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 +/- 12 deg, true spin-orbit angle psi = 16.1(-9.7)(+8.0) deg), revealing an aligned orbit consistent with quiescent disk migration. For K2-237b, we find lambda = 91 +/- 7 deg and psi = 90.5(-6.2)(+6.8) deg, indicating a nearly perfect polar orbit, which suggests a history consistent with disk-free migration, contrasting with previous studies inferring disk 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 of preferential orbital orientations. All three systems are compelling targets for future atmospheric characterization, and these dynamical constraints will be vital for a comprehensive understanding of their formation and evolution.