Gemstone formation as in Uranus and Neptune: Researchers have confirmed the existence of diamond showers in ice planets through "gaudy" experiments and at the same time have shown a new possibility for the production of nanodiamonds for technology. Apparently, simple bottle plastic can serve as a raw material, since it contains the element oxygen, which, according to the test results, stimulates the formation of exotic diamonds.
Huge, icy and mysterious: What goes on inside ice planets like Neptune and Uranus, which are believed to be very common in the universe? It is clear that extreme conditions prevail inside: the pressure is a million times greater than in the earth's atmosphere and while the outer layers are frosty, temperatures of several thousand degrees Celsius prevail in the depths. For some time now, researchers have been conducting experiments to investigate what processes this could lead to in the hydrocarbon-rich matter inside the exotic worlds. To do this, the scientists led by Dominik Kraus from the Helmholtz-Zentrum Dresden-Rossendorf create conditions in the laboratory that are similar to those found in the ice planets. To do this, they shoot strong laser flashes at material samples, heating them up to 6000 degrees Celsius for fractions of a second. This also creates a shock wave that compresses the matter to millions of times the atmospheric pressure.
"So far we have carried out such tests with foils made of hydrocarbons," says Kraus. "We were already able to determine that tiny diamonds, so-called nanodiamonds, form under the extreme pressure." But so far the researchers have not investigated the role played by an element that, along with carbon and hydrogen, is also likely to be found frequently in the interior of the ice planets: oxygen . An astonishingly profane-looking material offered itself to answer this question: PET – the plastic that plastic bottles are made of. "PET has a good ratio of carbon, hydrogen and oxygen to simulate what happens in ice planets," explains Kraus.
Oxygen promotes diamond formation
The team carried out the tests at the SLAC National Accelerator Laboratory in California. In addition to the possibility of generating the pressure wave, it also offers the corresponding analysis technology: A special X-ray laser can be used to examine what happens when the intense laser flashes hit a PET film. In concrete terms, the researchers were able to use X-ray diffraction to determine whether nanodiamonds formed and the so-called small-angle scattering showed how quickly they grew. It was shown that oxygen promotes diamond formation: "Due to its influence, oxygen accelerated the separation of carbon and hydrogen and thus promoted the formation of nanodiamonds," says Kraus. "This allowed the carbon atoms to come together better and form diamonds."
According to the scientists, the proof of the positive effect of oxygen supports the assumption that it literally rains diamonds inside ice giants. On Neptune and Uranus, however, they will probably be much larger than the nanodiamonds produced in experiments - some even reaching millions of carats. The scientists emphasize that this not only applies to the two ice planets in our solar system, but also to the many others in the universe. From the study of planets around distant stars, it is now clear that this category is very common.
New manufacturing process
As the researchers report, they came across another interesting aspect: Presumably, so-called superionic water is formed together with the diamonds: "The oxygen atoms form a crystal lattice in which the hydrogen nuclei move freely," explains Kraus. Since the cores are electrically charged, superionic water can conduct electrical currents and thus contribute to the formation of the magnetic field of the ice giants. In further experiments, the team hopes to be able to clearly demonstrate the existence of this exotic form of water mixed with diamonds.
In addition to fundamental findings for planetary research, Kraus and his colleagues emphasize that their work can also develop practical potential: A new possibility for the production of nanometer-sized diamonds is emerging. They are already being used in grinding and polishing agents and are regarded as promising elements in various technical areas of application. "So far, nanodiamonds have been made by blowing up carbon with explosives," explains Benjamin Ofori-Okai of the SLAC National Accelerator Laboratory. "However, this creates nanodiamonds of various sizes and shapes that are difficult to control." With the help of their process, they could be manufactured more precisely and cleanly in the future. "Because with the X-ray laser, we have a laboratory tool with which the size growth of the diamonds can be precisely controlled," says Kraus.
Source: Helmholtz Center Dresden-Rossendorf, SLAC National Accelerator Laboratory, specialist article: Science Advances, doi: 10.1126/sciadv.abo0617