Capture of Interstellar Objects and Binaries

Abstract: Interstellar objects (ISOs) can become gravitationally bound to the solar system, enabling multiple observations. If these bound ISOs exist, they provide valuable opportunities to generalize models of planetesimal formation, composition, and ejection beyond our solar system. We explore two mechanisms for ISO capture: gravitational braking (primarily with Jupiter) and the Hills mechanism with the Sun. Using N-body simulations, we investigate ISO capture rates, ejection probabilities, and the resulting orbital elements. Our simulations suggest that approximately 10 ISOs may currently be bound to the solar system, with the vast majority captured through gravitational braking by Jupiter. These objects are bound by a Tisserand parameter with respect to Jupiter less than three, tend to have high eccentricities, semi-major axes larger than Jupiter's, and inclinations modestly biased toward the prograde direction. This region is sparsely populated by observed solar system objects. By comparing known solar system objects to the most probable orbital elements of our simulated ISOs, we identify 18 candidate objects in the current solar system population that may be bound ISOs captured by Jupiter. For the Hills mechanism, we find it to be a viable but less common capture pathway, typically producing isotropic inclinations and perihelia less than one au. Based on these characteristics, we identify seven additional candidate objects for ISOs captured through the Hills mechanism.