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Seasonal variation in atomic D/H of the upper Mars atmosphere is a tracer for lower atmospheric dynamics

Presentation #307.07 in the session Characterizing the Martian Atmosphere, All the Way Up (Oral Presentation)

Published onOct 23, 2023
Seasonal variation in atomic D/H of the upper Mars atmosphere is a tracer for lower atmospheric dynamics

The Imaging UltraViolet Spectrograph (IUVS) instrument on the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission measures the ratio of atomic deuterium (D) to hydrogen (H), Ratomic, in the upper martian atmosphere. Recent results reveal that Ratomic is found to be larger than the ratio in water, Rwater, mostly in the latter half of the year (Ls=180 to 360 , southern spring through fall). This enhancement suggests a link to atmospheric escape and water loss, as water is the primary reservoir of D and H on Mars, but the exact mechanism causing the enhancement has not yet been well-defined. In this work, we use a fully coupled 1D photochemical model to propose an explanation for the driving cause of the Ratomic enhancement. We find that Ratomic can be enhanced up to 15-25x the Earth ratio due to either warm thermospheric temperatures, which reduce the supply of high-altitude H, or extra water in the mesosphere (~100 km), which both supplies high-altitude H and enables greater escape of the same. We also find that a greater relative proportion of H escapes compared with D, indicating a pathway for re-enrichment of the exchangeable water reservoir of Mars. This presentation will summarize our results and discuss the relevant physics at play, and conclude with suggestions for ways to combine multiple datasets from MAVEN and other Mars assets with modeling efforts to better understand the link between Ratomic and the martian water inventory. We will also comment on possibilities for utilizing a similar approach for either H & D or other isotope systems at other planets and moons with atmospheres.

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