Abstract

Abstract. Because of the small planetary magnetic field as well as proximity to the Sun that leads to enhanced solar wind pressure as compared to Earth, the magnetosphere of Mercury is very dynamical and at times subjected to promi-nent compression. We investigate the dynamics of magneto-spheric ions during such compression events. Using three-dimensional single-particle simulations, we show that the electric field induced by the time varying magnetic field can lead to significant ion energization, up to several hundreds of eVs or a few keVs. This energization occurs in a nona-diabatic manner, being characterized by large enhancements of the ion magnetic moment and bunching in gyration phase. It is obtained when the ion cyclotron period is comparable to the field variation time scale. This condition for nonadia-batic heating is realized in distinct regions of space for ions with different mass-to-charge ratios. During compression of Mercury’s magnetosphere, heavy ions originating from the planetary exosphere may be subjected to such an abrupt en-ergization, leading to loading of the magnetospheric lobes with energetic material.