The Effect of Enhanced Hydrogen on Non-Thermal Escape of Atoms

We have investigated the effect of enhanced hydrogen densities on photochemical escape mechanisms from the Martian atmosphere. We find that reduced escape rates of heavy atoms (O, C, N) result from two causes: the destruction of ions, which are the sources and many non-thermal escape mechanisms, such as dissociative recombination and ion-molecule reactions, and the increasing fraction of H and H2 in the exosphere at earlier times. Hydrogen is thought to escape at a much higher rate than O, C, and N, and thus in previous epochs, the thermosphere should consist of a larger fraction of these light gases. A very large amount of H and H2 in the exosphere will raise the height of the exobase and dominate the absorption of EUV radiation, and the escape of species by processes such as photodissociation of molecules will be reduced.