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Science and technology.科技。

本文摘要:Science and technology.科技。


Science and technology.科技。The search for alien life找寻外星生物Twinkle, twinkle, little planet闪光吧,小行星An undervalued optical trick may help to find life in other solar systems一个不被人推崇的光学方法有可能能协助找寻其他太阳系的生命MOST astronomical telescopes employ reflection to focus starlight. A concave mirror creates an image from this light using a design pioneered in the 17th century, by Sir Isaac Newton. Those telescopes that do not employ reflection use refraction. They have a system of lenses, an idea first used to look at the stars by Galileo.大部分天文望远镜都是运用的焦点星光的反射原理。早在17世纪,艾萨克.牛顿就开创性的利用这个光,让凹透镜产生了一个图像。

那些不利用光线的望远镜利用的是反射。他们有透镜系统。利用透镜系统的点子最先是伽利略用来观测星星的。But there is a third way to focus light. A century and a half after Newton, and more than two after Galileo, a Frenchman called Augustin-Jean Fresnel worked out that you can do it using diffraction. A set of concentric rings, alternately transparent and opaque, will scatter and spread light waves in a manner that causes them to reinforce each other some distance away, and thus form an image. The rings are known as a zone plate. And Fresnels countryman, Laurent Koechlin, of the Midi-Pyrenees observatory, thinks zone plates are the way to find out if there is life on other planets.但还不存在第三种探讨光源的方法。


这些的环被称作波带片。法国南比利牛斯天文台劳伦.凯什兰指出波带片可以用来找寻其他星球上否不存在生命。Seeing oxygen in another planets atmosphere would be a giveaway of biological activity because the gas is so reactive that it needs to be continuously renewed. That would almost certainly mean something akin to photosynthesis was going on, for no known non-biological process can produce oxygen from common materials in sufficient quantity. Looking at such an atmosphere, though, is tricky. Stars are so much brighter than the planets which orbit them that their light overwhelms the small amount reflected from a planets surface. And this is where Fresnel comes in.在其他星球的大气层找到氧气则指出这个星球上有生物活动,因为氧气是一种十分活跃的气体,所以他必须不时的改版。



Fresnel telescopes have not been developed in the past because the image formed by one that was large enough to rival a useful-sized reflecting telescope would be several kilometres from the zone plate. But Dr Koechlin does not worry about that, because his Fresnel telescope will be in space. Free of the confounding effects of the Earths own atmosphere, it will be able to isolate images of alien planets, make spectra of the light from their air, and examine those spectra for the characteristic dark lines that are caused by part of the light being absorbed by particular gases-oxygen among them.过去,菲涅尔设计的望远镜还生产不出来,因为要想要使散射望远镜的大小和长时间用于的光线望远镜大小完全相同,它所产生的图像就不会距离波带片数千米近。然而,凯什兰博士并不为此担忧,因为他的菲涅尔望远镜将不会在太空中。

瓦解了地球大气层的误解效应,望远镜将需要分离出来外星生物的图像,在他们的大气中制作出来光谱,并且为这些有特点的暗线检查光谱。这些暗线部分是由类似气体——大气中的氧气——所吸取的光产生的。Plate tectonics行星结构地质学Space telescopes are nothing new, of course, and several more are in the works (see article). But existing plans to photograph extrasolar planets in this way involve orbiting arrays of reflecting telescopes all pointing in exactly the same direction. An array is needed because a single mirror big enough to do the job of separating star from planet would be too large to launch. The problem is the word exactly. It means just that. The formation would have to fly with a precision of a few billionths of a metre.当然,太空望远镜并不是什么新事物,并且早已有几个早已在用于中了(闻文章)。


而问题就出有在精准上。它就如字面意思一样,要精准到十亿分之一米。Using a zone plate instead of a mirror gets around this. Because the plate is flat, it can be made of plastic and folded up for launch. Size thus ceases to be an issue. And although a second satellite containing the eyepiece (a special lens that also uses Fresnel optics, and a camera to record the image) must fly at the focus, the accuracy required is only hundredths of a metre, not billionths. That, Dr Koechlin reckons, gives Fresnel optics a big advantage over Newtonian ones.用波带片替换镜面在轨道运营。



To test the idea, he and an international consortium of his colleagues have built a ground-based prototype. This is a piece of copper foil 20cm square that has 696 rings, a portion of which is reproduced above. Because it is this small, its focal length is only 18 metres. In order that the foil does not fall apart, each transparent ring is actually a series of curved slots in the copper rather than a continuous gap. This, though, does not affect the systems optical properties and it can, indeed, see small, faint objects that are near large, bright ones.为了检测这一点子,他和他各国的同事创建了一个陆基的雏形。这是一片20平方厘米的铜箔,它有696个环。铜箔的一部分是再造的。

因为它体积稍小,所以它的探讨只有18米。为了不想铜箔前行,每一个半透明的环实质上都是铜箔里的一系列的曲线轮槽,而不是倒数的空隙。尽管如此,这并不影响整个系统的视觉特性,并且,它也显然需要看到极大且暗淡的恒星旁边那些小型且黯淡的物体。When Dr Koechlin and his team pointed it at Mars they could distinguish that planets two tiny moons-a task which would require a Newtonian telescope with a mirror at least 30cm across. And when they aimed at Sirius they could see the dim white-dwarf which orbits what is the brightest star in the night sky. Extrapolating from these results, they think that an orbiting zone plate measuring somewhere between 15 metres and 40 metres across will be enough to distinguish the spectrum of an Earthlike planet at a distance of 30 light-years. With that, they should be able to find out if mankind really does have any next-door neighbours, and Fresnel will have come into his own at last.当凯什兰博士和他的团队观测火星时,他们可以辨别火星的两个微小卫星——这样的任务如果是利用牛顿的望远镜则必须一个直径最多长达30厘米的镜面。





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