了解宇宙是如何运行的（2010）

and they actually do create melt pools
融化变成熔岩坑
liquid rock on the floors of these impact craters
有些熔岩坑炽热了好几万年
and some of those craters can glow hot
有的熔岩坑甚至热了几十万年
for tens of thousands, hundreds of thousands of years in some cases
要是当时你在地球上
if you were actually on the earth at that time
你就会看到满天的尘埃巨幕
there would have been enormous balls of dust
不断涌上大气层
continuously thrown into the atmosphere
天空会浓云密布 一篇昏暗
the sky would be hazy, cloudy
地面则到处山脉起伏
and the terrain would be mountainous
密布着陨石坑和熔岩
from the rims of craters all around, rocky
这是相当恐怖险恶的环境
and a wholly unpleasant place to be
现在地球的伤疤已经平复
today, the scars have healed
冰河推进又退后
glaciers advance and retreat
火山爆发
volcanoes erupt
风和水抹去了这个星球过去的痕迹
wind and water erase our planet's dust
但只要我们抬头观测 还是能看到证据
but the evidence is still visible if we look up
看看月亮
look at the moon
每晚满是坑坑洼洼的月亮都会高挂夜空
every night, you see the moon coming out and it's pockmarked
这是因为太阳系形成之后
because for about a billion years
大约有十亿年的时间 一切都很混乱
after the solar system was formed, there was chaos
2011年 Nasa的斯皮策空间望远镜
in 2011, nasa's spitzer space telescope
在另一颗恒星附近发现了这种撞击现象
reveals this kind of bombardment around another star
天文学家发现巨大的气体和尘埃圆盘
astronomers see a vast disk of gas and dust
环绕着年轻的恒星左辖
circling a young star called eta corvi
大量的冰彗星和小行星
this may be evidence of icy comets and asteroids
冲向类太阳系内
swarming into its inner solar system
40亿年前
four billion years ago
我们的太阳系也发生了同样的事情
the same thing was happening in our solar system
大量的物质 小行星和彗星
there was a wave of material, asteroids and comets
从太阳系外席卷而来
that swept in from the outer solar system
这些物质很可能来自于木星和土星等外行星
it turns out it probably came from jupiter and saturn the outer planets
他们在绕日运行是
as they were orbiting the sun
产生了引力的交互作用
they were interacting with each other gravitationally
就像是复杂的舞蹈
a very complicated dance
木星每绕日三圈
jupiter goes around the sun three times
土星就会绕日两圈
every two times that saturn does
所以它们在向外漂移时
and so, when they would migrate outwards
会紧紧地靠在一起
they'd be locked in this resonance
距离非常的近
they'd be very close to each other
就在它们漂移时
and at some point, as they were moving around
它们的引力合二为一
their gravitational powers basically combined
它们对轨道周围物质的影响变得更大了
got a little bit better at affecting the material around them
这两颗气体巨行星联合起来
together, the two inner gas giants
把天王星和海王星这两颗气体巨行星
sling the two outer gas giants, uranus and neptune
抛了出去
even farther out
天王星和海王星的位置互换了
uranus and neptune swap places
海王星撞上了太阳系外的
neptune slams into the frozen dust and gas
冰质尘埃和气体
in the solar system's outer reaches
冰质碎屑便往太阳系内
scattering icy debris far and wide
四面八方飞射
in the inner solar system
这些碎屑撞上了小行星带
this debris collides with the asteroid belt
数十亿颗彗星和小行星
billions of comets and asteroids swarm
纷纷飞过地球 月球和其他内行星的轨道
across the orbits of the earth, moon, and other inner planets
如果这种情况持续下去
if that had persisted
就不可能演化出生命
then life never could have evolved
一直到几亿年之后
only after a few hundred million years
生命才有可能在地球上出现
was it possible for life on earth to develop
但是这场破坏也蕴含了生命的种子
but this destruction contains the seeds of creation
因为冰质彗星带来了非常珍贵的东西
because the icy comets deliver a precious cargo
木星会定期扰动
jupiter periodically disturbs
外太阳系的天体 主要是含水的天体
objects in the outer solar system, largely water objects
它会将这项天体抛向地球
and directs the towards the earth
这如果在现在发生 会引发末日浩劫
nowadays, that would be a disaster
但实际上 就地球上的水来说
but in fact, if you look at the water on earth,
如今你在地球上看到的水很可能
it's quite likely that almost all of the water on earth
都是来自被木星抛到地球的冰块
that's now here came from ice that impacted upon the earth directed here by jupiter
每个海洋 每条河流
every ocean, every river
甚至每滴雨水 都是因为木星才能存在
every drop of rain may owe its existence to jupiter
这颗气体巨行星甚至有可能播下了生命的种子
the gas giant may have even sowed the seeds of life itself
组成生命的基本化学物质 或许就是跟着慧星来到地球的
the chemical building blocks of life may have hitched a ride to earth on-board a comet
要是没有木星 生命就无法出现
without jupiter, life would have never started
就算出现也无法存活
and it would have never survived
这段轰炸期在38亿年前结束
the main bombardment ended 3.8 billion years ago
但威胁并未消失
but a threat remains
每天 Nasa的近地天体计划
every day, nasa's near-earth objects program scans the skies
负责扫描天空寻找危险的小行星和彗星
for potentially dangerous asteroids and comets
目前他们发现了一万多个危险天体
so far, they've spotted over 10,000
只要有一个撞上地球就会引发大灾难
and it only takes one to cause a catastrophe
虽然直径只有3英里（约4.8公里）
just three miles wide
这颗小彗星却足以毁灭地球上的生命
this small comet is big enough to wipe out life on earth
幸运的是 木星能够阻止它
luckily, jupiter is in the way
从很多方面来看
jupiter acts, in a lot of ways
木星就像内太阳系的带刀侍卫
like the protector of the inner solar system
它引领附近的彗星
by shepherding comets in its vicinity
将它们跑出太阳系外
ejecting them from the solar system
木星保护了地球的安全
jupiter helps protect the earth itself
太阳系天体的运动
in a sense, the way objects move in a solar system
有点像竞速滑轮溜冰运动
is a little bit like a roller derby
这些天体沿着相同的方向
you've got all of these objects moving around the sun
不断地绕太阳运行
in the same direction, going around and around and around
但是天体有引力 彼此间有交互作用
but they have gravity, and they can interact with each other
想象这位白衣选手
imagine this skater in white
就是一颗从外太阳系来的冰质彗星
is an icy comet racing in from the outer solar system
黑衣选手是气体巨行星
the skaters in black are the gas giants
彗星越过了行星的轨道
the comets veer across the planets' orbits
直到它碰上木星
until it encounters jupiter
木星的速度比彗星要快
jupiter moves faster than the comet
然后这颗气体巨行星的引力
then, the giant planet's gravity
会抓住这颗彗星 像弹弓一样把彗星弹射出去
grabs it and gives it an assist in a slingshot maneuver
彗星得到了一些木星的动能
the comet steals some of jupiter's momentum
速度变快并改变方向
accelerates, and changes direction
木星能让彗星加速并将其甩出太阳系
jupiter can fling it out of the solar system
彗星就这样被甩开
by giving it that extra velocity
并被驱逐出太阳系
and it goes away. it's ejected
木星将危险天体甩出去 守卫地球
jupiter slings objects out and stands guard
每年 木星被彗星和小行星撞击的次数
every year, 200 times more comets and asteroids
是地球的200倍
smash into jupiter than the earth
这里一定要有一位像治安官的角色
something had to be there like a sheriff
像赶走流氓一样 赶走碎屑
to clean out all the riffraff and clean out all the debris
而这位治安官就是木星
and that's the planet jupiter
要是没有木星 我脚下可能会有
if it wasn't for jupiter, right where i'm standing
巨大的陨石坑
there might be gigantic meteor impact crater
没有木星 我们肯定没办法
without jupiter, most certainly
在这里讨论它
we wouldn't be here to talk about it
我们的生存依赖木星
our lives depend on jupiter
因为木星对于地球生命的演化
because of the incredibly important role
扮演着相当重要的角色
that jupiter's played in the evolution of life on earth
所以我们在寻找
when we look at exoplanets
系外行星的生命迹象时
when we look for life elsewhere in the universe
或许不要只寻找适合居住的行星
we may not need to look just for those habitable planets
还要寻找跟木星一样
we may need to look for jupiters or objects
能够保护我们的天体
like them that have saved them, as jupiter saved us
木星是我们太阳系成功的关键所在
jupiter is the secret behind our solar system's success
它让生命得以出现在地球上
it makes life on earth possible and helps protect that life
并且保护了这些生命 或许还能孕育出外星生命
it may even nurture life, alien life
木星影响的范围
jupiter dominates its neighborhood
广达数百万英里 还至少有67颗卫星绕它运行
for millions of miles, looming over at least 67 moons
最大的木卫三比水星还要大
from ganymede which is larger than the planet mercury
而最小的卫星直径只有一英里（约1.6公里）
to a rock barely a mile across
最内侧的卫星 岩石比较多
the innermost moons are more rocky rich
而最外侧的卫星 冰比较多