Observations of high manganese layers by the Curiosity rover at the Kimberley, Gale crater, Mars
Wednesday, 17 December 2014: 5:15 PM
The Curiosity rover spent sols 606-630 analyzing an outcrop in a region dubbed the Kimberley. Three rock targets at this location were found to have Mn concentrations strongly elevated above that of martian primary crust: Stephen (sols 611, 619, 630), Neil (sol 619), and Mondooma (sol 625). Stephen and Neil are adjacent to one another and appear as more resistant, fin-like layers subparallel to sedimentary bedding, and are interpreted as bedding-parallel mineralized fractures. Mondooma is located in the same bedrock unit a few meters away and has a similar geological context. After dust cleaning by ChemCam, Stephen and Neil exhibited dark, shiny surfaces. The dust-cleared surface of Mondooma is also dark and exhibits an angular, shallow fracture pattern. ChemCam observations indicate high Mn concentrations (~20-40 wt% MnO) for all three targets in which Mn abundances are higher in the first shots and decrease systematically with succeeding shots (i.e. increasing depths). The Alpha Particle X-ray Spectrometer (APXS) also analyzed Stephen (sols 627, 629) and observed elevated manganese abundances (~4 wt% MnO) that are the highest detected by that instrument in Gale thus far. APXS data show that Stephen also exhibits relatively high Ni abundances (~1000 ppm) that correlate with Mn. The difference between the two instruments’ measurements is likely due to differences in interaction volumes and footprint areas (1.7 cm APXS versus ~400 μm ChemCam). In addition to these three high Mn targets, other fin-like features are observed throughout the unit. Based on morphology and chemistry, these thin Mn-rich fins likely represent fracture-filling authigenic minerals emplaced by secondary fluids percolating through the strata. The appearance and correlation between Mn and Ni strongly suggest the presence of Mn-oxide phase(s). Mn-oxides are important because they require extremely strong oxidants and sufficient volumes of liquid water to form. Environments of Mn cycling on Earth are uniformly habitable and Mn-oxides provide for the microbial respiration of a wide variety of reduced compounds. Thus, these results suggest that Mars may have hosted a broader range of habitable environments than previously recognized.