Tidal Heating at Europa Using the Multifrequency Analysis of Tidal Heating Toolkit

Abstract

We evaluate the thermal response of Europa’s ice shell to the gravity perturbation of Jupiter using a comprehensive toolkit (dubbed Multifrequency Analysis of Tidal Heating, MATH) that evaluates tidal heating and heat flow in planetary bodies. The tidal heating source is radially resolved and can capture the temperature-dependent pattern of heat production with depth. We use MATH to examine the steady-state thermal profiles through a conductive Europan ice shell, considering the tidal effects of long-term eccentricity variations, obliquity, libration, and nonsynchronous rotation (NSR). In each case, we vary the shell thickness, calculate the combination of tidal heating generated within the shell and heat flux into the shell base that would maintain that thickness, and track the resulting surface heat flux. We find that Europa’s ice shell should be, on average, no more than 12–17 km thick, due to long-term eccentricity variations, and could be even thinner if the basal heat flux is nonnegligible. These results are more consistent with inferences from Europa’s surface geology than previous tidal heating studies that used simplified interior models, a globally averaged tidal heating rate, and/or constant eccentricity. We also find that, for a given stable shell thickness, the surface heat flow remains fairly consistent even as other parameters are varied, perhaps providing an additional method for constraining ice shell thicknesses on ocean-bearing moons. Although Europa’s tidal heat budget and shell thickness seem relatively insensitive to constant obliquity, libration, and NSR, moons in closer-in orbits may be more sensitive to these other effects and should be further explored.