Can convection in Europa's ocean translate interior tidal heating patterns to the ice-ocean boundary?

Abstract

Several icy moons of Jupiter and Saturn, including Europa and Enceladus, host liquid water oceans buried beneath their icy crusts. Geological features of the ice crusts as well as large-scale variations of the ice thickness are often attributed to endogenic processes within the ice. However, the ice shell is also coupled to the rocky interior via the convective ocean which controls heat and material exchanges. The amount of tidal heating in Europa's silicate mantle is highly uncertain, and heterogeneous. We investigate the effect of heterogeneous tidal heating in the silicate mantle on rotating thermal convection in the ocean and its consequences on ice shell thickness. Using global direct numerical simulations, we show that, under the assumption of no salinity or ocean-ice shell feedbacks, convection largely transposes the latitudinal variations of tidal heating from the seafloor to the ice, leading to a higher oceanic heat flux in polar regions. Longitudinal variations are efficiently transferred when boundary-driven thermal winds develop, but are reduced in the presence of strong zonal flows and may vanish in planetary regimes. We investigate the impact on ice shell thickness using the conductive equilibrium model of Nimmo et al. (2007) (doi: 10.1016/j.icarus.2007.04.021). We find that if spatially homogeneous radiogenic heating is dominant in the silicate mantle, the ocean’s contribution to ice shell thickness variations is negligible compared to tidal heating within the ice. If tidal heating is instead dominant in the mantle, the situation is reversed and the ocean controls the pole-to-equator thickness contrast, as well as possible longitudinal variations.