Move over Jupiter and Saturn, a crap load of diamonds could be found in two of the most mysterious places in the Solar System: Uranus and Neptune. Researchers using the Linac Coherent Light Source at Stanford have demonstrated in the lab -- with one of the brightest sources of X-rays on the planet -- that the depths of these ice giants are perfect for the formation of diamonds.
Image: Greg Stewart/SLAC National Accelerator Laboratory
The scientists behind this are excited as it's the first time this effect has been reproduced in a lab environment similar to the lower reaches of the icy giants' atmospheres. Scientist have long wondered about the effects of having copious amounts of hydrogen, helium and methane (which give the outer planets their distinctive blue hue), and whether these chemical circumstances are ideal for diamond formation.
"This [condition] will generate diamond precipitation inside such celestial bodies," Dominik Kraus, a researcher with Helmholtz-Zentrum Dresden-Rossendorf in Dresden and author on the paper told Gizmodo in an email. "This means that there is not necessarily a pure diamond core but certainly a large diamond envelope around the rocky cores that are supposed to exist inside Neptune and Uranus."
On Jupiter and Saturn, the current thinking goes like this: When storms roll through clouds of methane molecules, lightning strikes cause carbon atoms to disassociate from their chemical bonds. When they collect in the air, you get clouds of soot which then sink into the lower atmosphere, being put under more and more pressure. That pressure is what squeezes the carbon into graphite and then again into diamond. It's also under the effect of gravity, so it would truly fall to the middle of the planet as "diamond rain".
On Uranus and Neptune there could be a cloud layer where a sea of hot methane forms which then separates in a high pressure environment causing the resulting carbon to squeeze into diamond.
But we've never actually recreated those conditions in a lab. Until now.
Using a tool called the Matter in Extreme Condition instrument, the scientists shocked a thin polystyrene sheet with a laser blast which produced pressure of up to 150 gigapascals. That laser heated the material to about 6000 Kelvin, which is very hot, but not hot enough to melt diamond. Since the polystyrene is a hydrocarbon polymer, it happily breaks up into its constituent hydrogen and carbon atoms which then are compressed. For an incredibly short moment, this causes nanodiamonds to form.
Because scientists are now able to reproduce an environment similar to the one located about 10,000km in the interior of Neptune and Uranus, further research could show us if there are more stable options beyond diamond precipitation.
"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," said Kraus. "But most theories suggest that diamond would remain solid, at least inside Neptune and Uranus, but this may be different for some exoplanets."
It's pretty hard to actually test what's being created in real time with the laser pulse, so that's where the ultrabright X-rays come in. Think of it like an incredibly bright and extremely short -- firing only for 50 femtoseconds -- camera flash.
"We can only produce this exotic state for about a nanosecond and during this time we need enough X-rays to probe it," said Kraus. "We then do simple X-ray diffraction (that's the method how nearly every crystal structure is identified) and we got a surprisingly clear diamond signal."
Previous experiments either never really provided direct evidence of this process, or results from the method used to normally compress carbon, diamond anvils, was not clear enough. "The problem with diamond anvil cell experiments is that it is very difficult to distinguish tiny pieces of diamond created from hydrocarbons to diamond pieces that might stem from the comparably huge diamond anvils themselves," said Kraus.