The Mysterious Interior of Uranus: Final Report of the 2023 KISS Study

Abstract

Determining the internal structure of Uranus is a key objective for planetary science. Knowledge of Uranus’s bulk composition and the distribution of elements is crucial to understanding its origin and evolutionary path. In addition, Uranus represents a poorly understood class of “intermediate-mass planets” (intermediate in size between the relatively well studied terrestrial and gas giant planets), which appear to be very common in the Galaxy. As a result, a better characterization of Uranus will also help us to better understand exoplanets in this mass and size regime.

Recognizing the importance of Uranus, a Keck Institute for Space Studies (KISS) workshop was held in September 2023 to investigate how we can improve our knowledge of Uranus’s internal structure in the context of a future Uranus mission that includes an orbiter and a probe. The scientific goals and objectives of the recently released Planetary Science and Astrobiology Decadal Survey were taken as our starting point. We reviewed our current knowledge of Uranus’s interior and identified measurement and other mission requirements for a future Uranus spacecraft, providing more detail than was possible in the Decadal Survey’s mission study and including new insights into the measurements to be made. We also identified important
knowledge gaps to be closed with Earth-based efforts in the near term that will help guide the design of the mission and interpret the data returned.

Our report focuses on the following topics:
• Uranus’s atmosphere (noble gas, elemental, and molecular abundances and the pressure-temperature profile)
• Its gravity field and interior models
• The planet’s magnetic field, heat flux, and energy balance
• The potential for Uranian seismology

In the words of the Decadal Survey, the Uranus Flagship mission can produce “transformative, breakthrough science across a broad range of topics.” We argue that to fulfill its promise, great progress should be made in terms of mission design, theoretical calculations, numerical modeling, experiments, ground-based observations, and bringing communities together to plan the mission and interpret the data it returns.

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