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'{{short description|Star in the constellation Aquarius}} {{Starbox begin | name = Gliese 876 }} {{Starbox image | image = {{Location mark | image = Aquarius constellation map.svg | width = 320 | float = center | position = right | mark = Red Circle(small).svg | mark_width = 10 | x = 335 | y = 560 }} | caption = Location of Gliese 876 in Aquarius (red dot) }} {{Starbox observe | epoch = J2000.0 | constell = [[Aquarius (constellation)|Aquarius]] | ra = {{RA|22|53|16.73258}}<ref name="GaiaDR3"/> | dec = {{DEC|−14|15|49.3041}}<ref name="GaiaDR3"/> | appmag_v = 10.15<ref name="van Leeuwen2007"/> | pronounce = {{IPAc-en|ˈ|ɡ|l|iː|z|ə}} }} {{Starbox character | class = M4V<ref name=lurie/> | r-i = 1.22{{citation needed|date=March 2018}} | v-r = 0.30{{citation needed|date=March 2018}} | b-v = {{val|1.597|0.035}}<ref name=Anderson_Francis_2012/> | u-b = 1.15{{citation needed|date=March 2018}} | variable = [[BY Draconis variable|BY Draconis]]<ref name=gcvs/> }} {{Starbox astrometry | radial_v = {{val|−2.09|0.15}}<ref name="GaiaDR3"/> | prop_mo_ra = {{val|957.715|0.041}} | prop_mo_dec = {{val|−673.601|0.031}} | pm_footnote = <ref name="GaiaDR3"/> | parallax = 214.0380 | p_error = 0.0356 | parallax_footnote = <ref name="GaiaDR3"/> | absmag_v = 11.81<ref name=Anderson_Francis_2012/> }} {{Starbox detail | mass = {{val|0.346|0.007}}<ref name="Pineda2021"/> | radius = {{val|0.372|0.004}}<ref name="Pineda2021"/> | luminosity = 0.01309{{±|0.00011}}<ref name="Pineda2021"/> | gravity = 4.89<ref name="bean2006"/> | temperature = {{val|3201|20|19|fmt=commas}}<ref name="Pineda2021"/> | metal_fe = {{val|+0.19|0.17}}<ref name=apj748_2_934/> | rotation = 96.9<ref name="correia2010"/> [[day]]s | rotational_velocity=0.16,<ref name="correia2010"/> | age_gyr = 0.1–9.9<ref name="correia2010"/><ref name="saffe2005"/> }} {{Starbox catalog | names = {{odlist | BD=-15°6290 | G=156-057 | HIP=113020 | V=IL&nbsp;Aquarii | LHS=530 | Ross=780 }}, GCTP 5546.00, Vys 337 }} {{Starbox reference |Simbad=Gliese+876|sn=Gliese 876 |Simbad2=GJ+876+d|sn2=d |Simbad3=GJ+876+c|sn3=c |Simbad4=GJ+876+b|sn4=b |Simbad5=GJ+876+e|sn5=e | NSTED = Gliese+876 | ARICNS = 01870 | EPE = Gliese+876 }} {{Starbox end}} '''Gliese 876''' is a [[red dwarf]] approximately 15 [[light-year]]s away from [[Earth]] in the [[constellation]] of [[Aquarius (constellation)|Aquarius]]. It is one of the closest known stars to the [[Sun]] confirmed to possess a [[planetary system]] with more than two planets, after [[Gliese 1061]], [[YZ Ceti]], [[Tau Ceti]], and [[Luyten's Star]]; as of 2018, four [[extrasolar planet]]s have been found to orbit the star. The planetary system is also notable for the orbital properties of its planets. It is the only known system of orbital companions to exhibit a near-triple conjunction in the rare phenomenon of [[Orbital resonance#Types of resonance|Laplace resonance]] (a type of resonance first noted in [[Jupiter]]'s inner three [[Galilean moons]]). It is also the first extrasolar system around a [[normal star]] with measured [[coplanarity]]. While planets b and c are located in the system's [[habitable zone]], they are [[giant planet]]s believed to be analogous to [[Jupiter]]. ==Distance and visibility== Gliese 876 is located fairly close to the [[Solar System]]. According to [[astrometry|astrometric]] measurements made by the [[Hipparcos]] [[satellite]], the star shows a [[parallax]] of 213.28 [[Minute of arc|milliarcsecond]]s,<ref name="van Leeuwen2007"/> which corresponds to a distance of {{Convert|4.69|pc|ly|lk=on}}.<ref name="correia2010"/> Despite being located so close to Earth, the star is so faint that it is invisible to the [[naked eye]] and can only be seen using a [[telescope]]. ==Stellar characteristics== [[File:ILAqrLightCurve.png|thumb|left|A [[Photometric_system#Photometric_letters|visual band]] [[light curve]] for IL&nbsp;Aquarii, adapted from Hosey ''et al.'' (2015)<ref name="Hosey"/>]] As a red dwarf, Gliese 876 is much less massive than the Sun: estimates suggest it has only 35% of the mass of the Sun.<ref name="Pineda2021"/> The surface [[temperature]] of Gliese 876 is cooler than the Sun and the star has a smaller radius.<ref name="johnson1983"/> These factors combine to make the star only 1.3% as [[luminosity|luminous]] as the Sun, and most of this is at [[infrared]] [[wavelength]]s. Estimating the age and [[metal-rich|metallicity]] of cool stars is difficult due to the formation of [[diatomic molecule]]s in their [[atmosphere]]s, which makes the [[stellar spectrum|spectrum]] extremely complex. By fitting the observed spectrum to model spectra, it is estimated that Gliese 876 has a slightly lower abundance of heavy elements compared to the Sun (around 75% the solar abundance of [[iron]]).<ref name="bean2006"/> Based on [[chromosphere|chromospheric]] activity the star is likely to be around 6.5 to 9.9 billion years old, depending on the theoretical model used.<ref name="saffe2005"/> However, its membership among the young disk population suggest that the star is less than 5 billion years old but the long rotational period of the star implies that it is at least older than 100 million years.<ref name="correia2010"/> Like many low-mass stars, Gliese 876 is a [[variable star]]. Its [[variable star designation]] is IL Aquarii and it is classified as a [[BY Draconis variable]]. Its brightness fluctuates by around 0.04 [[apparent magnitude|magnitudes]].<ref name="gcvs"/> This type of variability is thought to be caused by large [[starspot]]s moving in and out of view as the star rotates.<ref name="bopp1973"/> Gliese 876 emits X-rays like most Red Dwarfs would do.<ref name="schmitt1995"/> ==Planetary system== ===Observation history=== [[File:Gliese876Orbits.svg|thumb|right|upright=1.2|The orbits of the planets of Gliese&nbsp;876. Note that the strong gravitational interactions between the planets causes rapid orbital precession, so this diagram is only valid at the stated epoch.]] On June 23, 1998, an extrasolar planet was announced in [[orbit]] around Gliese&nbsp;876 by two independent teams led by [[Geoffrey Marcy]] and Xavier Delfosse.<ref name="Marcy1998"/><ref name="delfosse1998"/><ref name="Keck press release a"/> The planet was designated [[Gliese 876 b|Gliese&nbsp;876&nbsp;b]] and was detected by [[Doppler spectroscopy]]. Based on luminosity measurement, the circumstellar habitable zone (CHZ) is believed to be located between 0.116 and 0.227&nbsp;AU.<ref name="jones2005"/> On January 9, 2001, a second planet designated [[Gliese 876 c]] was detected, inside the orbit of the previously-discovered planet.<ref name="Keck press release b"/><ref name="Marcy2001"/> The relationship between the [[orbital period]]s initially disguised the planet's radial velocity signature as an increased [[eccentricity (orbit)|orbital eccentricity]] of the outer planet. Eugenio Rivera and Jack Lissauer found that the two planets undergo strong gravitational interactions as they orbit the star, causing the [[orbital elements]] to change rapidly.<ref name="Rivera2001"/> On June 13, 2005, further observations by a team led by Rivera revealed a third planet, designated [[Gliese 876 d|Gliese&nbsp;876&nbsp;d]] inside the orbits of the two Jupiter-size planets.<ref name="Rivera2005"/> In January 2009, the mutual inclination between planets b and c was determined using a combination of radial velocity and [[astrometry|astrometric]] measurements. The planets were found to be almost coplanar, with an angle of only 5.0{{±|3.9|2.3}}° between their orbital planes.<ref name="bean2009"/> On June 23, 2010, astronomers announced a fourth planet, designated [[Gliese 876 e|Gliese&nbsp;876&nbsp;e]]. This discovery better constrained the mass and orbital properties of the other three planets, including the high eccentricity of the innermost planet.<ref name="Rivera2010"/> This also filled out the system inside e's orbit; additional planets there would be unstable at this system's age.<ref name="Gerlach">{{cite journal|last1=Gerlach|first1=Enrico|last2=Haghighipour|first2=Nader|arxiv=1202.5865|date=2012|title=Can GJ 876 host four planets in resonance?|bibcode=2012CeMDA.113...35G|doi=10.1007/s10569-012-9408-0|volume=113|issue=1 |journal=Celestial Mechanics and Dynamical Astronomy|pages=35–47|s2cid=119210665}}</ref> In 2014, reanalysis of the existing radial velocities suggested the possible presence of two additional planets, which would have almost the same mass as Gliese 876 d,<ref name="Jenkins2014"/> but further analysis showed that these signals were artifacts of dynamical interactions between the known planets.<ref name="Hara2017">{{cite journal |arxiv=1609.01519|doi=10.1093/mnras/stw2261 |title=Radial velocity data analysis with compressed sensing techniques |year=2017 |last1=Hara |first1=Nathan C. |last2=Boué |first2=G. |last3=Laskar |first3=J. |last4=Correia |first4=A. C. M. |journal=Monthly Notices of the Royal Astronomical Society |volume=464 |pages=1220–1246 }}</ref> In 2018 a study using hundreds of new radial velocity measurements found no evidence for any additional planets.<ref name="Millholland2018"/> If this system has a comet disc, it is undetectable "brighter than the fractional dust luminosity 10⁻⁵" of a recent Herschel study.<ref name="nodebris">B. C. Matthews; forthcoming study promised in {{Cite journal|arxiv=1211.4898|title=A DEBRIS Disk Around The Planet Hosting M-star GJ581 Spatially Resolved with Herschel|journal=Astronomy and Astrophysics|date=2012|author=J.-F. Lestrade|display-authors=etal|doi = 10.1051/0004-6361/201220325|bibcode = 2012A&A...548A..86L|volume=548|pages=A86|s2cid=53704989}}</ref> None of these planets [[Astronomical transit|transit]] the star from the perspective of Earth, making it difficult to study their properties.<ref>As of 2006: {{cite journal|journal=The Astrophysical Journal|last1=Shankland|first1=PD|display-authors=etal|url=http://schwab.tsuniv.edu/papers/apj/gj876_2/reprint.pdf|volume=653|issue=1|pages=700–707|date=2006 |title=On the search for transits of the planets orbiting Gliese 876|doi=10.1086/508562|arxiv = astro-ph/0608489 |bibcode = 2006ApJ...653..700S |hdl=10211.3/170010|s2cid=875634}}. No transit has been found as of 2012, either; so they are unlikely.</ref> GJ 876 is a candidate parent system for the [[ʻOumuamua]] object. The trajectory of this interstellar object took it near the star about 820,000&nbsp;years ago with a velocity of 5&nbsp;km/s, after which it has been perturbed by six other stars.<ref>{{cite journal | title=Investigating the dynamical history of the interstellar object 'Oumuamua | last1=Dybczyński | first1=Piotr A. | last2=Królikowska | first2=Małgorzata | journal=Astronomy & Astrophysics | volume=610 | id=L11 | pages=12 | date=February 2018 | arxiv=1711.06618 | bibcode=2018A&A...610L..11D | doi=10.1051/0004-6361/201732309 | s2cid=119513894 }}</ref> ===Orbital arrangement=== Gliese 876 has a notable orbital arrangement. It is the first planetary system around a normal star to have mutual inclination between planets measured without transits (previously the mutual inclination of the planets orbiting the [[pulsar]] [[PSR B1257+12]] had been determined by measuring their gravitational interactions<ref name="konacki2003"/>). Later measurements reduced the value of the mutual inclination,<ref name="correia2010"/> and in the latest four-planet models the incorporation mutual inclinations does not result in significant improvements relative to coplanar solutions.<ref name="Rivera2010"/> The system has the second known example of a Laplace resonance with a 1:2:4 resonance of its planets. The first known example was Jupiter's closest [[Galilean moons]] - [[Ganymede (moon)|Ganymede]], [[Europa (moon)|Europa]] and [[Io (moon)|Io]]. Numerical integration indicates that the coplanar, four-planet system is stable for at least another billion years. This planetary system comes close to a triple [[Conjunction (astronomy and astrology)|conjunction]] between the three outer planets once per orbit of the outermost planet.<ref name="Rivera2010"/> ===Planets=== The outermost three of the known planets likely formed further away from the star, and migrated inward.<ref name=Gerlach/> {{OrbitboxPlanet begin | table_ref = <ref name="Millholland2018"/><ref name="Uncertainties" group="note"/> }} {{OrbitboxPlanet | exoplanet = [[Gliese 876 d|d]] | mass_earth = {{val|7.55|0.23}} | period = {{val|1.937793|0.000008}} | semimajor = {{val|0.021838|0.000000063|0.000000065}} | eccentricity = {{val|0.057|0.039}} | inclination = {{val|53.06|0.85}} }} {{OrbitboxPlanet | exoplanet = [[Gliese 876 c|c]] | mass = {{val|0.8357|0.0085}} | period = {{val|30.0972|0.0071|0.0073}} | semimajor = {{val|0.136044|0.000021|0.000022}} | eccentricity = {{val|0.2571|0.0019}} | inclination = {{val|53.06|0.85}} }} {{OrbitboxPlanet | exoplanet = [[Gliese 876 b|b]] | mass = {{val|2.6595|0.0299|0.0296}} | period = {{val|61.1057|0.0074}} | semimajor = {{val|0.218627|0.000017}} | eccentricity = {{val|0.0325|0.0016|0.0017}} | inclination = {{val|53.06|0.85}} }} {{OrbitboxPlanet | exoplanet = [[Gliese 876 e|e]] | mass_earth = {{val|15.8|1.7}} | period = {{val|123.83|0.7|0.66}} | semimajor = {{val|0.3501|0.0013|0.0012}} | eccentricity = {{val|0.03|0.023|0.024}} | inclination = {{val|53.06|0.85}} }} {{Orbitbox end}} ; Gliese 876 d {{main|Gliese 876 d}} Gliese 876 d, discovered in 2005, is the innermost known planet. With an estimated mass 7.55 times that of the [[Earth]], it is possible that it is a dense [[terrestrial planet]]. ; Gliese 876 c {{main|Gliese 876 c}} Gliese 876 c, discovered in 2001, is a 0.84 Jupiter-mass giant planet. It is in a 1:2 [[orbital resonance]] with the planet b, taking 30.097 days to orbit the star. The planet orbits within the habitable zone. Its temperature makes it more likely to be a Class III planet in the [[Sudarsky extrasolar planet classification]].<ref name="SudarskyBurrows2003">{{cite journal|last1=Sudarsky|first1=David|last2=Burrows|first2=Adam|last3=Hubeny|first3=Ivan|title=Theoretical Spectra and Atmospheres of Extrasolar Giant Planets|journal=The Astrophysical Journal|volume=588|issue=2|year=2003|pages=1121–1148|issn=0004-637X|doi=10.1086/374331|doi-access=free|arxiv=astro-ph/0210216|bibcode=2003ApJ...588.1121S|hdl=10150/280087|quote=<span style="font-family:LatinModern;"><small>'''GJ 876'''b and c are both Class '''III''' planets because their temperatures are too cool for a silicate layer to appear in the troposphere, but too hot for '''H₂O''' to condense ... Given somewhat lower incident irradiation than that of our scaled Kurucz model for '''GJ 876''', or given an observation of '''GJ 876'''b at apastron, some water condensation may occur in its outermost atmosphere, rendering it a '''Class II EGP'''.</small></span>}}</ref> The presence of surface liquid water is possible on sufficiently massive satellites should they exist. ; Gliese 876 b {{main|Gliese 876 b}} Gliese 876 b, discovered in 1998, is around twice the mass of [[Jupiter]] and revolves around its star in an orbit taking 61.106&nbsp;[[day]]s to complete, at a distance of only 0.219&nbsp;[[Astronomical unit|AU]], less than the distance from the Sun to [[Mercury (planet)|Mercury]].<ref name="butler2006"/> Its temperature makes it more likely to be a Class II or Class III planet in the Sudarsky model.<ref name="SudarskyBurrows2003"/> The presence of surface liquid water is possible on sufficiently massive satellites should they exist. ; Gliese 876 e {{main|Gliese 876 e}} Gliese 876 e, discovered in 2010, has a mass similar to that of the planet [[Uranus]] and its orbit takes 124 days to complete. ==See also== * [[List of nearest stars]] * [[Gliese 581]] * [[List of extrasolar planets]] ==Notes== {{reflist|group="note"|refs= <ref name="Uncertainties" group="note">Uncertainties in the planetary masses and semimajor axes do not take into account the uncertainty in the mass of the star.</ref> }} ==References== {{Reflist|refs= <ref name="GaiaDR3">{{Cite Gaia DR3|2603090003484152064}}</ref> <ref name=Anderson_Francis_2012>{{cite journal | last1=Anderson | first1=E. | last2=Francis | first2=Ch. | title=XHIP: An extended hipparcos compilation | journal=Astronomy Letters | volume=38 | issue=5 | pages=331 | year=2012 | bibcode=2012AstL...38..331A | arxiv=1108.4971 | doi=10.1134/S1063773712050015 | s2cid=119257644 }}</ref> <ref name="bean2006">{{cite journal | last1=Bean | first1=Jacob L. | last2=Benedict | first2=G. 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Nick | title=Prospects for Habitable "Earths" in Known Exoplanetary Systems | journal=The Astrophysical Journal | volume=622 | issue=2 | pages=1091–1101 |date=April 2005 | doi=10.1086/428108 | bibcode=2005ApJ...622.1091J |arxiv = astro-ph/0503178 | s2cid=119089227 }}</ref> <ref name="Keck press release a">{{cite press release | title=Astronomers find planet orbiting nearby star | date=June 1, 1998 | publisher=W. M. Keck Observatory | location=Kamuela, Hawaii | url=http://www.keckobservatory.org/astronomers_find_planet_orbiting_nearby_star/ | access-date=August 13, 2019 }}</ref> <ref name="Keck press release b">{{cite press release | title=Two new planetary systems discovered | date=January 9, 2001 | publisher=W. M. Keck Observatory | location=Kamuela, Hawaii | url=http://www.keckobservatory.org/two_new_planetary_systems_discovered/ | access-date=August 13, 2019 }}</ref> <ref name="konacki2003">{{cite journal | last1=Konacki | first1=Maciej | last2=Wolszczan | first2=Alex | title=Masses and Orbital Inclinations of Planets in the PSR B1257+12 System | journal=The Astrophysical Journal | volume=591 | issue=2 | pages=L147–L150 |date=July 2003 | doi=10.1086/377093 | bibcode=2003ApJ...591L.147K |arxiv = astro-ph/0305536 | s2cid=18649212 }}</ref> <ref name="Marcy1998">{{cite journal | title=A Planetary Companion to a Nearby M4 Dwarf, Gliese 876 | last1=Marcy | first1=Geoffrey W. | last2=Butler | first2=R. Paul | last3=Vogt | first3=Steven S. | last4=Fischer | first4=Debra | last5=Lissauer | first5=Jack J. | display-authors=1 | journal=The Astrophysical Journal Letters | volume=505 | issue=2 | pages=L147–L149 | year=1998 | arxiv=astro-ph/9807307 | bibcode=1998ApJ...505L.147M | doi=10.1086/311623 | s2cid=2679107 }}</ref> <ref name="Marcy2001">{{cite journal | title=A Pair of Resonant Planets Orbiting GJ 876 | last1=Marcy | first1=Geoffrey W. | last2=Butler | first2=R. 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Please return them to the reflist once they have been correctly cited in the main article. <ref name="zhou2008">{{cite conference | last1=Zhou | first1=Ji-Lin | last2=Lin | first2=Douglas N. C. | title=Migration and Final Location of Hot Super Earths in the Presence of Gas Giants | conference=Exoplanets: Detection, Formation and Dynamics, Proceedings of the International Astronomical Union, IAU Symposium | volume=249 | pages=285–291 |date=May 2008 | bibcode=2008IAUS..249..285Z }}</ref> --> <ref name=lurie>{{cite journal|doi=10.1088/0004-6256/148/5/91|arxiv=1407.4820|title=The Solar Neighborhood. Xxxiv. A Search for Planets Orbiting Nearby M Dwarfs Using Astrometry|journal=The Astronomical Journal|volume=148|issue=5|pages=91|year=2014|last1=Lurie|first1=John C|last2=Henry|first2=Todd J|last3=Jao|first3=Wei-Chun|last4=Quinn|first4=Samuel N|last5=Winters|first5=Jennifer G|last6=Ianna|first6=Philip A|last7=Koerner|first7=David W|last8=Riedel|first8=Adric R|last9=Subasavage|first9=John P|bibcode=2014AJ....148...91L|s2cid=118492541}}</ref> }} ==External links== {{commons category}} * {{Cite APOD |title=A Dangerous Sunrise on Gliese 876d |access-date=2008-06-21 |date=2008-05-21}} * {{Cite APOD |title=A planet for Gliese 876 |access-date=2008-06-21 |date=1998-06-26}} * {{cite web |url=http://www.solstation.com/stars/gl876.htm |title=Gliese 876 / Ross 780 |access-date=2008-06-21 |work=SolStation}} * {{cite web |url=http://www.obs-hp.fr/www/nouvelles/gl876.html |title=Gliese 876 : THE CLOSEST EXTRASOLAR PLANET |access-date=2008-06-21 |work=Observatoire de Haute Provence}} * {{cite web |url=http://news.bbc.co.uk/2/hi/science/nature/4089534.stm |title=Smallest extrasolar planet found |access-date=2008-06-21 |work=[[BBC News]] |date=2005-06-13}} * [http://aladin.u-strasbg.fr/AladinPreview?-c=22+53+16.7339-14+15+49.322&ident=V*+IL+Aqr&submit=Aladin+previewer Image Gliese 876] * [http://www.lpl.arizona.edu/~rory/research/xsp/dynamics/ Extrasolar Planet Interactions] by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona {{Gliese 876|state=collapsed}} {{nearest systems|4}} {{Stars of Aquarius}} {{Sky|22|53|16.7|-|14|15|49|15.3}} {{Good article}} {{DEFAULTSORT:Gliese 876}} [[Category:Gliese 876| ]] [[Category:Aquarius (constellation)]] [[Category:BY Draconis variables]] [[Category:Durchmusterung objects|BD-15 6290]] [[Category:Hipparcos objects|113020]] [[Category:Local Bubble]] [[Category:M-type main-sequence stars]] [[Category:Planetary systems with four confirmed planets]] [[Category:Gliese and GJ objects|0876]] [[Category:TIC objects]] [[Category:Objects with variable star designations|Aquarii, IL]]'