Candidate Captured Interstellar Objects in the Solar System

Abstract

Interstellar objects (ISOs) provide direct probes of planetesimal formation and ejection in other planetary systems. While most ISOs that pass through the Solar System escape it after a single passage, a small fraction can become temporarily bound through gravitational interactions. We develop a self-consistent semi-analytic framework that couples analytic modeling of the interstellar object flux near Jupiter with N-body simulations of capture and long-term dynamical evolution, allowing us to predict the steady-state phase-space distribution of bound interstellar objects. Using an analytic model to construct initial conditions and N-body integrations to simulate capture and ejection, we compute capture rates and orbital distributions consistent with previous analytical estimates, finding a mean capture interval of approximately 220 years. We show that post-capture survival strongly reshapes the observable population: although capture initially favors prograde orbits, long-term stability is dominated by highly inclined objects that encounter planets less frequently and thus are less likely to be ejected. The resulting steady-state population is therefore concentrated at high inclinations, providing a potential dynamical discriminant for identifying candidates. However, most captured objects occupy semimajor axes comparable to the inner Oort cloud, making them difficult to distinguish from native long-period comets. The predicted phase-space distribution contains 122 known Solar System objects within the highest-density region of our model.