Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p52a..04b&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P52A-04
Mathematics
Logic
[0343] Atmospheric Composition And Structure / Planetary Atmospheres, [5410] Planetary Sciences: Solid Surface Planets / Composition, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Landing site selection for future missions, including sample return missions, requires a complete understanding both of the detailed local geology and the regional geological, geophysical, and geochemical context. Orbital imaging and spectroscopic instruments provide essential data about physical properties, local geology, and mineralogy, but only the Mars Odyssey Gamma-Ray Spectrometer (GRS) provides geochemical context by mapping the composition of the Martian near-surface environment. The GRS has provided elemental concentration maps of Mars from approximately 52○ south to 52○ north. Elements for which maps are available are K, Th, Si, Fe, Ca, Cl, and H, with S and Al in preparation. This is an excellent mix of incompatible elements (K, Th), major elements (Si, Fe, Ca, Al), and elements affected by aqueous processes (H, Cl, S). These data provide information on Martian bulk composition, crust formation and evolution, the composition of the dominant types of igneous rocks, and the intensity of aqueous alteration events. The data show that the surface composition is not uniform even in areas that are heavily mantled in surficial materials, thus arguing against surficial mantling materials originating from a globally homogenized dust component. The implication of this result is that the surficial materials are locally derived and represent the chemical characteristics of the surface rocks. The global K/Th ratio is consistent with previous estimates of Martian bulk composition, a critical component in testing models for planetary accretion. Its relatively narrow range (95% of the surface has K/Th between 4000 and 7000) indicates that aqueous alteration of the surface occurred in short duration events that did not fractionate K from Th. Basalts and sediments derived from basalts make up most of the Martian crust. These observations contribute to addressing fundamental problems in planetary and specifically Martian science, including the evolution of the Martian crust and mantle, planetary accretion, and the role of water on the Martian surface, and emphasize the need for continued direct chemical measurements of the surface, perhaps using orbital elemental measurements as guides for site selection. The GRS gamma-ray data have had a significant and unexpected impact on Mars atmospheric science and general circulation models used to predict Mars’ atmospheric dynamics. We found that Ar is enriched over the winter poles due to the transport of atmosphere into the polar region to replenish the CO2 condensed out of the atmosphere to form the seasonal cap. In the case of the south pole, the enrichment is a factor of six, but surprisingly around LS = 90○, even as the cap is continuing to grow, the Ar diffuses out of the polar region. These data show the value of long-term atmospheric monitoring from orbit.
Boynton Willam V.
McLennan Scott M.
Newsom Horton E.
Sprague Ann L.
Taylor Jacob
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