Numerical Simulations of Convection in Europa’s Ice Shell: Implications for Surface Fea-

Europa’s icy surface displays numerous small (530 km-diameter) pits, spots, and uplifts with topography of 100-300 m [1-5]. Although several formation models exist for these features, the most popular is that they result from deformation of the lithosphere by convection in the underlying ice [1,2,6,7,13]. However, it is unclear whether convection can produce topography of the appropriate wavelength, height, and surface expression. Here we present numerical simulations of convection in Europa’s ice shell including temperaturedependent viscosity and tidal heating. Ice shells 15 and 50 km thick are considered, consistent with several estimates of the shell thickness on Europa [8-10]. The convection produces 100-200 m-deep pits with 10-20 km diameter–consistent with some of the observed features– when the lithospheric viscosity is 10–10 times greater than that of the underlying ice, but greater or smaller viscosity contrasts lead to topography insufficient to explain the observed pits and uplifts. When compared with plausible lithospheric stiffnesses, the results suggest that Europa’s widest pits and uplifts could result from convection; however, features with diameters < 5 km require other formation mechanisms. The convection induces stresses > 1 bar, which exceeds the inferred strength of Europa’s crust [11] and indicates the likelihood of surface disruption.