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

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.