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Spin vector alignment of Koronis family asteroids


Studies of asteroid families—groups of asteroids that formed from the fragmentation of larger bodies—are of broad interest to solar system researchers because they can provide insights into collisional processes, as well as the interior structures, strengths, and compositions of asteroids. It is generally accepted that members of the Koronis family were created by collisional disruption of a homogeneous parent body1 and therefore share the same formation age and subsequent collisional history. The temporal variations in observed brightnesses of the Koronis family members (a consequence of their rotation) are, however, larger than expected2. Preferential alignment of spin vectors had been proposed2 as a possible explanation, but recent modelling3 predicted that family formation yields random spin vectors among the resulting fragments. Both hypotheses have been untested by observations. Here I show that the actual distribution of spin vectors among the largest members of the Koronis family falls within markedly nonrandom ‘spin clusters’. Reconciling models of family formation and evolution with the unexpected alignments of spin obliquities and correlations with spin rates presents a new challenge in understanding asteroid collisional processes.

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Figure 1: Light curves of (311) Claudia showing the doubly periodic change in brightness as it rotates once in 7.531 h.
Figure 2: Effect of changing illumination geometry on the observed mean brightness of (158) Koronis during a 36-day interval in 1994.
Figure 3: Spin angular momentum in the Koronis family of asteroids.


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I thank R. Binzel for advice and encouragement, and M. Kaasalainen, L. Crespo da Silva, M. Lyndaker and M. Krc̆o for contributions at various stages of this work.

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Correspondence to Stephen M. Slivan.

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Slivan, S. Spin vector alignment of Koronis family asteroids. Nature 419, 49–51 (2002).

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