THE discovery by Voyager I of a thin flat stream of rocks orbiting Jupiter at a radius of some 130,000 km, or ∼2RP (Rp = 6.677 × 109 cm = present polar radius), in its equatorial plane opens a new avenue of information in our understanding of the formation of the Solar System. Each of the major planets which possesses a regular satellite system also possesses a ring system. Theories for the formation of the major planets should therefore address themselves to this phenomenon of the co-appearance of rings and regular satellite systems, especially in considering the question whether Neptune, which has no regular satellites, may also not have a ring. We suggest here that Jupiter's rocky belt formed through condensation from a gaseous disk which was shed by the rotating gaseous envelope that originally contracted to form that planet. The four galilean satellites were formed from gaseous rings which were shed by the same envelope at an earlier and more turbulent stage in its evolution. It is possible that Jupiter may possess another rocky satellite belt at orbital radius 4RP1.