Superionic Ice Created: Mimicking Uranus and Neptune Conditions

In a groundbreaking experiment, physicists have successfully synthesized a predicted form of superionic ice, effectively recreating the extreme conditions found deep within ice planets like Uranus and Neptune. This exotic state of water, which is part liquid and part solid within a crystal lattice with mobile hydrogen atoms, offers new insights into the composition and behavior of celestial bodies in our solar system.

The research team, led by Alexis Forestier of Paris-Saclay University, subjected ultrapure water to temperatures reaching approximately 4,274 degrees Fahrenheit (2,357 degrees Celsius) and pressures up to two million times Earth's sea-level atmospheric pressure. These conditions were achieved using powerful synchrotron X-rays, compressing the water within a diamond anvil cell. The experiment aimed to validate theoretical predictions about a specific phase of ice, known as ice X, transitioning into a superionic state under immense duress.

"Exploring the phase diagram of water ice under pressure has continuously driven leading-edge experimental developments over the past century," the scientists stated in their findings published in Physical Review Letters. "This state is directly relevant for ice giant planetary interiors," they added, highlighting the significance of their work for planetary science.

A Glimpse into Alien Ice Worlds

The creation of this superionic ice marks a significant step in understanding the enigmatic interiors of ice giants. These planets, unlike Earth, are primarily composed of heavier elements than hydrogen and helium, including significant amounts of water, ammonia, and methane, often referred to as "ices" despite existing in fluid states under internal planetary conditions. Simulating these conditions in a laboratory allows scientists to test theories about their structure, magnetic fields, and atmospheric phenomena.

Previously, scientists had confirmed the existence of superionic ice in 2018, but recreating it under conditions specifically relevant to the internal pressures and temperatures of Uranus and Neptune has been a major challenge. The experiment reported that the predicted superionic state for ice X emerged above approximately 2,780 degrees F (1,526 degrees C) and 200 gigapascals. As pressure and heat intensified, the ice crystals shifted configurations, adopting a hexagonal close-packed structure composed of oxygen atoms, with hydrogen atoms flowing freely. This behavior was observed to be analogous to that of compressed noble gases.

The study acknowledges that definitively proving this form of ice exists within Uranus and Neptune will require further advancements, potentially taking decades. However, the successful laboratory synthesis provides crucial empirical data that will refine existing planetary models. Understanding the properties of such exotic ices is key to comprehending the complex physics governing the deep interiors of these distant worlds, including their potential for generating magnetic fields and internal heat.

This research is part of a larger scientific effort to classify and understand the myriad forms of ice. To date, scientists have identified 22 distinct types of ice, each with unique properties dictated by temperature and pressure. The most recently identified, ice XXI, was confirmed in 2025. Each new phase discovered, particularly those formed under extreme conditions, expands our knowledge base and aids in the interpretation of astrophysical observations. The insights gained from recreating superionic ice on Earth serve as a vital bridge between theoretical planetary science and observable cosmic phenomena.