Sedna and the Oort Cloud Around a Migrating Sun
  Recent numerical simulations have demonstrated that the Sun's dynamical
history within the Milky Way may be much more complex than that suggested by
its current low peculiar velocity. In particular, the Sun may have radially
migrated through the galactic disk by up to 5-6 kpc. This has important
ramifications for the structure of the Oort Cloud, as it means that the solar
system may have experienced tidal and stellar perturbations that were
significantly different from its current local galactic environment. To
characterize the effects of solar migration within the Milky Way, we use direct
numerical simulations to model the formation of an Oort Cloud around stars that
end up on solar-type orbits in a galactic-scale simulation of a Milky Way-like
disk formation. Surprisingly, our simulations indicate that Sedna's orbit may
belong to the classical Oort Cloud. Contrary to previous understanding, we show
that field star encounters play a pivotal role in setting the Oort Cloud's
extreme inner edge, and due to their stochastic nature this inner edge
sometimes extends to Sedna's orbit. The Sun's galactic migration heightens the
chance of powerful stellar passages, and Sedna production occurs around ~20-30%
of the solar-like stars we study. Considering the entire Oort Cloud, we find
its median distance depends on the minimum galactocentric distance attained
during the Sun's orbital history. The inner edge also shows a similar
dependence but with increased scatter due to the effects of powerful stellar
encounters. Both of these Oort Cloud parameters can vary by an order of
magnitude and are usually overestimated by an Oort Cloud formation model that
assumes a fixed galactic environment. In addition, the amount of material
trapped in outer Oort Cloud orbits can be extremely low and may present
difficulties for models of Oort Cloud formation and long-period comet
production.
