Lab-Made Planetary Ice Reveals Secrets Hidden Inside Uranus and Neptune

A New Kind of Ice, Born in a Lab

Deep inside planets like Neptune and Uranus, ice is nothing like the frozen cubes you drop into a cold drink. Under immense heat and pressure, it enters a weird state known as superionic ice. Now, scientists have confirmed an entirely new form of that exotic ice — one that had long been predicted but never directly observed — and the discovery could reshape our understanding of two of the solar system's most mysterious worlds.

Researchers led by Alexis Forestier from the French Alternative Energies and Atomic Energy Commission used a device called a diamond-anvil cell to squeeze a microscopic sample of water between two diamonds, heated the sample with lasers using specially prepared boron-doped diamonds to absorb the energy, and then studied the material with an X-ray beam at the European Synchrotron Radiation Facility. At the highest pressure, the water sample was only around 12 micrometers wide — a speck barely visible to the naked eye, yet capable of mimicking conditions at the heart of a distant planet.

What Makes This Ice So Strange

In this exotic phase, oxygen atoms lock into a solid grid while hydrogen nuclei flow freely through it like a liquid, allowing it to conduct electricity. That combination — simultaneously solid and liquid-like — is what makes superionic ice so alien. It doesn't behave like anything we encounter in everyday life, and until recently, scientists weren't sure exactly what crystal structure it took at the most extreme pressures.

X-ray diffraction at the European Synchrotron Radiation Facility revealed that the oxygen atoms had locked into a hexagonal pattern known as hexagonal close-packed (hcp). Above 200 gigapascals and 1,800 Kelvin, this form became the dominant phase of superionic ice, replacing the face-centered cubic (fcc) phase. According to the paper, the process resembles the behavior of compressed noble gases. The study was published in Physical Review Letters on September 9, 2026.

Scientists have now discovered a total of 22 types of ice, with the most recent being ice XXI in 2025. This number includes ice Ih — the same stuff as the cubes in your iced coffee and the snow on mountaintops. Variations in pressure and temperature push water into distinct crystalline forms, and most have only been created and observed inside lab settings.

Why Neptune and Uranus Have Such Weird Magnetic Fields

Data on the densities of Uranus and Neptune indicate that these planets contain unusual internal layers often described as "hot ices." These regions sit beneath outer atmospheres of hydrogen and helium and above solid cores. Scientists believe these layers are made up of water, methane, and ammonia. However, the extreme conditions in these environments likely force these familiar compounds into exotic and unfamiliar forms.

Those ice giants have odd magnetic fields — they tilt sharply and show multiple poles. Scientists suspect the flow of superionic material, with its mobile protons, helps generate those fields. But models needed better data on exactly which crystal structures form at different depths. Because the hexagonal form may have different electrical and mechanical properties from the cubic one, the discovery could change how scientists model those planetary interiors.

A Long Road Ahead — But a Giant Step Forward

The idea of superionic water is not new — scientists predicted its existence more than 30 years ago. The first strong evidence appeared in 2018, followed by experiments in 2019 that allowed researchers to examine its atomic structure directly. This latest work builds on that foundation by confirming a specific structural transition that previous experiments had only theorized.

It will likely take decades of scientific advancements — if not longer — to irrefutably prove that the ice in Neptune or Uranus is like this. That's something the team acknowledges in the paper, where the researchers invite future theoretical work on the plasticity and conductivity of superionic ice. The hcp form could have different mechanical and ionic-conduction properties compared to the fcc phase, so the results could have implications for models of Uranus, Neptune, and their exoplanet brethren. As scientists push further into the extreme physics of planetary interiors, each confirmed data point brings us closer to understanding worlds that, so far, only one spacecraft has ever visited.