The Tidal Response of Europa

The tidal response of Europa to a time-varying potential is determined by solving the quasi-static equilibrium equations for a body composed of several uniform, Maxwell viscoelastic layers. Models in which Europa's surface ice extends all the way to the silicate mantle have weak tidal responses (∼1 m vertical deflection) while models in which a liquid “ocean” underlies the ice have about 30 m peak vertical deflection. The phase-lag of the tidal response is very small (<2°) in the case of an ocean, but may be large if there is no ocean and the ice has a viscosity around 1013 Pa s. For models with an ocean, the product of the thickness and strength of the ice determines the tidal response, making it difficult to determine the thickness of the ice by observing the tidal deflection of Europa.