Mathematics – Logic
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p22a0061r&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #P22A-0061
Mathematics
Logic
3672 Planetary Mineralogy And Petrology (5410), 5400 Planetology: Solid Surface Planets, 5410 Composition, 5470 Surface Materials And Properties
Scientific paper
Thermophysically and compositionally distinct layers are exposed in the walls and floor of Ares Vallis ( ˜1000 km upstream from the Pathfinder landing site) and in an unnamed 20 km-diameter crater north of Ares Vallis (7.4 N, 340.4 E). Nighttime temperatures exceed 219 K in some areas; these temperatures are consistent with bedrock surfaces. THEMIS daytime radiance images over this region were selected for spectral analysis. A decorrelation stretch (DCS) was applied to each image using several different band combinations, in an effort to reveal any mineralogic variations that are present. Relative to many low-albedo regions on Mars, Ares Vallis displays a high degree of spectral variability at sub-TES-pixel resolution ( ˜3 km). Three primary spectral units are readily identified in the DCS images. Extensive spectral analysis with TES and THEMIS data indicates that these color units represent surface dust, basalt and an olivine-rich unit. The olivine-rich layer is exposed along a ˜250 km stretch of the outflow channel floor, and also in the wall and ejecta of the nearby unnamed crater. It is ˜50-100 m thick and is overlain by ˜1.5 km of crust. This thickness is comparable to that of other olivine-rich units found in Ganges Chasma and Nili Fossae [1-3]. The olivine-rich layer within the crater is ˜100 m thick, and the bottom of the layer is separated by 400 m of elevation from the top of the olivine-rich layer near the floor of Ares Vallis. The olivine-rich layer in the crater is likely part of the same layer as that within the floor of Ares Vallis, and was simply uplifted during the impact that formed the crater. MOLA data is being used in conjunction with THEMIS data to better establish the stratigraphy of exposed units in this region.
The spectral variation in Ares Vallis illustrates that the crust of Mars is compositionally-layered at sub-kilometer scales, and provides an excellent example of how TES and THEMIS can be used together as a high spectral/spatial resolution tool for lithologic mapping. The stratigraphy and geologic relationships of Ares Vallis units will be presented, as well as the geologic implications for the history of this region. [1] Hoefen T. M. et al., Bull. Am. Aston. Soc., 32(1118), abstract 62.03, 2000; [2] Hamilton, V. E. et al., Meteor. Planet. Sci., in press, [3] Christensen P. R. et al., Science, 300, p. 2056-2061, 2003.
Bandfield Joshua L.
Christensen Per Rex
Rogers David
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