Tilting the Solay System in its parent star cluster

Abstract Except for Mars, all the Solar System’s planets reside roughly in the same plane which is tilted relative to the Sun’s equatorial plane by roughly six degrees. We explore whether the tilt could be caused by the interactions between the Solar System and neighbouring stars in their birth cluster. We first run star cluster N-body simulations, varying, within the inferred range of parameters for the Solar System’s parent cluster, the total number of stars, cluster radius and binarity, recording neighbouring stars of the Solar System at high cadence. We then evolve the Solar System’s giant planets, in their current, as well as in a compact and a resonant configuration, mimicking the primordial Solar System, under the gravitational effects of the neighbouring stars as recorded in the cluster simulations. We find two pathways to tilt the planets’ orbits: a companion, either later acquired during cluster evolution or primordial, may reorient all the planets’ orbits gradually as a rigid body, maintaining their mutual coplanarity; the other possibility is to instantaneously rotate the planets’ orbital planes via deep stellar scatterings which usually break the coplanarity. Overall, for different cluster and Solar System models, the probabilityof tilting the planets’ orbits abovesix degrees is typically less than a tenth of a per cent is the Sun is born single. If the Solar System has a distant companion upon its formation, the chance is of the order of ten per cent, and sparsely populated clusters lie toward the high end.