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Origin of asteroid rotation rates in catastrophic impacts

Love, Stanley G. and Ahrens, Thomas J. (1997) Origin of asteroid rotation rates in catastrophic impacts. Nature, 386 (6621). pp. 154-156. ISSN 0028-0836. doi:10.1038/386154a0.

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The rotation rates of asteroids, which are deduced from periodic fluctuations in their brightnesses, are controlled by mutual collisions. The link between asteroid spin and collision history is usually made with reference to impact experiments on centimetre-scale targets, where material strength governs the impact response. Recent work, however, indicates that for objects of the size of most observed asteroids (≥1 km in diameter), gravity rather than intrinsic strength controls the dynamic response to collisions. Here we explore this idea by modelling the effect of impacts on large gravitating bodies. We find that the fraction of a projectile's angular momentum that is retained by a target asteroid is both lower and more variable than expected from laboratory experiments, with spin evolution being dominated by 'catastrophic' collisions that eject ~50 per cent of the target's mass. The remnant of an initially non-rotating silicate asteroid that suffers such a collision rotates at a rate of ~2.9 per day, which is close to the observed mean asteroid rotation rate of ~2.5 d^(–1). Moreover, our calculations suggest that the observed trend in the mean spin frequency for different classes of asteroids (2.2 d^(–1)for C-type asteroids, 2.5 d^(–1) for S-type, and 4.0 d^(–1) for M-type) is due to increasing mean density, rather than increasing material strength.

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Additional Information:© 1997 Nature Publishing Group. Received 10 October 1996; accepted 21 January 1997. We thank P. Farinella for suggesting this line of study, and A. W. Harris and H. J. Melosh for reviews of this Letter. The Cray supercomputer used in this investigation was provided by funding from the NASA Offices of Mission to Planet Earth, Aeronautics, and Space Science; the research itself was supported by NASA.
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Issue or Number:6621
Record Number:CaltechAUTHORS:20141024-102735165
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50779
Deposited By: Tony Diaz
Deposited On:24 Oct 2014 18:08
Last Modified:10 Nov 2021 19:00

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