A Preponderance of Perpendicular Planets

Observing the Rossiter–McLaughlin effect during a planetary transit allows determination of angle λ between sky projections star's spin axis and planet's orbital axis. Such observations have revealed large population well-aligned systems smaller misaligned systems, with values ranging up to 180°. For subset 57 we can now go beyond projection determine 3D obliquity ψ by combining data constraints on line-of-sight inclination Here show that do not span full range obliquities; they preference for nearly perpendicular orbits (ψ = 80°–125°) seems unlikely be statistical fluke. If confirmed further observations, this pile-up polar is clue about unknown processes excitation evolution.