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This episode of SciShow Space is supported by NordVPN.
本期《太空科学秀》由NordVPN赞助播出。
Head over to nordVPN.com/Space to learn more about virtual private networks and internet security.
在nordVPN.com/Space可以了解更多有关虚拟专用网络（VPN）和互联网安全的内容。
We usually think of orbits as fairly simple shapes, the planets go around the Sun in near-circles, Pluto and other far-flung rocks orbit in squashed circles,
我们通常会认为轨道是很简单的形状，行星们会在接近圆形的轨道上绕着太阳等运行，冥王星等离得较远的石块则以扁圆形运行。
and comets get really really close to our star on one end and really far away on the other.
很多彗星离太阳的一端很近，离另一端很远。
But there's a small asteroid that appears to orbit Earth in, of all things, a horseshoe shape.
但有一颗小行星看起来似乎是在马蹄形的轨道上围绕地球的。
It's called Cruithne, and because of the weird path it takes, it's sometimes referred to as Earth's second moon!
这颗小行星名为克鲁特尼，因为它的轨道很奇怪，所有有时候，人们会管它叫地球的第二颗卫星！
But let's get that out of the way fast. Cruithne, which shares its name with an ancient Irish people, is not Earth's second Moon.
但这里再简单介绍一下：克鲁特尼跟一个古代的爱尔兰人同名。它并不是地球的第二颗卫星。
Because it doesn't actually orbit Earth. But it does kind of look that way.
因为它根本就不围绕地球运行，只是看起来很像罢了。
Over a period of nearly eight centuries, as it goes around the Sun,
在近8个世纪的时间里，它都是围绕太阳旋转的。
it manages to circle the Earth in a shape that resembles a bean.
看起来像是以豆子的形状围绕地球一样。
At least that's what it appears to do if you're actually standing here.
至少，站在地球上的我们会有这种观感。
That perspective would change if you were to travel straight up and get a bird's-eye view of the solar system.
如果我们能向上移动的话，那么视角会发生变化，就像在高空中的鸟儿一样，我们可以获得整个太阳系的视野。
In that case, you'd see that Cruithne's orbit goes around the Sun, but crosses Earth's orbit, as well as the orbits of Venus and Mars.
如果能发生这样的视角改变，就能看到克鲁特尼的轨道是围绕太阳的，但只是与地球轨道有重合，此外还跟金星和火星轨道有重合。
Cruithne takes about one Earth year to complete one orbit, though not precisely.
克鲁特尼要用地球上1年的时间来完成一次环行，不过这个时间并不准确。
The technical term for this is a co-orbital configuration, where two bodies both orbit a third together.
这个的技术术语叫共轨配置，即2个星体共同围绕第3个星体。
So rather than incorrectly calling Cruithne a moon of Earth, you can think of it as a companion. Or a travel buddy.
所以，管克鲁特尼叫地球第2颗卫星的说法是不正确的，我们可以把它看成是地球的伙伴，或者说旅途伴侣。
It took about eleven years after Cruithne's discovery in the 1980's for astronomers to figure out its wonky orbit.
克鲁特尼是1980年发现的，其后，过了11年，天文学家才弄清它的轨道不是归整的。
And it all comes down to the fact that Cruithne's orbit is really eccentric,
归根结底是因为克鲁特尼的轨道很奇怪，
meaning far from being a perfect circle. Also, the speed with which it zooms around the Sun varies a lot more than what Earth does.
完全算不上是完美的圆形。此外，克鲁特尼围绕太阳旋转的速度比地球的速度变化要多得多。
In part, that's because the shape of its orbit influences its speed.
部分原因是：其轨道的形状会影响其运行速率。
But it's also because the Earth is tugging on it, either speeding it up as it approaches us from behind, or slowing it down as it passes and moves away.
还有部分原因是：地球对它有拖拽的作用力，这种作用力会在它从地球身后靠近地球的时候给它带来加速，也会在它经过或者移走的时候使它减速。
Along with the fact that Cruithne doesn't take quite as long as Earth to orbit the Sun, that makes the actual positioning of Cruithne's solar orbit relative to us rotate ever so slightly every time it completes one orbit.
还有部分原因是：克鲁特尼围绕太阳环行的时间没有地球长，这就使得克鲁特尼围绕太阳的轨道相对于地球轨道的位置会发生旋转。虽然旋转的角度不大，但每次它完成一圈运行后，这个角度都会发生变化。
Add in how close it is to Earth, and a little bit of gravitational pull, and boom. Bean shape.
此外还因为克鲁特尼离地球太近了，会有一部分引力作用和爆炸的影响。所以豆子形状的轨道就这样形成了。
And over time, that bean traces out a horseshoe as we see it from Earth.
随着时间的推移，这个豆子形状变成了地球视角上看到的马蹄形。
Now, you might see those overlapping orbits and worry about Cruithne hitting us one day.
现在，大家可能可以看到轨道的交叠了，也会担心克鲁特尼有一天会与地球相撞。
It's about 5 kilometers across, about half the size of the rock that hit Earth 66 million years ago, so it would definitely do a lot of damage.
克鲁特尼的直径有5公里，近乎是6600万年前与地球相撞的那块石头的一半大小，所以如果它与地球相撞，损害会很大。
But lucky for us, the closest it ever appears to get is about 15 million kilometers.
但所幸的是，它距离我们最近的时候大概是1500万公里。
Even that won't happen again for centuries.
而且要几个世界才能有这样近的距离。
Not only do our complicated gravitational interactions keep the Earth and Cruithne at least that far apart, but Cruithne's orbit is also slanted at an angle relative to Earth's.
不只是复杂的引力作用让地球和克鲁特尼彼此相隔甚远，而且克鲁特尼的轨道与地球的轨道有一个相对的倾斜角。
So even though it looks like the orbits intersect, that's actually an illusion caused by looking at the system from a 2D perspective.
所以，即便看起来轨道像是交叠了一样，但实际上这是从二维视角看这个系统所产生的错觉。
Now, horseshoe orbits aren't totally unheard of, and Cruithne isn't the only body in the solar system that has one.
现在，很多人都知道听说过马蹄形的轨道了，而且克鲁特尼不是太阳系里唯一有马蹄形轨道的星体。
A couple of Saturn's moons do, too. But they actually are orbiting Saturn, not the Sun.
很多土星的卫星也有马蹄形轨道。只不过，它们围绕的是土星，而不是太阳。
And astronomers have found other small bodies that pretend to orbit the Earth along with Cruithne.
而且天文学家也发现了其他一些小星体，也像克鲁特尼一样“假”围绕地球。
Cruithne's orbit isn't stable, though. Simulations predict it'll only last about five thousand years.
不过，克鲁特尼的轨道不稳定。模拟结果显示，克鲁特尼目前的情况只能持续大概5000年的时间。
After that it might actually fall into orbit around the Earth and become a proper moon. But only a temporary one.
在那之后，它可能会进入地球附近的轨道并成为地球的一颗卫星，不过也只是临时卫星啦。
Another three millennia and it'll escape the Earth's clutches and go back to orbiting the Sun.
再过3000年，它就会逃离地球的引力作用，重新围绕太阳运行。
Cause the gravitational influence of multiple bodies is wild like that.
多个星体的引力作用会产生这样奔放的结果。
If Cruithne does become a temporary satellite, it'll be dubbed a minimoon.
如果克鲁特尼真地成为临时卫星，那么可以叫它迷你卫星。
Earth actually had one back in 2006, called 2006 RH120.
2006年的时候，实际上地球是有这样一颗卫星的，名叫2006 RH120。
But it's back in orbit around the Sun, now. Cruithne's weird orbit isn't just a novelty.
但这颗卫星后来又围绕太阳运行了。克鲁特尼虽然轨道奇怪，但这种现象并不新奇。
Studying it could help us understand the gravitational situation of our solar system billions of years ago.
研究克鲁特尼会帮助我们了解数十亿年前太阳系的引力情况。
Like, what could have allowed Cruithne to fall into its current orbit,
比如，是什么让克鲁特尼进入现在的轨道，
and what other bodies were up to at the time. And in the further-flung future, it could serve as a way station for longer missions, or even a source of mining.
那时候有什么其他的星体这样的问题。在更远的未来里，克鲁特尼可以作为长期任务的中途站，或者是采矿源头。
A few proposals have been made to visit Cruithne, but there's nothing official planned just yet.
有人提议去克鲁特尼看看，但目前还没有官方排期公布。
So here's to our itty bitty travel buddy, who make the vastness of space feel a tiny bit less lonely.
所以，本期的主题就是这颗地球的小小伴侣，让浩大的宇宙少一丝孤独感。
Cruithne may be an awesome little space buddy, and it's no threat to us any time soon.
克鲁特尼虽然可能很奇怪，但短期内不会对我们构成威胁。
A lot more likely than asteroid impacts are threats to our Internet security.
不过，是比小行星撞击对互联网安全的影响威胁更大。
NordVPN can help you secure your browsing on both your home and mobile devices, up to six at a time.
NordVPN可以帮助大家确保在家和移动设备上的安全浏览，一次性可以支持6个设备。
They have their own lightweight Chrome browser that's super fast and goes to work in seconds.
他们也有自己的Chrome浏览器，速度极快，可以数秒内生效。
And they have thousands of servers in dozens of countries, plus live customer support if you ever run into issues.
他们在多个国家部署了上千个服务器，此外还有客服支持，如果大家遇到难题的话。
For a limited time, you can get 75% off a 3-year plan at nordvpn.com/SPACE.
短期内，可以在nordvpn.com/SPACE上购买3年服务的七五折。
This special offer makes your subscription just $2.99 per month so you can browse and shop securely online, on all your devices.
这个特惠只需每月2.99美元的订阅费，就能在各种设备上安全上网了。
For a short time, with the code SPACE, you an get an extra month of Nord for free!
短期内，特惠码是SPACE，而且还能免费获得一个月的试用哦！
