Mercury’s magnetosphere–solar wind interaction for northward and southward interplanetary magnetic field: Hybrid simulation results

Abstract

Analysis of global hybrid simulations of Mercury’s magnetosphere–solar wind interaction is presented for northward and southward interplanetary magnetic field (IMF) orientations in the context of MESSENGER’s first two encounters with Mercury. The global kinetic simulations reveal the basic structure of this interaction, including a bow shock, ion foreshock, magnetosheath, cusp regions, magnetopause, and a closed ion ring belt formed around the planet within the magnetosphere. The two different IMF orientations induce different locations of ion foreshock and different magnetospheric properties: the dayside magnetosphere is smaller and cusps are at lower latitudes for southward IMF compared to northward IMF whereas for southward IMF the nightside magnetosphere is larger and exhibits a thin current sheet with signatures of magnetic reconnection and plasmoid formation. For the two IMF orientations the ion foreshock and quasi-parallel magnetosheath manifest ion-beam-driven large-amplitude oscillations, whereas the quasi-perpendicular magnetosheath shows ion-temperature-anisotropy-driven wave activity. The ions in Mercury’s belt remain quasi-trapped for a limited time before they are either absorbed by Mercury’s surface or escape from the magnetosphere. The simulation results are compared with MESSENGER’s observations.