A primordial atmospheric origin of hydrospheric deuterium enrichment on Mars

Climatic scenarios allowed. The initial climate and the lifetime of the primordial greenhouse depend on the H2 inventory. Extreme ultraviolet (EUV) radiation from the young Sun can escape on time scales of millions of years. Calculating the escapement with the energy-limited approximation (Watson et al., 1981) gives a loss rate of »2.5 bar/Myrs. In such scenarios, the first Mars experiences habitable conditions (

astro-ph.EP

The deuterium to hydrogen ratio (D/H or 2H/1H) of Martian atmospheric water (~6x standard mean ocean water, SMOW) is higher than that of known sources, requiring planetary enrichment.

A recent measurement by NASA’s Mars Science Laboratory Curiosity rover of clays >3 Gyr yields a ~3x SMOW D/H ratio, demonstrating that most enrichment occurs early in Mars’ history. As on Venus, Mars’ D/H enrichment is thought to reflect the preferential loss to space of 1H (protium) over 2H (deuterium), but the overall environmental context of large and early hydrogen losses remains to be determined.

Here we apply a recent model of the evolution of the primordial atmosphere to Mars, relate the magmatic ocean from the accretion epoch to a later water-ocean epoch, and calculate the behavior of deuterium for comparison with the record observed. We find that ~2-3x hydrospheric deuterium enrichment is produced if the Martian magma ocean chemically reduces to last equilibrium with the primordial atmosphere, making H2-CO the initially dominant species, with minor abundances of H2O-CO2. Reducing gases – especially H2 – can cause greenhouse warming and prevent an ocean of water from freezing immediately after the magmatic ocean epoch.

Moreover, the pressure-temperature conditions are high enough to produce an ocean-atmosphere H2O-H2 isotopic equilibrium such that surface H2O strongly concentrates deuterium relative to H2, which preferentially absorbs protium and escapes from the atmosphere. primordial atmosphere. The proposed scenario of H2-rich primordial outgassing and escape suggests significant (>Myr) durations of chemical conditions on the Martian surface conducive to prebiotic chemistry immediately after Martian accretion.

Kaveh Pahlevan, Laura Schaefer, Linda T. Elkins-Tanton, Steven J. Desch, Peter R. Buseck

Comments: 5 digits
Subjects: Terrestrial and planetary astrophysics (astro-ph.EP)
Cite as: arXiv:2209.10635 [astro-ph.EP] (or arXiv:2209.10635v1 [astro-ph.EP] for this release)
https://doi.org/10.48550/arXiv.2209.10635
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Related DOI:
https://doi.org/10.1016/j.epsl.2022.117772
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Submission History
By: Kaveh Pahlevan
[v1] Wed, Sep 21, 2022 8:05:34 PM UTC (1,313 KB)
https://arxiv.org/abs/2209.10635
Astrobiology, Astrochemistry,

About Lucille Thompson

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