The effect of an asymmetric core on convection in Enceladus' ice shell: Implications for south polar tectonics and heat flux

Abstract

Enceladus exhibits a strong tectonic contrast between its south polar terrain (SPT), which is young and geologically active, and its northern hemisphere, which is relatively ancient and stable. Previous global three‒dimensional (3‒D) spherical models of convection exhibit patterns that are symmetrical around the equator and fail to explain the formation of a hemispheric dichotomy. Here we present global 3‒D spherical models of convection in Enceladus' ice shell to show that convection in Enceladus' ice shell with plasticity and irregular core geometry can self‒consistently generate a hemispheric dichotomy in tectonics and heat flux. With a spherical core, convection produces global overturning, which cannot explain the regional confinement of Enceladus' current tectonic activity to the SPT. Models with appropriate nonspherical core geometry and plasticity tend to produce overturning confined to the SPT or regional overturning in different regions at different times, which can explain the tectonic dichotomy and local age differences on Enceladus. Our models predict heat flows up to 5–10 gigawattts (GW) during active episodes, consistent with Cassini observations.