Two UA planetary scientists have worked out the dynamics of the early Solar System to demonstrate that the asteroid belt [right, white ring] is a result of the orbits of Jupiter and Saturn migrating, ejecting asteroids and creating a modern day asymmetry in their distribution.
David A. Minton & Renu Malhotra published a report in Nature yesterday that found "the particular pattern of missing asteroids is characteristic of the pattern of Jupiter's and Saturn's migration."
Minton said, "The patterns of depletion are like the footprints of wandering giant planets preserved in the asteroid belt."
This work confirms other studies that show the four giant planets (Jupiter, Saturn, Uranus, and Neptune) "formed in a more tightly compacted configuration, and then Jupiter moved slightly closer to the sun, while the other giant planets moved farther apart from each other and farther away from the sun."
Ref: A record of planet migration in the main asteroid belt, David A. Minton & Renu Malhotra, Nature 457, 1109-1111 (26 February 2009) | doi:10.1038/nature07778