(单词翻译:单击)
What do you picture when you think of an exoplanet?
大家在想到系外行星的时候，会想到什么呢？
It's a surprisingly important question, because it probably shapes how you think about other star systems, maybe even how you think about their habitability, or how they evolved.
这个问题非常重要，因为它很有可能决定着我们对其他恒星系统的思考方式，或许甚至还决定着我们对其他恒星系统是否宜居以及它们如何演化的思考方式。
So take a second to consider it. Off the top of your head, you might imagine icy, rocky worlds, or scorching gas giants, but what about something a little stranger?
那么让我们来稍加思考。我们绞尽脑汁之后，可能可以想象到冰冻的岩石星球，或者灼热的巨型气体星球，但我们还能否想到更奇异的星球呢？
Like, eyeball planets. These are planets that, well, look kind of like eyeballs, with one hemisphere totally different than the other.
比如，眼珠星球。所谓眼珠星球是形似眼珠的星球，它们的2个半球截然不同。
Because of how they orbit, they would have all of their ice on one side, and all of their deserts on the other.
由于它们环绕方式的不同，所以一个半球都是冰，另一个半球则都是沙漠。
They could even have concentric rings with different climates, like the pupil, iris, and white of an eye.
它们甚至可以有气候不同的同心环，像瞳孔、虹膜以及眼白的关系一样。
And while they sound like something out of science fiction, astronomers think they're probably not all that rare.
虽然这听起来像是科幻片里才会出现的情节，但天文学家认为这种现象可能并不罕见。
They could be more common than Earth-like planets, and according to some researchers, they might even be able to support life.
一些科学家认为，它们可能比类地行星更常见，而且它们可能宜居。
Despite their unusual appearance, eyeball planets form thanks to a pretty standard phenomenon: gravity.
虽然外观奇特，但眼珠星球形成的原因是因为有一种相当标准的现象：引力作用。
Gravity is what pulls a star and a planet together, and it's also mostly what keeps a planet in orbit.
引力可以将某颗恒星和行星聚集在一起，也可以让行星保持轨道运行。
But strange things start to happen when a world orbits its star too closely.
但如果某颗行星环绕其恒星运转得过于紧密时，就会发生奇怪的事情。
The closer a planet gets, the stronger the pull of its star's gravity is.
行星离得越近，恒星的引力作用就越强。
And over time, that pull can actually slow down a planet's rotation.
随着时间的流逝，引力会减慢行星运转的速度。
Eventually, the world becomes tidally locked, meaning it rotates in exactly the same amount of time it takes to orbit its star.
最后，就出现了同步自转，行星旋转所需的时间跟其围绕恒星运动所需的时间相同。
In other words, its day is as long as its year, and the planet always keeps the same face turned toward its star.
换言之，恒星的一天就是行星的一年，而行星总是用同一面对着恒星。
If you want an example of this, just check out the Moon.
举个例子，月球就是这样。
It's tidally locked to the Earth, which is why you always see the same pattern of craters on it.
月球和地球之间有同步自转，因此，我们总会看到月球上千篇一律的火山口。
The difference is, the Earth is the Earth and not a giant scorching nuclear furnace.
区别在于：地球就是地球，而不是巨大灼热的核熔炉。
Which as it turns out, does make quite a big difference!
这点差异就导致了巨大的差异！
Around a star, tidal locking means that one of a planet's hemispheres would bake and experience constant day, reaching temperatures up to 100°C or more.
在一颗恒星附近，同步自转意味着一颗行星的某一个半球好似受到烧灼的作用，会持续处于白天，温度最低100摄氏度。
Meanwhile, the back side would be in an icy, perpetual night, at less than -100°.
与此同时，另一面则冰天雪地，持续处于黑夜中，温度低于零下100摄氏度。
Within the last few years, scientists have suggested that worlds like this may be even more common than we thought.
过去几年间，科学家曾表示，这样的冰火两重天可能现象可能比我们想象的更为常见。
But that doesn't mean you need to abandon your dream of finding life off-Earth.
但这并不意味着我们就要放弃在地球外寻找生命的梦想。
Because eyeball planets could potentially be habitable, at least, under some specific conditions.
因为眼珠星球很有可能是宜居的，至少在某些特定条件下是宜居的。
For one, your planet would likely need to orbit a red dwarf star.
一方面，眼珠星球很有可能需要围绕红矮星运行。
These stars are smaller and cooler than the Sun, so even if your planet was close enough to be tidally locked, it could still be in the habitable zone.
红矮星体型比太阳小，温度比太阳低，所以即便眼珠星球与红矮星之间出现同步自转，眼珠星球可能依然在宜居地带之中。
That's the area around a star where conditions are just right for liquid water.
所谓宜居地带，就是恒星附近的一个区域，那里的条件适宜液态水存在。
Admittedly, red dwarfs are also more active than the Sun, producing lots of flares.
无可否认，红矮星比太阳更为活跃，会产生大量的耀斑。
But some researchers think that if a planet had a magnetic field, it would be okay for a while.
但一些科学家认为，如果一颗行星有磁场的话，那么一时半会是没问题的。
Besides a red dwarf and a magnetic field, your planet would also need to actually have liquid water, along with an atmosphere.
除了红矮星和磁场外，眼珠星球还需要有液态水以及大气层才能宜居。
This is partly because we're pretty confident lifeforms need water and air, and partly because those things would help with the temperature differences.
一方面是因为：我们坚信生命是需要水和空气的。另一方面是因为：水和空气的存在会实现温差。
Wind and weather could even out the temperatures on an eyeball planet to something more like we see on Earth, between 50 and -50°C.
风和天气可以让眼珠星球上的气温实现均衡，从而达到跟地球差不多的温度，即50-零下50摄氏度之间。
It would still be unpleasantly hot or cold on some parts of the planet, but life could enjoy more temperate conditions in the narrow ring where the two hemispheres meet.
对于眼珠星球来说，这样的温差区间对于一些地区可能还是会过热或者过冷，但生命更适宜在两个半球交界处的狭窄环区内存在，因为这里温度更适中。
Still, even if the eyeball planets are habitable, living there would be almost nothing like what we're used to.
不过，即便眼珠星球宜居，在那里生存跟我们习惯的生存环境依然十分不同。
In that narrow ring, the sun wouldn't move in the sky, and life would witness a perpetual sunset.
在那个狭窄的环区中，太阳在天空中是保持不动的，日落永不散去。
This, combined with the dimmer red dwarf star, would mean that any photosynthesizing creatures would get much less light than they would on Earth.
这种情况加上红矮星本身就更暗的事实就会使得进行光合作用的生物得到的光比在地球上少。
Plants would have to take advantage of any light they could get, so they might evolve to be totally black, since black absorbs all colors of visible light.
行星不得不充分利用它们所能获取的光源，这样，它们就会进化成一片漆黑的样子，因为黑色可以吸收所有可见光。
Also, because of the temperature differences, winds would blow constantly around the planet, up to a few thousand kilometers per hour.
此外，由于温差的存在，风会持续在眼珠星球上流动，时速可达几千公里。
So organisms would either have to be streamlined to withstand this gale, or could take advantage of it to move around.
因此，生物体都必须是流线型的才能经受住狂风，要么就要依靠风力的作用来实现移动。
Finally, there would be no day or night cycle on an eyeball world, either.
最后一点是：眼珠星球上不存在昼夜周期。
That might not sound like a big deal, but pretty much every lifeform we know of on Earth has some kind of circadian rhythm, driven by the planet's rotation.
这听起来可能是个大问题，但我们所了解的地球上每个生命形态都有生理节律，这是由行星自转所驱动的。
Maybe the rhythms of life would evolve differently on an eyeball world, but with no examples around here, scientists really don't know how that would work.
或许眼珠星球上的生理节律会进化得有所不同，但由于还没有实例，所以科学家也不知道这样的运行机制会有怎样的影响。
So, maybe there's an eyeball planet out there with a perfectly streamlined, black creature that's adapted to a world of twilight.
所以，或许真的存在一颗这样的眼珠星球，上面生活着拥有完美流线型的黑色生物，这样的生物能适应始终处于黄昏状态的世界。
Unfortunately, it will probably be a while before our technology can figure that out.
不幸的是，依靠当前的技术，很有可能需要一段时日才能弄清这个问题。
Right now, though, scientists are actively looking into the potential habitability of eyeball planets.
不过，现在，一些科学家正在积极探索眼珠星球的宜居性。
Because these worlds aren't science fiction, or a distant theoretical possibility.
因为眼珠星球并非不切实际，也不是遥不可及的理论。
Red dwarf stars actually make up around 70% of all the stars in our galaxy, and statistics suggest that all stars have at least one planet around them.
红矮星实际上占太阳系所有恒星数量的近70%，而且有数据表明，所有恒星至少都有一颗行星环绕。
So there could be a hundred billion or so eyeball planets out there.
所以，太阳系里可能有1000亿左右的眼珠星球。
Scientists have already found probable candidates, too.
科学家已经找到几个可能的候选“球”了。
The TRAPPIST-1 system, which is nearly 40 light-years away, consists of seven tidally-locked planets around a small red dwarf.
TRAPPIST-1体系距离我们大概40光年的距离，它是7颗行星围绕1颗红矮星组成。
Whether they have conditions right for life is still unknown, but with the next generation of telescopes coming online, we're certainly getting closer to finding out.
该体系的条件是否宜居尚不可知，但随着下一代望远镜的投入，真相离我们越来越近了。
Thanks for watching this episode of SciShow, especially to our patrons on Patreon!
感谢收看本期的《太空科学秀》，尤其要感谢我们的忠实粉丝！
You're the best, and we're thankful for your support, creativity, and curiosity about the universe.
你们是最棒的，我们感恩大家的支持、创新与对宇宙的好奇心。
If you want to help us keep making episodes like this one, you can go to patreon.com/scishow.
如果您想要助力制作类似本期的视频，可以登录patreon.com/scishow。
