Hagai B. Perets, M. B. N. Kouwenhoven
In recent years several planets have been discovered at wide orbits (>100 AU)
around their host stars. Theoretical studies encounter difficulties in
explaining their formation and origin. Here we propose a novel scenario for the
production of planetary systems at such orbits, through the dynamical recapture
of free floating planets (FFPs) in dispersing stellar clusters. This process is
a natural extension of the recently suggested scenario for the formation of
wide stellar binaries. We use N-body simulations of dispersing clusters with
10-1000 and f_FFP=0.5-2 to study this process. We find that planets are
captured into wide orbits, ~100-10^6 AU, and a thermal eccentricity
distribution. Typically, 3-6x(f_FFP/1) % of all stars capture a planetary
companion (f_FFP is the number of FFP per star). The planetary capture
efficiency is comparable to that of capture-formed stellar-binaries, and shows
a similar dependence on the cluster size and structure. The capture efficiency
is almost independent of the specific planetary mass; planets as well as
sub-stellar companions of any mass can be captured, where the capture
efficiency decreases with increasing cluster size. For a given cluster size the
capture efficiency increases with the host/primary mass. More than one planet
can be captured around the same host, and planets can be captured into binary
systems. We also expect planets to be captured into pre-existing planetary
systems as well as around compact objects, if these formed early enough before
the cluster dispersal. In particular, stellar black holes have a high capture
efficiency (>50 % and 5-10x(f_FFP/1) % for capture of stars and planetary
companions, respectively) due to their large mass. Finally, although rare, two
FFPs or brown dwarfs can become bound and form a FFP-binary system with no
stellar host through this process.
View original:
http://arxiv.org/abs/1202.2362
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