  We use numerical N-body simulations of the Orion Nebula Cluster (ONC) to
investigate the destruction of protoplanetary disks by close stellar encounters
and UV radiation from massive stars. The simulations model a cluster of 4000
stars, and we consider separately cases in which the disks have fixed radii of
100 AU and 10 AU. In the former case, depending on a star's position and orbit
in the cluster over 10^7 years, UV photoevaporation removes at least 0.01 Msol
from its disk, and can remove up to 1 Msol. We find no dynamical models of the
ONC consistent with the suggestion of Storzer and Hollenbach that the observed
distribution and abundance of proplyds could be explained by a population of
stars on radial orbits which spend relatively little time near Theta 1C Ori
(the most massive star in the ONC). Instead the observations require either
massive disks (e.g. a typical initial disk mass of 0.4 Msol) or a very recent
birth for Theta 1C Ori. When we consider the photoevaporation of the inner 10
AU of disks in the ONC, we find that planet formation would be hardly affected.
Outside that region, planets would be prevented from forming in about half the
systems, unless either the initial disk masses were very high or they formed in
less than ~ 2 Myr and Theta 1C Ori has only very recently appeared. We also
present statistics on the distribution of minimum stellar encounter
separations. This peaks at 1000 AU, with less than 10% of stars having had an
encounter closer than 100 AU after 10^7 years. We conclude that stellar
encounters are unlikely to play a significant role in destroying protoplanetary
disks. In the absence of any disruption mechanism other than those considered
here, we would thus predict planetary systems like our own to be common amongst
stars forming in ONC-like environments.
