Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

The same frequency of planets inside and outside open clusters of stars


Most stars and their planets form in open clusters. Over 95 per cent of such clusters have stellar densities too low (less than a hundred stars per cubic parsec) to withstand internal and external dynamical stresses and fall apart within a few hundred million years1. Older open clusters have survived by virtue of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when they formed. Such clusters represent a stellar environment very different from the birthplace of the Sun and other planet-hosting field stars. So far more than 800 planets have been found around Sun-like stars in the field2. The field planets are usually the size of Neptune or smaller3,4,5. In contrast, only four planets have been found orbiting stars in open clusters6,7,8, all with masses similar to or greater than that of Jupiter. Here we report observations of the transits of two Sun-like stars by planets smaller than Neptune in the billion-year-old open cluster NGC6811. This demonstrates that small planets can form and survive in a dense cluster environment, and implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars in the Galaxy.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: The colour–magnitude and colour–period diagrams for NGC6811.
Figure 2: Transit light curves.
Figure 3: Distribution of planetary properties.


  1. 1

    Lada, C. J. & Lada, E. A. Embedded clusters in molecular clouds. Annu. Rev. Astron. Astrophys. 41, 57–115 (2003)

    ADS  Article  Google Scholar 

  2. 2

    The Extrasolar Planets Encyclopaedia. (2012)

  3. 3

    Mayor, M. et al. The HARPS search for southern extra-solar planets XXXIV. Occurrence, mass distribution and orbital properties of super-Earths and Neptune-mass planets. Astron. Astrophys. (submitted); preprint at

  4. 4

    Howard, A. et al. Planet occurrence within 0.25 AU of solar-type stars from Kepler. Astrophys. J. Suppl. 201, 15–35 (2012)

    ADS  Article  Google Scholar 

  5. 5

    Fressin, F. et al. The false positive rate of Kepler and the occurrence of planets. Astrophys. J. 766, 81–99 (2013)

    ADS  Article  Google Scholar 

  6. 6

    Sato, B. et al. A planetary companion to the Hyades giant Epsilon Tauri. Astrophys. J. 661, 527–531 (2007)

    ADS  Article  Google Scholar 

  7. 7

    Lovis, C. & Mayor, M. Planets around evolved intermediate-mass stars. I. Two substellar companions in the open clusters NGC2423 and NGC4349. Astron. Astrophys. 472, 657–664 (2007)

    ADS  Article  Google Scholar 

  8. 8

    Quinn, S. et al. Two “b”s in the beehive: the discovery of the first hot Jupiters in an open cluster. Astrophys. J. 756, L33–L36 (2012)

    ADS  Article  Google Scholar 

  9. 9

    van Saders, J. L. & Gaudi, B. S. Ensemble analysis of open cluster transit surveys: upper limits on the frequency of short-period planets consistent with the field. Astrophys. J. 729, 63–76 (2011)

    ADS  Article  Google Scholar 

  10. 10

    Pace, G., Pasquini, L. & Francois, P. Abundances of four open clusters from solar stars. Astron. Astrophys. 489, 403–412 (2008)

    CAS  ADS  Article  Google Scholar 

  11. 11

    Fischer, D. A. & Valenti, J. The planet-metallicity correlation. Astrophys. J. 622, 1102–1117 (2005)

    CAS  ADS  Article  Google Scholar 

  12. 12

    Meibom, S. The Kepler Cluster Study. Bull. Am. Astron. Soc. 43, (AAS Meeting 218) abstr. 311.03. (2011)

  13. 13

    Yi, S. et al. Toward better age estimates for stellar populations: the Y2 isochrones for solar mixture. Astrophys. J. Suppl. 136, 417–437 (2001)

    ADS  Article  Google Scholar 

  14. 14

    Girardi, L., Bressan, A., Bertelli, G. & Chiosi, C. Evolutionary tracks and isochrones for low- and intermediate-mass stars: from 0.15 to 7 MO, and from Z = 0.0004 to 0.03. Astron. Astrophys. 141 (Suppl.). 371–383 (2000)

    CAS  ADS  Google Scholar 

  15. 15

    Jenkins, J. M. et al. Overview of the Kepler Science Processing Pipeline. Astrophys. J. 713, L87–L91 (2010)

    ADS  Article  Google Scholar 

  16. 16

    Meibom, S. et al. The Kepler Cluster Study: stellar rotation in NGC6811. Astrophys. J. 733, L9–L12 (2011)

    ADS  Article  Google Scholar 

  17. 17

    Janes, K., Barnes, S. A., Meibom, S. & Hoq, S. NGC6811: an intermediate-age cluster in the Kepler field. Astron. J. 145, 7–21 (2013)

    ADS  Article  Google Scholar 

  18. 18

    Weiss, L. M. et al. The mass of KOI-94d and a relation for planet radius, mass, and incident flux. Astrophys. J. 768, 14–32 (2013)

    ADS  Article  Google Scholar 

  19. 19

    Scally, A. & Clarke, C. Destruction of protoplanetary discs in the Orion nebula cluster. Mon. Not. R. Astron. Soc. 325, 449–456 (2001)

    ADS  Article  Google Scholar 

  20. 20

    Bonnell, I. A. et al. Planetary dynamics in stellar clusters. Mon. Not. R. Astron. Soc. 322, 859–865 (2001)

    ADS  Article  Google Scholar 

  21. 21

    Smith, K. W. & Bonnell, I. A. Free-floating planets in stellar clusters? Mon. Not. R. Astron. Soc. 322, L1–L4 (2001)

    ADS  Article  Google Scholar 

  22. 22

    Fregeau, J. M., Chatterjee, S. & Rasio, F. A. Dynamical interactions of planetary systems in dense stellar environments. Astrophys. J. 640, 1086–1098 (2006)

    CAS  ADS  Article  Google Scholar 

  23. 23

    Adams, F. C., Proszkow, E. M., Fatuzzo, M. & Myers, P. C. Early evolution of stellar groups and clusters: environmental effects on forming planetary systems. Astrophys. J. 641, 504–525 (2006)

    CAS  ADS  Article  Google Scholar 

  24. 24

    Malmberg, D. et al. Close encounters in young stellar clusters: implications for planetary systems in the solar neighbourhood. Mon. Not. R. Astron. Soc. 378, 1207–1216 (2007)

    ADS  Article  Google Scholar 

  25. 25

    Spurzem, R., Giersz, M., Heggie, D. C. & Lin, D. N. C. Dynamics of planetary systems in star clusters. Astrophys. J. 697, 458–482 (2009)

    ADS  Article  Google Scholar 

  26. 26

    Haisch, K. E., Lada, E. A. & Lada, C. J. Disk frequencies and lifetimes in young clusters. Astrophys. J. 553, L153–L156 (2001)

    CAS  ADS  Article  Google Scholar 

  27. 27

    Kroupa, P. The IMF of simple and composite populations. Astron. Soc. Pacif. Conf. Ser. 390, 303–315 (2008)

    Google Scholar 

  28. 28

    Gautier, T. N. et al. Kepler-20: a Sun-like star with three sub-Neptune exoplanets and two Earth-size candidates. Astrophys. J. 749, 15–33 (2012)

    ADS  Article  Google Scholar 

Download references


Kepler was competitively selected as the tenth Discovery mission. Funding for this mission is provided by NASA’s Science Mission Directorate. S.M. acknowledges support through NASA grant NNX09AH18A (The Kepler Cluster Study) and from the Kepler mission via NASA Cooperative Agreement NCC2-1390. G.T. acknowledges support through NASA’s Kepler Participating Scientist Program grant NNX12AC75G. L.A.R. acknowledges NASA support through Hubble Fellowship grant HF-51313.01-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555.

Author information




S.M. is the Principal Investigator of The Kepler Cluster Study and led the writing of the paper and the effort to identify members of NGC6811. He worked with G.T. and F.F. on characterization and validation of Kepler-66b and Kepler-67b, and with K.J. and S.A.B. on determination of the properties of NGC6811. G.T. developed the BLENDER software used to validate the planets, and determined the stellar properties of the host stars. F.F. worked on the BLENDER validation of the two planets and the Monte-Carlo simulation of the cluster yield. D.W.L. contributed follow-up spectroscopy of host stars. J.F.R. performed the light-curve analysis to extract the planet characteristics. D.R.C. provided constraints on angular separation of potential background blends from adaptive optics imaging. S.T.B. performed pixel-level centroid analysis. C.E.H. assisted in running BLENDER on the NASA Pleiades supercomputer. L.A.R. modelled the planets’ interior structure to constrain the range of possible masses and compositions. K.J. led the supporting photometric study from which the bulk properties of NGC6811 are derived. S.A.B. participated in the acquisition of ground-based spectroscopic and photometric data on NGC6811. G.W.M. and H.I. obtained and analysed high-resolution Keck HIRES spectra of the host stars used for the BLENDER analysis. D.A.F. analysed HIRES spectra using the Spectroscopy Made Easy software. S.B.H. and E.P.H. obtained and analysed speckle observations of the host stars. J.M.J. led the efforts of data collection, data processing and data review that yielded the Kepler time series photometry. S.C.S. did spectroscopic analysis of stellar members of NGC6811 to aid in the determination of cluster parameters including metallicity. J.C. obtained adaptive optics imaging observations.

Corresponding author

Correspondence to Søren Meibom.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Text and Data 1-4, Supplementary Figures 1-3 and additional references. (PDF 3389 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Meibom, S., Torres, G., Fressin, F. et al. The same frequency of planets inside and outside open clusters of stars. Nature 499, 55–58 (2013).

Download citation

Further reading


    • Andrea Miglio
    • , Léo Girardi
    • , Frank Grundahl
    • , Benoit Mosser
    • , Nate Bastian
    • , Angela Bragaglia
    • , Karsten Brogaard
    • , Gaël Buldgen
    • , William Chantereau
    • , William Chaplin
    • , Cristina Chiappini
    • , Marc-Antoine Dupret
    • , Patrick Eggenberger
    • , Mark Gieles
    • , Robert Izzard
    • , Daisuke Kawata
    • , Christoffer Karoff
    • , Nadège Lagarde
    • , Ted Mackereth
    • , Demetrio Magrin
    • , Georges Meynet
    • , Eric Michel
    • , Josefina Montalbán
    • , Valerio Nascimbeni
    • , Arlette Noels
    • , Giampaolo Piotto
    • , Roberto Ragazzoni
    • , Igor Soszyński
    • , Eline Tolstoy
    • , Silvia Toonen
    • , Amaury Triaud
    •  & Fiorenzo Vincenzo

    Experimental Astronomy (2021)

  • Planet host stars in open clusters

    • XiaoLing Yang
    • , YuQin Chen
    •  & Gang Zhao

    Science China Physics, Mechanics & Astronomy (2015)

  • The robustness of planet formation

    • William F. Welsh

    Nature (2013)


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.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing