Lunar exploration

月球探索

There is now cast-iron evidence for water on the Moon

現(xiàn)在有確鑿的證據(jù)表明月球上有水

詞匯

cast-iron/鑄鐵的；堅(jiān)固的

And it may be more widespread than previously suspected

而且它的分布范圍可能比之前想象的更廣

Oct 26th 2020 |?

IF HUMAN BEINGS?should ever wish to build bases on the Moon, those bases will need water. Residents will require it not only for their own sustenance but also as a raw material for rocket fuel to power adventures farther afield—Mars, for example. Given the cost of blasting things off the surface of Earth, however, such a base would be best served by finding its water locally. A pair of studies published on October 26th, in Nature Astronomy, will therefore raise the hopes of would-be lunar settlers.

如果人類希望在月球上建立基地，那些基地將需要水。居民們不僅需要它維持生計(jì)，還需要它作為火箭燃料的原材料（盲猜這里是指水電解氫氣壓縮氫氣作為燃料），為更遠(yuǎn)的太空探險(xiǎn)提供動(dòng)力，比如火星。然而，考慮到把東西從地球表面炸開的成本，這樣一個(gè)基地最好是在當(dāng)?shù)卣业剿?。因此?0月26日發(fā)表在《自然天文學(xué)》雜志上的兩項(xiàng)研究為未來的月球定居者帶來了希望。

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One, led by Paul Hayne of the University of Colorado, Boulder, shows that more of the Moon’s surface is in perpetual shadow than was previously believed. This matters because ice—the form in which any lunar water is likely to exist—would be stable and long-lived in such cold, shaded regions. Most of the lunar surface is bathed in harsh ionising radiation from the sun, so any water molecules present would swiftly be torn apart or disappear into space. But Dr Hayne’s work calculates that there are around 40,000 square kilometres of these ice-preserving “cold traps” on the Moon.

由博爾德科羅拉多大學(xué)的Paul Hayne領(lǐng)導(dǎo)的一項(xiàng)研究表明，月球表面存在永久陰影的部分比之前認(rèn)為的要多。這一點(diǎn)很重要，因?yàn)楸谠虑蛏峡赡艽嬖谒尸F(xiàn)的形式——在這樣寒冷、陰暗的地區(qū)能夠穩(wěn)定和長期存在的。月球表面的大部分區(qū)域都沐浴在來自太陽的強(qiáng)烈電離輻射中，因此任何存在的水分子都會(huì)迅速地被撕裂或消失在太空中。但根據(jù)Hayne博士的研究計(jì)算，月球上大約有40000平方公里的這些保存冰的“寒冷陷阱”。

詞匯

perpetual /永久的；不斷的

Harsh/嚴(yán)厲的；嚴(yán)酷的

Ionising/使電離，使離子化

Swiftly/很快地，急速

?注：?cold trap在本文多次出現(xiàn)，字面理解是“寒冷陷阱”，但是可以理解為那種可以把水分困住的小的寒冷的坑坑洼洼地帶。

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The other investigation, led by Casey Honniball of the Goddard Space Flight Centre in Maryland, a branch of NASA, America’s space agency, confirms the presence of water molecules (H2O) on the Moon’s surface. Previous evidence could not distinguish such molecules from hydroxyl radicals (OH), which are subunits of water that are normally chemically bonded to other substances. Intriguingly, these water molecules are on sunlit parts of the surface, away from any cold traps.

另一項(xiàng)由馬里蘭州戈達(dá)德太空飛行中心的Casey Honniball領(lǐng)導(dǎo)的調(diào)查證實(shí)了月球表面存在水分子(H2O)。戈達(dá)德太空飛行中心是美國宇航局的一個(gè)分支機(jī)構(gòu)。以前的證據(jù)無法區(qū)分這種分子和羥基自由基(OH)，羥基自由基是水的亞基，通常與其他物質(zhì)通過化學(xué)方式結(jié)合。有趣的是，這些水分子位于表面陽光照射的部分，遠(yuǎn)離任何寒冷的束縛處。

詞匯

Hydroxyl/羥基，氫氧基

Subunit/ 亞組；副族

?Intriguingly/有趣地；有魅力地

sunlit /陽光照射的；被日光照射了的

Sea of showers

海的沐浴

Despite the Moon being Earth’s closest and most studied celestial neighbour, the presence of water there was confirmed only recently, by a gradual accumulation of evidence. In 1999 a NASA?craft called Cassini?detected hints of the stuff as it flew past on its way to Saturn. The hints became stronger a decade later when Chandrayaan 1, an Indian probe, flew to the Moon. An American instrument on board, the Moon Mineralogy Mapper (M3), employed a spectrometer to examine sunlight reflected back from the lunar surface. M3 found that infrared light of a specific wavelength—three microns—was being absorbed by the surface. This is an absorption pattern shown by water, but also by hydroxyl.

盡管月球是離地球最近的天體，也是被研究最多的天體，但月球上存在水的說法直到最近才被逐漸積累的證據(jù)證實(shí)。1999年，美國宇航局的一艘名為“卡西尼號(hào)”的飛船在飛往土星的途中飛過土星時(shí)發(fā)現(xiàn)了這些物質(zhì)的跡象。10年后，當(dāng)印度探測器“月船一號(hào)”(Chandrayaan 1)飛向月球時(shí)，這種暗示變得更加強(qiáng)烈。月球礦物制圖儀(M3)搭載的美國儀器使用了光譜儀來檢測從月球表面反射回來的太陽光。M3發(fā)現(xiàn)波長為3微米的紅外光被表面吸收。這是水和羥基的吸收模式。

詞匯

?celestial /天上的，天空的

?Probe/探針；調(diào)查

?Mineralogy/ 礦物學(xué)；礦物學(xué)書籍

Spectrometer/光譜儀

Infrare/ 紅外線； 紅外線的

??

In October 2009, a few months after the results from M3 had been published, NASA?crash-landed the spent stage of an Atlas V rocket into Cabeus, a crater near the Moon’s south pole. They chose?Cabeus because it was known to have areas in perpetual shadow. The impact was followed minutes later by LCROSS, the Lunar Crater Observation and Sensing Satellite, its cameras trained on the site taking pictures and measurements of the resulting cloud of debris.

2009年10月，就在M3的結(jié)果公布幾個(gè)月后，美國國家航空航天局(NASA)的阿特拉斯5號(hào)(Atlas V)火箭硬著落撞上了月球南極附近的Cabeus隕石坑。他們選擇了Cabeus，因?yàn)樗杏谰玫年幱皡^(qū)域。幾分鐘后，月球隕坑觀測和傳感衛(wèi)星LCROSS也產(chǎn)生了撞擊，它的照相機(jī)在撞擊現(xiàn)場拍攝了照片，并測量了撞擊產(chǎn)生的碎片云。

詞匯

Debris/碎片，殘骸

Previous scans of the Moon’s south pole in the 1990s, by NASA?missions called Clementine?and Lunar Prospector, had indicated large amounts of hydrogen were present in the region, though it was unclear what form this hydrogen took. LCROSS?was designed to find out. The crash excavated 350 tonnes of lunar regolith, creating within Cabeus a crater 20 metres wide and generating a plume that rose 10km from the surface. Among the ejecta, LCROSS?detected the characteristic three-micron spectroscopic signal, but still could not distinguish whether the cause was water or hydroxyl.

早在上世紀(jì)90年代，美國宇航局的“克萊門汀”號(hào)和“月球探勘者”號(hào)任務(wù)就對(duì)月球南極進(jìn)行了掃描，結(jié)果顯示該地區(qū)存在大量的氫，盡管尚不清楚這些氫的形態(tài)。LCROSS（上文：月球隕坑觀測和傳感衛(wèi)星）的設(shè)計(jì)就是為了找出答案。這次撞擊挖掘了350噸的月球風(fēng)化層，在Cabeus內(nèi)部形成了一個(gè)20米寬的隕石坑，并從月球表面升起了10公里的羽狀物。在這些噴出物中，LCROSS探測到了具有特征的三微米光譜信號(hào)，但仍然無法區(qū)分其原因是水還是羥基。

詞匯

?Plume/羽毛；羽毛裝飾物；卷流

?Regolith/ 風(fēng)化層；表皮土

Ejecta/噴出物；排泄物

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One way to tell the difference is to look for missing light at six microns, too—for only water molecules absorb at this wavelength. So that was what Dr Honniball set out to do. In 2018 she commandeered the only instrument capable of making the relevant measurement—the 2.5-metre-wide Stratospheric Observatory for Infrared Astronomy (SOFIA) telescope, which sits on board a modified Boeing 747 that can fly it to an altitude of 13km. This is above 99.9% of the water vapour in Earth’s atmosphere, which would otherwise obscure any infrared signal reflected from the Moon.

一種區(qū)分的方法是尋找缺失的6微米的光——因?yàn)橹挥兴肿幽芪者@個(gè)波長。這就是Honniball博士著手做的事情。2018年，她征用了唯一能夠進(jìn)行相關(guān)測量的儀器——2.5米寬的平流層紅外天文觀測臺(tái)(SOFIA)望遠(yuǎn)鏡，該望遠(yuǎn)鏡安裝在一架改裝過的波音747飛機(jī)上，可以飛到13千米的高度。這超過了地球大氣中99.9%的水蒸氣，否則這些水蒸氣就會(huì)掩蓋從月球反射的任何紅外信號(hào)。

詞匯

?vapour /蒸發(fā)，汽化

?

SOFIA?normally observes distant celestial objects, such as black holes. Instead, Dr Honniball pointed it towards Clavius, a crater about 75° south of the Moon’s equator, and which, perhaps coincidentally, was the fictional site of an American Moonbase in “2001: A Space Odyssey”. She found an absorption line at six microns in the reflected sunlight. This confirmed that, here at least, between one and four parts in 10,000 of the material of the lunar surface is water.

【平流層紅外天文觀測臺(tái)】通常觀測遙遠(yuǎn)的天體，比如黑洞。相反，Honniball博士將它指向Clavius，一個(gè)位于月球赤道以南75度的隕石坑，也許巧合的是，它是《2001太空漫游》中虛構(gòu)的美國月球基地所在地。她發(fā)現(xiàn)在反射的太陽光中有一條6微米的吸收線。這至少證實(shí)了月球表面每10000個(gè)物質(zhì)中有1到4個(gè)是水。

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How useful such water would be for future missions depends, though, not only on how much of it there is but also on how it is stored in the regolith. One possibility is that it exists as ice crystals in microscopic voids between regolithic grains. If that is true, lunar settlers could simply heat the regolith up to liberate its water. Dr Honniball thinks, however, that the water she has found is more likely to be trapped in tiny glassy beads that form when the lunar surface is hit by micrometeorites.

然而，這些水對(duì)未來的任務(wù)有多有用，不僅取決于水的總量，還取決于水在表層土中的儲(chǔ)存方式。一種可能的存在形式是以冰塊晶體存在于風(fēng)化樣式顆粒的空洞中。如果這是真的，月球居民可以簡單地加熱風(fēng)化層釋放其水分。然而，Honniball博士認(rèn)為，她發(fā)現(xiàn)的水更有可能被困在微小的玻璃珠中，這些珠子是在月球表面被微隕石撞擊后形成的。

?Crystal/晶體

Void/無效的；空的；空洞

Regolith/風(fēng)化層

Grain/谷物；紋理；晶粒

?

The theory behind this idea is that the solar wind, which is composed largely of protons, the nuclei of hydrogen atoms, continuously deposits that element into the regolith. Some of this hydrogen then reacts with oxygen atoms present as part of lunar minerals. That leads to the creation of hydroxyl radicals. When a micrometeorite hits the Moon, the impact vaporises the regolith. Everything is lifted into space, where the hydroxyls combine to form water molecules. These molecules are then encapsulated within drops of rapidly cooling regolith as it falls back to the surface.

這一想法背后的理論是，太陽風(fēng)主要由質(zhì)子(氫原子的原子核)構(gòu)成，不斷地將質(zhì)子元素沉積到風(fēng)化層中。其中一些氫會(huì)與作為月球礦物的一部分的氧原子發(fā)生反應(yīng)。這導(dǎo)致了羥基自由基的產(chǎn)生。當(dāng)一顆微隕石撞擊月球時(shí)，其影響蒸發(fā)了風(fēng)化層。所有物質(zhì)都被提升到太空中，在那里，羥基結(jié)合形成水分子。這些分子隨后被封裝在迅速冷卻的風(fēng)化層中，這些風(fēng)化層回落到表面。

詞匯

nuclei /核心，核子

Vaporis/汽化，蒸發(fā)

Sea of cold

寒冷的海洋

Extracting water from such beads would not be straightforward. A more promising source is the ice thought to exist in cold traps. Dr Hayne’s team used high-resolution images from NASA’s Lunar Reconnaissance Orbiter?to identify potential cold traps all across the Moon’s surface. There are more than had been hoped for, and they range in size from several kilometres to a few centimetres across. Most, as expected, are found near the poles, where the sun, when visible, remains near the horizon and shadows are consequently long. But a small number also exist at lower latitudes, created by craters or other surface variations that might be small but nevertheless maintain shadows where the temperatures stay low enough to accumulate ice.

從這些珠子中提取水分并非易事。一個(gè)更有希望的來源是冰被認(rèn)為存在于寒冷的陷阱中。Hayne博士的團(tuán)隊(duì)利用美國宇航局月球勘測軌道飛行器的高分辨率圖像來識(shí)別月球表面所有潛在的寒冷陷阱。它們的數(shù)量比預(yù)期的要多，大小從幾公里到幾厘米不等。正如預(yù)期的那樣，大部分陷阱被發(fā)現(xiàn)在兩極附近，在那里，太陽在可見的時(shí)候，仍然在地平線附近，因此陰影很長。但也有一小部分存在于低緯度地區(qū)，這是由隕石坑或其他表面變化造成的，這些變化可能很小，但卻在溫度低到足以積冰的地方保留了陰影。

Just because cold traps exist, however, does not mean they have trapped anything. Finding out if they have, and also answering the questions left open by Dr Honniball’s work, requires further examination of the regolith itself. In November 2023 NASA?hopes to launch a mission called VIPER?(Volatiles Investigating Polar Exploration Rover) to the Moon’s south pole. This craft will be armed with instruments designed to prospect the landing area for minerals and ice.

然而，僅僅因?yàn)楹涞南葳宕嬖冢⒉灰馕吨鼈儾东@了任何東西。要想知道它們是否存在，以及回答Honniball博士的工作遺留下來的問題，需要對(duì)風(fēng)化層本身進(jìn)行進(jìn)一步的檢查。美國宇航局希望在2023年11月發(fā)射一項(xiàng)名為“毒蛇（縮寫是VIPER，該詞又有‘毒蛇’的意思）”(揮發(fā)性極地探測探測器)的任務(wù)到月球的南極。這艘飛船將配備用于探測著陸區(qū)域礦物和冰的儀器。

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Both Dr Honniball’s and Dr Hayne’s results, then, give mission planners something to think about—not least those involved in NASA’s Artemis project to land people on the Moon some time this decade. Deciding where to site a base, should one ever be built, has always been a balance between the availability of water for food and fuel, and of sunlight for power. The idea of doing so at the south pole, to provide the water, would have come at the cost of astronauts having to work and live in pitch-dark conditions where temperatures rarely exceed -160°C. The possibility that better-lit and marginally less hostile parts of the lunar surface might have water as well will be a welcome prospect.

因此，無論是Honniball博士還是Hayne博士的研究結(jié)果，都給了計(jì)劃制定者一些值得思考的東西——不僅僅是那些參與了NASA的 Artemis項(xiàng)目的人，該項(xiàng)目旨在在這十年的某個(gè)時(shí)間將人類送上月球。決定在哪里建立基地，如果一個(gè)基地已經(jīng)建成，一直是一個(gè)平衡之間的水和燃料的可用性，以及太陽能的可用性。為了提供水，在南極這樣做的想法，代價(jià)是宇航員必須在漆黑的環(huán)境中工作和生活，那里的溫度很少超過零下160攝氏度。倘若在月球表面光照較好且不那么惡劣的地方也有水，這將是一個(gè)受歡迎的前景。