[Home]Extrasolar planet

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An extrasolar planet is a planet orbiting around a different star than the sun. The first extrasolar planets were reported in 1993, orbiting the pulsar PSR 1257+12. Subsequent investigation has determined that they are only planets in the technical sense of "sub-brown dwarf masses orbiting an object that is or once was a star"; it is believed that they are unusual remnants of the supernova that produced the pulsar, and did not form as conventional planets do.

The first "real" extra-solar planet was announced on October 6, 1995 by [Michael Mayor]? and [Didier Queloz]?; the primary star was [51 Pegasi]?. Since then dozens of planets have been detected, many by a team lead by [Geoffrey Marcy]? at the University of Southern California, Berkeley.

There are two main methods of detecting extra-solar planets, which are too faint to be detected by present conventional optical means. The first involves measuring the displacement in the parent star's spectral lines due to the doppler effect induced by the planet orbiting the star and moving it through mutual gravitation. The second involves catching the planet as it passes in front of the star's tiny disk -- [gravitational micro-lensing]? will cause the light of the star to "blip" in a distinctive way, and do so periodically as the planet completes multiple orbits. The second method is theoretically more sensitive, but is newer and has scored fewer successes. It also depends on the plane of the planet's orbit being aligned with the line of sight between the star and the Earth. As a result, any number of stars with planets that are not so aligned will be missed.

On November 27, 2001, astronomers using the [Hubble Space Telescope]? announced that they had detected the atmosphere of the planet orbiting HD 209458, from its absorption of light when passing in front of its star.

See below for a list of stars with extrasolar planets.

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Confirmed extrasolar planets

The following is a list of main sequence stars with confirmed extrasolar planets. Note that the masses of the planets are lower bounds only. If a planet is detected by the spectral line displacement method referred to above, no information is gained about the inclination of the planet's plane of orbit around its star, and a value for this is needed to calculate the mass. It has become customary to arbitrarily assume that the plane is exactly lined up with the line of sight from Earth (this produces the lowest possible mass consistent with the spectral line measurements).

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Last edited December 17, 2001 9:00 pm by Malcolm Farmer (diff)