51 Pegasi b (unofficially dubbed Bellerophon, later named Dimidium):    Dimidium is an extrasolar planet in the constellation of Pegasus. It was the first exoplanet to be discovered. It orbits the sun, 51 Pegasi.

This exoplanet is nicknamed Bellerophon in honor of the Greek hero who tamed the winged horse Pegasus.

The discovery of 51 Pegasi b on 6 Octobver 1995 marked a breakthrough in astronomical research.  

The mass of 51 Pegasi b is . That is  0.472 ± 0.039 times the mass of Jupiter (M_J).

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51 Pegasi b is the prototype for a class of planets called hot Jupiters. A  is a class of exoplanets that is inferred to be physically similar to Jupiter but has a very short orbital radii compared to our solar system's Jupiter.		This artist’s view shows the hot Jupiter exoplanet 51 Pegasi b, sometimes referred to as Bellerophon, which orbits a star about 50 light-years from Earth in the northern constellation of Pegasus (The Winged Horse). 51 Pegasi b was the first exoplanet around a normal star to be found in 1995. Twenty years later this object was also the first exoplanet to be be directly detected spectroscopically in visible light. By ESO/M. Kornmesser/Nick Risinger (skysurvey.org) - ESO website, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=39719418