Fully coupled photochemistry of the deuterated ionosphere of Mars and its effects on escape of H and D

Abstract

Although deuterium (D) on Mars has received substantial attention, the deuterated ionosphere remains relatively unstudied. This means that we also know very little about non-thermal D escape from Mars, since it is primarily driven by excess energy imparted to atoms produced in ion-neutral reactions. Most D escape from Mars is expected to be non-thermal, highlighting a gap in our understanding of water loss from Mars. In this work, we set out to fill this knowledge gap. To accomplish our goals, we use an upgraded 1D photochemical model that fully couples ions and neutrals and does not assume photochemical equilibrium. To our knowledge, such a model has not been applied to Mars previously. We model the atmosphere during solar minimum, mean, and maximum, and find that the deuterated ionosphere behaves similarly to the H-bearing ionosphere, but that non-thermal escape on the order of 8000-9000 cm${}^{-2}$s${}^{-1}$ dominates atomic D loss under all solar conditions. The total fractionation factor, $f$, is $f=0.04$--0.07, and integrated water loss is 147--158 m GEL. This is still less than geomorphological estimates. Deuterated ions at Mars are likely difficult to measure with current techniques due to low densities and mass degeneracies with more abundant H ions. Future missions wishing to measure the deuterated ionosphere in situ will need to develop innovative techniques to do so.

37 pages, 8 figures, published in Journal of Geophysical Research: Planets

References in corpus (4)

• Precipitation of Energetic Neutral Atoms and Induced Non-Thermal Escape Fluxes from the Martian Atmosphere
• Higher Martian atmospheric temperatures at all altitudes increase the D/H fractionation factor and water loss
• Nonthermal hydrogen loss at Mars: Contributions of photochemical mechanisms to escape and identification of key processes
• Non-thermal production and escape of OH from the upper atmosphere of Mars

Cited by in corpus (1)

• Nonthermal hydrogen loss at Mars: Contributions of photochemical mechanisms to escape and identification of key processes