Abstract
Saturn’s moon Enceladus has a global subsurface ocean and a porous rocky
core in which water-rock reactions likely occur; it is thus regarded as
a potentially habitable environment. For icy moons like Enceladus, tidal
heating is considered to be the main heating mechanism, which has
generally been modeled using viscoelastic solid rheologies in existing
studies. Here we provide a new framework for calculating tidal heating
based on a poroviscoelastic model in which the porous solid and
interstitial fluid deformation are coupled. We show that the total
heating rate predicted for a poroviscoelastic core is significantly
larger than that predicted using a classical viscoelastic model for
intermediate to large (> 10 14 Pa.s) rock viscosities. The
periodic deformation of the porous rock matrix is accompanied by
interstitial pore fluid flow, and the combined effects through viscous
dissipation result in high heat fluxes particularly at the poles. The
heat generated in the rock matrix is also enhanced due to the high
compressibility of the porous matrix structure. For a sufficiently
compressible core and high permeability, the total heat production can
exceed 10 GW-a large fraction of the moon’s total heat budget without
requiring unrealistically low solid viscosities. The partitioning of
heating between rock and fluid constituents depends most sensitively on
the viscosity of the rock matrix. As the core of Enceladus warms and
weakens over time, pore fluid motion likely shifts from pressure-driven
local oscillations to buoyancy-driven global hydrothermal convection,
and the core transitions from fluid-dominated to rock-dominated heating.