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 A new analysis of samples returned by the Apollo astronauts suggests that there is virtually no chance that water ever existed beneath the lunar surface.

 新一輪采樣分析表明，實(shí)際上水不可能存在于月球表面之下。這些樣品是執(zhí)行阿婆羅航天計(jì)劃的宇航員帶回來的。

 Scientists have been arguing for decades about whether the moon contains significant quantities of water. Theoretically, it should because the moon was once part of Earth. (It was created by a catastrophic collision between our planet and a Mars-size body over 4 billion years ago.) Yet initial chemical analyses in the 1970s and '80s of rocks that had been brought back by the Apollo missions turned up virtually no evidence of lunar water. More recently, using improved equipment to examine the molecular constituents of the rocks, researchers have found minute quantities of hydrogen—an indicator of water. (The LCROSS spacecraft, which slammed into a perpetually shaded lunar crater last fall, turned up evidence of water ice on the surface, but that ice was presumably deposited by an ancient comet impact.) It's an important riddle to solve, as researchers would like to use lunar water to manufacture rocket fuel for future deep-space missions.

 幾十年來，關(guān)于月球上是否存在大量的水，科學(xué)家們一直爭論不休。從理論上，月球上應(yīng)該存在水，因?yàn)樗堑厍虻囊徊糠?，它?/span>40多億年前一顆火星大小的天體跟地球之間發(fā)生毀滅性的撞擊之后而產(chǎn)生的。然而，二十世紀(jì)七八十年代對(duì)阿婆羅航天行動(dòng)帶回的巖石進(jìn)行了初步的化學(xué)分析，實(shí)際上當(dāng)時(shí)并沒有發(fā)現(xiàn)月球水的跡象。后來，研究人員利用改良設(shè)備檢測了巖石的分子組分，發(fā)現(xiàn)了少量的氫，標(biāo)志著水的存在。去年秋季，LCROSS太空船撞擊到一個(gè)永遠(yuǎn)處于陰影中的隕石坑中，發(fā)現(xiàn)了表層中擁有水冰的跡象，但是那些水冰可能是由于古代的彗星撞擊而積存下來的。這是一個(gè)需要解開的重大謎團(tuán)，因?yàn)檠芯咳藛T想利用月球水為未來的航天行動(dòng)制造火箭燃料。

 Now, a team has attempted to solve the mystery by comparing the ratio of two isotopes, or forms, of chlorine in lunar and terrestrial rocks. The scientists had performed similar analyses on Earth rocks and on meteorites, so they decided to duplicate the research on the lunar samples. The researchers reported online 5 August in Science that based on the difference in chlorine ratios, the moon has basically zero subsurface water.

 目前，一個(gè)研究小組企圖通過對(duì)比月球巖石和陸地巖石中氯元素的兩種同位素來解開這個(gè)謎團(tuán)。以前研究人員對(duì)地球巖石和隕石做過類似的分析，因此他們決定對(duì)月球巖石進(jìn)行同樣的研究。研究人員在8月5日的《科學(xué)》（Science）雜志在線版上報(bào)道：根據(jù)氯元素比率存在的差異可以說明月球基本上不存在地下水。

 Geochemist and lead author Zachary Sharp of the University of New Mexico, Albuquerque, explains that the chlorine isotope ratio is a highly reliable indicator of the amount of hydrogen a planetary body contains. On Earth, primordial volcanic eruptions brought up lava containing huge amounts of volatile substances such as carbon dioxide, sulfur, water vapor, and chlorine. As the lava cooled, those gases leaked into the atmosphere—but they also interacted, and they left behind traces of that interaction, in the form of isotope ratios, which betray their relative quantities. On Earth's surface, the chlorine isotope ratio is uniform because the element interacts so readily with hydrogen. But on the moon, there's a wide variety in that ratio—what Sharp calls "scatter"—something that could not have happened if the moon contained significant amounts of hydrogen.

 該研究的首要發(fā)起人、新墨西哥大學(xué)（位于阿爾伯克基）化學(xué)家扎卡里·夏普解釋說，氯同位素比率可以極為準(zhǔn)確地表明一顆行星含有氫元素的量。在地球上，原始的火山爆發(fā)所噴出的熔巖中包含大量的揮發(fā)性物質(zhì)，如二氧化碳、硫、水蒸氣和氯。隨著熔巖的冷卻，這些氣體泄漏到大氣之中。但是這些氣體之間也發(fā)生相互反應(yīng)，這種反應(yīng)的痕跡卻以同位素比率的形式遺留下來，這樣也就透露出各種氣體的相對(duì)含量。在地球表面，氯同位素比率是一致的，因?yàn)槁仍胤浅７€(wěn)定地跟氫元素發(fā)生反應(yīng)；而在月球上，氯同位素比率差異很大，夏普稱之為“呈離散狀態(tài)”，如果月球上包含大量的氫，這種差異是不可能產(chǎn)生的。

 The ratio variability was a "completely unexpected and initially quite bewildering" result, Sharp says. The bottom line, he says, is that "the only process we are aware of that could cause such large isotope scatter is if the hydrogen content of the moon is 10,000 to 100,000 times less than [on] Earth."

 夏普說：“這種比率差異是一個(gè)完全意想不到的結(jié)果，起初給我們?cè)斐闪藰O大的困惑。”他說：“起碼，現(xiàn)在我們知道造成同位素比率差異如此巨大的唯一條件是：月球上的氫元素含量比地球上少10,000至100,000倍。”

 On its face, the paper presents a strong argument for a water-free moon, says planetary scientist David Stevenson of the California Institute of Technology in Pasadena. "But years of observation of geochemistry have taught me that caution is wise," he says, "whether it be for the earlier claims on water or this latest work on chlorine isotopes."

 帕薩迪納市加州理工學(xué)院的行星科學(xué)家大衛(wèi)·斯蒂文森稱：表面上看，該研究論文提供了一個(gè)強(qiáng)有力的論據(jù)，證明了月球上沒有水?！暗嵌嗄甑牡厍蚧瘜W(xué)觀測讓我認(rèn)識(shí)到，”他說，“不管對(duì)于早期有水的主張還是對(duì)于這項(xiàng)氯同位素的最新研究，謹(jǐn)慎一些總是明智的。”