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When we look at life on Earth, we see rich, diverse ecosystems powered by our host star, the Sun.
每次看着地球上的生命时，可以看到有丰富多样的生态系统是我们的恒星太阳提供的能量。
So, when we think about life elsewhere in the universe, we usually imagine something pretty similar:
所以，当我们思考宇宙其他地方的生命时，我们通常会想到非常相似的东西。
an Earth-like planet orbiting at an Earth-like distance from a Sun-like star.
一个像地球一样的行星在与地球和太阳相似的距离上环行。
But we now know that there are billions of planets in our galaxy that look nothing like this.
但我们现在知道，在太阳系中有数十亿颗行星长得跟地球一点儿都不像。
In fact, there are billions of rogue planets that aren't orbiting a star at all.
实际上，有很多颗行星四处飘荡，而且也不环绕任何恒星飞行。
It's thought they formed inside star systems like regular planets, but were then somehow ejected from their original orbit and flung into deep space.
我们认为他们是在恒星体系中形成的，就像一般的行星一样，但不知怎么地却从原来的轨道发射到深空中去了。
The sheer abundance of these planets has led some scientists to wonder if life could emerge without a star.
这些行星五花八门，这让一些科学家好奇生命是否可以在没有恒星的情况下产生。
And, though obviously we don't have conclusive evidence, there's actually good reason to think it could.
虽然我们现在还没有结论性的证据，但实际上有很好的理由可以认为答案是肯定。
It's hard to imagine anything thriving with no star because our sun is so vital to life on Earth.
很难想象在没有恒星的情况下如何生机活泼，因为太阳对地球而言就十分重要。
But it turns out that a star's light and heat might not be deal-breakers.
但最终我们发现，恒星的光和热可能不是交易人。
For instance, while the life we're most familiar with is powered by sunlight, there are plenty of living things that survive without it.
比如，虽然我们最熟悉的生命是由日光提供能量的，但有很多生物可以在没有日光的情况下存活。
In fact, for at least a little while, no life on Earth used sunlight as an energy source.
实际上，至少在有那么一段时间里，地球上没有任何生命是用日光作为能源的。
The molecular tools to perform photosynthesis arose after the first microbes.
在第一批微生物出现之后，分子才能进行光合作用。
And that's part of why multiple hypotheses on how life first emerged involve some pretty dark places.
有多个假设是关于最早出现的生命涉及到一些黑暗处的，而上面提到的这些就是部分原因。
Like, today, we know of a large number of microorganisms that live deep underground, where they survive off chemical reactions in the surrounding rocks.
比如，今天，我们都知道有很多微生物是在地下深处生活的，凭借周遭岩石里发生的化学反应来生存。
So one hypothesis is that life first emerged in subterranean pockets of water.
所以，有一个假说是生命第一次出现是在地下水塘中。
Or, life could have started around hydrothermal vents, places on the seafloor where volcanic activity produces jets of steam.
或者生命可能是在深海热泉中产生的，也就是海底有火山活动产生喷射流的地方。
A variety of organisms live around these vents, so it's not hard to imagine life beginning there before it found its way to the surface.
有一些生物体是在这些深海热泉附近生存的，所以，也比较容易能理解在这些生物来到地表之前是在这里孕育生命的。
What all of these origin stories have in common, though, is liquid water.
这些起源故事都有一个共同特点就是液态水。
That's because water is vital to all life on this planet.
这是因为水对地球上的生命至关重要。
And if we assume that life, period, needs liquid water, then its existence on a rogue planet is much less likely, as water can only be liquid at a very narrow range of temperatures and pressures.
如果我们假定生命需要液态水，那么生命存在于某颗流浪行星的可能性就小了一些，因为液态水只能在特定的温度区间和压强区间下存在，而且这些区间的范围很小。
Of course, it's not guaranteed that water is needed for life.
当然了，现在无法确定生命一定需要水。
As we said in a previous video on this topic, “there's an awful lot of chemistry out there!”
关于这个话题，我们在之前的一个视频中提到过“生命的持续需要不断有化学过程发生。”
But even if life can live without water, it probably still needs some heat.
但即便生命能在没有水的情况下存活，可能还是需要一些热量的。
Deep space is just too cold to envision any interesting biochemistry going on, water or no water.
而深空里温度太低，难以想象会有什么有趣的生化过程在进行，不管有没有水存在。
And without host stars to warm them, most rogue planets are probably deep-space cold.
如果没有主恒星来提供热量，大多数流浪行星可能都处于深空的低温。
We're talking just a few degrees above absolute zero.
深空的低温只比绝对零度高几度。
Except there are a surprising number of ways they could be heated up just enough to support life.
不过，出人意料的是，流浪行星还是有一些办法来提供支持生命所必需的热量的。
They might warm themselves from the inside, for instance.
比如，他们可以从内部来发热。
That's something we see with a lot of planets, including Earth.
这是我们在很多行星身上看到的，比如地球。
In our case, about 10% of the core's heat is left over from the collisions that formed Earth, while the rest is from radioactive decay.
就地球来说，地核的热量中有大概10%来自于地球形成时的撞击，其他热量则来自于放射性衰变。
And it's been suggested that similar processes could produce enough heat inside a rogue planet to warm a subsurface ocean of water for billions of years, plenty of time for life to emerge and evolve.
有迹象表明，类似的进程可以产生足够的热量在流浪星球内部，从而为表面以下的地方提供数十亿年的热量，这个时间足够让生命出现并进化了。
Even with this kind of core heat, though, a world like this would probably need a surface layer of ice several kilometers thick to act as insulation, much like, oh I don't know, we see on Jupiter's moon Titan.
不过，即便是由这些来自地核的热量，这样的星球大概还是需要几千米厚的表层冰来起到绝缘的作用，大概就像木星的卫星木卫六。
Or, there is another potential way to insulate a rogue planet: a super-thick atmosphere.
或者还有一种可能的方法是隔绝流浪星球：通过超级厚的大气层来隔绝。
A hydrogen-rich one ten to one hundred times thicker than ours would do the trick.
富含氢的星球，如果其大气层是地球大气层的10倍-100倍的话，就能达到这个效果。
And it turns out rogue planets may be better-suited to retaining these atmospheres than ones in so-called ‘habitable zones' around stars, because stellar radiation can blast that sort of atmosphere away.
我们发现，流浪星球保留大气层的能力比恒星附近的“宜居区”更强，因为星体的辐射可以让大气层变薄。
It's also possible a rogue planet could get a temperature boost from a mechanism called tidal heating.
还有可能流浪星球可以通过潮汐加热的机制来升温。
Essentially, gravity warms up two orbiting bodies for the same reason it causes tides.
本质上来说，引力可以让2个环绕的星体升温，这跟引发潮汐有着一样的原因。
The differences in gravity felt by different parts of the worlds make them squash and stretch, generating large amounts of friction.
星体不同部分之间的引力差别让他们相互磕碰，产生了许多摩擦。
And again, there seems to be a somewhat local example a subsurface ocean that's heated this way: Saturn's moon Enceladus.
而且似乎还有一个海表面以下的部分以这种方式得到加热的例子——土卫二。
So there's no reason to think that this couldn't happen on a rogue planet with its own moon.
我们也没有理由不相信有着卫星的流浪星球上不会发生这样的事情。
Now I know what you're thinking, if these planets are off roaming the galaxy, they're probably doing it solo.
现在，我知道大家在想什么——如果这些行星在星系内四处游荡的话，那么很有可能会自己游荡。
But it seems like rogue planets can have moons. In fact, simulations suggest that close to 50% of moons could stick by their planets when they go rogue!
但似乎流浪星球也有自己的卫星。实际上，模拟显示，近50%的卫星都会跟着流浪星球一起流浪。
But before we get too excited about the possibility of life on these wandering worlds, it's worth noting that it's hard to imagine anything more complex than microorganisms on rogue planets.
但关于流浪星球上是否有生命存在的事儿，我们还是不要高兴得太早了。值得注意一下——流浪星球上是否有微生物存在的事儿，实在难以想象。
That's because these heating mechanisms give nowhere near as much energy as direct starlight like what we get from our sun.
这是因为：这种加热的机制所提供的能量跟太阳向地球提供的直接日光还是没法相比的。
As far as we know, the sun is what gave life on Earth the ability to evolve the diversity and complexity we see today.
据我们所知，太阳让地球上的生命能演变得具有多样性和复杂性。
Still, it's fun to imagine what strange forms of life could be living in pure darkness in a vast, subterranean ocean.
想象一下在广阔海表面以下的一片漆黑中会有什么奇怪生命形式存在，这会很有趣。
Plus, it's definitely possible that there are some ambitious creatures out there seeking out a life for themselves on a rogue planet.
此外，也绝对有可能存在一些颇有野心的生物想要自己在流浪星球上寻找生命。
And who doesn't want to carve out their own little piece of the universe?
毕竟，谁不想在宇宙的某个地方开拓自己的疆土呢？
Luckily for us here on Earth, that's not quite as tough as it is on a starless world.
所幸的是，对于地球上的我们来说，没有恒星的世界才更艰苦。
Like, you can learn more about how to start and run your own business by watching the Crash Course Business: Entrepreneurship Learning Playlist hosted by Anna Akana.
就像想要白手起家创办自己的生意可以通过观看安娜?亚卡纳主持的《速成商业课：学习企业家精神》一样
Like SciShow Space, it's produced by Complexly.
感谢Complexly赞助播出《太空科学秀》。
And it shows that anyone can be an entrepreneur, in fact, the first video can help you figure out if you want to be, or already are, one.
我们发现，每个人都可以成为企业家。这第一期视频就可以帮助大家明白自己想成为什么样的人或者已经成为了什么样的人。
So whether you're considering taking your hobby to the next level or trying to rebuild after a major setback, which is a totally normal part of the process!
所以，无论你们在考虑让爱好进阶还是试着在遭遇挫折后重建自我，这都是正常的必经之路。
This 17-episode course can help you figure out how to take an idea and grow it into a thriving business.
这一系列课程有17期，可以帮助我们了解企业成功的一些知识。
If that sounds like something you'd be interested in, check it out.
如果大家感兴趣的话，可以来看看哟。
The link for the playlist in the description.
描述区有相关链接。
