Lunar exploration

月球探索

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

现在有确凿的证据表明月球上有水

词汇

cast-iron/铸铁的；坚固的

And it may be more widespread than previously suspected

而且它的分布范围可能比之前想象的更广

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.

如果人类希望在月球上建立基地，那些基地将需要水。居民们不仅需要它维持生计，还需要它作为火箭燃料的原材料（盲猜这里是指水电解氢气压缩氢气作为燃料），为更远的太空探险提供动力，比如火星。然而，考虑到把东西从地球表面炸开的成本，这样一个基地最好是在当地找到水源。因此，10月26日发表在《自然天文学》杂志上的两项研究为未来的月球定居者带来了希望。

 

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.

由博尔德科罗拉多大学的Paul Hayne领导的一项研究表明，月球表面存在永久阴影的部分比之前认为的要多。这一点很重要，因为冰——水在月球上可能存在所呈现的形式——在这样寒冷、阴暗的地区能够稳定和长期存在的。月球表面的大部分区域都沐浴在来自太阳的强烈电离辐射中，因此任何存在的水分子都会迅速地被撕裂或消失在太空中。但根据Hayne博士的研究计算，月球上大约有40000平方公里的这些保存冰的“寒冷陷阱”。

词汇

perpetual /永久的；不断的

Harsh/严厉的；严酷的

Ionising/使电离，使离子化

Swiftly/很快地，急速

 注： cold trap在本文多次出现，字面理解是“寒冷陷阱”，但是可以理解为那种可以把水分困住的小的寒冷的坑坑洼洼地带。

 

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.

另一项由马里兰州戈达德太空飞行中心的Casey Honniball领导的调查证实了月球表面存在水分子(H2O)。戈达德太空飞行中心是美国宇航局的一个分支机构。以前的证据无法区分这种分子和羟基自由基(OH)，羟基自由基是水的亚基，通常与其他物质通过化学方式结合。有趣的是，这些水分子位于表面阳光照射的部分，远离任何寒冷的束缚处。

词汇

Hydroxyl/羟基，氢氧基

Subunit/ 亚组；副族

 Intriguingly/有趣地；有魅力地

sunlit /阳光照射的；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.

尽管月球是离地球最近的天体，也是被研究最多的天体，但月球上存在水的说法直到最近才被逐渐积累的证据证实。1999年，美国宇航局的一艘名为“卡西尼号”的飞船在飞往土星的途中飞过土星时发现了这些物质的迹象。10年后，当印度探测器“月船一号”(Chandrayaan 1)飞向月球时，这种暗示变得更加强烈。月球矿物制图仪(M3)搭载的美国仪器使用了光谱仪来检测从月球表面反射回来的太阳光。M3发现波长为3微米的红外光被表面吸收。这是水和羟基的吸收模式。

词汇

 celestial /天上的，天空的

 Probe/探针；调查

 Mineralogy/ 矿物学；矿物学书籍

Spectrometer/光谱仪

Infrare/ 红外线； 红外线的

  

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的结果公布几个月后，美国国家航空航天局(NASA)的阿特拉斯5号(Atlas V)火箭硬着落撞上了月球南极附近的Cabeus陨石坑。他们选择了Cabeus，因为它有永久的阴影区域。几分钟后，月球陨坑观测和传感卫星LCROSS也产生了撞击，它的照相机在撞击现场拍摄了照片，并测量了撞击产生的碎片云。

词汇

Debris/碎片，残骸

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.

早在上世纪90年代，美国宇航局的“克莱门汀”号和“月球探勘者”号任务就对月球南极进行了扫描，结果显示该地区存在大量的氢，尽管尚不清楚这些氢的形态。LCROSS（上文：月球陨坑观测和传感卫星）的设计就是为了找出答案。这次撞击挖掘了350吨的月球风化层，在Cabeus内部形成了一个20米宽的陨石坑，并从月球表面升起了10公里的羽状物。在这些喷出物中，LCROSS探测到了具有特征的三微米光谱信号，但仍然无法区分其原因是水还是羟基。

词汇

 Plume/羽毛；羽毛装饰物；卷流

 Regolith/ 风化层；表皮土

Ejecta/喷出物；排泄物

 

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.

一种区分的方法是寻找缺失的6微米的光——因为只有水分子能吸收这个波长。这就是Honniball博士着手做的事情。2018年，她征用了唯一能够进行相关测量的仪器——2.5米宽的平流层红外天文观测台(SOFIA)望远镜，该望远镜安装在一架改装过的波音747飞机上，可以飞到13千米的高度。这超过了地球大气中99.9%的水蒸气，否则这些水蒸气就会掩盖从月球反射的任何红外信号。

词汇

 vapour /蒸发，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.

【平流层红外天文观测台】通常观测遥远的天体，比如黑洞。相反，Honniball博士将它指向Clavius，一个位于月球赤道以南75度的陨石坑，也许巧合的是，它是《2001太空漫游》中虚构的美国月球基地所在地。她发现在反射的太阳光中有一条6微米的吸收线。这至少证实了月球表面每10000个物质中有1到4个是水。

  

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，这些水对未来的任务有多有用，不仅取决于水的总量，还取决于水在表层土中的储存方式。一种可能的存在形式是以冰块晶体存在于风化样式颗粒的空洞中。如果这是真的，月球居民可以简单地加热风化层释放其水分。然而，Honniball博士认为，她发现的水更有可能被困在微小的玻璃珠中，这些珠子是在月球表面被微陨石撞击后形成的。

 Crystal/晶体

Void/无效的；空的；空洞

Regolith/风化层

Grain/谷物；纹理；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.

这一想法背后的理论是，太阳风主要由质子(氢原子的原子核)构成，不断地将质子元素沉积到风化层中。其中一些氢会与作为月球矿物的一部分的氧原子发生反应。这导致了羟基自由基的产生。当一颗微陨石撞击月球时，其影响蒸发了风化层。所有物质都被提升到太空中，在那里，羟基结合形成水分子。这些分子随后被封装在迅速冷却的风化层中，这些风化层回落到表面。

词汇

nuclei /核心，核子

Vaporis/汽化，蒸发

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.

从这些珠子中提取水分并非易事。一个更有希望的来源是冰被认为存在于寒冷的陷阱中。Hayne博士的团队利用美国宇航局月球勘测轨道飞行器的高分辨率图像来识别月球表面所有潜在的寒冷陷阱。它们的数量比预期的要多，大小从几公里到几厘米不等。正如预期的那样，大部分陷阱被发现在两极附近，在那里，太阳在可见的时候，仍然在地平线附近，因此阴影很长。但也有一小部分存在于低纬度地区，这是由陨石坑或其他表面变化造成的，这些变化可能很小，但却在温度低到足以积冰的地方保留了阴影。

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，仅仅因为寒冷的陷阱存在，并不意味着它们捕获了任何东西。要想知道它们是否存在，以及回答Honniball博士的工作遗留下来的问题，需要对风化层本身进行进一步的检查。美国宇航局希望在2023年11月发射一项名为“毒蛇（缩写是VIPER，该词又有‘毒蛇’的意思）”(挥发性极地探测探测器)的任务到月球的南极。这艘飞船将配备用于探测着陆区域矿物和冰的仪器。

 

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，无论是Honniball博士还是Hayne博士的研究结果，都给了计划制定者一些值得思考的东西——不仅仅是那些参与了NASA的 Artemis项目的人，该项目旨在在这十年的某个时间将人类送上月球。决定在哪里建立基地，如果一个基地已经建成，一直是一个平衡之间的水和燃料的可用性，以及太阳能的可用性。为了提供水，在南极这样做的想法，代价是宇航员必须在漆黑的环境中工作和生活，那里的温度很少超过零下160摄氏度。倘若在月球表面光照较好且不那么恶劣的地方也有水，这将是一个受欢迎的前景。