Saturn’s moon Titan has long been considered one of the archetypal ocean worlds of the outer Solar System, with multiple geophysical observations from NASA’s Cassini mission historically interpreted as evidence for a global subsurface ocean. Establishing the presence of such oceans, however, relies on indirect measurements that probe the interiors of icy moons, for example through observations of their gravity and magnetic fields, as well as their orientation and rotational state. In this seminar, I will first review the techniques used to detect subsurface oceans using spacecraft data, with a focus on how planetary gravity fields are measured through precision orbit determination and Doppler tracking. I will discuss how these geophysical measurements are used to infer the interior structure properties and the presence of liquid layers inside icy moons. I will then present a reassessment of Titan’s interior based on improved gravity field measurements derived from Cassini Doppler data. These new results reveal unexpectedly strong tidal energy dissipation within Titan’s interior and motivate a reinterpretation of other geophysical constraints, challenging the long-standing interpretation that Titan hosts a subsurface ocean. While reconciling all the geophysical measurements at Titan has historically been challenging, I will show that the available observations can be simultaneously explained with an interior model in which Titan’s hydrosphere is largely frozen, without a present-day global ocean. Finally, I will discuss the broader implications of this revised interior configuration for Titan’s thermal and orbital evolution, and for interpreting ocean signatures across other icy satellites in the outer Solar System.