The Many Fates of Pluto's Subsurface Ocean

A continuously increasing number of objects in our solar system have been classified as “ocean worlds,” harboring recent or past subsurface oceans of liquid water. These discoveries raise the potential of persistent habitability even in the frigid environments of the outer solar system. The presence of subsurface oceans within the largest and most tidally dissipative icy moons is consistent with the current understanding of their heat budgets, but suggestions of present-day oceans within smaller moons and Kuiper Belt Objects are harder to reconcile with simple thermal evolution models. It has been suggested that a methane clathrate layer within Pluto's shell would insulate a subsurface ocean and extend its lifetime. However, insulating effects have not been considered in the context of an ice shell experiencing solid-state convection, a key geodynamic process for ocean world evolution. We have therefore developed a 1-Dimensional (1D) thermal evolution model for an icy body with a time-evolving ice shell composition, to investigate the effects of basal methane clathrate incorporation on convective vigor and interior evolution. We apply our model to Pluto, a mid-sized icy world with relatively few complicating factors. We find that the addition of methane clathrate to a convecting ice shell can result in complex feedback mechanisms, causing nonlinear variation in maximum ocean thickness and temperature. This work takes a first step toward understanding both the thermal evolution of, and material transport within, compositionally complex ice shells. These results have implications for the longevity of subsurface oceans and the related habitability of these worlds.