Jupiter, Saturn, and the edge of chaos

When Saturn's orbital elements are slightly changed from their present valu es, the motion of the jovian planets enters a large, robustly chaotic zone associated with the 2:5 mean-motion near-resonance between Jupiter and Satu rn. The transition to chaos is through large increases in the secular frequ ency associated with Saturn's perihelion, while the other secular frequenci es do not change appreciably The chaotic zone is closer in the orbital elem ents' phase space to their current values than the range taken on by these values. It is plausible, therefore, to suspect that passages through such c haotic zones did occur throughout the history of the Solar System. (C) 1999 Academic Press.