科學(xué)美國(guó)人60秒聽(tīng)力練習(xí)：海水來(lái)自彗星

　　科學(xué)美國(guó)人60秒英文文本

　　Earth's surface is dominated by oceans. But where did all that water come from?

　　Asteroids and comets smashing into the early Earth have long been thought to be a promising source. But measurements of Halley's Comet and five others threw cold water on the idea that comets provided a large share of the oceans. Because the chemical signatures of the comets did not match the oceans. Specifically, the ratio of heavy hydrogen, or deuterium, to regular hydrogen was too high in the comets.

　　But now astronomers have gotten a glimpse of a comet with a different origin, and it matches the oceans much better. They used the Herschel space telescope to examine Comet Hartley 2, which originated in the Kuiper Belt. Halley and its ilk came from a distant swarm of comets called the Oort Cloud.

　　At a planetary science meeting last week in France, and in a study in Nature, the researchers announced that Comet Hartley 2 has the same deuterium-to-hydrogen ratio as ocean water. [Paul Hartogh et al., "Oceanlike water in the Jupiter-family comet 103P/Hartley 2"]

　　So maybe comets did play a major role in delivering Earth's oceans. Something to ponder next time you have a day at the beach.

　　科學(xué)美國(guó)人60秒中文翻譯：

　　地球表面大部分都是海洋，它們從哪里來(lái)?

　　一直以來(lái)人們認(rèn)為海水可能來(lái)自早期墜入地球的小行星和彗星。但是針對(duì)哈雷彗星和其他五顆彗星的觀測(cè)結(jié)果給這一結(jié)論大潑冷水。因?yàn)檫@些彗星的化學(xué)成分比例和海水并不相似。具體而言，在彗星中，重氫，或者說(shuō)是氘以及氫的含量更高。

　　但是現(xiàn)在天文學(xué)家們得以觀測(cè)一顆來(lái)自不同地區(qū)的彗星。它的化學(xué)成分比例和海水非常吻合。他們使用赫歇爾太空鏡來(lái)觀測(cè)哈特利2號(hào)，這顆來(lái)自柯伊伯帶的彗星。而哈雷彗星及其同類彗星則來(lái)自遙遠(yuǎn)的奧爾特彗星云。

　　上周，在法國(guó)舉行的行星科學(xué)會(huì)議上，研究人員在一個(gè)《自然》雜志(舉辦的)研究會(huì)中宣布，哈特利2號(hào)具有和海水相似的氘氫比例。[Paul Hartogh等，“木星家族的103號(hào)彗星哈特利2號(hào)上有類似海水存在”]

　　下次當(dāng)你在沙灘漫步時(shí)也許會(huì)想起，說(shuō)不定這些海水(真的)來(lái)自彗星。

　　surface n.表面

　　smash v. 撞擊

　　chemical signatures 化學(xué)成分

　　originate vi.起源于

　　deuterium-to-hydrogen ratio 氘氫比例