Jupiter – when young and sprightly

At www.dailygalaxy.com/my_weblog/2011/06/jupiter-was-once-where-mars-is-tod… … NASA has a new model, as in a computer simulation, of how the early solar system may have formed in which the orbit of Jupiter once migrated towards the Sun and back outward again. It is likened to the course of a sailing boat when it tacks around a bhoy. In fact, both Jupiter and Saturn, it is being suggested, may have had orbits taking them closer to the Sun – but when they came close to each other this set in motion the back tracking – as if repulsed (when previously attracted). This idea has been dreamed up, it would seem, because Mars presents a problem to the theorists – they think it should be larger than what it is. In addition, they need to explain the existence of the asteroid belt – why did it not acrete. It is thought it is composed of dry rocky objects from the inner solar system (Mars missing dimensions) and icy objects from the outer solar system (presumably meaning comets or something similar).