51 Pegasi b
An artist's impression of 51 Pegasi b (center) and its star (right). | |
| Discovery | |
|---|---|
| Discovered by | Michel Mayor and Didier Queloz |
| Discovery site | OHP, France |
| Discovery date | 6 October 1995 |
| Radial velocity (ELODIE) | |
| Designations | |
| Dimidium | |
| Orbital characteristics | |
| Aphelion | 0.0534 AU (7,990,000 km) |
| Perihelion | 0.0520 AU (7,780,000 km) |
| 0.0527 ± 0.0030 AU (7,880,000 ± 450,000 km) | |
| Eccentricity | 0.013 ± 0.012 |
| 4.230785 ± 0.000036 d 101.5388 h | |
Average orbital speed | 136 km/s |
| Star | 51 Pegasi |
| Physical characteristics | |
| 1.2±0.1 RJ | |
| Mass | 0.46±0.02 MJ |
| Temperature | 1,250 K |
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.