Monday, October 18, 1993 JUPITER I 8:30 - 10:00 AM South Ballroom Chair(s): P. Yanamandra-Fisher D. Gautier West R. A.* Karkoschka E. Tomasko M. G. Cunningham C. Wide-Field Camera Observations of Jupiter's Stratospheric Haze and Ammonia Cloud We observed Jupiter in early March of 1992 with the Wide Field Camera on the Hubble Space Telescope. We obtained images at UV wavelengths (284, 336, and 368 nm), blue (413 nm), red continuum (656 nm), and in the 889-nm methane band. The findings thus far indicate (1) jovian stratospheric haze extinction optical depth increases by about an order of magnitude from a minimum near latitude -40 degrees to maxima in polar regions, (2) there is a hemispheric asymmetry in the haze distribution such that the increase is most rapid between -50 degrees and -70 degrees, and between +30 degrees and +70 degrees, (3) stratospheric haze particles are strongly absorbing in the UV at high latitudes but not at low latitudes, (4) the wavelength dependence of the optical depth is similar to that of 0.16 micron radius spheres at high latitudes, but implies larger particles at low latitudes, (5) extinction optical depth of the underlying tropospheric ammonia cloud is approximately constant between latitudes -60 degrees and +40 degrees, but drops rapidly to near 0 poleward of those latitudes, (6) the north and south polar hood regions seen in the 889-nm images have distinctly different appearances, with considerable longitudinal structure seen only in the north. The loss of ammonia cloud opacity at high latitude correlates well with the magnitude of downwelling at the 270-mbar level indicated by the stratospheric circulation model of West et al. (Icarus 100, 245-259, 1992). Trafton L. M.* West R. A. Atreya S. K. Beebe R. F. Caldwell J. J. Owen T. C. HST Observations of the Spatial Variation of Gases and Aerosols in Jupiter's Atmosphere As part of a coordinated effort to obtain integrated dynamical and spectroscopic observations of Jupiter and Saturn, we have obtained spatially resolved spectra of Jupiter using the HST Faint Object Spectrograph with 0.5" and 1" circular apertures to sample selected regions along the central meridian and near the limb. The spectra span the wavelength range 1800-3200 Angstroms, covered by two gratings, G270H and G19OH, with resolutions from 1.8 -4.6 Angstroms. Various features were targeted in the blind pointing mode (1" pointing accuracy). The mostly northern hemisphere spectra, reduced to local reflectivities, are compared and contrasted. We report interim results for the 1992 apparition, taken in May. Evidence of a stratospheric absorber at 6 N includes limb darkening, which becomes more pronounced at shorter wavelengths. The spectra show a surprisingly marked variation of atmospheric haze content and haze properties with latitude. At low latitudes, a dramatic change is observed over a fairly small latitude interval. The presence of such gradients sets limits on the strength of the meridional circulation. At least in the northern hemisphere, Jupiter's upper atmospheric NH3 appears to be concentrated at lower latitudes. We investigate this in the context of a meridional circulation model. Cunningham C. C.* Caldwell J. J. HST Spectra of the Outer Planets I. The Grating Scatter Problem in the FOS Ultraviolet spectra of red objects, including planets, obtained with the HST Faint Object Spectrograph (FOS) are significantly affected below 2100 Angstroms wavelength by grating scatter of visible wavelength photons. Below 1800 Angstroms, the grating scatter dominates the signal. The HST Goddard High Resolution Spectrograph (GHRS) includes a low-resolution mode (G140L) that complements the FOS capability. Since the GHRS has "solar-blind" blind detectors, that would be the preferred mode for many planetary spectroscopy programs with the HST at short wavelengths. However, a partial electronic failure within the GHRS rendered the G140L inoperative soon after launch, so that the characteristics of the FOS below 2000 Angstroms have become a critical issue. Systematic ways to compensate for the effects of its grating scatter are required. Fortunately, the problem can be quantified. In May 1991, before the GHRS failure, the G2V solar analog star 16 Cygni B was observed with both the FOS ("blue" side) and the GHRS, throughout the wavelength range 1600-3300 Angstroms. As expected, the GHRS spectra of the solar analog star agreed well with independent observations of the Sun (Van Hoosier et al., Astron. Lett. Commun., 27, 163-168, 1988) throughout the entire spectral range, proving the reliability of the GHRS for this type of observation. The FOS observations have subsequently been used to develop techniques for correctly removing the instrumentally scattered, long-wavelength light. Additional FOS observations, using both its "blue" and "red" sides, of other stars previously observed with the GHRS are now scheduled. Repairing the GHRS is one of the items to be attempted during an STS maintenance visit to the HST, currently scheduled for launch on December 2, 1993. Barnet C. D.* Cunningham C. C. Caldwell J. J. HST Spectra of the Outer Planets II. Calibration and Other Problems Observations of Jupiter (May 1992-July 1993), Saturn (December 1992), Uranus (June 1992), and Neptune (August 1992) were made by the HST Faint Object Spectrograph (FOS) (1800-3300 Angstroms) and the Goddard High Resolution Spectrograph (GHRS) (1600-1850 Angstroms). The Jupiter and Saturn spectra sample the equatorial central meridian, equatorial limb, and the north pole (Saturn only). Spectra of Uranus and Neptune were only obtained at the center- of-disk. The FOS spectra were systematically processed to remove background grating scatter (see previous abstract) and to account properly for effects due to spherical aberration in the HST primary optics. Regions of overlap between FOS and GHRS spectra for Jupiter and Saturn indicate some absolute calibration problems. The calibration of planetary spectra is complicated by spherical aberration, since planetary targets overfill the spectrograph apertures. The standard data processing from the Space Telescope Science Institute applies a correction for aberration that assumes a point source is being observed. An additional systematic effect occurs when spectra from different gratings (FOS) or from different settings of the same grating (GHRS) are combined to produce an extended spectral range. The effect is consistent with a slight misalignment of the dispersion direction of the gratings with respect to the detector diode array, such that some light from the overfilled apertures is lost from diodes at the ends of the array. The effect is not seen in stellar spectra. Further calibration uncertainties are suggested by comparison with earlier spectra from the International Ultraviolet Explorer. Comparisons of the HST observations over the spectral range of 2100 Angstroms to 3300 Angstroms with earlier IUE measurements will be discussed. Subtle differences between the HST and IUE reflectivities exist. However, no significant changes in the reflectivity have occurred within the last decade with the exception of Saturn. This will be discussed in the context of the recent equatorial disturbance (Fall 1990). Caldwell J. J.* Cunningham C. C. Barnet C. D. HST Spectra of the Outer Planets III. Interpretation The HST spectra described above were ratioed both to HST spectra of the solar analog, 16 Cyg B, and to SUSIM/SpaceLab 2 solar data to derive albedo curves over the spectral range of 1600 Angstroms to 3300 Angstroms. In general, 16 Cyg B provided better cancellation of solar Fraunhofer features above 2000 Angstroms than did SUSIM, but SUSIM was better at shorter wavelengths. The reflectivity ratios are compared to vertically inhomogeneous models of the planetary atmospheres to determine abundances of minor and trace species therein. The models are sensitive to aerosol concentrations. All four giant planets show the influence of acetylene absorption. In particular, Uranus and Neptune have C2H2 abundances comparable to those previously determined from IUE observations. The HST spectra confirm that the abundances of C2H2 are very similar on Uranus and Neptune. Only Jupiter shows features due to NH3. The absence of NH3 on Saturn is in agreement with earlier TDla observations, and is a consequence of Saturn having lower tropospheric temperatures than Jupiter. No other species have been positively identified in the spectra above 1800 Angstroms, although some interesting possibilities are being considered. Attempts have been made to extend the spectra of Jupiter and Saturn to shorter wavelengths using a moderate resolution grating that is still operative on the GHRS. For Saturn, this was only marginally successful. For Jupiter, observations that have the potential to detect stratospheric CO have been made and will be discussed. Raman scattering within the solar Fraunhofer features at 2800 Angstroms (MgII) and 2850 Angstroms (MgI) are apparent in all spectra. Reuter D. C.* Deming D. Fast K. Thermal Wave Structure on Jupiter: Io Tidal Forcing As part of our continuing investigation of thermal wave structures on Jupiter we have obtained a series of 20-micrometer images of the planet using the cryogenically cooled grating spectrometer in the Goddard postdisperser in a stand-alone configuration. The observations were made from 3 to 7 May, 1993 using a 10 (spectral) x 50 (spatial) element BIB array at a spectral resolving power of about 1000 and a spatial resolution of 2 to 4 arcsec. Most of the observations were obtained in the equatorial region; however, occasional full- disk scans were performed. In addition to thermal wave structures of the type previously observed [e.g., 1] these data provide a sensitive probe of the thermal signature of tidal forcing due to Jupiter's moon Io. The strongest indicator of tidal motion is expected to be a wavenumber 2 mode that is locked to Io's orbital motion. Under the assumption that the deep atmosphere is neutrally buoyant only a weak response is expected to tidal forcing; however, it has recently been suggested [2,3] that even for small values of stratification the response is greatly increased. Thus measures of the amplitude of the tidal motion or sensitive upper limits to that amplitude, provide probes of the planetary structure. [1] Deming D. et al. (1989) Ap. J., 343, 456. [2] Ioannou P. J. and Lindzen R. S. (1993) Ap. J., 406, 252. [3] Ioannou P. J. and Lindzen R. S. (1993) Ap. J., 406, 266. . Bjoraker G. L.* Jennings D. Reuter D. McCabe G. Temperature Retrievals for Jupiter's South Pole Using H2 Quadrupole Emission at 17 Micrometers We observed Jupiter at 17 micrometers from the IRTF telescope on Mauna Kea using a new grating spectrometer developed at Goddard, known as CELESTE. We measured the 587.03 cm^-1S(1) quadrupole line of H2 in emission at high spectral resolution (Delta nu=0.08 cm^-1) for a region near Jupiter's South Pole (60 degrees South, 110 degrees System III longitude) on 7 March 1993, UT. At line center most of the emission originates from Jupiter's lower stratosphere between 10 and 60 mbars. The continuum produced by pressure- induced absorption by H2 sounds the tropopause at 100 mbar. These observations are useful because spatial variations in H2 emission from Jupiter are due solely to temperature changes rather than composition gradients. In addition, the H2 quadrupole line sounds a poorly understood part of the atmosphere. Voyager IRIS spectra of Jupiter sampled the 1 mbar region (using CH4) and 100- 200 mbar (using pressure-induced H2); however, temperature retrievals between 10 and 100 mbars are quite uncertain except at the spatial locations sampled by the radio occultation experiment. We retrieved a temperature profile intermediate between the Voyager 1 ingress and egress profiles. The ingress and egress temperatures at 30 mbar, which pertain to Jupiter's equator in 1979, were 135 and 115 K, respectively. Our south polar profile is consistent with -125 K at 30 mbar, using the Goorvitch & Chackerian S(1) line strength (Icarus 32, pp. 348-361, 1977). We have laboratory measurements of H2 absorption at high resolution and for long path lengths. Analysis is underway to improve estimates of the S(1) line strength. Beebe R.* Sada P. Conrath B. Observational Constraints for Great Red Spot Models Analysis of the highest-resolution Voyager imaging (ISS) and infrared (IRIS) data has been carried out, and improved navigational information has been utilized in a correlative study. These combined data indicate that the organized azimuthal flow is constrained in a sharply delineated collar 2300- 4500 km in width around the perimeter of the Great Red Spot (GRS). Lower- resolution Voyager observations indicate that the collar vorticity is replenished by the absorption of small westward translating eddies that are deflected around the spot. The central portion of the GRS, extending 12,000 km in longitude and 4500 km in latitude, contains smaller-scale structures with typical velocities of 5 m/sec that are suggestive of 2-D turbulence. Derived quantities from the IRIS data reveal a reduced H2 para fraction and enhanced ammonia gas and ammonia ice above the center of the spot. A temperature difference of approximately 10 K between the center of the GRS and its surroundings is indicated. These observations, along with the color ratio of the spot to its surroundings in groundbased observation at 889/7l5 nm, are consistent with a model of the GRS with a central region of elevated clouds surrounded by a constrained collar about the flanks of the raised center. If adiabatic heating is balanced by radiative cooling, the mean net upward velociy is approximately 5 x 10^-3 cm/sec. If the outward flow extends over a depth of one pressure scale height, then the divergent velocity is aproximately 1 cm/sec. The implications of the observations within the framework of current GRS models will be discussed. Hockey T.* Borucki W. Motion of the S-shaped Features Associated with Jovian Lightning Activity Studies of Voyager spacecraft images of Jupiter have revealed only one lightning storm that corresponds in latitude and longitude to a recognizable daytime feature: a pair of distinctive S-shaped clouds in the "disturbed region" of the planets northern hemisphere. If it is possible for a storm occurring at the water cloud level to affect the overlying ammonia cloud layer, then understanding these features may lend insight into the mechanism that controls the location of the lightning activity. We discuss the morpholoyg, dynamics, and development of the S-shaped feature. The data were culled from the collection of Voyager 2 images made before and at closest encounter. Images were selected that showed the features on each rotation of the planet while they were visible to the Voyager cameras. Discrete morphologies within the features are identified. Latitude and longitude measurements were made of each of these points for each image in which they appear. These measurements form the basis of a model of the motion of the features. The work of the first author is supported in part by a NASA JOVE Program fellowhsip. POSTERS Cochran W. D. Baines K. H. A High Resolution Spectral Atlas of Jupiter: 6000-7500 Angstroms We have obtained a high spectral resolution (R = 60000) map of selected regions of Jupiter in the wavelength region 6000-7500 Angstroms. Data were obtained using the Sandiford Cassegrain Echelle spectrograph on the McDonald Observatory 2.1m telescope on 1-3 May 1993 UT. Spatially resolved spectra of belts and zones were obtained along the central meridian. In addition, spectra were obtained of the South Equatorial Belt disturbance, the Great Red Spot, and dark spots in the North Equatorial Belt. Selected samples of the 160 spectra obtained will be shown. The data are of sufficient spectral resolution and signal/noise to allow isolation of individual H2, CH4, and NH3 rotational features for analysis. The distribution of the equivalent widths of several of these lines over the planet will be presented. These data will allow the pressure levels of the ammonia cloudtop near 600 mbars and the deepest tropospheric cloudtop near 3 bars to be obtained unambiguously for all of the re Borunov S. Dorofeeva V. Khodakovsky I. Drossart P. Lellouch E. Encrenaz Th. Phosphorus Compounds in the Atmosphere of Jupiter The only phophorus compound that has been detected in the jovian atmosphere from groundbased, airborne, and spacecraft observations is PH3. Abundance of PH3 is much larger than thermochemical equilibrium abundance at the levels of detection and it is possible to use these measurements for determination of the strength of convective mixing in the deep atmosphere of Jupiter. Here results of thermochemical equilibrium and chemical kinetic calculations are presented, including a sensitivity study to variations of elemental abundances of phophorus and oxygen. In contrast to what was found by Fegley and Prinn (1985, Ap.J., 299, 1067) in all the cases that are analyzed it is found that PH3 is mixed up from levels where the temperature is significantly lower than 1240 K. Clapp M. L. Miller R. E. FTIR Spectroscopy of Ammonia and Hydrazine Aerosols: Implications for Planetary Atmospheres We have recently obtained infrared extinction measurements for ammonia and hydrazine aerosols formed by homogeneous nucleation under conditions approximating the atmospheres of Jupiter and Saturn. The resulting extinction is very sensitive to particle size, phase (solid, liquid, etc.), and in some cases, shape. Indeed, comparison of Mie theory and Discrete Dipole Approximation calculations with observed spectra reveal a shape effect in the 9.4 micrometer region of the ammonia aerosol spectrum. This shape effect leads to an overall decrease in the peak absorption and may be responsible for the lack of observed condensed ammonia features in these atmospheres. We have also studied hydrazine and mixed ammonia/hydrazine aerosols using this technique. Both ammonia and hydrazine exhibit supercooled liquid phases at higher temperatures and are highly crystalline at lower temperatures when nucleated independently. When mixed aerosols are formed at lower temperatures, the spectra are perturbed, indicating the production of an amorphous solid aerosol. We have also observed the freezing of supercooled ammonia onto a hydrazine core as well as the coating of hydrazine particles by ammonia vapor. Representative spectra as well as their interpretation will be discussed. Huber L. F. Beebe R. F. Simon A. A. Danielson G. E. Limaye S. Zonal Wind Measurements Utilizing Hubble Space Telescope Wide Field/Planetary Camera Images Hubble Space Telescope Wide Field/Planetary Camera observations of the equatorial region of Jupiter in the Planetary Camera mode in broadband filters and in a narrow band filter centered on the deep methane absorption band at 889 nm have been deconvolved using both Lucy and Wiener algorithms. Pairs of images separated by 20 hours have been map projected and zonal winds have been derived for +20 to -30 degrees planetographic latitude. A discrepancy in the magnitude of the zonal winds near -7 degrees latitude between the measurements in the broadband F718M red filter and the narrow band FX89N methane filter is detected. The magnitude of this difference is approximately 30 +- 12 ms^-1. Comparison of the cloud morphology indicates that the clouds in the 718 nm image are strongly sheared near -7 degrees where the winds compare with those measured in low resolution Voyager images. In contrast the 889 nm image reveals chevron structures that extend +-2 degrees in latitude relative to the 718 nm shear zone. No discrepancy is seen at the corresponding northern latitude. Color vs. latitude across the equatorial zone indicate that the ammonia cloud deck is elevated and the two filters probe to the same depth at +7 degrees while the nonsimilar cloud pattern and color ratio near -7 degrees indicate that the cloud tracers in the two filters occur at different altitudes. This work is based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support was provided by NASA through grant number GO- 2560.01-87A from Space Telescope Science Institute. Carlson B. E. Lacis A. A. Rossow W. B. Thermal Structure, Cloud Structure, and Gas Composition of the Great Red Spot We have analyzed the Voyager IRIS observations of the Great Red Spot (GRS) in order to gain a better understanding of its thermal structure, cloud structure, and gas composition. As a starting point for this investigation, we have defined a GRS spectral ensemble and have compared the average GRS spectrum with the average spectra corresponding to the belt and zone spectral ensembles that we have previously analyzed (e.g., Carlson et al., 1992, Astrophys. J. 388, 648). These comparisons reveal large differences in the spectra in the region of the S(sub)l(O) hydrogen line (near 602 cm^-l). This region of the spectrum is sensitive to pressures near 0.15 bar. We can further refine the location of these differences by using the emission angle variability of the IRIS measurements to improve our height discrimination. Comparison of spectral ensembles at higher emission angles reveals smaller and structureless differences in the region of the S(sub)1(O) hydrogen line, suggesting that the differences are confined to lower altitudes (i.e., upper tropospheric). Using the radiative transfer model described in Carlson et al. (1993, JGR, 98, 5251) we have analyzed the GRS spectra. Our thermal inversion procedure is similar to the standard inversion procedures described in Conrath et al. (1970); however, we have replaced weighting functions with normalized contribution functions, which more accurately depict the peak emission level. Consistent with previous investigations, we find that the upper troposphere is colder in the GRS. Similarly, consistent with the results of Griffith et al. (1992, Icarus, 98, 82) we find that the abundance of NH3 above the 0.3-bar level is depleted relative tothat found in the STrZ, while the PH3 abundance is comparable. In contrast with previous results, we find some spectral indications for a slight enhancement of NH3 in the 1-2 bar region relative to that in the surrounding STrZ. The dynamical, microphysical, and chemical implications of these results are discussed. Drossart P. Lecacheux J. Measurement of the Differential Rotation of Jupiter at Several Wavelengths in the Visible Images of Jupiter were acquired in the visible through interferential filters, at 8300 Angstroms(continuum), 8900 Angstroms(strong CH4 band) and 7250 A(weak CH4 band) from the 1 m reflector at Pic-du-Midi observatory. Mosaics within cylindrical projection, covering about 270 degrees of longitude, are obtained from images recorded during the nights of 1993 February 18 and 20, corresponding to a 50 hours time lag. The comparison between the two projections allows us to measure the horizontal wind velocities to an accuracy of about 10 m/s, between 30 degrees S and 30 degrees N latitudes. Wind velocities are obtained from several methods, following Limaye (Icarus, 1986), in particular by correlations between the two projections. At first order, the wind velocities are very similar to the Voyager wind profile, despite the very different aspect of the SEB at time of observations. Comparing the observations at two different wavelengths (in particular 8900 and 8300 Angstroms) shows no significant differences, despite the different aspect of the Jupiter images at these wavelengths. A comparison of images at 8900 Angstroms and 8300 Angstroms after processing with a contour enhancement numerical filter shows also that, despite the very different contrasts at both wavelengths, the contours of the cloud structures are nevertheless very similar. We conclude that the features responsible of the correlations in the wind profiles observed in the visible are the same, and that the spatial distribution of the high altitude clouds, predominent in the images at 8900 Angstroms, does not alter the appearance of the underlying cloud structure. Guillot T. Morel P. Gautier D. Chabrier G. Non-Adiabatic Models of Jupiter and Saturn Contrary to the usual assumption that the fluid envelope of the giant planets are fully convective, new calculations have shown that the radiative opacity in the deep atmosphere of Jupiter, Saturn, and Uranus (around the 1000-3000 K temperature levels), are small enough to permit the transfer of internal energy by radiation rather than by convection. We present here a numerical code developed to study the internal structure of Jupiter and Saturn, in which the Schwarzschild criterion determines whether the temperature gradient is radiative or adiabatic. The four differential equations of internal structure are solved by using an implicit collocation method based on a B-spline basis. The relative abundances of hydrogen and helium as well as the mass and the composition of the central core of rocks and ices are adjusted in order to reproduce the radius of the planet and the observed moments of the external gravitational field. The results are compared to current adiabatic models. We discuss the consequences of the occurrence of a radiative zone in the envelope of Jupiter and Saturn on their internal structure and their evolution. Conrath B. J. Gierasch P. J. Para Hydrogen Remote Sensing in the Atmospheres of the Outer Planets Knowledge of the para hydrogen fraction f(sub)p on the outer planets has important implications for atmospheric dynamics and energetics. In the present study, the problem of the retrieval of vertical structure of f(sub)p from Voyager IRIS data is addressed using direct inversion techniques. Contribution functions appropriate to the retrieval of the vertical structure of f(sub)p on Jupiter and Neptune have been calculated and are found to have half-widths of about 1.3 pressure scale heights. If the temperature profile and opacity sources are known a priori, then f(sub)p can be obtained between approximately 200 and 700 mbar on Jupiter and between 100 and 800 mbar on Neptune with vertical resolutions approaching 0.75 pressure scale height. However, simultaneous retrieval of temperature and cloud and gaseous opacities, along with f(sub)p, requires "redundant" spectral regions that sense the same atmospheric layer but possess differing sensitivities to the various parameters. This condition is poorly met at pressures greater than about 350 mbar on Jupiter and throughout most of the Neptunian upper troposphere, resulting in highly ill-posed retrieval problems with physically plausible but non-unique solutions. Between approximately 200 and 350 mbar on Jupiter, limited vertical structure information on f(sub)p can be unambiguously obtained, and results for this atmospheric region are presented. In some locations, such as the North Tropical Zone, correlation between large upper level values of f(sub)p and large 45-micrometer cloud optical depths is found, while in other areas such as the Great Red Spot, a strong anti- correlation between these parameters is observed. The dynamical implications of the results are discussed. Dowling T. E. An Explicit Planetary Isentropic-Coordinate Atmospheric Model for Jupiter, Saturn, Uranus, and Neptune We describe a new global, multilayer atmospheric model for the giant planets, called the EPIC model, and present applications to Jupiter, Saturn, Uranus, and Neptune that illustrate the model's strengths and weaknesses. The model uses finite differencing and an explicit timestep in order to run efficiently on massively parallel processors. We use an nCUBE 2 with 512 processors. The timestep is the 3rd Order AdamsBashforth timestep, which is appropriate for both the advective and diffusive terms, does not require restarting, and is more accurate than the leap-frog timestep. The horizontal differencing follows the Arakawa and Lamb scheme, which conserves total energy and total enstrophy. The vertical differencing follows the Hsu and Arakawa scheme, which uses potential temperature, a function of entropy and hence a conserved quantity for adiabatic motions, as the vertical coordinate. The result is one fewer prognostic equation, since the thermodynamic equation is incorporated into the coordinate system, and the elimination of vertical velocities except for diabatic motions, which improves accuracy. Giant planets benefit from the advantages of isentropic coordinates without suffering from the major disadvantage that is encountered with terrestrial planets, namely the intersection of the coordinate surfaces with the solid lower boundary. Instead, the convectively adjusted fluid interior of a giant planet makes the lower boundary a coordinate surface. Global models of Jupiter's atmosphere require approximately 10 x 10 more grid points than comparable models of Earth's atmosphere, because on both planets the deformation radius is 1000 km, but Jupiter's radius is 10 times bigger than Earth's. We typically run with 512 x 256 horizontal grid points and from 4 to 10 vertical layers. The model incorporates Voyager vertical temperature soundings and zonalwind profiles, and employs Newtonian cooling with realistic radiative cooling times. It simulates the long-term dynamical response of giantplanet atmospheres to events like comet impacts, and provides numerical weather prediction. It also provides a framework for testing the dynamical importance of proposed latent-heat sources, including ortho-para conversion and cumulus heating. The primary goal is to model the formation of zonal-wind profiles and long-lived vortices in a realistic manner. Lederer S. M. Marley M. S. Albedo Inhomogeneities and Jovian Seismology Mosser et al. (A & A (1993) 267, 604) have reported the detection of p-mode oscillations of Jupiter from Fourier Transform Spectrometer observations made at the CFHT. Detected modes had periods ranging from 8 to 17 minutes. However, their observations are also sensitive to flux variations produced by spatially periodic albedo features rotating with the planet. Such features, if present, could produce a spurious seismological signal. To investigate the magnitude of longitudinally periodic albedo features in wavelengths corresponding to methane absorption, we studied images of Jupiter taken through an 0.889-micrometer methane absorption filter at the Tortugas Mountain Observatory in Las Cruces, NM. Images from three consecutive nights within the 1991 observing run of Mosser et al. were analyzed for periodic albedo features. Average dN values within a circular region (analogous to the aperture employed by Mosser et al.) 15 degrees in diameter and centered on 7.5 degrees N latitude were calculated as a function of longitude and converted to the time of the meridian crossing, assuming solid-body rotation of Jupiter. Based on a periodogram analysis of this dataset, we see no albedo features that could produce a spurious seismological signal. We do, however, see a possible periodicity in one set of data corresponding to a 60-minute period. This may be related to the visible plume structures. Periodic albedo features with amplitudes >~1.5% would be detected in our analysis. To more fully investigate periodic jovian albedo inhomogeneities, we are now employing a dataset better suited for a time series analysis from the 1993 Jupiter opposition. Limits on the magnitude of albedo features that may hinder methane-band seismological observations of Jupiter will be presented. Schinder P. J. Flasar F. M. A Reexamination of the Radio Occultation Technique for Determining the Structure of Planetary Atmospheres We have performed a major reexamination of the radio occultation technique for determining the structure of planetary atmospheres. We derive from relativistic first principles the equations describing the propagation of the radio signal from the spacecraft to the Earth, both inside and outside the target atmosphere. In particular, we use the relativistically covariant eikonal equation (to order (v/c) in a frame comoving with a chosen point in the atmosphere) to determine the path of the ray through the differentially moving atmosphere. The atmosphere is assumed to be axisymmetric but not necessarily spherical. We examine the propagation of systematic errors in the retrieval of vertical profiles of refractivity, pressure, and temperature. Such systematic errors include uncertainties in the geopotential and isopycnal surfaces arising from uncertainties in the zonal winds, in the gravitational field, and in the position of the rotational pole. We focus in particular on the atmospheres of Titan, Saturn, and Neptune. We will discuss potential errors in the shape of the retrieved T-P profiles, which for the latter two can affect the atmospheric helium abundance determination obtained from the combined analysis of thermal infrared and radio occultation data. Monday, October 18, 1993 MARS SURFACE I 8:30 - 10:00 AM North Ballroom Chair(s): J. F. Bell III G. A. Swayze Lee S. W.* Clancy R. T. James P. B. Monitoring Regional Albedo Features on Mars: Results from the Hubble Space Telescope The Pioneer Venus Ultraviolet Spectrometer obtained extensive series of images of Venus in the 4th Positive system of carbon monoxide. The (0,1) band at 160 nm is excited by ionospheric processes and by resonance fluorescence of sunlight, while the (14,4) and (14,3) bands at 139 nm and 136 nm are produced by an accidental resonance between the (14,0) band and solar Lyman-alpha (the 136-nm feature is also contaminated by the photoelectron-excited 3P-5S multiplet of atomic oxygen). The 160-nm feature is emitted near 150 km, whereas the 139-nm and 136-nm features are emitted two or three scale heights lower. Thus the morphology of the images depends on the horizontal distribution of carbon monoxide in the lower and middle thermosphere. An earlier study (Alexander et al., 1993) of images in the 3P-3S resonance triplet of atomic oxygen at 130 nm showed that in the upper thermosphere, oxygen at high latitudes is more abundant in the afternoon than in the morning, but that on the equator this effect is less pronounced. Their interpretation invoked the dissipation of gravity waves generated in the middle atmosphere, a mechanism proposed by Alexander (1992) to explain the thermospheric superrotation. A preliminary inspection of the carbon monoxide images at all three wavelengths shows similar trends. Since the variations of the densities of CO and O across the sunlit disk are dynamically controlled, we will examine the images for evidence of changes in the dynamical regime with position and altitude. Referemces: Alexander M. J. (1992) Geophys. Res. Lett., 19, 2207. Alexander M. J. et al. (1993) JGR, 98, 10849. Singer R. B.* Miller J. S. Merenyi E. Evidence for a Global Compositional Dichotomy on Mars The north-south morphologic and age dichotomy is a profound aspect of Mars geology. Yet there has been limited evidence for compositional variations that correlate with this geomorphic division. This has been interpreted by many to indicate that current surface materials on Mars are globally distributed, largely homogenized, and generally unrelated to the underlying crust. Recent evidence, however, has shown that this is not the case. There is significant regional and local compositional variation around the planet (e.g. Bell et al. JGR 95 1990; Singer et al. Bull. AAS 22 1990; Singer and Miller LPI 92?2 1991; Mustard et al. JGR 98 1993; Murchie et al. LPSC XXIV 1993; Geissler et al. Icarus in press 1993; Merenyi et al., Icarus submitted, 1993). The manifestations of these variations in remotely sensed data are often subtle. We conclude, however, that a global compositional pattern is emerging. This result is based on the synthesis of various recent results by us and others, with emphasis on a series of visible and near-IR (0.44-1.02 micrometers) spectral images obtained by us during the 1988 apparition (Singer et al. LPSC XXI 1990). In summary, both high and low albedo materials currently exposed in the ancient highlands show more bulk crystalline hematite, implying weathering or other alteration that proceeded further toward equilibrium than in most of the lowlands. This may be a consequence of exposure age, but might also be related to differences in geologic processes and/or climate. Northern plains low-albedo regions, such as Acidalia Planitia and Oxia Palus are also different in their mafic composition than observed low-albedo regions on older terrains. Near-IR Fe^2+ pyroxene bands are observed centered between 0.92 and 0.99 micrometers for highland exposures, while Acidalia, a large rocky plain in the northern lowlands, does not show a band minimum shortward of 1 micrometer (where our data end). Various interpretations are possible for Acidalia, but we cannot yet choose among these with available data. What is clear, however, is that there is now evidence for compositional differences that correlate with the long-known global morphologic dichotomy on Mars. We can also conclude that (a) the surface of Mars has not been completely resurfaced and homogenized by aeolian action; (b) not all heavily weathered deposits are the same as each other or the global dust. Arabia, in particular, appears compositionally distinct from other large northern bright regions; (c) the composition of at least some of the basaltic lavas in the northern plains differs markedly from those to the south. Bell J. F. III* Pollack J. B. Crisp D. Geballe T. R. Cruikshank D. P. High Resolution K-Band Spectroscopy of Mars During 1990 and 1993 High spectral resolution telescopic observations of Mars were obtained during the 1990 and 1993 oppositions from Mauna Kea Observatory. During 1990, the IRTF CGAS spectrometer was used to observe ten 500-km regions at a spectral resolution of 1200-1500 from 2.10 to 2.47 micrometers [1]. These data were obtained simultaneously with near-IR imaging spectroscopic measurements discussed elsewhere [2]. During 1993, the UKIRT CGS4 spectrometer was used to obtain multi-pixel slit images of Mars at a spectral resolution of 350 from 2.04 to 2.46 micrometers. The 1993 data range from 500-1000 km spatial resolution and encompass about 70 spectra in total. Flux calibration (to within +-20%) of both of these datasets has been performed using IR standard stars. Many interesting absorption features can be seen in these data sets. Most prominent are the strong CO2 R-branch band near 2.05 micrometers and a weaker CO2 band near 2.15 micrometers. Also, a broad but weak absorption in the 2.3 to 2.4 micrometer region can be seen and is attributed to atmospheric CO. The presence of these features in our flux calibrated data will allow us to accurately model the relative contributions of the martian atmosphere and surface. As well, the presence of both strong and weak atmospheric bands may allow us to quantitatively derive the dust opacity during both oppositions [2,3]. Less prominent absorption bands are also seen in the data, and these features are tentatively assigned to mineralogic absorptions either on the surface or in the airborne dust. These bands are indicated in Table 1, along with the so- called "scapolite" bands observed by Clark et al. during the 1988 opposition [4]. There is enough overlap among the datasets from different oppositions to indicate that the features observed just outside of the martian atmospheric CO region are probably real and are probably due to martian bisulfate- and/or bicarbonate-bearing minerals, as proposed in [4]. Features observed inside the CO region require additional modeling to adequately separate the gaseous vs. mineralogic components [i.e., 5]. There is evidence in a few of the spectra for weak features near 2.20 and 2.25 micrometers, consistent with previous interpretations of weak phyllosilicate and/or bisulfate/bicarbonate absorptions in these regions [2,4,6]. More specific mineralogic inferences from all of these data will be possible only after more detailed modeling and understanding (not "removal") of Mars atmosphenc absolptions. Table 1, which appears here in the hard copy, shows Mars K-band absorption features detected in 1988, 1990, and 1993. Referernces: [1] Bell J. F. III and Crisp D. (1992) MSA7T Kona Workshop, LPI Contribution 787, 1-3. [2] Bell J. F. III and Crisp D. (1993) Icarus, in press. [3] Crisp D. and Bell J. F. III (1990) LPS XXIV, 343-344.[4] Clark R. N. et al., JGR, 95, 14463-14480. [5] Encrenaz T. and Lellouch E. (1990) JGR, 95, 14589-14593. [6] Murchie S. et al., (1993) Icarus, in press. Merenyi E.* Edgett K. S. Singer R. B. A New Type of Weathered, Immobile Soil Unit on Mars In the past few years, extensive VIS-NIR spectral analysis work has been done to investigate the compositional variability of the martian soils. Recent research by Pinet and Chevrel (JGR, 95, 1990) from high-spatial-resolution CCD imagery at selected wavelengths, by Mustard et al. (JGR, 98, 1993), Murchie et al. (LPSC XXIV), from high-spatial- and spectral-resolution Phobos ISM data, by Singer et al. (LPSC XXI, 1990), Singer and Miller (MSATT, 1991), Miller and Singer (LPSC XXIV, 1993), Bell et al. (JGR, 95, 1990; LPSC XXI, 1990), Merenyi et al. (LPSC XXIII 1992; Icarus, submitted) from high-spectral-resolution telescope imaging has shown a considerable variation of surface materials among bright regions as well as across dark albedo units. It has generally been observed and argued that dark regions exhibit greater variability than bright regions. Dark region spectra show evidence for mafic mineralogy, bright units are more altered. There are also examples of areas where the spectral properties strongly correlate with the physical characteristics of the soil. Here we follow up on previous work regarding a medium albedo unit, Deucalionis Regio, centered at (245 degrees W, 15 degrees S), which seems to be covered with a previously unreported type of soil. It is distinguished from the surrounding classic regions of Arabia, Sinus Meridiani, Oxia, and Acidalia in the 0.4-1.0-micrometer range. The spectra suggest that this area contains more pyroxene than Arabia and less than Sinus Meridiani. The crystalline hematite content appears greater than either in Arabia or Meridiani. Yet, Deucalionis cannot be modeled as a simple mixture of the nearby dark and bright units. Its physical characteristics, as derived from Viking IRTM data, indicate an immobile soil, maybe cemented by salts. We expect to test the mineralogical distinction with Mars Observer Thermal Emission Spectrometer in the future. The geographic extent of the spectral and physical anomalies show strong spatial correlation, which suggests a possible genetic tie. Very similar spectral and physical properties seem to be spatially correlated over another large area, Noachis. The anomaly of Deucalionis Regio was brought to our attention by the analysis of a telescopic spectral image. Recent work on another, similar image cube confirms the previous results. Geissler P. E.* Singer R. B. Search for Small Scale Ferric Oxide Mineral Deposits on Mars In preparation for the arrival of Mars Observer, we have begun a program of systematic examination of the Viking Orbiter multispectral imaging data for evidence of color anomalies indicative of ferric oxide mineralization. The motivation for this study is the interpretation of color anomalies observed in the central Valles Marineris to be due to local concentrations of hematite (alphaFe2O3) [1-3]. The mineralization occurs in two small depressions on the margins of Hesperian-aged layered deposits in West Candor Chasma. The distinct coloration is caused by the absorption edge of Fe3+ in hematite at 0.53 micrometers, which coincides with the Viking green filter center wavelength [4,5]. On Earth, concentrations of iron oxides similar to the mineralized zone in West Candor Chasma are formed through a variety of geologic processes, many of which may have occurred on Mars as well. Hematite is a major component of many gossans (supergene ore deposits) produced by weathering of near-surface orebodies. Volcanism also frequently results in local concentrations of hematite, as oxidation rinds on basaltic rocks and cinders or as hematitic soils produced by a combination of water and heat in regions of hydrothermal alteration. Ferruginous sandstones and latentes are cemented by mixtures of poorly crystalline hematite, goethite (alphaFeOOH) and hydrated iron oxides resulting from oxidation and precipitation of dissolved iron by surface- or ground-water. Identification of OH- or H2O-bearing ferric oxides inferred from Vilking 3-color observations and data expected from Mars Observer would be especially significant as new evidence for the past existence of water on Mars. Geologic features small enough to have escaped detection by telescopic scrutiny --like the 20-km-long depressions in West Candor Chasma--may exist in many parts of Mars and hold important clues to the composition and chemical environment of its surface. References: [1] Geissler and Singer (1992) LPI Tech. Rept. 92-04, 12-14. [2] Singer et al. (1992) Bull. A.A.S., 24, 977. [3] Komatsu et al. (1993) JGR, 98, 1110511121. [4] Singer (1982) JGR, 87, 10159-10168. [5] Sherman et al. (1982) JGR, 87, 10169-10180. McLarty J. E.* Singer R. B. Are Antarctic Dry-Valley Altered Volcanics Spectrally Consistent with Mars? Weathered or otherwise altered volcanic materials from the dry valleys of Antarctica have often been considered as reasonable analogs to martian rocks and soils, based on similarities in temperature and humidity (Gibson, JGR, 28 1983; Berkley, PLPS, 12B, 1981). To our knowledge, however, little spectroscopic work has been done to compare these terrestrial materials with known spectral properties of the surface of Mars. For this reason we have undertaken a spectral study of Antarctic samples of a particular core previously analyzed by Berkley and Drake (Icarus, 45, 1981). These samples were recovered by the Dry Valley Drilling Program (DVDP) on Ross Island, Antarctica. They are olivine-bearing alkalic basaltic tuffs, a composition predicted by some for martian lavas. They are also of interest because the climate on Ross Island parallels permafrost terrains on Mars. The samples are from DVDP hole number 2 unit 11, and are numbered 25 through 33 (omitting 27), with depth increasing with sample number. Spectral reflectance (relative to halon) from 0.35 to l.lO micrometers was measured for powdered samples of these units using the new laboratory spectrometer at the Planetary Image Research Lab (PIRL). The sample spectra show a range in both Fe3+ abundance and mineralogy. The samples at the top of the core (26 and 27) show clear evidence of bulk crystalline hematite, with diagnostic bands at 530 and 860 nm. Spectral evidence for crystalline hematite decreases further down the core. Most (if not all) of these samples contain poorly crystalline or very finely crystalline (nanophase) ferric oxide, as demonstrated by steep but relatively featureless spectral slopes from the near-UV to the near-IR. The steepness of this slope increases toward the bottom of the core, indicating a somewhat higher overall Fe3+ content than upper units (but less crystalline hematite). This sequence indicates a range of temperature (and/or humidity conditions) under which alteration occurred, with the most mature alteration at the top of the sequence. Samples from units 28 and 29 are very similar spectrally to telescopic spectra of high-albedo regions on Mars, and to Hawaiian palagonitic Mars analogs. None of these Antarctic samples shows evidence of hydroxylated ferric oxides, implying alteration involving relatively little water. This is consistent with the findings of Berkley and Drake (1981) that clay minerals are not abundant in these samples, and also consistent with the apparent low abundance of crystalline clay on the surface of Mars. Moersch J.* Nicholson P. Squyres S. Van Cleve J. Lee P. Hayward T. Houck J. Miles J. Thermal Infrared Observations of Mars During the 1993 Opposition Using the newly-developed SpectroCam-10 instrument on the Hale 200" telescope at Palomar Observatory, we obtained images and spectra of Mars in the thermal infrared during the 1993 opposition. Images were taken using a set of six wide band filters centered at 7.9, 8.8, 9.8, 10.3, 11.7, and 12.5 micrometers at three times over the course of the night of 11 January. Spatially resolved slit spectra with a wavelength resolution of Lambda/Delta Lambda = 200 between 7.5 and 13.5 micrometers were also obtained covering the entire disk. Seeing on the night of the observations in this spectral region was about 0.75", corresponding to a resolution of 350 km on the surface of Mars at the sub- Earth point. To analyze the data, we have developed a thermal model that uses finite difference techniques to solve the time-dependent one-dimensional heat diffusion equation for surface temperatures and then blackbody radiances over the entire planet on a 2 x 2 degree grid. The inputs to the model are thermal inertia, albedo, and geometry of insolation at each grid point. Running the model with a spatially uniform thermal inertia of 6.5 x 10^-3 cal cm^-2 s^-1/2 K^-l and and an average albedo of 0.21, we produced synthetic "average" Mars images. The actual images were then divided by the "average" images to remove most of the center-to-limb brightness gradient and reveal more subtle surface features. Many well-known features are readily apparent in such ratioed images, including Syrtis Major, Hellas, Sinus Meridiani, Argyre, and Acidalia. Using the Viking-derived thermal inertias and albedos as inputs to the model, a second set of spatially inhomogeneous synthetic Mars images was created. When the observed images are divided by these inhomogeneous images, the results are mostly flat, but a few significant features remain. In at least one case, we have identified the cause of one of these features to be a change in the albedo of the surface since Viking. However, other features may be related to absorption in the martian atmosphere, or to non-unit emissivity of materials on the planet's surface. Because of our high spectral and spatial resolution, it may be possible to interpret any emissivity features that may be found in terms of surface geochemistry. We will discuss these possibilities using Planck curve normalized color ratio fits as well as analysis of the spectral data. Clark R. N.* Christensen P. Barbera P. Swayze G. Moore S. Betts D. Comparison of Mid-Infrared Emission Spectra with Spectra Computed from Reflectance: Verification of Kirkoff's Law Thirty-four mineral samples (phyllosilicates, micas, amphiboles, feldspars, pyroxenes, pyroxenoids, and olivines), have been measured in emittance and reflectance to test Kirkoff's Law: emittance = 1 - reflectance. Samples were measured in emission at the Arizona State U, Mars Observer Thermal Emission Spectrometer facility. Emission measurements, from 5 to 25 micrometers, were measured on cooled and heated samples in a dry nitrogen atmosphere. Black body reference and liquid nitrogen (zero level) background were also measured. The emissivity spectrum was then computed by fitting and ratioing a black body to the calibrated maximum radiance measured from the sample. The reflectance of the same sample set was measured from 1.8 to 25 micrometers in biconical reflectance at the USGS Denver Spectroscopy Lab. Ideally, the measurement would be done with an integrating sphere, but a sphere would limit the possible wavelength coverage. Our biconical measurement integrates about 50% of the hemisphere and should be a close approximation to that from a sphere. The samples were also measured on a near infrared spectrometer from 2.4 to 2.5 micrometers with an integrating sphere as a check on the reflectance levels from the midinfrared instrument. Emittance was calculated using Kirkoff's law. Comparison of the emittance spectra show good agreement within the sample set limitation. There are differences observed, but they can be explained by sample variability. The same sample was measured, removed from the sample cup, reloaded into the cup and measured again several times. In general, the differences observed by repeated measurements are greater than the disagreement between measured emittance and emittance calculated from reflectance. No artifacts similar to those reported by others are observed with Kirkoff's Law. Swayze G. A.* Clark R. N. King T. V. V. Gallagher A. Calvin W. M. The U.S. Geological Survey, Digital Spectral Library: Version 1: 0.2 to 3.0 Micrometers We have developed a digital reflectance spectral library, library management software, and spectral analysis software. The library includes 500 spectra of 447 samples (some samples include a grain size series) measured from approximately 0.2 to 3.0 micrometers. The spectral resolution (FWHM) of the reflectance data is <=4 nm in the visible (0.2-0.8 micrometers) and <=10 nm (0.8-2.35 micrometers) in the NIR. All spectra were corrected to absolute reflectance using an NBS Halon standard. Library software enables users to search on parameters (e.g., chemical formulae, chemical analyses, purity of samples, mineral groups, etc.) as well as spectral features. Minerals from sulfide, oxide, hydroxide, halide, carbonate, nitrate, borate, phosphate, and silicate groups are represented. X-ray and chemical analyses are tabulated for many of the entries, and all samples have been evaluated for spectral purity. The library also contains end and intermediate members for the olivine, garnet, scapolite, montmorillonite, muscovite, jarosite, and alunite solid-solution series. We have included representative spectra of H20 ice, kerogen, ammonium-bearing minerals, rare-earth oxides, desert varnish coatings, kaolinite crystallinity series, kaolinite/smectite series, zeolite series, and an extensive evaporite series. Because of the importance of vegetation to terrestrial studies we have include 17 spectra of tree leaves, bushes, and grasses. The library and software will be available as U.S.G.S. Open File reports. Software will allow PC users to convert the binary data to ASCII files. Additionally, an ftp binary file will be on line at the U.S.G.S. in Denver. Users may build customized libraries for their own instruments using the library software. We are currently extending spectral coverage out to 150 micrometers and will make this library available on CD-ROM. POSTERS Kerchner V. C. An Autonomous Software Agent for Feature Extraction from Mars Images Apple's new Digital Graduate Student(TM) (DGS) system for the Macintosh(R) is a modular construction set for building distributed scientific applications. At first glance, DGS resembles other component-based analysis systems such as IRIS Explorer(TM) or AVS(TM). However, DGS extends this metaphor to include a rich component user interface, the use of concurrently running applications as components, arbitrary levels of component hierarchy, distributed and remote processing, and network interfaces to Unix(R), VMS(R), and DOS(R). Many data import/export types are supported, such as HDF and FITS. DGS applications may include "hot links" to other scientific applications such as Mathematica(TM) and Spyglass(TM). DGS is currently under development, and is expected to be released in May of 1994. As a test case for DGS, an autonomous agent capable of recognizing and counting arbitrary features (e.g., craters) in spacecraft photographs was constructed. Neural net technology was used to construct a programmable scanner that could be trained to recognize arbitrary bitmaps in images. Training sets of artificial, random craters with adjustable parameters were input to the net until it was capable of recognizing features in simulated images with acceptable accuracy. A complete autonomous agent capable of reading multiple images, extracting features, and compiling coordinates and statistics in background mode was then constructed and used to locate actual features in Viking and Mariner images of Mars. This agent can be trained to recognize arbitrary features in any image, and can be used "as is" or modified as desired. Hansen G. B. The Spectral Absorption of CO2 Ice in the Thermal Infrared Accurate absorption coefficients of CO2 ice in the thermal infrared are needed for enhancing the analysis of Mars Observer measurements of the surface deposits and clouds in the martian polar regions by the TES and PMIRR instruments. The spectral absorption of CO2 ice has been previously measured in the infrared wavelengths 2.5-26 micrometers by Ditteon and Kieffer (JGR, 84, 8294, 1979), but only two strong absorptions at 90 and 150 micrometers have been measured at wavelengths longer than 26 micrometers (Kuan, Ph.D. Thesis, U. Southern Cal., 1969). I am measuring transmission through long (2-100 mm) crystals of CO2 in the wavelength region 20 to 50 micrometers, using a Fourier Transform Spectrometer. My previous work (Hansen, Bull. A.A.S., 24, 978, 1992) revealed a large amount of spectral detail and many weak, narrow lines in the "transparent" wavelength regions of the near infrared. To resolve similar structure in the thermal infrared, I am using a maximum spectral resolution of 0.2 wavenumbers. I am able to measure absorption only in spectral regions where CO2 ice is relatively transparent (absorption coefficient in the range 0.001-30 cm^-l). These regions are significant in the study of radiative transfer in dense scattering media, such as the permanent and seasonal polar deposits on Mars, in that low absorption implies low emissivity (Warren, et al., JGR, 95, 14717, 1990). Head J. N. Dark Materials in the Cerberus Region, Mars: Local Sources? Previously, we have successfully modeled one scene within the Cerberus region as a variable areal mixture of Bright and Dark materials (Head et al. 1992 LPSC 23 509-510). The Dark material was interpreted largely as a sand sheet overlying the bright plains material, consistent with the most recent geologic maps (Greeley and Guest 1987, Geologic Map of the Eastern Equatorial Region of Mars). In principle, the Dark material could be either locally or externally derived-many dark streaks emanate from scarps and crater splotches, indicating the former. However, it was unclear whether these sources represented currently eroding, primary bedrock (cf Veverka et al. 1976 Icarus 27 241-253, Geissler et al. 1990, JGR, 95, 14399-14413), or merely the latest episode of transport of externally derived aelion material (cf. Lee et al. 1982, JGR, 87, 10025-10041). We now have evidence that the local sources may represent outcrops of prirnary bedrock. The best-studied example is in the splotch crater Mj (12N, 201W), which has been examined using Viking apoasis multispectral images from orbits 506 and 609. A well-defined, roughly rectangular area covering ~80km^2 has the following properties: it is distinctly darker in the violet filter images than the adjacent Dark materials; it has the lowest Red/Violet ratio of any unit in the scene (RIV = 1.93 for i = 16, e = 14, phase = 29); it requires a relatively much higher Shade fraction in linear mixture models constructed from imaging from both orbits, and its photometric response is distinguishable from that of adjacent material. Three much smaller (~1km^2) similar areas occur within large (>20km) crater splotches in the 609 series images, although the small size precludes any judgements about photometric response. It is possible that these effects are due to induration. However, the scarps (Cerberus Rupes), which are morphologically not depositional, exhibit characteristics similar to the "smaller" areas (including the difficulty in determining photometric response). We have identified several large crater splotches with darker (violet filter) interior areas for which we have repeat coverage. These will be examined to determine if they also have these linear mixing model and photometric properties. Klassen D. R. Howell R. R. Bell J. F. III Spectral Imaging of Mars in the 2-micron Region We obtained near infrared images of Mars on 26-28 January 1993 and 12-13 February 1993 using a near-infrared camera at the Wyoming Infrared Observatory. These images cover most of the 2.0- to 2.5-micrometer range, with a resolution of approximately 1.3%. The images from some nights achieve subarcsecond spatial resolution, corresponding to better than 400 km. Approximately 50% of the planet was imaged, over the longitude range 170-270 degrees and 50-135 degrees. The 2-micrometer region is known to contain features primarily due to carbon dioxide gas and ice, as well as water ice and carbon monoxide. Our observing program was the first to use this particular camera with its circular- variable-filter, and this configuration introduced some instrumental problems that we are currently trying to calibrate and correct. However, the preliminary reduction of the images show considerable detail. The classical albedo features and the polar cap are very obvious, showing high contrast. The longitudes observed complement those obtained earlier by Bell and Crisp 1993 (Icarus, in press). We hope to use these images to extend that earlier study of the surface and atmosphere. Monday, October 18, 1993 JUPITER II 10:30 - 12:00 NOON South Ballroom Chair(s): C. D. Barnet G. L. Bjoraker Orton G.* Friedson J. Yanamandra-Fisher P. Baines K. Kaminski C. Momary T. Infrared Characterization of the Early Stages of the 1993 SEB Revival: Temperature Structure and Vertical Cloud Distribution Images of Jupiter were made between 1.6 and 18 micrometers from the NASA/IRTF to map the spatial distribution and time dependence of temperatures at 20 and 250 mbar and the vertical distribution and thickness of clouds between 0.01 and 5 bars. In the current apparition, observations were obtained in 1992 October and are scheduled through 1993 August. Observations on April 24-27 supported the World Astronomy Day #2 (Jovian Atmospheric Reference) campaign and characterized the early stages of the violent South Equatorial Belt Disturbance and the SEB revival, which began April 7. The 250-mbar temperature of the initial outbreak location was about 0.5 K lower than its surroundings (at 4500 km resolution), as was a broader region some 15 degrees eastward. This upwelling had transported particles detectable near 2 micrometers about the 100-mbar level, but not up to the 10-mbar level. Both regions had cloud reflectivity and 5-micrometer radiance indistinguishable from the surrounding zone-like SEB. To the immediate west of each, however, were regions of darker cloud albedo and brighter 5-micrometer radiance. This coincidence implies that areas immediately west of the upwelling material were reduced of particles with bright albedos and providing significant 5-micrometer opacity, most probably at the 600-mbar level. It is the reduction of this cloud material that was one key to "reviving" the SEB to its more usual appearance in the ensuing months. Yanamandra-Fisher P. A.* Hoffmann W. Friedson A. J. Orton G. S. Duetch L. K. Hora J. Fazio G. G. Shivanandan K. 1993 SEB Revival: Expansion Phase Post-SEB revival images of Jupiter were recorded at 4.6, 8.56, and 13.0 micrometers at Steward Observatory, Using the Mid-Infrared Array Camera (MIRAC) on 3-6 June 1993 to map the longitudinal regeneration of the South Equatorial Belt (SEB) at the 250- and 600-mbar and as deep as 5 bar levels. These observations were recorded almost 2 months after the initial violent and dramatic onset of the SEB Revival, which occurred on 7 April 1993. Longitudinal recovery of the SEB is observed at the 13.0 micrometer level (near 500-mbar level) and the two equatorial belts (NEB and SEB) appear comparable. The 8.56 micrometer data, sensitive to the upper NH3 ice cloud deck, reveal that the SEB is comparable to the NEB throughout the hemisphere preceding of the Great Red Spot (GRS), but has not recovered fully at other longitudes. However, the 4.6 micrometer data, sensitive to the radiances from the deeper levels of the atmosphere and cloud tops, show that the SEB is reviving as two distinct components--northern (SEBn) and southern (SEBs). The SEBn is evident at all longitudes, albeit very faintly and with a hint of structure, but the SEBs exhibits longitudinal inhomogeneity. These data imply that the SEB revival occurs on different timescales at various pressure levels and is still ongoing. Halthore R. N.* Allen J. E. Jr. DeCola P. L. On the Nondetection of the V3 Band of Methane on Jupiter High-resolution spectra of Jupiter in the 3.3-micrometer region have failed to reveal either the continuum or the line emissions that can unambiguously be attributed to the V3 band of methane (Drossart et al., 1993; Kim et al., 1991). Broadband V4 emission, on the other hand, is easily observable either from space or from the ground. With the help of two simple nonLTE models--a two-level model and a three-level model--we explore factors such as collisional relaxation due to hydrogen and solar pumping of the V3 levels that affect the emitted line intensities. Both models use previously measured experimental values of relaxation coefficients. Predicted V3 line intensities are shown to be 1 to 3 orders of magnitude below the 3-sigma noise level of previous observations for 2- and 3-level models respectively. For a methane mixing ratio of 2 x 10^-3, applicable to levels below the homopause, a value of 320 K is derived as an upper limit to the temperature. Lee Y. T.* Allen M. Yung Y. L. Solar System Hydrocarbon Photochemistry: Impact of New CH4 Ly-Alpha Photodissociation Quantum Yields The observed abundances of C2H6 and C2H2 in the atmospheres of the outer planets are simulated by current photochemical models with various degrees of success. Since the ultimate source of C2 hydrocarbons is methane, which is the most abundant carbon species in these atmospheres, different photolysis pathways of CH4 may result in different distributions of C2 hydrocarbons. Recent measurements of the primary product channels in CH4 photodissociation at Lyman-alpha (Mordaunt et al., J. Chem. Phys., 98, 2054 (1993)) have been used in new calculations of C2 species. The preliminary results for the atmosphere of Jupiter indicate that the recently reported CH4 photodissociation quantum yields lead to a reduction in C2 abundances. The C2H6/C2H2 ratios are mainly affected by the chemical mechanism of hydrogenation from C2H2 to C2H6 and are less sensitive to the specific choice of CH4 dissociation pathways. Calculations of C2 abundances for other solar system atmospheres will also be discussed. Gautier D.* LeCluse C. Robert F. Laboratory Determination of Deuterium Exchange Rates Between CH4 and H2: Application to Giant Planets In the gaseous envelopes of the giant planets, hydrogen is mainly in the form of H2 and deuterium in form of HD. However, because of the difficulty to properly detect HD spectral lines, the D/H ratio in hydrogen (noted (D/H)H2) is inferred from the CH3D/CH4 ratio through the relation: (D/H)H2 = [1 / (4 f) ] CH3D/CH4 (1) where f is the kinetic fractionation factor. f is usually estimated from theoretical calculations (Beer & Taylor, 1972; Fegley & Prinn, 1988). Since pressure and temperature vary rapidly in the tropospheres of these planets, f varies with the atmospheric depth z and depends upon the vertical atmospheric velocity v. We report here on laboratory measurements of the isotropic exchange rate constants between CD4 and H2. They permit us to evaluate the rate of the reaction: HD + CH4---->k(T) H2 + CH3D (2) where k(T) stands is the isotopic exchange rate constant for 1 atom. The variation between k(T) and the temperature has been determined experimentally: k(T) = 6.1 10^-25 exp(4.4 10^3/T) cm^3 sec^- (3) Using the formula (4) derived from the standard kinetic isotope exchange equation: d(f) / dz = P(z) . k(T(z)) [alpha(T(z)) - f] . v^-1 (4) (where alpha is the isotopic fractionation factor under thermodynamical equilibrium and z the atmospheric depth) we have calculated numerically the profile of f(z). Accordingly, the f values to be used in equation (1) are: 1.157, 1.288, 1.441, and 1.355 for Jupiter, Saturn, Uranus, and Neptune, respectively. The (D/H)H2 values in these planets are then derived from the most recent determination of CH3D/CH4 ratios. It appears that, even in Uranus and Neptune, (D/H)H2 seems to be only moderately enriched relative to the Protosolar value, recently revised by Geiss (1993) who proposes: (D/H)Protosolar = (2-6 +- 1) x 10^-5. References: [1] Geiss (1993) pre-print. [2] Beer & Taylor (1973) Astrophys. J., 179, 309-327; Fegley & Pnnn (1988) Asrophys. J. 326, 490-508. Varanasi P.* High-resolution Laboratory Data on the Infrared Spectral Lines of Methane and Other Hydrocarbons Needed in Studies of the Jovian Atmosphere Observed infrared spectra of the Jovian atmosphere contain a wealth of information on the spectral lines of CH4 and of several hydrocarbons that are created by the photodissociation of CH4. Accurate retrieval of atmospheric properties is dependent upon the availability of reliable laboratory data on the spectral lines of interest at the appropriate temperatures. Here we present absolute intensities, collision-broadened half-widths, and pressure- induced shifts on several lines in the fundamental bands of ^12CH4, ^13CH4, ^12CH3D, ^12C2H2, ^12C^13CH2, and ^12C2H4. Using a tunable diode laser spectrometer as well as a state-of-the-art Fourier transform spectrometer and He and H2 as broadening gases, the data have been obtained at several temperatures appropriate to the Jovian atmosphere. The data are useful in the spectroscopic determination of H:D and ^13C:^12C in the planetary atmosphere. Supported by the Planetary Atmospheres Branch of the Solar System Exploration Division of NASA under Grant-in-Aid No. NAGW-1894. Spilker T. R.* Hydrogen Broadening of Ammonia's Inversion Spectrum Microwave spectral measurements have been made on ammonia's inversion spectrum, broadened by hydrogen, at temperatures of 203 and 298 K and pressures from 0.5 to 4.5 atm. Over the range of conditions covered, the data most closely agree with predictions of the absorptivity formalism by Spilker [1990] as compared with predictions of the Van Vleck/Weisskopf [1945] and the Berge and Gulkis [1976] formalisms. Small systematic variations between the data and Spilker formalism predictions suggest minor adjustments to that formalism, which would increase its accuracy. This would bring the accuracy of our knowledge of the microwave absorptive behavior of ammonia more in line with the best opacity measurement accuracies for giant planet atmospheres. Results from this program will find immediate application in the interpretation (or reinterpretation) of radio astronomical and radio occultation data from observations of the giant planets, especially Jupiter and Saturn. They will also play an important role in the design of radio experiments for future missions to the giant planets. This research was done while the author held a NASA/National Research Council Research Assistantship at the Jet Propulsion Laboratory. Baguhl M.* Grun E. Linkert G. Linkert D. Siddique N. Identification of Small Dust Impacts in the Ulysses Dust Detector Data: Relevance to Jupiter Dust Streams Since October 1990 the dust detector onboard the Ulysses spacecraft recorded impacts of cosmic dust particles. A very rigid scheme has been applied so far to identify dust impacts from the noise background. These data with large signal amplitudes previously led to the identification of interstellar dust and of dust streams from Jupiter (Grun et al., Nature, 362, 428, 1993). Additional data with small signal amplitudes could be extracted from the noise background using coincidence arguments. In the time period from October 28, 1990 to December 31, 1992, 637 additional impacts have been identified. The total amount of reliably identified dust impact data increases by a factor of about 3. This increase permits a better statistical analysis especially of the Jupiter dust streams, which consist mostly of small and fast particles. Additional dust streams have been identified between the already known streams before and after Jupiter flyby. The dependence of the deflection from the Jupiter direction, the stream intensity and width on Jupiter distance support the assertion that they have been emitted from the jovian system. Io and Jupiter's gossamer ring has been proposed previously as a source of the dust. The relevance of the newly identified streams for the models is discussed. Eshleman V. R.* Gurrola E. M. Analytic Power-Law, Exponential, and Isothermal Models of Planetary Atmospheres The benchmark of analytic models of planetary atmospheres assumes isothermal ideal gas with constant scale height, so that both pressure and density decrease exponentially with radius. These combined exponential-isothermal attributes are well known to be incompatibile for real atmospheres since they require the strength of gravity to be constant with radius. For more realistic inverse-square gravity, unique analytic models are tractable if pressure is exponential, if density is exponential, or if the atmosphere is isothermal, but no two of these properties can apply to the same model. Although the above models can have useful appplications, all four leave much to be desired in problems related to occultation observations of tenuous planetary atmospheres. For example, the observable phase and frequency in radio occultations and the refractivity-controlled signal intensity in both stellar and radio studies of such atmospheres, can all be related to S/V, S'/V', and S"/V". Here S and V represent the density integrated along infinite tangential and semi-infinite veltical paths through the atmosphere, respectively, and the primes denote differentiation with respect to their common minimum radius. For the above four models, these three ratios involve complicated and different mixes of terms such as modified Bessel, modified Struve, exponential, and power functions of radius or its inverse. While remaining analytic, these results are not convenient to use. However, the complexities are unnecessarily obfuscating since there is a singular model with inverse-square gravity where S/V = S'/V' = S"/V" = a constant. It is neither isothermal nor exponential but pressure, density, temperature, pressure scale height, density scale height, S and its derivatives, and V and its derivatives all have the same functional form as powers of radius. We are particularly interested in this model as the fundamental unit for developing a superposition-ofmodels technique that can provide analytic representations of complex atmospheric structures and corresponding features of remote-sensing measurements. POSTERS Chanover N. J. Beebe R. F. Kuehn D. M. Temporal Development of the SEB Disturbance in Jupiter's Atmosphere Low-resolution Voyager 2 mosaics constructed by C. Avis and A. Collins at JPL have been used to characterize typical convective activity within Jupiters South Equatorial Belt (SEB). Between May 27 and June 8, 1979, three bright convective bubbles emerged 83 degrees, 104 degrees, and 106 degrees west of the Great Red Spot (GRS) respectively. The average north-south expansion rate of these bubbles was roughly 3 m/s, although at their onset they underwent a much more violent expansion, when they expanded roughly two degrees of latitude in two rotations of the planet. The resulting white clouds dispersed to the extent that they would not be visible at groundbased resolution in a time span of roughly eight days. Within that time they drifted eastward and expanded in longitude. An SEB Disturbance was observed on April 9, 1993, with the Tortugas Mountain Observatory at NMSU. An eight-color series of images was taken with a 24-inch telescope and full longitudinal coverage was obtained. This observation was followed by systematic monitoring of the disturbance over a period of 65 days. By May 7, 1993, the disturbance had developed to the point that five distinct bright clouds were visible to the east of the GRS. The extent to which the development of the 1993 cloud pattern is consistent with the Voyager convection is examined in detail. Center-to-limb reflectivity of the bright clouds is interpreted as vertical structure using the multilayered multiple scattering atmosphere model of Kuehn (Kuehn and Beebe, Icarus, 101, 2, 282). Sanchez-Lavega A. Gomez J. M. Miyazaki I. Lecacheux J. Colas F. Laques P. The Life Cycles of the Jovian SEB and New Phenomena Observed During the April 1993 Outburst The historical records and our own observations of Jupiter during the last twenty years are analyzed together to characterize the life cycles of the South Equatorial Belt (~ -20 degrees to -l0 degrees) in the 0.35-1.0 micron range. During the last century the SEB has suffered regular but aperiodic changes in its structure. We present a comparative study of their morphology, motions and characteristic times for their evolution patterns. Four major sequential phases can be distinguished: (a) Zone-like ("fade") status usually accompanied by a darkening of the EZs (from -10 degrees to 0 degrees) and by a uniform, very red and contrasted GRS; (b1) Outbreak of a bright white spot and development of a planetary-scale disturbance (SEBD); (b2) Disturbance interaction with the GRS and subsequent propagation of the activity to adjacent latitudes (EZs and STRZ Disturbances); (c) Quiescent belt-like status, with minor outbreaks of white cloud activity. Phase (b2) is not always observed. We also describe and document new phenomena observed during the 1993 April outburst phase: (1) A large low albedo uniform veil westward of GRS suggesting dispersion of cloud elements when interacting with the GRS and injection of particles to high altitudes; (2) A series of diagonal streaks crossing the equatorial region (a manifestation of waves triggered by the outburst ?), and (3) The retard in the development of the SEBD southern branch with the formation of a very dark spot to the northwest of the GRS. All these new patterns are probably related to the unusual proximity of the outbreak site, of only 20 degrees, to the east edge of the GRS. Molina A. Moreno F. Ortiz J. L. CCD Observations of Jupiter and Saturn During 1992-1993 Several sets of Jovian and Saturnian images covering the 0.3-1 micrometer spectral range are shown. The observations were carried out during 1992 and 1993 using the CCD camera of the 1.5m telescope at Calar Alto and that of the 2.5m Nordic Optical Telescope at La Palma (Spain). The high quality of some of these images allow us to study different atmospheric parameters. Specially interesting are the March to June 1993 Jovian images, which show the development of several features relationated with the 1993 South Equatorial Belt revival. Momary T. W. Baines K. H. Orton G. S. Jupiter's Polar Hoods and Prominent Temperate Latitude Features: An Assessment of Temporal Variability Between the 1992 and 1993 Apparitions Near-infrared imagery acquired at wavelengths within deep H2 and CH4 absorption bands reveal prominent polar hoods and, at temperate latitudes in both the northern and southern hemisphere, anomously bright, localized features ("spots"; each is 3-5 times brighter than their surroundings). We have observed such features at sub-arcsec resolution during the past two apparitions (23 Feb 1992 and 25 April 1993) with the ProtoCAM near-ir camera at the NASA/IRTF. We find that both polar hoods grew both significantly brighter and more extensive in area during this period. The northern hood is approximately 60% brighter in 1993 compared to 1992 at 2.14 micrometers, indicating perhaps a significant increase in the vertical column abundance of stratospheric aerosols. A distinctive asymmetrical shape is apparent in data acquired in both years, with increased asyrmmetry in 1993. Specifically, the hood boundary extends southward to 51 degrees lat at 319 degrees lon (System III), but only to 63 degrees lat at 184 degrees lon. When viewed from intermediate longitudes, the north polar hood appears "cocked", much as reported from 0.89-micrometer observations by W. Pryor (personnel communication). In contrast, the southern hood does not appear "cocked" in either year. One bright, localized spot was observed at northern temperate latitudes each year. In 1992, the northern spot was located 35.6 N lat and spanned 4*2 degrees in latitude and longitude. The 1993 spot was at 34.7 N lat, but was significantlylarger (8*6 degrees). In 1992, two southern spots were observed, co-located at 27.5 degrees S. lat. Each was significantly larger than their northern counterpart (~9*4 degrees). In 1993, a southern spot was located at 29.1 degrees S and extended 5.3 * 7.0 degrees. Finally, a brightening in the region of the SEB revival was centered at 10.7 degrees S lat, 322.4 degrees lon on 25 April 1993, spanning 5.0*6.3 degrees. Monday, October 18, 1993 MARS SURFACE II 10:30 - 12:00 NOON North Ballroom Chair(s): J. F. Bell III G. A. Swayze Miller J. S.* Singer R. B. Laboratory Reflectance of Ferric Mineral Mixtures: Application to Regional Mapping of the Martian Surface We are conducting a suite of laboratory reflectance measurements of ferric mineral mixtures to support analysis of our martian spectral imaging dataset (Singer et al., LPSC XXI, 1164, 1990). Our dataset was obtained during the 1988 and 1990 oppositions, and covers substantially all of Mars south of 40 degrees N with spectral coverage from 0.44 to 1.0 micrometers. The lab measurements will cover this range, focusing on the spectral regions near 0.53 micrometers and 0.86 micrometers, the location of absorption bands characteristic of Fe^3+ in hematite. Understanding the behavior of these spectral features when hematite is mixed with spectral dilutents of high and low albedo, and with martian surface analog materials will be useful for interpreting visible and near-infrared spectroscopy of the martian surface. Past investigations have revealed the detailed shape of crystalline hematite in ratio spectra of Meridiani Sinus to Acidalia Planitia (Singer and Miller, BAAS 23, 1174,1991). The characteristic hematite features are subtle in the original spectra and differences in strength are hard to see by overlaying. The ratio technique has proved useful in spectral comparisons for highlighting differences in spectral contribution from specific minerals. We have attempted to quantify the strength and map the distribution of hernatite spectral features on the martian surface to help in understanding regional geology and weathering history. These efforts have been complicated by the variation over the martian surface in relative strength of the two main hematite absorption features centered near 0.53 micrometers and 0.86 micrometers, and the strong positive (red) slope of martian reflectance spectra in the visible. These factors motivate us to gain a better understanding of the bchavior of Fe^3+ in spectral mixtures through laboratory spectral analyses. Objectives of the lab measurements include determining the behavior of the 0.53 micrometer and 0.86 micrometer features in mixtures of varying dilutions and in ratios of mixture spectra. Mixture components will include hematite, montmorillionite clay, oxidized and unoxidized basalt, and amorphous or nanocrystalline Fe^3+-containing palagonite. The shape and strength of the hematite Fe^3+ features will be observed in mixtures with high and low albedo spectral dilutents, as well as with martian spectral analog materials. These determinations will support a better quantification of the hematite spectral features, which will be applied to improve the quality and interpretability of regional mapping in our telescopic data set, and should be applicable more generally to analysis of visible and near-IR spectroscopy of Mars. Lee P.* Thomas P. C. Veverka J. Calvo S. Discovery of Longitudinal Dunes on Mars The features are resolved in three adjacent high-resolution (30 m/pxl) Viking Orbiter frames (525B11, B12, B13) and occur over an area of at least 900 km^2 in the northern circumpolar erg. The dunes appear as closely-spaced (~100 m) sets of subparallel linear ridges in the vicinity of a small (D = 6.5 km) impact crater. They reach several kilometers in length and occasionally display kinks and Yshaped junctions. As evidenced by a morphological continuum between the longitudinal dunes and the (transverse) barchane dunes present in the same area, the former appear to originate from the latter by modification of the barchane horns in a bimodal wind regime. While longitudinal dunes account for more than half of all the dunes in the sand seas on Earth, early studies noted that they were strikingly absent on Mars (Breed et al. 1979; Tsoar et al. 1979, JGR, 84). Because longitudinal dunes represent masses of passing sand in transit across a desert surface and are themselves usually transitory bedforms, their virtual absence on Mars implied that much of the available saltating material had already been stabilized in sites of accumulation. However, the localized occurrence of longitudinal dunes reported here suggests that aeolian processes involving saltation likely remain active in at least restricted areas of the northern circumpolar erg. The identification of these features as longitudinal dunes will be confirmed using very high resolution (2 m/pxl) Mars Observer images. Clifford S. M.* Mars: Thermal and Hydraulic Considerations Regarding the Fate of Water Discharged by the Outflow Channels to the Northern Plains The identification of possible shorelines in the martian northern plains suggests that the water discharged by the circum-Chryse outflow channels may have led to the formation of transient seas, or possible even an ocean, covering as much as a third of the planet. Speculations regarding the possible fate of this water have included local ponding and re-infiltration into the crust; freezing, sublimation, and eventual cold-trapping at higher latitudes; or the in situ survival of this frozen water to the present day--perhaps aided by burial beneath a protective cover of eolian sediment or lavas. However, consideration of the thermal behavior of water above and beneath the martian surface, and the kilometer or more hydraulic head difference between the water discharged from the channel source region and confined beneath the frozen crust of the northern plains, precludes any local mechanism for the significant reassimilation of flood water by either the frozen crust or the underlying regional aquifer under climatic conditions resembling those of today. On the other hand, neither cold-trapping at higher latitudes nor the subsequent freezing and burial of flood waters can be ruled out. It is important to note, however, that in the case of burial, thermal processes will rapidly redistribute any H2O present at depth into the overlying mantle--a process that will continue until the pore volume of the depositional layer is saturated throughout. These results further constrain the identification of geologically reasonable sinks for the water discharged by the outflow channels and may provide further insight to the subsequent geomorphic evolution of the northern plains. Hartmann W. K.* Survey of Lunar and Martian Cratering Record: Modifying the Current Paradigm Lunar and martian cratering data were reviewed in preparation for Mars Observer data analysis. Two standard format graphs of crater number/km2 vs. diameter have been developed, which allow quick and easy comparison of cratering data from different planetary geological provinces and also avoid the relatively illegible steep slope published by some workers. As I reported earlier, the lunar survey leads to significant modification of the paradigm that was used by the Voyager team to interpret planetary and satellite crater diameter distributions. The Voyager team reported that on the "relative plot" or "R-plot" format, lunar uplands generally are represented by what I call a V-shaped curve. They also found this shape of curve on some outer planet satellites, and interpreted it as the signature of a unique (ancient?) population of projectiles. This is probably incorrect. The V shape does not represent the lunar uplands generally. It is associated with regions that have ancient intercrater plains. Spectral evidence (including Galileo data) indicate these plains were mostly formed by flooding by ancient basaltic lavas, now covered by a veneer of highland dust. Models show how flooding can produce the V shape. These results will affect future interpretations and prepare the way for Mars Observer studies of martian cratering records from old and young martian regions. Mariner era interpretations stressed cratering evidence for an early erosive era followed by fairly abrupt climate change to current conditions. More recent work posits other interpretations. The small crater population, to be resolved by MO, will be especially informative in clarifying the issue, in dating channels, and perhaps in permitting searches for effects of a possible ancient denser atmosphere. Barlow N. G.* Martian Impact Craters as Indicators of the Subsurface Distribution of Volatiles The fluidized ejecta morphology surrounding the majority of fresh impact craters on Mars has been attributed to either impact into near-surface volatiles (Carr et al., 1977, JGR, 82) or by interaction of the ejecta with the thin martian atmosphere (Schultz, 1992, JGR, 97). A multifaceted study has been undertaken to determine the distribution and quantifiable qualities of the various ejecta morphologies in an attempt to constrain their manner of formation. Evidence to date supports the theory that near-surface volatiles (most likely H2O) are the primary cause of the fluidized ejecta morphologies observed on the planet. Five major ejecta morphologies are considered: single-lobe rampart (SL), double-lobe rampart (DL), multiple-lobe rampart (ML), radial (Rd), and diverse (Di). The three rampart morphologies are of the fluidized type, the radial morphology is more similar to typical lunar-type ejecta patterns, and the diverse morphology is a combination of fluidized and radial morphologies. The sizes and distributions of 3819 craters >=8 km diameter reveal a number of correlations. SL morphologies are primarily associated with craters in the 8- to 20-km diameter range in the equatorial regions, but cover a larger diameter range (up to 65 km) at higher latitudes. ML morphologies are found surrounding craters in the 1645-km-diameter range in the equatorial region, but are rare to nonexistent at higher latitudes. DL craters cover the 8-50-km-diameter range and are primarily found in the 30 degrees-60 degrees N latitude range. Rd craters are found globally for craters >60 km. Di morphologies are very localized in extent and cover the diameter range between ML and Rd morphologies. Few correlations between terrain type and ejecta morphology were discovered. Studies to determine variations in ejecta morphology with elevation are in progress. In addition, sinuosities of the fluidized morphologies were computed and ML morphologies are more sinuous than SL or DL morphologies (~1.2 for ML compared to 1.1 for SL or DL, where 1.0 is a circular morphology). Inner lobes of DL and ML craters are generally less sinuous than outer lobes. When depth-diameter relationships are computed, the observed diameter-latitude trend for SL and ML craters correlates well with the proposed areal and vertical distribution of subsurface H2O on Mars. According to this scenario, SL morphologies result from impact into ice whereas ML morphologies indicate influence from liquid water reservoirs at depth. The higher sinuosities for ML craters can be explained by an decrease in the clast/volatile ratio in the martian equatorial substrate. The observations are more consistent with the buried volatile model than with the ejecta-atmosphere interaction model. de Grenier M.* Pinet P. C. Chevrel S. Visible and Near-Infrared Reflectance Geometric Corrections of the Martian Surface and Implications for Spectral and Spectro-Imaging Mappings A nearly global visible (VIS) and near infrared (NIR) coverage of the martian surface has been achieved during the last 1988 and 1990 oppositions, by spectro-imaging telescopic means implemented at the 2-m telescope of Pic du Midi (France). The spectral observation focused on the 0.56-1.05-micrometer domain with a spectral resolution (R = lOO) and spatial resolution (100-300 km). Taking advantage of the substantial spatial overlapping existing within our data and resulting, for a given wavelength dataset, in a 15 to 25 degree martian longitude interval between the corresponding subterrestrial points, we propose a well-constrained estimate of the Minnaert exponent k for different wavelengths. This estimate is produced by minimizing the brightness difference rms residual of about 400,000 martian surface elements, observed under different geometric conditions and distributed across the available martian surface mapping in several separate overlapping frames. The phase angle is almost constant in these observations and ranges below 5 degrees. The incidence and emergence angle values of the dataset, due to the observation geometry, range from 0 to 90 degrees in a coupled behavior, and are predominantly distributed toward the low angle values (0-45 degrees). The results indicate that the mean value of exponent k varies from 0.59 to 0.68, with the rms residual varying from 4 to 11% when the wavelength is successively 0.56, 0.73, 0.91, 0.98 micrometers. The 4% residual means nearly all of the data spectral variance is explained and is consistent with the predominant effect of atmospheric attenuation known to occur in the VIS domain. The important NIR residual suggests that in addition to the geometric limb-darkening attenuation effect, there is a surface material contribution. Indeed, when considering the 0.98-micrometer wavelength, the k mean va1ue over the eastern hemisphere varies from 0.64 to 0.72 in relation to the proportion of dark and bright regions. This trend is consistent with a more precise analysis revealing a systematic k linear increase from low to high albedo areas. A linear regression fit of the dataset permits us to establish the following albedo (A)-dependent laws on the Minnaert coefficient, for the three wavelengths: 0.73 micrometers, k = (0.631 + 0.003).A + (0.500 + 0.003), 0.15 < A < 0.38 0.91 micrometers, k = (0.920 + 0.001).A + (0.397 + 0.002), 0.13 < A < 0.41 0.98 micrometers, k = (1.074 + O.OOl).A + (0.356 + 0.002), 0.15 < A < 0.41 These results allow presently to correct reflectance geometric variations and to produce VIS and NIR geometric albedo extended mosaics of the surface within a 3% to 8 % consistency. It also shows that one has to take into account the wavelength and albedo-dependent behavior of the Minnaert coefficient in the use of the spectroscopic and imaging data before any interpretation, a first estimate of the associated discrepancy between corrected and uncorrected data amounting up to 5 to 10% under certain conditions. Hayashi J. N.* Jakosky B. M. Haberle R. M. Atmospheric Effects on the Thermally Derived Albedo of Mars Haberle and Jakosky (1991) investigated the effect on thermal inertia of including a dusty C02 atmosphere and sensible heat exchange with the surface as opposed to the previously assumed constant atmospheric contribution equal to 2% of the maximum solar insolation (Kieffer et al. 1973, 1977; Palluconi and Kieffer 1981). We have utilized the Haberle and Jakosky model to investigate the effects on the thermally derived albedo. The thermally derived albedo together with the thermal inertia provides the best match for the observed temperatures. At low dust opacities, the 2% model derived albedo underestimates the Haberle and Jakosky model-derived surface albedo. This is most pronounced at low albedos and is attributed to the effects of CO2 in the atmosphere. For a constant low surface albedo and increasing dust opacity in the Haberle and Jakosky model, the thermal behavior is matched by an increasing albedo in the 2% model. This effect is attributed to scattering by dust in the atmosphere. For a constant high surface albedo and increasing dust opacity in the Haberle and Jakosky model, the thermal behavior is matched by a decreasing albedo in the 2% model. This effect is attributed to heating of the atmosphere by the dust. At low dust opacities, the 2% albedo adequately estimates the Haberle and Jakosky model mean planetary albedo. However, increasing the dust opacity increases the slope of the Haberle and Jakosky planetary albedo vs. 2% albedo to greater than 1. This change in slope is contrary to that of the observed albedo vs. the 2% albedo, which has an approximate slope less than 1. All of our model runs had a ratio of the dust infrared to visible optical depth equal to 0.5, consistent with Haberle and Jakosky (1991). We are currently exploring the effect of changing the dust properties on the slope of the Haberle and Jakosky planetary albedo vs. the 2% albedo. Zent A. P.* Quinn R. Laboratory Measurement of Co-Adsorption of H2O and CO2 Under Mars-like Conditions We are completing the first laboratory measurements of the simultaneous adsorption of CO2 and H2O on Mars-analog materials at temperatures and panial pressures appropriate to Mars. In laboratory experiments reported in the chemical engineering literature, H2O displaces CO2 from adsorption sites very effectively at temperatures and partial pressures higher than appropriate for Mars (e.g., Carter and Husain, Chem. Eng. Sci., 29, 267-273). While both species are present in the martian atmosphere and pore gases, climate models, which invoke regolith adsorbate as a volatile reservoir are based on laboratory experiments in which only one adsorbate is used. Future models must be augmented in order to account for the competition for a finite number of adsorption sites. At temperatures below the frost point however, H2O adsorbate may be segregated into ice, allowing more effective competition by CO2. In addition, the seasonal thermal wave passing through the shallow regolith may force in situ phase changes in H2O, and change the number of adsorption sites available for visitation by CO2. We find that CO2 is displaced from adsorption sites by the presence of H2O under Mars-like temperatures as long as H2O ice is absent. The implications for models of the martian cliate will be discussed. In general, high atmospheric pressure regimes during periods of high obliquity must be considered less likely. The inventory of CO2 adsorbed in the regolith must also be revised downward. We will present new estimates of the total exchangeable CO2 in the atmosphere-cap-regolith system. Wisdom J.* Touma J. The Chaotic Obliquity of Mars Numerical integration of the rotation of Mars with the chaotically evolving planetary system over 100 m.y. shows large chaotic variations in the obliquity of Mars. In our integrations the obliquity of Mars varies from about 10 degrees to 50 degrees on timescales of several million years. The chaos is associated with repeated separatrix crossings of a chaotically pulsating secular spin-orbit resonance. POSTERS Pierazzo E. Singer R. B. Britt D. T. Doose L. R. Smith P. H. Tomasko M. G. Keller H. U. Knudsen J. M. Soderblom L. A. Geologic Remote Sensing Science on Mars from MESUR Pathfinder The Imager for MESUR Pathfinder (IMP) is an innovative stereoscopic multispectral camera system based on a single CCD detector (see Britt et al., this volume). The CCD has a standard silicon spectral response, dropping off sharply below wavelengths of 0.4 micrometers and above about 1.0 micrometers. Fortunately this spectral region is well suited to studying alteration products and processes (including weathering) in dust, soil, and rocks, based on visible and near-IR spectral characteristics related to Fe^3+ abundance and mineralogy. At longer wavelengths (~0.8 to 1.0 micrometers) the system is sensitive to spectral features of Fe^2+ in mafic materials such as pyroxenes and basalts, and is capable of discriminating among various compositions and mineralogies. Mission constraints on cost, weight, and data rate required us to keep the design simple and limit the number of bandpasses for geologic remote sensing to 8. Optimization of location and width of these bandpasses has therefore been crucial for spectra discrimination of minerals, rocks, and soils known (or suspected) to occur on the surface of Mars. The science capabilities of this camera system are therefore excellent, both to guide the rovermounted Alpha/Proton/X-ray spectrometer to specific targets of interest and to remotely investigate and map the terrain surrounding the landing site. Initial bandpass positions were chosen based on prior knowledge, then refined analytically through modeling with laboratory and telescopic spectra. The first three bands are at 0.45, 0.53, 0.60 micrometers, for two reasons. First, the band centers are similar to Viking Orbiter and wlll facilitate comparisons at different spatial scales. Second, as proven with Viking images and telescopic spectroscopy, this combination is excellent for detecting subtle differences among ferric oxides and oxyhydroxides, and is especially sensitive to buLlc crystalline hematite. The fourth band, at 0.75 micrometers, corresponds to a reflectance maximum for many Fe3+ minerals. The fifth band (0.86 micrometers) is located at an absorption in crystalline hematite, while the sixth band (0.90 micrometers) is closer to the absorption for hydroxylated ferric oxides. The seventh and eighth bands (0.95 and 1.0 micrometer) help define the long-wavelength shoulder of the near-IR Fe^3+ bands. The fifth through eighth bands (0.86 to 1.0 micrometer) are also designed to characterize Fe^2+ absorptions diagnostic of pyroxenes and other mafic minerals. For low- to moderate-Ca pyroxenes the absorption minimum location can be estimated. For materials with minima at 1 micrometer and longer, such as high-Ca pyroxenes and olivine, we can characterize the short wavelength side of the absorption. Band widths vary from 30 to 50 nm, chosen to minimize exposure times in all channels. Modeling of bandpass width shows little difference in interpretive capability between narrow filters (10 nm) and the broader filters in IMP. Hauber E. Neukum G. Age Determinations of Valles Marineris Interior Deposits, Mars The large canyon system of the Valles Marineris offers a unique view into the upper part of the martian crust. Canyon walls, canyon floor, and various interior deposits like landslides or layered deposits represent a complex assemblance. Knowledge about the time and the mechanisms of emplacement of these materials is important in order to understand the sequence of geologic processes, which has led to the present state of the region. Of special interest are the absolute and relative ages of the different geologic units. While the surrounding plains are sufficiently large to yield well based crater retention ages, the small size of the interior deposits makes it difficult to get reliable crater counts. In detail, these tiny and sometimes not clearly separated units that formed subsequently to the ongin of the canyon itself consist of layered deposits, landslides, irregular floor deposits, fractured floor material, and surficial deposits (Lucchitta et al., in Mars, Univ. of Ariz. Press, 1992). Yet, only landslides have been dated by crater counting in an early work by Lucchitta (JGR 84, No. B14, 1979). In most cases, however, relative ages have been determined on the basis of stratigraphic positions. Our goal has been to define crater retention ages in the western part of the Valles Marineris, i.e., in Ius and Tithonium Chasmata. To this purpose, about 100 high-resolution Viking-Orbiter images have been map-projected and compiled to image mosaics covering the entire western Valles Marineris and parts of Noctis Labyrinthus. Using this image base as well as low-resolution color data, geologic units have been mapped and craters have been counted on these units. The results have been evaluated through application of the cratering chronology model of Neukum and Hiller (JGR 86, No. B4, 1981). Butler B. J. Muhleman D. O. Slade M. A. Results from 1992 and 1993 VLA/Goldstone 3.5 cm Radar Data In an attempt to further understand the surface and subsurface of Mars, radar experiments were undertaken during the most recent opposition. The motivation was threefold: first, we wanted to compare the radar return from the residual north polar ice cap (RNPIC) to that of the residual south cap (RSPIC). Second, we wanted to obtain data for those longitudes that we did not sample in our experiment in 1988. And finally, we wanted to verify results from our 1988 experiment (the 1988 experiment is explained in Muhleman, et. al., Science, 253, 1508-1513,1991). The experimental setup was similar to that described in Muhleman, et. al., with the exception of the transmitted power from the Goldstone antenna, which has been increased from 350 kW to 460 kW. We performed experiments on 3 dates: December 9, 1992 (subearth latitude, phi,~12 degrees), December 29, 1992 (phi ~9 degrees), and January 12, 1993 (phi ~6 degrees). Only the SS echo (or so- called "depolarized") data have been fully reduced to this point, and discussion will be limited to that data. Also, the December 9 data were compromised by transmission problems, and the only result from that date was an indication that the RNPIC was not nearly as efficient a backscatterer as the RSPIC. As far as verification of the 1988 results, we found that "Stealth" was still present, and the volcanic regions (Tharsis and Elysium) were still the most highly reflective regions on the planet, excluding the RSPIC. Global fits of the SS backscatter data have been made, incorporating all of the data taken thus far (including the 1988 data). Significant results are: "Stealth" is the least reflective region on the planet, but there are other regions which exhibit depressed reflectivities. The RSPIC is the most reflective region on the planet. The RNPIC has a slight enhancement in reflectivity in selected regions, but reflectivities are much less than those for the RSPIC. The reduced reflectivity can be explained by assuming that the ice is contaminated by silicate inclusions, with a volume fraction of ~50%. Other highly reflective regions are mostly contained in the Tharsis and Elysium volcanic regions. New global SS radar reflectivity maps will be shown. Lucey P. G. Williams T. Horton K. Rafert J. B. SMIFTS: A Cryogenically Cooled, Spatially Modulated, Imaging, Fourier Transform Spectrometer We describe a novel cryogenically cooled, spatially modulated, imaging, Fourier transform interferometer spectrometer for spectral measurement in the 1-5 micrometer range. Using spatial modulation and a detector array to sample the interferogram, the instrument employs no moving parts to obtain spectra. It is extremely robust and potentially more reliable than other interferometers in addition to taking advantage of the multiplexing afforded by array detectors. The instrument technology possesses a unique combination of characteristics that form a niche for spectral measurement not commonly recognized but of great potential value. These characteristics include broad wavelength range, wide field of view, simultaneous measurement of all spectral channels, compactness, no moving parts, and moderate resolution (lambda/Delta lambda = 100-1000). We will present test data derived from the instrument. The spatially modulated FTS spectral measurement technology has been described by several authors including Yoshihara and Kitade (1967), Okamoto et al. (1984), Barnes (1985), and Smith and Schempp (1991). The spectrometer requires no moving parts, is compact, and enjoys a number of advantages over other spectral data collection technologies such as gratings and tunable filters. The unique combination of characteristics define an important niche for remote sensing spectral data acquisition. In the simplest mode of operation, the spectral resolution is determined by the number of elements in the detector array and the cutoff frequency. Our implementation of the instrument employs an Amber Engineering 256 by 256 InSb element detector array, which enables a 10,000 wavenumber (1 micrometer) cutoff frequency and therefore a spectral resolution of 76 cm^-1. We will list and discuss the characteristics of the SMIFTS for spectral measurement, describe the interferometer technology upon which the instrument is based, and other optics essential to the instrument performance, and describe the cryogenically cooled implementation of this technology. Jakosky B. M. Henderson B. G. Mellon M. T. Chaotic Obliquity and the Nature of the Martian Climate Recent analysis of the martian obliquity shows that it is chaotic on timescales longer than 10^7 years. This suggests that the obliquity might have been as high as 60 degrees within the last 10^7 years and that it would almost certainly have been this high within the last 10^8 years. Using our polar-cap thermal models (Icarus, 102, 286,1993), we have calculated polar temperatures and water-ice sublimation at obliquities up to 60 degrees. At the highest obliquities, up to a meter of water ice could sublime each martian year, and the entire thickness of the polar deposits could sublime in under 10^4 years. This ice would presumably condense where it would be most stable-at middle and equatorial latitudes. Additionally, CO2-H2O clathrate hydrate is currently stable in the polar deposits at depths below a few meters. If the caps actually contain clathrate, the CO2 would be released as the caps sublime; if the caps are predominantly clathrate, then they could contain the equivalent of one bar of CO2. This CO2 would then be released at the highest obliquities, where it would remain predominantly atmospheric. This CO2 (i) could provide a sink for the putative early CO2 atmosphere, which provided some greenhouse warming and (ii) could be responsible for occasional warmer climates during recent epochs. Clearly, these results are very speculative, as conditions would be so different from those input into the model that the polar-cap temperatures, the water (and CO2) sublimation, and the climate would be very different from what we can predict. Stephens S. K. Stevenson D. J. Rossman G. R. Keyser L. F. Carbonate Formation on Mars: Latest Experiments and Models Laboratory simulations and computer models of martian CO2 storage may answer some fundamental questions about martian climate history and surface weathe?g. Could carbonate formation have reduced CO2 pressure from a hypothetical >1 bar to the present 7 mb in 3-4 b.y.? We address this and other problems with on- going pressure-drop (PD) experiments, coupled with various analytical techniques and modeling. Recent PD experiments exposed silicate powder (surface area ~3 m2/g) to 1 bar CO2 at ~20 degrees C for periods of 101-2 days. "Damp" (1 ml(sub)H2O for each 5 g(sub)silicate) results fall into 2 groups: [1] diopside (~CaMgSi2O6) and olivine ((Mg,Fe)2SiO4), [2] quartz (SiO2) and plagioclase (~CaAl2Si2O8). Group [1] shows rapid short-timescale (<3 days) CO2 pressure drop (Delta P) and slow long-tau Delta P, while group [2] gives Delta P ~ 0. "Dry" (no H2O), "vapor" (4 micro l), "damp," and "wet" (5 ml) diopside runs yield generally increasing Delta P for all taus. Results suggest adsorption (and other physical storage) and irreversible reaction (with CO2 + H2O); any reaction beyond a surface layer has not yet been investigated; and differences between [1] and [2] point to a thermodynamic or crystal structure role. Applying long-tau rates of <2.7 x 10^-5 g(sub)CO2/g(sub)silicate/day h(sub)regolith ~100 m, a limit of <75 mb/yr can be placed on CO2 uptake for a warm, wet Mars. We will use SEM to test for possible crack diffusion, and further PD runs (e.g., T < 0 degrees C, P < 1 bar, or using igneous glass) to characterize reaction mechanisms. Additional results involve an X-ray photoelectron spectroscopy (XPS) experiment and Fourier transform infrared spectroscopy (FTIR) analysis. Using XPS, a pristine diopside cleavage surface exposed to conditions similar to a "vapor" PD run shows no added carbonate, and FTIR spectra after the PD run show a change due to <1 wt% of an unidentified carbonate phase. These findings are interesting; we plan further analysis. Models of Martian CO2 history using experimental rates will address several issues: What is the effect of other sources or sinks on weathering timescales? Is Delta P affected more by gradual or catastrophic processes? Does carbonate decomposition (from rapid burial and shallow isotherms) stop early due to waning thermal flux? Where are martian carbonates? TITLE-ONLY PRESENTATIONS Britt D. T. Doose L. R. Singer R. B. Smith P. H. Tomasko M. G. Keller H. U. Knudsen J. M. Soderblom L. A. The Imager for MESUR Pathfinder (IMP) During the winter and spring 1993 the IMP team under Peter H. Smith (PI) competed in and won the JPL-supervised competition to provide the imager for the MESUR Pathfinder Mars lander. The IMP instrument is a binocular CCD-based imager with a 12-position filter wheel and full azimuth/elevation pointablity. The camera has a 12-cm stereo separation between the "eyes" and the optics are set (f/18, focal length 23 mm) so that the camera does not require active focusing (depth of field 0.65 m to infinity). The CCD uses frame transfer to shutter images electronically, eliminating another moving part. The active sensing area is 256 x 256 pixels in each "eye". The field of view for each eye is 14.4 degrees square and the IFOV is 1.0 mrad. The maximum resolution on the ground will be approximately 0.6 mm. The camera will sit on a deployable "jack-in-the-box" mast that can extend as much as a meter above the lander. Since the camera has full functionality in the stowed as well as the deployed configuration, it is possible to greatly expand the stereo baseline by taking panoramas both before and after mast deployment. The 12-position filter wheel is only on the right "eye" and contains eight filters optimized for Mars surface geology, three filters for atmospheric water vapor and dust measurements, and one broadband filter for stereo imaging with the other eye. Science experiments planned for the IMP include filter-wheel spectral mapping of the landing site to determine compositional variation and identify mineralogical units as targets for further investigation using the rover-based Alpha/Proton/X-ray spectrometer. Spectral mapping will also study weathering processes and products in the dust, soil, and rock. Included in the instrument package is J.M. Knudsen's magnetic properties experiment that will use up to five magnets of differing strengths to identify magnetic minerals in the martian dust. Stereo imaging and panoramas will study the large- and small-scale structure of the landing site, rock and dune features, and any erosional features. Additional images will be taken to study time-variable phenomena such as frost, dune formation, and seasonal changes. The instrument is also designed for a number of significant atmospheric studies. These include measurements of atmospheric water vapor, atmospheric dust, optical depth, and the size, shape, absorption spectra, and vertical distribution of dust in the atmosphere. Additional measurements include imaging a "wind sock" to estimate wind direction and imaging cloud patterns. Monday, October 18, 1993 INVITED TALK 1:30 - 2:20 PM Grand Ballroom Chair(s): G. Orton Moreno F.* The World Astronomy Days #2 Project: Preliminary Results on Groundbased Multispactral Imaging Analysis of Recent Changes in the Jovian Atmosphere The project #2 of the so-called World Astronomy Days of the IAU concerns the creation of a physical map through remote sounding of its atmospbere during the 1993 apparition. This apparition has been characterized by rapid changes in various jovian regions, the most remarkable being the South Equatorial Belt disturbance (SEBD). In this paper a preliminary analysis of this and other active regions is made from the dynamical evolution and photometric properties of features mostly based on 0.37-0.95 microns groundbased sub-arcsec imagery acquired using a large format CCD camera at the 1.52m spanish telescope at Calar Alto Observatory at various dates from March to June, 1993. Monday, October 18, 1993 INVITED TALK 2:20 - 3:00 PM Grand Ballroom Chair(s): G. Orton Shoemaker E. M.* Shoemaker C. S. Levy D. H. Collision of P/Shoemaker-Levy 9 with Jupiter The discovery of an impending collision of a comet with a planet is a unique event in the annals of astronomy. Detection of P/Shoemaker-Levy 9 in orbit around Jupiter and of two other comets (P/Gehrels 3 and P/Helin-Roman- Crockett) shortly after their escape from jovicentric orbit suggests that the steady population of comets brighter than H(sub)1 = 7 that are captured in orbit around Jupiter is about one. Collision of such comets with Jupiter probably occurs about once per century. If the pre-1992 precursor of P/SL 9 was substantially larger than the nuclei of P/G 3 and P/HRC, as seems likely, impact of an object with the energy of P/SL 9 may occur with a frequency of about once per millenium. Low-velocity encounters with the Jovian system evidently occur about an order of magnitude more frequently than calculated by the linearized two-body method of Opik. Collisions with Jupiter and the Galilean satellites are correspondingly more frequent. Collisions of comets on free heliocentric orbits are several times more frequent than collisions of comets captured as jovian satellites. Dimensions of the nuclei of P/SL 9 are not yet well established. If the largest objects are about 5 km in diameter, as much as 10 megatons total energy may be delivered to Jupiter's atmosphere. If the nuclei are smaller, however, the total energy could be one or two orders of magnitude lower. It is anticipated that impact of some of the largest nuclei, in July 1994, will be detectable from the Voyager and Galileo spacecraft. A campaign to study the nuclei is needed in order to predict observable effects of the collisions. The train of nuclei appears to be oriented at an angle to the orbit of the comet, and some objects may escape impact. Monday, October 18, 1993 Comet P/Shoemaker-Levy 9 and It's Impact on the Jovian System 3:30 - 5:30 PM Grand Ballroom Chair(s): E. M. Shoemaker, C. S. Shoemaker, D. H. Levy Jewitt D.* Luu J. Chen J. Physical Properties of Split Comet Shoemaker-Levy 9 We describe an ongoing program of observations of the split comet Shoemaker- Levy 9, designed to elucidate its basic physical and dynamical properties prior to the 1994 impact with Jupiter. The observations are taken under subarcsecond seeing conditions from Mauna Kea, and include both charge-coupled device images and spectra. To date, at least 21 separate nuclei have been identified (see below). Each nucleus supports a weak coma, so that photometry is able to yield only upper limits to the sizes of the underlying nuclei. CCD spectra show no evidence for molecular emission features due to CN, C2, or C3. The photometric and kinematic evolution of the fragments will be discussed, based on observations from the 1993 March to August observing window. Weaver H. A.* Feldman P. D. A'Hearn M. F. Arpigny C. Brown R. A. Helin E. F. Levy D. H. Marsden B. G. Meech K. J. Larson S. M. Noll K. S. Scotti J. V. Sekanina Z. Shoemaker C. S. Shoemaker E. M. Smith T. E. Storrs A. D. Yeomans D. K. Zellner B. HST Observations of Comet Shoemaker-Levy (1993e) Comet Shoemaker-Levy (1993e) was observed by the Hubble Space Telescope (HST) during July, 1993. The first observation executed successfully on July 1, and the second is scheduled for July 28. During the observation on July 1 four images were obtained with the PC using the F555W filter (similar to V-band) and exposure times of 100, 400, 700, and 700 s. Each nucleus is surrounded by a (roughly) spherical coma. The spatial brightness distribution of the coma is significantly flatter than the rho^-1 profile that is typically observed for comets having r~1 AU, so the coma is not due to the steady-state production of dust flowing outward from the nucleus. In order to estimate the magnitudes of the individual nuclei, the contribution from the coma must first be subtracted. Our initial attempts to subtract the coma result in the following preliminary estimates for the observed nucleus V magnitudes for the six brightest nuclei (starting from the southwest end and moving along the train to the northeast end): 23.8, 23.2, 23.5, 23.5, 24.0, and 23.5 with a relative uncertainty of ~0.1. The absolute value is dependent on the coma subtraction, and we believe that the numbers quoted are conservative lower limits to the true values. Assuming that the nuclei have a geometric albedo and color equal to that of the nucleus of P/Halley, and that the phase law is asteroidal, then an upper limit on the diameter of the largest nucleus is ~5 km. A 16 min. FOS spectrum covering the spectral region from 2223-3278 Angstroms was also obtained in order to search for gaseous emission from OH. Only scattered solar continuum radiation was detected, and the 3 sigma limit on the OH emission corresponds to an upper limit on the water production rate of about 3 x 10^27 s^-1. Chodas P. W.* Yeomans D. K. The Upcoming Collision of Comet Shoemaker-Levy 9 with Jupiter In late July 1994, the more than a dozen pieces of comet ShoemakerLevy 9 will likely collide with Jupiter. Using observations of the comet's central region over the interval from March 17 through June 26, preliminary orbital calculations have been carried out in a heliocentric frame and a backward integration of the comet's motion indicates that on July 8, 1992, the comet passed to within 1.6 Jupiter radii north of the planet's center, a distance that is well within this planet's Roche limit. The resultant tidal forces are the likely cause of the comet's splitting into multiple fragments. Prior to this Jupiter close approach, the comet was in a highly eccentric orbit about Jupiter itself. A forward extrapolation of this comet's motion and position uncertainties suggests that the center of the comet's train of particles has a high probability of colliding with Jupiter on July 20-21, 1994. When viewed in a heliocentric frame, the orbit of this comet resembles that of Jupiter. However, the comet is currently in a very eccentric (e > 0.99) and highly inclined (I = 83 degrees) Jupiter orbit with an apojove of 0.33 AU. Assuming a Jupiter radius of 69,700 km, Jupiter entry occurs on about July 20.5, 1994 at a relative velocity of 60 km/s. At entry, the Sun-Comet-Jupiter angle will be 64 degrees (night side) at a Jovicentric latitude of -45 degrees. As additional astrometric data become available, the comet's orbit will be improved and the rather uncertain Jupiter collision circumstances updated. Zahnle K.* MacLow M.-M. Chyba C. F. Some Consequences of the Collision of a Comet and Jupiter At the time we write this, comet Shoemaker-Levy IX (1993e) is expected to strike Jupiter on July 21 1994 (IAU circular 5800; D. K. Yeomans, pers. comm.). Based on the assumption that the fragments are as dark as P/Halley, the largest may be 10 km across (G. Shoemaker, pers. comm.). If so, the collisions will release some 10^31 ergs, which is comparable to the energy released by the Cretaceous-Tertiary (K-T) impact to the detriment of the dinosaurs et al. The energy to be released scales with the size of the fragments; a 1-km fragment would release only 10^28 ergs. Here we present model results of the catastrophic disruption and consequent explosion of cometary bodies hitting Jupiter. The model is directly based on our models of similar phenomena occurring on Earth. In these models we integrate equations describing aerodynamic drag and ablation of a spreading, fragmenting impactor. Ten kilometer comets explode at about the 100 bar level. One kilometer comets explode at about the 5 bar level. In either case the resulting fireball will rise bouyantly out of the atmosphere on a time scale of a minute. The fireball will lift with it water and other less volatile volatiles that are presently trapped below the visible cloud cover. The predicted Jovian impact qualifies as a serendipitous possible test of these models, although it may have more primal resonances as well. Marley M. S.* The Seismological Impact of Comet Shoemaker-Levy The impact of Comet Shoemaker-Levy (1993e) into Jupiter's atmosphere will release energies of l0^3l to 10^28 ergs (assuming impactor diameters of 1 to 10 km). A portion of this energy will be carried away as acoustic waves. A shock wave with an initial characteristic period of about 1 to 3 min (Zahnle et al., submitted) is generated by the explosive destruction of the comet. With distance from the explosion the shock dissipates into a pressure wave and the wave period increases. Acoustic waves will also be excited by the rapidly rising fireball resulting from the explosion. Downward-propagating components of the wave front will refract upward at various depths in the planet. Upon reaching the upper troposphere, those waves with periods longer than the acoustic cutoff period (about 4 min for Jupiter) will reflect downward and become trapped in the planet. These waves will excite the acoustic oscillation modes of the planet. Observed Jovian acoustic modes (Mosser et al. (1993) A & A 267:604) have reported periods of 8 to 17 minutes and energies of about 10^28 ergs/mode. Since the comet-produced acoustic waves will have predominantly shorter periods and comparable or smaller energies, the influence of the comet impact on the observable p-mode spectra may be small. However, those waves with periods less than the acoustic cut-off period will, after refraction in the interior, propagate upward past the tropopause. These waves will break, delivering energy and momentum into the stratosphere. The locations of stratospheric perturbations on the opposite side of the planet will reflect the paths taken by these waves. An annular "shadow zone" with no short-period wave paths connected to the impact point will be produced by the lower sound speed in Jupiter's core. Time- and spatially resolved observations of stratospheric temperature following the impact may thus provide a diagnostic of Jupiter's interior structure. Ahrens T. J.* Takata T. O'Keefe J. D. Comet Shoemaker-Levy 9 Impact on Jovian Atmosphere Dispersed fragments of Shoemaker-Levy 9 are expected to impact Jupiter in July 1994. Impact is expected because the predicted orbit intersects ~4 x 10^4 km from Jupiter's center. The largest of some 10 dispersed fragments are reported to have a diameter of 10 km. These fragments are expected to penetrate the jovian atmosphere with the initial velocity of 60 km/s at an angle of 40 degrees from the zenith. We have conducted three-dimensional numerical simulations of cometary penetration into the jovian atmosphere using the Smoothed Particle Hydrodynamics (SPH) method. The SPH method is a fully Lagrangian method and suitable for describing the motion of a highly distorted impactor. Hydrogen and an equation of state for ice are used to describe the jovian atmosphere and the icy comet respectively. We predict the energetics of energy transfer to the jovian atmosphere, the amount and distribution of cometary materials inserted into Jupiter's atmosphere, and the degree of atmospheric ionization, its radiative signature as a function of time, versus atmospheric height. We predict the light available, which could be reflected by the Galilean satellites and hence be immediately visible to the Earth upon impact. Postimpact events, which include focused free oscillations, may be observable from the Earth. A 10-km-diameter cometary fragment suffers ablation and vaporization during penetration. Transfer of ~50% of the kinetic energy to the jovian atmosphere occurs within a few hundred kilometers below th