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Exoplanets could be made of diamonds, unlike anything in our solar system

As telescopes become more powerful and techniques for detecting distant exoplanets become more sophisticated, astronomers continue to discover strange and bizarre worlds that seem like something out of science fiction. There are planets with iron rain or with yellow skies, those shaped like a football or where a year lasts just a week.

Now, in a concept straight out of a dream, new research shows that our universe could host planets made of diamonds.

Researchers at Arizona State University looked at a specific type of planet which is high in carbon. Most planets are formed from the same cloud of gas which formed their stars, and therefore have similar composition. So you end up with planets like Earth which has a low ratio of carbon to oxygen, making diamonds (which are composed of carbon) a relative rarity.

But other planets form around stars with different compositions, where the ratio of carbon to oxygen is much higher. The researchers wanted to know what would happen inside these planets, so they pressed samples of silicon carbide between diamonds in water and exerted massive pressure on them. The silicon carbide reacted with the water and turned into diamond and silica as well.

This means that if water were present on these carbon-rich planets, that carbon could be converted to diamond and silicate, meaning the inside of the planets would be rich in diamonds. “These exoplanets are unlike anything in our solar system,” lead author Harrison Allen-Sutter of Arizona State University’s School of Earth and Space Exploration said in a statement.

llustration of a carbon-rich planet with diamond and silica as main minerals.
Illustration of a carbon-rich planet with diamond and silica as main minerals. Water can convert a carbide planet into a diamond-rich planet. In the interior, the main minerals would be diamond and silica (a layer with crystals in the illustration). The core (dark blue) might be an iron-carbon alloy. Shim/ASU/Vecteezy

There is a downside to the glittering promise of a diamond planet, however — the interior of these planets would be so hard that they couldn’t be geologically active, and therefore couldn’t create an atmosphere and couldn’t support life.

Even so, finding these planets could be a boon for scientific knowledge. “Regardless of habitability, this is one additional step in helping us understand and characterize our ever-increasing and improving observations of exoplanets,” said Allen-Sutter.

“The more we learn, the better we’ll be able to interpret new data from upcoming future missions like the James Webb Space Telescope and the Nancy Grace Roman Space Telescope to understand the worlds beyond our own solar system.”

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