Money might not grow on trees here on Earth, but on Neptune and Uranus, diamonds do fall from the sky. That's according to scientists using the Linac Coherent Light Source at Stanford, who have recreated atmospheric conditions from our solar system's two outermost planets in the lab, and found that the rain there isn't made of water. It's made of diamonds, reports Gizmodo.

Scientists have long suspected that the conditions might be right for diamond rain in the outer planets, but without a probe capable of investigating, proving that the phenomenon is real has depended on being able to reproduce the proper conditions in the lab. This is the first time such a feat has been possible.

In order to rain diamonds, an atmosphere with the right mix of hydrogen, helium and methane is required. That's what we see on Neptune and Uranus (their distinctive blue coloration is due to this unique atmospheric mixture).

“This [condition] will generate diamond precipitation inside such celestial bodies,” explained Dominik Kraus, author on the paper, to Gizmodo. “This means that there is not necessarily a pure diamond core but certainly a large diamond envelope around the rocky cores that are supposed to exist inside Neptune and Uranus.”

Researchers used a tool called the Matter in Extreme Condition instrument to place a hydrocarbon polymer under immense pressure. This caused it to break up into its constituent hydrogen and carbon atoms and, for an extremely short instance, form into nanodiamonds.

These conditions ought to be similar to conditions on Uranus and Neptune, where there should be cloud layers where hot methane seas can form. These methane seas are then squeezed into diamonds by the immense pressures generated by the planets.

Interestingly, diamond rain might not be the only flashy consequence of these planets' otherworldly conditions. It's also within the realm of theoretic possibility that there are oceans of liquid carbon close to their cores, with diamond icebergs floating in them. "But most theories suggest that diamond would remain solid, at least inside Neptune and Uranus, but this may be different for some exoplanets,” suggested Kraus.

Whatever the case, the intrigue surrounding our mysterious outer planets just got a lot more extraordinary.