William Polycarpe (IMCCE, France)

Title: Iapetus, the key to the whole system ?

Abstract : Iapetus possesses all the attributes and characteristics of the whole system of Saturn. It is mysterious and very complex. In my doctoral study I have been runing numerical and semi-analytical simulations of a past mean motion resonance between Titan and Iapetus. The goal was to expose the consequences of a fast tidal migration for Titan and find an explanation for the eccentricity and the inclination of Iapetus’ orbit. The outcomes of simulations depend on the rate of migration and, consequently, there are constraints on the quality factor of Saturn at Titan’s frequency. The resonance allows Iapetus to pass from a circular orbit to an eccentric orbit and from its local Laplace plane to a tilted orbit. A few simulations show consistency in the orbital elements of Iapetus today.

A long semi-analytic expansion was performed to run fast simulations but alternative approaches can be taken. Inverting the order of Taylor and, eventually Fourier, expansions of the direct part of the disturbing function yields a series which is more suited to the resonance with Titan and the inclined orbit of Iapetus. More work is waiting to be done and the goal would be to obtain a universal formalism for the expansion.

The migration of Titan is becoming a reality today and, here again, further studies need to be carried out concerning, for example, the rotation of Iapetus.