Opportunity Microscopic Imager Results from the Western Rim of Endeavour Crater, Mars

Thursday, 17 December 2015
Poster Hall (Moscone South)
Kenneth E Herkenhoff, USGS Astrogeology Science Center, Flagstaff, AZ, United States, Raymond E Arvidson, Washington University in St Louis, St. Louis, MO, United States, David W Mittlefehldt, NASA Johnson Space Center, Houston, TX, United States, Robert J Sullivan Jr, Cornell University, Ithaca, NY, United States and Athena Science Team
Opportunity has been exploring exposures of Noachian-age rocks along the rim of Endeavour crater since August 2011, motivated by orbital spectral evidence for phyllosilicates at multiple locations along the crater’s rim. As reported previously, Opportunity discovered multiple bright linear features at “Cape York” that have been interpreted as veins of Ca sulfate deposited in bedrock fractures, and in-situ measurements are consistent with the presence of smectite clays in rocks and veneers on the east side of Cape York. The inferred neutral pH and relatively low temperature of the fluids involved in multiple phases of alteration would have provided a habitable environment if life existed on Mars at that time. Because Opportunity can no longer directly sense phyllosilicate mineralogy with the MiniTES or Mössbauer spectrometers, it is focusing on characterizing outcrop multispectral reflectance with Pancam, chemistry with the Alpha Particle X-ray Spectrometer and microtexture with the Microscopic Imager (MI) of potential phyllosilicate host rocks.

While traversing the western side of “Murray Ridge,” Opportunity found outcrops of breccia that are similar in texture and chemical composition to the Shoemaker Formation rocks exposed at Cape York. MI images of the breccias show cm-size angular clasts in fine-grained matrix, consistent with an impact origin. At “Cook Haven,” the rover wheels overturned a few rocks, exposing dark Mn-rich coatings and haloes on brighter sulfates (Figure 1), which suggest aqueous precipitation followed by interaction with a strong oxidant. The dark, resistant coatings on “Thessaloniki” are less than about 0.1 mm thick, barely resolved in places by MI stereogrammetry. Opportunity’s mission continues, with the rover exploring more exposures of phyllosilicates detected from orbit on “Cape Tribulation.” The latest MI results, including observations in “Marathon Valley,” will be presented at the conference.