The Trajectory of 3I/ATLAS Through the Inner Solar System: Close Encounters and Possible Collisions

Abstract 3I/ATLAS is the third interstellar object (ISO) identified to date. Unlike other known ISOs, 3I/ATLAS travels on a nearly ecliptic, retrograde orbit ( i ≈ 175°). This trajectory, combined with a small perihelion distance ( q ≈ 1.36 au), directs it through the relatively dense populated regions of the main-belt asteroids (MBAs) and near-Earth asteroids (NEAs), moving counter to their general prograde motion. This work focused on an investigation of close encounters and assessment of collision probabilities between 3I/ATLAS and the populations of MBAs/NEAs. The N -body numerical integration was performed to identify close approaches within distance ≤0.03 au on the time range from 2025 August 1 till 2026 April 1 (3I/ATLAS’s heliocentric distance exceeded the Jupiter’s orbit). The Monte Carlo (MC) simulations were used to estimate collision probabilities, accounting to the orbital uncertainties of asteroids which have the smallest approach distances. Performed search identified 736 MBAs and 31 NEAs that will have a close approach with 3I/ATLAS at a physical distance of ≤0.03 au. While no direct collisions are predicted based on nominal orbits, our analysis highlights the case of MBA 2020 BG107. Due to its high orbital uncertainty, its 3 σ positional ellipsoid at the time of the encounter is larger than the nominal approach distance to 3I. The collision probability is estimated at 0.025% within our MC simulations. The results could be extrapolated in regard to the solar system comets from Oort cloud on parabolic or hyperbolic orbits, as dynamically (except the velocity) they are similar to the interstellar objects.