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Wednesday, August 4, 1999 Published at 17:21 GMT 18:21 UK


A chip off the old block

Asteroid Braille as seen from the receeding Deep Space 1 probe

By BBC News Online Science Editor Dr David Whitehouse

Asteroid Braille, visited last week by the Deep Space One spaceprobe, is a chip off a larger asteroid say scientists.

Professor Eileen Ryan, a member of the Deep Space One project team, said they believe that Braille broke off a much larger Asteroid called Vesta in a cosmic collision millions of years ago.

[ image: Its camera was fooled]
Its camera was fooled
Deep Space 1 passed about 26 km (16 miles) from Braille last week. During the close pass an infrared spectrometer was able to measure the composition of the asteroid, finding it to be identical to Vesta.

At 2.2 km (1.3 miles) Braille is a mere speck compared with the much larger Vesta, which has a diameter of about 500 km (310 miles.)

Braille has a lava-like crust that suggests they both belonged to a body that contained a tremendous heat source, rather like Earth's core.

Ryan said Vesta, discovered in 1807, and two smaller asteroids were thought to have been the only asteroids in the solar system containing volcanic matter until the fly-by of Braille.

"We believe there may have been a giant impact on Vesta some time in its past. There is a trail of fragments - a trail of bread crumbs if you will - following it. It is probable that Braille achieved an escape velocity which booted it out of the asteroid belt and put it into a different orbit, a near-Earth orbit," she said.

Deputy mission manager Marc Rayman explained the only problem during the Braille fly-by was the failure of a camera that was to take pictures of the asteroid as Deep Space 1 approached.

"The asteroid was in total shadow, the sun was below and because of its angle of rotation the camera was fooled into thinking there was nothing there," he said.

But after passing the asteroid its other side was brightly lit and the camera was able to capture images of it.

That is why DS1 sent back only one blurred picture of Braille as it was travelling away from it.

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