Pressurized oceans and the eruption of liquid water on Europa and Enceladus

It is difficult for liquid water to erupt onto the surface of icy satellites, such as Europa and Enceladus, because liquid water is more dense than ice. If the ice shell thickens, the volume expansion of ice upon freezing increases pressure in the subsurface ocean. The excess pressure is determined by a balance between compression of ocean water and elastic expansion of the ice shell. We show that on Europa the freezing of ∼ 1–10 km of ice generates tangential stresses that exceed the tensile strength of ice. Excess pressure, however, is insufficient for liquid water to erupt to the surface. Within smaller icy satellites, such as Enceladus, ocean pressure can become large enough to cause an eruption of large amounts of liquid water.