DPS 34th Meeting, October 2002
Session 3. Mars Surface
Oral, Chair(s): N. Barlow and E.Z. Noe-Dobrea, Monday, October 7, 2002, 9:30-11:00am, Room M

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[3.05] Spectral variability in the layered terrain of Melas Chasma: Possible evidence for hydroxides using MGS/TES

E.Z. Noe Dobrea, J.F. Bell III (Cornell University), M.J. Wolff (Space Science Institute), M.D. Smith (NASA Goddard Space Flight Center)

In an attempt to constrain the mineralogy of both “anomalous soils” (identified as having a stronger 3-\mum absorption than “normal” soils of comparable reflectance) as well as the putative hydrogen-bearing mineral phase seen at equatorial latitudes in both ground-based near-IR spectra and Mars Odyssey GRS/NS measurements, we have performed band-depth analyses of Mars Global Surveyor Thermal Emission Spectrometer (MGS/TES) data in spectral regions where absorptions caused by metal hydroxides and oxyhydroxides could exist. We searched mid-infrared spectral databases to identify the most potentially diagnostic spectral regions to examine. Possible diagnostic spectral features outside the 500-800 cm-1 saturated CO2 absorption include an ~1100 cm-1 absorption found in hydroxylated aluminosilicates such as boehmite, and an ~890 cm-1 absorption found in ferrous oxyhydroxides (e.g., goethite) and aluminum hydroxides (e.g., gibbsite and diaspore), but absent in other hydroxides (e.g., magnesium hydroxides). Accurate atmospheric modeling is required because the 1100 cm-1 region includes some CO2 and dust absorption, and the 890 cm-1 region includes minor H2O absorption.

In our preliminary results, which concentrate on the Melas Chasma region of Valles Marineris, we find band-depths of up to 0.6% (4\sigma above the noise level). These are about 3 times greater in the interior deposits than in the surrounding plains (as would be expected from atmospheric absorption), but are coherently variable within the deposits, precluding a solely atmospheric cause. The variability in the interior of the Chasma tends to be associated with 1) geologic features (such as the interior layered deposits), where band-depths may vary by a factor of 2 on the scale of tens of kilometers); and 2) surface temperature variations (on a scale of tens to one hundred kilometers). Despite the latter association, there does not seem to be a larger-scale correlation between band-depth and temperature: the difference between the floor of the Chasma and the surrounding plains is evident in the band-depth map but not in the temperature map, whereas the band-depth map does not show the strong variability between the floor and the walls leading to the plains that is readily apparent in the temperature map. We present new work involving a full radiative atmospheric correction and spectral deconvolution of the regions of interest in order to futher constrain the surface mineralogy.

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.