UC Santa Cruz

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 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 to explain the dissipation. We further demonstrate that Eriss ice shell must be convecting to be sufficiently dissipative, which distinguishes it from Plutos conductive shell. The difference is likely due to Eriss apparent depletion in volatiles compared with Pluto, perhaps as the result of a more energetic impact.