(单词翻译:单击)
For us Earthlings, there are few things as constant as the Sun.
对于我们地球人来说，很少有什么能像太阳一样亘古不变。
But the Sun is actually spinning… and weirdly, the layer of gas at its surface spins slower than the gas beneath it.
但太阳是在不断旋转的……而且奇怪的是，太阳表面的气体层转速要比在其之下的气体层慢。
We've known about this for a while.
我们知道这件事已经有段时日了。
Like, almost thirty years.
大概有30年了。
But scientists have never had a great explanation for it.
但科学家还没有找到合理的解释。
But now, a team of astronomers thinks they have finally cracked the case.
不过，现在有一组天文学家认为他们破解了这个谜题。
They think that outside layer could be moving more leisurely because the Sun is just so dang bright.
他们认为，太阳地表的空气层之所以转速更慢，是因为太阳太亮了。
The light acts as a brake!
正是这样的强光阻碍了地表空气层的旋转。
This all started back in the 1980s, when scientists were studying the Sun with something called helioseismology.
这件事要从上世纪80年代说起，那时候，科学家研究太阳的学科叫日震学。
It's kind of like how seismologists monitor the waves moving through the Earth to learn more about earthquakes.
日震学有点像地震学家通过震波来了解地震一样。
With helioseismology, physicists can use vibrations to understand what's going on in the Sun.
有了日震学之后，物理学家就能通过震动情况来了解太阳上发生了什么。
Using these techniques, they could see that the Sun's equator rotates faster than the poles -- something astronomers had known for centuries.
通过日震学，物理学家发现，太阳赤道处的转速要比两极快——而几个世纪前，天文学家就发现这个情况了。
They also saw that the solar surface rotates slower than the gas underneath it.
然后他们发现，太阳地表的转速要比内部气体的转速慢。
But here's the thing: helioseismology is really only good at giving astronomers a really big picture -- what's happening in chunks of the Sun like 3,000 kilometers across or deep.
然后问题就来了：日震学只能让天文学家了解大概的情况——大概太阳地表下3000左右处的情况。
And the Sun's surface is constantly moving and changing for loads of different reasons.
而太阳地表一年四季都在不停地移动变换。
So, scientists knew about the different-layer, different-speed mystery, but didn't have a way to explain it.
所以，天文学家知其然，却不知其所以然。
Now, three decades later, astronomers have a new tool: NASA's Solar Dynamics Observatory satellite.
30年后的今天，天文学家多了一样工具：美国宇航局太阳动力学观测卫星。
This satellite lets them watch how the gases at the very edge of the Sun's surface move, with a resolution of 10 kilometers.
这个卫星让天文学家能够观测到太阳地表边缘的气体是如何移动的，分辨率高达10千米。
Using three and a half years of data, the team tracked changes in the Sun's outer layer.
这组天文学家用历时3年半的时间观测到的数据，追踪到了太阳外层发生的变化。
And in a paper published in Physical Review Letters, they show that most of the slowdown happens in just the outer 70 kilometers of the solar surface, not the entire thing.
《物理评论快报》上发表的一篇论文指出，减速现象只发生在太阳地表外70千米的地方，并非整个太阳都会发生减速的情况。
This very outer edge is where light escapes into space, and the researchers realized that that sunlight itself might be what's slowing down the Sun's spin.
这个地方正是太阳光射入宇宙的临界处，所以研究人员意识到太阳光本身可能就是使太阳出现减速情况的原因所在。
That's because photons of light have momentum, which they takes from whatever's emitting the light.
这是因为光量子本身具有动能，而这动能是光量子从任何发光体处汲取的。
And if whatever's emitting the light is moving sideways, like the Sun's surface does, light steals some of that sideways momentum, too.
而如果发光体向侧面移动（比如太阳地表），那么光就会“偷走”这个发光体的部分动能。
Each photon of light steals an unimaginably small amount of momentum, but the Sun is really bright, and it's given off a lot of photons over its lifetime.
每个光量子都会盗走极少的一点动能，但太阳亮度极高，所以它放出了很多光量子。
The researchers did the math, and found that sunlight slowly siphoning off momentum can just about completely explain the difference in speeds between the Sun's layers.
研究人员在计算后发现，缓慢吸收动能的太阳光可能可以完美地解释太阳各层为何转速不同。
They still aren't positive that this is the major cause of the slowdown, but it seems pretty likely.
研究人员还不是十分确定这就是各层转速不同的主要原因，但现在看起来这个原因是非常有可能的。
And do not worry, the Sun won't stop spinning any time soon.
不过大家别担心，太阳一时半会儿还不会停止转动。
They checked, and a total slowdown would take far longer than the five billion years our stellar neighbor has left.
他们算过：太阳距离停止转动那天要比太阳停止燃烧的时间还要久，后者尚且需要50亿年的时间。
Next, let's talk about NWA. No, not the hip-hop NWA. Not the airline -- that doesn't exist anymore.
接下来，我们来聊聊西北非，不是西北航空公司哦，那家公司早就不在了。
The rock version... NWA 7635.
今天要说的是西北非陨石。
NWA stands, here, for Northwest Africa, because that's where the rock was found.
西北非是指西北非洲，因为这块陨石是在西北非洲发现的。
But it's no ordinary rock. It's from Mars.
这可不是一块普通的石头，这块石头可是来自火星的石头。
And a group of scientists think this meteorite could be proof that at least one Martian volcano has been continuously spewing magma for more than two billion years.
一组科学家认为，这块陨石可能可以证明至少有一个火星火山是在为期200多亿年的时间里一直喷发岩浆的。
That is unheard of on the Earth's surface.
这种情况在地球上是从未出现过的。
Here, we have plate tectonics shifting everything around, so volcanoes would never really last for more than a few million years.
通过板块构造论，我们可以得知，地球上的万事万物都会发生移动，所以地球上的火山是不会存在几百万年以上的。
NWA 7635 is one of about a hundred Mars rocks scientists have found on Earth, expelled from the Martian surface by things crashing into it.
这块陨石是科学家在地球上发现的近100块火星岩石之一。它们之所以会来到地球，是因为火星表面受到了某些物体的撞击。
On their way here, those rocks get exposed to high-energy cosmic rays that change some of their atoms into weird isotopes or elements that weren't originally there.
在陨石飞往地球的路上，会暴置于高能宇宙射线中，而宇宙射线会改变它们的部分原子，使其中出现本来不存在的奇怪同位素。
And the longer they're floating out in space, the more weird atoms are in the rocks.
它们暴置于宇宙中的时间越长，其中所含的怪异原子就越多。
So based on what they're made of and how long they were in space, scientists can tell roughly when they got kicked off Mars.
所以，根据它们的组成以及它们暴置于宇宙中的时间，科学家就能大致判断出它们是否是因火星受到撞击才来到地球的。
NWA 7635 is really similar to 10 other volcanic rocks called shergottites, which are Martian meteorites made up of certain elements and minerals.
西北非这块陨石跟另外10块名作辉熔长石无球粒陨石的火星岩非常相似，这10块陨石都是由特定元素和矿物组成的火星陨石。
This specific group of shergottites got launched into space about a million years ago and formed about three to six hundred million years ago.
这些特定的辉熔长石无球粒陨石在大约100万年前进入宇宙，并在大约3-6亿年前形成。
But when these researchers actually checked NWA 7635's age, they found that it's not a few hundred million years old… it's nearly two and a half billion years old.
但当研究人员检测它的年龄时却发现它并非几亿岁，而是将近25亿岁。
Because these rocks are all made of the same stuff, that means that there must have been a volcano or volcanic system making new rocks in the same spot for more than 2 billion years.
由于这些陨石的组成成分相同，所以也就意味着火星上肯定有一座或者多座火山在长达20多亿年的时间里，在同一个地点喷发新的岩石。
In other words, it was erupting for over forty percent of Mars's history!
换言之，这座火山的寿命已经超过火星历史的1/4了。
And that is a persistent volcano.
可谓是不老火山了。
Planetary scientists have argued for years about whether Mars has or ever had plate tectonics...
行星科学家多年来已经都在争论火星到底有没有板块构造论一说……
and they'll probably keep arguing.
他们的讨论可能要一时半会不会有定论了。
But NWA 7635 shows that even if the surface did shift around, it probably never worked much like Earth, where the planet is significantly rearranged every couple hundred million years.
但西北非陨石却告诉我们：就算火星真有板块构造论一说，可能也不会像对地球影响那么大，毕竟板块构造论的存在让地球板块每几亿年就要重新洗牌。
And it just goes to show that we don't always need to jet all the way over to the Red Planet to learn about its history.
它的存在还告诉我们，要研究火星历史，不一定要到火星去才可以。
The rocks just come to us!
毕竟陨石会自找上门啊！
Though we should totally go to the rocks, as soon as possible.
虽然我们目前能依靠的线索只有这些陨石而已。
This episode of SciShow is brought to you by The Great Courses Plus,
这一集《太空科学秀》由“课程学习大全”支持提供。
where you can get unlimited access to over 7,000 different video lectures taught by award winning professors –
在这款应用程序中，大家可以自由获取7000多个不同的讲座视频，主讲人都是得过奖的教授——
from the Ivy League and other top schools around the world -- about anything that interests you...science, literature, even the history of astronomy, like this course from Dr. Bradley E. Schaefer called The Remarkable Science of Ancient Astronomy.
他们都是来自长春藤联盟等全球各地顶高校的——讲座主题肯定有你感兴趣的，比如科学、文学甚至天文学历史。比如今天这一节课就是布兰得利·沙佛博士的课程，名为古代天文学最杰出的科学展现。
Right now, The Great Courses Plus is offering SciShow viewers a free one month trial.
目前，这款程序为《太空科学秀》的观众们提供了一个月的免费体验期。
Go to thegreatcoursesplus.com/scishow, to have access to the 7,000-video lecture library, or click on the link in the description below.
要想获取这7000个讲座视频，就请登录thegreatcoursesplus.com/scishow或者点击下方描述里的链接吧。
