Alexis Coyette (UNamur)

Title: Modeling the rotation of Titan

Abstract: Observation of the rotation of synchronously rotating satellites can help to probe their interior. We study here the variations in rotation rate and the polar motion of Titan due to (1) the gravitational force exerted by Saturn at orbital period and (2) exchanges of angular momentum between the seasonally varying atmosphere and the solid surface. The deviation of the mass distribution from hydrostaticity can significantly increase the diurnal libration and decrease the amplitude of the seasonal libration. By including a large spectrum of atmospheric perturbations, the smaller than synchronous rotation rate measured by Cassini in the 2004–2009 period (Meriggiola et al., 2016) could be explained by the atmospheric forcing. The effect of the non-hydrostatic mass distribution is less important for polar motion, which is more sensitive to flow in the subsurface ocean. For some interior models of Titan, the amplitude of its polar motion can be resonantly amplified. Future observations of the polar motion of Titan could help constraining some properties of its interior structure as the ice shell thickness and ocean density.