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Alexander Mustill. Profile picture.

Alexander Mustill

Researcher

Alexander Mustill. Profile picture.

Company for the Ultra-high Density, Ultra-short Period Sub-Earth GJ 367 b: Discovery of Two Additional Low-mass Planets at 11.5 and 34 Days

Author

  • Elisa Goffo
  • Davide Gandolfi
  • Jo Ann Egger
  • Alexander J. Mustill
  • Simon H. Albrecht
  • Teruyuki Hirano
  • Oleg Kochukhov
  • Nicola Astudillo-Defru
  • Oscar Barragan
  • Luisa M. Serrano
  • Artie P. Hatzes
  • Yann Alibert
  • Eike Guenther
  • Fei Dai
  • Kristine W.~F. Lam
  • Szilárd Csizmadia
  • Alexis M.~S. Smith
  • Luca Fossati
  • Rafael Luque
  • Florian Rodler
  • Mark L. Winther
  • Jakob L. Rørsted
  • Javier Alarcon
  • Xavier Bonfils
  • William D. Cochran
  • Hans J. Deeg
  • Jon M. Jenkins
  • Judith Korth
  • John H. Livingston
  • Annabella Meech
  • Felipe Murgas
  • Jaume Orell-Miquel
  • Hannah L.~M. Osborne
  • Enric Palle
  • Carina M. Persson
  • Seth Redfield
  • George R. Ricker
  • Sara Seager
  • Roland Vanderspek
  • Vincent Van Eylen
  • Joshua N. Winn
Show all

Summary, in English

GJ 367 is a bright (V ≈ 10.2) M1 V star that has been recently found to host a transiting ultra-short period sub-Earth on a 7.7 hr orbit. With the aim of improving the planetary mass and radius and unveiling the inner architecture of the system, we performed an intensive radial velocity follow-up campaign with the HARPS spectrograph—collecting 371 high-precision measurements over a baseline of nearly 3 yr—and combined our Doppler measurements with new TESS observations from sectors 35 and 36. We found that GJ 367 b has a mass of M b = 0.633 ± 0.050 M ⊕ and a radius of R b = 0.699 ± 0.024 R ⊕, corresponding to precisions of 8% and 3.4%, respectively. This implies a planetary bulk density of ρ b = 10.2 ± 1.3 g cm−3, i.e., 85% higher than Earth’s density. We revealed the presence of two additional non-transiting low-mass companions with orbital periods of ∼11.5 and 34 days and minimum masses of M c sin i c = 4.13 ± 0.36 M ⊕ and M d sin i d = 6.03 ± 0.49 M ⊕, respectively, which lie close to the 3:1 mean motion commensurability. GJ 367 b joins the small class of high-density planets, namely the class of super-Mercuries, being the densest ultra-short period small planet known to date. Thanks to our precise mass and radius estimates, we explored the potential internal composition and structure of GJ 367 b, and found that it is expected to have an iron core with a mass fraction of 0.91 − 0.23 + 0.07 . How this iron core is formed and how such a high density is reached is still not clear, and we discuss the possible pathways of formation of such a small ultra-dense planet.

Department/s

  • Astrophysics

Publishing year

2023-09-01

Language

English

Publication/Series

Astrophysical Journal Letters

Volume

955

Issue

1

Document type

Journal article

Publisher

IOP Publishing

Topic

  • Astronomy, Astrophysics and Cosmology

Keywords

  • Exoplanet detection methods
  • Exoplanet systems
  • Exoplanets
  • Extrasolar rocky planets
  • Astrophysics - Earth and Planetary Astrophysics

Status

Published

Project

  • A unified picture of white dwarf planetary systems
  • Consolidating CHEOPS and preparing for PLATO: Exoplanet studies in the 2020s

ISBN/ISSN/Other

  • ISSN: 2041-8213