It May Rain Diamonds Inside Neptune and Uranus

Scientists have finally simulated the long-proposed shower of gems

Diamond Rain
Greg Stewart / SLAC National Accelerator Laboratory

Diamonds may rain down deep within Neptune and Uranus.

The physics of these “ice giants” differ greatly from that of Earth. These planets have a solid core surrounded by icy oceans made up of hydrocarbons, water and ammonia. Deep inside these planets, some 6,200 miles from the surface, the pressure is so intense physicists have long speculated that a shower of diamonds may form. Now, as Nicola Davis reports for The Guardian, a new experiment simulating this process has provided the first evidence that this diamond rain is possible.

Past researchers have tried to simulate this “diamond rain” before, Davis reports, but were never able to produce the immense pressures that are expected in the interiors of ice giants. So an international team of scientists tried a new approach.

According to a press release, the team exposed polystyrene, a type of plastic composed of carbon and hydrogen, to shock waves produced by a high-powered optical laser and x-rays. The shock waves compressed the plastic at pressures of 150 gigapascals and temperatures of over 9,000 degrees Fahrenheit. This intense reaction broke the bonds between the hydrogen and carbon molecules and compressed carbon atoms into a microscopic diamond. The research appears in the journal Nature Astronomy.  

“The experimental time is very short,” Dominik Kraus, of the German research laboratory Helmholtz-Zentrum Dresden-Rossendorf tells Davis. “That we saw this very clear signature of diamonds was actually very, very surprising.”

Kraus, lead author of the study, tells Bryson Masse of Gizmodo that there is likely a large envelop of diamond rain around the cores of Neptune and Uranus. And it’s possible the interiors of the planets are even weirder.

“If the temperature is high enough close to the core (some calculations predict that) it could also be ‘oceans of liquid carbon’ with gigantic ‘diamond icebergs, swimming on top of it,” Kraus says. “But most theories suggest that diamond would remain solid, at least inside Neptune and Uranus, but this may be different for some exoplanets.”

The diamond rain could also solve another mystery about the ice giants, Davis reports. Uranus and Neptune are hotter than most models predict, but Kraus explains that since the diamonds are heavier than the surrounding hydrocarbon medium in which they form, they would sink towards the planet's core over thousands of years. Those sinking stones would create friction, giving off heat, which would produce the temperature boost.

Aside from improving planetary modeling, the new simulation could have practical applications. Currently, tiny artificial diamonds used in electronics and surgical tools are created by blasting. This new laser-based process could lead to a more precise and efficient method of creating the tiny gems.

Editor's Note August 23, 2017: An earlier version of this article mistakenly suggested ammonia and water were types of hydrocarbons.

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