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51 Pegasi b
From Wikipedia, the free encyclopedia
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This article or section is missing citations or needs footnotes. Using inline citations helps guard against copyright violations and factual inaccuracies.(September 2007) |
 51 Pegasi b (artist's conception) |
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| Discovery | |
|---|---|
| Discovered by: | Mayor and Queloz |
| Discovery site: | California, United States |
| Discovery date: | 1995 |
| Detection method(s): | Radial velocity |
| Orbital characteristics | |
| Semi-major axis: | 0.0527 ± 0.0030 AU |
| Eccentricity: | 0.013 ± 0.012 |
| Orbital period: | 4.230785 ± 0.000036 d |
| Angular distance: | 3.537 mas |
| Longitude of the periastron: | 58° |
| Time of periastron: | 2,450,001.51 ± 0.61 JD |
| Semi-amplitude: | 55.94 ± 0.69 m/s |
| Physical characteristics | |
| Mass: | >0.472 ± 0.039 MJ |
51 Pegasi b (or 51 Peg b for short) is the first planet discovered around a sun-like star outside the solar system. It is the prototypical hot Jupiter. It orbits the star 51 Pegasi in the Pegasus constellation.
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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.
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, with estimated temperatures of around 1000 degrees Celsius (1800 degrees Fahrenheit), 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.
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 earlier, rocky-planet model was utilized as a setting by Hal Clement in the story "Exchange Rate".
The exoplanet's discovery was announced on October 6, 1995 by Michel 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.
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.
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.
- Extrasolar planet
- List of stars with confirmed extrasolar planets
- PSR 1257+12, the first star discovered with exoplanets.
- Mayor et al. (1995). "A Jupiter-mass companion to a solar-type star". Nature 378: 355-359.
- Butler, R. et al. (2006). "Catalog of Nearby Exoplanets". The Astrophysical Journal 646: 505 – 522. (web version)