Or maybe younger.

Its home star may have been in another galaxy altogether, perhaps it was brought here when our Milky Way collided or merged with another galaxy, which we know has happened several times in the past. Its present orbit may offer clues to its origins, but they would not be conclusive. Who knows how many perturbations from other encounters these objects have encountered in the past?

There are some interesting discussions on these objects in https://www.centauri-dreams.org/

Now, a study presented at the recent meeting of the Royal Astronomical Society in Durham hints that Comet 3I/ATLAS may be something special indeed. Specifically, the comet may pre-date the formation of our solar system by over three billion years.

Already, each of the three known interstellar objects—1I/ ‘Oumuamua, 2I/ Borisov, and 3I/ATLAS—have proven to be distinctive examples in their own right.

Comet 3I/ATLAS appears to hail from the outer thick disk of the Milky Way, versus the thin inner disk where stars like our Sun typically reside. Astronomers extrapolate this from the relatively steep path of 3I/ATLAS’s orbit around the galaxy. Ancient stars tend to reside in the Milky Way’s thick disk population. If 3I/ATLAS formed and was subsequently ejected from such a system long ago, it could be on the order of over seven billion years old.

A side-view simulation of our Milky Way Galaxy, showing the orbit of 3I/ATLAS (in red) versus our Sun. Credit: M. Hopkins/Ōtautahi-Oxford team. Base map: ESA/Gaia/DPAC/Stefan Payne-Wardenaar. CC-BY-SA 4.0.