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Space rock is chip off the old block

作者:尹汴    发布时间:2019-03-07 04:03:10    

By Jeff Hecht in Boston THE small asteroid visited by NASA’s Deep Space 1 probe on 29 July appears to be a chip off one of the largest and best-known asteroids: Vesta, which is 525 kilometres across. Although Deep Space 1’s cameras were pointing the wrong way when the craft zoomed by asteroid Braille (New Scientist, 7 August, p 13), it did record an image from 14 000 kilometres away some 15 minutes later. The spectrum of light given off by the asteroid suggests it has the same composition as Vesta. Vesta has a shallow crater with a diameter of 460 kilometres around its South Pole, indicating that it lost a sizeable chunk of rock from its surface after a collision. “It’s a good conjecture that Braille came from the hole,” says Bonnie Buratti, of the Jet Propulsion Laboratory in Pasadena. If so, Braille has been thrown right out of its former orbit: Vesta orbits between Mars and Jupiter, but Braille comes within 45 million kilometres of the Earth. Deep Space 1’s snapshot suggests that Braille is between 1 and 2 kilometres across, and consists of three distinct lobes. However, Rick Binzel of the Massachusetts Institute of Technology warns that shadows can fool the eye. “But it certainly looks like a pair of lobes,

 

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