Origin and Fate of Mars' Protoatmosphere and Atmosphere

Escape of the martian protoatmosphere and initial water inventory

Authors:

1. N.V. Erkaev (a, b)
2. H. Lammer (c)
3. L. Elkins-Tanton (d)
4. A. Stökl (e)
5. P. Odert (c, h)
6. E. Marcq (f)
7. E.A. Dorfi (e)
8. K.G. Kislyakova (c)
9. Yu.N. Kulikov (g)
10. M. Leitzinger (h)
11. M. Güdel (e)

Affiliations:

a. Institute for Computational Modelling, 660041 Krasnoyarsk 36, Russian Academy of Sciences, Russian Federation

b. Siberian Federal University, 660041 Krasnoyarsk, Russian Federation

c. Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria

d. Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington DC 20015, USA

e. Institute for Astronomy, University of Vienna, Türkenschanzstraße 17 1180 Vienna, Austria

h. Institute of Physics, IGAM, University of Graz, Universitätsplatz 5, A-8010 Graz, Austria

f. LATMOS, Université de Versailles Saint-Quentin-en-Yvelines, Guyancourt, France

g. Polar Geophysical Institute, Russian Academy of Sciences, Khalturina 15, 183010 Murmansk, Russian Federation

Abstract:

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 View the MathML source 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 View the MathML source to View the MathML source 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 View the MathML source. After the solidification of early Mars' magma ocean, catastrophically outgassed volatiles with the amount of View the MathML source H2O and View the MathML source CO2 could have been lost during View the MathML source, 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 View the MathML source. 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 View the MathML source ago, when the solar XUV flux decreased to values that have been less than 10 times that of today's Sun.