The past and future obliquity of Saturn as Titan migrates

Vol. 647
10. Planets and planetary systems

The past and future obliquity of Saturn as Titan migrates

The rotation axis of Saturn is tilted with respect to its orbital plane. The authors of the present study show that the past migration of Titan can explain this axial tilt. Titan has been drifting away from Saturn since its formation at a rate which the Cassini mission measured. The present study extends this previous work by simulating millions of trajectories to quantify this phenomenon and link the axial tilt of Saturn with the migration rate of Titan. These many simulations cover the uncertainty range on the migration rate of Titan, on the initial obliquity of Saturn, and on its moment of inertia. They show that the initial obliquity of Saturn was much smaller than its current value, and that the migrating Titan helped trap the precession of the rotation axis of Saturn into a secular resonance with Neptune. This resonance is in turn responsible for the tilt of Saturn. This study also looks into the future evolution of the spin axis of Saturn, suggesting that its obliquity is still increasing and could reach a much higher value of 55 to 65° within 5 Gyrs.