I believe the common thinking is that the giant gravity wells of Jupiter, Saturn, and the Sun are often considered a shield for the inner Solar System planets.

I believe the common thinking is that the giant gravity wells of Jupiter, Saturn, and the Sun are often considered a shield for the inner Solar System planets. Thus, given enough time (10 million years per the article) these wells attract and destroy a vast majority of free rocks, preventing them from threatening Earth. But (my conjecture) if there's far more random junk flying around out there, that's going to force a re-think of how we guarantee the safety of space travel past the Moon.