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Published June 30, 2016 | Submitted + Supplemental Material
Journal Article Open

A Neptune-sized transiting planet closely orbiting a 5–10-million-year-old star


Theories of the formation and early evolution of planetary systems postulate that planets are born in circumstellar disks, and undergo radial migration during and after dissipation of the dust and gas disk from which they formed. The precise ages of meteorites indicate that planetesimals—the building blocks of planets—are produced within the first million years of a star's life. Fully formed planets are frequently detected on short orbital periods around mature stars. Some theories suggest that the in situ formation of planets close to their host stars is unlikely and that the existence of such planets is therefore evidence of large-scale migration. Other theories posit that planet assembly at small orbital separations may be common. Here we report a newly born, transiting planet orbiting its star with a period of 5.4 days. The planet is 50 per cent larger than Neptune, and its mass is less than 3.6 times that of Jupiter (at 99.7 per cent confidence), with a true mass likely to be similar to that of Neptune. The star is 5–10 million years old and has a tenuous dust disk extending outward from about twice the Earth–Sun separation, in addition to the fully formed planet located at less than one-twentieth of the Earth–Sun separation.

Additional Information

© 2016 Macmillan Publishers Limited. Received 11 March 2016. Accepted 22 April 2016. Published online 20 June 2016. We thank S. Metchev, K. Batygin, B. Benneke, K. Deck, J. Fuller and A. Shporer for discussions, M. Ireland for software used in the aperture masking analysis, and A. Kraus for contributing to the 2011 Keck/NIRC2 data acquisition. T.J.D. is supported by an NSF Graduate Research Fellowship under Grant DGE1144469. E.A.P. is supported through a Hubble Fellowship. I.J.M.C. is supported through a Sagan Fellowship. A.W.H. acknowledges funding from NASA grant NNX16AE75G and NASA Research Support Agreement 1541779. This paper includes data collected by the Kepler mission, funded by the NASA Science Mission directorate. Some data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA. We acknowledge the important cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community and we are fortunate to be able to conduct observations from this mountain. Author Contributions: T.J.D. noted the object as a young star, prepared the light curve, validated the transit, and led the overall analysis and the writing of the paper. L.A.H. analysed the 2015 and 2016 Keck/HIRES spectra, participated in team organization, performed general analysis, and contributed substantially to the writing of the paper. E.A.P. analysed raw K2 photometry and validated the transit, provided general guidance on exoplanets and false positives, and contributed substantially to the writing of the paper. J.M.C. was involved in the K2 proposal that included the object, and was principal investigator on the 2011 Keck/NIRC2, 2015 Keck/HIRES, and ALMA observations of the object. I.J.M.C. led the transit fitting and VESPA analysis. A.M.C. analysed the raw K2 photometry and validated the transit. A.W.H. and H.T.I. obtained, reduced, and analysed the 2016 Keck/HIRES spectra. D.R.C. led the clear aperture adaptive optics contrast curve analysis for the 2016 and 2011 data. C.A.B. wrote the proposal for 2016 Keck/NIRC2 follow-up of K2 sources and participated in the observations of the object. S.H. analysed the Keck/NIRC2 aperture masking data and assessed the temperature of the circumstellar dust. J.E.S. provided a rotational velocity analysis and calculated the kinematic distance. S.A.B. took the 2015 Keck/HIRES spectrum and analysed the ALMA data (referred to, but published separately in ref. 27). The authors declare no competing financial interests. Reviewer Information: Nature thanks A. Collier Cameron and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Attached Files

Submitted - 1606.06729.pdf

Supplemental Material - nature18293-sf1.jpg

Supplemental Material - nature18293-sf2.jpg

Supplemental Material - nature18293-sf3.jpg

Supplemental Material - nature18293-sf4.jpg

Supplemental Material - nature18293-sf5.jpg

Supplemental Material - nature18293-st1.jpg


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