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M. Bro{\v z}, D. Vokrouhlick{\' y} (Univ. Prague), P. Farinella (Univ. Trieste), W.F. Bottke (Cornell Univ.)
The Yarkovsky effect, a tiny non--gravitational recoil force due to the anisotropy in the surface temperature of spinning and orbiting bodies, can affect significantly the dynamical evolution of small asteroids (up to \approx 20~km in diameter), since it results in a slow, but secular drift of their semimajor axes. While both analytical [1] and numerical [2] estimates of the drift rate have been recently obtained, it has also been recognized that the total mobility in semimajor axis needs to account for the collisional reorientation of the spin axes. Moreover, another dynamical mechanism may affect the semimajor axis drift when an asteroid fragment is en route toward the principal resonances in the main belt: the interaction with a web of higher--order, thin and relatively weak resonances. Temporary captures in these resonances may result in a significant deceleration of the overall Yarkovsky mobility, especially when the underlying semimajor axis drift is slow. Beyond some size threshold to be specified, small asteroids slowly leak from the main belt along these higher--order resonances, which at the same time are fed by the Yarkovsky effect [3,4]. On the other hand, smaller fragments may avoid to be trapped and eventually reach the main escape routes from the belt (\nu6, 3:1, 5:2 resonances), but with time scales affected by the interaction with the high--order resonances. We have now integrated the orbits of hundreds of asteroid fragments of different sizes over \approx 150~Myr, in order to assess quantitatively the resonance--Yarkovsky interaction effects. We have explored the effectiveness of the capture process into the weak resonances as well as the possibility that the Yarkovsky drift might lead a fraction of the small fragments to ``jump''/``cross'' over the main ones.
\vskip 2mm\noindent References: [1] Farinella et al. 1998, Icarus 132, 378. [2] Bottke et~al. 1999, Icarus, submitted. [3] Migliorini et~al. 1998, Science 281, 2022. [4] Farinella and Vokrouhlický 1999, Science 283, 1507.
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