Simulation of the atomic deuterium density and escape at Mars and comparison
with MAVEN/IUVS observations
J-Y. Chaufray, LATMOS, Paris, France, F. Gonzalez-Galindo, IAA, CSIC, Granada, Spain, M. Vals, L. Rossi, F. Montmessin, F. Lefevre, F. Leblanc, R. Modolo, LATMOS, Paris, France, F. Forget, E. Millour,
LMD, Paris, France, G. Gilli, M. Lopez-Valverde, IAA, CSIC, Granada Spain, M. Mayyasi, Boston University, MA, USA

References:
Introduction:
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 D/H ratio measured on Earth
is measured in its atmosphere. 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.
After the first detections of the deuterium Lyman-α
emission from Earth (Bertaux et al. 1992, Krasnopolsky et al. 1998), the mission MAVEN performed
the first systematic observations of the atomic deuterium Lyman-α emission around Mars showing a
brightness of several hundreds of Rayleigh near Mars
winter solstice (Clarke et al. 2017, Mayyasi et al.
2017), much larger than the Earth detections done
near aphelion (~ 20 – 50 Rayleighs). This seasonal
variation of the deuterium Lyman-α brightness is
consistent with the variations of the hydrogen
Lyman-α brightness observed from Mars Express
(Chaffin et al. 2014, Chaufray et al. 2021), HST
(Clarke et al. 2014), and MAVEN/IUVS (Clarke et
al. 2017, Chaffin et al. 2018) and should result from
the processes transporting the water vapor from the
lower atmosphere to the upper atmosphere (Vals et
al. 2022).
This work:
In this work we will present preliminary simulations
of the deuterium abundance in the Martian upper
atmosphere using a 3D time dependent global circulation model, its extension in the exosphere, and a
comparison of the simulated D Lyman-α brightness
with the brightness measured by MAVEN/IUVS
(Mayyasi et al. 2017). We will also present first results of the simulated non-thermal escape of H and D
produced by collisions between hot oxygen with H,
D, H2 and HD as well as the escape of planetary H+
and D+ driven by the solar wind interaction. We will
compare the D and H thermal escape rate with the
non-thermal escape rates.

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