William Polycarpe (Paris Observatory)

Title: Is Titan responsible for Iapetus’ orbit ?

Abstract: Latest astrometrical results on Saturnian moons show evidence for high migration rates (Lainey et al. 2012; 2016). The tidal dissipation in the planet is responsible for those large orbital expansions and should therefore be much stronger than usually expected. The idea of significant tidal dissipation in the massive core (Remus et al. 2012) and the convective envelope (Le Guenel et al. 2015; Fuller et al. 2016) of the planet has been brought forward as a likely explanation.
Nevertheless, high changes in semi-major axes of the moons shuffle up the ideas we had on the past evolution of the system of Saturn. In particular, depending on tidal mechanisms at play, several Mean Motion Resonances could have been crossed just a few million years ago.
In the frame of high tidal migration, we investigate the consequences of the past 5:1 mean motion resonance between Titan and Iapetus, which could have happened between 5 and 500 million years ago. Numerical simulations show that the most common outcome for Iapetus is to be ejected, as Titan migrates through the resonance. However, if Titan has a very high recession (Q <2000), Iapetus may survive the resonance and come out of it with an eccentricity consistent with today’s value. The effect on Iapetus’ inclination is still under investigation.