Editing Alpha Centauri (section)

== Planetary system ==
The Alpha Centauri system as a whole has two confirmed planets, both of them around Proxima Centauri. While other planets have been claimed to exist around all of the stars, none of the discoveries have been confirmed.

=== Planets of Proxima Centauri ===
{{Main|Proxima Centauri b|Proxima Centauri c|l2=c|Proxima Centauri d|l3=d}}
{{See also|Proxima Centauri#Planetary system}}

Proxima Centauri b is a terrestrial planet discovered in 2016 by astronomers at the [[European Southern Observatory]] (ESO). It has an estimated [[minimum mass]] of 1.17 {{Earth mass|link=y}} ([[Earth mass]]es) and orbits approximately 0.049 [[Astronomical unit|AU]] from Proxima Centauri, placing it in the star's [[Circumstellar habitable zone|habitable zone]].<ref name="proxima b discovery paper">{{cite journal|bibcode=2016Natur.536..437A|title=A terrestrial planet candidate in a temperate orbit around Proxima Centauri|journal=Nature|volume=536|issue=7617|pages=437–440|last1=Anglada-Escudé |first1=Guillem|last2=Amado|first2=Pedro J.|last3=Barnes|first3=John|last4=Berdiñas|first4=Zaira M.|last5=Butler|first5=R. Paul|last6=Coleman|first6=Gavin A. L.|last7=de la Cueva|first7=Ignacio|last8=Dreizler
|first8=Stefan|last9=Endl|first9=Michael|last10=Giesers|first10=Benjamin|last11=Jeffers|first11=Sandra V.|last12=Jenkins|first12=James S.|last13=Jones|first13=Hugh R. A.|last14=Kiraga|first14=Marcin |last15=Kürster|first15=Martin|last16=López-González|first16=María J.|last17=Marvin|first17=Christopher J.|last18=Morales|first18=Nicolás|last19=Morin|first19=Julien|last20=Nelson|first20=Richard P. |last21=Ortiz|first21=José L.|last22=Ofir|first22=Aviv|last23=Paardekooper|first23=Sijme-Jan|last24=Reiners|first24=Ansgar|last25=Rodríguez|first25=Eloy|last26=Rodríguez-López|first26=Cristina|last27=Sarmiento
|first27=Luis F.|last28=Strachan|first28=John P.|last29=Tsapras|first29=Yiannis|last30=Tuomi|first30=Mikko|first31=Mathias|last31=Zechmeister|display-authors=3|year=2016|arxiv=1609.03449|doi=10.1038/nature19106
|pmid=27558064|s2cid=4451513|url=https://www.nature.com/articles/nature19106}}</ref><ref name=Mascareno2020>{{cite journal|arxiv=2005.12114|last1=Suárez Mascareño|first1=A.|last2=Faria|first2=J. P. |last3=Figueira|first3=P.|title=Revisiting Proxima with ESPRESSO|journal=Astronomy & Astrophysics|year=2020|volume=639|page=A77|doi=10.1051/0004-6361/202037745|bibcode=2020A&A...639A..77S|s2cid=218869742 |display-authors=et al.}}</ref>

The discovery of Proxima Centauri c was formally published in 2020 and could be a [[super-Earth]] or [[mini-Neptune]].<ref name="proxima c scientific american">{{cite magazine|title=A Second Planet May Orbit Earth's Nearest Neighboring Star|url=https://www.scientificamerican.com/article/a-second-planet-may-orbit-earths-nearest-neighboring-star/|magazine=Scientific American|first=Lee|last=Billings|date=12 April 2019|access-date=2 August 2020}}</ref><ref name="proxima c discovery paper">{{cite journal|last1=Damasso|first1=Mario|last2=Del Sordo|first2=Fabio |display-authors=et al. |title=A low-mass planet candidate orbiting Proxima Centauri at a distance of 1.5&nbsp;AU |journal=Science Advances |date=January 2020 |volume=6 |issue=3 |page=eaax7467|doi=10.1126/sciadv.aax7467|pmid=31998838|pmc=6962037 |bibcode=2020SciA....6.7467D|doi-access=free}}</ref> It has a mass of roughly 7 {{Earth mass}} and orbits about {{nobr|1.49 AU}} from Proxima Centauri with a period of {{convert|1928|days|years}}.<ref name="proxima c mass">{{cite journal|last1=Benedict|first1=G. Fritz|last2=McArthur|first2=Barbara E.|title=A Moving Target — Revising the Mass of Proxima Centauri c|journal=Research Notes of the AAS|date=June 2020|volume=4|issue=6|page=86|doi=10.3847/2515-5172/ab9ca9|bibcode=2020RNAAS...4...86B|s2cid=225798015 |doi-access=free }}</ref> In June 2020, a possible direct imaging detection of the planet hinted at the presence of a large ring system.<ref name="proxima c imaging">{{cite journal|last1=Gratton |first1=Raffaele|last2=Zurlo|first2=Alice|last3=Le Coroller|first3=Hervé|display-authors=et al.|title=Searching for the near-infrared counterpart of Proxima c using multi-epoch high-contrast SPHERE data at VLT |journal=Astronomy & Astrophysics|date=June 2020|volume=638|page=A120|doi=10.1051/0004-6361/202037594 |bibcode=2020A&A...638A.120G |arxiv=2004.06685|s2cid=215754278}}</ref> However, a 2022 study disputed the existence of this planet.<ref name="Artigau2022">{{cite journal |bibcode=2022AJ....164...84A |title=Line-by-line Velocity Measurements: An Outlier-resistant Method for Precision Velocimetry |last1=Artigau |first1=Étienne |last2=Cadieux |first2=Charles |last3=Cook |first3=Neil J. |last4=Doyon |first4=René |last5=Vandal |first5=Thomas |last6=Donati |first6=Jean-François |last7=Moutou |first7=Claire |last8=Delfosse |first8=Xavier |last9=Fouqué |first9=Pascal |last10=Martioli |first10=Eder |last11=Bouchy |first11=François |last12=Parsons |first12=Jasmine |last13=Carmona |first13=Andres |last14=Dumusque |first14=Xavier |last15=Astudillo-Defru |first15=Nicola |last16=Bonfils |first16=Xavier |last17=Mignon |first17=Lucille |journal=The Astronomical Journal |date=2022 |volume=164 |issue=3 |page=84 |doi=10.3847/1538-3881/ac7ce6 |doi-access=free |arxiv=2207.13524 }}</ref>

A 2020 paper refining Proxima b's mass excludes the presence of extra companions with masses above {{Earth mass|0.6}} at periods shorter than 50 days, but the authors detected a radial-velocity curve with a periodicity of 5.15 days, suggesting the presence of a planet with a mass of about {{Earth mass|0.29}}.<ref name=Mascareno2020/> This planet, Proxima Centauri d, was detected in 2022.<ref name="Faria2022">{{cite journal |last1=Faria |first1=J. P. |last2=Suárez Mascareño |first2=A. |last3=Figueira |first3=P. |last4=Silva |first4=A. M. |last5=Damasso |first5=M. |last6=Demangeon |first6=O. |last7=Pepe |first7=F. |last8=Santos |first8=N. C. |last9=Rebolo |first9=R. |last10=Cristiani |first10=S. |last11=Adibekyan |first11=V. |display-authors=2 |date=January 4, 2022 |title=A candidate short-period sub-Earth orbiting Proxima Centauri |url=https://www.eso.org/public/archives/releases/sciencepapers/eso2202/eso2202a.pdf |journal=Astronomy & Astrophysics |publisher=European Southern Observatory |volume=658 |pages=17 |arxiv=2202.05188 |bibcode=2022A&A...658A.115F |doi=10.1051/0004-6361/202142337 |doi-access=free |last35=Tabernero |last23=Lo Curto |first18=X. |last19=Ehrenreich |first19=D. |last20=González Hernández |first20=J. I. |last21=Hara |last15=Cabral |first22=J. |first28=G. |last24=Lovis |first23=G. |first17=P. |first24=C. |last25=Martins |first25=C. J. A. P. |last26=Mégevand |first26=D. |last27=Mehner |first27=A. |last28=Micela |first21=N. |last18=Dumusque |last17=Di Marcantonio |first30=N. J. |first36=S. |last31=Pallé |first31=E. |last32=Poretti |first32=E. |last33=Sousa |first33=S. G. |last34=Sozzetti |first34=A. |last36=Udry |first15=A. |first29=P. |last37=Zapatero Osorio |first16=V. |first37=M. R. |first14=S. C. C. |last14=Barros |first13=R. |last13=Allart |first12=Y. |last12=Alibert |last30=Nunes |last29=Molaro |last16=D'Odorico |last22=Lillo-Box |first35=H.}}</ref><ref name="Artigau2022"/>

=== Planets of Alpha Centauri A ===
{{Main|2 = Alpha Centauri Ab}}
[[File:Candidate1 Discovery.png|thumb|upright=1.6|The discovery image of Alpha Centauri's candidate Neptunian planet, marked here as "C1"]]
{{Orbitbox planet begin
|name=Alpha Centauri A
|period_unit=day
}}
{{OrbitboxPlanet hypothetical
|exoplanet=[[Alpha Centauri Ab|b]]
|semimajor= 1.1
|period= ~360
|mass_earth= 9~35{{efn|
These mass limits are calculated from the observed radius of {{nobr|{{math| 3.3~7}} {{Earth radius|link=n}}}} applied to the equation quoted, and presumably used, to calculate the planet mass from the planet radius in the Wagner ''et al'' 2021 paper:<ref name="WagnerBoehle2021"/> {{nobr|{{math| ''R'' ∝ ''M''{{sup|&thinsp;0.55}} }} }} (although this radius-mass relationship is for low-mass planets and not for larger gas giants). Therefore {{nobr| {{math| 3.3{{sup|1.82}} {{=}} 8.77 }} {{Earth mass|link=n}} }} and {{nobr|{{math| 7{{sup|1.82}} {{=}} 34.52}} {{Earth mass|link=n}}.}} The {{nobr| {{mvar|M}}{{sub|{{math|sin ''i''}}}} ≥ 53 {{Earth mass|link=n}} }} is for a planet at the outer edge of the conservative habitable zone, {{nobr|2.1 AU}}, and so the upper mass limit is lower than that for the C{{sub|1}} planet at just {{nobr|1.1 AU}}.
}}
|radius_earth= 3.3~7
|inclination= ~65 ± 25
}}
{{Orbitbox end}}

In 2021, a candidate planet named Candidate 1 (or C1) was detected around Alpha Centauri A, thought to orbit at approximately {{nobr|1.1 AU}} with a period of about one year, and to have a mass between that of Neptune and one-half that of Saturn, though it may be a dust disk or an artifact. The possibility of C1 being a background star has been ruled out.<ref>{{cite web | url = https://www.theguardian.com/science/2021/feb/10/astronomers-hopes-raised-by-glimpse-of-possible-new-planet-alpha-centauri| title = Astronomers' hopes raised by glimpse of possible new planet? |access-date=2022-01-16| work=[[The Guardian]] | date=10 February 2021 |first=Ian |last=Sample}}</ref><ref name="WagnerBoehle2021">{{cite journal |last1=Wagner |first1=K. |last2=Boehle |first2=A. |last3=Pathak |first3=P.|last4=Kasper |first4=M.|last5=Arsenault|first5=R. |last6=Jakob|first6=G.|last7=Käufl|first7=U. |last8=Leveratto|first8=S.|last9=Maire|first9=A.-L.|last10=Pantin |first10=E.|last11=Siebenmorgen |first11=R.|last12=Zins|first12=G. |last13=Absil|first13=O. |last14=Ageorges |first14=N. |last15=Apai |first15=D. |last16=Carlotti|first16=A. |last17=Choquet|first17=É.|last18=Delacroix|first18=C.|last19=Dohlen|first19=K.|last20=Duhoux|first20=P.|last21=Forsberg|first21=P.|last22=Fuenteseca|first22=E.|last23=Gutruf|first23=S.|last24=Guyon|first24=O.|last25=Huby|first25=E.|last26=Kampf|first26=D.|last27=Karlsson|first27=M.|last28=Kervella|first28=P.|last29=Kirchbauer|first29=J.-P.|last30=Klupar|first30=P. |last31=Kolb|first31=J.|last32=Mawet|first32=D.|last33=N'Diaye|first33=M.|last34=Orban de Xivry|first34=G.|last35=Quanz|first35=S. P.|last36=Reutlinger|first36=A.|last37=Ruane|first37=G.|last38=Riquelme |first38=M. |last39=Soenke|first39=C.|last40=Sterzik|first40=M.|last41=Vigan|first41=A.|last42=de Zeeuw|first42=T. |display-authors=6 |title=Imaging low-mass planets within the habitable zone of α Centauri |journal=Nature Communications|date=10 February 2021|volume=12|issue=1|page=922|doi=10.1038/s41467-021-21176-6|pmid=33568657|pmc=7876126|doi-access=free|arxiv=2102.05159|bibcode=2021NatCo..12..922W}} [https://www.youtube.com/watch?v=Da2EMPuGu00&feature=youtu.be Kevin Wagner's (lead author of paper?) video of discovery]</ref> If this candidate is confirmed, the temporary name C1 will most likely be replaced with the scientific designation Alpha Centauri Ab in accordance with current naming conventions.<ref name="IAUNamingRules">{{cite web|url=https://www.iau.org/public/themes/naming_exoplanets/|title=Naming of Exoplanets|publisher=International Astronomical Union|access-date=24 July 2021}}</ref>

GO Cycle 1 observations are planned for the [[James Webb Space Telescope]] (JWST) to search for planets around Alpha Centauri A, as well as observations of [[Epsilon Muscae]].<ref name=":0">{{Cite web |title=1618 Program Information |url=https://www.stsci.edu/cgi-bin/get-proposal-info?observatory=JWST&id=1618 |access-date=2022-09-01 |website=www.stsci.edu |archive-date=1 September 2022 |archive-url=https://web.archive.org/web/20220901094214/https://www.stsci.edu/cgi-bin/get-proposal-info?observatory=JWST&id=1618 |url-status=dead }}</ref> The coronographic observations, which occurred on July 26 and 27, 2023, were failures, though there are follow-up observations in March 2024.<ref>{{Cite web |title=Visit Information |url=https://www.stsci.edu/cgi-bin/get-visit-status?id=1618&markupFormat=html&observatory=JWST |access-date=2022-09-01 |website=www.stsci.edu |archive-date=1 September 2022 |archive-url=https://web.archive.org/web/20220901094234/https://www.stsci.edu/cgi-bin/get-visit-status?id=1618&markupFormat=html&observatory=JWST |url-status=dead }}</ref> Pre-launch estimates predicted that JWST will be able to find planets with a radius of 5 {{Earth radius|link=true}} at {{nobr|1–3 AU}}. Multiple observations every 3–6 months could push the limit down to 3 {{Earth radius}}.<ref>{{Cite journal |last1=Beichman |first1=Charles |last2=Ygouf |first2=Marie |last3=Llop Sayson |first3=Jorge |last4=Mawet |first4=Dimitri |last5=Yung |first5=Yuk |last6=Choquet |first6=Elodie |last7=Kervella |first7=Pierre |last8=Boccaletti |first8=Anthony |last9=Belikov |first9=Ruslan |last10=Lissauer |first10=Jack J. |last11=Quarles |first11=Billy |last12=Lagage |first12=Pierre-Olivier |last13=Dicken |first13=Daniel |last14=Hu |first14=Renyu |last15=Mennesson |first15=Bertrand |date=2020-01-01 |title=Searching for Planets Orbiting α Cen A with the James Webb Space Telescope |url=https://ui.adsabs.harvard.edu/abs/2020PASP..132a5002B |journal=Publications of the Astronomical Society of the Pacific |volume=132 |issue=1007 |pages=015002 |doi=10.1088/1538-3873/ab5066 |arxiv=1910.09709 |bibcode=2020PASP..132a5002B |s2cid=204823856 |issn=0004-6280}}</ref> Post-launch estimates based on observations of [[HIP 65426 b]] find that JWST will be able to find planets even closer to Alpha Centauri A and could find a 5 {{Earth radius}} planet at {{nobr|0.5–2.5 AU}}.<ref>{{Cite journal |last1=Carter |first1=Aarynn L. |last2=Hinkley |first2=Sasha |last3=Kammerer |first3=Jens |last4=Skemer |first4=Andrew |last5=Biller |first5=Beth A. |last6=Leisenring |first6=Jarron M. |last7=Millar-Blanchaer |first7=Maxwell A. |last8=Petrus |first8=Simon |last9=Stone |first9=Jordan M. |last10=Ward-Duong |first10=Kimberly |last11=Wang |first11=Jason J. |last12=Girard |first12=Julien H. |last13=Hines |first13=Dean C. |last14=Perrin |first14=Marshall D. |last15=Pueyo |first15=Laurent |date=2023 |title=The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems I: High-contrast Imaging of the Exoplanet HIP 65426 b from 2 to 16 μm |journal=The Astrophysical Journal Letters |volume=951 |issue=1 |pages=L20 |doi=10.3847/2041-8213/acd93e |arxiv=2208.14990 |bibcode=2023ApJ...951L..20C |doi-access=free }}</ref> Candidate&nbsp;1 has an estimated radius between {{nobr|3.3–11 {{Earth radius}}}}<ref name=WagnerBoehle2021/> and orbits at {{nobr|1.1 AU}}. It is therefore likely within the reach of JWST observations.

=== {{anchor|Unconfirmed planets}}Planets of Alpha Centauri B ===
{{Main|Alpha Centauri Bb}}

The first claim of a planet around Alpha Centauri B was that of [[Alpha Centauri Bb]] in 2012, which was proposed to be an Earth-mass planet in a 3.2-day orbit.<ref name="Dumusque"/> This was refuted in 2015 when the apparent planet was shown to be an artifact of the way the [[Doppler spectroscopy|radial velocity]] data was processed.<ref>{{cite news |last=Wenz |first=John |date=2015-10-29 |title=It turns out the closest exoplanet to us doesn't actually exist |magazine=Popular Mechanics |url=https://www.popularmechanics.com/space/a18003/no-alpha-centauri-b-planet/ |access-date=2018-12-08}}</ref><ref>{{cite news |title=Poof! The planet closest to our Solar system just vanished |date=2015-10-29 |website = National Geographic News |url=https://news.nationalgeographic.com/2015/10/151028-planet-disappears-alpha-centauri-astronomy-science/ |url-status=dead |access-date=2018-12-08 |archive-url=https://web.archive.org/web/20151030010115/http://news.nationalgeographic.com/2015/10/151028-planet-disappears-alpha-centauri-astronomy-science/ |archive-date=30 October 2015 }}</ref><ref name=Rajpaul2016>{{cite journal |first1=Vinesh |last1=Rajpaul |first2=Suzanne |last2=Aigrain |first3=Stephen J. |last3=Roberts |date=19 October 2015 |title=Ghost in the time series: No planet for {{nobr|alpha Cen B}} |journal=Monthly Notices of the Royal Astronomical Society |volume=456 |issue=1 |pages=L6–L10 |arxiv=1510.05598 |bibcode=2016MNRAS.456L...6R |doi=10.1093/mnrasl/slv164 |doi-access=free |s2cid=119294717}}</ref>

A search for [[astronomical transit|transits]] of planet Bb was conducted with the [[Hubble Space Telescope]] from 2013 to 2014. This search detected one potential transit-like event, which could be associated with a different planet with a radius around {{Earth radius|0.92|link=y}}. This planet would most likely orbit Alpha Centauri B with an orbital period of 20.4&nbsp;days or less, with only a 5% chance of it having a longer orbit. The median of the likely orbits is 12.4&nbsp;days. Its orbit would likely have an eccentricity of 0.24 or less.<ref name=Demory2015>{{cite journal |last1=Demory |first1=Brice-Olivier |last2=Ehrenreich |first2=David |last3=Queloz |first3=Didier |last4=Seager |first4=Sara |last5=Gilliland |first5=Ronald |last6=Chaplin |first6=William J. |last7=Proffitt |first7=Charles |last8=Gillon |first8=Michael |last9=Guenther |first9=Maximilian N. |last10=Benneke |first10=Bjoern |last11=Dumusque |first11=Xavier |last12=Lovis |first12=Christophe |last13=Pepe|first13=Francesco |last14=Segransan |first14=Damien |last15=Triaud |first15=Amaury |last16=Udry |first16=Stephane |display-authors=6 |date=June 2015 |title=Hubble Space Telescope search for the transit of the Earth-mass exoplanet Alpha Centauri Bb |journal=Monthly Notices of the Royal Astronomical Society |volume=450 |issue=2 |pages=2043–2051 |arxiv=1503.07528 |bibcode=2015MNRAS.450.2043D |doi=10.1093/mnras/stv673 |doi-access=free |s2cid=119162954}}</ref> It could have lakes of molten lava and would be far too close to Alpha Centauri B to harbour [[extraterrestrial life|life]].<ref>{{cite news |last=Aron |first=Jacob |title=Twin Earths may lurk in our nearest star system |magazine=[[New Scientist]] |url=https://www.newscientist.com/article/dn27259-twin-earths-may-lurk-in-our-nearest-star-system/ |access-date=2018-12-08}}</ref> If confirmed, this planet might be called {{nobr|Alpha Centauri Bc}}. However, the name has not been used in the literature, as it is not a claimed discovery.

=== Hypothetical planets ===
Additional planets may exist in the Alpha Centauri system, either orbiting Alpha Centauri A or Alpha Centauri B individually, or in large orbits around Alpha Centauri AB. Because both stars are fairly similar to the Sun (for example, in age and [[metallicity]]), astronomers have been especially interested in making detailed searches for planets in the Alpha Centauri system. Several established planet-hunting teams have used various [[radial velocity]] or star [[Astronomical transit|transit]] methods in their searches around these two bright stars.<ref name="universetoday.com">{{cite news |title=Why haven't planets been detected around Alpha Centauri? |date=2008-04-19 |website=[[Universe Today]] |url=http://www.universetoday.com/2008/04/19/why-havent-planets-been-detected-around-alpha-centauri/ |access-date=19 April 2008 |url-status=live 
|archive-url=https://web.archive.org/web/20080421040845/http://www.universetoday.com/2008/04/19/why-havent-planets-been-detected-around-alpha-centauri/ |archive-date=21 April 2008 }}</ref> All the observational studies have so far failed to find evidence for [[brown dwarf]]s or [[gas giant]]s.<ref name="universetoday.com"/><ref>{{cite web |url=http://www.ucsc.edu/news_events/text.asp?pid=2012|title=Nearby star should harbor detectable, Earth-like planets |date=7 March 2008 |first=Tim |last=Stephens |work=News & Events |publisher=UC Santa Cruz |access-date=19 April 2008|archive-url=https://web.archive.org/web/20080417004113/http://www.ucsc.edu/news_events/text.asp?pid=2012| archive-date=17 April 2008|url-status=dead}}</ref>

In 2009, computer simulations showed that a planet might have been able to form near the inner edge of Alpha Centauri B's habitable zone, which extends from {{nobr|0.5–0.9 AU}} from the star. Certain special assumptions, such as considering that the Alpha Centauri pair may have initially formed with a wider separation and later moved closer to each other (as might be possible if they formed in a dense [[Open cluster|star cluster]]), would permit an accretion-friendly environment farther from the star.<ref name=Thebault-2009>{{cite journal|last1=Thebault |first1= P.|last2=Marzazi |first2= F.|last3=Scholl |first3= H.|year=2009 |title=Planet formation in the habitable zone of alpha centauri B|journal=Monthly Notices of the Royal Astronomical Society|volume=393|issue=1|pages=L21–L25|arxiv=0811.0673|bibcode=2009MNRAS.393L..21T |doi=10.1111/j.1745-3933.2008.00590.x|doi-access= free|s2cid=18141997}}</ref> Bodies around Alpha Centauri A would be able to orbit at slightly farther distances due to its stronger gravity. In addition, the lack of any brown dwarfs or gas giants in close orbits around Alpha Centauri make the likelihood of terrestrial planets greater than otherwise.<ref name="lackofany">{{cite journal|last1=Quintana |first1= E. V.|last2=Lissauer |first2= J. J.
|last3=Chambers |first3= J. E.|last4=Duncan |first4= M. J.|title=Terrestrial Planet Formation in the Alpha Centauri System|journal=Astrophysical Journal|year=2002|volume=576|issue=2|pages=982–996|doi=10.1086/341808
|bibcode=2002ApJ...576..982Q|citeseerx=10.1.1.528.4268|s2cid= 53469170}}</ref> A theoretical study indicates that a radial velocity analysis might detect a hypothetical planet of {{Earth mass|1.8|link=y}} in Alpha Centauri B's [[Circumstellar habitable zone|habitable zone]].<ref name=guedesetal2008>{{cite journal|first1=Javiera M.|last1=Guedes|first2=Eugenio J.|last2=Rivera|first3=Erica|last3=Davis|first4=Gregory|last4=Laughlin
|first5=Elisa V.|last5=Quintana|first6=Debra A.|last6=Fischer|title=Formation and Detectability of Terrestrial Planets Around Alpha Centauri B|journal=Astrophysical Journal|volume=679|issue=2|pages=1582–1587
|arxiv=0802.3482|doi=10.1086/587799|bibcode=2008ApJ...679.1582G|year=2008|s2cid=12152444}}</ref>

Radial velocity measurements of Alpha Centauri B made with the [[High Accuracy Radial Velocity Planet Searcher]] [[spectrograph]] were sufficiently sensitive to detect a {{Earth mass|4|link=y}} planet within the habitable zone of the star (i.e. with an orbital period P = 200 days), but no planets were detected.<ref name="Dumusque">{{cite journal|last1=Dumusque|first1=X.|last2=Pepe |first2= F.|last3=Lovis |first3= C. |last4=Ségransan |first4= D.|last5=Sahlmann |first5= J.|last6=Benz |first6= W.|last7=Bouchy |first7= F.|author8-link=Michel Mayor|last8=Mayor |first8= M.|author9-link=Didier Queloz|last9=Queloz |first9= D.|author10=Santos, N.|author11-link=Stéphane Udry|last11=Udry |first11= S.|title=An Earth mass planet orbiting Alpha Centauri B|journal=Nature|volume=490|issue=7423|pages=207–211|date=17 October 2012 |url=http://www.eso.org/public/archives/releases/sciencepapers/eso1241/eso1241a.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.eso.org/public/archives/releases/sciencepapers/eso1241/eso1241a.pdf |archive-date=2022-10-09 |url-status=live|doi=10.1038/nature11572|access-date=17 October 2012|bibcode=2012Natur.491..207D|pmid=23075844|s2cid=1110271}}</ref>

Current estimates place the probability of finding an Earth-like planet around Alpha Centauri at roughly 75%.<ref name=miniature>{{cite AV media |last1=Billings |first1=Lee |title=Miniature Space Telescope Could Boost the Hunt for "Earth Proxima" |medium = video |website=[[Scientific American]] (scientificamerican.com) |url=http://www.scientificamerican.com/article/miniature-space-telescope-could-boost-the-hunt-for-earth-proxima-video/ }}</ref> The observational thresholds for planet detection in the habitable zones by the radial velocity method are currently (2017) estimated to be about {{Earth mass|53}} for Alpha Centauri A, {{Earth mass|8.4}} for Alpha Centauri B, and {{Earth mass|0.47}} for [[Proxima Centauri]].<ref name=Zhao2018>{{cite journal |last1=Zhao |first1=L. |last2=Fischer |first2= D. |last3=Brewer |first3= J. |last4=Giguere |first4= M. |last5=Rojas-Ayala |first5= B. |date=January 2018 |title=Planet detectability in the Alpha Centauri system |journal=[[Astronomical Journal]] |volume=155 |issue=1 |page=12 |arxiv=1711.06320 |doi=10.3847/1538-3881/aa9bea |doi-access=free |bibcode=2018AJ....155...24Z |s2cid=118994786 |url=http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1711.06320 |access-date=29 December 2017 }}</ref>

Early computer-generated models of planetary formation predicted the existence of [[terrestrial planet]]s around [[Circumbinary planet|both Alpha Centauri A and B]],<ref name=guedesetal2008/><ref name=Quintna-Lissr-2007/> but most recent numerical investigations have shown that the gravitational pull of the companion star renders the accretion of planets difficult.<ref name=Thebault-2009/><ref>{{cite journal |first1 = M. |last1 = Barbieri |first2 = F. |last2 = Marzari |first3 = H. |last3 = Scholl |year=2002|title=Formation of terrestrial planets in close binary systems: The case of {{nobr|α Centauri A}} |journal=[[Astronomy & Astrophysics]] |volume=396 |issue=1 |pages=219–224 |doi=10.1051/0004-6361:20021357 |bibcode=2002A&A...396..219B|arxiv=astro-ph/0209118|s2cid=119476010}}</ref> Despite these difficulties, given the similarities to the Sun in [[spectral type]]s, star type, age and probable stability of the orbits, it has been suggested that this stellar system could hold one of the best possibilities for harbouring [[extraterrestrial life]] on a potential planet.<ref name="Wiegert">{{cite journal |first1=P.A. |last1=Wiegert |first2=M.J. |last2=Holman |year=1997 |title=The stability of planets in the Alpha Centauri system |journal=The Astronomical Journal |volume=113 |pages=1445–1450|bibcode=1997AJ....113.1445W |doi=10.1086/118360 |arxiv=astro-ph/9609106 |s2cid=18969130}}</ref><ref name=lackofany/><ref>{{cite journal |first1=J.J. |last1=Lissauer |first2=E.V. |last2=Quintana |first3=J.E. |last3=Chambers |first4=M.J. |last4=Duncan |first5=F.C. |last5=Adams |year=2004 |title=Terrestrial planet formation in binary star systems |journal=Revista Mexicana de Astronomía y Astrofísica |series = Serie de Conferencias |volume=22 |pages=99–103 |bibcode=2004RMxAC..22...99L |arxiv=0705.3444}}</ref><ref name=Quintna-Lissr-2007>{{cite book |last1=Quintana |first1=Elisa V. |last2=Lissauer |first2=Jack J. |year=2007 |section=Terrestrial planet formation in binary star systems |title=Planets in Binary Star Systems |editor-first=Nader |editor-last=Haghighipour |publisher=Springer |pages=265–284 |isbn=978-90-481-8687-7 |url=https://books.google.com/books?id=kyf7vgv6FSYC&pg=PA265}}</ref>

In the [[Solar System]], it was once thought that [[Jupiter]] and [[Saturn]] were probably crucial in perturbing [[comet]]s into the inner Solar System, providing the inner planets with a source of water and various other ices.<ref name=Croswell>{{cite magazine |last=Croswell |first=Ken |date=April 1991 |title=Does Alpha Centauri have intelligent life? |magazine=[[Astronomy Magazine]] |volume=19 |issue=4 |pages=28–37 |bibcode=1991Ast....19d..28C }}</ref> However, since isotope measurements of the [[deuterium]] to [[hydrogen]] (D/H) ratio in comets [[Halley's Comet|Halley]], [[Comet Hyakutake|Hyakutake]], [[Comet Hale–Bopp|Hale–Bopp]], 2002T7, and Tuttle yield values approximately twice that of Earth's oceanic water, more recent models and research predict that less than 10% of Earth's water was supplied from comets. In the {{nobr|α Centauri}} system, Proxima Centauri may have influenced the planetary disk as the {{nobr|α Centauri}} system was forming, enriching the area around Alpha Centauri with volatile materials.<ref>{{cite web |first=Paul |last=Gilster|date=5 July 2006 |title=Proxima Centauri and habitability |website=Centauri Dreams |url=http://www.centauri-dreams.org/?p=726 |access-date=12 August 2010}}</ref> This would be discounted if, for example, {{nobr|α Centauri B}} happened to have [[gas giant]]s orbiting {{nobr|α Centauri A}} (or vice versa), or if {{nobr|α Centauri A}} and B themselves were able to perturb comets into each other's inner systems, as Jupiter and Saturn presumably have done in the Solar System.<ref name=Croswell/> Such icy bodies probably also reside in [[Oort cloud]]s of other planetary systems. When they are influenced gravitationally by either the gas giants or disruptions by passing nearby stars, many of these icy bodies then travel star-wards.<ref name=Croswell/> Such ideas also apply to the close approach of Alpha Centauri or other stars to the Solar system, when, in the distant future, the [[Oort Cloud]] might be disrupted enough to increase the number of active comets.<ref name=Matthews/>

To be in the [[habitable zone]], a planet around Alpha Centauri A would have an orbital radius of between about 1.2 and {{val|2.1|ul=AU}} so as to have similar planetary temperatures and conditions for liquid water to exist.<ref name=Kaltenegger2013>{{cite journal  |last1=Kaltenegger |first1=Lisa |last2=Haghighipour |first2=Nader |year=2013 |title=Calculating the habitable zone of binary star systems. I.&nbsp;S-type binaries|journal=[[The Astrophysical Journal]] |volume=777 |issue=2 |page=165 |bibcode=2013ApJ...777..165K |arxiv=1306.2889 |s2cid=118414142  |doi=10.1088/0004-637X/777/2/165 |doi-access=free }}</ref> For the slightly less luminous and cooler {{nobr|α Centauri B}}, the habitable zone is between about 0.7 and {{val|1.2|u=AU}}.<ref name=Kaltenegger2013/>

With the goal of finding evidence of such planets, both Proxima Centauri and {{nobr|α Centauri AB}} were among the listed "Tier-1" target stars for [[NASA]]'s [[Space Interferometry Mission]] (S.I.M.). Detecting planets as small as three Earth-masses or smaller within two AU of a "Tier-1" target would have been possible with this new instrument.<ref name="numbers">{{citation-attribution|1={{cite press release |url=http://www.jpl.nasa.gov/news/features.cfm?feature=1209 |title=Planet hunting by numbers |publisher=Jet Propulsion Laboratory|date=18 October 2006|access-date=24 April 2007 |archive-date=4 August 2010 |archive-url=https://web.archive.org/web/20100804160702/http://www.jpl.nasa.gov/news/features.cfm?feature=1209 |url-status=dead}} }}</ref> The S.I.M. mission, however, was cancelled due to financial issues in 2010.<ref>{{cite web|last1=Mullen|first1=Leslie|title=Rage Against the Dying of the Light|url=http://www.astrobio.net/exclusive/4005/rage-against-the-dying-of-the-light|date=2 June 2011|work=Astrobiology Magazine|access-date=7 June 2011|archive-url=https://web.archive.org/web/20110604121537/http://www.astrobio.net/exclusive/4005/rage-against-the-dying-of-the-light|archive-date=4 June 2011|url-status=dead}}</ref>

=== Circumstellar discs ===
Based on observations between 2007 and 2012, a study found a slight excess of emissions in the 24&nbsp;[[Micrometre|μm]] (mid/far-infrared) band surrounding {{nobr|α Centauri AB}}, which may be interpreted as evidence for a sparse [[circumstellar disc]] or dense [[interplanetary dust cloud|interplanetary dust]].<ref name="Wiegart2014"/> The total mass was estimated to be between {{10^|-7}} to {{10^|-6}} the mass of the [[Moon]], or 10–100 times the mass of the Solar System's [[zodiacal cloud]].<ref name=Wiegart2014/> If such a disc existed around both stars, {{nobr|α Centauri A's}} disc would likely be stable to {{nobr|2.8 AU,}} and {{nobr|α Centauri B's}} would likely be stable to {{nobr|2.5 AU }}<ref name=Wiegart2014/> This would put A's disc entirely within the [[frost line (astrophysics)|frost line]], and a small part of B's outer disc just outside.<ref name=Wiegart2014>
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