Escape of the martian protoatmosphere and initial water inventory

N. V. Erkaev (1) , H. Lammer (2) , L. Elkins-Tanton (3) , A. Stökl (4) , P. Odert (2, 5) , Emmanuel Marcq (6) , E. A. Dorfi (4) , K. G. Kislyakova (2) , Yu. N. Kulikov (7) , M. Leitzinger (5) , M. Güdel (4)

1 ICM SB RAS - Institute of Computational Modelling of the Russian Academy of Sciences
2 IWF - Space Research Institute of Austrian Academy of Sciences
3 Department of Terrestrial Magnetism [Carnegie Institution]
4 Institute for Astronomy [Vienna]
5 IGAM - Institute for Geophysics, Astrophysics and Meteorology [Graz]
6 PLANETO - LATMOS
7 PGI - Polar Geophysical Institute of Russian Academy of Sciences

Latest research in planet formation indicate that Mars formed within a few million years (Myr) and remained a planetary embryo that never grew to a more massive planet. It can also be expected from dynamical models, that most of Mars' building blocks consisted of material that formed in orbital locations just beyond the ice line which could have contained of H2O. By using these constraints, we estimate the nebula-captured and catastrophically outgassed volatile contents during the solidification of Mars' magma ocean and apply a hydrodynamic upper atmosphere model for the study of the soft X-ray and extreme ultraviolet (XUV) driven thermal escape of the martian protoatmosphere during the early active epoch of the young Sun. The amount of gas that has been captured from the protoplanetary disk into the planetary atmosphere is calculated by solving the hydrostatic structure equations in the protoplanetary nebula. Depending on nebular properties such as the dust grain depletion factor, planetesimal accretion rates and luminosities, hydrogen envelopes with masses to could have been captured from the nebula around early Mars. Depending of the before mentioned parameters, due to the planets low gravity and a solar XUV flux that was ∼100 times stronger compared to the present value, our results indicate that early Mars would have lost its nebular captured hydrogen envelope after the nebula gas evaporated, during a fast period of . After the solidification of early Mars' magma ocean, catastrophically outgassed volatiles with the amount of H2O and CO2 could have been lost during , if the impact related energy flux of large planetesimals and small embryos to the planet's surface lasted long enough, that the steam atmosphere could have been prevented from condensing. If this was not the case, then our results suggest that, the timescales for H2O condensation and ocean formation may have been shorter compared to the atmosphere evaporation timescale, so that one can speculate that sporadically periods, where some amount of liquid water may have been present on the planet's surface. However, depending on the amount of the outgassed volatiles, because of impacts and the high XUV-driven atmospheric escape rates, such sporadically wet surface conditions may have not lasted longer than . After the loss of the captured hydrogen envelope and outgassed volatiles during the first 100 Myr period of the young Sun, a warmer and probably wetter period may have evolved by a combination of volcanic outgassing and impact delivered volatiles ago, when the solar XUV flux decreased to values that have been <10 times that of today's Sun.

Mots clés: Early mars; Protoatmospheres; Atmospheric escape; Evolution

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]; Planétologie et astrophysique de la terre [astro-ph.EP]

N. V. Erkaev, H. Lammer, L. Elkins-Tanton, A. Stökl, P. Odert, et al.. Escape of the martian protoatmosphere and initial water inventory. Planetary and Space Science, 2014, 98, pp.106-119. ⟨10.1016/j.pss.2013.09.008⟩. ⟨hal-00864122⟩