Article | Published:

An Earth-mass planet orbiting α Centauri B

Nature volume 491, pages 207211 (08 November 2012) | Download Citation



Exoplanets down to the size of Earth have been found, but not in the habitable zone—that is, at a distance from the parent star at which water, if present, would be liquid. There are planets in the habitable zone of stars cooler than our Sun, but for reasons such as tidal locking and strong stellar activity, they are unlikely to harbour water–carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult, because such a signal is overwhelmed by stellar perturbations. Here we report the detection of an Earth-mass planet orbiting our neighbour star α Centauri B, a member of the closest stellar system to the Sun. The planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star (one astronomical unit is the Earth–Sun distance).

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The data presented here were obtained with the ESO 3.6-m telescope at La Silla Paranal Observatory, Chile. We thank the Swiss National Science Foundation (FNRS) for continuous support. We thank R. Mardeling for English revision. N.S. and X.D. acknowledge support by the European Research Council/European Community under FP7 through Starting Grant agreement number 239953, as well as from Fundacao para a Cîencia e a Tecnologia (FCT) through programme Cîencia 2007 funded by FCT/MCTES (Portugal) and POPH/FSE (EC), and in the form of grants PTDC/CTE-AST/098528/2008 and PTDC/CTE-AST/098604/2008.

Author information


  1. Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, CH-1290 Sauverny, Switzerland

    • Xavier Dumusque
    • , Francesco Pepe
    • , Christophe Lovis
    • , Damien Ségransan
    • , Johannes Sahlmann
    • , François Bouchy
    • , Michel Mayor
    • , Didier Queloz
    •  & Stéphane Udry
  2. Centro de Astrofìsica da Universidade do Porto, Rua das Estrelas, P-4150-762 Porto, Portugal

    • Xavier Dumusque
    •  & Nuno Santos
  3. Physikalisches Institut Universitat Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland

    • Willy Benz
  4. Institut d’Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis Boulevard Arago, F-75014 Paris, France

    • François Bouchy
  5. Departamento de Fìsica e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, P-4169-007 Porto, Portugal

    • Nuno Santos


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F.P., C.L., W.B., F.B., M.M., D.Q., N.S. and S.U. obtained data under the ESO programme ‘Searching for Earth-analogs around nearby stars with HARPS’. The HARPS spectrograph was designed and built by F.P., C.L., W.B., F.B., M.M., D.Q. and S.U. C.L. and D.S. performed the reduction of the data. Data analysis was carried out by X.D., J.S., F.P., D.S. and C.L. All the work was supervised by S.U. All authors discussed the results and contributed to the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Xavier Dumusque or Francesco Pepe.

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    Supplementary Information

    This file contains Supplementary Text and Data 1-9, Supplementary Figures 1-13, Supplementary Tables 1-2 and additional references.

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    Supplementary Data

    This text file contains all data used in our analysis, in tab-separated format.

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