Clara Sousa-Silva: The fingerprints of life beyond Earth | TED

翻译人员: George Sze 校对人员: Alvin Lee

It's my job to find aliens, so as you might guess,

我的工作是寻找外星人， 所以你们大概会猜想，

I spent a lot of time thinking about them,

我花了很多时间来思考他们，

imagining little green women

想象小小的绿色的女外星人

meeting up with their friends, commuting to work.

跟朋友见面，通勤上下班。

And that gets me thinking about alien astronomers

这让我联想到外星的天文学家，

trying to find us in their night sky.

他们可能也正在仰望夜空，寻找我们。

If these alien astronomers had looked in our direction

如果这些外星天文学家 在上个世纪望向我们，

in the last century,

they would have been really excited to detect unequivocal signs of technology.

他们会为发现明确的 科技迹象而兴奋不已。

But what if they looked ten thousand years ago,

但如果他们是在一万年前发现地球，

before we showed signs of civilization?

而彼时尚未出现文明的迹象呢？

Would they shrug in disappointment and go look elsewhere for life?

他们会失望地耸耸肩， 再去别处寻找生命吗？

No, and neither should we.

答案是否定的， 我们也同样不应该这样做。

Instead, we can look for other signs of life.

与之相反， 我们可以寻找其他的生命迹象。

For example, if those alien astronomers had looked our way 10,000 years ago,

例如，如果那些外星天文学家 在一万年前看向地球，

they might notice that even without signs of civilization,

他们可能会注意到， 即使没有文明的迹象，

we still looked slightly unusual.

地球仍然有些不寻常之处。

For one, we have a thick and temperate atmosphere,

一方面， 地球有厚实而温和的大气层，

but more notably,

但更值得注意的是，

we have suspiciously large amounts of oxygen in the atmosphere.

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

对于我的外星同行来说， 这会是一个非常鼓舞人心的生命迹象，

because the composition of the Earth's atmosphere

因为像地球这样的大气组成

can only sustain itself through a biological cycle.

只能通过生物循环来自我维持。

So can we do the same to them?

那么对地外文明， 我们能不能也这样做？

I'm certainly trying.

我正是在努力这么做。

I am a quantum astrochemist,

我是一名量子天体化学家，

which means I study the quantum interactions

我研究的是 太空中分子与光的量子相互作用。

between molecules and light in space.

我们看不到这些分子， 甚至看不到它们所在的行星。

We can't see these molecules or even the planets they're on.

But when life from a star goes through an alien atmosphere,

但是当来自某个恒星系的生命 穿越外星大气层时，

each molecule within it leaves a unique fingerprint

其中的每个分子都会 在星光中留下一个独特的指纹，

in the starlight that I can see from here.

我在地球上就可以看到。

And I look for the fingerprints

我会寻找特定的分子指纹，

of molecules that could be associated with life,

它们可能与生命或生命迹象有关，

or biosignatures,

like complex pollutants or oxygen.

比如复杂的污染物或氧气。

在地球环境中， 氧气是一种完美的生命迹象，

In the context of Earth, oxygen is a wonderful biosignature,

但氧气并不难生成。

but oxygen is not that hard to make.

So, for example, if our sun had different levels of radiation

例如，如果我们的太阳 能产生多种等级的辐射，

or if our oceans were evaporating from a runaway greenhouse effect,

或者海洋因温室效应失控而蒸发，

then large amounts of oxygen could accumulate in our atmosphere

那么即便没有生物参与，

without biology,

大气中也可能有大量氧气，

and then oxygen would be a false positive for life.

这时的氧气就成了错误的生命迹象。

So maybe oxygen won't be the solution to finding life beyond Earth,

所以要想寻找地外生命， 氧气就大概不能作为判定依据，

but then what is?

那什么能作为依据呢？

Well, my specialty is to look for unusual molecules

我的专长是寻找那些特殊的分子， 它们的生命迹象误报率较低，

that have fewer false positives for life

because they're so difficult to make that they're rarely made spontaneously.

因为它们很难自然生成。

And my favorite of those unusual molecules is phosphine.

在这些特殊分子中， 我最喜欢的是磷化氢。

When I first started working on phosphine about a decade ago,

大约10年前， 我刚开始研究磷化氢的时候，

people had a hard time thinking of it as a biosignature at all.

人们根本不把它看作生命迹象。

Instead, it was known

相反，它是因为恶臭难闻而出名，

for being this horrific, foul-smelling molecule

that messes with life's ability to use oxygen,

而且它还能破坏生命使用氧气的能力，

making it a really effective killer.

这一点让它成为了高效的杀手。

Because of this fatal interaction with oxygen metabolism,

由于它对氧气代谢的致命影响，

phosphine is used widely as a pesticide

磷化氢被广泛用作杀虫剂，

and sadly for the same reason it was used many times in chemical warfare.

可悲的是， 它也多次被用在化学战中。

Phosphine can be made in the lab,

磷化氢可以在实验室中制造，

也能在气态巨行星的极端环境中产生，

and it's also produced in the extreme environments

found inside gas giants like Jupiter and Saturn.

比如木星和土星。

But on rocky planets like the Earth, it is rarely created accidentally.

但在地球这样的固体行星上， 它很少会自然产生。

所以我们对在地球上 找到磷化氢根本不抱希望。

So we don't really expect to find phosphine on Earth at all.

And yet we do.

然而我们找到了。

We find it in small amounts throughout the globe,

我们发现地球上的磷化氢总量很少，

and in some places in strangely large quantities,

然而在某些地方含量却出奇的高，

places like swamps and rice fields and lake beds

比如沼泽、稻田、湖床，

and the excrements and guts of most animals.

大多数动物的排泄物和内脏中 也有它们的身影。

And what all of these ecosystems have in common

这些生态系统的共同点是

is that they all host organisms that are not reliant on oxygen,

都生活着不依赖氧气的生物，

so phosphine can't hurt them.

因此磷化氢伤害不了它们。

Indeed, phosphine seems to be safely and enthusiastically produced

事实上，在所有这样的贫氧生态系统中， 磷化氢似乎都能安全、高效地产生。

in all of these oxygen-poor ecosystems.

So I figured, maybe other planets with life less reliant on oxygen than ours

所以我想，也许其他星球的生命 不像我们一样这么依赖氧气，

could also have phosphine, but as a really popular biosignature.

那里就可能有磷化氢， 磷化氢就可以作为一种普遍的生命迹象了。

And here's the best thing about phosphine.

磷化氢最好的特点就在于，

Because it's so hard to make on rocky planets like the Earth,

在像地球这样的固体行星上 很难天然产生，

it has almost no false positives for life.

因此它的生命误报率极低。

So I started considering what telescopes we would need

所以我开始考虑 要用什么样的望远镜

to detect phosphine on planets in our galactic neighborhood.

来探测我们银河系附近 行星上的磷化氢。

Because if we did, I predicted it could only mean life.

因为如果我们探测到了， 我觉得那就意味着生命。

I was imagining a distant planet,

我想象在一个遥远的星球，

a oxygen-poor tropical paradise

一个贫氧的热带天堂，

with a phosphine-rich biosphere that we might one day be able to detect.

有一个富含磷化氢的生物圈， 将来的某天我们能探测到它。

But turns out phosphine was a little more exciting

但事实证明磷化氢 比我最初设想的更令人兴奋，

than I had initially envisaged

because a few months after I finished this work

因为在我完成这项工作几个月后，

an astronomer, Jane Greaves, reached out to me

天文学家简·格里夫斯联系到我，

asking for help with interpreting a telescope signal seen here in white.

想要我帮忙解释 这里用白色标注的望远镜信号。

Then months later, another signal, seen here in orange,

几个月后，另一个信号， 用橙色标注的，

that seemed to indicate that phosphine might be present not on a distant planet,

似乎表明磷化氢可能 并不在遥远的行星上，

but right next door, on the clouds of Venus.

而就在我们的近邻，金星的云层里。

所以我们成功了吗？

So did we do it?

Did we find life beyond Earth? We don't know.

我们发现地外生物了吗？ 我们不知道。

这些金星观测数据初步而杂乱，

These Venus observations were noisy and preliminary,

so we still need to confirm, without a doubt,

所以我们仍然需要进一步确认

that the signal is real,

该信号是否真实无误，

and if it is, we need to make sure

如果确实是真的，我们还要进一步

it's not another molecule mimicking phosphine's fingerprint.

排除其他类磷化氢分子的可能性。

And if it is unambiguously phosphine,

如果明确是磷化氢，

we still need to figure out what or who is making it,

我们还需要弄清楚 是什么或谁在产生它，

因为也许生命真的是最好的解释，

because maybe it's true

that life is the best explanation for the presence of phosphine

为什么磷化氢会在金星上存在，

on a planet like Venus.

但那也可能是错的，

But maybe that's wrong

and there's an exotic but not biological way of making phosphine

可能存在一种奇特的、 非生物学的方法能产生磷化氢，

that no one has thought of yet.

目前还不为人所知。

Either way, as much as I love phosphine,

不管怎样， 尽管我很喜欢磷化氢，

I don't think that's how we'll find life.

但我不认为能凭它找到生命。

The detection of life will likely not come from a single molecule.

生命的发现很可能不会源自单个分子。

No matter how special it is.

无论这个分子有多特殊。

We'll have to detect a whole biosphere producing a complex network of gases

我们必须探测整个生物圈， 它会产生一个复杂的气体网络，

that together form a message that reads: “We’re alive!”

共同发出一条信息：“我们是活的！”

As the Venus story shows,

正如金星的故事所示，

the detection of life will likely be uncertain,

生命的探测有很大不确定性，

but Venus is the perfect lab for us to test our theories of biospheres

但金星是一个完美的实验室， 来检验和解释我们的生物圈理论。

and how to interpret them.

If we learn to understand the atmosphere of Venus

如果我们能设法搞明白 金星的大气层及其包含的信息，

and the message it contains,

then we can find out if we got it right by going there and checking.

然后就可以通过实地检测来检验。

And we'll do that at the end of the decade.

我们将在十年内实现这一点。

但这不会是我们最后一次

But this will not be the last time

that we have the discovery of a biosignature

在潜在宜居星球上发现生命特征，

on a potentially habitable planet,

and next time we won't be able to just go there and check.

而下次很可能无法进行实地检测。

So my biggest concern

所以我最担心的

is not that we will fail to find a habitable planet in our lifetimes.

不是在有生之年找不到宜居星球。

My biggest concern is that we'll point our very expensive telescopes

而是我们将极其昂贵的望远镜

directly at an inhabited planet

径直对准了有生命的行星，

但却对此浑然不知。

and just not know we did it.

But I am determined to not miss life.

但我决意避免错过这些生命。

So, yes, I will look for the unambiguous but quite unlikely signs of technology

所以，我会寻找指标明确， 却不太能证明技术发展迹象的东西，

like complex pollutants.

比如复杂的污染物。

And I'll look for the pleasant and familiar

我也会寻找喜闻乐见的、熟悉的

but potentially misleading signs of life, like oxygen.

但很可能会有误导性的 生命迹象，比如氧气。

And of course, I'll keep looking

当然，我也会继续寻找

for the strange and scary biosignatures like phosphine.

像磷化氢这样 奇怪又有点骇人的生命特征。

But crucially, I will look for all the molecules

但至关重要的是， 我会寻找所有的特定分子，

that can together paint a holistic picture of a biosphere.

它们能共同描绘 某个生物圈的整体图景。

所有这一切，只为某天 我们看到了生命，不至于浑然不觉。

All of this so that one day we'll know life when we see it.

Thank you.

谢谢大家。