Astronomers have discovered the smallest planet outside our Solar System, and the first that is undoubtedly rocky like Earth. Measurements of unprecedented precision have shown that the planet, Kepler 10b, has a diameter 1.4 times that of Earth, and a mass 4.6 times higher. However, because it orbits its host star so closely, the planet could not harbour life.
The discovery has been hailed as "among the most profound in human history". A pioneer of the hunt for exoplanets, Geoffrey Marcy, from the University of California Berkeley, said that Kepler 10b represented "a planetary missing link, a bridge between the gas giant planets we've been finding and the Earth itself, a transition... between what we've been finding and what we're hoping to find".