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A. Rossi (ISTI-CNR), F. Marzari (University of Padova), D.J. Scheeres (University of Michigan)
The statistical evolution of NEO rotation states accounting for Earth and Venus flybys was studied with a Monte Carlo simulation. Different spin components of the NEO population were evolved over 4.5 Byrs to find their steady states: fast rotators (6.37 hr periods) and intermediate rotators (11.27 hr) from the main belt, and slow rotators from the main belt and comet populations (27.46 hr). The cumulative effect caused average rotation periods to decrease for all components analyzed. This effect pushes fast rotating rubble pile asteroids over the disruption limit and causes more of them to experience a sub-disruption event that could modify their physical structure. For monolithic asteroids, the spin up effect is self-limiting, with a strong cut-off between 2-3 hours. This has two implications: it is not necessary to invoke the rubble pile hypothesis to recover a cut-off in spin period, and planetary flybys cannot account for the extremely rapid rotation rates of some asteroids. The Aten sub-class of asteroids was evaluated separately; due to increased interactions with the planets the spin up effect is more pronounced and disruptions increase. While some asteroids spin periods are significantly increased, the overall effect of planetary flybys does not significantly enhance the long rotation period tails in the distributions; thus this effect cannot cause the excess of slow rotators in the NEO population. Planetary flybys also cause asteroids to enter a tumbling state, with the majority of them having fast spin rates that will damp out relatively swiftly.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.