Ice Giants Revisited: Uranus And Neptune As Magma Ocean Worlds
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.
Schematic showing the layered structure of Neptune and Uranus as proposed here (not to scale). — astro-ph.EP
Edward D. Young, Sarah P. Marcum, Aaron Werlen, Paula N. Wulff
Comments: Extensively expanded and revised version of an earlier, shorter preprint on Research Square; 26 pages, 10 figures; submitted to The Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2606.18219 [astro-ph.EP] (or arXiv:2606.18219v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2606.18219
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Submission history
From: Edward Young
[v1] Tue, 16 Jun 2026 17:48:23 UTC (15,420 KB)
https://arxiv.org/abs/2606.18219
Astrobiology, exoplanet,
