A seven-planet resonant chain in TRAPPIST-1

Abstract

The TRAPPIST-1 system is the first transiting planet system found orbiting an ultracool dwarf star1. At least seven planets similar in radius to Earth were previously found to transit this host star2. Subsequently, TRAPPIST-1 was observed as part of the K2 mission and, with these new data, we report the measurement of an 18.77 day orbital period for the outermost transiting planet, TRAPPIST-1 h, which was previously unconstrained. This value matches our theoretical expectations based on Laplace relations3 and places TRAPPIST-1 h as the seventh member of a complex chain, with three-body resonances linking every member. We find that TRAPPIST-1 h has a radius of 0.752 R and an equilibrium temperature of 173 K. We have also measured the rotational period of the star to be 3.3 days and detected a number of flares consistent with a low-activity, middle-aged, late M dwarf.

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Figure 1: Long cadence K2 light curve of TRAPPIST-1 detrended with EVEREST.
Figure 2: Entire systematics-corrected K2 dataset with low-frequency trends removed.

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Acknowledgements

This paper includes data collected by the K2 mission. Funding for the K2 mission is provided by the NASA (National Space and Aeronautical Administration) Science Mission directorate. This research has made use of NASA’s Astrophysics Data System, the SIMBAD database and VizieR catalogue access tool operated at Centre de Données astronomiques de Strasbourg, Strasbourg, France. The data presented in this paper were obtained from the Mikulski Archive for Space Telescopes. R.L. and E.A. acknowledge support from NASA grant NNX14AK26G and from the NASA Astrobiology Institute’s Virtual Planetary Laboratory Lead Team, funded through the NASA Astrobiology Institute under solicitation NNH12ZDA002C and Cooperative Agreement Number NNA13AA93A. E.A. acknowledges support from NASA grant NNX13AF62G and National Science Foundation grant AST-1615315. E.K. acknowledges support from a National Science Foundation Graduate Student Research Fellowship. B.-O.D. acknowledges support from the Swiss National Science Foundation in the form of a Swiss National Science Foundation Professorship (PP00P2-163967). E.B. acknowledges funding by the European Research Council through ERC grant SPIRE 647383. D.L.H. acknowledges financial support from the UK Science and Technology Facilities Council. M.S. and K.H. acknowledge support from the Swiss National Science Foundation. A.B. acknowledges funding support from the National Science Foundation under award no. AST-1517177 and NASA under grant no. NNX15AI75G. J.L. acknowledges funding from the European Research Council under the European Unions Horizon 2020 research and innovation programme (grant agreement no. 679030/WHIPLASH). M.G., E.J. and V.V.G. are Fonds National de la Recherche Scientifique (F.R.S.-FNRS) Research Associates. S.N.R. thanks the Agence Nationale pour la Recherche for support via grant ANR-13-BS05-0003-002 (grant MOJO). The research leading to these results has received funding from the European Research Council under the FP/2007-2013 European Research Council Grant Agreement no. 336480 and from the Actions de Recherche Concertée (ARC) grant for Concerted Research Actions, financed by the Wallonia–Brussels Federation. S.B.H. wrote science cases to the K2 project office to include TRAPPIST-1 in the campaign 12 field and to make the raw data public upon downlink. D.F.M. is a Sagan Fellow.

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Authors

Contributions

R.L. and M.S. led the detrending efforts with EVEREST and the Gaissian process-based pipeline, with inputs from E.A., J.G.I, E.K. and D.F.M. R.L. performed the preliminary manual search for transits of TRAPPIST-1 h and the Δχ2 search, with input from E.A, E.K. and D.F.M. S.L.G. took care of the K2 data handling. B.-O.D. led the collaboration, wrote the K2 proposal and performed an independent transit search and Markov Chain Monte Carlo analysis of the K2 dataset. E.A. and D.F. led the dynamics and architecture of the system with inputs from S.N.R. and B.-O.D. E.B. took care of the tidal simulations. C.S.F, V.V.G., A.B., D.L.H. and B.M.M. conducted the work on stellar properties and variability and determined the stellar rotation period. S.N.R. led the formation and migration section. F.S., J.L. and M.T. worked on the atmospheric nature of TRAPPIST-1 h. G.B. and T.B. helped with the handling of the uncalibrated K2 fits files. Figures were prepared by R.L., A.H.M.J.T., J.G.I., E.B and E.K. M.G., E.J., A.H.M.J.T., L.D., J.d.W, S.L., Y.A., Z.B., P.M., K.H. and D.Q. contributed to the discovery and characterization of the TRAPPIST-1 system. All authors participated in the writing and commented on the paper.

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Correspondence to Rodrigo Luger.

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The authors declare no competing financial interests.

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Luger, R., Sestovic, M., Kruse, E. et al. A seven-planet resonant chain in TRAPPIST-1. Nat Astron 1, 0129 (2017). https://doi.org/10.1038/s41550-017-0129

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