Interaction of Europa With the Jovian Magnetosphere

We have developed a time-dependent 3D MHD model to investigate the time varying periodic interaction between the Jovian magnetosphere and the atmosphere of Europa. The temporal variations are caused by periodic variations of the magnetospheric plasma and magnetic fields at Europa. As an important and new feature, periodic induced magnetic fields, caused by electromagnetic induction in a potential subsurface ocean, are included. The time-dependent MHD-flow problem and the internal induction problem are solved simultaneously. We examine the interdependency of both effects and find that the induced magnetic fields influence the plasma interaction, e.g. by causing time varying asymmetries in the plasma density and the current density outside Europa and in the magnitude of the currents. By comparing our results to the Galileo spacecraft measurements, we place the so far strongest constraints on the conductivity and thickness of Europa's subsurface ocean.