Jupiter as a Sniper Rather Than a Shield

Do jovian-like planets in a planetary system shield habitable planets from impact events, or might they instead deliver potential impactors from the outer fringes of planetary system to its habitable zone? Using our Solar System as a testbed, we simulated the trajectories, and tracked the orbital evolutions and close encounter history, of 40,000 particles -- 10,000 in each of the outer planet gaps and 10,000 in the Kuiper Belt - with a highly accurate 13^th order modified Stormer integrator. The planetesimals were initially on low-eccentricity orbits, hence no threat to impact any of the terrestrial planets. Nevertheless, we found that through a series of close planet/planetesimal encounters, a significant fraction of planetesimals were successively handed down -- with increasingly smaller perihelion distances - to the inner Solar System. In our simulations Jupiter was, in fact, responsible for the vast majority of the encounters that kicked outer planet material into the terrestrial planet region. Our simulation suggests that instead of shielding the terrestrial planets, Jupiter was, in fact, taking "pot shots".