Osborn, H. P., Santerne, A., Barros, S. C. C., Santos, N. C., Dumusque, X., Malavolta, L., Armstrong, D. J., Hojjatpanah, S., Demangeon, O., Adibekyan, V., Almenara, J. -M, Barrado, D., Bayliss, D., Boisse, I., Bouchy, F., Brown, D. J. A., Cameron, A. C., Charbonneau, D., Deleuil, M., Delgado Mena, E., Díaz, R. F., Hébrard, G., Kirk, J., King, G. W., Lam, K. W. F. et al. 2017. "K2-110 b: a massive mini-Neptune exoplanet." Astronomy and Astrophysics, 604 A19. https://doi.org/10.1051/0004-6361/201628932.
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 a mass 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 likelydisc-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%.
