Rethinking the Composition of Uranus and Neptune: New Insights from the University of Zurich

A groundbreaking study from researchers at the University of Zurich and the NCCR PlanetS is reshaping our understanding of the solar system’s outer planets, Uranus and Neptune. Traditionally classified as ice giants, these planets may actually possess a more rocky composition than previously believed, challenging long-held assumptions about their interiors.

The solar system’s planets are typically categorized into three groups: the four terrestrial rocky planets (Mercury, Venus, Earth, and Mars), the gas giants (Jupiter and Saturn), and the ice giants (Uranus and Neptune). However, recent findings suggest that the classification of Uranus and Neptune as ice-rich may be overly simplistic. The research team, led by Ph.D. student Luca Morf, emphasizes that their study does not definitively categorize these planets as either water-rich or rock-rich, but rather opens up the possibility for a range of compositions.

Published in the journal Astronomy & Astrophysics, the study employs an innovative simulation process that combines empirical and physical modeling techniques to explore the interiors of Uranus and Neptune. Morf explains that previous models suffered from either excessive assumptions or oversimplifications. Their unique approach begins with a random density profile and iteratively refines it to match observational data, leading to a more nuanced understanding of the planets’ compositions.

The results indicate that Uranus and Neptune could be either water-rich or rock-rich, a finding that aligns with the recent understanding of Pluto as being rock-dominated. This shift in perspective not only alters our view of the ice giants but also provides new insights into their complex magnetic fields. Unlike Earth, which has distinct north and south magnetic poles, the magnetic fields of Uranus and Neptune are more intricate, featuring multiple poles. The researchers propose that “ionic water” layers within these planets could generate magnetic dynamos that account for this complexity.

Despite these promising findings, uncertainties remain, particularly regarding how materials behave under the extreme pressures and temperatures found deep within planetary interiors. Morf acknowledges the need for further research to refine their models and address these unknowns.

The implications of this study extend beyond theoretical discussions; they highlight the necessity for new space missions to Uranus and Neptune. Current data is insufficient to definitively categorize these planets, and dedicated missions could provide the crucial information needed to uncover their true nature. Professor Ravit Helled, the project’s initiator, stresses that both planets could be classified as rock giants or ice giants, depending on future model assumptions.

As researchers continue to explore the mysteries of our solar system, this study marks a significant step toward a deeper understanding of Uranus and Neptune. By challenging established classifications and opening the door to new possibilities, the University of Zurich’s research is poised to influence the future of planetary science and exploration.