51 Pegasi b
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| Extrasolar planet | List of extrasolar planets | |
|---|---|---|
 |
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| Parent star | ||
| Star | 51 Pegasi | |
| Constellation | Pegasus | |
| Right ascension | (α) | 22h 57m 28.0s |
| Declination | (δ) | +20° 46′ 08″ |
| Apparent magnitude | (mV) | 5.49 |
| Distance | 50.1 ly (15.4 pc) |
|
| Spectral type | G4V | |
| Orbital elements | ||
| Semimajor axis | (a) | 0.0527 ± 0.0030 AU |
| Periastron | (q) | 0.0520 AU |
| Apastron | (Q) | 0.0534 AU |
| Eccentricity | (e) | 0.013 ± 0.012 |
| Orbital period | (P) | 4.230785 ± 0.000036 d (0.01158306 y) |
| Argument of periastron |
(ω) | 58° |
| Time of periastron | (T0) | 2,450,001.51 ± 0.61 JD |
| Semi-amplitude | (K) | 55.94 ± 0.69 m/s |
| Physical characteristics | ||
| Minimum mass | (m sin i) | 0.472 ± 0.039 MJ (150 M⊕) |
| Discovery information | ||
| Discovery date | 6 October 1995 | |
| Discoverer(s) | Michel Mayor and Didier Queloz |
|
| Detection method | Radial velocity (ELODIE) | |
| Discovery site |  Haute-Provence |
|
| Discovery status | Published | |
| Other designations | ||
| Database references | ||
| Extrasolar Planets Encyclopaedia |
data | |
| SIMBAD | data | |
51 Pegasi b, also unofficially named Bellerophon and or abbreviated as 51 Peg b, is an extrasolar planet approximately 50 light-years away in the constellation of Pegasus. 51 Pegasi b was the first planet to be discovered orbiting a Sun-like star (namely 51 Pegasi) and is the prototype for a class of planets called hot Jupiters.
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[edit] Name
The name 51 Pegasi b is the official astronomical name of the planet. As with all extrasolar planets, the 'b' is used to indicate that this planet was the first discovered companion of its parent star. Further undiscovered companions of 51 Pegasi would be designated c, d, e, f, and so on. All extrasolar planets have lowercase letter to differentiate from companion stars in the system (which are designated with an uppercase letter).
Though not officially recognized, the name "Bellerophon" is commonly used for the planet.[1] This name comes from the Greek hero Bellerophon, who tamed Pegasus (the Winged Horse). This has direct relations with the constellation in which lies the planet (Pegasus). This name is usually used as the informal name to show the similarities to the planets of the Solar system. Only two other extrasolar planets were given unofficial or informal names ("Osiris" and "Methuselah").
[edit] Discovery
The exoplanet's discovery was announced on October 6, 1995 by Michel Mayor and Didier Queloz in Nature,[2] using the radial velocity method at the Observatoire de Haute-Provence with the ELODIE spectrograph.
After the announcement, on October 12, 1995, confirmation came from Geoffrey Marcy from San Francisco State University and Paul Butler from the University of California, Berkeley using the Hamilton Spectrograph at the Lick Observatory near San Jose in California.
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.
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.
[edit] Physical 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, and moves at an orbital speed of 136 km/s, yet has a minimum mass about half that 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.
Assuming the planet is perfectly grey with no greenhouse or tidal effects, and a Bond albedo of 0.1, the temperature would be 1265K (around 1000 degrees Celsius / 1800 degrees Fahrenheit). This is between the predicted temperatures of HD 189733 b and HD 209458 b (1180-1392K), before they were measured.[3]
It was initially assumed that 51 Pegasi b is a terrestrial planet, but it is now believed to be a gas giant. It is sufficiently massive that its thick atmosphere is not blown away by the star's solar wind.
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.
The planet is tidally locked to its star, always presenting the same face to it.
The planet (with Upsilon Andromedae b) is deemed a candidate for direct imaging by Planetpol.[4] It is also a candidate for "near-infrared characterisation.... with the VLTI Spectro-Imager".[3]
The earlier, rocky-planet model was utilized as a setting by Hal Clement in the story "Exchange Rate".
[edit] See also
[edit] References
- ^ http://jumk.de/astronomie/exoplanets/51-pegasi.shtml
- ^ Mayor, Michael; Queloz, Didier (1995). "A Jupiter-mass companion to a solar-type star". Nature 378 (6555): 355–359. doi:.
- ^ a b Renard, S.; Absil, O.; Berger, J. -P.; Bonfils, X.; Forveille, T.; Malbet, F. (2008). "Prospects for near-infrared characterisation of hot Jupiters with the VLTI Spectro-Imager (VSI)". arΧiv: 0807.3014v1 [astro-ph].
- ^ Lucas, P. W.; Hough, J. H.; Bailey, J. A.; Tamura, M.; Hirst, E.; Harrison, D. (2007). "Planetpol polarimetry of the exoplanet systems 55 Cnc and tau Boo". arΧiv: 0807.2568v1 [astro-ph].
- Butler et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal 646 (1): 505–522. doi:. http://www.iop.org/EJ/article/0004-637X/646/1/505/64046.html. (web version)
[edit] External links
- "51 Pegasi". SolStation. http://www.solstation.com/stars2/51pegasi.htm. Retrieved on 2008-07-03.
- "51 Peg". Exoplanets. http://media4.obspm.fr/exoplanets/base/etoile.php?nom=51+Peg.
- ""Bellerophon" - 51 Pegasi b". Extrasolar Visions. http://www.extrasolar.net/planettour.asp?StarCatId=&PlanetId=1. Retrieved on 2008-07-03.
- "The First Extrasolar Planet around a Solar-type Star". University of Geneva. http://obswww.unige.ch/~udry/planet/51peg.html. Retrieved on 2008-07-03.
- "The Planet Around 51 Peg". Lick Observatory. http://exoplanets.org/esp/51peg/51peg.shtml. Retrieved on 2008-07-03.
