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An extrasolar planet (or exoplanet) is a planet which orbits a star other than the Sun, and therefore belongs to a planetary system other than our solar system.
Although extrasolar planets were long posited, no planets orbiting main sequence stars were discovered until the 1990s. The discovery of extrasolar planets raises the question of whether they support extraterrestrial life.
Discoveries regarding extrasolar planets were first published in 1989 [1] [2], when variations in the radial velocities of HD 114762 and γ Cep were explained as being caused by sub- brown dwarf masses, possibly giant planets (11 MJ & 2-3 MJ respectively). γ Cep had been the subject of a paper [3] the year before, but the question of a planetary companion as the cause was left open. Subsequent work in 1992 however concluded that no planet was likely present [4]. The case for HD 114762 has yet to be disproven.
The Polish astronomer Aleksander WolszczanAleksander Wolszczan (born 1946) is a Polish astronomer. Educated in Poland he moved in 1982 to the USA to work at Cornell University in Ithaca and Princeton University. Later he became an astronomy professor at the University of Pennsylvania in Philadelp also claimed to have found the first extrasolar planets in 19931993 is a common year starting on Friday and marked the Beginning of the International Decade to Combat Racism and Racial Discrimination (1993-2003 Events January January 1 Czechoslovakia divides. Establishment of independent Slovakia and Czech Republic., later confirmed, orbiting the pulsarCrab Nebula pulsar, showing surrounding nebular gases stirred by the pulsar's magnetic field and radiation. A pulsar which originally stood for pulsating radio source is a rapidly rotating neutron star, whose electromagnetic radiation is observed in regul PSR 1257+12PSR 1257+12 PSR B1257+12 ''PSR 1300+1240 ''PSR J1300+1240 is a pulsar, located 2630 light years distant, at 13 00 01. 00 right ascension, +12 40. 00 declination, as seen from Earth, in the constellation Virgo, using J2000 coordinates, hence the alternate. They are believed to be formed from the unusual remnants of the supernovaRemnant of Kepler's Supernova, SN 1604. A supernova is a type of stellar explosion which appears to result in the creation of a new star upon the celestial sphere. Nova" is Latin for "new"). The "super" prefix distinguishes this from a nova, which also in that produced the pulsar, in a second round of planet formation; or the rocky cores that remain of gas giants that survived the supernova, and spiralled in to their current orbits.
Extrasolar planets around solar-type stars began to be discovered in large numbers during the late 1990s as a result of improved telescopeNice Observatory. A telescope is perhaps the most important astronomical tool; such technology gathers (and focuses) electromagnetic radiation. Telescopes increase the apparent angular size of objects, as well as their apparent brightness. Galileo Galilei technologyTechnology ( Gr. tau;εχνολογια < τεχνη "craftsmanship" + λογος "word, reckoning" + the suffix ια) has more than one definition., such as CCD and computer-based image processing. Such advances allowed for more accurate measurements of stellar motion , allowing astronomers to detect planets, not visually (the luminosity of a planet being too low for such detection), but by measuring gravitational influences upon stars (see astrometrics and radial velocity method ). In addition, extrasolar planets can be detected by measuring the variance in a star's apparent luminosity, as a planet passes in front of it (see eclipse).
The first definitive extrasolar planet around a main sequence star was announced on October 6, 1995 by Michel Mayor and Didier Queloz; the primary star was 51 Pegasi. Since then dozens of planets have been detected, and original claims from the late 1980s confirmed, many by a team led by Geoffrey Marcy at the University of California's Lick and Keck Observatories. The first system to have more than one planet detected was Upsilon Andromedae. The majority of the detected planets have highly elliptical orbits.
As of mid 2004, there were 108 known planetary systems around main sequence stars, containing at least 123 known planets. In July, 2004, it was announced that Hubble had been used to detect an additional 100 planets, but the presence of these planets could not yet be confirmed. Besides this, many observations point to the existence of millions of comets also in extrasolar systems.
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