PLATOSpec's first results: planets WASP-35b and TOI-622b are on aligned orbits, and K2-237b is on a polar orbit

Abstract

The spin-orbit angle between a stellar spin axis and its planetary orbital axis is a key diagnostic of planetary migration pathways, yet the mechanisms shaping the observed spin-orbit distribution remain incompletely understood. Combining the spin-orbit angle with atmospheric measurements has emerged as a powerful method of studying exoplanets that showcases the synergy between ground- and space-based observations. We present the Rossiter-McLaughlin effect measurements of the projected spin-orbit angle ($\lambda$) for three gaseous exoplanets using the newly commissioned PLATOSpec instrument on the E152 Telescope at La Silla Observatory. For WASP-35b, we determine $\lambda = 1_{-18}^{+19}$ deg, demonstrating PLATOSpec's capabilities through excellent agreement with HARPS-N literature data. We provide the first spin-orbit measurements for TOI-622b ($\lambda =-4 \pm 12$ deg, true spin-orbit angle $\psi = $16.1$^{+8.0}_{-9.7}$ deg), revealing an aligned orbit consistent with quiescent disc migration. For K2-237b, we find $\lambda = 91 \pm 7$ deg and $\psi = $90.5$^{+6.8}_{-6.2}$ deg, indicating a nearly perfect polar orbit, which suggests a history consistent with disc-free migration, contrasting previous studies inferring disc migration. TOI-622b populates a sparsely populated region of sub-Jovian planets with measured spin-orbit angles orbiting stars above the Kraft break, while K2-237b's polar configuration strengthens tentative evidence for preferential orbital orientations. All three systems are compelling targets for future atmospheric characterization, where these dynamical constraints will be vital for a comprehensive understanding of their formation and evolution.