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"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 2+ 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 ~ 0.44 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.