Researchers say the discovery of a diamond planet gives us the first glimpse of a world with a different chemistry to Earth.

'55 Cancri e' is thought to be composed mainly of diamond
Image Caption: The rocky planet is orbiting a sun-like star

A planet about 40 light years away and twice the size of Earth is made largely out of diamond, astronomers have said.

The rocky planet, called 55 Cancri e, which is in the constellation of Cancer, is orbiting a sun-like star that is visible with the naked eye.

Discovered by a US-Franco research team, the planet's radius is twice that of Earth's and its mass eight times greater. Temperatures on its surface reach 3,900 degrees Fahrenheit (1,648 Celsius).

"The surface of this planet is likely covered in graphite and diamond rather than water and granite," said Nikku Madhusudhan, the Yale researcher whose findings are due to be published in scientific journal The Astrophysical Journal Letters.

The study, with Olivier Mousis at the Institut de Recherche en Astrophysique et Planetologie in Toulose, France, estimates that at least a third of the planet's mass could be diamond.


"This is our first glimpse of a rocky world with a fundamentally different chemistry from Earth," Dr Madhusudhan said.

He added that the discovery of the carbon-rich planet means distant rocky planets can no longer be assumed to have chemical constituents, interiors, atmospheres, or biologies similar to Earth.


He said: "Planets are much more complex. This diamond-rich super-Earth is likely just one example of the rich sets of discoveries that await us as we begin to explore planets around nearby stars."