On the surface sputtering effects of magnetospheric charged particles at mercury

A simple model of the atomic sodium exosphere is used in conjunction with a magnetospheric field model to study the ion trajectories of Na⁺ ions in the magnetosphere of Mercury. It is found that low-energy (< 3 keV) ions usually encounter the planetary surface at high latitude as a result of the finite size of the planet and the E × B drift pattern of the ions. On the other hand, high-energy (> 10 keV) particles tend to hit the planetary surface on the nightside hemisphere at low latitudes. Such precipitation patterns of the exospheric ions might have important implication on the recent observations of enhancement of sodium emissions at high-latitude regions of Mercury.