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Simulation of deuterium and hydrogen loss on Mars by thermal, photochemical and solar wind processes

Presentation #318.07 in the session Mars’s Story as Told and Influenced by Dust and Water (Oral Presentation)

Published onOct 23, 2023
Simulation of deuterium and hydrogen loss on Mars by thermal, photochemical and solar wind processes

The D/H ratio is a key parameter to understand the atmospheric evolution of a planet. On Mars a D/H ~ 5 times larger than the ratio on Earth is measured. This large ratio can be explained by a preferential escape of the hydrogen compared to the deuterium due to its lower mass. However, while the thermal escape (Jeans escape) is strongly mass dependent other non-thermal processes are less mass dependent and would impact the time needed to fractionate the water from the terrestrial value to the current value.

In this work, we will present new simulations obtained by coupling 3 models to estimate the hydrogen and deuterium escape. The 3D Martian Planetary Climate Model (PCM-Mars) is used to compute the Jeans escape rate of D, H, H2 and HD, as well as the ion and neutral densities below the exobase are computed using at spring equinox. A 3D exospheric model is used to compute the escape rate of H and D due to photochemical reactions in the ionosphere and the escape rates of H, D, H2 and H2 induced by the collisions between the hot oxygen and these atmospheric species. Finally, a 3D hybrid model of the Martian induced magnetosphere is used to compute the escape of H+ and D+ produced by photoionization and charge exchange with the solar wind protons. The contribution of each process and the derived fractionation factor will be presented and discussed.

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