Wiki: Exoplanet
http://en.wikipedia.org/wiki/Exoplanet
An exoplanet or extrasolar planet is a planet that orbits a star other than the Sun, a stellar remnant, or a brown dwarf. More than 1900 exoplanets have been discovered (1906 planets in 1202 planetary systems including 480 multiple planetary systems as of 28 March 2015).[2] There are also rogue planets, which do not orbit any star and which tend to be considered separately, especially if they are gas giants, in which case they are often counted, like WISE 0855−0714, as sub-brown dwarfs.[3]
The Kepler space telescope has also detected a few thousand[4][5] candidate planets,[6][7] of which about 11% may be false positives.[8] There is at least one planet on average per star.[9] Around 1 in 5 Sun-like stars[a] have an "Earth-sized"[b] planet in the habitable zone,[c] with the nearest expected to be within 12 light-years distance from Earth.[10][11] Assuming 200 billion stars in the Milky Way,[d] that would be 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if red dwarfs are included.[12] The rogue planets in the Milky Way possibly number in the trillions.[13]
