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D. Nesvorny, W.F. Bottke, L. Dones, H.F. Levison (Soutwest Research Institute)
Much of what we observe in the asteroid belt today is the result of collisions between asteroids. Ideally, the orbit and size distributions of ejecta from these events can be used to help us understand the physics of large-scale collisions that helped shape the planets at early epochs. Unfortunately, this understanding has been hampered because observed clusters of collisional fragments (called asteroid families) are very old and thus have undergone significant evolution since their formation.
Here we report the discovery of a previously unidentified recent disruption event in the asteroid belt 5.8 million years ago. This marks the first time that such a break-up event has been precisely dated. Our discovery offers an excellent opportunity for physical studies of high-velocity collisions because the observed structure has apparently suffered limited dynamical and collisional erosion. The orbits and sizes of the thirty nine identified fragments of the disrupted \approx 25-km-diameter parent body yield an unusual size-frequency distribution, with two large, similarly sized bodies and a continuum among the 2-7 km bodies. The low impact-generated ejection velocities measured among the ejecta and the correlation between sizes and ejection velocities suggest that gravitational reaccumulation may have been common. These data may be used to validate numerical models of large-scale collisions.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.