'Diamond rain' on giant icy planet may be more common than previously thought

‘Diamond rain’ on giant icy planet may be more common than previously thought

The researchers studied a material more similar to the composition of ice giants and found that oxygen promotes the formation of diamond rain. The team also found evidence that, in combination with diamond, the recently discovered water phase, often described as “hot black ice”, can form.Credit: Greg Stewart/SLAC National Accelerator Laboratory

“Diamond rain,” a long-hypothesized type of bizarre precipitation on ice giant planets, may be more common than previously thought, a new study finds.


In an earlier experiment, researchers simulated the extreme temperatures and pressures found deep in the ice giants Neptune and Uranus and observed the formation of diamond rain for the first time.

Scientists at the Department of Energy’s SLAC National Accelerator Laboratory and their colleagues studied this process in a new material more similar to the chemical makeup of Neptune and Uranus, and they found that the presence of oxygen makes diamonds more likely, allowing them to form and grow in a wider range of conditions and on more planets.

The new study more fully shows how diamond rain forms on other planets, and on Earth, could lead to a new way of making nanodiamonds, which have applications in drug delivery, medical sensors, non-invasive surgery, sustainable Manufacturing and quantum electronics.

“The earlier paper is the first time we’ve directly seen any mixture form a diamond,” said Siegfried Glenzer, director of the High Energy Density Division at SLAC. “Since then, a lot of experiments have been done on different pure materials. But inside planets, It’s a lot more complicated; there are more chemicals in the mixture. So, we wanted to figure out here what the effects of these additional chemicals are.”

The team, led by Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the University of Rostock in Germany and École Polytechnique in France in collaboration with SLAC, is today in scientific progress.

Start with plastic

In previous experiments, the researchers studied a plastic material made from a mixture of hydrogen and carbon, key components of the overall chemical composition of Neptune and Uranus. But in addition to carbon and hydrogen, ice giants also contain other elements, such as large amounts of oxygen.

In recent experiments, the researchers used PET plastic — commonly used in food packaging, plastic bottles and containers — to more accurately reproduce the composition of these planets.

“PET has a good balance between carbon, hydrogen and oxygen and can simulate the activity of icy planets,” says HZDR physicist Dominik Kraus, professor at the University of Rostock.

Making nanodiamonds out of plastic bottles

In the experiment, a simple sheet of PET plastic was shot with a laser. An intense laser flash hitting a sample of foil-like material briefly heats it to 6,000 degrees Celsius, creating shock waves that compress the material to millions of times atmospheric pressure within a few nanoseconds. Scientists were able to determine that tiny diamonds, so-called nanodiamonds, formed under extreme pressure. Credit: HZDR/Blaurock

Oxygen is a diamond’s best friend

The researchers used a high-power optical laser at SLAC’s Linac Coherent Light Source (LCLS) Extreme Conditioning Matter (MEC) instrument to generate shock waves in PET. They then probed what was happening in the plastic with X-ray pulses from the LCLS.

Using a method called X-ray diffraction, they watched the atoms of the material rearrange into small diamond regions. They also used another method called small-angle scattering, which was not used in the first paper, to measure the speed and size of the growth of these regions. Using this additional method, they were able to determine that these diamond regions were several nanometers wide. They found that nanodiamonds were able to grow at lower pressures and temperatures than previously observed, thanks to the presence of oxygen in the material.

“The role of oxygen is to accelerate the splitting of carbon and hydrogen, thereby promoting the formation of nanodiamonds,” Krauss said. “This means that carbon atoms can combine more easily and form diamonds.”

'Diamond rain' on giant icy planet may be more common than previously thought

On the Matter for Extreme Conditions (MEC) instrument at the SLAC Linac Coherent Light Source, researchers reproduced the extreme conditions found on Neptune and Uranus and observed the formation of diamond showers.Image credit: Olivier Bonin/SLAC National Accelerator Laboratory

frozen planet

The researchers predict that the diamonds on Neptune and Uranus will be much larger than the nanodiamonds produced in these experiments — possibly weighing millions of carats. Over thousands of years, diamonds may have slowly sank into the planet’s ice and gathered into a thick layer of bling around the solid planetary core.

The team also found evidence that in combination with diamond, superionic water may also form. This recently discovered water phase, often described as “hot black ice,” exists at extremely high temperatures and pressures. Under these extreme conditions, water molecules split, oxygen atoms form a lattice, and hydrogen nuclei float freely in the lattice. Because these free-floating nuclei are electrically charged, superionic water can conduct electrical currents and could explain the unusual magnetic fields on Uranus and Neptune.

The findings could also impact our understanding of planets in distant galaxies, as scientists now believe ice giants are the most common form of planets outside our solar system.

“We know that the Earth’s core is primarily composed of iron, but many experiments are still investigating how the presence of lighter elements alters the conditions for melting and phase transitions,” said SLAC scientist and collaborator Silvia Pandolfi. “Our experiments show how these elements can change the conditions under which diamonds form on ice giants. If we want to model planets accurately, we need to get as close as possible to the actual composition of the planet’s interior.”

diamond in rough

The study also points to a potential route to producing nanodiamonds by laser-driven shock compression of inexpensive PET plastic. While already included in abrasives and polishes, in the future these tiny gems could be used in quantum sensors, medical contrast agents and reaction accelerators for renewable energy sources.

“The current way to make nanodiamonds is to use a pile of carbon or diamond and blow it up with explosives,” said SLAC scientist and collaborator Benjamin Ofori-Okai. “This produces nanodiamonds of various sizes and shapes, and it is very difficult to control. What we’re seeing in this experiment is different reactivity of the same species at high temperature and pressure. In some cases, diamond appears to form faster than others, suggesting that the presence of these other chemicals can speed up the process “Laser production could provide a cleaner, more controlled way to produce nanodiamonds. If we can engineer ways to change some things about reactivity, we can change their speed, form, and therefore how big they are.”

Next, the researchers are planning to conduct similar experiments using liquid samples containing ethanol, water and ammonia (the main components of Uranus and Neptune), which will bring them closer to understanding exactly how diamond rain forms on other planets.

“The fact that we can recreate these extreme conditions and see how these processes work on a very fast, very small scale is exciting,” said SLAC scientist and collaborator Nicholas Hartley. “Adding oxygen allows us to do more than ever before. Anytime is closer to seeing the full picture of these planetary processes, but there is more work to be done. This is a step towards getting the most realistic mixtures and understanding how these materials really behave on other planets.”


Scientists create ‘diamond rain’ that forms inside icy giant planet


More information:
Zhiyu He et al., Diamond formation kinetics in shock-compressed CHO samples recorded by small-angle X-ray scattering and X-ray diffraction, scientific progress (2022). DOI: 10.1126/sciadv.abo0617. www.science.org/doi/10.1126/sciadv.abo0617

Provided by SLAC National Accelerator Laboratory

Citation: ‘Diamond Rain’ on Giant Frozen Planet May Be More Common Than Previously Thought (September 2, 2022), September 3, 2022 from https://phys.org/news/2022-09-diamond-giant -icy-planets-common retrieved .html

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