Chaos in the solar system

The physical basis of chaos in the solar system is now better understood: I n all cases investigated so far, chaotic orbits result from overlapping res onances. Perhaps the clearest examples are found in the asteroid belt. Over lapping resonances account for its Kirkwood gaps and were used to predict a nd find evidence for very narrow gaps in the outer belt. Further afield, ab out one new "short-period" comet is discovered each year. They are believed to come from the "Kuiper Belt" (at 40 AU or more) via chaotic orbits produ ced by mean-motion and secular resonances with Neptune. Finally, the planet ary system itself is not immune from chaos. In the inner solar system, over lapping secular resonances have been identified as the possible source of c haos. For example, Mercury, in 10(12) years, may suffer a close encounter w ith Venus or plunge into the Sun. In the outer solar system, three-body res onances have been identified as a source of chaos, but on an even longer ti me scale of 10(9) times the age of the solar system. On the human time scal e, the planets do follow their orbits in a stately procession, and we can p redict their trajectories for hundreds of thousands of years. That is becau se the mavericks, with shorter instability times, have long since been ejec ted. The solar system is not stable; it is just old!.