Confirmation of the hot super-Neptune TOI-672 b with NIRPS and HARPS

Insights into the Neptunian desert around M dwarfs

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
² Department of Physics & Astronomy, McMaster University, 1280 Main St W, Hamilton, ON, L8S 4L8, Canada
³ Department of Physics, The University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
⁴ Observatoire de Genève, Département d’Astronomie, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁵ Institut Trottier de recherche sur les exoplanètes, Département de Physique, Université de Montréal, Montréal, Québec, Canada
⁶ Light Bridges S.L., Observatorio del Teide, Carretera del Observatorio, s/n Guimar, 38500 Tenerife, Canarias, Spain
⁷ Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁸ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁹ Observatoire du Mont-Mégantic, Québec, Canada
¹⁰ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹¹ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
¹² Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095, USA
¹³ Department of Physics, University of Toronto, Toronto, ON M5S 3H4, Canada
¹⁴ Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Campus Universitário, Natal, RN, 59072-970, Brazil
¹⁵ Department of Physics, McGill University, 3600 rue University, Montréal, QC, H3A 2T8, Canada
¹⁶ Department of Earth & Planetary Sciences, McGill University, 3450 rue University, Montréal, QC, H3A 0E8, Canada
¹⁷ Centre Vie dans l’Univers, Faculté des sciences de l’Université de Genève, Quai Ernest-Ansermet 30, 1205 Geneva, Switzerland
¹⁸ European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
¹⁹ Space Research and Planetary Sciences, Physics Institute, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
²⁰ Consejo Superior de Investigaciones Científicas (CSIC), 28006 Madrid, Spain
²¹ Bishop’s University, Dept of Physics and Astronomy, Johnson-104E, 2600 College Street, Sherbrooke, QC, J1M 1Z7, Canada
²² Department of Physics, Engineering Physics, and Astronomy, Queen’s University, 99 University Avenue, Kingston, ON K7L 3N6, Canada
²³ Department of Physics and Space Science, Royal Military College of Canada, 13 General Crerar Cres., Kingston, ON K7P 2M3, Canada
²⁴ Center for astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
²⁵ Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada (Madrid), Spain
²⁶ Boyce Research Initiatives and Education Foundation, 3540 Carleton St., San Diego, CA 92106, USA
²⁷ El Sauce Observatory, Coquimbo Province, Chile
²⁸ European Southern Observatory (ESO), Av. Alonso de Cordova 3107, Casilla 19001, Santiago de Chile, Chile
²⁹ Department of Astronomy, Westlake University, Hangzhou 310030, Zhejiang Province, PR China
³⁰ University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, 81679 Munich, Germany
³¹ Department of Physics and Astronomy, University of Waterloo, 200 University W, Waterloo, ON N2L 3G1, Canada
³² Perth Exoplanet Survey Telescope, Perth, Western Australia, Australia
³³ American Association of Variable Star Observers, Cambridge, USA

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Received: 1 December 2025
Accepted: 10 March 2026

Abstract

The Neptunian desert is a distinct lack of Neptune-sized planets at short orbital periods, purportedly carved by photoevaporation and tidal circularisation following high-eccentricity migration. Constraining these processes and how they vary across different hoststar spectral types requires detailed characterisation of the planets in the desert and around its boundaries. In this study, we confirm the planetary nature of a massive super-Neptune identified by TESS around the M0 dwarf TOI-672. We analysed photometry from TESS and ExTrA and precise radial velocity measurements taken with the recently commissioned Near-InfraRed Planet Searcher (NIRPS) and HARPS spectrographs. We measured a planetary orbital period of 3.634 days, a radius of 5.31_−0.26^+0.24 R_⊕, and mass of 50.9_−4.4^+4.5 M_⊕. Our findings place TOI-672 b within the Neptunian ridge, a pile-up of planets from 3-5 days at the Neptunian desert boundary. We used a novel approach to determine the desert boundaries in period-radius space and instellation-radius space, and for the first time, we compared the Neptunian desert boundaries for planets orbiting FGK versus M dwarf stars. We determined that the boundary ridge shifts slightly inwards from 3.3 ± 1.4 days for FGK host stars to 2.2 ± 1.0 days for M dwarf host stars. Statistically, these values do not significantly differ from each other, and the shift to shorter periods for M dwarf planets is smaller than what theoretical photoevaporation models predict. We also find that TOI-672 b is a single-planet system within the sensitivity limits of our RV and TTV datasets.