Title: Hotter Than Molten Steel: Hexagonal Close-Packed "Superionic Ice" Confirmed in the Lab
October 7, 2026
A team led by physicist Alexis Forestier of France's Alternative Energies and Atomic Energy Commission (CEA) trapped microscopic water samples between two diamond tips — a diamond anvil cell — crushing them to 230 gigapascals, about 2.3 million times Earth's atmospheric pressure at sea level, while lasers heated the samples past 4,000°F. Probing with an extremely narrow synchrotron X-ray beam, the diffraction pattern showed oxygen atoms locked into a hexagonal close-packed (hcp) lattice — a structure predicted on paper but never unambiguously observed in a lab. The findings were published in Physical Review Letters.
The strangeness is the "superionic" state: oxygen atoms sit in a rigid crystal lattice like a solid, while hydrogen nuclei flow through it like a liquid — and conduct electricity. Scientists had already made face-centered cubic (fcc) superionic ice in the lab (ice XVIII). The new experiments show that above 200 gigapascals and 1,800 kelvin, the hcp arrangement replaces fcc as the dominant phase. The difference is mainly how the dense oxygen layers stack: ABCABC in fcc, ABAB in hcp. For context, above roughly 60–80 GPa, ordinary ice X has a body-centered cubic structure — water ice is known in more than 20 crystalline phases.
This isn't just lab curiosity. The same conditions exist deep inside Uranus and Neptune, whose magnetic fields are famously weird — tilted and off-center, as Voyager 2 observed during its flybys in the 1980s. A leading hypothesis says those fields come not from a central dynamo like Earth's, but from electric charge flowing through superionic ice closer to the planets' surfaces. Superionic ice conducts well — the free-flowing hydrogen carries charge — so understanding the new phase's electrical properties could reshape models of what happens inside these planets.
The team identified the hcp structure from five classes of diffraction peaks, and found that hcp and fcc can coexist rather than being separated by a sharp boundary. The next step is measuring the new phase's electrical conductivity and thermal expansion precisely, and feeding those parameters into planetary interior models. Ice giants are among the most common exoplanet types — understanding Uranus and Neptune is a key to understanding huge numbers of planets across the galaxy. For a sense of scale, the pressure at Earth's center is about 360 gigapascals — this experiment's 230 GPa is already in the same league.
Sources: New Scientist, IFLScience, Phys.org, ScienceAlert, Science News Today, Hackaday