Hydrogen generation from ferrous saponite: molecular-geochemical insights into early Martian environment

Abstract

Leading-edge surveys by Mars rovers enable us to apply geochemical techniques like laboratory experiments and modeling to reproduce early Martian environments. While widespread hydrated minerals support an aqueous early Mars, the mechanism achieved clement environment that can possess liquid water on its surface has been debated. One prominent effect that compensated for the greenhouse effect of CO₂ is collision-induced absorption (CIA) caused by mixing molecular hydrogen into the atmosphere. Here, we propose ferrous saponite as a new hydrogen source through the reduction of hydrogen sulfide. Our hydrothermal experiments showed a significant hydrogen generation from the reaction between laboratory synthesized ferrous saponite and hydrogen sulfide. STXM (Scanning Transparent X-ray Microscopy) analysis supports the formation of pyrite particles and oxidation of saponite in mineral phases, supporting that the reduction of sulfur by ferrous saponite caused hydrogen production. As sulfur content in the Martian mantle is high and ferrous saponite is a ubiquitous aqueous alteration product on early Mars, this reaction could have provided hydrogen into the early Martian atmosphere.