ABSTRACT
Since we know comparatively little about extrasolar planetary systems, our main emphasis in this chapter must be just to explain what we know about the Solar System. However, although it is possible that the Solar System may be special in terms of its general complexity, any tenable theory for the basic Solar System must also be able to explain the existence of other planets. Current estimates put the proportion of sun-like stars with planets from about 20% up to 50%, and a plausible theory must accommodate this.
