LARGE-SCALE CHAOS AND MARGINAL STABILITY IN THE SOLAR-SYSTEM

Large scale chaos is present everywhere in the solar system. It plays a major role in the sculpting of the asteroid belt and in the diffusio n of comets from the outer region of the solar system. All the inner p lanets probably experienced large scale chaotic behavior for their obl iquities during their history. The Earth obliquity is presently stable only because of the presence of the Moon, and the tilt of Mars underg oes large chaotic variations from 0 degrees to about 60 degrees. On bi llion years time scale, the orbits of the planets themselves present s trong chaotic variations which can lead to the escape of Mercury or co llision with Venus in less than 3.5 Gyr. The organization of the plane ts in the solar system thus seems to be strongly related to this chaot ic evolution, reaching at all time a state of marginal stability, that is practical stability on a time-scale comparable to its age.