Key facts
- Discovered by
- Michel Mayor and, Didier Queloz
- Discovery site
- OHP , France
- Discovery date
- 6 October 1995 ; 30 years ago ( 6 October 1995 )
- Detection method
- Radial velocity ( ELODIE )
- Alternative names
- Dimidium
- Semi major axis
- 0.052 344 942 (2) au (7,830,691.9 km)
- Eccentricity
- <0.0063
- Orbital period sidereal
- 4.230 7966 ± 0.000 0027 days
- Inclination
- 49.8° +5.8°, −5.7°
- Semi amplitude
- 55.77 ± 0.15 km/s
- Star
- 51 Pegasi
- Mean radius
- 1.07 ± 0.14 R J
Article
51 Pegasi b, officially named Dimidium (/dɪˈmɪdiəm/), is an extrasolar planet approximately 50 light-years (15 parsecs) away in the constellation of Pegasus. It was the first exoplanet to be discovered orbiting a main-sequence star, the Sun-like 51 Pegasi, and marked a breakthrough in astronomical research. It is the prototype for a class of planets called hot Jupiters.
In 2017, traces of water were discovered in the planet's atmosphere. In 2019, the Nobel Prize in Physics was awarded in part for the discovery of 51 Pegasi b.