Thermal–orbital evolution of Eris

The large Kuiper Belt object (KBO) Eris is nearly as big as Pluto and has a small moon, Dysnomia. Constraints on the system’s spin and orbit characteristics were recently used to argue for a dissipative Eris, requiring a differentiated structure but not necessarily a subsurface ocean. Here, we model the thermal history of Eris coupled to its spin–orbital evolution, finding a subsurface ocean is preferred in order for Eris to be sufficiently dissipative. Spinning down Eris without an ocean is difficult, requiring a warm convecting ice shell protected by a thick insulating layer and very dissipative anelastic behavior in ice. Oceans make up 77%–100% of successful thermal–orbital evolution models, depending on the parameters assumed, which increases to $>$98% when the Andrade $\beta$ parameter for ice is restricted to $\beta \le 3\times 10^{-11}$ Pa⁻¹ s${}^{-0.25}$. Oceans freeze over by the present day unless insulation (porosity, gas clathrates) or antifreeze are present.