Mineral Mapping of High Priority Landing Sites for MSL and Beyond Using Mars Express OMEGA and HRSC Data

Kurzfassung

High priority candidate landing sites for the Mars Science Laboratory (MSL) mission have been proposed by various researchers, their significance based largely on spectroscopic and geomorphic evidence for aqueous processes. Specifically, seven candidate landing sites are under consideration for MSL at the time of this writing: Mawrth Vallis, Nili Fossae, southern Meridiani Planum, Eberswalde Crater, Holden Crater, Gale Crater, and Miyamoto Crater. While only one of these sites can be visited by MSL, the other sites remain among the most compelling localities on Mars for future in-situ exploration by ESA's ExoMars mission or an international Mars sample return mission. We have produced regional scale mineral maps of these sites using data from the Mars Express Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA). Visible images from the High Resolution Stereo Camera (HRSC) are used as a map base. OMEGA infrared band parameters are used to identify and map pyroxene, olivine, oxides, sulfates, phyllosilicates, and other hydrated phases. OMEGA visible channel data also provide color information, which gives an estimate of dust cover and additional insights into the mineralogy of altered deposits. The dustiest site is Gale Crater and the least dusty is Nili Fossae. The strongest signature of phyllosilicates occurs in Mawrth Vallis, followed by Nili Fossae. However, Nili Fossae also has some of the strongest olivine signatures on the planet. One fundamental difference between the Nili Fossae and Mawrth Vallis sites is that in Mawrth Vallis, phyllosilicate-bearing, light-toned rocks contain no evidence for primary phases in OMEGA data, but in the Nili Fossae area, phyllosilicates, olivine, and pyroxene are mixed at the subpixel level. South Meridiani Planum shows hydrated plains in contact with ancient, pyroxene-bearing, slightly altered, older bedrock. Patchy deposits of phyllosilicates are found in Miyamoto Crater, but their geologic context is not clear at this time. Only weak evidence for alteration is seen at Gale Crater at OMEGA resolution. While Eberswalde and Holden Craters contain fluvial landforms clearly diagnostic of aqueous processes, the surface mineralogy of each site is dominated by pyroxene. Only small, localized exposures of phyllosilicates are seen in Holden, and Eberswalde contains little evidence for alteration in OMEGA data. Based on OMEGA mineralogy and geologic context from HRSC data, we consider three sites to be the most compelling. Mawrth Vallis provides the strongest alteration signatures on the planet, with phyllosilicate minerals tied to a thick, diverse stratigraphic section of ancient bedrock. In Nili Fossae, there is the opportunity to study primary crust and altered, impact-excavated terrain in close proximity. At south Meridiani Planum, the geologic contact between sulfate-bearing terrain and ancient, phyllosilicate-bearing bedrock can be explored and sampled. At all three of these sites, it is possible to immediately address mission objectives without driving because the spacecraft can land on altered terrain using technology available for MSL.