Tidal heating did not dry out io and europa

Abstract

The Galilean satellites exhibit a clear trend in composition from the rocky Io, close to Jupiter, to the icy and distant Callisto. Proposed causes of this trend can be roughly divided by when the trend developed-either as a result of the material accreted, as a byproduct of the accretion process, or due to the subsequent diverging evolution of the moons. While the first two options have been heavily favored in the existing literature and were therefore studied previously, in this work, we directly address the last of these possibilities. To do so, we determine the range of plausible tidal heating experienced by these moons and how efficiently that energy could be converted into mass loss. We find that while the total tidal energy does exceed the energy required to lose an ice shell, the loss process would have to be highly energy efficient. Examining a range of loss processes, we find that only in extreme cases could enough mass be lost from Europa and no cases where enough mass could be lost from Io. We conclude that this compositional gradient must have been in place by the end of accretion.