  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 ~0.1-0.2 wt. % 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 >=3x10^{19} g to <=6.5x10^{22} g 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 ~0.1-7.5 Myr. After the solidification of early Mars'
magma ocean, catastrophically outgassed volatiles with the amount of ~50-250
bar H2O and ~10-55 bar CO2 could have been lost during ~0.4-12 Myr, 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... (continued)
