Uranus orbiter and probe: a radio science investigation to determine the planet’s gravity field, depth of the winds and tidal deformations

Uranus is the proposed target of NASA's next large-scale mission. The orbiter and probe concept is generating considerable interest in identifying top-priority objectives and the associated instruments essential for addressing the most pressing science questions. In particular, the interior structure and atmosphere of the planet are currently very poorly understood and objectives pertaining to investigating Uranus's deeper regions and composition are very highly ranked. Traditionally, gravity science has served as the primary mean for probing the depths of planetary bodies and inferring their internal density distributions. In this work, we present precise numerical simulations of an onboard gravity science experiment designed to determine Uranus's gravity field and tidal deformations, which would offer a rare view into Uranus's interior. We delve into the mission's orbital planning, discussing crucial parameters such as the number of pericenter passes, orbital inclination, and periapsis altitude necessary to meet the measurement requirements for a Uranus orbiter. Our findings suggest that eight close encounters may be sufficient to determine the zonal gravity field up to J_8, if certain conditions are met. This level of precision would allow for the decoupling of the gravity field components due to uniform and differential rotation. Furthermore, we find that the expected 3-sigma accuracy on Uranus's degree-2 tidal Love number is ~0.01. This parameter offers valuable information about Uranus's inner state, and may allow us to discriminate between a liquid and solid core, shedding light on crucial aspects of the planet's formation and evolution.