HR: 0800h
AN: P11A-0957    [Abstracts]
TI: A Global View of Martian Surface Compositions With MGS-TES Revisited: Regional-scale Spectral Deviations From Surface Types 1 and 2
AU: * Rogers, D
EM: adr@asu.edu
AF: Dept. of Geological Sciences, Arizona State University, Campus Box 6305, Tempe, AZ 85287-6305 United States
AU: Bandfield, J L
AF: Dept. of Geological Sciences, Arizona State University, Campus Box 6305, Tempe, AZ 85287-6305 United States
AU: Christensen, P R
AF: Dept. of Geological Sciences, Arizona State University, Campus Box 6305, Tempe, AZ 85287-6305 United States
AB: Previous global studies of martian low-albedo regions with MGS-TES data have identified 2 global spectral endmembers: Surface Type 1, which has been interpreted as basalt to basaltic-andesite, and Surface Type 2, which has been interpreted as either basaltic-andesite to andesite or basalt with alteration minerals or coatings. Using the 2 global endmembers plus the Meridiani Planum hematite spectrum, all low-albedo surfaces can be modeled with spectral RMS errors $<$0.5% at a spatial resolution of 1 pixel per degree (ppd), indicating that there are no regions of extreme spectral differences, such as those that would be caused by a large exposure of carbonate. However, spectral shape deviations from either global endmember that might be caused by small but geologically-significant differences in the characteristic mineralogy of Surface Types 1 and 2, such as a 10% increase in pyroxene abundance, would still be modeled reasonably well (RMS error $<$0.5%) with only the global endmembers. Model fits of spectra from regions that were previously mapped as mixtures of Surface Types 1 and 2 are often greatly improved if a set of mineral endmembers is used instead of the 2 global endmembers, indicating that Surface Types 1 and 2 may not account for all low-albedo regions on Mars. We have re-examined TES spectra from martian low-albedo regions to identify subtle spectral deviations from Surface Types 1 and 2 and found that in some regions, deviations occur in widespread but coherent distributions. Three regions have been found to have deviations from these spectral shapes across multiple orbits; the characteristic spectral shapes of these regions cannot be well-modeled using only Surface Types 1 and 2. Note that these regions are different than the local-scale exposures of olivine- and quartz-rich surfaces that have been previously-reported. The differences in the spectral shapes of these regions indicate that they may differ in primary mineralogy or alteration history from areas that exhibit the typical spectral character of Surface Types 1 and 2. When the characteristic spectral shapes of these regions are added to the global endmember set and used to model surface emissivity at 1 ppd, the distributions of Surface Types 1 and 2 are refined. Geologic context is an important consideration when interpreting the high-silica component of surfaces that exhibit Surface Type 2 spectral character (e.g. primary glass vs. secondary amorphous silica or zeolites); this work will help to clarify the distributions of the previously-identified surface types, and will identify the presence and distribution of newly-distinguished mineralogic assemblages.
DE: 5410 Composition
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting