  We examine a low energy mechanism for the transfer of meteoroids between two
planetary systems embedded in a star cluster using quasi-parabolic orbits of
minimal energy. Using Monte Carlo simulations, we find that the exchange of
meteoroids could have been significantly more efficient than previously
estimated. Our study is relevant to astrobiology as it addresses whether life
on Earth could have been transferred to other planetary systems in the solar
system's birth cluster and whether life on Earth could have been transferred
here from beyond the solar system. In the solar system, the timescale over
which solid material was delivered to the region from where it could be
transferred via this mechanism likely extended to several hundred million years
(as indicated by the 3.8-4.0 Ga epoch of the Late Heavy Bombardment). This
timescale could have overlapped with the lifetime of the Solar birth cluster
(~100-500 Myr). Therefore, we conclude that lithopanspermia is an open
possibility if life had an early start. Adopting parameters from the minimum
mass solar nebula, considering a range of planetesimal size distributions
derived from observations of asteroids and Kuiper Belt Objects and theoretical
coagulation models, and taking into account Oort Cloud formation models, the
expected number of bodies with mass > 10 kg that could have been transferred
between the Sun and its nearest cluster neighbor could be of the order of
1E14-3E16, with transfer timescales of 10s Myr. We estimate that of the order
of 3E8 x l(km) could potentially be life-bearing, where l(km) is the depth of
the Earth crust in km that was ejected as the result of the early bombardment.
