Precise masses in the WASP-47 system

Andrew Vanderburg, Juliette C. Becker, Lars A. Buchhave, Annelies Mortier, Eric Lopez, Luca Malavolta, Raphaëlle D. Haywood, David W. Latham, David Charbonneau, Mercedes López-Morales, Fred C. Adams, Aldo Stefano Bonomo, François Bouchy, Andrew Collier Cameron, Rosario Cosentino, Luca Di Fabrizio, Xavier Dumusque, Aldo Fiorenzano, Avet Harutyunyan, John Asher JohnsonVania Lorenzi, Christophe Lovis, Michel Mayor, Giusi Micela, Emilio Molinari, Marco Pedani, Francesco Pepe, Giampaolo Piotto, David Phillips, Ken Rice, Dimitar Sasselov, Damien Ségransan, Alessandro Sozzetti, Stéphane Udry, Chris Watson

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We present precise radial velocity observations of WASP-47, a star known to host a hot Jupiter, a distant Jovian companion, and, uniquely, two additional transiting planets in short-period orbits: a super-Earth in a ≈19 hr orbit, and a Neptune in a ≈ 9 day orbit. We analyze our observations from the HARPS-N spectrograph along with previously published data to measure the most precise planet masses yet for this system. When combined with new stellar parameters and reanalyzed transitphotometry, our mass measurements place strong constraints on the compositions of the two small planets. We find unlike most other ultra-short-period planets, the inner planet, WASP-47 e, has a mass (6.83 ± 0.66 M) and radius (1.810 ± 0.027 R) inconsistent with an Earth-like composition. Instead, WASP-47 e likely has a volatile-rich envelope surrounding an Earth-like core and mantle. We also perform a dynamical analysis to constrain the orbital inclination of WASP-47 c, the outer Jovian planet. This planet likely orbits close to the plane of the inner three planets, suggesting a quiet dynamical history for the system. Our dynamical constraints also imply that WASP-47 c is much more likely to transit than a geometric calculation would suggest. We calculate a transit probability for WASP-47 c of about 10%, more than an order of magnitude larger than the geometric transit probability of 0.6%.
Original languageEnglish
Article number237
Number of pages14
JournalAstronomical Journal
Issue number6
Publication statusPublished - 17 Nov 2017


  • Planets and satellites: composition
  • Planets and satellites: detection
  • Planets and satellites: dynamical evolution and stability
  • Planets and satellites: fundamental parameters
  • Planetes and satellites: gaseous planets
  • Planets and satellites: interiors


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