Published online by Cambridge University Press: 25 April 2016
The aggregation of a large number of planetesimals into a single body is a problem that has proved to be a stumbling block for many theories of planetary formation. This difficulty has mainly arisen because of the tendency of an orbiting stream of bodies to disperse over the equatorial plane as a result of the combined effects of collisions and gravitational interactions (Trulsen 1972; Brahic 1975). Once such a chaotic distribution of orbiting bodies has developed, it is extremely difficult for these bodies to subsequently accumulate into a single entity. This problem does not arise, however, when aggregation takes place within a differentially rotating gaseous ring as proposed by Prentice (1978). It has been shown previously (Hourigan 1977) that the gas drag overcomes the disruptive nature of collisional interactions, resulting in the formation of a thin concentrated torus of orbiting bodies.