Impact induced surface heating by planetesimals on early Mars

¹ Department of AstrophysicsUniversity of Vienna, Türkenschanzstrasse 17, 1180 Wien, Austria
e-mail: thomas.maindl@univie.ac.at
² Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
³ Institut für Astronomie und Astrophysik, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
⁴ Physikalisches Institut, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 14, 72076 Tübingen, Germany
⁵ Institute of Physics, IGAM, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
⁶ Institute for Computational Modelling, Russian Academy of Sciences, 660041 Krasnoyarsk 36, Russian Federation
⁷ Siberian Federal University, 660041 Krasnoyarsk, Russian Federation

Received: 22 May 2014
Accepted: 13 November 2014

Abstract

Aims. We investigate the influence of impacts of large planetesimals and small planetary embryos on the early Martian surface on the hydrodynamic escape of an early steam atmosphere that is exposed to the high soft X-ray and extreme-ultraviolet (EUV) flux of the young Sun.

Methods. Impact statistics in terms of number, masses, velocities, and angles of asteroid impacts onto early Mars are determined via n-body integrations. Based on these statistics, smoothed particle hydrodynamics (SPH) simulations result in estimates of energy transfer into the planetary surface material and the resulting surface heating. For the estimation of the atmospheric escape rates we applied a soft X-ray and EUV absorption model and a 1D upper atmosphere hydrodynamic model to a magma ocean-related catastrophically outgassed steam atmosphere with surface pressure values of 52 bar H₂O and 11 bar CO₂.

Results. The estimated impact rates and energy deposition onto an early Martian surface can account for substantial heating. The energy influx and conversion rate into internal energy is probably sufficient to keep a shallow magma ocean liquid for an extended period of time. Higher surface temperatures keep the outgassed steam atmosphere longer in vapor form and therefore enhance its escape to space within ~0.6 Myr after its formation.