The browser you are using is not supported by this website. All versions of Internet Explorer are no longer supported, either by us or Microsoft (read more here:

Please use a modern browser to fully experience our website, such as the newest versions of Edge, Chrome, Firefox or Safari etc.


Judith Korth



Super-Earth of 8 M in a 2.2-day orbit around the K5V star K2-216


  • C. M. Persson
  • M. Fridlund
  • O. Barragán
  • F. Dai
  • D. Gandolfi
  • A. P. Hatzes
  • T. Hirano
  • S. Grziwa
  • J. Korth
  • J. Prieto-Arranz
  • L. Fossati
  • V. Van Eylen
  • A. B. Justesen
  • J. Livingston
  • D. Kubyshkina
  • H. J. Deeg
  • E. W. Guenther
  • G. Nowak
  • J. Cabrera
  • Ph Eigmüller
  • Sz Csizmadia
  • A. M.S. Smith
  • A. Erikson
  • S. Albrecht
  • Alonso Sobrino
  • W. D. Cochran
  • M. Endl
  • M. Esposito
  • A. Fukui
  • P. Heeren
  • D. Hidalgo
  • M. Hjorth
  • M. Kuzuhara
  • N. Narita
  • D. Nespral
  • E. Palle
  • M. Pätzold
  • H. Rauer
  • F. Rodler
  • J. N. Winn

Summary, in English

Context. Although thousands of exoplanets have been discovered to date, far fewer have been fully characterised, in particular super-Earths. The KESPRINT consortium identified K2-216 as a planetary candidate host star in the K2 space mission Campaign 8 field with a transiting super-Earth. The planet has recently been validated as well. Aims. Our aim was to confirm the detection and derive the main physical characteristics of K2-216 b, including the mass. Methods. We performed a series of follow-up observations: high-resolution imaging with the FastCam camera at the TCS and the Infrared Camera and Spectrograph at Subaru, and high-resolution spectroscopy with HARPS (La Silla), HARPS-N (TNG), and FIES (NOT). The stellar spectra were analyzed with the SpecMatch-Emp and SME codes to derive the fundamental stellar properties. We analyzed the K2 light curve with the pyaneti software. The radial velocity measurements were modelled with both a Gaussian process (GP) regression and the so-called floating chunk offset (FCO) technique to simultaneously model the planetary signal and correlated noise associated with stellar activity. Results. Imaging confirms that K2-216 is a single star. Our analysis discloses that the star is a moderately active K5V star of mass 0.70 ± 0.03 M and radius 0.72 ± 0.03 R. Planet b is found to have a radius of 1.75-0.10 +0.17 R and a 2.17-day orbit in agreement with previous results. We find consistent results for the planet mass from both models: Mp ≈ 7.4 ± 2.2 M from the GP regression and Mp ≈ 8.0 ± 1.6 M from the FCO technique, which implies that this planet is a super-Earth. The incident stellar flux is 2.48-48 +220 F. Conclusions. The planet parameters put planet b in the middle of, or just below, the gap of the radius distribution of small planets. The density is consistent with a rocky composition of primarily iron and magnesium silicate. In agreement with theoretical predictions, we find that the planet is a remnant core, stripped of its atmosphere, and is one of the largest planets found that has lost its atmosphere.

Publishing year





Astronomy and Astrophysics



Document type

Journal article


EDP Sciences


  • Planetary systems
  • Planets and satellites: Atmospheres
  • Planets and satellites: composition
  • Stars: individual: K2-216
  • Techniques: photometric
  • Techniques: radial velocities




  • ISSN: 0004-6361