There is great book entitled Rogue Asteroids and Comets. It makes the point that Comets might present the greater risk, ultimately. They are not terribly visible until they reach the inner Solar System. Some of them are truly enormous. Many comets have orbits with periods of millions of years.

We have a deep ancestral fear of Comets and Asteroids. Note our word "Dis-aster" meaning bad star.

scott712