The planets in our Solar System have long been categorized based on their composition: the terrestrial rocky planets like Mercury, Venus, Earth, and Mars, followed by the gas giants Jupiter and Saturn, and finally, the ice giants Uranus and Neptune. However, new research from the University of Zurich (UZH) suggests that Uranus and Neptune might be more rocky than previously thought. This study does not definitively classify the two planets as either water-rich or rock-rich but challenges the notion that they are predominantly ice-rich.
The announcement comes as the UZH scientific team developed a unique simulation process to explore the interiors of Uranus and Neptune. “The ice giant classification is oversimplified as Uranus and Neptune are still poorly understood,” explains Luca Morf, a PhD student at the University of Zurich and lead author of the study. “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.”
A New Perspective on Planetary Composition
This development follows the discovery that Pluto, a dwarf planet, is rock-dominated in composition, adding weight to the new hypothesis. The UZH team began their research by creating a random density profile for the planetary interiors. They then calculated the gravitational fields consistent with observational data to infer possible compositions, repeating the process to achieve the best match between models and data.
With their agnostic yet fully physical model, the team found that the potential internal composition of these “ice giants” is not limited to ice, typically 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. This new range of internal compositions shows that both planets could be either water-rich or rock-rich.
Implications for Magnetic Fields
The study also brings new insights into the puzzling magnetic fields of Uranus and Neptune. Unlike Earth, which has clear North and South magnetic poles, these planets have more complex magnetic fields with more than two poles. “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,” explains Helled.
The Call for New Space Missions
While the results are promising, some 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 plans to expand the models in the future.
Despite these uncertainties, the new findings pave the way for potential interior composition scenarios, challenging long-held assumptions and guiding future material science research under 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 Helled.
Looking Forward
The move represents a significant shift in our understanding of the outer planets and underscores the need for further exploration. As the scientific community continues to debate the true nature of Uranus and Neptune, the call for new missions becomes increasingly urgent. Such missions could provide the detailed data necessary to resolve these mysteries and potentially rewrite our understanding of the Solar System’s formation and evolution.
Meanwhile, the study opens up a new realm of possibilities for planetary science, encouraging researchers to reconsider the composition and characteristics of other celestial bodies. As we advance our technologies and methodologies, the secrets of the cosmos may gradually unfold, offering a clearer picture of the universe we inhabit.
