Code to track coupled orbital-rotational evolution of a planet and satellite

The large Kuiper Belt Object Eris is tidally locked to its small companion Dysnomia. Recently obtained bounds on the mass of Dysnomia demonstrate that Eris must be unexpectedly dissipative in order for it to have despun over the age of the solar system. Here we show that Eris must have differentiated into an ice shell and rocky core in order to explain the dissipation. We further demonstrate that Eris's ice shell must be convecting to be sufficiently dissipative, which distinguishes it from Pluto's conductive shell. The difference is likely due to Eris's apparent depletion in volatiles compared with Pluto, perhaps as the result of a more energetic impact.