Hemisphere coupling in Enceladus' asymmetric plasma interaction

Abstract

The recently discovered neutral gas plume around the south pole of Enceladus introduces a pronounced north‐south asymmetry in the plasma interaction of Saturn's magnetosphere with Enceladus. In this work we present an analytic model for such an asymmetric interaction for both an Alfvénic and a unipolar inductor far field model including the Hall effect. We find that even though both hemispheres of Enceladus are not directly connected through magnetic field lines, both hemispheres are electromagnetically coupled, that is, the perturbations of the velocity and magnetic fields generated around the south polar plume are mapped in a modified way into the northern hemisphere. This hemisphere coupling creates surface currents on the magnetic flux tube determined by field lines tangent to the body of Enceladus. The surface currents are accompanied by a magnetic field discontinuity across the flux tube on both hemispheres, that is, a discontinuity across the northern and the southern wings. The Cassini spacecraft has not yet crossed this boundary, which we here predict. The diameter and other properties of the discontinuity are diagnostic of plume properties and might be even diagnostic of electrodynamic induction in a potential subsurface ocean on Enceladus. Our model is also applicable to other satellite plasma interactions where similar asymmetries can occur such as Io or extra solar planets.