The team of the Kepler mission have just announced the discovery of a new exoplanet, Kepler 10b. It's about 1.4 times the size of the Earth, 4.6 times as massive and has an average density of 8.8g/cm^3....basically it's a giant iron wrecking ball with a thin veneer of silicates. A super Mercury, if you will. Here's the link to the physical parameters of the system...
http://kepler.nasa.gov/Mission/discoveries/kepler10b/
and the discovery page....
http://kepler.nasa.gov/news/nasakepl...News&NewsID=94