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 t he accumulation of solid matter entrained in a gaseous protoplanetary disk. We model part of this process starting from small particles susp ended 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 planetesi mal swarm is the major result of this study, inasmuch as it provides i nsight into the large-scale character of the emerging planetary system . The model simultaneously keeps track of the evolution of gas and sol id particles due to gas-solid coupling, coagulation, sedimentation, an d evaporation/condensation. For simplicity, we concentrate on solids m ade 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 cond itions 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 l ow-mass, low-concentration case that starts with a disk of 0.02 M. ext ending 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 fou nd in our solar system.