51 Pegasi b

51 Pegasi b
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Name	51 Pegasi b
Caption	Artist's impression of a hot Jupiter like 51 Pegasi b orbiting its host star.
Discovered	6 October 1995
Discovery site	Observatoire de Haute-Provence
Discoverers	Michel Mayor and Didier Queloz
Discovery method	Radial velocity
Alt names	Dimidium, Bellerophon
Apsis	astron
Semimajor gm	0.052
Period	4.23077 d
Eccentricity	0.013
Star	51 Pegasi
Mass	≥0.46 M<sub>J</sub>
Single temperature	~1200 K
Atmosphere composition	Likely contains water vapor, carbon monoxide

51 Pegasi b is an extrasolar planet located approximately 50 light-years away in the constellation of Pegasus. It was the first exoplanet discovered orbiting a Sun-like star, a detection that revolutionized the field of astronomy and inaugurated the modern era of exoplanet science. The planet is classified as a hot Jupiter, a gas giant orbiting extremely close to its parent star, 51 Pegasi.

Discovery and detection

The landmark discovery of 51 Pegasi b was announced on 6 October 1995 by astronomers Michel Mayor and Didier Queloz of the University of Geneva. Using the ELODIE spectrograph on the 1.93-meter telescope at the Observatoire de Haute-Provence in France, the team employed the radial velocity method to detect the star's subtle wobble. This motion, with a period of just 4.2 days, revealed the gravitational influence of an unseen companion. The finding was swiftly confirmed by a team led by Geoffrey Marcy and R. Paul Butler using the Lick Observatory, validating the extraordinary result. The discovery challenged prevailing planetary formation theories and earned Mayor and Queloz the 2019 Nobel Prize in Physics.

Physical characteristics

As a prototypical hot Jupiter, 51 Pegasi b is a gas giant with a minimum mass of about half that of Jupiter. Its true mass and radius are not precisely known due to the unknown orbital inclination, but its composition is presumed similar to Jupiter and Saturn. Theoretical models suggest it is heavily irradiated and likely inflated by the intense heat from its nearby star. The planet's existence so close to 51 Pegasi forced a major revision of models, introducing concepts like planetary migration and orbital resonance. Its discovery implied that such large planets could form in the outer protoplanetary disk and subsequently migrate inward.

Orbit and rotation

51 Pegasi b orbits its host star at a mere 0.05 astronomical units, about one-eighth the distance of Mercury from the Sun. It completes a full revolution every 4.23 Earth days, resulting in a searingly hot environment. The orbit is nearly circular, with very low eccentricity. This close proximity results in probable tidal locking, meaning one hemisphere permanently faces the star while the other remains in perpetual darkness. Such a configuration creates extreme temperature contrasts between the planet's permanent day and night sides.

Atmosphere and climate

The atmosphere of 51 Pegasi b is a subject of intense study in the field of exoplanetology. Spectroscopic observations, including those from the Spitzer Space Telescope and the Hubble Space Telescope, have probed its composition. Studies suggest the presence of molecules like water vapor and carbon monoxide, though without evidence of methane, which may be thermally dissociated. The climate is defined by extreme radiative forcing, with estimated dayside temperatures around 1200 K. Atmospheric circulation models predict powerful supersonic winds redistributing heat from the permanent dayside to the nightside.

Significance and impact

The detection of 51 Pegasi b is one of the most significant milestones in modern astronomy. It proved that planets could exist around solar analogs and that the radial velocity technique was a powerful tool for finding them, directly inspiring projects like the High Accuracy Radial Velocity Planet Searcher (HARPS). This discovery ignited the exoplanet gold rush, leading to the confirmation of thousands of worlds by missions such as Kepler and the Transiting Exoplanet Survey Satellite (TESS). It fundamentally altered the scientific perspective on planetary system architecture and paved the way for the search for Earth-like planets and the study of extraterrestrial life.

Category:Exoplanets Category:Hot Jupiters Category:Pegasus (constellation) Category:Exoplanets discovered in 1995