Diamond rain and superionic water are among the most dramatic theories put forward to explain the mysterious interiors of our solar system’s ice giants, Uranus and Neptune. But a planetary scientist at the University of California, Berkeley, has proposed an intriguing alternative: The interiors of these planets are composed of layers, and the materials are separated from each other, like oil and water. This separation could explain the planets’ unusual magnetic fields and cast doubt on previous theories about their interiors.

A multi-layered model for frost giants

In the article published in Proceedings of the National Academy of SciencesBurkhard Militzer, a professor of Earth and planetary science at the University of California, Berkeley, proposes that the interiors of Uranus and Neptune consist of two different layers. Beneath the planets’ thick hydrogen-helium atmospheres lies a deep ocean of water-rich materials, above a highly compressed, hydrocarbon-rich liquid composed of carbon, nitrogen, and hydrogen.

Militzer’s computer simulations show that water (H₂O), methane (CH₄) and ammonia (NH3) naturally split under extreme pressures and temperatures inside these planets. This separation occurs because hydrogen is compressed from methane and ammonia, forming immiscible layers.

“I can say that we now have a good theory of why Uranus and Neptune have really different fields, and they are very different from Earth, Jupiter, and Saturn,” Militzer explained. “It’s like oil and water, except the hydrogen-rich layer is on top and the heavier material is at the bottom.”

Magnetic fields and convection

The theory provides a potential explanation for the irregular magnetic fields of Uranus and Neptune discovered by NASA’s Voyager 2 mission in the 1980s. Unlike Earth’s strong bipolar magnetic field, which results from convection in the planet’s liquid outer core, Uranus and Neptune have irregular magnetic fields.

Convection, the process by which hot material rises and cooler material sinks, creates magnetic fields in the interiors of planets. The absence of a large-scale convection layer midway between Uranus and Neptune indicates that the materials inside are layered and unmixed.

In Militzer’s model, the upper water-saturated layer likely convections, producing the observed irregular magnetic field, while the deeper, hydrocarbon-rich layer remains stationary and layered, preventing global convection.

Extreme conditions of Uranus and Neptune

Militzer’s discovery came after a decade of research. A decade ago, he used 100-atom computer models to simulate the behavior of elements in the interiors of planets but was unable to recreate the formation of layers. Last year, he increased the number of atoms in his model to 540 using machine learning and more powerful computing tools.

This allowed him to model the behavior of materials under extreme pressures and temperatures inside Uranus and Neptune (3.4 million times Earth’s atmospheric pressure and temperatures of about 4,750 Kelvin (8,000°F)).

“One day I looked at the model and saw that water had separated from carbon and nitrogen,” Militzer said. “What I couldn’t do 10 years ago has happened now.”

The model showed that as pressure increases with depth, hydrogen becomes compressed, forming a stable layer of carbon-nitrogen-hydrogen material, almost like a plastic polymer. This hydrocarbon-rich layer lies beneath the water-rich convective layer.

Gravitational fields measured by Voyager 2

When Militzer modeled the gravitational effects of multi-level Uranus and Neptune, the results matched the gravitational fields measured by Voyager 2 nearly 40 years ago. His model predicts that a water-saturated layer about 5,000 miles thick lies beneath Uranus’ 3,000-mile-thick atmosphere. Beneath this layer is a similarly thick, hydrocarbon-rich layer with a rocky core about the size of Mercury. Although larger than Uranus, Neptune has a thinner atmosphere but similar layers rich in water and hydrocarbons. Its rocky core is slightly larger, about the size of Mars.

Implications for exoplanets

If Militzer’s theory is correct, it has implications beyond our solar system. Planets similar in size to Uranus and Neptune, often called sub-planets of Neptune, are among the most common types of planets found around other stars. These exoplanets may also have layered interiors with different chemical compositions and magnetic fields.

“If other star systems have a composition similar to ours, the ice giants around these stars may have similar internal structures,” Militzer said.

Interiors of Uranus and Neptune

Militzer hopes to work with experimental physicists to recreate the extreme conditions inside Uranus and Neptune in the laboratory. By testing the behavior of liquids with fundamental ratios found in the proto-solar system, researchers can test whether immiscible layers form naturally.

Future space missions may also provide conclusive evidence. NASA’s proposed mission to Uranus could include a Doppler camera to measure planetary oscillations. According to Militzer, a layered planet vibrates at different frequencies than a planet whose interior is entirely convective. His next project involves calculating these fluctuations using his own computational model.

Characteristics of Uranus and Neptune

Militzer’s findings challenge popular theories about Uranus and Neptune, such as the idea of ​​diamond rain in the planets’ interiors or the exotic properties of superionic water.

“I asked my colleagues, ‘What do you think explains the fields of Uranus and Neptune?’ “They might say, ‘Maybe it’s rain of diamonds, but maybe it’s a property of water that we call superionic,'” Militzer said. “From my perspective, that’s unbelievable. “But if we’re separating this distinction into two separate layers, that might explain it.”

Militzer’s multilevel model offers a comprehensive description of the properties of Uranus and Neptune, from their magnetic fields to their gravitational signatures. The study, which identifies the separation of water-rich and hydrocarbon-rich layers as a key factor, improves our understanding of ice giants and opens up new opportunities to explore the planet’s interior. Future laboratory experiments and space missions may confirm these findings; It not only sheds light on the mysteries of Uranus and Neptune, but may also provide insights into the structure of similar planets in the galaxy.