Satellite Formation: Supply of Solid Material to Circumplanetary Disks

Most of the major natural satellites around the giant planets in our solar system are classified into “regular satellites,” with orbits that are nearly circular and in the equatorial planes of their parent bodies. The satellites are thus thought to form in circumplanetary disks. However, the origin and the properties of such disks are not well understood. Recently, some hydrodynamic simulations showed that gas flow accreting toward the planet forms a disk‐like structure in the course of the gas‐capturing process that creates gas giant planets. Thus, circumplanetary disks are inevitably formed as by‐products of the formation of gas‐giant planets. In order to form satellites, however, solid material needs to be supplied to the circum‐planetary disks. In this period, most of solid material are in the form of planetesimals or their fragments, not micron‐size dust. So, the motions of these large objects are basically independent of gas flow, and the objects need to be captured by the gas drag within the circumplanetary disks. In order to examine the supply rate of solid material to circumplanetary disks, we calculated the rate of delivered mass of solid materials by using an analytic calculation with some assumptions. We find that the supply of solid materials tend to be concentrated in the inner regions of such disks, which implies that the dust‐to‐gas ratio can change with distance from the planet and become larger at the inner region. We discuss this effect on the process of satellite formation.