The Interior Dynamics of Water Planets

TL;DR

This paper models the internal structure and dynamics of water-rich super-Earths, exploring surface regimes, ice mantle convection, and implications for observable features.

Contribution

It provides a comprehensive model of water planet interiors, including surface regimes, ice mantle convection, and their effects on atmospheric observables.

Findings

Identification of regimes for subsurface liquid oceans and ice tectonics.

Ice mantle overturn timescales range from 0.1 to 100 million years.

Planetary radius and overturn times depend on total mass and water fraction.

Abstract

The ever-expanding catalog of detected super-Earths calls for theoretical studies of their properties in the case of a substantial water layer. This work considers such water planets with a range of masses and water mass fractions (2 to 5 M_Earth, 0.02% to 50% H2 O). First, we model the thermal and dynamical structure of the near-surface for icy and oceanic surfaces, finding separate regimes where the planet is expected to maintain a subsurface liquid ocean and where it is expected to exhibit ice tectonics. Newly discovered exoplanets may be placed into one of these regimes given estimates of surface temperature, heat flux, and gravity. Second, we construct a parameterized convection model for the underlying ice mantle of higher ice phases, finding that materials released from the silicate iron core should traverse the ice mantle on the timescale of 0.1 to 100 megayears. We present the dependence of the overturn times of the ice mantle and the planetary radius on total mass and water mass fraction. Finally, we discuss the implications of these internal processes on atmospheric observables.