The new intruder of the Solar System is perhaps among the oldest comets

The new intruder in the Solar System , the recently discovered interstellar comet 3I/Atlas , could be very ancient . It could in fact come from a region of the Milky Way very different from our own, namely the so-called ' thick disk ' of the galaxy, where stars are more than 10 billion years old . This is the first time that such an origin has been suspected for a celestial body and, if confirmed , it could make comet 3I/Atlas one of the oldest ever seen. This is what emerges from an international study led by the University of Oxford, shared on the arXiv website and submitted to The Astrophysical Journal Letters for publication. The researchers, led by astrophysicist Matthew Hopkins, applied a model developed for the study of interstellar objects to reconstruct the trajectory of 3I/Atlas up to its point of origin in the Milky Way . The model, developed by British and New Zealand astronomers, uses data from the European Space Agency's Gaia mission combined with models of the Milky Way's disk chemistry and object motion to map populations of interstellar objects. At the time of its discovery , comet 3I/Atlas was traveling at a speed of 57 kilometers per second , on a trajectory that will take it just inside the orbit of Mars for its closest approach to the Sun in October 2025 , before exiting the Solar System. According to the model, this velocity is consistent with an origin located in the Milky Way's thick disk , the puffy part surrounding the main thin disk. The thin disk is home to most of the Milky Way's stars, including the Sun; the thick disk , on the other hand, contains about 10% of the galaxy's stars , and most are more than 10 billion years old . If this were confirmed , it would mean that 3I/Atlas would be much older than the Solar System : researchers have estimated its age to be between 7.6 and 14 billion years . The Sun , by comparison, is only 4.6 billion years old . This finding makes it extremely unlikely that 3I/Atlas and the other two interstellar visitors known to date ( ʻOumuamua discovered in 2017 and the comet 21/Borisov detected in 2019) come from the same place . Indeed, 3I/Atlas appears to be the first known interstellar intruder from the Milky Way's thick disk.