Re: How do the planets protect Earth from asteroids and comets?

The short answer is that most of the planets do not protect us; however, Jupiter deflects many new comets as they enter the inner reaches of the solar systm from the Oort Cloud or Kuiper Belts. Many incoming comets are accelerated by Jupiter into hyperbolic orbits, and so ejected out of our region, or, conversely, are slowed down so as to become inner system objects and fall into the sun. Shoemaker Levy 9, by contrast, was ripped apart by Jupiter and ended its journey at that location, thanks to Jupiter's massive gravity. Without Jupiter, we would suffer a flux of comets maybe 100 times the current rate; it is questionable whether such a flux would have been compatible with the evolution of advanced life forms! The Inner asteroid belts, however, may yield new impactors of the Apollo, Amor, and Aten types by collision/breakups