51 Pegasi b
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.
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 |
Detection method | Radial velocity (ELODIE) |
| Designations | |
Alternative names | Dimidium |
| Orbital characteristics | |
| Aphelion | 0.0534 AU (7,990,000 km) |
| Perihelion | 0.0520 AU (7,780,000 km) |
Semi-major axis | 0.0527 ± 0.0030 AU (7,880,000 ± 450,000 km) |
| Eccentricity | 0.013 ± 0.012 |
Orbital period (sidereal) | 4.230785 ± 0.000036 d 101.5388 h |
Average orbital speed | 136 km/s |
| Star | 51 Pegasi |
| Physical characteristics | |
Mean radius | 1.9±0.3 RJ |
| Mass | ≥0.472 ± 0.039 MJ |
| Temperature | 1284 ± 19 K |
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.
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