What transpires inside planets like Uranus and Neptune? An innovative experiment was carried out to find out by a global team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the University of Rostock, and France’s École Polytechnique. They used intense laser flashes to study what occurred when they shot a laser at a thin sheet of simple PET plastic.

As a consequence, the scientists were able to support their prior hypothesis that diamonds really do rain within the ice giants at the edge of our solar system. Another was that this technique would provide a brand-new approach to making nanodiamonds, which are needed, for example, in very sensitive quantum sensors. The team’s findings were recently published in Science Advances.

Extreme conditions occur in the interior of large icy planets like Neptune and Uranus, with pressure millions of times higher than on Earth and temperatures that can reach several thousand degrees Celsius. However, states like these can be briefly reproduced in the lab by using intense laser flashes to hit a sample of a film-like material, heat it to 6,000 degrees Celsius in the blink of an eye, and create a shock wave that compresses the material to a million times the atmospheric pressure for a few nanoseconds.

“Up to now, we used hydrocarbon films for these kinds of experiments,” explains Dominik Kraus, a physicist at HZDR and professor at the University of Rostock. “And we discovered that this extreme pressure produced tiny diamonds, known as nanodiamonds.”

However, since ice giants also contain significant quantities of oxygen, in addition to carbon and hydrogen, it was only partially able to replicate the interior of planets using these films. When looking for suitable film material, the researchers stumbled upon an everyday substance: PET, the resin used to make ordinary plastic bottles.

“PET has a good balance between carbon, hydrogen, and oxygen to simulate the activity in ice planets,” Kraus explains.

The team carried out their research using the Linac Coherent Light Source (LCLS), a powerful, accelerator-based X-ray laser, at the SLAC National Accelerator Laboratory in California. They utilized it to analyze what transpires when powerful laser flashes hit a PET film while simultaneously using two measuring techniques: X-ray diffraction to detect if nanodiamonds were created and so-called small-angle scattering to see how fast and how big the diamonds grew.