spacetoday.net: Kepler discovers rocky exoplanet

Posted: Tue, Jan 11, 2011, 7:43 AM ET (1243 GMT)
Kepler-10b illustration (NASA)

Scientists announced Monday the discovery of the first "unequivocally rocky" extrasolar planet with a density similar to iron. The planet, designated Kepler-10b, is about 1.4 times the diameter of the Earth but 4.6 times the mass, giving it a density of 8.8 grams per cubic centimeter. That density, scientists said, means the planet is certainly a rocky world, and not a gaseous planet. NASA's Kepler spacecraft detected the planet by observing brief, periodic decreases in brightness as the planet transited across the star's disk as seen from the spacecraft. The planet orbits very closely to the star, completing one orbit in just over 20 hours, giving it an estimated surface temperature of 1,500 degrees Celsius.