Formation of the planets

A timetable for an evolutionary sequence of processes, which begins with the formation of the solar nebula being nearly in equilibrium and ends with formation of planets and satellites, is presented. Four main stages are discussed: (1) the collapse of a cloud and the formation of a gas disk rotating around the protosun which is nearly in a state of thermal and dynamical equilibrium under the influence of solar gravity and radiation; (2) the fragmentation of a thin dust layer due to gravitational instability; (3) the collapse of atmospheres of molecular hydrogen onto protoplanets which have grown above a limit of about ten earth masses; and (4) the disappearance of the gas component of the disk due to the solar wind and ultrviolet radiation, which are thought to have been very strong during thy T Tauri stage of the sun.