Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p53a1437r&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P53A-1437
Other
3934 Optical, Infrared, And Raman Spectroscopy, 5220 Hydrothermal Systems And Weathering On Other Planets, 5410 Composition (1060, 3672), 5464 Remote Sensing, 6225 Mars
Scientific paper
The Mars Exploration Rover (MER) Spirit has discovered surprisingly high concentrations of amorphous silica in the Inner Basin of the Columbia Hills. As described by Squyres et al. (2008, Science, 320, 1063), within a topographic lowland called Eastern Valley, Spirit's Alpha Particle X-Ray Spectrometer (APXS) measured a composition of >90 wt.% silica at the soil feature "Gertrude Weise", a record high for Mars. The Mössbauer spectrum of this target is featureless. APXS measurements of light-toned nodular outcrops also show high silica concentrations (up to ~72 wt.%), which in some locations co-exist with sulfur-rich soils. Miniature Thermal Emission Spectrometer (Mini-TES) results from the soils and nodules are consistent with opal-A. These deposits have been found adjacent to "Home Plate", a layered plateau interpreted as the product of explosive volcanism. The silica-rich soils and nodules are consistent with sinters and/or residues formed in a hydrothermal system, and may be related to the same hydrovolcanic activity that produced Home Plate. We have begun to map the distribution of high-silica materials in Gusev Crater more extensively using remote sensing, in order to understand the regional extent of possible hydrothermal activity. Spirit's Pancam instrument has collected visible to near-infrared relative reflectance spectra of the region in 11 unique wavelengths. We find that a distinct absorption feature at the longest Pancam wavelength (1009 nm) appears to be characteristic of the high-silica soils and nodules. By mapping the occurrence of this feature with other spectral parameters in Pancam images, we can remotely identify potential amorphous silica deposits elsewhere in the Columbia Hills. Here we present a map with our proposed regional distribution of silica-rich materials within the rover's Gusev Crater traverse area. The mineralogic origin of the 1009nm feature is enigmatic; reflectance spectra of amorphous silica are typically featureless in near-infrared wavelengths (as are spectra of TiO2, which was also detected by the MER team in APXS data of the Gusev high-silica soils). For comparison, we have performed laboratory analyses of silica sinters and residues from hydrothermal sites at Wairakei, New Zealand and Geysir, Iceland. Based on spectral mixing models with these and other mineral spectra from digital spectral libraries, we hypothesize that the presence of water or OH, either free (trapped in pore spaces) or bound in a mineral structure (perhaps from a minor species produced together with the high-silica materials), is responsible for the spectral feature observed by Pancam.
Bell Jon F.
Cloutis Edward A.
Rice Melissa S.
Wang Anzhong
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