View source for Gliese 581 d

{{Planetbox begin 
| name = Gliese 581 d
}}
{{Planetbox image
| image = Gliese 581 d-v1.jpg
| caption = An artist's impression of Gliese 581 d and speculative moons.
}}
{{Planetbox star 
| star = [[Gliese 581]]
| constell = [[Libra (constellation)|Libra]]
| RA = {{RA|15|19|26}}  
| DEC = {{DEC|&minus;07|43|20}}
| app_mag = 10.55
| dist_ly = 20.3 ± 0.3
| dist_pc = 6.2 ± 0.1
| class = M3V
}} 
{{Planetbox orbit 
| period = 83.6 ± 0.7<ref name="udry">{{cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007A%26A...469L..43U&db_key=AST&nosetcookie=1|title=The HARPS search for southern extra-solar planets. XI. Super-Earths (5 and 8 M<sub>⊕</sub>) in a 3-planet system|author=Udry, S.; Bonfils, X.; Delfosse, X.; Forveille, T.; Mayor, M.; Perrier, C.; Bouchy, F.; Lovis, C.; Pepe, F.; Queloz, D.; Bertaux, J.-L.|journal=[[Astronomy and Astrophysics]]|volume=469|issue=3|year=2007|pages=L43 – L47|doi=10.1051/0004-6361:20077612|accessdate=2008-08-18}}</ref>
| semimajor = 0.25<ref name="udry" />
| eccentricity = 0.20 ± 0.10<ref name="udry" />
| arg_peri = 295 ± 28<ref name="udry" />
| semi_amp = 2.52 ± 0.17<ref name="udry" />
| t_peri = 2,452,936.9 ± 9.2<ref name="udry" />
}}
{{Planetbox character
| minimum_mass_earth = 7.7<ref name="udry" />
}} 
{{Planetbox discovery 
| discovery_date = [[24 April]] [[2007]]
| discoverers = [[Stéphane Udry|Udry]] et al.
| discovery_method = [[Radial velocity]]
| discovery_site = {{flag|Chile}}
| discovery_status = Published<ref name=udry />
}}
{{Planetbox reference
| star=Gliese+581
| planet=d
}}
{{Planetbox end}}

'''Gliese 581 d''' ({{pron-en|ˈɡliːzə}}) is an [[extrasolar planet]] approximately 20 [[light-year]]s away in the [[constellation]] of [[Libra (constellation)|Libra]].  Because of its mass, the planet is classified as a [[super-Earth]] planet. In late April 
2009 new observations by the original discovery team concluded that the planet is within the habitable zone where liquid water could exist.
== Discovery ==

The planet was discovered by the team of [[Stéphane Udry]] of the [[Geneva Observatory]] in [[Switzerland]] using the [[HARPS]] instrument on the [[European Southern Observatory]] 3.6 meter [[telescope]] in [[La Silla]], [[Chile]] on [[24 April]] [[2007]]. Udry's team employed the [[radial velocity]] technique, in which the size and [[mass]] of a [[planet]] are determined based on the small perturbations it induces in its parent star’s [[orbit]] via [[gravity]].<ref name=udry/>

The team is confident that the planet exists but recognizes that unlikely events could mimic its existence.  They believe the issue will be settled by upcoming studies.

Dynamical simulations of the Gliese 581 system assuming that the orbits of the three planets are [[coplanarity|coplanar]] show that the system becomes unstable if its component masses are so high as to correspond to an overall inclination angle of 10° or less.<ref>{{cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2008A%26A...479..277B&db_key=AST&nosetcookie=1|author=Beust, H. et al.|title=Dynamical evolution of the Gliese 581 planetary system|journal=[[Astronomy and Astrophysics]]|volume=479|issue=1|year=2008|pages=277–282|doi=10.1051/0004-6361:20078794|accessdate=2008-08-20}}</ref> For Gliese 581 d, the upper bound of its mass must be half that of 581 b; that is, 581 d's maximum is 44 Earth masses.<ref>Dividing the m sin i by "Sin(10/180 * PI)" on a radian-configured processor.</ref> At this mass it must be held together with a central heavy-element core like [[Saturn]] and maybe even [[HD 149026 b]].

== Climate and habitability ==

It was originally thought that Gliese 581 d orbits outside the theoretical [[habitable zone]] of its star.  However, further studies released in April of 2009 confirmed that the planet is within the habitable zone where liquid water could exist. According to Stephan Udry " d could be covered by a deep ocean, it is the first serious waterworld candidate."“Gliese 581 d is probably too massive to be made only of rocky material, but we can speculate that it is an icy planet that has migrated closer to the star,” .<ref>[http://www.space.com/scienceastronomy/070618_mm_gliese_581d.html SPACE.com - Hopes Dashed for Life on Distant Planet<!-- Bot generated title -->]</ref><ref>{{cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007A%26A...476.1365V&db_key=AST&nosetcookie=1|title=The Habitability of Super-Earths in Gliese 581|author=von Bloh, W.; Bounama, C.; Cuntz, M.; Franck, S.|journal=[[Astronomy & Astrophysics]]|volume=476|pages=1365 – 1371|doi=10.1051/0004-6361:20077939|accessdate=2008-08-18|year=2007}}</ref> Scientists originally believed that Gliese 581 d would be too cold for [[liquid]] [[water]] to exist, and therefore could not support [[life]] in forms as existing on Earth. However, since Earth's temperature would be about -18°C<ref>{{cite web|url=http://lwf.ncdc.noaa.gov/oa/climate/globalwarming.html#q1 |title=Global Warming Frequently Asked Questions |publisher=Lwf.ncdc.noaa.gov |date=2008-05-08 |accessdate=2009-01-18}}</ref> without any greenhouse gases, and due to a theorized [[greenhouse effect]] of Gliese 581 d, research now suggests that [[atmospheric]] conditions on the planet could create [[temperature]]s at which liquid water can exist, and therefore the planet may be capable of supporting life.<ref>http://arxiv.org/abs/0712.3219v4</ref><ref>{{cite web|url=http://www.centauri-dreams.org/?p=1625 |title=Centauri Dreams » Blog Archive » Gliese 581d: A Habitable World After All? |publisher=Centauri-dreams.org |date=2007-12-13 |accessdate=2009-01-18}}</ref><ref>{{cite web|author=Posted at 12:06 AM in Space Exploration |url=http://www.dailygalaxy.com/my_weblog/2007/06/another_super_e.html |title=New 'Super Earth 2' Discovered in Constellation Libra |publisher=Dailygalaxy.com |date=2007-06-15 |accessdate=2009-01-18}}</ref>

On 21 April 2009, [[European Organisation for Astronomical Research in the Southern Hemisphere|ESO]] announced, together with the discovery of [[Gliese 581 e]], that they had refined the models of Gliese 581 d's orbit, discovering it lay well within the habitable zone.<ref>{{cite web|url=http://www.eso.org/public/outreach/press-rel/pr-2009/pr-15-09.html|title=Lightest exoplanet yet discovered|publisher=eso.org|date=2009-04-21|accessdate=2009-04-21}}</ref>

== References ==
{{reflist|2}}

== External links ==

{{commonscat|Gliese 581}}

{{Gliese 581}}
{{Sky|15|19|26|-|07|43|20|20.3}}

[[Category:Extrasolar planets]]
[[Category:Libra constellation]]
[[Category:Super-Earths]]
[[Category:Terrestrial planets]]
[[Category:Exoplanets discovered in 2007]]

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