Detection of rapid orbital expansion of Saturn's moon Titan

The gravitational pull exerted on Saturn by each of its moons raises a tidal bulge on the gas giant. Because of poorly understood dissipative processes happening in the host planet, the tidal bulge is not directed along the direction of the moon. This allows the transmission of energy from the rotation of the planet to the orbits of the moons, causing them to migrate outward. The classical tidal theory predicts a small migration rate for Titan and the middle-sized moons of Saturn. However, previous analyses, (V.Lainey 2012, V.Lainey 2017), evidenced that the mid-sized moons of the Saturn system are migrating faster than expected. Using two completely independent approaches we constrained the outward migration of Titan, obtaining a large orbital expansion. This fact suggests that the moon was formed significantly closer to Saturn and it has migrated by a substantial amount, over the lifetime of the solar system. The estimated values are not compatible with a constant quality factor for Saturn. Although, the estimated outward migration is consistent with the resonance locking tidal theory. This fact motivates a revision of the evolutionary history of the Saturn's moon system.