SECULAR DYNAMICS OF ASTEROIDS IN THE INNER SOLAR-SYSTEM

In the last three years we have carried out numerical and semi-analyti cal studies on the secular dynamical mechanisms in the region (semimaj or axis a < 2 AU) where the NEA orbits evolve. Our numerical integrati ons (over a time span of a few Myr) have shown that: (i) the Linear se cular resonances with both the inner and the outer planets may play an important role in the dynamical evolution of NEAs; (ii) the apsidal s ecular resonance with Mars could provide an important dynamical transp ort mechanism by which asteroids in the Mars-crossing region eventuall y achieve Earth-crossing orbits; (iii) in this region, due to the inte raction with the terrestrial planets, the Kozai resonance can occur at small inclinations, with the argument of perihelion omega librating a round 0 degrees or 180 degrees, providing a temporary protection mecha nism against close approaches to the planets. The location of the line ar secular resonances in this zone has also been obtained by an automa tic procedure using a semi-numerical method valid for all values of th e inclinations and eccentricities of the small bodies, and also in the case of libration of the argument of perihelion. A map of the secular resonances in the (a, i) plane shows - in agreement with the numerica l integrations - that all the resonances with the terrestrial and gian t planets are present and also that some of them overlap. Thus the way is now open to fully take into account secular resonances in modellin g the dynamical evolution of NEAs.