The Kepler satellite concludes Campaign 1 of its exoplanet observation mission and begins Campaign 2, which extends the mission to 2016. Kepler has so far discovered 997 confirmed planets in over 400 alien planetary systems, and a further 3,216 are still unconfirmed (based on past confirmations, it is estimated that 90% of these will be confirmed). Some of these are terrestrial and in the Goldilocks belt, potentially habitable. Given Kepler’s limited field of view (about the size of the palm of a hand held out at arm’s length, between Lyra, Cygnus, and Aquila, the famous Summer Triangle), and the technique used (occultation), and extrapolating to the entire Milky Way, the number of potentially habitable planets around solar-type stars can be estimated at 17 billion. The closest is “only” 12 light-years away.
