A high-pressure phase of atomic hydrogen predicted theoretically to form at the center of Jupiter, Eric Weisstein's World of Astronomy was first produced in the laboratory by Weir et al. (1996), at a pressure of 93-180 GPa and temperature of 2200-400 K.
References
Ladbury, R. "Livermore's Big Guns Produce Liquid Metallic Hydrogen." Phys. Today 49, 17-18, May 1996.
Weir, S. T.; Mitchell, A. C.; and Nellis, W. J. Phys. Rev. Let. 76, 1860, 1996.
