  It is believed that satellites of giant planets form in circumplanetary
disks. Many of the previous contributions assumed that their formation process
proceeds similarly to rocky planet formation, via accretion of the satellite
seeds, called satellitesimals. However, the satellitesimal formation itself
poses a nontrivial problem as the dust evolution in the circumplanetary disk is
heavily impacted by fast radial drift and thus dust growth to satellitesimals
is hindered. To address this problem, we connected state-of-the-art
hydrodynamical simulations of a circumplanetary disk around a Jupiter-mass
planet with dust growth and drift model in a post-processing step. We found
that there is an efficient pathway to satellitesimal formation if there is a
dust trap forming within the disk. Thanks to the natural existence of an
outward gas flow region in the hydrodynamical simulation, a significant dust
trap arises at the radial distance of 85~R$_{\rm J}$ from the planet, where the
dust-to-gas ratio becomes high enough to trigger streaming instability. The
streaming instability leads to the efficient formation of the satellite seeds.
Because of the constant infall of material from the circumstellar disk and the
very short timescale of dust evolution, the circumplanetary disk acts as a
satellitesimal factory, constantly processing the infalling dust to pebbles
that gather in the dust trap and undergo the streaming instability.
