PRELIMINARY MODELS OF MINERALOGIES FROM NEAR-SURFACE WATER-ROCK SIMULATIONS AT THE NILI FOSSAE REGION, MARS

Using fundamental aqueous geochemical principles and a Gibbs Free Energy minimization strategy, we provide new support for habitable microenvironments in the near-subsurface of Mars, hosted in Fe- and Mg-rich rock units containing the mineral serpentine. We modeled reactions of published Martian meteorite and Jezero Crater igneous rock compositions and reasonable planetary waters using Geochemist's Workbench ver 12.0. Meteorite compositions for ALH 77005, Nakhla, and Chassigny, and Perseverance sites, Máaz and Séítah, were used as solid phase inputs. Six plausible Mars groundwaters (NaClO4, Mg(ClO4)2, Ca(ClO4)2, Mg(ClO4)2, Mg-Na2(ClO4)2, Ca-Na2(ClO4)2, Mg-Ca(ClO4)2, Mars wet chemistry experiments from Rosy Red) were aqueous phase inputs. Geophysical conditions were appropriate for near-subsurface Mars (273.15-373.15 K, 101.3 kPa, <10 m depth). Mineral products were dominated by phyllosilicates such as serpentine group minerals in most reaction paths, but differed in some trace minerals, and modeled solutions varied in physicochemical properties, major ion compositions, and gas fugacities; the evolving habitability of pore spaces in subsurface groundwater percolation systems was assessed. Models anchored to the Chassigny composition produced the overall highest H2 fugacity. Models using the Rosy Red Mars experimental fluid as solution input produced the highest sustained CH4 fugacity, with the maximum CH4 derived from the reaction of this water type with ALH 77005. Of critical importance are the mineral occurrences of serpentine and saponite, which have been directly observed using CRISM spectral data, can indicate consistent aqueous H2 and CH4 production and suggest a sustained (if long ago) bioenergetic niche for microbial life for modeled bioenergetic reaction paths.