Reconstructing Habitable Environments on a Late Noachian Icy Mars: Causes, Frequencies and Durations of Melting, Fate of Meltwater, and Biological Insights from the McMurdo Dry Valleys. James W. Head, Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912 USA

Abstract:

Recent global climate models for Late Noachian Mars have underlined the difficulty of producing and sustaining a “warm and wet” early Mars, suggesting instead a cold and icy late Noachian climate dominated by stable ice sheets in the highlands and a horizontally stratified hydrological system. If Late Noachian Mars was “cold and icy”, how can one explain the origin and distribution of the extensive valley networks and abundant open basin lakes? Could periodic or catastrophic melting of highland ice sheets produce the observed features? Are there areas where the horizontally stratified hydrological system is breached to enable communication with the groundwater system below? Would such scenarios lead to habitable environments? Analogs of aqueous environments and biological settings from the McMurdo Dry Valleys are combined with assessment of several top-down and bottom-up melting mechanisms for the Late Noachian Icy Highlands to outline predictions for the location and duration of potential habitable environments. Explored are 1) the volumes of ice available and the possibility that ice distribution and thickness are “supply-limited”, 2) the areal distribution of available ice, 3) the total amount of meltwater necessary to account for the observed features, 4) the predicted duration of aqueous production and longevity of aqueous environments under different melting scenarios, 5) the predicted geomorphic features formed by these mechanisms, and 6) similarities of these predicted features to the distribution and morphologic/morphometric characteristics of observed valley networks and open-basin lakes. The results are interpreted in the context of known habitable environments in the Mars-like hyperarid, hypothermal McMurdo Dry Valleys, comparing and assessing the locations of meltwater production and biological activity, the stratification of the hydrological system, and communication with the groundwater system below. Predictions are made for remote sensing signatures of these environments that might be recognized on Mars as candidates for ExoMars and Mars 2020 landing sites.