HOME WEB NEWS IMAGES CLASSIFIEDS YELLOW PAGESPOLLS - SURVEYS WIKI COUNTRIES PHOTOS US UK INDIA
Cities Stocks Weather Movies Coupons Travel Blogs Health Horoscope Maps ASIA EUROPE Classifieds Yellow Pages
 1
|
An artist\'s concept of a planetary system
A planetary system consists of the various non-stellar objects orbiting a star such as planets, moons, asteroids, meteoroids, comets, and cosmic dust.p. 394, The Universal Book of Astronomy, from the Andromeda Galaxy to the Zone of Avoidance, David J. Dsrling, Hoboken, New Jersey: Wiley, 2004. ISBN 0471265691.p. 314, Collins Dictionary of Astronomy, Valerie Illingworth, London: Collins, 2000. ISBN 0-00-710297-6. The Sun together with its planetary system, which includes Earth, is known as the Solar System.p. 382, Collins Dictionary of Astronomy.p. 420, A Dictionary of Astronomy, Ian Ridpath, Oxford, New York: Oxford University Press, 2003. ISBN 0-19-860513-7.
Contents |
Planetary systems are generally believed to form as part of the same process which results in star formation. Some early theories involved another star passing extremely close to the Sun, drawing material out from it which then coalesced to form the planets. However, the probability of such a near collision is now known to be far too low to make this a viable model. Accepted theories today argue that a protoplanetary disk forms by gravitational collapse of a molecular cloud and then evolves into a planetary system by collisions and gravitational capture.planetary systems, formation of, David Darling, entry in The Internet Encyclopedia of Science, accessed on line September 23, 2007.
Some planetary systems may form differently, however. Planets orbiting pulsars—stars which emit periodic bursts of electromagnetic radiation—have been discovered by the slight variations they cause in the timing of these bursts. Pulsars are formed in violent supernova explosions, and a normal planetary system could not possibly survive such a blast—planets would either evaporate, or the sudden loss of most of the mass of the central star would see them escape the gravitational hold of the star. One theory is that existing stellar companions were almost entirely evaporated by the supernova blast, leaving behind planet-sized bodies. Alternatively, planets may somehow form in the accretion disk surrounding pulsars.Planet formation scenarios, Philipp Podsiadlowski, pp. 149–165, in Planets around pulsars; Proceedings of the Conference, California Inst. of Technology, Pasadena, Apr. 30-May 1, 1992, edited by J. A. Phillips, J. E. Thorsest, and S. R. Kulkarni, ASP Conference Series, 36, 1993.
Artist\'s concept of a distant planetary system
Our solar system compared with the planetary system of 55 Cancri
 | This astronomy related article is a stub. You can help Wikipedia by expanding it. |
This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia
