Recent tectonic activity on Pluto driven by phase changes in the ice shell

The New Horizons spacecraft has found evidence for geologic activity on the surface of Pluto, including extensional tectonic deformation of its water ice bedrock see Moore et al. (2016). One mechanism that could drive extensional tectonic activity is global surface expansion due to the partial freezing of an ocean. We use updated physical properties for Pluto and simulate its thermal evolution to understand the survival of a possible subsurface ocean. For thermal conductivities of rock less than 3 W m−1 K−1, an ocean forms and at least partially freezes, leading to recent extensional stresses in the ice shell. In scenarios where the ocean freezes and the ice shell is thicker than 260 km, ice II forms and causes global volume contraction. Since there is no evidence for recent compressional tectonic features, we argue that ice II has not formed and that Pluto's ocean has likely survived to present day. Key Points The partial freezing of a subsurface ocean is likely driving recent extensional tectonic activity on Pluto If the ice shell is thicker than 260 km and the ocean freezes completely, ice II forms and causes global volume contraction The lack of compressional tectonic features suggests that ice II did not form and Pluto's ocean may have survived to present day