Cracking Europa’s shell: How ice thickness and convection drive surface-interior dynamics

Europa’s geologically young surface, characterised by extensional and subsumption bands, hints at dynamic ice tectonics and active interactions between the moon’s surface and its interior. Potentially, a key driver of this activity is the convection within Europa’s icy shell. Ice shell convection can facilitate and promote the mobility of Europa’s ice surface, the evolution of its topography as well as thermochemical mixing within the shell itself. Yet, critical aspects of Europa’s ice shell, such as its thickness and composition and how these vary across the surface and with depth, remain elusive, limiting our understanding of Europa’s icy dynamics and its surface evolution. In this work, we present state-of-the-art numerical models of convection in an icy shell with composite viscosity, visco-elastic-plastic deformation, and a free-surface top boundary condition using the finite element code ASPECT. We explore a range of ice properties informed by current the literature and find that the ice shell thickness plays a pivotal role in determining the onset, style and longevity of convection. Notably thicker ice shells encourage chaotic convection with high Rayleigh numbers, leading to the formation and peeling of ‘icy slabs’. These results provide new insights into the dynamic behavior of Europa’s icy shell and its implications for surface-interior coupling.