NIRPS tightens the mass estimate of GJ 3090 b and detects a planet near the stellar rotation period

¹ Institut Trottier de recherche sur les exoplanètes, Département de Physique, Université de Montréal, Montréal, Québec, Canada
² Department of Physics & Astronomy, McMaster University, 1280 Main St W, Hamilton ON, L8S 4L8, Canada
³ Department of Physics, University of Toronto, Toronto, ON M5S 3H4, Canada
⁴ Observatoire de Genève, Département d’Astronomie, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁵ Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁶ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁷ Planétarium de Montréal, Espace pour la Vie, 4801 av. Pierre-de Coubertin, Montréal, Québec, Canada
⁸ Observatoire du Mont-Mégantic, Québec, Canada
⁹ European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
¹⁰ University Observatory, Faculty of Physics, Ludwig-MaximiliansUniversität München, Scheinerstr. 1, 81679 Munich, Germany
¹¹ European Southern Observatory (ESO), Av. Alonso de Cordova 3107, Casilla 19001, Santiago de Chile, Chile
¹² Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹³ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
¹⁴ Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095, USA
¹⁵ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹⁶ Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Campus Universitário, Natal, RN 59072-970, Brazil
¹⁷ Department of Physics, McGill University, 3600 rue University, Montréal, QC H3A 2T8, Canada
¹⁸ Department of Earth & Planetary Sciences, McGill University, 3450 rue University, Montréal, QC H3A 0E8, Canada
¹⁹ Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, Fortaleza, Brazil
²⁰ Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada (Madrid), Spain
²¹ Centre Vie dans l’Univers, Faculté des sciences de l’Université de Genève, Quai Ernest-Ansermet 30, 1205 Geneva, Switzerland
²² Space Research and Planetary Sciences, Physics Institute, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
²³ Consejo Superior de Investigaciones Científicas (CSIC), 28006 Madrid, Spain
²⁴ Bishop’s Univeristy, Dept of Physics and Astronomy, Johnson-104E, 2600 College Street, Sherbrooke, QC J1M 1Z7, Canada
²⁵ Department of Physics, Engineering Physics, and Astronomy, Queen’s University, 99 University Avenue, Kingston, ON K7L 3N6, Canada
²⁶ Department of Physics and Space Science, Royal Military College of Canada, 13 General Crerar Cres., Kingston, ON K7P 2M3, Canada
²⁷ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
²⁸ Departamento de Física da Faculdade de Ciências da Universidade de Lisboa, Edifício C8, 1749-016 Lisboa, Portugal
²⁹ Centre of Optics, Photonics and Lasers, Université Laval, Québec, Canada
³⁰ Herzberg Astronomy and Astrophysics Research Centre, National Research Council of Canada, Canada
³¹ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
³² Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
³³ Center for astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
³⁴ NASA Exoplanet Science Institute, IPAC, California Institute of Technology, Pasadena, CA 91125, USA
³⁵ George Mason University, 4400 University Drive, Fairfax, VA 22030, USA
³⁶ Division of Astrophysics, Department of Physics, Lund University, Box 118, 22100 Lund, Sweden
³⁷ SETI Institute, Mountain View, CA 94043, USA; NASA Ames Research Center, Moffett Field, CA 94035, USA
³⁸ York University, 4700 Keele St, North York, ON M3J 1P3, Canada
³⁹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴⁰ University of British Columbia, 2329 West Mall, Vancouver, BC, Canada, V6T 1Z4, Canada
⁴¹ Western University, Department of Physics & Astronomy and Institute for Earth and Space Exploration, 1151 Richmond Street, London, ON N6A 3K7, Canada
⁴² Light Bridges S.L., Observatorio del Teide, Carretera del Observatorio, s/n Guimar, 38500 Tenerife, Canarias, Spain
⁴³ Department of Physics, The University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁴⁴ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
⁴⁵ Subaru Telescope, National Astronomical Observatory of Japan (NAOJ), 650 N Aohoku Place, Hilo, HI 96720, USA
⁴⁶ Department of Astronomy & Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
⁴⁷ Laboratoire Lagrange, Observatoire de la Côte d’Azur, CNRS, Université Côte d’Azur, Nice, France

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Received: 16 August 2025
Accepted: 15 December 2025

Abstract

We present an updated characterization of the planetary system orbiting the nearby M2 dwarf GJ 3090 (TOI-177; d=22 pc), based on new high-precision radial velocity (RV) observations from NIRPS and HARPS. With an orbital period of 2.85 d, the transiting sub-Neptune GJ 3090 b has a mass we refine to 4.52 ± 0.47 M_⊕, which, combined with our derived radius of 2.18 ± 0.06 R_⊕, yields a density of 2.40_−0.30^+0.33 g∉cm⁻³. The combined interior structure and atmospheric constraints indicate that GJ 3090 b is a compelling water-world candidate, with a volatile-rich envelope in which water likely represents a significant fraction. We also confirm the presence of a second planet, GJ 3090 c, a sub-Neptune with a 15.9 d orbit and a minimum mass of 10.0 ± 1.3 M_⊕, which does not transit. Despite its proximity to the star’s 18 d rotation period, our joint analysis using a multidimensional Gaussian process (GP) model that incorporates TESS photometry and differential stellar temperature measurements distinguishes this planetary signal from activity-induced variability. In addition, we place new constraints on a non-transiting planet candidate with a period of 12.7 d, suggested in earlier RV analyses. This candidate remains a compelling target for future monitoring. These results highlight the crucial role of multidimensional GP modelling in disentangling planetary signals from stellar activity, enabling the detection of a planet near the stellar rotation period that could have remained undetected with traditional approaches.