51 Pegasi b (also written as 51 Peg b) is the first planet discovered around a sun-like star outside of the solar system. It is the prototypical hot Jupiter. It orbits the star 51 Pegasi in the Pegasus constellation. The semi-major axis of an ellipse In geometry, the term semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolas. ... The astronomical unit (AU or au or a. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... A day (symbol: d) is a unit of time equal to 24 hours. ... Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ... Map of Earth showing lines of longitude, which appear curved and vertical in this projection, but are actually halves of great circles Longitude, sometimes denoted by the Greek letter λ, describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. ... Another view of Keplerian orbital elements. ... Another view of Keplerian orbital elements. ... The Julian day or Julian day number (JDN) is the number of days that have elapsed since 12 noon Greenwich Mean Time (UT or TT) on Monday, January 1, 4713 BC in the proleptic Julian calendar . ... Mass is a property of a physical object that quantifies the amount of matter it contains. ... Adjective Jovian Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... In classical geometry, a radius of a circle or sphere is any line segment with one endpoint on the circle (i. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ... The cubic meter (symbol m³) is the SI derived unit of volume. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. ... 1995 (MCMXCV in Roman) was a common year starting on Sunday of the Gregorian calendar. ... Infrared image of the star GQ Lupi (A) orbited by a planet (b) at a distance of approximately 20 times the distance between Jupiter and our Sun. ... Michel Mayor (born 12 January 1942) is a professor in the Department of Astronomy at the University of Geneva. ... Didier Queloz, born 23 February 1966, is a Geneva-based astronomer with a prolific record in finding extrasolar planets. ... Presentation of the solar system (not to scale) The solar system comprises the Earths Sun and the retinue of celestial objects gravitationally bound to it. ... Artists impression of roaster extrasolar planet HD 209458b (Osiris). ... 51 Pegasi (Flamsteed designation, HIP 113357 in the Hipparcos Catalogue, HD 217014 in the Henry Draper Catalogue) is the name of a Sun-like star 14. ... Pegasus is a northern constellation, named after the mythological Pegasus. ...

The name

The official name of the exoplanet is 51 Pegasi b; the 'b' is used to indicate that it is the first companion of its parent star. Further companions would be designated c, d, and so on. It has been nicknamed "Bellerophon", after Bellerophon, the Greek hero who tamed Pegasus (the Winged Horse), referring to the constellation of Pegasus in which the planet is located. Bellerophon killing Chimera Bellerophon (bearing darts) was a hero from Greek mythology whose greatest feat was to kill the Chimera, a monster usually depicted as with a lions head, a goats body, and a serpent-tail. ... Pegasus on roof of Poznań Opera House In Greek mythology, Pegasus (Pegasos) was a winged horse that was the foal of Poseidon, in his role as horse-god, and the Gorgon Medusa. ... Orion is a remarkable constellation, visible from most places on the globe at one time or another during the year. ... Pegasus is a northern constellation, named after the mythological Pegasus. ...

Characteristics

After its discovery, many teams confirmed the planet's existence and obtained more observations of its properties. It was discovered that the planet orbits the star in around 4 Earth days, and is much closer to it than Mercury is to our Sun, suffering temperatures of around 1000 degrees Celsius (1800 degrees Fahrenheit), yet is about half the mass of Jupiter (about 150 times that of the Earth). At the time, the presence of a huge world so close to its star was not compatible with theories of planet formation and was considered an anomaly. However, since then, numerous other 'hot Jupiters' have been discovered (see 55 Cancri and τ Boötis, for example), and astronomers are revising their theories of planet formation to account for them by studying orbital migration. Atmospheric characteristics Atmospheric pressure trace Potassium 31. ... A degree Celsius (°C) is a unit of temperature named after the Swedish astronomer Anders Celsius (1701-1744), who first proposed a similar system in 1742. ... Fahrenheit is a temperature scale named after the German physicist Gabriel Fahrenheit (1686–1736), who proposed it in 1724. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... The accretion theory, in astrophysics, is a scientific theory of the formation of our Solar system. ... 55 Cancri (abbreviated 55 Cnc; Bayer designation ρ1 Cancri, Rho-1 Cancri) is a nearby 6th magnitude star in the constellation Cancer. ... Tau Boötis (Ï„ Boo / Ï„ Boötis) is a 4th magnitude star in the constellation of Boötes. ...

It was initially assumed that 51 Pegasi b is a terrestrial planet, but it is now known to be a gas giant. It is sufficiently massive that its thick atmosphere is not blown away by the star's solar wind. A terrestrial planet or telluric planet is a planet which is primarily composed of silicate rocks. ... A gas giant is a large planet that is not composed mostly of rock or other solid matter. ... The plasma in the solar wind meeting the heliopause For the British comic, see Solar Wind (comic). ...

51 Pegasi b probably has a greater radius than Jupiter despite its lower mass. This is because its superheated atmosphere must be puffed up into a thick but tenuous layer surrounding it. Beneath this, the gases that make up the planet would be so hot that the planet would glow red. Clouds of silicates may exist in the atmosphere. In classical geometry, a radius of a circle or sphere is any line segment with one endpoint on the circle (i. ... In chemistry, a silicate is a compound consisting of silicon and oxygen (SixOy), one or more metals, and possibly hydrogen. ...

The planet is tidally locked to its star, always presenting the same face to it. Tidal locking makes one side of an astronomical body always face another, like the Moon facing the Earth. ...

(It may be of interest to note that the earlier, rocky-planet model was utilized as a setting by Hal Clement in the story "Exchange Rate".)

Discovery process

The exoplanet's discovery was announced on October 6, 1995 by Michael Mayor and Didier Queloz in Nature, volume 378, page 355, using the radial velocity method at the Observatoire de Haute-Provence with the Elodie spectrograph. Infrared image of the star GQ Lupi (A) orbited by a planet (b) at a distance of approximately 20 times the distance between Jupiter and our Sun. ... October 6 is the 279th day of the year (280th in Leap years). ... 1995 (MCMXCV in Roman) was a common year starting on Sunday of the Gregorian calendar. ... Michel Mayor (born 12 January 1942) is a professor at the Department of Astronomy at the University of Geneva. ... Didier Queloz, born 23 February 1966, is a Geneva-based astronomer with a prolific record in finding extrasolar planets. ... Nature is one of the oldest and most reputable scientific journals, first published on 4 November 1869. ... Sound waves emanating from an ambulance moving to the right. ... The Observatoire de Haute-Provence (OHP) was created in 1937 as a national facility for French astronomers although the first plans for a privately financed observatory date from as early as 1923. ...

After the announcement, on October 12, 1995, confirmation came from Dr. Geoffrey Marcy from San Francisco State University and Dr. Paul Butler from the University of California, Berkeley using the Hamilton Spectrograph at the Lick Observatory near San Jose in California. October 12 is the 285th day of the year in the Gregorian calendar (286th in leap years). ... 1995 (MCMXCV in Roman) was a common year starting on Sunday of the Gregorian calendar. ... Image:Geoff marcy. ... San Francisco State University is a branch of the California State University system. ... Categories: Astronomers stubs | Astronomers ... University of California, Berkeley The University of California, Berkeley (also known as California, Cal, UCB, UC Berkeley, The University of California, or simply Berkeley) is a public, coeducational university situated east of the San Francisco Bay in Berkeley, California, overlooking the Golden Gate. ... The Lick Observatory is an astronomical observatory, owned and operated by the University of California. ... Nickname: Capital of Silicon Valley Motto: Official website: http://www. ... Official language(s) English Capital Sacramento Largest city Los Angeles Area  - Total  - Width  - Length  - % water  - Latitude  - Longitude Ranked 3rd 410,000 km² 402. ...

Discovery method

The planet was discovered using a sensitive spectroscope that could detect the slight, regular velocity changes in the star's spectral lines of around 70 metres per second. These changes are caused by the planet's gravitational effects from just 7 million kilometres distance from the star. A spectroscope is a device which measures the spectrum of light. ...

This discovery of this first exoplanet established a milestone in astronomical research, as it forced astronomers to realize that giant planets could exist in short period orbits. Once astronomers realized that it was worth looking for giant planets with the currently available technology, much more telescope time was devoted to radial velocity planet searches, and hence many more exoplanets in the Sun's neighbourhood have been discovered.

See also

• Extrasolar planet
• List of stars with confirmed extrasolar planets
• PSR 1257+12, the first star discovered with exoplanets.

Infrared image of the star GQ Lupi (A) orbited by a planet (b) at a distance of approximately 20 times the distance between Jupiter and our Sun. ... The following are lists of stars with confirmed extrasolar planets. ... PSR 1257+12 (also catalogued as PSR B1257+12,PSR 1300+1240 and PSR J1300+1240) is a pulsar located 2630 light years from Earth. ...

External links

• Current Notes from the Extrasolar Planet Encyclopedia
• Extrasolar Visions: Information and pictures
• Velocity curve and information from the Geneva based Planet Search Team
• Velocity curves and information from the California & Carnegie Planet Search Team
• solstation entry