Claim: Uranus and Neptune have oceans that are 5000 miles deep

The hidden interiors of Uranus and Neptune have long puzzled scientists who try to understand how these distant ice giants formed and evolved.

Past proposals included the possibility of diamond rain falling through their cores or super-ionic water lurking beneath their bluish exteriors.

Each idea sparked interest, yet questions persisted about the unusual nature of these planets’ magnetic fields and internal structures.

Recent work proposes a different view. After many years of study and advanced computer simulations, a new theory suggests that materials in Uranus and Neptune could separate into layers as pressures rise.

Burkhard Militzer, a professor of Earth and planetary science at the University of California, Berkeley, has put forth a model that challenges older notions and draws on the principles of immiscibility – when substances refuse to mix, like oil and water.

Layered interiors and magnetic fields

Militzer believes that under the extreme conditions found in the deep layers of these planets, ingredients such as water (H₂O), methane (CH₄), and ammonia (NH₃) behave in unexpected ways.

“We now have, I would say, a good theory about why Uranus and Neptune have really different fields, and it’s very different from Earth, Jupiter, and Saturn,” Militzer explained.

“It’s like oil and water, except the hydrogen-rich layer goes on top, and the heavier material stays below.”

His findings also align with magnetic field readings collected by NASA’s Voyager 2 in the 1980s. Instead of a tidy, dipolar field like Earth’s, Uranus and Neptune show disorganized magnetic fields.

Militzer’s model proposes that the water-rich layer under the atmospheres can move enough to create these irregular fields, while the deeper hydrocarbon-rich layer remains stable and resists mixing.

Extreme pressures and new simulations

Militzer used computer models to simulate conditions at pressures reaching 3.4 million times Earth’s atmospheric pressure and temperatures around 8,000°F.

A decade ago, he ran calculations with 100 atoms but could not confirm layered separation.

Recently, he expanded those simulations to 540 atoms, leveraging machine learning and stronger computing power.

“One day, I looked at the model, and the water had separated from the carbon and nitrogen,” he said. “What I couldn’t do 10 years ago was now happening.”

As depth increases, hydrogen is squeezed out of methane and ammonia, creating a carbon-nitrogen-hydrogen fluid that sits below a water-rich zone.

According to Militzer’s gravity calculations, this layering matches readings taken by Voyager 2 nearly 40 years ago.

Beneath Uranus’ 3,000-mile-thick atmosphere, the model points to a 5,000-mile-thick layer of water-rich fluid. A hydrocarbon-rich layer of similar thickness lies underneath, ending at a rocky core roughly the size of Mercury.

Neptune follows the same layout but has a thinner atmosphere and a slightly larger rocky core, about the size of Mars.

Why does any of this matter?

Ice giants comparable to Uranus and Neptune appear to be common in other star systems, where they are often referred to as sub-Neptune exoplanets.

“If other star systems have similar compositions to ours, ice giants around those stars could well have similar internal structures,” Militzer noted.

He sees this model as a way to explain varied planetary magnetic fields beyond our solar neighborhood.

Militzer aims to collaborate with experimental physicists to test these concepts in the lab.

By recreating the extreme conditions of water, methane, and ammonia in the right proportions, researchers could discover whether layers form on their own.

He believes this work could confirm the immiscible behavior that sets the stage for the stability of these deep planetary zones.

Diamond rain is cool, but not important

Talk of diamond rain and super-ionic water once captured imaginations, but Militzer’s simulations question those ideas.

“If you ask my colleagues, ‘What do you think explains the fields of Uranus and Neptune?’ they may say, ‘Well, maybe it’s this diamond rain, but maybe it’s this water property which we call super-ionic,’” he said.

“From my perspective, this is not plausible. But if we have this separation into two separate layers, that should explain it.”

Upcoming space missions might shed more light on the issue. A proposed NASA trip to Uranus could carry instruments to measure the planet’s vibrations through Doppler imaging.

A non-mixing interior would jiggle in different ways than one with full convection. Militzer plans to use his computational model to predict those vibrations, offering a fresh way to confirm or refute his layered theory.

What’s next for Uranus and Neptune?

This perspective on Uranus and Neptune adds a personal dimension to the centuries-long quest to understand our solar system.

Each discovery builds on a chain of data, from telescopes to spacecraft, and now advanced simulations.

Militzer’s decade of effort offers an approach that explains how water and hydrocarbon fluids might settle into distinct bands deep inside these ice giants.

His findings suggest a layered format that explains their odd magnetic fields and gravitational measurements.

The model supplies a framework for designing experiments, planning future probes, and even exploring how exoplanets might evolve.

By identifying the presence of two immiscible layers – one water-rich and one made of highly compressed hydrocarbons – this theory marks another step toward unraveling Uranus and Neptune’s secrets, one simulation at a time.

The full study was published in the journal Proceedings of the National Academy of Sciences.

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