Two Harvard scientists announced on the 27th of January '17 that they have produced metallic hydrogen. Their feat, which has eluded physicists for more than 80 years, marks an important breakthrough in physics, not only because it demonstrates a fundamental new property of the most abundant element in the universe, but because the metallic form is predicted to remain a superconductor at room temperature. If that turns out to be true, and an efficient means of producing it can be devised, the applied uses of metallic hydrogen could be transformative: superconductors, for example, transmit electricity without resistance and could be used to create lossless, superconducting magnetic storage for the electrical grid, and frictionless maglev trains. Space travel, too, could be fundamentally changed, because the substance’s predicted properties as a rocket fuel would open even the most distant planets in the solar system to exploration.