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

TL;DR

This paper uses high-resolution Hall MHD simulations to reveal how Hall electric fields influence Ganymede's magnetosphere, affecting currents, plasma flows, and observable magnetic structures, providing insights beyond resistive MHD models.

Contribution

It demonstrates the significant global effects of Hall electric fields in Ganymede's magnetosphere through comprehensive simulations, highlighting phenomena not captured by resistive MHD.

Findings

Development of intense field-aligned currents along separatrices.

Formation of ion drift belts circulating plasma.

Observable features like double magnetopause and Alfvénic ion jets.

Abstract

We 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 currents in the reconnection plane accelerate ions to the local Alfv\'en 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 Alfv\'enic ion jet extending across the upstream magnetopause and an asymmetric pattern of magnetopause Kelvin-Helmholtz waves.