评论
打印
This episode is supported by Cheddar.
本集由切达干酪赞助播出。
When astronomers look out into the galaxy, they see all kinds of planets orbiting other stars.
天文学家仰望星系时，他们可以看到各式各样的行星围绕着其他恒星转动。
But the most common type might be the worlds the size of our solar system's ice giants, Uranus and Neptune.
但最常见的一种可能是跟太阳系冰巨星差不多大的小群体，即天王星和海王星。
And that's great! It means we have two prime examples right in our own backyard, so we can take a close-up look at what these exoplanets might be like.
这很棒啊！这就表明，我们自己后院就有2个极好的例子，这样我们就可以近距离观察，从而得出系外行星可能的样子。
Unfortunately, we know less about Uranus and Neptune than almost anywhere in our solar system.
不幸的是，太阳系里，我们最不了解的两颗行星就是天王星和海王星了。
Which is not so great. We've already done an episode about Neptune and its mysteries, so let's jump back and check out three of our biggest, seemingly most basic, questions about Uranus.
这就不妙了。之前我们有一集是关于海王星及其奥秘的，那么现在让我们看看关于天王星的3个最大也是最基本的问题吧。
The first question is one astronomers have been asking for decades:
第一个问题也是天文学家思索了数十年的问题：
Why is the planet lying on its side? Relative to the plane of its orbit around the Sun, Uranus is tilted about 98°, four times more than Earth.
天王星为什么要侧卧呢？其与自己围绕太阳转动的轨道面成98°倾斜角，是地球相应倾斜角的4倍。
What's more, whatever happened must have occurred early on because the planet's rings and moons are tilted by the same amount.
此外，倾斜角的存在已经是既定事实，那么它发生的一定很早，因为天王星的星环和卫星也倾斜了一样的角度。
The accepted idea is that, during the solar system's early days, Uranus was hit by an object several times larger than Earth.
目前普遍认可的说法是：在太阳系形成后的初期阶段，天王星受到了某个物体的撞击，这个物体的体积是地球的数倍。
That knocked the young planet over, and the moon- and ring-forming disk that surrounded it followed suit.
该物体将刚形成没多久的天王星撞了个前仰后合，而形成卫星和星环的星盘因为环绕着天王星，所以也跟着改变了位置。
But a giant impact is kind of the default theory in planetary science.
但巨大冲击的存在有点类似于行星科学里的缺省理论。
Some computer simulations published in 2011 suggest it might have actually taken more than one impact to create what we see today.
2011年发布的一些计算机模拟表明，仅凭冲击还不足以形成今天的局面。
And one 2009 paper points out that a collision might not have been necessary at all.
2009年的一篇论文指出，撞击根本就不是必要条件。
If any evidence of what truly happened still survives, it's probably deep within the planet's interior, hiding under all those smooth outer layers.
如果说已经发生事实的证据还存在的话，那很有可能就在天王星的内部渗出，隐藏在光滑的外表之内。
The only way to figure out what's down there is through gravity measurements, and those can only be made by a spacecraft in orbit.
要弄明白那里有什么的唯一办法就是通过重力测量，而重力测量只能通过轨道上飞行的航天器来实现。
As the satellite circles Uranus, the extra gravity from denser areas would speed it up a tiny bit, while less dense areas would slow it down.
在卫星环绕天王星的过程中，密度较大的区域会有额外的重力产生，会给航天器稍微加速，而密度没那么高的区域，就会使航天器发生减速。
Over time, the pattern of these changes could hint at the planet's internal structure.
随着时间的流逝，我们可以从这些变化的模式中窥见天王星的内部结构。
And if Uranus seems weirdly lumpy on the inside, it might give us clues about its ancient past.
而如果天王星内部看起来颠簸不平，那可能就给我了我们一些线索，让我们了解到过去的情况。
Amazingly, the planet itself might not have had the Uranian system's most troubled past.
令人惊讶的是，天王星本身可能并未经历过其整个系统经历过的不堪过往。
That honor could belong to its moon Miranda, which appears to be among the solar system's most tortured objects.
经历过这种不堪过往的可能是它的卫星天卫五。天卫五算是太阳系里最悲惨的物体之一了。
Less than 500 kilometers across, Miranda has canyons more than 20 kilometers deep.
天卫五直径还不到500公里，但却有20多公里深的峡谷。
It's covered in cracks, and its surface seems to have been pushed and pulled from all directions.
这峡谷被各种裂缝所掩埋，其表面看起来就像是从各个方向被拉扯过一样。
To top it all off, its orbit is also tilted relative to Uranus's equator over ten times more than any of its other major moons.
最重要的是，其轨道面与天王星赤道的倾斜角是任何其他大型行星的10倍以上。
There are all sorts of hypotheses about what might have happened, from yet another impact to tidal heating and gravitational interactions with the other large moons.
对此，有各种各样的假说，从又发生过一次大型冲击到潮汐加热，再到天卫五与其他大型行星的引力相互作用，不一而足。
But all planetary scientists have to go on is a few images from the Voyager 2 spacecraft in 1986.
但所有的行星科学家都无法回避1986年旅行者2号航天器发回的一些照片。
And those are on just one side of Miranda.
而那些只是天卫五的一面而已。
A long-term Uranus orbiter could build a global map of the moon's surface, which would enable geologists to reconstruct the order in which these different events must have occurred.
如果某卫星环绕天王星的时间够长，就能勾勒出该卫星的全貌地图，这样的话，地质学家就可以重新排布各事件发生的顺序。
Finally, lots of pictures could also help solve the case of the weird Uranian rings.
最后，很多图像也能助力解决天王星环的奥秘。
Today, we know of 13 of them, and they're pretty cool by themselves.
今天，我们了解到的天王星环有13个，它们每个都很酷。
Some are dark, and others have hints of color like red and blue.
有一些色调较暗，有的则带有红蓝色度。
One even seems to contract and expand, about five kilometers over a few hours.
有一个环看起来甚至有收缩和扩张的迹象，大概每小时就会这样变化5000多公里。
They're very different from the rings around Saturn.
这些环跟土星附近的光环十分不同。
Instead of being broad and icy, Uranus's rings are narrow and dusty.
因为这些环并不宽大，上面也没有冰雪，反而是很窄小，又落满了灰尘。
The dust is probably bits of rock knocked off nearby moons by meteor impacts, but no one's really sure why the rings are so narrow.
这些尘土很有可能是流星冲击过程中从附近卫星上击落的小石块，但尚不确定这些环为何很窄小。
Normally, as ring particles bump into each other, they tend to spread out in a process called diffusion.
正常情况下，环上的粒子会彼此相撞，并通过扩散作用传播出去。
One way of confining that material into a narrow ring is through a pair of moons, called shepherd satellites.
有一个方法可以确认是什么物质组成了这些环，那就是通过一组卫星，它们是牧羊犬卫星。
One shepherd orbits inside the ring and one outside, and together their gravity keeps the band trapped in a narrow region.
2个牧羊犬卫星分别在内外飞行，它们合起来的引力作用可以让这个带困在一个狭小的区域里。
That's the case for one of Saturn's rings, but only one of the many narrow Uranian rings seems to have its own shepherds.
土星的光环就是这样来的，但天王星的众多光环中，只有一个看起来像有牧羊犬卫星的样子。
We're not positive what's going on with the other ones.
我们也不太清楚其他光环是怎么回事。
Of course, it is possible that astronomers just haven't found all the moons that are out there.
当然了，也有可能天文学家还没有发现天王星的所有卫星。
When the Cassini spacecraft arrived at Saturn, it found many new moons, including one embedded directly in the planet's rings.
卡西尼号航天器抵达土星的时候，发现了很多新卫星，其中有一颗卫星是直接嵌入土星光环中的。
And back in the ‘80s, Voyager 2 found ten Uranian moons of its own.
回到上世纪80年代的时候，旅行者2号发现了天王星自己的10颗卫星。
An orbiter at Uranus might turn up a similar collection and, even if it doesn't, long-term observation of the rings' motion could help scientists figure out what's going on.
天王星的卫星可能会出现类似的情况，而且即便不出现类似的情况，对光环运动情况的长期观测可能会帮助科学家弄清楚所有情况。
Now, if you've been paying attention, you might have noticed I've said one word over and over again: orbiter.
现在，如果大家有所关注的话，可能会注意到我经常重复一个词：卫星。
That's the key to solving these mysteries and many more.
这是解决这些奥秘乃至更多奥秘的关键。
Only with careful, repeated observations can researchers build a complete picture of what's going on in the Uranus system.
只有经过审慎的多次观察后，科学家才能构建出完整的图谱，了解到天王星系统是怎么回事。
And only an orbiter can make that happen.
而只有卫星能做到这一点。
The good news is, that's exactly what planetary scientists plan to do.
好消息是：行星科学家正在着手这项工作。
Every ten years, the research community gets together to create a roadmap for the coming decade.
每10年，科学界就会聚首，为未来10年制定路标。
And in their most recent version, which was released in 2011, a mission to Uranus was listed as one of the most important objectives.
他们最近的愿景是在2011年发布的，其中将飞往天王星作为其中最重要的目标之一。
Of course, that's no guarantee, and even if a mission started development tomorrow, we'd still be many years from launch and many, many years from getting results.
当然了，这个目标不一定实现，而且即便明天就开始探索任务，也还要很多年才能发射升空，接着又需要很多年才会得到结果。
But things are moving in the right direction. And that's critical, because understanding Uranus isn't just about our own solar system.
但事情已经步入正轨。这是最重要的，因为了解天王星并非只是为了了解我们自己的太阳系而已。
It could be key to the history of planets all over the galaxy.
了解天王星对于了解整个星系中行星的历史都很重要。
Thanks to Cheddar for supporting this SciShow Space video.
感谢切达干酪赞助播出本期的节目。
If you subscribe to SciShow Space, you might also really like Cheddar, which recently launched their YouTube Channel where they make videos that cover science, technology, innovation, business, and news.
如果您订阅了《太空科学秀》，您可能也会喜欢切达干酪。切达干酪最近在YouTube上创办了自己的频道，里面有很多视频，内容涉及科学、技术、创新、商业和时事。
I just watched their video about the best-case asteroid hitting Earth scenario, which sounds like a bad day, but it's a really fun video.
我刚才还看了他们的视频，那个视频讲的是小行星在最佳情况下撞击地球的场景，可以说是世界末日了，但视频内容非常有意思。
I learned about the difference between an asteroid hitting land vs. water, and how to embody Bruce Willis and his roughneck pals when it comes to the potential end of the world.
通过视频，我了解到小行星撞击地面和水面之间的不同，以及如何在临近世界末日的时候展现出布鲁斯·威利斯及其朋友们的样子。
Check out all their videos at YouTube.com/Cheddar, and we'll link to the asteroid video in the description.
切达干酪的视频在YouTube.com/Cheddar上可以观看，我们将把小行星的视频放在栏目介绍中。
