Abstract

One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization. Recently, three Earth-sized planets were detected that transit (that is, pass in front of) a star with a mass just eight per cent that of the Sun, located 12 parsecs away1. The transiting configuration of these planets, combined with the Jupiter-like size of their host star—named TRAPPIST-1—makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities1,2,3. Here we report the results of a photometric monitoring campaign of that star from the ground and space. Our observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers. This architecture suggests that the planets formed farther from the star and migrated inwards4,5. Moreover, the seven planets have equilibrium temperatures low enough to make possible the presence of liquid water on their surfaces6,7,8.

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Acknowledgements

This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. The material presented here is based on work supported in part by NASA under contract no. NNX15AI75G. TRAPPIST-South is a project funded by the Belgian Fonds (National) de la Recherche Scientifique (F.R.S.-FNRS) under grant FRFC 2.5.594.09.F, with the participation of the Swiss National Science Foundation (FNS/SNSF). TRAPPIST-North is a project funded by the University of Liège, and performed in collaboration with Cadi Ayyad University of Marrakesh. The research leading to these results has received funding from the European Research Council (ERC) under the FP/2007-2013 ERC grant agreement no. 336480, and under the H2020 ERC grant agreement no. 679030; and from an Actions de Recherche Concertée (ARC) grant, financed by the Wallonia–Brussels Federation. The VLT data used in this work were taken under program 296.C-5010(A). UKIRT is supported by NASA and operated under an agreement among the University of Hawaii, the University of Arizona, and Lockheed Martin Advanced Technology Center; operations are enabled through the cooperation of the East Asian Observatory. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University (JMU) in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, with financial support from the UK Science and Technology Facilities Council. This paper uses observations made at the South African Astronomical Observatory (SAAO). M.G., E.J. and V.V.G. are F.R.S.-FNRS research associates. B.-O.D. acknowledges support from the Swiss National Science Foundation in the form of a SNSF Professorship (PP00P2_163967). E.A. acknowledges support from National Science Foundation (NSF) grant AST-1615315, and NASA grants NNX13AF62G and NNH05ZDA001C. E.B. acknowledges that this work is part of the F.R.S.-FNRS ExtraOrDynHa research project and acknowledges funding by the European Research Council through ERC grant SPIRE 647383. S.N.R. thanks the Agence Nationale pour la Recherche (ANR) for support via grant ANR-13-BS05-0003-002 (project MOJO). D.L.H. acknowledges financial support from the UK Science and Technology Facilities Council. The authors thank C. Owen, C. Wolf and the rest of the SkyMapper team for their attempts to monitor the star from Australia; from UKIRT, the director R. Green and the staff scientists W. Varricatt and T. Kerr; the ESO staff at Paranal for their support with the HAWK-I observations; JMU and their flexibility as regards the Liverpool Telescope schedule, which allowed us to search actively for the planets, and to extend our time allocation in the face of amazing results; for the William Herschel Telescope, C. Fariña, F. Riddick, F. Jímenez and O. Vaduvescu for their help and kindness during observations; and for SAAO, the telescopes operations manager R. Sefako for his support.

Author information

Affiliations

  1. Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, Bat. B5C, 4000 Liège, Belgium

    • Michaël Gillon
    • , Emmanuël Jehin
    • , Artem Burdanov
    • , Laetitia Delrez
    • , Catarina S. Fernandes
    • , Valérie Van Grootel
    •  & Pierre Magain
  2. Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK

    • Amaury H. M. J. Triaud
  3. University of Bern, Center for Space and Habitability, Sidlerstrasse 5, CH-3012 Bern, Switzerland

    • Brice-Olivier Demory
  4. Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK

    • Brice-Olivier Demory
    • , Laetitia Delrez
    •  & Didier Queloz
  5. Astronomy Department, University of Washington, Seattle, Washington 98195, USA

    • Eric Agol
  6. NASA Astrobiology Institute’s Virtual Planetary Laboratory, Seattle, Washington 98195, USA

    • Eric Agol
  7. Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA

    • Katherine M. Deck
  8. NASA Johnson Space Center, 2101 NASA Parkway, Houston, Texas 77058, USA

    • Susan M. Lederer
  9. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA

    • Julien de Wit
  10. Spitzer Science Center, California Institute of Technology, 1200 E California Boulevard, Mail Code 314-6, Pasadena, California 91125, USA

    • James G. Ingalls
    •  & Sean J. Carey
  11. NaXys, Department of Mathematics, University of Namur, 8 Rempart de la Vierge, 5000 Namur, Belgium

    • Emeline Bolmont
  12. Laboratoire AIM Paris-Saclay, CEA/DRF–CNRS–Univ. Paris Diderot - IRFU/SAp, Centre de Saclay, F- 91191 Gif-sur-Yvette Cedex, France

    • Emeline Bolmont
  13. Laboratoire d'astrophysique de Bordeaux, Université Bordeaux, CNRS, B18N, Allée Geoffroy Saint-Hilaire, F-33615 Pessac, France

    • Jeremy Leconte
    • , Sean N. Raymond
    •  & Franck Selsis
  14. Laboratoire de Météorologie Dynamique, Sorbonne Universités, UPMC Univ Paris 06, CNRS, 4 Place Jussieu, 75005 Paris, France

    • Martin Turbet
  15. Laboratoire LPHEA, Oukaimeden Observatory, Cadi Ayyad University/FSSM, BP 2390 Marrakesh, Morocco

    • Khalid Barkaoui
    •  & Zouhair Benkhaldoun
  16. Center for Astrophysics and Space Science, University of California San Diego, La Jolla, California 92093, USA

    • Adam Burgasser
  17. Leicester Institute for Space and Earth Observation, Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK

    • Matthew R. Burleigh
    •  & Aleksander Chaushev
  18. Astrophysics Research Institute, Liverpool John Moores University, Liverpool L3 5RF, UK

    • Chris M. Copperwheat
  19. Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK

    • Daniel L. Holdsworth
  20. South African Astronomical Observatory, PO Box 9, Observatory, 7935, South Africa

    • Enrico J. Kotze
  21. Space and Astronomy Department, Faculty of Science, King Abdulaziz University, 21589 Jeddah, Saudi Arabia

    • Yaseen Almleaky
  22. King Abdullah Centre for Crescent Observations and Astronomy, Makkah Clock, Mecca 24231, Saudi Arabia

    • Yaseen Almleaky
  23. Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, CH-1290 Sauverny, Switzerland

    • Didier Queloz

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Contributions

M.G. leads the ultracool dwarf transit survey that uses the TRAPPIST telescope and led the photometric follow-up of the star TRAPPIST-1; he also planned and analysed most of the observations, led their scientific exploitation, and wrote most of the manuscript. A.H.M.J.T. led the observational campaign using the La Palma telescopes (the Liverpool Telescope, LT, and William Herschel Telescope, WHT). C.M.C. managed the scheduling of the LT observations, and Ar.B. performed the photometric analysis of the resulting LT and WHT images. B.-O.D. led the TTV/dynamical simulations. E.A. and K.M.D. performed independent analyses of the transit timings. J.G.I. and S.J.C. helped to optimize the Spitzer observations. B.-O.D., J.G.I. and J.d.W. performed independent analyses of the Spitzer data. M.G., E.J., L.D., Ar.B., P.M., K.B., Y.A. and Z.B. performed the TRAPPIST observations and their analysis. S.M.L. obtained the director’s discretionary time on UKIRT, and, with E.J., managed the preparation of the UKIRT observations. M.T., J.L., F.S., E.B. and S.N.R. carried out atmospheric modelling for the planets and worked on the theoretical interpretation of their properties. V.V.G. managed the SAAO observations performed by C.S.F., M.R.B., D.L.H., A.C. and E.J.K. All co-authors assisted with writing the manuscript. A.H.M.J.T. prepared most of the figures.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Michaël Gillon.

Reviewer Information Nature thanks D. Deming and I. Snellen for their contribution to the peer review of this work.

Extended data