We find that free-floating planets can remain bound to an open cluster
for much longer than was previously calculated: of the order of the
cluster half-mass relaxation timescale as opposed to the crossing-time.
This result is based on N-body simulations performed with the
new GRAPE-6 special purpose hardware and is important
in the context of the preliminary detection of a population of free-floating
sub-stellar objects in the globular cluster M22.
The planets in our N-body study are of Jupiter mass and are initially
placed in circular orbits of between 0.05 and 50 AU about a parent
star whose mass is chosen from a realistic initial mass function.
The presence of the free-floating planets is the result of dynamical
encounters between planetary systems and the cluster stars.
Most planets are liberated from their parent star in, or near, the cluster
core, and then drift outwards on a timescale of ~ 108-9 year.
This still implies the existence of many (~ 100) planets per star
if the M22 result is confirmed.