Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p54a..02a&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P54A-02
Physics
[5400] Planetary Sciences: Solid Surface Planets, [5460] Planetary Sciences: Solid Surface Planets / Physical Properties Of Materials, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Opportunity has been traversing the plains of Meridiani since January 25, 2004, acquiring remote sensing and in-situ observations of soils, cobbles, and bedrock, together with atmospheric observations. This paper provides an overview of discoveries between sols 511 (July 1, 2005) and 2300 (July 13, 2010), complementing a similar paper by Squyres et al., [2006] covering results from the initial phase of the mission. Use of the Alpha Particle X-Ray Spectrometer to measure atmospheric argon shows the importance of the southern seasonal ice cap in controlling atmospheric dynamics, with inter-annual variations evident over the three Mars years of observations. The plains are partially covered by aeolian ripples produced by easterly winds during a previous epoch with enhanced Hadley cell circulation. During the current climatic regime, fine-grained particles continue to be reworked locally and trapped. Ripple surfaces are composed of basaltic sand mixed with varying amounts of dust and hematitic concretions. Cobbles examined by Opportunity include iron and stony iron meteorites and both sedimentary and basaltic impact ejecta. Hematite-rich deposits in fractures within ejecta from Concepcion crater, together with iron oxide deposits on meteorites, imply on-going aqueous alteration at low rates. Measurements of sulfate-rich rock strata within the walls of Erebus and Victoria craters provide compelling evidence of sand deposition by wind, with local reworking within ephemeral lakes. We continue to search for the lacustrine facies that would confirm or refute the hypothesis that the sands were produced in an acid-sulfate evaporitic environment. Rocks examined in the upper walls of Victoria and Endurance craters also show enrichment of Cl and a decrease in Mg and S with increasing depth. This pattern implies that regional-scale aqueous alteration took place before formation of these craters. Opportunity has been traversing toward the rim of the 20 km wide Endeavour crater. This crater predates the formation of the layered sedimentary rocks examined by Opportunity, and analysis of CRISM data shows that clay minerals are exposed on its rim. CRISM data also indicate the presence of hydrated sulfate minerals in sedimentary rocks adjacent to the rim, unlike the anhydrous surfaces of outcrops observed thus far by Opportunity. Thus, with continuing mechanical health, Opportunity will reach a terrain markedly different from anything examined to date.
Arvidson Ray E.
Athena Team
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