Catastrophic disruption of icy bodies with sub-surface oceans

Several icy bodies in the outer Solar system have extensive internal oceans. In several bodies the oceans are believed to be so extensive they decouple the interior core from the icy surface. A major evolutionary driver in the Solar System is high speed impacts – which lead to cratering or even disruption of the target body. Here we consider how the presence of an internal ocean modifies the energy density needed to disrupt an icy body with an internal ocean. We find that in laboratory experiments on decimetre scale bodies, the energy density to cause disruption is 16.25 ± 1.35 J kg−1, compared to 18.0 ± 0.7 J kg−1 for solid ice bodies. This suggests that for the purposes of impacts the bodies behave as if a solid with the same density. Predictions of the lifetimes of such icy bodies against impact disruption thus need not take the interior ocean into account.