Time-varying interaction of Europa with the jovian magnetosphere: Constraints on the conductivity of Europa's subsurface ocean

Abstract

We study the conductivity distribution inside Europa by using a time-dependent 3D-model of the temporal periodic interaction between Europa and the jovian magnetosphere. The temporal variations are caused by periodic variations of the magnetospheric plasma and magnetic fields at Europa. We develop a model which describes simultaneously the 3D plasma interaction of Europa's atmosphere with Jupiter's magnetosphere and the electromagnetic induction in a subsurface conducting layer due to time-varying magnetic fields including their mutual feedbacks. We find that inclusion of the magnetic field perturbations caused by the interaction with Jupiter's magnetospheric plasma is important for interpreting Galileo's magnetic field measurements near Europa. This leads to improved constraints on the conductivity and thickness of Europa's subsurface ocean. We find for the conductivity of Europa's ocean values of 500 mS/m or larger combined with ocean thicknesses of 100 km and smaller to be most suitable to explain the magnetic flyby data. In summary, this results in the following relation: electrical conductivity × ocean thickness ⩾ 50 S / m km . It is shown that the influence of the fields induced by the time variable plasma interaction is small compared to the induction caused by the time-varying background field, although some aspects of the plasma interaction are changed appreciably.