Wednesday, June 17, 2026

A Hot Hypothesis For Neptune And Uranus

Normally, I don't write much about planetary astronomy, not because there's anything wrong with the discipline, but because I'm concerned mostly with the quest to determine the fundamental laws of physics, and planetary astronomy is basically unrelated to that. But this paradigm shifting interpretation of the data regarding Uranus and Neptune deserves a mention.
Uranus and Neptune are commonly interpreted as volatile-rich "ice giants", an assumption that underpins most interior models. 
Here we show that their observed radii, bulk densities, gravitational harmonics, normalized moments of inertia, intrinsic luminosities, and key features of their atmospheric compositions are consistent with interiors comprising supercritical, hydrogen-rich magma oceans overlain by H2-rich envelopes. 
Our results, based on three fit parameters for each planet, provide a parsimonious explanation for the structures, thermal states, and atmospheric chemistries of Uranus and Neptune. We find that the Solar System's ice giants are better understood as magma-ocean giants, with origins parallel to those of sub-Neptune gas-dwarf planets. A continuum among gas dwarf planets permits Neptune and Uranus to serve as accessible, data-driven test cases for structure models and material properties used to understand sub-Neptunes.
Edward D. Young, Sarah P. Marcum, Aaron Werlen, Paula N. Wulff, "Ice Giants Revisited: Uranus and Neptune as Magma Ocean Worlds" arXiv:2606.18219 (June 16, 2026).

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