Band Formation and Ocean‐Surface Interaction on Europa and Ganymede

Geologic activity in the outer H2O ice shells of Europa and Ganymede, Galilean moons of Jupiter, may facilitate material exchange between global water oceans and the icy surface, fundamentally affecting potential habitability and the future search for life. Spacecraft imagery reveals surfaces rich with tectonic bands, predominantly attributed to the extension of brittle ice overlaying a convecting ice layer. However, the details of band‐forming processes and links to potential ocean‐surface exchange have remained elusive. We simulate ice shell faulting and convection with two‐dimensional numerical models and track the movement of “fossil” ocean material frozen into the base of the ice shell and deformed through geologic time. We find that distinct band types form within a spectrum of extensional terrains correlated to lithosphere strength, governed by lithosphere thickness and cohesion. Furthermore, we find that smooth bands formed in weak lithosphere promote exposure of fossil ocean material at the surface. Plain Language Summary The strength of rigid near‐surface ice on Europa and Ganymede determines the terrains formed where the surface has pulled apart, and certain terrains can contain material originating in the subsurface ocean. Key Points Bands and groove lanes on Europa and Ganymede form within a spectrum of morphologies controlled by lithosphere strength “Fossilized” ocean material accreted to the base of the ice shell may be exposed at the surface after high strain, notably in smooth bands Lithosphere thickness and cohesion loss are primary controls on the surface expression of tectonic deformation