Workshop Overview:

This Study Program will bring together theorists, observers, experimentalists, and mission architects to draft an innovative yet practical plan for determining the interior structure of Uranus. This Study will lead to a fully integrated approach, crossing scientific and engineering disciplines, to overcome the traditional limitations of determining a giant planet's interior structure.

Understanding the internal structure and composition of planets in our solar system is critical for understanding their origin and evolution. This knowledge is also important for characterizing exoplanets for which we may only know their mass and radius. As a result, determining these properties of Uranus is a high-priority objective for the Uranus Flagship mission recommended by the recently released Planetary Science and Astrobiology Decadal Survey. Unfortunately, the internal structure of planets cannot be measured directly. Instead, it is inferred from various measurements, typically gravity, magnetic field, and, at Saturn, ring seismology. Bulk composition also comes from the gravity data and measurements of the atmosphere. For both composition and internal structure, however, the indirect nature of the measurements and theoretical uncertainties prevent convergence on a unique solution.

To address our goal of determining the interior structure of Uranus, we will produce an integrated plan that outlines a series of calculations together with observations that, if implemented, will be able to discriminate among competing models for Uranus's interior structure. That plan will likely include:

• Recommended laboratory measurements of Equations of State and of the optical, thermal, and physical properties of key species and compounds.
• Identification of important dynamical, chemical, and condensation processes not accounted for in current atmospheric models.
• Identification of discriminators of Uranus formation models that might be found on other bodies (e.g., the composition of outer solar system small bodies).
• Identification of what measurements of the Uranus system to make, and how to make them, in order to discriminate among competing interior models.

The workshop's final product will be a mutually-supporting list of experiments, models, and observations that will best determine Uranus's interior structure and bulk composition.