Diamond rain may be common on giant icy planets

A new study led by Department of Energy’s SLAC National Accelerator Laboratory has found that “diamond rain” – a long-hypothesized exotic type of precipitation occurring on giant icy planets such as Uranus and Neptune – could be more common than previously thought. The analysis revealed that the presence of oxygen could make diamond formation more likely, allowing them to form and grow in many conditions throughout a variety of planets. These findings could help scientists fabricate nanodiamonds more efficiently, which would have a major impacts and applications in drug delivery, medical sensors, noninvasive surgery, sustainable manufacturing, and quantum electronics.

In an earlier study, the team mimicked the extreme temperatures and pressures from deep inside icy giants to observe diamonds as they formed. “The earlier paper was the first time that we directly saw diamond formation from any mixtures,” said co-author Siegfried Glenzer, the director of the High Energy Density Division at SLAC. “Since then, there have been quite a lot of experiments with different pure materials. But inside planets, it’s much more complicated; there are a lot more chemicals in the mix. And so, what we wanted to figure out here was what sort of effect these additional chemicals have.”

While in their previous research, the scientists studied a plastic material consisting of a mixture of hydrogen and carbon – which are key components of Uranus and Neptune’s chemical make-up – in more recent experiments they included other critical elements present in icy giants, such as oxygen, by using PET plastics. “PET has a good balance between carbon, hydrogen, and oxygen to simulate the activity in ice planets,” said study lead author Dominik Kraus, a professor of Physics at the University of Rostock.

Using high-power optical lasers and innovative methods such as X-ray diffraction and small-angle scattering, the experts investigated how the atoms of the material rearranged into small diamond regions, and measured how fast these regions grew. They discovered that, when oxygen was present, the nanodiamonds were able to grow at lower temperatures and pressures than previously thought. “The effect of the oxygen was to accelerate the splitting of the carbon and hydrogen and thus encourage the formation of nanodiamonds,” Kraus explained. “It meant the carbon atoms could combine more easily and form diamonds.”

According to the scientists, diamonds on Neptune and Uranus would become much larger that those produced in these experiments and, over thousands of years, they might slowly sink through the planets’ ice layers, assembling into a thick layer of bling around the solid planetary core.

In future studies, the team aims to include liquid samples containing ethanol, water, and ammonia – what icy giants are largely made of – to better understand how diamond rain forms on such planets. “The fact that we can recreate these extreme conditions to see how these processes play out on very fast, very small scales is exciting,” said co-author and SLAC scientists Nicholas Hartley. 

“Adding oxygen brings us closer than ever to seeing the full picture of these planetary processes, but there’s still more work to be done. It’s a step on the road towards getting the most realistic mixture and seeing how these materials truly behave on other planets,” he concluded.

The study is published in the journal Science Advances. 

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By Andrei Ionescu, Earth.com Staff Writer