Fork me on GitHub
an open source database of all discovered extrasolar planets

Alpha Centauri

The planetary system Alpha Centauri hosts at least 5 planets. Note that the system is a multiple star system. It hosts at least 3 stellar components.

  System parameters
Primary system name Alpha Centauri
Alternative system names Rigil Kentaurus, Rigil Kent, alpha Cen B, Toliman, Bungula, Proxima Centauri
Right ascension 14 39 36.204
Declination -60 50 08.23
Distance [parsec] 1.295±0.004
Distance [lightyears] 4.224±0.015
Number of stars in system 3
Number of planets in system 5



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: 15000 AU
    •  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
          •  Proxima Centauri, stellar object
            •  Proxima Centauri b, planet, semi-major axis: 0.049+0.004−0.005 AU
              •  Proxima Centauri c, planet
                •  Proxima Centauri d, planet, semi-major axis: 0.0289±0.0002 AU

              PlanetsPlanets in the system

              This table lists all planets in the system Alpha Centauri.

                Proxima Centauri b Proxima Centauri c Proxima Centauri d Alpha Centauri B b Alpha Centauri B c
              Alternative planet names α Centauri C b, GL 551 b, HIP 70890 b, Proxima b α Centauri C c, GL 551 c, HIP 70890 c, Proxima c α Centauri C d, GL 551 d, HIP 70890 d, Proxima d 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 Astronomers using ESO telescopes and other facilities have found clear evidence of a planet orbiting the closest star to Earth, Proxima Centauri. The long-sought world, designated Proxima b, orbits its cool red parent star every 11 days and has a temperature suitable for liquid water to exist on its surface. This rocky world is a little more massive than the Earth and is the closest exoplanet to us — and it may also be the closest possible abode for life outside the Solar System. Proxima c is a Super-Earth about 7 times as heavy as Earth, orbiting at roughly 1.5 astronomical units (220,000,000 km) every 1,900 days (5.2 yr). Due to its large distance from Proxima Centauri, the exoplanet is unlikely to be habitable, with a low equilibrium temperature of around 39 K. The planet was first reported by Italian astrophysicist Mario Damasso and his colleagues in April 2019. Damasso's team had noticed minor movements of Proxima Centauri in the radial velocity data from the ESO's HARPS instrument, indicating a possible additional planet orbiting Proxima Centauri. In 2020, the planet's existence was confirmed by precovery images from Hubble c. 1995, making it the first and closest planet ever to be directly imaged. Due to the differences in how its light shines throughout its orbit, the planet is speculated to have a ring system. This planet has been found using a large set of observations taken with the ESPRESSO spectrograph at the VLT. This candidate planet is the third detected in the system and the lightest yet discovered orbiting this star. At just a quarter of Earth’s mass, the planet is also one of the lightest exoplanets ever found. The analysis of subsets of the ESPRESSO data, the activity indicators, and chromatic RVs suggest that this signal is not caused by stellar variability but instead by a planetary companion. 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). 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.
              Lists Confirmed planets; Planets in binary systems, S-type Confirmed planets; Planets in binary systems, S-type Confirmed planets; Planets in binary systems, S-type Retracted planet candidate; Planets in binary systems, S-type Controversial; Planets in binary systems, S-type
              Mass [Mjup] 0.0037±0.0003 0.022±0.003 ( 8.2±1.6 )·10-4 0.0036±0.0003 N/A
              Mass [Mearth] 1.17±0.09 7.0±1.0 0.26±0.05 1.13±0.09 N/A
              Radius [Rjup] N/A N/A N/A N/A 0.084±0.005
              Radius [Rearth] N/A N/A N/A N/A 0.94±0.06
              Orbital period [days] 11.1843±0.0007 1929±20 5.122+0.002−0.036 3.2357±0.0008 < 20.4000
              Semi-major axis [AU] 0.049+0.004−0.005 N/A 0.0289±0.0002 0.0400 N/A
              Eccentricity < 0.3500 N/A 0.04+0.15−0.04 0.00 < 0.2400
              Equilibrium temperature [K] 234+6−14 N/A N/A N/A N/A
              Discovery method RV RV RV RV transit
              Discovery year 2016 2019 2022 2012 2015
              Last updated [yy/mm/dd] 16/08/22 20/08/29 22/02/10 20/08/29 15/11/17

              starStars in the system

              This table lists all stars in the system Alpha Centauri.

                Proxima Centauri Alpha Centauri A Alpha Centauri B
              Alternative star names α Centauri C, GL 551, HIP 70890, Proxima 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] 0.12±0.02 1.100±0.006 0.907±0.006
              Radius [RSun] 0.141+0.022−0.019 1.227±0.005 0.865±0.006
              Age [Gyr] N/A N/A N/A
              Metallicity [Fe/H] N/A 0.20±0.02 0.23±0.03
              Temperature [K] 2900±100 5790±30 5260±50
              Spectral type M5.5V G2 V K1 V
              Visual magnitude N/A 0.0100 1.330

              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).

              PlutoMercuryMarsVenusEarthNeptuneUranusSaturnJupiterProxima Centauri bProxima Centauri cProxima Centauri dAlpha 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.

              Proxima Centauri

              Habitable zoneProxima Centauri bProxima Centauri cProxima Centauri d

              Alpha Centauri B

              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
              Diamondraph 54761256+TheDeathStar3(at) 1
              Hanno Rein hanno(at) 20
              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 useful.


              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.