Escape of the martian protoatmosphere and initial water inventory

Author(s)

N V Erkaev, Helmut Lammer, Linda T. Elkins-Tanton, Alexander Stökl, Ernst Dorfi, Manuel Güdel

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 ~0.1-0.2wt.% of H

₂O. 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 ≥3×10

¹⁹g to ≤ times 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 ~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 ~0.1-7.5Myr. After the solidification of early Mars' magma ocean, catastrophically outgassed volatiles with the amount of ~50-250bar H and ~10-55bar CO could have been lost during ~0.4-12Myr, 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 H;bsubesub 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 ~0.4-12Myr. 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 ~4.0±0.2Gyr ago, when the solar XUV flux decreased to values that have been <10 times that of today's Sun.

Organisation(s)

Department of Astrophysics

External organisation(s)

Carnegie Institution for Science, Russian Academy of Sciences, Österreichische Akademie der Wissenschaften (ÖAW)

Journal

Planetary and Space Science

Volume

98

Pages

106 - 119

No. of pages

14

ISSN

0032-0633

DOI

https://doi.org/10.1016/j.pss.2013.09.008

Publication date

08-2014

Peer reviewed

Yes

Austrian Fields of Science 2012

103003 Astronomy, 103004 Astrophysics

Keywords

ASJC Scopus subject areas

Astronomy and Astrophysics, Space and Planetary Science

Portal url

https://ucrisportal.univie.ac.at/en/publications/escape-of-the-martian-protoatmosphere-and-initial-water-inventory(89ab7ec5-1b2a-480d-b509-ddcf207a2ef3).html