Letter | Published:

A resonant chain of four transiting, sub-Neptune planets

Nature volume 533, pages 509512 (26 May 2016) | Download Citation

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Abstract

Surveys have revealed many multi-planet systems containing super-Earths and Neptunes in orbits of a few days to a few months1. There is debate whether in situ assembly2 or inward migration is the dominant mechanism of the formation of such planetary systems. Simulations suggest that migration creates tightly packed systems with planets whose orbital periods may be expressed as ratios of small integers (resonances)3,4,5, often in a many-planet series (chain)6. In the hundreds of multi-planet systems of sub-Neptunes, more planet pairs are observed near resonances than would generally be expected7, but no individual system has hitherto been identified that must have been formed by migration. Proximity to resonance enables the detection of planets perturbing each other8. Here we report transit timing variations of the four planets in the Kepler-223 system, model these variations as resonant-angle librations, and compute the long-term stability of the resonant chain. The architecture of Kepler-223 is too finely tuned to have been formed by scattering, and our numerical simulations demonstrate that its properties are natural outcomes of the migration hypothesis. Similar systems could be destabilized by any of several mechanisms5,9,10,11, contributing to the observed orbital-period distribution, where many planets are not in resonances. Planetesimal interactions in particular are thought to be responsible for establishing the current orbits of the four giant planets in the Solar System by disrupting a theoretical initial resonant chain12 similar to that observed in Kepler-223.

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Acknowledgements

We thank A. Howard and G. Marcy for their role in obtaining spectra, and E. Agol, J. Lissauer, and J. Bean for comments on the manuscript. This material is based on work supported by NASA under grant numbers NNX14AB87G (D.C.F.), NNX12AF73G (E.B.F.) and NNX14AN76G (E.B.F.) issued through the Kepler Participating Scientist Program. E.B.F. received support from NASA Exoplanet Research Program award NNX15AE21G. D.C.F. received support from the Alfred P. Sloan Foundation. C.M. was supported by the Polish National Science Centre MAESTRO grant DEC-2012/06/A/ST9/00276.

Author information

Affiliations

  1. Department of Astronomy and Astrophysics, The University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA

    • Sean M. Mills
    •  & Daniel C. Fabrycky
  2. Institute of Physics and CASA*, University of Szczecin, Wielkopolska 15, 70-451 Szczecin, Poland

    • Cezary Migaszewski
  3. Torun Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, 87-100 Torun, Poland

    • Cezary Migaszewski
  4. Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, Pennsylvania 16802, USA

    • Eric B. Ford
  5. Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA

    • Eric B. Ford
  6. Center for Astrostatistics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA

    • Eric B. Ford
  7. University of California at Berkeley, Berkeley, California 94720, USA

    • Erik Petigura
    •  & Howard Isaacson
  8. California Institute of Technology, Pasadena, California 91125, USA

    • Erik Petigura

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Contributions

S.M.M. performed the photodynamic, stability, tidal dissipation and spectral evolution analyses and led the paper authorship. D.C.F. designed the study, performed TTV and Laplace-angle libration analysis, and assisted writing the paper. C.M. performed the migration analysis, assisted in initial data fitting and contributed to the writing of the paper. E.B.F. advised on the DEMCMC analysis and paper direction. E.P. and H.I. obtained and analysed the spectra. All authors read and edited the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Sean M. Mills.

Kepler data are publicly available at http://archive.stsci.edu/kepler/.

Extended data

Supplementary information

Text files

  1. 1.

    Supplementary Data

    This file contains Supplementary Table Dataset 1, a tsv file of predicted transmit times for Kepler-223. Columns: [Transit_Number] \t [Time_(BJD-2454900)] \t [1-Sigma_Uncertainty_(d)]. Description: Transits times and errors are estimated from integrations of the randomly selected 107 year-stable chains from the posterior. Transit times are listed quarterly (the nearest transit time every 3 months) and extend for 10 years past the end of the Kepler mission. The transits of each planet are given sequentially and indexed from 0 at BJD 2455700, the data epoch used in our fits.

  2. 2.

    Supplementary Data

    This file contains source data for Extended Data Table 1.

  3. 3.

    Supplementary Data

    This file contains source data for Extended Data Table 2.

  4. 4.

    Supplementary Data

    This file contains source data for Extended Data Table 3.

Zip files

  1. 1.

    Supplementary Data

    This file contains the source code compressed into zip format.

About this article

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DOI

https://doi.org/10.1038/nature17445

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