M. Ramsey, Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, PA

S. Wright, Department of Geological Sciences, Arizona State University, Tempe, AZ

Data from the Earth-orbiting Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Mars-orbiting Thermal Emission Imaging System (THEMIS) instruments are highly complimentary in both spatial and spectral resolution. Therefore, ASTER serves as an excellent, longer-term analog for data currently being returned from THEMIS. Thermal infrared (TIR) data from ASTER were used in this study to identify the lithologic distribution of the Meteor Crater ejecta blanket and the surrounding (~3 km) plain. Samples of the primary lithologies collected at Meteor Crater during detailed fieldwork provided an opportunity to ground-truth both the ASTER data as well as previously acquired airborne TIR data. The compositional unit mapping agrees well with these past studies considering the effects of resolution degradation from 3 m/pixel (airborne) to 90 m/pixel (ASTER). The work at Meteor Crater also has direct bearing on the interpretation of THEMIS data collected over many similarly-sized impact sites on the surface of Mars. These small impact craters have not been studied in detail in the past due to the low spatial resolution of orbiting TIR instruments. We used the same data analysis methodology as that applied to Meteor Crater, to examine THEMIS TIR data of Winslow Crater (provisionally-named), a small (~ 1 km) impact crater in Syrtis Major. The crater rim and ejecta blanket were found to contain larger block sizes and a lower albedo than the surrounding ejecta-free plain, indicating a young impact age and little to no accumulation of windblown dust. Using both TES and THEMIS data, the composition of the rim, ejecta, and surrounding plain was determined to be dominated by basalt. However a pre-impact stratigraphy of layered igneous rocks has also been identified at this site. Results from this work are now being extended to other fresh-appearing impact sites on Mars. It is expected that the high spatial resolution of THEMIS TIR data coupled with the potential of recent impacts from small meteorites, can be used to map the upper stratigraphy at various locations on Mars. These studies could also be used to help better constrain models for the: approximate age of the impacts, thermophysical properties of similar ejecta blankets, and regolith to dust thicknesses at these sites.

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Submitted: American Geophysical Union Fall Meeting
Invited: P17: Thermal Infrared Remote Sensing of Mars From TES and THEMIS
Date: December 5 - 9, 2004