The Multi-planet System TOI-5624: Four Transiting Sub-Neptunes With An Outer Companion Revealed By Transit-timing Variations

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 P_b≈3.4, P_c≈7.9, P_d≈13.7, and P_e≈21.5 days, later confirmed by additional TESS and CHEOPS photometry in 2024-2025.

After analysing the TESS & CHEOPS photometric data, we extracted and modelled the HARPS-N & SOPHIE RV time series using two independent methodologies both within an MCMC 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.

We present the discovery of four transiting sub-Neptunes with radii of R_b=2.314±0.035R_⊕, R_c=2.474±0.042R_⊕, R_d=3.584+0.051−0.050R_⊕, and R_e=3.247+0.042−0.043R_⊕ and masses of M_b=9.4±1.4M_⊕, M_c=4.8±1.9M_⊕, M_d=4.9±2.2M_⊕, and M_e=8.9+2.9−3.0M_⊕.

Our photometric analysis reveals that the outermost transiting planet TOI-5624 e shows significant TTVs. We find 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 label this non-transiting planet as TOI-5624 f and find its minimum mass to be M_fsinif=13.0±3.7M_⊕.

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 been previously 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.

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

Comments: Accepted for publication in A&A. 22 pages (13 in the main text), 4 figures (+9 in the Appendix), 2 tables (+7 in the Appendix). Abstract abridged to satisfy the arXiv submission requirements
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2604.15035 [astro-ph.EP] (or arXiv:2604.15035v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2604.15035
Focus to learn more
Submission history
From: Andrea Bonfanti
[v1] Thu, 16 Apr 2026 14:04:19 UTC (6,147 KB)
https://arxiv.org/abs/2604.15035

Astrobiology, Exoplanet,