Cosmogony of the solar system

This report is intended to cover research on solar system origin over the last 4 years. Emphasis has been placed on the physics of planetary accumulation mechanisms, although pertinent references on the chemistry of mineral condensation and cometary research are included. The most ambitious attempt to model the solar nebula to date is the 1973 paper of Cameron and Pine [1973]. This model is characterized by a large mass (∼2 M S ) and is modeled as a collapse of spherical distribution of gas with an angular momentum per unit mass estimated from the assumption of fully developed turbulent motion. A disk structure is determined by requiring a radial and vertical balance of forces, i.e., gravitational, centrifugal, and pressure gradient forces. The most striking and controversial feature of the model is the absence of a central concentration of material representing the protosun. Rather, the sun forms as a secondary process of angular momentum redistribution via Eddington‐Sweet type circulation currents during which the inner portion of the nebula contracts and the outer portion expands radially. The large mass of the system is justified on two counts: there must be sufficient material to allow angular momentum redistribution, and a T ‐tauri phase has presumably ejected a few tenths of a solar mass from the system. Another noteworthy attribute of the model is the presence of a vertical convection zone between ∼1 and ∼10 AU due to the opacity of condensed iron grains.