(单词翻译:单击)
This episode is brought to you by Squarespace.
本期节目是由“Squarespace”为您带来的。
A decade or so ago, the title of this video would have sounded ridiculous.
这个视频的标题在大约10年前可能听起来很滑稽。
The first planet outside of our solar system was only confirmed in 1992.
第一颗太阳系外行星是在1992年确定的。
And when I was in high school and college, we'd only found a handful of exoplanets.
我在高中和大学的时候，我们只发现了几颗太阳系外行星。
For all we knew, stars with planets around them were super rare.
据我们所知，周围有行星的恒星非常罕见。
But now, it seems everywhere we look, planets litter star systems.
但现在，我们似乎到处都能看到这种恒星，星系中到处都是行星。
And, indeed, it seems increasingly likely that almost 100% of stars have planets around them.
确实，几乎所有的恒星都有行星围着它们，这种可能性越来越大。
It's taken a while to get a good idea of how common it is for a star to have planets around it, because we just didn't have enough data.
我们花了很长时间才了解到有行星围绕的恒星是多么普遍，因为之前我们没有足够的数据。
For a long time, we mainly detected exoplanets using the radial velocity method,
很长一段时间，我们主要用径向速度法来探测系外行星，原理是：
where the gravitational pull from a planet orbiting a star makes the star wobble slightly,
一颗围绕恒星运转的行星引力会使恒星微微摆动，
which changes the wavelength of the light we detect from Earth.
从而改变我们从地球上探测到的光波长度。
So far, we've detected more than 600 exoplanets this way.
到目前为止，我们用这种方法已经探测到600多颗系外行星。
Problem is, most of the planets we can detect using the radial velocity method are hot Jupiters:
但有一个问题，我们用径向速度法探测到的大多数行星都是“热木星”，
giant planets orbiting very close to their stars.
“热木星”是巨大的行星，围绕它们的恒星超近距离运行。
Since they're so big and orbit so close, they cause bigger, shorter wobbles that are easier for us to detect.
由于它们体积巨大，轨道又近，摆动幅度大、速度快，更容易被探测到。
The other issue is that the radial velocity method doesn't really work for stars farther than about a hundred light-years from Earth.
另一个问题是，径向速度法对远离地球一百多光年的恒星不起作用。
Beyond that, it's just too hard to see the wobbles.
超过这个距离，我们很难看到摆动。
They don't have enough of an effect on the wavelength of the light we detect.
它们对我们探测到的光波长度没有太大影响。
So the radial velocity method doesn't tell you much about how common planets are that aren't hot Jupiters, or about stars farther away from Earth.
所以，径向速度法只能测“热木星”，但其他种类的行星更为常见，它也无法测离地球远的恒星状况。
Which is why the transit method has been so useful.
这就是凌日变光观测法有用的原因。
A transit is when a planet's orbit takes it between its parent star and Earth.
当一颗行星运行到它的母星和地球之间时就会发生变化。
As it passes in front of its star, the light we detect from the star dims a little.
当它在恒星前面经过时，我们从恒星上探测到的光会变暗一点儿。
The Kepler space telescope looks for exoplanets using the transit method.
开普勒太空望远镜用凌日变光观测法寻找系外行星。
Since it launched in 2009, it's found more than 2,000 confirmed exoplanets.
自2009年发射以来，它发现了2000多颗确认的系外行星。
It's still harder to spot smaller planets with the transit method, but at least it's easier than using the radial velocity method.
通过凌日变光观测法发现较小的行星仍然很困难，但至少比径向速度法简单多了。
And the transit method works for planets that are much farther away,
而且凌日变光观测法适用于更远的行星，
because even if it's too far for us to see the effects of the star's wobble,
因为即使距离太远，我们无法看到恒星摆动的影响，
the planet will still have a measurable dimming effect.
但行星仍然会有一个可测量的变暗效应。
We've used the transit method to find plenty of planets hundreds of light-years from Earth.
我们用凌日变光观测法已经发现了很多颗距地球数百光年以外的行星。
So the transit method is a pretty successful way to find exoplanets, but it still has its limitations.
所以凌日变光观测法是发现系外行星非常成功的的方法，但它仍有局限性。
Mainly, if a planet doesn't pass between its star and Earth, you're not gonna detect it.
主要一个就是如果行星不在恒星和地球中间经过，你就无法探测到它。
For example, astronomers were able to find that system of 7 Earth-sized planets around the star TRAPPIST-1 using the transit method
比如，天文学家们利用凌日变光观测法发现了一个星系，有7颗地球大小的行星环绕着恒星TRAPPIST-1，
because the planets have relatively close orbits that just so happen to take them between their parent star and Earth.
因为行星的轨道相对较近，所以它们恰好在母星和地球之间的轨道上运行。
But if they weren't lined up so perfectly, we never would have detected them.
但如果它们的排序不是那么完美的话，我们就无法探测到它们。
Now we've found so many exoplanets using the transit method that it's pretty clear that planets around other stars are really common,
现在我们使用凌日变光观测法已经发现了许多系外行星，很明显，其他恒星周围有行星很常见。
at least within a few thousand light-years of Earth.
至少距地球几千光年的范围内是这样。
When it comes to finding planets that around stars that are really far away, like, tens of thousands of light-years,
在寻找非常遥远的围绕恒星运行的行星时，如成百上千光年远，
our best bet is to use gravitational microlensing.
我们最好的方法是使用引力微透镜。
That's where the gravity from a star with a planet orbiting it warps the light we detect from a second star behind it.
有行星围绕的恒星引力会扭曲我们从它背面探测到的第二颗恒星的光。
It doesn't let us see the planet, but it lets us know it's there.
它不会让我们看到行星，但能让我们知道它在哪儿。
So far, we've only been able to use microlensing to find a few dozen exoplanets,
到目前为止，我们用微透镜只找到了几十颗系外行星，
because the chances of two distant stars lining up in just the right way are incredibly low.
这是因为两颗遥远的恒星以正确方式排列的可能性非常低。
Still, it's the best method we have right now to find exoplanets far from Earth,
然而，它是我们目前发现远离地球的系外行星的最好方法。
and we might even be able to use it to find some outside of the Milky Way, in the nearby Andromeda galaxy.
我们甚至可以用它来发现银河系之外、仙女座星系附近的一些东西。
With so many limitations to our exoplanet-detection methods, we aren't going to see exoplanets around every star.
既然我们的系外行星检测方法有这么多的局限性，我们就不会在每颗恒星周围发现系外行星。
But it seems like practically every star could have them.
但似乎每颗恒星都有行星。
We used to think there were some exceptions.
我们曾考虑过例外。
For example, astronomers once thought that binary star systems weren't gravitationally stable enough for planets to form and survive.
比如，天文学家一度认为双子星系的引力不稳定，不足以支撑行星的形成和生存。
But then we found planets around binary stars.
但我们在双子星附近发现了行星。
Astronomers also used to think that blue giant stars, which are huge, hot, bright,
天文学家也曾认为蓝巨星非常巨大、炎热和明亮，
and don't stick around for very long, were too intense for planets to form around them.
对于行星来说不能太久逗留，因为活动剧烈而不能形成。
The matter the planets would form from would be blown apart before it could condense.
形成行星的物质在凝结之前就会被吹散。
But then we found protoplanetary disks, the disks of rock and gas and dust that planets form from, around blue giant stars.
但随后我们发现了原行星盘，它是由形成行星的岩石、气体和灰尘构成的，围着蓝巨星运转。
Whenever we think there's an environment where planets can't form, it turns out we're wrong.
无论什么时候我们认为一个环境不足以形成行星时，事实都会证明我们错了。
So, are there any stars out there without planets?
所以，存在没有行星的恒星吗？
I mean, probably. It's a big universe.
我想可能吧。宇宙这么大呢！
But based on all the exoplanets we've found in the last couple of decades,
但基于我们最近几十年发现的所有系外行星，
it seems like almost every single star could have planets, and probably does.
几乎每颗恒星都有行星，或许有可能。
Because of the limitations of the tools we have used thus far,
因为我们迄今使用工具的局限性，
and the relatively short time we've had access to those tools,
和相对较短时间内我们接触到的这些工具，
we don't yet have the most accurate picture of the average star system in the universe.
我们对宇宙中的普通星系还没有非常清晰的认识。
But it has become clear that planets are a natural feature of stellar formation,
但很明显，行星是恒星形成的自然特征，
they are common, they are everywhere, and they are just waiting to be discovered.
它们很普通、到处都是，只是等着被人发现。
Which is why you should subscribe to SciShow Space, because when they are discovered, we will let you know!
这就是为什么你要订阅太空科学秀了，因为它们一旦被发现，我们就会告诉你！
Also, you might have a thing that you're thinking about doing, maybe you're already doing it.
你可能有考虑要做的事，或许你已经做了。
Would it be better if it had a website?
那么有一个网站不是更好吗？
Well, this episode was made possible by Squarespace,
本期节目是由“Squarespace”制作的，
which is a company that makes it really quite easy to create a custom, professional, dynamic website that works on both mobile and desktop.
它是一个工厂，很容易就能建立一个专门、专业且随时更新的网站，在手机和电脑上都能使用。
I was once upon a time a web designer for a living,
我曾经是一个网络设计师，
and people would pay me thousands of dollars for websites that are much less cool than Squarespace's award winning templates.
人们会支付给我数千美元来制作网站，这些网站不比“Squarespace”的打赏区酷！
Whether you're an entrepreneur, a musician, an artist, designer, or a scientist,
不管你是企业家、音乐家、艺术家、设计师还是科学家，
a website from Squarespace can help you be taken seriously, get clients, and get hired.
来自“Squarespace”的网站可以帮助您认真对待，获得客户和工作。
Make your next move by visiting Squarespace.com, and use the code "SPACE" for 10% off your 1st order.
访问Squarespace.com，制定下一步行动，输入“SPACE”后，第一单给你打九折。
