The role of the Hall effect in the global structure and dynamics of planetary magnetospheres: Ganymede as a case study

Abstract

AbstractWe present high‐resolution Hall MHD simulations of Ganymede's magnetosphere demonstrating that Hall electric fields in ion‐scale magnetic reconnection layers have significant global effects not captured in resistive MHD simulations. Consistent with local kinetic simulations of magnetic reconnection, our global simulations show the development of intense field‐aligned currents along the magnetic separatrices. These currents extend all the way down to the moon's surface, where they may contribute to Ganymede's aurora. Within the magnetopause and magnetotail current sheets, Hall J × B forces accelerate ions to the local Alfvén speed in the out‐of‐plane direction, producing a global system of ion drift belts that circulates Jovian magnetospheric plasma throughout Ganymede's magnetosphere. We discuss some observable consequences of these Hall‐induced currents and ion drifts: the appearance of a sub‐Jovian “double magnetopause” structure, an Alfvénic ion jet extending across the upstream magnetopause, and an asymmetric pattern of magnetopause Kelvin‐Helmholtz waves.