How thick are Europas icy outer shell and its possible ocean?
The sum of theoretical and observational data indicate that Europa’s the icy shell is ~15 to 25 km thick, overlying an ocean approximately 80 km deep. A comprehensive theoretical estimate of the ice shell thickness is given by Ojakangas and Stevenson (1989), who look at the influences of tidal and radiogenic heating. They find that the ice shell should be an average thickness of ~20 to 30 km. Unintuitively, they find that the radiogenic heat from the rock-rich interior of Europa would not make the ice shell much thinner, because there is a feedback: more heat from the interior thins the ice shell, and so there is less total tidal heating of the ice shell, so the ice shell does not thin significantly overall. More recently, Bill McKinnon has investigated this further: in modeling significant tidal heating of the rocky interior, he finds that the ice shell can become no less than ~10 km thick.
