[Simon Green]

Nitpick: First known interstellar visitor. I'm confident that there have been plenty of such encounters over the last few billion yeara.

[BradyLS]

I agree. You have but to look at the Asteroid Belt (failed planet or destroyed by a strike?), the near-rolling axial tilt of Neptune, and the strange orbit of Pluto and to easily imagine how interstellar bodies visiting our solar system have influenced.