"Hot oxygen corona at Mars"
V.I.
Shematovich (Institute of Astronomy RAS)
M.Ya. Marov, M.A. Krestyanikova (Keldysh
Institute of applied Mathematics, RAS)
Abstract:
The
processes of the kinetics and transport of hot oxygen atoms in the
transition region (from thermosphere to exosphere) of the Matrian upper
atmosphere will be discussed in this report. A reaction of dissociative
recombination of the main ionospheric ion Î2+ with
thermal electrons in Martian ionosphere is a main photochemical source of
hot oxygen atoms. Oxygen atoms are formed in this exothermic reaction with
an excess of kinetic energy ~ 0.4—4 eV and their energy is lost in an
elastic and inelastic collisions with ambient thermal atmosphere gas.
Detailed calculations of formation, collisional kinetics and transport of
hot oxygen in transitional region (from thermosphere to exosphere) of
upper atmosphere of Mars are presented. These calculations were conducted
using the developed by authors method of stochastic modeling of the
kinetics and transport of suprathermal atoms. Kinetic energy distribution
functions were calculated using the differential cross sections for
collisions of hot oxygen atom with ambient atmosphere. It has been shown
that exosphere is populated by substantial amount of hot oxygen atoms with
kinetic energies less than escape energy 2 eV, i.e., hot oxygen corona is
formed. Comparison with the previous models of hot oxygen corona shows
that our model is characterized by higher escape fluxes and higher
abundances in the outer regions of oxygen corona at Mars. The input of
exothermic photochemistry (with a dominant role of dissociative
recombination of the molecular oxygen ion) into the water loss rate from
Mars was estimated and its dominant role in the evolution of the Martian
atmosphere is discussed.