When and why formation of large bodies in circumstellar discs could take place?

Abstract

We outlined the scenario of the planetary system formation, where large bodies are formed on the stage of massive discs. On this stage the whole of factors: chemical composition, chemical catalytic reactions, the disc self- gravitation, the increased ratio of solids to gas surface density, adiabatic gas cooling provides favorable conditions for gravitational instabilities development. Gravitational instabilities in multiphase medium can lead to planetesimal and planetary embryo formation.