Poro-viscoelastic tidal heating of Io

TL;DR

This paper models Io's interior as a two-phase system to evaluate tidal heating, revealing shear dissipation as the dominant process and Darcy dissipation as secondary under realistic conditions.

Contribution

It introduces a self-consistent model combining poro-viscous and poro-elastic theories to quantify tidal heating in Io's partially molten mantle.

Findings

Shear dissipation dominates tidal heating in Io.

Darcy dissipation can exceed shear heating only at high melt fractions and ultra-low viscosities.

Compaction contributes minimally, at most 1% of observed heating.

Abstract

Io's tidally driven global volcanism indicates widespread partial melting in its mantle. How this melt participates in the interior dynamics, and, in particular, the role it plays in tidal dissipation, is poorly understood. We model Io's tidal deformation by treating its mantle as a two-phase (solid and melt) system. By combining poro-viscous and poro-elastic compaction theories in a Maxwell framework with a consistent model of tidal and self-gravitation, we produce the first self-consistent evaluation of Io's tidal heating rate due to shearing, compaction, and Darcy flow. We find that Darcy dissipation can potentially exceed shear heating, but only for large (0.05 to 0.2) melt fractions, and if the grain size is large or melt viscosity ultra-low. Since grain sizes larger than 1cm are unlikely, this suggests that Darcy dissipation is secondary to shear dissipation. Compaction dissipation is maximised when the asthenosphere is highly resistive to isotropic stresses, but contributes at most 1% of Io's observed heating rate. This work represents a crucial step toward a self-consistent quantitative theory for the dynamics of Io's partially molten interior.