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A closely packed system of low-mass, low-density planets transiting Kepler-11

Abstract

When an extrasolar planet passes in front of (transits) its star, its radius can be measured from the decrease in starlight and its orbital period from the time between transits. Multiple planets transiting the same star reveal much more: period ratios determine stability and dynamics, mutual gravitational interactions reflect planet masses and orbital shapes, and the fraction of transiting planets observed as multiples has implications for the planarity of planetary systems. But few stars have more than one known transiting planet, and none has more than three. Here we report Kepler spacecraft observations of a single Sun-like star, which we call Kepler-11, that reveal six transiting planets, five with orbital periods between 10 and 47 days and a sixth planet with a longer period. The five inner planets are among the smallest for which mass and size have both been measured, and these measurements imply substantial envelopes of light gases. The degree of coplanarity and proximity of the planetary orbits imply energy dissipation near the end of planet formation.

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Figure 1: Light curves of Kepler-11, raw and detrended.
Figure 2: Detrended data of Fig. 1 shown phased at the period of each transit signal and zoomed to an 18-h region around mid-transit.
Figure 3: Transit timing variations and dynamical fits.
Figure 4: Transit probabilities as a function of relative orbital inclinations of planets orbiting Kepler-11.
Figure 5: Mass–radius relationship of small transiting planets, with Solar System planets shown for comparison.

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Acknowledgements

Kepler was competitively selected as the tenth Discovery mission. Funding for this mission is provided by NASA’s Science Mission Directorate. We thank the many people who gave so generously of their time to make the Kepler mission a success. A. Dobrovolskis, T. J. Lee and D. Queloz provided constructive comments on the manuscript. D.C.F. and J.A.C. acknowledge NASA support through Hubble Fellowship grants HF-51272.01-A and HF-51267.01-A, respectively, awarded by STScI, operated by AURA under contract NAS 5-26555.

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Authors and Affiliations

Authors

Contributions

J.J.L. led the research effort to confirm and validate candidates as planets, assisted in the dynamical study, developed most of the interpretation and wrote much of the manuscript. D.C.F. performed dynamical analysis on transit times and derived planetary masses, derived dynamical constraints on mutual inclinations, performed long-term stability calculations, and wrote much of the Supplementary Information. E.B.F. measured transit times, including special processing for Q6 data, checked for transit duration variations, contributed to the interpretation, and supervised transit probability and relative inclination analysis. The following seven authors contributed equally: W.J.B. developed photometers, observational techniques, and analysis techniques that proved Kepler could succeed, participated in the design, development, testing and commissioning of the Kepler mission and in the evaluation of the candidates that led to the discovery of this system. F.F. modelled Kepler transit light curves as false positives leading to the rejection of blend scenarios for hierarchical triple and background configurations. G.W.M. obtained and reduced spectra that yielded the properties of the star. J.A.O. measured planet radii and impact parameters. J.F.R. performed transit searches to identify candidates, multi-candidate light curve modelling to determine stellar and planetary parameters, and transit timing measurements. G.T. modelled Kepler transit light curves as false positives, leading to the rejection of blend scenarios for hierarchical triple and background configurations. W.F.W. measured transit times and O-C curves and used Monte Carlo simulations to determine robust uncertainties. The remaining authors listed below contributed equally: N.M.B. directed target selection, KOI inspection, tracking, and vetting. S.T.B. supported centroid and light curve analysis and participated in validation discussions. L.A.B. took and analysed the first reconnaissance spectrum of the target star. D.A.C. worked on the definition and development of the Science Operations Center analysis pipeline. J.A.C. assisted in the determination of transit times and durations from the Kepler photometry. D.C. provided advice on blender analysis. J.L.C. supported the science operations to collect the Kepler data. W.D.C. obtained, reduced and analysed reconnaissance spectroscopy. J.-M.D. participated in blend studies. E.W.D. provided optical, electronic and systems support for flight segments, commissioning work, and discussions regarding validation of small planets. M.N.F. reviewed light curves and centroid time series and participated in verification and validation of the science pipeline. J.J.F. modelled the interior structure and mass-radius relationships of the planets and wrote the text on interpreting planetary structure. T.N.G. performed follow-up observation support and commissioning work. J.C.G. worked on the design of the Kepler focal plane and associated charge-coupled device (CCD) imagers and electronics. R.L.G. performed difference-image-based centroid analysis as means of discriminating against background eclipsing binary stars. M.R.H. led the team responsible for the scientific commissioning and operation of the instrument, and processing the data to produce light curves. J.R.H. developed operations procedures and processed Kepler data to produce light curves. M.J.H. developed the trending algorithm and helped in assembling and writing up the results. D.G.K. designed and developed major portions of the Kepler mission. D.W.L. led reconnaissance spectroscopy, stellar classification and the preparation of the Kepler Input Catalog. E.L. modelled the interior structure and mass–radius relations of the planets. S.McC. wrote software to manage and archive pixel and flux time series data. N.M. modelled the interior structure and mass–radius relations of the planets. R.C.M. performed transit probability versus relative inclination analysis. E.V.Q. wrote software to calibrate the pixel data to generate the flux time series. D.R. conducted data analysis and interpretation. D.S. performed calculations using stellar evolution models to determine stellar parameters. D.R.S. developed and used code to measure transit times. J.H.S. worked on validation of analysis methods and composition of text.

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Correspondence to Jack J. Lissauer or Daniel C. Fabrycky.

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Supplementary Information

The file contains Supplementary Text, Supplementary References, Supplementary Tables 1-6 and Supplementary Figures 1-12 with legends. (PDF 1254 kb)

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Lissauer, J., Fabrycky, D., Ford, E. et al. A closely packed system of low-mass, low-density planets transiting Kepler-11. Nature 470, 53–58 (2011). https://doi.org/10.1038/nature09760

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