The ice giant planets of Neptune and Uranus might have just the right conditions to rain diamonds. Unfortunately we can’t go and check ourselves, so we have to rely on laboratory recreations of their atmospheres to find out. And so that’s exactly what a team of physicist did: they used a vaporized form of common plastics to find out how quickly and how easily diamonds could grow in those kinds of conditions.
Diamond rain is a crazy idea, but it’s crazy enough that it just might work. The upper atmospheres of Uranus and Neptune, the ice giants of the solar system, have exactly the right pressures and temperatures needed to cause this interesting phenomenon. In the middle layers of the atmosphere, individual carbon atoms can glue onto each other to form larger structures, which we know as diamonds. Once the diamonds are large enough they can make their way down to the lower levels of the atmosphere. At some point it becomes too hot for them to remain solid, and so they sublimate back into their individual carbon atoms which then float back up to the upper layers.
It’s just like the water cycle on the earth, but instead of involving water vapor and raindrops, it involves carbon and diamonds.
Unfortunately we do not have the technology to probe the atmosphere of these planets, so the only way to tell if these worlds rain diamonds is to attempt to recreate the atmospheric conditions of those planets in the laboratory. Recently, a team was able to produce nanometer scale diamonds in the lab, but those results were rather limited because the experimental setup only included carbon and hydrogen.
Now, a team based at the U.S. Department of Energy’s SLAC National Accelerator Laboratory included the presence of oxygen, which is abundant in the atmospheres of the ice giants.
“The earlier paper was the first time that we directly saw diamond formation from any mixtures,” said Siegfried Glenzer, 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.”
To generate the right atmosphere the team turned to PET plastic, which you might recognize as a common substance for food containers and bottles. “PET has a good balance between carbon, hydrogen and oxygen to simulate the activity in ice planets,” said Dominik Kraus, a physicist at HZDR and professor at the University of Rostock.
The researchers found that including oxygen in the mix sped up the diamond formation process and made it easier for diamonds to form. “The effect of the oxygen was to accelerate the splitting of the carbon and hydrogen and thus encourage the formation of nanodiamonds,” Kraus said. “It meant the carbon atoms could combine more easily and form diamonds.”
While it’s not yet a perfect recreation of the ice giant atmosphere, it is much closer than previous experiments. And this result gives us a nudge in the right direction that diamonds really are forming in those worlds.
The researchers could only grow diamonds for a fraction of a second. But in the atmospheres of Uranus and Neptune, diamonds would have all the time in the world to form. It’s quite possible, the researchers say, that the diamonds currently forming in Uranus and Neptune could weigh millions of carrots.
So if you’re in the market for some new bling, you know where to look.