文章轉載自 世紀君 21世紀英文報

經過半個多世紀的探測，各種證據已讓人們相信，月球上是有水存在的。但月球水的含量、來源等仍是需要研究的問題。

光譜儀探測也是更加先進的方式。此前，來自光譜儀的數據都是從距離月球表面遙遠的月球上空觀測到的，人類還從未在月球表面原位直接進行過水的探測。

如今，我國嫦娥五號探測器攜帶的月球礦物光譜分析儀，第一次有機會在月表近距離、高分辨地探測水的信號。

采樣區一噸月壤約含一百二十克水

據《科技日報》報道，基于嫦娥五號攜帶的“月球礦物光譜儀”探測的數據，中科院地質與地球物理研究所等單位的研究人員首次獲得了月表原位條件下的水含量。他們發現，嫦娥五號采樣區的水含量在120ppm（百萬分之一）以下，而從別的地方濺射到采樣區的更古老巖石中的水含量約為180ppm。這就相當于1噸月壤中大約有120克水，1噸巖石中大約有180克水。相關研究成果1月8日在線發表于《科學·進展》。

An illustration in the paper shows the lunar lander's sampling site and the samples it takes. [Photo/Xinhua]

Chinese scientists published results of in-situ detection of water signals on the moon by the Chang'e 5 lunar lander, lending new evidence to the dryness of the satellite.

The study published on Saturday in the peer-reviewed journal Science Advances revealed that the lunar soil at the landing site contains less than 120 ppm water or 120g water per ton, and a light, vesicular rock carries 180 ppm, which are much drier than that on Earth.

A device onboard the lunar lander measured the spectral reflectance of the regolith and the rock and detected water on the spot for the first time.

需要說明的是，“光譜儀所探測到的‘水’是指礦物里的水分子或者羥基，在一定條件下才能轉化為我們喝的水。”論文第一作者、中科院地質地球所副研究員林紅磊解釋道。

和普遍意義上的液態水不同，光譜儀在月面探測到的“水”都藏在巖石中，水分子代表稍微加熱就可以跑出來的“結合水”，羥基則代表需要較高溫度才能析出的“結構水”。

Lin Honglei, the first author of the study and an associate researcher at the Chinese Academy of Sciences' Institute of Geology and Geophysics, said detecting water signals, like water molecules and hydroxyl, is different from finding actual liquid water.

Scientists would need to treat rock and soil with heat to extract water molecules and hydroxyl from them and turn it into liquid water, he said.

Technicians monitor the status of Chang'e 5 probe at the Beijing Aerospace Flight Control Center, Dec 1, 2021. [Photo/Xinhua]

月壤中的水絕大部分來自太陽風

嫦娥五號探測器攜帶了月球礦物光譜分析儀，在采樣過程中獲取了月表的光譜。“光譜儀是靠發現羥基或者水分子的明顯吸收特征來測量水。”中科院上海技物所研究員何志平介紹，“通過分析3微米附近的光譜特征，就可以識別月表水并獲得水含量。”

The water content can be estimated since the water molecule or hydroxyl absorbs at a frequency of about three micrometers, according to researchers from the Chinese Academy of Sciences (CAS).

那么，這些水從何而來？科研人員解釋，結合樣品分析，月壤中的水絕大部分是太陽風的貢獻——太陽風里有很多氫，轟到月面與月壤里的氧結合形成了羥基或者水分子。

It was the solar wind that contributed to the most humidity of lunar soil as it brought hydrogen that makes up the water, the researchers said.

和月壤中的水含量相比，巖石中多出來的60ppm水又來自哪里？科研人員推測，巖石是來自于比嫦娥五號著陸點本地玄武巖更古老的區域，多出來的水可能代表了月球內部水。“而月壤中的含水量較低，可能是嫦娥五號著陸區月幔較干或經歷了大量脫氣的過程，這與風暴洋地區長期的火山噴發是一致的。”林紅磊說。

The additional 60 ppm water in the rock may originate from the lunar interior, according to the researchers.

Therefore, the rock is estimated to hail from an older, more humid basaltic unit before being ejected onto the landing site to be picked up by the lunar lander.

The study revealed that the moon had turned drier within a certain period, owing probably to the degassing of its mantle reservoir.

月表水的分布可能與緯度高度相關，嫦娥五號是目前返回樣品中緯度最高的，這對研究月表水的分布及來源具有重要意義。論文通訊作者之一、地質地球所研究員林楊挺表示，嫦娥六號、嫦娥七號未來將在原位和軌道尺度繼續探測月表水的含量、分布，本研究成果也將為嫦娥六號、嫦娥七號的科學目標實現提供支撐。

Lin Yangting, one of the study's co-authors, said China's next two lunar missions-Chang'e 6 and Chang'e 7-hope to examine the content and distribution of lunar surface water at the same site in greater detail.

The latest discovery can serve as a foundation for the two future missions to achieve their scientific objectives, he said.

綜合來源：科技日報，新華網，央視網

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