TOI-5678b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS

Ulmer-Moll, S.; Osborn, H. P.; Tuson, A.; Egger, J. A.; Lendl, M.; Maxted, P.; Bekkelien, A.; Simon, A. E.; Olofsson, G.; Adibekyan, V.; Alibert, Y.; Bonfanti, A.; Bouchy, F.; Brandeker, A.; Fridlund, M.; Gandolfi, D.; Mordasini, C.; Persson, C. M.; Salmon, S.; Serrano, L. M.; ... (2023). TOI-5678b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS. Astronomy and astrophysics, 674, A43. EDP Sciences 10.1051/0004-6361/202245478

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A large sample of long-period giant planets has been discovered thanks to long-term radial velocity surveys, but only a few dozen of these planets have a precise radius measurement. Transiting gas giants are crucial targets for the study of atmospheric composition across a wide range of equilibrium temperatures and for shedding light on the formation and evolution of planetary systems. Indeed, compared to hot Jupiters, the atmospheric properties and orbital parameters of cooler gas giants are unaltered by intense stellar irradiation and tidal effects. We identify long-period planets in the Transiting Exoplanet Survey Satellite (TESS) data as duo-transit events. To solve the orbital periods of TESS duo-transit candidates, we use the CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability period aliases in order to discard or confirm a transit event at a given period. We also collect spectroscopic observations with CORALIE and HARPS in order to confirm the planetary nature and measure the mass of the candidates. We report the discovery of a warm transiting Neptune-mass planet orbiting TOI-5678. After four non-detections corresponding to possible periods, CHEOPS detected a transit event matching a unique period alias. Joint modeling reveals that TOI-5678 hosts a 47.73 day period planet. TOI-5678 b has a mass of 20 (+-4) Me and a radius of 4.91 (+-0.08 Re) . Using interior structure modeling, we find that TOI-5678 b is composed of a low-mass core surrounded by a large H/He layer with a mass of 3.2 (+1.7, -1.3) Me. TOI-5678 b is part of a growing sample of well-characterized transiting gas giants receiving moderate amounts of stellar insolation (11 Se). Precise density measurement gives us insight into their interior composition, and the objects orbiting bright stars are suitable targets to study the atmospheric composition of cooler gas giants.

Item Type:

Journal Article (Original Article)


08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences > Theoretical Astrophysics and Planetary Science (TAPS)
08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute
10 Strategic Research Centers > Center for Space and Habitability (CSH)
08 Faculty of Science > Physics Institute > NCCR PlanetS

UniBE Contributor:

Ulmer-Moll, Solène Chloé, Osborn, Hugh Patrick, Egger, Jo Ann, Simon, Attila, Alibert, Yann Daniel Pierre, Mordasini, Christoph, Rieder, Martin, Benz, Willy, Broeg, Christopher, Demory, Brice-Olivier Denys, Fortier, A., Thomas, Nicolas, Venturini Corbellini, Julia Elisa


500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics
000 Computer science, knowledge & systems
500 Science




EDP Sciences




Danielle Zemp

Date Deposited:

15 Apr 2024 11:32

Last Modified:

15 Apr 2024 11:32

Publisher DOI:





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