  Chiang et al. 2006, hereafter C06 have recently proposed that the observed
structure of the Kuiper belt could be the result of a dynamical instability of
a system of ~5 primordial ice giant planets in the outer Solar System.
According to this scenario, before the instability occurred, these giants were
growing in a highly collisionally damped environment according to the arguments
in Goldreich et al. (2004a,b, hereafter G04). Here we test this hypothesis with
a series of numerical simulations using a new code designed to incorporate the
dynamical effects of collisions. We find that we cannot reproduce the observed
Solar System. In particular, G04 and C06 argue that during the instability, all
but two of the ice giants would be ejected from the Solar System by Jupiter and
Saturn, leaving Uranus and Neptune behind. We find that ejections are actually
rare and that instead the systems spread outward. This always leads to a
configuration with too many planets that are too far from the Sun. Thus, we
conclude that both G04's scheme for the formation of Uranus and Neptune and
C06's Kuiper belt formation scenario are not viable in their current forms.
