GJ 3090 b: one of the most favourable mini-Neptune for atmospheric characterisation

J. M. Almenara, X. Bonfils, J. F. Otegi, O. Attia, M. Turbet, N. Astudillo-Defru, K. A. Collins, A. S. Polanski, V. Bourrier, C. Hellier, C. Ziegler, F. Bouchy, C. Briceno, D. Charbonneau, M. Cointepas, K. I. Collins, I. Crossfield, X. Delfosse, R. F. Diaz, C. DornJ. P. Doty, T. Forveille, G. Gaisné, T. Gan, R. Helled, K. Hesse, J. M. Jenkins, E. L.N. Jensen, D. W. Latham, N. Law, A. W. Mann, S. Mao, B. McLean, F. Murgas, G. Myers, S. Seager, A. Shporer, T. G. Tan, J. D. Twicken, J. Winn

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3 Scopus citations


We report the detection of GJ 3090 b (TOI-177.01), a mini-Neptune on a 2.9-day orbit transiting a bright (K = 7.3 mag) M2 dwarf located at 22 pc. The planet was identified by the Transiting Exoplanet Survey Satellite and was confirmed with the High Accuracy Radial velocity Planet Searcher radial velocities. Seeing-limited photometry and speckle imaging rule out nearby eclipsing binaries. Additional transits were observed with the LCOGT, Spitzer, and ExTrA telescopes. We characterise the star to have a mass of 0.519 ± 0.013 Mâ ? ? and a radius of 0.516 ± 0.016 Râ ? ? . We modelled the transit light curves and radial velocity measurements and obtained a planetary mass of 3.34 ± 0.72 ME, a radius of 2.13 ± 0.11 RE, and a mean density of 1.89-0.45+0.52 g cm-3. The low density of the planet implies the presence of volatiles, and its radius and insolation place it immediately above the radius valley at the lower end of the mini-Neptune cluster. A coupled atmospheric and dynamical evolution analysis of the planet is inconsistent with a pure H-He atmosphere and favours a heavy mean molecular weight atmosphere. The transmission spectroscopy metric of 221-46+66 means that GJ 3090 b is the second or third most favorable mini-Neptune after GJ 1214 b whose atmosphere may be characterised. At almost half the mass of GJ 1214 b, GJ 3090 b is an excellent probe of the edge of the transition between super-Earths and mini-Neptunes. We identify an additional signal in the radial velocity data that we attribute to a planet candidate with an orbital period of 13 days and a mass of 17.1-3.2+8.9 ME, whose transits are not detected.

Original languageEnglish (US)
Article numberA91
JournalAstronomy and Astrophysics
StatePublished - Sep 1 2022

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Planetary systems
  • Stars: individual: GJ 3090
  • Techniques: photometric
  • Techniques: radial velocities


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