Hot oxygen and carbon escape from the martian atmosphere

The escape of hot O and C atoms from the present martian atmosphere during low and high solar activity conditions has been studied with a Monte-Carlo model. The model includes the initial energy distribution of hot atoms, elastic, inelastic, and quenching collisions between the suprathermal atoms and the ambient cooler neutral atmosphere, and applies energy dependent total and differential cross sections for the determination of the collision probability and the scattering angles. The results yield a total loss rate of hot oxygen of 2.3 – 2.9 × 10 25 s − 1 during low and high solar activity conditions and is mainly due to dissociative recombination of O2+ and CO2+. The total loss rates of carbon are found to be 0.8 and 3.2 × 10 24 s − 1 for low and high solar activity, respectively, with photodissociation of CO being the main source. Depending on solar activity, the obtained carbon loss rates are up to ~40 times higher than the CO2+ ion loss rate inferred from Mars Express ASPERA-3 observations. Finally, collisional effects above the exobase reduce the escape rates by about 20–30% with respect to a collionless exophere.