Neptune in the sky with diamonds

An international collaboration of scientists has revealed that ice giants create large amounts of diamonds.

Using an ultra-strong X-ray laser and other facilities at the Stanford Linear Accelerator Centre (SLAC) in the US, the researchers simulated conditions found inside ice giants. During the experiment, they observed hydrocarbon fission and subsequently, carbon converting into diamonds.

Dr Dominik Kraus, head of a research group at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), said: “So far, no one has been able to directly observe these sparkling showers in an experimental setting. In our experiment, we exposed a special kind of plastic – polystyrene, which also consists of a mix of carbon and hydrogen – to conditions similar to those inside Neptune or Uranus.”

Digging for diamonds

Icy planets consist of a solid core wrapped in thick layers of ice, composed largely of hydrocarbons, water and ammonia. For years, scientists theorised that extreme pressures underneath the planet’s crust splits hydrocarbons and converts carbon into diamonds. These then sink further into the planet’s interior. In order to test this, two shock waves were driven through the plastic polystyrene samples. At a pressure of 150 gigapascals and temperatures of about 5,000°C, these waves compressed the samples. The first, smaller slower wave was overtaken by another stronger second wave, with most of the diamonds forming when both waves overlap.

This process occurred within a fraction of a second, so the researchers used ultrafast X-ray diffraction to record the diamonds’ creation and the chemical processes involved. Based on this information, the scientists believe the diamonds formed on the ice giants are larger and sink down to their planet’s core over thousands of years.

These experiments will help shape astrophysicists’ understanding of exoplanets – currently measurements and estimations are based on understanding these planets’ mass and radius. The first is calculated based on positional changes of the planet’s mother star and the radius is derived from the shadow cast as the planet passes a star.

In addition to astrophysical developments, there are possible practical applications. The nanodiamonds created in this experiment can be used in electronic instrumentation, medical procedures or as cutting materials for industrial use. Currently, these diamonds are produced via blasting, but laser-based production could signify a cleaner and more controlled process.

The paper was published in Nature Astronomy.