Letter | Published:

Unbound or distant planetary mass population detected by gravitational microlensing

Nature 473, 349–352 (19 May 2011) | Download Citation

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Abstract

Since 1995, more than 500 exoplanets have been detected using different techniques1,2, of which 12 were detected with gravitational microlensing3,4. Most of these are gravitationally bound to their host stars. There is some evidence of free-floating planetary-mass objects in young star-forming regions5,6,7,8, but these objects are limited to massive objects of 3 to 15 Jupiter masses with large uncertainties in photometric mass estimates and their abundance. Here, we report the discovery of a population of unbound or distant Jupiter-mass objects, which are almost twice () as common as main-sequence stars, based on two years of gravitational microlensing survey observations towards the Galactic Bulge. These planetary-mass objects have no host stars that can be detected within about ten astronomical units by gravitational microlensing. However, a comparison with constraints from direct imaging9 suggests that most of these planetary-mass objects are not bound to any host star. An abrupt change in the mass function at about one Jupiter mass favours the idea that their formation process is different from that of stars and brown dwarfs. They may have formed in proto-planetary disks and subsequently scattered into unbound or very distant orbits.

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Acknowledgements

The MOA collaboration thanks the JSPS and MEXT of Japan, and the Marsden Fund of New Zealand, for support. D.P.B. acknowledges support by the NSF and NASA. The OGLE collaboration is grateful for funding from the European Research Council Advanced Grants Program.

Author information

Affiliations

  1. Department of Earth and Space Science, Osaka University, Osaka 560-0043, Japan.

    • T. Sumi

  2. Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan.

    • T. Sumi
    • , K. Kamiya
    • , F. Abe
    • , A. Fukui
    • , K. Furusawa
    • , Y. Itow
    • , K. Masuda
    • , Y. Matsubara
    • , N. Miyake
    • , M. Motomura
    • , M. Nagaya
    • , S. Nakamura
    • , T. Okumura
    •  & T. Sako

  3. Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA.

    • D. P. Bennett

  4. Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland 0745, New Zealand.

    • I. A. Bond
    • , W. Lin
    • , C. H. Ling
    •  & W. L. Sweatman

  5. Department of Physics, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.

    • C. S. Botzler
    • , N. Rattenbury
    • , P. J. Tristram
    •  & P. C. M. Yock

  6. Department of Physics and Astronomy, University of Canterbury, Christchurch 8140, New Zealand.

    • J. B. Hearnshaw

  7. Mt John University Observatory, University of Canterbury, PO Box 56, Lake Tekapo 8770, New Zealand.

    • P. M. Kilmartin

  8. School of Chemical and Physical Sciences, Victoria University, Wellington 6140, New Zealand.

    • A. Korpela
    •  & D. J. Sullivan

  9. Department of Physics, Konan University, Nishiokamoto 8-9-1, Kobe 658-8501, Japan.

    • Y. Muraki

  10. Nagano National College of Technology, Nagano 381-8550, Japan.

    • K. Ohnishi

  11. Cavendish Laboratory, Cambridge University, J. J. Thomson Avenue, CB3 0HE Cambridge, UK.

    • Y. C. Perrott

  12. Tokyo Metropolitan College of Industrial Technology, Tokyo 116-8523, Japan.

    • To. Saito

  13. Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland.

    • A. Udalski
    • , M. K. Szymański
    • , M. Kubiak
    • , G. Pietrzyński
    • , R. Poleski
    • , I. Soszyński
    •  & K. Ulaczyk

  14. Universidad de Concepción, Departamento de Astronomia, Casilla 160–C, Concepción, Chile.

    • G. Pietrzyński

  15. Institute of Astronomy, Cambridge University, Madingley Road, CB3 0HA Cambridge, UK.

    • Ł. Wyrzykowski

Consortia

  1. The Microlensing Observations in Astrophysics (MOA) Collaboration

  2. The Optical Gravitational Lensing Experiment (OGLE) Collaboration

Authors

    Contributions

    T.S. and K.K. conducted data reduction and statistical analysis. A.U. produced OGLE-III light curves. I.A.B. generated the extended MOA-II light curves. D.P.B. conducted the detailed analysis of binary events. T.S. wrote the manuscript. D.P.B. and I.A.B. edited the manuscript. All other authors contributed to the observation and maintenance of observational facilities, discussed the results and commented on the manuscript.

    Competing interests

    The author declare no competing financial interests.

    Corresponding author

    Correspondence to T. Sumi.

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    DOI

    https://doi.org/10.1038/nature10092

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