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. Siegfried Glenzer 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.

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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.