Titan's Obliquity as evidence for a subsurface ocean?

TL;DR

This paper proposes a new Cassini state model for Titan that includes a subsurface ocean, which better explains Titan's observed obliquity and rotation state, providing evidence for a liquid water ocean beneath its ice shell.

Contribution

The study introduces a Cassini state model incorporating a subsurface ocean, improving agreement with observations and supporting the existence of Titan's hidden ocean.

Findings

Better match between observed obliquity and model predictions with a subsurface ocean

Supports the hypothesis of a liquid water ocean beneath Titan's ice shell

Strengthens the case for Titan's internal ocean based on rotational dynamics

Abstract

On the basis of gravity and radar observations with the Cassini spacecraft, the moment of inertia of Titan and the orientation of Titan's rotation axis have been estimated in recent studies. According to the observed orientation, Titan is close to the Cassini state. However, the observed obliquity is inconsistent with the estimate of the moment of inertia for an entirely solid Titan occupying the Cassini state. We propose a new Cassini state model for Titan in which we assume the presence of a liquid water ocean beneath an ice shell and consider the gravitational and pressure torques arising between the different layers of the satellite. With the new model, we find a closer agreement between the moment of inertia and the rotation state than for the solid case, strengthening the possibility that Titan has a subsurface ocean.