Evolution of Exospheric Suprathermal Oxygen over Martian History

As a part of a global effort, the dynamics of the flow of energetic particles through the Martian upper atmosphere has been studied. Being the most important reaction, the dissociative recombination (DR) of O2+ is responsible of most of the production of hot atomic oxygen deep in the thermosphere of Mars. To understand the Martian exosphere, it is then necessary to employ a global kinetic model which can include a self-consistent description of both thermosphere collisional region and exospheric collisionless domain. In this study, we have used our Direct Simulation Monte Carlo (DSMC) model in combination with the 3D Mars Thermosphere General Circulation Model (MTGCM) of Bougher et al. [2006, Geophys. Res. Lett., 33, doi:10.1029/2005GL024059.] to describe self-consistently the region of the upper thermosphere where the exosphere is generated, the entire exosphere, and its feedback into the thermosphere generally. Along with the effect of ionization, the DSMC method allows us to provide 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 this physical problem we examined several of the most limiting cases spanning spatial and temporal domains. The contribution of the different physical and chemical escape processes was studied and compared for the present but also earlier Mars epochs characterized by different solar inputs (1 EUV, 3 EUV and 6 EUV) for Equinox conditions [Zhang et al., 1993, JGR, 98].