Astronomers find planet made of diamond

The rocky planet, called 55 Cancri e, orbits a sun-like star in the constellation of Cancer and is moving so fast that a year there lasts a mere 18 hours.

Discovered by a US-Franco research team, its radius is twice that of Earth's but it is much more dense with a mass eight times greater.

It is also incredibly hot, with temperatures on its surface reaching 1,648 degrees Celsius.

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

The study - with Olivier Mousis at the Institut de Recherche en Astrophysique et Planetologie in Toulose, France - estimates that at least one-third of the planet's mass, the equivalent of about three Earth masses, could be diamond.