StartsWithABang writes: For the past three years, Kepler has been looking at 150,000 stars, searching for planetary transits. The science haul has been huge, but mostly larger planets close in to their parent stars. Nevertheless, a few rocky, habitable-zone planets have been discovered. Whether we take optimistic or pessimistic estimates, what do we expect for the rest of the galaxy? At minimum, some 6 billion habitable-zone, rocky planets. And likely many more!