了解宇宙是如何运行的（2010）

How the Universe Works S06E08

Part 4 Dec. 22, 2021, 7:23 p.m.

最后的残余地幔
of Mercury's lost mantle.
如果我们能发现祝融小行星，那将为我们
If we were to discover
vulcanoids, that would offer us
提供一个全新的研究对象种群
an entirely new population
of objects to study.
这些物质可以为水星本身的形成
This material could offer
some rather unique insight
提供一些相当独特的见解
into the formation
of Mercury itself.
一场巨大的正面撞击是我们对水星怪异结构的
A giant head-on impact
has been our best explanation
最好的解释
for Mercury's weird structure.
但现在有一个关于水星缺失的地幔
But now there's a
startling new theory
惊人的新理论
for Mercury's missing mantle.
它被偷了，但谁是小偷？
It was stolen,
but who is the thief?
多年来，我们一直认为
For years,
we assumed that Mercury lost
水星在一次巨大的正面碰撞中失去了大部分地幔
most of its mantle
in a giant head-on collision.
但信使号♥飞船却颠覆了一切
But the messenger spacecraft
turned everything on its head.
通过发射探测器来研究水星表面
One of the exciting things
that we've learned
我们最近了解到的一件
about Mercury recently
令人兴奋的事情
by sending probes
to study its surface
它的表面散落着我们认为
is that its surface
is littered with material
不应该存在的物质
that we didn't think
should be there,
我们称之为挥发物
things that we'd call volatiles.
挥发物是像钾这样的化学元素
The volatiles are chemical
elements like potassium.
之所以它们被认为不稳定……
They're called volatile...
因为它们在高温下很容易蒸发
Because they evaporate
easily in high temperatures,
这种高温正好是巨大撞击产生的那种温度
just the sorts of temperatures
generated by a giant impact.
如果我必须用一个词来形容水星
If I had to describe
Mercury in a word,
那就是“惊讶”
it would be "surprising."
新的想法是，一个较小的物体撞上了水星
The idea was that a smaller
object ran into Mercury
撞掉了物质
and knocked off material.
好吧，这的确会使它失去物质
Well, that actually would work
to make it lose material,
但它也会产生大量的热量
but it would also generate
a lot of heat,
正因为如此，水星上的挥发性物质
and because of that, the
volatile materials on Mercury
也同样会失去
would also have been lost.
但今天，我们看到它们还在那里
But today, we see that
they're still there.
所以这意味着大多数关于水星如何形成的基本设想
So it meant that most of the
basic scenarios that have been
都被证明是错误的
laid out for how Mercury was
assembled had been disproven.
我们必须从头开始
We had to go back
to the drawing board
重新思考水星是如何形成的
and rethink how
Mercury was assembled
以及水星是如何进化的
and how Mercury evolved.
水星是如何失去地幔
How did Mercury lose its mantle
而保留这些挥发物的？
but retain these volatiles?
水星就像是一起侦探案件
Mercury is like
a detective case.
我们有了尸体也有一些线索
We have the body.
We have some clues,
但我们必须把它们拼凑起来
but we really have to
piece it together.
行星科学家埃里克·阿斯帕格
Planetary scientist Erik Asphaug
解开了这个巨大的谜题
tackles this giant riddle.
最初的想法是
The original idea was that
水星被比它本身更小的东西击中
Mercury was hit by something
smaller than itself.
但无论水星的形成过程是什么
But whatever process
made Mercury
它都以某种方式保存了
somehow preserved
all these volatiles
这些本应蒸发并消失的挥发物
that should have
vaporized and gone.
埃里克有一个大胆的猜想
Erik has a bold alternative,
肇事逃逸
a hit-and-run collision.
在“肇事逃逸”的碰撞理论中
In the hit-and-run collision
idea, you actually have
水星实际上是在不失去所有挥发物的情况下
Mercury hitting something
bigger than itself
撞击了比它自身更大的物体
without losing
all of its volatiles.
撞击更大的物体可能听起来更糟糕
Hitting something
bigger may sound even worse,
但这完全取决于你如何撞击它
but it all depends
on how you hit it.
在早期的太阳系里，有很多成员
In the early solar system,
there were a lot of players,
就像曲棍球比赛一样，事情变得残酷起来
and just like a hockey match,
things got brutal.
你会看到星子通过碰撞生长
You would have had planetesimals
growing through collisions.
较大的天体会占据主导地位
The bigger objects
would have dominated
因为它们不仅会撞上较小的天体
because not only are they
running into smaller objects,
还会通过引力将较小的天体吸引到自己身上
they're drawing them
to themselves gravitationally,
而两个天体会将大部分物质卷走
and two objects will sweep up
most of the matter.
这两个物体就是金星和地球
Those two objects
became Venus and Earth.
地球和金星是内太阳系的
Earth and Venus
are the enforcers
执法者
of the inner solar system,
消灭了大部分竞争对手
wiping out most
of the competition.
哇！
Whoo!
小水星是最后剩下的玩家之一
Little Mercury is one
of the last players left,
它可能会与地球正面交锋
and it could have
a faceoff with Earth.
水星是这个事件中的小东西
Mercury is the little guy
in this thing,
这个冰球是我们的挥发物
and this hockey puck
is our volatiles.
那个小个子高速冲进来
The little guy comes in
at a high speed
迎面撞上了那个大个子
and has a head-on collision
with the big guy.
这是灾难性的
It is catastrophic.
但现在假设
But suppose now,
instead of hitting him
他不是迎面撞他
in a head-on collision,
而是侧击他
he hits him in a glancing blow.
所以他可能会弄掉一些设备
So he might knock off
a little bit of equipment,
但水星继续前进，并保留着他的冰球
but Mercury just keeps on going
and keeps his hockey puck.
正面撞击会产生冲击波穿过水星
A head-on impact would send
a shockwave across Mercury,
融化整个表面
melting the entire surface.
但侧击就没那么猛烈了
But a glancing blow
is less ferocious.
你摩擦碰撞的东西越多
The more grazing
you hit something,
你带来的能量就越少，它就越不暴♥力♥
the less energy you bring
to bear, the less violent it is.
在摩擦碰撞中
In the grazing collision
is where piece of the surface
物体表面的一部分被摩擦掉并炸向太空
has grazed off
and blasted into space,
而物体的另一个半球基本上不受影响
and the other hemisphere of
the body is largely unaffected
让一些原始物质
and allowed some
primordial material
留在表面上
to remain on the surface.
水星的大部分地幔被剥离了
Most of Mercury's
mantle is stripped away,
但这种掠食冲击
but this grazing impact
并没有向星球发出冲击波
doesn't send a shockwave
through the planet,
所以挥发性物质和足够多的地幔一起留下来
and so the volatiles remain
along with enough of the mantle
以一层薄薄的岩石外层重塑这个世界
to reshape this world
with a thin outer layer of rock.