A multiarc approach to detecting Uranus normal modes via Doppler tracking of a 5 planetary orbiter

Uranus is the proposed target of NASA’s next large-scale mission, offering a unique opportunity to advance our understanding of ice giant systems. The planet hasn’t been visited by a spacecraft since Voyager 2, and fundamental questions about its interior structure, atmospheric composition, and magnetosphere remain unanswered. As part of the strategy to address these knowledge gaps, a gravity science experiment is strongly recommended for the future Uranus Orbiter and Probe (UOP) mission. The primary objective is to accurately determine the planet’s gravity field and tidal parameters, providing crucial insights into its internal structure. However, these parameters alone may not be sufficient to fully constrain Uranus’s density gradients and core structure. Complementary approaches are being considered, such as the study of normal modes. These global-scale planetary oscillations have been observed in Saturn and possibly Jupiter, are directly linked to interior properties and may be observable using a gravity science instrument. Yet, Uranus’s normal mode frequencies and amplitudes remain unknown, posing a challenge for their detection via gravitational seismology. Here, we draw comparisons with Saturn’s observed oscillations and conduct numerical simulations of the orbit determination process at Uranus. The goal is to assess whether an orbiter on a realistic trajectory can detect planetary oscillations and determine how many orbits would be required. This work is useful for designing UOP trajectories and contributes to a more comprehensive understanding of ice giants, both within our solar system and beyond.