THE KIRKWOOD GAP AT THE 2 1 COMMENSURABILITY WITH JUPITER - NEW NUMERICAL RESULTS/

In this paper it is pointed out that the 2/1 resonance with Jupiter is not completely empty of asteroids. However, among the ten bodies pres ently in the 2/1 resonance with e<0.5, only four have a quite regular orbit and moderate eccentricity and inclination. The integration of th e evolution of the orbits of 24 fictitious particles over 1 Gyr shows that in the 2/1 resonance all orbits diffuse chaotically. In some part s of the resonance, however, the diffusion speed is very slow, so that some bodies can survive at least 1 Gyr without becoming Mars crosser. From the global chart of diffusion, some hypotheses are discussed abo ut the origin of the four ''regular'' asteroids, as well as on the dep letion of the Themis family members in the 2/1 resonance. (C) 1996 Ame rican Astronomical Society.