Two warm Earth-sized exoplanets and an Earth-sized candidate in the M5V-M6V binary system TOI-2267

¹ Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
² Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
³ Dpto. Física Teórica y del Cosmos. Universidad de Granada. 18071. Granada, Spain
⁴ Avature Machine Learning, Spain
⁵ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁶ Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
⁷ Department of Physics & Astronomy, Vanderbilt University, 6301 Stevenson Center Ln., Nashville, TN 37235, USA
⁸ Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
⁹ Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile
¹⁰ Observatoire Astronomique de l’Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
¹¹ Lund Observatory, Division of Astrophysics, Department of Physics, Lund University, Box 118, 22100 Lund, Sweden
¹² European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹³ Center for Astrophysics and Space Sciences, UC San Diego, UCSD Mail Code 0424, 9500 Gilman Drive, La Jolla, CA 92093-0424, USA
¹⁴ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 1800 Sherman, Evanston, IL 60201, USA
¹⁵ Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
¹⁶ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁷ Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38200, La Laguna, Tenerife, Spain
¹⁸ School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
¹⁹ Institut Trottier de recherche sur les exoplanètes, Université de Montréal, 1375 Ave Thérèse-Lavoie-Roux, Montréal, QC H2V 0B3, Canada
²⁰ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
²¹ Lomonosov Moscow State University, Sternberg Astronomical Institute, Universitetskij pr. 13, Moscow 119234, Russia
²² NASA Ames Research Center, Moffett Field, CA 94035, USA
²³ Bay Area Environmental Research Institute, Moffett Field, CA 94035, USA
²⁴ NASA Exoplanet Science Institute, Caltech/IPAC, Mail Code 100-22, 1200 E. California Blvd., Pasadena, CA 91125, USA
²⁵ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
²⁶ Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK
²⁷ Department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
²⁸ Magdalen College, University of Oxford, Oxford OX1 4AU, UK
²⁹ Paris Region Fellow, Marie Sklodowska-Curie Action
³⁰ AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, 91191 Gif-sur-Yvette, France
³¹ Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA
³² Universidad Nacional Autónoma de México, Instituto de Astronomía, AP 70-264, Ciudad de México 04510, Mexico
³³ Department of Astrophysical and Planetary Sciences, University of Colorado Boulder, Boulder, CO 80309, USA
³⁴ Institute for Particle Physics and Astrophysics, ETH Zürich, Wolfgang-Pauli-Strasse 2, 8093 Zürich, Switzerland
³⁵ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
³⁶ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
³⁷ NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
³⁸ Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Faculty of sciences Semlalia, Cadi Ayyad University, Marrakech, Morocco
³⁹ Observatoire du Mont-Mégantic, Université de Montréal, Montréal H3C 3J7, Canada
⁴⁰ SETI Institute, Mountain View, CA 94043 USA/NASA Ames Research Center, Moffett Field, CA 94035, USA
⁴¹ Universidad Nacional Autónoma de México, Instituto de Astronomía, AP 106, Ensenada 22800, BC, Mexico

^★ Corresponding authors: sgzuniga@uliege.be; pozuelos@iaa.csic.es

Received: 7 March 2025
Accepted: 18 August 2025

Abstract

We report the discovery of two warm exoplanets orbiting the cool binary system TOI-2267, composed of the M5 (TOI-2267A) and M6 (TOI-2267B) stars, whose angular separation is 0.384 arcsec, corresponding to a projected distance of only about 8 au at 22 pc from the Solar System. To confirm the planetary nature of these objects, we combined photometry from the Transiting Exoplanet Survey Satellite (TESS) and ground-based facilities together with high-resolution images, archival data, and statistical validation in our analyses. From the current data set, we cannot unambiguously determine which star of the binary the planets orbit. These planets are Earth-sized with radii of 1.00±0.11 and 1.14±0.13 R_⊕ for TOI-2267 b (P = 2.28 d) and TOI-2267 c (P = 3.49 d), respectively, when orbiting TOI-2267A, whereas the radii are of 1.22±0.29 and 1.36±0.33 R_⊕ when orbiting TOI-2267B. In addition to the signals attributed to TOI-2267 b and c, the TESS data reveal a third strong signal with a periodicity of 2.03 d (TOI-2267.02). Although statistical analyses support its planetary nature, ground-based follow-up observations did not detect this signal. Its status therefore remains that of a planetary candidate, with an Earth-size of 0.95±0.12 R_⊕ or 1.13±0.30 R_⊕ when orbiting TOI-2267A or B, respectively. If this candidate is confirmed, dynamical analyses indicate that all three planets cannot orbit the same star. The most plausible configurations are b–c or .02–c orbiting the same star, while the .02–b case is unlikely due to strong instabilities. The proximity of b and c to a first-order 3:2 mean motion resonance suggests they likely orbit the same star, with .02 orbiting the other component. This scenario would make TOI-2267 the most compact binary system known to host planets, with both components harbouring transiting worlds, and offer a unique benchmark for studying planet formation and evolution in compact binary environments.