High Quality Content by WIKIPEDIA articles! 51 Pegasi b, also unofficially named Bellerophon and or abbreviated as 51 Peg b, 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 Sun-like star and is the prototype for a class of planets called hot Jupiters. The name 51 Pegasi b is the official astronomical name of the planet. As with all extrasolar planets, the 'b' is used to indicate that this planet was the first discovered companion of its parent star. Further undiscovered companions of 51 Pegasi would be designated c, d, e, f, and so on. All extrasolar planets have lowercase letter to differentiate from companion stars in the system.