Irregular moon: Difference between revisions
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In [[Astronomy]], an '''irregular satellite''' is a [[natural satellite]] following an inclined, sometimes retrograde orbit and believed to be captured as opposed to a regular satellite, formed ''in situ''. |
In [[Astronomy]], an '''irregular satellite''' is a [[natural satellite]] following an inclined, sometimes [[retrograde]] orbit and believed to be captured as opposed to a regular satellite, formed ''in situ''. |
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[[Image:TheIrregulars.svg|thumb|400px|Irregular satellites of Jupiter (red), Saturn (yellow), Uranus (green) and Neptune (blue)]] |
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Eighty-six irregular satellites have been discovered since 1997 orbiting all four giant planets. Only [[Phoebe (moon)|Phoebe]] the largest irregular satellite of Saturn and [[Himalia (moon)|Himalia]], the largest irregular satellite of Jupiter and a dozen others have |
Eighty-six irregular satellites have been discovered since 1997 orbiting all four giant planets. Only [[Phoebe (moon)|Phoebe]] the largest irregular satellite of Saturn and [[Himalia (moon)|Himalia]], the largest irregular satellite of Jupiter and a dozen others have been discovered earlier. |
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There's no widely accepted precise definition of the irregular satellite. Typically, the semi-major axis is compared with the [[Hill sphere]] (the gravitational influence sphere) <math>r_H</math>. |
There's no widely accepted precise definition of the irregular satellite. Typically, the semi-major axis is compared with the [[Hill sphere]] (the gravitational influence sphere) <math>r_H</math>. |
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Irregular satellites have semi-major axes greater than 0.05 <math>r_H</math> and [[apoapsis]] up to 0.65 <math>r_H</math>. <ref =name=Sheppard2006> [[Scott S. Sheppard]] ''Outer irregular satellites of the planets and their relationship with asteroids, comets and Kuiper Belt objects'' Asteroids, Comets, Meteors, Proceedings of the 229th Symposium of the International Astronomical Union held in Búzios, Rio de Janeiro, Brasil August 7-12, 2005, Edited by Daniela, L.; Sylvio Ferraz, M.; Angel, F. Julio Cambridge: Cambridge University Press, 2006., pp.319-334. [http://arxiv.org/abs/astro-ph/0605041 Preprint.] </ref> |
Irregular satellites have semi-major axes greater than 0.05 <math>r_H</math> and [[apoapsis]] up to 0.65 <math>r_H</math>. <ref =name=Sheppard2006> [[Scott S. Sheppard]] ''Outer irregular satellites of the planets and their relationship with asteroids, comets and Kuiper Belt objects'' Asteroids, Comets, Meteors, Proceedings of the 229th Symposium of the International Astronomical Union held in Búzios, Rio de Janeiro, Brasil August 7-12, 2005, Edited by Daniela, L.; Sylvio Ferraz, M.; Angel, F. Julio Cambridge: Cambridge University Press, 2006., pp.319-334. [http://arxiv.org/abs/astro-ph/0605041 Preprint.] </ref> |
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The diagram illustrates the orbits of the irregular satellites of the giants planets discovered so far. The semi-major axes are expressed as a fraction of the planet’s Hill sphere’s radius and the inclination is represented on Y axis. The satellites above the X axis are prograde, the satellites beneath are retrograde. |
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===References=== |
===References=== |
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Revision as of 22:42, 27 July 2006
In Astronomy, an irregular satellite is a natural satellite following an inclined, sometimes retrograde orbit and believed to be captured as opposed to a regular satellite, formed in situ.
Eighty-six irregular satellites have been discovered since 1997 orbiting all four giant planets. Only Phoebe the largest irregular satellite of Saturn and Himalia, the largest irregular satellite of Jupiter and a dozen others have been discovered earlier.
There's no widely accepted precise definition of the irregular satellite. Typically, the semi-major axis is compared with the Hill sphere (the gravitational influence sphere) . Irregular satellites have semi-major axes greater than 0.05 and apoapsis up to 0.65 . [1]
The diagram illustrates the orbits of the irregular satellites of the giants planets discovered so far. The semi-major axes are expressed as a fraction of the planet’s Hill sphere’s radius and the inclination is represented on Y axis. The satellites above the X axis are prograde, the satellites beneath are retrograde.
References
- ^ Scott S. Sheppard Outer irregular satellites of the planets and their relationship with asteroids, comets and Kuiper Belt objects Asteroids, Comets, Meteors, Proceedings of the 229th Symposium of the International Astronomical Union held in Búzios, Rio de Janeiro, Brasil August 7-12, 2005, Edited by Daniela, L.; Sylvio Ferraz, M.; Angel, F. Julio Cambridge: Cambridge University Press, 2006., pp.319-334. Preprint.
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