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Modelling and measuring the variations of D/H and 18O/16O in Martian water vapour

Presentation #318.05 in the session Mars’s Story as Told and Influenced by Dust and Water (Oral Presentation)

Published onOct 23, 2023
Modelling and measuring the variations of D/H and 18O/16O in Martian water vapour

Numerous lines of evidence suggest that liquid water was once abundant on the surface of Mars, which later migrated to the crust or escaped to space throughout history. Clues about the evolution of the water reservoir are held in the isotopic ratios of atmospheric gases, which carry information about the long-term processes that have shaped the Martian climate. However, to understand these present-day values the isotopic imprints from long-term processes must be disentangled from the fractionation taking place at present due to several atmospheric processes, such as surface-atmosphere exchange or photochemical reactions.

We report measurements of the D/H and 18O/16O isotopic ratios in water vapour made in 2018 and 2019 by the EXES (Echelon-Cross-Echelle Spectrograph) instrument onboard the SOFIA (Stratospheric Observatory for Infrared Astronomy) aircraft, when Mars was close to southern summer solstice (Ls=274°) and northern spring equinox (Ls=13°). In addition, we compare the observations with the expectations from the condensation-induced fractionation of both D/H and 18O/16O modelled using a Mars Global Circulation Model and evaluate whether other processes such as atmospheric exchange with the Martian regolith may be inducing isotopic fractionation at diurnal timescales.

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