The multi-planet system TOI-5624: four transiting sub-Neptunes with an outer companion revealed by transit-timing variations
Year: 2026
Type: article
Abstract: Context. Following the 2022 alert of a TESS object of interest transiting TOI-5624 (a G7 V star ∼ 100 pc away), a CHEOPS campaign in 2023 detected four planetary signals at Pb ≈ 3.4, Pc ≈ 7.9, Pd ≈ 13.7, and Pe ≈ 21.5 days. These signals were later confirmed by additional TESS and CHEOPS photometry in 2024-2025. Aims. By using TESS and CHEOPS photometry, along with HARPS-N and SOPHIE high-resolution spectra, we determined the planet properties and performed a dynamical analysis of the system. Methods. After analysing the photometric data, we extracted and modelled the radial velocity (RV) time series using two independent methodologies, both within a Markov chain Monte Carlo framework. We further integrated the N-body equations of motion, while simultaneously fitting the transit times and the detrended RVs, to dynamically characterise the system. Results. We present the discovery of four transiting sub-Neptunes with radii of Rb = 2.314 ± 0.035 R⊕, Rc = 2.474 ± 0.042 R⊕, Rd = 3.584−0.050+0.051 R⊕, and Re = 3.247−0.043+0.042 R⊕, along with masses of Mb = 9.4 ± 1.4M⊕, Mc = 4.8 ± 1.9M⊕, Md = 4.9 ± 2.2M⊕, and Me = 8.9−3.0+2.9 M⊕. Our photometric analysis revealed that the outermost transiting planet TOI-5624e shows significant transit-timing variations (TTVs). Indeed, we found a robust Keplerian signal in the RV time series close to the 2:1 period commensurability with TOI-5624 e, which explains the TTV pattern exhibited by TOI-5624 e according to our dynamical analysis. We labelled this non-transiting planet as TOI-5624 f and determined its minimum mass to be Mf sin if = 13.0 ± 3.7 M⊕. Conclusions. Among the known systems hosting more than four planets, the remarkable precision with which the radii have been measured (<1.7%) and the firm assessment (>3σ) of the mass for at least three planets has previously been reached only for TRAPPIST-1. Additional photometric observations will enable a better sample of the TTV modulation and a more robust dynamical determination of the masses.
Authors: A. Bonfanti, D. Gandolfi, P. Leonardi, H. P. Osborn, L. M. Serrano, G. Hébrard, N. Billot, A. Bekkelien, G. Olofsson, C. Broeg, D. Nardiello, S. G. Sousa, T. G. Wilson, A. C. M. Correia, C. Pezzotti, A. Brandeker, L. Fossati, M. Gillon, M. Stalport, B. Akinsanmi, Y. Alibert, R. Alonso, J. Asquier, T. Bárczy, D. Barrado, S. C. C. Barros, W. Baumjohann, W. Benz, L. Borsato, A. Castro-González, A. Collier Cameron, Sz. Csizmadia, P. E. Cubillos, M. B. Davies, M. Deleuil, X. Delfosse, A. Deline, O. D. S. Demangeon, B.-O. Demory, A. Derekas, F. Destriez, B. Edwards, D. Ehrenreich, A. Erikson, A. Fortier, M. Fridlund, K. Gazeas, M. Güdel, M. N. Günther, N. Hara, N. Heidari, A. Heitzmann, Ch. Helling, K. G. Isaak, T. Keller, L. L. Kiss, D. Kitzmann, J. Korth, G. Lacedelli, K. W. F. Lam, J. Laskar, A. Lecavelier des Etangs, A. Leleu, M. Lendl, D. Magrin, P. F. L. Maxted, M. Mecina, B. Merín, C. Mordasini, V. Nascimbeni, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, D. Piazza, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, N. C. Santos, G. Scandariato, D. Ségransan, A. E. Simon, A. M. S. Smith, S. Sulis, Gy. M. Szabó, S. Udry, S. Ulmer-Moll, V. Van Grootel, J. Venturini, F. Verrecchia, E. Villaver, N. A. Walton, S. Wolf, D. Wolter, T. Zingales
Institutions: Centre National de la Recherche Scientifique, Institut d'Astrophysique de Paris, Université Pierre-et-Marie-Curie, Aix-Marseille Université, Observatoire de Haute-Provence, University of Geneva, Stockholm University, AlbaNova, University of Bern, Universidade do Porto, Institute of Astrophysics and Space Sciences, Centro de Astrofísica da Universidade do Porto, University of Warwick, Centro de Física da Universidade de Coimbra, University of Coimbra, University of Liège, Universidad de La Laguna, Instituto de Astrofísica de Canarias, European Space Agency, European Space Research and Technology Centre, Centro de Astrobiología, Osservatorio Astronomico di Padova, National Institute for Astrophysics, University of St Andrews, Osservatorio Astrofisico di Torino, Lund University, Laboratoire d’Astrophysique de Marseille, Institut de Planétologie et d'Astrophysique de Grenoble, Université Grenoble Alpes, Eötvös Loránd University, Université Paris Cité, Université Paris Sciences et Lettres, Observatoire de Paris, Sorbonne Université, Space Research Organisation Netherlands, Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR), Leiden University, University of Vienna, National and Kapodistrian University of Athens, Graz University of Technology, Leiden Observatory, Chalmers University of Technology
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7155812702
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