  Circumplanetary particle disks would be created in the late stage of
planetary formation either by impacts of planetary bodies or disruption of
satellites or passing bodies, and satellites can be formed by accretion of disk
particles spreading across the Roche limit. Previous N-body simulation of lunar
accretion focused on the formation of single-satellite systems from disks with
large disk-to-planet mass ratios, while recent models of the formation of
multiple-satellite systems from disks with smaller mass ratios do not take
account of gravitational interaction between formed satellites. In the present
work, we investigate satellite accretion from particle disks with various
masses, using N-body simulation. In the case of accretion from somewhat less
massive disks than the case of lunar accretion, formed satellites are not
massive enough to clear out the disk, but can become massive enough to
gravitationally shepherd the disk outer edge and start outward migration due to
gravitational interaction with the disk. When the radial location of the 2:1
mean motion resonance of the satellite reaches outside the Roche limit, the
second satellite can be formed near the disk outer edge, and then the two
satellites continue outward migration while being locked in the resonance.
Co-orbital satellites are found to be occasionally formed on the orbit of the
first satellite. Our simulations also show that stochastic nature involved in
gravitational interaction and collision between aggregates in the tidal
environment can lead to diversity in the final mass and orbital architecture,
which would be expected in satellite systems of exoplanets.
