Non-thermal Escape Of The Martian CO2 Atmosphere Over Time: Constrained By Ar Isotopes

The ion escape of Mars’ CO2 atmosphere caused by its dissociation products C and O atoms is simulated from present time to ≈4.1 billion years ago (Ga) by numerical models of the upper atmosphere and its interaction with the solar wind.

The planetward-scattered pick-up ions are used for sputtering estimates of exospheric particles including 36Ar and 38Ar isotopes. Total ion escape, sputtering and photochemical escape rates are compared. For solar EUV fluxes ≥3 times that of today’s Sun (earlier than ≈2.6 Ga) ion escape becomes the dominant atmospheric non-thermal loss process until thermal escape takes over during the pre-Noachian eon (earlier than ≈4.0-4.1 Ga).

If we extrapolate the total escape of CO2-related dissociation products back in time until ≈4.1 Ga we obtain a theoretical equivalent to CO2 partial pressure of more than ≈3 bar, but this amount did not necessarily have to be present. The fractionation of 36Ar/38Ar isotopes through sputtering and volcanic outgassing from its initial chondritic value of 5.3, as measured in the 4.1 billion years old Mars meteorite ALH 84001, until the present day can be reproduced for assumed CO2 partial pressures between ≈0.2-3.0 bar, depending on the cessation time of the Martian dynamo (assumed between 3.6-4.0 Ga) – if atmospheric sputtering of Ar started afterwards.

H. Lichtenegger, S. Dyadechkin, M. Scherf, H. Lammer, R. Adam, E. Kallio, U.V. Amerstorfer, R. Jarvinen

Comments: 70 pages (including 18 pages of supplement), 20 figures and 20 tables (including 12 figures and 15 tables in the supplement), resubmitted to Icarus
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2105.09789 [astro-ph.EP] (or arXiv:2105.09789v1 [astro-ph.EP] for this version)
Submission history
From: Manuel Scherf
[v1] Thu, 20 May 2021 14:38:55 UTC (4,798 KB)
https://arxiv.org/abs/2105.09789
Astrobiology