The GAPS Programme at TNG. LXXX. Characterisation of the 400 Myr old multi-planet system K2-233
Abstract
Understanding exoplanet physical properties is crucial for characterising their atmospheres and internal composition. Precise planetary masses are essential for constraining bulk densities and interiors, particularly in young systems hosting planets within or near the radius valley, where atmospheric mass loss may strongly shape their evolution. Here we revise the masses of the three transiting planets orbiting K2-233, a young (∼ 400 Myr) active K-type star. We combine 70 HARPS-N observations from the GAPS/ArMS Large Programme with 124 archival HARPS observations, K2 light curves, and TESS photometry obtained during our radial-velocity monitoring. We explore several Multi-GP configurations to mitigate the strong stellar activity and find that the inferred planetary masses depend significantly on the adopted activity-modelling strategy, yielding several physically viable solutions rather than a uniquely preferred one. We model the long-term atmospheric evolution of K2-233 d and find significant atmospheric mass loss. Depending on its internal composition and atmospheric properties, the planet is expected to evolve towards either a low-mass sub-Neptune retaining a thin envelope (Rp ∼ 1.71-1.84 R⊕) or a bare-core super-Earth (Rp ∼ 1.95 R⊕) on Gyr timescales. Our interior-structure models suggest that K2-233 b and c are likely iron-dominated, while K2-233 d retains a substantial H/He atmosphere.
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BibTeX
@misc{fardella2026gaps,
title = {{The GAPS Programme at TNG. LXXX. Characterisation of the 400 Myr old multi-planet system K2-233}},
author = {V. Fardella and S. Benatti and R. Spinelli and D. Locci and G. King and M. Baratella and K. Biazzo and S. Desidera and D. Barbato and M. C. D'Arpa and L. Naponiello and A. Petralia and M. Damasso and O. Barragán and C. Di Maio and A. Maggio and G. Piccinini and A. Bonomo and I. Carleo and R. Claudi and M. Gonzales and A. Harutyunyan and A. F. Lanza and L. Malavolta and L. Mancini and G. Mantovan and D. Nardiello and M. Rainer and A. Sozzetti and T. Zingales},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.09954},
eprint = {2610.09954},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.09954},
}
RIS
TY - UNPB
TI - The GAPS Programme at TNG. LXXX. Characterisation of the 400 Myr old multi-planet system K2-233
AU - V. Fardella
AU - S. Benatti
AU - R. Spinelli
AU - D. Locci
AU - G. King
AU - M. Baratella
AU - K. Biazzo
AU - S. Desidera
AU - D. Barbato
AU - M. C. D'Arpa
AU - L. Naponiello
AU - A. Petralia
AU - M. Damasso
AU - O. Barragán
AU - C. Di Maio
AU - A. Maggio
AU - G. Piccinini
AU - A. Bonomo
AU - I. Carleo
AU - R. Claudi
AU - M. Gonzales
AU - A. Harutyunyan
AU - A. F. Lanza
AU - L. Malavolta
AU - L. Mancini
AU - G. Mantovan
AU - D. Nardiello
AU - M. Rainer
AU - A. Sozzetti
AU - T. Zingales
PY - 2026
DA - 2026/10/09
PB - arXiv
DO - 10.48550/arxiv.2610.09954
UR - https://arxiv.org/abs/2610.09954
AB - Understanding exoplanet physical properties is crucial for characterising their atmospheres and internal composition. Precise planetary masses are essential for constraining bulk densities and interiors, particularly in young systems hosting planets within or near the radius valley, where atmospheric mass loss may strongly shape their evolution. Here we revise the masses of the three transiting planets orbiting K2-233, a young (∼ 400 Myr) active K-type star. We combine 70 HARPS-N observations from the GAPS/ArMS Large Programme with 124 archival HARPS observations, K2 light curves, and TESS photometry obtained during our radial-velocity monitoring. We explore several Multi-GP configurations to mitigate the strong stellar activity and find that the inferred planetary masses depend significantly on the adopted activity-modelling strategy, yielding several physically viable solutions rather than a uniquely preferred one. We model the long-term atmospheric evolution of K2-233 d and find significant atmospheric mass loss. Depending on its internal composition and atmospheric properties, the planet is expected to evolve towards either a low-mass sub-Neptune retaining a thin envelope (R_p ∼ 1.71-1.84 R_⊕) or a bare-core super-Earth (R_p ∼ 1.95 R_⊕) on Gyr timescales. Our interior-structure models suggest that K2-233 b and c are likely iron-dominated, while K2-233 d retains a substantial H/He atmosphere.
ER -