Photochemical Escape of Atomic Carbon from Mars

We have modeled the escape fluxes of atomic carbon from the Martian atmosphere for low and high solar activities due to various photochemical escape mechanisms, including photodissociation of CO, dissociative recombination of CO+, electron impact dissociation and dissociative ionization of CO, photodissociative ionization of CO, and dissociative charge transfer of O++ to CO. Only photodissociation of CO and dissociative recombination of CO+ are found to be important, and the time-averaged escape flux is predicted to be controlled by the high solar activity values. The computed global average escape fluxes of C due to photodissociation of CO at low and high solar activities are 1.65 × 105 and 1.8 × 106 cm−2 s−1, respectively, and those for dissociative recombination are 2.9 × 104 and 6.2 × 105 cm−2 s−1, respectively. The other sources contribute \u3c10% to the total. The photochemical escape rates are slightly larger than those estimated for sputtering by O+ pickup ions in the present era. If current estimates are correct, however, sputtering will dominate the escape in earlier epochs when the solar wind is predicted to have been much stronger. Ion outflow may also constitute an important loss mechanism if escape rates are on the order of their predicted upper limits