Resolve the fundamental composition and interior-structure uncertainties of Uranus and Neptune

Determine the atmospheric composition, bulk composition, and internal structure of Uranus and Neptune in order to resolve fundamental uncertainties about their formation, evolution, and atmospheric structure.

Background

The introduction identifies the limited observational record for Uranus and Neptune—particularly the absence of a dedicated spacecraft mission—as a major obstacle to characterizing these planets. The unresolved atmospheric and bulk compositions and internal structures impede understanding of their formation and thermal evolution and motivate the proposed need for a dedicated Uranus Orbiter and Probe mission.

References

As a result, there are still many open questions regarding the formation, evolution, interiors, and atmospheric structures of Uranus and Neptune.

— The atmospheric vertical structure of Uranus and Neptune from thermochemical models: the impact of model assumptions  (2608.13157 - Douçot et al., 13 Aug 2026) in Section 1, Introduction

It is unclear if such a massive compositional gradient is consistent with the circulation strengths of the ice giants, and longer-wavelength resolved observations are necessary to obtain a firm grasp on the relative S/H and N/H values.

— Microwave Remote Sensing of Giant Planet Atmospheres: Considerations for Saturn and Uranus Orbiter Missions  (2608.20669 - Akins et al., 21 Aug 2026) in Section 2.3, page 4