51 Pegasi b

51 Pegasi b is a gas giant that orbits the Sun-like star 51 Pegasi every 4.2 days. Its 1995 discovery established the first exoplanet orbiting a main-sequence star.

Radial-velocity method: An exoplanet detection technique that measures periodic shifts in a star’s spectral lines caused by orbital motion. Michel Mayor and Didier Queloz detected 51 Pegasi b through its host star’s repeating Doppler shifts.
Michel Mayor: A Swiss astronomer who co-discovered 51 Pegasi b with Didier Queloz. Mayor led the observational program that found the planet in 1995.
Extrasolar planet: A planet that orbits a star other than the Sun, or a stellar remnant. 51 Pegasi b was the first confirmed member of this broad class around a main-sequence star.
Jupiter: The largest planet in the Solar System, a gas giant orbiting the Sun every 11.86 years. 51 Pegasi b is broadly Jupiter-like in mass but orbits vastly closer to its star.
Hot Jupiter: A gas giant that orbits very close to its star and completes an orbit in days or weeks. 51 Pegasi b became the prototype for this unexpectedly close-in class of planets.
Didier Queloz: A Swiss astronomer who co-discovered 51 Pegasi b with Michel Mayor. Queloz helped identify the repeating stellar velocity signal that established the discovery.
Exoplanet detection: The methods used to find planets beyond the Solar System. Its discovery demonstrated that precision measurements could reveal planets around ordinary stars.
HD 209458 b: A hot Jupiter discovered in 1999 that became the first exoplanet observed transiting its star. Unlike 51 Pegasi b, it crosses its star from Earth’s viewpoint, enabling direct measurements of its atmosphere.
51 Pegasi: A Sun-like star in the constellation Pegasus, located about 50 light-years from Earth. This star’s motion revealed the planet and anchors its unusually short orbit.
Observatoire de Haute-Provence: A French astronomical observatory in southeastern France. Mayor and Queloz made the observations there that revealed 51 Pegasi b.

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Exoplanet atmosphereBroader topic: Its discovery established hot Jupiters as a surprising planetary population and opened a major target class.