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Alpha Centauri

The planetary system Alpha Centauri hosts at least 2 planets. Note that the system is a multiple star system. It hosts at least 2 stellar components.

  System parameters
Primary system name Alpha Centauri
Alternative system names Rigil Kentaurus, Rigil Kent, Toliman, Bungula
Right ascension 14 39 36.204
Declination -60 50 08.23
Distance [parsec] 1.342±0.004edit
Distance [lightyears] 4.376±0.015
Number of stars in system 2
Number of planets in system 2



This artist's impression shows the planet orbiting the star Alpha Centauri B, a member of the triple star system that is the closest to Earth. Alpha Centauri B is the most brilliant object in the sky and the other dazzling object is Alpha Centauri A. Our own Sun is visible to the upper right. The tiny signal of the planet was found with the HARPS spectrograph on the 3.6-metre telescope at ESO's La Silla Observatory in Chile. Credit: ESO/L. Calcada

ArchitectureArchitecture of the system

This list shows all planetary and stellar components in the system. It gives a quick overview of the hierarchical architecture.

  •  Stellar binary, semi-major axis: 23.52±0.05 AU, 79.912±0.011 years
    •  Alpha Centauri A, stellar object
      •  Alpha Centauri B, stellar object
        •  Alpha Centauri B b, planet, semi-major axis: 0.0400 AU
          •  Alpha Centauri B c, planet

        PlanetsPlanets in the system

        This table lists all planets in the system Alpha Centauri.

          Alpha Centauri B b Alpha Centauri B c
        Alternative planet names GJ 559 B b, HR 5460 b, HD 128621 b, HIP 71681 b, Albertus Alauda, alf Cen B b GJ 559 B c, HR 5460 c, HD 128621 c, HIP 71681 c, alf Cen B c
        Description Alpha Centauri is one of the brightest stars in the southern sky (in fact, it is a triple system). The planet candidate Alpha Centauri Bb was announced as the nearest exoplanet to Earth and also the lightest exoplanet ever discovered around a Sun-like star. The candidate was detected using the HARPS instrument on the 3.6-metre telescope at ESO's La Silla Observatory in Chile. The planet's existence was challenged by Hatzes (2013) and was shown to be likely an artifact caused by the data sampling by Rajpaul et al. (2015).edit A possible transit event was detected in Hubble Space Telescope photometry of Alpha Centauri B while searching for transits of the planet candidate Alpha Centauri Bb. This may be due to the presence of a roughly Earth-sized planet in an orbit less than 20 days.edit
        Lists Controversial; Planets in binary systems, S-type
        Mass [Mjup] 0.0036±0.0003edit N/A
        Mass [Mearth] 1.13±0.09 N/A
        Radius [Rjup] N/A 0.084±0.005edit
        Radius [Rearth] N/A 0.92±0.06
        Orbital period [days] 3.2357±0.0008edit < 20.4000edit
        Semi-major axis [AU] 0.0400edit N/A
        Eccentricity 0.00edit < 0.2400edit
        Equilibrium temperature [K] N/A N/A
        Discovery method RV transit
        Discovery year 2012 2015
        Last updated [yy/mm/dd] 15/11/17

        starStars in the system

        This table lists all stars in the system Alpha Centauri.

          Alpha Centauri A Alpha Centauri B
        Alternative star names alf Cen A, α Cen A, α Centauri A, Alpha-1 Centauri, alf01 Cen, α1 Cen, α1 Centauri, Rigil Kentaurus A, Rigil Kent A, Toliman A, Bungula A, Gliese 559 A, GJ 559 A, HR 5459, HD 128620, HIP 71683, TYC 9007-5849-1, CD-60 5293 A, CPD-60 5483 A, WDS J14396-6050 A, RHD 1 A alf Cen B, α Cen B, α Centauri B, Alpha-2 Centauri, alf02 Cen, α2 Cen, α2 Centauri, Rigil Kentaurus B, Rigil Kent B, Toliman B, Bungula B, Gliese 559 B, GJ 559 B, HR 5460, HD 128621, HIP 71681, TYC 9007-5848-1, WDS J14396-6050 B, RHD 1 B
        Mass [MSun] 1.100±0.006edit 0.907±0.006edit
        Radius [RSun] 1.227±0.005edit 0.865±0.006edit
        Age [Gyr] N/A N/A
        Metallicity [Fe/H] 0.20±0.02edit 0.23±0.03edit
        Temperature [K] 5790±30edit 5260±50edit
        Spectral type G2 V K1 V
        Visual magnitude 0.0100edit 1.330edit

        Planet sizes

        The following plot shows the approximate sizes of the planets in this system The Solar System planets are shown as a comparison. Note that unless the radius has been determined through a transit observation, this is only an approximation (see Lissauer et al. 2011b).

        PlutoMercuryMarsVenusEarthNeptuneUranusSaturnJupiterAlpha Centauri B bAlpha Centauri B c

        Habitable zone

        The following plot shows the approximate location of the planets in this system with respect to the habitable zone (green) and the size of the star (red). This is only an estimate, using the star's spectral type and mass. Note that if no green band is shown in the plot, then the planet's orbit is far outside the habitable zone. The equations of Selsis, Kasting et al are used to draw the inner and outer boundaries.

        Habitable zoneAlpha Centauri B bAlpha Centauri B c

        referencesScientific references and contributors

        Links to scientific papers and other data sources


        This table lists all links which are relevant to this particular system. Note that this is just a summary. More references to the scientific publications and comments can be found in the commit messages. To see these, head over the github or click here to directly go to the git blame output of this system. In the left column of the output you can see the commit message corresponding to each parameter. It also lists the date of the last commit and the person making the changes. Within the commit message, you will find a link to the scientific publication where the data is taken from. Note that this is a new feature and not all system parameters might have a reference associated with it yet. Please help making this catalogue better and contribute data or references!

        Open Exoplanet Catalogue contributors

        Contributor E-mail Number of commits
        Andrew Tribick ajtribick(at) 2
        Christian Sturm Sol-d(at) 1
        Hanno Rein hanno(at) 11
        Marc-Antoine Martinod marc-antoine.martinod(at) 1

        This table lists all people who have contributed to the Open Exoplanet Catalogue. Please consider contributing! Click here to find out how. You can also view all commits contributing to this file on github.

        xmlData download

        You can download the xml file corresponding to this planetary system, which is part of the Open Exoplanet Catalogue. All information on this page has been directly generated from this XML file. You can also download the entire catalogue over at github. If you prefer to download the dataset as an ASCII tables, you might find the oec_tables repository usefule.


        If you spot an error or if you can contribute additional data to this entry, please send an e-mail to Please include the corrected xml file and a reference to where the new data is coming from, ideally a scientific paper. If you are fluent with git and github, you can also create a pull request or open an issue on the Open Exoplanet Catalogue repository. Please include the reference to the relevant scientific paper in your commit message.