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Blasting plastic with powerful lasers can create tiny diamonds. Similar processes may occur at the high temperatures and pressures found within planets, which could help explain why Uranus and Neptune are so strange.

Researchers have been able to create nanodiamonds before by shining lasers at a mixture of carbon and hydrogen, but it required extraordinarily high pressures. at SLAC National Accelerator Laboratory in California and his colleagues found that by using a simple plastic called PET – commonly used to make bottles and other containers – which contains carbon, hydrogen and oxygen, they could make diamonds in much less extreme conditions.

When they fired a powerful laser at the plastic, it heated up to temperatures between 3200°C and 5800°C and the shock waves generated by the laser pulse brought the plastic to pressures upwards of 72 gigapascals – equal to one-fifth the pressure in Earth’s core. This separated the hydrogen and oxygen from the carbon, leaving behind tiny diamonds a few nanometres across and a form of water called superionic water, which conducts electricity more easily than regular water.

This happened at lower pressures than in previous experiments using other materials, says Glenzer, and like PET, the interiors of giant planets contain oxygen as well as carbon and hydrogen.

“What that means is that diamonds are probably everywhere,” says Glenzer. “If it happens at lower pressures than previously seen, it means they’re inside Uranus, inside Neptune, inside some moons such as Titan, which contain hydrocarbons.”

Such diamonds forming in Neptune’s mantle and then sinking towards its core, generating friction and heat in the process, could explain why the planet is unexpectedly hot. And within Uranus, pockets of superionic water left over from diamond formation could be conducting electric currents, which might have something to do with the strange shape of its magnetic field.

One next step is to include this process in models of those worlds and see if it can account for some of their many mysteries, says Glenzer. Another is to collect the nanodiamonds after they form. Similar materials are already used in industrial abrasive processes and could be useful in many scientific applications, but are generally produced by detonating explosives.

“In the other experiments, where the necessary pressure was much higher, the conditions were so extreme and dynamic that the diamonds ended up falling apart,” says Glenzer. “Now that we’ve found a way to make the diamonds at lower pressure, we may have a chance to actually harvest the diamonds.”