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The Spin States of Small Near-Earth Asteroids

Wednesday, May 7, 2008
Tom
Statler (Ohio University)

Large asteroids, with diameters of 150 meters or larger, all have rotation periods longer than 2 hours, corresponding to the spin limit for gravitationally bound "rubble piles." Small asteroids, on the other hand, do not. A population of fast-rotating objects is seen among the near-Earth Asteroids (NEAs) smaller than 150 m. Neither the source, nor the interpretation, of this rapid rotation is clear. For objects of this size in the inner Solar System, torques produced by the radiation-recoil (YORP) effect modify the spin rates and axial obliquities on timescales of 106 to 107 years, which coincide with the objects' typical lifetimes. Neither the actual spin rate distribution nor the axial obliquity distribution is known, because of the obvious difficulties in observing asteroids the size of office buildings at multi-megamile distances. In this talk, I will report on preliminary results from observations of approximately 40 NEAs with diameters between 20 and 500 meters, showing that the actual spin rate distribution is quite different from what has previously been thought. I will discuss the implications of these results for the evolution of asteroid spins and possible constraints on material strength.

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