双语阅读地球外有生命存在吗一起来找证据

　　地球外有没有生命存在？如果有，我们要通过什么来判断？本次的演讲者是哈佛大学和史密森学会天体物理中心量子天体化学家克拉拉·苏萨-席尔瓦（Clara Sousa-Silva），主要研究能被远程探测到的分子与光的相互作用。我们一起来看看是什么样的发现令她如此兴奋。
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　　The Fingerprints of Life Beyond Earth
　　地球外生命存在的印迹
　　It’s my job to find aliens, so as you might guess, I spent a lot of time thinking about them, imagining little green women meeting up with their friends, commuting to work. And that gets me thinking about alien astronomers trying to find us in their night sky.
　　我的工作是寻找外星人。如你们所想，我花了很多时间琢磨他们，想象小小的绿皮肤女性和朋友们聚会，通勤上班。这也让我想到，外星的天文学家们是不是也尝试在他们的夜空中寻找我们。
　　If these alien astronomers had looked in our direction in the last century, they would have been really excited to detect unequivocal signs of technology. But what if they looked 10,000 years ago, before we showed signs of civilization? Would they shrug in disappointment and go look elsewhere for life?
　　如果外星的这些天文学家曾在上世纪看向地球，他们可能会为探测到明确的科技迹象而兴奋不已。但如果他们是在一万年前，在我们还没有任何文明迹象的时候看向地球的呢？他们会失望地耸耸肩，然后去别的地方寻找生命吗？
　　No, and neither should we. Instead, we can look for other signs of life. For example, if those alien astronomers had looked our way 10,000 years ago, they might notice that even without signs of civilization, we still looked slightly unusual. For one, we have a thick and temperate atmosphere.
　　不会的，我们也不会。相反，我们会寻找其他的生命迹象。比如，假设外星天文学家们早在一万年前就看向地球，他们也许会注意到，尽管没有任何文明的迹象，这里看起来仍然有点儿不同寻常。其一，这里有很厚的大气层和温和的气候。
　　But more notably, we have suspiciously large amounts of oxygen in the atmosphere. This would be a really encouraging sign of life for my alien colleagues because the composition of the Earth’s atmosphere can only sustain itself through a biological cycle. So can we do the same to them? I’m certainly trying.
　　但更值得注意的是，大气中氧气的含量高得出奇。而地球大气的构成只能通过生物循环来维持，这对我的外星同行们来说无疑是个非常鼓舞人心的生命迹象。那么，我们能对他们做同样的探测吗？我正在努力尝试。
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　　I am a quantum Astro-chemist, which means I study the quantum interactions between molecules and light in space. We can’t see these molecules or even the planets they’re on. But when life from a star goes through an alien atmosphere, each molecule within it leaves a unique fingerprint in the starlight that I can see from here.
　　我是一名量子天文化学家，主要研究太空中分子与光的相互作用。我们无法看到这些分子，也看不到它们所在的星球。但当某个恒星的生命穿过外星大气时，它的每一个分子都会在星光中留下独特的痕迹，这些痕迹我从这里就能够看到。
　　And I look for the fingerprints of molecules that could be associated with life, or biosignatures, like complex pollutants or oxygen. In the context of Earth, oxygen is a wonderful biosignature, but oxygen is not that hard to make.
　　我寻找的是与生命相关的分子痕迹，或是结构复杂的污染物和氧气这样的生物印记。在地球，氧气是不错的生物印记，但是它并不难产生。
　　So, for example, if our sun had different levels of radiation or if our oceans were evaporating from a runaway greenhouse effect, then large amounts of oxygen could accumulate in our atmosphere without biology, and then oxygen would be a false positive for life.
　　举例来说，如果太阳的辐射值发生变化或者温室效应失控导致海水蒸发，即使没有生物也会有大量的氧气在大气中聚集，那样的话，氧气就无法证明这里有生命存在了。
　　So maybe oxygen won’t be the solution to finding life beyond Earth, but then what is? Well, my specialty is to look for unusual molecules that have fewer false positives for life because they’re so difficult to make that they’re rarely made spontaneously.
　　所以，探测氧气或许并不是判断地球外是否有生命的有效途径。那什么才是呢？我的专长是寻找那些不寻常的分子，它们很难产生，更无法自发产生，足以证明生命存在。
　　And my favorite of those unusual molecules is phosphine. When I first started working on phosphine about a decade ago, people had a hard time thinking of it as a biosignature at all. Instead, it was known for being this horrific, foul-smelling molecule that messes with life’s ability to use oxygen, making it a really effective killer.
　　这些不寻常的分子中，我最喜欢的就是膦。我对膦的研究大约开始于十年前，那时人们并不视其为生物标记。相反，膦是一种有毒分子，气味难闻，会扰乱生物利用氧气的能力，最终导致死亡。
　　Because of this fatal interaction with oxygen metabolism, phosphine is used widely as a pesticide and sadly for the same reason it was used many times in chemical warfare. Phosphine can be made in the lab, and it’s also produced in the extreme environments found inside gas giants like Jupiter and Saturn.
　　由于与氧代谢的致命反应，膦被广泛用作杀虫剂。可悲的是，也正因如此，化学武器中也常见到膦的身影。人们可以在实验室中合成膦，像木星、土星这些气态巨星的极端环境里也能产生膦。
　　But on rocky planets like the Earth, it is rarely created accidentally. So we don’t really expect to find phosphine on Earth at all. And yet we do. We find it in small amounts throughout the globe, and in some places in strangely large quantities, places like swamps and rice fields and lake beds and the excrements and guts of most animals.
　　但像地球这样的岩态行星很难自发产生膦，所以我们并没想过能在地球上找到膦。但是，我们发现，膦在全球范围内分布较少，可在一些地方，比如沼泽地、稻田和湖床，还有大多数动物的排泄物和内脏里，膦的含量惊人。
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　　And what all of these ecosystems have in common is that they all host organisms that are not reliant on oxygen, so phosphine can’t hurt them. Indeed, phosphine seems to be safely and enthusiastically produced in all of these oxygen-poor ecosystems.
　　这些生态系统的共同点是都含有不依赖氧气的生物，而膦不能伤害它们分毫。事实上，这些氧气稀薄的生态环境似乎在安稳且源源不断地产生着膦。
　　So I figured, maybe other planets with life less reliant on oxygen than ours could also have phosphine, but as a really popular biosignature. And here’s the best thing about phosphine. Because it’s so hard to make on rocky planets like the Earth, it has almost no false positives for life.
　　所以我想，也许有的生命并不像我们那么依赖氧气，这样的星球上可能会有膦，而且膦是一种普遍的生物印记。用膦探测生命，最好的一点在于，它在地球这种岩态行星上很难产生，所以几乎不会出现误报。
　　So I started considering what telescopes we would need to detect phosphine on planets in our galactic neighborhood. Because if we did, I predicted it could only mean life. I was imagining a distant planet, a oxygen-poor tropical paradise with a phosphine-rich biosphere that we might one day be able to detect.
　　于是我开始思考什么样的望远镜才能观测到银河系附近行星上的膦。因为一旦观测到，那将意味着有生命存在。我想象着有朝一日会发现某个遥远的星球，那里有富含膦的生物圈，是一个氧气稀薄的热带天堂。
　　But turns out phosphine was a little more exciting than I had initially envisaged because a few months after I finished this work an astronomer, Jane Greaves, reached out to me asking for help with interpreting a telescope signal seen here in white. Then months later, another signal, seen here in orange, that seemed to indicate that phosphine might be present not on a distant planet, but right next door, on the clouds of Venus.
　　对膦的观测结果比我最初的预设更令人兴奋，就在我结束这项工作几个月后，天文学家简·格里夫斯找到了我，请我协助解读望远镜看到的信号，这里用白色显示。过了几个月，又有了另一个信号，这里用橙色显示，这似乎意味着膦可能就出现在离我们不远的星球，就在我们的邻居——金星的云层上。
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　　So did we do it? Did we find life beyond Earth? We don’t know. These Venus observations were noisy and preliminary, so we still need to confirm, without a doubt, that the signal is real, and if it is, we need to make sure it’s not another molecule mimicking phosphine’s fingerprint.
　　那么，我们成功了吗？我们在地球之外找到生命了吗？我们并不确定。这些只是对金星的初步观察，很可能存在干扰，所以仍然需要确认。但毋庸置疑的是，信号是真实的，如果是这样，我们需要确认不是其他分子在模仿膦的痕迹。
　　And if it is unambiguously phosphine, we still need to figure out what or who is making it, because maybe it’s true that life is the best explanation for the presence of phosphine on a planet like Venus. But maybe that’s wrong and there’s an exotic but not biological way of making phosphine that no one has thought of yet.
　　如果这确实是膦的痕迹，我们还得弄清楚是什么或者是谁制造出的膦。也许膦出现在金星这样的星球上的最好解释就是，这些星球上有生命存在。但也许并非如此，也许膦还有一种不寻常的非生物产生途径，只是人们未曾想到。
　　Either way, as much as I love phosphine, I don’t think that’s how we’ll find life. The detection of life will likely not come from a single molecule. No matter how special it is. We’ll have to detect a whole biosphere producing a complex network of gases that together form a message that reads: ＂We’re alive!＂
　　无论如何，不管我多么喜欢膦，我都不认为这是发现外星生命的方式。探测生命不太可能仅凭一种分子，无论它有多特殊。我们必须探测整个生物圈产生的复杂气体网络，它们整体生成了一个信息：我们是活着的！
　　As the Venus story shows, the detection of life will likely be uncertain, but Venus is the perfect lab for us to test our theories of biospheres and how to interpret them. If we learn to understand the atmosphere of Venus and the message it contains, then we can find out if we got it right by going there and checking. And we’ll do that at the end of the decade.
　　金星的故事告诉我们，对生命迹象的探测可能是不确定的，但我们可以利用金星这个完美的实验室，来验证并解释关于生物圈的理论。如果我们掌握并理解了金星的大气层和其中蕴含的信息，那么之后，我们就可以去实地勘察我们的判断是否正确，这也是我们将在十年后做的事情。
　　But this will not be the last time that we have the discovery of a biosignature on a potentially habitable planet, and next time we won’t be able to just go there and check. So my biggest concern is not that we will fail to find a habitable planet in our lifetimes. My biggest concern is that we’ll point our very expensive telescopes directly at an inhabited planet and just not know we did it.
　　这绝不会是我们最后一次在潜在的宜居星球发现生物印记，下次我们也不能只是去实地勘察。所以我最担心的不是在有生之年找不到宜居星球，而是我们用造价不菲的望远镜对准了一颗星球，却浑然不知它就是我们要找的宜居星球。
　　But I am determined to not miss life. So, yes, I will look for the unambiguous but quite unlikely signs of technology like complex pollutants. And I’ll look for the pleasant and familiar but potentially misleading signs of life, like oxygen. And of course, I’ll keep looking for the strange and scary biosignatures like phosphine.
　　但我决不会错过任何可能的生命。所以，没错，我会继续寻找明确但不太可能找到的技术信号，比如，结构复杂的污染物；我会继续寻找让人愉快又熟悉、但可能误导人们的生物信号，比如氧气。当然，我还会一直寻找像膦一样奇怪又可怕的生物印记。
　　But crucially, I will look for all the molecules that can together paint a holistic picture of a biosphere. All of this so that one day we’ll know life when we see it.
　　此外至关重要的是，我会寻找所有能够共同描绘出生物圈整体风貌的分子，而这一切都是为了有一天我们一看就知道，这就是生命。
　　Thank you.
　　谢谢。