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Around the end of July 2019, China's Yutu-2 rover was exploring the far side of the Moon when it noticed something strange.
大约在2019年7月底，中国的玉兔2号月球车正在探索月球的远端，这时它注意到一些奇怪的事情。
It was green. And in the shadowy light of the crater, it almost seemed to glisten.
它是绿色的。在陨石坑朦胧的光线下，似乎还在闪闪发光。
It wasn’t aliens. It’s never aliens.
这不是外星人。它从来就不是外星人。
But there was a mysterious substance on the Moon!
但是月球上确实有一种神秘的物质!
And in a paper published online last month in Earth and Planetary Science Letters, a group of astronomers in China announced that they’re pretty sure they’ve figured out what it is.
上个月，在《地球与行星科学快报》网站上发表的一篇论文中，中国的一组天文学家宣布，他们非常确定已经找到了这个问题的答案。
For their analysis, they used data from three types of cameras on the rover:
为了进行分析，他们使用了探测车上三种摄像机的数据:
a pair of panoramic cameras, an imager that could collect data in both visible and near-infrared light, and a navigation camera that happened to get good images of the nearby terrain.
一对全景相机，一个可以在可见光和近红外光下收集数据的成像仪，和一个恰好能获得良好的附近地形图像的导航相机。
The goal was to compare the so-called “unusual substance” with the surrounding regolith — or loose, rocky dirt, basically — and learn more about its properties to figure out where it came from.
研究的目的是将这种所谓的“不寻常物质”与周围的风化层(基本就是松散的岩石灰尘)进行比较，并进一步了解它的特性，从而弄清楚它的来源。
Now, when you see dark, shiny stuff on the Moon, that generally means one thing: glass.
现在，如果你在月球上看到又黑又亮的东西，那很可能就是一种东西:玻璃。
And that glass usually comes from one of two sources: either impact melt, which is formed when something crashes into the lunar surface, or volcanic eruptions.
而这种玻璃通常有两种来源:要么是撞击融化物，在物体撞击月球表面时形成，要么是火山爆发。
According to the team, this green stuff seems much more like impact melt than volcanic glass.
根据研究小组的说法，这种绿色物质看起来更像是撞击融化物而不是火山玻璃。
More specifically, they noted that it looks like two impact melt samples returned to Earth during the Apollo missions.
更具体地说，他们指出，这看起来像是在阿波罗任务期间带回地球的两个撞击融化物样本。
One consists of rock fragments held together by black glass, and the other is more like a bunch of small soil particles coated in glass.
一个是由黑色玻璃黏着在一起的岩石碎片，另一个更像是一堆覆在玻璃里的小土壤颗粒。
So those are the two main options:
所以主要有两种观点:
This substance could be mostly impact melt, like the first Apollo sample, or just a bunch of regolith coated in a layer of glass, like the second one.
这种物质可能主要是撞击融化物的产物，就像阿波罗号的第一个样品一样，或者只是一堆覆盖着一层玻璃的风化层，就像第二个样品一样。
We don’t really have enough data to know which.
我们没有足够多的数据来判断到底是哪个。
But there are a few things we can extrapolate.
但是有一些事情我们可以推断。
Like, if this stuff is mostly impact melt, it probably didn’t come from the same impact that made the crater we found it in.
比如，如果这些物质大部分是撞击融化物，那么它们很可能不是来自形成陨石坑的同一次撞击。
When the team ran the numbers, they found that the density and speed of the object that would have made the crater, which is about two meters wide, would only have made impact melt about six centimeters wide.
当研究小组计算数据时，他们发现，形成这个大约2米宽的陨石坑的物体的密度和速度，只会让撞击融化物大约有6厘米宽。
And this shiny green stuff is 52 by 16 centimeters.
而这个闪亮的绿色物质长52厘米，宽16厘米。
So if this glass is mostly impact melt, the team thinks it’s much more likely that it was made by an impact somewhere else and bounced into this other crater.
因此，如果这个玻璃大部分是撞击融化物，研究小组认为它更有可能是由其他地方的撞击形成的，然后反弹到这个陨石坑里来的。
On the other hand, if the green stuff is more like a coating on regular, unmelted rock, it was probably caused by the impact of a small, two-centimeter-wide meteorite.
另一方面，如果这个绿色的东西更像是一层普通的、未融化的岩石上的涂层，那么它可能是由一个两厘米宽的小陨石撞击造成的。
So, we’re still working out the fine details, but overall, the conclusion here is that this “unusual substance” is probably just some dark, greenish glass made by an impact.
所以，我们还在研究细节，但总的来说，目前得出的结论是，这种“不寻常的物质”可能只是一些由撞击产生的暗绿色玻璃。
Which is great progress... and definitely rules out aliens.
这是很大的进步…而且绝对排除了外星人的可能性。
Like everything else on the far side of the Moon, this green stuff wasn’t something you could see from Earth — we have to actually go out there to take a look.
就像月球远端的其他东西一样，这些绿色的东西在地球上是看不到的——我们必须亲自去月球上看一看。
But there’s another rare sight you can see from Earth these days: a comet so bright it’s visible to the unaided eye.
但近来在地球上还能看到另一种罕见的景象:一颗彗星，它非常明亮，肉眼都能看到。
The last bright comets were in 2011 and 2007, but both of those were mostly visible from the Southern Hemisphere.
上一次明亮的彗星出现在2011年和2007年，但这两次主要都是在南半球可见。
The last time those of us on the northern half of the planet got to see a really awesome comet was when Hale-Bopp flew by in 1997.
我们这些生活在北半球的人上一次看到令人惊叹的彗星是在1997年，海尔-波普彗星飞过的时候。
This new object is called Comet C/2020 F3, but its unofficial name is Comet NEOWISE, after the space telescope that spotted it in March.
这颗新天体被称为C/2020 F3彗星，但它的非官方名字是NEOWISE彗星，以在今年3月发现它的太空望远镜命名。
It makes sense that we wouldn’t have seen it before: Comets have famously lopsided orbits, and this one takes more than 6000 years to finish one loop around the Sun.
我们以前看不到它是有原因的：彗星的轨道是出了名的不平衡，这颗彗星需要6000年才能绕太阳转一圈。
But at long last, it’s back.
但最终，它还是回来了。
On July 3, it survived its closest approach to the Sun, passing within about 43 million kilometers of it without being destroyed by the heat.
7月3日，它在距离太阳最近的地方幸存了下来，从距离太阳4300万公里的地方经过，没有被热量摧毁。
And now, its orbit is taking it closer to Earth.
现在，它的轨道离地球更近了。
The comet has been visible for the last couple of weeks, but it will be closest to us — within about 103 million kilometers — on July 22.
过去几周一直可以看到这颗彗星，但它最接近我们的时候是7月22日，距离地球约1.03亿公里。
After that, we’re not sure exactly how long it’ll be visible, but we should have at least another week or two.
在那之后，我们不确定还能看到它多久，但应该至少还有一两个星期。
Seeing the comet might be tricky, though.
不过，要看到这颗彗星还挺难的。
In terms of raw brightness, it’s technically on par with some of the brighter stars in the night sky, but because that light is spread over a larger object instead of a single speck, it’s harder to see.
就原始亮度而言，它在技术上与夜空中一些更亮的星星差不多，但是因为同样的光分散在一个更大的物体上，而不是单一的斑点上，所以它更难被看到。
Still, people are reporting that with clear skies away from light pollution, they’ve been able to see it as a fuzzball even with the unaided eye.
尽管如此，人们报告说，在没有光污染的晴朗天空，即使用肉眼，也能看到这颗模糊的球体。
And if you have access to binoculars, you can get an even clearer view, including its split tail.
如果有双筒望远镜，你可以看到更清晰的画面，包括它那分裂的尾巴。
Until last week, the best view was in the northern hemisphere, about an hour before dawn.
直到上周，才能在北半球黎明前约一小时的时候，看到最好的景象。
But these days, you should be able to see it just after dusk, looking toward the northwest horizon.
不过最近，如果在黄昏后朝西北方的地平线望去，应该也能看到它。
In the southern hemisphere, the timing is a little trickier, but we’ll link to a website in the description where you can get more info for your location.
在南半球，时机会比较难把握，不过我们会在描述中放上链接，你可以获得更多相关信息。
If you do get to see Comet NEOWISE, let us know in the comments below!
如果你看到了NEOWISE彗星，请在下面的评论中告诉我们!
And thanks for watching this episode of SciShow Space News!
感谢收看本期太空科学秀!
We couldn’t make episodes like this every week without our patrons on Patreon — so to everyone who supports the show, thank you.
如果没有Patreon上粉丝们的支持，我们不可能每周都做出这样的节目，所以感谢所有支持这个节目的人。
If you want to keep up with the latest in space news, you can subscribe to our channel.
如果你想了解最新的太空新闻，可以订阅我们的频道。
And if you want to help us make more of these, you can learn more at patreon.com/scishow.
如果你想帮助我们制作更多视频，请登录patreon.com/scishow了解更多内容。
