Proxima Centauri: Difference between revisions

Based on a parallax of {{val|768.0665|0.0499|u=mas}}, published in 2020 in [[Gaia Data Release 3]], Proxima Centauri is {{convert|4.2465|ly|pc AU|lk=on}} from the Sun.<ref name="Gaia3" /> Previously published parallaxes include: {{val|768.5|0.2|u=mas}} in 2018 by Gaia DR2, {{val|768.13|1.04|u=mas}}, in 2014 by the [[Research Consortium On Nearby Stars]];<ref name="lurie2014">{{cite journal |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. |year=2014 |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 |arxiv=1407.4820 |bibcode=2014AJ....148...91L |doi=10.1088/0004-6256/148/5/91 |s2cid=118492541}}</ref> {{val|772.33|2.42|u=mas}}, in the original [[Hipparcos]] Catalogue, in 1997;<ref name="aaa323_L49">{{cite journal |last1=Perryman |first1=M. A. C. |last2=Lindegren |first2=L. |last3=Kovalevsky |first3=J. |last4=Hoeg |first4=E. |last5=Bastian |first5=U. |last6=Bernacca |first6=P. L. |last7=Crézé |first7=M. |last8=Donati |first8=F. |last9=Grenon |first9=M. |last10=Grewing |first10=M. |last11=van Leeuwen |first11=F. |date=July 1997 |title=The Hipparcos catalogue |journal=Astronomy and Astrophysics |volume=323 |pages=L49–L52 |bibcode=1997A&A...323L..49P |last12=van der Marel |first12=H. |last13=Mignard |first13=F. |last14=Murray |first14=C. A. |last15=Le Poole |first15=R. S. |last16=Schrijver |first16=H. |last17=Turon |first17=C. |last18=Arenou |first18=F. |last19=Froeschlé |first19=M. |last20=Petersen |first20=C. S.}}</ref> {{val|771.64|2.60|u=mas}} in the Hipparcos New Reduction, in 2007;<ref name="hipparcos">{{cite journal |bibcode=2007A&A...474..653V |title=Validation of the new Hipparcos reduction |journal=Astronomy and Astrophysics |volume=474 |issue=2 |pages=653–664 |last1=Van Leeuwen |first1=F. |year=2007 |doi=10.1051/0004-6361:20078357 |arxiv=0708.1752|s2cid=18759600 }}</ref> and {{val|768.77|0.37|u=mas}} using the [[Hubble Space Telescope]]{{'s}} [[fine guidance sensor]]s, in 1999.<ref name="apj118" /> From Earth's vantage point, Proxima Centauri is separated from Alpha Centauri by 2.18 degrees,<ref name="apj121">{{cite journal |last1=Kirkpatrick |first1=J. D. |last2=Davy |first2=J. |last3=Monet |first3=David G. |last4=Reid |first4=I. Neill |last5=Gizis |first5=John E. |last6=Liebert |first6=James |last7=Burgasser |first7=Adam J. |year=2001 |title=Brown dwarf companions to G-type stars. I: Gliese 417B and Gliese 584C |journal=The Astronomical Journal |volume=121 |issue=6 |pages=3235–3253 |arxiv=astro-ph/0103218 |bibcode=2001AJ....121.3235K |doi=10.1086/321085 |s2cid=18515414}}</ref> or four times the angular diameter of the full [[Moon]].<ref>{{cite web |last=Williams |first=D. R. |date=February 10, 2006 |title=Moon Fact Sheet |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html |access-date=October 12, 2007 |series=Lunar & Planetary Science |publisher=NASA}}</ref> Proxima Centauri has a relatively large proper motion—moving 3.85&nbsp;[[arcseconds]] per year across the sky.<ref>{{cite conference |last1=Benedict |first1=G. F. |last2=Mcarthur |first2=B. |last3=Nelan |first3=E. |last4=Story |first4=D. |last5=Jefferys |first5=W. H. |last6=Wang |first6=Q. |last7=Shelus |first7=P. J. |last8=Hemenway |first8=P. D. |last9=Mccartney |first9=J. |title=Astrometric stability and precision of fine guidance sensor #3: the parallax and proper motion of Proxima Centauri |url=http://clyde.as.utexas.edu/SpAstNEW/Papers_in_pdf/%7BBen93%7DEarlyProx.pdf |pages=380–384 |access-date=July 11, 2007 |first10=Wm. F. |last10=Van Altena |first11=R. |last11=Duncombe |first12=O. G. |last12=Franz |first13=L. W. |last13=Fredrick |work=Proceedings of the HST calibration workshop}}</ref> It has a [[radial velocity]] towardtowards the Sun of 22.2&nbsp;km/s.<ref name="KervellaThévenin2017" /> From Proxima Centauri, the Sun would appear as a bright 0.4-magnitude star in the constellation [[Cassiopeia (constellation)|Cassiopeia]], similar to that of [[Achernar]] or [[Procyon]] from [[Earth]].<ref group="nb">The coordinates of the Sun would be diametrically opposite Proxima Centauri, at α={{RA|02|29|42.9487}}, δ={{DEC|+62|40|46.141}}. The absolute magnitude ''M_v'' of the Sun is 4.83, so at a parallax ''π'' of 0.77199 the apparent magnitude ''m'' is given by 4.83 − 5(log₁₀(0.77199) + 1) = 0.40.

Proxima Centauri has been suspected to be a companion of the Alpha Centauri [[binary star]] system since its discovery in 1915. For this reason, it is sometimes referred to as Alpha Centauri&nbsp;C. Data from the [[Hipparcos]] satellite, combined with ground-based observations, were consistent with the hypothesis that the three stars are a [[gravitationally bound]] system. Kervella et al. (2017) used high-precision radial velocity measurements to determine with a high degree of confidence that Proxima and Alpha Centauri are gravitationally bound.<ref name="KervellaThévenin2017" /> Proxima Centauri's orbital period around the Alpha Centauri&nbsp;AB [[barycenter]] is {{val|547000|6600|4000}} years with an eccentricity of {{val|0.5|0.08}}; it approaches Alpha Centauri to {{val|4300|1100|900|u=AU}} at [[periastron]] and retreats to {{val|13000|300|100|u=AU}} at [[apastron]].<ref name="KervellaThévenin2017" /> At present, Proxima Centauri is {{convert|12947|±|260|AU|e12km|2|abbr=unit}} from the Alpha Centauri&nbsp;AB barycenter, nearly to the farthestfurthest point in its orbit.<ref name="KervellaThévenin2017" />

| table_ref={{efn|<ref name=Guillem2016>{{cite journal

}}</ref><ref name=Li-2017/><ref name="Damasso2020"/><ref name="KervellaArenou2020">{{cite journal|last1=Kervella|first1=Pierre|last2=Arenou|first2=Frédéric|last3=Schneider|first3=Jean|title=Orbital inclination and mass of the exoplanet candidate Proxima c|journal=Astronomy & Astrophysics|volume=635|year=2020|pages=L14|issn=0004-6361|arxiv=2003.13106|doi=10.1051/0004-6361/202037551|bibcode= 2020A&A...635L..14K|s2cid=214713486}}</ref><ref name="Suárez MascareñoFaria2020" /><ref name="BenedictMcArthur2020">{{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=16 June 2020 |volume=4 |issue=6 |page=86 |doi=10.3847/2515-5172/ab9ca9 |bibcode=2020RNAAS...4...86B |s2cid=225798015 |doi-access=free }}</ref><ref name="FariaSuárezMascareñoSilva2022"/>}}

As of 2022, three planets (one confirmed and two candidates) have been detected in orbit around Proxima Centauri, with one possibly being among the lightest ever detected by radial velocity ("d"), one close to Earth's size within the [[habitable zone]] ("b"), and a possible [[gas dwarf]] that orbits much fartherfurther out than the inner two ("c"), although its status remains disputed.

Proxima Centauri b, or Alpha Centauri Cb, orbits the star at a distance of roughly {{convert|0.05|AU|e6km|abbr=unit}} with an orbital period of approximately 11.2 Earth days. Its estimated mass is at least 1.1707 times that of the [[Earth]].<ref name="BA2017FariaSuárezMascareñoSilva2022">{{cite journal |last1=Bixel |first1=A. |last2=Apai |first2=D. |title=Probabilistic Constraints on the Mass and Composition of Proxima b |journal=The Astrophysical Journal Letters |date=February 21, 2017 |volume=836 |issue=2 |pages=L31 |doi=10.3847/2041-8213/aa5f51 |issn=2041-8205 |hdl=10150/623234 |arxiv=1702.02542|s2cid=119469149 |doi-access=free |bibcode=2017ApJ...836L..31B }}</ref> Moreover, the equilibrium temperature of Proxima Centauri&nbsp;b is estimated to be within the range where water could exist as liquid on its surface; thus, placing it within the [[habitable zone]] of Proxima Centauri.<ref name="Guillem2016" /><ref name="NYT-20160824">{{cite news |last=Chang |first=Kenneth |title=One star over, a planet that might be another Earth |url=https://www.nytimes.com/2016/08/25/science/earth-planet-proxima-centauri.html |date=August 24, 2016 |work=[[New York Times]] |access-date=August 24, 2016}}</ref><ref name="telegraph20160824">{{Cite news |last1=Knapton |first1=Sarah |title=Proxima b: Alien life could exist on 'second Earth' found orbiting our nearest star in Alpha Centauri system |url=https://www.telegraph.co.uk/science/2016/08/24/proxima-b-alien-life-could-exist-on-second-earth-found-orbiting/ |archive-url=https://ghostarchive.org/archive/20220112/https://www.telegraph.co.uk/science/2016/08/24/proxima-b-alien-life-could-exist-on-second-earth-found-orbiting/ |archive-date=12 January 2022 |url-access=subscription |url-status=live |work=The Telegraph |publisher=[[Telegraph Media Group]] |access-date=August 24, 2016 |date=August 24, 2016}}{{cbignore}}</ref>

Proxima Centauri c is a candidate [[super-Earth]] or [[gas dwarf]] about 7 Earth masses orbiting at roughly {{convert|1.5|AU|km}} every {{convert|1900|days|years}}.<ref name="SA-20190412" /> If Proxima Centauri b were the star's Earth, Proxima Centauri c would be equivalent to Neptune. Due to its large distance from Proxima Centauri, it is unlikely to be habitable, with a low equilibrium temperature of around 39 K.<ref name="ProximaC" /> The planet was first reported by Italian astrophysicist Mario Damasso and his colleagues in April 2019.<ref name="ProximaC">{{cite web |title=Possible 2nd Planet Spotted Around Proxima Centauri |url=https://www.space.com/proxima-centauri-possible-second-exoplanet.html |first=Mike |last=Wall |work=Space.com |date=April 12, 2019 |access-date=April 12, 2019}}</ref><ref name="SA-20190412">{{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=April 12, 2019 |access-date=April 12, 2019}}</ref> Damasso's team had noticed minor movements of Proxima Centauri in the [[Methods of detecting exoplanets#Radial velocity|radial velocity]] data from the ESO's HARPS instrument, indicating a possible additional planet orbiting Proxima Centauri.<ref name="ProximaC" /> In 2020, the planet's existence was confirmed by Hubble [[astrometry]] data from {{Circa|1995}}.<ref name="McDonald">{{cite web |url=https://mcdonaldobservatory.org/news/releases/20200602 |title=Texas Astronomer Uses 25-year-old Hubble Data to Confirm Planet Proxima Centauri c |last=Benedict |first=Fritz |date=June 2, 2020 |website=McDonald Observatory |publisher=University of Texas}}</ref> A possible direct imaging counterpart was detected in the infrared with the [[Spectro-Polarimetric High-Contrast Exoplanet Research|SPHERE]], but the authors admit that they "did not obtain a clear detection." If their candidate source is in fact Proxima Centauri c, it is too bright for a planet of its mass and age, implying that the planet may have a [[ring system]] with a radius of around 5 {{Jupiter radius|link=y}}.<ref name="Gratton2020" /> A 2022 study disputed the radial velocity confirmation of the planet.<ref name="ArtigauCadieux2022"/>

{{stack|[[File:Proxima Centauri and its planet compared to the Solar System.jpg|thumb|upright=1.2|Overview and comparison of the orbital distance of the [[habitable zone]].]]}}