A study of suprathermal oxygen atoms in Mars upper thermosphere and exosphere over the range of limiting conditions

Abstract

As a part of a global effort, the dynamics of energetic particles flowing through the martian upper atmosphere is studied. Most of the production of hot atomic oxygen occurs deep in the day-side thermosphere of Mars, where dissociative recombination (DR) of O 2 + ion is the dominant source. The study of an upper atmosphere is complicated by the change in the flow regime from a thermospheric collisional to an exospheric collisionless domain. To understand the martian exosphere, it is then highly desirable to employ a global kinetic model that includes a self-consistent description of both thermospheric and exospheric regions. In this work, a combination of our Direct Simulation Monte Carlo (DSMC) model [Tenishev, V., Combi, M.R., 2005. Monte-Carlo model for dust/gas interaction in rarefied flows. AIAA, 2005–4832] and the 3D Mars Thermosphere General Circulation Model (MTGCM) [Bougher, S.W., Bell, J.M., Murphy, J.R., Lopez-Valverde, M.A., Withers, P.G., 2006. Geophys. Res. Lett. 32, doi:10.1029/2005GL024059. L02203] is used to describe self-consistently the exosphere and the upper thermosphere. Along with the effect of ionization, the model provides profiles of density and temperature, atmospheric loss rates and return fluxes as functions of the Solar Zenith Angle (SZA) for all cases considered. To present a complete description of the effects of a 3D thermosphere onto the exosphere, several of the most limiting cases spanning spatial and temporal domains are examined. Along with solar activity variability, the influences of position on the planet and of different seasons are investigated and their relative contribution to the atmospheric loss is shown to be of the same order.