  We study the influence of outer Solar System architecture on the structural
evolution of the Oort Cloud (OC) and the flux of Earth-crossing comets. In
particular, we seek to quantify the role of the giant planets as "planetary
protectors". To do so, we have run simulations in each of four different
planetary mass configurations to understand the significance of each of the
giant planets. Because the outer planets modify the structure of the OC
throughout its formation, we integrate each simulation over the full age of the
Solar System. Over this time, we follow the evolution of cometary orbits from
their starting point in the protoplanetary disk to their injection into the OC
to their possible re-entry into the inner planetary region. We find that the
overall structure of the OC, including the location of boundaries and the
relative number of comets in the inner and outer parts, does not change
significantly between configurations; however, as planetary mass decreases, the
trapping efficiency (TE) of comets into the OC and the flux of comets into the
observable region increases. We determine that those comets that evolve onto
Earth-crossing orbits come primarily from the inner OC but show no preference
for initial protoplanetary disk location. We also find that systems that have
at least a Saturn-mass object are effective at deflecting possible
Earth-crossing comets but the difference in flux between systems with and
without such a planet is less than an order of magnitude. We conclude by
discussing the individual roles of the planets and the implications of
incorporating more realistic planetary accretion and migration scenarios into
simulations, particularly on existing discrepancies between low TE and the mass
of the protoplanetary disk and on determining the structural boundaries of the
OC.
