Most known extrasolar planets (exoplanets) have been discovered using the radial velocity1,2 or transit3 methods. Both are biased towards planets that are relatively close to their parent stars, and studies find that around 17–30% (refs 4, 5) of solar-like stars host a planet. Gravitational microlensing6,7,8,9, on the other hand, probes planets that are further away from their stars. Recently, a population of planets that are unbound or very far from their stars was discovered by microlensing10. These planets are at least as numerous as the stars in the Milky Way10. Here we report a statistical analysis of microlensing data (gathered in 2002–07) that reveals the fraction of bound planets 0.5–10 au (Sun–Earth distance) from their stars. We find that of stars host Jupiter-mass planets (0.3–10 MJ, where MJ = 318 M and M is Earth’s mass). Cool Neptunes (10–30 M) and super-Earths (5–10 M) are even more common: their respective abundances per star are and . We conclude that stars are orbited by planets as a rule, rather than the exception.

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Support for the PLANET project was provided by the HOLMES grant from the French Agence Nationale de la Recherche (ANR), the French National Centre for Scientific Research (CNRS), NASA, the US National Science Foundation, the Lawrence Livermore National Laboratory/National Nuclear Security Administration/Department of Energy, the French National Programme of Planetology, the Program of International Cooperation in Science France–Australia, D. Warren, the German Research Foundation, the Instrument Center for Danish Astronomy and the Danish Natural Science Research Council. The OGLE collaboration is grateful for funding from the European Research Council Advanced Grants Program. K.Ho. acknowledges support from the Qatar National Research Fund. M.D. is a Royal Society University Research Fellow.

Author information


  1. Probing Lensing Anomalies Network (PLANET) Collaboration, Institut d’Astrophysique de Paris, Université Pierre & Marie Curie, UMR7095 UPMC–CNRS 98 bis boulevard Arago, 75014 Paris, France

    • A. Cassan
    • , D. Kubas
    • , J.-P. Beaulieu
    • , M. Dominik
    • , K. Horne
    • , J. Greenhill
    • , J. Wambsganss
    • , J. Menzies
    • , A. Williams
    • , U. G. Jørgensen
    • , D. P. Bennett
    • , M. D. Albrow
    • , V. Batista
    • , S. Brillant
    • , J. A. R. Caldwell
    • , A. Cole
    • , Ch. Coutures
    • , K. H. Cook
    • , S. Dieters
    • , D. Dominis Prester
    • , J. Donatowicz
    • , P. Fouqué
    • , K. Hill
    • , N. Kains
    • , S. Kane
    • , J.-B. Marquette
    • , R. Martin
    • , K. R. Pollard
    • , K. C. Sahu
    • , C. Vinter
    • , D. Warren
    • , B. Watson
    •  & M. Zub
  2. Institut d’Astrophysique de Paris, Université Pierre & Marie Curie, UMR7095 UPMC–CNRS 98 bis boulevard Arago, 75014 Paris, France

    • A. Cassan
    • , D. Kubas
    • , J.-P. Beaulieu
    • , V. Batista
    • , Ch. Coutures
    •  & J.-B. Marquette
  3. Astronomischen Rechen-Instituts (ARI), Zentrum für Astronomie, Heidelberg University, Mönchhofstrasse 12–14, 69120 Heidelberg, Germany

    • A. Cassan
    • , J. Wambsganss
    •  & M. Zub
  4. European Southern Observatory, Alonso de Cordoba 3107, Vitacura, Casilla 19001, Santiago, Chile

    • D. Kubas
    •  & S. Brillant
  5. Scottish Universities Physics Alliance (SUPA), University of St Andrews, School of Physics & Astronomy, North Haugh, St Andrews, KY16 9SS, UK

    • M. Dominik
    •  & K. Horne
  6. University of Tasmania, School of Maths and Physics, Private bag 37, GPO Hobart, Tasmania 7001, Australia

    • J. Greenhill
    • , A. Cole
    • , S. Dieters
    • , K. Hill
    • , D. Warren
    •  & B. Watson
  7. South African Astronomical Observatory, PO Box 9 Observatory 7935, South Africa

    • J. Menzies
  8. Perth Observatory, Walnut Road, Bickley, Perth 6076, Australia

    • A. Williams
    •  & R. Martin
  9. Niels Bohr Institute and Centre for Star and Planet Formation, Juliane Mariesvej 30, 2100 Copenhagen, Denmark

    • U. G. Jørgensen
    •  & C. Vinter
  10. Optical Gravitational Lensing Experiment (OGLE) Collaboration, Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

    • A. Udalski
    • , M. K. Szymański
    • , M. Kubiak
    • , R. Poleski
    • , I. Soszynski
    • , K. Ulaczyk
    • , G. Pietrzyński
    •  & Ł. Wyrzykowski
  11. Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

    • A. Udalski
    • , M. K. Szymański
    • , M. Kubiak
    • , R. Poleski
    • , I. Soszynski
    • , K. Ulaczyk
    • , G. Pietrzyński
    •  & Ł. Wyrzykowski
  12. University of Notre Dame, Physics Department, 225 Nieuwland Science Hall, Notre Dame, Indiana 46530, USA

    • D. P. Bennett
  13. University of Canterbury, Department of Physics & Astronomy, Private Bag 4800, Christchurch 8140, New Zealand

    • M. D. Albrow
    •  & K. R. Pollard
  14. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA

    • J. A. R. Caldwell
    •  & K. C. Sahu
  15. Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, PO Box 808, California 94550, USA

    • K. H. Cook
  16. Department of Physics, University of Rijeka, Omladinska 14, 51000 Rijeka, Croatia

    • D. Dominis Prester
  17. Technical University of Vienna, Department of Computing, Wiedner Hauptstrasse 10, 1040 Vienna, Austria

    • J. Donatowicz
  18. Laboratoire Astrophysique de Toulouse (LATT), Université de Toulouse, CNRS, 31400 Toulouse, France

    • P. Fouqué
  19. European Southern Observatory Headquarters, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany

    • N. Kains
  20. NASA Exoplanet Science Institute, Caltech, MS 100-22, 770 South Wilson Avenue, Pasadena, California 91125, USA

    • S. Kane
  21. Microlensing Observations in Astrophysics (MOA) Collaboration, Department of Earth and Space Science, Osaka University, Osaka 560-0043, Japan

    • T. Sumi
  22. Department of Earth and Space Science, Osaka University, Osaka 560-0043, Japan

    • T. Sumi
  23. Universidad de Concepción, Departamento de Fisica, Casilla 160-C, Concepción, Chile

    • G. Pietrzyński
  24. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

    • Ł. Wyrzykowski
  25. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

    • J.-P. Beaulieu


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A.Ca. led the analysis and conducted the modelling and statistical analyses. A.Ca. and D.K. selected light curves from 2002–07 PLANET/OGLE microlensing seasons, analysed the data and wrote the Letter and Supplement. D.K. computed the magnification maps used for the detection-efficiency calculations. J.-P.B. and Ch.C. wrote the software for online data reduction at the telescopes. J.-P.B. led the PLANET collaboration, with M.D., J.G., J.M. and A.W.; P.F. and M.D.A. contributed to online and offline data reduction. M.D. contributed to the conversion of the detection efficiencies to physical parameter space and developed the PLANET real-time display system with A.W., M.D.A. and Ch.C.; K.Ho. and A.Ca. developed and tested the Bayesian formulation for fitting the two-parameter power-law mass function. J.G. edited the manuscript, conducted the main data cleaning and managed telescope operations at Mount Canopus (1 m) in Hobart. J.W. wrote the original magnification maps software, discussed the main implications and edited the manuscript. J.M., A.W. and U.G.J. respectively managed telescope operations in South Africa (South African Astronomical Observatory 1 m), Australia (Perth 0.61 m) and La Silla (Danish 1.54 m). A.U. led the OGLE campaign and provided the final OGLE photometry. D.P.B, V.B., S.B., J.A.R.C., A.Co., K.H.C., S.D., D.D.P., J.D., P.F., K.Hi., N.K., S.K., J.-B.M., R.M., K.R.P., K.C.S., C.V., D.W., B.W. and M.Z. were involved in the PLANET observing strategy and/or PLANET data acquisition, reduction, real-time analysis and/or commented on the manuscript. T.S. commented on the manuscript. M.K.S., M.K., R.P., I.S., K.U., G.P. and Ł.W. contributed to OGLE data.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to A. Cassan or A. Cole.

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    Supplementary Information

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