Metallic hydrogen is a phase of hydrogen in which it behaves like an electrical conductor. This phase was predicted in 1935 on theoretical grounds by Eugene Wigner and Hillard Bell Huntington.
At high pressure and temperatures, metallic hydrogen can exist as a partial liquid rather than a solid. It is thought to appear in large quantities in the hot and gravitationally compressed interiors of Jupiter and Saturn, as well as in some exoplanets.