Temporal Changes in Europa's Ice Shell Thickness: Insights From Models of Convection

Abstract Europa is characterized by a thin ice I h shell overlying a subsurface ocean and a large solid core. Estimates of the outer ice shell's thickness range from a few kilometers to several tens of kilometers, with strong implications for Europa's thermal and geological history. Here, we model the thermal evolution of Europa's ice shell using a parameterized convection approach that explicitly accounts for internal heat release. We explore changes in the thickness of this ice shell as a function of ice reference viscosity, tidal heating, and ocean composition. We further consider the effect of cyclical variations in tidal heating in response to changes in the eccentricity of Europa's orbit. Our calculations show that the ice shell thickness is mostly influenced by both the ice viscosity and tidal heating. While significant in the absence of tidal heating, the ocean composition has no or little influence when such heating is accounted for. For dissipated tidal power and viscosity around 1 TW and 10 14 Pa·s, respectively, which are within the expected range of values for these parameters, our calculations predict an ice shell thickness in the range of 20–45 km including, at the top part of this shell, a stagnant lid ∼10 km in thickness. These values are in agreement with recent estimates of impact basin morphology. Our calculations further indicate that a 10% change in orbital eccentricity may trigger variations in the ice shell thickness of approximately 15 km, which further helps to reconcile estimates based on geological features and modeled thermal history.