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A terrestrial planet candidate in a temperate orbit around Proxima Centauri

Naturevolume 536, pages437–440 (2016)Cite this article

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Abstract

At a distance of 1.295 parsecs1, the red dwarf Proxima Centauri (α Centauri C, GL 551, HIP 70890 or simply Proxima) is the Sun’s closest stellar neighbour and one of the best-studied low-mass stars. It has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun2 and a mass of about 12 per cent of the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is about 83 days (ref.3) and its quiescent activity levels and X-ray luminosity4 are comparable to those of the Sun. Here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface5.

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Figure 1: Detection of a Doppler signal at 11.2 d.
Figure 2: All of the data sets phase-folded at the 11.2 d signal.
Figure 3: Time series obtained during the PRD campaign.

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Acknowledgements

We thank E. Gerlach, R. Street and U. Seemann for their support to the science preparations. We thank P. Micakovic, M. M. Mutter (QMUL), R. Ivison, G. Hussain, I. Saviane, O. Sandu, L. L. Christensen, R. Hook and the personnel at La Silla (ESO) for making the PRD campaign possible. The authors acknowledge support from the following funding grants: Leverhulme Trust/UK RPG-2014-281 (H.R.A.J., G.A.-E. and M.T.); MINECO/Spain AYA-2014-54348-C3-1-R (P.J.A., C.R.-L., Z.M.B. and E.R.); MINECO/Spain ESP2014-54362-P (M.J.L.-G.); MINECO/Spain AYA-2014-56637-C2-1-P (J.L.O. and N.M.); J.A./Spain 2012-FQM1776 (J.L.O. and N.M.); CATA-Basal/Chile PB06 Conicyt (J.S.J.); Fondecyt/Chile project #1161218 (J.S.J.); STFC/UK ST/M001008/1 (R.P.N., G.A.L.C. and G.A.-E.); STFC/UK ST/L000776/1 (J.B.); ERC/EU Starting Grant #279347 (A.R., L.F.S. and S.V.J.); DFG/Germany Research Grants RE 1664/9-2 (A.R.); RE 1664/12-1 (M.Z.); DFG/Germany Colloborative Research Center 963 (C.J.M. and S.D.); DFG/Germany Research Training Group 1351 (L.F.S.); and NSF/USA grant AST-1313075 (M.E.). Study based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programmes 096.C-0082 and 191.C-0505. Observations were obtained with ASH2, which is supported by the Instituto de Astrofísica de Andalucía and Astroimagen. This work makes use of observations from the LCOGT network. We acknowledge the effort of the UVES/M-dwarf and the HARPS/Geneva teams, who obtained a substantial amount of the data used in this work.

Author information

Authors and Affiliations

  1. School of Physics and Astronomy, Queen Mary University of London, 327 Mile End Road, London, E1 4NS, UK

    Guillem Anglada-Escudé, Gavin A. L. Coleman, Richard P. Nelson, Sijme-Jan Paardekooper & John P. Strachan

  2. Instituto de Astrofísica de Andalucía – Consejo Superior de Investigaciones Científicas, Glorieta de la Astronomía S/N, Granada, E-18008, Spain

    Pedro J. Amado, Zaira M. Berdiñas, Marίa J. López-González, Nicolás Morales, José L. Ortiz, Eloy Rodríguez & Cristina Rodrίguez-López

  3. Department of Physical Sciences, Open University, Walton Hall, Milton Keynes, MK7 6AA, UK

    John Barnes

  4. Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, 20015, Washington DC, USA

    R. Paul Butler

  5. Astroimagen, C. Abad y Lasierra, 58 Bis, Ibiza, 6-2, 07800, Spain

    Ignacio de la Cueva

  6. Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, Göttingen, 37077, Germany

    Stefan Dreizler, Benjamin Giesers, Sandra V. Jeffers, Christopher J. Marvin, Ansgar Reiners, Luis F. Sarmiento & Mathias Zechmeister

  7. McDonald Observatory, the University of Texas at Austin, 2515 Speedway, C1400, Austin, 78712, Texas, USA

    Michael Endl

  8. Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile

    James S. Jenkins

  9. Centre for Astrophysics Research, Science & Technology Research Institute, University of Hertfordshire, Hatfield, AL10 9AB, UK

    Hugh R. A. Jones & Mikko Tuomi

  10. Warsaw University Observatory, Aleje Ujazdowskie 4, Warszawa, Poland

    Marcin Kiraga

  11. Max-Planck-Institut für Astronomie, Königstuhl 17, Heidelberg, 69117, Germany

    Martin Kürster

  12. Laboratoire Univers et Particules de Montpellier, Université de Montpellier, Place E. Bataillon—CC 72, Montpellier, 34095, Cédex 05, France

    Julien Morin

  13. Department of Earth and Planetary Sciences, Weizmann Institute of Science, 234 Herzl Street, Rehovot, 76100, Israel

    Aviv Ofir

  14. Astronomisches Rechen-Institut, Mönchhofstrasse 12–14, Heidelberg, 69120, Germany

    Yiannis Tsapras

Authors
  1. Guillem Anglada-Escudé
  2. Pedro J. Amado
  3. John Barnes
  4. Zaira M. Berdiñas
  5. R. Paul Butler
  6. Gavin A. L. Coleman
  7. Ignacio de la Cueva
  8. Stefan Dreizler
  9. Michael Endl
  10. Benjamin Giesers
  11. Sandra V. Jeffers
  12. James S. Jenkins
  13. Hugh R. A. Jones
  14. Marcin Kiraga
  15. Martin Kürster
  16. Marίa J. López-González
  17. Christopher J. Marvin
  18. Nicolás Morales
  19. Julien Morin
  20. Richard P. Nelson
  21. José L. Ortiz
  22. Aviv Ofir
  23. Sijme-Jan Paardekooper
  24. Ansgar Reiners
  25. Eloy Rodríguez
  26. Cristina Rodrίguez-López
  27. Luis F. Sarmiento
  28. John P. Strachan
  29. Yiannis Tsapras
  30. Mikko Tuomi
  31. Mathias Zechmeister

Contributions

In the author list, after G.A.-E., the authors are listed in alphabetical order. G.A.-E. led the PRD campaign, observing proposals and organized the manuscript. P.J.A. led observing proposals and organized and supported the Instituto de Astrofisica de Andalucía team through research grants. M.T. obtained the early signal detections and most of the Bayesian analyses. J.S.J., J.B., Z.M.B. and H.R.A.J. participated in the analyses and obtained activity measurements. Z.M.B. also led observing proposals. H.R.A.J. funded several co-authors via research grants. M. Kuerster and M.E. provided the extracted UVES spectra, and R.P.B. re-derived radial velocity measurements. C.R.-L. coordinated photometric follow-up campaigns. E.R. led the ASH2 team and related reductions (M.J.L.-G., I.d.l.C., J.L.O. and N.M.). Y.T. led the LCOGT proposals, campaign and reductions. M.Z. obtained observations and performed analyses on HARPS and UVES spectra. A.O. analysed time series and transit searches. J.M., S.V.J. and A.R. analysed stellar activity data. A.R. funded several co-authors via research grants. R.P.N., G.A.L.C., S.-J.P., S.D. and B.G. did dynamical studies and studied the planet formation context. M. Kiraga provided early access to time series from the ASAS survey. C.J.M. and L.F.S. participated in the HARPS campaigns. All authors contributed to the preparation of observing proposals and the manuscript.

Corresponding author

Correspondence toGuillem Anglada-Escudé.

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Competing interests

The authors declare no competing financial interests.

Additional information

Reviewer Information

Nature thanks A. Hatzes and D. Queloz for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Figure 1 Window function.

a–c, Window function of the UVES (a), HARPS pre-2016 (b) and HARPS PRD (c) data sets. The same window function applies to the time series of Doppler and activity data. Peaks in the window function are periods at which aliases of infinite period signals would be expected. The green vertical lines mark the period of the planet candidate at 11.2 d.

Extended Data Figure 2 Signal searches on independent radial velocity data sets.

a–c, Likelihood-ratio periodograms searches on the radial velocity (RV) measurements of the UVES (a), HARPS pre-2016 (b) and HARPS PRD (c) subsets. The periodogram with all three sets combined is shown inFig. 1. The black and red lines represent the searches for the first and second signals, respectively. The green vertical lines mark the period of the planet candidate at 11.2 d.

Extended Data Figure 3 Signal searches on the photometry.

a–d, Likelihood-ratio periodograms searches for signals in each photometric ASH2 photometric band (a,b) and LCOGT bands (c,d). The two sinusoid fits to the ASH2 Sii series (P1 = 84 d,P2 = 39.1 d) are used later to construct theFF′ model to test for correlations of the photometry with the radial velocity data. The black, red and blue lines represent the search for the first, second and third signal respectively. The green vertical lines mark the period of the planet candidate at 11.2 d.

Extended Data Figure 4 Signal searches on the width of the spectral lines.

a,b, Likelihood-ratio periodogram searches on the width of the mean spectral line as measured bym2 for the HARPS pre-2016 (a) and HARPS PRD data (b). The signals in the HARPS pre-2016 data are comparable to the photometric period reported in the literature and the variability in the HARPS PRD run compares quite well to the photometric variability. The black, red and blue lines represent the search for the first, second and third signal, respectively. The green vertical lines mark the period of the planet candidate at 11.2 d.

Extended Data Figure 5 Signal searches on the asymmetry of the spectral lines.

a,b, Likelihood-ratio periodogram searches on the line asymmetry as measured bym3 from the HARPS pre-2016 (a) and HARPS PRD (b) data sets. Signal beating at around 1 yr and 0.5 yr is detected in the HARPS pre-2016 data, which is possibly related to instrumental systematic effects or telluric contamination. No signals are detected above the 1% threshold in the HARPS PRD campaign. The black and red lines represent the search for the first and second signals respectively. The green vertical lines mark the period of the planet candidate at 11.2 d.

Extended Data Figure 6 Signal searches on the chromosphericS-index.

a,b, Likelihood-ratio periodogram of theS-index from the HARPS pre-2016 (a) and HARPS PRD (b) campaigns. No signals were detected above the 1% threshold. The green vertical lines mark the period of the planet candidate at 11.2 d.

Extended Data Figure 7 Signal searches on the spectroscopic Hα index.

a–c, Likelihood-ratio periodogram searches of Hα intensity from the UVES (a), HARPS pre-2016 (b) and HARPS PRD (c) campaigns. No signals were detected above the 1% threshold. The green vertical lines mark the period of the planet candidate at 11.2 d.

Extended Data Figure 8 Radial velocities and chromospheric emission during a flare.

a–d, Radial velocities (a) and equivalent width measurements of the Hα (b), Na doublet lines (c) and theS-index (d) as a function of time during a flare that occurred the night of 5 May 2013. The time axis is days sincejd = 245417.0 d. No trace of the flare is observed in the radial velocities. Error bars in the radial velocities correspond to 1σ errors. The formal 1σ errors in the equivalent width measurements are comparable to the size of the points.

Extended Data Figure 9 Probability distributions for the activity coefficients versus the signal amplitude.

a–n, Marginalized posterior densities of the activity coefficients versus the semi-amplitude of the signal for UVES (a), HARPS pre-2016 (b–f), HARPS PRD campaign (g–k) and the photometricFF′ indices for the PRD campaign only (l–n). Each panel shows equiprobability contours containing 50%, 95% and 99% of the probability density around the mean estimate, and the corresponding standard deviation of the marginalized distribution (1σ) in red. The blue bar shows the zero value of each activity coefficient. OnlyCF′ is found to be substantially different from zero.

Extended Data Table 1 Complete set of model parameters

Supplementary information

Supplementary Data

This zipped file contains the time-series used in the paper. All time-series are given as plain ASCII/CSV files (columns separated by commas) and follow the same format. See the README file within the zip folder for details. (ZIP 62 kb)

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Anglada-Escudé, G., Amado, P., Barnes, J.et al. A terrestrial planet candidate in a temperate orbit around Proxima Centauri.Nature536, 437–440 (2016). https://doi.org/10.1038/nature19106

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  1. Guillem Anglada

    The authors would like to acknowledge useful discussions and quantitative feedback provided by Dr. Javier Pascual Granado and Prof. Rafael Garrido at IAA/CSIC on the mathematical properties of time-series under the section "Methods. Further tests on the signal" during the preparation of the manus cript.

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