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R.N. Clark, T Hoefen (USGS), J Moore (NASA Ames)
Approximately 3 years worth of Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) day-side, nadir-pointed, 10-wavenumber data have been culled from the TES database and projected into image cubes at full TES spatial resolution of ~3 km per pixel to provide near global coverage (to +/- 60 degrees latitude). Only the best, artifact free, spectra were selected for assembly but this still gave > 80% surface coverage. Multiple observations of the same area on the Martian surface were averaged. The hyperspectral image cubes were calibrated to radiance using internal black-body measurements and space measurements. Apparent emissivity was derived for each pixel using temperatures in the TES database. Atmospheric gas absorptions were removed and ancillary data were registered with the images, including albedo and MOLA topographic elevation. Spectral features were searched for using least squares feature analysis with reference spectral library features. The search was limited to regions of the TES spectra free of strong gas and dust absorptions and where TES has a high signal-to-noise ratio. The most spectrally abundant features found in the TES data to date are those due to pyroxenes, olivine, hematite and a possible sulfate. Searches for outcrops of other minerals, including carbonates, quartz, and those present in hydrothermal alteration systems have produced no definitive evidence of their presence. Such minerals, if they exist on Mars, are either significantly smaller than a TES pixel, or are buried by dust. Olivine maps a range of compositions, from FeO content <10 to 60 wt%, in different regions of Mars, and appears stratified in outcrops at certain elevations. Olivine composition tends to increase in iron with higher elevations on a global average. The correlation suggests the possibility that Fe-rich olivine was preferentially incorporated into stratigraphically younger units by fractional crystallization of mantle melts. The implications of this compositional stratification are under study but may indicate changing volcanic conditions over Martian geologic history. Funded by NASA MGS.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.