Thursday, 17 December 2015
Poster Hall (Moscone South)
Raymond E Arvidson1, Steven W Squyres2, Ralf Gellert3, Kenneth E Herkenhoff4, David W Mittlefehldt5, Larry S Crumpler6, Scott M McLennan7, William H Farrand8, Bradley L Jolliff9, Richard V Morris5 and The Athena Science Team, (1)Washington University in St Louis, St. Louis, MO, United States, (2)Cornell University, Ithaca, NY, United States, (3)University of Guelph, Guelph, ON, Canada, (4)USGS Astrogeology Science Center, Flagstaff, AZ, United States, (5)NASA Johnson Space Center, Houston, TX, United States, (6)NM Museum Ntrl History & Sci, Albuquerque, NM, United States, (7)Stony Brook University, Stony Brook, NY, United States, (8)Space Science Inst, Boulder, CO, United States, (9)Washington University, Saint Louis, MO, United States
The Opportunity Rover is in its 11th year of exploration, currently exploring the Cape Tribulation rim segment of the ~22 km wide Noachian Endeavour Crater and its tilted and fractured outcrops. A key target for Opportunity’s measurements has been the Spirit of Saint Louis crater (SoSL), which is ~25 m wide, oval in plan view, shallow, flat-floored, and has a slightly raised rim. SoSL crater is surrounded by an apron of bright, polygonally-shaped outcrops and is superimposed on a gentle swale in Cape Tribulation. Rocks in a thin reddish zone on the rim are enriched in hematite, Si, and Ge, and depleted in Fe, relative to surrounding rocks. Apron rocks include an outcrop also enriched in Si and Ge, and slightly depleted in Fe. In general rocks in the crater and apron have elevated S levels relative to Shoemaker formation breccias, tracking values observed in the Cook Haven (gentle swale superimposed on Murray Ridge and site of Opportunity’s 5th winter site) and the Hueytown fracture (running perpendicular to Cape Tribulation) outcrops. SoSL crater lies just to the west of Marathon Valley, a key target for exploration by Opportunity because five separate CRISM observations indicate the presence of Fe/Mg smectites on the upper valley floor. Opportunity data show that low relief, relatively bright, wind-scoured outcrops dominate the valley floor where not covered by scree and soil shed from surrounding walls. Initial reconnaissance shows that the outcrops are breccias with compositions similar to the typical SoSL crater apron and floor rocks, although only the very upper portion of the valley has been explored as of August 2015. Pervasive but modest aqueous alteration of Endeavour’s rim is implied by the combination of CRISM and Opportunity data, providing insight into early aqueous processes dominated in this location by relatively low water to rock ratios, and at least in part associated with enhanced fluid flow along fractures.