The Orbital Geometries and Stellar Obliquities of Exoplanet-Hosting Multi-Star Systems

The current orbital geometries of exoplanet systems offer a fossilized record of the systems’ dynamical histories. A particularly rich set of dynamical mechanisms is available to exoplanets residing in multi-star systems, which may have their evolution shaped by the gravitational influence of bound stellar companions. In this work, we examine the joint distribution of stellar obliquities and orbital orientations for transiting exoplanets residing within astrometrically resolved binary and triple-star systems. We leverage existing constraints on stellar obliquities in exoplanet systems, together with astrometric measurements from Gaia DR3, to uncover a set of fully-aligned, “orderly” exoplanet systems that exhibit evidence of both spin-orbit and orbit-orbit alignment. We also find evidence that the observed distribution of orbit-orbit orientations in our sample is more strongly peaked toward alignment than an isotropic distribution. Our results may be indicative of efficient viscous dissipation by nodally recessing protoplanetary disks, demonstrating a regime in which stellar companions produce and maintain order in planetary systems, rather than enhancing misalignments.