Mars

Quantifying The Bioavailable Energy In An Ancient Hydrothermal Vent On Mars And A Modern Earth-based Analogue

By Keith Cowing
Press Release
biorxiv.org
September 18, 2022
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Quantifying The Bioavailable Energy In An Ancient Hydrothermal Vent On Mars And A Modern Earth-based Analogue
Gibbs energies of the 85 reactions considered in this study for the noted mixing ratios of hydrothermal vent fluid and seawater in the Strytan hydrothermal system. The measured chemical composition of Strytan vents was used as the hydrothermal fluid. Reactions are colored by electron acceptor or donor (left versus right side). The electron donors and acceptors are grouped when applicable with other donors or acceptors that have similar reaction equations that may differ slightly in product stoichiometry (e.g., CO2 – and HCO3 – ). Reactions listed as “other” represent dissociation reactions (e.g. reaction 51: 2NO-3: 3 → 2NO-2 + 02.
biorxiv.org

Putative alkaline hydrothermal systems on Noachian Mars were potentially habitable environments for microorganisms. However, the types of reactions that could have fueled microbial life in such systems and the amount of energy available from them have not been quantitatively constrained.

In this study, we use thermodynamic modeling to calculate which catabolic reactions could have supported ancient life in a saponite-precipitating hydrothermal vent system in the Eridania basin on Mars. To further evaluate what this could mean for microbial life, we evaluated the energy potential of an analogue site in Iceland, the Strytan Hydrothermal Field (SHF).

Results show that out of the 85 relevant redox reactions that were considered, the highest energy-yielding reactions in the Eridania hydrothermal system were dominated by methane formation. By contrast, Gibbs energy calculations carried out for Strytan indicate that the most energetically favorable reactions are CO2 and O2 reduction coupled to H2 oxidation.

In particular, our calculations indicate that an ancient hydrothermal system within the Eridania basin could have been a habitable environment for methanogens using NH4+ as an electron acceptor. Differences in Gibbs energies between the two systems were largely determined by oxygen – its presence on Earth and absence on Mars. However, Strytan can serve as a useful analogue for Eridania when studying methane producing reactions that do not involve O2.

Competing Interest Statement
The authors have declared no competing interest.

Holly R. Rucker, Tucker D. Ely, Douglas E. LaRowe, Donato Giovannelli, Roy E. Price
doi: https://doi.org/10.1101/2022.09.09.507253

PDF: https://www.biorxiv.org/content/10.1101/2022.09.09.507253v1.full.pdf

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