Redox evolution, climate and geochemistry on early Mars

Abstract:

Reconciling the evidence for past liquid water and redox variability on Mars with models of atmospheric evolution remains a major challenge. Here we present new stochastic modeling we have performed to investigate Mars’ coupled climate and redox evolution. Via an atmosphere evolution model incorporating episodic injection of reducing greenhouse gases, slow oxidation due to hydrogen escape, and short-term heating due to bolide impacts, we show that Mars could have transitioned repeatedly from reducing (H2-rich) to oxidizing (O2-rich) atmospheric conditions during the Noachian and Hesperian periods. Our model predicts a generally cold early Mars. If background CO2 levels are high enough (1-2 bar 3.5 Gya), it nonetheless exhibits episodic warm intervals sufficient to degrade crater walls, form valley networks and create other fluvial/lacustrine features. Transient buildup of O2-rich atmospheres can help explain the occurrence of oxidized mineral species such as manganese oxides at Meridiani Planum and Gale Crater. The Noachian–Hesperian “phyllosilicate–sulfate transition” can also be interpreted as an outcome of increasing planetary oxidation, decreasing groundwater availability and waning bolide impactor flux, which dramatically slowed the remobilization and thermochemical destruction of surface sulfates. Here we present our key model results and discuss their implications for observations by future missions, including NASA’s Perseverance rover.