ИСТИНА

Observations of Calcium column densities in Mercury’s exosphere exhibit a scale height consistent with a temperature > 50,000 K, and with a source located mainly on the dawnside of the planet. It was suggested that the originating process is due to MMIV (Micro- Meteoroids Impact Vaporization), but previous estimations were not able to justify the observed intensity and energy. We use an exospheric Monte Carlo model to simulate the 3D spatial distribution of the Ca-bearing molecule and atomic Ca generated by the MMIV process. The exospheric energetic Ca component derives from the shock-induced nonequilibrium dissociative ionization and neutralization of Ca+ during the vapor cloud expansion, while a low energy Ca component is generated later by the photo-dissociation of the Ca-bearing molecules released by MMIV. Since the exact temperature, the photolysis lifetimes of the produced molecules and the excess energy during photolysis processes are still not well constrained values, we investigate diferent model assumptions. We simulate the seasonal variation of Ca distribution and altitude profile of Ca and Ca-bearing molecules comparing the theoretical calculations with data observations. This study permits to find the set of model input parameters able to reproduce the observed Ca content. The work is a meant to be a step forward in the understanding of the MMIV process at Mercury; furthermore, the model is a strong and useful tool to the scientific community for the interpretation for data as well a for observational strategies of the ESA/JAXA BepiColombo mission, that will start its nominal mission phase in 2026.