Abiotic Formation of Methane and Prebiotic Molecules on Mars and Other Planets

We explored the photocatalytic (UV-driven) reduction of CO2 on mineral surfaces in acidic conditions and observed the production of methane. Based on our measured laboratory reaction rates, we estimate a 2.81 × 107 cm–2 s–1 methane surface flux on the current-day Mars. We also estimate a Martian methane destruction rate of 2.37 × 105 cm–2 s–1, which is 2 orders of magnitude less than the production rate. The flux of the photochemically produced methane therefore seems sufficient to explain the background levels of methane detected on Mars. This photocatalytic reduction is part of a proposed novel reaction network tightly bound to the chemistry of CO2 in planetary atmospheres described in this paper. The emergent methane-enriched atmosphere can be transformed by high-energy-density events on rocky planets to nucleic acid bases and amino acids. Finally, destructive processes, such as volcanic eruptions or lightning storms, can turn the synthesized products back into CO2 in any step. This proposed scenario should be, in our opinion, included in models of exoplanetary chemistry.