High Quality Content by WIKIPEDIA articles! 51 Pegasi b (abbreviated 51 Peg b), sometimes though unofficially named Bellerophon, is an extrasolar planet approximately 50 light-years away in the constellation of Pegasus. 51 Pegasi b was the first planet to be discovered orbiting a main sequence star, the Sun-like 51 Pegasi (the first exoplanets at all were dicovered in 1992 by Aleksander Wolszczan around pulsar PSR 1257), and marked a breakthrough in astronomical research. It is the prototype for a class of planets called hot Jupiters.