Are the Jovian Planets “Failed” Stars?

Abstract

THERE are three distinct types of object in the Solar System—the Sun is a star ; the terrestrial planets (Mercury, Venus, Earth/Moon, Mars) are solid bodies ; and the Jovian planets (Jupiter, Saturn, Uranus, Neptune) are cold gaseous bodies. The nature of Pluto is not established and Pluto will be discounted for my purposes here. It is surely no accident that the solid members of the planetary system lie nearer the Sun than the gaseous members. The most distant terrestrial planet (Mars) is 1.52 AU from the Sun whereas the nearest Jovian planet (Jupiter) is 5.20 AU from the Sun (1 AU = 1.496 × 10⁸ km). As yet no agreed view of planetary formation exists. Most theories involve a single process for all the planets (see, for example, ref. 1). I suggest that the division of the planetary bodies into solid and gaseous types may imply different formation mechanisms. In particular I suggest that the terrestrial planets formed in a high density shell surrounding the proto-Sun and that the Jovian planets are the remnants of other attempts to form stars contemporaneously with the Sun.