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This episode is sponsored by The Great Courses Plus.
本期《太空科学秀》由“课程学习大全”赞助播出。
Saturn's beautiful rings might be the most recognizable thing in all of astronomy, but it won't be that way forever.
土星美丽的光环可能是天文史上最有辨识度的存在之一，但不会永远都是如此。
In 2018, planetary scientists realized that the rings are disappearing way faster than previously expected.
2018年，行星科学家们发现，土星光环消失的速度比预想的要快很多。
In fact, some researchers went as far as to say this was the “worst-case scenario.”
实际上，一些科学家甚至说这是“最坏的情况。”
Now, before the wave of grief overwhelms you, remember that this is astronomy.
现在，先别顾着伤心，我们要记住这是天文学的常态。
In this case, way faster means that the rings may only be around for another hundred million years or so.
就土星的情况来说，光环消失的速度更快就意味着光环可能还会存在大概几亿年的时间。
What might be even more surprising about this research is that it suggests Saturn's rings might also only be around a hundred million years old, billions of years younger than some astronomers have suspected.
该研究可能更让人吃惊的一点是：研究表明，土星光环可能也只存在了大概几亿年的时间，其年龄比一些天文学家预想的要小。
That complicates our understanding of where the rings might have come from in the first place.
这加大了我们了解土星光环从何而来的难度。
And it's making some people wonder if, maybe, the ring system we see today isn't the only one Saturn has ever had.
也让一些人猜测我们今天看到的星环是否是土星曾有过的唯一星环。
Those 2018 results were thanks to NASA's Cassini mission, which wrapped up in 2017.
上述是2018年的研究结果，该结果的得出要感谢美国宇航局卡西尼号太空船。卡西尼号于2017年结束了任务。
As the mission came to an end, scientists sent the spacecraft between Saturn and its rings for the very first time.
在卡西尼号任务要接近尾声时，科学家首次将它派到土星和土星光环之间。
During these final orbits, Cassini detected material falling from the innermost ring onto the planet's upper atmosphere, the first direct measurements of what scientists called ring rain.
在这最后阶段的环行中，卡西尼号勘测到了最里面的星环上会脱落一些物质到土星的大气层中，这是科学家第一次进行直接的测量，这种现象称为环雨。
And the data were backed up by astronomers using the giant Keck telescope in Hawaii.
该数据得到了科学家的证实，科学家用到的工具是位于夏威夷的大型望远镜凯克。
Material falls from the rings for a bunch of reasons, including random collisions between ring particles and particles getting dragged around by Saturn's magnetic field.
环雨的出现是有诸多原因的，比如星环粒子与土星磁场吸引的其他粒子发生了不规则碰撞。
We've actually seen evidence of this process since the 1980s, so that part of Cassini's discovery wasn't surprising.
实际上，自上世纪80年代以来，我们已经观测到环雨的一些证据，所以卡西尼号的这个发现成果并未让我们感到惊讶。
What did catch scientists off guard, though, was how effective ring rain seems to be.
而真正让科学家吃惊的是：环雨的速度非常之快。
Cassini and Keck's observations allowed scientists to more accurately calculate the rate Saturn's rings are losing material,
卡西尼号和凯克望远镜的观测结果让科学家可以更精准地计算土星环产生环雨的速率。
and they found it could be anywhere from around 5,000 to 45,000 kilograms per second.
通过计算，他们发现，环雨产生的速率大概在5000-4.5万公里/秒之间。
And that has some significant implications.
这个计算结果给了我们很多重要的提示。
Researchers have used that new number to run time forward and backward in computer simulations, and they've found that it would only take around a hundred million years for what we see today to disappear.
研究人员通过最新计算的结果反复进行计算机模拟计算，随后，他们发现，大概只需要几亿年的时间，土星环就会彻底消失。
But even more significantly, you'd only have to go back about a hundred million years for Saturn's inner rings to have as much material as the largest one does today.
但更为重要的是：土星环只用了几亿年的时间就变成了目前为止最大的星环。
Scientists think that's a pretty good estimate for how old the ring system might be.
科学家认为，这可以帮助我们估测土星环的年龄。
It's a rough guess, but that value matches other lines of evidence, like how clean the rings seem to be.
这只是一个大致的猜测，但这个值与其他证据吻合，比如土星环有多干净。
Either way, what's clear is that the rings are young compared to the four and a half billion-year age of the solar system, and that kind of throws a wrench in things.
无论是哪种情况，现在很明显的一点是：土星环年龄很小，跟已经有45亿年历史的太阳系比相距甚远，而这一点阻碍了我们的研究进程。
See, Saturn's rings are the outlier in the solar system.
毕竟，土星环不属于太阳系的一部分。
Not only are they much larger than those of other outer planets, but they're also made of nearly pure ice instead of dust and rock.
土星环不仅要比其他外部的行星更大，而且土星环也是由几乎纯冰，而非尘土和岩石组成的。
Whatever formed them needs to account for this purity.
无论组成土星环的是什么，其纯度都是无可置疑的。
And that eliminates many options, since most objects in space contain a mix of ice, rock, and metal.
这就否掉了很多可能性，因为宇宙里的大多数物体都是冰、岩石和金属的混合体。
The problem is, some of the best hypotheses that do explain the purity really only make sense if the rings are as old as the solar system.
问题在于：虽然有一些假设看起来很有可能性，但这些假设虽然能解释纯度的问题，但却需要一个前提——土星环跟太阳系年龄相仿。
Like, one idea is that the rings are the icy outer layers of a large moon that was torn apart by Saturn's gravity.
比如，有一个假说认为：土星环是土星某个大型卫星的外层，该外层由冰组成。而该卫星则因土星的引力作用而四分五裂。
But in order for a moon that size to get close enough to Saturn to be ripped apart, there would have to be a disk of debris around Saturn, and that disk only lasted a short time after the planet formed.
但土星的卫星要离土星足够近才能被图形的引力作用所撕裂，这样的话，该卫星必须是土星附近由残骸组成的圆盘，而土星形成后，这个圆盘只存在了很短的一段时间。
Another possibility is that a large asteroid or comet destroyed a medium-sized moon like Mimas, which contains very little rock or metal.
还有一个假说认为：曾有一颗巨大的小行星或者彗星摧毁了中等大小的卫星，比如土卫一，而其中含有很少的岩石或者金属。
But again, that kind of big collision was much more common billions of years ago than a hundred million years ago.
但这种撞击在几十亿年前才比较常见，而在几亿年前是很少见的。
Researchers aren't totally out of ideas, though.
而除了这些假说之外，科学家现在还没有什么头绪。
One hypothesis that might make more sense is a pair of smaller moons colliding in the recent past, similar to how some scientists think the rings of Uranus formed.
有一个更有可能的假说认为：不久前，两颗小型微型相撞，其撞击方式与天王星光环的撞击方式类似。
The gravity of a passing comet might be enough to nudge one object into the orbit of another, and most of Saturn's small moons seem to be nearly pure ice, anyway.
若是有彗星经过，那彗星的引力应该足以让一个物体进入另一颗星体的轨道中，而土星诸多小型卫星中的大多数似乎都是由纯冰组成的。
Unfortunately, the models for this idea aren't all that supportive so far, so it might be back to the drawing board.
不过，该假说的模型证实力度较弱，所以我们可能还是要从头来过。
Scientists will likely be researching their hypotheses for a while, but there's actually another, even bigger question raised by Cassini's discoveries:
科学家可能还要颇费些时日才能找到合理的假说，但还有另一个假说提出了更大的问题，这个问题是由卡西尼号的发现成果所引发的：
If the rings are so young and short-lived, why are we so lucky that we get to be around when they are?
如果光环存在时间不长并且生命周期很短的话，那我们为何能如此幸运的看到光环。
Astronomers hate feeling lucky, because it sometimes means that they're not looking hard enough for the deeper answer.
科学家不相信走狗屎运的说法，因为有时候这说明科学家没有足够努力地挖掘深层次原因。
So many don't think this is a coincidence.
所以很多科学家认为这不是一个巧合。
Like, maybe these rings are recent, but what we see is actually just the latest iteration of a process that has happened multiple times in Saturn's history.
因为就算这些光环是最近才形成的，但我们现在看到的只是最近某个过程的反复迭代，而这个迭代过程在土星历史上已发生过多次。
Maybe Saturn has spent the last four billion years collecting and destroying one ring system after another.
或许土星过去40亿年间一直在收集并摧毁一个又一个星环系统。
If that's true, it might also mean that the other outer planets have had large rings in the past, too, but they just don't right now.
如果该说法为真，那么这可能意味着其他外部的行星以前可能也曾有过大型光环，但现在却没有了。
There are a lot of questions left to answer here, but they're ones scientists are actively investigating,
还有很多疑问有待解开，这些疑问就交给科学家去研究了。
and they could lead to a new understanding of how ring systems form, and what our solar system looked like not that long ago.
这些疑问的研究可能会让我们对星环系统的形成方式有新的理解，也让我们能对不久之前太阳系的样子有新的了解。
Oh, and in case you're still mourning the future loss of the rings, there is one last bit of good news:
对了，为了调解一下大家可能为土星环消失的悲伤心情，这里有一个好消息：
Even once the main rings have disappeared, Saturn won't be entirely ringless!
即便主环消失，土星也不会一个星环都没有的！
The dusty G ring and Phoebe ring are constantly being replenished by debris knocked off nearby moons, and the E ring is composed of ice particles ejected by the geysers on Enceladus.
满是灰尘的G环和土卫九的光环一直在接收残骸源源不断的补充，这些残骸的来源是附近的其他卫星。此外，E环是由冰粒子组成的，而冰粒子是由土卫二的间歇泉放出的。
So there still will be rings! Everything will be alright.
所以，星环是肯定会有的！这都不是事儿。
And who knows, maybe by then another planet will have some new bling to show off!
而且，谁能说得准那时候会不会有另一颗行星有着闪亮的光环呢！
If you're interested in learning more about space science and how to understand it, you can check out The Great Courses Plus!
如果您有兴趣继续了解空间科学的知识及原理，您可以访问“课程学习大全”。
It's a subscription-based, on-demand video learning service, and it is full of some seriously impressive lectures and courses.
“课程学习大全”可以订阅并根据大家的需求帮助大家通过视频进行学习，其中有些课程让人印象非常深刻。
You can watch a lecture from professors at Ivy League universities, other great schools worldwide, or experts from places like National Geographic, The Smithsonian, and the Culinary Institute of America.
在上面，大家可以观看常青藤大学等全球知名大学的讲座，也可以听《国家地理》、史密森尼学会、美国烹饪学院等专家的讲座。
They have more than 11,000 video lectures to choose from, and you can learn just about anything.
上面有1.1万多个视频可供大家挑选，内容包罗万象。
They have courses on science, math, history, literature, and even hobbies, like cooking or photography.
课程涉及科学、数学、历史、文学甚至爱好（比如烹饪和摄影）。
If you want learn more about the inventions that have helped us explore space, you could watch a course called Space, Technology, and Discovery.
如果您想了解更多的发明创造以帮助我们更好地探索宇宙的话，您可以观看《太空、科技与发现》节目。
It opens with an episode about the Curiosity rover, so you know I am immediately on board.
该节目的首期就介绍了好奇号探测器，我对这个就很感兴趣。
Right now, The Great Courses Plus is giving SciShow viewers the chance to try their content for free!
目前，“课程学习大全”为《太空科学秀》的观众朋友们提供了一个机会，可以免费试看其课程。
And if you choose to subscribe after the trial, you will be supporting SciShow, too.
如果您在试看后订阅的话，也是对我们节目的支持了。
To learn more, you can visit thegreatcoursesplus.com/SciShowSpace, or click the link in the description to start a free trial.
想要了解的更多的话，可以访问thegreatcoursesplus.com/SciShowSpace，或者点击下方的链接来进行免费试看哦。
