Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p13a1247j&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P13A-1247
Other
[5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6225] Planetary Sciences: Solar System Objects / Mars, [6240] Planetary Sciences: Solar System Objects / Meteorites And Tektites
Scientific paper
The Mars Exploration Rover Opportunity used the Pancam stereo camera to image the Fe-Ni meteorite “Block Island” extensively in 11 visible/near-infrared (434-1009 nm) bands to document variations in color and texture beginning on Sol 1961 (July 30, 2009). Pancam spectra of the meteorite suggest that a relatively thick coating of nanophase ferric-rich dust contaminated the surface of this rock, as well as nearby soil units. This resulted in positive 535 nm band depths on Block Island, compared to negative 535 nm bands observed on less dusty surfaces on Heat Shield rock (sol 352; Jan. 19, 2005), the other Fe-Ni meteorite measured by Opportunity. Despite the dust coating, distinct color variations were observed across the surface of Block Island, including intermittent to more contiguous occurrences of smooth materials with “purple” hues in Pancam false-color RGB representations using 434 nm, 535 nm, 753 nm bands (and distinct in decorrelation stretches using the same bands). These materials exhibited lobate margins that appeared to coat the underlying meteorite surface. Using Pancam images to colorize Microscopic Imager (MI) frames confirmed that the dark-toned, lobate, smooth surfaces observed in MI images were purple-colored in false-color composites. Although the surfaces underlying the purple materials exhibited a weak 535 nm band, they also exhibited a featureless, positive slope between 670 nm and 900 nm, consistent with laboratory spectra of Fe-Ni meteorites. By comparison, the purple coatings on Block Island exhibited stronger 535 nm band depths, and slightly stronger absorptions in the 860 nm region. These spectral features are consistent with a more oxidized surface, likely containing a mixture of nanophase ferric materials. Preliminary APXS data suggest that the purple coatings are enriched in Mg, Br, and Zn relative to the rest of the meteorite, while Mössbauer data are consistent with phases of nanophase ferric oxide (e.g., np-hematite). These data, in combination with comparisons with terrestrial fusion crust compositions, suggest that the purple coating materials may represent an altered or secondary weathering coating partially eroded by aeolian abrasion, rather than a remnant fusion crust. Opportunity planned to circumnavigate Block Island and image the rock from multiple orientations. It is expected that Pancam data acquired during this traverse will provide a comprehensive view of the rock at more than 2 locations and sample regions on the back (south) side of the meteorite. This should also provide a useful photometric data set comprised of different solar incidence and Pancam emission angles to expand the phase angle coverage for comparison to the highly forward-scattering surfaces observed on Heat Shield rock.
Ashley James W.
Bell Jon F.
Calvin Wendy M.
Farrand William H.
Herkenhoff Ken E.
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