HR: 0800h
AN: P21A-0129    [Abstracts]
TI: VNIR spectral classes of rocks in the Columbia Hills, Gusev Crater, Mars as observed by the Mars Exploration Rover Spirit's Pancam
AU: * Farrand, W H
EM: farrand@spacescience.org
AF: Space Science Institute, 4750 Walnut Street, #205, Boulder, CO 80301 United States
AU: Bell, J F
EM: jfb8@cornell.edu
AF: Department of Astronomy, Cornell University, 610 Space Sciences Building, Ithaca, NY 14853 United States
AU: Johnson, J R
EM: jrjohnson@usgs.gov
AF: USGS Astrogeology Research Program, Flagstaff Field Center 2255 N. Gemini Drive, Flagstaff, AZ 86001 United States
AB: The Mars Exploration Rover Spirit has been examining the Columbia Hills in Gusev Crater for over 400 martian sols and has observed a number of texturally, chemically, mineralogically and spectrally distinct rocks- both in situ and out of place. This paper reports on the discrimination of these rocks into spectral classes using the rover's Panoramic Camera or Pancam. The Pancam has 11 spectrally unique channels in the Visible and Near Infrared (VNIR) (400 to 1010 nm) spectral range. Six spectral classes were determined as of sol 419 of the mission and these include plains basalts typified by the rock Adirondack, lower West Spur rocks, a larger number of rocks higher on the West Spur (Clovis-class), rocks on the northwest flank of Husband Hill (Wishstone-class and Peace-class), rocks near the crest of Husband Hill (Watchtower-class). Among the Cumberland Ridge rocks examined after sol 419, the Larry's Lookout outcrop includes Watchtower-class rocks, the Jibsheet outcrop has rocks with similar spectral characteristics to the Watchtower class, and the Methuselah outcrop is similar in spectral character to the Wishstone and Lower West Spur classes. Higher on Husband Hill, low albedo rocks, some with specular reflecting surfaces and some with a clast and matrix texture were observed in the Voltaire region, and the clasts and matrix materials are spectrally distinct from each other. Diagnostic NIR features of these classes include a shallow long wavelength band center at, or longer than, 1000 nm in the Clovis-class, a deeper absorption centered at 930 nm in Lower West Spur and Wishstone-class rocks, and an absorption centered at 900 nm with a steep increase in reflectance going out to the 1000 nm band in the Watchtower class. There is also a correspondence between Mössbauer measurements of Fe³⁺/Fe_Total and Pancam measurements of 535 nm band depth. Tentative assignments can be made of minerals/materials responsible for these spectral features. The West Spur/Clovis-class resemble glass-dominated tuffs. Features in Watchtower-class rocks indicate higher fractions of hematite. Lower West Spur, Wishstone-class, and related (e.g., Methuselah outcrop) rocks have a deeper NIR absorption consistent with a significant pyroxene fraction. The variety of spectral features observed by Pancam is consistent with diverse lithologies that reveal a complicated history likely involving a series volcanic and impact related events, interspersed by various amounts of aqueous alteration during the evolution of the Columbia Hills complex.
DE: 5460 Physical properties of materials
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 5494 Instruments and techniques
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: Fall Meeting 2005