Titan’s spin state as a constraint on tidal dissipation

Tidal dissipation in satellites affects their orbital and rotational evolution and their ability to maintain subsurface oceans. However, a satellite's dissipation rate, parameterized by <i>k</i>₂<i>/Q</i>, is hard to measure and is only known for the Moon and Io. Here, we use Titan's measured departure from its expected rotation state to infer <i>k</i>₂<i>/Q</i> and its boundary layer dissipation parameter <i>K/C</i>_s. Over the likely range of ocean and ice shell thicknesses, we infer a <i>K</i>/<i>C</i>_s of 6.3 × 10^-14 s^-1 to 2.4 × 10^-10 s^-1, a <i>k</i>₂<i>/Q</i> of 0.058 to 0.12, and a minimum dissipation factor <i>Q ≈ 5</i>. Titan's dissipation parameters are one to two orders of magnitude larger than the Moon's and suggest an interior with a low effective viscosity. Titan's dissipation rate implies that its eccentricity and inclination are damping rapidly, consistent with an excitation within the last ~350 Myr. The forthcoming Dragonfly lander could measure Titan's tidal response, and JUICE could use our approach to determine Ganymede's <i>k</i>₂<i>/Q</i>.