Two massive rocky planets transiting a K-dwarf 6.5 parsecs away

Michaël Gillon, Brice-Olivier Demory, Valérie Van Grootel, Fatemeh Motalebi, Christophe Lovis, Andrew Collier Cameron, David Charbonneau, David Latham, Emilio Molinari, Francesco A. Pepe, Damien Ségransan, Dimitar Sasselov, Stéphane Udry, Michel Mayor, Giuseppina Micela, Giampaolo Piotto, Alessandro Sozzetti

Research output: Contribution to journalArticlepeer-review

34 Citations (Scopus)


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.
Original languageEnglish
Article number0056
Number of pages6
JournalNature Astronomy
Publication statusPublished - 2 Mar 2017


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