HR: 16:30h
AN: P24A-03    [Abstracts]
TI: VNIR spectral features observed by the Mars Exploration Rover Opportunity in hematite-bearing materials at Meridiani Planum
AU: * Farrand, W H
EM: farrand@spacescience.org
AF: Space Science Institute, 4750 Walnut St Suite 205, Boulder, CO 80301 United States
AU: Bell, J F
EM: jfb8@cornell.edu
AF: Cornell University, Department of Astronomy, 402 Space Sciences Building, Ithaca, NY 14853-6801 United States
AU: Morris, R V
EM: richard.v.morris1@jsc.nasa.gov
AF: NASA, Johnson Space Center, Code SN3, 2101 NASA Road 1, Houston, TX 77058 United States
AU: Joliff, B L
EM: blj@levee.wustl.edu
AF: Washington University, Department of Earth and Planetary Sciences, Campus Box 1169 1 Brookings Dr, St. Louis, MO 63130-4899 United States
AU: Squyres, S W
EM: squyres@astrosun.tn.cornell.edu
AF: Cornell University, Department of Astronomy, 402 Space Sciences Building, Ithaca, NY 14853-6801 United States
AU: Souza, P A
EM: paulo.antonio.souza@cvrd.com.br
AF: Companhia Vale do Rio Doce, Av. Dante Micheline 5.500 Ponta de Tubarao Jardim Camburi, 29090 900 Caixa, Vitoria es Brasil, 8001 Brazil
AB: The Mars Exploration Rover Opportunity was sent to Meridiani Planum based largely on MGS TES spectroscopic evidence of a large surface exposure of coarse grained gray hematite. The presence of hematite at Meridiani Planum has been confirmed through thermal infrared spectroscopy by the rover's Mini-TES instrument and by in-situ measurements by its Moessbauer (MB) spectrometer. Several types of hematite, as expressed by differences in MB spectral parameters, have been associated with various rocks and soils examined in Eagle crater and on the surrounding plains. The host materials include the small spherules (informally known as "blueberries") littering the floor of Eagle crater and the plains of Meridiani, the outcrop rock itself, specific types of soils, and two measurements on unique rocks in the Shoemaker's Patio area of Eagle crater. At the visible to near infrared (VNIR) wavelengths covered by the rover's multispectral Panoramic camera (Pancam), gray hematite is spectrally neutral. However, multispectral observations by Pancam of some of these hematite-bearing materials show discernable spectral features. Specifically, portions of the outcrop visible in the walls of Eagle crater display a strong 535 nm absorption feature. This feature resembles a similar feature in laboratory spectra of red hematite, but the characteristic 860 nm absorption of red hematite is either absent or is instead replaced by a longer wavelength absorption centered on Pancam's 900 nm channel. The blueberries display a deep and broad absorption centered on 900 nm and as well as an increase in reflectance in the 1009 nm band. The shape of the absorption feature in the blueberries is consistent with that seen in red hematite, but again the band minimum is displaced to a longer wavelength than would be expected for red hematite. The blueberries also lack the prominent absorption at the shortest wavelengths that would be expected of red hematite. The unique hematite-bearing (or coated) rocks at Shoemaker's Patio lack the very strong 535 nm band depth of other portions of the outcrop but still have a stronger 535 nm feature than most of the outcrop. Interestingly, VNIR spectra more consistent with that expected for red hematite have been found in cuttings released by grinding into outcrop by the rover's Rock Abrasion Tool. The cause of the observed spectral features in the portions of outcrop with strong 535 nm band depths and of the reddish rocks in the Shoemaker's Patio area is believed to be attributable either to red hematite mixed with other Fe3+ - bearing phases (such as jarosite and/or schwertmannite) or, at the longer wavelengths, with Fe2+ - bearing phases (such as pyroxenes). Determination of the nature of these iron-bearing materials will further elucidate the geologic, aqueous and diagenetic history of the rocks at Meridiani Planum.
DE: 5460 Physical properties of materials
DE: 5464 Remote sensing
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting