B. S. Lakeland, A. Mortier, R. D. Haywood, S. Ulmer-Moll, Z. Garai, A. Vanderburg, J. A. Egger, D. A. Turner, D. Kubyshkina, A. C. M. Correia, H. P. Osborn, L. A. Buchhave, L. Malavolta, A. Bonfanti, W. Boschin, A. Collier Cameron, A. Castro-González, R. Cosentino, M. Damasso, X. Dumusque, D. Ehrenreich, Z. Essack, S. Filomeno, L. Fossati, D. Gandolfi, M. Gillon, C. Hedges, M. Lopez-Morales, G. Lacedelli, M. Lendl, J. Maldonado, G. Mantovan, A. F. Martinez Fiorenzano, P. F. L. Maxted, C. Mordasini, B. Nicholson, S. O'Brien, L. Palethorpe, E. Palle, M. Pinamonti, D. Rapetti, I. Ribas, N. C. Santos, A. M. Silva, A. Sozzetti, M. Stalport, G. Szabo, S. Udry, M. Vezie, C. A. Watson, T. Wilson
Abstract
We present the discovery and characterization of two transiting exoplanets orbiting the metal-poor, solar-type star TOI-5788. From our analysis of six TESS sectors and a dedicated CHEOPS programme, we identify an inner planet (TOI-5788 b; P=6.340758±0.000030d) with radius 1.528±0.075R⊕ and an outer planet (TOI-5788 c; P=16.213362±0.000026d) with radius 2.272±0.039R⊕. We obtain 125 radial-velocity spectra from HARPS-N and constrain the masses of TOI-5788 b and c as 3.72±0.94M⊕ and 6.4±1.2M⊕, respectively. Although dynamical analyses indicate that a third planet could exist in a stable orbit between 8 and 14 d, we find no evidence of additional planets. Since the TOI-5788 system is one of the few systems with planets straddling the radius gap, and noting that there are even fewer such systems around metal-poor stars, it is a promising system to constrain planet formation theories. We therefore model the interior structures of both planets. We find that TOI-5788 b is consistent with being a rocky planet with almost no envelope, or having an atmosphere of a high mean molecular weight. We find that TOI-5788 c is consistent with both gas-dwarf and water-world hypotheses of mini-Neptune formation. We model the atmospheric evolution history of both planets. While both scenarios are consistent with the atmospheric evolution of TOI-5788 c, the gas-dwarf model is marginally preferred. The results of the atmospheric evolution analysis are not strongly dependent on stellar evolution. This makes the system a promising target to test internal structure and atmospheric evolution models.
Keywords
methods: data analysis / techniques: photometric / techniques: radial velocities / planets and satellites: detection / stars: individual (TOI-5788 / TIC42883782)
Monthly Notices of the Royal Astronomical Society
Volume 546, Issue stag158, Page 19
2026 March
