Earth sees its own fair share of incoming projectiles from space, but it’s extremely rare to find an event that poses any real threat to Earth or its life. Most of this safety comes from that fact that space is inconceivably large; the possibility of being hit by an asteroid that could do any real damage is astronomically low (yeah, pun intended).
In a 1994 paper, planetary scientist George Wetherill postulated that Jupiter’s immense size could be partially to thank for keeping large bodies from reaching the inner planets of the solar system and possibly colliding with Earth. Recently, however, Kevin Grazier of NASA’s Jet Propulsion Laboratory ran simulations of the solar system and found strong evidence that we may have Saturn to thank as well for keeping us safe.
His tests showed that the most asteroids were deflected out of our system only when both Saturn and Jupiter were in the solar system. A solar system with either Jupiter or Saturn in it would produce a much larger asteroid belt and would keep many of these smaller bodies in closer, more dangerous proximity to our home rather than being flung into space due to the larger, combined gravity of both giant planets.
Photo courtesy of NASA and seeker.com