Global evolution of solid matter in turbulent protoplanetary disks .2. 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. We model 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 0.24 M. 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 250 A.U. from the star. The high-mass model 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.