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Prior close stellar encounters of 3I/ATLAS

Ascertain whether 3I/ATLAS experienced previous close stellar encounters prior to its current passage through the Solar System, beyond the past ~10 Myr in which no close encounters were found.

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Background

The authors reference analyses showing no close stellar flybys within the past 10 Myr (~500 pc), but they explicitly state that earlier close passages cannot be ruled out. Establishing whether such encounters occurred would inform ejection scenarios, dynamical history, and the high incoming velocity of 3I/ATLAS.

Determining past stellar interactions could also help constrain the physical evolution of the object during its interstellar transit, including implantation and surface processing by cosmic rays.

References

On the other hand, during its long journey we know it didn't encounter close stellar systems, during at least 500 pc, but we cannot rule out previous stellar encounters, even closer than it is now experiencing to the Sun in our solar system.

— Spectrophotometric evidence for a metal-bearing, carbonaceous, and pristine interstellar comet 3I/ATLAS (2511.19112 - Trigo-Rodríguez et al., 24 Nov 2025) in Section 1, Introduction