K2-110 b: a massive mini-Neptune exoplanet

H. P. Osborn, A. Santerne, S. C. C. Barros, N. C. Santos, X. Dumusque, L. Malavolta, D. J. Armstrong, S. Hojjatpanah, O. Demangeon, V. Adibekyan, J.-M. Almenara, D. Barrado, D. Bayliss, I. Boisse, F. Bouchy, D. J. A. Brown, A. C. Cameron, D. Charbonneau, M. Deleuil, E. Delgado MenaR. F. Díaz, G. Hébrard, J. Kirk, G.W. King, K. W. F. Lam, D. Latham, J. Lillo-Box, T. M. Louden, C. Lovis, M. Marmier, J. McCormac, E. Molinari, F. Pepe, D. Pollacco, S. G. Sousa, S. Udry, S. R. Walker

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26 Citations (Scopus)


We report the discovery of the exoplanet K2-110 b (previously EPIC212521166b) from K2 photometry orbiting in a 13.8637d period around an old, metal-poor K3 dwarf star. With a V-band magnitude of 11.9,K2-110 is particularly amenable to RV follow-up. A joint analysis of K2 photometry and high-precision RVs from 28 HARPS and HARPS-N spectra reveal it to have a radius of 2.6 ± 0.1R⊕ and amass of 16.7 ± 3.2M⊕, hence a density of 5.2± 1.2 g cm-3, making it one of the most massive planets yet to be found with a sub-Neptune radius. When accounting for compression, the resulting Earth-like density is best fitted by a 0.2M⊕ hydrogen atmosphere over an 16.5M⊕ Earth-like interior, although the planet could also have significant water content. At 0.1 AU, even taking into account the old stellar age of 8 ± 3 Gyr, the planet is unlikely to have been significantly affected by EUV evaporation. However the planet likely disc-migrated to its current position making the lack of a thick H2 atmosphere puzzling. This analysis has made K2-110 b one of the best-characterised mini-Neptunes with density constrained to less than 30%.
Original languageEnglish
Article numberA19
Number of pages8
JournalAstronomy & Astrophysics
Early online date27 Jul 2017
Publication statusPublished - Aug 2017


  • Planets and satellites
  • Detection


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