Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p23c0066b&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P23C-0066
Physics
5464 Remote Sensing, 5470 Surface Materials And Properties
Scientific paper
One objective of the THEMIS instrument on the Mars Odyssey spacecraft is to determine the mineralogy of deposits associated with aqueous environments. Sulfate minerals are important indicators of such environments. Orbital data at Mars suggest the occurrence of near surface water. This hydration may be associated with hydrated sulfate species that have been observed in situ and by orbital measurements. OMEGA data has identified sulfates at several locations and TES data may indicate the presence of sulfates at Aram Chaos. Additionally, analysis of martian surface materials (e.g. modeling of APXS chemistry and linear un-mixing of the mini-TES data) by the Mars Exploration Rovers suggests sulfates are present. These results are especially compelling at the Opportunity landing site where sulfate identification corresponds with light-toned outcrops that appear prevalent throughout Meridiani Planum. Several regions in Meridiani Planum were selected for analysis with THEMIS data based on the presence of light toned outcrops and previous detections. Sulfate analysis was performed using the combination of THEMIS VIS geomorphology and THEMIS TIR mineralogy. In the thermal infrared region of the spectrum, sulfates have deep, well-defined features in the 8-10 micron region that vary in position based on chemistry and hydration state. Compared to a pure basalt spectrum, at THEMIS spectral resolution the affect of the addition of sulfates is to steepen the slope of the spectral shape between band 3 and band 4. The slope between bands 4 and 5 varies depending on hydration state. Therefore, the spectral shape between bands 3 and 4 gives sulfate detection while the shape between 4 and 5 aids in identification. To detect these sometimes subtle spectral shape changes, band math algorithms were used to both detect and identify sulfates in THEMIS data. THEMIS images near the landing site, where light-toned outcrops appear to be confined to mainly crater walls, did not show a change in the spectral shape consistent with sulfate minerals. However, in several TIR images analyzed, the results of the band math algorithms correspond well with light toned outcrops in VIS images. In these regions the light-toned surface materials are pervasive indicating that this method can work well for the detection of sulfate materials at the martian surface, but may be constrained by spatial resolution.
Baldridge Alice
Christensen Paul
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