Assessing the accuracy in the determination of Uranus gravity field with the UOP mission

The Uranus Orbiter and Probe (UOP) mission, prioritized by the 2023-2032 Decadal Survey, represents a critical step in understanding ice giant interiors, a class of planets left unexplored since the Voyager 2 flyby. This work investigates the potential for a dedicated gravity science experiment to resolve Uranus's hidden internal structure by measuring its gravitational field.

Through a comprehensive multi-arc covariance analysis conducted using the MONTE software, we evaluate the performance of three different candidate orbital families depending on pericenter altitude and latitude, as well as inclination and period. These families are designed to balance the high gravitational sensitivity of low-altitude periapsis passes with the operational safety constraints imposed by Uranus’s ring system. We specifically assess the recovery accuracy of zonal harmonics (J_l) and degree-2 tidal Love number (k_22) the latter being a pivotal indicator of whether the Uranian interior is fluid or partially solid.

Furthermore, following recent discoveries of seismic effects at Jupiter and Saturn, we incorporate a model of planetary normal modes (f-modes and p-modes) into the spacecraft dynamical model. We explore the detectability threshold of these acoustic oscillations and their potential to bias static gravity field estimations. By simulating various excitation scenarios and frequency envelopes, we identify orbital inclinations and periods that optimize the decorrelation between static, tidal, and dynamic gravitational signals. Our results demonstrate that a strategic selection of orbital parameters, specifically targeting polar inclinations and non-resonant periods, can advance our understanding of Uranus, potentially confirming the existence of a stratified or frozen core.

 

This work has been supported in part by the Italian Space Agency under contract n. 2024-5-HH.0.