We present a detailed theoretical analysis of a non-thermal escape of molecular hydrogen from Mars induced by collisions with hot atomic oxygen from martian corona. To accurately describe the energy transfer in O + H2(v,j) collisions, we performed extensive quantum-mechanical calculations of state-to-state elastic, inelastic, and reactive cross sections. The escape flux of H2 molecules was evaluated using a simplified 1D column model of the martian atmosphere with realistic densities of atmospheric gases and hot oxygen production rates for the low solar activity conditions. An average density of the non-thermal escape flux of H2 of 1.9×105 cm−2s−1 was obtained considering energetic O atoms produced in dissociative recombinations of O2+ ions. Predicted rovibrational distribution of the escaping H2 was found to contain a significant fraction of higher rotational states. While the non-thermal escape rate was found to be lower than Jeans flux for H2 molecules, the non-thermal escape rates of HD and D2 are significantly higher than their respective Jeans rates. The accurate values of non-thermal escape fluxes of different molecular isotopes of H2 may be important in analyses of evolution of the martian atmosphere. The described molecular ejection mechanism is general and expected to contribute to atmospheric escape of H2 and other light molecules from planets, satellites, and exoplanetary bodies.
@article{arxiv.1112.0730,
title = {Non-thermal escape of molecular hydrogen from Mars},
author = {Marko Gacesa and Peng Zhang and Vasili Kharchenko},
journal= {arXiv preprint arXiv:1112.0730},
year = {2013}
}