Seasonal Enhancement in Upper Atmospheric D/H at Mars Driven by Both Thermospheric Temperature and Mesospheric Water

E. M. Cangi, M. S. Chaffin, R. V. Yelle, B. S. Gregory, J. Deighan

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

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 23× 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.

Original languageEnglish (US)
Article numbere2023GL106793
JournalGeophysical Research Letters
Volume51
Issue number4
DOIs
StatePublished - Feb 28 2024

Keywords

  • deuterium
  • diffusion
  • dynamics
  • escape
  • mars
  • photochemistry

ASJC Scopus subject areas

  • Geophysics
  • General Earth and Planetary Sciences

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