Metallic hydrogen is a phase of hydrogen in which it behaves as an electrical conductor. This phase was predicted theoretically in 1935, but has not been reliably produced in laboratory experiments due to the requirement of high pressures, on the order of hundreds of gigapascals. At these pressures, hydrogen might exist as a liquid rather than solid. Liquid metallic hydrogen is thought to be present in large amounts in the gravitationally compressed interiors of Jupiter, Saturn, and in some of the newly discovered extrasolar planets. History Theoretical predictions Metallization of hyd...