‘Diamond rain’ found on Uranus has been recreated on Earth – and it could help solve our growing energy crisis
Deep within the icy planets on the edges of our solar system, diamond rains are a’ falling. Carbon and hydrogen squeezed together by astronomical pressures beneath the surfaces of Uranus and Neptune form solid diamonds that sink irrevocably towards the core.
Here on Earth, scientists have been able to mimic the conditions of these distant worlds for the first time, using shock waves, intense optical lasers and X-ray pulses to create and observe the formation of diamond rain.
Researchers at Stanford University’s SLAC National Accelerator Laboratory took polystyrene plastic, made from a mixture of hydrogen and carbon, to simulate the chemical makeup of Uranus and Neptune. To imitate the conditions of these planets at depths of more than 5,000 miles (8,000km), the team used high-powered optical lasers to fire pairs of shock waves into the material.
The first shock wave is slower and smaller than the second, which overtakes it at a crucial point of overlap. During this moment, when the pressure is at its peak, the molecules are compacted together, which results in diamond structures.
Because this extremely high level of pressure is unsustainable beyond a fraction of a second, the lab-made diamonds materialise over only the briefest of moments. Previous attempts to create them were unable to observe the diamond structure formation in real-time, but the researchers at SLAC recorded the chemical reaction by using the lab’s X-ray free-electron laser: the Linac Coherent Light Source (LCLS).
“For this experiment, we had LCLS, the brightest X-ray source in the world,” said Siegfried Glenzer, professor of photon science at SLAC and a co-author of the paper, published in Nature Astronomy. “You need these intense, fast pulses of X-rays to unambiguously see the structure of these diamonds, because they are only formed in the laboratory for such a very short time.”
The pulses of the LCLS last a few femtoseconds (quadrillionths of a second), which is short enough to record the creation of the diamond rain. Consequently, the scientists could see that almost every carbon atom in the plastic was incorporated into diamonds that measured a few nanometres wide.
Those sizes might not be any good for an engagement ring, but the scientists predict that conditions on Neptune and Uranus could grow these structures to diamonds weighing at more than a million carats. They also believe that, over the course of thousands of years, these enormous diamonds will sink through the planets’ icy layers to create a thick layer around the core.
Diamond rain could have a number of applications both within and outside of astronomy. Knowing how elements fuse together under different pressures can provide essential information on how scientists calculate the relationship between a planet’s mass and radius, for example. Waltzing over to Neptune and peering inside is currently impossible, so these experiments offer an important glimpse to the inner workings of these distant worlds.
One potential reaction could be that these falling diamonds generate heat as they sink towards the core – creating a source of energy for the planet.
“Matter-clumping in these types of high-pressure conditions is a force to be reckoned with”
There’s also scope for these lab-made nanodiamonds to one day be harvested for a variety of commercial purposes, from medicine to electronics. Further to this, knowing more about what happens when matter is compressed at extreme pressures is useful for research into fusion power. Squeezing hydrogen atoms to create helium is a process that fuels our own sun, and there’s scope for SLAC’s research to be used by the handful of organisations racing to translate this into an controllable power source for Earth.
“Simulations don’t really capture what we’re observing in this field,” noted Glenzer. “Our study and others provide evidence that matter-clumping in these types of high-pressure conditions is a force to be reckoned with.”
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