At 2 Million Atmospheres, Water Stacks Itself Into Hexagonal Ice

Deep inside Uranus and Neptune, at pressures that would make your skull a distant memory, water doesn't melt. It goes superionic: oxygen atoms lock into a crystal lattice while hydrogen ions flow through them more like a liquid. It's ice. It's also kind of a liquid. It's a whole thing.

Scientists have confirmed that under even more extreme conditions, the oxygen atoms stack themselves into a structure nobody had directly seen in superionic ice before.

Researchers already knew of two arrangements. At lower pressures, the oxygen atoms form one kind of cubic lattice. Squeeze harder and they shift into another. But experiments at the European Synchrotron Radiation Facility pushed water beyond 200 gigapascals, roughly 2 million times normal atmospheric pressure, while heating it to thousands of degrees.

There, the oxygen atoms packed themselves into a hexagonal close-packed structure. At 219 gigapascals and about 2,630 K, roughly 4,300 degrees Fahrenheit or 2,360 degrees Celsius, that hexagonal form became dominant.

Those conditions may exist deep inside Uranus and Neptune. That matters because both planets have notoriously strange, lopsided magnetic fields that scientists have been trying to explain since Voyager 2 flew past in the 1980s. If this form of superionic ice conducts electricity differently from the structures used in existing models, it could help explain what is happening inside them.

Same H₂O. Entirely different ice.

Read the full story at European Synchrotron Radiation Facility, September 11, 2026

Hot Take: Water was already showing off with more than 20 forms of ice. Apparently it had one more in its pocket.