Early evolution of the birth cluster of the solar system
  The solar system was most likely born in a star cluster containing at least
1000 stars. It is highly probable that this cluster environment influenced
various properties of the solar system like its chemical composition, size and
the orbital parameters of some of its constituting bodies. In the Milky Way,
clusters with more than 2000 stars only form in two types - starburst clusters
and leaky clusters - each following a unique temporal development in the
mass-radius plane. The aim is here to determine the encounter probability in
the range relevant to solar system formation for starburst or leaky cluster
environments as a function of cluster age. N-body methods are used to
investigate the cluster dynamics and the effect of gravitational interactions
between cluster members on young solar-type stars surrounded by discs. Using
the now available knowledge of the cluster density at a given cluster age it is
demonstrated that in starburst clusters the central densities over the first
5Myr are so high (initially > 10^5 Msun pc^{-3}) that hardly any discs with
solar system building potential would survive this phase. This makes a
starburst clusters an unlikely environment for the formation of our solar
system. Instead it is highly probable that the solar system formed in a leaky
cluster (often classified as OB association). It is demonstrated that an
encounter determining the characteristic properties existing in our solar
systems most likely happened very early on (< 2Myr) in its formation history
and that after 5Myr the likelihood of a solar-type star experiencing such an
encounter in a leaky cluster is negligible even if it was still part of the
bound remnant. This explains why the solar system could develop and maintain
its high circularity later in its development.
