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Uranus and Neptune May Be Far Rockier Than the 'Ice Giant' Label Suggests

A University of Zurich 'agnostic' gravity-based model finds current observations allow either rock‑rich or ice‑rich interiors.

Overview

  • The peer‑reviewed study by Luca Morf and colleagues appears in Astronomy & Astrophysics and was conducted with the NCCR PlanetS team.
  • Researchers iteratively generated random interior density profiles, matched them to observed gravity, and retained only solutions that stayed thermodynamically and compositionally consistent.
  • The resulting models permit broad compositions for both planets, challenging the assumption that ice‑heavy interiors are required by existing data.
  • Layers of ionic water in the models can host magnetic dynamos that reproduce the observed non‑dipolar fields, with Uranus’s dynamo region deeper than Neptune’s.
  • Within current measurement uncertainties, allowed rock‑to‑water mass ratios span roughly 0.04–4 for Uranus and about 0.20–<2 for Neptune, underscoring the need for dedicated missions to resolve the true compositions.