HR: 09:11h
AN: P31A-03    [Abstracts]
TI: Albedo and Multispectral Properties of Rocks and Soils at Gusev and Meridiani from the Mars Exploration Rover Pancam Imaging Systems
AU: * Bell, J F
EM: jfb8@cornell.edu
AF: Cornell University, Dept. of Astronomy, 402 Space Sciences Bldg., Ithaca, NY 14853 United States
AB: The Mars Exploration Rover Pancam multispectral imaging systems have been operating for over an Earth year on the martian surface, acquiring more than 48,000 high resolution 400 to 1100 nm images at hundreds of locations along more than 6 km of total rover traverse odometry as of early February 2005. Multispectral images at these wavelengths can be used to assess the geologic context and topography in Gusev crater and Meridiani Planum and to provide constraints on the mineralogy and physical properties of iron-bearing rocks and fines. The use of color information (near-UV to near-IR) has been particularly important in deciding where to make more detailed elemental and mineralogic measurements using the rovers' in situ instruments. The Pancam multispectral properties of Gusev plains rocks and soils are dominated by a strong ferric absorption edge indicating the presence of significant nanophase dust coverings or coatings on all surfaces. Soils exposed by wheel actions or rock interiors exposed by RAT abrasion have weaker (or no) ferric bands and near-IR reflectances consistent with the presence of relatively pristine ferrous phases like pyroxene or olivine. Columbia Hills materials display more geomorphologic evidence for alteration than plains materials, but their Pancam spectra are generally similar to plains materials, even in areas where in situ measurements have detected low abundances of alteration phases like hematite and goethite. The average albedo of Gusev materials is 0.25+/-0.05, varying between 0.20 for dark wind streaks and 0.30 for brighter hollows. The Pancam multispectral properties of rocks and soils at Meridiani Planum display a wider range of diversity. Dark soils exhibit near-IR spectral slopes consistent with the presence of ferrous minerals, and similar to disturbed subsurface soils at Gusev. Rarer bright soils (some of which underly darker soils) are ferric rich and spectrally similar to homogeneous global dust. Some of the ubiquitous spherules are bluer than typical soils, some are gray and consistent with the spectral properties of coarse-grained hematite at Pancam wavelengths, and some exhibit near-IR spectra indicating the presence of a different ferric oxide (possibly an oxyhydroxide or oxyhydroxysulfate). Some small dark cobbles exhibit relatively gray spectra and occasional glints, suggesting either that they are also carriers of coarse-grained hematite, have glassy coatings, or have polished surfaces. Bright outcrop rocks have a strong ferric absorption edge and weak 900 nm band that probably indicates the presence of an aeolian dust component and/or a nanophase ferric oxyhydroxide within the materials identified as sulfur- and chlorine-rich by in situ measurements. Two large dark rocks have been encountered so far in the plains. One, Bounce Rock, has a Pancam spectrum that exhibits one of the strongest "1 micron" absorption features ever measured on the surface, indicating a significant relatively pristine ferrous component, subsequently identified as pyroxene from Moessbauer and Mini-TES measurements. The other, Heat Shield Rock, has Pancam spectra consistent with a dusty Fe-rich meteorite. The average albedo of Meridiani plains materials is 0.12+/-0.01. Bright, dusty ripples and wind streaks exhibit albedos ranging from 0.19 to 0.29, and bright reddish outcrop rocks exhibit an average albedo around 0.25. This presentation will summarize the observations used to identify these different spectral classes of materials, their occurrence and distribution, and their implications for the origin and evolution of materials at both landing sites.
UR: http://marswatch.astro.cornell.edu/pancam_instrument/
DE: 6200 PLANETOLOGY: SOLAR SYSTEM OBJECTS (New field)
DE: 6225 Mars
DE: 6297 Instruments and techniques
SC: Planetary Sciences [P]
MN: 2005 Joint Assembly