3I/ATLAS: In Search Of The Witnesses To Its Voyage

3I/ATLAS is the third interstellar object discovered to date, following 1I/’Oumuamua and 2I/Borisov.

Its unusually high excess velocity and active cometary nature make it a key probe of the Galactic population of icy planetesimals. Understanding its origin requires tracing its past trajectory through the Galaxy and assessing the possible role of stellar encounters, both as a potential origin and a perturber to its orbit.

We integrated the orbit of 3I/ATLAS backward in time for 10 Myr, together with a sample of Gaia DR3 stars with high-quality astrometry and radial velocities, to identify close passages within 2 pc. We identify 93 nominal encounters, 62 of which are significant at the 2σ level. However, none of these encounters produced any meaningful perturbation.

The strongest perturber Gaia DR3 6863591389529611264 at 0.30 pc and with a relative velocity of 35 km s−1, imparted only a velocity change of |Δv|≃5×10−4 km s−1 to the orbit of 3I/ATLAS.

Our results indicate that no stellar flybys within the past 10 Myr and 500 pc contained in Gaia DR3 can account for the present trajectory of 3I/ATLAS or be associated with its origin. We further show that 3I/ATLAS is kinematically consistent with a thin-disk population, despite its large peculiar velocity.

X. Pérez-Couto, S. Torres, E. Villaver, A. J. Mustill, M. Manteiga

Comments: Submitted to ApJL, 12 pages, 5 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2509.07678 [astro-ph.EP](or arXiv:2509.07678v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2509.07678
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Submission history
From: Santiago Torres
[v1] Tue, 9 Sep 2025 12:44:21 UTC (802 KB)
https://arxiv.org/abs/2509.07678
Astrobiology