Metallic hydrogen
Metallic hydrogen is hydrogen squeezed until it turns into a metal. Jupiter holds a layer of it deep inside; on Earth, no lab has made a sample that everyone accepts.
In 1935 physicists predicted that hydrogen, crushed hard enough, would become a metal, and Jupiter is thought to hold it deep inside. Wigner and Huntington put the pressure needed at 25 gigapascals. Labs have since reached 425, seventeen times that, and seen hydrogen turn opaque without yet showing it conducts. A sample claimed as solid metal in 2017 was lost when the diamonds squeezing it failed, and nobody knows whether it is still there or has turned back into gas.
Sources
- Militzer et al., "Juno Spacecraft Measurements of Jupiter's Gravity Imply a Dilute Core", Planetary Science Journal, 2022
- NASA Science, Juno mission
- Eremets and Drozdov, "Comments on the claimed observation of the Wigner-Huntington Transition to Metallic Hydrogen", arXiv, 2017
- DESY, "On the way to metallic hydrogen", 2025
- Ji et al., "Ultrahigh-pressure crystallographic passage towards metallic hydrogen", Nature, 2025 (Lund University record)
- Silvera and Dias, "Metallic Hydrogen", Inference, 2021
- The Harvard Crimson, "First Sample of Solid Metallic Hydrogen Lost", 2017
- Phys.org, "Researchers find evidence for metallic hydrogen at 425 gigapascals", 2020
- Physics World, "Has metallic hydrogen been made at long last?"
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