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

¹ Astronomical Institute of the Czech Academy of Sciences, Fričova 298, 25165 Ondřejov, Czech Republic
² European Southern Observatory, Karl-Schwarzschild-str. 2, 85748 Garching, Germany
³ Astronomical Institute of Charles University, V Holešovičkách 2, 180 00 Prague, Czech Republic
⁴ Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Av. Diagonal las Torres 2640, Peñalolén, Santiago, Chile
⁵ Millennium Institute for Astrophysics, Santiago, Chile
⁶ Institute of Physics, Faculty of Science, Pavol Jozef Šafárik University, Park Angelinum 9, 040 01 Košice, Slovakia
⁷ Dipartimento di Fisica, La Sapienza Università di Roma, Piazzale Aldo Moro 5, Roma 00185, Italy
⁸ Steward Observatory, The University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA
⁹ Center of Astro Engineering, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-043 Santiago, Chile
¹⁰ Department of Electrical Engineering, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-043 Santiago, Chile
¹¹ Department of Theoretical Physics and Astrophysics, Masaryk Univesity, Kotlářrská 2, 60200 Brno, Czech Republic
¹² Institute of Plasma Physics of Czech Academy of Sciences, U Slovanky 2525/1a, 182 00 Praha 8, Czech Republic
¹³ Thüringer Landessternwarte, 07778 Tautenburg, Germany

^★ Corresponding author: zak@asu.cas.cz

Received: 26 June 2025
Accepted: 13 August 2025

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 (λ) for three gaseous exoplanets using the newly commissioned PLATOSpec instrument on the E152 Telescope at La Silla Observatory. For WASP-35b, we determine λ = 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 (λ = −4 ± 12 deg, true spin-orbit angle ψ = 16.1_−9.7^+8.0 deg), revealing an aligned orbit consistent with quiescent disk migration. For K2-237b, we find λ = 91 ± 7 deg and ψ = 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.