Diamond is more than a dazzling gem—the extremely hard form of carbon makes up the pellet that encases fuel for inertial confinement fusion, and scientists believe it rains down deep inside ice giant planets like Neptune and Uranus. In both cases, the material experiences enormous pressures. Until now, experiments and simulations have disagreed about how it actually behaves under those conditions.

In a new study, published in Nature Physics, researchers at Lawrence Livermore National Laboratory (LLNL) document how diamond melts under pressures three times greater than conditions at Earth’s core.

“We were able to take tiny diamond samples and shock-compress them to temperatures hotter than the surface of the sun and to pressures higher than the centers of Neptune and Uranus—and still measure atomic structure, temperature, density and optical reflectivity,” said author and LLNL scientist Marius Millot.