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V. Carruba, J. A. Burns (Cornell University), W. Bottke, D. Nesvorny' (Southwest Research Institute), V. Zappala' (Astronomical Obs. Torino)
Asteroid families are generally believed to result from the break-up of a parent body, with the smallest fragments traveling the furthest from the cluster's center (Cellino et al. 1999). One problem with this scenario is that the ejection velocities inferred for the fragments from the observed dispersions in their current proper orbital elements seem to be consistently higher than those predicted by collisions in laboratory experiments and hydrocode simulations (Fujiwara et al. 1989, Benz and Asphaug 1999). In addition, there are large members (D > 20 km) of the Adeona, Chloris, Dora, and other families (Zappalá 2001, private communication) that have unusually high values of apparent ejection velocities, and could be classified as interlopers. This may be explained if family members were launched with low ejection velocities, and then diffused to their current locations. While chaotic diffusion from mean-motion resonances can account for the mobility in proper e and i, the only mechanisms that can cause changes in proper semimajor axis are the Yarkovsky effect and close encounters among asteroids.
We have investigated the degree to which large asteroid-family fragments could be further scattered by close encounters with the four most massive asteroids in the Main Belt (1 Ceres, 2 Pallas, 4 Vesta, and 10 Hygiea). We performed several N-body simulations over 500 Myr of members (and of test particles simulating the initial conditions after break-up). We studied the Adeona, Gefion, and Dora families because they seem to have a spherical symmetric ejection velocity field and they are close in proper element space to 1 Ceres, which previous studies showed to be the primary internal perturber of the Main Belt.
While close encounters seem unable to significantly alter the semimajor axis distribution of most simulated bodies, individual asteroids can be significantly moved (up to 0.015 AU/500 Myr) from their original positions. Also, close encounters have stimulated chaotic diffusion of several other asteroids by injecting them into mean-motion resonances, thereby changing the e and i distributions of the families.
The author(s) of this abstract have provided an email address for comments about the abstract: vc27@cornell.edu