Researchers have successfully synthesized a hexagonal close-packed phase of water ice, providing new data to help scientists understand the mysterious interiors of ice giants like Neptune and Uranus.
For planetary scientists, the cores of distant worlds like Neptune and Uranus remain frustratingly out of reach. Lacking the ability to probe these interiors directly. researchers have long relied on surface scans and complex extrapolations to guess what sits at the center of our solar system’s ice giants. We have known for years that these cores are primarily composed of rock and ice. but the specific behavior of water under such crushing gravity remained a theoretical gap.
Alexis Forestier and their research team have now closed that gap. revealing what happens when water is subjected to the extreme conditions found deep within a planet. In findings published in a Physical Review Letter paper. with a corresponding ArXiv preprint. the team recreated these intense pressures to witness water transform into a new structural phase.
To bridge the distance between Earth and the ice giants. the team utilized a diamond anvil to exert extreme force on a water sample. They employed synchrotron x-ray diffraction to monitor the molecular shifts within the sample as the pressure mounted. The experiment required more than just crushing force; by using the laser heating feature of the diamond anvil. the team pushed the temperature to approximately 2. 000K while maintaining pressures exceeding 200 GPa.
This process unveiled the hexagonal close-packed (HCP) phase of water ice. For decades. the phase diagram of water has been known to hold far more complexity than the ice familiar to life on Earth. At pressures above 80 GPa, water forms ice X, characterized by a body-centered cubic (BCC) oxygen sublattice. The discovery of the HCP phase. following previously identified face-centered cubic (FCC) structures. confirms that the packing of the oxygen sublattice shifts significantly as pressure intensifies. Observations showed a transitionary mixed FCC-HCP phase occurring at intermediate pressures.
The findings provide a vital new data point for the study of ice giants. though they do not offer a complete map of those distant cores. Instead. they act as a foundational clue. helping experts refine their models of how water behaves in its own sprawling galaxy of phases under the immense weight of gravity.
planetary science water ice hexagonal close-packed diamond anvil Neptune Uranus physics research