View source for Gliese 581

{{short description|Star in the constellation Libra}}
{{Use dmy dates|date=May 2021}}
{{Starbox begin}}
{{Starbox image
|image={{Location map|100x100|AlternativeMap=Libra_constellation_map.svg
|alt=Gliese 581 is located in the constellation Libra
|caption=Location of Gliese 581 in the constellation [[Libra (constellation)|Libra]]|border=infobox|mark=Red_pog.png|width=280
|label=Gliese 581
|position=left
|lat=83
|long=44.2
}}|caption=
}}
{{Starbox observe
| epoch                = J2000.0
| constell             = [[Libra (constellation)|Libra]]<ref name="NASA">{{cite web|last1=Smith|first1=Yvette|title=NASA and NSF-Funded Research Finds First Potentially Habitable Exoplanet|url=http://www.nasa.gov/topics/universe/features/gliese_581_feature.html|website=nasa.gov|publisher=NASA|access-date=9 June 2016|archive-date=10 March 2013|archive-url=https://web.archive.org/web/20130310091735/http://www.nasa.gov/topics/universe/features/gliese_581_feature.html|url-status=dead}}</ref>
| ra                   = {{RA|15|19|26.82694}}<ref name="GaiaDR3"/>
| dec                  = {{DEC|−07|43|20.1895}}<ref name="GaiaDR3"/>
| appmag_v             = 10.56&nbsp;to&nbsp;10.58{{refn|group=note|Gliese 581 is classified as a [[BY Draconis variable]] in the [[General Catalogue of Variable Stars]].<ref>{{cite journal |last=Lopez-Morales |first=M. |display-authors=etal |date=2006 |title=Limits to Transits of the Neptune-mass planet orbiting Gl 581 |journal=[[Publications of the Astronomical Society of the Pacific]] |volume=118 |pages=1506–1509 |doi=10.1086/508904 |quote=V* HO Lib ... BY Draconis |arxiv=astro-ph/0609255 |bibcode=2006PASP..118.1506L |issue=849|s2cid=15156619 }} (page 2 of pre-print submitted 9 September 2006)</ref> This catalog gives a maximum magnitude of 10.56 and minimum of magnitude 10.58 for a relatively low 20 mmag (0.020 magnitudes) variability.<ref>{{cite web |publisher=[[Sternberg Astronomical Institute]] |title=General Catalogue of Variable Stars Query results |url=http://www.sai.msu.su/groups/cluster/gcvs/cgi-bin/search.cgi?search=HO+Lib |access-date=27 April 2009 |archive-date=23 September 2021 |archive-url=https://web.archive.org/web/20210923213559/http://www.sai.msu.su/groups/cluster/gcvs/cgi-bin/search.cgi?search=HO+Lib |url-status=live }}</ref> For full data see [http://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/html/ data description] and {{cite web |publisher=Sternberg Astronomical Institute |url=http://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/iii.dat |title=The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars |access-date=27 April 2009 |archive-date=20 June 2017 |archive-url=https://web.archive.org/web/20170620004609/http://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/iii.dat |url-status=dead }} }}
}}
{{Starbox character
| type = [[Main sequence]]
| class                = M3V<ref name="bonfils">{{Cite journal |doi=10.1051/0004-6361:200500193 |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 |issue=3 |pages=L15–L18 |year=2005 |last1=Bonfils |first1=Xavier |last2=Forveille |first2=Thierry |last3=Delfosse |first3=Xavier |last4=Udry |first4=Stéphane |last5=Mayor |first5=Michel |last6=Perrier |first6=Christian |last7=Bouchy |first7=François |last8=Pepe |first8=Francesco |last9=Queloz |first9=Didier |last10=Bertaux |first10=Jean-Loup |bibcode=2005A&A...443L..15B |arxiv=astro-ph/0509211 |s2cid=59569803 }}</ref>
| b-v                  = 1.61<ref name="sb0">{{ cite simbad | title=GJ 581 | access-date=21 August 2008 }}</ref>
| variable             = [[BY Draconis variable|BY Dra]]<ref name=gcvs>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref>{{refn|group=note|In 1994 Edward Weis concluded that Gliese 581, like half the 43 dwarf M stars he studied over a multi-year period, showed long term variability (and page 1137, Fig 1 shows Gliese 581 had magnitude 10.58 in 1982 and between 10.57 and 10.56 from 1985 to 1990).<ref>{{cite journal |last=Weis |first=E. W. |date=1994 |title=Long term variability in dwarf M stars |journal=[[The Astronomical Journal]] |volume=107 |issue=3 |pages=1138 |bibcode=1994AJ....107.1135W |doi=10.1086/116925 }}</ref> Bonfils noted in 2005 that Gliese 581 "has been classified as a variable star (HO Lib), but its variability (Weis 1994) is only marginally significant. If real it would be on a time scale of several years, with short term variability being at most ~0.006 mag."<ref>[[#bonfils|Bonfils]] page L15</ref> Measurements by [[Microvariability and Oscillations of STars telescope|MOST]] showed short term variability of about 5 mmag (half a percent) over a period of a few weeks.<ref>{{cite web |last=Matthews |first=J. M. |display-authors=etal |date=2007 |title=MOST Exoplanet System Photometry |url=http://nexsci.caltech.edu/workshop/2007/Matthews.pdf |pages=80 |access-date=27 April 2009 |archive-date=7 October 2022 |archive-url=https://web.archive.org/web/20221007015654/https://nexsci.caltech.edu/workshop/2007/Matthews.pdf |url-status=live }}</ref>}}
}}
{{Starbox astrometry
| radial_v             = {{val|−9.75|0.16}}<ref name="GaiaDR3"/>
| prop_mo_ra           = {{val|−1221.278|(37)}}
| prop_mo_dec          = {{val|−97.229|(27)}}
| pm_footnote          = <ref name="GaiaDR3"/>
| parallax             = 158.7183
| p_error              = 0.0301
| parallax_footnote    = <ref name="GaiaDR3"/>
| absmag_v             = 11.6<ref>From apparent magnitude and parallax.</ref>
}}
{{Starbox detail
| mass                 = {{val|0.295|0.010}}<ref name="vonStauffenberg2024"/>
| radius               = {{val|0.302|0.005}}<ref name="vonStauffenberg2024"/>
| luminosity_bolometric= {{val|0.012365|(68)}}<ref name="vonStauffenberg2024"/>
| luminosity_visual    = 0.002<ref group="note" name="luminosity_visual" />
| temperature          = {{val|3500|26|fmt=commas}}<ref name="vonStauffenberg2024"/>
| gravity              = {{val|4.97|0.11}}<ref name="vonStauffenberg2024"/>
| metal_fe             = {{val|−0.08|0.07}}<ref name="vonStauffenberg2024"/>
| rotation             = {{val|132.5|6.3|u=d}}<ref name=mnras452_3_2745 /> or {{val|148.1|0.9|u=d}}<ref name="Engle2023"/>
| rotational_velocity  = <2.0<ref name="vonStauffenberg2024"/>
| age_gyr              = {{val|9.5|1.5}}<ref name="Engle2023"/>
}}
{{Starbox catalog
| names                = {{odlist | V=HO Lib | BD=-07 4003 | GJ=581 | HIP=74995 | LFT=1195 | LHS=394 | LPM=564 | LTT=6112 | NLTT=39886 | TIC=36853511 | TYC=5594-1093-1 | Wolf=562}}<ref name=sb0 />
}}
{{Starbox reference
|Simbad                = gl+581|sn=The star
|Simbad2               = gl+581+e|sn2=e
|Simbad3               = gl+581+b|sn3=b
|Simbad4               = gl+581+c|sn4=c
|Simbad5               = gl+581+d|sn5=d
|Simbad6               = gl+581+f|sn6=f (artifact)
|Simbad7               = gl+581+g|sn7=g
}}
{{Starbox end}}

'''Gliese 581''' ({{IPAc-en|ˈ|ɡ|l|iː|z|ə}}) is a [[red dwarf]] star of [[stellar classification|spectral type]] M3V which hosts a planetary system, {{convert|20.5|ly|pc|lk=on|abbr=off}} away from [[Earth]] in the constellation [[Libra constellation|Libra]]. Its estimated mass is about a third of that of the [[Sun]], and it is the 101st closest known star system to the Sun.<ref name="Reylé2021"/> Gliese 581 is one of the oldest, least active M dwarfs known. Its low stellar activity improves the likelihood of its planets retaining significant [[atmosphere]]s, and lessens the sterilizing impact of [[solar flare|stellar flare]]s.<ref name="auto">{{cite web|url=http://hpf.psu.edu/2014/07/03/gliese-581/|title=Gliese 581 and the Stellar Activity Problem|date=3 July 2014|access-date=16 December 2018|archive-date=29 April 2019|archive-url=https://web.archive.org/web/20190429054406/http://hpf.psu.edu/2014/07/03/gliese-581/|url-status=live}}</ref>

==History of observations==
Gliese 581 is known at least from 1886, when it was included in [[Eduard Schönfeld]]'s ''Southern {{lang|de|Durchmusterung}} (SD)''—the fourth part of the ''{{lang|de|[[Bonner Durchmusterung]]}}''. The corresponding designation is BD -7 4003.<ref>{{cite web |url=http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-source=I/119&zone=-7&num=4003 |title=BD -7 4003 |work=Southern Durchmusterung |last=Schönfeld |first=Eduard |year=1886 |display-authors=etal |access-date=15 October 2015 |archive-date=23 December 2015 |archive-url=https://web.archive.org/web/20151223095256/http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-source=I/119&zone=-7&num=4003 |url-status=live }}</ref>

==Characteristics==
[[File:SunGliese581.png|thumb|left|upright=1.2|Size of the Sun (left) and Gliese 581 (right)]]
[[File:Gliese 581.gif|thumb|left|The star]]
The name ''Gliese 581'' refers to the catalog number from the 1957 survey ''[[Gliese Catalogue of Nearby Stars]]'' of 965 stars located within 20 [[parsec]]s of the [[Earth]]. Other names of this star include ''BD-07° 4003'' ([[Durchmusterung|BD catalogue]], first known publication) and ''HO Librae'' ([[variable star designation]]). It does not have an individual name such as ''[[Sirius]]'' or ''[[Procyon]]''.<ref name="sb0" /> The star is a [[red dwarf]] with [[stellar classification|spectral type]] M3V, located 20.5 [[light-year]]s away from [[Earth]]. It is located about two degrees north of [[Beta Librae]], the brightest star in the [[Libra constellation]]. Its mass is estimated to be approximately a third that of the [[Sun]], and it is the 101st closest known [[star system]] (including [[brown dwarf]]s) to the Sun.<ref name="Reylé2021"/>

An M-class dwarf star such as Gliese 581 has a much lower mass than the Sun, causing the core region of the star to fuse hydrogen at a significantly lower rate. From the apparent magnitude and distance, astronomers have estimated an effective temperature of 3200 K and a visual [[luminosity]] of 0.2% of that of the Sun.<ref name="Sel3">{{Cite journal |doi=10.1051/0004-6361:20077612 |arxiv=0704.3841 |title=The HARPS search for southern extra-solar planets XI. Super-Earths (5 and 8&nbsp;{{Earth mass}}) in a 3-planet system |journal=Astronomy & Astrophysics |volume=469 |issue=3 |pages=L43–L47 |last1=Udry |first1=Stéphane |last2=Bonfils |first2=Xavier |last3=Delfosse |first3=Xavier |last4=Forveille |first4=Thierry |last5=Mayor |first5=Michel |last6=Perrier |first6=Christian |last7=Bouchy |first7=François |last8=Lovis |first8=Christophe |last9=Pepe |first9=Francesco |last10=Queloz |first10=Didier |last11=Bertaux |first11=Jean-Loup |year=2007 |bibcode=2007A&A...469L..43U |s2cid=119144195 |url=http://exoplanet.eu/papers/udry_terre_HARPS-1.pdf |url-status=dead |archive-url=https://web.archive.org/web/20101008120426/http://exoplanet.eu/papers/udry_terre_HARPS-1.pdf |archive-date=October 8, 2010 }}</ref> However, a red dwarf such as Gliese 581 radiates primarily in the [[infrared|near infrared]], with peak emission at a wavelength of roughly 830 [[nanometre|nm]] (estimated using [[Wien's displacement law]], which assumes the star radiates as a [[black body]]), so such an estimate will underestimate the star's total luminosity.<ref name="bonfils" /> (For comparison, the peak emission of the Sun is roughly 530&nbsp;nm, in the middle of the visible part of the spectrum.) When radiation over the entire spectrum is taken into account (not just the part that humans are able to see), something known as the bolometric correction, this star has a [[absolute magnitude|bolometric luminosity]] 1.2% of the [[solar luminosity|Sun's total luminosity]].<ref name="Pineda2021" /> A planet would need to be situated much closer to this star in order to receive a comparable amount of energy as the Earth. The region of space around a star where a planet would receive roughly the same energy as the Earth is sometimes termed the "[[Goldilocks phenomenon|Goldilocks Zone]]", or, more prosaically, the [[habitable zone]]. The extent of such a zone is not fixed and is highly specific for each [[planetary system]].<ref>{{cite journal |doi=10.1051/0004-6361:20078091 |bibcode=2007A&A...476.1373S |title=Habitable planets around the star Gl 581? |journal=[[Astronomy and Astrophysics]] |volume=476 |issue=3 |year=2007 |pages=1373–1387 |last1=Selsis |first1=Franck |last2=Kasting |first2=James F. |last3=Levrard |first3=Benjamin |last4=Paillet |first4=Jimmy |last5=Ribas |first5=Ignasi |last6=Delfosse |first6=Xavier |arxiv=0710.5294 |s2cid=11492499 |ref=Selsis |url=https://hal.archives-ouvertes.fr/hal-00182743 |access-date=4 November 2018 |archive-date=4 November 2018 |archive-url=https://web.archive.org/web/20181104170049/https://hal.archives-ouvertes.fr/hal-00182743 |url-status=live }}</ref> Gliese 581 is a very old star. Its slow rotation makes it very inactive, making it better suited than most red dwarfs for having habitable planets.<ref name="auto"/>

Gliese 581 is classified as a [[variable star]] of the [[BY Draconis variable|BY Draconis]] type, and has been given the variable star designation HO Librae. This is a star that exhibits variability because of the presence of [[star spot]]s combined with the rotation of the star. However, the measured variability is close to the margin of error, and, if real, is most likely a long term variability.<ref name="bonfils"/> Its brightness is stable to 1%.<ref>{{cite journal |last=Dragomir |first=D. |display-authors=etal |date=2012 |title=A Search for Transits of GJ 581e and Characterization of the Host Star Variability Using MOST Space Telescope Photometry |journal=[[The Astrophysical Journal]] |volume=759 |issue=1 |pages=2f |doi=10.1088/0004-637X/759/1/2 |arxiv=1211.0577 |bibcode=2012ApJ...759....2D |s2cid=54956486 }}</ref> Gliese 581 emits X-rays.<ref>{{cite journal |last1=Schmitt |first1=J. H. M. M |last2=Fleming |first2=T. A |last3=Giampapa |first3=M. S. |date=1995 |title=The X-Ray View of the Low-Mass Stars in the Solar Neighborhood |journal=[[The Astrophysical Journal]] |volume=450 |issue=9 |pages=392–400 |bibcode=1995ApJ...450..392S |doi=10.1086/176149 |doi-access=free }}</ref>

==Planetary system==

{{Orbitbox planet begin
| table_ref = <ref name="debris"/><ref name="vonStauffenberg2024"/>
}}
{{Orbitbox planet
| exoplanet = [[Gliese 581e|e]]
| mass_earth = {{val|2.48|0.70|0.42}}
| semimajor = {{val|0.02799|0.0003}}
| period = {{val|3.1481|0.0004}}
| eccentricity = {{val|0.012|0.015|0.008}}
| inclination = {{val|47|15|13}}
}}
{{Orbitbox planet
| exoplanet = [[Gliese 581b|b]]
| mass_earth = {{val|20.5|6.2|3.5}}
| semimajor = {{val|0.0399|0.0005}}
| period = {{val|5.3686|0.0001}}
| eccentricity = {{val|0.0342|0.009|0.010}}
| inclination = {{val|47|15|13}}
}}
{{Orbitbox planet
| exoplanet = [[Gliese 581c|c]]
| mass_earth = {{val|6.81|0.21|1.16}}
| semimajor = {{val|0.0718|0.0008|0.0009}}
| period = {{val|12.9211|0.0008|0.0007}}
| eccentricity = {{val|0.032|0.027|0.021}}
| inclination = {{val|47|15|13}}
}}
{{OrbitboxPlanet disk
| disk = Debris disk
| periapsis = 25 ± 12 AU
| apoapsis =  >60
| inclination = 30° – 70
}}
{{Orbitbox end}}

The Gliese 581 planetary system is the gravitationally bound system comprising the star Gliese 581 and the objects that orbit it. The system is known to consist of at least three planets discovered using the [[radial velocity method]], along with a [[debris disk]]. The system's notability is due primarily to early [[exoplanetology]] discoveries, between 2008 and 2010, of possible [[terrestrial planets]] orbiting within its [[habitable zone]] and the system's relatively close proximity to the [[Solar System]] at 20 light years away. However, its observation history has been controversial due to false detections, and the radial velocity method yields little information about the planets themselves beyond their orbit and mass.

The confirmed planets are believed to be located close to the star with near-circular orbits. In order of distance from the star, these are [[Gliese 581e]], [[Gliese 581b]], and [[Gliese 581c]]. The letters represent the discovery order, with b being the first planet to be discovered around the star.

=== Observation history ===
The first announcement of a planet around the star was [[Gliese 581b]] discovered by astronomers at the [[Observatory of Geneva]] in Switzerland and [[Grenoble University]] in France. Detected in August 2005 and using extensive data from the ESO/[[HARPS]] spectrometer it was the fifth planet to be discovered around a red dwarf.<ref name="bonfils" /> Further observations by the same group resulted in the detection of two more planets, [[Gliese 581c]] and [[Gliese 581d]].<ref name="Sel3" /><ref>{{cite news |date=25 April 2007 |title=New 'super-Earth' found in space |url=http://news.bbc.co.uk/1/hi/sci/tech/6589157.stm |work=[[BBC News]] |access-date=20 October 2008 |archive-date=10 November 2012 |archive-url=https://web.archive.org/web/20121110172300/http://news.bbc.co.uk/2/hi/science/nature/6589157.stm |url-status=live }}</ref><ref name="bbc">{{cite news |last1=Rincon |first1=P. |last2=Amos |first2=J. |date=21 April 2009 |title=Lightest exoplanet is discovered |url=http://news.bbc.co.uk/1/hi/sci/tech/8008683.stm |work=[[BBC News]] |access-date=21 April 2009 |archive-date=24 April 2009 |archive-url=https://web.archive.org/web/20090424061149/http://news.bbc.co.uk/1/hi/sci/tech/8008683.stm |url-status=live }}</ref> The orbital period of Gliese 581d was originally thought to be 83 days but was later revised to a lower value of 67 days.<ref name="mayor" /> The revised orbital distance would place it at the outer limits of the habitable zone, the distance at which it is believed possible for [[liquid water]] to exist on the surface of a planetary body, given favourable atmospheric conditions. Gliese 581d was estimated to receive about 30% of the intensity of light the Earth receives from the Sun. By comparison, sunlight on Mars has about 40% of the intensity of that on Earth, though if high levels of [[carbon dioxide]] are present in the planetary atmosphere, the greenhouse effect could keep temperatures above freezing.<ref>{{cite journal |last1=von Bloh |first1=W. |date= 2008|title=Habitability of Super-Earths: Gliese 581c and 581d |doi=10.1017/S1743921308017031 |journal=Proceedings of the International Astronomical Union |volume=3|pages=503–506 |arxiv=0712.3219 |display-authors=1 |last2=Bounama |first2=C. |last3=Cuntz |first3=M. |last4=Franck |first4=S.|bibcode=2008IAUS..249..503V |s2cid=113406160 }}</ref>

The next discovery was the inner planet [[Gliese 581e]], also by the Observatory of Geneva and using data from the HARPS instrument, was announced on 21 April 2009.<ref name="mayor" /> This planet, at a [[minimum mass]] of 1.9 Earths, was at the time the least massive confirmed exoplanet identified around a main-sequence star.<ref name="bbc" />

On 29 September 2010, astronomers using the [[Keck Observatory]] proposed two additional planets, Gliese 581f and [[Gliese 581g]], both in nearly circular orbits based on analysis of a combination of data sets from the HARPS and [[High Resolution Echelle Spectrometer|HIRES]] instruments. The proposed planet Gliese 581f was thought to be a 7 Earth-mass planet in a 433-day orbit and too cold to support liquid water. The candidate planet Gliese 581g attracted more attention: nicknamed Zarmina's World by one of its discoverers,<ref name="Vogt 2010"/> the predicted mass of Gliese 581g was between 3 and 4 Earth-masses, with an orbital period of 37 days. The orbital distance was calculated to be well within the star's habitable zone, though the planet was expected to be tidally locked with one side of the planet always facing the star.<ref name="Vogt 2010"/><ref>{{cite press release | date=29 September 2010 | title=Keck Observatory discovers the first Goldilocks exoplanet | url=http://keckobservatory.org/news/keck_observatory_discovers_the_first_goldilocks_exoplanet/ | publisher=[[Keck Observatory]] | access-date=29 September 2010 | archive-date=22 August 2013 | archive-url=https://web.archive.org/web/20130822183158/http://keckobservatory.org/news/keck_observatory_discovers_the_first_goldilocks_exoplanet/ | url-status=dead }}</ref> In an interview with Lisa-Joy Zgorski of the [[National Science Foundation]], Steven Vogt was asked what he thought about the chances of life existing on Gliese 581g. Vogt was optimistic: "I'm not a biologist, nor do I want to play one on TV. Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say that ... the chances of life on this planet are 100%. I have almost no doubt about it."<ref name="Press Release 10-172 - Video"/>

Two weeks after the announcement of the discovery of {{nowrap|Gliese 581f}} and {{nowrap|Gliese 581g}}, astronomer [[Francesco Pepe]] of the Geneva Observatory reported that in a new analysis of 179 measurements taken by the [[HARPS]] spectrograph over 6.5 years, neither planet ''g'' nor planet ''f'' was detectable,<ref>{{Cite web |last=Kerr |first=Richard A. |title=Recently Discovered Habitable World May Not Exist |work=Science Now |publisher=[[American Association for the Advancement of Science|AAAS]] |date=12 October 2010 |url=https://www.science.org/content/article/recently-discovered-habitable-world-may-not-exist |access-date=24 January 2018 |archive-date=6 April 2023 |archive-url=https://web.archive.org/web/20230406004501/https://www.science.org/content/article/recently-discovered-habitable-world-may-not-exist |url-status=live }}</ref><ref>{{Cite web|last=Mullen|first=Leslie|title=Doubt Cast on Existence of Habitable Alien World |work=Astrobiology |date=12 October 2010 |url=https://www.astrobio.net/meteoritescomets-and-asteroids/doubt-cast-on-existence-of-habitable-alien-world/ |access-date=24 January 2018  |url-status=usurped |archive-url=https://web.archive.org/web/20180125015326/https://www.astrobio.net/meteoritescomets-and-asteroids/doubt-cast-on-existence-of-habitable-alien-world/ |archive-date=2018-01-25}}</ref> and the relevant measurements were included in a paper uploaded to the arXiv preprint server, though still unpublished in a refereed journal.<ref>{{cite arXiv |eprint=1109.2505 |last1=Forveille |first1=Thierry |last2=Bonfils |first2=Xavier |last3=Delfosse |first3=Xavier |last4=Alonso |first4=Roi |last5=Udry |first5=Stéphane |last6=Bouchy |first6=François |last7=Gillon |first7=Michaël |last8=Lovis |first8=Christophe |last9=Neves |first9=Vasco <!-- de Matos Ferreira Mendes --> |last10=Mayor |first10=Michel |last11=Pepe |first11=Francesco |last12=Queloz |first12=Didier |last13=Santos |first13=Nuno C. |last14=Ségransan |first14=Damien |last15=Almenara |first15=José M. |last16=Deeg |first16=Hans-Jörg |last17=Rabus |first17=Markus |title=The HARPS search for southern extra-solar planets XXXII. Only 4 planets in the Gl~581 system |date=September 12, 2011 |class=astro-ph.EP }}</ref> The non-existence of Gliese 581f was accepted relatively quickly: it was shown that the radial velocity variations that led to the claimed discovery of Gliese 581f were instead associated with the stellar activity cycle rather than an orbiting planet.<ref name="Robertson2013">{{cite journal|title=Hα Activity of Old M Dwarfs: Stellar Cycles and Mean Activity Levels for 93 Low-mass Stars in the Solar Neighborhood|author1=Robertson, Paul |author2=Endl, Michael |author3=Cochran, William D. |author4=Dodson-Robinson, Sarah E. |journal=The Astrophysical Journal|volume=764|issue=1|pages=article id. 3|date=2013|bibcode=2013ApJ...764....3R|doi=10.1088/0004-637X/764/1/3|arxiv = 1211.6091 |s2cid=119178575 }}</ref> Nevertheless, the existence of planet g remained controversial: Vogt responded in the media that he stood by the discovery<ref>{{Cite news|last=Grossman|first=Lisa|title=Exoplanet Wars: "First Habitable World" May Not Exist|magazine=[[Wired (magazine)|Wired]]|date=12 October 2010|url=https://www.wired.com/wiredscience/2010/10/gliese581g-may-not-exist|access-date=12 October 2010|archive-date=13 October 2010|archive-url=https://web.archive.org/web/20101013075724/http://www.wired.com/wiredscience/2010/10/gliese581g-may-not-exist/|url-status=live}}</ref><ref>{{cite news|last=Wall|first=Mike|title=Astronomer Stands By Discovery of Alien Planet Gliese 581g Amid Doubts|work=[[Space.com]]|date=13 October 2010|url=http://www.space.com/scienceastronomy/gliese-581g-discoverer-responds-101013.html|access-date=13 October 2010|archive-date=1 July 2012|archive-url=https://web.archive.org/web/20120701180603/http://www.space.com/9324-astronomer-stands-discovery-alien-planet-gliese-581g-doubts.html|url-status=live}}</ref> and questions arose as to whether the effect was due to the assumption of circular rather than eccentric orbits<ref>{{Cite news|last=Cowen|first=Ron|title=Swiss team fails to confirm recent discovery of an extrasolar planet that might have right conditions for life|work=[[Science News]]|date=13 October 2010|url=http://www.sciencenews.org/view/generic/id/64308/title/Existence_of_habitable_exoplanet_questioned|access-date=13 October 2010|archive-date=29 September 2012|archive-url=https://web.archive.org/web/20120929062842/http://www.sciencenews.org/view/generic/id/64308/title/Existence_of_habitable_exoplanet_questioned|url-status=dead}}</ref> or the statistical methods used.<ref>{{cite arXiv|eprint=1012.3754|title=Dos and don'ts of reduced chi-squared|author1=Rene Andrae|author2=Tim Schulze-Hartung|author3=Peter Melchior|date=2010|class=astro-ph.IM}}</ref>

Bayesian analysis found no clear evidence for a fifth planetary signal in the combined HIRES/HARPS data set,<ref>{{Cite journal |arxiv=1101.0800 |author1=Gregory |title=Bayesian Re-analysis of the Gliese 581 Exoplanet System |journal=Monthly Notices of the Royal Astronomical Society |volume=415 |issue=3 |pages=2523–2545 |date=2011|doi=10.1111/j.1365-2966.2011.18877.x |doi-access=free |bibcode=2011MNRAS.415.2523G |s2cid=38331034 }}</ref><ref>{{cite journal |arxiv=1102.3314 |author1=Mikko Tuomi |title=Bayesian re-analysis of the radial velocities of Gliese 581. Evidence in favour of only four planetary companions |date=2011 |doi=10.1051/0004-6361/201015995 |volume=528 |journal=Astronomy & Astrophysics |page=L5 |bibcode=2011A&A...528L...5T|s2cid=11439465 }}</ref> though other studies led to the conclusion that the data did support the existence of planet g, albeit with strong degeneracies in the parameters as a result of the first eccentric harmonic with the outer planet Gliese 581d.<ref>{{cite arXiv |eprint=1011.0186 |author1=Guillem Anglada-Escudé |title=Aliases of the first eccentric harmonic : Is GJ 581g a genuine planet candidate? |date=2010|class=astro-ph.EP }}</ref>

On 27 November 2012, the European Space Agency announced that the Herschel space observatory had discovered a [[comet]] belt "at 25 ± 12 AU to more than 60 AU".<ref name="debris"/> It must have "at least 10 times" as many comets as does the Solar system. This likely rules out [[Saturn]]-mass planets beyond 0.75 AU.<ref>{{cite news|title=Do missing Jupiters mean massive comet belts?|url=http://www.esa.int/SPECIALS/Herschel/SEMVDXDQZ9H_0.html|date=27 November 2012|author=ESA Herschel|access-date=27 November 2012|archive-date=30 November 2012|archive-url=https://web.archive.org/web/20121130193628/http://www.esa.int/SPECIALS/Herschel/SEMVDXDQZ9H_0.html|url-status=live}}</ref> However another (undiscovered) planet further out, say a Neptune-mass planet at 5 AU, might be required to keep the comet belt replenished.<ref name="debris"/>

Using the assumption that the noise present in the data was correlated (red noise rather than white noise), Roman Baluev called into question not only the existence of planet g, but Gliese 581d as well, suggesting there were only three planets (Gliese 581b, c, and e) present.<ref>{{cite journal | title=The impact of red noise in radial velocity planet searches: Only three planets orbiting GJ581? |author=Roman Baluev |journal=Monthly Notices of the Royal Astronomical Society |volume=429 |issue=3 |pages=2052–2068 | arxiv=1209.3154 |date=2013|bibcode = 2013MNRAS.429.2052B |doi = 10.1093/mnras/sts476 |doi-access=free }}</ref><ref>{{cite news|last1=Carlisle|first1=Camille|title=The Planet That is No More|url=http://www.skyandtelescope.com/astronomy-news/planet-that-is-no-more/|date=3 July 2014|newspaper=Sky & Telescope|access-date=4 July 2014|archive-date=7 July 2014|archive-url=https://archive.today/20140707135350/http://www.skyandtelescope.com/astronomy-news/planet-that-is-no-more/|url-status=live}}</ref> This result was further supported by a 2014 study, whose authors argued that [[Gliese 581d]] is "an artifact of stellar activity which, when incompletely corrected, causes the false detection of the planet ''g''."<ref name="SCI-20140703"/><ref name="NYT-20140708" /> While a response was published questioning the methodology of this study,<ref>{{Cite web|url=https://www.sciencedaily.com/releases/2015/03/150306102602.htm|title='Habitable' planet GJ 581d previously dismissed as noise probably does exist|website=ScienceDaily|access-date=4 January 2021|archive-date=31 May 2022|archive-url=https://web.archive.org/web/20220531032412/https://www.sciencedaily.com/releases/2015/03/150306102602.htm|url-status=live}}</ref><ref name="SCI-20150306"/><ref name="Astronomy Now">{{cite news |title=Reanalysis of data suggests 'habitable' planet GJ 581d really could exist |url=http://astronomynow.com/2015/03/09/reanalysis-of-data-suggests-habitable-planet-gj581d-really-does-exist/ |date=9 March 2015 |work=[[Astronomy Now]] |access-date=27 May 2015 |archive-date=20 May 2015 |archive-url=https://web.archive.org/web/20150520175016/http://astronomynow.com/2015/03/09/reanalysis-of-data-suggests-habitable-planet-gj581d-really-does-exist/ |url-status=live }}</ref> all subsequent studies of the radial velocity data have confirmed the stellar, rather than planetary, origin of the signal corresponding to Gliese 581d,<ref name="Robertson2015"/><ref name="Hatzes2016"/><ref name="Trifonov2018"/><ref name="Dodson-Robinson2022"/> though some dispute has remained.<ref name="Cuntz2024"/>

A 2024 study, in addition to confirming evidence for a three-planet system, determined the [[orbital inclination]] of the planets. This allowed their true masses to be determined; previously only [[minimum mass]]es were known. The planets' true masses are about 30% greater than their minimum masses.<ref name="vonStauffenberg2024"/>

=== Planets ===
[[File:GJ581orbits.svg|thumb|250px|The orbits of the Gliese 581 planetary system, based on a 2009 study which proposed a four-planet model (e, b, c, d).<ref name="mayor"/> In the picture, Gliese 581c is the third planet from the star.]]
Analysis of the radial velocity data has produced several models for the orbital arrangement of the system. 3-planet, 4-planet, 5-planet and 6-planet models have been proposed to address the available radial velocity data, with the current consensus being a 3-planet model (e, b, c).<ref name="SCI-20140703"/><ref name="Trifonov2018"/><ref name="vonStauffenberg2024"/><ref>{{cite web |title=GJ 581 |url=https://exoplanetarchive.ipac.caltech.edu/overview/GJ%20581 |website=[[NASA Exoplanet Archive]] |access-date=1 January 2022 |archive-date=11 May 2021 |archive-url=https://web.archive.org/web/20210511181349/https://exoplanetarchive.ipac.caltech.edu/overview/GJ%20581 |url-status=live }}</ref> Most of these models predict, however, that the inner planets are close in with circular orbits, while outer planets, particularly Gliese 581d, should it exist, are on more elliptical orbits.

Models of the habitable zone of Gliese 581 show that it extends from about 0.1 to 0.25 AU. The three confirmed planets orbit closer to the star than the inner edge of the habitable zone, while planets g and d would have orbited within it.<ref name="SCI-20140703"/>

==== Gliese 581e ====
{{Main|Gliese 581e}}
Gliese 581e is the innermost planet and, with a mass of 2.5 Earth masses, is the least massive of the three.<ref name="vonStauffenberg2024"/> Discovered in 2009, it is also the most recent confirmed planet to have been discovered in this system.<ref name="mayor"/> It takes 3.15 days to complete an orbit. Initial analyses suggested that the planet's orbit is quite elliptical but after correcting the radial velocity measurements for stellar activity, the data now indicate a circular orbit.<ref name="SCI-20140703"/>

==== Gliese 581b ====
{{Main|Gliese 581b}}
Gliese 581b is the most massive planet known to be orbiting Gliese 581 and was the first to be discovered.<ref name=bonfils /> It is about 20 times the mass of Earth and completes an orbit in 5.37 days.<ref name="vonStauffenberg2024"/>

==== Gliese 581c ====
{{Main|Gliese 581c}}
Gliese 581c is the third planet orbiting Gliese 581. It was discovered in April 2007.<ref name="Sel3" /> In their 2007 paper, Udry et al. asserted that if Gliese 581c has an Earth-type composition, it would have a radius of 1.5R<sub>🜨</sub>, which would have made it at the time "the most Earth-like of all known exoplanets".<ref name="Sel3" /> A direct measurement of the radius cannot be taken because, viewed from Earth, the planet does not [[astronomical transit|transit]] its star. The mass of the planet is 6.8 times that of Earth.<ref name="vonStauffenberg2024"/> The planet initially attracted attention as being potentially habitable, though this has since been discounted.<ref name="greenhouse">{{cite journal |last=von Bloh |first=W. |display-authors=etal |date=2007 |title=The Habitability of Super-Earths in Gliese 581 |volume=476 |pages=1365–71 |bibcode=2007A&A...476.1365V |doi=10.1051/0004-6361:20077939 |journal=Astronomy and Astrophysics |issue=3 |arxiv=0705.3758 |s2cid=14475537 }}</ref> The mean blackbody surface temperature has been estimated to lie between −3&nbsp;°C (for a Venus-like [[albedo]]) and 40&nbsp;°C (for an Earth-like albedo),<ref name="Sel3" /> however, the temperatures could be much higher (about 500 degrees Celsius) due to a [[runaway greenhouse effect]] akin to that of [[Venus]].<ref name="greenhouse" /><ref name="von Bloh 2008 503–506">{{cite journal |last=von Bloh |first=W. |display-authors=etal |date=2008 |title=Habitability of Super-Earths: Gliese 581c & 581d |journal=Proceedings of the International Astronomical Union |volume=3 |issue=S249 |pages=503–506 |doi=10.1017/S1743921308017031 |arxiv=0712.3219 |bibcode=2008IAUS..249..503V |s2cid=113406160 }}</ref> Some astronomers believe the system may have undergone [[planetary migration]] and Gliese 581c may have formed beyond the [[frost line (astrophysics)|frost line]], with a composition similar to icy bodies like [[Ganymede (moon)|Ganymede]]. Gliese 581c completes a full orbit in just under 13 days.<ref name="Sel3" />

==== Doubtful and disproven planets ====
===== Gliese 581g =====
{{main|Gliese 581g}}
Gliese 581g, unofficially known as Zarmina's World,<ref name="Vogt 2010"/> was a candidate [[exoplanet]] claimed to orbit Gliese 581, but its existence was ultimately refuted.<ref name="SCI-20140703"/> It was thought to orbit with a period of 36.6 days at a distance of 0.146 AU, placing it within the habitable zone, and to have a minimum mass of {{val|3.1|ul=Earth mass}}.<ref name="Vogt 2010"/>
===== Gliese 581d =====
{{main|Gliese 581d}}
Gliese 581d is a possible candidate exoplanet thought to orbit Gliese 581, which is frequently heavily disputed,<ref name="SCI-20140703"/><ref name="NYT-20140708">{{cite news |last=Quenqua |first=Douglas |title=Earthlike Planets May Be Merely an Illusion |url=https://www.nytimes.com/2014/07/08/science/earthlike-planets-may-be-merely-an-illusion.html |date=7 July 2014 |work=[[The New York Times]] |access-date=8 July 2014 |archive-date=29 March 2019 |archive-url=https://web.archive.org/web/20190329064605/https://www.nytimes.com/2014/07/08/science/earthlike-planets-may-be-merely-an-illusion.html |url-status=live }}</ref><ref name="SCI-20150306"/> as it has been argued by a number of studies to be a false positive originating from stellar activity.<ref name="Robertson2015"/><ref name="mnras452_3_2745"/><ref name="Hatzes2016"/><ref name="Trifonov2018"/><ref name="Dodson-Robinson2022"/><ref name="vonStauffenberg2024"/> The planet's minimum mass is thought to be {{val|6.98|ul=Earth mass}} and its radius, assuming an Earth-like composition, is estimated (assuming the planet's existence) to be {{val|2.2|ul=Earth radius}}, making it a [[super-Earth]]. Its orbital period is thought to be 66.87 days long, with a semi-major axis of 0.21847 AU, with an unconstrained eccentricity. Previous analyses suggested that the planet (if existing) orbits within the star's [[habitable zone]], where the temperatures are just right to support life.<ref name="scidaily2011">{{cite web |date=16 May 2011 |title=First Habitable Exoplanet? Climate Simulation Reveals New Candidate That Could Support Earth-Like Life |url=https://www.sciencedaily.com/releases/2011/05/110516080124.htm |work=[[ScienceDaily]] |access-date=16 May 2011 |archive-date=31 December 2019 |archive-url=https://web.archive.org/web/20191231180446/https://www.sciencedaily.com/releases/2011/05/110516080124.htm |url-status=live }}</ref><ref name="greenhouse" /><ref name="von Bloh 2008 503–506" />

===== Gliese 581f =====
Gliese 581f was a candidate exoplanet claimed to orbit Gliese 581,<ref name="Vogt 2010"/> but its existence was ultimately refuted.<ref name="Robertson2013"/> It was thought to orbit with a period of 433 days at a distance of 0.758 AU, and to have a minimum mass of {{val|7.0|ul=Earth mass}}.<ref name="Vogt 2010"/>

=== SETI ===
The Gliese 581 system has been the target of both [[Search for extraterrestrial intelligence|SETI]] and Active SETI searches for extraterrestrial life.
[[A Message from Earth]] (AMFE) is a high-powered digital radio signal that was sent on 9 October 2008, toward Gliese 581c. The signal is a digital time capsule containing 501 messages that were selected through a competition on the social networking site Bebo. The message was sent using the Yevpatoria RT-70 radio telescope radar telescope of the National Space Agency of Ukraine. The signal will reach Gliese 581 in early 2029.<ref>Moore, Matthew (9 October 2008). "Messages from Earth sent to distant planet by Bebo". .telegraph.co.uk. Archived from the original on 11 October 2008. Retrieved 9 October 2008.</ref>

Using optical SETI, [[Ragbir Bhathal]] claimed to have detected an unexplained pulse of light from the direction of the Gliese 581 system in 2008.<ref>{{Cite web|url=https://www.space.com/9303-claim-alien-signal-planet-gliese-581g-called-very-suspicious.html|title=Claim of Alien Signal from Planet Gliese 581g Called 'Very Suspicious'|first=Denise|last=Chow|date=11 October 2010|website=Space.com|access-date=19 May 2021|archive-date=19 May 2021|archive-url=https://web.archive.org/web/20210519214142/https://www.space.com/9303-claim-alien-signal-planet-gliese-581g-called-very-suspicious.html|url-status=live}}</ref>

In 2012, the International Centre for Radio Astronomy Research at Curtin University in Perth, Gliese 581 was precisely targeted by Australian Long Baseline Array using three radio telescope facilities across Australia and the Very Long Baseline Interferometry technique, however no candidate signals were found.<ref>{{cite web|url=https://www.universetoday.com/95598/first-seti-search-of-gliese-581-finds-no-signs-of-et/|title=First SETI Search of Gliese 581 Finds No Signs of ET - Universe Today|date=5 June 2012|access-date=4 January 2021|archive-date=27 February 2021|archive-url=https://web.archive.org/web/20210227043819/https://www.universetoday.com/95598/first-seti-search-of-gliese-581-finds-no-signs-of-et/|url-status=live}}</ref>

=== Debris disk ===
At the outer edge of the system is a massive debris disk containing more comets than the Solar System. The debris disc has an inclination between 30° and 70°.<ref name="debris"/> If the planetary orbits lie in the same plane, their masses would be between 1.1 and 2 times the minimum mass values.<ref group="note">The radial velocity method allows the determination of the minimum mass which is the product of the true mass with the sine of the orbital inclination, denoted <var>m</var>&nbsp;sin&nbsp;<var>i</var>. In general the inclination is unknown. For a given inclination, the true mass is therefore the minimum mass multiplied by 1/sin&nbsp;<var>i</var>.</ref> This is supported by a 2024 study, which found an inclination for the planetary orbits of about 47°.<ref name="vonStauffenberg2024"/>

==See also==
* [[Habitability of red dwarf systems]]
* [[Lists of exoplanets]]
* [[Gliese 876]]

==Notes==
{{Reflist|group=note|refs=

<ref group="note" name="luminosity_visual">Taking the absolute magnitude of Gliese 581, <math>\begin{smallmatrix}M_{V_{\ast}}=11.59\end{smallmatrix}</math>, with the absolute magnitude of the Sun, <math>\begin{smallmatrix}M_{V_{\odot}}=4.83\end{smallmatrix}</math>, the visual luminosity can be calculated from, <math>\begin{smallmatrix}\frac{L_{V_{\ast}}}{L_{V_{\odot}}}=10^{0.4\left(M_{V_{\odot}} - M_{V_{\ast}}\right)}\end{smallmatrix}</math> .</ref>

}}
{{clear}}

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<ref name="Press Release 10-172 - Video">NSF. [https://www.nsf.gov/news/news_videos.jsp?cntn_id=117765&media_id=68454&org=NSF Press Release 10-172 – Video] {{Webarchive|url=https://web.archive.org/web/20210211090625/https://www.nsf.gov/news/news_videos.jsp?cntn_id=117765&media_id=68454&org=NSF |date=11 February 2021 }}. Event occurs at 41:25–42:31. See {{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=29 September 2010 |url=https://www.nytimes.com/2010/09/30/science/space/30planet.html?_r=1 |title=New Planet May Be Able to Nurture Organisms |work=[[The New York Times]] |access-date=30 September 2010 |archive-date=14 September 2017 |archive-url=https://web.archive.org/web/20170914035005/http://www.nytimes.com/2010/09/30/science/space/30planet.html?_r=1 |url-status=live }}</ref>

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<ref name="Dodson-Robinson2022">{{Cite journal |last1=Dodson-Robinson |first1=Sarah E. |last2=Delgado |first2=Victor Ramirez |last3=Harrell |first3=Justin |last4=Haley |first4=Charlotte L. |date=2022-04-01 |title=Magnitude-squared Coherence: A Powerful Tool for Disentangling Doppler Planet Discoveries from Stellar Activity |journal=The Astronomical Journal |volume=163 |issue=4 |pages=169 |doi=10.3847/1538-3881/ac52ed |arxiv=2201.13342 |bibcode=2022AJ....163..169D |s2cid=246430514 |issn=0004-6256 |doi-access=free }}</ref>

<ref name="Engle2023">{{Cite journal |last1=Engle |first1=Scott G. |last2=Guinan |first2=Edward F. |date=September 2023 |title=Living with a Red Dwarf: The Rotation-Age Relationships of M Dwarfs |journal=[[The Astrophysical Journal Letters]] |volume=954 |issue=2 |pages=L50 |doi=10.3847/2041-8213/acf472 |doi-access=free |arxiv=2307.01136 |bibcode=2023ApJ...954L..50E}}</ref>

<ref name="Cuntz2024">{{Cite journal |last1=Cuntz |first1=Manfred |last2=Engle |first2=Scott G. |last3=Guinan |first3=Edward F. |date=January 2024 |title=The Once-canceled Habitable-zone Super-Earth Gliese 581d Might Indeed Exist! |journal=[[Research Notes of the AAS]] |volume=8 |issue=1 |page=20 |doi=10.3847/2515-5172/ad1de4 |doi-access=free |bibcode=2024RNAAS...8...20C}}</ref>

<ref name="vonStauffenberg2024">{{cite journal|last1=von Stauffenberg|first1=A.|last2=Trifonov|first2=T.|last3=Quirrenbach|first3=A.|last4=Reffert|first4=S.|last5=Kaminski|first5=A.|last6=Dreizler|first6=S.|last7=Ribas|first7=I.|last8=Reiners|first8=A.|last9=Kürster|first9=M.|last10=Twicken|first10=J. D.|last11=Rapetti|first11=D.|last12=Caballero|first12=J. A.|last13=Amado|first13=P. J.|last14=Béjar|first14=S. V. J.|last15=Cifuentes|first15=C.|last16=Góngora|first16=S.|last17=Hatzes|first17=A. P.|last18=Henning|first18=Th.|last19=Montes|first19=D.|last20=Morales|first20=J. C.|last21=Schweitzer|first21=A.|display-authors=3|title=The CARMENES search for exoplanets around M dwarfs. Revisiting the GJ 581 multi-planetary system with new Doppler measurements from CARMENES, HARPS, and HIRES|journal=Astronomy & Astrophysics|date=2024-06-05|issn=0004-6361|arxiv=2407.11520|doi=10.1051/0004-6361/202449375|page=|bibcode=2024A&A...688A.112V }}</ref>

}}

==External links==
{{Wikinews|First earthlike planet outside solar system discovered | Discovery of smallest exoplanet yields 'extraordinary' find}}
{{Commons category|Gliese 581}}
* [http://www.space.com/scienceastronomy/070424_hab_exoplanet.html Major Discovery: New Planet Could Harbor Water and Life] {{Webarchive|url=https://web.archive.org/web/20101224061707/http://www.space.com/scienceastronomy/070424_hab_exoplanet.html |date=24 December 2010 }} Space.com
* [http://www.solstation.com/stars/gl581.htm Gliese 581 / HO Librae] {{Webarchive|url=https://web.archive.org/web/20081010163609/http://www.solstation.com/stars/gl581.htm |date=10 October 2008 }} Solstation.com
* [https://web.archive.org/web/20120510094317/http://exoplanet.eu/star.php?st=Gl+581 ''Extrasolar Planets Encyclopaedia'': Gl 581]
* [http://www.astronomycast.com/astronomy/planets/extrasolar-planets/ep-202-the-planets-at-gliese-581/ AstronomyCast: Gliese 581] {{Webarchive|url=https://web.archive.org/web/20101016071718/http://www.astronomycast.com/astronomy/planets/extrasolar-planets/ep-202-the-planets-at-gliese-581/ |date=16 October 2010 }}
* [https://web.archive.org/web/20081223194115/http://www.satsig.net/seticalc.htm SETI Range Calculator]
* [http://www.sciam.com/article.cfm?articleID=25A261F0-E7F2-99DF-313249A4883E6A86&chanID=sa007 All Wet? Astronomers Claim Discovery of Earth-like Planet] {{Webarchive|url=https://web.archive.org/web/20071013164438/http://www.sciam.com/article.cfm?articleID=25A261F0-E7F2-99DF-313249A4883E6A86&chanID=sa007 |date=13 October 2007 }}, [[Scientific American]]
* [http://webarchive.nationalarchives.gov.uk/20100604044125/http%3A//cc.joensuu.fi/%7Etniemi/starmaps/GJ581.png Position of Gliese 581 marked on local space] (Top right corner)
* [http://www.allthesky.com/constellations/lib35.html Photo of Constellation Libra with Gliese 581] {{Webarchive|url=https://web.archive.org/web/20090206043707/http://allthesky.com/constellations/lib35.html |date=6 February 2009 }}
* [http://cosmographica.com/gallery/extrasolar/Gliese581c/index.html Artist conceptions of planets of Gliese 581] {{Webarchive|url=https://web.archive.org/web/20110928044147/http://cosmographica.com/gallery/extrasolar/Gliese581c/index.html |date=28 September 2011 }}
* [https://web.archive.org/web/20070617225754/http://gnews.wustl.edu/gn131/gliese581c.htm Speculation about geology/geochemistry of Gliese 581c] [http://geochemsoc.org/ ''The Geochemical Society''] {{Webarchive|url=https://web.archive.org/web/20090411110655/http://www.geochemsoc.org/ |date=11 April 2009 }}
* [http://news-info.wustl.edu/news/page/normal/9607.html Computer models suggest planetary and extrasolar planet atmospheres – A gas, gas, gas] {{Webarchive|url=https://web.archive.org/web/20080705130225/http://news-info.wustl.edu/news/page/normal/9607.html |date=5 July 2008 }} [[Washington University in St. Louis]]
* [http://www.lpl.arizona.edu/~rory/research/xsp/dynamics/ Extrasolar Planet Interactions] {{Webarchive|url=https://web.archive.org/web/20160505160348/http://www.lpl.arizona.edu/~rory/research/xsp/dynamics/ |date=5 May 2016 }} by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona
* [https://web.archive.org/web/20071023075235/http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20070424/new_planet_070424/20070424?hub=SciTech Earth-like planet found that may support life] Ctv.ca
* [http://members.misty.com/don/g581.html Gliese 581 – The "Red Dwarf" and implications for its "earthlike" planet Gliese 581c] {{Webarchive|url=https://web.archive.org/web/20101205160305/http://members.misty.com/don/g581.html |date=5 December 2010 }}
* [http://video.foxnews.com/v/1301110758001/earths-twin-discovered/ Earth's Twin Discovered?] {{Webarchive|url=https://web.archive.org/web/20111201170804/http://video.foxnews.com/v/1301110758001/earths-twin-discovered/ |date=1 December 2011 }}

{{Gliese 581}}
{{Stars of Libra}}
{{Extraterrestrial life}}
{{Portal bar|Stars|Spaceflight|Outer space|Solar System}}
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{{Good article}}

{{DEFAULTSORT:Gliese 581}}
[[Category:Gliese 581| ]]
[[Category:M-type main-sequence stars]]
[[Category:BY Draconis variables]]
[[Category:Libra (constellation)]]
[[Category:Planetary systems with three confirmed planets]]
[[Category:Circumstellar disks]]
[[Category:Gliese and GJ objects|0581]]
[[Category:Hipparcos objects|074995]]
[[Category:Objects with variable star designations|Librae, HO]]
[[Category:Durchmusterung objects|BD-07 4003]]
[[Category:TIC objects|36853511]]
[[Category:Wolf objects|0562]]