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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.
我的工作是寻找外星人，所以你可能猜到了，我花了很多时间思考有关外星人的事，想象外星人和她们的朋友聚会、上班。
And that gets me thinking about alien astronomers trying to find us in their night sky.
外星的天文学家也想在他们的夜空中找到我们。
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.
如果这些外星天文学家开始从上个世纪寻找我们，他们会发现明确的科技迹象，同时会非常兴奋。
But what if they looked ten thousand years ago, before we showed signs of civilization?
但如果他们是一万年前开始寻找我们的呢，那时候我们还没有文明的迹象呢。
Would they shrug in disappointment and go look elsewhere for life?
他们会不会失望地耸耸肩，换一个找寻的目标呢?
No, and neither should we. Instead, we can look for other signs of life.
他们不会失望的，我们也不应失望。相反，我们可以寻找其他生命迹象。
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.
例如，如果那些外星天文学家在1万年前观察过我们，他们可能会注意到，即使没有文明的迹象，我们看起来仍然有自己的特色。
For one, we have a thick and temperate atmosphere, but more notably, we have suspiciously large amounts of oxygen in the atmosphere.
首先，我们有一个厚而温和的大气层，但更值得注意的是，我们的大气中有大量的氧气。
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.
对于我的外星同事来说，这将是一个鼓舞人心的生命迹象，因为地球大气层的构成只有通过生物循环才能维持下去。
So can we do the same to them? I'm certainly trying.
那我们能对他们做同样的事吗?这就是我在尝试的事情。
I am a quantum astrochemist, which means I study the quantum interactions between molecules and light in space.
我是一名量子天体化学家，我研究的是空间中分子与光之间的量子相互作用。
We can't see these molecules or even the planets they're on.
我们看不到这些分子，甚至看不到它们所在的行星。
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.
但当恒星上的生命穿过外星大气层时，其中的每个分子都会在星光下留下独特的图谱，我从地球上就能观察到它们。
And I look for the fingerprints of molecules that could be associated with life, or biosignatures, like complex pollutants or oxygen.
我寻找可能与生命有关的分子指纹，或生物特征，比如复杂的污染物或氧气。
In the context of Earth, oxygen is a wonderful biosignature, but oxygen is not that hard to make.
在地球上，氧气是一种奇妙的生物特征，但制造氧气并不难。
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.
例如，如果我们的太阳有不同程度的辐射，或者如果我们的海洋因为失控的温室效应而蒸发，那么大量的氧气就会在没有生物的情况下积聚在我们的大气中，氧气就会成为生命存活着的假信号。
So maybe oxygen won't be the solution to finding life beyond Earth, but then what is?
也许氧气不是寻找地球外生命的解决方案，但那什么是呢?
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.
我的专长是寻找对生命有较少假阳性反应的不寻常分子，因为它们很难制造，它们很少是自发产生的。
And my favorite of those unusual molecules is phosphine.
这些不寻常的分子中我最喜欢的是磷化氢。
When I first started working on phosphine about a decade ago, people had a hard time thinking of it as a biosignature at all.
大约十年前，当我第一次开始研究磷化氢时，人们很难把它看作是一种生物特征。
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.
相反，它以可怕的、恶臭的分子而闻名，它扰乱了生命使用氧气的能力，使它成为真正有效的杀手。
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.
由于这种与氧代谢的致命相互作用，磷化氢被广泛用作杀虫剂，可悲的是，出于同样的原因，它在化学战中被多次使用。
Phosphine can be made in the lab, and it's also produced in the extreme environments found inside gas giants like Jupiter and Saturn.
磷化氢可以在实验室中制造，也可以在木星和土星等气体巨星内部的极端环境中产生。
But on rocky planets like the Earth, it is rarely created accidentally.
但在像地球这样的岩石行星上，它很少是偶然产生的。
So we don't really expect to find phosphine on Earth at all. And yet we do.
所以我们并不指望在地球上找到磷化氢。 然而，我们确实这样做了。
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.
在全球范围内，我们发现它的数量很少，而在一些地方，它的数量出奇地多，比如沼泽、稻田、湖床以及大多数动物的粪便和内脏。
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.
所有这些生态系统的共同之处在于它们都有不依赖氧气的生物，所以磷化氢对它们造成伤害。
Indeed, phosphine seems to be safely and enthusiastically produced in all of these oxygen-poor ecosystems.
事实上，在所有这些缺氧的生态系统中，磷化氢似乎都能安全而大量产生。
