The first rocky exoplanet

Today the discovery of the first definitely rocky exoplanet — as well as the smallest planet discovered to date — was announced.  The Kepler 10b press release was made this morning by Dr. Natalie Batalha at the American Astronomical Society (AAS) meeting in Seattle.  At 1.4 Earth radii and 4.6 Earth masses, it has an average density of 8.8 g/cc (a bit smaller than the density of the Earth’s core).  It’s not habitable, though: with a period of only 0.84 days, it orbits quite close to its host star and will thus be extremely hot.  Kepler 10b is the first Earth-like planet and 8th confirmed planet discovered by the Kepler mission.