SESSION 01 ....... Comet Shoemaker-Levy 9 I Monday, 8:30 - 10:00 Crystal Ballroom M. Festou and H.A. Weaver, Moderators 01.01 Weaver H. A.* Noll K. S. Storrs A. D. Smith T. E. A'Hearn M. F. Arpigny C. Feldman P. D. Boice D. C. Stern S. A. Lamy P. L. Larson S. M. Levy D. H. Scotti J. V. Marsden B. G. Meech K. J. Shoemaker C. S. Shoemaker E. M. Sekanina Z. HST Monitoring of Comet P/Shoemaker-Levy 9 The Hubble Space Telescope (HST) first observed comet P/Shoemaker-Levy 9 (SL9) on 1 July 1993, and then began a systematic monitoring campaign in late January 1994 that continued through the impact week in mid-July 1994. During the campaign a total of 39 HST orbits were devoted to imaging of the comet, and 6 orbits were devoted to UV spectroscopy with the Faint Object Spectrograph (FOS) in the wavelength range from 2223 - 3278 nagstrom. The images were used to estimate the sizes of the nuclei, examine carefully the near-nucleus morphology to search for further fragmentation events and outgassing activity, monitor the temporal variability, and measure the V-R colors in the inner comae of several nuclei. Results from several different image deconvolution analyses indicate that the diameters of the larger nuclei were in the range of about 2 - 4 km (assuming a geometric albedo of 4%), but all of these techniques impose constraints on the core behavior of the coma brightness profile that are not necessarily valid. Most of the nuclei displayed spherically symmetric comae of approximately 0."6 in radius from July 1993 until mid-July 1994, at which time the comae became highly elongated along the direction of the train. There is clear evidence for continuing fragmentation of the nuclei subsequent to the July 1992 breakup of the original body, which seems to argue against the "swarm" model for most of the fragments. The spectroscopic observations of SL9 have not shown any evidence for OH emission, which might be expected if SL9 is a water-laden object. Spectra taken on 14 July 1994 show strong Mg II emission in one two-minute segment followed by a three-fold increase in the continuum about 18 min after the appearance (and disappearance) of Mg II. The continuum enhancement lasted for less than 20 min. These latter spectral observations were made when SL9 was about 50 R(sub)J from Jupiter and may correspond to the time when the comet crossed the Jovian magnetopause. 01.02 Benner L. A. M.* McKinnon W. B. Dynamical Evolution of P/Shoemaker-Levy 9 We have investigated the orbital evolution of P/Shoemaker-Levy 9 by integrating its motion in the general four-body Sun-Jupiter-Saturn-comet problem, using the orbital elements determined by D.K. Yoemans and P.W. Chodas (posted on the P/Shoemaker-Levy 9 public account). We have now simultaneously integrated nineteen fragments (posted February, 1994) back to the 1992 perijove to test the effects of self-gravity (suggested by Benz and Asphaug) and possibly constrain the masses of the fragments. A general convergence within approximately 0.2 R(sub)J of the train center shortly after perijove is observed, but in general, improved orbital elements are necessary to achieve a more compact convergence, so no constraint on the fragment masses can be inferred yet. Prior to perijove, Shoemaker-Levy passed through the inner halo of Jupiter's ring at approximately 1.6 R(sub)J. Collisions with ring particles may have weakened the nucleus and assisted tidal disruption, or caused the disruption as the comet is apparently not strength dominated. The motion of each fragment was treated as a test case of the pre-disruption parent body's evolution and was integrated backward. Capture durations vary between approximately 6 and approximately 40 P(sub)J (P(sub)J = 1 jovian year), with a median near approximately 9 P(sub)J. The motion of the comet is chaotic, with a Lyapunov time of approximately 30 yr, so no definitive capture date can be inferred. The only robust inference for its pre-encounter heliocentric origin is that the orbit was not one of either high inclination or high (>0.5) eccentricity. Secular solar perturbations cause Shoemaker-Levy's jovicentric orbit to alternate between intervals of low eccentricity (e similar to 0.1 - 0.3) and high inclination (i similar to 90 degrees), and near-parabolic eccentricity and lower (either prograde or retrograde) inclinations (while its jovicentric semimajor axis and angular momentum perpendicular to Jupiter's orbital plane are approximately constant). Consequently, prior to disruption Shoemaker-Levy's perijove oscillated from a maximum of approximately 0.15 AU to a minimum well within the orbit of Callisto, indicating multiple earlier close flybys may have occurred. Ultimately solar perturbations increased Shoemaker-Levy's eccentricity and decreased its perijove sufficiently for disruption in 1992 and collision in 1994. This work supported by NASA grant NAGW-432 and NGT-50629. 01.03 Lisse C. M.* A'Hearn M. F. Esterle P. A. McFadden L. A. Weaver H. A. Woodney L. M. Modeling of UBVRIJK' Observations of P/Shoemaker-Levy 9: Implications for the Dust Size Distribution, Emission History, and Icy Composition Comet P/Shoemaker-Levy 9 was observed in the UBVRIJK passbands from January 1994 through its July 1994 impact with Jupiter from the Kitt Peak National Observatory (KPNO), Cerro Tololo Interamerican Observatory (CTIO), and the NASA/Infared Telescope Facility (IRTF). Extended comae and dust tails many arc-seconds in extent were detected for 10 of the cometary nuclei. Observations to date have yielded only non-detection upper limits for gas production from the comet. But the observed pre- impact dust in the tails, trails, and debris fan associated with 1993e had to originate at some point in time and space, presumably at/near the July 1992 perijove that first captured the comet into a Jupiter-centered orbit and fractured the parent body. The lack of activity due to low local equilibrium temperatures suggests that any observed dust has a substantial icy component to its composition. The behavior of the dust during the July 1994 impact will place strong constraints on its properties, and demonstrate its behavior in a strong magnetic field environment. We have fit the UBVRIJK images to modified Finson-Probstein/Monte Carlo dynamical models. These models calculate the classical orbit of a dust particle experiencing the gravitational influence of the Sun and Jupiter and the radiation pressure of the Sun. The observed dust tail is then fit by adjusting the rate of dust emission vs time, the velocity of dust emission vs. particle size (Beta), and the particle size (Beta) distribution. The models are poorly constrained unless observations over a large angular scale and a large time range (>1 month) are made. We present preliminary conclusions concerning the emission history and dust particle size distribution of P/Shoemaker-Levy 9 from the dynamical models. We have also combined the images into spectra. We fit the spectra using a Mie scattering code modified to allow for porous spheres, multi- component dust, and various particle size distributions. Cross-checks to the particle size distributions found by the dynamical modeling are made. We present preliminary conclusions concerning the silicate:carbon:ice composition of the grains. 01.04 Ahrens T. J.* Takata T. Friedson A. J. Orton G. S. Radiative Signatures and Plumes from Impact of Comet Shoemaker-Levy 9 on Jupiter Pre-impact diameters of Comet Shoemaker-Levy 9 fragments (SL9) are computed by comparing observed maximum height of plumes and their radiance with detailed Smoothed Particle Hydrodynamic (SPH) modeling of impact in three dimensions [Takata et al., Icarus, 109, 3-19, 1994; Ahrens et al., GRL 21, 1087-1090 and 1551-1553, 1994a,b]. Comparison between preliminary absolute peak radiances of the plume from impact of fragment R observed by the NASA/Infrared Telescope Facility SL9 Team with the MIRAC2 camera (Hoffmann et al., Infr. Phys. Tech. 35, 175, 1993) at 7.85, 10.3 and 12.2 microns with SPH power versus wavelength yields (using logarithmic interpolation at 10 microns) a diameter of approximately 1.3 km. In contrast, maximum plume height after impact is directly proportional to fragment energy, for example, inferred from images of the G impact recorded by the Hubble Space Telescope (Hammel et al. 1994, Science, in prep.) yields a height above the ammonia cloud deck of approximately 3300 km. Interpolating previously maximum plume height calculated for 0.4 and 2 km diameter fragments yields a fragment diameter of 1.7 km (assuming a density of 1 g/cm^3). Using these values to calibrate the relative sizes of fragments [Weaver et al., Science, 263, 787, 1994] yields an estimate of the progenitor SL9 diameter of 3 to 3.4 km and a total impact energy of 2.5 to 3.6 x 10^30 ergs or 6 to 9 x 10^7 Mton of TNT equivalent impact energy for the entire SL9 fragment chain. The SL9 progenitor diameter is less than the seven short-period comet nucleii in Luu's [Pub. Astron. Soc. Pac. 106, 425, 1994] catalog. Comparisons between other aspects of the SPH model, such as the penetration depth, will be made as new observational data become available. 01.05 Schenk P.* McKinnon W. B. Characteristics of Split Comets: The Fossil Record from Crater Chains on Callisto and Ganymede Crater chains on the surface of Jupiter's large moons Callisto and Ganymede represent a unique sample of ancient, tidally split comets. These impressively straight chains, or catena, can be up to 700 km long and consist of between 6 and 30 impact craters. No other type of crater clustering has been recognized. Characteristics of these chains closely resemble those of P/Shoemaker-Levy 9 at the time of discovery. Positions of craters within chains exhibit no more than one crater diameter deviation from the best-fit line through the chain. The largest craters are located in the center portion of the chain. The chains approximate great circles but can have curves equivalent to 30 degrees colatitude small circles, consistent with nonvertical impact of a linear chain on a rotating sphere. A reexamination of the Voyager images and detailed mapping indicates that there is a total of 8 such chains on Callisto that are clearly unrelated to secondary cratering (3 additional chains are classified as of uncertain origin). Assuming a mean surface age of 4 b.y. for Callisto, we obtain a frequency of 1 splitting event every 150 to 200 years. Three similar chains have also been identified on the younger surface of Ganymede. We have begun a study of the detailed morphology of these craters in order to assess the role of dispersed comet fragments on cratering in the Jovian system, and to characterize the internal properties of comets/asteroids and their fragmentation. Craters within these chains range from 4 to 36 km in diameter. Using appropriate scaling laws, and an impact velocity of approximately 15 km/s at Callisto, we calculate cometary fragment size range of 0.2 to several km, assuming a density of 1 gm/cm^3. Crater morphology may also provide limits on the structure of individual fragments. Central peaks, rimwall slopes and flat floors are recognizable in all the crater chains (within the resolution limits) and have dimensions consistent with those of normal craters. This implies that split comet fragments are not loosely bound disrupted clusters (like many secondary craters), although they may range from solid cohesive fragments to closely bound rubble piles. 01.06 Hammel H. B.* Dowling T. E. Harrington J. Mills J. R. Beebe R. F. Simon A. A. Huber L. F. Ingersoll A. P. Toigo A. Orton G. S. West R. A. De Jong E. Karkoschka E. Kuehn D. M. HST Imaging of Jupiter's Atmosphere in July 1994: Dynamical Effects from the Impact of Comet P/Shoemaker-Levy 9 In mid July 1994, fragments of the comet P/Shoemaker-Levy 9 plunged into Jupiter over a period of several days. We used the Hubble Space Telescope to image Jupiter before, during, and after the impacts to search for atmospheric phenomena created during the collisions. Many effects on Jupiter's atmosphere were detectable. For four separate events (A, E, G, and W), fireball plumes were detected rising above the limb of Jupiter; some of these plumes reached heights of 4000 kilometers. The plumes were visible in Jupiter's shadow, probably in thermal emission; above the shadow, they reflected sunlight. We observed several fresh impact sites, and detected transient expanding rings around several sites, most likely caused by horizontal propagation of an atmospheric wave. Estimates of the propagation speed will be reported. Thin ejecta blankets sometimes extended up to 16,000 km from the impact sites. The distribution of material was asymmetric; the patterns were consistent with ejection back along the sloping path of the incoming projectile. Several features evolved throughout the week of impacts due to the jovian winds. We also imaged impact sites over a period of several weeks to watch the long-term effects of atmospheric circulation on impact-created debris. In this talk, we will present an overview of the dataset and the results from our program. Detailed interpretation of the data will be presented in other talks in the session. These NASA/ESA Hubble Space Telescope observations were supported in part through grant GO-5624.08-93A from the Space Telescope Science Institute (operated by AURA Inc. under NASA contract NAS5-26555). 01.07 de Pater I.* Graham J. R. Jernigan G. Brown M. Liu M. Marcus P. Fomenkova M. Ingersoll A. Orton G. Infrared Observations of the Comet SL9/Jupiter Impacts at Keck We observed the SL9 impact with Jupiter on July 16-21 with the near- infrared camera (NIRC) mounted on the W.M. Keck telescope. We focused on imaging experiments, at wavelengths between 1 and 4 micrometers. Our most significant observation is the continuous monitoring of the fragment R event at 2.3 micrometers. Monitoring began 25 minutes before the impact of R, and continued until 22 minutes after. The resultant movie has approximately 8 frames per minute, and shows two flashes at the approximate time of impact, followed by the plume rotating into view. We will show and discuss the movie and lightcurve of the R event. In addition, we will show images of Jupiter's disk at 7 different infrared wavelengths which show the time evolution and vertical structure in the atmosphere of the various impact sites. We further have images of several cometary fragments (M, K, and W), and of Jupiter's ring (during impacts C and M, and afterwards). 01.08-INV Belton M. J. S. Chapman C. R.* Johnson T. V. Heffernan C. M. Klaasen K. P. Galileo Imaging Team Galileo Imaging of the Shoemaker-Levy 9 Impact Sites The Galileo Solid State Imaging SSI Camera was used to observe directly the impacts of fragments K, N, V, and W. To capture any sufficiently bright bolides, fireballs, or other L luminous phenomena with different sensitivities and time resolutions, two new camera modes were implemented -- an on-chip mosaicking of 2 1/3 sec. time-lapsed images and a diagonal drift-scan mode. Brief samples of data from the K, N, and W impacts have been returned to Earth. A luminous event has been detected for K from approximately 10:24:15 to 10:25 UT, reaching a peak brightness (in the near-IR) about 10% that of E total Jupiter (as seen from the same vantage point, 50 deg. phase, 1.5 AU from Jupiter). An event was observed for W, commencing at 8:06:12 UT, and lasting for at least 2 more images taken at 2 1/3 sec. intervals, which reached a peak brightness about 1% the brightness of Jupiter (green filter). Data return for the N impact is not yet sufficient to determine whether or not there is an indication of an event. We have decided not to return data for V, which were taken in a less favorable observing mode. It is not yet clear which parts of the impact phenomenology have been observed for K and W (e.g. bolide or fireball) but we expect to have much additional data available for at least the K impact by the time of the DPS presentation. We will also describe plans for returning the remaining data during the months extending to the end of January 1995. 01.09 Martin T. Z.* Tamppari L. Orton G. S. Claypool I. Travis L. Galileo PPR Observations of Shoemaker-Levy 9 The Galileo spacecraft Photopolarimeter Radiometer (PPR), a hybrid visual/thermal IR instrument designed primarily to measure properties of the Jovian atmosphere, was employed for SL9 as a staring high-speed photometer at 945 and 678 nm, taking advantage of Galileo's direct view of the impact point. Jupiter subtended 0.6 mrad within the 2.5 mrad circular field of view. The PPR was able to acquire data at times when no other Galileo optical instruments could operate. The impacts of fragments B, H, L, Ql, and S were observed for 41 m each with a sample time of 0.23 sec. The H, L, and Ql events provided good light curve and timing information. Initial flashes occurred at these times (for eardlbased observers): H: 1994/199 19:31:58 UTC L: 1994/200 22:16:48 Ql: 1994/201 20:13:52 These data likely represent thermal emission from the brief initial pass of comet fragments through the atmosphere, followed immediately by an expanding and cooling "fireball." The Ql flash appeared 3x brighter at 678 nm than at 945 nm, with a faster decay at the shorter wavelength. Initial temperatures above 10^4 K are implied. (A graph of these events appears on hard copy.) 01.10-P Yeomans D. K. Chodas P. W. Comet Shoemaker-Levy 9 in Orbit About Jupiter The collision of comet Shoemaker-Levy 9 with Jupiter has focused attention upon the cometary formation process and the history of cometary motions within the solar system. At least some comets appear to be extremely fragile structures. In addition to the Jupiter tidal disruption of comet Shoemaker-Levy 9s on July 7, 1992, comet Brooks 2 was disrupted by Jupiters tidal forces in 1886. Although Brooks 2 was not captured by Jupiter, temporary captures of periodic comets by Jupiter are not particularly unusual. During the 1800-2200 time period, the following periodic comets either have been, or will be, in temporary orbit about Jupiter: Shoemaker-Levy 9, Helin-Roman-Crockett, Oterma, Gehrels 3, Smirnova-Chernykh, Haneda-Campos, Helin (1987w), and Kojima. Apart from the record close Jupiter approach of comet SL-9 on July 7, 1992 (1.3 Rj) and the collision in July 1994, the next closest Jupiter approach was that of Gehrels 3 in August 1970. Although Gehrels 3 did not pass closer than 3 Rj to Jupiter, its osculating perijove distance for an epoch in February 1971 was temporarily well below Jupiters radius. Although only comet Shoemaker-Levy 9 collided with Jupiter, solar perturbations on comets in Jupiter orbit can easily reduce a comets perijove distance to allow a collision. Using the orbital history of Shoemaker-Levy 9 as an example, the Jupiter capture process is discussed. 01.11-P Rettig T. W. Hahn J. Tegler S. C. Mumma M. J. DiSanti M. Hubble Space Telescope Observations of Comet Shoemaker-Levy 9 Subnuclei: Solid Bodies or Swarms? We present a preliminary analysis of comet Shoemaker-Levy 9 images taken with the Hubble Space Telescope Wide Field (WF) and Planetary Cameras (PC) during January, March, May, June and July 1994. The WF and PC images have resolutions of 0.10 and 0.046 arc sec, respectively. The high spatial resolution of the images allows us to probe the dust distribution in the inner coma of each subnucleus through an examination of continuum surface brightness distributions. We are using the observed magnitude variations and surface brightness distributions of the inner comae to determine whether the various impacting subnuclei consisted of kilometer sized central bodies or swarms of meter-sized cometesimals. We suggested (Rettig et al. BAAS 1994) that as the original cometary nucleus approached perijove in 1992, the nucleus fragmented into a cloud of cometesimals that was quickly stretched out in a 'tube' along the tidal direction. After leaving the Roche limit, the decreasing tidal force permitted self-gravity to re-focus material to form (approximately 20) 'swarms'. Depending on swarm mass and particle relative velocities, several types of comet 'fragments' may have developed. The swarms might have gravitationally re-collapsed into central subnuclei or they may have remained as loosely bound swarms of particles that could have been disrupted at large distances from Jupiter, prior to impact. For subnuclei that consisted of loosely formed swarms of particles, the effects of tidal disruption were predicted to be observable prior to Jovian impact as variations in both surface brightness distributions and magnitudes. Even the recondensed subnuclei were expected to disrupt again at the tidal limit and were not expected to penetrate much below the stratospheric levels of the Jovian atmosphere. Evidence of swarm-like structures will provide information on the physical structure of comet nuclei and will provide constraints on comet accretion processes that existed some 4.5 billion years ago. This research is supported by an STScI grant to the University of Notre Dame. 01.12-P Rauer H. Osterloh M. Low Resolution Spectra of Comet Shoemaker-Levy 9 (1993e) The activity of cometary nuclei is found to be restricted to descrete areas on the surface. The difference between active and inactive regions may be caused by the evolution of the comet during its perihelion passages, or may be linked to processes during its formation. Assuming comets are made of several planetesimals, physical and/or chemical differences between the cometesimals may cause the observed differences in activity. Up to now, the question of homogeneity of cometary nuclei could not be addressed in measurements of comets. The break-up of comet Shoemaker-Levy 9 into a chain of individual nuclei offers the unique possibility to study possible differences of parts of a cometary nucleus. Low resolution spectra (16 angstrom/pixel) of comet Shoemaker-Levy 9 have been obtained on April 15 1994 at the 2.2m telescope at ESO, La Silla, using EFOSC 2. The spectral range covers 3600 angstrom - 9200 angstrom. The slit of 5.7 arsec length and 5 arcsec width was placed along the train of nuclei. In this way 11 spectra of the train have been obtained to search for possible differences in the dust colour of the individual nuclei. 01.13-P Chen J. Jewitt D. Luu J. Mauna Kea Observations of Split Comet Shoemaker-Levy 9 Split comet Shoemaker-Levy 9 has been observed from Mauna Kea at regular intervals since its discovery in March 1993. Systematic observations with a charge-coupled device on the University of Hawaii 2.2 meter telescope show the photometric and morphological evolution of the fragments over the 16 month pre-impact period. Apart from the progressive separation of the fragments, the most prominent change observed is the decrease in the amount of dust associated with the comet. Individual dust tails became prominent in early 1994 but subsequently faded. As we reported at last year's DPS meeting, no clear evidence for embedded nuclei can be discerned in the Mauna Kea data. Spectra from the 3.6 meter CFHT and 10 meter Keck telescopes were obtained to search for gas (OH, CN, N(sub)2^+, CO^+) in the 3000 angstrom to 4500 angstrom wavelength region. No evidence for emission was found. We will present an overview of the temporal development of the fragments prior to their plunge into Jupiter. 01.14-P Peterson B. A. Wehinger P. A. Wyckoff S. Spectroscopy of Comet Shoemaker-Levy 9 and Jupiter Spectroscopic observations of Comet Shoemaker-Levy 9 and Jupiter were acquired during the period 1994 July 16-23 using the Mt. Stromlo Obs. 1.9-meter telescope and a long slit CCD spectrograph. We shall compare the spectra of the fragments of comet Shoemaker-Levy 9 with those of P/Halley observed at similar heliocentric distances (4.8 AU). In addition, we report on slit spectra taken at the eastern limb of Jupiter in an attempt to search for evidence of the effects of the collision of selected larger fragments in the outermost layers of the Jovian atmosphere. This research is supported in part by the NASA Solar System Exploration Division and the NSF U.S.-Australian Cooperative Science Program. 01.15-P Chernova G. P. Birkle K. Kiselev N. N. Jockers K. Imaging Photometry, Polarimetry and Color of Comet Shoemaker-Levy 9 Comet Shoemaker-Levy 9 was observed with the ESO 1m-telescope and the focal reducer of the Max-Planck-Institute for Aeronomy from April 27 to May 1. During this interval the phase angle wa.s always less than 0.4 degrees. ,About 60 useful images of 5 minutes duration were obtained in the g, r, and i filters of the Gunn system. The field of view was 14.5 x 9.6 arcmin and the scale 1.6 arcsec pixel^-l. For the night of April 27/28 the following Gunn g magnitudes have been derived (the fluxes are taken in square boxes of 5 x 5 pixels, i.e. 8 x 8 arcsec, corresponding to 21000 x 21000 km at the comet): 20.6 A(21), 20.0 B(20), 20.2 C(l9), 19.3 E(17), 19.6 F(16),18.4 G(15),18.8 H(14),18.5 K(12),18.9 L(ll),l9.1 P2(8b), 19.3 R(6), 18.9 S(5), 19.5 W(1). The Gunn G magnitude of P1, Q1 and Q2 together, measured in a square box of 11 x 11 arcsec is 17.7. The colors of the individual comet fragments are the same within the error limits. This indicates a homogeneous nucleus of the parent comet. In the night from May 12 to May 13 comet Shoemaker-Levy 9 was observed with the prime focus camera of the 3.5m-telescope of the German-Spanish Astronomica1 Center, Calar Alto, Spain, through a rotatable polaroid and a filter similar to the R filter of the Cousins system in order to obtain a polarimetry map of the comet. At that time the phase angle was 2.6 degrees. Four images of 20 minutes duration were secured, with polarization directions 0 degrees, 45 degrees, 90 degrees, and 135 degrees. The field of view was 7 x 7 arcmin and the scale 0.41 arcsec pixel^-l. Since the night was not photometric it will not be possible to extract an accurate polarization map but we might be able to judge about polariza.tion differences between the individual nuclei and their tails and to compare them with the color variations. 01.16-P Yabe T. Xiao F. Zhang D.-L. Sasaki S. Kobayashi N. Abe Y. Terasawa T. Effect of EOS on Break-up of Shoemaker-Levy 9 Entering the Jovian Atmosphere Break-up of Comet Shoemaker-Levy 9 entering Jovian atmosphere was studied with highly accurate hydrocode ExCIPHER[1] by changing the equation of state (EOS) of the comet[2]. The comet of radius 1.5km was completely destroyed around the atmospheric pressure of 10 bar which is shallower than that of the other simulations[3,4]. Furthermore, the behavior of break-up is quite different from them. This behavior depends on the type of EOS . For hard material like water and ice, the impact of Jovian atmosphere caused incompressible surface wave propagating along the comet surface thus enhancing ablation loss even at a low pressure atmosphere. For ideal EOS, however, the surface wave did not appear since the comet was compressed upon impact and hence the ablation loss around 5 bar was quite low. Although the comet was broken into moderate pieces at 10 bar, most of the energy had already been lost well before the break-up. Surprisingly, however, the final disintegration occurred around 10 bar for tested EOS and even for planar geometry. This may be because the disintegration is triggered by a hole created along the central axis and the comet is torn off when the atmospheric gas penetrates through the comet causing turbulent now behind it. A hole of this kind can easily develop because even a small concave structure can grow into a larger one by the focusing of flow through conical geometry. The subsequent explosion process was also simulated by the same code. In the first 100 second, a plume followed by a fireball propagates above 1000 km and then the plume alone is ejected higher in the sky like an umbrella. The rest part expands quite slowly over 10000 km and this structure lasts for more than 1000 second. These two sequences might be related to the two subsequent increases of observed infrared signals. [1] Yabe, T. et al. (1994) Nucl. Des. Engnrg. in press. [2] Yabe, T. et al. (1994) J.Geomag.Geoelec. 46, 657-662. [3] Mac Low, M. and Zahnle, K (1994) Ap. J. Lett. in press. [4] Ahrens, TJ. et al. (1994) Geophys. Res. Lett. 21, 1087-1090. 01.17-P Wyckoff S. Ferro A. Spectroscopic Observations of Comet Shoemaker-Levy 9 and Jupiter Long slit spectra of selected fragments of Comet Shoemaker-Levy 9 and of Jupiter were acquired with the 4.5-meter Multiple-Mirror Telescope using the red channel spectrograph. Observations were obtained during the week of the SL9's collision with Jupiter. The spectra of the fragments will be characterized. We shall compare the SL9 spectra with those of P/Halley observed at similar heliocentric distances (4.8 AU). This research is supported in part by the NASA Solar System Exploration Division. 01.18-P Festou M. C. Lelouch E. On the Detection of Gaseous Species in Comet Shoemaker-Levy 9 Prior to Its Impact with Jupiter Comet P/Shoemaker-Levy 9 was observed on five consecutive nights with the 30m IRAM antenna, from 16 July till 21 July 1994. The instrumental setting allowed to simultaneously monitor the gaseous emissions of CO and HCN in the 2 mm window until the comet disappeared behind the planet disc, then to switch to another observing program. If in July 1994 the comet sub nuclei break as they did in 1992 after entering the Roche limit of the planet, then a large cloud of dust particles will form and slowly expand into space. Large amounts of gas might be released, either at the time of breakup or immediately after, when large areas of fesh comet snow are exposed to sunlight. Such an event could occur anywhere during the last hour prior to the impact. At the time of impact, this cloud might be up to about 1,000 km in diameter, and very bright, especially in CO light. The observing geometry is such that the comet activity at mm wavelengths can be monitored until the last few minutes before the impacts, maximizing thus the chances to detect a gaseous emission from the comet. This paper will be given only if positive results are obtained. 01.19-P McFadden L. A. A'Hearn M. F. Esterle P. A. Lisse C. M. Weaver H. A. Woodney L. M. Multi-Wavelength Imaging of Comet P/Shoemaker-Levy 9: January-July, 1994 We have acquired multi-wavelength images of Comet P/Shoemaker-Levy 9 from January-July using three telesopes for seven observing runs in order to monitor the brightness of the fragments, the dust tails, trails, and debris fan. Wide-field (FOV = 1 degree^2) CCD images with UBVRI filters were acquired with the 0.6m Schmidt telescopes at Kitt Peak National Observatory (KPNO) February, April, and June, 1994 and Cerro Tololo Interamerican Observatory (CTIO) in March and June, 1994. Moderate-field (FOV=1 arcmin^2) near-infrared images with J and K filters were acquired with the 3m NASA-Infrared Telescope Facility at Mauna Kea in January, May, and July, 1994. The 256 x 256 InSb array camera, NSFCam was used at the IRTF. The brightness of the nuclei are in the range 20- 21 magnitudes/arcsec^2. The data will be analyzed for temporal brightness variations of the nuclei, tails, dust trails, and debris fan. Comparison with the colors of the Sun, comets McNaught-Russell (1993v), Takamizawa-Levy (1994f) and asteroid 23 Thalia, also observed with this equipment, will be made. We anticipate finding evidence of ice grains that can be seen using broad-band visible and near-IR imaging although if icy grains and dust are intimately mixed, these observations may not be an appropriate diagnostic of water ice. This work was supported by NSF and NASA. 01.20-P Chodas P. W. Yeomans D. K. Comet Shoemaker-Levy 9 Impact Times and Impact Geometries The fragments of Comet Shoemaker-Levy 9 impacted Jupiter July 16-22, 1994, within 10 minutes of the final predicted impact times. Post-impact estimates of the impact times appear in the table below. These estimates are based upon direct observations by the Galileo spacecraft (for fragments H, K, L, and W), the times at which the Hubble Space Telescope observed impact plumes, the times at which infrared flashes were observed from the ground, the longitudes of impact features seen in HST images, and the relative impact times predicted from astrometry. The table also gives l-sigma uncertainties in minutes. Fragment Impact Time Fragment Impact Time (UT) (UT) A July 16 20:11 +/-3 N July 20 10:31 +/-4 B July 17 02:50 +/-6 P2 July 20 15:23 +/-7 C July l7 07:12 +/-4 Q2 July 20 19:44 +/-6 D July 17 11:54 +/-3 Ql July 20 20:13 +/-3 E July 17 15:11 +/-3 R July 21 05:33 +/-3 F July 18 00:33 +/-5 S July 21 15:15 +/-5 G July 18 07:32 _+/-2 T July 21 18:10 +/-7 H July 18 19:32 +/-1 U July 21 21:55 +/-7 K July 19 10:24 +/-1 V July 22 04:22 +/-5 L July 19 22:16 +/-1 W July 22 08:06 +/-1 The impacts occurred on the night side of the planet near the morning terminator, varying from 9 degrees past the limb as seen from the Earth for fragment A to 4 degrees for W. Fragment W passed behind Jupiter's limb only 5 seconds before impact, at an altitude of only 200 km above the l-bar level. The Jovicentric latitudes of the impacts ranged from 43.1 degrees S for fragment A to 44.2 degrees S for W. The longitudes of the impacts relative to the midnight meridian varied more widely, from 64 degrees to 71 degrees. The velocity of the fragments at impact was about 61 km/s, the incidence angle was about 43 degrees, and the azimuth angle of the velocity vector was about 15 degrees west of north. The time required for Jupiter's rotation to bring the impact sites into Earth view varied from 19 minutes for A to 9 minutes for W. 01.21-P Asphaug E. Benz W. Size and Density of Comet Shoemaker-Levy 9 Deduced by Modelling Break-up of the Parent 'Rubble Pile' The fragments of comet Shoemaker-Levy 9 produced a display more spectacular than many dared to hope; equally surprising was the wide variation in impact magnitude. In our prediction paper [1], a heterogeneous chain of "rubble swarms" is created when a parent comet with bulk density about 0.7 g/cc and grain density about 0.9 g/cc suffers tidal disruption and self-gravitational reaccretion along the 1992 perijove trajectory. Higher density parents reaccrete into one dominant clump, and parents with bulk density about 0.5 g/cc form about 20 clumps of nearly equal mass. We can explain the uniform crater chains on Ganymede and Callisto and the recent impacts into Jupiter by the same mechanism if the bulk density of comets is 0.6 +/- 0.1 g/cc, with SL-9 slightly denser than average. Many rejected this idea as soon as the first bolide struck, claiming that strength was needed to penetrate the deep atmosphere -- in spite of the fact that models predicting deep penetration [2] did not generally include strength. Spectroscopic evidence eventually showed that the impacts were, after all, quite shallow, bursting near the 1 bar level. It was also claimed, in spite of calculations to the contrary [3], that Jupiter's tide would disperse a strengthless bolide prior to atmospheric entry. This is also not true. The final issue concerns the size of the parent comet. Huge impact scars might seem to require very large impactors, yet three models including our own [1,4,5] conclude that the parent comet diameter was less than 2 km. We must strive to understand how a comparatively small mass creates such a big blemish. A typical rubble-swarm in our model is over 10 km in diameter before the final encounter with Jupiter, with a loosely-packed (approximately 0.1 g/cc) "core" about 1 km across. These approximately 10^14 g swarms each deposit approximately 2x10^27 ergs. While the core can be treated as a single entity in airburst models, the outer swarm must be treated as many independent impactors. A 1 km 0.1 g/cc bolide explodes near the one bar level [6], whereas a 100 m approximately 1 g/cc grain explodes about 100 km higher, two seconds earlier. Hundreds of smaller bursts, each depositing 10 to 100 Mt over a wide area before the approximately 3 Gt explosion of the central bolide, could play an important role in fireball and plume evolution. [1] Asphaug, E. and Benz, W., Nature 370 1994. [2] Takata, T. et al., Icarus, in press. [3] Yanagisawa, M. and Konno, T., LPSC XXV 1994. [4] Solum, J.C., Nature 370 1994. [5] Scotti, J.V. and Melosh, H.J., Nature 365 1993. [6] Zahnle, K. and Mac Low, M. M., Icarus 1994. 01.22-P Barker E. S. Cochran W. D. Cochran A. L. Na C. Pryor W. Baines K. H. Briley M. Smith V. Spectrophotometry and High-Dispersion Spectroscopy of Jupiter's Southern Latititudes During the Impact Period We report on visible spectrophotometry and high dispersion spectroscopy taken of Jupiter during the impact period (17 July - 23 July 1994 UT). Spectrophotometric observations were obtained using the longslit CCD spectrograph (ES2) on the 2.1m telescope to cover the 0.55 to 1.08 micron wavelength range. A seeing limited spatial resolution of about 1- 2 arcsec was achieved resulting in a spectral resolution of about 10 angstrom. The spectrograph slit was rotated to allow spatial sampling along and adjacent to the impact latitude (-44 degrees S). This scenario allowed sampling of impact regions and unperturbed regions as functions of both time and location. Spectrophotometric calibration of the low resolution dataset via standard stars and solar analogs will be used to provide absolute calibration of the narrow-band CCD images taken concurrently in the 6190 angstrom and 8930 angstrom CH4 bands by the McDonald Team on the 0.76m telescope (see adjacent poster paper) . The high resolution spectroscopy was done on the 2.7m telescope with a cross-dispersed echelle spectrograph, giving nearly complete spectral coverage between 0.40 and 1.05 microns. The coude slit was 1.2 x 8.1 arcsec permitting spatial resolution of the impact latitude in either a N-S or E-W direction. An R=60,000 allowed resolution of individual rotational CH4 lines in the impact region spectra. We will report on changes in the morphology of the continuum and the CH4 bands between 0.6 and 1.0 microns. For example, the observed impact regions appeared as bright features only in the strongest CH4 absorption regions within the 8930 angstrom band and conversely as dark features in the weaker absorption regions. Both the low- and high- dispersion spectra covered a range of CH4 band or line strengths which will aid in the determination of the altitude distribution of the condensates formed as a result of the impacts. 01.23-P Cochran A. L. Baines K. H. Barker Barker E. S. Cochran W. D. Frueh M. Kim S. Kim Y. Kudari A. Lester D. F. Na C. Pryor W. Gyorgyey Ries J. Trafton L. Whipple A. L. Wiant J. A Synopsis of McDonald Observatory Imaging Observations of Jupiter Before, During, and After the Shoemaker-Levy 9 Impact We report on optical CCD and IR images of Jupiter which were obtained at McDonald prior to the impacts of Shoemaker-Levy 9, during impacts, about one week following the last impact, and almost one month after the last impact. The CCD observations were obtained through narrow-band filters which isolate the 6190 and 8900 Angstrom CH4 bands and the adjacent continuum regions at 6040, 7640 and 8290 Angstrom. A barlow lens was utilized to expand the image on the chip so that Jupiter mostly filled the chip. The CCD observations before the impacts were obtained on the 0.9-m telescope, while the CCD observations during and after the impacts were obtained with the 0.8-m telescope. During the impacts and the following time, we obtained at least some data on each of 15 "nights" (we started observing as early as 4pm). The IR images were obtained on the 2.7-m telescope using a NICMOS3 array (Rokcam) with filters to isolate the 1.5 micrometer NH3 band, the 2.3 micrometer CH4 band, the 2.12 micrometer H2 S(0) pressure induced dipole absorption and the continuum at 1.58 micrometer and short K-band. Rokcam observations were obtained on 11 nights during and following the impacts. In addition to the CCD and Rokcam observations, we obtained about 14 hours of real-time video observations using the Lunar Laser Ranging 0.8-m telescope. In the course of our observations, we observed the flash associated with the impact of fragment R. Observations were obtained during several other impact periods but no flashes were detected. We compare images of the planet obtained with the CCD and Rokcam, including a movie in some wavelengths. We also show a time sequence of certain longitudes of Jupiter. Cross-cuts of the images for different wavelengths are compared to show how the morphology of the spots, bands, etc. change with latitude and wavelength. 01.24-P Lupishko D. F. The Results of the Ukraine Observation Program of Shoemaker-Levy 9 Collision with Jupiter The photometric, polarimetric, spectral, photographic and radio observations of Jupiter before, during and after the collision are carried out at the observatories of Ukraine, Middle Asia and Northern Caucasus. The spatial and time variations of polarization characteristics of atmosphere aerosol, the photometric profiles and the moments of flashes in Jupiter atmosphere, the changes in the structure of atmosphere cloud layer, the data on the state of Jupiter magnetosphere during the collision and Jupiter photographs of high spatial resolution (0.3 - 0.5 arc sec)are supposed to be obtained. All the results are going to be reported. This work was supported by grant of National Space Agency of Ukraine. 01.25-P Kleshchonok V. V. Churyumov K. I. Photoelectric Observations of Io and Europa in the Course of Fall Down of Secondary Nuclei A, H, Q2, Q1 and T of Comet D/SL-9 on to Jupiter Observations of the Jupiter satellites within the program for investigation of the comet D/SL-9 - Jupiter collision were held with the electrophotometer installed on the AZT-14 (D=0.5m) telescope at the Lesniki station of the Kiev University Astronomical Observatory. The electrophotometer worked in the regime of photon counting with registration on the PC IBM. In the course of observations standard UBVR filters were used. Temporal control tie was hand-made according to exact signals time. Circumstances for observations did not reveal changes in the satellites brightnesses which could be linked with reflection of light of fireball in the Jupiter atmosphere, with the exception of the nucleus fall down Q2. Here, two events that can be tied with the outburst during the nucleus fall down were found out. The first event has the following parameters: filter B, the outset of the outburst at 19:32:09 UT, continuity of the outburst 2.7 sec, the amplitude 0.12 mag [l]. Parameters of the second event: filter B, the outset at 19:48:10 UT, the continuity - 1.0 sec, the amplitude 0.11 mag. The second flash seems more probable both in continuity and it being close to the predicted time of the nucleus fall down Q2 on to Jupiter [2]. 1. Churyumov K.I. Io brightens. The Siderial Times, 1994, No. 10, p.5, IAU XXIInd General Assembly, The Hague. 2. Yeomans D.K., Chodas P.W. Comet SL-9 impact times. Interoff. memorand., 1994, 314.10-87. 01.26-P Larson S. Scotti J. Howell E. Marcialis R. Nolan M. Winsiewski W. A'Hearn M. Wellnitz D. Campins H. Rabinowitz D. Butner H. Tapia S. Vilas F. Doherty P. Bessell M. Brosch N. Liebowitz E. Gilmore A. Kervin P. Africano J. Levine S. Schuster W. Martin P. Verveer A. Moreno F. Molina A. Rutten R. Kidger M. The Comet Impact Network Experiment (CINE) The Comet Impact Network Experiment (CINE), an international collaboration designed to observe phenomena associated with the impact of Comet Shoemaker-Levy 9 with Jupiter was successfully deployed at the 4.2-m WHT at La Palma, Spain; the 2.5-m at Las Campanas, Chile; the 1.5- m at San Pedro Martir, Mexico; the 1.2-m of the Air Force Maui Optical Station, Hawaii; the 1.0-m at Mt. John Obs., New Zealand; the 1.0-m at Siding Spring Obs., Australia; the 0.6-m telescope at Perth Obs., Australia; a 1.0-m Air Force GEODSS telescope on Diego Garcia; and the 1.0-m telescope at the Wise Obs., Israel. Coronagraphic/spectrographic transfer optics were constructed to reduce the scattered light from Jupiter and normalize plates scales with the various facility CCD cameras. The main objectives were to 1) provide astrometric positions of the nuclei just prior to impact, 2) look for evidence of cometary particle fragmentation as the comet enters the Jovian magnetic field, 3) look for evidence of further breakup as the comet crosses its Roche limit, 4) obtain time-resolved spectra of the meteor flashes reflected off the satellites, 5) look for evidence of material ejected from the impact, 6) observe changes in the Jovian cloud morphology, and 7) look for evidence of dust capture and interaction with the Jovian ring. The project was implemented through the local observer-collaborators who applied for telescope time and provided the technical information needed to interface the coronagraphs with the telescopes and CCDs, and observers who accompanied the coronagraphs to the sites. This project was supported by the NASA Planetary Astronomy Program, the USAF Space Command and the various host institutions. 01.27-P Wellnitz D. D. A'Hearn M. F. Martin R. Comet SL9 Interactions with Jupiter as Observed from Perth, Australia The results of planned observations of the interactions of Comet Shoemaker-Levy 9 with Jupiter, using the University of Maryland CCD Imaging System for Comets (CISCo) on the Lowell Telescope at the Perth Observatory in Western Australia, will be reported. Planned observations include coronographic imaging of the cometary fragments as they approach and impact Jupiter, fast CCD imaging of satellites of Jupiter near the predicted times of cometary fragment impacts, imaging of the atmospheric fireball if it rises above the limb of Jupiter, coronographic imaging of the Jovian ring to observe the interaction of the cometary dust tail with the ring, imaging of Jupiter with various filters in the continuum and in methane absorption bands of various depths to search for cloud formation in the stratosphere after the fireball starts to cool, and low-resolution spectrographic imaging of Jupiter to search for changes in the absorption features in appropriate areas of Jupiter. This work is being supported by NASA and NSF funds. 01.28-P Jockers K. Observations of Jupiter's Atmosphere in the K-Band During the Shoemaker-Levy 9 Encounter Using ESO's infrared camera IRAC2B at the German/ESO 2.2m telescope at La Silla, Chile, observations of Jupiter's atmosphere were performed from July 16 to 24, 1994 (8 nights). The IRAC2B camera employs a NICMOS- 3 array with 256 x 256 pixel of a size of 40 microns. A scale of 0.27 arcsec pixel^-l was used. Regrettably not a single impact was observed. Filter images were taken through two interference filters with center wavelengths 2.105 and 2.365 microns, and FWHM 0.037 and .088 microns respectively. These wavelengths are located at the flank and in the centre of a deep methane absorption band. While at 2.105 microns some of the Jovian clouds are still visible, Jupiter's disk is practically black at 2.365 microns and even the Great Red Spot, which extends to great height, is barely visible. In both filters the impact clouds appear in emission and have about the same brightness. This indicates that the clouds must be located at atmospheric heights unaffected by methane absorption. They are remarkably stable but in the course of a few days are getting sheared by Jupiter's velocity field. Narrow-band images of spectral resolution approximately equal to 1000 were obtained with an imaging Fabry-Perot-Interferometer in the "hot" band of H(sub)3^+ at 2.093 microns and in the H2 quadrupole line at 2.121 microns. Both lines are sensitive to temperature enhancement in the outer layers of the Jovian atmosphere. Usually the "hot" band of H(sub)3^+ can be observed only when the auroral heating is particularly strong. Quick look data show no evidence for the presence of the emissions. The paper will present the time evolution of the impact clouds as observed with the interference filters. In addition we will provide evidence for the detection or non-detection of tlle H(sub)3^+ and H2 quadrupole line in tlle interferograms. 01.29-P Klavetter J. J. Petmecky S. Levine S. Near-IR Reflection Observations of the Shoemaker-Levy 9 Fireballs We observed the SL9 impacts into Jupiter from the San Pedro Martir Observatory (SPMO), administered by the Observatorio Astronmica Nacional (OAN) located in Baja, Mexico. This presentation will concentrate on the near IR observations made from the 2.1 meter telescope using the Camila IR imager. We will report on the dramatic impact spots/plumes observed from the SPMO/OAN site, including the L and R (and perhaps M and W) fragments. We will show the dramatic increase in brightness from our time series imaging, including photometry of the spots/plumes. The morphology of the spots is dramatically different at the wavelengths observed, from 1.1 microns to 2.3 microns, with the spots being essentially invisible at the smaller wavelength bands. We will show images from filters throughout this range and place temperature limits on the thermal continuum radiation observed. 01.30-P Wasserman L. H. Buie M. W. Millis R. L. Imaging of Shoemaker-Levy 9 Impact Phenomena from Northeastern Australia We will be conducting imaging observations of the Shoemaker-Levy 9 impact on Jupiter from Northeastern Austrailia from 1994 July 12-25. Our observations will be made with our portable Celestron 14" telescope with the Occultation CCD camera system that was presented at last year's DPS meeting. The system has now been retro-fitted with an automated 10 position filter wheel and a new optical mode for an image scale of approximately 0.5"/pix. Our two primary goals are (1) to take extensive sets if images to monitor the Jovian atmosphere for any changes caused by the impacts, and (2) to attempt to observe the flashes from the impacts in reflection off of a well-placed satellite. Current predictions indicate that from our location, four impact occur in darkness. One of these is the only impact that occurs with Europa in eclipse where a flash may be seen. Our system can quickly cycle through the filter set for multi-spectral imaging of Jupiter. At the time of fragment impacts, we can quickly re- configure and take high-frame rate data (up to 5 Hz) for the flashes. We have also developed a spectroscopic mode that can be used to derive the color temperature evolution of the prompt flash, provided enough signal is generated from the impacts. We will present results from our efforts and will provide a catalog of the dataset for interested people. This work was funded by NSF grant AST-9322449. 01.31-P Lazzaro D. Moreira J. K. Foryta D. W. P/Shoemaker-Levy 9 Impact: Observations at the Pico-dos-Dias Observatory We report the observations planned at the Observatorio do Pico-dos-Dias (Itajuba, Brazil) for the impact on Jupiter of comet Shoemaker-Levy 9 (SL9) expected to occur on July 94 (Marsden, 1993, IAU Circular No. 5801; S Green, 1993, IAU Circular No. 5807). Since the impact of the 20-22 fragments of SL9 are expected to take place on the side of Jupiter away from the Earth, we plan to observe the reflected light of the bolide and/or fireball, subsequent to each impact, from a suitably placed Galilean satellite. A rapid photometer mounted on a 60cm telescope will probably be able to detect these phenomena using an integration time of 0.1 seg. With this instrument we expect an impact detectability limit of 14.5 to 12.5 magnitudes (V), whether or not the observed satellite is in eclipse. Assuming a luminosity efficiency of 3% we estimate that the above magnitudes correspond to a fragment diameter of 100-200m. A lower luminosity efficiency will necessarily increase these diameters up to 1- 2 km, which would be just the greatest fragments. The final aim of these observations is the obtention of some data relevant to determine the fragment distribution of SL9. We pretend, by the time of the meeting, to carry out at least preliminary reductions in order to deduce the size of the fragments from the observed signals (if any!!). 01.32-P Glenar D. A. Hillman J. J. Le Louarn M. Drummond J. D. Narrow-band Visible and IR Imagery of Jupiter During the Comet Shoemaker/Levy-9 Collision Series We observed the Southern hemisphere of Jupiter on several nights during the Jupiter SL/9 impact sequence, using the Coude focus at the Kirtland Air Force Base, 1.5-meter adaptive optics telescope. The objectives were to identify condensed volatiles in the high atmosphere at the locations of the impact sites, track the motions of these sites as they transit the disk, and examine their breakup. Multispectral images were acquired in the CH4 bands at 725 and 890 nm, the NH3 bands at 645 and 790 nm and in their adjacent continua using a tunable acousto-optic imaging spectrometer and silicon CCD at the focal plane, with a spectral resolution (Lambda/Delta Lambda) of 380 to 530. The stratosphere near 10 mbar was simultaneously sounded by imaging in the deep 2.35 micrometer CH4 band using a NICMOS-3 camera with cooled narrow band filter. All observations were photometrically calibrated and reduced to absolute reflectivity (I/F) using close coincidence standard stars and published solar intensities. A summary of the major results is presented. This work was supported by the NASA Planetary Instrument Definition and Development Program and the GSFC Directors Discretionary Fund. 01.33-P Woodney L. M. Meier R. A'Hearn M. F. Wellnitz D. Smith T. High-speed Photometry of the Jovian Satellites During Comet P/Shoemaker-Levy 9's Impact with Jupiter At Mt. Singleton, West Australia, a high-speed photometer and a 14 inch Celestron were used to look for flashes off Io or Europa during the expected impact times of D, E, K, and N. The observations were made in broad-band white light. Io was well monitored during the impact time of D and no flashes are apparent. There is a possible effect at the time of impact of E, but due to problems with tracking caused by high winds, we can not yet rule out contamination from Jupiter in the aperture. Comparison with results from other observers may resolve this uncertainty. No flashes were observed for the impact of fragment K, which occurred while Europa was in eclipse, or for fragment N. The brightness of the monitored satellites changed by less than approximately 10%. Careful analysis should allow us to look for small effects and better constrain upper limits. 01.34-P Stuwe J. A. Schulz R. Encrenaz Th. A'Hearn M. F. Shoemaker-Levy 9 and Its Impact sites on Jupiter We report on observations in the visible spectral range of P/Shoemaker- Levy 9 before and Jupiter after the impact. SL-9 was observed with the ESO Multi Mode Instrument (EMMI) at the 3.5-m New-Technology-Telescope (NTT) at La Silla, Chile, on July 1 and 2, 1994, two weeks before its impact on Jupiter. Highly resolved images of the entire cometary train were obtained in B, V, R, and I. A comparative study of the individual fragments in terms of color, brightness and morphological appearance will be presented. Due to the large field of view of the instrument all fragments could be imaged in one frame. The comparison of the individual fragments relative to each other is therefore not affected by errors due to changing observational conditions. The large spatial scale (approximately equal to 1200 km pixel^-1) on the other hand allows the detailed analysis of the dust distribution around the individual sub- nuclei. The dust distribution around some fragments appears to be elongated slightly towards the direction of Jupiter. Additionally, we obtained long-slit spectrophotometric observations of SL-9 on both dates using EMMI in the dichroic medium dispersion mode (DIMD), which allowed the parallel use of a blue- and a red-sensitive CCD covering a spectral range of 3200 angstrom less than lambda less than 10400 angstrom (3.5 angstrom pixel^-l). The slit was aligned along the cometary train from fragment K to fragment S. The spectra of fragments K, L, P, Q, and S were searched for the CN (0-0) emission band at 3875 angstrom. No CN emission feature was detected for either fragment and we therefore present 3-sigma upper limits on the CN production rates. After the impact Jupiter was imaged on two nights (July 23/24 and 25/26, 1994) with the NTT and the Superb Seeing Imager (SUSI) in six different filters to study the appearance of the impact sites in different spectral ranges. The time difference of two days (approximately 5 Jupiter rotations) between both observational series also allows the investigation of the temporal evolution of the impact sites. 01.35-P Rogers J. H. Jupiter's Visible Clouds Following the Comet Impacts Imaging and visual observations of Jupiter after the comet impacts showed extremely dark spots, which were the darkest features on the planet and in some cases grew larger than the Great Red Spot. The size of each visible 'scar' was roughly in proportion to the reported magnitude of the fireball. The scars always appeared at least as dark near the limb as when fully on the disk. For example, sites H and Q1 were observed coming onto the disk one hour after the impacts, and became darker on subsequent days, with an apparently black core. There were no systematic motions (less than ten degrees per month) relative to the S.S.S. Temperate Current or System III. There was evidence for diverse local motions, viz: increase then decrease in longitude of site E; eastward and westward expansion of site K/W; northward extension of site H. Most sites have lasted over a month, although site A disappeared within 2 weeks. Most sites were beginning to fade after 10-20 days, while grey patches were appearing outside the previous boundaries of some sites. By late August, sites A and C had disappeared, and sites Q1, H, and E were reduced to indistinct condensations on a dusky belt which extended all round the planet at the impact latitude. The three largest complexes -- K/W, L, and D/G/S -- were still very large and dark in late August but had changed shape; dark material had spread for tens of degrees preceding the original boundaries of K/W and L. Before the impacts, five dark patches around 40 deg.S had been tracked in the S.S. Temperate Current. They appear to be part of compensatory changes south of the STB following its revival in 1993. These dark patches remained visible as the impact sites faded. This report is the result of observations by amateur observers in several countries, especially: F. Balella (Italy), M. Bosselaers and colleagues (Belgium), D. Bruton and R. Schmude (USA), R. Bullen (UK), E. Colombo (Italy), P. Devadas and Mrs. Komala (India), M. Foulkes (UK), H. Gross (Germany), C. Hernandez (USA), J. Lancashire (UK), R.J. McKim (USA), H-J. Mettig (Germany), H. Miles (UK), I. Miyazaki (Japan), T. Platt (UK), J. Rogers (UK), G. Teichert (France), D. Troiani (USA), J. Warell (Sweden). 01.36-P Phillips C. B. Mueller B. E. A. Broad-Band CCD Photometry of Jupiter's Impact Scars Observations of Comet P/Shoemaker-Levy 9's impact on Jupiter were made using the 36-inch telescope on Kitt Peak on July 20 and 22 (UT), during the impacts, and on August 3 (UT) as a follow-up night. Images were taken using a Harris UBVRI filter set and a 3.5 magnitude neutral density filter, which was placed directly in front of the filter wheel. The telescope was set to f/13.5 which resulted in a resolution of 0.384"/pixel, and the images clearly show the dark impact scars. Preliminary analysis has resulted in color composites which show both structure within the spots, and changes in color due to the spots' aging between the July and August observation dates, as the August follow-up date was chosen to include the same rotational phase of Jupiter. We are also obtaining relative photometry of the impact scars in relation to Jupiter's Galilean satellites and the undisturbed northern hemisphere of the planet. We hope to trace the brightness evolution of the spots to provide a quantitative counterpart to the qualitative visual spreading of the impact scars during the two weeks spanned by our observations. 01.37-P Moreno F. Molina A. Ortiz J. L. Munoz O. Kidger M. del Rosario J. C. Larson S. Campins H. Consequences of the Comet Shoemaker-Levy 9 Impact on the Jovian Atmosphere from UV to Near-Infrared Imagery The impact sites of the fragments of the comet Shoemaker-Levy 9 in the Jovian atmosphere were studied at UV through near-infrared imagery at various telescopes in Spain. Prior to the impact sequence, systematic observations were obtained in order to get a Jovian atmospheric reference. Methane band imaging at the center of the absorption features of different strengths will help to study the height dependence in the aerosol content and dynamic properties of the stratosphere. Particularly, we present here some preliminary results from CCD images obtained using the 4.2 m William Herschel Telescope at La Palma. These images were obtained during very good sky conditions and sub-arcsec resolution on 16-22nd of July. Low and high resolution (0.34 Angstrom/pixel) spectra were also obtained with the WHT using the ISIS spectrograph. These observations have been made as a part of the Comet Impact Network Experiment. 01.38-P McGhee C. Gierasch P. Goodman J. Hayward T. Moersch J. Nicholson P. Squyres S. Van Cleve J. Matthews K. Neugebauer G. Weinberger A. Orton G. Observations of the Shoemaker-Levy 9 Impacts from Palomar Using the 256 x 256 InSb Camera We observed the effects on the jovian atmosphere of the collision of comet Shoemaker-Levy 9 in July and August 1994, using near-infrared imaging at the Palomar 200-inch with the Caltech near-IR Cassegrain camera. This camera permits imaging through broadband J, H, K, or L' filters, or two narrowband (R = lambda/delta lambda about 70) circular variable filters tunable between 1.5 and 5.2 microns. Our observations focussed on the spatial distribution and temporal evolution of the impact sites, and their near-infrared spectral characteristics. Observations were made from 15-27 July UT and from August 16-19 and 28- 29. On each night after July 21, several complete sequences of broadband and narrowband images at 17 selected wavelengths in the 2.0-2.4 micron and 3.0-4.0 micron regions were obtained. In narrowband images of Jupiter in the strong methane bands at 2.2-2.4 microns and 3.2-3.5 microns the reflected light from the main tropospheric cloud deck is almost competely suppressed, revealing the signatures of the stratospheric hazes. Observations at 2.0-2.35 microns of the increasing strength of the CH4 absorptions provide an altitude estimate of about 10 mb for these hazes. The 2.3 micron images from July 24-25, August 17-19, and August 28-29 have been assembled into mosaics which show the complete distribution of the impact hazes as well as their temporal evolution. The longitudes of nine distinct features, associated with impacts G, R, Q1, H, E, A, C, K and L have been measured in the July data, and found to be consistent (within 3 degrees) with impact site longitudes reported by Ingersoll et al. from HST images. With the exception of R, all features remain identifiable in the August data, albeit considerably altered in shape and size. By late August, sites G, H, and E extended over about 20 degrees in longitude, while Q1, C, K and L retained compact cores. These well-defined features show a mean eastward drift relative to System III of about 13 degrees over 24 days, or 5.5 ms^-1. The more diffuse structures appear to map the zonal wind profile in the middle stratosphere. This work was supported by a grant from the NASA Planetary Astronomy program. 01.39-P Foust J. A. Hammel H. B. Elliot J. L. Meech K. J. Patten B. M. Observations of the Impact of Comet Shoemaker-Levy 9 Using a High-Speed CCD Camera Although the fragments of comet Shoemaker-Levy 9 impacted on the far side of Jupiter as seen from Earth, two phenomena associated with the impact events were postulated to be visible: the impact flash, reflected off an appropriately placed satellite such as Io; and a plume or fireball from the impact site that rises beyond the Jovian limb and into direct view from Earth. Both of these phenomena require observations with high time resolution and accurate timing to provide details on the depth and magnitude of the explosions. We observed the impacts and Jupiter using a high-speed CCD camera mounted on the University of Hawaii Planetary Patrol 0.61-m telescope at Mauna Kea Observatory. This system is capable of taking five or more images per second over a small field and utilizes a Global Positioning Satellite (GPS) receiver to provide accurate timing, making this an ideal system to carry out observations of impact flashes and plumes. Of the four impacts potentially visible from Mauna Kea, weather conditions permitted us to observe two, impacts C and R. High-speed imaging of Io, Europa, and Ganymede during the time of impact C showed no visible change in the R band brightness of the satellites. High-speed imaging of the limb of Jupiter in B band during impact R showed no strong signal for a plume or fireball at visible wavelengths. A more thorough analysis of the observations is being conducted to look for small (order approximately 1%) brightness variations and set upper limits on the brightness of the impact effects at visible wavelengths. 01.40-P Drossart P. Barucci A. Colas F. Crovisier J. Fulchignoni M. Lecacheux J. Roos-Serote M. Roques F. Observations of Jupiter at Pic-du-Midi During the SL9 Impacts Period Observations of Jupiter have been conducted at Pic-du-Midi, first at the 2 meter Bernard Lyot telescope with the spectrometer MU-SICOS, working in the red part of the visible spectrum between 540-880 nm at a spectral resolving power of 38000, second on the 1 meter telescope with the CCD imaging system Astriane, working in the visible and the near infrared (J-H-K filters). The main results are: (1) Several emission lines have been detected on impacts L and Ql in spectra taken on July 19 at 22:42 UT (impact L) and on July 20 at 20:24 UT (impact Ql). The strongest lines are the Na doublet at 589.0 and 589.6 nm . Other detected lines, not present in Jupiter spectra before impacts are due to Li (670.8 nm), K (766.5 nm), Ca (657.3 nm) and H alpha (656.3 nm). These lines are observed in spectra less than 30 min after impact and disappear totally in less than 1 hour after impact. (2) CCD images show the evolution of the impact sites at several time scales. Images in K filter show the complete sequence of the impacts, in particular, impacts H, L and Ql. A flash appears first at the limb, which is observed in all the bands (J-H-K). Then, a bright emission feature appears in filter K, which should correspond to the raise of the plume in the high atmosphere of Jupiter, slowly decreasing. In the long term, the evolution of the dark cloud is followed in various filters in the visible (including interferential methane filter). These images will be reduced to provide the albedo of the dark clouds in standard photometric filters. 01.41-P Gehrels T. Scotti J. V. Spacewatch Observations and Astrometry of P/Shoemaker-Levy 9 Observations were made up to the time of impact, mostly with the Spacewatch Telescope which is the 0.9-m Newtonian Reflector of the Steward Observatory on Kitt Peak. The astrometry was used for the orbit and impact predictions. Size estimates are being updated; ours are smaller than generally used in the modelling. 01.42-P Lambert J. V. Africano J. L. Nishimoto D. L. Nolan R. A. Kervin P. Medrano R. Five Micron Observations of the Comet Shoemaker-Levy 9 Jupiter C, F, and R Impacts from the Air Force Maui Optical Station (AMOS) Near infrared, 4.8 - 5.05 micron, imagery of the C, F, and R fragment impacts of Comet Shoemaker-Levy 9 on Jupiter was collected using the Enhanced Longwave Spectrometer/Imager (ELSI) on the 1.6-meter AMOS telescope at the Air Force Maui Optical Station. The impact sites were visible only after they reached the planet's limb, then faded rapidly, within ten minutes, leaving persistent spots slightly brighter than the surrounding area. These spots appeared to lag the corresponding dark impact spots observed in visible imagery recorded using the 1.2-meter MOTIF telescope by ten to fifteen degrees in rotation. Extensive visible and infrared observations were also made during the periods between observable impacts. Several northern hemisphere spots and other structures not apparent in the pre-impact five micron imagery were observed. Five micron light curves for the impacts and infrared and visible imagery will be presented. A relative intensity light curve for the R-fragment impact is plotted and available in hard copy. 01.43-P Olson K. M. Mumma M. J. Simulations of the Breakup and Dynamical Evolution of Comet Shoemaker/Levy 9 Employing a Swarm Model We investigated the dynamical evolution of a swarm of fragments produced by tidal disruption of the nucleus of comet Shoemaker-Levy 9, for comparison with observed properties of the nuclear train. We take the initial state of Ihe comet nucleus to be a loose agglomeration of macroscopic cometesimals, each bound more strongly internally than to each other. Tidal disruption of the nucleus near perijove then produces an initial swarm of these cometesimals (approximately 10^6 particles), with possibly one sizable core remaining. We performed gravitational N- body simulations of the subsequent dynamical evolution of this initial swarm, and explicitly accounted for collisions between swarm particles, gravitational interactions among them, and interaction with the tidal field of Jupiter. We used an N-body tree code designed for highly parallel computers, and ran a large number of simulations with particle numbers ranging from 16,384 up to 131,072. The volume filling factor of the pre-split nucleus was allowed to vary from 0.001-1.0. We find that the initial swarm is tidally stretched into an elongated structure which grows in length as the simulation proceeds. We also find that in ALL cases the swarm becomes gravitationally unstable and a number of clumps of bodies form. The time at which the instability sets in (relative to periJove), the number of clumps which form, and the nature of the clumps depend on assumptions about the detailed collisional process between bodies. When the pre-split nucleus is optimally packed (filling factor = 1) and the colliding particles are treated as hard spheres, the instability does not set in until 78 hours (approximately 41 Rj) after periJove. When the radius of each body is 0.5 of that in the optimally packed case, and some dissipation is added to the collisions, the initial swarm of particles is very unstable and distinct clumps form very soon after periJove (approximately 9 hrs, approximately 7.6 Rj). We have found no cases to date which were not unstable to some degree at some point in the simulation. In general, we find that a collection of gravitationally and collisionally interacting particles is gravitationally unstable as it passes through the tidal field of Jupiter for a large range of the parameters considered by our model. This tends to support the theory that comet Shoemaker-Levy 9 was initially fragmented into a large number (10^5 - 10^6) of small cometesimals and also has implications for the structure of comets in general. We find it difficult to draw detailed conclusions about the initial state of the comet before breakup owing to the fact that clumps of particles form for a large range of the free parameters of the model. These clumps are similar in number and spacing to the observed 'string of pearls' observed prior to impact with Jupiter. They explain in a simple way virtually all of the observed properties demonstrated by the 'fragments' up to and including disruption in the Jovian stratosphere. This work was supported by the NASA Planetary Astronomy Program RTOP 196-41-54 and by the NASA/ESS HPCC program. 01.44-P Tozzi G. P. Richichi A. Ferrara A. Calamai G. IR Photometric Observations of the Impact of Comet SL9 with Jupiter The impacts of fragments A, H, Q 1, Q2, T, and U of the comet Shoemaker- Levy 9 (1993e) with Jupiter have been observed in the IR with the 2.2m telescope of the Calar Alto Observatory. The sampling rate of the fast photometer was typically 100-500 Hz, thus allowing us to follow with high time resolution the evolution of the phenomena. The filters used were a broad band K (lambda(sub)0 = 2.20 microns, delta lambda = 0.47 micron), and a narrow band ice filter (lambda(sub)0 = 3.12 micron, delta lambda = 0.14 micron). The diaphragm was in all cases 15 arcsec. During impact A, we monitored the luminosity of Europa at K. No evidence of significant variations were revealed, within a dynamic range of 6-7 mag of the satellite's brightness (0.4%-0.1%). During all other events, we monitored directly Jupiter's disk, centering at the expected impact point. While no evidence of enhanced emission was revealed for the T and U impacts, the H and Q impacts gave origin to increases in luminosity which at the peak exceeded the emission of the planet's surface (in our diaphragm) by a factor of approximately 25 - 50. We present the corresponding lightcurves, which extend over about 0.5-1 hr with a (rebinned) resolution of 1 s. It is noteworthy that in both cases a small "precursor" event is seen, at approximately 1-2 minutes after the predicted and measured impact time and about 10 minutes before the actual development of the fireball. It is also interesting to note that while the Q1 fireball was extremely bright, the Q2 fireball apparently did not produce significant emission. Another interesting feature is the presence of a plateau in the decreasing part of the lightcurve, especially pronounced in the case of the H fireball. Comparison with other lightcurves taken at different wavelengths will be shown and possible interpretation will be given. 01.45-P Wiedemann G. Encrenaz Th. Schultz R. Stuewe J. A. Drossart P. Crovisier J. Near-Infrared Spectroscopy of Jupiter at the Time of SL9 Impact Near-IR spectra of Jupiter have been recorded with the IRSPEC imaging spectrometer at the 3.5m NTT (ESO, La Silla), with the 4.4 arcsec slit aligned along the parallel of impacts (latitude l= -44 degrees). After the last impact, spectra were also recorded in the Northern hemisphere at l=+44 degrees (see Schulz et al, this issue). Spectra were recorded around the H2 S(1) quadrupole line at 2.12 microns, and around the 3.533 micron H(sub)^+ line. Most of the impact sites (and later their images at l=+44 degrees) were easily detected at 2.12 microns. Shortly after the impacts, spectra recorded in the 2.107-2.135 micron range with a resolving power of 2000 show a drastic increase of the signal and a change in slope, with a maximum peaking toward shorter wavelengths. The simplest explanation is that there is a very strong scattering over a newly formed stratospheric haze. This strong component sometimes hides the H2 quadrupole line, which is detected when the continuum is low enough. These data are being analysed to derive information about the particle size and the stratospheric temperature at pressure levels of about 0.1-1 microbar. Emission lines of H(sub)3^+ were detected in the 3.501-3.566 micron range, with a resolving power of 1700, over many impact sites. As a general rule, these emissions were stronger over more evolved sites, as compared to the fresh impact sites. In the case of strongest emissions, the multiplet of H(sub)3^+ previously detected in auroral regions was observed, which will allow the determination of both the H(sub)3^+ column density and the stratospheric temperature around 10-100 nanobars. 01.46-P Xie X. Olson K. Mumma M. J. Constraints on the Masses and Sizes of SL9 Fragments We have performed N-body simulations of the infall of the fragments of comet Shoemaker/Levy 9 from apoJove to shortly before impact with Jupiter. These simulations assumed that each fragment is itself composed of a large number of small bodies (the swarm model). It was also assumed that the bodies interact solely through their self gravitational interactions and also with the tidal field of Jupiter. Collisions between the bodies have been ignored for this set of simulations. The swarm of bodies is assumed to be initially in vireal equilibrium at apoJove and then follows an orbit which will bring it into collision with Jupiter. For this study we have varied the swarm mass (10^l3 - 10^l5 gms) as well as its radii (10 -100 km) to determine for what range of these parameters the swarms hold together and would impact the surface of Jupiter as a more or less solid object. The simulations show that for the range of masses considered here and a critical size of approximately 10 km, the swarms remain bound up until a few days before impact. 01.47-P Reitsema H. J. Hubbard W. B. Roques F. Peyrot A. Vignand M. Coordinated Imaging of SL-9 Impact Events: Observations from Les Makes, La Reunion High time resolution photometric observations of impact events and imaging of impact sites were obtained from four globally-distributed distributed sites using similar CCD systems. We report here data obtained from Ile de La Reunion (at latitude -21:11:57, longitude E55:24:35, elevation 995 m) which complete the observing net which also included sites in Hawaii, Chile and Australia. Data were obtained each night from 15 July to 24 July with the 36 cm telescope of the Observatoire des Makes and seven filters covering B, V, R, and two methane bands and corresponding continuum bands. Impact events A, E, H, and S were observed with 0.4-sec time resolution during the impact times, while slower multi-wavelength image sequences were taken during impact events P, Q2, and T. Rapid image sequences of events A, E, and S were obtained in the methane 890 nm filter, while the rapid image sequence of event H was obtained using the B filter. However ongoing analyses of impact events have yet to show any discrete signal from any of these atmospheric entry events. Dark atmospheric disturbances and occasional bright methane features were imaged at impact locations. The poster will display representative images and data. Supported by NASA Grants NAGW-1555 and NAGW-4072. 01.48-P Max C. Gavel D. Johansson E. Bissinger H. An J. Lawrence T. Olivier S. Liu M. Bradford W. Impacts of Comet Shoemaker-Levy: Speckle Imaging in the Visible Using the 3 Meter Telescope at Lick Observatory We performed speckle imaging of the impacts of Comet Shoemaker-Levy 9 with Jupiter at the Lick Observatory 3 meter telescope, from July 19 through 22, 1994. Images were obtained at wavelengths of 0.55, 0.7, and 0.85 microns. Using exposure times of 200 - 300 msec, we are able to obtain high resolution images using a bispectral speckle reconstruction algorithm from 20 to 40 individual speckle frames. We were able to obtain continuous data over periods of 3 to 4 hours for several of the impact points, and have made time-lapse movies following the rotation and evolution of the impact spots. Features such as the dark "eyebrow" and the interior darker region of the impact points are clearly distinguished. In this presentation we shall show both images and videos of our speckle reconstructions, and shall present preliminary conclusions concerning the evolution of impact point structure over periods of hours to days. This research was supported by the US Department of Energy under contract No. E-7405-ENG-48 to the University of California, and by the Institute of Geophysics and Planetary Physics at LLNL. 01.49-P Lopez-Moreno J. J. Rodriguez J. Formisano V. CCD Images of the Shoemaker-Levy 9 Impacts on Jupiter from Sierra Nevada Observatory A continuous coverage with CCD observations has been performed by using the 1.52 telescope of the Sierra Nevada Observatory in Granada, Spain, during the week (16-22 July) of the SL9 impacts. The telescope was equipped with a direct CCD with filters and with a multispectral imaging system (VNIR) covering from 350 to 1005 nm. During this period a daily average of 50 CCD images during the 3 hours of visibility of Jupiter were taken. We have also made observations of the impact regions some days after the collisions (26, 27 and 29 July) in which the remaining of the impacts were still clearly visible. The CCD was equipped with 6 filters covering the visible spectrum from 426 to 829 nm. We present here some results on the evolution of the spot H from its first appearance (H0) in July 18 to its seven passage (H7) on July 21. We present ratio of the images at ammonia (648 nm) and methane (727 nm) bands to the one obtained in the continuum at 635 nm and make estimations of the depth of the features for each appearance. This work was supported by CICYT under grants ESP-93-0338 and ESP-1290- C02-01. SESSION 02 ....... Comet Shoemaker-Levy 9 II Monday, 10:30 - 12:00 Crystal Ballroom Reta Beebe and William B. Hubbard, Moderators 02.01 Noll K. S.* McGrath M. Weaver H. A. Atreya S. Caldwell J. J. Trafton L. Yelle R. Hubble Space Telescope Spectroscopic Observations of Jupiter After the Impact of Comet SL9 Dramatic changes in Jupiter's UV spectrum were recorded with Hubble Space Telescope's (HST) Faint Object Spectrograph (FOS) and High Resolution Spectrograph (HRS) following the impact of fragment G. Darkening at all wavelengths and absorption and emission from a wide variety of molecules and atoms were observed. In particular four different sulfur-containing molecules were identified in quantities that indicate the major source of sulfur is almost certainly Jupiter. This observation provides a constraint on the depth of penetration of the fragments and is also the first observation of sulfur in Jupiter. A ratio of an 18 July FOS spectrum of the G impact site 3 hours after impact to one obtained on 14 July effectively removes the solar spectrum and normal jovian absorptions. The ratio shows strong absorption bands of S2, CS2, and NH3; evidence for H2S is also present in the shape of the absorption near 210 nm. The estimated column abundance of S2, N about l0^l9 cm^-2 corresponds to a mass of sulfur of m similar to 10l4g in our 0.9 arcsec field of view. This lower limit is a significantly greater mass of sulfur than could be present in a l km diameter impactor. The second post-impact FOS spectrum was obtained on 21 July, approximately 30 minutes after the impact of fragment S. In this spectrum we identify all the molecules identified in the 18 July spectrum. In addition we observe strong, narrow emission lines from MgII, MgI, SiI, FeI, and CS. Lower limits for the abundances of the metal atoms are about l part in 10^6 of a l0^14 g impactor, easily consistent with expected abundances of these elements in the impactors. The remaining two FOS spectra obtained in August, on 9 August and 23 August, show an increase in NH3 relative to the CS2 absorption while the S2 is no longer detectable. We searched for Si- and 0- containing molecules in both EIRS and FOS spectra. Derived upper limits indicate that very little of either element is present in gas-phase species after the impacts. This evidence may constrain the initial elemental abundances of the impactor, i.e. SL9 may have been a low-volatile object. This research is supported by grant GO-5624.12-93A from the Space Telescope Science Institute. Significant contributions to this work were made by Paul Feldman, Chris Barnet, Diane Gilmore, Scott Edgington, Ed Smith, and by Alex Storrs, Andy Lubenow, David Taylor, and many others at STScI. 02.02 Yelle R. V. McGrath M. Noll K. Weaver H. Atreya S. Caldwell J. Trafton L. Spectroscopic Constraints on the Evolution of Sulfur-Bearing Molecules in the Jovian Atmosphere Ultraviolet spectroscopic observations of Jupiter's atmosphere subsequent to the impact of comet p/Shoemaker-Levy 9 (SL9) have detected the sulfur-bearing molecules S2, CS2, CS, and H2S. Several observations were carried out with the Hubble Space Telescope Faint Object Spectrograph (FOS) in the region from 170 to 330 nm with a spectral resolution of 0.4 nm. A spectrum from the G impact site obtained on 18 July 1994 has as its most prominent feature a series of absorption bands from 250-300 nm which are clearly due to the S2 (B-X) transition. In the 190-220 nm region this spectrum also contains absorption features due to CS2 as well as absorption features attributed to NH3 and H2S. Spectra obtained under similar viewing conditions on 9 and 24 August 1994 continue to show the NH3, CS2, and H2S absorption features but the S2 absorption is greatly reduced or absent. Spectra acquired from Jupiter's limb on 21 July 1994 show the absorption features mentioned above but also contain emission features due to CS and several metallic species. Noll et al. (this session) will present an overview of FOS results and implications. This presentation will focus on the ramifications of FOS spectroscopy on the post-impact evolution of the sulfur-bearing species. The observed changes in the spectra may be due to spatial inhomgeneities or temporal changes. In this talk we will explore the latter possibility. The S2 bands are the sulfur analogs of the O2 Schumann- Runge band system which plays a critical role in terrestrial atmospheric chemistry. Absorption in these S2 bands leads to production of atomic sulfur, which will react with ambient atmospheric species further altering the composition of the atmosphere. This research is supported by grant GO-5624.12-93A from the Space Telescope Science Institute. Significant contributions to this work were made by Paul Feldman, Chris Barnet, Diane Gilmore, Scott Edgington, and Ed Smith, and by Alex Storrs, Andy Lubenow, David Taylor, and many others at STScI. 02.03 Lellouch E.* Paubert G. Moreno R. Festou M. Bockelee-Morvan D. Colom P. Crovisier J. Encrenaz T. Gautier D. Marten A. Despois D. Strobel D. Millimeter-Wave Observations of the Jupiter/Comet Shoemaker-Levy 9 Collision from IRAM 30-m Telescope: CO, CS, and OCS Millimeter-wave observations of the collision of comet Shoemaker-Levy 9 with Jupiter were conducted at the IRAM 30-m telescope on July 17-28, 1994. These observations led to the detection of emission lines of CO at 230.538 GHz and CS at 244.935 GHz on a number of impact sites (C,E,G,H,K,L,Q+G for CO; K,L,Q+G,W for CS). The typical linewidth (FWHM) is 2 MHz, suggesting a primarily collisional broadening (with a probable contribution due to velocity smearing within the impact sites) and indicating a formation level of about 1 mbar. For a few sites, the lines were monitored over several days, providing information on their temporal evolution. Generally, the lines appear to be weak immediately after impact (0.1-0.2 K antenna temperature contrast), then to increase to reach a maximum (0.5-1 K) one or two days after impact, then to decrease. In particular, on impact site Q+G, the decay of the emissions from July 21 to July 23 and 25 was observed. On July 28, the CO and CS lines were detected in absorption, with perhaps an emission core in the case of CO. All these variations probably result from a combination of variations in (i) the horizontal extent of the sites (ii) the vertical distribution of the molecules and (iii) the temperature profile. We also report the probable detection of OCS at 218.903 GHz on impact site W on July 22, and upper limits on CO^+, CH3OH, HC3N, H2S, SO2, CN, and H2CO. Very preliminary modelling, assuming entire deposition/formation of the molecules near 1 mbar, suggests that the strongest CO and CS lines require approximately 10^14g of CO and 5 x 10^11g of CS. On impact site W, the lines indicate about 1.5 x 10^11g of CS and 1.5 x 10^12g of OCS. The corresponding relative abundances (in volume) for CS:OCS:CO are about 1:7:350. A cometary origin for the O and S seen in CO, CS, and OCS seems therefore plausible at the present stage. 02.04 Encrenaz Th.* Schulz R. Stuewe J. A. Wiedemann G. Drossart P. Crovisier J. Detection of 3.5 Micron CH4 emission at the Time of SL9-H Impact: An Estimate of Rotational Temperatures We have monitored Jupiter in the 3.501-3.566 micron range shortly after the impact of fragment H, using the IRSPEC imaging spectrometer at the 3.5m NTT (ESO, La Silla). The resolving power was 1700; the 4.4 arcsec slit was aligned along the parallel of impacts, and the pixel size along this axis was 2.2 arcsec. Our observations started on July 18, UT 19:46, i.e. 13 mn after the impact, at a rate of 1 image per minute. A very strong emission was detected over the whole spectral range, due to high J-value multiplets of the CH4 nu(sub)3 band (J=14 to J=18). The signal intensity decreased exponentially with a timescale of about 5 minutes, and was detectable for about 30 minutes. At the beginning of the sequence, the CH4 emission extends over about 10 arcsec along the slit. The slope of the emission shows drastic variations over the emission regions, corresponding to a large range of rotational temperatures. Assuming, as a first step, that methane lines are unsaturated, the rotational temperature, in the first image, is estimated to about 700K at the center (emission peak). On the edge (leading side), a different spectrum is observed, with a much weaker intensity, which may indicate different temperature profiles in the center and on the edge. A modeling of these emissions is in progress, which will give important constraints on the temperature profiles at the impact site and around. 02.05 Friedson A. J.* Goguen J. D. Orton G. S. Hoffmann W. F. Dayal A. Deutsch L. K. Wells W. K. Hora J. L. Spitale J. N. Fazio G. G. Thermal Infrared Observations of the Impact of Fragment R at the IRTF The impact of fragment R was observed at thermal infrared wave-lengths of 7.8, 10.3 and 12.2 micrometers from the NASA/Infrared Telescope Facility on July 21 (UT), using the MIRAC2 mid-infrared array camera (Hoffmann et al., Infrared Phys. Technol. 35, 175, 1993). Thermal emission at the three wavelengths was sampled sequentially using a 2% circular variable filter, with an average time interval of 17 seconds between observations at different wavelengths. Continuous imaging of Jupiter in this mode began at 5:08 UT and extended to 5:55 UT. Clear evidence for enhanced emission from the impact region first appears at 5:41 UT, with the peak in fireball emission at all three wavelengths occurring 3.5 minutes later. The excess flux at each wavelength then falls to less than 20% of the peak value over a period of about 4-5 minutes. Results based on preliminary calibrations of the 7.8 and 10.3 micrometer excess flux indicate a source color temperature of 3650 +ll00/-600 K and, on the assumption that the source was optically thick, a solid angle of 1.5 +/- 0.5x1O^-l4 sr (equivalent to that subtended by a sphere about 110 km in diameter) at the time of peak emission. Fifty seconds later, the color temperature has fallen to 2050 +l50/-200 K and the solid angle is 3.2 +/- 0.6x1O^-l4 sr (equivalent spherical diameter about 160 km). Work in progress includes i) refining the absolute calibrations, particularly for the 12.2 micrometer data; ii) including the calibrated 12.2 micrometer data in the analysis to determine whether the excess fluxes follow a black body spectrum; and iii) least-squares fitting a physical model of the fireball to the data as a function of time. 02.06 Livengood T. A.* Bjoraker G. L. Kostiuk T. Romani P. N. Kaufl H. L. Wiedemann G. Ivchenko N. Mosser B. Sauvage M. Thermal-Infrared Imaging of the SL9 Impact Sites Using TIMMI at the European Southern Observatory We present initial results from a successful program of thermal-IR imaging that was conducted as part of the European Southern Observatory SL9 observing campaign using the Thermal-Infrared Multimode Instrument (TIMMI) on the 3.6m telescope, during and following the collision of comet Shoemaker-Levy 9 with Jupiter. We obtained complete or nearly- complete 10 micron light curves during the A and H fragment impacts (3.26-second sampling), and extensive multiwavelength imaging of impact sites after the initial explosive phenomena, with filters at 5, 7.8,10.1,10.65,12.1, and 13.3 microns. Observations extended up to seven nights following the last impacts, with spatial sampling of 0.63 or 0.47 arcsec per pixel on a 64 x 64 pixel detector array. Many impact sites were still discernible as of our last observations, possibly due to either the persistence of non-equilibrium species (e.g., NH3), heating by aerosols in the stratosphere, or simply long radiative time constants for gaseous emission. The impact sites are sufficiently large that their spatial extent is resolved in these images. These observations were conducted jointly with a program of B. Mosser (related abstract, this meeting). TAL acknowledges support as an NRC Research Associate at NASA/GSFC during this work. 02.07 Halthore R.* Bjoraker G. Livengood T. Allen J. Jr. Kostiuk T. Stolovy S. Herter T. Kaufl U. Energy Deposited in the Jovian Stratosphere by the Impacts of Comet Shoemaker-Levy 9 Light curves in the 7.7 micrometer band observed using the Kuiper Echelle Grating Spectrometer (KEGS), for the G and K impact sites of comet Shoemaker-Levy9 on Jupiter show a rapid cooling of the hot core in the stratosphere. As the impact sites become visible over the limb, temperatures of the hot cores derived from the water emission lines are seen to be in the 500 K range (Bjoraker et al., this meeting). The horizontal size of the hot core can be estimated using the methane emission at 7.7 micrometers provided methane abundance is not altered in the hot spot. From the light curves in the methane emission, the temporal evolution of the size and temperature of the hot core are obtained. Results will be compared with those of TIMMI camera (ESO), an imaging instrument that observed the impacts in the 10 micrometer band. TIMMI will allow us to study the long term evolution of the impact sites. 02.08 Bjoraker G. L.* Herter T. Gull G. Stolovy S. Pirger B. Detection of Water in the Fireball of Fragments G and K of Comet Shoemaker-Levy 9 We observed Jupiter on 17-19 July 1994 using the Kuiper Airborne Observatory (KAO) deployed out of Melbourne, Australia. The KAO Echelle Grating Spectrometer uses a Si:As BIB array with 20 spatial and 128 spectral elements at a resolving power of 9000. The principal objectives were to search for H20 emission lines near 22 and 24 micrometers and to measure the stratospheric temperature using CH4 emission lines at 7.7 micrometers. It was necessary to switch between these 3 wavelengths during each flight. At the peak of the fireball for the G and K fragments, the intensity of the CH4 emission lines increased by a factor of 30 from pre-crash levels. Within the 7.67-7 72 micron bandpass, we detected 3 emission lines of H20. The lower state energy levels of these transitions are populated only at high temperatures (about 5OO K). The intensity of the water lines dropped by an order of magnitude in 15 minutes. Spectra at 22 and 24 micrometers were obtained after the peak of each fireball. No dramatic change in either the continuum level or depths of telluric H20 lines were observed. The long wavelength channels are sensitive to the temperature of the upper troposphere and to large amounts of modestly heated water. We conclude that the water came from the impactor, not from Jupiter, based on a combination of KAO and ground-based data. A quantitative estimate of the water abundance will be required before determining whether the impactor was a comet or an asteroid. 02.09 Sprague A. L.* Hunten D. M. Witteborn F. C. Kozlowski R. W. H. Wooden D. H. Bjoraker G. KAO Observations of Jupiter During and Following the Impact of Comet SL-9 Fragments R and W Using HIFOGS (4.9-9.4 and 9.3-14.5 Micrometers) Observations of Jupiter during and following the impacts of two segments of Comet Shoemaker-Levy-9 were made July 21 and July 22 1994 from the Kuiper Airborne Observatory using the High Efficiency Infrared Faint Object Grating Spectrograph (HIFOGS) [1]. An emission peak at 6.6 micrometers identified as H20 is prominent following the R impact and is seen in spectra following W. Line ratios indicate that the water temperature is near 500K. The Q branch of the 7.8 micrometer band of CH4 rapidly rose to 11 times brighter (5^h 45^m) than pre-impact measurements. It decayed by 25% in the next 3 minutes (by 5^h 48^m) following the R impact. A large increase was also seen at these wavelengths following W but the factor is not yet known. Also seen is a large emission increase of acetylene at 13.7 micrometers following both impacts and other, unidentified emissions. The KAO new out of Melbourne, Australia. HIFOGS has cryogenically cooled aperture and filter wheels, grating, and a linear array of 120 Bi-doped Si detectors. To increase the spectral range slightly, and to increase the resolution (decrease the wavelength sampling increment), standard stars and Jupiter were measured at four grating settings spanning wavelengths of 4.9 to 9.4 micrometers and 9.3 to 14.5 micrometers. Residual telluric absorptions are removed by calibrating to spectra of alpha CMa and alpha Cen when possible or by using atmospheric transmissions generated by the HITRAN data base and the NASA Ames ATRAN program. Spectral shape is removed by correcting ratios using alpha CMa which has been well-characterized using the KAO in previous flights. 1. Witteborn F.C. et al. Astro. Soc. Pacific Conf. Series Astro. IR Spec. Conf. 365-372 (1993). 2. Cohen et al. Astro. J. 104, 5, 2030-2044 (1992). 3. Cohen et al. Astro. J. 104, 5, 2045-2052 (1992). 02.10-P Harrington J. Dowling T. E. Hammel H. B. Mills J. R. Hoffmann W. F. Dayal A. Wells K. Sprague A. Hora J. L. Deutsch L. K. Fazio G. G. Baines K. H. Friedson A. J. Orton G. S. Yanamandra-Ficher P. A. IRTF and HST Observations of the Dynamic Response of Jupiter's Atmosphere to the Impact of Comet Shoemaker-Levy 9 We present images of Jupiter to be obtained immediately before and for several weeks after fragments of comet Shoemaker-Levy 9 impact the planet. We report dynamical effects of the impacts on the atmosphere. If sufficient energy is deposited in the atmosphere, the predicted behavior, including inertia-gravity wave excitation and vortex generation, acts as an atmospheric probe that constrains structure and dynamics. Imaging of reflected sunlight with the Hubble Space Telescope (HST) Wide-Field and Planetary Camera 2 (2159, 2553, 3344, 4090, 5407, 8922, 9534 Angstrom) and NASA Infrared Telescope Facility (IRTF) NSFCAM facility camera (1-3 micrometers) probes the upper ammonia cloud level (approximately 150 mbar). Imaging of thermal emission with NSFCAM (4-5 micrometers) and the Arizona/SAO/NRL Mid-Infrared Array Camera (5-20 micrometers) on the IRTF probes the stratosphere and troposphere (approximately 30-500 mbar) with a vertical resolution of 1-2 scale heights. 02.11-P Zahnle K. Mac Low M.-M. More Consequences of the Collision of a Comet and Jupiter The pieces of the former Comet Shoemaker-Levy 9 struck Jupiter during the week of July 16-22 1994. We divide the general impact phenomena into four phases. (1) Atmospheric entry should have been accompanied by an entry flash, probably only detectable by the Galileo spacecraft. (2) Aerodynamic forces cause the impactor to explode. We show that the apparent altitude of the explosions is consistent with the analytical model proposed by Zahnle and Chyba et al, with numerical models calculated by Mac Low and Zahnle and Yabe et al., and with dynamically- based estimates of fragment masses suggested by Scotti and Melosh and Asphaug and Benz. (3) The explosion produces a fireball that propagates most quickly up the wake, as predicted by Takata et al. and Crawford et al. The fireball's luminosity fades over a timescale of 30-60 seconds. (4) Each explosion produced a plume that reached thousands of kilometers above the cloudtops. The plumes appear to have been dusty and so illuminated when they reached sunlight. The plumes rose and fell over a period of ten or twenty minutes, governed by the simple laws of ballistics. When plume material (dust) fell back on the atmosphere it was reheated and glowed brightly in the thermal infrared for a period of order ten to twenty minutes; a large fraction of the impact energy was spent thus. Geometry introduces additional factors that complicate interpretation of the observed light curves. 02.12-P De Jong E. M. Ingersoll A. P. Toigo A. Video Representation of Shoemaker-Levy 9 Impact We present a video animation of the five phases: entry, plume, pressure wave, internal gravity wave, and long-lived vortex following the impact of comet Shoemaker-Levy 9 into Jupiter. The entry phase lasts a few seconds and ends when the bolide has lost its initial kinetic energy. The plume (fireball) phase lasts a few minutes and ends when the ejecta have fallen back and the strong shock waves have dissipated. The pressure wave phase lasts for 1-2 hours and ends when the waves' amplitude drops to unobservable levels. The gravity wave phase lasts for 1-2 days and ends when the wavefronts have been broken up by the zonal winds and the waves' amplitudes have fallen to unobservable levels. The vortex phase may last indefinitely if the vortex can adjust to a stable configuration in the zonal shear flow. We have borrowed heavily from numerous authors and, where necessary, have parameterized their results. The objective in producing the video is educational -- to provide physical insight into the various phenomena and their interrelations in space and time. References: T. Ahrens et al. GRL 21,1087 (1994), J. Harrington et al. Nature 368, 525 (1994), D. Hunten et al. GRL 21, 1091 (1994), A. Ingersoll et al. GRL 21, 1083, (1994), M. Marley Ap. J. Lett. 427, L63 (1994), K. Zahnle and M.-M. Mac Low Icarus 108, 1 (1994) 02.13-P Marley M. S. Dayal A. Deutsch L. K. Fazio G. G. Hoffmann W. F. Hora J. L. Hunten D. M. Sprague A. L. Sykes M. V. Walter C. Wells K. W. A Search for Seismic Waves Launched by the Impact of Comet Shoemaker-Levy/9 The impact and explosion of each fragment of comet Shoemaker-Levy/9 (1993e) into Jupiter's atmosphere was predicted to launch an acoustic "seismic" wave that would probe the interior structure of the planet. We attempted to detect the thermal infrared signature of this wave as it returned to the visible atmosphere after refraction in the interior of Jupiter. To do so the mid-infrared array camera MIRAC2 was deployed on the IRTF to search for perturbations in the 7.8 micrometer CH4 stratospheric emission feature following several impacts. The planned S/N ratio of 100 per pixel in an exposure of 140 sec would have allowed detection of the approximately 0.1K temperature fluctuations expected after impacts exceeding approximately 10^28 erg. Owing to uncooperative weather, the seismic wave search was conducted only in the aftermath of the moderate-sized R impact and technical problems limited the exposure time. Our dataset thus consists of 240 7.85 micrometer images of Jupiter obtained in the 90 minutes after the impact. The seismic wave was expected to appear as a growing ring centered on the impact site during this time period. No such structure is obvious in our current, slightly-processed images. With substantial further reduction and analysis we expect to either detect the wave feature or place an upper limit on its stratospheric temperature amplitude and, ultimately, the impact energy. 02.14-P Lognonne Ph. Billebaud F. Vauglin I. Merlin Ph. Sybille F. Mosser B. Lagage P. O. Gautier D. Drossart P. Seismic Waves Generated by the SL-9 Impact The 10 micron camera from the Observatoire de Lyon was mounted on CFHT between July 21 and July 27 1994. Due to hurricane Emilia, no observations were done July 21, e.g. for the last impacts V and W and only post-impact data were obtained between July 23 and July 27. 5 hours of continuous observations were recorded in the 10.57-12.94 micron filter between July 24 and 27, at a rate of one image every 30 seconds, for a search of trapped pressure waves with period greater than 5.5 minutes, and several images were taken with 4.5-5, 9.16-10.08 microns and CVF filters for a search of slow thermal changes, related either to gravity waves or non-reversible heating of the Jovian atmosphere due to surface waves. The post impact seismic program on CFHT was coordinated with two other telescopes, all using the same type of instrument: TIMMI camera at the 3.6-m telescope at ESO (Chili), and CAMIRAS, from CEA, at the NOT (Canary Islands). The analysis of these data is under progress. Synthetic simulations on the excitation of normal modes and surface wave have shown that the post-impact seismic waves are observable for impacts with energy greater than 10^{21} J. However, the seismic waves are strongly focused at the antipode and a seismic signature at the antipode remains possible for lower impact energies [Lognonne et al., 1994]. If positive, seismic observation will allow the inversion of a profile of seismic velocity. From the amplitude of seismic signals, it will also be possible to give a range for the explosion released by the impact. 02.15-P Collins M. D. McDonald B. E. Kuperman W. A. Siegmann W. L. Jovian Acoustics and Comet Shoemaker-Levy 9 A three-dimensional acoustic model that handles spatially varying acoustic parameters and wind fields has been developed and applied to model global-scale sound propagation from the impact sites of the fragments of Comet Shoemaker-Levy 9. To achieve these modeling capabilities, it was necessary to neglect nonlinear effects. Although nonlinear effects are important near the impact sites, the spatial distribution of compressional wave energy predicted by the linear model should be qualitatively representative. The vertical dependence of the acoustic parameters and the latitudinal dependence of the wind are known from Voyager data. The Jovian atmosphere contains a sound channel, which is a layer of relatively low sound speed that ducts acoustic energy by refraction and contains the cloud layers. Since several of the fragments exploded just above or within the cloud layers, a great deal of acoustic energy was released in the sound channel. The zonal winds consist of cells that blow in opposite directions and act as acoustic waveguides. The acoustic model predicts that energy in the sound channel is pinched into well-defined beams by the zonal winds. The two strongest beams form in wind cells to the east and west of the impact sites and remain well defined at great distances from the impact sites. Since these beams are caused by geometric effects and delimited by acoustic shadow regions, they should be the most prominent acoustic features away from the impact sites. Images from the Hubble Space Telescope show evidence of cylindrical acoustic wave fronts propagating in the sound channel near the impact sites. Processed data might reveal structured wave fronts away from the impact sites. This work was supported by ONR. 02.16-P Maillard J. P. Drossart P. Bezard B. de Bergh C. Lellouch E. Martin A. Caldwell J. Owen T. Atreya S. Waite H. Yelle R. FTS Spectroscopy of the SL9 Impact Sites on Jupiter The collision of comet Shoemaker-Levy 1993e with Jupiter has been observed with the Fourier Transform Spectrometer at the CFHT. A 2.5- arcsec aperture (corresponding to 8000 km on Jupiter) has been selected, and the impact sites were observed by offset guiding on a galilean satellite. The goal of the observations was a search for modifications of the jovian composition after the impacts, at tropospheric and stratospheric levels. As a priority, the 4.7-micron window was observed to search for modifications of CO, with a resolution up to 0.1 cm^-l. In the same spectral range signatures from PH3 and CH3D are also present. Impact sites B, C, F, G and L were observed in this spectral range, showing increased cloud opacity but no dramatic changes in the spectral absorptions. Two fragments (C and R) were monitored at the time of the impact, directly observable from Hawaii, in a 3.3-micron filter covering the 2850-3020 cm^-l range, with a resolution up to 0.19 cm^-l. This region is dominated by the R-branch of the nu(sub)3 band of methane which blocks all the solar reflected light in normal jovian spectra. For both impacts an emission peak appeared at 3000 cm^-1 with further structures between 2860 and 2950 cm^-1, lasting less than 20 min. Preliminary simulations with a 500-K temperature profile down to the 10- micronbar level and normal below, indicate that these structures could possibly be due to methane emission. Additional observations were made in the 2.2-micron window on fresh impact sites (G and H) allowing the detection of a haze continuum and of the pressure-induced spectrum of H2. 02.17-P Korsun P. P. Sizonenko Yu. V. High-resolution Spectra of the Satellite Reflections During the Comet Shoemaker-Levy 9 Impacts on Jupiter Long-slit CCD spectra of Jupiter were obtained with the 2.6-m telescope of Crimean Astrophysical Observatory, ZTSh, on 19-22 July, 1994. One set of the observations was carried out at Nasmith focus and the wavelength region covered 4600-10,250 angstroms at a resolution of 4.5 angstroms. The other one was carried out at coude focus and the spectra extended over various parts of the same spectral region at a resolution ranging from 0.2 to 0.8 angstroms. The spectrometer slit was aligned along the parallel of the impact to provide a spatial analysis in this direction. Combined investigations of Nasmith spectra, both the spatial profiles for different spectral regions and extracted spectra for different sites of the crash latitude, show that the impact spots have some spectral peculiarities. The main results of our investigations we can summarize as All impact sites have low albedo with respect to undisturbed surface of Jupiter in at least 4600-8000 angstroms wavelength region. No obvious changes in the spots spectra shape are apparent, except for 4600-5700 angstroms region where albedo of the spots slightly increase to the blue. Observed spots showed considerably less methane absorption in the 8900- angstrom band. Such effect was somewhat lower in the 1-micrometer CH(sub)4 band from the H and D+G+S+R sites spectra and no detected in the other observed methane bands. We are grateful to R. E. Hershberg, Yu. F. Mal'kov, and V. I. Pronik (CrAO) for their support and assistance in our observations. 02.18-P Wannier P. G. Spilker T. R. Submillimeter Observations of the SL-9 Impact from KAO We will use a heterodyne submillimeter radio receiver on NASA's Kuiper Airborne Observatory to measure the abundance and vertical distribution of water in the Jovian stratosphere immediately following the collision of comet Shoemaker-Levy. Our specific target is the 548 GHz line of ^18O water, minimizing interference by terrestrial water. The Jovian stratosphere is normally dry but water vapor, once introduced, will persist for relatively long periods, possibly years. Water may be injected by the fireball following a deep penetration, or by sublimation of cometary ice. After injection, lateral stratospheric circulation should distribute the water over the planetary disk within a few days. The heterodyne technique yields very high resolution (upsilon/delta upsilon approximately equal to 10^6) spectra that can be used to infer both depths of the observed water, from pressure broadening, and longitudinal distributions, from timing and Doppler shifts. 02.19-P Orton G. Baines K. Friedson J. Goguen J. Yanamandra-Fisher P. A'Hearn M. Esterle P. Lisse C. Weaver H. Wellnitz D. Hoffmann W. Hunten D. Dayal A. Sprague A. Sykes M. Wells K. Marley M. Fazio G. Deutsch L. Hora J. Jewitt D. Joseph R. Deming D. Kostiuk T. Bjoraker G. Fast K. Livengood T. Zipoy D. Griffith C. Dowling T. The NASA/IRTF SL9 Observing Campaign The NASA Infrared Telescope Facility campaign (July 12 - August 7, 1994, supplemented by later observations) used near- and middle-infrared cameras NSFCAM and MIRAC2, near- and middle-infrared spectrometers CSHELL and IRSHELL, and the Goddard heterodyne spectrometer in several investigations. (1) Fragment K was observed an hour before its impact. (2) The impact fireballs were investigated from fragments C (2.248 microns), G (2.295 and 4.780 microns) and R (7.85, 10.30 and 12.20 microns). (3) Particulates high in the stratosphere at impact lasted for many weeks. (4) Temperatures were perturbed between 10 and 400 mbar pressure. (5) The temperature field was searched for seismic waves, and both the temperature and cloud field were searched for inertia-gravity waves. (6) The north polar H(sub)3^+ aurora brightened after the impacts; the stratospheric hot spot was suppressed during the impacts. (7) NH3 was transported into the stratosphere, C2H4 and C2H6 abundances was enhanced, and tropospheric PH3 was depleted. (8) Little influence of the increased dust environment on Jupiter's ring was detected in the near infrared. 02.20-P Smythe W. D. Carlson R. W. Weissman P. R. Hui J. Segura M. E. Baines K. H. Matson D. L. Johnson T. V. Leader F. E. Taylor F. W. Encrenaz T. Drossart P. Galileo Infrared Observations of the Shoemaker/Levy-9 Impacts of Jupiter A direct view of the impact sites of the comet fragments from the Galileo spacecraft allows a study of the fireball expected to occur during the first minutes following each impact. Predicted temperatures of a few thousand degrees place the spectral emission within the wavelength range (0.7 to 5.2 microns) of the Near Infrared Mapping Spectrometer, which will observe several of the events in seventeen wavelength bands. The spectral bands chosen exhibit differing gas opacities and allow sounding at various depths in the atmosphere. These spectral positions include the Jovian spectral windows (e.g. 2.7 and 5 micron windows and shorter wavelength continuum regions) and a band for H(sub)3^+ emission. To ensure observation of the impacts, given spacecraft pointing errors, the scan platform will dither across Jupiter with a 5 second period. Data will be recorded for 64 minutes for 4 impacts, although only a portion of these data will be selected for playback. Initial pecks at the data for the G and R impacts show that the scan platform and the NIMS instrument operated correctly. Normal Jupiter spectra were obtained. Approximately the first 3 minutes of the G impact spectra are expected to be available in time for the DPS meeting. Preliminary results of the spectral properties and time development of an observed fireball will be presented. 02.21-P Kim S. Dumas C. Orton G. Brooke T. Spencer J. Spectroscopic Study of the SL9 Impact Areas of Jupiter with the CTIO IRS We obtained spectra of Jupiter's atmosphere in the 3 - 5 micron region with the newly modified Infrared Spectrometer (IRS) on the 1.5-m telescope at the Cerro Tololo Inter-American Observatory (CTIO) between July 16 and 25, 1994 (UT), during and after the impacts of fragments of comet Shoemaker-Levy 9. Analyzing the spectra of the impact sites, we have found the following: (1) The upsilon(sub)3 band of CH4 has been shown in emission on the major impact areas; (2) The spectral characteristics of the impact clouds are very similar to that of the usual polar haze. The polar haze is dark in UV and visible ranges, and bright in methane bands in the visible range. The polar haze is bright between 1.5 and 4 microns, wherever CH4 absorption is strong. The reason why the impact areas are bright in the CH4 bands is that the impact cloud altitude is high (approximately 1 mbar as we reported previously. See DePoy et al., this conference), so that there is less CH4 absorption above the impact clouds than above the normal cloud layers; (3) We found brighter global H(sub)3^+ emissions than the normal condition. In contrast, we found no significant increase in the H(sub)3^+ emissions at the major impact sites, and frequently we did not detect H(sub)3^+ emissions finding only CH4 upsilon(sub)3 band emissions at the major impact sites. We are now investigating the following possible phenomena: ( 1 ) CH4 upsilon(sub)3 band emissions at other latitudes, (2) altered vertical and hortzontal distributions of atmospheric molecules, haze particles, and cloud levels; (3) the presence of new molecules and comparisons with model calculations; and (4) vertical mixing ratios and temperatures of tropospheric molecules to determine whether fragment penetration is deep enough to cause tropospheric mixing. As a part of a network of internationally coordinated observations, including other near-infrared spectroscopic obsetvations in the U.S. southwest, Hawaii and Australia we are comparing our observations with other observers' results to shape a unified scenario of the impacts. 02.22-P Dinelli B. Miller S. Achilleos N. Lam H. Tennyson J. Jagod M.-F. Oka T. Geballe T. Brooke T. Ballester G. Trafton L. Infrared Spectroscopic Studies of the Impacts of Fragments B and C of Comet Shoemaker Levy-9 The effects of the Fragment B and C impacts of SL9 on Jupiter were monitored at wavelengths around 3.5 microns, sensitive to ionospheric H(sub)3^+ emission, using the CGS4 long-slit spectrometer on UKIRT. Data obtained prior to the impacts, with the slit aligned east-east along the S45 region, showed that emission from the western region of the planet was somewhat stronger than that from the east. But this pattern was reversed with the approach and impact of Fragment B, even though this fragment made hardly any impact deeper into Jupiter's atmosphere. The Fragment C impact gave rise to emission due to high-J lines of methane (principally P(18) and P(l9) of upsilon(sub)3), at intensities which were at least two orders of magnitude greater than the ambient ionospheric H(sub)3^+ emission. The most intense H(sub)3^+ line (upsilon(sub)2 R(3,3)) in our spectra also appeared to brighten by this amount. But, since the CH4/contiupsiloupsilonm emission swamped the weaker lines we were monitoring, we cannot be sure that all this intensity is due to H(sub)3^+. Initial fitting of CH4 lines to our spectra suggests that temperatures in the plume some 15 miupsilontes after nominal impact were around 1300K, falling to about half this during the next 40 miupsilontes. But CH4 fits the spectra we obtained poorly, indicating that other -- thus far unidentified -- species may be important. 02.23-P Crawford D. A. Boslough M. B. Robinson A. C. Trucano T. G. Numerical Simulations of Fireball Growth and Material Motion During Comet Shoemaker-Levy 9 Impact on Jupiter The CTH shock-physlcs code ls used to study two- and three-dimenslonal representations of the impacts of Comet Shoemaker-Levy 9 on Jupiter. The simulations are divided into two closely linked parts. The first part consists of two- and three-dimensional simulations of entry, deformation and breakup of the cometary fragments. Realistic material models incorporating melting, vaporization, dissociation and ionization of the comet fragments and Jovian atmosphere are used. The comet fragments are modeled as 1-, 2- and 3-km spheres of fully dense (0.95 g/cc) and porous (0.3 g/cc) water ice, porous silicate (1.0 g/cc) and distended clouds of unbound water and silicate fragments (average density 0.01-0.2 g/cc). Depth of penetration and energy deposition per unit altitude are tabulated for comparison with other models. The second part of the simulation takes, as its input, material location, velocity, pressure,,temperature and density from re-entry, deformation and breakup studies. These are mapped into a three- dimensional computational mesh for rendition of fireball growth and evolution. Lagrangian tracer particles track the motion of cometary debris and Jovian atmospheric constituents. At 120 seconds after the impact of a fully dense 3-km cometary ice fragment (M = 1.4 x 10^16 g), the total mass of the resulting fireball above the 1-bar level is 6.8 X 10^l6 g (4.9M) with 0.2% (1.5 x 10^14 g, 0.01M) of the fireball as impactor material. At this time, 4.4 x 10^l6 g (3.1M) of atmosphere has been uplifted above the l-bar level from below the tops of the Jovian water clouds. Assuming a 10^-3 relative abundance of water in the water clouds, our simulation shows that approximately 4 x 10^13 g of water (0.003M) has been entrained in the lower portion of the fireball. Dependence of material motion over the range of fragment models described above will be discussed. This work is supported by the National Science Foundation under Agreement No. 9322118 and performed at Sandia National Laboratories supported by the U.S. Department of Energy under contract DE-AC04- 94AL85000. 02.24-P Biraud Y. G. Cuisenier M. Marten A. Rosenqvist J. Moreau D. Muller C. Balega I. Chuntonov G. Maslov I. Near Infrared Photometric Observations of the Comet SL9-Jupiter Collision at the Zelenchuk Observatory Near infrared observations of the comet impacts with Jupiter have been performed at the SAO 6-m telescope (Zelenchuk/Caucasus) using a Fourier spectrometer. Because of an unpredictable technical problem, the observations were limited to spectro-photometry between 3.3 and 4.2 microns with a resolving power around 300. Observations were performed on July 17, 19, 22, and 27, consisting of a total integration time of 3 hours. The K and W impacts were mainly monitored. Preliminary results did not show any obvious variability of the 3-4 microns low resolution Jovian spectra but a more detailed investigation of these data will be reported in order to determine possible _small_ variations of the Jupiter'continuum. In addition to infrared spectra, CCD cameras provided visible information on the location, shape, and size of the impacts. After filtering and digitization, a spatial resolution of 0.4 arcsecond could be attained. 02.25-T Trafton L. M. Atreya S. K. Noll K. S. McGrath M. A. Weaver H. F. Caldwell J. J. Yelle R. V. Comet SL9-Jupiter Impact Events: HST Search for Enhanced Stratospheric CO and H2S During the SL9-Jupiter impact events, HST will obtain exploratory spectra of the impact sites. One objective is to detect and measure cometary and photochemically enhanced CO and H(sub)2S in Jupiter's stratosphere. This will be attempted using the GHRS to obtain spectra of the 4th Positive bands of CO in emission and the FOS to get spectra of the H2S absorption bands from 2000 - 2700 Angstrom. The potential enhancement of CO from these sources is significant and diagnostic of the cometary CO + H20 content, and of the photochemistry between the Jovian hydrocarbons and uplifted Jovian H20. The H2S is diagnostic of the cometary sulfur abundance, and possibly of the reservoir of Jovian sulfur. SESSION 03 ....... Comet Shoemaker-Levy 9 III Monday, 1:30 - 3:30 Crystal Ballroom A Cindy C. Cunningham and Glenn Orton, Moderators 03.01 Mac Low M.-M.* Zahnle K. Comparison Between Observations and Numerical Models of the Impact of Comet Shoemaker-Levy 9 on Jupiter We present our latest numerical models of the impact of comet Shoemaker-Levy 9 on Jupiter and compare to the observations. We use the astrophysical gas dynamics code ZEUS to model the initial entry, explosion, and plume development for a period of 10 minutes after impact of each fragment. We show that if the incoming fragments had diameters of order 0.5 km as suggested by Asphaug & Benz, we can give a consistent model of the observations. Our entry models show that these small fragments explode in the ammonia cloud layer, explaining the observations of ammonia but no water. Published models predicting deeper penetration were flawed by inadequate resolution. The light curves from the resulting 10^27 erg explosions are as dim as observed by Galileo. Finally, our plume models show that these explosions are still large enough to spread cometary material over distances of 10,000 km in the upper stratosphere, as observed. This work was supported by the NSF through grant AST 93-22509, and by NASA through grant NAGW-2379. Computations were perfomed at the Pittsburgh Supercomputing Center. 03.02 Gurwell M. A.* Muhleman D. O. Philips J. A. Grossman A. W. Millimeter Imaging of the Comet P/Shoemaker-Levy 9 Impacts on Jupiter Observations were made during each transit of Jupiter during the impact events of comet SL9 using the OVRO millimeter interferometer (located near Big Pine, CA). The data were taken in the 3.0 mm continuum (July 16, 17, 22, 23) and the 3.38 mm continuum (July 18-21). The latter observations include spectral correlator data centered on the HCN(1-0) transition. These OVRO observations are part of a larger effort to measure the microwave response of Jupiter to the impacts, and include observations taken at the BIMA millimeter interferometer and the Very Large Array. The main source of opacity at millimeter wavelengths is gaseous ammonia, with the weighting function peaking near 0.8 bars. Pre-impact modeling had suggested that the fragments of SL9 would penetrate to well below this level. This penetration would perturb the vertical ammonia distribution at and near the impact site, affecting the millimeter brightness temperature in spatially localized regions on Jupiter. We are currently in the midst of the arduous reduction of this large dataset, but at this point we see no obvious effects of the cometary impacts in maps of the continuum brightness temperature. Our current maps are of poor SNR, due to rapid phase fluctuations of the Earth's atmosphere; however, we will soon be able to correct this substantially in the dataset. This will allow us to construct much improved maps of the continuum of Jupiter, increasing our sensitivity to more subtle effects that the comets may have had. If our current results stand, the lack of discernable variation in the continuum brightness temperature has important implications for the depth to which the fragments penetrated, on the size of the perturbed regions in the atmosphere at that depth, and on the structure of the impacting bodies themselves. In addition, using the spectral correlator data we will set at least an upper limit for HCN in the stratosphere. 03.03 Owen T.* Griffin M. J. Marten A. Matthews H. E. Naylor D. A. Davis G. R. Han B. Bockelee-Morvan D. Colom P. Crovisier J. Gautier D. Lellouch E. Strobel D. Orton G. de Pater I. Sanders D. Atreya S. JCMT Observations of the Collision of Comet Shoemaker-Levy 9 with Jupiter Using heterodyne techniques, we observed Jupiter with the JCMT at frequencies corresponding to lines of HCN, H2CO and CO. We tracked seven different impact locations during the entire period of the collision of the comet. A beam-switching procedure was adopted and we checked that no emission feature was present at the symmetric northern position. We will report on the detection of HCN emission lines at the impact sites visible from Earth during our observing run. The first detection was that of fragment C on July 17 UT only one hour after impact. On the following days, we succeeded in observing similar narrow lines of HCN at the impact locations F, G, H, A, P2 and R. At the end of our observations, impact sites had accumulated to such an extent that several of them were usually contained within our 14" or 21" beam, at 354 and 267 GHz, respectively. We will present a time history of the emitting regions from a careful analysis of the recorded spectra of the HCN lines as well as of the other lines we observed. Despite the poor weather conditions, our JCMT observations are the only submillimeter detections of HCN during the SL9-Jupiter collision. 03.04 Kostiuk T.* Fast K. E. Zipoy D. Bjoraker G. L. Buhl D. Espenak F. Romani P. N. Livengood T. A. Goldstein J. J. Very High-Resolution Spectroscopy of the Jovian Stratosphere in the Wake of the SL9 Impacts We will present results from very high spectral resolution (lambda/delta lambda approximately equal to 10^6) studies of molecular emission from Jupiter's stratosphere at the latitude of the SL9 fragment impacts. Observations were conducted just following the impact period (23 July UT) and several days after the impacts (26 and 29 July UT), to study the chemical and thermal alteration of Jupiter's stratosphere and the reestablishment of equilibrium after the impacts. Measurements were made with the Goddard Infrared Heterodyne Spectrometer (IRHS) at the Coude focus of the NASA IRTF. Selected spectral intervals were investigated near 11 micrometers, which include individual rovibrational lines of H20 and NH3, two non-equilibrium species that may be injected into the stratosphere, as well as emission lines of the equilibrium-state species C2H6. No significant H20 lines were observed. Ammonia emission lines were identified and abundances determined from the precise transition frequencies and true lineshapes measured at this resolution. From the linewidth it was determined that NH3 was present at pressures less than 10 mbar in the stratosphere near the Q and K impact sites at least 7 days after the last impact. Emission lines of C2H6 were also measured and showed no significant enhancement, implying no apparent simple temperature increase in the stratosphere after a few days. Interpretation of these results regarding NH3 abundance distribution, lifetime, and Jovian stratospheric temperature will be discussed. 03.05 Orton G.* Friedson J. Yanamandra-Fisher P. Baines K. Hoffmann W. Dayal A. Deutsch L. Fazio G. Hora J. Hammel H. Harrington J. Jovian Atmospheric Structure Investigation in the NASA IRTF SL9 Campaign We explored changes in Jupiter's atmospheric structure due to comet gragments by imaging the planet between 5 and 21 micrometers using the Mid-Infrared Array Camera (MIRAC2) in the NASA Infrared Telescope Facility SL9 campaign. Assuming uniform mixing of both CH4 and H2 at the impact sites several minutes after impacts, we derived temperatures near the 10-mbar region of the stratosphere via CH4 emission at 7.85 microns and between 100 and 400 mbar in the troposphere via the collision-induced absorption of H2 at 13.00, 17.2, 17.8 and 20.8 microns. We find stratospheric warming by as much as 4 K at sites sampled within 30 hours of impact. However, the time scale for cooling is on the order of days - much shorter than expected from radiative cooling. Similar observations in the troposphere showed warming by as much as 4 K at 100 mbar and 1.5 K at 400 mbar. The 400-mbar temperature perturbations also disappear on a time scale of days, but the largest 100-mbar perturbations cool to roughly half their initial amplitude in 18 days. There are also major differences in the amplitude of the perturbations associated with the various impact sites. For example, the E impact site had barely any detectable perturbation of 100-mbar temperatures. We also mapped cloud pertubations at 5.00 and 8.57 microns and mapped NH3 gas variability near 10.57 microns. We found little evidence for perturbations of the 600-mbar NH3 cloud or deeper clouds. On the other hand, most impact sites had strong 10.74-micron emission arising from NH3 gas transported into the stratosphere, forming the most persistent thermal infrared signature at the impact sites. 03.06 Griffith C. A.* Orton G. Noll K. Kelly D. Lacy J. Zahnle K. Bezard B. Mid-IR Spectroscopy and Ammonia Images of K Impact Site We have observed the SL9 comet's crash into Jupiter at the NASA Infrared Telescope Facility (Mauna Kea, Hawaii), with the U. Texas mid-infrared echelle spectrometer IRSHELL. This spectrometer was used at a spatial resolution of 1 arcsec and a spectral resolution of approximately 15000. We detected ammonia emission at wavelengths of 908 and 945 cm^-l over the K impact site at several times after impact; 10 hours, 5 days and 10 days later. The emission observed within a week of impact can be most easily simulated by an NH3 mixing ratio of 4.3 x 10^-8, which is constant in altitude above the tropopause and equal to the value at the tropopause. For the quiescent atmosphere, the NH3 abundance falls off rapidly with altitude in the stratosphere as a result of photochemical destruction. This situation is consistent with a scenario in which the impactor penetrated at least as deep as the tropopause. The ammonia rose following the hot gas of the explosion into the the stratosphere, where we have detected its presence. The emission decreases over a week timescale, consistent with depletion of NH3 from photolysis and diffusion. Emission from C2H4 was also observed, consistent with a mixing ratio of about 5 x 10^-9. We searched for evidence of H2S and HCN several hours after the K impact and found no signature of these molecules. 03.07 Brooke T. Y.* Orton G. S. Crisp D. Friedson A. J. Bjoraker G. Near-Infrared Spectroscopy of the Shoemaker-Levy 9 Impact Sites with UKIRT: CO, NH3, and Haze Layers Spectra of impact sites in select regions in the 3-5 micrometer range were obtained with the CGS4 spectrometer at the United Kingdom Infrared Telescope atop Mauna Kea, Hawaii on July 19, 20, 26, 28 UT 1994, generally long after actual impact. These are being used to determine the depth of impact effects in Jupiter's atmosphere. The spectral resolution was 1.5 x 10^4 with the echelle grating, and 10^3 in low resolution. The slit was approximately aligned with the impact latitudes. CO: Echelle spectra of several impact sites were obtained in absorption lines of CO near 4.7 micrometers. The effects on the CO line depths are still being assessed but were not large. However, CO emission was detected at the L site on Jul 20 at 2:20 UT, over 4 hours after impact. NH(sub)3: Echelle spectra of the K/W impact sites were obtained in a little studied region: the NH(sub)3 nu(sub)1 Q-branch at 3.0 micrometers on Jul 28 at 5:00 UT. The sites were brighter in reflected sunlight than adjacent regions. Different absorption depth changes in the NH(sub)3 Q-branch compared to lines of other molecules are seen. The spectra will provide unique new estimates of the effective height of the haze layer and the NH(sub)3 abundance. Haze layers: Low resolution spectra of the E, H, and G impact sites at 3.3 micrometers were obtained on Jul 19 at 8:10 UT. Although bright against Jupiter's CH4 absorption, the actual reflectivities are low, approximately a few percent. 03.08 Nicholson P. D.* Gierasch P. Goodman J. Hayward T. McGhee C. Moersch J. Squyres S. Van Cleve J. Matthews K. Neugebauer G. Weinberger A. Bjoraker G. Conrath B. Orton G. Principal Results from Palomar Observations of the Shoemaker-Levy 9 Impacts Observations of the impacts of the SL-9 fragments on Jupiter were carried out with the 5-meter Hale telescope at Palomar Observatory using two instruments: the near-IR Cassegrain InSb camera (lambda 2 - 4 microns) and SpectroCam-10, a mid-IR imaging spectrometer (lambda 5 - 18 microns). Dual-wavelength lightcurves at 3.5 microns and approximately 4.6 microns were obtained for the R impact on 21 July under good conditions, interspersed with periodic lambda 8 - 14 micron spectra. A faint signal of approximately 30 sec duration was detected at 2.3 microns (but not at 4.6 microns) at the expected time of the V impact. No detectable signal was seen from the B or U impact. The near-IR camera was also used to monitor the reflectivity spectra and temporal evolution of the stratospheric aerosol clouds resulting from the impacts. Spectra at 2.0 - 2.35 microns clearly show the signature of methane but not molecular hydrogen, and suggest an effective aerosol pressure level of approximately 10 mb. Follow-up observations on 16-19 August show that the brighter impact sites remained distinct, but had drifted 12-15 degrees eastward relative to System III, suggesting a mean wind speed of 5 ms^-1 at this altitude and -44 degrees planetocentric latitude. SpectroCam-10 was used in three modes: narrowband imaging at 7.9, 8.8 and 10.3 microns to monitor the spatial extent and evolution of the impact-heated regions in the upper troposphere and stratosphere; low-resolution (lambda/delta lambda = 100) long-slit spectroscopy to map the perturbed regions at 8-14 microns; and high-resolution (lambda/delta lambda = 2000) spectroscopy at selected wavelengths for thermal retrievals and to probe the vertical distribution of CH4, NH3, and PH3. We will present an overview of the principal results from these observations. Detailed results and catalogs of the data are presented in companion papers by Gierasch et al., Hayward et al., and McGhee et al. This research was supported by a grant from the NASA Planetary Astronomy Program. 03.09 Gierasch P.* Goodman J. Hayward T. McGhee C. Moersch J. Nicholson P. Squyres S. Van Cleve J. Matthews K. Neugebauer G. Bjoraker G. Conrath B. Orton G. A Physical Interpretation of the SL-9 Impacts Observed from Palomar Post-impact 8 to 14 micron spectra and images of SL-9 impact sites and the neighboring regions, obtained with SpectroCam-10 on the Hale telescope, are used to infer atmospheric properties. Temperature in the middle stratosphere and in the middle troposphere is deduced from spectral bands near 8 and 12 microns sensitive to methane and hydrogen opacity. The vertical distribution of ammonia and phosphine is deduced from spectral regions near 10 microns. Aerosol opacity at 8 microns and longer wavelengths does not noticeably differ between impact sites and neighboring regions. A few days after impacts, over areas on the order of 2000 km in diameter centered on impact sites, the stratospheric temperatures are elevated, tropospheric ammonia is depleted, and ammonia and phosphine appear in the stratosphere at concentrations more than two orders of magnitude above their usual values. From near infrared imaging data, obtained with the Cal Tech Near Infrared Cassegrain Camera on the same telescope, we find that aerosols visible at wavelengths near 2.3 microns are at a pressure level of approximately 10 mb. 03.10 Ingersoll A. P.* Kanamori H. Waves from the Shoemaker-Levy 9 Impacts on Jupiter Press release images (1,2,3,4) from the Hubble Space Telescope (HST) reveal narrow circular rings around the G impact site. The rings' circular shape and outward expansion implies that they are waves. Contrast is produced by stratospheric particles that appear bright in a methane filter. Here, following Kanamori (5) and Ingersoll et al. (6), we compute the properties of waves generated by explosions at various depths in Jupiter' s atmosphere. The observable properties are group velocity, pulse width, and amplitude in the stratosphere. Explosions near the tropopause mainly excite acoustic waves trapped in the sound channel at the temperature minimum. Deeper explosions mainly excite gravity waves trapped in the stable layer near the water cloud (6). Both waves have narrow pulse width, but the acoustic wave travels several times faster than the gravity wave. Untrapped waves (7) have lower amplitude and broader pulse width. The most prominent ring in the HST images matches the speed of the trappped acoustic wave, while the less prominent ring matches the speed of the trapped gravity wave. The relative amplitude of the two waves suggests that the impacts did not reach the Jovian water cloud. 1. Chapman, C.R. Nature, 370, 245 (1994). 2. Cowen, R. Science News, 146, 68 (1994). 3. Kerr, R.A. Science, 265, 601 (1994). 4. Wakefield, J. EOS, 75, 337 (1994). 5. Kanamori, H. Geophys. Res. Lett., 20, 2921 (1993). 6. Ingersoll, A.P. et al. Geophys. Res. Lett., 21, 1083 (1994). 7. Harrington, J. et al. Nature, 368, 525 (1994). 03.11 Mosser B.* Sauvage M. Lagage P. O. Lognonne Ph. Gautier D. Drossart P. Livengood T. Kaufl H. U. Billebaud F. Marley M. Belmonte J. A. Roca-Cortes T. Seismological Consequences of the SL 9 Comet Impact Thermal images of the Jovian disk have been recorded with the TIMMI infrared camera based at the 3.6-m telescope at ESO (Chile), in order to monitor the thermal fluctuations due to the seismic waves excited by the comet impact (Lognonne et al. 1994). Data analysis of impacts A, B, F and H is under progress (B has not been detected, and F only marginally). During the 2 hours following each impact, a quasi- continuous series of images has been recorded at the rate of about 1 image each 3 seconds. A broad band filter [9-->10.4 micrometer] has been used, sensitive to the tropospheric levels around the 0.5 bar level. About 10,000 images of the full disk of Jupiter have been recorded without nodding, in order to obtain the high acquisition frequency required for the observation of the high frequency primary waves excited by the impact. The detection of the arrival times of these waves will be possible for all impacts greater than 10^20 degrees J (Lognonne et al. 1994). The resulting hodograms will permit to infer the sound speed profile in the planetary fluid envelope. Twenty hours observations have been recorded in the 6 days following the impact period, in order to search for pressure modes (resonant waves with periods greater than 5.5 minutes). The nodding technique has been used, with an acquisition rate of about 1 image per minute. The data will be mixed with the ones obtained in slmilar conditions at the NOT with the CAMIRAS camera developed by the Service d'Astrophysique (Saclay) and at the CFHT with the C10 micrometer camera developed in the Observatoire de Lyon. The combination of the 3 different sets of data gives 40 hours observations, and is necessary to reduce the window effect. Data reduction will be similar to the one commonly used in helioseismology. The seismological observations may provide the first measurement of the density profile through the whole planetary interior, and could permit to discriminate between the poorly constrained current interior models of the planet. 03.12 Lagage P. O.* Galdemard Ph. Jouan R. Masse P. Pantin E. Sauvage M. Olofsson G. Huldtgren M. Belmonte J. A. Regulo C. Roca Cortes T. Rodriguez Espinosa J. M. Selby M. Vidal L. Mosser B. Gautier D. 10 Micrometer Observations of SL9 Impacts with CAMIRAS at NOT From July 15th to July 27th, Jupiter was imaged with CAMIRAS, the Saclay mid-IR camera, mounted on the 2.5m Nordic Optical Telescope (La Palma island). The 10-13 micron filter and the 0.9" PFoV (total field: 57"x57") were used. The weather conditions were fine. Out of the 8 impacts observed (A, E, F, H, L, Q, T, U), five were clearly detected (A, E, H, L, Q). Light curves with a time resolution of 1 second, will be presented. Mid- IR observations are an indispensable complement to shorter wavelength measurements, for example to obtain indication about the impact site temperature. We will insist particularly on the brightest impact, the L impact, which shows first a faint precursor peak (the plume?) around 22:18 UT, followed by a huge spot, at its maximum 12 minutes later. At this stage, with an intensity of 15 000 Jy, the spot was one of the brightest mid-IR source in the sky. The brightness decreases rapidly with, around 22:36, an intringuing plateau lasting for a few minutes. The prime aim of the observations was the search for thermal fluctuations associated with seismic waves excited by the comet fragments. Direct information about the internal structure of Jupiter can be derived from the arrival times of the waves at various distances from the impact. The data analysis is underway. The post impact observations will be used in coordination with the mid- IR observations at ESO and CFHT to search for Jupiter pressure modes (see Mosser et al.). 03.13-P Steffes P. G. DeBoer D. R. Smith W. W. Observations of the Jovian Microwave (5cm) Emission During and Subsequent to the Collision with Comet Shoemaker-Levy 9 A student-faculty observational project has been undertaken whereby the 5 cm continuum emission from Jupiter is being monitored both before and after the collision of Comet Shoemaker - Levy 9. Disk-averaged flux density variations of 0.5% are detectable with the system developed, which uses a 30-meter radio telescope at the Georgia Tech Woodbury Research Facility, 65 miles south of Atlanta. This facility has been developed by a team including over 50 students. The 5 cm flux from Jupiter is largely thermal (75%) and will be subject to variations depending on the depth of the comet's penetration, as well as the redistribution and spreading of microwave absorbers carried up from the deeper atmosphere by the vertical shock waves. The non- thermal, synchrotron emission at 5 cm (approximately 25%), could likewise be affected by the injection of either cometary material or Jovian atmospheric constituents into the magnetosphere. As with any continuum measurement, large bandwidths (>500 MHz) are desirable so as to increase sensitivity. However, spectral crowding in the centimeter wavelength range has made it more difficult to obtain interference-free observing spectrum, especially given the large number of spaceborne transmitters. New approaches for addressing this problem are presented. This work was supported by the NASA Planetary Atmospheres Program under Grant NAGW-533. 03.14-P Grossman A. W. White S. M. Muhleman D. O. Gurwell M. A. Microwave Imaging of Jupiter's Troposphere During Impact with Comet P/Shoemaker-Levy 9 We report on the results from a world-wide campaign to acquire high- resolution, microwave images of thermal emission from Jupiter's troposphere, before, during, and after impact with fragments of comet P/Shoemaker-Levy 9. Interferometric observations were obtained at wavelengths of 3cm and 6cm from the Very Large Array (VLA) and the Australia Telescope (AT). At these wavelengths, gaseous ammonia is the primary source of opacity in Jupiter's troposphere. It is also the principal condensate. Therefore changes in brightness temperature are indicative of changes in ammonia abundance and relative humidity. The corresponding weighting functions at these wavelengths probe the pressure levels 1-5 bars, below the optically thick cloud deck. Preliminary images at centimeter wavelength clearly show the expected zone-belt structure. Two prominent features in the radio data are a distinctly bright band at the position of the North Equatorial Belt (NEB) and a corresponding dark band at the position of the Equatorial Zone (EZ). The 30K brightness temperature difference (at a wavelength of 6cm) between these two regions, interpreted within the context of a radiative transfer model requires that the NH3 mixing ratio decrease by a factor of two from the EZ to the NEB. At the latitude of the impacts there are no discernable features at a level of 3-5K within a 3000-5000 km beam-width. This constrains the change in the average NH3 abundance within this region to value of less than 10%, although larger changes in NH3 abundance are allowed in a smaller region. These limits may constrain the depth of penetration of the comet fragments. Work continues to reduce the full complement of data taken during the week of impacts and to improve the sensitivity and quality of the images. 03.15-P Sada P. V. McCabe G. Deming D. Bjoraker G. Jennings D. Loewenstein R. F. Continuing Thermal-Infrared Spectroscopic Observations of Jupiter and Comet Shoemaker-Levy 9 Fragment Collision Sites The collisions between comet Shoemaker-Levy 9 and Jupiter created large atmosphe These observations will be used to retrieve temperature and species abundance in The preliminary results of this study will be presented. u@ 03.16-P Matthews C. N. Hydrogen Cyanide Polymers from the Impact of Comet Shoemaker-Levy 9 on Jupiter Hydrogen cyanide polymers--heterogeneous solids ranging in color from yellow to orange to red to black--may be among the organic macromolecules most readily formed within the solar system. The non- volatile black crust of comet Halley, for example, might consist largely of such polymers arising from HCN formed by photolysis of methane and ammonia. It seems likely, too, that HCN polymers are a major constituent of the dark solids detected spectroscopically by Cruikshank et al. on other comets and on some asteroids and planetesimals. Comet outbursts attributed by Rettig et al. to exothermic internal polymerization of HCN may even be a contributory cause of the fragmentation observed for comet Shoemaker-Levy 9. HCN polymerization could account also for the yellow- orange-red coloration of Jupiter. Laboratory studies by Matthews et al. of these ubiquitous compounds point to the presence of polyamidine structures synthesized directly from hydrogen cyanide. These would be converted by water to polypeptides which can be further hydrolyzed to alpha-amino acids. Other polymers and multimers with ladder structures derived from HCN would also be present. The impact of comet Shoemaker-Levy 9 with Jupiter--a collision between two possible sources of HCN polymers--would be expected to disperse some polymeric cyanide material as well as to produce pyrolysis and hydrolysis compounds such as nitrogen heterocycles, nitriles, polypeptides and amino acids. Spectroscopic detection of these predicted products and of the parent polymers of HCN would strengthen significantly the hypothesis that cyanide polymerization is a preferred pathway for prebiotic and extraterrestrial chemistry. 03.17-P Hayward T. L. Gierasch P. Goodman J. McGhee C. Moersch J. Nicholson P. Squyres S. Van Cleve J. Matthews K. Neugebauer G. Weinberger A. Miles J. Orton G. Ten Micron Images and Spectra of the Shoemaker-Levy 9 Impacts Observed from Palomar We present lambda = 5 to 13 micron observations of several SL-9 impacts made with SpectroCam-10 at Palomar Observatory from July 15 to 24 and August 15 to 18. On the 5-m Hale Telescope, the diffraction limit of 0.5" at 10 microns provided excellent views of the impact sites. Our 8.8 and 10.3 mmicron broad-band images illustrate the morphological structure and evolution of several sites from soon after the impact to about one month later. In many spots the thermal infrared structure closely resembles the near-IR appearance. Low-resolution 8 to 13 micron spectra show strong thermal continuum emission in young spots which slowly decays over the following days and weeks. High resolution spectra (R = 2000) in lines of H2S, NH3, and PH3 show features such as line inversions in several of the larger impact sites. We will also discuss 5 micron images and 8-13 micron low-resolution spectra of the R impact. The emphasis of this paper will be to catalog and describe the observational results; detailed physical interpretations will be presented in companion papers by Nicholson et al. and Gierasch et al., and the Palomar near-IR observations will be discussed by McGhee et al. This research was supported by a grant from the NASA Planetary Astronomy program. 03.18-P Meadows V. Crisp D. Orton G. Brooke T. Spencer J. AAT Observations of Shoemaker Levy-9 Collisions with Jupiter We will use the Infrared Imaging Spectrometer (IRIS) on the 3.9m Anglo- Australian Telescope (AAT) to observe the collisions of the fragmented comet Shoemaker Levy-9 (SL9) with Jupiter on July 16-22. This southem hemisphere site (31.28 S) is advantageous because Jupiter will be at -12 degrees declination, and at least 6 impacts can be observed from this longitude (149.07 degrees E). The impacts of fragments D, K, N, and W will occur after sunset, while the impacts of C and G will be visible before sunset. IRIS is versatile, near-infrared (0.9 to 2.5 micrometer) camera/spectrometer with a 128 by 128 HgCdTe (NICMOS 2) detector. For imaging at f/15, the IRIS pixel scales are 0.61 and 1.94 arcsec. K-band images of comet fragments will be used for astrometry, and to search for evidence of further tidal disruption before impact. Long-exposure images will be used to monitor interactions between the SL9 dust veil and the Jovian magnetosphere and ring. Impact events will be monitored by rapid- sampling K-grism spectroscopy (2 to 2.4 micrometers). In this mode, IRIS provides a spatial resolution of 0.6 arcsec/pixel along a 60 arcsec slit, a spectral resolution of approximately 300, and readout times as short as 0.5 seconds. For all fragments except K, the slit will be placed across the limb at the impact latitude to provide time-resolved spectra of the fireball as it rises above the limb. For fragment K, the slit will be placed across the disk of Europa, which will be in eclipse. Once the impact sites rotate into view, drift-scanning will be used to produce spectral images of the Jovian disk. Images extracted within strong CH4 and H2 bands will constrain the abundance, vertical distribution, and horizontal motions of aerosols produced by the impacts. These image cubes will also be used to search for trace gases of cometary and tropospheric origin (H20, CO, H2S, etc.) deposited in the stratosphere by the impacts. Finally, the K-band cubes will monitor variations in the weak H2 and H3+ auroral emission associated with the impacts. 03.19-P Bockelee-Morvan D. Colom P. Despois D. Gautier D. Biver N. Crovisier J. Encrenaz T. Gerard E. Lellouch E. Marten A. Owen T. Strobel D. Molecular Observations of the Jupiter/Comet Shoemaker-Levy 9 Collision at the Swedish/ESO Submillimetre Telescope and the Nancay Radio Telescope Millimeter line observations of the Jupiter/comet Shoemaker-Levy 9 collision were performed with the Swedish/ESO Telescope (SEST, La Silla, Chile) from July 18 to July 23 1994. Using alternatively the 3 mm, 1.3 mm and 0.8 mm receivers, we searched for line signatures of several species at various impact sites, CO (230 GHz and 345 GHz), HCN (266 GHz), HCO^+ (89 GHz), SiO (86 GHz), SO2 (246 GHz), ArH^+ (246 GHz) and ArH(sub)3^+ (246 GHz). In addition, in late July, after the impacts, and in mid-August, we observed the 1667 and 1665 MHz transitions of the OH radical at the Nancay telescope. A quicklook analysis does not reveal any obvious detection. Further reductions are in progress. A report will be presented. 03.20-P Caldwell J. J. Barnet C. Noll K. S. McGrath M. Weaver H. A. Atreya S. Trafton L. Yelle R. HST/GHRS Spectra of Jupiter's from 1610 to 1830 Angstrom During the SL-9 Encounter The G140L grating in the GHRS and its associated detector (D1) onboard the Hubble Space Telescope have 500 spectral diodes or width 0.57 angstrom. During and after the SL-9 encounter period, a total of ten spectra of Jupiter were obtained with the G140L in two spectral ranges: 1251-1537 angstrom and 1541-1828 angstrom. We report here on the four spectra taken at the latter spectral range, but restrict our discussion to wavelengths longer than 1610 angstrom. This wavelength approximately separates shorter wavelengths where emission occurs (predominantly from H2) from longer ones where reflected sunlight dominates. Consistent with other UV observations during the SL-9 event, we find that the general reflectivity of Jupiter is significantly lower than it is at normal times, Within our restricted spectral range, C2H2 has previously been determined to be the strongest molecular absorber, and several characteristic bands have been detected during SL-9 around 1750 angstrom. However other absorbers, possibly continuum and/or molecular, appear to be present. A continuing investigation seeks to determine the nature and identity of these additional absorbers. 03.21-P Kundu A. Grossman A. W. de Pater I. Millimeter Wave Observations of the Effects of Shoemaker-Levy 9 on the Jovian Troposphere We present radio interferometric images of Jupiter in the 3mm thermal continuum before, during and after the Shoemaker-Levy 9 collision. The data were obtained using the Berkeley-Illinois-Maryland array (BIMA), a six-antenna millimeter interferometer that operates in the 3mm band with an 800 Mhz wide continuum. We observed Jupiter continuously from 15-24 July at 101 Ghz with a bandwidth of 725 Mhz . However we tuned to the HCN line at 88.6318 Ghz from the 19 to the 21 of July when preliminary reports from other observers suggested a detection of HCN. Our synthesized images of Jupiter have an angular resolution of 4 arcsecs, and sensitivity of 1 K. As of yet we have not discovered any localized or large scale change in the thermal emission in the millimeter range. We have not found any evidence of a HCN line in onr data. Our observations are very sensitive to any vertical motion in the Jovian troposphere associated with the impact at a level of 0.5-2.5 bars. Thus our observations can place unique upper bounds to the depth to which collision induced effects occured. Consequently, useful constraints can be obtained on the size and composition of the cometary fragments. 03.22-P Vervack R. J. Jr. Collins J. Holberg J. B. Sandel B. R. Herbert F. Dessler A. J. Forrester W. T. Broadfoot A. L. Voyager 2 UVS Observations of Jupiter During the Comet Shoemaker-Levy 9 Impact Events The Voyager 2 Ultraviolet Spectrometer (UVS) observed Jupiter during the Comet Shoemaker-Levy 9 impact events. Observations began on July 8 and continued through August 15 with approximately 18 hours of real-time data collected each day. Data were collected for impacts A, B, C, D, F, G, H, L, Q1, Q2, R, T, U, V, and W, as well as during the predicted impact times for the "missing" fragments J and M. Data from impacts E, K, N, P1, P2, and S were not collected because they occurred during gaps in scheduled ground-station coverage. The Voyager 2 UVS is sensitive over the 500-1700 angstrom range with a spectral resolution of approximately 18 angstrom. The time resolution of these observations is 3.84 seconds. Although Voyager 2 had a relatively direct view of the Jovian hemisphere where the impacts occurred, the spacecraft was 40.9 AU from Jupiter. An examination of the UVS spectra revealed no obvious signal from the comet fragment impacts. At present, we can quote a provisional upper limit of 2x10^35 photons/sec or 2X10^24 ergs/sec integrated over the wavelength range 1340-1670 angstrom for the radiated power escaping the Jovian atmosphere. This wavelength range was chosen because it is relatively free of absorption by atmospheric H2 and the primary hydrocarbon CH4. We expect to improve this upper limit and to relate this power to various emission scenarios. This work was supported by NASA Grant NAGW-3657. 03.23-P Moses J. I. Allen M. Gladstone G. R. The Aftermath: Effects of Shoemaker-Levy on Jovian Photochemistry The impact of Comet P/Shoemaker-Levy 9 (SL9) with Jupiter caused cometary material and tropospheric Jovian air to be injected into Jupiter's stratosphere. Atomic and molecular species that are not commonly found in the Jovian stratosphere can now participate in atmospheric photochemistry. Observations suggest that relatively few new gaseous oxygen species were introduced to the stratosphere following the impacts but that sulfur and nitrogen species were greatly enhanced. We have examined the short- and long-term photochemical evolution of sulfur and nitrogen compounds in the Jovian atmosphere. We begin our calculations approximately a half hour after an impact, after the material in the ejecta plume has splashed back down into the atmosphere. The results of several shock chemistry models as well as the reports of the various nitrogen and sulfur species observed immediately after the impacts provide our initial composition. We find that the sulfur species observed initially are short-lived -- S2 and CS2 are photolyzed in less than a day, and H2S in less than a week. Several interesting sulfur species are formed in the hours and days following the impacts. Particularly noteworthy are CS, CH2S, CH3SH, CH3SCH3, CH3SSCH3; ring species such as elemental sulfur, C2H4S, and C3H6S; and polysulfide chains such as HSxH. The nitrogen photochemistry is somewhat less intricate. Ammonia (NH3) is photolyzed in about a week, but the photolysis products are recycled back to NH3 or form hydrazine (N2H4). Molecular nitrogen is very stable in the Jovian stratosphere and will not participate in the photochemistry. If HCN is produced in sufficient quantities during the impact, its photolysis may dominate the production of nitriles and more complex nitrogen compounds. Many of the sulfur and nitrogen compounds formed after the impacts will condense in Jupiter's stratosphere. The atmosphere will take years to relax fully back to its unperturbed state. 03.24-P Billebaud F. Drossart P. Vauglin I. Merlin P. Sibille F. Lognonne P. Mosser B. Lagage P.-O. Lellouch E. Gautier D. 10 Micron Observations of Hydrocarbon Emissions in Jupiter's Atmosphere After the Impacts of Comet P/Shoemaker-Levy 9 Using the French national 10-micron array camera installed on CFHT, we recorded images in hydrocarbon bands around 10 micron after the impacts of the fragments of comet P/Shoemaker-Levy 9. We used the circular variable filter of the instrument which provides a spectral resolving power lambda/delta lambda similar to 50. Jupiter was mapped at the following wavelengths: 7.93 microns (CH4, P branch of the upsilon(sub)4 band), 12.18 microns (C2H6, upsilon(sub)9 band), and 13.7 microns (C2H2 upsilon(sub)5 band). The observations cover the period from July 24 to July 27 and provided several sequences of observations at the mentioned wavelengths, allowing us to cover the whole planetary disk. The spatial sampling was 0.8 arcsec per pixel. A preliminary analysis of a sequence of observations at 7.93 microns shows CH4 emissions associated with the impact regions. The spatial distribution of these emissions, and its temporal evolution will be characterized. The comparison of the emissions of the different hydrocarbon bands should help determining the atmospheric levels affected by the impacts. 03.25-P Knacke R. F. Geballe T. R. Noll K. S. Brooke T. Y. Infrared Spectra of the R Post-Impact Events of Comet Shoemaker-Levy 9 We obtained a series of 2.20-2.41 micron spectra of the R event of Comet Shoemaker-Levy 9 shortly after the impact. Spectra taken with the UKIRT telescope span a 45 minute interval, spaced roughly 1-2 minutes apart. Before the event, spectra of Jupiter's limb at 44 deg south showed reflected solar llght with mainly CH4 absorption. Within about two minutes the flux rose by approximately two orders of magnitude and the spectrum developed a classic CO 2-0 bandhead profile at 2.295 microns. Other CO bandheads were not clearly visible either because they were weak or were blended with other emission features (probably CH4). Subsequent spectra, obtained at 1-2 minute intervals, showed a progressive weakening of the continuum and the CO emmission. The 2-0 profile was absorbed at the long wavelength side, apparently by cooler CO on the outside of the blast, until finally CO emission and absorption faded away. The entire episode was over in approximately ten minutes. We will discuss interpretation and modeling of the spectra. This work was supported by NASA grant NAGW 2194. 03.26-P Marten A. Moreno R. Paubert G. Wild W. Colom P. Crovisier J. Rosenqvist J. New Heterodyne Millimeter Observations of Jupiter Performed After the Collision of Comet SL9 with the Planet Emission lines of CO and CS have been observed at 230 and 245 GHz with the IRAM 30m radiotelescope located near Granada, Spain, during the comet Shoemaker-Levy 9 collision with Jupiter, (c.f. Lellouch et al., this issue). The IRAM 30m has continued its monitoring of Jupiter at several fragment locations a long time after the last impacts using the same observing procedure. We report here on new detections of CO and CS lines, unambiguously observed _in absorption_ at the same frequencies. We have checked whether these features might be artefact effects in the observational procedure and conclude they are not. We present a summary of all observations carried out after July 28th and discuss the significant aspects of the recorded spectra. A comparison of our results with other previous millimeter observations of Jupiter will be done. Since the spectral signatures of carbon compounds did not disappear rapidly, we will propose a coherent scenario of their formation in the upper atmosphere of Jupiter. We are indebted to M. Grewing and M. Guelin for providing this unique opportunity of monitoring Jupiter during extra time periods of observations with the IRAM 30m Telescope. 03.27-P Formisano V. Bellucci G. Lopez Moreno J. J. Multispectral Imaging of the Shoemaker-Levy 9 Impacts on Jupiter from Sierra Nevada Observatory The impact of comet Shoemaker-Levy 9 on Jupiter has been observed from the Sierra Nevada Observatory, in Granada, Spain with a 1.5 meter telescope and two instruments: a CCD camera and a multispectral imaging system (VNIR) with cooled CCD. Observations have been carried out from July 16 to July 22. This paper concerns mostly with multispectral images and related spectra ( 400 - 1050 nm ). The cometary dark spots are clearly visible; the preliminary study of the spectra shows that the major effect seen in our data is a decrease of the albedo, or a decrease of the continuum in the spots compared with the nearby -43 degrees band. The spectra are essentially coincident around 800 nm, and they diverge going toward 400 nm. The spot spectra show less deep methane bands and occasionally deeper ammonia band ( at 640 nm ) with respect to the nearby regions at the same latitudes. Several other small spectral differences are being studied. This work was supported by ASI and CSIC grants. 03.28-P Naylor D. A. Davis G. R. Griffin M. J. Marten A. Holland W. S. Matthews H. E. Han B. Bockelee-Morvan D. Colom P. Crovisier J. Gautier D. Lellouch E. Strobel D. Orton G. Owen T. de Pater I. Sanders D. Atreya S. Broadband Submillimetre Observations of the Collision of Comet Shoemaker-Levy 9 with Jupiter from JCMT In addition to the JCMT heterodyne observations of the collision of Comet Shoemaker-Levy 9 with Jupiter reported by our group at this meeting, a polarizing Fourier Transform Spectrometer was used to conduct a broadband spectral survey of the encounter. Despite the poor weather experienced throughout the run, spectra were obtained in the atmospheric windows centred on 750, 850 and 1100 microns. To minimise baseline variations, which can contaminate the transformed spectra in a Fourier spectrometer, instead of trying to track the impacts around the planet, the telescope pointing was fixed at the central meridian of Jupiter at a latitude determined by the beam size in such a way to minimise baseline variations due to any tracking errors. In this mode impact sites were observed as they moved through the telescope field of view. Bad weather prevented us from obtaining pre-collision reference data at the impact latitudes. Reference spectra were obtained by observing the planet at an equivalent offset position in the northern hemisphere. While the 750 and 850 micron band spectra appear featureless, spectra in the 1100 micron band reveal a repeatable broad, and therefore possibly tropospheric, absorption feature of the order of 5% of the continuum background. These results will be presented and their correlation with impact sites discussed. 03.29-P Vasilyev V. P. Sergeev V. A. Calculation of the Comet-Jupiter Collision Wave Response The Jovian atmosphere wave response belongs to direct consequences of the comet-Jupiter collision. Relatively slow warm-up with surface vaporization should prevent to explosion of the fragment as a unit. On the other hand sufficiently rapid attainment of breaking impact stress should result in this intensive failure. These above principal concurrence factors determine the wave disturbances source structure in the Jovian atmosphere. We assume that the source have a heat nature and stretched drop-like geometry with longitudinal temperature inhomogeneity. On the basis of such model using the calculations of Jovian atmosphere oscillation spectra outside the impact was performed. The most probable existence of the two main amplitude,increasing regions in the oscillation power spectra is shown. The first region relates the wavelengths close to the cutoff frequency and the other one relates to the periods near the 10 D/C, where D is a fragment diameter and C is the sound velocity. So far as the cutoff period monotonously increases in the undertropopause layers the depth of the impact for every fragment can be determined by the peculiarities of the observed low-frequency peak. 03.30-P Betz A. L. Boreiko R. T. Bester M. Danchi w. C. Hale D. D. Stratospheric Ammonia in Jupiter as a Result of Comet SL-9 Several spectral lines of ammonia in the 10 micron band were monitored in Jupiter between July 16 and August 8, 1994, covering the period of fragment collisions from comet SL-9. Narrow line emission was detected from impact sites E, G, H, K, L, and Ql, while only upper limits were obtained at the A and C sites and other selected locations on the planet's surface outside of the impact areas. The strongest emission was seen from the G site, where the aQ(2,2), aQ(6,6), and the aQ(9,8) lines of ^14NH(sub)3 were detected. Over a period of days following the impact, Rayleigh-Jeans antenna temperatures were about 2 K for the first two lines, corresponding to a brightness temperature of 200 K if the emission fills the 1.5 arcsec beam. Observed linewidths were about 1.7 km/s (FWHM) at the beginning of the period and closer to 2-3 km/s toward the end. The narrow linewidths are definitive indicators that the emission occurs well above the tropopause. The lack of equivalently strong emission from water vapor which is expected to be much more abundant than ammonia in cometary ice leads us to conclude that the observed ammonia is an impact induced upwelling of material from the troposphere of Jupfiter where ammonia has long been known to be a significant constituent. This result helps establish minimum penetration depths for impact fragments producing detectable NH3 emission. This work was supported by NASA Grant NAGW-3196 (U. CO) and ONR grant N00014-89-J-1583 and NSF grants AST-9016474, AST-9119317, AST-9321289 (UCB). SESSION 04 ....... Solar System Formation I Monday, 1:30 - 3:30 Crystal Ballroom B A. P. Boss and W. D. Cochran, Moderators 04.01 Berman A. F.* Kary D. M. Lissauer J. J. Single Pass Planetary Feeding Zones We have calculated accretion and rotation rates of planets growing on eccentric orbits within uniform surface density planetesimal disks for a variety of orbital inclinations and planet and planetesimal eccentricities (Berman and Kary 1993, B.A.A.S., 25, 1121). Accretion occurs from two bands which are nearly symmetrically placed about the planet's orbit. We have found that the extent of a planet's single pass feeding zones depends only upon the sum of the eccentricities of the planet and the planetesimals and their mutual inclination. The inner band is a bit narrower than the outer band and is located slightly closer to the planet. For 2-D simulations, the interior limits move slightly closer to the planet with increasing eccentricity, and the exterior limits move away from the planet and become comparable to (e(sub)1 + e(sub)2) a for large eccentricities. Different simulations with the same maximum relative eccentricity produce very similar limits of the planet's single passage feeding zone. Were we to extend our simulations over many synodic periods, we expect the feeding zone would expand more rapidly for larger planetary eccentricity (with e(sub)1 + e(sub)2 fixed), as the Jacobi parameter, which is constant when e(sub)1 = 0, tends to vary more rapidly as e(sub)1 increases. Inclination reduces the mean effect of the planet's gravity, and thus moves the interior limits slightly closer to the planet and the exterior limits significantly closer to the planet. This research was supported in part by NASA-PG&G. 04.02 Ward W. R.* Hahn J. M. Rettig T. W. Resonant Trapping in a Self-Gravitating Planetesimal Disk A planetesimal's orbit will decay due to the solar nebula gas drag. Such an object approaching a massive secondary (a protoplanet) will experience strong gravitational perturbations at the secondary's outer Lindblad resonances. If perturbations can compensate for the orbital energy and angular momentum lost by the planetesimal due to gas drag, orbit decay is halted and the planetesimal is trapped in a stable orbit at the resonance. Past examinations (Weidenschilling and Davis 1985, Malhotra 1993, Kary et. al. 1993) show an isolated test particle can be trapped at resonance provided the planetesimal size is larger than a critical value, or, equivalently, the secondary's mass exceeds a certain threshold. We present results of an alternate treatment of this problem that considers the collective gravitational effects of numerous disk particles present at a resonance. As a consequence of the planetesimal disk's self-attraction, the secondary launches spiral density waves at its Lindblad resonances. Energy and angular momentum deposited there by the secondary are transported away by wave action, significantly reducing its ability to trap particles. Provided the waves are able to propagate out of the resonance zone and damp to the gas and/or particle disk before reflecting at at the Q-barrier and returning to resonance, particle trapping is not possible for a significant range of solar nebula parameters. This provision that the waves transport the energy and angular momentum out of the resonance zone ultimately determines whether particle trapping can occur. Particle trapping in a self-gravitating disk is possible only if (i) waves vigorously damp in the resonance zone via linear or non-linear viscous dissipation, (ii) the particles' dispersion velocity is too high to support wave propagation, or (iii) gas drag and/or viscous damping of spiral waves is too weak to prevent their reflection and return to resonance. In the last instance, the returning waves are re-absorbed by the particles at resonance. The range of solar nebula parameters (particularly the secondary's mass as well as the disk particle size in a unimodal disk, or the particle size distribution for a more general disk) for which collective effects prevent resonant trapping will be discussed. 04.03 Dominik C.* Tielens A. G. G. M. Coagulation in Oblique Collisions Between Micron-sized Grains It is now well established, that coagulation plays an important role in the formation of planetesimals in the solar nebula. Especially the first growth step from (sub)micron sized grains to cm sizes is undoubtly due to this process. Nevertheless, the physics of coagulation is still poorly understood. In a recent paper, Chokshi et al. (1993) have studied the head-on collision between two micron-sized grains and derived sticking probabilities by considering adhesive forces and elastic waves excitation. We have now extended this study towards oblique collisions. In these collisions, tangential forces in the contact area can give rise to sliding or rolling of the spheres over each other, a process that proves to be decisive for the structure of the formed aggregates. We have studied the effects of tangential forces, rolling and sliding friction in an adhesive contact between two elastic, adhesive spheres. We find, that both sliding and rolling depend strongly on the properties of the grain materials. In collisions with initial velocities only slightly smaller than the rebounce velocity, rolling or sliding can be sustained until a grain formed several contacts with an aggregate. Thus, grains will generally not stick where they hit, and the solar nebula aggregates might have been more compact that previously assumed. References A. Chokshi, A.G.G.M. Tielens, D. Hollenbach, 1993, APJ 407, 806. 04.04 Weidenschilling S. J.* Formation of Cometesimals and Planetesimals: Numerical Results The analytie model of formation of "rubble pile" comets (Nature 368, 721) envisions a two-stage process of eollisional coagulation followed by gravitational instability of a layer of macroscopic bodies. The instability mechanism requires that the layer exceeds a critical density delta*; also, the drag-induced radial velocity dispersion must be sufficiently small. Numerical simulations including time-dependent settling and coagulation, particle size distribution, and shear-induced turbulence are in good agreement with analytical predictions. Starting from dispersed dust at 30 AU, instability is reached after ~-9 x 10^4 y when the median particle size is ~-15 delta*. About 2/3 of the total solids are in the dense layer, and the optical thickness has declined to ~-10% of the initial value. Application of the same model to silicates at 3 AU results in instability after ~-10^4y for a layer of 40 m bodies containing ~-1/3 of the total surface density of solids. If local shear is the only source of turbulence, it delays but does not prevent gravitational instability. Global (e.g., convective) turbulence corresponding to alpha <~10^-6 has little effect. Turbulence with alpha >~ 10^-4 has serious consequences; thickening of the particle layer lowers the coagulation rate and also keeps the deviation of the gas from keplerian rotation at a large value, resulting in rapid orbital decay. If the solar nebula contained regions of high and low turbulence, there would be a strong tendency for solids to accumulate in the low-turbulence regions. 04.05 Cassen P.* Meteoritic Constraints on Models of the Solar Nebula: The Abundances of Moderately Volatile Elements The "moderately volatile" elements are those which condense (or evaporate) in the temperature range 650 - 1350 K, as a mix of material with solar abundances is cooled (or heated) under equilibrium conditions. Their relative abundances in chondritic meteorites are solar (or "cosmic", as defined by the composition of CI meteorites) to within a factor of several, but vary within that range in a way that correlates remarkably well with condensation temperature, independent of chemical affinity. It has been argued that this correlation reflects a systematically selective process which favored the accretion of refractory material over volatile material from a cooling nebula. Wasson and Chou (Meteoritics 9, 69-84, 1974, and Wasson and co-authors in subsequent papers) suggested that condensation and settling of solids contemporaneously with the cooling and removal of nebular gas could produce the observed abundance patterns, but a quantitative model has been lacking. We show that the abundance patterns of the moderately volatile elements in chondritic meteorites can be produced, in some degree of quantitative detail, by models of the solar nebula that are designed to conform to observations of T Tauri stars and the global conservation laws. For example, even if the local surface density of the nebula is not decreasing, condensation and accretion of solids from radially inflowing gas in a cooling nebula can result in depletions of volatiles, relative to refractories, like those observed. The details of the calculated abundance patterns depend on (but are not especially sensitive to) model parameters, and can exhibit the variations that distinguish the meteorite classes. Thus it appears that nebula characteristics such as cooling rates, radial flow velocities, and particle accumulation rates can be quantitatively constrained by demanding that they conform to meteoritic data; and the models, in turn, can produce testable hypotheses regarding the time and location of the formation of the chondrite parent bodies and the planets. 04.06 Wetherill G. W.* Formation of Extra-Solar Terrestrial Planets During the past decade significant progress has been made in quantitatively modeling the formation of planetary systems with surface densities and stellar masses similar to those of our solar system. These models have been successful in explaining a number of observable features, particularly in the terrestrial planet and the asteroidal regions. These same models have been extended to include a range of stellar masses and preplanetary disk densities. Disk surface densities, lifetimes, and temperature distributions are not well defined theoretically or observationally, but it is likely that they are quite variable even for young stars of the same mass. This investigation represents a tentative study of the sensitivity of planetary systems to variations in these parameters. 150 simulations have been made, based on the Monte Carlo model described earlier (Wetherill, Icarus 100, 307, 1992), for stellar masses of 0.5, 1.0, and 1.5 solar masses. These are grouped according to several sets of calculations: 1. Surface density independent of stellar mass. 2. Surface density proportional to stellar mass. 3. One solar mass stars with varying surface density. 4. Variation of the position of "Jupiter." 5. Variation in the power law dependence of the surface density. It is found that in general the number of final planets (~4) interior to 5 AU is insensitive to variation in these assumptions. With a "Jupiter" at 5 AU, Earth-Venus mass terrestrial planets are concentrated between 0.7 and 1.3 AU, with little dependence on stellar mass. Higher surface densities tend to lead to larger planets, sometimes ~2 Earth masses. A more distant Jupiter permits formation of large planets in the asteroidal region, whereas a less distant Jupiter inhibits the formation of terrestrial planets. One solar mass stars usually have an Earth mass planet in the habitable zones of Kasting et al (Icarus, 101, 108, 1993). Both the larger and smaller stars appear to be less likely to have habitable terrestrial planets, but they are not completely excluded. This work was supported by NASA grants NAGW-1969 and NAGW-3928. 04.07 Canup R. M.* Esposito L. W. Formation of the Moon from an Impact-generated Disk In light of geological and dynamical evidence, the "Giant-Impact" scenario has emerged as a nearly consensus view of lunar origin. Detailed simulations of the impact of a Mars-sized body with Earth have demonstrated the plausibility of formation of a proto-lunar disk following a large impact event. A series of works by a group composed of Cameron, Benz, Slattery, and Melosh (1986,1987,1989, 1991,1994) have modeled the impact event and subsequent ejection of material into orbit about the Earth. Their work predicts radial disk profiles, which are relatively insensitive to the specifics of an impact, and finds that most ejected material is typically located within the classical Roche limit for silicate densities. While the formation of an impact-produced disk has been convincingly modeled, subsequent lunar formation from the disk has not. Indeed, the processes leading from the creation of a protolunar disk to its accumulation into a single, large Moon are not obvious, since protosatellite disks in the outer solar system have evolved into systems of multiple moons and rings. Past works have proposed that multiple moonlets which formed at various radial locations in the protolunar disk evolved inlo crossing orbits via tidal interaction with the Earth, (e.g., Cameron 1986). Tidal orbital evolution requires that the innermost "moonlet" which, forms in the disk be the most massive in order for all moonlets to eventually evolve into colliding orbits (e.g., Cameron 1986, Cameron and Benz, 1991). This is contrary to expectations from Canup and Esposito (1994), who find that tidal effects in a region extending approximately one planetary radii beyond the classical Roche limit greatly limit and alter accretional growth processes. In the "Roche Zone", like-sized bodies cannot remain gravitationally bound as they physically overflow their mutual Hill sphere. Accretion in the inner protolunar disk would therefore be expected to result in a distribution of multiple small moonlets (who are precluded from accreting with one another due to the tidal forces of the planet), while accretion in the outer disk would be much more efficient. This implies that the largest bodies in an impact-generated disk would naturally form in the outer disk, which is contrary to the condition needed for all moonlets to eventually evolve into crossing orbits to form a single Moon. We will present results of our tidal accretion model applied to realistic initial conditions in an impact-generated disk. Conditions that could lead to the accumulation of the disk into a single body will be discussed. This work is supported by the Cassini Science Project and the Patricia Roberts Harris fellowship program. 04.08 Lissauer J. J.* Analytic Calculations Relevant to the Origin of the Rotation of Giant Planets Jupiter and Saturn. obtained most of their rotational angular momenta via hydrodynamic accretion of gas from the protoplanetary disk. Detailed calculations of such flows are quite complicated, and cannot at present yield unique, generally applicable results because of substantial uncertainties in the properties of both the protoplanetary disk and the growing giant planets themselves. Fortunately, it is possible to make some simple analytic estimates of the spin angular momentum accreted by a gas giant planet. These calculations ignore planetary gravity, which may be far less important than it is for the rotation of terrestrial planets because growing gas planets occupy a large fraction of their Hill Spheres, i.e., they are distended "fluffy" objects. The results are illuminating because they provide both order of magnitude estimates of the amount of rotational angular momentum attainable by growing giant planets and qualitative measures of the sensitivity of giant planet rotation to pressure and surface density variations in the protoplanetary disk and the orbital eccentricity of the growing planet itself. This work was supported by NASA PG&G grant NAGW-l 107. 04.09 Foster P. N.* Boss A. P. Shock-Induced Collapse of the Presolar Nebula We model the formation of the early solar nebula through shock-triggered collapse of a molecular cloud core. We examine the plausibility of initiating collapse with the shock wave from an asymptotic giant branch (AGB) star wind. This choice for the shock is motivated by meteoritical evidence. Noble gas isotopic anomalies in SiC presolar grains point to synthesis in an AGB star. Furthermore, Ca,Al-rich refractory inclusions have isotopic anomalies that can be explained by synthesis in an AGB star no more than several million years before the formation of the inclusion. This suggests passage of an AGB wind through the presolar molecular cloud near the time collapse began. Previous studies of clouds struck by shock waves have generally found that supernovae are not a viable triggering mechanism, because such energetic shocks shred the cloud through Rayleigh-Taylor (RT) and Kelvin-Helmholtz (KII) instabilities (e.g., Klein, McKee, and Colella 1994). Our first goal is therefore to determine if AGB shocks can induce collapse without destroying the cloud. Secondly, we follow the shock/cloud interface to determine if this scenario can inject isotopically anomalous grains from the AGB wind into the solar nebula. Boss (1994) and Boss and Foster (1994) used 3D hydrodynamical models to show that AGB winds are capable of inducing collapse and injecting significant amounts of grains. However, these 3D models were limited in their ability to follow the instabilities that tore apart the clouds in the supernovae shock simulations. Here, we calculate much higher spatial resolution 2D models, which are capable of following the RT and KH instabilities. Further, we employ a new hydrodynamics code (VH-1:Lindahl) which was designed to handle shock waves (Collela and Woodward 1984). With this code, we have reproduced the supernova-shock cloud shredding results. Preliminary results for the AG13-shock are promising for initiating collapse. Shocking a Bonnor-Ebert sphere (n(sub)c = 10^6cm^-3) with a 20 km/s AGB wind results in the cloud being crushed onto the symmetry axis. By the time the shock has passed the cloud, roughly 0.7 cloud crushing times, the central density has increased by a factor of 5, high enough to ensure sustained collapse. This research was partially supported by NASA grants NAGW-3413 and NAGW-1410. 04.10 Ruzmaikina T. V.* Reprocessing of the Presolar Dust Aggregates in the Accretional Shock Laboratory studies of a variety of extraterrestrial materials provide an evidence that the inner solar system, including most of the asteroid belt, had been subjected to temperatures 1200 - 1400 K. A large amount of the organics in the dust of comet Halley, and isotopic anomalies in the outer solar system, assume that the outer early solar system might preserve significant amount of the interstellar dust, including ices. This paper studies impulsive heating of the presolar dust and gas in the accretional shock produced by infalling gas and dust at the surface of the solar nebula. The peculiarity of the shock in the solar nebula is fast cooling of the gas, resulting in a sharp density gradient in the postshock region, and the density increase up to two orders of magnitude. Millimeter-size dense grains, embedded in the infalling gas, have such an inertia that they cross the region of cooling without deceleration, and are heated by the drag through the cooled and compressed postshock gas. In the inner part of the solar nebula, up to distances of the asteroidal belt, these silicate grains are heated to > 1600 K were melted and then solidified in ,~ 10^3 s, plausibly forming chondrules. In the outer part of the solar nebula, where the temperature of the infalling gas is low enough to preserve presolar organic material and ices, the accretional shock can cause melting, evaporation, and chemical changes of volatile components of dust aggregates. Also, the presence of liquid water or vapor could cause oxidation of less volatile components, such as Fe. The intensity of heating of aggregates and the extent of region of their evaporation in the outer solar system are also dependent on the size and structure of the aggregates. Large dense grains of ice could be melted at distances up to >= 30 AU. Smaller (say <= micrometer-size grains) and very low dense dust aggregates are heated to lower temperatures. Such particles preserve interstellar water ice beyond 5 to 10 AU, and organics beyond 3 to 5 AU. The outer solar system must contain a mixture of interstellar ices, and ices which were evaporated in the accretional shock and recondensed again. 04.11 Dyt C. P.* Prentice A. J. R. Modelling of Supersonic Turbulent Convection in the Solar Atmosphere A new method of flux corrected transport in two dimensions has been developed Wo by extending the work of Zalesak (J. Comp. Phys. 31, 335, 1979). The code has been applied to the problem of turbulent compressible convection in the solar atmosphere with a view to understanding the origin of the planetary system. The numerical simulation is carried out for an ideal gas on a uniform mesh between two horizontal stress-free boundaries. The initial density-temperature gradient is chosen to be strongly super-adiabatic, corresponding to polytropic index m = 1. The initial density ratio between the lower and upper boundaries is 11:1. This thermal instability quickly leads to a structure consisting of several convective cells dominated by narrow fast-moving downflows and broad slower-moving M upwellings. Supersonic speeds and shocks occur near the head of the downflows. C The flows are time dependent and persist for several sound crossing times. Al These calculations confirm the findings of Cattaneo et al. (Astrophys. J. 349, L63, 1990) that supersonic convection can develop in stellar atmospheres. The most important discovery we report here is that supersonic convection induces a E concentration of the gas towards the lower boundary (z = 1) and a rarefying near the top (z = 0). For the typical density profiles shown below, corresponding to a Rayleigh number of 4.76 x 10^5, the average density ratio between the lower and upper boundaries is 17:1. The peak Mach speed is about 1.5. These results confilm a basic premise of the theory of planetary system origin due to one of us (AJRP, Astr. Astrophys. 27, 23.7, 1973; Moon & Planets 19, 341, 1978) that supersonic convection caused the contracting proto-solar cloud to become very centrally condensed. This work is supported by the ARC. Y? ? Al 04.12 Chamberlain J. W.* Blowoff of Planetary Atmospheres: Supersonic Solutions of the Solar-Wind Equations We re-examine the inviscid solar-wind equations with heat conduction from below, and establish a fundamentally new approach for finding solar and planetary solutions. Although the problem is fourth order, only two independent integration constants can be assigned, since two boundary conditions that are required to specify well-behaved supersonic solutions determine the values of the other two constants. The Noble and Scarf (1963) solar-wind models are essentially accurate for practical purposes, but in a fundamental sense they are not self-consistent. The ratio of thermal energy to gravitational potential at the supersonic point, (kTr/GMm)s, must lie between 0.4375 and about 0.405 to permit stable supersonic solutions for ionized hydrogen. For planets with diatomic molecular atmospheres, the range is lower but still quite narrow. These limits seriously constrain the physical conditions wherein hydrodynamic "blowoff" of planetary atmospheres can develop. In addition, an atmosphere having blowoff conditions is adiabatically unstable just above the sonic level. 04.13-P Kary D. M. Lissauer J. J. Gas Drag and the Origin of the Trojan Asteroids The origin of Trojan asteroids, which librate about Jupiter's L(sub)4 and L(sub)5 points, presents a long-standing puzzle in planetary dynamics. Models of Trojan asteroid origin are usually based on the assumption that they were inserted into their present orbits as a result of collisions after the formation of Jupiter. However, Peale (1994, Icarus 106 308) has shown that the Lagrange points could be stable in the presence of the solar nebula, opening up the possibility that nebular gas drag played a role in inserting asteroids into the Lagrange points. We find that a planetesimal can have a close encounter with a planet which inserts it into the 1/1 resonance. When the planet is on a circular orbit, the encounter leaves the planetesimal in a low eccentricity orbit (due to conservation of the Jacobi constant) which allows a second close encounter with the planet. The symmetry of the two encounters means the planetesimal is ejected into an inferior orbit. However, when the planet has an eccentric orbit, the planetesimal can be inserted into the resonance with a large eccentricity. This in turn introduces an asymmetry into the planetesimal's orbital evolution and prevents the second close encounter. The planetesimal instead goes through a decaying libration about the L(sub)5 point. In the case of planetesimals approaching a 10^-6M solar mass planet with an eccentricity e >/= 0.02, then ~ 10% of the migrating bodies can be thrown into the 1/1 resonance and decay down to the L(sub)5 point. Further collisional evolution is still required to redistribute material to the L(sub)4 point. This work was supported in part through NASA Planetary Geology and Geophysics Grant # NAGW-2061 at UCSB and # NAGW-1107 at SUNYSB. 04.14-P Sasaki S. Nagahara H. Kitagami K. Nakagawa Y. Shock Heating During Solar Nebula Formation and Origin of Isotopic Fractionation in CAI and Chondrules Mass-dependent isotopic fractionations of Mg, Si, O have been observed in some CAI grains. Recently mass-dependent Mg isotopic fractionation is also found in olivine condrules of Allende meteorites by SIMS study [1]. Large Mg isotopic fractionation is considered to have been caused by evaporation or condensation process but conditions (T, P, t) have not been discussed in detail. Shock heating process through the vertical accretion of cloud gas in the solar nebular formation is pursued numerically solving ratiative transfer precisely with frequency dependence [2]. From a widespread initial density distribution, peak temperature could be higher than 1700K at the asteroidal zone (a = 2.8AU). Outward radiation from shocks heats up the less-dense off-disk region, where pressure is 10^-8-10^-7 [bar]. Evaporation experiments of forsterite (Mg2SiO4) at various PH2 conditions [3] show that evaporation rate at PH2 > 10^-5 [bar] is much higher than that at PH2 < 10^-6 [bar]. When the evaporation speed is comparable to the diffusion speed, enrichment of heavier isotopes in evaporation residues is expected. At a low pressure (PH2 < 10^-6 [bar]), longer duration (10^4-10^5 min at 1700-1800 K) (or slower rate of temperature change) is preferable for the isotopic fractionation. Typical distance for Mg isotopic fractionation is in the order of 10 micrometers, which would be compatible with size of precursor grains of CAIs and chondrules-before aggregation. Since the evaporation rate is likely to be higher than Mg diffusion rate at a higher pressure (PH2 > 10^-5 [bar]), Mg isotopic fractionation would not take place. Evaporative fractionation of Mg isotopes should have proceeded in less-dense environment, which is compatible with the shock heating during solar nebula formation. References: [1] Koga A. et al. (1994) LPSC XXV, 723-724. [2] Kitagami K. (1994) Master thesis, Univ. Tokyo. [3] Nagahara H. (1994) LPSC XXV, 965-966. 04.15-P Levy E. H. Ruzmaikina T. V. Ip W. Tidal Origin in the Solar Tilt In a view of the flatness of the solar system, the origin of the substantial deviation between the solar rotational axis and the angular momentum vector of the planetary system (approximately 7 degrees) needs a special explanation. The very inhomogeneous distribution of angular momentum in the solar system suggests that there was significant exchange of angular momentum and mass between the Sun and the solar nebula. Such an exchange tends to keep the rotational axis of the Sun normal to the plane of the protoplanetary disk. We consider the possibility that the plane of the protoplanetary disk became tilted, with to respect to its initial position coinciding with the equatorial plane of the Sun, as a result of tidal forces exerted by a passing star(s) early in the history of the solar system. The figure, which appears here in the hard copy, shows the magnitude of tilt produced by a one solar mass star moving at 5 km/s and at an angle of 45 degrees with respect to the undisturbed disk. The vertical axis gives the final ratio of the Y and Z components of angular momentum as a function of the impact parameter R (sub) O(shown on the horizontal axis); the radius of the disk is taken to be 50 AU. The initially thin disk of planetesimals is thickened as the orbital inclinations are pumped by the encounter with the star; the resulting disk thickness increases outward. Because of the consequent increase of encounter velocities in planetesimal collisions, such an encounter could have a significant influence on subsequent planet accumulation in the outer solar system, possibly halting accumulation of a planet beyond the orbit of Neptune. The probability of such an encounter could be high if the solar system formed in a dense molecular core with a high efficiency of star formation. This work was supported in part by grants from NASA. SESSION 05 ....... Comet Shoemaker-Levy 9 IV Monday, 4:00 - 5:30 Crystal Ballroom A Kevin H. Baines and Philip Nicholson, Moderators 05.01 West R. A.* Friedson A. J. Baines K. H. Seymour M. Karkoschka E. Hammel H. B. Wide-Field/Planetary Camera 2 Observations of Jupiter's Stratospheric Haze and Ammonia Cloud: Post Impact We observed Jupiter in July and August of 1994 with the Wide Field/Planetary Camera 2 on the Hubble Space Telescope. The first observations were obtained just prior to the first of the large impacts by fragments of comet Shoemaker-Levy 9. The final images occurred a month after the last of the large impacts. We obtained images at UV wavelengths (218, 255, and 336 nm), blue (413 nm), near-IR continuum (953 nm), and in the 889-nm methane band. The principal scientific objectives of this program are to use the cloud particles formed by the impacts as tracers of the Jovian stratospheric circulation and as a tool for studying particle microphysical processes in the stratosphere. The design of our observations emphasizes emission angle coverage (repeated observations as Jupiter rotates) and coverage at wavelengths (UV and methane bands) sensitive to vertical location, over time scales from hours to weeks. Our first attempts to model some of the dense core regions indicate that the debris material, which is dark at all continuum wavelengths, is consistent with particles in the size range 0.15-0.3 micrometers mean radius having an imaginary refractive index that varies from about 0.006 in the near-IR to about 0.02 at 270 nm. In the dense core regions the optical depth of the particles is in the range 5-2 depending on whether the material is distributed between a few mbar and 400 mbar, or only goes as deep as 200 mbar. The material in the dense core regions is distributed at least as deep as 200 mbar and at least as high as a few mbar. There is a decrease in optical depth by about a factor of 2 within a few days after impact, but substantial optical depth remains in the stratosphere in late August. \vfill\eject\end 05.02 Baines K. H.* Friedson A. J. Orton G. S. Yanamandra-Fisher P. Drossart P. Esterle P. Hammel H. Harrington J. Lisse C. Miller S. Achilleos N. Momary T. Noll K. Shure M. The Effect of SL9 on Jupiter's Vertical AerosolStructure: Observational Results from IRTF Near-Infrared Imaging Near-infrared images of Jupiter have been analyzed to determine changes of the planet's vertical aerosol structure wrought by the SL9 impacts. The use of multiple wavelengths in regions of varied atmospheric molecular absorption between 1.6 and 3.4 microns allows us to derive aerosol opacities and altitude distributions from the high stratosphere to the 3-bar level of the troposphere. The impact sites are detectable in all absorption bands with reflectivities many times higher than from clouds in the pre-impact atmosphere. This includes the 3.3-micron CH4 fundamental band where no aerosols have been previously detected, indicating that aerosols are present at the levels of several mbar total pressure. Our preliminary analysis concentrated on analyzing images in the 2.14-micrometer H2 collision-induced fundmental band taken over several weeks. From July 21 to August 7, the spatial extent of the well-isolated Q1 feature changed by less than 10% (aproximately 900 km), comparable to the fluctuations in night-to-night seeing. During this same time, the brightness of the cores of G, L, and Q1 did not change more than 10%, but the brightness of the H impact site decreased by 20%. A vertical aerosol model structure with bright 0.25-micron particles distributed uniformly between 1 and 200 mbar is consistent with both our near-infrared observations and with visible/red Hubble Space Telescope images (West et al., 1994, BAAS this issue). Specifically, in the core of the G impact site, we find particle column densities of 3.0 +/-0.5 x 10^8 cm-2, corresponding to optical thicknesses of 2.4 +/-0.4 and 0.085 +/-0.015 at 0.89 microns and 2.14 microns, respectively. 05.03 Harris W. M.* Ballester G. E. Barker J. Clarke J. T. Combi M. Jessup K. L. Kozyra J. Vincent M. Budzien S. Emerich C. Prange R. Gladstone G. R. Hall D. T. Fireman G. F. Livengood T. A. McGrath M. A. Talavera A. Woodney L. Early Results from the IUE Shoemaker-Levy Observing Campaign: Temporal Evolution of the FUV/NUV Albedo in the Impact Regions The collision of the remnants of comet Shoemaker-Levy 9 with Jupiter appears to have had significant effects on the structure of the Jovian upper atmosphere that were caused by the passage of fragments through high altitude regions, and by the upwelling of debris and gas from the lower atmosphere. We present the initial results of our IUE observing program to monitor the temporal development of the impact sites in the first hours after a collision. During this period significant evolution of the chemical composition of the upper atmosphere is believed to occur as the upwelled material cools and mixes with the background atmosphere. Our observational technique made use of the IUE small aperture to obtain a series of quick spatially isolated spectra of the E, G, K, S, and W impact sites while they were on the approaching limb, at the central meridian, and rotating out of the field of view. Spectra were obtained using both the SWP and LWP cameras, with exposure times optimized to get good signal to noise in the 1700-1950 angstrom, 2300-2550 angstom, and 2500-3200 angstrom band passes. Because of the 3" diameter of the aperture and the 5" resolution of the IUE telescope, these data provide the general characteristics of the impact sites rather than the detailed structure near the center. We will show results indicating large scale changes in the albedo during the first 5 hours after an impact. This places a lower limit on the initial size of the affected region, and provides information about the nature of the absorbing material. We also present results regarding the rate of evolution in the spot albedo as a function of wavelength, and discuss the longer term evolution of selected impact sites. This work is funded by Nasa grant NAGW-4009 to the University of Michigan. 05.04 Stapelfeldt K.* Ballester G. Clarke J. Harris W. Trauger J. Crisp D. Brooke T. Weaver H. Prange R. Emerich C. Bertaux J.-L. Ben Jaffel L. HST FUV Imaging of Jupiter's Upper Atmosphere Around the Time of the Comet Impact During the impact of comet Shoemaker-Levy-9 with Jupiter a combination of gases from Jupiter's lower atmosphere, cometary matter, and their photochemical by-products were deposited in the upper atmosphere. Due to the presence of scattering haze, dust, and UV absorbing molecules the sites of the fragment impacts appear dark in the reflected sunlight over 1400-2100 angstrom in images obtained with the Wide Field Planetary Camera 2 (WTPC2) using the Na Wood's filter (F160W). Due to Rayleigh scattering by molecular hydrogen, far UV images probe only the upper atmospheric levels (down to around the 100 mbar levels, above the low stratosphere haze layer). Motion of the dark clouds provides information on the magnitude and direction of the circulation in these high altitude regions. During the impact week, evolution in the morphology and contrast of the clouds was observed. Material was carried zonally by the upper atmospheric winds, starting to form a dark band at the impact latitude, and latitudinal motion was also observed that differed between impact sites. The dark clouds associated with the impact sites of fragments A, C and E were observed the most. One interesting feature appeared about two weeks after the first impact, where some material associated with impact sites A and E seemed to have migrated north and to be somewhat detached from the rest of that concentrated at the impact latitude. This may reflect the effect of different wind patterns/speeds at the different upper atmosphere altitude levels. In addition to the comet related phenomena, the WFPC2 far-UV images obtained in May 1994 with our Guaranteed Time Observer program, as well as Guest Observer images obtained during the comet campaign, have revealed various features in the solar light reflected by the Jovian upper atmosphere: a) banded structure that does not exactly follow the visible bands in the lower atmosphere, b) high altitude dark material associated with the Great Red Spot, and c) some structure in the dark polar haze. This work is supported by STScI grant GO-5624,18-93A to U. Michigan. 05.05 Clarke J.* Ballester G. Trauger J. Stapelfeldt K. Crisp D. WFPC2 Investigation Definition Team Prange R. Emerich C. Ben Jaffel L. Bertaux J. L. Weaver H. Far-UV Imaging of Jupiter's Aurora with the HST/WFPC 2 Before and During the Impacts of Comet Shoemaker/Levy A series of far-UV images of Jupiter have been obtained with the Wide Field Planetary Camera 2 on the Hubble Space Telescope using the Na Wood's filter. The first UV images were obtained on 19 May 1994 over bandpasses including 1150-2100 angstrom, 1300-2100 angstrom, and 1650- 2100 angstrom. The images show bright aurora at both north and south poles, with emissions from H Ly alpha (1216 angstrom) and the H2 Werner and Lyman band series (1150-1650 angstrom), in addition to Rayleigh scattered solar continuum across the disk with pronounced polar darkenings which are asymmetric between the north and south polar regions. There is considerable structure in the north aurora, with a complete auroral oval and additional emission inside the oval. The observed emissions are up to approximately 100 kR in brightness, with a limiting sensitivity of roughly 1-10 kR. A more extended series of shorter exposures was obtained on 31 May 1994 with 10 min. exposures covering roughly 5 hours (1/2 Jovian rotation). These images show localized auroral emission structures which change dramatically on short time scales, with features which are mainly co-rotating with Jupiter. Additional far-UV images of Jupiter were obtained over 7 days during the impacts of Comet Shoemaker/Levy. These images show pronounced darkenings in the reflected solar continuum at the impact sites, with spatial structure which evolves with the local upper atmospheric winds over the week-10 days following the impacts. Jupiter' s aurora are apparent in each far-UV image, with the northern oval and changing emission structures along and inside the the oval. In addition, we detect UV emission from the foot of the Io flux tube on each occasion when Io is on the sunlit side of Jupiter. During the impact week two image series revealed auroral emission structures that may be connected with the impact events: northern auroral arcs near the magnetic conjugate point from the K impact site roughly 45-54 min. after the impact, and a variable southern emission feature apparently associated with the R fragment before its impact. This work is supported by grants STScI GO- 5624.18-93A and JPL 959122 to the Univ. of Michigan. 05.06 Hall D. T.* Gladstone R. Herbert F. Lieu R. Thomas N. EUVE Observations of Jupiter: Effects of Comet SL-9 The Extreme Ultraviolet Explorer satellite conducted extensive observations of the Jupiter system before, during and after the arrival of the fragments of Comet Shoemaker-Levy 9. Approximately 500,000 seconds of data were acquired in 1994. Previous observations of the Jupiter system revealed that electron-impact generated line emission from oxygen and sulfur ions resident in the Io plasma torus dominate the spectrum in the 300-730 angstrom range; these emissions dimmed moderately after the impact events, and no new torus emissions were detected. Unexpectedly, following several of the impacts, EUVE detected transient brightening events in planetary atomic helium resonance emission, HeI 584 angstrom, which was not detected before the impacts (I < 1 Rayleigh), although it was measured by the Voyager UVS instruments during 1979 (I is about equal to 4 Rayleigh). After the impacts of fragments H and K the HeI 584 angstrom brightness increased to about 25 Rayleigh, (arbitrarily assuming that the atmospheric He enhancement covered 10% of Jupiter's disk). The brightening events indicate that the impacts lifted substantial amounts atomic helium to high altitudes in Jupiter's atmosphere, above much of the molecular hydrogen gas that would have absorbed the emitted HeI 584 angstrom photons. 05.07 Schulz R.* Encrenaz Th. Stuwe J. A. Wiedemann G. Spatial Distribution of Jovian Near-IR Emissions Associated with the SL-9 Impact: Evidence for Northern Counterparts Between July 16 and 31, 1994, Jupiter was monitored in the nearIR with the IRSPEC spectrometer at the ESO 3.5-m NTT, at La Silla, Chile. We concentrated on the H2 S(1) quadrupole line at 2.12 microns and the H3 multiplet at 3.5 microns, which both occur at low pressure levels, very high in the stratosphere. During the week of impacts the 4."4 slit was aligned along the parallel of the impact sites. This allowed to search into the immediate implications of each impact to the Jovian atmosphere at the time of event and to study the evolution of the older impact sites additionally present in the spectra. Fragments B, F, and H were observed at time of impact. The impact of B was observed at 2.12 microns and H was watched in the 3.5 micron region. For details on the H event see Encrenaz et al., this issue. For impact F we recorded data in 3 spectral regions (3.3 microns, 3.5 microns, 2.1 microns) within two hours after impact. Since F almost fell on impact site E, both sites could only be distinguished by their distinctly different spectra in the 2.1 micron region. The spectrum of F was characterized by a strong featureless continuum, whereas the already evolved site E showed little continuum, but a strong H2 line. After July 22, emissions clearly associated to the impacts were detected in the 2.1 micron and 3.5 micron regions also in the northern hemisphere (lat.: +44 degrees). The emissions were not uniformly distributed in longitude, but concentrated at the longitudes of the brightest impact sites. They could result from the transfer of charged particles along the Jovian magnetic field lines. The mapping of the entire planet in H2 and H(sub)3^+ showed their distribution on the Jovian disk. As expected the H(sub)3^+ emission was strongest in the auroral regions and was also strong at the impact sites and their northern counterparts. Apart from these regions it was extremely weak, although the strongest H(sub)3^+ line at 3.533 microns could be detected at all latitudes. 05.08 Waite J. H., Jr.* Gladstone G. R. Na C. Stern S. A. Franke K. Bagenal F. Clarke J. T. Fabian A. C. Brandt W. N. X Ray Emissions Produced as a Result of the Impact of Comet Shoemaker-Levy 9 with Jupiter Rontgensatellit (ROSAT) high-resolution imager (HRI) observations of Jupiter made before and during the impact of comet Shoemaker-Levy 9 with Jupiter indicate the emission of x rays from northern mid-latitudes in association with the K, P2, and W fragment impacts. The emissions appear to originate at the north magnetic conjugate footprints corresponding to southern latitude impact sites. This suggests a mechanism whereby the comet impact produces in situ acceleration of electrons and/or magnetospheric perturbations of trapped radiation belt electrons that precipitate into the weaker surface magnetic field region associated with the northern magnetic conjugate footpoint. Interaction of the electrons with the upper atmosphere subsequently produces x ray emissions through a bremsstrahlung process. 05.09 Dessler A. J.* Hill T. W. Effects of Comet Impact on the Jovian Magnetosphere As expected from observational estimates of dust concentration and upper limits for gas production from Comet Shoemaker--Levy--9, direct effects on the Jovian magnetosphere were slight [Dessler and Hill, GRL 21, 1043, 1994]. However, three unexpected effects of the comet impacts have been reported: (1) approximately a 25% increase in the intensity of decimetric radio emission (synchrotron radiation from trapped relativistic electrons); (2) mid-latitude auroral UV emission features in the northern hemisphere; and (3) x-ray emissions, also from mid- latitudes in the northern hemisphere. The reported auroral features are somewhat poleward of the northern footprint of the magnetic field line that connects to the K impact site, according to available models of Jupiter's intrinsic magnetic field, and the position of the source of the x-ray emissions is consistent with that of the more highly resolved auroral features. We propose that these three phenomena are different manifestations of a single cause: namely, ionospheric motions driven by the impacts of SL-9 fragments on the Jovian atmosphere. The impacts produce ionospheric winds that interact with the Jovian magnetic field. An ionospheric wind of 1 km/s produces a vxB electric field approximately 0.5 V/m and a potential of more than 1 MV across the region of impact-driven wind. The resulting magnetic-field-aligned Birkeland current system accelerates electrons into the conjugate atmosphere to produce the observed auroral arcs. The vxB electric f1eld also "stirs" the magnetosphere near L = 2 (the region where decimetric emissions are produced), which, because radio emission is sensitive to radial magnetospheric motions, needs only a small displacement of the relativistic electrons already present to account for the observed decimetric enhancement. Thus, the one mechanism of splash-induced winds explains the two auroral arcs and the associated x-ray feature in the northern hemisphere as well as the increase in decimetric radio emissions from the inner magnetosphere. This work was supported in part by NSF grant ATM-9322360. 05.10-P DePoy D. L. Spencer J. R. Orton G. S. Dumas C. Kim S. J. Near-IR Observations of the Comet Crash from Cerro Tololo We used the 1-2.5 micrometer Ohio State Infrared Imager Spectrometer (OSIRIS) to observe the Shoemaker-Levy 9 impacts from the CTIO 4-meter- telescope in Chile. We obtained 1.58, 1.7, and 2.3 micrometer images and 1-2.5 micrometer cross-dispersed R=500 spectra of the impact sites during the following times in July (given in fractional days): 16.95- 17.15; 17.93-18.15; 19.00; 22.80-22.90; and 23.18; also a few images near days 25.0 and 27.0. Continuous movies at 1.7 or 2.3 microns during the B and F impacts showed no detectable effects due to these events, though clouds caused brief interruptions, and all other impact events were clouded out. In the CH4 filters, considerable structure was seen in the high altitude clouds produced at many of the impact sites. The few spectra of the impact site clouds so far reduced show weak K-band CH4 absorptions, probably due to CH4 above the impact clouds: simple reflecting-layer models assuming normal atmospheric CH4 abundances above the impact sites give cloud altitudes in the 1 mbar range, though there is considerable variation in the strength of the CH4 bands between spectra. 05.11-P Chanover N. J. Marley M. S. Severson S. A. Hereld M. Near-Infrared Observations of Comet Shoemaker-Levy 9 Impacts We collected near-infrared images of Jupiter with the Astrophysical Research Consortium's 3.5 m telescope at Apache Point, NM, on the nights of July 15, 16, 18, 19, and 20, 1994. The GRIM II near-infrared GRism spectrometer/IMager was used to image Jupiter at several near-infrared wavelengths with narrow-band filters centered at 1.58, 1.70, 1.99, 2.122, 2.22, and 2.36 microns and in K band. These data are used to place limits on the vertical extents of the ejecta created by the comet impacts. We compare the relative heights of the clouds created at impact sites H, D/G, and E in an effort to characterize the ejecta created by several different impacts. We also plan to integrate the APO dataset with simultaneously obtained methane band and continuum images from the Tortugas Mountain Observatory 0.6 m telescope, which span the spectral region from 450 to 968 nm (see Kuehn et al., this issue). This work was supported in part by NASA grant NAGW-1802. 05.12-P Kuehn D. M. Beebe R. F. Murrell A. S. Vertical Structure Models for the Impact Regions on Jupiter of Comet Shoemaker-Levy 9 The Tortugas Mountain Station of the NMSU Observatory continued its monitoring of atmospheric changes on Jupiter throughout the 1994 observing season. Intensity calibrated images in broadband blue, green, red, and near IR wavelengths as well as narrow band images of Jupiter in visible and near-IR methane absorption bands were taken prior to, during and after the Shoemaker-Levy 9 impacts in July 1994. Hubble Space Telescope images obtained at similar wavelengths before, during and after the impacts will be used as well. In particular, calibrated ground-based observations were obtained for 20 July 1994 and 25 July 1994. These high resolution (PSF FWHM approximately 1 arc sec for groundbased imaging), photometrically calibrated images are used to retrieve vertical structure information. Vertical structure models were constructed by fitting scans of constant latitude (limb darkening with a multilayer, radiative transfer model incorporating multiple scattering. We are especially interested in the vertical structure of the localized and resolved cloud disturbances arising from the comet impacts. The scale of the time variation of any vertical structure detected will also be of interest if it is possible to detect. 05.13-P Morozhenko A. V. Use of Consequences of the Comet Shoemaker-Levy 9 Collision with Jupiter for Study of Nature of Deep Atmospheric Layers of Jupiter and of the Cometary Materials Consequences of the collision which would be observed up to 1995 can be changes of upper cloud layer of Jovian atmosphere and formation aerosol haze of cometary origin. It is shown that this phenomena can be found most effectively with simultaneous measurements of polarization and reflectivity in several spectral ranges of continuum for wavelength from 0.30 to 0.80 microns and in contours of different methane absorption bands. The measurements for the most powerful band at 0.889 microns make it possible to find haze at the level of optical thickness near 0.02. 05.14-P Beebe R. F. Simon A. A. Huber L. F. Comparison of Cloud Structure in Jupiter's Southern Hemisphere at the Time of Shoemaker-Levy 9 Impacts with Voyager Data Images with filter F336W (333+/-18 nm), F410M (409+/-07 nm), and F547M (545+/-24 nm) or F555W (533+/-61 nm) obtained with the Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) are compared with 1979 Voyager 1 and 2 ultraviolet (325+/-45 nm), violet (400+/-50 nm) and green (550+/-15 nm) images of similar spatial resolution. The extent of alteration of typical cloud systems or generation of anomalous structures associated with the comet is investigated. The expanded wavelength coverage of WFPC2 (200-325 and 600-1000 nm) is utilized to test the hypothesis that the dual morphology (turbulent spiraling aspect or bright central region edged with a wavelike pattern) of cyclonic structures at 28-44 degrees South latitude is due to differences in stratospheric cloud cover. Support for this work is provided by NASA through the SL-9 Campaign of the Space Telescope Science Institute, which is operated by the Assoc. of Univ. for Research in Astronomy, Inc., under contract NAS5-2G555. 05.15-P Yanamandra-Fisher P. A. Orton G. S. Gillam S. Young J. W. Kanamori T. Spitale J. N. Grasdalen G. Fisher R. F. Visual and Methane Band Observations of the Impact of Fragment R on Jupiter from Table Mountain Observatory Observations of Jupiter during the impact week of comet Shoemaker-Levy 9 were recorded at the JPL/Table Mountain Observatory (TMO) from 21 - 25 July 1994 (UT) using a visual CCD camera at several wavelengths: B and V filters and four methane bands at 0.89 microns, 0.945 microns, 0.75 microns, 0.727 microns. The impact of fragment R was continuously observed in the 0.89 micron methane band on 21 July 1994 from 5:00 to 6:00 UT at 50 second intervals. Observations of Jupiter in the other filters were acquired pre- and post-R impact. We saw evidence for several limb-brightening events between 5:30 UT and 5:45 UT, with the impact site rotating onto the planet about 6:00 UT. The material appears very bright at 0.89 microns, but is dark at all the other wavelengths, indicating the deposition of material in the stratosphere. Current work is focussed on the improvement of absolute calibration, determination of center-to-limb variations at several wavelengths to constrain optical properties of the stratospheric particles; evolution of the R impact site and correlative analysis with near-infrared and thermal infrared observations (from 1.65 microns - 20 microns) of Jupiter, acquired at the NASA/InfraRed Telescope Facility during the same time interval. 05.16-P Musatenko S. I. Borovkov O. V. Ivchenko V. N. Kotsarenko A. N. Possible Effects in Radio-frequency Emission of Jupiter on its Interaction with Comet Shoemaker-Levy Relying on study of radio-frequency emission of nearterrestial space in ultra-short wave range and its connection with different helioheophysical disturbances, the following effects would be expected in radio-frequency emission during interaction process of magnetosphere, ionosphere and atmosphere of Jupiter with the comet Shoemaker-Levy. 1. The radio-frequency emission fluxes bound to increase in the centimeter and decimeter wave ranges. 2. The polarization degree in decimeter wave range will decrease and next recover. 3. The radiobursts fluctuations dealing with orbiting of the planet will decrease. 4. The discharges type of thunderstorm ones are occurred due to big quantity of dust. The implantation of the cometary fragments in the Jupiter atmosphere, their motion and explosions will produce powerful shock and acoustic waves. Propagation of these waves would cause fluctuations of radiobursts in the centimeter wave range. Our line of investigation will be consist in searching for abovementioned effects. 05.17-P de Pater I. Heiles C. Wong M. Maddalena R. J. Strom R. LePoole R. Spoelstra T. Bird M. Neidhoefer J. Funke O. Price M. Kesteven M. Bolton S. J. Klein M. J. Galopeau P. Gerard E. Lecacheux A. Dulk G. Leblanc Y. Hunstead R. W. Campbell-Wilson D. Ye T. Jupiter's Synchrotron Radiation Throughout the SL9 Impacts Jupiter's microwave emission has been observed throughout the SL9 impact period by many different telescopes. We will discuss the synchrotron radiation data obtained with the 140-foot NRAO telescope in Green Bank (20 cm), at Westerbork (20, 90 cm), Effelsberg (2.8, 6, and 11 cm), Parkes (20 cm), NASA DSN (13 cm), Nancay (20, 18, 9 cm), the Australia Telescope (13, 20 cm), the Molonglo Observatory Synthesis Telescope (36 cm) and the Very Large Array (20, 90 cm). The flux density increased by roughly 20-30% during the week of impacts at most wavelengths. We will present graphs of the total flux density as well as the spectral index as a function of time at wavelengths between 2.8 and 90 cm. In addition, we will show a few representive images, which emphasize the brightness distribution and changes therein during the week of cometary impacts. 05.18-P Shemansky D. E. Matheson P. L. Festou M. A. Noll K. S. Weaver H. A. Upper Limits on the Amount of SL-9 Dust Contained in the Inner Jovian Magnetosphere as Inferred from HST FOS Observations Much of the dust and gas that accompanied the SL-9 comet into the Jovian magnetosphere missed impacting Jupiter itself and continued through the magnetosphere. Some material, particularly small dust grains, may have become trapped in the magnetosphere when the qv x B force associated with the grains charge was large compared to gravity. Horanyi, (GRL, 21, 1039-1042, 1994), has shown that the Io plasma torus is a likely accumulation region for such grains. Molecular gases released in the encounter processes have very short life times against dissociation and ionization in the inner magnetosphere and can contribute plasma to the magnetosphere also. The Hubble Space Telescope Faint Object Spectrograph (FOS) has been used to observe the inner magnetosphere near the time of impact of the SL-9 comet. We present results from these observations and discuss limits on the amount of dust present in the inner magnetosphere. A specific search for SiIII has been made because of this ions strong 2,1 transitions at 1892 Angstroms and because detection of silicon in the torus would be unambiguously of cometary origin. CIII also has a nearby line at 1910 Angstroms. Other strong SiIII transitions would be effectively masked by OII, SIV, or hydrogen Lyman alpha radiation. The nominal baseline criterion for detection by FOS at the 5 Rayleigh level requires a column density of only 7 x 10^10 cm^-2. Silicon is sourced from dust grains by ion impact sputtering and from energetic electron induced dissociative reactions on grain surfaces. Estimated production rates of silicon are low. The density of micron sized dust in the Io plasma torus necessary to produce an observable effect is of order 10^-8 cm^-3. As of this writing, such dust densities are unlikely. If the comet dust is ice-coated, as is likely at 5 AU, OH may be the dominant product for energetic particle impacts. FOS observations searching for OEI in the inner magnetosphere of Jupiter near the time of the impacts may see some signal from diffuse cometary sources. 05.19-P Carsenty U. Mottola S. Braatz E. Neukum G. Imaging of the Jovian Upper Atmosphere and the Io Torus During the Encounter with Comet Shoemaker-Levy 9 A group of observers from the DLR institute for Planetary Exploration (Berlin, Germany) will observe the encounter of the large fragments of Comet Shoemaker-Levy 9 with Jupiter, using the 60cm Bochum telescope, the DLR CCD Camera (lk x lk) and a set of narrow band interference filters. Imaging of Jupiter in the CH4 absorption bands (893nm,727nm) and comparison with the "off" band (750nm), will enable us to monitor the Jovian upper atmosphere and detect transient events as well as permanent features, and study the interaction of the atmosphere with the cometary fragments. Imaging of the Io plasma torus in the emission lines of NaI, [SII], and [SIII] will enable us to study the interaction of the cometary fragments with the Jovian magnetic field. The nights before July 16 will be used to test our observing strategy and to obtain a baseline of Jupiter data before the encounter. We will implement an observing strategy which will enable us to observe transient events as well as permanent effects of the encounter. 05.20-P McGrath M. A. Weaver H. A. Hall D. T. Schneider N. M. Thomas N. Harris W. M. Livengood T. A. Prange R. P/S-L9 Related Observations of the Io Plasma Torus During the comet P/Shoemaker-Levy 9 encounter with the Jovian system several sets of ultraviolet spectroscopic observations of the Io plasma torus will be performed with both the Hubble Space Telescope and the International Ultraviolet Explorer satellite. The scientific objectives of these observing programs are two-fold: (1) search for new species, particularly silicon and carbon, associated with the increased amounts of dust being injected into the Jovian magnetosphere by the comet; and (2) monitor the well-studied UV emissions from sulfur and oxygen ions for any indication of significant change. The unambiguous detection of either carbon or silicon would be indicative of comet remnants, since the most sensitive UV spectroscopy of the torus to date with the Hopkins Ultraviolet Telescope in December 1990 has failed to detect either, and provides very stringent upper limits on their abundances. Variability by as much as a factor of two in the line brightnesses on time scales of weeks to months has been observed in both the UV and visible ion emissions. Observed line brightnesses within the previously measured range of variability will imply little impact by the comet on the system, while variations outside this range may imply a fundamental change such as that seen during the Pioneer 10 flyby in which the "torus" was apparently only partial. We will report on the findings of the planned observations. 05.21-P Hicks M. Grundy W. Fink U. Spectral Imaging of the Io Plasma Torus and Spectrophotometry of the G Impact Site In March of 1994 we began a program of spectral observations of the Io torus taken with our long-slit CCD spectrograph in a survey mode. By moving the slit across the plane of sky between exposures we are able to construct image cubes capturing all emissions between 0.5 and 1.0 micrometer and thus derive two-dimensional flux calibrated maps of emissions of Na D (5890 angstrom), S^+ (67l6 angstrom) S^++ (9530 angstrom), etc. We first obtained baseline observations of the Io torus before its interaction with P/Shoemaker-Levy 9, during the impact event as well as post impact. Our technique has the advantage over traditional filter imaging in that we are able to observe a wide spectral range simultaneously and search for emission changes which are not necessarily predicted. Weather factors prevented us from obtaining emission maps in the midst of the impact events. Some additional data was obtained Sept 6. At the time that this abstract is being prepared we are only in the first stages of data reduction. Preliminary analysis is showing time-variant phenomena. Images of the torus at 5890 angstrom show an enhancement of the total column density of Na D in the torus by a factor of three between April 14 UT and June 12 UT, unrelated to effects by the comet. This may be correlated to volcanic activity on Io before or at this later date. It may be possible that our studies can serve as an indirect monitor of geologic activity. In addition to studies of the torus, on July 22 UT, four days after its collision with Jupiter, we observed the impact site of Fragment G with our long slit spectrographic system. We present a calibrated spectrum from 0.5 to 1.0 microns with a resolution of approximately l0 angstrom. This spectrum should prove quite useful to help observers using relatively wide methane filters do a proper job of continuum subtraction on their images. When we compare the spectrum of the impact site with the bright zonal material adjacent we see an approximately 10% brightening in the saturated region of the 8900 angstrom methane band as well as a gentle reddish slope at shorter wavelengths. We hope that our spectrum will assist in constraining models of the impact sites, namely the height of the aerosols and their optical depths. This work was supported by NASA grant NAGW 1549. 05.22-P Niciejewski R. J. Roesler F. L. Scherb F. Oliversen R. J. Observations of the Extended Sodium Cloud in the Jovian System During the Encounter with Comet Shoemaker-Levy 9 High resolution spectrometric measurements of the sodium D emission rate in the vicinity of Jupiter were conducted prior to, during, and following the encounter with Comet Shoemaker-Levy 9. This paper will present preliminary results from the measurement campaign and comment on the magnitude of any change in the sodium magneto-nebula (zeno-corona). 05.23-P Prange R. Emerich C. Rego D. Ballester G. E. Clarke J. T. Harris W. M. Livengood T. Zarka P. Ben Jaffel L. Beust H. Dougherty M. K. Southwood D. Miller S. Gerard J. C. Ip W. Horanyi M. McGrath M. Paresce F. Talavera A. Trauger J. Staplefeldt K. Crisp D. Auroral Signature of the Interaction of Comet Shoemaker-Levy 9 with the Jovian Magnetosphere Observations of the FUV auroral emission of Jupiter have been performed during the traversal of the Jovian magnetosphere by comet SL9 fragments, together with an extensive set of preimpact (baseline) and postimpact (relaxation) observations, using HST image complemented by IUE observations. As part of this effort, we anticipate to identify the interaction of the comet dust coma with magnetospheric plasma in specific configurations where conjugate south/north auroral signatures are expected using FOC images before and after comet in magnetosphere, plus images looking for auroral arcs associated with P fragment. 05.24-P Budzien S. A. Livengood T. A. Fireman G. F. Harris W. M. Ballester G. E. McGrath M. A. Prange R. M. Talavera A. Early Results from the IUE Shoemaker-Levy Observing Campaign: Temporal and Spatial Variability of the Jovian Ultraviolet Aurora A comprehensive observation program of Jupiter was successfully executed by the International Ultraviolet Explorer spacecraft SL9 science team. Observations were conducted before, during, and after the impacts of the comet Shoemaker-Levy 9 fragments with the Jovian atmosphere. These impact events provided a unique opportunity to investigate the response of the Jovian aurora to impulsive forcing on the magnetosphere. Relevant processes capable of altering the auroral brightness or morphology may include changes in ionospheric conductivity due to ion chemistry of cometary volatiles or upwelling Jovian atmosphere, and modifications of the co-rotation efficiency in the Io plasma torus due to loading by gas and dust from the comet. The collisionally-excited far-ultraviolet H2 emissions from the north and south aurora were monitored, and no dramatic changes in auroral morphology, brightness, or variability were observed, although early indications are that the south auroral intensity may have been somewhat lower than usual during the impact period. Comparison with the typical temporal and spatial variability will be made in light of more than 15 years of IUE observations of Jupiter's aurora. SAB is supported by a fellowship from the Office of Naval Research. 05.25-P Miller S. Achilleos N. Lam H. Tennyson J. Jagod M.-F. Oka T. Geballe T. Joseph B. Baines K. Orton G. Ballester G. Trafton L. The Effect of the SL9 Impact on Jupiter's Aurorae Spectra obtained on UKIRT and images from NASA's IRTF show that the impact of Comet Shoemaker Levy-9 had a profound effect on the auroral emissions of Jupiter as measured in infrared wavelengths sensitive to the H(sub)3^+ molecular ion. In comparison with images and spectra taken in previous years, the aurorae immediately prior to impact appeared fairly normal. This situation continued at least until July 20; observations immediately after the Fragment C impact (July 17) showed no noticeable effect, for example. But spectra taken on July 25 at UKIRT show a very considerable enhancement of the northern aurora -- particulally in the region ,of the maximum emission (circa cml 150 degrees). Preliminary analysis shows that this is due to a tenfold increase in the column density of H(sub)3^+, rather than an enhancement in temperature. In comparison with previous years, the southern aurora appears slightly depressed. Subsequent UKIRT spectra and images taken on the NASA IRTF show this situation continuing at least until August 3. But later images show the relative strengths of the north and south auroral zones returning to pre-impact levels. 05.26-P Harris W. M. Ballester G. E. Barker J. Clarke J. Combi M. Vincent M. Gladstone R. Kozyra J. Prange R. Bibring J.-P. Emerich C. Ip W. Miller S. Rego D. Southwood D. Talavera A. Dougherty M. Livengood T. A. Budzien S. A. Espenak F. Fireman G. F. Kostiuk T. McGrath M. A. Feldman P. D. Hall D. T. Strobel D. F. Moos H. W. Woodney L. M. Observing the Impact of Comet Shoemaker-Levy with Jupiter Using the IUE Satellite We describe our program to observe the effects of the impact of comet Shoemaker-Levy with Jupiter using the IUE satellite. Four different groups from the US and Europe combined their efforts into a single science team with more than 450 hours of total satellite time between June and September. The IUE spectral range from 1150-3300 angstrom provided us with the most complete FUV/NUV coverage available during the encounter, and the nearly continuous IUE duty cycle allowed direct observation of all of the major impacts. During the course of this program we were able to study comet related effects and to perform long sought for simultaneous observations with the FOC, WFPC-II, EUVE, and NSFCAM. The Jovian upper atmospheric and magnetospheric phenomena that were monitored during this period include: > The temporal evolution of the NUWFUV impact site albedos. > The zonal and meridional migration of this new material by stratospheric and thermospheric winds. > The Jovian auroral emission intensity, optical depth, and relative strength between the north and south zones. > The high altitude equatorial Ly-alpha enhancement. > The visible intensity of the Galilean satellites during the impacts using the IUE targeting camera to search for evidence of a reflected 'flash'. > The characteristics of the lo plasma torus. > FUV emission from the developing impact plumes and their magnetically conjugate regions in the northern hemisphere. 05.27-P Nazarchuk H. K. Shulman L. M. The Preliminary Results of Spectral Monitoring of Jupiter and Its Satellites During the Comet Impacts The spectra of the Jovian satellites and the auroral zone of Jupiter are obtained at 6-meter telescope to look for the Balmer and other emissions expected in the impact phenomena. 05.28-P Lam H. A. Miller S. Tennyson J. Geballe T. R. Trafton L. Condition Mapping of the Jovian Ionosphere Using H3+ as a Probe--Baseline for the SL9 Impact Observation Medium resolution spectra were taken in April 1993 using CGS4 mounted on UKIRT. The data were fitted with theoretical H^+(sub)3 spectra to obtain temperatures and column densities. The results show that the H^+(sub)3 auroral temeratures were higher than those on the body of the planet. H^+(sub)3 emission is found at all latitudes with large enhancement at the poles. Earlier work reporting elevated temperature around 102 degrees Central Meridian Longitude (CML) have not been repeated here. Spectra taken with the slit along the equator detected H^+(sub)3 emission right the way across the planet. Taking into account the line of sight effect it was found that the setting limb has a higher concentration of H^+(sub)3 than at other CMLs. This work will act as the baseline for the upcoming SL9 campaign . 05.29-P Gerasimov M. V. Dikov Yu. P. Yakovlev O. I. Wlotzka F. Laboratory Approach to Impact of Meteorites and Comets on Planetary Atmospheres Early evolution of planets was characterized by high-temperature processing of planetary matter in impacts during planetary accretion. High-temperature processing of planetary matter and complex heterogeneous chemistry during impacts provided production of multiple chemical products which could be significant for initial global evolution of a planet. The use of a powerful pulse laser is a reliable method for laboratory simulation of high-temperature (3000-5000 K) pulse processes such as hyper-velocity impact of large meteorite or a comet, etc. In a cycle of our experimental works we have investigated chemical processes which accompany high-temperature transformation of different basic minerals, rocks, and meteorite matter. Special attention was made for investigation of chemical effects of counteraction of hot ejecta with planetary atmosphere. Obtained results indicate extensive chemical processes involving hot ejecta and atmospheric gases and can give a certain understanding of the early evolutionary trends of primitive atmosphere, ocean and of silicate matter. An approach is also done to simulate experimentally the counteraction of a comet with reduced atmosphere. 05.30-P Gomez J. M. Lecacheux J. Colas F. Laques P. Rouan D. Tiphene D. Sanchez-Lavega A. Observations of the SL9 Impact on Jupiter from 0.4 to 2.16 Microns at Pic-du-Midi Observatory We present the time-resolved photometric light curves at 2.16 microns and films of the impacts of fragments H, L Q1 and S of comet SL9 with Jupiter. At least three different phases are seen during the brightness increase and up to its maximum of impacts H and L, whereas only a steady increase is observed during the impact S. Photometric data in the nearby bands at 1.25 microns (J) and 1.65 microns (H) are also given. We have determined the spectral reflectivity from 0.4 to 2.16 microns (continuum and methane bands) of cloud system G and L as measured on 20 July, as well as their center-to-limb dependence. The tracking of the features in the red since their formation and up to September, has allowed to characterize their morphology changes and motions. The main spots associated to each impact remained nearly stationary in System II (i.e. their zonal velocities relative to the internal rotation perior -- System III -- were westward with u = -1 to -4 m/s). However the most remarkable features (complexes G/D/S/R and K/W, and spot L) showed a zonal expansion with velocities in the range u = 1 m/s to 31 m/s. Besides this, meridional motions have been detected within several impact regions, in particular within the complex G/D/S/R we have measured meridional velocities v = 6 m/s, both in the northward and southward directions from the impact center, reaching the cloud elements on 1 August the latitudes 61 deg South (bright SPR limit in the 890 nm methane band) and 37 deg S (STB). 05.31-P Scotti J. Larson S. Howell E. Marcialis R. Nolan M. Wisniewski W. A'Hearn M. Wellnitz D. Campins H. Rabinowitz D. Butner H. Tapia S. Vilas F. Doherty P. Bessell M. Brosch N. Liebowitz E. Gilmore A. Kervin P. Africano J. Levine S. Schuster W. Martin R. Verveer A. Moreno F. Molina A. Rutten R. Kidger M. Preliminary Results from CINE CINE, experiencing about 50% clear skies during the SL9/Jupiter impact week, amassed a large amount of data consisting of pre-impact images of the comet fragments, spectra of satellites during impact, direct images of the impact spots on Jupiter, and spectra of the spots. The comet had become too faint for useful studies of the interaction with the Jovian magnetic field, but the elongation of the inner coma by differential acceleration was observed within 1-2 days of impact. Positions of fragments E, G, L, P2 (8a and 8b),Ql,Q2, R, S, and W obtained at Las Campanas on 1994 July 16 near 04:00 UT and reduced with respect to the PPM astrometric catalogue generally indicate systematic residuals of -1" to -2" RA with respect to the pre-impact ephemeris, consistent with the impacts arriving approximately 10 minutes later than expected. With instrumental dead time averaging 50%, flashes of the impact meteor off salellites as continuum or spectral emissions were not observed at 2% of the satellite's brightness. The evolution of the impact spots were recorded with near continuous coverage during the impact period, and for over two months at less regular inlervals. High resolution methane-band images and high resolution long-slit spectra across the spots provide information on the impact cloud height. High resolution narrow-band methane images show the impact plume of H to be 750km above the limb less than 20 min. after impact. This project was funded by the NASA Planetary Astronomy Program, the USAF Space Command and the various host institutions. 05.32-T Scherb F. Retherford K. Smyth W. H. Woodward R. C. Comet Shoemaker-Levy 9 Impact with Jupiter: Observations of [OI]6300 and Na D2 Emissions from Io We plan to carry out observations of [OI]6300 and Na D(sub)2 (5890) emissions near Io during a three-week period centered on the Comet Shoemaker-Levy 9 impact with Jupiter. The observations will be carried out with the stellar spectrograph at the McMath-Pierce telescope on Kitt Peak. We will search for observable effects of the comet and its cloud of dust and gas on the interaction of the plasma torus with Io's atmosphere. This work was supported in part by NASA grant NAGW-3319. SESSION 06 ....... Solar System Formation II Monday, 4:00 - 5:30 Crystal Ballroom B A. F. Berman and P. Cassen, Moderators 06.01 Boss A. P.* Yorke H. W. Protoplanetary Disks, Mid-IR Dips, and Disk Gaps The flat-topped spectral energy distributions of certain T Tauri stars show evidence for significant dips at mid-infrared wavelengths (~10 micrometers) that could be explained by the existence of gaps in the protoplanetary disks believed to be orbiting these pre-main-sequence stars. Assuming an effective temperature depending on radius as T(sub)e is proportional to r^-q, Adams, Lada, and Shu (1988, Ap.J., 326, 865) showed that q ~ 0.5 disks lead to flat-topped spectra whose masses can be inferred by fitting to long wavelength (~mm) observations. Marsh and Mahoney (1992, Ap.J., 395, L115) showed that mid-IR dips could be caused by removing disk matter with T(sub)e ~ 300K, corresponding to Lambda ~ 10 micrometers (Wien's law). In this interpretation, the inferred disk gaps could then be taken as evidence for unseen companions (possibly of planetary mass) orbiting in the disk. Boss and Yorke (1993, Ap.J., 411, L99) then showed that mid-IR dips could also be caused by the effects of realistic dust grain opacities in a continuous disk. Using a detailed radiative hydrodynamical model of a 0.02 solar mass protoplanetary disk orbiting a solar-mass protostar (Boss 1993, Ap.J., 417, 351), b.y. showed that the non-power-law T(sub)e profile produced by the thermostatic action of the dust grain evaporation and condensation process in a disk without a gap leads to a mid-IR dip quite similar to that seen in the spectrum of T Tau itself. Using a refined technique for calculating the radiative equilibrium of the disks, we have now reproduced the initial result of b.y. for a 0.02 solar mass disk, and extended the calculations to disks with masses of 0.01 solar mass and 0.04 solar mass. The disks are assumed to be accreting matter from their envelopes (at ~10^-6-10^-5 solar mass/yr.) and hence are contracting vertically, a process that appears to be important to disk energy budgets; radial contraction occurs as well. The spectrum of the 0.04 solar mass disk shows a mid-IR hump (with a strong 10 micrometer absorption feature) because in this higher mass disk, a region with T(sub)e 250K extends to larger radii and so has a larger surface area. The 0.01 solar mass disk shows an even more pronounced mid-IR dip than the 0.02 solar mass disk because the T(sub)e profile contracts to smaller radii in a lower mass disk. The 0.01 solar masses disk leads to the best match to the spectrum of T Tau. This research was partially supported by NASA grant NAGW-1410. 06.02 Graham J. A.* Boss A. P. Clumpy Accretion During Early Stellar and Planetary Evolution Three types of astronomical observations are best explained by the existence of absorbing clumps of dust and gas that block stellar radiation while moving at high velocities within a few astronomical units of young pre-main sequence stars: (a) rapid variations in stellar luminosity independent of wavelength; (b) rapid changes in surface brightness of nearby reflection nebulae; and (c) rapid variations in spectral lines excited in circumstellar regions. Clumps with mass of the order of 10^22 grams appear to be required. Infalling motions predominate. As the clumps impact a protoplanetary disk, a localized, intense source of heat suitable for chondrule formation may occur. We have been studying especially closely the pre-main sequence variable star R CrA. New observations made this year at Las Campanas Observatory provide evidence that the clumps exist over a wide range of opacities. Optically thin clumps, which are responsible for circumstellar line variations, are more common than the optically thick clouds necessary to produce shadow effects on reflection nebulae. Multi-year AAVSO observations of R CrA indicate that the number density of clouds changes from year to year. While the origin of these clumps is presently unknown, they might arise from the return of material swept up by the outflowing stellar wind. This work has been supported by NASA Grant No. NAGW-2287 in the Origins of Solar Systems Research Program. 06.03 Tegler S.* Rettig T. Weintraub D. Pendleton Y. Whittet D. Kulesa C. Evidence for Chemical Processing of Pre-Cometary Icy Grains Around Pre-Main-Sequence Stars We report the detection of a broad absorption feature near 4.62 micrometers in the spectrum of the Taurus cloud source Elias 18. This pre-main-sequence source is the second in Taurus, the third in our survey, and the fifth known in the sky to show the broad 4.62 micrometers absorption feature. Of equal importance, this feature is not seen toward several other embedded sources in our survey, nor is it seen toward the source Elias 16, located behind the Taurus cloud. Laboratory experiments with interstellar ice analogs show that such a feature is associated with a complex C=N containing compound (called X(C=N)) that results from high energy processing of simple ice components into more complex, organic components. We find a non-linear anticorrelation between the abundance of X(C=N) and frozen CO in non-polar lattices. Because the abundances of frozen CO and H20 are strongly correlated with each other and with visual extinction toward sources embedded in and located behind the Taurus molecular cloud, these ice components usually are associated with intracloud material. Our results indicate that X(C=N) molecules result from chemical processing of dust grains dominated by non-polar icy mantles in the local environments of pre-main-sequence stars. Such processing of icy grains in the early solar system may be an important source of organic compounds observed in minor solar system bodies. This research is supported by NASA grants NAGW-3433 and NAGW-3385 to Notre Dame and Verderbilt Universitites. 06.04 Scholl H.* Lecavelier A. Roques F. How To Detect a Planet in the Disk of Beta-Pictoris? The Beta Pictoris disk exhibitsan inner clearing zone at a typical distance of 15-30 A.U. from the star. We had investigated numerically and analytically the possibility of dust confinement by a planet orbiting Beta Pictoris (Icarus, 108, 37 and 59, 1994). Above a critical planet mass of ~10^-5 stellar mass (5 Earth masses), the particles are trapped in outer mean motion resonances. This mechanism can create a steady state clearing zone extending inside the planet orbit. A depletion region corotating with the planet and just outside it creates an asymmetric feature in the dust disk. A moderate planet eccentricity (lO^-2) can generate large arc-like structures. We have improved this model, taking into account destructive collisions between the particles in order to compare it directly to the observations of the inner part of the disk. We show that, if the optical depth is smaller than a critical value, assymetric structures created by the planet are maintained in spite of collisions. These structures could be a way to reveal bodies otherwise invisible by direct imagery. 06.05 Cochran W. D.* Hatzes A. P. A Progress Report on the McDonald Observatory Search for Extra-Solar Planetary Systems The McDonald Observatory Planetary Search (MOPS) program is designed to detect planetary companions to solar-type stars by measuring the orbital motion of the star around the planetary system barycenter.We obtain regular synoptic observations of the variations in stellar radial velocity of a sample of 36 nearby F, G, and K dwarfs. Velocity measurements are made to a precision of about 10m/s^-1, which would be sufficient to detect a Jovian-mass planet around a solar-mass star. The MOPS was started in September 1987, and now has accumulated seven years worth of data. So far, no massive planets have been found with short period orbits. We present typical results from the program, place limits on the types of planets which can exist around program stars, and discuss difficulties that have been encountered and their solutions. We also present plans for future improvements in radial velocity precision and survey sample size. 06.06 Cullers D. K.* Statistical Model for Photometric Detection of Earth-Sized Planets A detector for Earth-sized planets orbiting other star which uses photometry must see changes in apparen stellar luminosity of order 10^-4. Such changes, lastin several hours, occur at regularly spaced intervals if cause by orbiting extra-solar planets intersecting the line of sight to a distant star. Detection must occur against background of random detector noise which causes fals positive events. For highly plausible assumptions about causes and amounts of background noise, an ideal folding detectio: algorithm finds Earth-sized planets after 3-4 years of observing, at signal/noise ratios of about 3.5. The noise model considers both instrument noise and that from fluctuations in stellar spectra. These latter are assessed using detailed records of solar luminosity fluctuations. It is found that the false alarm rate curve is a steep function of detector threshold while planetary detectability varies only slowly with this parameter. This work is supported by NASA. 06.07 Jenkins J. M.* Doyle L. R. Detection of Extrasolar Planets in Eclipsing Binary Systems: A New Cross-Correlation Technique The photometric detection of extrasolar planets in eclipsing binary systems takes advantage of the binary orbital plane (and presumably the planetary orbital plane) being parallel to the observer's line-of-sight. A second advantage is the unique photometric signature a planetary transit makes due to the changing configuration of the two stars, allowing it to be distinguished from intrinsic stellar brightness variations and other noise sources. The modeled convolution of planetary transits with the light curve of selected eclipsing binaries can be correlated with observational photometric data to retrieve planetary transit signatures significantly below the noise. The usual ground-based photometric limit of about 1% can therefore be exceeded. For the smallest few eclipsing binary systems ground-based detection of Earth-to-Neptune-sized planets should be possible with meter-class telescopes. We have run a series of numerical experiments for the binary system CM Draconis with twice Earth-sized planets in various circular orbits. A matched filter is constructed that maxirnizes the cross-correlation coefficient between the noise-corrupted observation and the model. Although it is rather large, the parameter space provides sufficient constraints to allow for unique detection of single planets even when the transit drops are well below the standard deviation of the measurement noise. In addition, it is possible to detect and isolate transit signatures of multiple planets, if the observations are carried out longer than two of the maximum orbital periods, and the planets are well separated. 06.08 Gautier D.* Lecluse C. Robert F. A Well-Mixed Solar Nebula: Constraints from Observed Deuterium Abundances in the Solar System Various objects of the Solar System are enhanced in deuterium with respect to the protosolar abundance value of 2.6 x 10 ^-5 (Geiss, in "Origin and Evolution of the Elements, Cambridge University Press, 1993 p. 89). This enrichment is frequently considered as resulting from ion-molecules reactions which occurred in the interstellar medium prior to the formation of the primitive solar nebula. This scenario implies that the solar nebula was not well-mixed since otherwise the ices enriched in deuterium would have lost their interstellar signature when moving towards the warm inner part of the nebula. We show that D/H ratios as high as 18 x 10 ^-5 can be reached in water in the nebula through molecular reactions, when taking into account the deuterium enrichment occuring at the gas-ice transition (Lecluse and Robert, Geochem. Cosmochem. Acta, 1994, in press). Accordingly, the D-enrichment observed in ocean water and in meteoritical clays as well as in the atmospheres of Uranus, Neptune, Titan and the Halley comet may have occurred in the nebula. This scenario is consistent with the wellmixed nebula models advocated by a number of authors (Prinn and Fegley, Astrophys. J, 249, 308, 1986, Prinn, Astrophys. J., 348, 725, 1990). On the other hand, enrichments observed in hydrocarbons and organic macromolecules embedded in carbonaceous chondrites have presumably an interstellar origin and have never been subsequently reprocessed in the nebula. 06.09 Gustafson B. A. S.* A New Analog to Light Scattering Laboratory at the University of Florida The absorption and scattering of sunlight by individual cosmic dust grains and aerosols as well as the emission of infrared light can be precisely simulated in the new scattering laboratory at the University of Florida. Following the design of the now defunct microwave analog facilities at the University of Florida and at the Ruhr University in Germany, the new facility uses the principle of electromagnetic similitude. Accurate measurements of single particle scattering and precise control of the target parameters is achieved by magnifying the wavelength and all particle dimensions by the same factor (~ 10^4) while keeping the complex index of refraction of the material constant. Custom designed antennas in a bistatic arrangement allow automatic filll w-waveband coverage corresponding to the range from blue to red using a network analyzer to record both scattered arnplitude and phase in the angular interval from O to 165 degree scattering angle. The broad wavelength coverage also allows the separation of the wanted signal from the background using time-gating technique to increase accuracy and boost the signal to noise ratio thus allowing scattering measurements from particles close to the Rayleigh size limit. The upper size limit is set by the extent of the flat portion of the wavefront which is of the order of 10^2 wavelengths. This work is supported by NASA's Planetary Atmospheres Program through grant NAGW-2482. 06.10-P Lumme K. Rahola J. Light Scattering by Porous Dust Aggregates in the Discrete-Dipole Approximation Electromagnetic scattering by various crystals and porous dust particles has long been a challenging problem in several astronomical applications including solar system objects as planetary atmospheres, cometary comae, asteroid regoliths and interplanetary dust particles. In regoliths and planetary atmospheres the particles strongly interact between each other whereas in comae and interplanetary space we see effectively the single scattering only. Quite recently there has been a new computational progress in the discrete-dipole approximation (DDA) shown by Lumme and Rahola (ApJ 425, p. 633, 1994). We are now able to compute light scattering in almost any geometry consisting up to 10^5 interacting elect dipoles. We are currently studying stochastic aggregates which are thought to model dust particles in the solar system. We show how the backscattering enhancement and the reversal of linear polarization develop as a function of the mean particle size, porosity and optical constants. Some well known photometric and polarimetric features, such as the opposition effect and the negative polarization seem to follow naturally from these computations. 06.11-P Mautner M. Leonard R. L. Deamer D. W. Meteorite Organics on the Early Earth: Hydrothermal Release, Prebiotic Properties and Microbial Activity The release, survival, prebiotic potential and microbial nutrient properties of meteorite materials are examined experimentally. Simulated undersea volcanic or impact-induced high temperature and pressure conditions are applied to powdered Murchison meteorite, and release 10% of the organics at 121 degrees C and 2.1 bars and 51% at 350 degrees C and 250 bars, the latter including some of the organic polymer. The hydrothermal release preserves prebiotic components such as carboxylic acids, amino acids and polycyclic aromatics. The released material is surface active, with surface pressures up to 2 x 10^-2 N/m and gives an expanded surface tension isotherm that suggests a mixture of amphiphilic components. One released component, nonanoic acid, forms vesicles. Meteorite powder processed at high temperatures inhibits microbial growth. However, the materials released at 121 degrees C are nutrients for the humic acid utilizing microorganism Pseudomonas maltophilia, and efficient nutrients for the oligotroph Flavobacterium oryzihabitans, which grows to a globular shape in the dilute 10^-3 mol/l meteorite extract medium and utilizes about 3% of the released organics. The observations suggest that meteorite organics can be released efficiently under early planetary conditions and are suitable for prebiotic synthesis, and for supporting microorganisms on the early Earth or those transported to other planetary environments. Hydrothermal and microbial processing may be potentially useful in the direct conversion of asteroid organics to biomass for space-based applications. SESSION 07 ....... Educational Outreach Invited Posters Monday, 5:30 - 6:30 07.01-P Buratti B. J. Brady L. E. Hanner M. S. Alvidrez R. F. Roettger E. E. `Teachers Touch the Sky:' A One Week Workshop for Teachers Grades 4-6 Space science is inherently interesting to students, less threatening to teachers than some other sciences, and interdisciplinary in nature. These features make it the ideal vehicle for teaching basic scientific concepts to children in a concrete and captivating manner. During the summer of 1994, JPL scientists will be holding a one week pilot workshop for 16 teachers in grades 4-6. We will walk the teachers through five hands-on activities which are all based on current projects in astronomy and space science at Caltech and the Jet Propulsion Lab. We will discuss ways of integrating the lessons into the teachers' own curriculum; the teaching of basic physical principals will be emphasized. The teachers will also learn of the resources NASA makes available to them, and they will have the opportunity to tour JPL's facilities and to talk to "real" scientists about their work. The workshops to be covered include the Venus topography box, cratering and mass,extinctions, and the construction of a small telescope. The approach will be "small science" in a supportive environment for teachers who in general have no background in science. FUNDED BY AN EDUCATIONAL SUPPLEMENT FROM NASA CODE Z. 07.02-P Cunningham C. C. Stiff T. Curriculum-based Science Education Using a Multi-media Platform A cooperative science education project with IBM, Canada, The Simcoe County Board of Education (SCBE), and the Institute for Space and Terrestrial Science (ISTS) has recently begun. The progress towards developing a multi-media, Ontario high school curriculum based demonstration product will be outlined. Concepts in space sciences will be used to teach basic concepts in math and science to Ontario students at the Grade 10 - OAC (Ontario Academic Credit) levels. The advantages of this product over other multi-media learning materials currently flooding the market will also be discussed. 07.03-P Limaye S. S. Sromovsky L. A. Krauss R. Wright E. Santek D. Fry P. Saunders R. S. McIDAS-eXplorer: A Software Environment for Analysis of Planetary Data A software environment for analysis of planetary data published by the Planetary Data System on CD-ROM volumes has been developed for UNIX and OS/2 2.1 operating systems. The environment allows convenient access, navigation, analysis, display and animation of planetary data by utilizing the full calibration and navigation data accompanying the planetary data. Support currently exists for Voyager images of the giant planets and their satellites, Magellan radar images (F-MIDR and C-MIDRs, global map products (GxDRs) and altimetry data (ARCDRs), Galileo SSI images of the earth, moon, Venus), Viking Mars images and MDIMs as well as most earth based telescopic images of solar system objects (FITS). The NAIF/JPL SPICE kernels are used for image navigation when available. For data without the SPICE kelnels (such as the bulk of the Voyager Jupiter and Saturn imagery and Pioneer Orbitel images of Venus), tools based on NAIF toolkit allow the user to navigate the images interactively. Multiple navigation types can be attached to a given image (e.g for ring navigation and planet navigations in the same image). Tools are available to perform common image processing tasks such as digital filtering, cartographic mapping, map overlays, data extraction. It is also possible to have different planetary radii for an object such as Venus which requires a different radius for the surface and for the cloud level. A graphical user interface based on Tcl-Tk scripting language is provided (UNIX only at present) for using the environment and also to provide on-line help. It is possible for end users to add applications of their own to the environment at any time. This work was supported by USRA Contract# 5555-08 under NASA's Applied Information Systems Research Program and by the Space Science and Engineering Center at University of Wisconsin-Madison. SESSION 08 ....... Mission Applications Posters Monday, 5:30 - 6:30 08.01-P Borucki W. Koch D. Dunham E. Cullers D. Webster L. Granados A. Ford C. Reitsema H. Cochran W. Bell J. FRESIP: A Discovery Mission Concept to Find Earth-sized Planets Around Solar Like Stars The current nebular theory postulates that planets are a consequence of the formation of stars from viscous accretion disks. Condensation from the accretion disk favors the formation of small rocky planets in the hot inner region, and the formation of gas giants in the cool outer region. Consequently, terrestrial-type planets in inner orbits should be commonplace (Wetherill, Science 253, 535, 1991). From geometrical considerations, Borucki and Summers (Icarus 58, 121, 1984) have shown that 1% of planetary systems resembling our solar system should show transits for Earth-sized (or larger) planets. Thus a photometric satellite that uses a wide field of view telescope and a large detector array to simultaneously monitor 5000 target stars should detect 50 planetary systems. To differentiate regularly recurring transits from statistical fluctuations of the stellar flux, one must observe over several orbital periods so that the false positive rate can be reduced to one event or less. A one-meter aperture telescope placed in a halo orbit about either the Ll or L2 Lagrange points and viewing perpendicular to both the orbital and ecliptic planes can view continuously for the required period because neither the Sun, Earth, or Moon would enter the fireld of view. Model calculations show that the observations should provide statistically significant estimates of the distributions of planetary size, orbital radius, coplanarity, and the frequency of planetary systems that have Earth-sized planets in inner orbits. Because approximately one half of the star systems observed will be binary systems, the frequency of planetary systems orbiting either one or both of the stars can also be determined. 08.02-P Hart H. M. Lubenow A. Wells E. N. Schultz A. B. Using Hubble Space Telescope to Observe Solar System Objects The HST pointing control system was designed to acquire and accurately track any solar system target with an apparent motion on the sky less than 0.21 arc-sec/second, including planets, planetary satellites, planetary surface features, comets, and asteroids. The apparent motion of a target is comprised of its geocentric motion and the parallax and aberration due to the motion of HST in orbit about Earth. The problems posed by the intrinsic motion of solar system targets are exaggerated by the small field of view and high spatial and spectral resolution of the instruments. In general, moving targets can be tracked to an accuracy better than 0.05" for the duration of an observation. Other constraints on the operation of the telescope include avoidance of bright objects that can damage the instruments, visibility of the communications satellites from HST, instrument operational constraints posed by the South Atlantic Anomaly, restrictions on spacecraft pointing to allow sufficient sunlight on the solar panels to maintain power, availability of guide stars for the duration of the observation, etc. Most of these constraints are invisible to an investigator proposing to use the HST, but they all affect the final schedule of observations, and sometimes can cause a particular observation to be unschedulable. This paper gives an overview of the steps needed and systems used to prepare, schedule, and execute observations of moving targets. The development state of new capabilities is outlined. Some suggestions are given to help investigators prepare to submit proposals. The preparation of this poster was supported by Space Telescope Science Institute. 08.03-P Russell C. T. Metzger A. Pieters C. Elphic R. C. McCord T. Head J. Abshire J. Phillips R. Sykes M. A'Hearn M. Hickman M. Sercel J. Kluever C. Rosenthal R. Purdy W. Maximizing the Scientific Return of Low Cost Planetary Missions Using Solar Electric Propulsion After many years of development solar electric propulsion is now a practical low cost alternative for many planetary missions. The ion thrusters and power processing units are now undergoing extended operational tests at NASA Lewis Research Center and a space flight in low earth orbit is being planned for the first flight of these thrusters. Moreover, a large commercial market is considering the use of these thrusters. Thus their availability and continued improvement seem assured. In response to the recent Discovery AO we and a number of colleagues have examined the scientific return from a mission to map the moon and then rendezvous with a small body. We have named this mission after Diana, the Roman goddess of the moon and the hunt. In planning this mission we found that solar electric propulsion was quite affordable under the Discovery cost guidelines, that many targets could be reached more rapidly with solar electric propulsion than chemical propulsion, that a large number of planetary bodies were accessible with modest propulsion systems, and that such missions were quite adaptable with generous launch windows which minimized mission risks. Moreover, solar electric propulsion is ideally suited for large payloads requiring a large amount of power. 08.04-P Tedesco E. F. Price S. D. Paxton L. J. Walker R. G. Planetary Astronomy with the Midcourse Space Experiment (MSX) Satellite The Midcourse Space Experiment (MSX) satellite, funded and managed by the Ballistic Missile Defense Organization (BMDO), will be a long-duration, "observatory" style measurement platform that will collect several terabytes of data on earth, earthlimb, and celestial backgrounds. In particular, observations of the zodiacal background, zodiacal dust bands, comet trails, asteroids, comets, Pluto, and targets of opportunity are planned. MSX will be launched into a polar orbit in late 1994. The spacecraft will carry a suite of state-of-the-art sensors, including a cryogenic infrared scanning radiometer and Fourier-transform spectrometer, several visible and ultraviolet imagers and five UV and visual spectrographic imagers. The optical sensors cover the spectrum from the far ultraviolet through the longwave infrared (0.11 to 28 micrometers). While the principal focus of MSX is to collect phenomenology data in support of ballistic missile defense objectives, it will also be capable of collecting well-calibrated data in support of a variety of civilian science objectives in earth and atmospheric remote sensing and astronomy. This presentation describes some of the instrumentation, discusses the planned observations, and outlines the approach to reducing, analyzing, and archiving the large database that will result from several years of data collection supporting a variety of scientific objectives. This work was supported under contract from the United States Air Force, Phillips Laboratory, Geophysical Directorate and the Ballistic Missile Defense Organization. SESSION 09 ....... Uranus and Neptune Tuesday, 8:30 - 10:00 Crystal Ballroom A C. de Bergh and H. B. Hammel, Moderators 09.01 Rages K. A.* Pollack J. B. Modeling Uranus' Temporal Variability Analysis of spatially resolved Voyager images of Uranus has shown that the subtle latitudinal banding seen on the planet is associated with substantial variations in the optical depth and single scattering albedo of the methane cloud layer above 1.3 bar [1]. Due to Uranus' extreme axial tilt, this latitudinal variation in the atmospheric scattering properties will account for some portion of the temporal variability seen by Lockwood et al. [2]. Models of Uranus' scattering atmosphere have been derived for seven latitudes between 0 degrees and 85 degrees S, using the spatially resolved Voyager data. Assuming that the northern hemisphere is a mirror image of the,southern hemisphere, changes in Uranus' aspect since 1g72 can account for only half the variation seen in the blue and 1/6 of the variation seen in the yellow by Lockwood et al. during that time. Varying only the optical depth and haze mixing fraction of the methane cloud also fails to reproduce the observed spectral dependence of Uranus' secular variation. It appears that some change in the wavelength dependence of the stratospheric haze absorption coefficient (darkening toward the red) will be necessary to fit the observations with a hemispherically symmetric model atmosphere. [1] Rages et al. (1991). Icarus 89, 359-367. [2] Lockwood et al. (1983). Astrophys. J. 266, 402-414. 09.02 Lyons J. R.* Constraints on Meteoroidal Influx Into the Upper Atmospheres of Uranus and Neptune Results from a recent analysis of meteoroid ablation rates in the atmosphere of Neptune (Moses, 1992) have been coupled with photochemical models of the upper atmospheres of Neptune and Uranus to yield estirnates of stratospheric water profiles as a function of meteoroid influx. Because water has never been detected in the upper atmospheres of the giant planets, the tangential column opacities of the model water profiles were compared with ultraviolet absorption measurements made by Voyager to determine maximum water influxes. For Uranus an upper limit of 4 x 10^6 water molecules cm^-2 sec^-l is obtained. For a Triton-like meteoroid composition (30% water ice by mass), this flux is consistent with an Oort-family particle population, but is not consistent with a large population of planet-family dust particles. For Neptune the model water profile is strongly dependent on the still uncertain eddy diffusion coefficient, making it difficult to rule out a large planet-family population of IDP's. However, an IDP population sufficiently large to account for the CO observed in Neptune's atmosphere can be ruled out. 09.03 Crisp D.* Trauger J. Stapelfeldt K. Brooke T. Clarke J. Ballester G. Evans R. WFPC2 Science Team Hubble Space Telescope Wide Field Planetary Camera 2 Observations of Neptune The Hubble Space Telescope Wide Field Planetary Camera 2 was used to observe Neptune on 28-29 June 1994. Planetary Camera images (0.046 arcsectpixel) of one hemisphere of the 2.3 arcsec disk were acquired in 7 spectral passbands (255, 300, 467, 588, 620, 673, and 890-nm). The opposite hemisphere was observed in a subset of these passbands (300nm - 673 nm). The near-UV images show an almost featureless limb-darkened disk There is also very little contrast at most visible wavelengths outside of the strong methane bands, but the 673-nm images reveal several features seen by Voyager 2^1, including the dark band near 60S latitude. We do not see the Great Dark Spot, but it would not be obvious if it were near the limb. Images in the strong methane bands at 619 and 890 nm show weak limb brightening, and several bright cloud features. The northern hemisphere is occupied by a single, bright, planet-encircling cloud band centered near 30N latitude. This may be the same bright feature discovered last fall in ground-based images of Neptune 2. The tropics also appear about 20% darker than the disk average at these wavelengths. The southern hemisphere includes two discrete bright features. The largest and brightest is centered at 30S latitude, alld extends for least 40 degrees of longitude, like the Bright Companion to the Great Dark Spot. There is also a thin cloud band at 45S latitude, which almost encircles the planet. An atmospheric radiative transfer model based on a multi-level, multi-stream discrete ordinate method is being used to analyze the center-to-limb profiles in these images to provide new constraints on the composition and vertical structure of the radiatively- active gases and aerosols in Neptune's atmosphere. References: 1) Smith et al. Science 246, 1422, (1989). 2) Harnmel el al. Bull. Arner. Astron. Soc., 25,1077, (1993). 09.04 Lockwood G. W.* Hammel H. B. Mills J. Variability of Neptune in 1994 Compared with 1989: Imaging, Spectra, and Photometry Neptune shows intrinsic variability on time scales ranging from days to years. To investigate causes of such variation, we compare spectra and photometry obtained in 1994 (contemporaneous with HST imaging) with 1989 ground-based and Voyager data. These include photoelectric photometry (Lowell), spectrophotometry of the 6190-Angstrom methane band (Lowell), near-infrared imaging and photometry at six wavelengths (Mauna Kea), and Voyager imaging and photometry. Periodic short-term variations correspond to the transit of the "Bright Companion" just south of the "Great Dark Spot." We present Voyager images and photometric sequences derived from them for several transit events, along with ground-based photometry of the same events. Changes in the amplitude of the variability is sometirnes due to changes in the Bright Companion and sometimes due to other transient features rotating with slightly different speeds. Our 1994 data include CCD spectra from 5500 to 8100 Angstroms and photoelectric photometry in visible light obtained on about a dozen nights in May and June. Our analysis addresses the questions: Has the amplitude of rotational modulation changed since 1989, which may indicate changes in the size and distribution of the features causing the variation? Do features detectable in images affect visible wavelength spectra? Is the steadily rising brightness of Neptune seen since 1985 associated with obvious changes in spectral features? NASA and NSF supported this research under grants NAGW-2385 (HBH) and ATM-9021100 (GWL), respectively. 09.05 Roques F.* Evidence for Saturated Gravity Wave Spectra in the Upper Atmospheres of Neptune and Titan from Ground-based Observations We have analyzed systematically stellar occultations by Neptune (observed at 0.89 and 2.2 micrometers between 1983 and 1991) and Titan (occultation of 28 Sagittarii, July 3rd 1989). They exhibit strong scintillation spikes, at pressure levels ranging from ~ 1 to 50 microbars. This scintillation translates, via an inversion technique, into local temperature fluctuations of a few to several K, over vertical distances of a fraction of a scale height, ~ 50 km (Hubbard et al., A.and A. 269, 541, 1993, Roques et al., A and A., 288, 985, 1994). Although the time variations of these features are not available, their spatial analysis can provide some clues as to their nature. First, the gradient of temperature delta T/delta z is bounded from below by the adiabatic lapse rate, i.e. ~ -1 K km^-l for both Neptune and Titan in the regions under study. This appears to be true at all the scales available from our observations, i.e. ~2-50 km in the vertical direction. We note a strong asymmetry between the negative and positive values of the gradient, the positive values being much steeper, reaching values as high as ~+2-5 K km^-l. Second, the power spectrum of the vertical temperature profiles, for both Neptune and Titan, exhibit a characteristic power law variation in m^-3 (where m is the vertical wavenumber) between vertical scales ,~ 2 and 50 km. The two points above strongly suggest the existence of breaking internal gravity waves in the upper stratospheres of both bodies. Further analysis of existing occultation lightcurves by other planets (Jupiter, Saturn, Uranus,...) is strongly recommended to look for similar structures. 09.06 de Bergh C.* Lellouch E. Tokunaga A. Gautier D. Marten A. Owen T. Rosenqvist J. Romani P. Search for CO Absorptions in Near-Infrared Spectra of Neptune Surprisingly large amounts of CO (mixing ratio of the order of 1O^-6) have been detected in the stratosphere of Neptune from millimeter measurements (Marten et al., Astrophys. J., vol.406, 285,1993; Rosen-qvist et al., Astrophys. J., vol. 392, L99, 1992). Measurements in the millimetric also showed that CO must be present in the troposphere of Neptune in comparable amounts (Marten et al., ibid; Guilloteau et al., Astron. Astrophys., vol. 279, 661, 1993; Naylor et al., Astron. Astrophys. Lett., submitted). On the contrary, CO has never been detected on Uranus. In August 1993, we obtained spectra of Neptune with the CSHELL instrument at the NASA-IRTF telescope on Mauna Kea (Hawaii) in order to look for absorptions of the 3-0 band of CO in the troposphere of Neptune. The spectra cover the range 6328-6348 cm^-l at a resolution of 20,000. Spectra of Uranus were recorded during the same run in order to help eliminating the methane absorptions present in the Neptune spectra. We find that the spectra of Neptune and Uranus at 1.6 micron look strikingly similar. Comparable methane absorptions are seen in both planetary spectra, in addition to numerous telluric features. There is no clear detection of CO absorptions in the spectrum of Neptune. A comparison with results from the millimetric measurements is presented. 09.07 DeBoer D. R.* Steffes P. G. Radiative Transfer Results for Neptune Microwave Emission Recently it has been shown that the microwave opacity of H2S is greater than previously modeled and that it could possibly be responsible for the microwave opacity in Neptune's troposphere measured by Voyager 2 radio occultation (DeBoer and Steffes Icarus 109, June 1994). This paper examines that proposal in greater detail by comparing results from a radiative transfer model with radio telescope and Voyager radio occultation observations. Sub-solar quantities of NH3 (< 5 ppm) are needed below the putative NH4SH cloud near 35 bars to match the relatively high brightness temperature near 1 GHz measured by the VLA (de Pater and Richmond, Icarus 80, 1-13, 1989). This value (5 ppm) also reproduces the sharp dip in emission measured above 1 GHz but requires that essentially no H2S be present throughout the entire atmosphere. Other abundance profiles which seem to better describe the measured spectrum between 100-200 GHz include relatively large H2S abundances along with NH3 depletions. These suffer at frequencies with weighting functions peaking near the NH4SH cloud (roughly 5-10 GHz). The microwave extinction due to NH4SH is currently poorly known and could possibly play a role at these frequencies. Both profiles yield absorptivities which are similar to those measured by Voyager 2 near 6 bars. This work was supported by the NASA Planetary Atmospheres Program under grant NAGW-533. 09.08-P Sromovsky L. A. Fry P. M. Hammel H. B. Spencer J. R. Shure M. Cloud Features in 1993 Images of Neptune at 1.6 and 2.2 Microns Using the NSFCAM at NASA's Infrared Telescope Facility, 76 near IR images of Neptune were acquired during a 2.5 hr period on 4 September 1993 (UT). Most were made with a 2.2 micron filter (K-band) at a scale of approximately 0.056 arc seconds/pixel, for which Neptune's equatorial diameter spans 41.4 pixels. In the best of these images the PSF had a FWHM of 0.4 arc seconds. Although strong methane absorption makes Neptune's atmosphere virtually invisible at 2.2 microns, discrete bright features indicative of high altitude clouds were seen in all of the images. Assigning latitudes to the observed features was complicated by image smear and the lack of a visible limb profile, but was facilitated by a star that appeared on each image within 10 arc seconds of Neptune. The PSF determined from the star image was used to deconvolve Neptune's image, greatly reducing the smear in some images. The motion of Neptune's cloud features relative to the star was also used in a non-linear regression algorithm to establish both the approximate pixel scale and the approximate feature latitudes, under the assumption that the features rotated about Neptune's axis at the same latitude-dependent rate that was defined by the Voyager observations (Sromovsky et al., Icarus 105, 1993). Latitudes were also estimated from one image at 1.6 microns (H-band) for which an atmospheric limb could be identified. Although the latitudes are still very preliminary, at least four discrete cloud features are visible, at approximate planetocentric latitudes of 55 degrees S, 40 degrees S, 10 degrees N and 25 degrees N. The brightest feature was near 10 degrees N. For comparison, HST images made during 1991 at 889 nm (Sromovsky et al., Bull. Am. Astron. Soc. 25, 1993) showed features at 66 degrees S, 50 degrees S, 6 degrees N, and about 30-45 degrees N, all at locations where Voyager saw features during 1989. Given the currently large uncertainties in the latitudes of features in the IRTF images and very limited temporal coverage, as well as spectral differences, it is not clear which of the 1993 features are related to those seen earlier in 1989 Voyager images and 1991 HST images. Imaging planned for 1994 will presumably clarify the nature of these 1993 features. 09.09-P Pryor W. R. West R. A. Aerosol Models of Neptune Applied to Voyager IRIS Radiometer Data Neptune's radiative energy balance can be derived by combining data from reflected sunlight with thermal emission data. We address the reflected sunlight problem. Aerosol models have been derived from Voyager PPS data [1], ground-based data [2], and Voyager camera data [3]. One additional available constraint on Neptune aerosol models is broadband IRIS radiometer data obtained at a variety of phase angles [4]. We apply the PPS aerosol models (derived to fit data at 0.265 micrometers and 0.75 micrometers) to broadband IRIS radiometer data (0.3-1.9 micrometers) to test their ability to reproduce the data. A comparison with other aerosol models will be discussed. Each aerosol model can be used to make predictions about the phase angle behavior of reflected sunlight in Neptune's atmosphere. An aerosol model that successfully reproduces the phase-angle behavior of the radiometer data can be used to obtain improved estimates of Neptune's phase integral, and its radiative energy balance. This work was supported by NASA's Neptune Data Analysis Program. 1Pryor, W.R., R.A. West,, K.E. Simmons, and M. Delitsky, Icarus 99, 302-317,1992. 2Baines, K.H., and H. B. Hammel, submitted to Icarus, 1994. 3Moses, J.I., K. Rages, and J.B. Pollack, submitted to Icarus, 1994. 4Pearl, J.C., and B.J. Conrath, JGR 96,18921-18930,1991. 09.10-P Bishop J. Romani P. N. Atreya S. K. Photochemical Modeling of Voyager UVS Solar Occultation Lightcurves Acquired at Neptune Ingress and egress occultations of the Sun by Neptune were recorded with the UVS instrument on Voyager 2 [Broadfoot et al. 1989, Science 246:1459]. Previous modeling of the 125-140 nm lightcurves indicated eddy mixing coefficient values of 3-10 x 10^6 cm^2 s^-1 near the 0.2 microbar level and methane mixing ratios in the lower stratosphere on the order of 1-3 x 10^-4 [Bishop et al. 1992, J. Geophys. Res. Planets 97:11681]. These results should be insensitive to photochemical details, provided methane is indeed the main source of opacity at these wavelengths. The UVS lightcurves at longer wavelengths (140-153 nm) are expected to be dominated by the opacity of C2 species (ethane, acetylene, ethylene) and perhaps higher order organics. At still longer wavelengths, H(sub)2 Rayleigh scattering is a major opacity source. We will present photochemical models giving good agreement with both sets of UVS l1ghtcurves at wavelengths 125-165 nm and with C(sub)2H(sub)6 and C(sub)2H(sub)2 abundances near 0.5 mbar derived from IRIS measurements [Bezard et al. 1991, J. Geophys. Res. 96:18961]. The current photochemical model incorporates several updates, including the recent revision in CH(sub)4 photolysis branching ratios at Lyman alpha [Mordaunt et al. 1993, J. Chem. Phys. 98:2054]. These model fits strongly suggest a reglon of enhanced eddy mixing near the 10 mubar level (K > 108 cm2 s-l), decreasing at higher altitudes. Comparisons between egress (~49 degrees S latitude) and ingress (61 degrees N) UVS results will be discussed, as 'well as the impact of uncertainties in mean stratospheric temperature and key reaction rates. In line with our earlier work, methane mixing ratios on the order of l0^-4 are required to obtain good agreement between the photochemical models and the UVS lightcurves. This work supported by NASA Contract NASW-4806. 09.11-P Conrath B. J. Gierasch P. J. Smith M. D. Ustinov E. A. Simultaneous Retrieval of Temperature and Para Hydrogen in Neptune's Atmosphere The possibility of the simultaneous retrieval of the temperature and the para hydrogen fraction in the atmosphere of Neptune by inversion of thermal emission spectra between 200 and 350 cm- 1 is investigated. The sensitivity of the spectral radiance at each wavenumber to the temperature and para hydrogen fraction at each atmospheric pressure level is obtained through the calculation of appropriate functional derivatives. The sensitivity of the radiance to the para hydrogen profile at atmospheric levels between 250 mbar and 850 mbar is of special interest; that in the spectral region between 200 and 245 cm^- 1 is anti-correlated with that between 245 and 300 c m ^- 1. In contrast, the sensitivity of the radiance to the atmospheric temperature is positively correlated in these spectral regions. This differing behavior permits independent information on the two atmospheric parameters to be obtained. An inversion algorithm for the simultaneous retrieval of temperature and para hydrogen profiles has been applied to data from the Voyager IRIS north/south mapping sequence. Small but apparently significant departures of the para hydrogen fraction from the thermodynamic equilibrium values are found. Implications of these results for the thermodynamics and dynamics of Neptune's upper troposphere are discussed. This work was supported in part by the NASA Planetary Atmospheres Program. 09.12-P LeBeau R. P. Dowling T. E. Simulations of Neptune's Atmospheric Dynamics We present three-dimensional circulation simulations of the atmosphere of Neptune using a global, primitive-equation model (the EPIC model) with ten vertical layers. The Voyager wind data initialize the cloud-top level, and various assumptions are made about the variation of wind strength above and below the clouds, the standard model using a sech^2 (theta) vertical variation similar to Leovy and Orsolini (1993, Icarus 106, 392-405). Our primary goal is to constrain the three-dimensional structure of Neptune's jet streams and vortices by forward modeling. The atmospheric dynamics of Neptune combine aspects found in the atmosphere of Jupiter and in that of Earth, providing an important bridge between the jovian and terrestrial regimes. Like Jupiter, Neptune has a large anticyclone, the Great Dark Spot, with an angular size and position similar to that of the Great Red Spot. On the other hand, the zonal winds of Neptune, Uranus and Earth each have a limited number of jets and a retrograde equatorial flow, in contrast to the multiple-jets and prograde equatorial flow found on Jupiter and Saturn. Our numerical models indicate that Neptune's atmospheric dynamics may be more global than on any other planet. We are investigating the role of thermodynamics in shaping the zonal winds, including moist thermodynamics and the latent heat effect of ortho-para hydrogen conversion. 09.13-P Mickelson M. E. Larson L. E. The Temperature Dependent Absorption Coefficient for Methane at 5430 Angstroms and 6190 Angstroms Improved quantitative values of the methane absorption coefficient in the visible and near infrared spectral regions are of vital importance in the modeling of the atmospheres of the outer planets and their satellites. We have extended previous laboratory measurements of the temperature dependent absorption coefficient of the visible methane bands at 6190 Angstrom and made new measurements for the 5430 Angstrom region. Spectra were obtained using a tunable dye laser system coupled to a cooled 3 m base length White-type cell. The laser operates with a line width of 0.016 cm^-l, and data were recorded at approximately one Angstrom intervals. Absorption coefficients derived from these data were averaged over 10 Angstrom intervals. The cooled cell was adjusted for an optical path of 288 m for the 6190 Angstrom band and 582 m for the one at 5430 Angstrom. These measurements were made at gas densities of 1.22, 0.74, and 0.25 amagats and at four temperatures down to 123K. The results are compared with previous laboratory measurements. The absorption coefficient was determined over a wavelength interval from 6000 to 6400 Angstrom and 5270 to 5600 Angstrom respectively for the two bands. As an independent check on absolute intensities, for one wavelength location in both pseudo-continuum regions of each band and at each temperature, signal absorption intensity was measured as a function of gas density by systematically freezing the methane out of the main cell into a small container held at LN2 temperature. This work was supported by NASA Planetary Atmospheres Program Grant NAGW-1765 and by the W.M. Keck Foundation. SESSION 10 ....... Clementine and Moons I Tuesday, 8:30 - 10:00 Crystal Ballroom B J. F. Bell, III and P. G. Lucey, Moderators 10.01 Pieters C. M.* Staid M. I. Fischer E. M. Tompkins S. He G. Clementine Science Team Products of the Impact Process: A Sharper View from Clementine Data The BMDO Clementine spacecralt spent a little more than two months orbiting the Moon during the spring of 1994 as part of an instrument and spacecraft integration test. Digital images were acquired for the surface using four co-aligned framing cameras sensitive to radiation from the visible to mid-infrared, each with a different spatial resolution and coverage. The NASA supported science team has been analyzing and validating these data for scientific applications. Our group has focused on the UVVIS camera which produced 5 channels of multispectral data from 0.4 to 1.0 micrometers. Calibration issues center on dark subtraction, flat fields, scattered light, frame transfer signal, and frame-to-frame registration. First-order corrections have been developed and initial multispectral data products have proven to be of good quality and provide an excellent tool for general unit definition of surface materials at a scale similar to Lunar Orbiter (200-500 m). The five UVVIS spectral channels are sensitive to variations of surface composition as well as to degree exposure (maturity). Using preliminary calibrations, five channel image cube mosaics have been produced for Giordano Bruno, Copemicus and Tycho. Although both Copemicus and Tycho contain extensive deposits of impact melt, the variety of material ejected from different depths have not been mixed beyond recognition at either crater. A primary scale of lithologic mixing at these two large craters appears to be on the order of 1-2 km; for a given local terrain type large blocks of mafic-rich material can be observed in close proximity to more feldspathic material. Copernicus exhibits substantially more heterogeneity than Tycho. The southern wall of Copernicus is particularly enriched in small mafic-bearing zones. Many of these also exhibit a low albedo and suggest a component of excavated basalt or dark mantle. The impact process does not homogenize lithologies within the crater since different quadrants of the wall at Copernicus remain distinct from neighboring sections. In contrast to the diversity of materials observed at large impact craters which probe deep into the crust, much of the spectral variation at the small fresh crater Giordano Bruno on the farside is due to the varying proportion of fresh material mixed with older weathering products (both presumably feldspathic). 10.02 Jakosky B. M.* Lucey P. G. Long-Wave Infrared (LWIR) Camera Observations of the Moon from Clementine The Clementine spacecraft included a long-wave infrared camera to map thermal emission from the lunar surface. The instrument uses HgCdTl detectors in a 128 x 128 actively cooled focal-plane array. The field of view is 1.0 x 1.0 degrees, corresponding to a resolution on the lunar surface of about 55 m/pixel at periapsis. The passband is centered at 8.75 microns. Preliminary estimates of the performance in orbit at the Moon indicate that the noise in the dark field observations is approximately 1 DN. The signal on the day side varies between 0 and 100 DN; the 1 DN noise corresponds roughly to a noise-equivalent uncertainty in the derived brightness temperature of 1 K at 400 K and 2 K at 300 K. Observations will be used to map the dayside thermal emission. Variations at low latitudes are due primarily to variations in the albedo, while those at higher latitudes include the effects of topography. In the polar regions, measurable emission comes from the sunlit areas only. In addition, special sequences were performed to observe sites of interest at multiple emission angles. The results will be used to derive estimates of surface roughness at multiple scales and of the thermal energy balance in the polar regions. In conjunction with Apollo 17 Infrared Scanning Radiometer observations of nightside thermal emission, the results will constrain particle size and the lunar thermal environment. 10.03 Hawke B. R.* Peterson C. A. Blewett D. T. Budney C. J. Coombs C. R. Lucey P. G. Smith G. A. Taylor G. J. Remote Sensing and Geologic Studies of the Aristarchus Region of the Moon The region that includes the Aristarchus Plateau and Montes Harbinger is one of the most geologically and compositionally diverse areas of the lunar surface. In the course of a continuing spectral study of the Aristarchus region, numerous near-IR (0.6- 2.5 micrometers) reflectance spectra were obtained for a wide variety of surface units and analyzed in order to extract compositional information. Both Earth-based and Clementine multispectral images were also utilized. The dominant surface unit is a regional dark mantle deposit (RDMD) of pyroclastic origin. Spectra for several portions of the RDMD exhibit nearly identical characteristics. These include steep infrared continua, low albedoes, and very broad absorptions centered longward of 1 micrometers. The spectra are indicative of uncrystallized Fe^2+-bearing glass. The RDMD exhibits an extremely homogeneous composition and contamination seems to be largely due to Aristarchus ejecta. Mare materials with various ages and compositions are present on and around the Plateau. A spectrum obtained for the wall of Vallis Schroteri clearly indicates the presence of fresh mare basalt. The spectra of highlands units in the Aristarchus region can be classified into two distinct categories which reflect very different mineralogies. One group is concentrated in the vicinity of Aristarchus crater and includes most of the spectra of the interior and exterior deposits of Aristarchus, the Cobra Head of Vallis Schroteri, and impact craters which expose highlands debris from beneath the RDMD on the Plateau. While this group can be divided into distinct subclasses, in general it can be characterized as having shallow infrared continuum slopes and fairly strong absorptions centered between 0.97 and 1.0 micrometers. These characteristics are indicative of a feldspar-bearing material which has a mafic assemblage dominated by Ca-rich pyroxene. The gabbroic composition of Imbrium ejecta exposed by small impact craters on the Aristarchus Plateau is very different from the noritic material emplaced by Imbrium southeast of the basin. The other group of spectra were obtained for widely separated locations in the region. These include Herodotus X, the southern rim crest of Aristarchus, and portions of the Agricola and Harbinger Mountains. The spectral characteristics of this group, chiefly the broad shallow absorption centered at or beyond 1 micrometer, are attributed to large amounts of olivine. 10.04 Duxbury T.* McEwen A. Eliason E. Edwards K. Smith D. Davies M. Clementine Global Geodetic/Cartographic Accuracy The Clementine Mission provided complete global lunar imaging coverage, which was augmented with LIDAR ranging data. The global imaging data, tahen by the UVVis Camera, had a ground resolution of about 100-150 m/pixel while the LIDAR data had a ranging resolution of 45 m. UVVis stereo imaging of the poles and other regions were obtained. HiRes Camera imaging had an effective resolution of about 20m, but this was not a global dataset. The Clementine spacecraft had two star trackers for attitude control (instrument pointing) having an accuracy of about 0.03 deg (1 sigma). The spacecraft orbit (periselene altitude of ~400 km) was reconstructed to an accuracy of better than lOOm along track and out-of-plane and better than 30m in range. Also, the instrument alignments and geometric properties were determined to an accuracy of better than 0.01 deg using star fields and locating the LIDAR footprint in image coordinates. Computing the lunar-fixed coordinates of any feature in a single UVVis image would yield an accuracy of about 200m (1 sigma), anywhere on the moon which represents a significant improvement in some areas having uncertainties of over 5 km. Additional improvement for Clementine can be made using standard photogrammetric techniques which takes advantage of averaging the randomness of pointing and orbit errors over the global datasets. A global cartographic control network can be produced having an absolute accuracy of 50m or better in latitude and longitude. An error in elevation, for those areas not covered by stereo imaging or by LIDAR could be as large as 1 km since variations in topography of +/- 10 km have been seen with LIDAR. Good correlation was found to exist between elevations derived from LIDAR and stereo imaging. Example of cartographic accuracy including imaging and LIDAR derived topography will be presented. Parts of this research were performed at the California Institute of Technology, Jet Propulsion Laboratory under the NASA Clementine Science Team Program. 10.05 Cook A. C.* Roatsch T. Oberst J. Hoffmann H. Jaumann R. Neukum G. Semi-Automated Extraction of DTMs for Studies of the Lunar Surface Using Apollo Metric and Clementine Stereo Pair Imagery A technique is described that has been used to semi-automatically generate Digital Terrain Models (DTMs) of the lunar surface using stereo pair images obtained from the Apollo metric cameras, and from the Clementine spacecraft. This involves using digital images of the Moon's surface (scanned from photographs in the case of Metric) for automated stereo matching with the "Gotcha" software developed at University College London. The resulting stereo disparity ( data are then passed through a camera model and, with the aid of some manually derived control points, a DTM can be produced. This entire process can be performed in under one day on a Sun Sparc 1 for a Metric stereo pair. Apollo Metric stereo imagery has a ground resolution of 25m and a height precision of 30m, but is limited in coverage to near equatorial regions. Clementine stereo imagery has a ground pixel size of 100m at best, and a height precision of the order of lkm over the majority of the Moon. However in the polar areas, and other regions that were iamged specifically for stereo, the height precision is improved to the order of 100m. The height information derived from the DTM yields important additional data for the geological interpretation of surface features like: depth to diameter ratio and volume studies for craters down to a diameter of l km, the thickness of lava flows and crater ejecta, and cross-sections through tectonic features and impact basin rings. In addition the DTM allows us to enhance the morphology of surface features that normally appear camouflaged by albedo markings or shading, and they can provide local slope information to support lunar surface photometric studies. Examples are given of a DTM covering the region to the west of Tsiolkovskiy from Apollo Metric, and experiments to stereo polar regions of the Moon from Clementine imagery. The goal of our future studies is to produce regional scale DTMs and controlled rectified colour image mosaics by combining Clementine data with other image data available for the Moon. 10.06 Blewett D. T.* Hawke B. R. Lucey P. G. Spudis P. D. Geologic and Compositional Studies of the Crisium Region of the Moon Using Earth-Based and Spacecraft Spectra and Images The Crisium basin is a multiring impact structure of Nectarian age centered at 17.5 degrees N, 58.5 degrees E. The basin rim consists of platform massifs, an unusual morphology possibly caused by post-impact structural modification. Other interesting features in the vicinity of Crisium include dark-halo impact craters, light plains units, probable cryptomaria, and geochemical anomalies identified with data from Apollo orbital X-ray and gamma-ray sensors. About 20 near-IR (0.6-2.5 micrometers) reflectance spectra for small areas in the Crisium region were obtained with Univ. of Hawaii telescopes and instruments at Mauna Kea Observatory (MKO). Spectral analysis focusing on the absorption band near 1 micrometer provides information on Fe^+2-bearing minerals present in the surfaces observed. In order to gain greater spatial coverage, multispectral images in the extended visible (~0.4- 1.1 micrometer) have been analyzed. The imagery includes that recorded by a CCD camera at MKO, as well as data from the Galileo and Clementine spacecraft. Our findings demonstrate that most circum-Crisium massifs are composed of noritic anorthosite, though the slightly steeper continuum slopes in some spectra with deeper bands may attest to the presence of anorthositic norite. A spectrum for the central peak of the crater Taruntius indicates the presence of a slightly more mafic (Fe,Mg-rich) composition; this material may have been excavated from beneath the Crisium ejecta deposit. Spectral and image mixing models show that certain areas mapped as light plains and "smooth terra" NE of Taruntius and in Palus Somni contain a significant component of mare basalt, i.e., cryptomaria are present. These areas have been identified as anomalous in orbital geochemical data sets (e.g., Mg/Al greater than the surrounding highlands). These units probably represent mare basalt deposits contaminated with highlands debris by nearby impacts. Another occurrence of smooth terra, to the SW of Crisium, also contains a large mare component. However, this area has a rugged topography and is thus unlikely to have been the site of a really extensive volcanic flows. Hence we propose that an episode of explosive activity emplaced a mantle of pyroclastic material in this area. 10.07 Bell J. F. III* Bregman J. D. Rank D. M. Temi P. Roush T. L. Hawke B. R. Lucey P. G. Pollack J. B. Mid-Infrared Imaging Spectroscopy of the Moon: 5.0 to 7.0 Micrometer Observations from the Kuiper Airborne Observatory We have obtained the first mid-IR imaging spectroscopic observations of the Moon. The data were obtained on the Kuiper Airborne Observatory (KAO) using a 128x128 Si:Ga array camera mounted in a LHe dewar. Images were obtained in October 1993 in 71 wavelengths from 5.0 to 7.0 micrometers using a cooled 1.5 percent resolution CVF filter. These observations were exploratory in nature, and thus only one small (3.4 arcmin) region of the Moon was imaged. This study site is located along the southwestern lunar limb near the craters Schickard, Baade, and Inghirami. Although this region covers only 1 percent of the projected area of the full Moon, it contains diverse geologic terrains, including mare basalt/impact crater melt, highlands, and possibly buried cryptonare. Thus it represents a useful test site for our preliminary investigation. The 5 to 7 micrometers wavelength region represents a transitional area of the spectrum between spectral regions dominated by reflected solar flux (< 3 micrometers) and emitted thermal radiation (> 8 micrometers). This wavelength range contains diagnostic mineral absorption features that can be used to discriminate among many different potential lunar rocks and minerals, including feldspar, olivine, pyroxene, and even quartz. Because of the Earth's atmosphere, these wavelengths are not accessible from groundbased telescopes. They can only be measured by spacecraft or by the KAO (39,000 feet altitude). Because of tbe exploratory nature of these observations, a rigorous calibration of the data is not possible. However, we have devised a relative calibration scheme that allows us to analyze the images for evidence of compositional variations and to assess the detectability of different rocks and minerals. This was accomplished by performing the best possible offset and flatfield corrections to the images, spatially coregistering the 71-channel image cube, and dividing out the average spectrum of all lunar pixels in the cube. This provides the best possible removal of instrumental and residual telluric artifacts in this data set. The resulting images show spatially coherent evidence for relative spectral variability at the +-10 percent level; some of this variability correlates with albedo/morphologic features (mostly craters), some does not. Residual instrumental problems prevent the interpretation of spectral features between 5.8 and 6.2 micrometers, but at other wavelengths, such as near 5.6 micrometers and 6.7 micrometers, spectral features are evident in ratio images and relative band depth maps. Spectral features diagnostic of plagioclase and pyroxene exist at these wavelengths, but continued refinement of the relative calibration is necessaly to determine whether it is these minerals that we have actually detected and mapped. At the very least it appears that the lunar surface is detectably heterogeneous at these wavelengths, which is encouraging for planned future, more detailed KAO and spacecraft mid-lR observations. 10.08 Henderson B. G.* Jakosky B. M. Mid-IR Spectral Effects of Near-Surface Thermal Gradients in Scattering Materials Radiative cooling of the near-surface of evacuated particulate materials can create significant thermal gradients in the uppermost layer where the emitted energy is generated. A near-surface thermal gradient will create emission features which are related to the spectral variation in the opacity since it determines the depth from which the emitted energy originates. We modeled this process for non-scattering materials and showed that near-surface thermal gradients increase spectral contrast and create emission maxima in the transparent regions of the spectrum (Henderson and Jakosky, submitted to JGR). However, the mid-infrared opacity of particulate materials is strongly affected by scattering as well as absorption. It is thus important to investigate this problem for scattering materials in order to interpret emission spectra of the surronding surfaces of warm airless bodies like the Moon and Mercury. We have examined the spectral effects of near-surface temperature gradients on thermal emission spectra using Hapke's emittance theory and numerical thermal gradient values from our previous model. Our results show that near-surface thermal gradients enhance spectral contrast and shift the wavelength location of the Christiansen peak to shorter wavelengths, consistent with the laboratory data obtained by Logan et al. (JGR, 78, 4983, 1973). This effect is due to increased scattered contribution from warmer material at depth in regions of low absorption. This result suggests that mid-IR spectral features due to a near-surface thermal gradient are understandable and diagnostic of composition so that mid-IR emission spectroscopy should be a useful tool for remote determination of planetary surface composition. 10.09 Clark P. E.* Trombka J. I. Multi-Variate Compositional Analysis Capabilities of Combined Geochemical Experiment Package The combined X-ray/Gamma-ray Experiment Package which flew on the Apollo 15 and 16 orbiters were provided data essential to the understanding to our nearest neighbor (1). Specifically made available were elemental compositional maps of the top (u (XRF) to cm (GRS)) of the lunar regolith, an extensively gardened mixture of surface and buried rocks. These compostionals maps show, by inference, the contribution of underlying geochemical terraines and rock types found at the landing sites. With these data (2,3,4,5), determinations of variations in surface chemistry and major rock components have been made on local (including landing sites and their surroundings), to regional (including entire mare or ancient basins), to gobal (including the entire 10% to 20% area of data coverage) scales (e.g., 6,7,8). Multi-dimensional classification techniques have been used to correlate XRF-derived Al and Mg data, combined with GRS-derived Fe, Ti, and Th data. Two methods of correlation, one supervised the other unsupervised, were developed. Such mapping of relationships between variables is particularly important in the case of Al and Mg, two elements with a complex relationship. One correlation technique involved simply creating a density plot (two dimensional array) from two dataset's values at a given pixel This 2D array llas then placed into a 3 x 3 matrix consisting of 9 equal sub-arrays containing an equal number of datapoints. The color assigned to each sub-array was selected aneonic device, to allow an instant estimate of the degree of positive or inverse correlation between the two datasets at a pixel. The resulting color correlation map showed the geographic distribution of the correlation. In this way, areas not correlated in the normal way, anomalous in regard to expected rock components near the surface, could be identified. The relationship between Al/Si and albedo, elevation, and Fe were thus illustrated on a global scale. Anomalies were found within the rings of Crisium, surrounding sites of recent impacts and buried basins. The technique was also used to indicate the nature of the distribution of Fra Hauro basalts and ANT suite rocks in the Hadley Apennine region. The second two-dimensional correlation technique developed was a supervised classification, constrained by compositional fields of major rock types occurring in the area of coverage. The population centers which appear on a density plot of the two datasets are average soils consisting of a mixture of major- components. In some cases, one major rock component clearly dominates. Thus, such a plot is divided into units based both on how population centers are distributed, and on how these fall relative to the compositional fields of typical rock components. Population centers are divided into two or more units to show how mixtures of coeponents are distributed geographically in typical areas in a given region. Such correlations were done in two highland regions, one in the eastern highlands the other on the far side. This technique has also been applied to global-scale correlations of Al/Si vs Fe,and Al\Si vs Mg/Si. As a result, buried basalt deposits, indicated by moderately sized areas with enhanced Ti, Ti, and/or Mg, have been shown to be widespread in near and farside highlands. Unsupervised cluster analysis was performed on all five datasets. The maximum likelihood classifier consisted of an algorithm which combined parallelpiped and Bayesian techniques. The algorithm was constrained to fit the data into the ten most significant classes. The resulting regional units included three mare units with correlation between basin age and Ti, the Hadley Apennine area the Undarum/Spumans area, and five highland areas with varying mafic components, most of which have been previously associated with highland volcanism. REFERENCES: Adler and Trombka (1970) Geochemical Exploration of the Planets; [2] Arnold et al (1977) Proc Lun Sci Conf 8th 945-948; [3] Bielefeld et al (1977) Proc Lun Sci Conf 8th, 901-908 [4] Hetzger et al (1977 Proc Lun Sci Conf 8TH, 949-999; [5] Davis (1980) JGR 85 3209-3224; [6] Clark et al (1981) Proc Lun Plan Sci Conf 12TH, 727-719; (7) Clark et al (1978 Proc Lun Plan Sci Conf 9th, 3015-3027; (8) Clark et a1 (1991) Earth Moon Plan 53, 93-107. 10.10-P Simpson R. A. Lichtenberg L. Asmar S. W. Clementine Bistatic Radar Experiment Two sets of bistatic radar experiments were conducted while Clementine (DSPSE) was in lunar orbit. In both cases, the spacecraft high-gain antenna was aimed toward a surface target region and the scattered signals were received at stations of the NASA Deep Space Network on Earth. The transmitted signals were right circularly polarized at Lambda=13 cm; both circular polarizations were received and recorded on the ground. On 9-10 April 1994 experiments were conducted in a "spotlight" mode over the south pole; on 23-24 April 1994 spotlight experiments were conducted over the north pole. Part of one quasi-specular track in the southem hemisphere was also obtained on the second set of observations. The primary objective was to investigate the scattering of radio waves in the polar regions, searching particularly for signatures characteristic of ice such as have been reported on Mars by Muhleman et al. (Science, 253, 1508-1513, 1991). Dates and times for the observations were chosen so that the experimental geometry would include the near-backscatter condition, allowing possible detection and measurement of coherent backscatter effects (Hapke, Icarus, 88, 407-417, 1990). Early examination of the data shows no strong ice-like response, in agreement with the results of Stacy (Cornell University, Ph.D. dissertation, 1993) who studied high-resolution Arecibo radar images of polar regions. But a broad enhancement of the scattering, such as may be inferred for Mercury's polar regions (Harmon et al., Nature, 369, 213-215, 1994), is not ruled out. Detail in the echo spectra can be matched with large features in Clementine mosaics and suggests that radar photometric functions and/or low-resolution radar images may be derived from these bistatic data with further analysis. 10.11-P Budney C. J. Lucey P. G. Structure of the Mare in Southwestern Oceanus Procellarum The total volume of mare basalts and the volumes of individual mare units are important parameters for constraining the history and extent of melting within the lunar mantle. How the mantle melted constrains models of the bulk composition and thermal history of the Moon. Mare basalt units have been spectrally mapped at low resolution from Earth and the Galileo spacecraft. The Clementine mission has provided high resolution multispectral digital data of most of the lunar surface. We intend to use these data to map and estimate the volumes of highland material and mare basalts of different compositions ejected from craters in southwestern Oceanus Procellarum. We will use these data to infer the depth and vertical structure of the mare, providing constraints on the nature, timing, and production efficiency of mare volcanism in the region. This work was supported by NASA grant NAGW1421. SESSION 11 ....... Jupiter I Tuesday, 10:30 - 12:00 Crystal Ballroom A T. A. Livengood and R. Halthore, Moderators 11.01 Thomas A.* Prange R. Ballester G. E. Harris W. M. Livengood T. Maurice S. Gerard J. C. Paresce F. Comparison of IUE and HST Diagnostic of the Jovian Aurorae Observation of FUV auroral emission from Jupiter have been performed for more than a decade using the earth-orbiting ultraviolet observatory IUE. One of the most striking characteristic of this emission is its modulation in magnetic longitude, which has be interpreted as control of auroral magnetospheric processes by the corotating asymetric magnetic field. Recent HST images using the FOC has not confirmed this typical modulation inferred from the IUE data. Using HST sequences of auroral images in the Lyman H(sub)2 bands, we present simulations of IUE response to the aurora. We show that they are consistent with IUE observations, and that the longitudinal modulation is at least partly due to geometrical effects in the IUE aperture. We discuss briefly consequences of this finding. 11.02 Gladstone G. R.* Waite J. H. Jr. Na C. Y. Franke K. Gerard J.-C. Grodent D. Some Aeronomical Implications of Jupiter's Aurora Recent observations of the jovian UV aurora with the HST Faint Object Camera detected H2 band emissions of up to ~ 10 MR. Simulations of these emissions suggest that the precipitating particle energy fluxes into the auroral region must be routinely ~ 100 erg cm^-2 s^-l, and occasionally as large as 1000 erg cm^-2 s^-l. For comparison, the available solar energy flux at wavelengths < 1600 is only ~0.5 erg cm^-2 s^-l at Jupiter. Such large energy inputs into a presumably low density region of the atmosphere must dramatically disturb the upper atmosphere both in the auroral regions and globally. UV auroras typically occur near the homopause region, which, if low-latitude model atmospheres are used as a guide, is about 350-400 km above the 1 bar pressure level. The pressure and density in the region of the homopause are about 0.2-1 microbar and 6 x 10^l2-3 x 10^l3 cm^-3, respectively. Unless the auroral heating rate (due to Joule heating as well as particle precipitation) nearly exactly overlaps the cooling rate (presumably dominated by CH4 and C2H2 IR radiation), then the expected exospheric temperatures are extraordinarily large. Assuming steady-state, the exospheric temperature expected for a column heating rate of 100 erg cm^-2 s^-1, with the peak heating rate only 100 km above the peak cooling rate, is ~ 8000 K. In this paper we present simulations of the FOC observations and investigate some of the aeronomical implications of Jupiter's powerful aurora. We also examine some other recent observations that seem to require extremely large auroral-region exospheric temperatures. 11.03 Baron R. L.* Owen T. Connerney J. Satoh T. Harrington J. Photometric Variability of the Jovian H3+ Aurora: A Strong Correlation with Solar Wind Ram Pressure Jupiter's 3.4 micron aurora was observed during the Ulysses spacecraft encounter spanning the first months of 1992. After careful removal of the consistent photometric changes due to Jovian rotation, the integrated intensity of each polar region and the planet as a whole (a quantity that changes markedly in tens of hours) show a strong correlation with the solar wind ram pressure as measured by the Ulysses spacecraft and projected to Jupiter. On the longer time scale of months, photometric changes up to a factor of three in magnitude are observed. A nearly quiescent state of the aurora appears to present itself just after the Ulysses encounter. This work was supported by NASA grant NASW 44 8 1 11.04 Satoh T.* Connerney J. E. P. Baron R. L. Owen T. Observations and Modeling of Jovian H3+ Aurorae Jovian H(sub)3^+ aurorae have been imaged (3.4 ,micrometers) on many nights during the spring of 1992 using the ProtoCAM array camera on NASA'S IRTF 3-m telescope at Mauna Kea, Hawaii. These high spatial resolution (subarcsec) and high signal-to-noise ratio (several hundreds) observations are compared with a distributed source model of the aurorae. The source model uses auroral ovals corresponding to the last closed field line (LCFL) computed using the GSFC O(sub)6 + current sheet model magnetic field, but allows the position (longitude and latitude of the oval center) and size of the ovals, the width, thickness, and height of the emitting area to be adjusted. Due to the positioning uncertainties in the planetary limbs (of the order of one pixel) and the changing seeing condition through the observations, slight image shift and different point-spread function (PSF) are also parameterized as well as the source-model parameters. Several different source distributions in the auroral region are examined as well as the uniform source distribution model. Model parameters (including image shift and PSF) are determined by utilizing the Generalized Inverse Method, so the difference between the observed and model-computed brightness in individual pixels of the images are minimized in a least square sense. We conclude the source model based on the 0(sub)6-LCFL oval can be a good first-order approximation to the Jovian H(sub)3+ aurora with the above parameters adjusted properly. We also discuss the difference between the northern and sourthern aurorae, as well as the short-term variability of the auroral structure. 11.06 Ben Jaffel L.* Vidal-Madjar A. Clarke J. T. Emerich C. Prange R. Gladstone R. McConnell J. Noll K. HST-GHRS Detection of the Deuterium Lyman Alpha Emission at the Limb of Jupiter We have obtained high resolution profiles of the H and D Lyman alpha lines emitted by the limb of the upper atmosphere of Jupiter, using the G160M grating and the LSA of the GHRS instrument on board the Hubble Space Telescope. The analysis of the resulting line shape provides, through our radiative transfer calculations, the possiblity for the first time to detect the deuterium Lyman Alpha emission at the planetary limb. This observation represents a new observational technique giving access to a possible new and independant evalution of the D/H ratio of the proto-solar nebula as well as direct informations related to the upper atmosphere physical parameters. 11.07 Emerich C.* Prange R. Ben Jaffel L. Clarke J. Ballester G. Gladstone R. Sommeria J. High Resolution Measurements of the H-Lyman Alpha Jovian Line After the Goddard High Resolution Spectrograph (GHRS) side 1 of the Hubble Space Telescope (HST) was repaired, high resolution measurements of the Jovian H-Ly alpha line have been performed during the Cycle-4 of HST. Different regions, in both hemispheres as well as in the "bulge" itself, have been selected and observed in order to spatially follow the propagation of possible turbulent therrnospheric motions which could be at the origin of the "bulge". The first results of our analysis will be presented and discussed. 11.08 Karkoschka E.* Spectrophotometry of the Jovian Planets and Titan: 300-1000 nm Full-disk albedo spectra of the Jovian planets and Titan are presented. They are based on observations taken in July, 1993 at the European Southern Observatory. The accuracy is 2 percent for relative and 4 percent for absolute albedos. The signal-to-noise ratio is approximately 1000 in the visible. Ultraviolet albedos are 10-15 percent higher than many published ones. UBV magnitudes were determined. They show some small temporal variations with respect to published magnitudes, mostly in the ultraviolet. The spectrum of each Jovian planet displays some 40-60 Raman scattering features. They can be explained by a Raman scattering model with five parameters adjusted for each planet. These parameters can be used in future radiative transfer calculations. A cold-temperature methane absorption spectrum has been determined which fits the observed methane features. Care has been taken to separate methane, ammonia, and hydrogen absorptions and Raman scattering features which superpose at many wavelengths. A strong absorption band at 933 nm wavelength in Jupiter's spectrum is possibly due to water, confirming a strong depletion of oxygen in the probed part of Jupiter's atmosphere. 11.09 Yair Y.* Levin Z. Tzivion S. Detailed Evaluation of Cloud Growth, Charge Separation, and Lightning Formation in Jupiter's Clouds We use an axysimmetric cloud model with detailed microphysics to study the formation and evolution of convective water clouds in the Jovian troposphere, and to calculate the electrical structure of these clouds. The model includes microphysical processes in both the liquid and ice phases: nucleation, diffusional growth, two-phase coagulation, freezing and sedimenation. Charge separation is based on the non-inductive ice-ice mechanism, and occurs due to interaction between graupel and ice particles in the presence of supercooled liquid drops. We calculate the space charge distributions and the electrical potentials and fields. Lightning is assumed to occur wherever the field exceeds the breakdown value for the ambient conditions. Results show that the Jovian water clouds are very efficient in separating electric charge. Electric fields reach values of 1.0-3.0 kV/cm as early as 30 minutes from the onset of ice formation in the cloud. We calculate the flash frequency by assuming that each lightning stroke neutralizes a 20 km channel within the cloud. The calculated rate is several flashes per minute. and most discharges are located in the upper part of the cloud at the 2 bar pressure level. The total energy per flash, calculated from the reduction in the elecrical energy density, is of the order of 10^l2J. Considering the optical efficiency of Jupiter's atmosphere, the calculated optical energy for these lightning flashes is 10^8-10^9J, in agreement with the analysis of Voyager's data. 11.10-P Grodent D. Gerard J. C. Dols V. The Spatial Distribution of the UV Color Ratio of the Jovian Aurora Observed with the FOC/HST Observations were made with the Faint Object Camera (FOC) on board Hubble in July 1993 to investigate the time variation and the color ratio distribution of the north UV Jovian aurora. Very bright discrete emission (up to 4 MR) was observed in the H2 Lyman bands with a considerable decrease 20 hours later. The morphology of the emission is compared in 3 different UV bandpasses to map for the first time the distribution of hydrocarbon absorption. Systematic differences are seen between the H2 Wemer and Ly-alpha morphology on one side and the H2 Lyman on the other side. A tentative interpretation in terms of the energy of the precipitating particles will be given. If available at the time of the meeting, first FOC images of the UV Saturn aurora will be briefly presented. 11.11-P Li Z. Hemtchinov V. Varanasi P. Intensity, Line Width, and Line Shift Measurements in the 10-micrometer and Pure Rotation Bands of 14NH3 and 15NH3 The need for the line intensity, width, and shift data at low temperatures of planetary interest on H(sub)2-, He-, and N(sub)2- broadened lines in the 10 micrometers and pure rotation bands of ^l4NH(sub)3 and ^l5NH(sub)3 has prompted us to measure many of them using a Fourier-transform spectrometer at several temperatures between 200 and 296 K. The variations of the line parameters with temperature and quantum numbers are considered. 11.12-P Clapp M. L. Miller R. E. Spectroscopy of Ammonia-Hydrazine and Ammonia-Water Mixed Aerosols Ammonia ice particles are thought to be the primary constituents of the upper clouds of Jupiter and Saturn, yet no direct evidence of this has been obtained from the infrared spectra of these planets. One possibility is that condensation of ammonia on a foreign core may alter the optical properties of the aerosol, masking its spectral features. Hydrazine is believed to be a byproduct of ammonia photochemistry in the Jovian stratosphere, and due to its low vapor pressure is a likely candidate for the formation of condensation nuclei. In a low temperature flow cell we have obtained spectra of ammonia coated hydrazine particles from 700 to 4000 cm^-1 (14.3 to 2.5 micrometers). The infrared spectra indicate that ammonia forms a crystalline coating on the hydrazine particles. This composite system can be successfully modeled using Mie theory and the published optical constants for ammonia. Crystalline hydrazine optical constants were derived by a novel technique based on aerosol extinction spectra which will also be described. The overall conclusion is that ammonia-hydrazine interactions are too weak to disrupt the ammonia spectral features. The ammonia water system is much different. The strong interaction between the ammonia and water molecules leads to efficient mixing of the ammonia into the ice core, resulting in significant perturbations to the ammonia spectrum. These spectra have been modeled using water ice optical constants also derived in this laboratory. 11.13-P Borysow A. Zheng C. Modeling of Collision-Induced Absorption Spectra of H2-H2 Pairs in the First Overtone Band A numerical method is presented [1] which generates the rotovibrational collision-induced absorption (RV CIA) spectra of H2-H2 pairs in the first overtone band of hydrogen, at temperatures from 20 to 500 K. The first overtone band of the rotovibrational CIA of H2-H2 pairs, typically referred to as the 1.2 micrometers, or (2-0) band, is associated with two cases, a "single" vibrational transition upsilon(sub)l = O ---> 0, upsilon(sub)2 = O ---> 2 (and similarly upsilon(sub)2 = 0 ---> 0, upsilon(sub)1 = 0 ---> 1) and "double" vibrational transitions, upsilon(sub)l = O ---> 1, upsilon(sub)2 = 0 ---> 1, where upsilon(sub)i are the vibrational quantum numbers of two interacting H2 molecules (i = 1 or 2). The first overtone band appears in the near infrared region, roughly between 7,500 and 10,000 cm^-l, which overlaps with the frequency range of NIMS (Galileo) and VIMS (Cassini) future observations. The method employs spectral model lineshapes, whose parameters are obtained from the lowest three, translational quantum mechanical spectral moments. The model spectra reproduce very closely the results of the quantum mechanical computations [2], which were based on the same input. They also show good agreement with the existing experimental data. The work is of interest for modeling the outer planets' atmospheres in the near infrared region of the spectrum. User friendly FORTRAN program utilizing the described method has been developed, and is available upon request from the authors. Acknowledgments: Partial support by NASA, Planetary Atmospheres Program, grant NAGW-10-74507 is gratefully acknowledged. [1] C. Zheng and A. Borysow, "Modeling of collision-induced infrared absorption spectra of H2-H2 pairs in the first overtone band at temperatures from 20 to 500 K", Icarus, 1994, submitted. [2] W. Meyer and A. Borysow and L. Frommhold, "The binary collision-induced first overtone band of gaseous hydrogen from first principles", Phys. Rev. A 47, 1993, 4065-4077. 11.14-P Ustinov E. A. Inverse Problems of Radiative Transfer and Inversion Methods of Data Interpretations: A General Approach to Formulation and Development The optical sounding of a planetary atmosphere, either remote or in situ, may be regarded as an observation of a field of radiation produced by the radiative transfer in the atmosphere. The nonlinear forward operator converting relevant atmospheric parameters into the measured radiative parameters is implemented by the radiative transfer computations with subsequent convolution with characteristics of the instrument. A general approach to the development of inversion methods of interpretation of data of optical sounding is discussed that is based on the formulation of the corresponding inverse problem of radiative transfer. This inverse problem is considered as an implementation of an inverse operator converting the measured data into the fields of the atmospheric parameters to be retrieved. Three cases are considered: explicit inversion of the forward operator (Case A), analytic expressions for the weighting functions through the atmospheric parameters (Case B), and, in a most general situation, these expressions involve the solutions of forward and adjoint problems of radiative transfer (Case C). Specific examples illustrating all three cases are considered. 11.15-P Garcia-Melendo E. Sanchez-Lavega A. Gomez J. M. Lecacheux J. Colas F. Parker D. Miyazaki I. Study of a New Form of Activity Within the Jovian North Temperate Eastward Jet Since the 1990 Disturbance in Jupiter's 24 deg N high-speed jet, the North Temperate Belt has been a prominent low albedo feature. During the period 1991-1994 a series of dark spots potruding into the NTrZ and running along the south edge of the NTB (average latitude 23.5 deg. N) have been tracked from more than 10000 CCD images taken at different wavelengths in the visible region (300 nm - 1000 nm). Some of these features are long enduring, persisting for two years or more, representing a record of longevity for the spots observed within the latitude of the NTB jet. Their velocity was in average 125 m/s although an oscillatory movement is appreciable in a latitude-longitude diagram with amplitude 1 deg. and spatial period 360 deg. The derived velocities relative to System III indicate deviations relative to the mean Voyager reference profile, which could be due to a real change in the profile, or to local motions of the features (wave propagation) or to vertical sheared motions since the features seems to be deep seated as they have high emissivity at 5 microns (G. Orton, priv. comminication) . 11.16-P Sanchez-Lavega A. Lecacheux J. Colas F. Parker D. Miyazaki I. Gomez J. M. A New Long-lived Anticyclonic Vortex in the South Tropical Zone of Jupiter A conspicuous synoptic scale vortex is being observed since 1983 in the South Tropical Zone of Jupiter. Its center has varied within the latitude range 19 deg S - 23 deg S, i.e. close to that of the GRS. The spot has showed an erratic motion with extreme zonal velocities of -3.5 m/s and 0 m/s relative to System III, and a changing color, being white most of the time (period 1983-1992, and 1994) but red in 1993. Images obtained under the 890 nm methane band in 1993 (red period) showed it to have a high albedo, resembling the GRS. The vortex has survived to the intense activity developed in the SEB-STrZ region following the SEB Disturbances of 1990 and 1?93. High resolution images obtained at Pic-du-Midi Observatory showed it to have a size of 8000-10000 km (East-West) times 6000 km (North-South) with an spiral shape band within it rotating anticyclonically. Because of its latitude location, longevity and morphology, this vortex represents an important clue to understand the nature of the GRS itself and other jovian vortices. 11.17-P Smith M. D. Gierasch P. J. Conrath B. J. Convective Adjustment on the Outer Planets Including Ortho-Para Hydrogen Conversion Convective adjustment and diffusive schemes based on terrestrial methods are extended to outer planet applications in order to develop an algorithm that can be used in dynamical modeling of outer planetary flows. Over the temperature range between 50 K and 250 K the delayed conversion of ortho-hydrogen to parahydrogen can have large effects on stratification. One dimensional modeling of atmospheric layers cooled from the top, as by radiation to space, is reported. After ortho- and para-hydrogen are mixed by a convective event, the ortho/para ratio begins to relax toward thermodynanlic equilibrium. The energy release during relaxation drives the atmosphere toward stability. On Jupiter, the influence of hydrogen conversion on convection is small. On Neptune the energy released by hydrogen conversion is large, and it shuts off convection. A time dependent structure ensues, with irregular occurrence of mixing events associated with temperature fiuctuations of 1 K or more. The mean thermal structure at levels where the temperature is less than about 250 K is significantly stable, in contrast to the predictions of conventional outer planet radiative-convective calculations. 11.18-P Fisher B. M. Jones B. Hudson H. S. Observations of Jovian Thermal Structure at Mid-Infrared Wavelengths The mid-infrared wavelengths offer a relatively clear view of the thennal structure of the Jovian troposphere and (as we confinn) some infonnation about the interior. We have conducted time-series imaging observations at 10 micrometers and 20 micrometers with a 16 X 64-element Si : As photoconductive detector array, using the 1.5 m UCSD/Minnesota telescope at Mt. Lemmon, Arizona (2776 m). The data have a basic one-minute interval between images to make p-mode searches possible, following the observing procedure pioneered by Deming et al. (1989). At 20 micrometers we obtained about 1200 good images during four clear nights over the interval 23 Feb. - 27 Feb. 1992, our best observing run. Each of these images has a signal-to-noise ratio of about two on the thermal features, which themselves have low contrast and carmot easily be seen in the raw data prior to flat-fielding and flattening of the limb darkening across the Jovian disk. We find the following properties: (a) At 20 micrometers the thermal features rotate at System III (the interior rate), as previously shown by Magalhaes et al. (1990); at 10 micrometers the rotation shifts between System I and System III as a function of latitude. (b) The spatial distribution of the features follows the band structure in latitude and has a semi-regular appearance in longitude. There is, however, no dominant preferred spatial frequency, nor are the spectral properties the same in N and S hemispheres. (c) Individual features evolve significantly in time over the S-day interval of the observations. The thermal features presumably represent the tropospheric signatures of deep-seated convective structures, but these properties have not yet been explained theoretically. This work was supported by NASA grant NGT-50776. 11.19-P Flasar F. M. Conrath B. J. Thermal Waves in Jupiter's Atmosphere We have reexamined the zonal structure of temperatures retrieved from the IRIS north-south mapping sequences of Voyager 1 and 2. This structure is dominated at several latitudes by the wavenumber-1 components in the upper troposphere that Magalhaes et al. (1990, Icarus, 88, 39-72) have determined to be quasi-stationary with respect to System III. We find that the strongest amplitudes of these waves tend to be located near nulls in the meridional profile of the zonal wind, extending usually into the cores of the eastward currents. Remarkably, the waves appear to extend coherently over latitude: We find little difference in the zonal phase of these waves with respect to System III over the latitude range 28 degrees N to 20 degrees S. Wavenumber-1 features identified beyond 25 degrees S have zonal phases that differ by approximately 180 degrees ; no statistically significant wavenumber-1 features have been identified at mid or high northern latitudes. All this suggests the possibility of a globally coherent wave field whose spatial structure is determined by the thermal stratification and winds of the mean atmosphere. We will present models of planetary waves to illustrate the possible ducting and tunneling properties of these waves. This work has been supported by the NASA/Planetary Atmospheres Program. 11.20-P Lederer S. M. Marley M. S. Mosser B. Chanover N. J. Beebe R. The Sensitivity of Jovian Seismological Observations to Albedo Features Schmider et al. (A&A 1991 248, 281) and Mosser et al. (A & A 1992 267, 604) report detection of Doppler shifts in reflected solar radiation from Jupiter induced by p-mode oscillations of the planet. We have considered the possibility that these observations may be recording albedo features in Jupiter's atmosphere rather than or in addition to Jovian oscillations. We have modeled the Fourier Transform Spestroscopy method of p-mode detection in detail using .889 micrometers methane-band images of Jupiter to test the albedo feature hypothesis. We found that the low frequency portion of the spectrum is strongly contaminated by the photometric signal of albedo features rotating with Jupiter. In particular, the equatorial plumes evident between 3 degrees N and 11 degrees N latitude create a signal at 250,mu Hz which coincides with signal apparent in the results of both Schmider et al. (1991) and Mosser et al. (1992). These plumes are also responsible for power at frequencies ranging from 180 mu Hz to 1070 ,mu Hz. Furthermore, features including white ovals at 33 degrees S are a likely source of signals ranging from 400 mu Hz to 1600 mu Hz. Although albedo features apparently are not responsible for the bulk of the higher frequency signal attributed to p-modes, they do appear to significantly affect the lower frequency portion of the power spectrum obtained by Mosser et al. Ideally, future observations of Jupiter will incorporate simultaneous imaging of Jupiter, thus eliminating any such ambiguity. 11.21-P Vidmatchenko A. P. Brightness Variations of Jupiter, Saturn, and Transparency Variations of the Earth Atmosphere An investigation of brightness variations of Jupiter, Saturn, and stars by mathematical spectral analysis has been made. Oscillation periods of the Earth T ~2.5, 3.6, 5.2, 7.1, 8.9, 11.2, 16.5, 20, 48, 104, and 208 min. with some variations from day to day are obtained. Most stable values are T ~ 20 and 104 min. Periods of brightness oscillations for Saturn (137 and 179 min.) and for Jupiter (142 min.) were obtained. We assumed that the last ones are free oscillations of giant planet's atmosphere. SESSION 12 ....... Moons II and Mercury Tuesday, 10:30 - 12:00 Crystal Ballroom B B. C. Flynn and T. L. Roush, Moderators 12.01 Wisdom J.* Touma J. Evolution of the Earth-Moon System The tidal evolution of the Earth-Moon system is reexamined. Several models of tidal friction are first compared in an averaged Hamiltonian formulation of the dynamics. With one of these models, full integrations of the tidally evolving Earth-Moon system are carried out in the complete, fully interacting, and chaotically evolving planetary system. Classic results on the history of the lunar orbit are confirmed by our more general model. A detailed history of the obliquity of the Earth which takes into account the evolving lunar orbit is presented. This work was supported in part by the NASA Planetary Geology and Geophysics program under grant NAGW-706, and by an NSF Presidential Young Investigator Award AST-8857365. 12.02 Hartung J. B.* Chi Scorpiid, Theta Ophiuchid and Corvid Meteorites are Giordano Bruno Ejecta If the orbit of meteoroids from a particular stream and the orbit of specific ejecta from a particular impact can be shown to be the same, then it is reasonable to conclude that the stream meteoroids were produced by the impact. The orbit of an object is specified by its position and velocity at a given time. Both the above named meteor streams and tne Giordano Brun impact occurred in June, so they are found to have the same position at a given time. The velocity magnitudes for stream meteoroids and impact ejecta are not determined precisely enough for a useful comparison of orbits. The velocity direction, or anti-radiant, of a meteor stream is specified by its observed radiant right ascension and declination (equatorial coordinates), which are generally known within a few degrees. Ejecta directions are specified by their azimuth and elevation angles (nautical coordinates). Ejecta elevation angles tend to be between 40 and 60 degrees, but can range widely during a single impact. Therefore, the elevation angle is of little value as a basis for comparing similar orbits. So, only the azimuth angle remains as a possible basis for establishing the similarity of two orbits. The azimuth of meteoroid motion is determined via a coordinate transformation, equatorial to nautical, and is uncertain by only few degrees. To express both the meteoroid and ejecta directions of motion in the same coordinate system requires knowledge of the location of the crater on the Moon and the time of the impact, both of which are accurately known for the crater, Giordano Bruno (lunar lat. = 36 deg. N.; long. = 103 deg. E 2100 hr. GMT: June 19, 1178, Julian calendar). Here an important assumption is made that the azimuths of the most abundant ejecta from the impact are the same as the azimuths of the most prominent rays extending from the crater. We find from the study of photographs and maps of the Moon that the azimuths of the three most prominent rays from Giordano Bruno to be 125 deg., 150 deg., and 237 deg. The azimuths, derived from observed radiants of the theta Ophiuchid, Ch Scorpiid and Corvid meteoroids are 123 deg., 155 deg., and 238 deg. respectively. The remarkable similarity of these three pairs of azimuths is beyond occurrence by chance and, therefore, provide a basis for the conclusion that these meteor streams were produced by the Giordano Bruno impact. These results are based on an assumption of simple two-body motion; no perturbations occurred to change the orbit parameters between the time of the impact and the time the meteor streams were observed. If perturbations did occur, which is likely, then additional streams, such as the Librids, June Bootids, June Lyrids, and Tau Herculids also may have been produced by the Giordano Bruno impact. 12.03 Gladman B. J.* Burns J. A. Lee P. Dynamical Evolution of Escaping Lunar Ejecta As more and more meteorites from the Moon and Mars are discovered, it is increasingly clear that the ejection of fragments from large bodies is easier than previously believed. Because few, if any, common source craters are plausible, at least a half dozen separate launch events have occurred in the last 10^5-10^6 years (Warrell, 1994, Icarus, in press). Since the lunar meteorite inventory is undoubtedly incomplete, one can argue for a reasonably large injected flux of lunar material into the near-Earth environs. We have undertaken a detailed study of the dynamical evolution of this ejected material through the use of numerical simulations. We bombard the Moon randomly with impactors that eject material at a variety of velocities above the lunar escape velocity. We find that some fraction of this material is delivered directly to the Earth, but most escapes quickly onto heliocentric orbits (as found by Gault, 1983, LPSC XIV, abstract). The material that reaches heliocentric orbit is then followed using the regularized mixed variable symplectic integration package of Levison and Duncan (1994, Icarus, 108, 18-36). We produce statistics regarding the fraction of the material eventually accreted by the Earth (and other planets), including the timescales involved, the entry velocity, and geometry. We hope to ultimately build a self-consistent model taking into account the primary impactor flux onto the Moon, launch efficiency for escaping material, and the available data from the lunar meteorites (cosmic ray exposure ages, strengths, sampling biases, etc.). 12.04 Stern S. A.* Flynn B. C. High-Resolution Imaging of the Lunar Sodium Exosphere I: Observing Technique The lunar Na atmosphere has been observed from Earth since its discovery in 1988. Both spectroscopy and wide-angle imaging has been used. We present a new imaging technique that takes advantage of a narrow-band Na interference filter, unique observing geometry, and good internal scattered light suppression to enable probing of the atmosphere over the lunar terminator. In this paper we describe our imaging technique and present clear evidence of this method's success at detecting the lunar Na exosphere. In paper II we present results of analysis of our data. The narrow-field (4x4 arcmin) imaging technique involves taking images just to the dark side of the lunar terminator with a 1-m-class telescope and a CCD. The lunar surface within the field-of-view (FOV) is then illuminated only by earthshine, allowing sufficient contrast for detecting atmospheric Na. By taking image strips along the terminator as the terminator moves across the lunar surface, the structure of the atmosphere can be mapped out over approximately two thirds of the lunar surface visible from the Earth. By covering both lunar mare and highland surface units, spatial variations due to inhomogeneous surface composition may be characterized. Furthermore, temporal variations due to dynamical transport across the FOV can be detected by taking a time-sequence of images over the same surface regions. The imaging technique described here complements other methods of observing the lunar atmosphere. Whereas spectroscopy is limited to observations off the lunar limb, the narrow-field technique can measure the atmosphere over roughly 70% of the Earth-facing hemisphere. Furthermore, wide-angle coronagraphic imaging has so far observed only the extended lunar atmosphere at distances greater than 0.5 lunar radii from the surface, whereas our narrow-field imaging technique can observe the atmosphere essentially down to the surface. 12.05 Simonelli D. P.* Veverka J. Thomas P. C. Helfenstein P. Switala A. Wisz M. Photometric Variations on Phobos: Reexamining the Viking Images Using techniques developed for analysis of Galileo Gaspra and Ida data (Simonelli et al. 1993, Icarus 103, 49-61) we have corrected clear-filter Viking images of Phobos for global-average limb-darkening and phase-angle effects, to investigate the range of albedos and extent of photometric diversity on the satellite. Normal reflectances range between ~ 0.06 and 0.10, with a mean value just above 0.07. Most of the surface has a normal reflectance near the global mean value; the higher reflectances are associated with the small fraction of the surface comprised of bright crater rims. Photometrically corrected images covering phase angles 1.5 degrees -47 degrees reveal that the contrast between the bright northeast rim of Stickney and the crater floor increases significantly with rising phase, a trend opposite to that seen for bright rims around small craters. Preliminary indications are that the Stickney contrast changes are due more to an atypical photometric behavior of the crater floor than to any unusual scattering behavior of Stickney's rim; Stickney's floor may have particles slightly more backscattering than average Phobos, or may have a higher than average macroscopic roughness. Because slumping has considerably modified Stickney' s floor, the processes that roughen this surface might be different from those proposed for dark markings in fresh crater floors elsewhere on the satellite (Goguen et al. 1978, GRL 5, 981-984). The photometric corrections described above were performed with a global-average Hapke function determined by fitting disk-resolved data from 22 clear-filter images (phase angles 1.5 degrees to 123 degrees). The average macroscopic roughness is well-constrained at 22 degrees, making Phobos somewhat smoother than Gaspra and comparable in roughness to the Moon. The results also confirm earlier indications that Phobos has a strong opposition surge-stronger, in fact, than those of Gaspra or the Moon. This work was supported by NASA grant NAGW-2186. 12.06 Hapke B. W.* Nelson R. M. Smythe W. D. Horne L. J. Herrera P. Gharakanian V. Preliminary Results of Studies of the Opposition Effect Using the JPL Long-Arm Photopolarimeter Using the new JPL goniometric photopolarimeter, which can measure the orthogonal components of reflectances of materials in linearly and circularly polarized light at phase angles as small as 0.2 degrees, we have studied the opposition effect (OE) in lunar soils and terrestrial powders. Previous measurements of lunar soils at phase angles larger than 1 degree showed that the lunar OE is caused primarily by coherent backscatter. High albedo powders have large OE's that are concave-upwards and independent of grain size. In low albedo powders the OE peak is truncated and flattened, as predicted by the coherent backscatter model of the OE. Major exceptions to the latter are the lunar soil samples, for which the OE's are concave-upward, with surges as large as 66%. The amplitudes of these OE peaks decrease as albedo increases, directly contrary to predictions of the coherent backscatter model; this implies that part of the lunar OE is caused by shadow hiding. The typical planetary, well-developed, wide branch of negative polarization, such as the moon's, is associated with a circular polarization ratio that decreases as the phase angle decreases, implying that this negative polarization is caused by shadow hiding. This research is support by grants from the NASA PG&G program. 12.07 Morgan T. H.* Killen R. M. Unsteady Diffusive Flows in the Mercurian Regolith Deep (~10 km) crustal release of gaseous Na and K has been invoked as both the source for these species in the exospheres of the Moon and Mercury and to explain observed temporal changes [1,2 and references therein]. Here we examine the temporal behavior of the flux at the surface that results from the sudden release of a large quantity of gas at depth in response to some crustal forcing event. With D(z) = D(sub)0 exp(z/lambda) [2] where z is the distance from the base of the crust and lambda is e-folding distance, and the loss at the surface of the regolith = Au(sub)s = -D{Du/Dx}(sub)s where u is the density of Na or K in the pores, we show that the Crank-Nickelson difference equation for the density, u(sub)j between any two consecutive time steps can be written. Equations 1 and 2 appear here in the hard copy. We examine solutions of these finite difference equations looking at the temporal behavior in terms of the quantity (L2/4* bar-D) in order to examine the possibility that deep crustal release could explain the observed temporal behavior of K. Supported by NASA grant NAGW 3824. References: [1] Sprague A. L. et al. (l990) Science, 249, 1140. [2] Killen R. M. and Morgan T. H. (1993) Icarus, 101, 293. 12.08 Kozlowski R. W. H.* Sprague A. L. Witteborn F. C. Cruikshank D. P. Wooden D. H. Mercury: Mid-Infrared (7.3-13.5 Micrometer) Spectroscopic Observations Showing Features Characteristic of Plagioclase Mid-infrared spectroscopic observations of the surface of Mercury are reported for the wavelength range 7.3 to 13.5 micrometers. The observed spectral radiance emanated from equatorial and low latitude regions between 110-130 degrees mercurian longitude. The area is primarily an intercrater plain. The spectra show distinct and recognizable features, the principal Chnstiansen emission peak being the most prominent. The Chnstiansen feature and overall spectral shape strongly suggests the presence of plagioclase (Ca,Na)(Al,Si)AlSi(sub)2O(sub)8. The emissivity maximum of albite typically falls near 7.7 and that of anonhite near 8.2 micrometers; the Mercury emission maximum is at 8.0 micrometers. Assuming a linear mixing model, and making adjustments for the vacuum environment, this corresponds to Ab(sub)(30-10) (bytownite). Labradonte is not ruled out. Both labradorite and bytownite are characteristic of igneous rocks of gabbroic composition and of anorthosites. Mercury observations were made at the NASA Infrared Telescope Facility (IRTF) 3.0 m telescope on Mauna Kea, Hawaii. The thermal IR spectra were obtained July 12, 1992 using the High Efficiency Infrared Faint Object Grating Spectrometer (HIFOGS) Witteborn et al. [1]. HIFOCS has cryogenicailly cooled aperture and filter wheels, grating, and a linear array of 120 Bi-doped Si detectors. To increase the spectral range slightly, and to increase the resolution (decrease the wavelength sampling increment), all standard stars and Mercury were measured at two grating settings. The first grating setting spanning wavelengths of 7.22 to 13.02 micrometers and the second 7.61 to 13.30 micrometers. The individual spectra have an average resolution of 0.048 micrometers. After the spectra from the two grating settings are interleaved, the spectral resolution is improved to 0.025 micrometers. Telluric absorptions were corrected for by using alpha Boo. All ratioed spectra were then corrected for the spectral shape of alpha Boo (K2 II) using a spectrum generated from several observations of alpha Boo from Kuiper Airbome Observatory, the IRTF, and the NASA 1.5 m telescope at Mt. Lemmon (Cohen et al. l 2]; Cohen et al.[3]). References: [1] Witteborn F.C., et al. Astro. Soc. Pacific Conf. Series Astro. IR Spec. Conf. 365-372 (1993). [2] Cohen et al. Astro. J. 104, 5, 2030-2044 (1992). [3] Cohen et al. Astro. J. 104, 5, 2045-2052 (1992). 12.09 Butler B. J.* Muhleman D. O. Slade M. A. VLA/Goldstone 3.5-cm Radar Observations of Mercury in 1994: South Polar and Other Results The discovery of deposits of ices at the poles of Mercury has profound implications for planetary science [1-4]. Studies of these deposits may provide clues about the distribution and type of impactors and the supply of volatiles in the early inner solar system, the state of the spin vector of Mercury in the past, and the thermal history of Mercury, among other things. The deposits have been mapped at both poles by the Arecibo radar telescope at 13-cm [2,4]. The north polar deposits have also been mapped at 3.5-cm [1,3]. In an attempt to map and characterize the south polar deposits at 3.5-cm, we performed two experiments when the south polar regions were visible. These experiments took place on Feb. 21 and 26 of 1994, when the subearth latitude was ~-10 degrees, giving a good view down into regions on the surface which remain in permanent shadow, the most likely regions to find the polar ice deposits [3]. Because of the extreme complexity of the data reduction involved in these experiments, the data have not been completely reduced yet. However, preliminary results indicate the presence of a south polar feature similar to that at the north pole. The peak radar cross section received in the same circular polarization as that transmitted (SS) on Feb. 21 was ~ 6.6%. Also seen in the SS data for that day are large cross section enhancements which we have called "radar basins" [3], one of which is located near the Kuiper crater. These features and their cause will be discussed, along with the south polar feature. 1 - Slade, Butler, and Muhleman, Science, 258, 635, 1992. 2 - Harmon and Slade, Science, 258, 640, 1992. 3- Butler, Muhleman, and Slade, JGR, 98, 15003, 1993. 4 - Harmon, et al., Nature, 36g, 213, 1994 12.10-P Magnusson P. Lumme K. Photomorphography Applied to Rough and Globally Concave Objects Photomorphography is a technique for inverslon of dlsk-integrated photometrlc observations to derlve global characterlstics of solid Solar System bodies (see Kaasalainen, Lamberg, Lumme, and Bowell 1992, Astron. Astrophys. 259, 318-332). A basic assumptlon ln thls technlque is that the object has a convex shape. Relaxation of this assumption makes the whole problem mathematically very intractable. We are studying the sensitivity of our results to departure from the convexity assumption. For example, for a simple model with homogeneous scattering and a global concavity on the equator the resulting synthetlc lightcurves at non-zero solar phases have a significant component in the first Fourier order. When interpreting this in terms of convex models one erroneously arrives at a strong albedo contrast and a shape that resembles neither the concave object nor its convex hull. We wlll dlscuss ways of overcoming this problem, or at least diagnosticise when there is a problem. 12.11-P Robertson S. Walch B. Horanyi M. Charging Characteristics of Simulated Lunar Regolith Dust Grains in a Plasma The charge on grains of simulated lunar regolith (MLS-1) has been measured in a plasma environment containing thermal electrons of a few eV temperature and a second component of nearly monoenergetic electrons with energy variable from 15 to 120 eV. Measurements are compared with the charging characteristics of glass spheres and copper dust in the same range of size (53-63 microns). The charging characteristics can be divided into three regimes: one in which the grains charge to a potential which repels the bulk of the thermal electrons, a regime of higher potential in which the thermal and the fast electrons are repelled, and a bi-modal regime in which grains may charge to either potential. The charging is described by a model which includes the currents of the thermal electrons, thermal ions, fast electrons and secondary emission induced by the fast electrons. 12.12-P Potter A. E. Morgan T. H. Gilliam L. Coronagraphic Observations of the Lunar Sodium Exosphere Near the Lunar Surface Imaging of the sodium exosphere was first accomplished by Flynn and Mendillo (Science, 261, 184 (1933)) using optical filters to isolate the sodium emission and occulting masks to block scattered moonlight. Their technique was limited to regions above about 1000 km., because of interference by scattered moonlight in the optics and sky. Images of the sodium exosphere near the surface are needed to resolve issues surrounding the origin of the sodium and its interaction with the surface (see Potter and Morgan, GRL, 1994, in press). In order to image the sodium exosphere near the lunar surface using the optical filter technique, extremely high rejection factors for scattered light are required. These are found only in special purpose instruments like the Evans 40 cm.,solar coronagraph at the National Solar Observatory at Sacramento Peak New Mexico. We report initial observations of the lunar sodium exosphere near the lunar surface, using the Evans coronagraph, a 2K x 2K CCD, and a 3 A bandwidth interference filter. Our results illustrate the difficulties involved in imaging observations close to the lunar surface, as well as the importance of these data to our understanding of the processes which form and modify the lunar sodium corona. The work was supported by the NASA Planetary Astronomy program. 12.13-P Belobrov A. V. Fuks I. M. Approximation of the Scattering Data from the Moon Recent theoretical results in the problem of the electromagnetic wave scattering by a rough surface offer new possibilities to determine interface parameters from the experimental data. Statistical parameters of the Moon's surface, e.g. spacial spectrum of the irregularities, has been found from comparison between the experimental and computational data obtained in the framework of different surface models. These results were compared with the well-known Hagfor's approximation model too. 12.14-P Nelson R. M. Horn L. J. Weiss J. R. Smythe W. D. Wright F. Hermes-The Mercury Orbiter Discovery Mission The Hermes Mercury orbiter is one of several missions that have been proposed to NASA under the Discovery program. If selected, Hermes would be launched in 1999 and would be inserted in a 200X15000 km., 12hr, elliptical orbit about Mercury. The tour to Mercury would include two Venus-Mercury flybys. The principal objectives of the mission are: surface mapping, surface composition and texture determination, mapping the magnetic and gravitational fields, understanding the distribution and abundances of atmospheric species, characterizing the species in Mercury's magnetosphere, and understanding the planet's interior. There are four instruments under consideration for the Hermes payload. These are: an imaging system, a magnetometer, an ultraviolet spectrometer, and a lidar. The imaging system will provide the measurements intended to study the large scale surface morphology and to distinguish between impact and volcanic landforms. Along with the ultraviolet spectrometer, it will be able to provide information on questions regarding the abundance of iron in the planet's crust. Both systems are able to search for water ice at Mercury's poles. The camera and the lidar provide several ways to measure the scattering properties of the regolith, and hence infer its texture. The Ultraviolet spectrometer will measure the abundance of species in the planet's tenuous atmosphere. The particle and fields investigations will provide information about the nature of the planet's interior and will characterize the material in the planet's magnetosphere. This work carried out at JPL under contract with NASA. 12.15-P Lopes-Gautier R. Baloga S. Nelson R. Volcanism on Mercury No volcanic features have yet been unambiguously identified on Mercury. However, Mercury presents an unusual opportunity to investigate the role of planetary volcanism in comparison with other planetary surface processes (e.g. cratering, thermal and orbital evolution) and constraints (e.g. composition, shape, and interior configuration). Advances in the understanding of effusive volcanism over the last decade now make it possible to constrain eruption rates, compositions, rheologic properties, thermal characteristics, and eruption style from dimensional and topographic information. We will elaborate these quantitative aspects of volcanism on Mercury on regional and global basis in light of the recent improvements in the current theories of lava emplacement. Particular attention is paid to the influence of regional differences in relation to compositional and topographic influences and the competition of volcanism with other surface processes. These results provide additional constraints on the orbital and thermal evolution of the planet and the interior processes. Presently, the ability to understand the interrelationship of planetary processes for Mercury is lirnited by data, rather than the theoretical capabilities. We will discuss potential remote sensing measurements that would improve the understanding of volcanism in relation to the other processes that formed the surface and interior processes. Presently, the ability to understand the interrelationship of planetary processes for Mercury is limited by the data, rather than the theoretical capabilities. We will discuss potential remote sensing measurements that would improve the understanding of volcanism in relation to the other processes that formed the surface and interior of the planet. 12.16-P Flynn B. C. Stern S. A. High-Resolution Imaging of the Lunar Sodium Exosphere II: Science Results We present results of analysis of lunar atmospheric imaging data obtained with the University of Texas McDonald Observatory 0.9-m telescope equipped with a CCD. Our imaging technique, described in paper I, employs high-resolution, narrow bandpass, and specific observing geometry to suppress scattered light and image the lunar atmospheric Na essentially down to the surface. We have conducted observations at McDonald with this technique in 1991, 1993, and 1994. We have analyzed the data by applying a simple collisionless exosphere model to obtain temperature and spatial distribution information. The model assumes spherical symmetry and a Maxwellian distribution. Image analysis completed to date yields evidence of (1) coexistent cold (thermal) and hot (suprathermal) Na populations; and (2) systematic variation in atmospheric temperature and surface fractional abundances with latitude. The data taken to date represent <10% of the visible lunar surface. Future observations will concentrate on obtaining data over the full extent of lunar surface that can be observed during the first quarter-full Moon and full Moon-last quarter observing windows. We will use our imaging technique to (1) make lunar Na "movies" over specific surface areas; (2) make full north-south Na image strips along the terminator over a wide range of lunar phases; and (3) extend imaging observations to lunar K, which has thus far only been detected through spectroscopy. SESSION 12A ....... INVITED TALK PLENARY Tuesday, 1:30 - 2:15 Crystal Ballroom M. A. McGrath, Moderator 12A.01-INV Gladstone G. R.* Planetary Science in the Extreme Ultraviolet No abstract available. SESSION 12B ....... INVITED TALK PLENARY Tuesday, 2:15 - 3:00 Crystal Ballroom D. M. Hunten, Moderator 12B.01-INV Ingersoll A. P.* S-L 9: What Happened? No abstract available. SESSION 13 ....... Jupiter II and Saturn Tuesday, 3:30 - 5:30 Crystal Ballroom A C. D. Barnet and B. Sicardy, Moderators 13.01 Bezard B.* Griffith C. Owen T. Lacy J. Search for Hydrogen Cyanide on Jupiter We present high spectral resolution observations of Jupiter recorded on January 21, 1991 at the NASA/Infrared Telescope Facility . The cryogenic echelle array spectrometer IRSHELL was used at a resolution of 0.08 cm^-l to search for the R(5) and R(ll) lines of HCN at 735.61 and 747.41 cm^-l. Signal-to-noise ratios of several hundred were achieved in the continuum. We do not find evidence for HCN absorption, in contrast to the pioneer observations of Tokunaga et al. (1981, Icarus 48, 283-289). Synthetic spectra have been generated using a HCN vertical profile limited by saturation in the upper troposphere. The calculated lines yield a poor agreement with Tokunaga et al.'s data for any value of the deep HCN mixing ratio. From our non-detection of the HCN lines and our re-analysis of Tokunaga et al.'s observations, we think that the previously reported detection of HCN in Jupiter is questionable. 13.02 Weisstein E. W.* Serabyn E. Detection of the PH3 J=3-2 Rotational Transition in Jupiter and Saturn We report the detection of absorption in the J = 3-2 lines of PH(sub)3 at 800.5 GHz in both Jupiter and Saturn. While PH(sub)3 has been detected in the infrared in both Jupiter and Saturn, and at mm wavelengths in Saturn (Weisstein and Serabyn 1994), the measurements presented here represent the first submillimeter confirmation of the presence of PH3 in Jupiter. Jupiter and Saturn were observed at the CSO in June 1994 with our FTS. A strong ~20% absorption feature with a FWHM ~ 10 GHz and line center of 800.6 GHz was observed in Jupiter. An even broader feature was detected at the same frequency in Saturn, but its large linewidth, combined with the cutoff in terrestrial atmospheric transition near 780 GHz, make this line's parameters more difflcult to determine. The observed lines are modeled in both giant planets using a radiative transfer code, and results concerning the distribution of PH(sub)3 in the Saturnian and Jovian stratospheres and upper tropospheres are derived. In the case of Saturn, additional constraints are provided by the previous detection of the J = 1-0 line. The enrichment of PH(sub)3 in Saturn relative to Jupiter is confirmed. In addition, new low-noise FTS continuum observations of Jupiter and Saturn between 330 and 950 GHz have yielded no further line detections, allowing new upper limits to be placed on the mixing ratios of species such as CO, HCN, HCP, and H(sub)2S in their upper atmospheres. 13.03 Varanasi P.* Li Z. Nemtchinov V. Laboratory Data on the IR Lines of 12CH4, 13CH4, 12CH3D, 12C2H2, and 12C13CH2 Observable in the Jovian Atmosphere Infrared observations of the Jovian atmosphere involve the study of the infrared spectral emission by CH(sub)4, its isotopes, and hydro-carbons which are created by its photodissociation. As laboratory data are needed on the spectral lines of interest at the appropriate temperatures to aid the astronomers, we present absolute intensities, collision-broadened half-widths, and pressure-induced shifts on lines belonging to thermal infrared bands of ^l2CH(sub)4, ^l3CH(sub)4, ^l2CH(sub)3D, ^l2C(sub)2H(sub)2 and ^l2C^l3CH(sub)2 obtained with a Fourier-transform spectrometer. Using He and H(sub)2 as broadening gases, the data have been measured at temperatures appropriate to the planetary atmosphere. 13.04 Romani P. N.* Monks P. S. Nesbitt F. L. Payne W. Stief L. J. Fahr A. Laufer A. H. Recent Rate and Product Measurements of the Reactions C2H3 + H2 and C2H3 + H--Importance for Photochemical Modeling of Hydrocarbons on the Outer Planets Recently the rate constant for the reaction C2H3 + H2 has been measured by a more direct method than any used previously. While only an upper limit at room temperature was determined, the rate is lower by at least a factor of 400 than that used in Allen et al. 1992 (Icarus, 100, 527). This reaction is potentially important in regulating the relative abundances of C2H2, C2H4, and C2H6 in the stratospheres of the Jovian planets. Specifically, this reaction converts C2H3 to C2H4 before it is either recycled to C2H2 or reacts further to form C3 and C4 hydrocarbons. The resultant C2H4 can be transformed to C2H6 by successive reactions with H or photodissociated back to C2H2. While the new rate constant for C2H3 + H is not significantly different from previous measurements, the determination of the yield of the combination product C2H4 (~25% at room temperature and ~1 mbar) is significant. Previously, the products were assumed to be solely C2H2 + H2, i.e., recycling C2H3 before it could be converted to C2H4. For photochemical modeling, the reduced conversion rate of C2H3 to C2H4 via H2 is partially offset by inclusion of the C2H4 product channel for C2H3 + H. We will present results from a 1-D hydrocarbon photochemical model with an emphasis on sensitivity to the extrapolation method chosen to bridge the pressure/temperature regime of laboratory measurements to those in the stratospheres of the outer planets. 13.05 Drossart P.* Forni O. Beuzit J. L. Baines K. Orton G. Structure of the Polar Haze of Jupiter from Ground-based Observations in 1994 Observations of the South polar regions of Jupiter at 2 microns have been conducted on 1994 March 27 and 29 with the adaptive optics system COME-ON+ on the 3.60 meter ESO telescope. By using a galilean satellite as a wavefront reference, as well as for accurate offset guiding, a spatial resolution better than 0.2 arcsec (for the PSF width) was obtained on Jupiter images at 2.07 and 2.12 micron, in the dipole induced absorption band of H(sub)2. At these wavelengths, the upper atmospheric levels of Jupiter are sounded between 5 and 70 mbar (Kim et al, Icarus, 1991). At this spatial resolution, the South polar haze appears to be non-uniform, and spatial structures in the polar haze are observed, corotating with Jupiter . A comparison will be made with images obtained one month later with NSFCAM on IRTF. These images are obtained during the nights of April 25 and 28. A global longitudinal survey has been obtained, at selected wavelengths between 1 and 5 micron. Morphological studies of the polar haze, in particular, can be made from these images, both in North and South polar regions. From the observations of each night, cylindrical mosaics can be built and cloud tracking will allow us to study the differential rotation of Jupiter at several wavelengths in the infrared. 13.06 Barnet C. D.* Caldwell J. J. Cunningham C. C. HST Spectra of Jupiter and Saturn: Characteristics of Stratospheric and Tropospheric Hazes Observations of Jupiter (May 1992-July 1993) and Saturn (December 1992) were made by the HST Faint Object Spectrograph (FOS) (1800-3300 angstrom) and the Goddard High Resolution Spectrograph (GHRS) (1600-1850 angstrom). The planetary spectra sample the equatorial central meridian, equatorial limb, and (Saturn only) the north pole. The FOS spectra were processed to remove background grating scatter and to account properly for effects due to spherical aberration in the HST primary optics. The planetary spectra were ratioed to HST spectra of the solar analog 16 Cyg B over the spectral range 1600-3300 angstrom. HST images at 3360 angstrom are used to derive limb-to-limb absolute reflectivity scans, I/F, for both Jupiter and Saturn. The absolute reflectivity ratios are compared to vertically inhomoge-neous models of the planetary atmospheres to determine abundances of minor and trace species therein. Both Jupiter and Saturn show the influ-ence of acetylene and phosphine absorption below 2300 angstrom. Only Jupiter shows features due to ammonia. Preliminary models of these data were discussed by Caldwell et al. (1993, BAAS 25, 1027). In this paper we will concentrate on the vertical distribution and op-tical characteristics of the hazes in these atmospheres. The wavelength dependent models at FOS wavelengths are most sensitive to aerosol parameters (e.g., particle size distribution, refractive index) and gas concentrations. The geometry dependent models of limb-to-limb reflec-tivity characteristics are most sensitive to particulate phase functions. Simultaneous utilization of both types of models are used to optimize our understanding of these atmospheres. 13.07 Gudkova T.* Mosser B. Gautier D. Guillot T. Provost J. Chabrier G. Jovian Seismology: Influence of the Troposphere Thermal Signature and Seismological Diagnosis In order to correctly interpret the seismological measurements recor\ded after the cometary impact on Jupiter, we have examined the following points: 1) The Jovian oscillation spectrum taking into account the planetary troposphere and stratosphere has been calculated for the first time. Direct numerical computations of planetary eigenfrequency pattern have been carried out for the fundamental modes and for non radial modes with radial order up to 20 and degree up to 30. The differences of the oscillation frequencies due to the addition of the tropospheric and the stratospheric levels strongly depend on the upper boundary condition. However, the corrections are simple functions of the eigenfrequency and the degree of the mode. These results are necessary for accurately interpreting the future seismological observations of Jupiter and Saturn. 2) The propagation of acoustic waves in the Jovian troposphere has been revisited, in order to estimate their thermal signature. The relation between this signature and the wave velocity depends strongly on the wave frequency and on the level of detection. 3) Different interior structure.models of Jupiter have been compared with the help of seismology. We have considered two groups of models: first, models based on different equation of state of hydrogen, and second, models with different descriptions of the mechanism of energy transport (fully adiabatic models and models with a radiative window). Our results show it is possible to test the giant planets interiors with the help of future seismological data, depending on the accuracy of the determination of the eigenfrequencies and on the degrees of the observed modes. 13.08 Hubbard W. B.* Porco C. C. Hunten D. M. Rieke G. H. Rieke M. J. McCarthy D. W. Haemmerle V. Haller J. McLeod B. Lebofsky L. A. Marcialis R. Holberg J. B. Landau R. Carrasco L. Elias J. Buie M. W. Persson S. E. Boroson T. West S. French R. G. Saturn's Mesospheric Temperature from 28 Sgr Occultations A full ensemble of immersion/emersion lightcurves from the occultation of 28 Sgr by Saturn in 1989 has been analyzed. From an accurate determination of the Saturn center of figure using fiducial ring features, the center is known a priori to within a few km. Thus we retrieve not only atmospheric temperatures but also absolute radial positions of the measurements with high accuracy. From the 11 best-calibrated lightcurves, we infer a mean temperature of 135 +- 5 K on a level surface corresponding to an equatorial radius of 60963 +- 3 km. The pressure corresponding to this level (isothermal fit) is 1.7 microbar. Saturn-centered latitudes ranging from -14.20 degrees to +6.25 degrees were probed. To fit the actual shape of the planet, we assumed that it was rotating on cylinders with the observed differential flow field as derived from cloud motions. There is considerable "topography" (several x 10 km) in the level surfaces over the range of latitudes probed, and this effect is included in the model. The self-consistencies of the inferred level-surface radii at half flux for each of the stations provide support.for the differentially-rotating model. Two of the stations, CTIO and Las Campanas, observed immersion through C-ring features. The features thus acted as a fiducial grating superimposed over the atmospheric modulation at these stations. Model lightcurves computed on the basis of the adopted mean temperature and center-of-figure solution agree very well with the data from these stations. This work has been supported by NASA grants NAGW-1555, NAGW-1876, NAGW-1368, by NSF Grant AST-8715373, and by others. 13.09 Allison M.* A Lower Isentropic, Iso-Potential Vorticity Model for the Deep Saturn Thermocline A simple conceptual model for the zonal winds of the outer planets is proposed with particular attention to the deep thermal structure of Saturn. A dynamic upper layer of well-mixed potential vorticity is assumed, with a static stability exponentially decreasing with height above a windless, isentropic interior. The schematic character of the geostrophically balanced potential temperature field is shown by the solid contours in the figure, with isotherms dashed (for every 20K). Quasi-uniform potential vorticity for the configured thermocline is consistent with a high-latitude alternation of jets over the interal deformation scale and cyclonic shear toward a strong equatorial jet. 13.10 Bosh A. S.* Saturn's Gravitational Harmonics We present a solution for Saturn's pole and radius scale derived from S occultation data sets, including 2 recent data sets acquired using the High Speed Photometer on the Hubble Space Telescope. This solution is used in an investigation of kinematic models for non-circular ringlets. Constraints from the location of the Titan ringlet (in an apsidal resonance with Titan) and the measured precession rates of the Maxwell and 1.495 Rs ringlets are combined with previously published constraints from Pioneer tracking data and satellite precession rate measurements (Null et al., 1981. Astron. J. 86, 456-468) to determine values for Saturn's gravitational harmonics: J(sub)2 = (16301 +/- 6) x lO^-6, J(sub)4 = (-894 +/- 9) x lO^-6, and J(sub) = (124 +/- 5) x 10^-6 (for Saturn equatorial radius 60330 km). Values of higher-order harmonics are held fixed: J(sub)8 = -10 X l0^-6, J(sub)10 = 2 X 10 ^-6, J(sub)12 = -0.5 X 10^-6, J(sub)14 = J(sub)16 =...= 0. The formal errors of the first three even gravitational harmonics are greatly reduced from those of Nicholson and Porco (1988, J. Geophys. Res. 93, 10209-10224), particularly the error in J(sub)6. J6 is now determined precisely enough to prDvide a useful constraint on models of Saturn's interior. The value we find for this quantity suggests that the interior may be in a state of complex rotation. 13.11-P Martyn M. D. Barnet C. D. Caldwell J. J. Hopkinson J. M. HST Spectra and Image of Saturn. Interpretation A Hubble Space Telescope (HSI) ultraviolet (F336W filter) images of Saturn in December 1992 shows a brightening on the limb at 35 degrees north latitude. At the time of these observations the phase angle was 4.85 degrees and the limb was on the sunset (east in system III) side of the planet. Reflectivity scans show that the limb is 4% brighter than the central meridian (cm) and the terminator is 15% brighter than the cm. We have utilized a vertically inhomogeneous model of Saturn's atmo-sphere to synthesize the absolute reflectivity, I/F. The model was opti-mized to fit HST/FOS spectra in the wavelength range of 1800-3200 angstrom for the equatorial and polar regions during the same observations (Caldwell et al. 1993, BAAS 25,1028). Limb-to-limb scans from the F336W image constrain the phase function of the hazes used in the model, while the FOS spectra constrain the altitude, optical depth, and single scattering albedo of the hazes. We have modeled limb-to-limb scans and FOS spectra taken at the same latitudes and extrapolated these models to show that the increase in reflectivity at 35 degrees latitude is consistent with the observational geometry. The imaging observations also, confirm differences in vertical structure between the north polar region and the equatorial regions. M. D. Martyn was supported by Natural Science and Engineering Research Council (NSERC) of Canada grant no. 5-50455. 13.12-P Ortiz J. L. Moreno F. Molina A. Methane Band Imaging of Saturn's Cloud Temporal Changes from 1991 to 1993 We present the latitudinal behavior of absolute reflectivity, molecular absorption and limb-darkening as derived from CCD Saturn images obtained at 6190 Angstrom, 6350 Angstrom, 7250 Angstrom, 7500 Angstrom, 8900 Angstrom, and 9500 Angstrom during four observing runs during the period 1991-1993. The observations were made at the 1.52-m telescope at Calar Alto and the 2.5-m Nordic Optical Telescope at La Palma. The limb-to-limb reflectivity scans at planetographic latitudes 0 degrees , 10 degrees , 20 degrees, 40 degrees, and 70 degrees have been analyzed in terms of multiple scattering radiative transfer models. The large changes in reflectivity at equatorial latitudes from 1991 to 1992 are interpreted as a considerable increase in the aerosol specific abundance at different levels within the extended tropospheric haze. 13.13-P Hillman J. J. Glenar D. A. Le Louarn M. Drummond J. D. Multispectral Imaging of Saturn Using the Kirtland 1.5 m Adaptive Optics Telescope Recent high spectral and spatial resolution imaging results obtained from observations of Saturn are shown and discussed in a preliminary fashion. These observational data were acquired using a newly developed multispectral array camera. Wavelength tuning is achieved by an acousto-optic tunable filter operating in the 0.6 to 1.0 micron region. Images were recently obtained using the 1.5 m laser beacon adaptive optics facility at the Starfire Optical Range, Albuquerque, NM, using a new image correlator intended for tracking extended (solar system) sources. Spectral images were taken in H2 (800 nm), NH3 (770 nm), and CH4 (725 and 890 nm), and corresponding adjacent continuum regions. Preliminary analysis of this data and a comparison with earlier works will be made. This work was supported by the NASA Planetary Instrument Definition and Development Program and the GSFC Director's Discretionary Fund. 13.14-P Momary T. W. Baines K. H. Saturn's Tropospheric and Stratospheric Aerosols: Probing Vertical Structure of Various Latitude Regions with an Analysis of Near-Infrared IRTF ProtoCAM Imagery Near-infrared imagery of Saturn acquired in August 1993 in H2 and CH4 absorption bands between 1.60 - 3.90 micrometers affords a means of probing the vertical distributions of aerosol layers in Saturn's troposphere and stratosphere. Our objective is to determine vertical structure and near-infrared optical properties of Saturn's aerosols, such as single scattering albedos and opacities, as well as to derive particle sizes and mass column abundances. We have initially used a simplified three-layer atmospheric model containing a clear gas layer, an NH3 haze layer, and an optically-thick, physically-thin NH3 cloud just below the haze. We have assumed a double Henyey-Greenstein phase function for the haze and cloud particles with f = 0.75, g(sub)1 = 0.7, and g(sub)2 = -0.3, and a H2 unsaturated molar fraction of 0.924. Three regions have been analyzed (the Equatorial Zone, the North Temperate region, and the North Tropical region) and preliminary results suggest that the aerosol burden in the EZ is either much greater and/or extends to a much higher altitude than in the other two regions. For example, for a haze opacity of 2.00 (i.e., an optically-significant layer based on recent findings of Karkoschka and Tomasko, 1992), we find that the EZ has a hazetop near 0.083 bars while the NTe and NTr regions are characterizedby a lower-lying hazetop near 0.160 bars. On the other hand, if we assume that all regions have a hazetop near 0.160 bars, then we find that the EZ's opacity is about 2.5 times that of the other regions. Tentatively, we find that the haze opacity for the NTe and NTr regions is less than 4.00, from which we can estimate that the particle radii are significantly smaller than 2 micrometers, consistent with the conclusions of Karkoschka and Tomasko (Icarus 106, 428-441, 1993). We are continuing to analyze these images, incolpoIating other wavelengths (such as an intermediatewavelength on the shoulder of the H2 1-0 S(l) pressure-induced absorption feature) and enhancing the model, in order to establish haze structures of these various axisymmetric regions on Saturn more fully. 13.15-P Del Rizzo D. A. Barnet C. D. Caldwell J. J. Saturn's Northern Polar Hexagon: Image Analysis and Color Differencing The Voyager spacecraft encounters with Saturn both occurred near the northern spring equinox and, therefore, were not at optimum geometry for observing Saturn's poles. Even so, Godfrey (1988, Icarus 76, 335) was able to construct mosaics of images to reveal Saturn's north polar hexagon and the associated spot at 76 degrees latitude. We have surveyed the Voyager 2 database and examined previously un-published images at high sub-spacecraft latitudes (+ 10 degrees to 20 degrees) and high spatial resolution. We have constructed high resolution polar projections from selected images in the violet and green filters. The appearance of the hexagon in these filters is significantly different; we interpret this as being due to a different vertical distribution of hazes between the region to the south and to the north of the hexagon. These images are consistent with the interpretation that the hexagon is an atmospheric cloud pattern associated with a complex planetary wave phenomena (Allison et al., 1990, Science 247, 1061). HST observations of the hexagon during Saturn's summer season clearly show the polar hexagon with its associated spot (Caldwell et al., 1993, Science 260, 326). Comparison of HST images with Voyager images taken through similar filters shows that the regions delineated by the hexagon boundary as well as the polar spot have the same color. This suggests that the hexagon and the polar spot remained unchanged during the 12 years between the Voyager and HST images, and supports the theory that the polar spot is linked to the rotation rate of the interior. We acknowledge the National Space Science Data Center (NSSDC) and the imaging team leader from the Voyager project, B. A. Smith, for provid-ing the Voyager images used in this analysis. We also acknowledge Prof. J.A. Westphal who was the original PI for the HST images considered here. D.A. Del Rizzo was supported by Natural Science and Engineering Research Council (NSERC) of Canada grant no. 5-50455. 13.16-P Achterberg R. K. Flasar F. M. Modeling of Planetary-Scale Waves in Saturn's Atmosphere Analysis of Voyager IRIS data has revealed the presence of quasi-stationary planetary scale waves of zonal wavenumber 2 and 4 at the tropopause level on Saturn (BAAS 25, 1055). These waves are strongest at latitudes between 30 degrees and 40 degrees north, decaying rapidly to the north and more slowly to the south, and are seen in data at 130 mbar pressure level, but not at 270 mbar. We have used a WKB raytracing model of planetary-scale Rossby wave propagation on a sphere to understand the behavior of the observed waves. Rossby waves near the tropopause at 35 degrees N are restricted to phase velocities between about -30 and +30 m/s (as Rossby waves propagate westward relative to the mean zonal flow with a maximum velocity dependent upon the static stability). Meridional confinement of the waves is caused by variations of the mean zonal flow; the strong equatorial jet creates a turning point near 30 degrees at which the wave is reflected. Propagation of the wave north of roughly 40 degrees is restricted by either a turning point or a critical layer (at which the wave is stationary with respect to the mean flow and is absorbed) depending upon its phase velocity. The observed rapid decay to the north is suggestive of a critical layer. Vertical propagation of upper trophospheric Rossby waves to pressures below about 200 to 300 mbar is inhibited by the vertical thermal structure of the atmosphere, consistent with the observations. The waves are, however, free to propagate upwards into the stratosphere. This work was supported by a grant from the NASA Planetary Atmospheres program. 13.17-P Weir A. L. A Search for Resonant Wavemodes in Outer Planet Atmospheres: Preliminary Results Longitudinally averaged 2D models of the upper troposphere and lower stratosphere of several outer planet atmospheres have been produced using temperature and velocity fields obtained during the Voyager encounters. These are being used to look for resonant equatorial and midlatitude planetary wavemodes. Results of this search will be presented and, where relevant, compared to observations. 13.18-P Schinder P. J. Flasar F. M. Sensitivity of the Radio Occultation Technique to Spacecraft Transmitter Power We investigate the sensitivity of the radio occultation technique to the power of signal produced by the on-board transmitter on the occulted spacecraft. This is done in anticipation of the Cassini mission to Saturn, where the S-band transmitter will be operating at roughly half the power of the Voyager 2 transmitter. We take an atmosphere of known structure and perform a synthetic occultation of a spacecraft on a known trajectory emitting a signal of known frequency, constructing a time series of the complex antenna voltage received by a receiver on the earth. For convenience, the atmosphere we choose is taken from our determination of the structure of the atmosphere of Saturn using the Voyager 2 ingress occultation, and the trajectory that of Voyager 2 during this occultation. The loss of power due to refractive defocusing of the signal from the spacecraft is fully accounted for as the ray from the spacecraft passes through the atmosphere. We perform a series of occultations by adding white noise at the antenna to the pure monochromatic signal from the space craft. In addition to the no noise case which forms the baseline, we perform a Monte Carlo series of occultations at the Voyager 2 free-space signal-to-noise ratio (SNR), one half that value (roughly the Cassini value), and one quarter that value (half the Cassini value). After the synthetic time series is produced, we use our standard radio occultation software to determine the run of temperature T vs. pressure P of the atmosphere from the synthetic time series. The end result is a series of plots of Delta T, the difference in temperature from a particular run from the known T of the atmosphere vs. P. From this we can determine the degradation in the retrieved temperature profile with decreasing SNR. Preliminary results done using the Titan atmosphere show that while the current planned band transmitter power for Cassini is probably adequate, a lowering of the power by a factor of two would result in unacceptably large errors. SESSION 14 ....... Mars Surface Tuesday, 3:30 - 5:30 Crystal Ballroom B G. B. Hansen and E. Merenyi, Moderators 14.01 Houben H.* Haberle R. M. Young R. E. Zent A. The Regolith-Dominated Martian Water Cycle Martian water vapor sublimes from the permanent north polar cap during the summer and is transported through the atmosphere to lower latitudes. It is an open question whether that water returns to the north pole at other seasons (i.e., whether the current annual cycle is closed) or if it is being transfered to other reservoirs, such as the south polar cap or the regolith. To answer this question we have developed a Mars Climate Model-a simplified atmospheric general circulation model capable of multi-annual simulations, coupled to a subsurface regolith. We have used this model to perform a suite of ten-year-long simulations of the current Martian water cycle. Each simulation begins with a dry atmosphere and a limitless supply of surface ice polewards of ~ 75 degrees N. In one set of simulations, all super-saturated atmospheric water vapor precipitates on the surface as frost where it is available to re-evaporate whenever conditions allow. In these simulations, the water cycle is not closed. Large quantities of water are deposited in seasonal frost caps (extending nearly to the equator in winter) and in a permanent cap near the south pole. After a decade, all latitudes have > 100 micrometers available as surface ice or in the atmospheric column. This situation bears little resemblance to Mars as we know it. In another set of simulations, surface ice and water vapor in the lowest atmospheric layer (~ 250 m thick) are in daily equlilibrium with a 1 cm thick layer of the regolith. In these simulations, adsorption is the dominant process and no ice deposits form outside the initial source region. Since the adsorptive capacity of the soil increases with the vapor pressure, the soil buffers the atmospheric water vapor column. A seasonal adsorbing layer forms in the northern mid-latitudes into which water is deposited in summer and from which it returns to the permanent cap in stages through the remainder of the year. These simulations are qualitatively quite Mars-like, though the typical water vapor column abundances of ~ 1 precipitable micrometer are a bit low compared to Viking observations. 14.02 Clifford S. M.* Mars: The Response of an Ice-Rich Crust to Burial by Volatile-Poor Materials Consideration of the martian valley networks, outflow channels, and various other surface features, suggests that the martian crust is water-rich and that it may host a planetary inventory of outgassed water equivalent to a global ocean 0.5 - 1 hn deep [Carr, Nature, 326, 30-35, 1987J. However, the geologic evidence also indicates that Mars has undergone extensive resurfacing including the production of up to 2 km of ejecta from impacts, as much as 0.5 km of extrusive volcanics, and an unknown (but potentially large) volumetric contribution of interbedded weathering and sedimentary deposits. Therefore, given the influence of crustal temperature on the stability and distribution of ground ice, and the effect of deposition on subsurface temperatures, the response of an initially ice-rich crust to burial by volatile-poor mantles has been considered - including potential changes in state, distribution, and modes of volatile transport. At the base of the cryosphere (that region of the crust where the temperature remains continuously below the freezing point of water), the added insulation provided by the emplacement of a depositional layer will result in the rise of the melting isotherm until thermal equilibrium is reestablished - resulting in the melting of any intervening ice and the subsequent drainage of meltwater into the lowermost porous regions of the crust. At the top of the ice-rich layer, the increase in local temperature will lead to the movement of the crustal 'cold-trap' into the overlying mantle -- causing the ice present at depth to be thermally redistributed until it has saturated the available pore space in the colder regolith, above. This redistribution may occur by three different processes that involve all three phases of water, these include: thermal vapor diffusion (where vapor migrates from the warmer depths to the colder near-surface crust), thermal liquid transport (in response to the temperature-induced gradient in soil water potential that can occur in the interfacial films between rock and ice), and regelation (the movement of ice through soil pores via pressure induced melting and refreezing). By these processes, an initially volatile-poor depositional mantle may -- on a geologically short time scale (whose duration depends on both mantle thickness and its thermophysical properties) -- become quickly charged with ice. The results of this analysis bave important implications for understanding the present distribution of ice within the near-surface crust and its potential geomolphic expression. 14.03 Zent A. P.* Quinn R. C. Jakosky B. M. Fractionation of Nitrogen Isotopes on Mars: The Role of the Regolith as a Buffer We have measured the adsorption of molecular nitrogen (N(sub)2) S on palagonite, and modeled the adsorbed nitrogen inventory on the martian regolith. We were motivated by the fact that models of isotopic evolution predict stronger N2 fractionation than reported by Viking. Possible scenarios for reconciling models with the observation include: a heavy C0(sub)2 atmosphere early in the planets' history; continued outgassing of N(sub)2 throughout the history of Mars; or a substantial adsorbed inventory. We are investigating the plausibility of the latter explanation. The adsorption measurements were made via a standard volumetric adsorption apparatus. We modeled the adsorption on the martian regolith by dividing the regolith into chunks, bounded every ten degrees of latitude, and with 10 depth steps. The partial pressure of N(sub)2- in the atmosphere E (16 Pa) is assumed to apply throughout the regolith, and the adsorptive coverage of each chunk is calculated separately and summed over the entire regolith. We parameterize the regolith in terms of its total depth and specific surface area; we consider specific surface areas between 10 and 100 m^2 g^-l, and regolith depths from 50 to 500 m. If fractionation models are to be reconciled with the observed fractionation solely through the presence of 7 an adsorbed N2 component, we a calculate that approximately 59 kg m^-2 of N(sub)2 must be adsorbed. We find that the regolilh reservoir of adsorbed N(sub)2 is less than 50 kg m^-2, and so inadequate to buffer the atmospheric isotopic composition. The most plausible explanations of the observed isotopic fractionation require that N(sub)2 have outgassed throughout martian history, or that early loss of N(sub)2 occurred at a lower rate, the consequence of a more massive atmosphere. There is supportive evidence for both explanations. 14.04 Lee S. W.* Clancy R. T. Martin T. Z. Spatial and Temporal Mapping of Regional Surface Albedo and Atmospheric Dust Opacity on Mars Past studies have demonstrated that aeolian processes are active over much of the surface of Mars; variations in regional albedo are indicative of active sediment transport in a region, while thermal inertia data are indicative of the degree of surface mantling by dust deposits. The visual and thermal data are therefore diagnostic of whether net erosion or deposition of dust-storm fallout is taking place at present and whether such processes have been active in a region over the long term. The earlier investigations have not corrected for the effects of atmospheric dust loading on observations of the martian surface, so quantitative studies of current sediment transport rates have included large elTors due to uncertainty in the magnitude of this "atmospheric component" of the observations. A radiative transfer model has been developed which allows corrections for the effects of atmospheric dust loading on observations of surface albedo to be made. This approach to determining "dust-corrected surface albedo" incorporates variable atmospheric dust opacity, the most recent dust particle properties (Clancy et al, JGR 1994, in press), and accounts for the lighting and viewing geometry of individual observations. The spatial and temporal variability of atmospheric dust opacity strongly influences the modeling results; we are making use of the method developed by T. Z. Martin (JGR 84, 10941-10949,1993) to determine dust opacity irom Viking IRTM thermal observations. This modeling approach allows the atmospheric dust opacity to be determined at the highest spatial and temporal resolution supported by the IRTM mapping data; maps of "dust-corrected surface albedo" and atmospheric opacity can be constructed at a variety of times for selected regions. Information on the spatial and temporal variability of both surface albedo and atmospheric opacity, and inferences of the amount of dust deposition/erosion related to such variability, result. Analyses of Viking IRTM mapping observations of the Syrtis Major region, spanning more than one martian year, will be presented. 14.05 Sunshine J. M.* Mustard J. F. Quantification of Variations in the Mafic Mineralogy of Mars Through MGM Analysis of ISM Spectra Absorptions near 1 and 2 micrometers in ISM imaging spectrometer data (0.77 to 3.14 Sm) indicate that calcic-pyroxenes exist in weakly altered volcanic terrains on the martian surface. Nili Patera (in Syrtis Major) and Eos Chasma (in Valles Marineris) exhibit distinct differences in absorption strength and shape, suggesting mineralogic differences. Here, we report on new efforts to place limits on these possible compositional variations by applying the Modified Gaussian Model (MGM) to ISM spectra. The MGM is a method for deconvolving spectra into their constituent absorption bands (Sunshine et al. JGR, 1990). However, because the absolptions in ISM spectra are relatively weak (5-15%), modeling efforts must be constrained through consistency with existing data bases and by incorporating experience with MGM analysis of laboratory spectra of pyroxene mixtures. Our initial goal was to test if the absorptions in ISM spectra are due to a single pyroxene, or to two?? To explore this hypothesis, we begin with simple models, making the fewest assumptions about constituents, and then proceed, as the data warrant, to more complex models. Examination of solutions in the context of laboratory data, focusing on critical comparisons between the known coupling in the 1 and 2 micrometer regions, have led to the conclusion that both the Nili and Eos regions contain two distinct pyroxene phases, a high- and a low-calcium pyroxene, as well as a ferric component. No compelling spectral evidence for an olivine was found. The differences in modal mineralogy between Nili and Eos have been quantified as a 20% increase in high-calcium pyroxene at Nili relative to Eos. MGM analysis of spectra from more altered regions near Nili and Eos have revealed quantifiable increases in the ferric component, while maintaining the differences in the modal ferrous mineralogy. Thus, we have demonstrated that the MGM can be used to examine crustal composition even through the veil of dust on Mars. 14.06 Merenyi E.* Calvin W. M. Singer R. B. Tracking Compositional and Physical Similarities from the Martian Equator to the South Polar Region In earlier works we characterized a previously unreported Martiar soil type that covers Deucalionis Regio (centered at [245 degrees W,15 degrees S]) and also appears in part of Noachis, 20 degrees W - 340 degrees W, 30 degrees S - 50 degrres C (Merenyi et al. under review, Icarus, Merenyi et al. PLPSC XXV). From analysis on a high spectral resolution telescopic image in the 0.4 -1.02 micrometer range (Singer et al. PLPSC , XXI), and on Viking IRTM data we concluded that this soil was compositionally and physically significantly different from the surrounding major surface units such as Arabia, Sinus Meridiani, Acidalium, Chryse, and that it was likely to be immobile and possibly cemented by salts. In a second telescopic image cube a south polar area was found where the spectra were virtually identical to those of the Deucalionis spectra longward of 0.7 micrometers. Based on works by Kaufman (1989), Christensen and Zurel JGR, 1984), Iwasaki et al. (1990) and others, the nature of the spectral deviation.under 0.7 micrometers suggested the sout polar spectra migh be seen through a thin layer of condensates. Preliminary analysis using the newly derived thermal inertia map for the south polar region by Paige and Keagan ( JGR, 1994) supported that Deucalioni and the S. Pole areas also show similar physical properties. The compositional and physical likeness raised the question of a possible genetic relationship between equatorial and south polar regions spanning the southern hemisphere of Mars. Here we present a more careful and detailed analysis that verifies the above spectral and physical similarities. Through rigorous Mi modeling, we show that the spectra from the south polar area described above can indeed be Deucalionis type spectra modified by atmospheric scattering. The possibility of an indurated surface is confirmed from the data of Paige and Keagan with more refined discussion regarding the comparison with mid-latitude thermal inertia maps and interpretation of the thermal inertia values. The existence of these similarities linking Deucalions, Noachis and some areas on the south polar region would provide a piece of evidence in the emerging picture of a global Martian compositional and morphological dichotomy. 14.07 Blaney D. L.* Crisp D. Martin T. Z. Analysis of the Mariner 6/7 Infrared Spectra of Mars The Mariner 6/7 Infrared Spectrometer experiment measured IR spectra of Mars between 1.9 - 14.4 llm. These data were recently restored, with improved radiometric and wavelength calibration and updated geometry [1]. Although collected in 1969, they are still the only spacecraft data available between 3.1 - 5 micrometers. The spacecraft6 tracks contain data from latitudes ranging from roughly + 20 degrees N to -80 degrees S, covering most of the geologic unit types on Mars. Spatial resolution was about 130 km at closest approach and spectral resolution was roughly 1-2%. We are reanalyzing this data set using modern atmospheric modeling techniques to remove atmospheric gas and dust effects in order to identify variations in surface mineralogy. A major concern in the earlier analysis of the Mariner 6/7 data set by Pimentel et al. 1974 [2] are differences in viewing geometry, dust opacity, and atmospheric absorption features. We are currently focusing on the spatial distribution of the 3 micrometers band caused by hydrated minerals on Mars Our first step has been to try and recreate the results of Pimentel et al. on the latitudinal dependance on the depth of the 3 ,micrometer band. Although our calibration differs due to use of different solar spectra, we still observe the same trends in the data the Pimentel et al. see. The most hydrated regions occur at latitudes > 50 degrees S and in the equatorial bright region while the least hydrated region was in Meridiani Sinus (lat -4.2 degrees S, 359 degrees E). Detailed modeling of the effects of the 2.75 micrometers CO2 absorption feature and of atmospheric dust, which may also have a 3 micrometer absorption feature, will be done to fully characterize the distribution of hydrates on Mars. 1. T.Z. Martin, Restoration ofthe Mariner 6/7 IR Spectrometer Data Set. Icarus,in press, 1994; 2. G.C. Pimentel et al. J. Geophys. Res. 11, 1 623,1 974. This work was done at JPL/ CALTECH, under contract to NASA. 14.08 Hansen G. B.* Low Brightness Temperatures of Martian Polar Deposits: New Insights from Recent Measurements of CO2 Ice The infrared thermal mapper (IRTM) instruments aboard both Viking orbiters made the first extensive measurements of infrared radiance during the Martian polar night. Early measurements of the south polar region in polar night showed brightness temperatures in the 20 micrometers band well below tne expected temperature of CO(sub)2 frost deposits (Kieffer, et al. (1976), Science, 193, 780; (1977), J. Geo-phys. Res., 82, 4249) Many explanations have been advanced for this behavior, including the low emissivity of the frost deposits, a position supported by the contemporary measurements of Ditteon and Kieffer ((1979), J. Geophys. Res., 84, 8289). Paige ((1985), PhD Thesis, Calif. Inst. of Tech., Pasadena, CA) used information from the 11 micrometers channel as well as the 20 micrometers channel in a detailed study of the polar night measurements in both the north and south, and called into question the emissivity argument due to the spatial and temporal variation of the two brightness temperatures. New measurements of the spectral transmission of CO(sub)2 ice indicate that in the spectral regions on either side of the strong l5 micrometers absorption, it is at least a factor of 10 times more transparent than reported by Ditteon and Kieffer. Furthermore, the absorption is higher across the 11 micrometers band than across the 20 micrometers band, indicating that the emissivity (and brightness temperature) will be higher in the 11 micrometers band, and moreover, that the relative emissivities in the two bands will vary with effective particle size. A radiative transfer model of pure CO(sub)2 frost with kinetic temperature 146 K gives the following nadir brightness temperatures (T(sub)B). Effective particle dia. T(sub)B ( 1 1 llm ) T(sub)B ( 20 micrometers ) 10 micrometers 119 . 2 K 97. 4 K 100 micrometers 130.8 K 111.3 K 1 mm 140.0 K 126.6 K 10 mm 144.3 K 139.0 K The addition of small amounts of water ice or dust raises the brightness temperatures considerably and may change the relative temperatures between the two bands. By varying the water ice and dust content and particle size, the observed spatial and temporal variations of brightess temperatures may be simulated. This work was supported JPL, Caltech, and NASA. 14.09 Slade M. A.* Jurgens R. F. Goldstone Radar Observations of the 1995 Mars Opposition As part of the International Mars Watch, Goldstone radar observations of Mars are planned during the 1995 Opposition (~Dec.'94-March'95). While much of the allocated time is already devoted to observations for Mars Pathfinder landing site validation, a small number of tracks could be made available for well-focused scientific objectives. During this opposition, the sub-Earth latitudes are in Mars' Northern hemisphere (Figure 1,) over terrain not previously examined with current sensitivity. The radar data types possible in 1995 will be described at he meeting. A good overview can be found in Chapter 20 of the book Mars (Keiffer et al., ed.; 1992). Informal observing proposals from any scientist with peer-reviewed Mars funding should be forwarded to Martin.A.Slade@jpl.nasa.gov by email. Data reduction can, in principle, be carried out over the Internet. A graduate student or postdoctoral fellow resident at JPL for short period is recommended, however, to become familiar with suite of software for data analysis. (Unfortunately, JPL cannot supply travel reimbursement due to the current NASA funding situation.) The Mars 1995 dataset should provide a significant increase in the knowledge about the surface and subsurface of Mars. We urge that you consider becoming involved with the acquisition and analysis of Mars radar data. Figure 1 appears here in the hard copy. 14.10 Pischel R.* de Niem D. Classification of Surface Features from Mars '96 HRSC and WAOSS Imagery Using Statistical Analysis and Image Processing Methods The analysis of surface features plays a key role for the understanding of the geology and the evolution of planets and small bodies. Statistical analysis methods are most important for the interpretation of geological structures. Digital image analysis approaches are used for systematic processing steps and interpretation suppport in order to handle huge data volumes as they are expected for the High Resolution Stereo Camera (HRSC) and Wide Angle Optoelectronic Stereo Scanner (WAOSS, imagery on the Mars '96 mission (approximately 200 GByte decom-pressed data). One of the main features of the HRSC and WAOSS cameras is there stereo capability. Images with a planimetric resolution of 10-20 m and an absolute height accuracy of 70 m are expected from the high resolution (HRSC) data. The goal of this study is to investigate how this HRSC high resolution image data and HRSC and WAOSS stereo image data can be used for the analysis of selected Martian surface features based on a combination of statistical methods and a pattern recognition approach. The use of this technique is shown for the case of crater detection and classification. An approximation approach is proposed which is applied to a combined digital image and digital elevation data set. A number of molphological features (crater form, peak height etc.) and crater parameters can be easily derived using the "approximated crater". One example for statistical analysis methods is the succeeding classification step which is based on feature information (e.g. existence of inner peaks) as well as on numerical data (e.g. curvature of the crater rim). Results are presented using Viking images and simulated data. 14.11 Stoker C.* Field Experiments Using Telepresence and Virtual Reality to Control Remote Vehicles: Application to Mars Rover Missions This paper will describe a series of field experiments to develop and demonstrate the use of Telepresence and Virtual Reality systems for controlling rover vehicles on planetary surfaces. In 1993, NASA Ames deployed a Telepresence-Controlled Remotely Operated underwater Vehicle (TROV) into an ice-covered sea environment in Antarctica. The goal of the mission was to perform scientific exploration of an unknown environment using a remote vehicle with telepresence and virtual reality as a user interface. The vehicle was operated both locally, from above a dive hole in the ice through which it was launched, and remotely over a satellite communications link from a control room at NASA's Ames Research center, for over two months. Remote control used a bi-directional Internet link to the vehicle control computer. The operator viewed live stereo video from the TROV along with a computer-generated graphic representation of the underwater terrain showing the vehicle state and other related information. The actual vehicle could be driven either from within the virtual environment or through a telepresence interface. In March 1994, a second field experiment was performed in which the remote control system developed for the Antarctic TROV mission was used to control the Russian Marsokhod Rover, an advanced planetary surface rover intended for launch in 1998. Marsokhod consists of a 6-wheel chassis and is capable of traversing several kilometers of terrain each day. The rover can be controlled remotely, but is also capable of performing autonomous traverses. The rover was outfitted with a manipulator arm capable of deploying a small instrument, collecting soil samples, etc. The Marsokhod rover was deployed at Amboy Crater in the Mojave desert, a Mars analog site, and controlled remotely from Los Angeles in two operating modes: (1) a Mars rover mission simulation with long time delay and (2) a Lunar rover mission simulation with live action video. A team of planetary geologists participated in the mission simulation. The scientific goal of the science mission was to determine what could be learned about the geologic context of the site using the capabilities of imaging and mobility provided by the Marsokhod system in these two modes of operation. I will discuss the lessons learned from these experiments in terms of the strategy for performing Mars surface exploration using rovers. This research is supported by the Solar System Exploration Exobiology, Geology, and Advanced Technology programs. 14.12 Paige D. A.* The Mars Polar Pathfinder Discovery Mission The Mars Polar Pathfinder is a Discovery-class mission whose primary scientific objective is to initiate the exploration of the Martian north polar ice deposits. On Earth, polar ice deposits have yielded detailed, continuous records of past climatic variability extending from the present to hundreds of thousands of years into the past. On Mars there is a strong theoretical basis for expecting significant astronomicaily-driven climate variations, and there is strong observational evidence that Mars experiences significant interannual climate variability as well. If the Martian polar ice caps and associated layered deposits are also found to contain records of past climatic variability, they will surely become major focal points for the scientific exploration of Mars in future decades. The Mars Polar Pathfinder is intended to take the first steps towards this ultimate goal by characterizing the basic composition and stratigraphy of the Martian north polar ice cap at a single landing site. As the name suggests, the Mars Polar Pathfinder Project derives considerable heritage from Mars Pathfinder. It employs the same Delta launch vehicle, and uses a close copy of the JPL-built Mars Pathfinder lander. The mission plan calls for launch in August 1998, and landing near the Martian north pole in November, 2000, which is just after the start of the Martian northern summer season. Once landed, the spacecraft will deploy its instruments and operate on the surface of the north polar water ice cap using solar power and direct to-earth communications for approximately 100 days. The strawman scientific payload for the Mars Polar Pathfinder includes: a descent imager, a meteorology package and a surface imager which together will survey the local environment at the landing site; an ice-sounding radar which will determine the internal structure and total depths of the polar ice deposits; a drill and borescope system, a robotic arm and ice/dust thermal analyzer which together will determine the basic composition and stratigraphy of near-surface layers. Other instruments being considered for inclusion on the payload include a thermal probe, a micro mass spectrometer, and an extraterrestrial resource utilization demonstration experiment. The Mars Polar Pathfinder can achieve its exciting scientific and mission objectives within the cost guidelines of the Discovery Program primarily because of its extensive heritage from the Mars Pathfinder Program. 14.13-T Hartmann W. K. Engel S. Studies of Ancient Mars and Titan Atmospheres Using the Cratering Record We find that there may be significant opportunities to study the past history of the atmospheres of Mars and Titan by using the cratering record on surfaces of different ages. Using a program originally developed by Chyba, Thomas, and Zahnle (1993), we have calculated minimum sizes of bolides that can make it through present atmospheres of Mars and Titan without exploding. This filtering produces an observable turndown in the crater diameter distribution on these bodies. Similar calculations have been made by Melosh and others for the present-day atmosphere, but our work differs by assuming higher past atmospheric densities to examine at what sizes the turndown occur for hypothetical ancient atmospheres of different density. For Mars, we conclude that if the atmosphere was ever denser than about 200-300 mb, cometary bolides and chondritic stony asteroids would be filtered by the atmosphere, producing a strong downturn in the cratering record near crater diameter 0.5-4 km (resembling that observed on Venus, but at smaller sizes). Only irons would make smaller craters. Titan has a massive atmosphere with a high scale height, and we find that it is comparable to the atmosphere of Venus in filtering effects. The smallest cometary bodies that would get through Titan's present atmosphere would produce a minimum crater size of tens of kilometers. This effect should be detected by Cassini radar. Competing theories picture either a denser or less dense ancient Titan atmosphere; tests of these theories may be possible, depending on the erosion state of Titan. Chyba, C., Thomas, P., and Zahnle, K. (1993) Nature 361, 40. 14.14-T Bell J. F. III Bornhoeft K. Lucey P. G. Pollack J. B. High Resolution 0.50 to 0.95 Micrometer Spectroscopy of Mars During 1990 We conducted visible to near-IR imaging spectroscopic observations of Mars from Mauna Kea Observatory during the 1990 opposition. Our goal was to complete imaging spectroscopic survey begun in 1988 by imaging regions of the planet centered the Amazonis-Elysium hemisphere not studied previously. The data were obtained on the University of Hawaii 2.2-m telescope using the Wide Field Grism Spectrogra instrument. We obtained approximately 10,000 spectra from 0.50 to 0.95 micrometers of regions of the surface visible on 9 and 10 November 1990 UT. The spatial scale of the data was 0.7 arcsec/pixel, corresponding to a resolution on Mars of 540 km/pixel at the sub-Earth point. Seeing conditions were not optimal, and thus the imaging aspect of this experiment was not very successful. We have concentrated on the interpretations of the spectra instead because they exhibit high S/N and reveal diagnostic absorption features. Telluric atmospheric correction and solar spectral removal were achieved using the Hardorp solar analog star Kappa Cet (G5V). The Mars / Kappa Cet spectra (~ Mars / Sun) show interesting features that support and enhance interpretations gleaned from previous observations. These features include: (1) a steep red 0.50 to 0.75 micrometers spectral slope both bright and dark regions, with a bright/dark ratio near unity at 0.50 micrometers and increasing to 1.5 to 2.0 near 0.75 micrometers; (2) a strong (for Mars) absorption feature in the 0.8 to 0.9 micrometers region, center near 0.86 micrometers in bright regions and near 0.89 in darker regions; (3) a weaker, partial absorption band or "cusp" in the spectra of both bright and dark regions, centered near 0.68 micrometers; and (4) a distinct difference between the near-lR spectral slope of dark regions (negative) and bright regions (flat). Our interpretation of these spectra is that the absorption band positions in the bright regions indicate the presence of a small arnount (less than 5%) of well-crystalline hematite that must occur in a matrix of much more poorly crystalline ferric-bearing materials which account for the overall color of Mars. The shift in band position observed between bright and dark regions and the negative 0.80 to 0.95 micrometers spectral slope are most likely caused by the presence of pyroxene-bearing materials in the dark regions that have ferrous absorption band positions longward of 0.9 micrometers. An alternate hypothesis, that the band shift is due to the presence of hydrous ferric oxides, is possible but less likely given the position of the near-UV absorption edge and the decreasing near-lR spectral slope. Because we observed a hemisphere dominated by bright, windblown materials and our spatial resolution was poor, there is certain to be a high amount of actual and effective spatial mixing occurring in the data, such that the spectral differences between regions are muted and even the darkest spectra measured have a substantial "bright" component to them. The only solution to this problem is increased spatial resolution, either utilizing improvements in groundbased techniques, spaceborne observatories, or Mars-orbiting spacecraft. All of these approaches will be attempted by many different groups over the next decade, which will greatly improve our understanding of Mars spectral heterogeneity. 14.15-P Erard S. Variability of the Surface Materials in the Equatorial Regions of Mars A systematic search for spectral variations was performed on imaging spectroscopic data of Mars acquired by ISM onboard Phobos-2. The dataset consists in nine observation sessions, each comprised of about 3,000 spectra of pixels 25 x 25 km^2 in size, from 0.77 to 3.15 micrometers. Following preliminary analysis of th the spectra were described by 5 to 7 spectral parameters as less sensitive as to photometric effects and atmospheric scattering. Those parameters are mostly related to iron mineralogy and hydration. They were checked on possible martian analogs to insure they allow characterization of mineralogical composition. The nine obselvation sessions were studied independently by means of analysis, with relatively high security levels. The analysis yielded 4-7 main units per session, some of them being macroscopic mixtures of pure end members. The corresponding spectral types were then used as input to a new analysis so as to get a global image of spectral variability in the observed regions. This study confirms the higher variability of dark regions and the diversity of bright materials, mostly related to the presence of different iron oxides. Current investigations focused on the interpretation of the materials in terms of mineralogical/chemical composition. This work was partly supported by an ESA fellowship. 14.16-P Cohen B. A. Singer R. B. Detectability of Siderite (FeCO3) in Martian Soil: An Experimental Investigation It has been postulated that the Martian surface could contain abundant carbonates [1,2], based on evidence that Mars once had both a substantial CO2 atmosphere and liquid water reservoirs. While only minor carbonate has been detected on the whole surface [3], buried carbonate sediments may be only locally exposed and observable with high spatial resolution sensors. If Mars did once support liquid water under a reducing CO2 atmosphere, metal ions would have been weathered from young volcanic rocks but would not have been rapidly oxidized as on Earth. This might have led to a saline, acidic ocean, where calcite (CaC03) and siderite (FeCO3) would form. Recently, the abundance of iron oxides on the surface has led to speculation that siderite could be at least as important as calcite [4]. This study examines the VIS-NIR reflectance spectra of siderite mixed with Martian surface analogs. The reflectance spectroscopic properties of calcite both by itself and in mixtures with palagonite have been investigated [5,6]. In addition to IR vibrational features, siderite has a very prominent, broad double band at about 1 micrometer [7]. Calcite and palagonite are relatively unabsorbing here. Samples used were natural siderite, palagonite, and calcite, mechanically mixed together. Analysis was performed from ,0.33 to 1.2 micrometers with the PIRL laboratory spectrophotometer (modified from a CARY-14). Both the depth and position of the l-micrometer band were found to shift regularly with increasing amounts of siderite. Mixtures of 20 wt% siderite with varying amounts of calcite and palagonite also exhibit good correlations between band depth/center and the percent CaC0(sub)3 in the mix. Experimentally, it is shown that siderite could be detected in a palagonite-like Martian soil in quantities as low as 6 wt% if there is no calcite present. A more likely scenario would be a carbonate deposit containing both iron and calcium carbonates; in this situation, even smaller amounts of siderite would be detectable, as siderite's l-micrometer band remains visible at much lower abundances when calcite is present. Vibrational bands are diagnostic of carbonate minerals, but VIS-NIR spectra are useful in making cation distinctions, and have potential for estimating the proportions of each phase. The IMP camera on Mars Pathfinder is sensitive to these features. REFERENCES: [1]Gooding (1978) Icarus 33, p.483. [2]Clark and VanHart (1981) Icarus 45, p.370. [3]Roush, et al. (1989) LPSCXX, p.928 [4]Banin et al. in Mars, ed. Kieffer et al. ( 1992: U of A Press) p. 594 [5]Blaney et al. ( 1987) LPSC XVIII, p. 87. [6]Wenrich and Christensen(1994)LPSC XXV,.p.1485 [7] Gaffey(1987)JGR 92 B2,p.l429. 14.17-P Barlow N. G. Impact Crater Depth-Diameter Ratios in Mangala Valles, Mars The author is continuing studies of the variations in impact crater depth- diameter ratios in selected regions of Mars. Results from the photoclinometric studies have previously been reported for the Arabia, Maja Valles, and Memnonia regions of Mars. The study has now been expanded to the Central Mangala Valles region, extending from 7S to 14.5S and 148W to 160W. Forty-five Viking Orbiter frames with resolutions between 45 and 50 m/px have been utilized in this analysis. The Davis and Soderblom photoclinometry technique, specifically designed for use with Viking Orbiter images of Mars, was used to determine crater depths and diameters for all craters >k km in diameter on the images. The depth-diameter ratios of fresh impact craters (identified by their morphologically fresh appearance, such as pristine ejecta blankets, sharp rim crests, and lack of obvious floor deposits) were determined based on the results of the photoclinometric analysis. The photoclinometric results were compared with results from shadow measurements--the two techniques provided results within 2% of each other. Simple craters (crater with diameters generally <6 km) within the Mangala Valles region of Mars have an average depth-diameter ratio of 0.20 (+/- 0.05). Complex craters display an average depth-diameter ratio of 0.08 (+/- 0.05). These ratios are similar to those obtained by this method for fresh impact craters in the Arabia and Maja Valles regions. Thus, the Medusae Fossae deposits in the Memnonia region are currently the only area where anomalous depth-diameter ratios have been identified. 14.18-P Hartmann W. K. Engel S. Chyba C. Sagan C. Mars Cratering Record as a Probe of Ancient Pressure Variations There are significant opportunities to study the past history of the atmosphere of Mars by analyzing the cratering record on surfaces of different ages [1]. As shown by the case of Venus, a dense enough atmosphere leaves a dramatic cutoff in the cratering record below a critical size. Dense as well as episodic ancient martian atmospheres (>>10 mb), proposed by many authors, could cause similar effects. Using a program originally developed by [2] and modified for Mars, we have calculated minimum sizes of bolides that can make it through present and hypothetical denser past atmospheres of Mars without exploding. This filtering produces observable downturn in the crater diameter distribution. Although calculations have been made by [3] for the present atmosphere, our work calculates the effect for various possible atmospheric densities that may have existed in the past. We conclude that if the atmosphere ever reached more than about 100-300 mb surface pressure, cometary bolides and chondritic stony asteroids would be filtered out by the atmosphere, generating a strong downturn in the cratering record near crater diameter 0.5-4 km (resembling that observed on Venus, but at smaller sizes). Only irons would get through to make smaller craters (representing only about 1% to 4% of the craters that would exist otherwise at small diameters). In the course of our work, we have studied examples of isolated crater clusters on Mars (typically tens of craters, D~700 to 1000 m). These are important because they may identify the threshold of breakup for weak cometary bodies--consistent with models of comet P/SL-9. References: [1] Chyba C. et al. (1992) BAAS, 24, 975. [2] Chyba C. et al. (1993) Nature, 361, 40. [3] Melosh H. J. (1989) Impact Cratering: A Geological Process, Oxford University. 14.19-P Savijarvi H. Thermal Inertia on Viking Sites in Mars The thermal inertia of the uppermost martian regolith has traditionally been determined indirectly by fitting surface temperatures predicted by thermal models to remotely sensed surface brightness temperatures. The soil models and their atmospheric forcing have been simplified and the surface temperatures derived from the brightness temperatures contain errors from various sources. We have recently coupled our dusty and moist Helsinki Mars Mesoscale Model (providing reasonable atmospheric forcing to the surface, [1,2]) with a numerically accurate regolith heat diffusion scheme [3]. By adjusting the model-produced temperatures to the direct Viking 1.6 m observations, an estimate of the ground thermal inertia is obtained as the function of reqolith depth. References: [1] Savijarvi H., Contr. Atmos. Phys., 64, 219-229. [2] Savijarvi H. and Siili T., J. Atmos. Sci., 50, 77-88. [3] Savijarvi H., Contr. Atmos. Phys., 65, 281-292. 14.20-P Neugebauer G. Machling M. Dorrer E. Zhou X. Hauber E. Hoffmann H. Jaumann R. Neukum G. Cartographic Representation of the Martian Surface: New Results for Digital Deshading and Reshading In preparation for map production using data from the forthcoming camera experiments onboard the Russian Mars'94/'96 missions (High Resolution Stereo Camera and Wide Angle Optoelectronic Stereo Scanner), a preliminary topographic image map of Tithonium Chasma, in the Valles Marineris, has been produced. Such maps are supposed to show all characteristics of a full topographic map, such as optimal true color representation, relief visualization by prevailing NW-illumination, appropriate topographic information (contour lines), map annotation, and legend. The input used to prepare the first experimental output in A4 format consisted of two sets of information: (1) a 1/500,000 topographic orthophoto mosaic (USGS 1980, Miscellaneous Investigations Series, Map I-1294); (2) monochromatic image data from the Viking Orbiter 1 mission with a pixel size of 60 m. The 200m contour lines of the topographic orthophoto mosaic were digitized and generalized with an equidistance of 500 m. A digital elevation model (DEM) was derived from the 200m contour lines. The image data were then mosaicked and co-registered to the DEM to match the map geometry. Since the azimuth and elevation of the Sun are known for the images, shadows could be simulated on the DEM and then removed, as far as possible, from the image mosaic. According to cartographic standards, the DEM was illuminated with a prevailing NW-illumination. In order to improve the impression of the surface relief, secondary illumination from different directions was added for NW-SE striking morphological features. In this preliminary work, color has been visually introduced to the DEM using Viking Lander data in order to produce the Cyan-Magenta-Yellow color separates for the printing process. However, it is planned to use color data from Viking Orbiter to generate near true color representation of the martian surface. During the map production, the image information has been printed as the black channel (K) in the CMYK model. In different experiments, the percentages of CMYK values have been varied to optimize the visibility of the superimposed contour lines as well as the underlying image mosaic.__ 14.21-P Wells W. K. Sprague A. L. Hunten D. M. Rizk B. Hill R. E. Mars: Observations of Seasonal Atmospheric Water Vapor Variations Ground-based high-resolution spectroscopic observations of water vapor in Mars atmosphere have been made using the 8189 Angstrom line. Strong seasonal variations are seen in the frames reduced to date Abundances at all latitudes are similar to those seen by the Viking MAWD experiment [1] and by Rizk et al. [2]. A simple latitudinal binning into northern, equatorial and southern regions shows strong seasonal variations. Summer values are a factor of two higher in the northern hemisphere than in the southern hemisphere. Nineteen nights of good data were obtained. Below are plotted the results of the eight reduced so far. References: [1]Jakosky and Farmer, JGR, 87, 2099, 1982. [2] Rizk et al. Icarus 9O 205, 1991 14.22-P Mumma M. J. DiSanti M. A. Atmospheric Water Vapor on Mars: A Search for Enrichment of HDO/H20 in the North Polar Cap We present latitudinally resolved spectra of Martian H20 and HD0, which permit us to address the question of whether HD0 is enriched in the polar ice caps. Existing models developed for the odd-hydrogen chemical cycle on Mars have neglected the role of transport within the atmosphere. We have been investigating this problem with the use of spatially-resolved global maps of C0, H20, HD0, and C degrees 2 absorption lines, to assess transport and photochemistry in the Martian atmosphere. We observed Mars UT 9 - 12 March 1993, using CSHELL (resolving power lambda \delta lambda ~2 x 10^4) at the IRTF. At this time L(sub)s 50, degrees or northern spring; thus the north polar cap would have just begun to sublimate. Based on Viking Orbiter MAWD measurements, virtually no water vapor is expected for southern latitudes, for this L(sub)s-value (Jakosky and Farmer 1982 JGR 87, 2999). A principal advantage in using modern array detectors such as CSHELL is that they provide simultaneous spatial coverage for extended objects. We onented the slit north-south, allowing full latitudinal coverage over the disk of Mars, and targeted the H20 111-000 band at 8820 cm^-l, and the HDO Vl band at 2720 cm^-l. Using spectra of the southernmost latitudes as calibrators, we present latitudinal maps of H20, and of HDO, which allow us to determine whether HDO is preferentially sequestered in the northern polar ice cap reservoir. 14.23-P West F. R. An Investigation of Advantages of Observing Mars from Antarctica in 1997, 1999, 2001, 2003, and 2005 Advantages of observing Mars from Antarctica near and during the upcoming opposition of 1997, 1999, 2001, 2003, and 2005 are investigated. Several Antarctic sites, including 90 degrees S (South Pole) and 82 degrees S (hig plateau) are investigated for the visibility of Mars above the horizon during these years. An important characteristic investigated is the possibility for keeping Mars under continuous observation for at least several weeks during Antarctic autumn and winter (March 21 through Sept. 23). Detailed calculations of periods when Mars is continuously above the horizon for more than a day and for other possibly favorable observing periods are summarized for the chosen observation sites. Projects that could benefit from prolonged continuous monitoring of Mars are studies of dust storm development and changes in its polar regions. Preliminary studies indicate that the 1997 and 2005 oppositions will not be favorable for such an observational project from Antarctica, but that the oppositions of 1999 and 2001 will be quite favorable. The opposition of 2003 promises to be excellent. SESSION 15 ....... Comets I Wednesday, 8:30 - 10:00 Crystal Ballroom A D. C. Boice and R. Meier, Moderators 15.01 Rodin A. V.* Vibration and Rotational Distribution of C2 in the Inner Coma of P/Halley: Update Analysis of the Results of VEGA Mission Emission in the bands Delta v = -1,0,1 of C(sub)2 Swan system measured by means of TKS spectrometer with scanning field of view during VEGA flyby has been analysed using line-by-line model involving 10 vibration levels and J up to 60. Inversion of low-resolution data on the entire band sequence permits to retrieve smoothed rotational structure of v' = 0 state as well as vibration population with an accuracy sufficient to reveal features specific for newborn molecules in the innermost fields of coma not available for ground-based spectroscopy. Spectra observed with line of sight impact parameter less than 300 km yield bimodal Bolzman distribution with inflection point around J'=30 and characteristic temperatures T(sub)l = 2730K and T(sub)2 = 5700 K. Since distribution variations for J<10 are left out of analysis and cold component cannot be model-independently retrieved, comparison with laboratory data combined with spatial fitting map by gas outflow modelling confirms an assumption that main source of C near the nucleus is two-step photodissociation of acetylene. In the framework of available accuracy, observed distribution relaxes to single Bolzman mode with T = 3300K at nucleocentric distance about 1500 km, according to a variety of models of C(sub)2 fluorescent equilibrium. However, quasi-3D section of the coma shows that an extended source associated with jet containing CHON particles contributes to radical production with thermal rotational population and lower vibration excitation initial states of remnants are probably controlled by evaporating phase. 15.02 Luu J.* Jewitt D. Colors of Centaurs and Trans-Neptunian Objects The planet-crossing orbits of the Centaurs are short-lived, implying that they must have originated elsewhere in the solar system. The newly discovered trans-Neptunian Kuiper Belt provides a possible source of the Centaurs, and of short-period comets. In this paper we present broad-band optical colors of the known Centaurs and of the brighter trans-Neptunian objects. The colors represent our first attempt to compare trans-Neptunians with each other, and with the three known Centaurs. The observations are complicated by the faintness of the trans-Neptunians (red magnitudes are in the range 22 to 24.5). Our main result is that the trans-Neptunians possess diverse colors, and that the striking red mantles of 5145 Pholus and 1993 HA2 are not representative of all Kuiper belt objects. Possible implications for the processing of surface materials on distant objects will be discussed. 15.03 Kolokolova L. O.* Studying Cometary and Asteroid Composition Using Stokes Parameters: Computations A new successive reflections method for computing the Stokes parameters light multiply scattered by rough surfaces and large fluffy particles suggested. The method is based on the order-of-scattering approach applied earlier to planetary atmospheres by Uesugi and Irvine (1970). We have obtained a good quantitative agreement between theoretical computations and laboratory measurements of the Stokes vector for powder samples (Degtyare and Kolokolova, 1992). In comparing theoretical computations and laboratory measurements, we analyzed data for all the four Stokes parameter as functions of the phase angle. We have shown that both linear and circular polarizations are sensitive to the chemical composition and texture of scattering particles, and that the third and fourth Stokes parameters are dependent on the particle shape and presence of anisotropic features on the surface. The dependence of the Stokes parameters on the refractive and absorption indices and structural properties have also been analyzed. We make some suggestions regarding the use of Stokes parameters in remote sensing of asteroid surfaces and cometary particles. References: Degtyarev V. and Koldlcolova L. (1992). Earth Moon Planets 34, 45. Uesugi A. and Irvine W. (1970). Astrophys. J. 159, 127. 15.04 Fomenkova M.* Larson S. Jones B. Pina R. Albedo Map of Comet Swift-Tuttle Comet Swift-Tuttle is an active short period comet. Quasisimultaneous images of this comet were obtained on Nov 09, 1991 and on Nov 17,1991 in the R-band (with the plate scale of 0.7"/pixel) and at 11.6 microns (with the plate scale of 0.8"/pixel). These data were used to produce albedo maps in accordance with [1]: gamma = 1/(1 + IR/VIS), where gamma is albedo, IR is the thermal emission image, and VIS is the reflected sunlight image. On Nov 09, the comet was in a quiescent state. The albedo map covers the 10^4 by 10^4 km region of the coma. The value of the albedo is 0.03 at the center of the coma and gradually increases with the distance from the nucleus up to 0.2. On Nov 17, the map covers the 3 x 10^4 by 3 x 10^4 km region of the coma. The comet had two pronounced jets. The albedo of the dust ranges from 0.05 up to 0.08 in the jets and from 0.12 up to 0.3 in the rest of the coma. The lowest albedo is in the downward jet which is the closest to the sunward direction. The albedo of particles in the upward jet is slightly higher. This behavior is consistent with the hypothesis that fresh dust, recently emitted from the nucleus, has on average lower albedo - due to the presence of either larger particles or darker (presumably organic) material, or both. After leaving the nucleus, the particles fragment or the volatile material decomposes due to heating and solar radiation, thus leading to an increase of the albedo. References: [1] O'Dell C. R. (1971) Ap J 166, 675-681; Ney E. P. (1982) In Comets (ed. L. Wilkening), pp. 323-340, U. of Arizona Press. 15.05 Jewitt D.* Luu J. The Solar System Beyond Neptune We are studying the trans-Neptunian solar system using deep imaging observations at optical wavelengths. Distant objects are identified by their slow, retrograde opposition motions. Thirteen trans-Neptunians have been identified at the time of writing (June 1994), mostly as part of a survey to magnitude 25 conducted on Mauna Kea. These are the first detected members of a trans-Neptunian swarm that comprises about 35,000 objects larger than 100 km in the 30 - 50 AU heliocentlic distance range. Vast numbers of smaller objects presumably exist below the limits of detection. The dynamical natures of the new objects are unclear. The best characterized (1992 QB1, 1993 FW) have perihelia near 40 AU, and so are relatively immune from strong Neptune perturbations (Neptune is at 30 AU). These objects, as well as the distant 1994 ES2, 1994 EV3 and 1994 JQl (heliocentric distances 46, 45 and 43 AU, respectively) are likely members of the predicted Kuiper Belt. Other objects at smaller distances (e.g. 1993 RO, RP, SB and SC, all near 32 - 35 AU) might be part of the Kuiper Belt, or could also be stabilized by gravitational resonance with Neptune either as trojans (1:1 resonance) or"Plutinos" (3:2 resonance). We will discuss the observational status of the solar system beyond Neptune. 15.06 Sykes M.* Cutri R. Moynihan P. Plath J. A Parallactic Mini-Survey of the Infrared Sky We are probing for distant members of the solar system in the Kuiper Belt and inner Oort Cloud using IRAS images constructed from scans of the sky at 60 and 100 micrometers. These would include hypothesized cometary collision debris and "local" cirrus. Cirrus is seen at all galactic latitudes and evidences structure at all spatial scales. It is likely that the solar system passes through or by these clouds as it orbits the galaxy. Parallactic distances probed by pairs of scans in the case where a source is seen to shift 3' correspond to a depth of 1500-3000 AU when using the larger baseline observations. To search for sources near the ecliptic we have developed a process by which survey images are "cleaned" of structures such as the zodiacal dust bands. 15.07 Haken M.* A'Hearn M. F. Feldman P. D. Secular Variation in Comet P/Encke Comet P/Encke, with the shortest period (~3.3 yr.) of any known comet, affords the best opportunity to study secular variation of brightness in comets. We have observed P/Encke with IUE over five consecutive apparitions, from 1980 to 1994, three times pre-perihelion and twice post-perihelion. Comparison of pre-perihelion data from the first (1980) and the last (1994) of the observed apparitions revealed no evidence of secular change in the outgassing rate of water, based on the OH emission at 3086 Angstroms. In particular, the secular fading, which some authors have reported was not confirmed. The maximum such variation consistent with our data is unclear, due to the fact that different cameras aboard IUE were used for the two sets of observations, and there exists no definitive assessment of the relative error in the absolute calibration of the two cameras. However, we can certainly set an upper limit on fading of 2.5% per revolution, and may be able to further constrain the possible size of this effect. To do so, we will reduce and compare spectra of standard stars taken with the two cameras to assess systematic differences. This work was supported by NASA's IUE program. 15.08 Eberhardt P.* Krankowsky D. The Electron Temperature in the Inner Coma of Comet P/Halley From the CH(sub)30H(sub)2^+/H(sub)30^+ and H(sub)30^+/H(sub)20^+ ratios measured by the Giotto Neutral Mass Spectrometer in the inner coma (distance < 20'000 km) of comet P/Halley we derive the electron temperature profile. The electron temperature T(sub)e increases gradually from ~ 100 K at 2000 km to approximately 10^3 K at 8500 km followed by a sharp increase to well above 10^4 K at 11'500 km. Then T(sub)e drops gradually to values below 10^4 K at 20'000 km. This profile is used for modeling the absolute H(sub)20^+, H(sub)30^+, and CH(sub)30H(sub)2^+ densities. We obtain excellent agreement between modeled and measured ion densities over the whole distance range from inside the contact surface to 20'000 km. Electron impact ionization plays no important role in this region. The up to fourfold ion density enhancement observed for distances between 10'000 and 20'000 km (pile-up region) is the result of the sharp Te increase coupled with very low radial ion velocities in this distance range. 15.09 Esterle P. A.* A'Hearn M. F. Comet Halley's Rotation from Observations of Dust Jets from Giotto and the Ground There is much debate among cometary astronomers as to the 'correct' rotational state of Comet P/Halley. Recently, two completely different models--a Fast Long Axis Mode with periods of 2.2 and 3.6 days, and a Slow Long Axis Mode with periods of 3.6 and 7.3 days--have been invoked to describe many observed phenomena. The most probable of each of these models have been tested against a series of ground-based and spacecraft observations of dust jets in Comet P/Halley. While the Fast Long Axis Mode can be used to explain the positions of some of the jets, it does not support enough of the observations. The Slow Long Axis Mode fits the observations quite well, and should be taken to be the correct state for Halley. This work was supported by NASA funds. 15.10-P Ferrante R. F. Moore M. H. Nuth J. A. III Laboratory Studies of Formaldehyde Polymerization in Cometary Ice Analogues Formaldehyde, H(sub)2CO, has been found in the coma of several comets, and its polymerized form, polyoxymethylene (POM), has been suggested as a possible constituent in the organic component of Comet Halley. Little experimental information is available on the processes connecting such species under appropriate conditions. We have used infrared spectroscopy to examine the thermal and radiation-induced polymerization of formaldehyde in mixtures with astrophysically relevant volatile molecules (H20, CH(sub)30H, etc.) deposited at low temperatures onto low density sub-micron amorphous silicate grains. Special focus on the effect of the condensation surface will be attained by comparison with results employing other substrates (Al, salt, inert surfaces, etc.); these silicate smokes have previously been shown to promote crystallization of such ices at temperatures well below those required with other surfaces. The experiments will progress from simple binary mixtures, with the ultimate aim of treating multi-component cometary ice analogues. The presence of Fe, Mg, and other metals in the silicates will also be examined in the future. *This work was supported by the NASA Planetary Atmospheres Program **Supported by the NASA Planetary Materials and Geochemistry Program 15.11-P Verkhoglyadova O. P. Paraboloidal Model of Formation of Envelopes and Rays in Cometary Ionosphere Three-dimension model of large-scale stratification of cometary ionosphere is studied. Given weak charged particle flows along the tail in the cometary ionosphere, an aperiodic filamentation instability [1] results in formation of paraboloidal plasma envelopes in the cometary head and regular ray structures in the plasma tail. The study is carried out in terms of linear magnetohydrodynamics in paraboloidal geometry of the cometary ionosphere [2]. This model enable to study the formation of both paraboloidal envelopes covering the cometary head and ray system in the tail. Near the cometary head the instability development gives rise to formation of a set of paraboloidal envelopes. Moving along the cometary tail one can obtain the system of quasiparallel rays directed along the tail axis. Shape, thickness and formation time of these plasma structures are discussed. References: [1] Verkhoglyadova O. P., Kotsarenko N. Ya., Pasko V. P., Churyumov K. T. (1993) Sov. Astron. Lett., 19(9), 823. [2] Schmidt H. U. and Wegmann R. (1991) In cometary plasma processes, (A. D. Johnstone ed.), Geophysical Monograph 61, AGU, 49. 15.12-P Boice D. C. Benkhoff J. Huebner W. F. A Dusty Coma Model for Long- and Short-Period Comets The mixing ratios of the minor constituents of frozen gases in the ice-dust conglomerate of the nucleus is a very important clue to the original composition of the solar nebula. The usual assumption has been that the mixing ratios of volatile species observed in the coma is the same as that in the nucleus when photolytic and gas-phase chemistry is taken into account. While this may be the case for a solidly compacted nucleus, it is doubtful for a low density, porous nucleus. Moreover, evidence from the P/Halley missions and laboratory experiments indicate that comet nuclei are very porous. We present multifluid, hydrodynamic si1nulations for the gas, dust, and plasma flow appropriate for long- and short-period comets. The results of a sophisticated nucleus surface layer model are used for the initial gas production rates of the volatile species released from the surface. The simulations are based on a spherically symmetric neutral coma model with detailed photolytic and gas-phase chemistry, dust entrainment by the gas, a separate energy balance for the electrons, separate flow of the neutral gas, fast neutral atomic and molecular hydrogen, dust fragmentation, and distributed coma sources of gas-phase species related to the dust. These simulations allow a study of how certain coma features, e.g., spatial distributions of coma species, neutral and electron tempera-tures, outflow velocities, etc., change with cometary gas production and dust-to-gas production rate. In comparison with observations, the simulations can give insights into the similarities aud differences of long- and short-period comets. 15.13-P Mueller B. E. A. A Numerical Study of Complex Spin States of Cometary Nuclei I investigated published light curve data of comets with respect to their periodicity with special emphasis on multiple periodicity analysis. The results were presented at the last DPS meeting [1]. The conclusion was that we did not have sufficient data for most of the observed comets to establish with certainty a pure or complex rotation. For this reason I analyzed numerically generated light curves for comets in pure and complex spin states using phase dispersion minimization (pdm) and fourier analysis with clean algorithm (windowCLEAN) methods [2]. The goal is to find the best strategy to observe the comets in order to detect complex motion (apart from getting continuous coverage) and to establish limits on the deviations from simple rotation that can be detected by windowCLEAN. 15.14-P Schleicher D. G. Sackey S. Ballou R. G. Spatial Distribution of Cometary Grains In order to better understand physical and chemical processes taking place within cometary comae, it is desirable to know the detailed spatial distribution of both the dust and the various gas species in a comet. In recent years it has become clear that a significant fraction of the "dust" coma is composed of material, which is neither inert nor unchanging. Rather, direct and indirect evidence of the existence of volatile grains as an additional source of cometary gas comes from the discoveries of CHON particles and collimated gas jets in Comet Halley. Analysis of radial brightness profiles of 14 comets by Baum, Kreidl, and Schleicher (1992) indicated that the majority of profiles were steeper than the canonical 1/rho, consistent with fading of the grains, perhaps caused by darkening or shrinking of the grains due to the sublimation of ices. In order to further investigate this phenomenon, we have an on-going program at Lowell Observatory of narrow-band CCD imaging of "bright" comets. In this paper, we will show that Comets P/Brorsen-Metcalf (1989 X) and Austin (1990 V) both have spatial profiles consistent with grain fading. Moreover, the deviation from a 1/rho profile for Comet Austin clearly evolves during the month of imaging. Possible causes of this evolution, such as declining production rates due to increasing heliocentric distance or effects due to the change in phase angle, will be presented. This research was supported by NASA, NSF, and the Research Corporation. 15.15-P Kiselev N. N. Jockers K. Chernova G. P. CCD Imaging Polarimetry of Comets P/Encke, P/Ashbrook-Jackson, and P/Schwassmann-Wachmann 2 (P/SW 2) Using single-aperture polarimetry Chernova et al. (1993) have shown that the phase dependence of polarization in comets with strong continuum follows one single curve within measurement error. Comets with reduced continuum in their spectrum also show reduced polarization and the values scatter significantly, in particular at large phase angles. In order to investigate the question if this result is caused by unwanted contribution of molecules to the measured polarization or if there is indeed a different kind of dust in the comets with low continuum, we have performed imaging polarimetry in comets P/Encke (low continuum) and P Ashbrook-Jackson and P/SW2 (both comets have strong continuum). The comets were observed at the lm-reflector of Observatory Hoher List. Germany, and at the 2m-RCC-telescope of the Bulgarian National Observatory. A red filter (lambda(sub)0 = 694 nm. FWHM = 76 nm) was used. It includes the faint molecular emissions of NH(sub)2 and H2O^+. Comet P/Encke was observed at phase angles 51.1 degrees and 80.5 degrees. The degree of polarization found in its sunward fan (10 - 14 degrees) is higher than in other parts of the coma. (4 - 7 degrees), but less tha.n the value observed in dust-rich comets at similar phase angles (22 %). In comets P/Ashbrook-Jackson and in P/SW 2 the polarization is similar to other dust-rich comets. We will discuss the evidence if the reduced polarization values found in comet P/Encke are caused by contribution of NH(sub)2 a.nd H20^+ or if the effect is real, i. e. caused by a different kind of dust grains. Reference: Chernova. G. P., Kiselev N. N., and Jockers K: 1993, Polarimetric characteristics of dust particles as observed in 13 comets: Comparison with asteroids. Icarus 103. 144-158. 15.16-P Keller H. U. Wellnitz D. D. Schulz R. Birch P. V. A'Hearn M. F. Gas and Dust Distribution in the Coma of Comet McNaught-Russell (1993v) A series of pre-perihelion images of Comet McNaught-Russell was obtained with the University of Maryland CCD camera system mounted on the 0.61-m Lowell Telescope at Perth Observatory, Australia. Observations in several different spectral ranges were taken on 13 nights between March 9th and March 27th, 1994, using standard IHW narrowband filters for CN, C(sub)2, C(sub)3, blue continuum, and red continuum, and a broad red bandpass (RG665). The images have been extinction corrected and relatively calibrated with appropriate standard stars. The light curves show short-term variabilities in brightness superimposed on the general increase due to the decreasing heliocentric distance. Surprisingly, preliminary morphological analysis shows distinct features in the coma pointing into the sunward hemisphere for CN and C(sub)2, but not for C(sub)3. Tlle images reflecting the distribution of dust also show no evidence for distinct features except for the already developed dust tail. The material distribution as well as the temporal evolution of the coma in all six components will be presented in a comparative analysis. 15.17-P Osip D. J. Schleicher D. G. Campins H. The Rotation State of 4015 Wilson-Harrington: Revisiting Origins for the Near-Earth Asteroids The rotational characteristics of Near-Earth Asteroids (NEA) have been found by some to be at least partially diagnostic of their origins. Binzel et al. (1992) compared the rotation periods of 32 NEAs with those of the only 5 well obselved cometary nuclei at that time and with those of their new sample of 32 main-belt asteroids of similar size (d < 5 km). They concluded that the spin rate and shape distributions of the small main-belt asteroids are statistically indistinguishable from those of the NEAs while the mean values for the comet sample were significantly different. Considering their available sample of cometary nuclei as representative, they concluded that their observations were consistent with 0-40% of the NEA population being derived from dormant or extinct cometary nuclei. CCD photometry perforrned on the comet-asteroid transition object 4015 Wilson-Harrington (W-H) during its most recent apparition have provided a new rotational light curve and an estimate of the rotational period of 6.1 +- 0.05 hours. The new rotation period and amplitude determined for W-H are within one standard deviation of the mean values calculated for the 32 small main belt asteroids by Binzel et al.; the rotation period is significantly shorter than those of the other comets previously considered. In addition, Campins et al. (1994) estimate an effective diameter of 4 km for W-H, similar to those of the NEA and asteroid samples, whereas the earlier studied comets averaged over 10 km in diameter. In short, the range in cometary nuclear properties is greater than indicated by the comets studied previously and although the statistics are still poor, the size and rotational properties of W-H do suggest that some fraction of NEAs are of cometary origin. 15.18-P Nazarchuk H. K. The Photometrical Evolution of Comets Numerical simulation of the orbital and secular photometric evolution of cometary nuclei has been carried out using a theory of formation and destruction of surface dust mantle. As a result of the simulation the next parameters were obtained: the equivalent radii of nuclei, dust content, the maximal size of the mineral particles embedded into the ice. The used model of evolution is rather sensitive to these parameters. The phorometric curves of eleven comets were calculated for more than 100 revolutions. All the investigated comets belonged to one of the next three types: the comet with the perihelion distance q>2 AU and low dust contents, the comet with q~1.5 AU and ~5% dust material, the comets with q~0.5 AU, the dust contents ~10% and large nuclei ~10 km. Each of these types has its own features of evolutions. 15.19-P Shulman L. M. Effect of the Solar Spectrum on Spectra of Comets If one has a comet spectrum with good enough resolution it is easy to take a gap between two deep neighbor solar absorption lines as an "emission" comet feature. The genuine physical characteristics of comet is not the distribution of energy in its spectrum but rather the dependence of the optical thickness of its atmosphere on the wave length. This function can be obtained by division of the comet spectrum by the spectrum of the Sun reduced to the same resolution. this procedure being applied to Comet Halley gave deficiency of the equivalent widths of the Fraunhofer's lines scattered by the cometary atmosphere. The luminescence of CHON particles has been proposed to explain this phenomenon. There is a suspicion (M. Mumma, private communication) that this effect may be caused by underresolution of the comet spectra. This problem is analyzed and discussed. 15.20-P Chorny G. F. Nazarchuk G. K. Luminescence of Organic Molecules in the Halley Comet It has been previously observed (December 1985, G. K. Nazarchuk) that there are two broad features with the centers at 3950 angstrom (-10, +40 angstrom) and 5100 angstrom (+/- 50 angstrom) in the continuum of the Halley comet. They are parts of the scattered solar continuum. The feature at 5100 angstrom has been observed as far as 2000 km from the nucleus. The feature at 3950 angstrom was more longlived and has been observed at the nucleocentric distances up to 20000 km. The assumption is that there are luminescence features of unknown origin. The luminescent spectra of some alternative sources in the optical regions are qualitatively analyzing: (a) the sputtering of water icy particles at temperature below 100 K by electrons with the energy between 20 and 300 eV; (b) continuous spectrum of C(sub)2H radical that arises under photolysis of the C(sub)2H(sub)2 molecules; (c) the photoluminescence of lonsdeleite crystals, which are the white grains of diamond and can be included in composition of graphite particles; (d) the photoluminescence of the polycyclic aromatic hydrocarbons (PAHs). The analysis shows that the possible contribution of (b) and (c) sources is sufficiently slight. Process (a) can contribute to the detail of 3950 angstrom if there are the regions in a cometary atmosphere in which the temperature of the icy particles is in the range from about 77 K to 100 K. The photoluminescence of the small PAHs, in environment where these PAHs are slightly pushed by H2O and OH molecules, is the most probable. The candidates among PAHs are anthracene (C14-H10), pyrene (C16-H10), anthrol (C14-H9-OH) and other small PAHs with adjacent O, OH, or H2O. 15.21-P Shvidkiy A. A. Kotsarenko N. Ya. Lizunov G. V. On the Theory of Generation of Electromagnetic Waves on Half-harmonics of Electron Cyclotron Frequency in Space Plasma Electrostatic plasma waves at half-harmonics of cyclotron frequency are of special interest. This kind of emission is observed in the Earth and planetary magnetospheres, including the Jupiter magnetosphere, some spectra of the Solar radiobursts, laboratory and active space plasma experiments, etc. From the theoretical point we have to do with a definite frequency spectrum of Bernstein modes. The problem is to explain its character, which is common for dissimilar plasmas. Particularly, the location of spectrum maximums near the (eta + l/2)omega(sub)c values (omega(sub)c is electron cyclotron frequency, eta = 1,2,3,...) is of interest. Earlier, a variety of mechanisms were invoked for this purpose. Most of them deal with the instabilities of special kinds of plasma distribution functions, like a loss cone, oscillatory, or temperature anisotropy functions. These approaches could explain isolated data, but not the general nature of phenomena. The purpose of this report is to show that a wave generation at frequencies omega = (eta + 1/2)omega(sub)c is.caused by interaction of electron flows with Bernstein modes. The linear theory of instability and estimation for the level of quasilinear instability saturation are developed. The essence is that the spectrum shape is determined by dispersion properties of these modes in themselves. An electron flow plays a role of the energy source only, providing the necessary sign of plasma wave dissipation. 15.22-P Churyumov K. I. Kleshchonok V. V. Spectral observations of Comets Scorichenko-George (1990 VI), Levi (1990 XX), Tanaka-Machholz (1991X), Swift-Tuttle (1992t) and Shaumasse (1992x) with the 6-M Reflector BTA Five comets Scorichenko George (1990 Vl), Levi (1990 XX), Tanaka-Machholz (1992 X), Swift-Tuttle (1992t) and P/Shaumasse (1992x) were observed with the 6-m renector BTA of Special Astrophysical Observatory of RAS in Nyzhny Arkhyz during 1990-1993. In the spectra of comet Scorichenko-George (1990 VI) obtained on March 26/27, 1990, emission bands of triplet and Asundi of neutral CO were found and emissions of the negative ion of the carbon C2- were discovered. In the spectra of comets Levi (1990 XX) (on March 23-24, 1990) and Tanaka-Machholz (1992t) (on April 29/30, 1992) typical cometary emissions (CN, C2 et al.) were identified. In the spectra of comet P/Schaumasse (1992x) (on March 14-15, 1993) anomaly relative gas productivity of the molecule of C3 (vs. molecule of CN) was found. Peculiarities of spectra of five comet are discussed. 15.23-T Xie X. Mumma M. J. Bockelee-Morvan D. Colom P. Crovisier J. Gerard E. Saturation of the OH 18-cm Lines in Comet Levy The optical depth of the 1667 MHz transition was found to be nonnegligible for comet Levy in Sept 02-03,1990, which leads to about a 25% reduction of its gas production rate from the initial value. The Monte Carlo method is used in simulating the observed line profile (Bockelee-Morvan et al. 1991), which was fitted with an angular distribution. The line simulation is based on the OH kinematic parameters obtained from a full Monte Carlo Particle Transport model (Xie, 1994) and incorporates the optical depth effect of the 18-cm lines in an expanding coma. SESSION 16 ....... Mars Atmosphere I Wednesday, 8:30 - 10:00 Crystal Ballroom B R. T. Clancy and R. E. Johnson, Moderators 16.01 James P. B.* Clancy R. T. Lee S. W. Martin L. J. Monitoring Mars with the Hubble Space Telescope: 1994 Observations Mars may be observed by the Hubble Space Telescope after August 6, 1994 when its elongation exceeds 50 degrees. A regular program of monitoring of the planet will begin at that time; Mars will be observed every 15 degrees of L(sub) using filters at 255, 336, 410, 502, and 673 nm. These observations will continue a program of HST observations of Mars which started in December, 1990. Comparison of our first 1994 observations (L(sub)s = 335 degrees) with the earliest WFPC images will be used to investigate the occurence of a major dust storm in the preceding summer reported by Clancey (private communication). Preliminary results of this comparison will be presented. This work was supported by STScI Grant GO-5493. 16.02 Rosenqvist J.* Titov D. Water Vapor Spatial Variations on Mars Inferred from ISM/Phobos 2 Observations The infared spectrometer aboard the Phobos 2 spacecraft provide a data bank constituted by 40,000 spectra of Mars in 1989 with a typical spatial resolution of 25 km. Although the spectral power was modest (60), the spectral range (0.76-3.15 microns) associated to a very high S/B (500-1000) pemits to detect H2O at five wavelengths (1.14, 1.38, 1.86, 2.55 and 3.0 microns). Different problems impose to use only two of them (1.86-2.55 microns). Because these bands could be contaminated by the surface, we should be very careful in interpreting these features. The correlations with the altitude of the surface and between the two bands are nevertheless a strong argument in favor of a quasi-pure atmosheric origin of these spectral features. We will discuss the results concerning the spatial variations of water vapor from place to place as a function of the albedo and the surface elevation and nature. 16.03 Titov D. V.* Rosenqvist J. Regolith Atmosphere Water Vapor Exchange on Mars: Evidences from the ISM (Phobos) Measurements and Theoretical Analysis The measurements of the infrared mapping spectrometer ISM ( Phobos2 orbiter provided valuable data on the atmospheric content on Mars, its spatial and local time variations /1/. Some peculiarities of vapour distribution were observed: l)a facto higher H20 mixing ratio above Tharsis volcanoes as compare surrounding plateau /2/; 2)a factor of 2+ / - 1 increase of the vapour column density from morning towards noon in some regions /1/; 3)positive correlation of the atmospheric water amount with the surface albedo and negative-with the thermal inertia /1/. These features were interpreted as a result of regolith-atmosphere vapour exchange caused by the diurnal surface temperature variations and differences in properties. A theoretical analysis of the diffusion equation led to the solution for the rate of water release to the atmosphere. Surface temperature and regolith buffering coefficient were found to be the main parameters, which control this process. Montmorillonite clay and basalt grains were found considered as possible analogs of the Martian regolith. The difference in their adsorbing properties results in significant variations of diffusion time scale: the response of the clay regolith to the diurnal temperature changes is much faster than that of basalt soil. The models, proposed on this basis, succeeded to explain observed peculiarities of the water vapour distribution on Mars. REFERENCES: l.J.Rosenqvist et al. Icarus, 98, 254-270, 1992. 2.D.V.Titov et al. Submitted to Planet. Space Sci., 1994. 16.04 Krasnopolsky V. A.* Bjoraker G. L. Mumma M. J. Jennings D. E. High-Resolution Spectroscopy of Mars at 3.7 and 8 Micrometers: D/H Ratio and Upper Limits to H2O2, CH4, H2CO and HCl A combination of the KPNO 4 m telescope and the Fourier Transform Spectrometer with the GSFC postdisperser was used to observe low-latitude regions of Mars in spectral ranges of 2650-2800 cm^-1 and 1229-1237 cm^-1 with resolving power nu/delta nu = 2.7 x 10^5 and 1.2 x 10^5, respectively. The main spectral features are isotopic lines of CO2, which make possible determination of the ^18O/^16O, ^17O/^16O and ^13C/^12C ratios on Mars. The,observed HDO lines result in the HDO abundance which being compared with that of H20 measured by the Vikings at the same season and latitudes yields an enrichment in the D/H ratio of a factor of 5.5 + 1 relative to the Earth. Substantial improvement of upper limits to mixing ratios of some species has been achieved: H2O2 < 35 ppb, CH4 < 170 ppb, H2CO < 5 ppb, HCl < 2 ppb. The H2O2 limit imposes some constraint to models of the martian photochemistry, while the other ones preclude any significant chlorine and CH4-H2CO atmospheric chemistries. Telluric absorptions correspond to abundances of H20 of 2 precipitable cm, CH4 of 2.0 ppm, N20 of 60 ppb, H2CO < 0.6 ppb, HCl < 0.4 ppb. All upper limits are given for the 2 sigma uncertainty. This work was supported by RTOP 196-41-54 under the NASA Planetary Astronomy Program. 16.05 Johnson R. E.* Pospieszalska M. K. Calculations of Pick-up Ion Sputtering of the Martian Atmosphere The importance of pick-up ions formed from escaping O atoms in the solar wind interaction region has been pointed out in a number of recent papers^1,2. Here we re-evaluate our initial estimates ^3,4 of the number of atoms ejected from the atmosphere per O+ ion incident onto the atmosphere. This is done using realistic cross sections in a Monte Carlo particle tracking calculation^4. Results will be shown for an atmosphere dominated by atomic 0. These are self-consistent calculations in that the expansion of the Martian corona due to the incident flux of ions is included in the calculation as well as the escape of 0. We will use these results to re-evaluate the pick-up ion impact flux and the direct loss of pick-up ions. That is, the sputter-expanded corona and enhanced escape flux act to stand-off the solar fields at larger distances from Mars, and the ion formation rate depends on the O densities in the ionization region. Therefore, the pick-up ion bombardment rate is also determined by the atmospheric sputtering yield^4 when sputter escape dominates other loss processes, as is the case in the early epochs^1. Evaluating this feed-back process will allow improved estimates of the atmospheric loss rate. REFERENCES: [l] J.Luhmann, R.Johnson, M.Zhang GRL 19, 2151, 1992 [2] B.Jalcosky, R.Pepin, R.Johnson, J.Fox, Icarus in press, 1994 [3] R.Johnson, JGR 97, 13911, 1992 [4] R.Johnson Space Sci.Rev., in press, 1994. 16.06 Kass D. M.* Yung Y. L. Atmospheric Loss from Mars Due to Solar Wind Induced Sputtering Since Mars does not have a strong intrinsic magnetic field, the atmosphere is eroded by solar wind induced sputtering. In this process, ions (especially O+) reimpact the upper atmosphere after being accelerated by the interaction of the solar wind and interplanetary magnetic field. In the process, they acquire significant amounts of energy (upwards of 1 keV) and will collisionally eject neutral elements of the atmosphere. Luhmann et al. (1991) showed that early solar system conditions, especially the much greater EUV solar flux and stronger solar wind, greatly increased the precipitating ion flux. They used a sputtering model to estimate that ~ 0.14 bar of CO2 and ~ 50 m of water could be lost over the last 3.5 Gyr of Martian history. We use a general Monte-Carlo type atmospheric sputtering model adapted to Mars to calculate the sputtering efflciencies. Excluding polyatomic dissociation, the model uses elastic collisions with anisotropic scattering functions. The model includes two major factors that the analytic model of Luhmann et al. appears,to have neglected. Their model appears to ignore some of the secondary collisions that allow particles to escape. It also treats C atoms as only having their own cross-section and not that of the full CO2 molecule. With our new sputtering efflciencies, we calculate that ~2.3 bars of CO2 and ~60 m of water have been lost over the last 3.5 billion years. One explanation for Martian geomorphology, notably the channels, is an early dense atmosphere to create a greenhouse. Such an atmosphere would require at least 0.5 bar of CO2 (e.g. McKay and Davis, 1991) and 50 m of water (Baker et al., 1992). The fate of such an early atmosphere is a significant problem for the greenhouse explanation. If the thick early atmosphere existed, the new sputtering losses of 2.3 bars of CO2 and 60 m of H20 could remove such an atmosphere over the history of the planet. Currently the best constraint is the atmospheric stable isotope data (Jakosky, 1991). Simple calculation, using just the current atmosphere, for C^l3 indicate that between 1 and 5 bars of CO2 need to be buried in the planet during the sputtering to match the isotope measurements. DMK was supported by an NFS Fellowship and this work was partly supported by NASA grant NAGW-1538. 16.07 Forget F.* Hourdin F. Talagrand O. Pollack J. B. Observations and Simulation of the Martian Polar Climate: Impact of the CO2 Clouds Analyzing thermal infrared observation from Viking IRTM and Mariner 9 IRIS, we have found strong evidences for the presence of CO2 and H20 clouds above the Martian polar caps during the polar night [1]. This study revealed that, by altering the thermal radiation emitted to space, these clouds have a strong impact on the thermal balance of the polar regions, lowering the amount of CO2 that condense during the fall and winter seasons. A strong hemispheric asymmetry was observed: in the northern hemisphere, C02 clouds were very common at most polar latitudes unlike in the southern hemisphere where they were less frequent below 80 degrees S. We have tried to take this impact into account in climate modeling with the Martian Global Circulation Model (GCM) of the Laboratoire de Meteorologie, Dynamique. For that purpose, we have first developed a simple scheme to simulate the condensation, advection, and possible sedimentation or sublimation of the CO2 ice particles in the GCM. This treatment is based on the calculations of the condensation rates of the CO2 in the cold polar atmosphere by the GCM and on clouds microphysics considerations. We have also derived a simple parametrization of the simulated polar clouds radiative properties from our analyses of the thermal infrared data. The results of our simulations can be compared with the Mariner 9 and Viking observations, and can also be validated by considering the ability of the model to reproduce the Viking Landers pressure curves, which mainly depend on its ability to simulate the climate of the polar region and the associated CO2 condensation/sublimation cycle [2]. References: [1] Forget and Pollack, Bull. of A.A.S., 25-3, p. lO70, 1993. Also, Paper submitted to JGR Planet, 1994. [2] See Hourdin et al., J.Atmos.Sci. 50, 3625-3640,1993, Pollack et al., JGR Planet 98(E2),3149-3181, 1993, Talagrand et al., this issue. 16.08 Talagrand O.* Forget F. Hourdin F. Martian Seasonal and Transient Pressure Variations: GCM Simulations and Viking Observations The Martian General Circulation Model (GCM) of Laboratoire de Meteorologie Dynamique (LMD) has been used to simulate the Martian Climate and analyze its sensitivity to various parameters (Hourdin et al., submitted to J. Geophys. Res.). Results of pluriannual simulations have been evaluated primarily on the basis of comparisons with the Viking surface pressure measurements. The model is able to reproduce rather accurately both the large seasonal variations and the rapid transient oscillations of the surface pressure. The seasonal variations are due to the change in the the atmospheric mass (resulting from the condensation of the CO2 atmosphere in the polar caps), but also to internal latitudinal mass redistributions associated with the atmospheric circulation (Hourdin et al., J. Atmosph. Sci., 50, 3625-2640, 1993). The simulated internal mass redistribution (found to be weakly sensitive to model parameters) can be used to retrieve the seasonal variations of the total atmospheric mass from the Viking pressure measurements. The periods (typically 2-5 sols) and the amplitudes of the transient eddies provide a useful diagnostic of the mid-latitude atmospheric circulation. The model is able to simulate the decrease of the amplitude of the eddies for increasing optical depths, as observed near northern winter solstice, particularily during the 1977-B global dust storm. Even without seasonal variations of the atmospheric dust content, the reduction of the transient activity for dusty conditions is maximum near northern winter solstice. For large dust amounts, the increase in the latitudinal extent of the Hadley circulation strongly reduces condensation at the edge of the forming cap. But in the same time, the reduction of the transient activity, responsible for latitudinal energy transport toward higher latitudes, reinforces strongly condensation at the pole. 16.09 Fanale F. P.* Postawko S. E. Mass Loading: A Key to the Early Mars Greenhouse? Carbon dioxide atmospheric greenhouse models for early Mars require massive CO2 atmospheres and are subject to cloud formation. Similarly, models augmenting the greenhouse with SO2 molecules run afoul of short SO2 atmospheric mean residence times (MRT) dictated by the rapid reaction with OH-. However, the MRT of SO2 is actually a variable which depends on the relative rate of SO2 supply and H20 resupply. Hesperian eruption rates can supply SO2 at global rates of 10^-9 to 10^-8 g cm^-2 sec^-l which could destroy the current atmospheric H20 inventory in days and the higher H20 inventories associated with greenhouse models in less than 1 month. This, together with recent models allowing wide obliquity variations, results in a wide range of plausible but unfamiliar models in which CO2 and H20 can be "traded off" against SO2. We assume than in early conditions CO2, H20, and SO2 are cold trapped at the same temperatures. For cap temperatures of 213K and 195K: PCO(sub)2 = 4 bars and 1 bar; PS0(sub)2 = 50 mb and 12 mb (when equilibrium with the cap is achieved); atmospheric H20 destruction time = 1 month to 2 days (for the highest eruption rate); SO2 mixing ratios are on the order of 10^-2. It is unlikely that the poles or regolith could resupply atmospheric H20 at a rate comparable to the SO2 supply rate. Indeed, the most viable source of H20 is the fissure eruption itself. However, it cannot supply the H20 directly and efficiently to the atmosphere as it does the SO2 owing to the local and regional cold trapping. Steady state between H20 and SO2 can be achieved by creation of an open water lake with a radius of approximately 200 km or, for an assumed ablation rate of 30 cm/yr, an ice covered lake of radius 900 km. SESSION 17 ....... Comets II Wednesday, 10:30 - 12:00 Crystal Ballroom A M. S. Hanner and M. H. Moore, Moderators 17.01 Grun E.* Comet Surface Probes for Rosetta The Rosetta spacecraft will deploy surface probes on a cometary nucleus with the goal to study the most primitive material in the solar system. The objectives of these surface probes are the in situ characterization of the chemical, mineralogical and physical properties of bulk surface material and the study of cometary processes at the surface of and within the nucleus. Four different scenarios of surface probes and their relationships to the objectives are discussed: (1) A battery-powered surface station carries a camera for morphologic and mineralogic studies and several sensors for compositional analysis of cometary surface material. It transmits pictures and compositional data for several hours after landing. (2) Two different surface regimes are known to exist on a cometary nucleus: inactive areas which are depleted of volatile materials and "active" areas which emit gas and dust at elevated insolation levels. Either multiple probes or a mobile probe are required to sample both regimes. (3) Comet material undergoes continuous thermal modifications due to variable insolation: volatile components are redistributed and depleted within the nucleus and finally leave the surface. In order to study these processes a long-term probe is necessary which both daily and seasonal variations of the physical and chemical properties of cometary materials. (4) The nucleus is thermally coupled to the exterior via a thin surface layer. Within an about meter-thick layer strong temperature variations and both physical and chemical modifications occur. Studying this heat transfer process and the corresponding material modifications will require a sub-surface probe. In order to understand the compositional data obtained at the surface all of these questions have to be addressed by the Rosetta Mission. Possible implementations of these objectives will be discussed. 17.02 Young E. F.* Collisional Evolution Within the Kuiper Belt Various populations of Kuiper Belt objects are studied with a simple computer simulation. Hill's equations (linearized equations of motion within a rotating reference frame) are used to describe the objects' trajectories. Borrowing a trick from Wisdom and Tremaine's treatment of particles in a ring (AJ 95 no. 3, 1988), this simulation tracks a local cluster of objects and models the rest of the Kuiper Belt as copies of this local cluster. The simulation is a useful tool for studying the following questions: What is the collision rate in the Kuiper Belt? What is the dust production rate in the Kuiper Belt, and what is the flux of dust into the inner solar system?. What initial populations are consistent with the current assumed Kuiper Belt population? What fraction of Kuiper Belt objects are the products of collisions? How does the size distribution evolve? Figure 1. appears here in the hard copy. This work was supported by the National Research Council Associateship Programs. 17.03 Capria M. T.* Coradini A. Capaccioni F. Espinasse S. Orosei R. Salomone M. Federico C. Differentiation Processes of a Comet Coming from the 'Kuiper Belt' We studied the evolution of a porous comet nucleus injected from the Kuiper belt to the inner Solar System. The comet undergoes different successive closeencounters with giant planets, becoming a "Jupiter family" comet. We have analyzed the differentiation of the nucleus and the conditions under which a dusty crust forms, during the dynamical evolution of the comet. Our nucleus is compose of a mixture, initially homegeneous of different ices and grains. Ices can be considered amorphous, due to the low temperature of the comet in its formation area. For the water ice, the transition amorphous-crystalline is followed in detail. We have used different values of conductivity for amorphus ice, different gas and dust concentrations, different initial conditions (presence or not of an original organic crust due to cosmic ray bombardment) in order to study how this choice affects the thermal evolution and the differentiation of the nucleus. The gas and dust emission is studied as well. 17.04 Coradini A.* Capaccioni F. Capria M. T. Orosei R. Salomone M. Federico C. Thermal Evolution of a Short Period Comet: Bidimensional Models The differentiation of comet-like body has been studied for several years by means of uni-dimension models allowing to solve the heat equation. These models allowed to study the importance of different parameters - such as porosity, dust content, presence of different gaseous components - on the thermal evolution and differentiation of the cometary nucleus. In this paper we present the thermal evolution of the comet nucleus obtained solving the hear equation in 2D in a spherical coordinate system. The nucleus is initially made by amorphous ice and orbits around the Sun at a distance of 50 A.U. The evolution differs from the unidimensional one mainly because the latitudinal insulation differences generate a temperature field in the interior of the nucleus that is strongly latitude dependent. We study the evolution of the nucleus taking into account also of the amorphous-crystalline ice transition. 17.05 Malhotra R.* The Origin of Pluto's Orbit: Implications for the "Kuiper Belt" Pluto's Neptune-crossing orbit owes its dynamical longevity to a reasonant libration of its perihelion 90 degrees away from Neptune's mean longitude. This peculiar orbit plausibly owes its origin to dynamical processes in the early Solar System. A resonance capture mechanism is possible during the loss of planetesimal mass from the vicinity of the giant planets [Malhotra, R. Nature 365:819-21 (1993)]. If this mechanism were in operation during the early history of the planetary system, the entire region between the orbit of Neptune and approximately 48 AU would have been swept by first order mean motion resonances. Thus, resonance capture would occur not only for Pluto, but quite generally for other trans-Neptunian "planetesimals". Furthermore, the dynamical erosion of the number density of small bodies in the "Kuiper Belt" (the putative source reservoir of short-period comets) would be greater than that suggested by recent studies of test particle orbital stability [Holman, M. & Wisdom, J. AJ 105:1987-99 (1993); Levison, H. & Duncan, M., ApJ 406:L35-38(1993)]. Theoretical predictions for the orbital distribution of trans-Neptunian small bodies will be presented. A significant implication for observational searches is that higher number density of objects may be found in very narrow regions interior to ~ 48 AU, in stable resonant orbits with non-random distribution of orbital elements. 17.06 Kotsarenko N. Ya.* Rapoport Yu. G. Verkhoglyadova O. P. Soliton Model of Formation of Condensations in the Cometary Plasma Tails Condensations are typical objects in the cometary ionosphere. We assume that they are stable dense structures caused by nonlinear solitary waves of alfven and magnetosonic wave branches which play an important role for space plasma objects. The high level of spectra density of the above waves in the cometary plasma is in favour of our assumption. In order to study the possibility of soliton formation mechanism for condensations, nonlinear dynamics of the magnetosonic waves is considered. The study is carried out in terms of a set of MHD-equations for ions and electrons of the cometary plasma. We study the one-dimensional wave propagation with angle theta to the external magnetic field. The reductive perturbation method for weakly dispersive and weakly nonlinear waves [1] is used. The KdV soliton is formed under the defined conditions for theta and for wave number of the initial magnetosonic wave. The estimation for solitary wave propagating with theta = 15 degrees in external magnetic field of 10 nT gives the spatial scale of magnetosonic soliton about ~=750 km which value agrees with the observational data. We propose that sperical plasma clouds maybe nonlinear solitary MHD-waves in the cometary ionsphere. [1] Kakutani T. (1974) Suppli. Progress of Theor. Phys., N-55, 97 17.07 Farnham T. L.* Meech K. J. Modelling of Comet P/Tempel 2 Using a Finson-Probstein Fitting Routine We have developed and are refining a kinetic model of cometary dust grains, which is based on the Finson-Probstein (F-P) technique, to study the particle populations in cometary dust tails. The appearance and morphology of a comet's dust tail are the result of the opposing forces of gravity and solar radiation pressure that act upon individual grains. Using the dynamics of the system, the surface density along the tail is determined by summing up the scattering contributions from all particles. By matching models to observed images, the various grain parameters can be determined. The main parameters are the particle size distribution, the dust production rates and the escape velocities. Our model is based of the original F-P work, however, several improvements have been incorporated into our model, including non-spherical emissions and more realistic scattering functions. The most recent refinement to the model is the implementation of a fitting process to determine the parameters which best reproduce the observed images. The fitting process will be based on the Levenberg-Marquardt method of solving non-linear least squares problems. It will have the capability of solving for a number of dust grain parameters, while at the same time determining how the individual parameters are interrelated in E producing the morpllology of the tail. This is important in the interpretation of the grain parameters, because changes in the appearance of the tail produced 1?! by altering one parameter can sometimes be corrected for by adjusting another. Comet P/Tempel 2 has been chosen as a test case for the fitting procedures, because it is a periodic comet that has been well-studied. Its rotation period is known to be 6.5 hours, and the direction of the rotation axis and the lag angle of the sublimation have both been calculated, so the orientation of the I? emission can be well-defined. We have data from 17 different observing runs a between March 1987 and March 1992 (spanning one full orbit). The full orbital coverage allows the development and dissipation of the tail to be observed as a Y fan shaped tail has formed by April 1988, and remains well defined until January 1989, when it begins to dissipate. There is excellent coverage of the comet D near its perihelion passage, which is the best time to constrain the properties A of the particles. The application of suitability tests indicates that P/Tempel 2 A is a good candidate for modelling using our technique, especially with the large time base that the images cover, It will make a good test candidate for the S fitting procedures because so much is already known about the properties of the nucleus. A review of the modelling process, with the details of the fitting D procedures will be presented, along with the results of the application of the S model to the observations of Comet P/Tempel 2. 17.08 Benkhoff J.* Huebner W. F. Influence of the Gas Flux on Temperature and Density in the Near Surface Layers of Comets We calculate the gas flux of the volatile icy components in the surface layer of a porous, short-period, Jupiter-class comet, in order to investigate the relationship of the observed relative molecular abundances in the coma with those in the nucleus. The model assumes a body containing dust, one major ice component (H20), and two minor components of higher volatility (C0 and CO2). The mass and energy equations for the different volatiles are solved simultaneously with appropriate boundary conditions. The model includes inward and outward flowing gas within the body, escape of outward flowing gas from the body, depletion of less volatile ices in outer layers, recondensation of gas in deeper, cooler layers, and changing porosity as a result of sublimation. The dust layer at the surface of the nucleus drastically reduces the sublimation flux of H20 at heliocentric distances less than about 3AU and keeps the the mixing ratio of the gas flux of mi