ROSS BEYER, University of Illinois

ADVISOR:Deborah Domingue, Lunar and Planetary Institute

"Correlation Between Volcanic Activity and Temporal Variability of the Satellite Io." The IUE spacecraft made observations of the galilean satellites for over a decade with the long wavelength prime (LWP) and long wavelength redundant (LWR) cameras. As spacecraft instruments were better understood, the calibration software for IUE's observations has been updated and refined. All LWP observations have been reprocessed using the new software, and reprocessing of LWR images has begun. Initial comparisons of spectra taken between 1984 and 1986 to spectra taken in 1995 show spatial and temporal variability on all four of the satellites.

This project will study Io in greater depth to correlate volcanic activity with temporal surface variability. In addition, IUE spectra will be compared to laboratory spectra of materials whose absorption bands have been detected. Spectral mixing models (such as those developed by Hapke in 1981, 1984, and 1986) will be applied to the laboratory data to attempt to match observed spectra of Io. Understanding how Io's surface materials are mixed will give insight to the geological processes altering the satellite's surface. Io's surface also varies from area to area, so this study will investigate whether this variability is caused by differences in the amount of mixing of surface materials or whether it is caused by different aereal units of each material.

The intern will correlate temporal changes with known areas of volcanic activity and will chronicle the activity of these volcanic areas from IR observations in the literature. Then, using the laboratory spectra supplied by Wagner et al. (1987), the student will compare observed spectra of Io to attempt to model mixing within Io's regolith. The laboratory dataset includes reflectance spectra of terrestrial, lunar, and meteoritic powders and frosts, and software to model mixing is currently being written.

PAUL COX, LeTourneau University

ADVISOR:Michael B. Duke, Lunar and Planetary Institute

"Theoretical and Experimental Investigation of Regolith/Ice Interactions in Lunar Cold Traps." In this project the intern will develop models of increasing complexity that describe the range of possible configurations of ice deposits at the lunar south pole. The intern will review previous work modeling the accumulation of ice in permanent lunar cold traps and the effects of micrometeoroid and meteoroid impact on ice, regolith, and ice/regolith mixtures. A mathematical modeling approach will be defined using various assumptions about ice accumulation rate and regolith turnover due to impact gardening and experiments that demonstrate critical parameters will be designed.

TANYA DI VALENTIN, University of Ottawa

ADVISOR:Michael E. Zolensky, NASA/Johnson Space Center

"Characterization of Iron-Nickel Sulfides Formed in the Solar Nebula." Sulfur is an important element, found in all galactic environments. The most common sulfur-containing minerals are Fe and Fe-Ni sulfides, which is the only group of minerals found in all extraterrestrial samples. There is a huge number of different sulfide minerals, but each has its own well-determined stability conditions. This means that, if we can determine which sulfides are present in a given sample, we can establish important physical-chemical constraints on the early solar system, giving us a better view of processes like planet formation and subsequent evolution. For this study, we will use an electron beam to determine the compositions of sulfides in the most primitive extraterrestrial material available: cometary and asteroidal particles collected in Earth's stratosphere called chondritic interplanetary dust particles (IDPs) and type 3 ordinary chondrites, and laboratory-produced analog materials. The small grain size of these sulfides (generally 15_50 nanometers across) will make transmission electron microscope analysis necessary here. The situation is easier for the type 3 chondritic meteorites for which scanning electron microscope and electron microprobe analyses will suffice. We have obtained artificially produced sulfides from experimental studies performed by Dante Lauretta and Bruce Fegley, our collaborators at Washington University. These samples result from the first realistic attempt to duplicate sulfide growth in the solar nebula in the laboratory, and promise a lot of surprises. We will analyze these samples by a combination of SEM and TEM techniques.

RYAN EWING, The Colorado College

ADVISORS: Paul Schenk, Steven Clifford, Allan Treiman, Lunar and Planetary Institute

"Stereo Topography of Mass-Wasting Deposits on Mars." Mars has a variety of unusual geologic landforms, including splosh craters, terrain softening, debris aprons, and other mass-wasting phenomena. Some of these features suggest water- or ice-rich rock or regolith. We ultimately seek to understand the role of subsurface water on Mars in the formation of these features. The goal of this project will involve making the first topographic measurements of some of those features formed by mass-wasting in order to determine local surface slope, surface profiles, and material thickness, all of which are unknown. Simple analytical models, pending more sophisticated modeling efforts, may be used to ascertain if these deposits are unusual mechanically, testing the idea that these deposits are water-rich. Two sites in Nilosyrtis Mensae have been selected as candidate features that can be mapped topographically. The intern will be responsible for selecting other sites to examine additional types of mass-wasting deposits. The intern will run a stereo autocorrelation program to generate stereo digital elevation models over target sites, using these to measure slope of deposit and scarp face and to calculate volumes. Simple mechanical models may be applied to these results to make a preliminary assessment of rheologic properties.

NANCY K. FORSBERG, Hofstra University

ADVISORS: Robert R. Herrick, Benjamin Bussey, Lunar and Planetary Institute

"The Effects of Impact Angle on the Shape of Lunar Craters." Using stereo photogrammetry techniques, the intern will generate and analyze high-resolution topography of selected lunar craters to determine the effects of impact angle on crater shape. A number of laboratory experiments have shown that different impact angles produce distinctive patterns in the ejecta blanket, and these patterns have been observed around craters on the Moon and the other terrestrial planets. These experiments also showed systematic changes in crater shape, but a lack of high-resolution topographic data for smaller fresh craters has prevented testing whether the laboratory shapes are mimicked by actual craters. The Clementine mission collected stereo imagery at approximately 100 meters resolution for roughly one-third of the lunar surface. This is sufficient resolution to
generate digital elevation models (DEMs) of topography with a few hundred meters horizontal resolution. Using a combination of manual and automatic matching techniques to find corresponding points on the stereo pairs, the student will generate DEMs for about 10 fresh lunar craters that are approximately 15 kilometers in diameter. Based on the pattern of ejecta, the craters are chosen to represent a range of impact angles at a single crater diameter. The 15 kilometer diameter is chosen so the craters are large enough for features to be easily resolvable in the DEMs but small enough to minimize the effects on crater shape from the modification stage associated with complex crater formation. The resulting DEMs will be analyzed for systematic variation in crater shape and rim height within and among the selected craters, and comparisons will be made with the laboratory data.

CATHERINE ROSS GRAHAM, Brown University

ADVISOR:David S. McKay, NASA Johnson Space Center

"Scanning Electron Microscope Studies of Carbonate Precipitates." A major goal of the exploration of Mars is to determine whether life has developed there. Recent data on martian meteorite ALH84001 reveal complex zoned carbonates that may be associated with martian microbial activity. The summer project will consist of a Scanning Electron Microscope (SEM) study of selected carbonates formed by precipitation at low temperatures in natural and laboratory environments on Earth. The objective is to try to understand the processes by which bacteria may play a role in the nucleation and growth of these carbonates and to determine whether they leave distinctive signs or fingerprints that can be found within or on the carbonate precipitates. We currently have a variety of appropriate terrestrial samples and plan to get more by summer. The intern project is to study representative samples of each of these materials with the scanning electron microscope (possibly supplemented by TEM studies of selected samples) and to characterize the morphology and chemistry of the carbonate precipitates and associated phases. Some samples will be selectively etched to reveal internal features. The project will also include a literature search on carbonates formed in recent natural environments. Results will contribute to investigations of possible life on Mars by providing new data on possible analogs and by developing new techniques for studying these materials. Important findings will also be incorporated into advanced planning for Mars robotic exploration and the landing site selection process for future missions.

KAREN JAGER, Pomona College

ADVISOR:Carlton C. Allen, Lockheed Martin Engineering & Science Co.

"Martian Surface Material Simulant." NASA is developing a simulant of the surface material of Mars to be used for testing analytical instruments, engineering designs, and spacesuits, as well as for museums and classrooms. An important part of this effort involves characterizing the simulant and comparing it to our current understanding of the martian surface. The intern will be a key participant in this effort, characterizing splits of the simulant by a wide variety of analytical techniques. The results will be compiled into a technical paper on which the intern will be a co-author.

MUTSUMI KOMATSU, University of Tokyo, Tokyo

ADVISOR:Arch Reid, Lunar and Planetary Institute

"Prior's Rules and the LL Chondrites." The range of textures and of mineral and bulk compositions within the LL chondrites has been interpreted as representative of a progressive metamorphic sequence (LL3_LL6) within a series of meteorites of near- constant bulk composition. Prior's Rules for the ordinary chondrites refer to the relationship that with decreasing metal content there is a corresponding increase in Ni content of the metal and in FeO content of the ferromagnesian silicates. The variability in ordinary chondrites is thus representative of a range of oxidation states (and oxygen contents) within an essentially constant bulk composition.
The project will use mineral composition data and mineral abundance data within individual LL chondrites to test whether Prior's Rules apply within the LL chondrite group. Polished thin sections from the Antarctic Meteorite Collection at JSC will provide the materials for the study, and these samples will be analyzed using electron microprobe facilities at JSC. These data will also be used to determine whether the metamorphic sequence LL4-LL6 is a sequence representing progressive annealing at successively higher temperatures, whether within each of the metamorphic types (4, 5, 6) there are progressive sequential differences, and the extent to which the type 4 to type 6 sequence is one of progressive oxidation, as suggested by McSween and Labotka (1993).

KACPER KORNET, Warsaw University

ADVISOR:Tomasz Stepinski, Lunar and Planetary Institute

"From Dust to Planetesimals — Global Evolution of Rocky Solids in the Solar Nebula." It is currently thought that planets formed from the accumulation of solid matter entrained in the solar nebula. This project concentrates on modeling this part of the accumulation process that starts from small particles suspended in the gaseous nebula and ends when most of the solid material aggregates into 1_10-km-sized planetesimals. The result of the project should be a theoretically derived surface density distribution of deposited rocky solids, a quantity that can also be inferred from the present-day planetary distribution of masses. The goal of the project is to determine whether theoretical models of the solar nebula can account for the large-scale architecture of the solar system.

SARAH KATHRYN NOBLE, University of Minnesota

ADVISOR:Gary E. Lofgren, NASA Johnson Space Center

"Experimental and Petrographic Study of Recycling in the Solar Nebula and the Origin of Chondrules." Chondrules form in the solar nebula during events that process the earliest materials that now comprise the materials in our solar system. Understanding the formation of chondrules gives insight into the physical processes taking place in the nebula. Recent work on chondrule formation suggests that nebular processes are more complicated than previously thought, involving a more complex set of recycling and aggregation processes among previously formed chondrules, chondrule fragments, and other components present in the nebula. These aggregates are chondrule precursors and have implications for determining chondrule composition and the ultimate processing of nebular materials. Work on this project will concentrate on analysis of experiments on the aggregation and partial-melting processes that form chondrules.

MATTHEW PRITCHARD, University of Chicago

ADVISOR:Walter S. Kiefer, Lunar and Planetary Institute

"The Effects of Lithospheric Rheology on Mantle Convection on Mars." An important issue in martian geophysics is the effect that the planet's lithosphere has on the gravity and topography produced by mantle convection. A purely elastic lithosphere will act to resist convective uplift, whereas in a more realistic visco-elastic lithosphere, viscous flow will relax elastic stresses over time, allowing a greater degree of convective uplift. The intern will assess the interaction between elastic and viscous processes in the martian lithosphere, leading to an improved understanding of how mantle convection affects the planet's topography and gravity.

BRADLEY THOMSON, Harvey Mudd College
ADVISORS:Paul D. Spudis, Benjamin Bussey, Lunar and Planetary Institute

"Geological Models of Lunar Impact Craters from Clementine Data." Multispectral and topographic data from the Clementine spacecraft allow us to map the composition of various lunar landforms. Impact craters are of particular interest because they excavate and expose interior portions of the Moon that would otherwise remain unseen. Craters of various sizes probe different levels of the crust and a systematic study of several individual craters should make it possible to reconstruct the three-dimensional geological structure of a region of the Moon.

In this project the intern will use Clementine multicolor image data to make compositional maps of the surface materials associated with several large impact craters, including Copernicus (97 kilometers diameter, 9°N, 21°W). In addition, the intern will use special stereo image coverage obtained by the Clementine spacecraft to make a digital terrain model (DTM) of each crater. These DTMs will be compared to previously compiled topographic maps and other DTMs for accuracy, as well as coordinated with the global topographic map provided by the Clementine laser altimetry. The stereo DTMs and the multispectral, compositional data will be merged into geological block models of the crust for at least two, and as many more as can be completed, regions of the Moon. From these data, the three-dimensional nature of a region of the lunar crust will be deduced. The project will involve digital image processing, geological mapping, and interpretation of remotely sensed compositional data.