The D/H Ratio and Implications for Escape of Water from the Upper Atmosphere of Mars - INSU - Institut national des sciences de l'Univers Access content directly
Conference Poster Year : 2022

The D/H Ratio and Implications for Escape of Water from the Upper Atmosphere of Mars

John T. Clarke
  • Function : Author
  • PersonId : 999760
Majd Mayyasi
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  • PersonId : 1032335
Jean-Yves Chaufray
Bruce Martin Jakosky
  • Function : Author
  • PersonId : 965550


The constituent atoms of water are known to escape the weak Martian gravity into space, while heavier water molecules largely remain in the atmosphere. A key indicator of water loss is the ratio of the isotopes deuterium to hydrogen since the lighter H escapes faster than D leading to a gradual increase in the D/H ratio of the remaining water. The present D/H ratio reflects the total water Mars has lost in its lifetime but deriving the depth of the primordial Martian water layer requires understanding the physical processes that control escape today to accurately extrapolate back in time. Observations of UV resonance line emissions from H and D with the MAVEN and Hubble Space Telescope (HST) missions provide the key atomic H and D densities and escape rates. There are strong repeated seasonal increases in the densities and escape fluxes of both H and D atoms each Martian year near perihelion, consistent with a strong upwelling of water tied to lower atmosphere dynamics needed to supply the atoms. Around perihelion there appear dramatic changes on time scales of a couple of weeks, providing strong constraints on the loss processes and relative amounts of H and D atoms. A process in addition to thermal escape is required to explain the observed changes in D density, likely from superthermal processes that produce hot atoms. This implies that at present D and H escape at close to their ratio in water, providing strong evidence for the scenario of a warm, wet primordial Mars with a large depth of water on its surface. These results will be presented and the implications will be discussed.
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Dates and versions

insu-03912809 , version 1 (25-12-2022)


  • HAL Id : insu-03912809 , version 1


John T. Clarke, Majd Mayyasi, Dolon Bhattacharyya, Jean-Yves Chaufray, Bruce Martin Jakosky, et al.. The D/H Ratio and Implications for Escape of Water from the Upper Atmosphere of Mars. AGU Fall Meeting 2022, Dec 2022, Chicago, United States. pp.P42F-2472. ⟨insu-03912809⟩
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