了解宇宙是如何运行的（2010）

How the Universe Works S01E08

Part 2 April 18, 2021, 7:58 p.m.

difference between survival and destruction.
太靠近行星, 会被引力摧毁
Get too close, and the planet's
gravity will rip a moon to shreds.
科学家相信木星年轻时
Scientists believe this is what happened
有不少卫星因此死亡
to many moons when Jupiter was young.
木星很可能曾有一批大的卫星
And it's very likely that Jupiter had
an entire conveyer belt of large moons
不过它们都被木星吞噬了
that when they formed only to be
swallowed up by the planet itself.
今天所见的戴维星是硕果仅存
The large moons we see
today are only the last ones
它们稳定下来, 不再转入死路
that were able to stabilise
right at the end of that process,
于是得以存活, 并留在今天的位置
stop their death spiral, and survive
into the position we see today.
但木星仍不断想把它们吃掉
But Jupiter keeps trying to eat them.
巨行星的引力不断拉扯周围的卫星
The gravity of the giant planets reaches
out and pulls hard on the orbiting moons.
把一些没有生命的岩体
It transforms them from
lifeless balls of rock...
变成奇异、变化多端的世界
into strange and dramatic worlds.
在我们的太阳系, 木星是最大行星
Jupiter is the largest
planet in our solar system.
有63颗卫星
It has 63 moons.
最大的4颗定名为「伽利略卫星」
The four largest are
called the Galilean moons,
纪念伽利略于1610年发现它们
named after the astronomer Galileo
who discovered them in 1610.
它们显示, 引力主宰卫星的形状
They show how gravity controls
both what moons look like
以及特性
and how they behave.
第一颗「伽利略卫星」是木卫一
The first of the Galilean moons, lo,
它的轨道最接近木星
orbits closest to the planet,
就在木星26万英里之上
just 260,000 miles above Jupiter.
大约相等于月球和地球的距离
That's about the same distance
as our moon is from Earth.
但木卫一不同月球, 没有撞击坑
But unlike our moon, the surface
of lo has no impact craters.
这显示, 卫星表面是新形成的
Scientists realised that
meant the surface was new,
但怎么可能呢?
but how could that be?
每次从宇宙飞船
Every time you look
at Io with a spacecraft
或望远镜望向木卫一
or even with a telescope,
总发觉它有少许不同
it, it, it's a little bit different.
木卫一的地质, 像行星天气的多变
So the geology on lo changes
like the weather on other planets.
真的很活跃
It's that active.
太空总署初次探索木卫一时
When NASA first sent probes to
fly past lo, they were shocked
见到数十座活火山, 大吃一惊
They saw dozens of active volcanoes.
这是木卫一超级火山爆发的片段
This is footage of an
erupting super volcano on lo,
直喷到太空200英里
blasting 200 miles into space.
人人都发出同一疑问:
Everyone had the same question:
卫星怎可能有活火山?
How could there be active
volcanoes on a moon?
答案很简单: 引力
The answer was simple: gravity.
木星引力强大, 可以把卫星挤压
Jupiter's gravity is so huge that
it reaches out and crunches the moon.
而且不只是木星的引力拉扯木卫一
And it's not just Jupiter's
gravity pulling on lo.
其它卫星经过时, 也把它拉动
Other nearby moons also
pull on it as they pass by.
于是木卫一的核心不断被拉来拉去
So the core of the moon is being
worked back and forth all the time.
这叫「潮汐摩擦」
It's called tidal friction
在木卫一核心产生极大热力
and it generates extreme
heat on lo's core.
好像把铁衣架扭曲, 直至折断一样
Almost like bending a wire
coat hanger until it breaks
可以感觉到衣架内的热力
and you feel the inside of the coat
hanger there, it feels rather warm.
潮汐摩擦力使木卫一内部发热
That tidal friction, that internal
friction heats the interior of lo
变成太阳系中
until it's become actually
最活跃的火山地带之一
one of the most volcanically
active worlds in the solar system.
不停的拉扯
The constant pushing and pulling
使木卫一内部温度高达数千度
generates temperatures thousands
of degrees high inside lo.
于是喷出大量的熔岩
It blasts out in gigantic
eruptions of lava.
木卫一是太阳系中
lo is the prime example of tidal forces
潮汐摩擦和引力互动的
and gravitational interactions
最佳例证
in the solar system.
它被木星不停的拉扯
It is constantly being pulled by Jupiter
也被其它卫星不停的拉扯
and it's constantly getting
pulled by the other moons as well.
于是产生大量热力
And so as a result, there's a
tremendous amount of heat created.
熔岩不断喷出, 重铺木卫一的表面
The floods of erupting lava
constantly resurface lo,
所以卫星上见不到撞击坑
which is why there are no visible
impact craters on this moon.
引力亦使附近的木卫二发热
Gravity also heats
lo's neighbour, Europa.
木卫二距离木星较远, 所以冷得多
Europa's orbit is farther away
from Jupiter, so it's much colder.
木卫二不喷熔岩, 它的表面是冰层
Instead of lava, the
surface of Europa is ice.
南极洲最低温纪录是零下128度
The lowest recorded temperature
in Antarctica is minus 128 degrees.
木卫二表面的温度更低一倍
Europa's surface is twice as cold.
但在冰层之下, 可能有水
But underneath all the ice,
there may be an ocean of water,
因同一潮汐摩擦作用而发热
heated by the same tidal
friction that makes lo volcanic.
木卫二的地表下, 几乎肯定有海洋
Europa has a subsurface
ocean almost certainly.
地表下海洋和岩石地幔相接
And that subsurface ocean is in
contact with the rocky mantle,
因此产生热力
which provides heat,
也可能产生养份, 支持生命
and also provides, probably,
appropriate nutrients to sustain life.
将来我们会探索木卫二冰层下状况
Someday we'll send a probe to
explore beneath the ice on Europa.
说不定会在温暖海洋内发现生物
And maybe we'll discover life forms
living there in warm Europan oceans.
在木卫一和木卫二之外
Out beyond lo and Europa
有接近60颗卫星
are nearly 60 more moons.
它们在远离木星的轨道上运行
They orbit much further
away from Jupiter
木星引力的效应比较弱
where the affects of the giant
planet's gravity are much weaker.
无法产生潮汐摩擦, 使卫星发热
Out here, it's too weak to generate
tidal friction and heat the moons.
所以这些遥远的世界寒冷而荒芜
So these remote worlds
are cold and barren.
但也不是平淡无奇
But not featureless.
它们有无数次撞击后留下的疤痕
They bear the scars of
countless collisions,
科学家相信
and scientists believe
最奇妙的卫星系统因撞击而形成
it was collisions that created the most
extraordinary moon system of them all.
土星拥有最不寻常的卫星系统
The planet with the most
unusual moon system is Saturn.
范围覆盖20万英里以上
It's spread out over
more than 200,000 miles.
严格来说, 它有超过十亿颗卫星
Technically, there are
more than a billion moons.
不错, 是十亿颗卫星
That's right, a billion moons.
它们集结起来, 组成土星环
And all together, they
make up Saturn's rings.
卫星可以是小如卵石的岩石或冰块
A moon can be a hunk of rock
or ice no bigger than a pebble
只要是围绕行星运行便合格
as long as it orbits a planet.
土星环由无数的岩石和冰块组成
The rings of Saturn are made of
countless pieces of rock and ice.
体积由卵石以至整座城市不等
They go from the size of a
pebble up to the size of a city.
土星环上有些颗粒
We don't refer to all
the ring particles...
宽度10至20米
that can get to be as big
as 10 to 20 metres across,
我们并不称为卫星
we don't refer to them
as individual moons,
但如果宽度达1至2公里
but when we find a body that is
maybe a kilometre or two across,
便可以开始称为卫星或小卫星
then you can start talking
about it as a moon or a moonlet.
土星环是最悠久的天文奥秘之一
Saturn's rings are one of the
oldest mysteries of astronomy.