The evolution of the solar system

Abstract

A brief description of the solar system is given which highlights those features that a plausible theory should explain. A review of theories up to 1960 sets the scene for the description of more modern work and also points out the major features for which explanations are difficult to find. The major obstacle, on which all the older theories founder, is the explanation of the distribution of angular momentum in the system whereby the planets with 0·14% of the mass possess 98% of the angular momentum. The other problem, which has been more recently emphasized by Hoyle, is the slow rotation of the Sun, which is difficult to explain in terms of it having condensed from material possessing the basic galactic rotation. The modern theories described are: Hoyle's nebula theory, which invokes the transfer of angular momentum by magnetic forces; the accretion theory, which proposes that planetary material was captured by the Sun from an interstellar cloud; McCrea's floccule theory, which describes the solar system as having formed from initial condensations of planetary mass; the capture theory, which proposes that the Sun captured planets from a tidal filament drawn out of a light star; a nebula theory proposed by Urey based on chemical evidence derived primarily from meteorites.