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Scientists investigate diamond planets 'unlike anything in our solar system'

A new experiment shows some exoplanets may be full of Earth's most wanted gemstone.

Amanda Kooser
Freelance writer Amanda C. Kooser covers gadgets and tech news with a twist for CNET. When not wallowing in weird gear and iPad apps for cats, she can be found tinkering with her 1956 DeSoto.
Amanda Kooser
2 min read

This sparkling illustration shows a carbon-rich planet with diamond and silica as the main minerals.

Dan Shim/ASU/Vecteezy

Diamonds might be a rare commodity here on Earth, but the wider universe doesn't seem to have any shortage of them. Just imagine the outrageous bling-rings you could make from an entire planet packed with the sought-after gemstone.

Researchers at Arizona State University and University of Chicago led a new study on carbon-rich exoplanets (planets located outside of our solar system) and found that some of these wild worlds might be made up of diamonds and silica. Diamonds are made of carbon. Here on Earth, silica is found in quartz and sand. 

"These exoplanets are unlike anything in our solar system," said ASU's Harrison Allen-Sutter, lead author of the paper published in The Planetary Science Journal, in a release last week.

What makes a diamond planet and what makes an Earth-like planet? Stars and planets are created from dust and gas clouds, but it's a matter of the ratio of certain gases that feed into their formation. "A star with a lower carbon-to-oxygen ratio will have planets like Earth, comprised of silicates and oxides with a very small diamond content (Earth's diamond content is about 0.001%)," ASU said.

Enlarge Image

This is what a diamond-anvil cell looks like. A sample is compressed between the two flat surfaces.

Dan Shim/ASU

Not all stars are just like our sun. Some have a higher carbon-to-oxygen ratio, which -- in combination with the presence of water -- could lead to carbon-rich planets. 

The research team took this idea a step further and tested it in a lab experiment using diamond-anvil cells. This is pretty much what it sounds like: two high-quality diamonds shaped like anvils are pointed at each other. 

The scientists mimicked the interior of carbide exoplanets by immersing silicon carbide in water and compressing it to a high pressure. The team added some laser heating into the mix. 

"As they predicted, with high heat and pressure, the silicon carbide reacted with water and turned into diamonds and silica," ASU said.

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This latest study builds on previous investigations into planets that may be full of diamonds. NASA has taken a closer look at 55 Cancri e, an exoplanet that earned the nickname "diamond planet" due to research that suggests it has a carbon-rich composition.

Even if we could reach these diamond exoplanets, they wouldn't be appealing places to visit. "While Earth is geologically active (an indicator of habitability), the results of this study show that carbon-rich planets are too hard to be geologically active and this lack of geologic activity may make atmospheric composition uninhabitable," ASU said.

Shine on, you crazy diamond planets.