Evolution of the outer solar system: possible structure beyond Neptune

The question of possible structure in the outer solar system (beyond Neptune) is considered in terms of the new cosmogonical model of planetary systems developed by N. N. Kozlov and the author. In zones of the protoplanetary cloud beyond Neptune, the evolutionary process could under certain conditions have culminated in the formation not of a planet but of an asteroid belt. It is suggested that this region may now contain undetected asteroid belts and that Pluto represents an asteroid from one of those belts. This hypothesis is an elaboration of Cameron's 1962 proposal that an appreciable amount of matter might exist immediately beyond Neptune's orbit