* Astronomy

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Asteroid (66391) 1999 KW4

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RE: Asteriod 66391 1999KW4

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1999 KW4

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RE: Asteriod 66391 1999KW4

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Researchers using the Arecibo Observatory's powerful radar have made the most detailed observations ever of a binary near-Earth asteroid (NEA) -- two clusters of rubble circling each other -- offering new clues about how such systems formed, the properties they share and the dynamics of their motion.
The observations, made by Steve Ostro, senior research scientist at the NASA/Caltech Jet Propulsion Laboratory in Pasadena (who earned his master's degree in engineering physics at Cornell), Jean-Luc Margot, assistant professor of astronomy at Cornell, and their colleagues, describe asteroid (66391) 1999 KW4 (called KW4). Their report appears in the latest issue (Nov. 24) of the journal Science.

The new data allow the most detailed shape models ever of a potentially hazardous asteroid. Alpha, KW4's larger component, is spinning so fast that particles on its surface feel themselves being pulled toward the equatorial ridge; that is, they fall toward the highest part of the surface.

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The first detailed images of a binary asteroid system reveal a bizarre world where the highest points on the surface are actually the lowest, and the two asteroids dance in each other's gravitational pull.

A binary asteroid is a system where two asteroids orbit around one another, like a mini Earth-moon system, said Daniel Scheeres, University of Michigan associate professor of aerospace engineering. The new results are scheduled to appear Oct. 12 in the journal Science in a pair of papers by Scheeres and Dr. Steven Ostro of the NASA/Caltech Jet Propulsion Laboratory.
The radar images of asteroid KW4 (the official full designation is 66391 1999 KW4) were obtained in May 2001, when the asteroid passed 4.8 million kilometres from Earth. Previously, KW4 was classified as a potentially hazardous asteroid (PHA) because of the proximity of the asteroid's orbit to Earth's orbit. The new observations show that there is no chance of KW4 hitting Earth within at least the next 1,000 years.

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