title: Escape of the martian protoatmosphere and initial water inventory.
abstract: Latest research in planet formation indicates that Mars formed within a few million years (Myr) and remained as 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 [Formula: see text] 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 [Formula: see text] to [Formula: see text] could have been captured from the nebula around early Mars. Depending on the before mentioned parameters, due to the planets low gravity and a solar XUV flux that was [Formula: see text] 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 [Formula: see text]. After the solidification of early Mars' magma ocean, catastrophically outgassed volatiles with the amount of [Formula: see text] H2O and [Formula: see text] CO2could have been lost during [Formula: see text], 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 also not lasted much longer than [Formula: see text]. 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 [Formula: see text] ago, when the solar XUV flux decreased to values that have been [Formula: see text] times that of today's Sun.
authors.affiliation: Institute for Computational Modelling, 660041 Krasnoyarsk 36, Russian Academy of Sciences, Russian Federation ; Siberian Federal University, 660041 Krasnoyarsk, Russian Federation.
authors.forename: N V
authors.initials: NV
authors.lastname: Erkaev
authors.affiliation: Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria.
authors.forename: H
authors.initials: H
authors.lastname: Lammer
authors.affiliation: Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington DC 20015, USA.
authors.forename: L T
authors.initials: LT
authors.lastname: Elkins-Tanton
authors.affiliation: Institute for Astronomy, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria.
authors.forename: A
authors.initials: A
authors.lastname: Stökl
authors.affiliation: Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria ; Institute of Physics, IGAM, University of Graz, Universitätsplatz 5, A-8010 Graz, Austria.
authors.forename: P
authors.initials: P
authors.lastname: Odert
authors.affiliation: LATMOS, Université de Versailles Saint-Quentin-en-Yvelines, Guyancourt, France.
authors.forename: E
authors.initials: E
authors.lastname: Marcq
authors.affiliation: Institute for Astronomy, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria.
authors.forename: E A
authors.initials: EA
authors.lastname: Dorfi
authors.affiliation: Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria.
authors.forename: K G
authors.initials: KG
authors.lastname: Kislyakova
authors.affiliation: Polar Geophysical Institute, Russian Academy of Sciences, Khalturina 15, 183010 Murmansk, Russian Federation.
authors.forename: Yu N
authors.initials: YN
authors.lastname: Kulikov
authors.affiliation: Institute of Physics, IGAM, University of Graz, Universitätsplatz 5, A-8010 Graz, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Leitzinger
authors.affiliation: Institute for Astronomy, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Güdel
keywords: Atmospheric escape; Early mars; Evolution; Protoatmospheres
references.citation: Science. 2012 Aug 10;337(6095):721-3
references.pmid: 22798405
references.citation: Nature. 2013 May 30;497(7451):607-10
references.pmid: 23719462
references.citation: Astrobiology. 2013 Nov;13(11):1030-48
references.pmid: 24283926
references.citation: Icarus. 1988;74:472-94
references.pmid: 11538226
references.citation: Icarus. 1990;84:502-27
references.pmid: 11538474
references.citation: Nature. 2007 Nov 22;450(7169):525-8
references.pmid: 18033291
references.citation: Nature. 2001 Jul 12;412(6843):228-36
references.pmid: 11449284
references.citation: Astrobiology. 2013 Nov;13(11):1011-29
references.pmid: 24251443
references.citation: Science. 1995 Jan 13;267(5195):213-7
references.pmid: 7809625
references.citation: Science. 2005 May 13;308(5724):1014-7
references.pmid: 15817816
references.citation: Nature. 2011 Jun 05;475(7355):206-9
references.pmid: 21642961
references.citation: Orig Life Evol Biosph. 2011 Dec;41(6):503-22
references.pmid: 22314970
references.citation: Nature. 2005 Feb 24;433(7028):842-4
references.pmid: 15729335
references.citation: Icarus. 1988;74:62-97
references.pmid: 11538227
references.citation: Planet Space Sci. 2011 Oct;59(13):1472-1481
references.pmid: 21969736
references.citation: Nature. 2002 Mar 7;416(6876):39-44
references.pmid: 11882886
references.citation: Science. 2005 Mar 11;307(5715):1576-81
references.pmid: 15718430