Classical analytic theories of the solar system indicate that it is stable,
but numerical integrations suggest that it is chaotic. This disagreement is
resolved by a new analytic theory. The theory shows that the chaos among the
Jovian planets results from the overlap of the components of a mean motion
resonance among Jupiter, Saturn, and Uranus, and provides rough estimates of
the Lyapunov time (10 million years) and the dynamical lifetime of Uranus
(10^{18} years). The Jovian planets must have entered the resonance after all
the gas and most of the planetesimals in the protoplanetary disk were removed.Comment: 19 pages, 3 figures, to appear in Scienc
