On the structure and evolution of the primordial solar nebula

A self-consistent accretion disc model is proposed for the primordial solar nebula. In this model convective motion not only transports energy in the z-direction but also provides a mechanism for viscous coupling in the disc so that energy stored in shear motion can be dissipated. We find that a steady state accretion disc model can be constructed. Conditions for the primordial solar nebula to contain the present planetary mass are obtained. The results presented here tend to favour the idea that the planets formed by the accumulation of planetesimals, rather than by gravitational instability, occurring on a scale comparable to their present mass. We conclude that the tidal influence of a growing planet on the disc, coupled with the conditions required for formation, automatically gives rise to an upper limit of |~\,10⁻³M_| for a planet's mass.