Recent Tectonic Activity on Pluto Driven by Phase Changes in the Ice Shell

TL;DR

This study models Pluto's thermal evolution to explore how phase changes in its ice shell, like ocean freezing and ice II formation, influence tectonic activity and surface geology.

Contribution

It provides updated physical parameters and simulations showing the likelihood of a surviving subsurface ocean and the absence of ice II formation on Pluto.

Findings

An ocean likely exists and has survived to present day.

Recent extensional tectonics are driven by surface expansion due to partial freezing.

Ice II formation is unlikely given the absence of compressional features.

Abstract

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.