Numerical and analytical model of Mercury's exosphere: Dependence on surface and external conditions

Analytical models of the Hermean exosphere for specific surface processes are described here. A numerical, Monte-Carlo model, for separately describing ion-sputtering, photon stimulated and thermal desorption from the surface of Mercury, is used to determine the trajectories of ejected particles, calculated by using the full equation of motion. These are accumulated into a matrix to obtain the spatial and energy distributions of atmospheric particles, assuming uniform surface concentration of the ejecta. Then, analytical models are obtained by fitting the numerical data with parametric functions.We focus on the effect of those physical quantities that are not well constrained in describing the role of the source processes, and on the global loss from the planet. Hence, we run several numerical simulations with different values of the source-associated physical quantities, studying the effect on the morphology of the exosphere for the various analytical-model parameters. In this way, it is possible to model the exosphere of Mercury, for each source separately, when different source configurations are involved. Moreover, we can investigate the role of each physical source quantity separately. This study shows possible strong variations in the Hermean exospheric profiles; hence, it demonstrates the importance of taking into account different surface or external conditions while modelling the Hermean exosphere.