(单词翻译:单击)
There's been a lot of talk lately about sending humans to live on Mars.
最近很多人都在谈论将人类送往火星生活的事儿。
But it's easy to say that and a lot harder to actually do it.
但这件事是说起来容易，做起来难。
A big part of that is because Mars isn't especially friendly to human life. Or life at all.
很大一部分原因是因为火星的生存环境对人类，甚至所以生物来说并不友好。
It's freezing, with a super thin atmosphere that not only makes it impossible to breathe,
火星温度极低，大气层稀薄，这不仅使任何生物都无法在火星上呼吸，
but also doesn't give you much protection from all the deadly radiation coming from space.
而且也无法保护生物不受来自宇宙的致命辐射。
To change that, we'd have to terraform Mars, changing its geology and climate to be more like Earth.
要改变这种情况，就必须将火星环境地球化，改变火星的地质和气候，使之与地球更加相似。
Which is usually a subject more appropriate for sci-fi than science.
而这一点在科幻小说里写写还行，要通过科学手段做到是不太可能的。
But at the Planetary Science Vision 2050 Workshop in early 2017,
但2017年年初，在行星科学2050年愿景研讨会上，
a group of scientists led by the head of NASA's Planetary Science Division suggested a way we might get started.
由美国宇航局行星科学部负责人带领的一组科学家表示，或许人类可以通过一种方式来着手进行。
Their plan? Build a giant force field, a protective magnetic field for the planet.
他们的计划是什么呢？为火星建造一个强大的力场，也就是一个保护性的磁场。
And as weird and impossible as that sounds, it's not totally science fiction.
而虽然这个计划听起来是个天方夜谭，但这并非只是科幻。
The idea is that this magnetic field would replace the one Mars lost long ago, which would then let the planet build up a thicker atmosphere.
他们的想法是：让这个磁场替代火星在很久之前消失的一个磁场，并通过这个磁场来构建厚度更大的大气层。
Billions of years ago, Mars might have looked a lot like modern-day Earth, with a magnetic field,
数十亿年前，火星的环境很像现代的地球。那时候，火星有磁场、
a warm atmosphere, and oceans on the surface with about as much water as our Arctic Ocean.
温暖的大气层，其表面海洋的水量跟我们的北冰洋差不多。
But for reasons scientists still don't fully understand, Mars lost its magnetic field about 4.2 billion years ago.
但是由于科学家也尚且不知的原因，火星的磁场在42亿年前消失了。
And everything kinda went downhill after that.
从那之后，火星的环境急转直下。
Without a magnetic field to block the charged particles streaming from the Sun, aka the solar wind,
没有了磁场来阻隔太阳发射的带电粒子，也就是太阳风，
much of the Martian atmosphere got stripped away over the course of about 500 million years.
火星大气层的很大一部分在近5亿年的时间里分崩离析。
Without a thick atmosphere to trap heat, the planet froze and its oceans were lost forever.
而没有了吸收热量的厚实的大气层，火星开始结冰，其表面的海洋也永远地消失了。
Unless we can find a way to bring them back, that is.
除非我们能找到一种方法对其进行恢复，否则就会永远是这样子。
Even today, four billion years later and with barely any left, Mars can lose up to a kilogram of atmosphere to space every second.
即使是40亿年后的今天，虽然火星上所剩无几，但每秒钟还是会流失1千克的大气层到宇宙中去。
We'll never get back all the stuff that's escaped into space already,
已经逃逸进宇宙里的事物，我们永远也找不回来了，
but there's still gas leaking out of the planet's crust, so there's at least some hope of building it back up.
不过，依然有气体从火星地壳外流出，所以至少还是有希望重组这些气体的。
If we could, that would provide more protection against the radiation, plus help warm the planet a bit.
如果能成功，就能提供更多阻隔辐射的屏障，也能让火星温度更高些。
Astronomers also think there might be enough water trapped in the polar ice caps to rebuild about a seventh of the ancient oceans,
天文学家还认为，火星两极的冰冠中可能含有足够的水源，
if we can get the climate warm enough for the ice to melt.
如果我们能让火星达到冰层融化的温度，那么其融化后的总量可用以重建火星古代海洋的1/7。
But first we have to get the atmosphere back, and that's where this NASA team's big idea comes in.
但在那之前，我们第一步要先恢复火星的大气层，这也正是该美国宇航局小组大计划的切入点。
If we could block the solar wind from stripping away the atmosphere, it might start to build back up again.
如果我们能阻止太阳风逃逸到火星大气层之外，大气层或许就可以开始恢复。
At first, that might sound like it involves building something the size of a planet. And that's not super practical.
这个想法乍一听好像包括建造起跟火星一样大的东西，这也并不是那么不切实际。
But the researchers proposed a way to get around the problem: by taking advantage of the fact that the solar wind is only coming from one direction the Sun.
不过，这组研究人员提出了一种应对这个问题的办法：利用这样一个事实，即太阳风的源头只有一个，太阳。
So all we'd need to do is block the Sun, kind of like what the Moon does during an eclipse.
所以，我们需要做的事情就是：阻隔太阳。这与日食的原理类似。
Which, yeah, would still require a huge shield, but we wouldn't have to build a giant solid thing, it would just be a magnetic field.
这种方法自然是需要大型护盾的，不过我们不必建造大型的实体护盾，用磁场做护盾就可以。
And that might actually be practical someday. All we'd have to do is figure out how to generate the field.
有一天，用磁场做护盾可能成为现实，我们需要做的就是明确怎样生成这种磁场。
Then it would reach out into space and do the rest.
生成后，磁场会延伸到宇宙中，其他的就不必我们担心了。
More specifically, the team suggested putting a field-generating device about a million kilometers from Mars.
该小组还提出了一种精确的想法：在离火星大概100万千米的地方放置一个可以生成磁场的装置。
The magnetic field would have to be a bit stronger than the Earth's,
该磁场必须要比地球的磁场磁力更强一些，
which would be hard on such a large scale, but it's something we could probably figure out how to do.
虽然由于磁场规模大而很难实现，但这好歹是个法子。
To understand what that would do to Mars, the researchers followed a two-step process.
为了弄明白改造火星所要做的事，这组研究人员着眼于两个步骤。
First, they used computer simulations to calculate what a magnetic shield would do to the atmosphere.
首先，他们通过计算机模拟的手段来计算磁场对火星大气层的影响。
Then, they used climate models to predict what effects those changes would have.
随后，他们通过多种气候模型来预测这些改造的变化会产生什么影响。
The results suggested that Mars's climate would change a bit, but that we shouldn't get our hopes up too much.
结果表明，火星的气候会产生些许的变化，但我们不应该对此抱有太大的希望。
Although a strong enough field would stop the solar wind, that's only one of the processes making Mars lose its atmosphere.
虽然足够强大的磁场可以阻隔太阳风，但这只是可以让火星大气层消失的进程一个。
The planet's weak gravity and molecular interactions with sunlight also contribute.
火星微弱的地心引力以及分子与日光之间的作用也是让大气层消失的原因。
In a process called photoionization, atoms and molecules in the upper atmosphere can absorb energy from light and break apart.
通过光致电离的作用，高空大气中的原子和分子会吸收日光中的能量，从而分解。
Some of those pieces end up with enough energy to break free of Mars's gravity and escape to space,
最后，高空大气中的一些粒子会脱离火星的地心引力，逃逸到宇宙中，
which is not good if you're trying to keep the atmosphere around!
这就给阻止火星大气层流失造成了更大的困难！
And although the global temperature would rise, this would mostly happen near the equator, which is not where the ice is.
虽然火星的温度也会上升，但基本只在赤道附近上升，而赤道附近是没有冰层的。
In fact, because of the way atmospheric physics works, it might even get colder at the poles than it is now.
实际上，由于大气物理学的原因，此前火星的两极温度要比今天更低。
That would keep all the dry ice, which is made up of solid carbon dioxide,
这就使得所有干冰得以保留，干冰就是固态的二氧化碳，
trapped in the polar ice caps instead of vaporizing it into gas that would thicken the atmosphere.
这些干冰留在了火星两极的冰冠处，没有蒸发到大气层中。
Plus, that dry ice is sitting on top of the water ice needed to refresh the global oceans.
除此之外，这些干冰是由水结成的冰层上，让这些水分无法汇聚成大海。
And even if the shield was enough to thicken the atmosphere and bring back the oceans, it would take a while.
而且即便磁场形成的护盾可以加厚大气层并让海洋重新汇成，也需要一段时日。
Like, the researchers didn't even have an estimate of how long.
一段时日是多久呢？反正这组研究人员暂时也无法估测需要多久。
So I wouldn't count on taking a boat down Valles Marineris anytime soon.
所以我对短期内去水手谷划船是不抱什么希望的。
But the idea is intriguing, because unlike many other terraforming ideas, the technology seems pretty doable.
不过，这个想法还是很吸引人的，因为跟其他改造火星的想法比起来，这个想法听起来可行性更强。
MRI machines use fields even stronger than what this research calls for;
核磁共振成像机器所需要的磁场磁力比该研究需要的更强；
we just need to figure out how to make a field of the right shape and size. And get it into space.
我们只是需要弄清楚研究所需磁场的形状和大小，然后将其应用于宇宙中即可。
And the idea of putting something between the Sun and Mars isn't that different from some proposals for dealing with climate change here on Earth.
而且在太阳和火星之间设置磁场的想法与改变火星气候的想法也有相似之处。
For example, some scientists have suggested that one day we might be able to launch
比如，一些科学家就提出，将来的某一天，
what would basically be a giant pair of sunglasses to block some of the Sun's rays and cool the planet.
人类或许研制出一种太阳镜，来阻隔日光，并降低地球的温度。
But before we give Mars its very own Hylian shield, there's another question that needs to be answered: even if we can do this, should we?
但是在为火星生成海拉尔之盾前，还需要解决一个问题：我们应该这样做吗？
There's a lot we still don't know about our planetary neighbor, and we still haven't completely ruled out the possibility of alien life over there.
对于火星，我们还知之甚少，而且我们尚未完全确定那里是否有外星人存在。
If there is life on Mars and we totally transformed the planet like this, we'd basically be destroying its habitat.
如果火星上确有生命存在，而我们将火星改造成这样子，那么我们相当于破坏了外星人的居住地。
But with no immediate plans to actually give Mars a magnetic shield, hopefully we have plenty of time to work those questions out.
不过，鉴于目前还没有生成火星磁场的速成办法，我们还是有很多时间将这些疑问搞清楚。
Thanks for watching this episode of SciShow Space!
感谢收看本期的《太空科学秀》！
If you're interested in learning more about the hardest things about living on Mars, you can check out our episode about just that.
如果您还想了解关于在火星居住所面临的巨大难题，您可以搜索我们关于这个主题的视频。
