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Thursday, 4 May, 2000, 17:59 GMT 18:59 UK
Astronomers see 'dog bone' asteroid
![]() Slowly spinning in space and shaped like a dog bone
By BBC News Online science editor Dr David Whitehouse
Astronomers have obtained extraordinary radar images of a giant, dog bone-shaped asteroid. The radar images are the first ever of an asteroid in the main asteroid belt between Mars and Jupiter.
"With its dog bone shape, Kleopatra has the most unusual shape we've seen in the Solar System," says Steven Ostro of Nasa's Jet Propulsion Laboratory, who led a research team using the 305-m (1,000-ft) Arecibo telescope. "Kleopatra could be the remnant of an incredibly violent collision between two asteroids that did not completely shatter and disperse all the fragments," Ostro says. Metal cores The astronomers used the mighty Arecibo telescope to bounce radar signals off the space rock. They decoded the echoes and transformed them into images.
The images were obtained when Kleopatra was about 171 million km (106 million miles) from Earth. The transmitted signal took about 19 minutes to make the trip to the asteroid and back. "Getting images of Kleopatra from Arecibo was like using a Los Angeles telescope the size of the human eye's lens to image a car in New York," Ostro says. Kleopatra is one of several dozen asteroids whose spectrum suggests they contain metal. They were once heated, melted and changed into a body that contained a core, mantle and crust, much like the Earth. Unlike Earth, these asteroids cooled and solidified throughout, and then were subjected to violent collisions that exposed their metallic cores. Separate lobes "The radar-based reconstruction of Kleopatra's shape shows the object's two lobes connected by a handle, forming a shape that resembles a distorted dumbbell, or dog bone," says R Scott Hudson of Washington State University.
Michael Nolan of Arecibo comments that the radar observations "indicated the surface of Kleopatra is porous and loosely consolidated, much like surface of the Moon, although the composition is different." He says: "Kleopatra's interior arrangement of solid metal fragments and loose metallic rubble, and the geometry of fractures within any solid components, are unknown. What is clear is that this object's collision history is extremely unusual." Ostro voices his amazement "that nature has produced a giant metallic object with such a peculiar shape." He says: "We can think of some possible scenarios, but at this point none is very satisfying. The object's existence is a perplexing mystery that tells us how far we have to go to understand more about asteroid shapes and collisions."
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