Librations and obliquity of the largest moons of Uranus

TL;DR

This paper investigates how libration and obliquity measurements of Uranus's largest moons can reveal their internal structure and potential subsurface oceans, aiding future planetary exploration and understanding of ocean worlds.

Contribution

It provides a detailed analysis of libration and obliquity for Uranus's major moons to detect internal oceans and differentiate their internal structures.

Findings

Libration amplitudes vary with internal composition.

Obliquity measurements can indicate subsurface oceans.

Models suggest detectable signals for future missions.

Abstract

Following the discovery of several ocean worlds in the solar system, and the selection of Uranus as the highest priority objective by the Planetary Science and Astrobiology Decadal Survey 2023-2032, the five largest moons of Uranus (Miranda, Ariel, Umbriel, Titania and Oberon) have been receiving renewed attention as they may also harbor a subsurface ocean. We assess how rotation measurements could help confirm the internal differentiation of the bodies and detect internal oceans if any. Because of the time-varying gravitational torque of Uranus on the flattened shape of its synchronous satellites, the latter librate with respect to their mean rotation and precess with a non zero obliquity. For a range of interior models with a rocky core surrounded by a hydrosphere, either solid or divided into an outer ice shell with a liquid ocean underneath, we compute their diurnal libration amplitude and obliquity.