Diamond Planets May Not be as Rare as Previously Thought: Carbon-Rich Exoplanets Discovered

Could "diamond" planets be far more common than previously thought? Scientists have discovered that carbon-rich planets, which could contain vast deposits of graphite or diamonds, may be abundant beyond Earth's solar system.

Exoplanets are planets that are located outside of the Earth's solar system. Although scientists usually argue that rocky exoplanets are like Earth and composed mainly of iron, oxygen, magnesium and silicon with only a small fraction of carbon, a discovery in October 2012 changed that. At that time, scientists argued that the exoplanet 55 Cancri e was likely covered in graphite and diamond.

Intrigued by this, the scientists decided to see whether other exoplanets could be carbon-based. The researchers developed an advanced model to estimate exoplanet composition. While previous models were based on static snapshots of the gaseous pools in which planets form, the new model tracked changes in the composition of the disk as it aged.

In the end, the researchers found that in disks with carbon-oxygen ratios greater than .8, carbon-rich planets can form farther from the center of the disk than previously thought. In addition, carbon-rich planets can form in disks with a carbon-oxygen ratio as low as .65. This, in particular, shows that there may be far more carbon-based exoplanets out there than previously thought.

"Despite relatively small amount of carbon on Earth, carbon has been critical for the emergence of life and the regulation of our climate through the carbon-silicate cycle," said John Moriarty, one of the researchers, in a news release. "It's an open question as to how carbon-rich chemistry will affect the habitability of exoplanets. We hope our findings will spark interest in research to help answer these questions."

There are currently more than 1,000 confirmed exoplanets and more than 3,000 exoplanet "candidates." This means that it's possible that quite a few of these could be "diamond" planets.

"An important question is whether or not our Earth is a typical rocky planet," said Debra Fischer, one of the researchers, in a news release. "Despite the growing number of exoplanet discoveries, we still don't have an answer to this question. This work further expands the range of factors that may bear on the habitability of other worlds."

The findings are published in The Astrophysical Journal.