Chemistry and evolution of gaseous circumstellar disks

An investigation of the chemical and physical processes which determine the composition and evolution of gas-rich circumstellar disks is reported. Strong mixing in a thermoclinic environment like an accretion disk leads to thermochemical disequilibration due to 'kinetic inhibition' induced by chemical time constants becoming longer than outward mixing time constants. In this case, species thermodynamically stable at high temperatures but not at low temperatures dominate at all temperatures in the disk. Nonaxisymmetric accretion of material at hypersonic speeds is a major forcing mechanism for mixing in the disk and can produce eddy speeds of 1 percent of the sound speed. The implications kinetic inhibition in the carbon, nitrogen, and anhydrous/hydrous silicate families has for the compositions of the terrestrial planets, giant planets, ice-rich satellites, Pluto, comets, meteorites, and asteroids are discussed.