Comparison of a Monte Carlo Calculation of the Escape Rate of C from Mars to that Obtained Using the Exobase Approximation

We have carried out 3-D Monte Carlo calculations of the escape rates of C from the Martian atmosphere due to several mechanisms, including dissociative recombination of CO ⁺ , photodissociation of CO, photodissociative ionization of CO and electron impact dissociation of CO. We utilize two differential collision cross sections: one isotropic in angle and the other a more realistic forward scattered distribution. We compare the results to those obtained using the traditional exobase approximation. We find that there are differences in the escape rates obtained by the two methods for different processes, both because of the nascent energy distribution of the C atoms and the altitude dependence of the mechanism. Significant escape is found to arise from below the exobase, and from particles initially released in the downward direction. The predicted total escape rate of C is reported and compared with previous calculations.