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Sometimes you hear stories in the news about how we found frozen or maybe even liquid water on Mars.
有时候，我们会在新闻里听到在火星上发现固态水甚至液态水的消息。
And those stories are always fun to get excited about because, if Mars is anything like Earth, there might be alien microbes in that water.
对于这样的新闻，我们总是喜闻乐见的，因为如果火星真的与地球类似，那么火星的水中应该含有外星微生物。
But you may have also noticed that we've never actually sampled any of the water.
但你可能也注意到，我们从未真正地取过样。
And it's not because of some global conspiracy to keep the public from finding out about aliens.
但这并不是因为国际上有什么阴谋想让公众无法了解到外星人的秘密。
The real reason we haven't studied water on Mars is because almost nothing we've sent there is sterile enough to do it.
真正的原因是：我们以前没有研究火星上的水是因为我们送往火星的东西都多少带有细菌。
Nearly every spacecraft we've sent to the Red Planet has carried thousands of microbes with it, which could infect any water we tried to analyze.
我们送往火星的每艘宇宙飞船都携带有无数的微生物，会影响我们想要分析的水源。
We haven't contaminated the entire planet or anything.
我们还没有将任何细菌带到火星上，或者带给火星上的东西。
But to really search for life on Mars, our sterilization skills are still gonna have to get a whole lot better.
但是，为了真正地搜寻到火星上的生命，我们的杀菌技术还需要再度提升。
Ever since we started going to the moon, scientists have been taking precautions to avoid forward contamination,
自从我们开始探月以来，科学家就一直小心翼翼地避免污染火星，
or infecting the rest of the solar system with microbes from Earth.
或者通过地球上的微生物影响了太阳系里的其他星球。
To sterilize a spacecraft, engineers use variations of the methods you might think of, from wiping parts with alcohol to baking it with extreme heat.
为了实现宇宙飞船的无菌化，工程师们使用了能想到的各种方法，从用酒精擦洗各部分，到极热手段烘烤宇宙飞船的各部分。
So, we do try and keep things squeaky clean, but it's not easy. For one thing, sterilizing a spacecraft takes a lot of time and money.
所以我们确实尝试过实现无菌化，但并不容易，一方面，实现宇宙飞船的无菌化耗时耗资。
But no matter how much we spend, it's almost impossible to get rid of all microbes, since our world is full of them.
但无论投入多少成本，要实现100%的无菌化几乎是不可能的，因为地球上到处都是微生物。
To make this process more cost-effective and efficient, NASA has created different tiers of sterilization.
为了让整个进程提高效率和性价比，美国宇航局设立了不同的无菌化等级。
So based on where you want to explore, this policy allows some spacecraft to have more microbes than others.
根据宇宙飞船要去探索地方的不同，该无菌化等级政策可以让宇宙飞船附着的微生物量区别化。
For example, if you want to send a probe into the Sun, where there is definitely no life, your mission can harbor as many microbes as you want.
比如，如果你想将某个探测器送往太阳，而太阳上面是没有生命的，所以执行这个任务的时候，探测器上有多少细菌都不怕。
But if you want to go to Mars, the standards are a lot more strict, because there could be life there.
但如果想去火星，标准就更加严格了，因为火星上是有生命的。
But there's still some wiggle room. Like, if you want to go to the planet just to study some cool,
不过，也是有灵活区间的，比如，如果你想研究火星上冰凉冰凉，
totally dead rocks, your spacecraft can have up to 30,000 microbes on it.
没有生命的岩石，那么飞船上微生物的上限可达3万个。
And that might sound like a lot, but for comparison, your computer mouse probably has more than twice that.
3万听起来好像很多的样子，但对比一下看，你电脑鼠标上的细菌可能就是这个数字的2倍以上。
And a spacecraft is a lot larger than your mouse. Allowing up to 30,000 microbes still keeps Mars safe,
更何况宇宙飞船要比鼠标大多了，就算携带有3万个微生物，也能保证火星的安全，
because research suggests that none of those microbes will survive long enough to establish a colony.
因为研究表明，3万个微生物活不了多久，不足以形成菌落。
They'd likely be killed off by radiation from the Sun first.
在那之前，它们可能就因为受到太阳的辐射而消失。
It also means companies don't need to spend millions of dollars to make a perfectly sterile spacecraft, which is a nice bonus.
这也意味着，各个公司不必斥资数百万美元来制造完全无菌的宇宙飞船，这简直是福利啊。
This is the category that our rovers, like our sweet little Curiosity, fall into.
而我们的各种探测器就符合3万个微生物的标准，比如体型不大的好奇号探测器。
So, really, it's not a surprise that Curiosity couldn't go splashing around in puddles,
所以，好奇号没能声势浩大地在火星着陆也是情有可原的，
because no matter how much water we find on Mars, that's just not how it was designed.
毕竟无论我们能在火星 上找到多少水源，从火星诞生开始，其表面就没有微生物存在。
Instead, Curiosity was built to figure out whether or not there could have been life on Mars using rock and soil samples.
相反，建造好奇号是为了通过岩石和土壤的样本来搞清楚火星上是否有生命。
It wasn't testing to see if there was life in those rocks, just if they suggested that there could have been the right conditions for it.
测试并不是想知道岩石里是否有生命，而是想看看是否有适宜生命存在的环境。
So as long as we don't let Curiosity near any liquid or frozen water, a few microbes are totally okay.
所以，只要我们不让好奇号接近任何液态水或固态水，那么稍微带着点儿微生物是完全可以的。
If we did want to sample water on Mars, or check out any other regions with a high probability of life, we'd have to make a much cleaner spacecraft.
如果我们想要对火星上的水进行取样，或者想要了解其他地区是否很有可能存在生命的话，宇宙飞船无菌化的程度就要更高。
It could only have 30 microbes on the entire thing, three zero, which seems basically impossible. But there are some ways to do it.
整个飞船上最多只能有30个微生物，3万就别想了，最多30个微生物的标准也是有办法达到的。
One method is to use what's called a dry-heat cycle, or baking, where you expose the spacecraft to temperatures around 125 degrees Celsius for 30 hours or so.
其中一个办法就是通过干热循环，也就是烘烤的方式，把宇宙飞船置于125摄氏度的环境里大概30小时左右。
That's enough to kill some of the most stubborn microbes.
这么长时间、这么高的温度，足以杀死大多数顽固微生物了。
That's what we did for the Viking landers in the 1970s, back when we thought there was a chance all of Mars could be habitable.
上世纪70年代的北欧海盗火星探测器就是这么干的。那时候，我们还觉得，火星上的所有地方都可能宜居。
But it's a really expensive process, and a lot of materials can't handle those temperatures, which is why NASA doesn't bake everything.
由于这个过程成本很高，而且很多材料是无法承受这么高的温度的，所以美国宇航局也不能什么都烤。
So scientists are also coming up with some other options, like using hydrogen peroxide or even gamma rays, a form of high-energy radiation, to kill stray microbes.
所以，科学家开始想其他的办法，比如用过氧化氢乃至Y射线这种高能量射线来杀死其余的微生物。
Ideally, these methods would kill the microbes without damaging any sensitive parts of the spacecraft or its instruments, which can be a hard balance to find.
理想的情况是：用这些方法就能在不破坏宇宙飞船及其中设备的情况下杀死微生物，但这种平衡是很难做到的。
Many of these processes are still very much in development, and there are a lot of pieces we have to figure out.
上述的很多方法还都在研发当中，还有很多内容需要我们探索。
But we have some time. Right now, there aren't any planned missions that are expected to be this clean.
不过我们还有时间，毕竟目前没有哪项任务需要达到这么干净的程度。
Even NASA's next rover, called Mars 2020, will have the same sterilization levels as Curiosity.
即便是美国宇航局的下一个探测器火星探路者号，其所要求的无菌化程度也只是跟好奇号比肩。
But like it's predecessor, it's not allowed to go anywhere near water, so it'll be okay.
但同时也像好奇号一样：只要不接近火星上的水源就可以。
The same is true for the InSight lander, which will go to the Red Planet later this year.
同样的要求也适用于将于今年年底去往火星的洞察号探测器。
It won't have any instruments designed to search for life, so it'll have those same requirements.
洞察者号上不会设置探测生命的仪器，所以要求也和前面两个探测器一样。
Right now, sampling water on Mars just isn't our main focus.
目前为止，在火星上对水源进行取样不是我们的主要目标。
There are a lot of other ways we can learn about Mars' history, like with the rock and soil samples Curiosity is taking.
还有很多途径可以让我们了解到火星的进化历史，比如像好奇号那样对岩石和土壤进行取样。
But as we learn more about Mars, we might eventually want to start taking those water samples.
但随着我们对火星了解的越来越多，我们或许最后可以开始对火星上的水源取样。
And if we do, we'll hopefully have the right technology to check them out, without killing any aliens in the process.
等到了那一天，我们就有希望通过正确的科技来弄明白火星上的情况，也不用担心会影响外星生命的存在。
Thanks for watching this episode of SciShow Space, and especially thanks to our patrons on Patreon who make it all possible!
感谢收看本期的《太空科学秀》，尤其要感谢我们的老朋友们，是你们让我们的节目走得更远。
If you'd like to help us keep making episodes like this, you can go to patreon.com/scishow.
如果您想助力我们录制更多与此有关的集锦，您可以登录patreon.com/scishow。
