Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p21c..06l&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P21C-06
Mathematics
Logic
5410 Composition (1060, 3672), 5415 Erosion And Weathering, 5462 Polar Regions, 5464 Remote Sensing
Scientific paper
The nearly global mapping provided at a scale of a few km by the OMEGA Vis/NIR imaging spectrometer on board Mars Express revealed that hydrated minerals on Mars are mostly observed in ancient terrains (Bibring et al., 2005). These discoveries led to the conclusion that surface water on Mars was mainly present early in the history of the planet, and that Mars has remained cold and dry during the last 3 billion years (Bibring et al., 2006). The observation by OMEGA of a very strong calcium sulfate signature (most likely dominated by gypsum) within the boundaries of the Olympia Planitia Dune field (Langevin et al., 2005) is a major puzzle as this geological feature is at most a few 100 m.y. old. An independent analysis of the OMEGA data (Horgan et al. 2007) confirmed the results of Langevin et al. (2005), in particular the identification of gypsum as the dominant mineralogical hydrated species in the dune field. The extended region richest in gypsum (~ 60 km x 200 km) remained unresolved at a resolution of 1 km/pixel (Langevin et al., 2006). With its 20 m resolution, CRISM, the Vis/NIR imaging spectrometer on board MRO, secured the relationship between the gypsum signature and the dune field as well as its absence over the "basal unit" (only a few pixels wide in OMEGA data) which is exposed between the dune field and the ice (Roach et al., 2007). CRISM showed that the gypsum signatures were highest over dune crests and weakest over exposed bedrock. Mineralogical modeling of the CRISM and OMEGA spectra shows that Gypsum represents at least 60% of the dune material in the eastern part of the Olympia field and decreases towards the western part. This lower limit has been raised since then by accounting for aerosol contributions which reduce the strength of absorption bands. The low albedo (< 20%) requires significant intimate and/or intra- mixture of dark material. The low thermal inertia (Herkenhoff and Vasavada, 1999) is difficult to reconcile with morphologic evidence for induration (Schatz et al., 2006). Weaker occurrences of the 1.93 µm OH stretch band have been observed in other northern and southern circumpolar locations. Sulfates and hydrated oxides provide much better matches for these signatures than phyllosilicates. The formation of large amounts of hydrated sulfates in the relatively young northern circumpolar terrains requires a source of sulfur (already present in soils? volcanic activity?) as well as water, which most likely is provided by outflows from the nearby polar cap (Fishbaugh et al., 2007). This process for generating hydrated minerals is distinct from that which was active during the first few hundred million years of the history of the planet. Bibring et al., Science 307, p. 1576-1581 (2005); Bibring et al., Science 312, p. 400-404 (2006); Feldman et al., Lunar Planet. Sci. 38 #2311 (2007); Fishbaugh et al., J. Geophys. Res. 112, E07002 (2007); Herkenhoff and Vasavada, J. Geophys. Res. 104, 16484. Horgan et al., 7th Int. Conf. on Mars #3241 (2007); Langevin et al., Science 307, p. 1581-1583 ; Langevin et al., Lunar Planet. Sci. 36 #1652 (2005) ; Roach et al., Lunar Planet. Sci. 38 #1970 (2007) ; Schatz et al., J. Geophys. Res. 111, E04006 (2006).
Bibring J.
Fishbaugh Kathryn E.
Gondet Brigitte
Langevin Yves
Murchie Scott
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