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O2 solubility in Martian near-surface environments and implications for aerobic life

Abstract

Due to the scarcity of O2 in the modern Martian atmosphere, Mars has been assumed to be incapable of producing environments with sufficiently large concentrations of O2 to support aerobic respiration. Here, we present a thermodynamic framework for the solubility of O2 in brines under Martian near-surface conditions. We find that modern Mars can support liquid environments with dissolved O2 values ranging from ~2.5 × 10−6 mol m−3 to 2 mol m−3 across the planet, with particularly high concentrations in polar regions because of lower temperatures at higher latitudes promoting O2 entry into brines. General circulation model simulations show that O2 concentrations in near-surface environments vary both spatially and with time—the latter associated with secular changes in obliquity, or axial tilt. Even at the limits of the uncertainties, our findings suggest that there can be near-surface environments on Mars with sufficient O2 available for aerobic microbes to breathe. Our findings may help to explain the formation of highly oxidized phases in Martian rocks observed with Mars rovers, and imply that opportunities for aerobic life may exist on modern Mars and on other planetary bodies with sources of O2 independent of photosynthesis.

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Fig. 1: Solubility of O2 in liquids on modern Mars as a function of temperature for 6.1 mbar.
Fig. 2: O2 solubilities in liquids on modern Mars for 6.1 mbar and 140–300 K compared with Earth today.
Fig. 3: Spatial variation of O2 solubility in Ca-perchlorate brines on modern Mars.
Fig. 4: Evolution of aerobic environments on Mars due to obliquity change for Ca-perchlorate brines.

Data availability

The generated data output from the climate model used for this study can be made available upon request from the authors.

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Acknowledgements

V.S. would like to dedicate this work in memory of A. S. Kubik who inspired so many to search for life on other worlds and brought so much life to this planet. V.S. thanks the Simons Foundation Collaboration on the Origins of Life for supporting this work (338555). A portion of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. W.W.F. acknowledges support of the David and Lucile Packard Foundation and Simons Foundation Collaboration on the Origins of Life, and L.M.W. the support of a NASA Earth Space and Science Fellowship. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center as well as the High-Performance Computing facilities of the Jet Propulsion Laboratory, Office of the Chief Information Officer.

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V.S., L.M.W. and W.W.F. conceptualized this study. M.M. ran the GCM simulations for all obliquities. V.S. developed the solubility model for all brines, extended the idea to a three-dimensional and time-dependent (obliquity-driven) solubility framework, led the writing of the manuscript and prepared all figures and tables. All authors contributed to the writing of the manuscript.

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Correspondence to Vlada Stamenković.

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Supplementary Methods, Supplementary Figures 1–4, Supplementary Tables 1–4.

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Stamenković, V., Ward, L.M., Mischna, M. et al. O2 solubility in Martian near-surface environments and implications for aerobic life. Nature Geosci 11, 905–909 (2018). https://doi.org/10.1038/s41561-018-0243-0

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