Scientists melt diamond at pressures beyond Neptune, solving a two-decade mystery

Researchers at Lawrence Livermore National Laboratory performed dynamic compression experiments at the University of Rochester's Laboratory for Laser Energetics, using the Omega Laser Facility to generate shock waves that melted diamond under extreme conditions. The measurements, taken within a billionth of a second, included X-ray diffraction data that revealed the material retained its diamond lattice until it turned liquid, contradicting earlier suggestions of an intermediate crystalline phase.

The observed melting temperature now agrees with quantum-mechanics-based simulations, resolving a discrepancy that had persisted for roughly two decades. The results suggest that the initial shock in inertial confinement fusion implosions can be less intense, which may increase fuel compressibility and boost fusion yield by up to threefold. Additionally, the data provide a more reliable basis for modeling the high-pressure interiors of Neptune and Uranus, where diamond rain is thought to occur. Future work will explore diamond behavior under multiple shock sequences using the National Ignition Facility.