CONFIRMATION OF RESONANT STRUCTURE IN THE SOLAR-SYSTEM

Using a semianalytical secular theory, Laskar (1989, Nature 338, 237-238) computed the orbits of the planets over 200 million years and found that their motion, and especially the motion of the inner planets, is chaotic, with a Liapunov exponent of 1/(5 Myr). It was found that this chaotic behavior originated in the existence of the resonances 2(g4 - g3) - (S4 - S3) and (g1 - g5) - (S1 - S2) between the main secular frequencies associated with the perihelia and nodes of the planets. The recent numerical integration of the Solar System over 6 Myr by Quinn et al. (1991, Astron. J. 101, 2287-2305) is in excellent agreement with the results of the secular theory and confirms the validity of the use of both solutions for orbital calculations related to Milankovich climate theory. The 6-Myr time span is too short to confirm the chaotic behavior directly, but the existence of the secular resonance 2(g4 - g3) - (S4 - S3) between the Earth and Mars is confirmed, and the behavior of the resonant argument shows very good quantitative agreement, thus providing strong indirect support that chaos is actually present. © 1992.