Subsurface ocean salinity and dissipation rate inferred from Enceladus ice shell morphology

TL;DR

This study uses scaling analysis and simulations to explore how ocean salinity and tidal mixing influence Enceladus's subsurface ocean circulation, heat transport, and dissipation, providing constraints on its ocean properties and habitability.

Contribution

It introduces a novel analysis linking ocean salinity and tidal mixing to circulation and heat transport constraints on Enceladus's subsurface ocean.

Findings

Ocean circulation is stronger at extreme salinity levels.

Tidal mixing enhances heat transport and circulation.

Enceladus's ocean acts as an efficient heat pump, limiting dissipation.

Abstract

The habitability of Enceladus' subsurface ocean and the detectability of potential biosignatures depend on efficient ocean circulation and suitable ocean conditions. Directly probing the ocean is challenging because it lies beneath a thick ice shell; however, the ice thickness distribution is relatively well constrained and provides indirect insight into the underlying ocean dynamics. This study investigates how ocean circulation and the associated heat transport depend on ocean salinity and tide-induced vertical mixing using scaling analysis, supported by numerical simulations. We find that ocean circulation and equatorward heat convergence are stronger under extremely high or low salinity conditions than under intermediate salinity, and both increase with tidal mixing rates. Because the poleward thinning of Enceladus' ice shell cannot be maintained in the presence of strong equatorward ocean heat transport, these results place constraints on the ocean salinity, diffusivity, circulation timescale, and ocean dissipation rate. Energetic analysis further shows that Enceladus' ocean behaves like an extremely efficient heat pump (inefficient heat engine), potentially transporting up to 1000 times more heat across latitudes than the energy dissipated within the ocean itself, thereby placing strong constraints on the ocean's energy dissipation rate.