Letter | Published:

Unbound or distant planetary mass population detected by gravitational microlensing

Nature volume 473, pages 349352 (19 May 2011) | Download Citation

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.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

References

  1. 1.

    & Jupiter-mass companion to a solar-type star. Nature 378, 355–359 (1995)

  2. 2.

    The Extrasolar Planets Encyclopaedia〉 (CNRS/LUTH—Paris Observatory, 2011)

  3. 3.

    in Exoplanets (ed. ) 79–110 (University of Arizona Press, 2011)

  4. 4.

    et al. A cold Neptune-mass planet OGLE-2007-BLG-368Lb: cold Neptunes are common. Astrophys. J. 710, 1641–1653 (2010)

  5. 5.

    et al. Discovery of young, isolated planetary mass objects in the σ Orionis star cluster. Science 290, 103–107 (2000)

  6. 6.

    et al. Young T-dwarf candidates in IC 348. Astron. Astrophys. 508, 823–831 (2009)

  7. 7.

    et al. Search for very low-mass brown dwarfs and free-floating planetary-mass objects in Taurus. Astrophys. J. 708, 770–784 (2010)

  8. 8.

    et al. Deep near-infrared imaging of the ρ Oph cloud core: clues to the origin of the lowest-mass brown dwarfs. Astrophys. J. 719, 550–560 (2010)

  9. 9.

    et al. The Gemini deep planet survey. Astrophys. J. 670, 1367–1390 (2007)

  10. 10.

    Gravitational microlensing by the galactic halo. Astrophys. J. 304, 1–5 (1986)

  11. 11.

    Gravitational lenses. Phys. Rev. 133, B835–B844 (1964)

  12. 12.

    et al. in Planets Beyond the Solar System and the Next Generation of Space Missions (ed. ) ASP Conf. Proc. 119, 95 (Astronomical Society of the Pacific, 1997)

  13. 13.

    & A new channel for the detection of planetary systems through microlensing. I. Isolated events due to planet lenses. Astrophys. J. 512, 564–578 (1999)

  14. 14.

    et al. Microlensing optical depth toward the Galactic Bulge from microlensing observations in astrophysics group observations during 2000 with difference image analysis. Astrophys. J. 591, 204–227 (2003)

  15. 15.

    The Optical Gravitational Lensing Experiment. Real time data analysis systems in the OGLE-III survey. Acta Astron. 53, 291–305 (2003)

  16. 16.

    et al. The Optical Gravitational Lensing Experiment—the optical depth to gravitational microlensing in the direction of the Galactic Bulge. Acta Astron. 44, 165–189 (1994)

  17. 17.

    et al. The MACHO project: microlensing optical depth toward the Galactic Bulge from difference image analysis. Astrophys. J. 541, 734–766 (2000)

  18. 18.

    et al. Galactic Bulge microlensing optical depth from EROS-2. Astron. Astrophys. 454, 185–199 (2006)

  19. 19.

    et al. Microlensing optical depth toward the Galactic Bulge using bright sources from OGLE-II. Astrophys. J. 636, 240–260 (2006)

  20. 20.

    & Stellar contribution to the Galactic Bulge microlensing optical depth. Astrophys. J. 592, 172–175 (2003)

  21. 21.

    et al. The initial mass function of the Galactic Bulge down to 0.15 M. Astrophys. J. 530, 418–428 (2000)

  22. 22.

    Galactic stellar and substellar initial mass function. Publ. Astron. Soc. Pacif. 115, 763–795 (2003)

  23. 23.

    Measuring the remnant mass function of the Galactic Bulge. Astrophys. J. 535, 928 (2000)

  24. 24.

    & A discontinuity in the low-mass initial mass function. Astrophys. J. 671, 767–780 (2007)

  25. 25.

    & Probing the spatial distribution of extrasolar planets with gravitational microlensing. Astrophys. J. 596, 1320–1326 (2003)

  26. 26.

    , & Formation, survival, and detectability of planets beyond 100 AU. Astrophys. J. 696, 1600–1611 (2009)

  27. 27.

    et al. Direct imaging of multiple planets orbiting the star HR 8799. Science 322, 1348–1352 (2008)

  28. 28.

    et al. Hot stars with hot Jupiters have high obliquities. Astrophys. J. 718, L145 (2010)

  29. 29.

    et al. The occurrence and mass distribution of close-in super-Earths, Neptunes, and Jupiters. Science 330, 653–655 (2010)

Download references

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.

    Supplementary information

    PDF files

    1. 1.

      Supplementary Information

      This file contains Supplementary Text and Data, Supplementary References, Supplementary Figures 1-11 with legends and Supplementary Tables 1-3.

    About this article

    Publication history

    Received

    Accepted

    Published

    DOI

    https://doi.org/10.1038/nature10092

    Further reading

    Comments

    By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.