Accessing Surface and Subsurface Habitable Environments of Ancient Mars

Abstract:

The martian Curiosity rover has characterized the Yellowknife Bay region as habitable based on the presence of sedimentary rocks, the array of elements essential to supporting life (CHNOPS), and indications of hydrologic activity either as a shallow stream bed or intermittently wet lake bed. However as an ancient site this surface was challenging for sustained habitability due to the radiation environment and unknown persistence of water. In contrast the shallow subsurface was potentially a longer lived environment sheltered from the harsh surface conditions. Yet our knowledge of subsurface environments is limited. Did the ancient subsurface of Mars encompass the full range of factors needed for habitability, what is the evidence for this, and was this preserved in the geologic record? Syntheses of global 0.4-5.0 µm spectroscopic observations from high (19 m/pixel CRISM) to moderate (1 km/pixel OMEGA) resolution VNIR data show diverse assemblages of aqueous minerals. The most common environment observed from orbit is a subsurface hydrothermal-type environment accounting for more than 70% of observed sites with hydrated silicates. The dominant hydrated mineral phase is smectite clay, implying a moderate pH environment and a thermal environmental <350°C. The heat source to drive hydrothermal systems could be crustal cooling following planet formation, conductive heat flow from the mantle, impact generated heat pulses, deuteric alteration and magmatism. Evidence of relatively rapid cooling of the crust after formation perhaps by hydrothermal circulation is provided by ancient topography preserved by a rigid crust. Exhumation of Noachian-aged phyllosilicate-rich terrains reveal abundant linear ridges resistant to erosion interpreted to be mineralized fraction zones in regional hydrothermal systems. The proposed landing site in Northeast Syrtis provides excellent access to both surface (Late Noachian fluvial systems with standing bodies of water) and subsurface (mineralized fracture zones) environments in an energy-rich setting (olivine-serpentine-magnesite mineral assemblages) I will synthesize these and new observations to assess the knowledge of subsurface environments and the relationship to surface environments in the Nili Fossae region and its prospects a landing site for Mars 2020.