科学美国人60秒:碎陨石-托福听力下载

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　　科学美国人60秒中英文翻译：碎陨石

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　　From the depths of space, an asteroid hurtles toward Earth. (Well, our general vicinity.)But this is no ordinary hunk of galactic debris. Because the body of this asteroid seems to defy gravity. It's bound by forces never observed on this scale in space.

　　That's not the plot of a new summer blockbuster. It's the result of a study in the journal Nature.

　　The asteroid in question is actually a kilometer-sized collection of rubble. In most cases, such space — faring pebble piles are held together by a combination of gravity and friction. But not so for our rocky interloper, dubbed "1950 DA." This asteroid is rotating so rapidly that its pieces should have flung apart long ago.

　　Now, by analyzing the 1950 DA's temperature and density, researchers conclude that cohesive forces called van der Waals attractions must be keeping the pieces clustered. Van der Waals forces may sound mysterious, but they're well known on the small scale for their weak influence within and between molecules.

　　Blasting the asteroid, Hollywood style, could overcome these forces. But that might leave us with hundreds of smaller killer space rocks to dodge. The good news is, the asteroid won't be in our area until 2880. So we have some time to figure it out.

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