New research challenges long-held assumptions about the composition of Uranus and Neptune, suggesting the “ice giant” designation may be a misnomer. A study led by researchers at the University of Zurich and the Center PlanetS in Bern indicates these planets may contain considerably more rock than previously thought,potentially reshaping our understanding of how giant planets form. The findings, published in December 2025, reconcile observed data with new physical models and align with recent discoveries regarding the rocky composition of Pluto [[1]].
Uranus and Neptune, long considered “ice giants,” may actually be primarily composed of rock, according to new modeling from researchers at the University of Zurich (UZH) and the Center PlanetS in Bern. The findings challenge conventional understanding of the solar system’s outermost planets and could reshape theories about planetary formation.
Previous models attempting to characterize Uranus and Neptune relied heavily on assumptions, while empirical models were often too simplistic to capture the complexity of these distant worlds, explained Luca Morf, a doctoral student at UZH and lead author of the study. “The models of representation of Uranus and Neptune were until now based on many hypotheses,” Morf said.
The new research combines both approaches, aiming to reconcile observed data – including gravitational fields, gravity measurements, internal pressure, and thermodynamics – with a more nuanced physical representation. This hybrid model has revealed a surprising possibility: the cores of Uranus and Neptune are significantly more rocky than previously believed.
“We’ve suspected this for about fifteen years, but now we can back it up with calculations,” said Ravit Helled, a professor at UZH. The findings align with recent discoveries about Pluto, the dwarf planet once considered the ninth planet, which is also predominantly rocky.
>> Read: The heart on the surface of Pluto comes from a gigantic impact and On Pluto, the volcanoes are made of ice
While the model provides compelling evidence, some uncertainties remain. Researchers acknowledge limited understanding of how materials behave under the extreme pressure and temperature conditions found at the core of a planet. “This could have an impact on our results,” Morf cautioned.
Chaotic Magnetic Fields
The study also sheds new light on the unusual magnetic fields of Uranus and Neptune. Unlike Earth’s relatively simple north-south magnetic poles, the magnetic fields of these ice giants are chaotic and possess multiple poles.
“Our models include layers known as ‘ionic water’[[ndlr – a unique state of water under high pressure and temperature, typical of the interiors of giant icy planets]that generate magnetic dynamos in locations that explain the observed non-dipolar magnetic fields,” Helled explained. “We also discovered that Uranus’s magnetic field originates from deeper within the planet than Neptune’s.”
The results of the study are expected to inform new scenarios regarding the internal composition of Uranus and Neptune. However, determining the precise makeup of these planets will require more than modeling; dedicated space missions are needed to gather direct observations. This research underscores the importance of continued exploration of our solar system’s outer reaches.
>> Read also: New moons discovered around Uranus and Neptune
Stéphanie Jaquet and the ats
