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An Earth-mass planet orbiting α Centauri B



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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Figure 1: Radial velocities of α Centauri B and fitting the long-timescale stellar signals.
Figure 2: Magnetic cycle of α Centauri B.
Figure 3: Fit of the rotational activity.
Figure 4: Periodograms of the radial-velocity residuals after removing the non-planetary signals.
Figure 5: Phase-folded radial-velocity curve with a period of 3.2357 d.


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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.

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Authors and Affiliations



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.

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Correspondence to Xavier Dumusque or Francesco Pepe.

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The authors declare no competing financial interests.

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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. (PDF 4834 kb)

Supplementary Data

This text file contains all data used in our analysis, in tab-separated format. (TXT 56 kb)

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Dumusque, X., Pepe, F., Lovis, C. et al. An Earth-mass planet orbiting α Centauri B. Nature 491, 207–211 (2012).

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