A recent study conducted by researchers at the University of Zurich indicates that the compositions of Uranus and Neptune might be less icy than previously assumed.
Uranus could be classified as an ice giant (left) or a rock giant (right), depending on the assumptions of the model. Image credit: Keck Institute for Space Studies / Chuck Carter.
“Uranus and Neptune remain poorly understood, making the designation of ice giants too simplistic,” states Dr. Luca Morf, a student at the University of Zurich.
“Models based on physical data incorporate too many assumptions, while empirical models fall short in complexity.”
“Our approach combines both methodologies to create an interior model that is unbiased, yet physically coherent.”
The research commenced with a stochastic density distribution inside the planets.
Subsequently, the team calculated the gravitational fields of the planets in alignment with observational data to infer their likely compositions.
The process was iterated to achieve the closest alignment between the model and the empirical data.
Employing a new, unbiased yet fully physical framework, scientists have revealed that the internal compositions of the solar system’s ice giants are not restricted to ice alone.
“We initially proposed this concept nearly 15 years ago, and now we possess a numerical framework to substantiate it,” remarked Professor Ravit Held of the University of Zurich.
“This expanded spectrum of internal compositions suggests both planets could be rich in water or minerals.”
The study also sheds light on the enigmatic magnetic fields of Uranus and Neptune.
In contrast to Earth’s defined north and south magnetic poles, the magnetic fields of Uranus and Neptune exhibit greater complexity, featuring multiple poles.
“Our model introduces a so-called ‘ionized water’ layer that generates magnetic dynamos that account for the observed non-dipolar magnetic fields,” noted Professor Held.
“Moreover, we discovered that Uranus’ magnetic field has a more profound origin compared to that of Neptune.”
While the findings are promising, some ambiguities linger.
“A significant challenge is that physicists still have limited understanding of how materials behave under the extreme pressure and temperature conditions in planetary cores, which could influence our conclusions,” Morf added.
Notwithstanding the uncertainties, these new findings open avenues for possible internal composition scenarios, challenging longstanding assumptions and informing future materials science research under planetary conditions.
“Depending on model assumptions, both Uranus and Neptune have the potential to be classified as rock giants or ice giants,” Professor Held remarked.
“At present, the data is insufficient to differentiate between the two, highlighting the necessity for dedicated missions to Uranus and Neptune to uncover their true natures.”
A paper detailing this research was published in this week’s journal Astronomy and Astrophysics.
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Luca Morf and Ravit Held, 2025. Ice or rock? Convection or stability? New interior models for Uranus and Neptune. A&A 704, A183; doi: 10.1051/0004-6361/202556911
Source: www.sci.news
