Deep inside the planet Neptune, the pressure is so extreme that carbon atoms are crushed into actual diamonds — which then rain downward in solid showers through the planet’s interior — and recent laboratory experiments have successfully recreated the conditions in which this happens, producing tiny synthetic diamonds in the process.

The interiors of the two ice giants of the outer solar system — Uranus, at about 2.9 billion kilometres from the Sun, and Neptune, at about 4.5 billion — are difficult to study by any direct means. The only spacecraft ever to visit either planet was Voyager 2, which flew past Uranus in January 1986 [...] The post Deep inside the planet Neptune, the pressure is so extreme that carbon atoms are crushed into actual diamonds — which then rain downward in solid showers through the planet’s interior —