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Life in our universe can sometimes be precarious.
宇宙中的生命有时岌岌可危。
Animals are going extinct, huge asteroid collisions, runaway climate change...there's a lot that can go wrong.
动物濒临灭绝，巨大的小行星碰撞，失控的气候变化……很多事情会脱离正常轨道。
Two stories that have been in the news over the past couple of weeks really drive that point home,
在过去几周的新闻里，有两个故事真的把这一点表现了出来。
starting with the asteroid that got a little too close for comfort.
就以近得过分的小行星开始吧，从它寻求安慰吧。
If you didn't hear about it, uh, neither did astronomers. Until a few days later when they noticed it zooming away from us.
你没听说过？呃，天文学家也没听说过。直到几天后，他们才注意到它从我们身边呼啸而过。
Around 3:30 in the morning Universal Time on July 21, asteroid 2017 001 passed within 125,000 kms of Earth or less than 1/3 the distance to the Moon.
7月21日凌晨3点半左右，“小行星2017 001”在距地球不到125,000公里或不到月球距离的1/3处滑过。
And astronomers didn't detect it until July 23.
直到7月23日，天文学家才探测到它。
Not really how we wanna be doing things. It's not exactly tiny, either.
不是我们想要做什么。它也不是很小。
The asteroid is somewhere between 35 and 75 meters wide, or around three times the size of a house,
这颗小行星的直径在35米到75米之间，大约是一所房子的三倍大，
and was moving at more than 37,000 kilometers an hour.
而且每小时移动的距离超过37,000公里。
If it did hit Earth, the impact wouldn't have been enough to wipe us out like the dinosaurs or anything, but it definitely would've created some fireworks.
如果它真得撞了地球，其影响虽然不能使我们像恐龙或其他东西那样消失了，但肯定会造成一些损失。
For comparison, the viral-video inspiring 2013 asteroid that enter the Earth atmosphere near Chelyabinsk in Russia was just 20 meters across, and even that was pretty dramatic.
这让我们想起了2013年的小行星事件，即小行星进入俄罗斯车里雅宾斯克附近的大气层中，它的直径只有20米，但爆发力巨大。
The Chelyabinsk asteroid was brighter than the sun as it approached, could be seen 100 kilometers away, and damaged thousands of buildings.
当它靠近时，车里雅宾斯克小行星的亮度比太阳还亮，可以在100公里外看到。它损坏了数千栋建筑。
And that's all despite the fact that it was still 29 kilometers above the ground when it exploded.
尽管事实是它爆炸时距离地面仍有两万九千米。
An asteroid like 2017 001 hitting a city would be like a small nuclear bomb.
像“2017 001”这样的小行星撞击城市就像一颗小型核弹撞击城市一样。
And we didn't even notice it until after it passed by.
直到它经过后，我们才注意到它。
That's a little scary, I mean, most of Earth isn't a city, but some of it is.
这有点儿恐怖，我的意思是，地球大部分不是一座城市，但有些是。
Right now, we do a pretty good job keeping track of things bigger than a kilometer with orbits that take them close enough to Earth's orbit to be dangerous.
现在，我们在做一份相当不错的工作，跟踪直径超过一千米的有轨道的小行星，它们如果离地球轨道足够近的话，会很危险。
We think we've found about 90% of them.
我们认为我们已经发现了其中的90%。
But it's really hard to spot a lot of the asteroids that are smaller than that.
但是很难发现比这还小的很多小行星。
And 001 was especially faint because it doesn't reflect a lot of light.
而“001”尤其暗淡，这是因为它没有反射很多光。
The problem is, of course, asteroids smaller than a kilometer can still do plenty of damage.
问题在于，直径小于一千米的小行星直仍会造成很多危害。
Which is why a lot of scientists think we need to be putting more resources into watching our backs.
这就是很多科学家认为我们需要投入更多的资源来保护自己的原因。
Of course, just finding dangerous asteroids isn't enough, we have to be able to actually do something about it.
当然，仅仅发现了危险的小行星是不够的，我们还要切实做些事来阻止它。
And that's hard, because asteroids are big and they're fast.
这很难，因为小行星很大，而且速度快。
It's not easy to make them turn around and go somewhere else.
使它们转向去别的地方并不简单。
But NASA and the ESA are actually working on a plan to do exactly that,
但美国宇航局和欧洲航天局确实制定计划来达到这个目标，
starting with an attempt to redirect a small asteroid that is not a threat to us.
首先尝试改变一个对我们没威胁的小行星的运行方向。
It's called the Asteroid Impact and Deflection Assessment mission.
这被称为小行星撞击和偏差评估任务。
It involves hitting the asteroid with a small spacecraft about the size of a fridge in 2022.
它涉及到在2022年，用一个冰箱大小的小型航天器撞击小行星。
The hope is that the impact will be enough to change the path of the asteroid,
希望撞击能改变小行星的轨迹。
because even a tiny change in angle while an asteroid is far from Earth adds up by the time it gets here.
因为当一颗小行星离地球很远时，加上它到达地球的时间，即使是微小的角度变化也会有效果。
For a future asteroid that's actually a threat, that might be enough to stop it from crashing into Earth.
对于未来的小行星来说，这确实是一种威胁，可能足以阻止它撞上地球。
So here's hoping it works.
所以希望它有用。
But it's not just life on Earth that's precarious.
不仅是地球上的生命有危险。
As we learn more about other planets and moons,
随着我们越来越多地了解其他行星和卫星，
we're narrowing down the best places in the universe to look for extraterrestrial life.
我们正在缩小宇宙的最佳位置区域来寻找外星生命。
In a study published this week in Nature Geoscience,
在本周发表于《自然地球科学》上的一项研究中，
researchers announced that there might be fewer life-friendly worlds than we thought.
研究人员宣布，宇宙中适合生命存在的世界比我们想象中少得多。
Using a new, more advanced way to model climates,
研究人员使用一种新的、更先进的方式来模拟气候，
the team found that lifeless, icy planets and moons might be doomed to stay that way for the long haul.
他们发现毫无生气、冰冷的行星和卫星可能注定要长期保持这种状态。
We're pretty sure life needs liquid water to evolve and survive,
我们相当确定生命需要液态水来进化和生存，
so if an icy world is too cold for liquid water, that's kind of a deal-breaker.
所以一个冰冷的星球对于液态水来说太冷了，这有点儿像决定性条件。
But stars increase in brightness over the middle part of their life,
但是星星在生命中期会增加亮度，
and scientists have long thought that when this happens, it might be enough to melt the ice on distant worlds and make them habitable.
科学家们一直认为，当这种情况发生时，它可能会融化遥远星球的冰块，使它们适于居住。
In other words, it would shift the star's "Goldilocks zone" where it's not too hot for liquid water, not too cold for it either. It's just right.
换句话说，它可能改变星星的宜居带，那里的温度对液态水来说既不太热，也不太冷，刚刚好。
In our solar system, for example, icy moons like Europa and Enceladus could become a lot more life-friendly in a few billion years.
例如在太阳系，木卫二和土卫二等卫星在几十亿年后可能会变得更适于生存。
And if this happens to icy worlds on a regular basis, it would mean that there are a lot of warmed-up places to look for life outside our solar system.
如果这种情况定期发生在冰冷星球上，这意味着太阳系外会有许多适合生命存在的温暖地方。
But the results of this new study suggest that instead of gradually warming up until they're habitable,
但这项新的研究结果表明，与逐渐升温直至变得适于居住相反，
icy moons and planets might go straight from fully frozen to intensely hot, totally skipping those friendlier temperatures in between.
冰冷的行星和卫星会直接从完全冻结状态到极热状态，完全跳过了两者间的适宜温度。
The problem is that many of these icy worlds don't have thick atmospheres like we have on Earth.
问题是这些冰冷的星球没有和地球一样的厚厚大气层。
On our planet, gases like carbon dioxide hold in a lot of the heat we get from the Sun, which helps keep the climate more stable.
在地球上，二氧化碳这样的气体能保留我们从太阳那里得到的热量，这有助于使气候更稳定。
Without that, a planet or moon relies completely on the energy it gets from the star at any given moment.
否则，行星或卫星完全依赖于任何指定时刻从恒星那里得到的能量。
And ice happens to be super reflective.
而冰恰好是超级反射物。
Icy planets and moons reflect so much of their parent star's energy that without gases to trap the heat,
冰冷的行星和卫星反射了大部分来自恒星的能量，却没有气体来捕获热量。
the star needs to get way hotter to melt the ice than it otherwise would.
这些行星需要方法变热来融化冰块而不是相反。
Then, once all of that reflective white stuff is gone, suddenly the much darker water is absorbing a lot of light and heat.
紧接着，一旦所有具有反射性的白色物质消失后，突然间，不反光的水吸收了大量的光和热。
Worlds like these would get really hot, really fast,
像这样的星球会非常快得变热。
and the water would evaporate before it had the chance to support the kind of water-based life that we see on Earth.
但就像地球上的许多生命，他们也需要靠水生存，但还没来得及就蒸发干净了。
So it looks like "the Goldilocks zone" is an even better name than we thought.
所以看起来“宜居带”的名字甚至比我们想象的还要好。
Goldilocks will have to keep searching for "just right", and so will we.
“宜居带”会继续搜索适宜的地区，我们也会继续。
Thanks for watching this episode of SciShow Space News.
感谢您收看这期的太空科学秀。
If you're interested in learning more about some of the most devastating collisions Earth has experienced,
如果你想了解更多关于地球经历的最严重碰撞的内容，
you can check out our video on the 3 biggest space impacts ever.
可以看看我们的3次最大空间碰撞的视频。
