Gliese 581: Difference between revisions - Wikipedia

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'''Gliese 581''' is an [[stellar classification|M2.5V]] [[red dwarf]] star located 20.40 [[light year|light years]] away from Earth, in the [[constellation]] [[Libra (constellation)|Libra]]. It has the [[variable star]] designation HO Librae. It is first known to have been published in the [[Durchmusterung|BD catalogue]] in [[1863]] by [[Friedrich Wilhelm August Argelander]] as BD-07° 4003. Its mass is estimated to be approximately a third of the Sun. At least three [[planets]] are believed to be orbiting this [[star]]. One, about [[Neptune]]-sized, was discovered in [[2005]].<ref>{{cite journal | url=http://www.edpsciences.org/papers/aa/full/2005/45/aahh223/aahh223.html |author=Bonfils et al.|title=The HARPS search for southern extra-solar planets, VI. A Neptune-mass planet around the nearby M dwarf Gl 581 |journal = [[Astronomy and Astrophysics]] | volume=443 | year=2005 | pages=L15-L18 }}</ref> Another, having 1.5 times the radius of Earth, was discovered in [[2007]].<ref name="Udry, Astronomy and Astrophysics, 2007">{{cite journal | url=http://obswww.unige.ch/~udry/udry_preprint.pdf |author=Udry et al.|title=The HARPS search for southern extra-solar planets, XI. An habitable super-Earth (5 M_⊕) in a 3-planet system |journal = [[Astronomy and Astrophysics]] | volume=preprint | year=2007 | pages=preprint }}</ref> The latter is notable as it is the first possibly rocky [[exoplanet]] discovered which lies within the [[habitable zone]] of a star. Observations of the star also revealed the possibility of a third planet with a mass of roughly 8 Earths, and an orbit of 84 Earth days.

== Planetary system ==

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=== Gliese 581 c ===

{{main|Gliese 581 c}}

Gliese 581 c is a planet believed to be of 50% greater radius than Earth and about five times as massive, orbiting within the habitable zone of its parent star. The mean surface temperature has been estimated to lie between -3&nbsp;°C (for an Earth-like [[albedo]]) and 40&nbsp;°C (for a venus-like albedo)<ref>{{cite journal | url=http://obswww.unige.ch/~udry/udry_preprint.pdf |authorname="Udry et al.|title=The HARPS search for southern extra-solar planets, XI. An habitable super-Earth (5 M_⊕) in a 3-planet system |journal = [[Astronomy and Astrophysics]], | volume=preprint | year=2007 | pages=preprint }}"></ref>, assuming a rocky composition and an Earth-like atmosphere, suggesting the possibility of liquid water on a solid surface. However, given the closer-orbiting Neptune-mass planet, the system has undergone planetary migration and Gliese 581 c may have formed beyond the snowline, with a composition similar to icy bodies like Ganymede. Gliese 581 c completes a full orbit in just 13 days.

Gliese 581 c orbits one of the hundred closest stars to Earth, which has led some to suggest that Earth-like planets are much more common than previously speculated.<ref>[http://www.iht.com/articles/2007/04/25/news/planet.php 20 light years away, the most Earthlike planet yet] IHT.com</ref>