Almenara, JM, Bonfils, X, Otegi, JF, Attia, O, Turbet, M, Astudillo-Defru, N, Collins, KA, Polanski, AS, Bourrier, V, Hellier, C, Ziegler, C, Bouchy, F, Briceno, C, Charbonneau, D, Cointepas, M, Collins, KI, Crossfield, I, Delfosse, X, Diaz, RF, Dorn, C, Doty, JP, Forveille, T, Gaisne, G, Gan, T, Helled, R, Hesse, K, Jenkins, JM, Jensen, ELN, Latham, DW, Law, N, Mann, AW, Mao, S, McLean, B, Murgas, F, Myers, G, Seager, S, Shporer, A, Tan, TG, Twicken, JD and Winn, J (2022) GJ 3090 b: one of the most favourable mini-Neptune for atmospheric characterisation. Astronomy and Astrophysics: a European journal, 665. ISSN 0004-6361

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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 M⊙ and a radius of 0.516 ± 0.016 R⊙. 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.

Item Type: Article
Additional Information: Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article is published in open access under the Subscribe-to-Open model. Subscribe to A&A to support open access publication.
Subjects: Q Science > QA Mathematics
Q Science > QB Astronomy
Q Science > QB Astronomy > QB460 Astrophysics
Q Science > QB Astronomy > QB600 Planets. Planetology
Q Science > QC Physics
Divisions: Faculty of Natural Sciences > School of Chemical and Physical Sciences
Related URLs:
Depositing User: Symplectic
Date Deposited: 09 Nov 2022 16:28
Last Modified: 09 Nov 2022 16:28

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