IP5 ~ Monday, May 22, 1995 ~ 1:30 PM

Recent Results on the Dynamics of the Solar System

Long-term integrations of the solar system has shown that the evolution of the solar system is chaotic with a Lyapunov time of only about 4-5 million years. A dramatic consequence of the chaotic orbital evolution is large chaotic variations in the tilt of the spin axis (the obliquity) of Mars. The obliquity of Mars varies from about 0 degrees to 60 degrees on time scales of several million years. The Lyapunov time is about 3 million years. The dynamical mechanism responsible for the chaotic evolution of the spin of Mars is that of "adiabatic chaos." The spin state of Mars is near a secular spin-orbit resonance with the solar system. Slow shift of the resonance associated with the chaotic evolution of the solar system drives Mars repeatedly across the separatrix of this secular spin orbit resonance, resulting in chaotic behavior.

Jack Wisdom
Earth, Atmosphere, and Planetary Sciences Department, Massachusetts Institute of Technology