There should be interstellar comets hiding in our solar system after making a journey of many light-years. Maybe we have already seen one but believed it was a “normal” comet formed in the solar system, according to Tom Hands, astrophysicist at the University of Zürich and member of the NCCR PlanetS.
Source:
https://phys.org/news/2019-12-capturing-alien-comets-simulating-rogue.html