Measurements suggest that non-thermal loss processes over geologic time have been significant in determining the abundance of nitrogen (N2) in the Martian atmosphere. Since N2 is involved in many photochemical reactions with the background atmosphere, knowledge of the escape properties of atomic nitrogen is necessary for the reconstruction of the ancient Martian thermosphere. In the traditional approach, all atoms produced at the base with energies greater than the escape energy and velocity vectors oriented upward are assumed to escape. This approximation, however, does not appropriately describe the escape properties of heavier species, such as nitrogen, carbon, and oxygen from upper atmospheres. Monte Carlo computations of the escape flux of atomic oxygen have been carried out previously for the Martian thermosphere. However, to date no studies using the Monte Carlo method have been employed for the escape of atomic nitrogen. This research project, directed by Dr. Sultan Hameed, is the first to carry out Monte Carlo computations for nitrogen escape fluxes for the low and high solar activity Martian atmospheres. In using the Monte Carlo method, invaluable insight will be gained into the processes leading to the escape of nitrogen and the evolution of the early Martian atmosphere. In particular, the energy and altitude distributions of escaping nitrogen atoms as well as the escape fractions will be computed for the present day low and high solar activity Martian atmospheres. Significant differences are expected for the low and high solar activity models, which should provide information on the long term variations of the escape fluxes. Also, the contribution of various escape mechanisms to the total flux of escaping nitrogen atoms is still relatively unknown, and this study will help to address those questions in greater detail. As N2 could have buffered the escape of other species in the past, quantifying the present day escape of nitrogen is important for reconstructing the ancient water inventory on Mars and could have played an important role in sequestering the early liquid water present on Mars. Since geological evidence appears to suggest that the Martian atmosphere was once capable of supporting liquid water on the surface, it is crucial that reliable time dependent models which incorporate the escape of atomic nitrogen are constructed to model past conditions.
Atomic nitrogen could also comprise a significant portion of the present day high solar activity Martian corona, and hence knowledge of the escape properties of nitrogen atoms could be used to predict coronal densities, which may be valuable for future aerobraking missions. The wider impact of this research will occur by the application of these findings to understand the evolution of other planetary bodies, such as Earth and Venus. ***
