Global evolution of solid matter in turbulent protoplanetary disks II. Development of icy planetesimals

It is currently thought that planets around solar-type stars form by the accumulation of solid matter entrained in a gaseous protoplanetary disk.Wemodel part of this process starting from small particles suspended in a gaseous disk, and ending up with most of the solid material aggregated into 1–10–km– sized planetesimals. The radial distribution of solid material circumnavigating a star in the form of the planetesimal swarm is the major result of this study, inasmuch as it provides insight into the large-scale character of the emerging planetary system. The model simultaneously keeps track of the evolution of gas and solid particles due to gas-solid coupling, coagulation, sedimentation, and evaporation/condensation. For simplicity, we concentrate on solids made up solely of water–ice. We have found that the radial distribution of mass locked into planetesimals is sensitive to initial conditions. Two illustrative examples corresponding to two different initial conditions are presented: a high-mass, high-concentration case that starts with a disk of 0.24M extending up to 15 A.U. from the star, and a low-mass, low-concentration case that starts with a disk of 0.02 M extending up to 250A.U. from the star. The high-massmodel leads to all solids being lost to the star; however, the low-mass model leads to a radial distribution of solid material quite reminiscent of what is found in our solar system.