Two massive rocky planets transiting a K-dwarf 6.5 parsecs away
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HD 219134 is a K-dwarf star at a distance of 6.5 parsecs around which several low-mass planets were recently discovered1,2. The Spitzer Space Telescope detected a transit of the innermost of these planets, HD 219134 b, whose mass and radius (4.5 M⊕ and 1.6 R⊕ respectively) are consistent with a rocky composition1. Here, we report new high-precision time-series photometry of the star acquired with Spitzer revealing that the second innermost planet of the system, HD 219134c, is also transiting. A global analysis of the Spitzer transit light curves and the most up-to-date HARPS-N velocity data set yields mass and radius estimations of 4.74 ± 0.19 M⊕ and 1.602 ± 0.055 R⊕ for HD 219134 b, and of 4.36 ± 0.22 M⊕ and 1.511 ± 0.047 R⊕ for HD 219134 c. These values suggest rocky compositions for both planets. Thanks to the proximity and the small size of their host star (0.778 ± 0.005 R ⊙ )3, these two transiting exoplanets — the nearest to the Earth yet found — are well suited for a detailed characterization (for example, precision of a few per cent on mass and radius, and constraints on the atmospheric properties) that could give important constraints on the nature and formation mechanism of the ubiquitous short-period planets of a few Earth masses.
Gillon , M , Demory , B-O , Van Grootel , V , Motalebi , F , Lovis , C , Cameron , A C , Charbonneau , D , Latham , D , Molinari , E , Pepe , F A , Ségransan , D , Sasselov , D , Udry , S , Mayor , M , Micela , G , Piotto , G & Sozzetti , A 2017 , ' Two massive rocky planets transiting a K-dwarf 6.5 parsecs away ' Nature Astronomy , vol 1 , 0056 . DOI: 10.1038/s41550-017-0056
© 2017, Macmillan Publishers/Springer Nature. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at www.nature.com / https://doi.org/10.1038/s41550-017-0056
Support for this work was provided by NASA. M.G. is grateful to NASA and SSC Director for having supported his searches for RV planets with Spitzer. M.G. and V.V.G. are Research Associates at the Belgian Scientific Research Fund (F.R.S.-FNRS). The research leading to these results has received funding from the ARC grant for Concerted Research Actions, financed by the Wallonia–Brussels Federation.
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