  The origin of the regular satellites ties directly to planetary formation in
that the satellites form in gas and dust disks around the giant planets and may
be viewed as mini-solar systems, involving a number of closely related
underlying physical processes. The regular satellites of Jupiter and Saturn
share a number of remarkable similarities that taken together make a compelling
case for a deep-seated order and structure governing their origin. Furthermore,
the similarities in the mass ratio of the largest satellites to their
primaries, the specific angular momenta, and the bulk compositions of the two
satellite systems are significant and in need of explanation. Yet, the
differences are also striking. We advance a common framework for the origin of
the regular satellites of Jupiter and Saturn and discuss the accretion of
satellites in gaseous, circumplanetary disks. Following giant planet formation,
planetesimals in the planet's feeding zone undergo a brief period of intense
collisional grinding. Mass delivery to the circumplanetary disk via ablation of
planetesimal fragments has implications for a host of satellite observations,
tying the history of planetesimals to that of satellitesimals and ultimately
that of the satellites themselves. By contrast, irregular satellites are
objects captured during the final stages of planetary formation or the early
evolution of the Solar System; their distinct origin is reflected in their
physical properties, which has implications for the subsequent evolution of the
satellites systems.
