New Findings Suggest Uranus and Neptune Are Not What They Seem

By University of Zurich December 13, 2025

Collected at: https://scitechdaily.com/new-findings-suggest-uranus-and-neptune-are-not-what-they-seem/

The Solar System is usually grouped into three main types of planets based on what they are made of: the four rocky terrestrial worlds (Mercury, Venus, Earth ,and Mars), the two massive gas giants (Jupiter and Saturn), and the pair of ice giants (Uranus and Neptune).

New research from a scientific team at the University of Zurich (UZH) suggests that Uranus and Neptune may not fit neatly into that final category. Their findings indicate that both planets could contain much more rock than previously assumed. The study does not argue that the two worlds must be water-rich or rock-rich; instead, it challenges the long-standing belief that an ice-heavy composition is the only viable explanation. This perspective is also supported by the discovery that the dwarf planet Pluto is primarily made of rock.

A New Approach to Modeling Planet Interiors

To investigate these possibilities, the researchers developed a specialized method for simulating the internal structures of Uranus and Neptune. “The ice giant classification is oversimplified as Uranus and Neptune are still poorly understood,” says Luca Morf, PhD student at the University of Zurich and lead author of the work. “Models based on physics were too assumption-heavy, while empirical models are too simplistic. We combined both approaches to get interior models that are both “agnostic” or unbiased and yet, are physically consistent.”

Their process begins with a randomly generated density profile for each planet. They then compute a gravitational field that matches observational data and use this to infer what the planets may contain. The steps are repeated many times to identify the versions that best agree with available measurements.

A Wider Range of Planetary Possibilities

Using this unbiased modeling framework, the University of Zurich team found that the internal structure of the Solar System’s so-called ice giants does not have to be dominated by ice (usually represented by water).

“It is something that we first suggested nearly 15 years ago, and now we have the numerical framework to demonstrate it,” reveals Ravit Helled, Professor at the University of Zurich, and initiator of the project. Their results indicate that either Uranus or Neptune could be rich in water or rich in rock depending on which models align with the observations.

New Clues About Puzzling Magnetic Fields

The research also sheds light on the complex magnetic fields of both planets. Unlike Earth, which has two clear magnetic poles, Uranus and Neptune have fields with multiple poles and unusual geometries. Helled explains that “Our models have so-called “ionic water” layers which generate magnetic dynamos in locations that explain the observed non-dipolar magnetic fields. We also found that Uranus’ magnetic field originates deeper than Neptune’s.” These insights offer new context for some of the most baffling features of the ice giants.

Why Future Missions Are Essential

Even with these advances, uncertainties remain. “One of the main issues is that physicists still barely understand how materials behave under the exotic conditions of pressure and temperature found at the heart of a planet, this could impact our results,” says Morf, who aims to refine the models further.

Despite these challenges, the work introduces promising new scenarios for the interiors of Uranus and Neptune and encourages a reevaluation of long-standing assumptions. It may also help guide future research into how materials behave under extreme planetary conditions. “Both Uranus and Neptune could be rock giants or ice giants depending on the model assumptions. Current data are currently insufficient to distinguish the two, and we therefore need dedicated missions to Uranus and Neptune that can reveal their true nature,” concludes Ravit Helled.

Reference: “Icy or rocky? Convective or stable? – New interior models of Uranus and Neptune” by Luca Morf and Ravit Helled, 10 December 2025, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202556911