For 80 years, researchers theorized that hydrogen could transform into a metal. This year, scientists at Sandia National Laboratories finally proved it.

They took deuterium, an isotope of hydrogen, and applied 3 million times the atmospheric pressure using the Z machine, shown above. After 200 nanoseconds, the liquid turned reflective, indicating it had become metallic.

20: Magnetic strength, in mega gauss, of the Z machine—20 million times greater than Earth's magnetic field

"The moment we got our first look at the data, we were very excited," says Mike Desjarlais, the team's lead theoretical physicist. "After the first several experiments, we had begun to wonder if we would ever see it."