Crustal control of dissipative ocean tides in Enceladus and other icy moons

TL;DR

This paper introduces a novel model combining the Laplace Tidal Equations with the membrane approach to analyze tidal dissipation in icy moons, revealing crustal constraints significantly reduce oceanic heat contribution and highlighting the importance of resonances.

Contribution

It presents the first comprehensive model of dissipative tides in subsurface oceans that accounts for crustal effects, applicable to all icy satellites with thin crusts and shallow oceans.

Findings

Oceanic dissipation is greatly reduced by crustal constraints.

Tidal resonances may influence heat flow in young or freezing oceans.

Crustal dissipation can differ from static predictions by up to a factor of two.

Abstract

Could tidal dissipation within Enceladus' subsurface ocean account for the observed heat flow? Earthlike models of dynamical tides give no definitive answer because they neglect the influence of the crust. I propose here the first model of dissipative tides in a subsurface ocean, by combining the Laplace Tidal Equations with the membrane approach. For the first time, it is possible to compute tidal dissipation rates within the crust, ocean, and mantle in one go. I show that oceanic dissipation is strongly reduced by the crustal constraint, and thus contributes little to Enceladus' present heat budget. Tidal resonances could have played a role in a forming or freezing ocean less than 100 m deep. The model is general: it applies to all icy satellites with a thin crust and a shallow ocean. Scaling rules relate the resonances and dissipation rate of a subsurface ocean to the ones of a surface ocean. If the ocean has low viscosity, the westward obliquity tide does not move the crust. Therefore, crustal dissipation due to dynamical obliquity tides can differ from the static prediction by up to a factor of two.