A Cold and Super-Puffy Planet on a Polar Orbit

We report the discovery of TOI-4507 b, a transiting sub-Saturn with a density $<0.3$ g/cm³ on a 105-day polar 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 30\,M_⊕ at $95%$ confidence. The radial velocities also exhibit the Rossiter-McLaughlin effect and imply that the star's equatorial plane is tilted by 82.0-2.4+2.6 deg with respect to the planet's orbital plane. With these characteristics, TOI-4507 b is one of longest-period planets for which the stellar obliquity has been measured, and is among the longest-period and youngest ''super-puff'' planets yet discovered.