A planetary system with a sub-Neptune planet in the habitable zone of TOI-2093

¹ Centro de Astrobiología, CSIC-INTA, Camino bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
² Departamento de Física de la Tierra y Astrofísica & IPARCOS Instituto de Física de Partículas y del Cosmos, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, Plaza de Ciencias 1, 28040 Madrid, Spain
³ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁴ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁵ Institut d’Estudis Espacials de Catalunya, 08860 Castelldefels, Barcelona, Spain
⁶ Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁷ Department of Physics, Ariel University, Ariel 40700, Israel
⁸ Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006, Australia
⁹ Astrophysics, Geophysics, And Space Science Research Center, Ariel University, Ariel 40700, Israel
¹⁰ Vereniging Voor Sterrenkunde, Oostmeers 122 C, 8000 Brugge, Belgium
¹¹ Public observatory ASTROLAB IRIS, Provinciaal Domein “De Palingbeek”, Verbrandemolenstraat 5, 8902 Zillebeke, Ieper, Belgium
¹² Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹³ Department of Astronomy & Astrophysics, University of Chicago, Chicago, IL 60637, USA
¹⁴ NHFP Sagan Fellow
¹⁵ Institut für Astrophysik und Geophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
¹⁶ NASA Ames Research Center, Moffett Field, CA 94035, USA
¹⁷ Research Institute for Advanced Computer Science, Universities Space Research Association, Washington, DC 20024, USA
¹⁸ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹⁹ Centro Astronómico Hispano en Andalucía, Observatorio Astronómico de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Almería, Spain
²⁰ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025, Pino Torinese, Italy
²¹ NASA Exoplanet Science Institute, Caltech/IPAC, Mail Code 100-22, 1200 E. California Blvd., Pasadena, CA 91125, USA
²² Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
²³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²⁴ Departamento de Ingeniería Topográfica y Cartografía, E.T.S.I. en Topografía, Geodesia y Cartografía, Universidad Politécnica de Madrid, 28031 Madrid, Spain
²⁵ Institut de Ciències de l’Espai, CSIC, c/ de Can Magrans s/n, Campus UAB, 08193 Bellaterra, Barcelona, Spain
²⁶ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziądzka 5, 87-100 Toruń, Poland
²⁷ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany

^★ Corresponding author: jsanz@cab.inta-csic.es

Received: 11 July 2025
Accepted: 12 September 2025

Abstract

Aims. We aim to confirm and measure the mass of the transiting planet candidate around the K5 V star TOI-2093, previously announced by the Transiting Exoplanet Survey Satellite (TESS) project.

Methods. We combined photometric data from 32 sectors between 2019 and 2024 with 86 radial velocity measurements obtained with the CARMENES spectrograph over a period of 2.4 years, along with a series of ground-based, broadband photometric monitoring campaigns to characterize the host star and the transiting planet candidate, as well as to search for additional planets in the system. Our data indicate that TOI-2093 is a main-sequence star located at a distance of 83 pc, with solar metallicity, and a rotation period of 43.8±1.8 d.

Results. We have confirmed the planetary nature of the TESS transiting planet candidate, named TOI-2093 c, through the detection of its Keplerian signal in the spectroscopic data. We measured a planetary radius of 2.30±0.12 R_⊕, a Neptune-like mass of 15.8_−3.8^+3.6 M_⊕, and an orbital period of 53.81149±0.00017 d. This makes TOI-2093 c the smallest exoplanet known in the habitable zone of a main-sequence FGK star. Given its size and relatively high density, TOI-2093 c belongs to a class of planets with no analog in the Solar System. In addition, the CARMENES data revealed the presence of a second planet candidate with a minimum mass of 10.6±2.5 M_⊕ and an orbital period of 12.836±0.021 d. This inner planet, which we designated TOI-2093 b, shows no detectable photometric transit in the TESS light curves. The orbital planes of the two planets are misaligned by more than 1.6° despite the near 4:1 mean-motion resonance of their orbital periods.