The High-Frequency Tidal Response of Ocean Worlds: Application to Europa and Ganymede

Europa and Ganymede, whose liquid water oceans are of uncertain thickness, are subject to tidal forces across a broad frequency spectrum. Tidal deformation is inherently frequency dependent, an effect which is enhanced when a subsurface ocean is present. We model the tidal response of Europa and Ganymede, taking into account ocean dynamics and the viscoelastic coupling to the ice shell. Tidal deformation at high frequencies - a result of moon-moon interactions - is resonantly amplified by ocean dynamics. We find the corresponding tidal Love numbers to be extremely sensitive to ocean thickness and weakly sensitive to ice shell thickness, shear modulus, and viscosity. Measuring these high-frequency deformations would provide a unique determination of ocean thickness, though the minimum sensitivity required to detect the relevant deformation (0.1 mm, 2 nGal) makes this an extreme challenge. Detection of a large signal on the order of centimeters would only be possible if the ocean was tuned to a particular thickness, which would suggest that moon-moon tides play a role in the thermal/orbital evolution of the moon. Scaling laws are also derived that predict the resonant enhancement of tidal Love numbers and associated tidal dissipation in the ocean and ice shell.