Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p43d1458m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P43D-1458
Mathematics
Logic
[5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The major clay units at Mawrth Vallis have been well-characterized by OMEGA and CRISM [1-6]. Here we extend this to HiRISE data, demonstrating that these units can be mapped in photographic data as well as through imaging spectroscopy. In HiRISE data the nontronite-bearing unit consists of two main textures: 2-5 m irregular polygons and irregular parallel fracture sets. In contrast, the montmorillonite-bearing unit consists of 0.5-1.5 m regular polygons (see figure below from HiRISE RED image PSP_007612_2045). These morphologies are consistent with previous outcrop-scale observations [1, 7]. Possibly, these polygons are due to freeze-thaw cycles, desiccation, loss of interlayer water, or a combination of these processes. In any case, the same processes must have occurred throughout the Mawrth Vallis region in order to produce such consistency. On the plains surrounding Mawrth Vallis, clear bed divisions are visible in the montmorillonite unit on both gradual and steep slopes (e.g. crater walls) but none are visible in the nontronite unit except in steep crater walls, implying that the beds in the montmorillonite unit may be better lithified than those in the older nontronite unit. Kaolinite, where identified by CRISM, appears bright and fractured in HiRISE imagery with no visible polygons. These morphologies are consistent across the entire 300 x 300 km central Mawrth Vallis region. Therefore, these units can be mapped in areas with some dust/sand cover that masks the CRISM spectrum or where there are no CRISM data available (see companion abstract by Parente et al. for details on automatic texture mapping). This discovery will provide future rover missions (such as MSL) with a more complete map of the major lithologic units, which will enhance and streamline mission planning. [1]Bishop, J. L., et al. (2008) Science, 321, 830-833. [2]Bibring, J.-P., et al. (2005) Science, 307, 1576-1581. [3]Loizeau, D., et al. (2009) Icarus, (in press). [4]McKeown, N. K., et al. (2009) JGR- Planets, (in press). [5]Noe Dobrea, E. Z., et al. (2009) JGR- Planets, (in revision). [6]Poulet, F., et al. (2005) Nature, 438, 632-627. [7]Wray, J. J., et al. (2008) GRL, 35, L12202.
Bishop Janice L.
McKeown Nancy K.
Parente Mimmo
Silver Eli A.
Wray James J.
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