— New research led by Yale University scientists suggests that a rocky planet twice Earth's size orbiting a nearby star is a diamond planet.The planet -- called 55 Cancri e -- has a radius twice Earth's, and a mass eight times greater, making it a "super-Earth." It is one of five planets orbiting a sun-like star, 55 Cancri, that is located 40 light years from Earth yet visible to the naked eye in the constellation of Cancer.