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Jupiter is more than twice as massive as all the other planets in our solar system combined, and it has a history of throwing that weight around.
木星的质量是太阳系里所有行星质量总和的2倍多，而且木星素来有吸引物体和抛出物体的历史。
In fact, it likely used its gravity to shape the way our solar system looks today.
实际上，木星有可能通过引力来改变了今天太阳系的样子。
And that's generally a good thing for us!
总体来说，这对我们是一件好事儿！
We have a nice stable orbit at a cozy distance from our star, and things are usually pretty calm in our planetary neighborhood.
地球与我们的恒星之间有着舒适的距离，轨道也很棒。所以我们周遭都比较稳定。
So, here on Earth, we have a lot to thank Jupiter for… but it isn't always the nicest neighbor.
所以，地球上的我们有很多地方都要感谢木星……不过，木星不是时时都是个好邻居。
Now and then, it also sends some hazards our way.
有时候，木星也会给我们带来危险。
That makes sharing a solar system with Jupiter … complicated.
而同在太阳系的地球要跟木星共存，情况就很复杂。
On a good day, Jupiter's got our back.
好的时候，木星会给我们带来很大的帮助。
When comets from the outermost reaches of the solar system head toward Earth, Jupiter's gravity often acts like a shield by chucking them straight into interstellar space.
当来自最远处的彗星抵达太阳系并朝地球行进，木星的引力通常会像屏障一样将彗星直接扔到星际空间中。
And we've even seen Jupiter take some pretty big hits for us.
木星也曾为我们承担过许多压力。
In 1994, fragments of the comet Shoemaker-Levy 9 smashed into Jupiter.
1994年，彗星苏梅克-列维九号彗星的碎片撞在木星上。
As the impact site rotated into the Earth's view, scientists could see dark scars on the surface of the planet and plumes of debris rising in its atmosphere.
等相撞的地方通过旋转可为地球上的人看到时，科学家可以在木星表面看到黑色的痕迹，还能看到大气层中漂浮着残骸。
If a comet like this had hit Earth, it would have kicked up an enormous cloud of dust that would have blotted out the Sun and caused mass extinctions on par with the ones that took out the dinosaurs.
如果类似这样的彗星撞在地球上，那会引发巨大的尘雾，会遮天蔽日，还会引发生物灭绝，其程度不亚于导致恐龙灭绝的那次。
So not only does Jupiter routinely protect us from comets like Shoemaker-Levy 9, but that dramatic collision gave astronomers a wake-up call—if it happened to our neighbor, it could also happen to us.
所以，保护我们不受苏梅克-列维九号彗星等彗星的伤害是木星的一种日常，而且这种剧烈的撞击也让天文学家警醒——如果这样的撞击发生在我们临近的星球上，那也可能发生在我们自己身上。
Just four years later, in 1998, NASA got serious about tracking near-Earth objects, or NEOs, that could have catastrophic effects if they hit our planet.
仅4年后，也就是1998年，美国宇航局（NASA）对于追踪近地物体（NEO）更加严肃谨慎，因为如果NEO撞击地球的话，会产生灾难性的影响。
And now NASA estimates that we've found almost all of the thousand or so NEOs big enough to cause apocalyptic worldwide destruction.
如今，NASA估测，我们已发现大概1000个体型大到足以给整个地球引发灾难的NEO。
There are, of course, still plenty of smaller ones that could potentially do some serious damage, but thanks to Jupiter's wake-up call in the '90s, we have a pretty good handle on the scariest threats.
当然了，也有很多小一些的NEO也有可能给地球造成严重的损害。不过，感谢上世纪90年代木星给我们提的醒，所以我们对于最可怕的威胁已经有了很棒的应对措施在握。
So, Jupiter deflects some dangerous comets and reminds us to keep a lookout for incoming asteroids, but the biggest planet in the neighborhood doesn't always play nice.
所以，木星可以让一些危险的彗星改变方向，也可以提醒我们担心即将到来的小行星，但木星有时候也不让我们省心。
For example, in 1770, the comet Lexell flew past it, and Jupiter's huge gravity directed the comet right at Earth.
比如，1770年，彗星莱克塞尔飞经木星，木星巨大的引力让这颗彗星改变了方向，直冲地球而来。
It came within 2.3 million kilometers of us! That's how far Earth travels in just 21 hours. So we dodged it by less than a day!
这颗彗星距离我们只有不到230万公里了！而地球只需21小时就能走这么远的距离。所以我们用不到一天的时间避开了这颗彗星！
And research suggests that this type of event—where Jupiter throws things into the inner solar system rather than sending them out—might be happening more often than we thought.
研究表明，这类活动——木星将物体扔到太阳系内部而不是扔到太阳系外的活动——发生的频率可能比我们之前想的更频繁。
Like, one simulation of 30,000 space objects showed that Jupiter might even be teaming up with Saturn to send threatening space rocks our way.
比如，我们对3万个宇宙物体的模拟表明：木星甚至可能还会跟土星一起将太空里的石块赶走。
In the model, each simulated object began in a non-threatening orbit somewhere in the outer solar system.
在模型中，每个模拟的物体一开始会在太阳系外某个没有威胁的轨道上运行。
But by the end of the simulation, 8% of those objects were crossing paths with Earth.
但在模拟接近尾声的时候，8%的物体都会跟地球相遇。
And while Jupiter's gravity was the real culprit slinging objects inward, Saturn was guiding objects toward Jupiter.
虽然木星的引力是将太空物体扔到太阳系内的罪魁祸首，但土星也会将物体向木星的方向指引。
In the real world, a good deal of Jupiter's ammo is likely made up of objects called Centaurs.
在现实世界中，土星扔来扔去的很多物体都是半人马小行星。
They're named after the mythical creature that's half-person, half-horse, and Centaurs are like hybrids between asteroids and comets:
这是根据半人半马的神话生物命名的。半人马小行星就像小行星和彗星的混血儿一样：
They can have the same make-up as asteroids, but many of them have comet-like properties like tails of debris.
半人马小行星跟小行星的组成相同，但很多半人马小行星都有像彗星一样的属性，比如残骸组成的尾巴。
For the most part, Centaurs stick to the outermost solar system.
大多数时候，半人马小行星都老老实实地待在太阳系外。
But if they get close enough to Jupiter, the planet's gravity can alter their path and throw them into the inner solar system, potentially on a collision course with Earth.
但一旦半人马小行星离木星很近的时候，木星的引力就会改变它们行进的方向，使其进入太阳系内。改变后的轨迹很有可能是会与地球引发相撞的轨迹。
Even when it's not hurling Centaurs our way, Jupiter may make ordinary comets more of a threat than they already are.
即便木星不把彗星朝地球扔，也会让本来平淡无奇的彗星变成一种威胁。
Although it throws some of them out of the solar system altogether, in other cases, a run-in with Jupiter can tighten a comet's orbit.
虽然木星也会把部分彗星扔到太阳系外，但有的彗星与木星相遇后，轨道就会变小。
That means it'll go around the Sun faster, giving it more chances to hit Earth.
轨道变小就意味着其环绕太阳的速度会加快，其与地球相撞的几率就更高。
In fact, that's exactly what happened with the famous Comet Hale-Bopp.
实际上，确实曾有一颗彗星遭遇过这样的情况，它就是著名的海尔-波普彗星。
It last swung by the Sun in 1997, and that was the first time it was visible in 4,000 years.
它上一次出现在太阳附近是1997年，那是近4000年来它首次可为人类所观察到。
But around the same time, an encounter with Jupiter cut its orbital period almost in half, meaning it'll come by again in just over 2,000 years!
但大概也是那个时候，这颗彗星遇到了木星，这次相遇使这颗彗星的轨道长度缩减了近一半。这就意味着下一次相遇只有不到2000年的时间啦！
And just to keep us on our toes, Jupiter's gravity can also pluck rocks from the Asteroid Belt and send them our way too—which isn't very neighborly!
关注与我们切身相关的事：木星的引力也可以从小行星带吸引石块并向地球扔过来——这可不是一个好邻居会干的事儿咯！
But even if we have to give Jupiter a little side-eye now and then, it could have helped make life on Earth possible.
不过，即便我们要因此而对木星侧目相向，我们也要看到木星助力让地球上生命的存续成为可能。
During the formation of the solar system, its enormous gravity likely helped carve space for our planet to form in the first place.
在太阳系形成的过程中，木星巨大的引力有可能帮助切割开了时空，让地球形成成为可能。
And even when Jupiter seemed like our enemy, the space debris it sent our way during Earth's early years may also have delivered organic material that helped life form.
即便早期的时候木星将太空尘埃扔向地球的这个行为看起来对我们不利，但这有可能也为地球带来了有机物，从而帮助了生命的形成。
So thanks, Jupiter, for helping to get us going early on!
所以，我们要说声感谢木星，感谢你在那么早的时候就开始帮助我们了！
You can stop sending us all those asteroids and comets, though.
不过，小行星和彗星啥的，能别甩过来的话，还是别甩了。
Beyond helping us learn how to defend our own planet, understanding Jupiter's role in our solar system could help us search for life beyond it.
除了帮助我们了解如何保护地球外，了解木星在太阳系中的作用也可以帮助我们搜寻太阳系外的生命。
When we look for habitable worlds orbiting other stars, it might be useful not just to look for Earth-like planets, but also to see what a Jupiter-like frenemy might be up to nearby.
在我们寻找其他恒星的行星是否宜居时，如果我们不将目光锁定在像地球一样的行星上，如果我们也能看看像木星这样让人欢喜让人忧的行星在附近起到了何种作用的话，那或许会有帮助。
Thanks for watching this episode of SciShow Space!
感谢收看本期的《太空科学秀》！
If you want to learn more about how Jupiter tosses its weight around in the solar system, you might like our video about the group of asteroids Jupiter has held prisoner—possibly for billions of years!
如果想了解更多木星在太阳系里反复扔东西的知识，你或许会喜欢我们的一期视频——这期视频讲解了被木星困在身边的一群小行星——可能已经困了数十亿年哦！
You can find out more about Jupiter's Trojan asteroids after this.
这个看完了的话，还可以从木星的特洛伊小行星上了解更多。
