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It's been more than 20 years since astronomers discovered the first planet orbiting a star beyond our own.
20多年前，天文学家发现了第一颗系外行星。
And today, there's a catalog of more than 3700 confirmed exoplanets, along with thousands more unconfirmed candidates.
今天，已登记在案的系外行星有3700多个，此外还有上千个尚未确认的星体可能是系外行星。
But now, we might have found the very first moon beyond our solar system, or an exomoon.
但现在，我们可能发现了太阳系外的第一颗系外行星了。
Last week, Science Advances published the first quote-unquote compelling evidence of a huge, Neptune-sized exomoon 8,000 light-years away.
上周，《科学进展》上发表了第一份所谓的实锤证据，他们指出，在8000光年外，有一颗跟海王星差不多大小的系外行星。
In 2017, data from the Kepler Space Telescope seemed to contain hints that an exomoon might be out there.
2017年，开普勒太空望远镜观测到的数据似乎在暗示着那里可能有一颗系外行星。
The data revealed that a body the size of a gas giant was orbiting a larger body called Kepler-1625b.
数据表明，有一个物体跟气体巨星的大小差不多。这个物体正在环绕一个更大的物体飞行，而更大的物体就是开普勒-1625b。
Now, two astronomers from Columbia University have used the even-stronger Hubble Space Telescope to further explore the system.
现在，来自哥伦比亚大学的两位天文学家通过更强大的哈勃太空望远镜进一步探索这个体系。
And from what they saw, it looks like that exomoon signature isn't some error in the data.
他们观测到，似乎这颗系外行星的信号并不是说明数据有什么问题。
In the new study, the team used the transit method to study 1625b.
在这项最新研究中，该小组通过中天法研究了开普勒-1625b。
In other words, they analyzed the light coming from its star and how it dims as the planet passes between the star and us.
换言之，他们分析了这颗恒星放出的光，以及当这颗行星运行到该恒星和地球之间的时候亮度变弱的方式。
The weird thing was, about 3.5 hours after the planet's transit ended, there was a smaller dip in brightness.
奇怪的是，这颗行星经过之后大概3.5小时，亮度有所下降。
That suggests the planet has a moon trailing it.
这表明，这颗行星后面有一颗卫星尾随。
To the disappointment of space nerds everywhere (including us) the team ran out of observation time before the potential moon had finished its own transit.
但让所有天文学家（包括我们这些非天文工作者）失望的是，在这颗可能是卫星的星体还没完成穿越之前，观测时间就到了。
So they don't have a full set of data to analyze.
所以，他们没有一整套数据可以分析。
The good news is, there is a little more data that supports the planet having a natural satellite: The planet's transit started over an hour earlier than was predicted.
好消息是：还有一部分多出来的数据可以让这颗行星有一颗自然卫星：该行星穿越的起始点提早了1小时。
That could happen if it had a moon tugging on it and changing the system's center of gravity.
这种情况可能的原因是：该行星后有卫星的引力在拖拽，这种引力改变了该体系的重心。
So far, all this evidence suggests this moon, if it exists, is comparable in mass and size to Neptune.
目前为止，所有证据都表明，假如这颗卫星存在的话，其质量和大小都可以跟海王星媲美。
By our standards, that's huge. But since the planet is around the same size as Jupiter and a few times more massive, it makes sense.
从各种标准来看，这颗卫星体型都非常巨大。但鉴于该行星的大小跟木星差不多，甚至比木星还要大上那么几倍，所以其卫星这么大也说得通了。
Then again, these properties aren't based on the strongest models, so there's still some uncertainty.
况且，这些特性是基于最强的模型，所以还是有一些不确定因素的。
It could be that our data is a bit off and that there isn't a moon at all.
有可能是我们的数据有所偏离，其实压根儿就没有卫星也说不准呢。
Instead, there could be a second planet in the system that's responsible, although there hasn't been any evidence of that so far.
也有可能这个体系里还有一颗行星在起作用，虽然目前为止还没有证据能证明这一点。
It's also possible that 1625b could just have a longer orbital period than we think.
还很有可能的情况是：1625b的轨道周期可能比我们预想的要长。
Or it could be orbiting at such a distance or angle that it's not transiting every time we look at it, which could be why our predictions were off this time.
也有可能它的运行距离和角度导致每次我们观测的时候，都不是它穿过的时间段。这也有可能是我们这次出现偏差的原因。
Right now, the authors of this paper confess this first exomoon has to survive years of scrutiny and follow-up before its existence can be confirmed.
现在呢，本文的几位作者坦言，这第一颗系外行星在我们确认它存在的很多年前就存在了，虽然这段空白期间，我们也一直在仔细地追踪观测。
But if it does end up being a moon beyond our solar system, it will be a really important target to continue studying.
但如果该星体最后经证实确实是太阳系外的卫星的话，这对于我们继续进行研究是非常重要的目标。
For example, since it's likely much, much larger than any moon in our system, it opens the question of how planetary systems form and evolve.
比如，鉴于该星体比太阳系里的任何一颗卫星都要大很多，所以，这就让我们想知道各行星体系是如何形成和发展的。
And the moon's origins at the moment are a total mystery.
目前，这颗卫星的起源还是个谜。
Like, was it captured, or did it form alongside its partner? At this point, we can only guess.
比如，我们既不了解它是否被俘获的，还是在小伙伴附近形成的。关于这个问题，我们现在还只能猜。
In other moon news, a study published online this week in Nature Geoscience predicts a decent chunk of Jupiter's moon Europa might be covered in giant ice blades!
再来说说其他跟卫星有关的新闻：本周，一项研究发表在了《自然地球科学》上。该研究预测了木卫二的很大一部分可能掩藏在了巨大的冰刃之下。
Officially, these blades are called penitentes. They're formed when large chunks of frozen water heat up and sublimate, turning directly from a solid into a gas.
这种冰刃叫penitentes，其形成条件是：固态水经加热后升华，直接从固态变为气态。
On Earth, we see this happen in places like the top of the Andes Mountains.
地球上只有安第斯山脉顶端这样的地方才能看到这种景象。
But we've also seen evidence of these blades on Pluto.
但我们也在冥王星上发现过这种冰刃的存在。
For penitentes to form, the environment has to be super dry and cold, the air has to be really still, and the sunlight has to hit the ice at just the right angle and for long enough periods of time.
要想让这种冰刃形成，环境就需要极度干冷，空气必须静止。太阳照射冰的角度也必须恰如其分，而且照射的时间段也必须足够久。
Then, the Sun's radiation causes heaps of water molecules to sublimate, carving deep depressions into the surface and turning everything really spiky.
而且，太阳的辐射会引起大量水分子升华，使其表面发生大量下陷，出现了各种尖状的形态。
In other words, the penitentes don't grow up like stalagmites do they're leftovers!
换言之，这种冰刃并不是像石笋一样成长的，他们是发生上述变化后的结果哦！
Eventually, penitentes smooth out or break apart, either from geologic activity beneath the surface or space debris smashing into them from above.
最后，这种冰刃变得平滑，要么四散瓦解，出现这种变化要么是因为地表下的地质活动，要么是因为空间碎片的撞击。
But the amount of time that takes can vary.
但所需的时间却是会变化的。
To learn more about Europa, astronomers wanted to determine the likelihood, location, and size of penitentes.
为了了解更多有关木卫二的信息，天文学家就需要确定冰刃形成的可能性、位置及其大小。
So they created a model. It took into account things like how Europa is tilted toward the Sun, its range of temperatures, and the reflectivity of its surface.
所以，他们创建了一个模型。该模型融合了很多元素，比如木卫二与太阳的倾斜角、温度变化情况、表面的反射率。
They also needed to estimate how often space debris would crash into Europa's surface, which would smooth out its features.
他们还需要估测空间碎片撞击木卫二表面的频率，因为这种撞击会让冰刃表面变得平滑。
According to their model, water could sublimate faster than erosion could smooth things out at latitudes below 23° or so.
从该模型可以得知，在纬度低于23°左右的时候，水升华的速度要比腐蚀作用让物体变平滑的速度更快。
That means, for a large band around Europa's equator, we'd likely see a healthy population of penitentes.
也就是说，木卫二赤道附近的很大一块地带上，很有可能会存在很多非常完好的冰刃群。
The team also calculated that, over 50 million years which is the average age of Europa's surface the blades could get up to 15 meters tall.
该小组还计算出一个结果：在5000万年的时间里，也就是木卫二表面形成的平均时间里，冰刃可以长到15米高。
That's three times taller than what we usually see on Earth.
这个高度是地球上冰刃高度的3倍。
Of course, all their stats are averages, and don't take into account local geologic features, or exactly how impurities in the ice will play a role.
当然了，这些数值都是平均值，还没有考虑到当地的地理特征，也就是杂质的影响。
So there may be more to the story. Unfortunately, our technology near Europa doesn't have the proper resolution to find photographic evidence of this spiky surface.
所以，这项研究还要继续下去。不幸的是，我们在木卫二附近的技术无法实现较高的清晰度，所以也就无法在可能满是冰刃的表面通过照片发现证据。
But there is both ground-based radar and thermal data from the 1990s Galileo probe that suggests penitentes could be there.
但上世纪90年代，地面雷达和伽利略号探测器发回的数据表明，这种冰刃就是存在的。
Studies like this are cool, but they're about more than just uncovering giant ice spikes on a far-flung moon.
这种研究很酷，但其意义并不只是揭示遥远卫星上的巨大冰刃而已。
To scientists and engineers, this kind of information is really important to know when planning a future lander mission to Europa.
对于科学家和工程师来说，这种信息是很重要的，因为通过它可以确定未来何时计划发射着陆器到木卫二上比较合适。
The moon is one of a few that scientists are almost definitely sure has a liquid water ocean beneath its surface.
这颗卫星很难得，因为总共也没有几颗卫星是科学家几乎断定表面下有液态海洋的。
And although there aren't any landers officially on the docket right now, we'll need all the information we can get when we are ready to go.
而且，虽然目前还没有这样的着陆器，但在设备研发出来之前，信息先要收集周全才是。
Thanks for watching this episode of SciShow Space News!
感谢收看本期的《太空科学秀》！
And thanks especially to our Patrons on Patreon.
也要感谢我们的老朋友们！
The things beyond our planet are beautiful and fascinating, and we love getting to explore them with you.
系外的世界很精彩，我们希望能继续跟大家一起探索了解。
