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

地球表面大部分都是海洋，它们从哪里来？

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.

一直以来人们认为海水可能来自早期坠入地球的小行星和彗星。但是针对哈雷彗星和其他五颗彗星的观测结果给这一结论大泼冷水。因为这些彗星的化学成分比例和海水并不相似。具体而言，在彗星中，重氢，或者说是氘以及氢的含量更高。

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.

但是现在天文学家们得以观测一颗来自不同地区的彗星。它的化学成分比例和海水非常吻合。他们使用赫歇尔太空镜来观测哈特利2号，这颗来自柯伊伯带的彗星。而哈雷彗星及其同类彗星则来自遥远的奥尔特彗星云。

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"]

上周，在法国举行的行星科学会议上，研究人员在一个《自然》杂志（举办的）研究会中宣布，哈特利2号具有和海水相似的氘氢比例。[Paul Hartogh等，“木星家族的103号彗星哈特利2号上有类似海水存在”]

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.

下次当你在沙滩漫步时也许会想起，说不定这些海水（真的）来自彗星。

surface n.表面
smash v. 撞击
chemical signatures 化学成分
originate vi.起源于
deuterium-to-hydrogen ratio 氘氢比例