Search For Past Stellar Encounters And The Origin Of 3I/ATLAS

3I/ATLAS, the third discovered interstellar object, has a heliocentric speed of 58 km/s and exhibits cometary activity.

To constrain the origin of 3I/ATLAS and its past dynamical evolution, we propagate the orbits of 3I/ATLAS and nearby stars to search for stellar encounters. Integrating orbits in the Galactic potential and propagating the astrometric and radial-velocity uncertainties of 30 million Gaia stars, we identify 25 encounters with median encounter distances less than 1 pc.

However, because the encounter speeds between 3I/ATLAS and each encounter exceed 20 km/s, none is a plausible host under common ejection mechanisms. We infer stellar masses for most stars and quantify the gravitational perturbations exerted by each individual star or each binary system on 3I/ATLAS. The strongest gravitational scattering perturber is a wide M-dwarf binary.

Among all past encounters, the binary’s barycenter and 3I/ATLAS reach the small encounter distance of 0.242 pc and the encounter speed of 28.39 km/s, 1.64 Myr ago. We further demonstrate that the cumulative influence of the stellar encounters on both the speed and direction of 3I/ATLAS is weak.

Based on the present kinematics of 3I/ATLAS to assess its origin, we find that a thin-disk origin is strongly favored, because the thin disk both exhibits a velocity distribution closely matching that of 3I/ATLAS and provides the dominant local number density of stars.

Yiyang Guo, Luyao Zhang, Fabo Feng, Zhao-Yu Li, Anton Pomazan, Xiaohu Yang

Comments: 11 pages, 5 figures, submitted to ApJL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2509.03361 [astro-ph.SR] (or arXiv:2509.03361v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2509.03361
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Submission history
From: Yiyang Guo
[v1] Wed, 3 Sep 2025 14:46:05 UTC (2,559 KB)
https://arxiv.org/abs/2509.03361
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