Constraining asymmetry in Europa's oceans

Abstract

Induced magnetic fields from Europa, measured by the Galileo spacecraft, provide the strongest evidence we have for the presence of a salty water ocean beneath the outer ice shell. The observed field is consistent with a global ocean layer with a high dissolved salt content. However, ice layer thickness, ocean depth, and salinity determined from induced magnetic field measurements are dependent on the model applied to represent the interior structure. Past studies attempting to constrain ocean properties have all assumed spherical symmetry, which is not expected for Europa and restricts the validity of the derived constraints. Quantifying the degree of potential asymmetry in the ocean and ice layer is critical to future exploration. Interpretation of magnetic measurements by the upcoming Europa Clipper mission, especially considering plume activity that may have degenerate signals, may be impossible without asymmetric interior models. In this work, we aim to identify constraints on the spatial asymmetry that may be present in Europa's oceans. Constraints will be determined as extremes in low-order spherical harmonics describing the ice-ocean boundary that are consistent with Galileo gravity and magnetometer measurements and realistic ocean parameters, assuming uniform ocean conductivity. Preliminary results and plans for future work will be presented.