Monte Carlo computations of the escape of atomic nitrogen from Mars

Abstract

Monte Carlo simulations were carried out to compute the escape flux of atomic nitrogen for the low and high solar activity martian thermospheres. The total escape of atomic nitrogen at low and high solar activities was found to be 3.03 × 10 5 and 1.32 × 10 6 cm −2 s −1 , respectively. The escape flux of atomic nitrogen at low and high solar activities from photodissociation of N 2 was found to be 2.75 × 10 5 and 9.90 × 10 5 cm −2 s −1 , respectively. The remainder of the contribution is from dissociative recombination, which is only important at high solar activity were it comprises about 25% of the total escape. The relative contributions to the total N escape flux from thermal motion of the background atmosphere, winds and co-rotation, and photoionization and subsequent solar wind pickup are also considered here. We find that the total predicted escape fluxes are observed to increase by 20 and 25% at low and high solar activities owing to thermal motion of the background atmosphere. At low and high solar activities, we find that the co-rotation and wind velocities combined translate to a maximum transferable energy of ∼0.0103 and 0.0181 eV, respectively, and that the total escape flux contribution from winds and co-rotation is negligible. Photoionization was found to be a minor process only impacting those source atoms produced with energies close to the escape energy, between 1.5 and 2 eV. The contributions to the total escape fluxes at low and high solar activities from photoionization and subsequent solar wind pickup are found to be about 8 and 13%, respectively.