Scientists have discovered that there is ice deep inside planets like Neptune and Uranus and want to find out what form it takes and how it behaves. They cannot dig for it and transport it all the way back to Earth, so they do the next best thing: recreate those extreme conditions in the lab.
That’s exactly what a team of scientists led by Alexis Forestier from the CEA, France’s Alternative Energies and Atomic Energy Commission, did. What they discovered could help us better understand the strange magnetic fields and deep interior layers of these distant worlds.
The weird world of hot ice
On those planets, ice is not like the frozen cubes you put into a cold drink. It enters a weird state known as superionic ice because of the immense heat and pressure it is under. 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. Scientists already knew this hot, conducting ice existed, but they did not know what specific crystal shapes it formed.
To find out, they squeezed tiny samples of ice between two ultra-hard diamonds inside a device called a diamond anvil cell. They heated this trapped ice with lasers to over 1,800 Kelvin. They subjected it to pressures reaching 230 gigapascals, more than 2 million times Earth’s atmospheric pressure.
And what they discovered was remarkable. 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, as the team detailed in their paper published in Physical Review Letters.
“We report the unambiguous observation of a novel H2O ice phase adopting an hcp oxygen sublattice,” the study authors commented.
What makes the research significant is that it could help us get a clearer picture of what is happening deep inside our solar system’s icy giants. In planets like Uranus and Neptune, superionic ice has been proposed as playing a role in generating their unusual magnetic fields. 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.
“The presence of an fcc-hcp martensitic transition in the superionic regime of warm dense ice may have implications for planetary models of Uranus and Neptune.” https://phys.org/news/2026-09-scientists-strange-ice-interiors-neptune.html
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