Manganese in Endeavour Crater Rim Materials, Mars, and Implications for Habitability

Wednesday, 17 December 2014: 5:45 PM
Raymond E Arvidson1, Jeffrey G Catalano1, Benton C Clark2, Woodward W Fischer3, John P Grotzinger3, Ralf Gellert4, Edward A Guinness1, Kenneth E Herkenhoff5, Jeffrey Roy Johnson6, Scott M McLennan7, Douglas W Ming8, Richard V Morris8, Steven W Squyres9 and Albert S Yen10, (1)Washington University in St Louis, St. Louis, MO, United States, (2)Space Science Institute Boulder, Boulder, CO, United States, (3)Caltech, Pasadena, CA, United States, (4)University of Guelph, Guelph, ON, Canada, (5)USGS Astrogeology Science Center, Flagstaff, AZ, United States, (6)Applied Physics Laboratory, Laurel, MD, United States, (7)Stony Brook University, Stony Brook, NY, United States, (8)NASA Johnson Space Center, Houston, TX, United States, (9)Cornell Univ, Ithaca, NY, United States, (10)NASA Jet Propulsion Laboratory, Pasadena, CA, United States
The Opportunity Mars rover wheels overturned two adjacent rocks and exposed underlying fracture-filling deposits while exploring the Murray Ridge rim segment of the Noachian-aged Endeavour Crater. These two small rocks, Pinnacle Island (~4 cm across) and Stuart Island (ranging from ~3 to 8 cm wide and ~10 cm long), were subsequently examined in detail to determine the textures, spectral reflectances (0.4 to 1.0 µm), and compositions of the fracture-filling materials. Relatively bright materials with a composition enriched in Mg, Fe, and S, and spectral features indicative of hydrated sulfates, are overlain with a dark, purple mineral phase or phases with a composition enriched in Mn, Ni, P, and Ca, all relative to underlying bedrock. Reflectance spectra for the dark, purple material are consistent with the presence of one or more Mn-oxide phases. Results indicate two aqueous events, one to deposit the Fe and Mg-rich sulfates, and one to deposit the Mn-rich mineral(s), perhaps with scavenging of Ni from the fluid. Ca and P-rich phases (e.g., Ca-phosphates) co-precipitated with Mn-bearing mineral(s) or were incorporated into one or more of them. Mixing of reducing ground waters with an oxidizing atmosphere or other waters likely produced both the S and Mn-enriched deposits. Oxidation of Mn, in particular, requires a very high potential oxidant relative to what is required for S or Fe oxidation. This suggests oxidation by O2 or species derived from O2. Mn-oxide phases would have provided highly favorable substrates for microbial respiration, making this period of aqueous flow through the fractures a potentially habitable environment. These results add to the evolving story of aqueous alteration of Endeavour’s rim rocks, including evidence for nontronite, montmorillonite, Ca-sulfate-rich veins, and hematitic concretions.