了解宇宙是如何运行的（2010）

How the Universe Works S06E02

Part 5 Dec. 22, 2021, 7:22 p.m.

科学家们发现了一层薄薄的气体雾
scientists spotted a thin haze of gas.
原来冥王星有大气层
Turns out, Pluto has an atmosphere.
但这种大气是暂时的
But this atmosphere is temporary
因为冥王星的轨道是椭圆形的
because Pluto's orbit is elliptical.
有时，它离太阳很远
Some of the time, it's far from the Sun.
其他时间则离太阳比较近，天气会变得暖和
Other times, it's much closer and warmer,
形成了一种冬夏两季的气候
creating a kind of winter and summer.
冥王星的大气层取决于季节
Pluto's atmosphere depends on the season.
在夏天，它足够暖和，就有一个大气层
In the summer, it's warm enough to have an atmosphere,
在冬天，大气层就冻结了
and in the winter, that atmosphere freezes out.
在绕太阳运行一圈的过程中
Over the course of just a single orbit around the Sun,
这些矮行星的表面
the surfaces of these dwarf planets
可能会发生显著的变化
may change significantly,
当它们远离太阳时
condensing and coding out atmosphere
它们的大气层会被压缩和凝结
when they're far from the Sun,
当它们靠近太阳时
having that atmosphere revolatilize
大气层会旋转和重新分布
and redistribute the surface when they're closer to the Sun.
目前冥王星处于夏季阶段
Pluto is currently in its summer phase.
在漫长的炎热的夏季里
The extra heat during the long super summer
额外的热量蒸发了表面的一些氮冰
evaporates some of the nitrogen ice on the surface,
于是形成了一个稀薄的大气
creating a thin, wispy atmosphere.
结果发现
It turns out that even though
尽管冥王星的大气层很薄，但仍有风存在
the atmosphere of Pluto is very thin, there is wind.
这风真的很轻
It's really light, but there's just enough wind
但只要有足够的风
to be able to carry particles with it once they start moving.
小颗粒就会开始移♥动♥，风就可以带走这些颗粒
The seasonal cycle
这有助于解释阋神星明亮的表明
could help explain Eris' brightness.
阋神星离太阳的距离
Eris is three times further away from the Sun
是冥王星的三倍远
than Pluto is,
但是当你把氮气体放在
but when you put a nitrogen atmosphere
离太阳三倍远的地方时
three times further away,
氮就会冻结在表面
that nitrogen freezes solid to the surface.
阋神星可能
Eris could be an indicator
就像冥王星进入冬季时一样
of what Pluto looks like when it enters its winter.
气体会结成冰，使得星球表面反射性变得更强
The gases will freeze, and it'll become even more reflective.
在冬季
In winter,
冥王星的沙丘
Pluto's dunes will be locked in place...
就会被锁定在冻结的地表
Frozen on the surface,
这与另一个矮行星的冰层特征不同
unlike the icy features of another dwarf planet
它会让火山消失
and the case of the vanishing volcanoes.
从远处看，这颗矮星谷神星
From afar, the dwarf planet Ceres
看起来均匀而沉闷
looks uniform and dull...
但近距离看，有一个巨大的特征出现在我们眼前
...but up close, one huge feature comes into view.
当我们开始绘制谷神星表面的地图时
One of the strangest objects that we saw
我们所看到的最奇怪的物体之一
when we began to map the surface of Ceres
有一种山，叫做阿胡娜·蒙斯（Ahuna Mons）
was something called Ahuna Mons.
这是一个奇怪的，突出的山
Now, this was a strange, jutting hill, very, very sharp sides,
有着非常，非常尖锐的侧面
and it didn't match any of the other terrain on Ceres.
与谷神星上的其他任何地形相比显得非常突兀
Ahuna Mons is a very peculiar feature on Ceres.
这是一座三英里高的山
This is a mountain that is standing three miles high,
在谷神星的整个表面上
and there's nothing else like it
没有任何其他东西能与它相比
on the entire surface of Ceres.
阿胡娜·蒙斯主宰着谷神星的景观
Ahuna Mons dominates the landscape of Ceres.
由于其陡峭的侧面和巨大的高度
With its steep sides and enormous height,
它看起来很像地球上的火山
it looks a lot like volcanoes on earth,
但地球上的火山仍然有地质活动
but earth is still geologically active.
谷神星很小，它的核心应该是早就冰结了
Ceres is so small, its molten core should be frozen solid.
行星科学家尼娜·兰扎（Nina Lanza）
Planetary scientist Nina Lanza
前往地球上火山活动最活跃的地方之一
heads to one of the most volcanically active places
冰岛
on earth... Iceland.
她用无人机俯瞰赫尔加菲火山
She has a drone's-eye view of mount Helgafell,
这座火山的形状与阿胡娜·蒙斯火山相似
a volcano similar in shape to Ahuna Mons.
所以这座火山被称为流纹岩穹顶
So this volcano is what's called a rhyolitic dome,
它是一种熔岩
and so it's a type of lava
通过地表裂缝被挤压出来
that kind of gets squeezed out through fissures,
然后形成这种泡泡状的穹顶
and then forms this kind of blobby dome feature
被从下面挤出的岩浆一点点推高
that gets pushed up by the magma coming up from beneath.
在地球上，炽热的岩浆泡会从地表裂缝中慢慢挤出
On earth, red-hot magma bubbles slowly
形成一座山坡陡峭的火山
out of cracks in the surface, building a steep-sided volcano.
但是像谷神星这样的矮行星太小了
But dwarf planets like Ceres are too small
没有一个炽热的熔岩核心来支持火山活动
to have a hot core of molten rock to power volcanism.
这些小星球上没有熔岩
There isn't molten rock on these smaller worlds
但上面有很多冰
that have a lot of ice on them.
相反，融化的是地表下的水
Instead, what's molten is water under the surface,
如果水能通过裂缝向上流动并在地表喷发
and if the water can work its way up through cracks
也会得到一座“火山”
and erupt out in the surface, you get a volcano.
但这是一座冷水火山
But it's a cold-water volcano.
我们称之为冰♥火♥山
We call these cryovolcanoes.
液态水从表面的裂缝中
Liquid water squeezes up
挤了上来
through fissures in the surface.
它很快就结冰了，然后建成了这座冰♥火♥山
It quickly freezes, building the mountain.
这座冰♥火♥山，可以看到它具有很年轻的特征
This volcano, you can see that it's a pretty young feature,
它并没有被侵蚀
and it's not very eroded.
在地球上
We expect on earth that wind and water
风和水会慢慢侵蚀这座山
will slowly erode this mountain away.
因为没有风或天气侵蚀谷神星的冰♥火♥山
With no wind or weather
所以冰♥火♥山一旦形成
to erode Ceres' cryovolcanoes, once created,
它们将在地表上
they should remain on the surface
停留达数十亿年
for billions of years.
胡娜·蒙斯很奇怪
Ahuna Mons is very strange
因为它是谷神星上唯一的一座高山
because it's the only tall mountain on Ceres.
为什么会这样？
Why should that be?
通常情况下，不会只有一座冰♥火♥山
You don't typically get just one of something.
应该有很多这样的火山
You should have dozens of them, and, in fact,
事实上，谷神星可能曾经有很多冰♥火♥山
Ceres may have had quite a few cryovolcanoes in the past,
但今天它们都消失了
but they're all gone today.
我们换个角度思考一下
Just to put that into perspective,
如果这是地球上的唯一的火山
imagine if this is the only mountain on earth.
为什么会只有一座山？
Why would there only be one mountain?
那是什么意思？
What would that mean?
这就引出了一个问题
This leads us to ask the question, you know,
你知道吗？谷神星上的火山正在消失
are the volcanoes on Ceres disappearing?
火山正在消失的想法……
The idea that volcanoes are vanishing...
听起来完全是科幻小说
It just sounds totally science fiction,
一点都不现实
and really, not realistic at all.
当然，火山不可能凭空消失
Of course, volcanoes can't just vanish,
事实上，在符合某些条件的情况下
but actually, in the right context,
确实可以发生这种事情
in certain scenarios, they actually can.
这个“魔术”的关键就是引力
The key to this magic trick... Gravity.
它能使固体变平
It can flatten solid matter.
至于多快
How quickly depends on
取决于材料的结构组成
the structural composition of the material.
如果你想在海滩上建一座沙堡
If you want to build a sand castle on the beach,
你就不能用干沙
you can't use dry sand.
它粘不到一起
It doesn't stick together,
所以你得在里面混合一点水
so you want to mix a little bit of water in there
这样当你建沙堡的时候
so that when you make the structure,
它就会粘在一起了
it holds together,
但是如果你加入了太多的水，它又会流走
but if you mix in too much water, it just dribbles away.
会会变成粘性流体
It viscously relaxes.
然后就会塌下来
It slumps.
就连冰岛的岩石火山
Even Iceland's rock volcanoes
也在自己的重压下慢慢崩塌
are slowly slumping under their own weight.
虽然想象起来很奇怪
Strange as it is to imagine this,
但我身后的那座火山
it turns out the mountain behind me
就在慢慢地往下塌
is actually slowly relaxing back down.
只是速度非常慢
It's just happening very slowly,
在人类的时间尺度上，我们无法直接观察到
not on a time scale that we can directly observe.
谷神星表面
It may be that there were many cryovolcanoes
可能有许多冰♥火♥山
on the surface of Ceres.