A Bimodal Orbital Geometry Distribution for Exoplanet-Hosting Multi-Star Systems

Stellar companions offer key dynamical pathways to flip and misalign planetary systems. However, their dynamical influence can also produce exquisitely aligned and “orderly” planetary systems through viscous dissipation during the protoplanetary disk phase. We combine the archival set of stellar obliquity measurements with astrometric constraints from Gaia DR3 to characterize the joint spin-orbit and orbit-orbit distributions of transiting exoplanets in wide binary- and triple-star systems. Through this work, we unveil an intriguing overabundance of extremely collinear systems — preferentially around cool stars (T_eff < 6100 K) — that are both spin-orbit and orbit-orbit aligned, such that they appear to be “flattened”. By contrast, we find that the geometries of exoplanets around hotter stars (T_eff > 6100 K) are more suggestive of von Zeipel-Kozai-Lidov secular evolution. We conclude by examining the implications of our findings, which are indicative of dynamically rich evolution across all stages.