The Behavior of Metal-rich Meteorites in the Thermal Infrared - Implications for Dust Thickness, Spectral Anomalies, and the Continued Remote Sensing of Meteorites on Mars Using Mini-TES.

Details The Behavior of Metal-rich Meteorites in the Thermal Infrared - Implications for Dust Thickness, Spectral Anomalies, and the Continued Remote Sensing of Meteorites on Mars Using Mini-TES. The Behavior of Metal-rich Meteorites in the Thermal Infrared - Implications for Dust Thickness, Spectral Anomalies, and the Continued Remote Sensing of Meteorites on Mars Using Mini-TES.

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p53a1433a&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P53A-1433

Other

1028 Composition Of Meteorites (3662, 6240), 1039 Alteration And Weathering Processes (3617), 1620 Climate Dynamics (0429, 3309), 1640 Remote Sensing (1855), 6225 Mars

Scientific paper

The scientific value of meteorites resting on the surface of Mars (or any other planetary body) lies in their hypersensitivity to chemical (aqueous) alteration. Reduced iron metal, present in some 88 percent of all terrestrial falls, will oxidize in water-contact to generate secondary iron oxide and oxyhydroxide products. The metal content ranges from <1 % for L ordinary chondrites [e.g. 1], to more than 20 % for H ordinary chondrites [e.g. 2], subequal volumes with silicate phases in the case of many stony-irons and CB chondrites [e.g. 3 & 4], to close to 100 % for irons (less sulfides, occasional silicates, and other trace non-metal fractions). Weathered meteorites thus assist in the assessment of paleoclimatic history and habitability potential at the locations where they are found. Understanding the behavior of metals in the infrared would be useful for interpreting spectra of these meteorite classes. TIR spectra of metal-rich meteorites are therefore being included in the thermal emission spectral library reported in [5]. Metal present in large volumes within such rocks appears to have both predictable and counterintuitive effects on spectral patterns, requiring further evaluation. The Miniature Thermal Emission Spectrometer (Mini-TES) instrument on the Mars Exploration Rovers has been effective in remote sensing iron meteorites because of their highly reflective behavior in the thermal infrared [6]. The radiance of an ideal metal is that of a graybody, demonstrating greatly reduced emissivity with greatly enhanced reflectivity. This can lead to a reflected spectrum of the environment. On Mars, reflected features tend to be those of the downwelling atmosphere. Although simulating this behavior has been difficult in the laboratory for natural surfaces because they tend to scatter the downwelling radiance, the effect has been recreated for a polished slab of the Canyon Diablo iron meteorite using an artificial quartz-based control. We have collected TIR measurements in concert with incremental Mars dust analog loading and determined that approximately one order of magnitude less dust is required to obscure the effect in the thermal infrared than in visible light. A maximum thickness of only 14 microns of dust is sufficient to completely obscure reflective effects evident on an undusted, polished slab surface. The result has implications for dust thicknesses coating the surfaces of the iron meteorite Meridiani Planum, found by the Opportunity rover at Meridiani Planum; and Alan Hills and Zhong Shan, found at Gusev Crater by the Spirit rover. Future evaluations of Mini-TES spectra will incorporate these findings as the search for weathered meteorites continues. References: [1] Pun A. et al. (1990) Meteoritics 25, 237-239. [2] McCoy T.J. (1990) Meteoritics 25, 77-79. [3] Weisberg M.K. et al. (2002) LPSC XXXIII, abstract 1551. [4] Ivanova M.A. et al. (2005) 68th Annual Meteoritical Society Meeting, abstract 5073. [5] Ashley J.W. and Christensen P.R. (2007) AGU Fall Meeting abstract 12506. [6] Schroder, C., et al. (2008), JGR 113, E06S22, doi:10.1029/2007JE002990.

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