THE EARTH-MOON SYSTEM AND THE DYNAMICAL STABILITY OF THE INNER SOLAR-SYSTEM

Evidence from self-consistent solar system n-body simulations is prese nted to argue that the Earth-Moon system (EM) plays an important dynam ical role in the inner solar system, stabilizing the orbits of Venus a nd Mercury by suppressing a strong secular resonance of period 8.1 Myr near Venus's heliocentric distance. The EM thus appears to play a kin d of ''gravitational keystone'' role in the terrestrial precinct, for without it, the orbits of Venus and Mercury become immediately destabi lized. The mechanism of the resonance, driven by the giant planets, is described. Approximate limits are provided for the mass and heliocent ric distance required of EM to perform this role, and results from sev eral additional empirical tests are reported. A number of avenues of f urther investigation are suggested.