Scientists have discovered a new form of ice that may help explain the mysterious interiors of the ice giant planets Neptune and Uranus. This research, led by Alexis Forestier from France's Alternative Energies and Atomic Energy Commission (CEA), recreated the extreme conditions found deep within these planets in a laboratory. Under immense heat and pressure, the ice transforms into a state known as superionic ice. In this state, oxygen atoms form a solid lattice, while hydrogen nuclei move freely like a liquid, allowing the ice to conduct electricity. To study the crystal structures formed by this superionic ice, the researchers used a diamond anvil cell to compress tiny ice samples and heated them with lasers to temperatures above 1,800 Kelvin—far hotter than the surface of the Sun. The pressure applied reached up to 230 gigapascals, which is more than 2 million times Earth's atmospheric pressure. Using X-ray diffraction at the European Synchrotron Radiation Facility, the team found that the oxygen atoms arranged themselves into a hexagonal pattern known as hexagonal close-packed (hcp). This hexagonal structure became the dominant form at pressures above 200 gigapascals and temperatures above 1,800 Kelvin, replacing a previously known cubic structure called face-centered cubic (fcc). The discovery could change how scientists model the interiors of Uranus and Neptune. The hexagonal form of superionic ice may have different electrical and mechanical properties compared to the cubic form, potentially affecting how these planets generate magnetic fields and transfer heat. This research highlights how the behavior of materials under extreme conditions can influence planetary dynamics. The findings, published in the journal Physical Review Letters, suggest that the transition between the fcc and hcp structures in superionic ice may play a role in the internal processes of Uranus and Neptune. This new understanding could lead to more accurate models of these distant planets, helping scientists better interpret data from space missions and future observations.