This handout illustration obtained by Reuters October 11, 2012, shows the interior of the planet 55 Cancri … LONDON (Reuters) - Forget the diamond as big as the Ritz. This one's bigger than planet Earth. Orbiting a star that is visible to the naked eye, astronomers have discovered a planet twice the size of our own made largely out 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 U.S.-Franco research team, its radius is twice that of Earth's with a mass eight times greater. That would give it the same density as Earth, although previously observed diamond planets are reckoned to be a lot more dense. It is also incredibly hot, with temperatures on its surface reaching 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 Nik...