A STABILITY STUDY OF ASTEROID FAMILIES NEAR THE 3:1 AND 5:2 RESONANCE WITH JUPITER

By using the D-criterion Lindblad (1992) has identified 14 asteroid families from a sample of 4100 numbered asteroids with proper elements from Milani and Knezevic (1990). Taxonomic types and other physical properties for a significant number of objects in five of the families show strong homogeneity within each family, further strengthening their internal relationship. To test the hypothesis of a common origin in, e.g., a catastrophic collision event, we have set out to integrate the orbits of the members of the Maria, Dora and Oppavia-Gefion families over some 10(6) years. The mean distance for the Mafia family is close to the 3:1 mean-motion resonance with Jupiter, while the other two families lie close to the 5:2 resonance. We used a simplified solar system model which included the perturbations by Jupiter and Saturn only and implemented Everhart's variable stepsize integrator RA15. All close encounters between the family members (within 0.1 AU) were recorded as well. Preliminary results from integrations over approximate to 4 x 10(5) years are presented here. The statistics of close encounters show pronounced peaks for several members within each family, while for others no significant levels above the background of random encounters or even very low frequencies were found. This indicates a subclustering within the families. Quite a lot of very close (< 0.005 AU) mutual encounters are found, which suggest that, at least for the larger members in a family, the mutual gravitational interactions could be of some importance for the real orbital evolutions. The encounter statistics between the Dora and Oppavia family members suggest a possible interrelationship between this two groups.