New Research Challenges Classification of Uranus and Neptune as Ice Giants
The composition of Uranus and Neptune might be less icy than previously thought, according to a groundbreaking study by scientists at the University of Zürich. The study challenges the long-held classification of these planets as ice giants, suggesting that their internal makeup could be more complex.
The research, led by Ph.D. student Luca Morf, highlights the limitations of current models. "The ice giant classification is oversimplified," Morf explains, "as Uranus and Neptune are still poorly understood. Models based on physics were too assumption-heavy, while empirical models are too simplistic."
To address this, the team combined both physics-based and empirical approaches. They started with a random density profile for the planetary interior and then calculated the gravitational field, using observational data to infer the composition. This iterative process aimed to create unbiased, yet physically consistent models.
The results are eye-opening. The scientists found that the internal composition of the ice giants is not limited to ice. "It is something we first suggested nearly 15 years ago," says Professor Ravit Helled, "and now we have the numerical framework to demonstrate it. The new range of internal composition shows that both planets can either be water-rich or rock-rich."
This discovery also sheds light on the planets' magnetic fields, which have long puzzled scientists. While Earth's magnetic field has clear North and South poles, Uranus and Neptune's fields are more complex, with more than two poles. The study's models suggest the presence of 'ionic water' layers, generating magnetic dynamos that explain the observed non-dipolar fields.
Furthermore, the research reveals that Uranus's magnetic field originates deeper than Neptune's, adding another layer of complexity.
Despite the exciting findings, 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," Morf notes. "This could impact our results."
Despite these uncertainties, the study opens up new possibilities for understanding the planets' interior composition. It challenges decade-old assumptions and paves the way for future material science research at planetary conditions. "Both Uranus and Neptune could be rock giants or ice giants depending on the model assumptions," Professor Helled concludes. "Current data are insufficient to distinguish the two, and we need dedicated missions to reveal their true nature."
The research was published this week in the journal Astronomy & Astrophysics, and it invites further exploration and discussion in the scientific community. The paper (https://www.aanda.org/articles/aa/full_html/2025/12/aa56911-25/aa56911-25.html) is available online for those eager to delve deeper into this fascinating topic.
