One-third of Sun-like stars are born with misaligned planet-forming disks.

Abstract

Exoplanets are organized in a broad array of orbital configurations^1,2 that reflect their formation along with billions of years of dynamical processing through gravitational interactions³. This history is encoded in the angular momentum architecture of planetary systems-the relation between the rotational properties of the central star and the orbital geometry of planets. A primary observable is the alignment (or misalignment) between the rotational axis of the star and the orbital plane of its planets, known as stellar obliquity. Hundreds of spin-orbit constraints have been measured for giant planets close to their host stars⁴, many of which have revealed planets on misaligned orbits. A leading question that has emerged is whether stellar obliquity originates primarily from gravitational interactions with other planets or distant stars in the same system, or if it is 'primordial'-imprinted during the star-formation process. Here we present a comprehensive assessment of primordial obliquities between the spin axes of young, isolated Sun-like stars and the orientation of the outer regions of their protoplanetary disks. Most systems are consistent with angular momentum alignment but about one-third of isolated young systems exhibit primordial misalignment. This suggests that some obliquities identified in planetary systems at older ages-including the Sun's modest misalignment with planets in the Solar System-could originate from initial conditions of their formation.