Planet Formation in Dense Star Clusters

Our Solar System's closest stellar neighbors are several light years
away, and most models of the Solar System's formation assume that we have 
always been isolated from other stars.  But a growing body of evidence suggests
that most stars and planets form in star clusters far more dense, where tens of
thousands of young stars are initially packed into the same volume of space as
between us and our closest stellar neighbors.  The Orion region is one such 
nearby dense stellar cluster, where UV radiation, clouds of gas, and encounters
with other stars can shape the future of planetary systems.  I will discuss 
recent observations and modeling of the formation of stars, disks, and planets
in dense star clusters such as Orion.

I will focus in particular on recent modeling (Throop and Bally, 2008)
that shows that young circumstellar disks can accrete large amount of gas
from the ISM during the 1-10 Myr after formation.  This late accretion of gas
may have substantial impact on the architecture and composition of planetary 
systems throughout the galaxy.