Magnetic Induction in Europa’s Ocean

The Galileo mission discovered a distorted magnetic field around Jupiter’s moon Europa that is best explained by induction in a subsurface ocean. NASA’s Europa Clipper mission will revisit the moon and measure the field with much higher precision. The data should yield field models with an error of about one nano Tesla (nT). We explore whether this is precise enough for detecting any induction due to zonal flows or the effects of conductivity variations caused by salinity gradients. Our tools comprise analytical solutions, the Matlab code SVzon, and the MHD code MagIC. Unfortunately, we find that both zonal winds and salinity gradients likely have signals well below the expected error level. For example, assuming an electrical conductivity of 10 S/m, flows with peak velocities of about 10 m/s are required to reach the one nT level, which seems excessively fast. We also explore the flows driven by the induction process itself via Lorentz forces. These flows are dominated by geostrophic zonal winds that are reminiscent of the Reynolds-stress driven winds observed in Jupiter’s or Saturn’s cloud decks. Balancing the Lorentz force with viscous drag indicates that these induction-driven flows in Europa’s ocean would remain very slow with velocities below 10^-5 m/sec. This is orders of magnitude slower than any convective driven flows.