Europa’s coupled ice–ocean system: Temporal evolution of a pure ice shell

Abstract

Europa’s icy surface likely overlies an ocean, but the ice thickness is not known. Here we model the temporal growth of a Europan shell of pure ice subject to varying ice–ocean heat fluxes, ice rheologies, and internal heating rates. Both constant and viscosity-dependent internal heating rates are included, yielding similar results for particular viscosities. A growing shell starting from an ice-free initial state transitions from conduction to convection at O(105) to O(107) years, with thicknesses of O(1–10) km. For low ice–ocean heat fluxes and larger viscosities, and in the absence of internal heating of the shell, the time to reach a steady-state thickness exceeds the estimated age of Europa’s surface, whence the shell may still be growing. We conclude by presenting a method for inferring estimates of ice–ocean heat fluxes (modulo uncertainties introduced by internal heating) and vertical ocean velocities from the ice-thickness measurements expected from the upcoming Clipper mission, assuming the shell is in a conductive steady state.