Pitfalls of tidal modelling and obliquity constraints on Titan's interior

A recent reanalysis of Cassini's data to measure Titan's tidal response suggested that the inferred tidal dissipation was too large for a global subsurface ocean to be present within Saturn's largest moon's interior, suggesting instead that the ice may directly transition to higher-pressure phases, of which a thick layer should remain near the melting point (Petricca et al., 2025). In this contribution, we demonstrate the peculiarities of tidal modelling in triaxial, synchronously rotating moons like Titan and show why the traditional representation of the diurnal tidal response in terms of a single (complex) tidal Love number may not readily provide useful constraints on the interior structure. We then proceed to a detailed analysis of the measured orientation of Titan's spin axis using a self-consistent model of tides and rotation variations tailored for icy satellites, and highlight the difficulties that can affect the accuracy of uncoupled models. Our results do not preclude the existence of a global subsurface ocean within Titan.