What lies beneath the thick, bluish atmospheres of Uranus and Neptune?
For decades, scientists have speculated about the mysterious interiors of these ice giants.
Now, a planetary scientist from the University of California, Berkeley, has proposed a groundbreaking theory: Uranus and Neptune have layered interiors that don’t mix, much like oil and water.
This new model helps explain the planets’ unusual magnetic fields and challenges older ideas about their compositions.
Burkhard Militzer, a professor of Earth and planetary science, suggests that beneath the clouds of Uranus and Neptune lie two distinct layers.
The first is a vast ocean of water, and below it is a highly compressed fluid made up of carbon, nitrogen, and hydrogen.
According to Militzer’s research, published in Proceedings of the National Academy of Sciences, these layers don’t mix because of the extreme pressures and temperatures inside the planets.
Using advanced computer simulations, Militzer found that the combination of water, methane, and ammonia naturally separates into two layers under these conditions.
The separation occurs because hydrogen is squeezed out of methane and ammonia, forcing the heavier materials into a distinct layer below the water-rich upper layer.
This layered structure could explain one of the biggest mysteries about Uranus and Neptune: their unusual magnetic fields.
Unlike Earth’s magnetic field, which is a strong, organized dipole created by convection in its liquid outer core, the fields of Uranus and Neptune are chaotic and disorganized.
The Voyager 2 spacecraft discovered this in the 1980s, leaving scientists puzzled.
Militzer’s model suggests that the two-layered interiors prevent large-scale convection, which is necessary to create a global magnetic field. Instead, the upper water-rich layer likely produces localized convection, leading to the disorganized magnetic fields observed by Voyager 2.
Militzer’s work builds on decades of research, but earlier attempts to explain the planets’ interiors didn’t succeed.
Ten years ago, his computer models using 100 atoms couldn’t replicate the separation of layers. However, recent advances in machine learning allowed him to simulate the behavior of 540 atoms, finally revealing the natural formation of layers under high pressure and temperature.
“When I looked at the new model, I saw that water had separated from carbon and nitrogen,” Militzer explained. “This was the breakthrough we needed to understand why these layers form.”
The denser, carbon-rich layer sits beneath the lighter, water-rich layer, creating a stable structure where only the upper layer convects. This prevents the large-scale movement needed for a traditional dipole magnetic field.
Militzer’s findings not only provide new insights into Uranus and Neptune but also have implications for exoplanets.
Planets similar in size to these ice giants, often called sub-Neptunes, are some of the most common exoplanets discovered. If they share a similar composition, this theory could help explain their structures as well.
To test his theory, Militzer hopes to collaborate with scientists conducting laboratory experiments that mimic the extreme conditions inside these planets. A proposed NASA mission to Uranus could also provide critical data.
By measuring the planet’s vibrations using a Doppler imager, scientists could determine whether Uranus has a layered interior or a convecting one. Militzer plans to refine his computational model to predict how these vibrations would differ.
This new theory offers a fresh perspective on Uranus and Neptune, reshaping our understanding of the solar system’s enigmatic ice giants and opening doors to uncovering the secrets of distant worlds.
