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Seasonal enhancement in upper atmospheric D/H at Mars driven by both thermospheric temperature and mesospheric water
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  • Eryn Cangi,
  • Michael Scott Chaffin,
  • Roger Yelle,
  • Bethan Sarah Gregory,
  • Justin Deighan
Eryn Cangi
Laboratory for Atmospheric and Space Physics

Corresponding Author:[email protected]

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Michael Scott Chaffin
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Roger Yelle
University of Arizona
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Bethan Sarah Gregory
University of Colorado Boulder
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Justin Deighan
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The D/H ratio in water on Mars, Rwater, is 4–6× the Earth ratio, signifying past water loss to space. Recently, measurements have revealed high values of the D/H ratio in hydrogen, Ratomic, in the thermosphere during southern summer. Here, we use a photochemical model to explore the potential drivers of Ratomic, testing three: thermospheric temperatures, excess mesospheric water, and changing insolation. We find that Ratomic can achieve values between 15× the Earth ratio (due to water) and 25× the Earth ratio (due to temperature). The effects arise because H escape is diffusion-limited, while D escape is energy-limited. Our results underscore how Ratomic reflects mesospheric dynamics, and the need for concurrent measurements of mesospheric water, thermospheric temperatures, and Ratomic to understand seasonal changes in the martian water cycle and atmospheric loss.
18 Oct 2023Submitted to ESS Open Archive
27 Oct 2023Published in ESS Open Archive