Giant Outer Transiting Exoplanet Mass (GOT’EM) survey

VII. TOI-6041: A multi-planet system including a warm Neptune exhibiting strong transit-timing variations

¹ Institut d’astrophysique de Paris, CNRS & Sorbonne Université, UMR 7095, 98bis boulevard Arago, 75014 Paris, France
² LTE, UMR8255 CNRS, Observatoire de Paris, PSL Univ., Sor-bonne Univ., 77 av. Denfert-Rochereau, 75014 Paris, France
³ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
⁴ ETH Zurich, Department of Physics, Wolfgang-Pauli-Strasse 2, 8093 Zurich, Switzerland
⁵ Department of Physics and Astronomy, University of New Mexico, 210 Yale Blvd NE, Albuquerque, NM 87106, USA
⁶ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
⁷ Space Research and Planetary Sciences, Physics Institute, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
⁸ Observatoire astronomique de l’Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁹ Observatoire de Haute-Provence, CNRS, Université d’Aix-Marseille, 04870 Saint-Michel-l’Observatoire, France
¹⁰ European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹¹ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
¹² Space Research Institute, Austrian Academy of Sciences, Schmiedl-strasse 6, 8042 Graz, Austria
¹³ Center for Astrophysics |Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹⁴ CFisUC, Departamento de Física, Universidade de Coimbra, 3004-516 Coimbra, Portugal
¹⁵ Caltech/IPAC-NASA Exoplanet Science Institute, 770 S. Wilson Avenue, Pasadena, CA 91106, USA
¹⁶ Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, 10125 Torino, Italy
¹⁷ Observatoire de Genève, Université de Genève, 51 Chemin Pegasi, 1290 Versoix, Switzerland
¹⁸ NASA Ames Research Center, Moffett Field, CA 94035, USA
¹⁹ Amateur Astronomer, 7507 52nd Place NE, Marysville, WA 98270, USA
²⁰ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
²¹ Instituto de Astrofisica e Ciencias do Espaco, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
²² Leiden Observatory, University of Leiden, Einsteinweg 55, 2333 CA Leiden, The Netherlands
²³ NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
²⁴ Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38200 La Laguna, Tenerife, Spain
²⁵ Departamento de Astrofísica, Universidad de La Laguna, Astrofísico Francisco Sanchez s/n, 38206 La Laguna, Tenerife, Spain
²⁶ Admatis, 5. Kandó Kálmán Street, 3534 Miskolc, Hungary
²⁷ Depto. de Astrofísica, Centro de Astrobiología (CSIC-INTA), ESAC campus, 28692 Villanueva de la Cañada (Madrid), Spain
²⁸ Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
²⁹ INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
³⁰ Department of Astronomy, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden
³¹ Institute of Space Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
³² Centre for Exoplanet Science, SUPA School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
³³ INAF, Osservatorio Astrofisico di Torino, Via Osservatorio, 20, 10025 Pino Torinese To, Italy
³⁴ Centre for Mathematical Sciences, Lund University, Box 118, 221 00 Lund, Sweden
³⁵ Aix Marseille Univ, CNRS, CNES, LAM, 38 rue Frédéric Joliot-Curie, 13388 Marseille, France
³⁶ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³⁷ ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland
³⁸ ELTE Gothard Astrophysical Observatory, 9700 Szombathely, Szent Imre h. u. 112, Hungary
³⁹ SRON Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA Leiden, The Netherlands
⁴⁰ Centre Vie dans l’Univers, Faculté des sciences, Université de Genève, Quai Ernest-Ansermet 30, 1211 Genève 4, Switzerland
⁴¹ Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
⁴² Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
⁴³ National and Kapodistrian University of Athens, Department of Physics, University Campus, Zografos 157 84 Athens, Greece
⁴⁴ Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
⁴⁵ Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁴⁶ Institute for Theoretical Physics and Computational Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
⁴⁷ Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521, USA
⁴⁸ Vanderbilt University, Department of Physics & Astronomy, 6301 Stevenson Center Ln., Nashville, TN 37235, USA
⁴⁹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, 1121 Budapest, Konkoly Thege Miklós út 15–17, Hungary
⁵⁰ ELTE Eötvös Loránd University, Institute of Physics, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁵¹ Institut d’astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis blvd. Arago, 75014 Paris, France
⁵² Astrophysics Group, Lennard Jones Building, Keele University, Staffordshire ST5 5BG, UK
⁵³ European Space Agency, ESA – European Space Astronomy Centre, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁵⁴ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziądzka 5, 87-100 Toruń, Poland
⁵⁵ INAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁵⁶ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁵⁷ Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK
⁵⁸ German Aerospace Center (DLR), Markgrafenstrasse 37, 10117 Berlin, Germany
⁵⁹ Institut fuer Geologische Wissenschaften, Freie Universitaet Berlin, Malteserstrasse 74-100, 12249 Berlin, Germany
⁶⁰ Institut de Ciencies de l’Espai (ICE, CSIC), Campus UAB, Can Magrans s/n, 08193 Bellaterra, Spain
⁶¹ Institut d’Estudis Espacials de Catalunya (IEEC), 08860 Castelldefels (Barcelona), Spain
⁶² Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁶³ HUN-REN-ELTE Exoplanet Research Group, Szent Imre h. u. 112., Szombathely 9700, Hungary
⁶⁴ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁶⁵ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
⁶⁶ Proto-Logic LLC, 1718 Euclid Street NW, Washington, DC 20009, USA
⁶⁷ SETI Institute, Mountain View, CA 94043 USA/NASA Ames Research Center, Moffett Field, CA 94035, USA

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Received: 1 August 2025
Accepted: 27 November 2025

Abstract

We present the characterisation of the TOI-6041 system, a bright (V = 9.84 ± 0.03) G7-type star hosting at least two planets. The inner planet, TOI-6041 b, is a warm Neptune with a radius of 4.55_−0.17^+0.18 R_⊕, initially identified as a single-transit event in TESS photometry. Subsequent observations with TESS and CHEOPS revealed additional transits, enabling the determination of its 26.04945_−0.00034^+0.00033 orbital period and the detection of significant transit-timing variations (TTVs), exhibiting a peak-to-peak amplitude of about 1 hour. Radial-velocity (RV) measurements obtained with the APF spectrographs allowed us to place a 3σ upper mass limit of 28.9 M_⊕ on TOI-6041 b. In addition, the RV data reveal a second companion, TOI-6041 c, on an 88 d orbit, with a minimum mass of 0.25 M_Jup. A preliminary TTV analysis suggested that the observed variations could be caused by gravitational perturbations from planet c; however, reproducing the observed amplitudes requires a relatively high eccentricity of about 0.3 for that planet. Our dynamical stability analysis indicates that such a configuration is dynamically viable and places a 1σ upper limit on the mass of TOI-6041 c at 0.8 M_Jup. An alternative is the presence of a third, low-mass planet located between planets b and c, or on an inner orbit relative to planet b – particularly near a mean-motion resonance with planet b – which could account for the observed variations. These findings remain tentative, and further RV and photometric observations are essential in to better constrain the mass of planet b and to refine the TTV modeling, thereby improving our understanding of the system’s dynamical architecture.