Illustration of the interior of 55 Cancri e — an extremely hot planet with a surface of mostly graphite surrounding a thick layer of diamond, below which is a layer of silicon-based minerals and a molten iron core at the center. (Image: Haven Giguere)

Illustration of the interior of ’55 Cancri e’ — an extremely hot planet with a surface of mostly graphite surrounding a thick layer of diamond, with a molten iron core at the center. (Image: Haven Giguere)

Scientists have found a planet outside of our solar system which could be a true diamond in the rough.

This gem of a planet is twice Earth’s size, according to the US-Franco team that found it, and its surface appears to be covered in graphite and diamond.

Researchers estimate that at least one-third of the new planet’s mass could be diamond.

The gemstone planet, called ’55 Cancri e’, has a radius twice that of Earth’s and a mass that’s eight times greater, making it a “super-Earth.”  The planet is one of five found orbiting ’55 Cancri’, a sun-like star about 40 light years from Earth.  Located in the constellation of Cancer, scientists say the star can be seen with the naked eye.

Astronomers first spotted the planet last year as it was transiting its star, which allowed them to measure its radius for the first time.  Using that information, along with their most recent estimate of its mass, researchers used computer modeling to speculate on the chemical composition of the planet.

Previous research revealed that the host star, 55 Cancri, has more carbon than it does oxygen, leading the US-French team to confirm that significant amounts of carbon and silicon carbide, with only a small amount of water ice, were available during the planet’s formation.

Star map showing the planet-hosting star 55 Cancri in the constellation of Cancer. The star is visible to the naked eye, though better through binoculars. (Image:Nikku Madhusudhan using Sky Map Online)

Star map showing the planet-hosting star 55 Cancri in the constellation of Cancer. The star is visible to the naked eye. (Image:Nikku Madhusudhan using Sky Map Online)

Astronomers initially assumed the diamond planet’s chemical composition was similar to Earth’s and that 55 Cancri e contained a substantial quantity of super-heated water.  However, according to Yale University researcher Nikku Madhusudhan, the new research suggests the planet has no water at all and is primarily made up of carbon – such as graphite and diamond – as well as iron, silicon carbide, and, possibly, some silicates.

The identification of a carbon-rich super-Earth means scientists can no longer assume that all distant rocky planets have chemical elements, interiors, atmospheres or biologies similar to Earth, according to Madhusudhan.

Which means there could be other gemstone planets out there just waiting to be discovered.