Sources of Clay‐Rich Sediment in Eberswalde Crater, Mars With Implications for Biopreservation Potential

Abstract

Introduction and Background Mars HabitabilityToday, the mean atmospheric pressure at the surface of Mars is ∼0.6 atm, and the mean surface temperature during the day has been shown to be ∼200 K (e.g., Schofield et al., 1997). Within this cold and thin atmosphere, liquid water is not thermodynamically stable, and most water on present-day Mars is locked in the cryosphere. However, abundant geologic evidence in the form of massive drainage networks (e.g., Barnhart et al., 2009;Hynek & Phillips, 2003), and numerous preserved fluvially constructed deposits (e.g., Ansan et al., 2011;Dibiase et al., 2013) indicate that at some point in Mars' history its climate was amenable to overland flow. Dating based on crater density in regions of fluvial incision and valley network formation indicates that most fluvial activity on the surface of Mars ceased prior to ∼3.5 Ga (Figure 1) (e.g., . Observations consistent with pervasive aqueous activity are not limited to stratigraphic or geomorphic expressions; there is also abundant spectrally observed evidence for water-rich conditions early in Mars history in the form of aqueous alteration minerals

Isotopic evidence of long-lived volcanism on Io

“…Io's mean density and moment of inertia indicate the presence of a core with possible compositions that range from pure Fe to an Fe-FeS eutectic mixture [which is ~25% sulfur by mass (30)]. These constraints, combined with experiments on equilibrium sulfur partitioning between metal and silicates, indicate that 80 to 97% of Io's initial sulfur inventory is in the core (20). Our measurement of 94 to 99% sulfur loss is therefore consistent with the fraction of noncore sulfur lost if Io has been losing mass at ~0.5 to 5 times its current rate over its entire 4.57-Gyr lifetime.…”

“…Io's atmosphere is thought to be well-mixed up to a boundary known as the homopause [altitude ~30 km (19)]. Between the homopause and another boundary known as the exobase (altitude ~600 km), molecular diffusion produces a gravitationally stratified atmosphere (20). In the exosphere (above the exobase), the atmosphere is collision-less.…”