We report the discovery of TOI-4507 b, a transiting sub-Saturn with a density < 0.2 g/cm3 on a 105-day prograde orbit around a 700 Myr old F star. The transits were detected using data from TESS as well as the Antarctic telescope ASTEP. A joint analysis of the light curves and radial velocities from HARPS, FEROS, and CORALIE confirmed the planetary nature of the signal by limiting the mass to be below 20 M⊕ at 95% confidence. The radial velocities also exhibit the Rossiter-McLaughlin effect and imply that the planet orbits the star in a prograde orbit with a sky-projected obliquity λ=−15−44+50 deg (∣λ∣<80 deg at 3σ). With these characteristics, TOI-4507 is one of the longest-period systems for which the stellar obliquity has been measured, and the planet is among the longest-period and youngest ''super-puff'' planets yet discovered.
@article{arxiv.2510.00102,
title = {A Cold and Super-Puffy Planet on a Prograde Orbit},
author = {Juan I. Espinoza-Retamal and Rafael Brahm and Cristobal Petrovich and Andrés Jordán and Thomas Henning and Trifon Trifonov and Joshua N. Winn and Erika Rea and Maximilian N. Günther and Abdelkrim Agabi and Philippe Bendjoya and Hareesh Bhaskar and François Bouchy and Márcio Catelan and Carolina Charalambous and Vincent Deloupy and George Dransfield and Jan Eberhardt and Néstor Espinoza and Alix V. Freckelton and Tristan Guillot and Melissa J. Hobson and Matías I. Jones and Monika Lendl and Djamel Mekarnia and Diego J. Muñoz and Louise D. Nielsen and Felipe I. Rojas and François-Xavier Schmider and Elyar Sedaghati and Guðmundur Stefánsson and Stephanie Striegel and Olga Suarez and Marcelo Tala Pinto and Mathilde Timmermans and Amaury H. M. J. Triaud and Stéphane Udry and Solène Ulmer-Moll and Carl Ziegler},
journal= {arXiv preprint arXiv:2510.00102},
year = {2025}
}
Comments
15 pages, 4 figures. Accepted for publication in ApJL