The multi-planet system TOI-5624: four transiting sub-Neptunes with an outer companion revealed by transit-timing variations
Journal article, 2026
Context. Following the 2022 alert of a TESS object of interest transiting TOI-5624 (a G7 V star similar to 100 pc away), a CHEOPS campaign in 2023 detected four planetary signals at P-b approximate to 3.4, P-c approximate to 7.9, P-d approximate to 13.7, and P-e approximate to 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 R-b = 2.314 +/- 0.035 R-circle plus, R-c = 2.474 +/- 0.042 R-circle plus, R-d = 3.584(-0.050)(+0.051)R(circle plus), and R-e = 3.247(-0.043)(+0.042)R(circle plus), along with masses of M-b = 9.4 +/- 1.4M(circle plus), M-c = 4.8 +/- 1.9M(circle plus), Md = 4.9 +/- 2.2M(circle plus), and M-e = 8.9(-3.0)(+2.9)M(circle plus). 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 M-f sin i(f) = 13.0 +/- 3.7 M-circle plus. 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 (>3 sigma) 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.
techniques: radial velocities
planets and satellites: fundamental parameters
techniques: photometric
stars: fundamental parameters
Author
A. Bonfanti
Austrian Academy of Sciences
D. Gandolfi
University of Turin
P. Leonardi
University of Trento
University of Padua
H. P. Osborn
University of Bern
Swiss Federal Institute of Technology in Zürich (ETH)
L. M. Serrano
University of Turin
G. Hebrard
Aix Marseille University
Pierre and Marie Curie University (UPMC)
N. Billot
University of Geneva
A. Bekkelien
University of Geneva
G. Olofsson
Stockholm University
C. Broeg
University of Bern
D. Nardiello
University of Padua
Istituto nazionale di astrofisica (INAF)
S. G. Sousa
University of Porto
T. G. Wilson
The University of Warwick
A. C. M. Correia
University of Coimbra
C. Pezzotti
University of Liège
A. Brandeker
Stockholm University
L. Fossati
Austrian Academy of Sciences
M. Gillon
University of Liège
M. Stalport
University of Liège
B. Akinsanmi
University of Geneva
Y. Alibert
University of Bern
R. Alonso
University of La Laguna
Instituto de Astrofísica de Canarias
J. Asquier
European Space Agency (ESA)
T. Barczy
Admatis
D. Barrado
Spanish National Research Council (CSIC)
S. C. C. Barros
University of Porto
W. Baumjohann
Austrian Academy of Sciences
W. Benz
University of Bern
L. Borsato
Istituto nazionale di astrofisica (INAF)
A. Castro-Gonzalez
University of Geneva
A. Collier Cameron
University of St Andrews
Sz. Csizmadia
German Aerospace Center (DLR)
P. E. Cubillos
Istituto nazionale di astrofisica (INAF)
Austrian Academy of Sciences
M. B. Davies
Lund University
M. Deleuil
Aix Marseille University
X. Delfosse
Grenoble Alpes University
A. Deline
University of Geneva
O. D. S. Demangeon
University of Porto
B. O. Demory
University of Bern
A. Derekas
Eötvös Loránd University (ELTE)
F. Destriez
Pierre and Marie Curie University (UPMC)
Paris Descartes University
B. Edwards
Netherlands Institute for Space Research (SRON)
D. Ehrenreich
University of Geneva
A. Erikson
German Aerospace Center (DLR)
A. Fortier
University of Bern
Malcolm Fridlund
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
K. Gazeas
National and Kapodistrian University of Athens
M. Gudel
University of Vienna
M. N. Gunther
European Space Agency (ESA)
N. Hara
Aix Marseille University
N. Heidari
Pierre and Marie Curie University (UPMC)
A. Heitzmann
University of Geneva
Ch. Helling
Technische Universität Graz
Austrian Academy of Sciences
K. G. Isaak
European Space Agency (ESA)
T. Keller
University of Bern
L. L. Kiss
Eötvös Loránd University (ELTE)
Hungarian Academy of Sciences
D. Kitzmann
University of Bern
J. Korth
University of Geneva
G. Lacedelli
Instituto de Astrofísica de Canarias
K. W. F. Lam
German Aerospace Center (DLR)
J. Laskar
Sorbonne University
A. Lecavelier des Etangs
Pierre and Marie Curie University (UPMC)
A. Leleu
University of Geneva
University of Bern
M. Lendl
University of Geneva
D. Magrin
Istituto nazionale di astrofisica (INAF)
P. F. L. Maxted
Keele University
M. Mecina
University of Vienna
B. Merin
European Space Agency (ESA)
C. Mordasini
University of Bern
V. Nascimbeni
Istituto nazionale di astrofisica (INAF)
R. Ottensamer
University of Vienna
I. Pagano
Istituto nazionale di astrofisica (INAF)
E. Palle
Instituto de Astrofísica de Canarias
University of La Laguna
G. Peter
German Aerospace Center (DLR)
D. Piazza
University of Bern
G. Piotto
Istituto nazionale di astrofisica (INAF)
University of Padua
D. Pollacco
The University of Warwick
D. Queloz
University of Cambridge
Swiss Federal Institute of Technology in Zürich (ETH)
R. Ragazzoni
University of Padua
Istituto nazionale di astrofisica (INAF)
N. Rando
European Space Agency (ESA)
H. Rauer
German Aerospace Center (DLR)
Freie Universität Berlin
I. Ribas
Inst Estudis Espacials Catalunya IEEC
Spanish National Research Council (CSIC)
N. C. Santos
University of Porto
G. Scandariato
Istituto nazionale di astrofisica (INAF)
D. Segransan
University of Geneva
A. E. Simon
University of Bern
A. M. S. Smith
German Aerospace Center (DLR)
S. Sulis
Aix Marseille University
Gy. M. Szabo
Eötvös Loránd University (ELTE)
S. Udry
University of Geneva
S. Ulmer-Moll
Leiden University
University of Liège
V. Van Grootel
University of Liège
J. Venturini
University of Geneva
F. Verrecchia
Agenzia Spaziale Italiana
Istituto nazionale di astrofisica (INAF)
E. Villaver
Instituto de Astrofísica de Canarias
University of La Laguna
N. A. Walton
University of Cambridge
S. Wolf
University of Bern
D. Wolter
German Aerospace Center (DLR)
T. Zingales
Istituto nazionale di astrofisica (INAF)
University of Padua
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 709 A265Exoplanet diversity with satellite studies
Swedish National Space Board (174/18), 2019-02-04 -- 2023-08-01.
Exoplanets from space -CHEOPS and PLATO ESA's next two projects (Phase 2)
Swedish National Space Board (177/19), 2020-01-01 -- 2022-12-31.
Swedish National Space Board (65/19), 2020-01-01 -- 2022-12-31.
Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
Subatomic Physics
DOI
10.1051/0004-6361/202558740