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Science 24 November 2006:
Vol. 314. no. 5803, p. 1213
DOI: 10.1126/science.314.5803.1213d
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This Week in Science

Of the various binary objects in space, binary asteroids are the smallest, as well as the closest for observation. Ostro et al. (p. 1276, published online 12 October; see the cover) used radar to map the binary Earth-approaching asteroid (66391) 1999 KW4 and deduce its physical properties. Alpha, the main component, is an unconsolidated aggregate and spins on its axis every 2.8 hours. The smaller companion, Beta, is elongated and denser than Alpha. Scheeres et al. (p. 1280, published online 12 October) model the coupled orbital and rotational dynamics of the system. Alpha is spinning at a rate near its break-up speed, and the authors suggest that the system may have been put into its excited state by a close pass with the Sun or Earth. The binary asteroid may have ultimately originated from the disruption of a rubble-pile precursor.




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