了解宇宙是如何运行的（2010）

How the Universe Works S01E07

Part 4 April 18, 2021, 7:57 p.m.

都是太阳系形成所剩下的
from the formation of the solar system.
太阳形成时太阳周围的星云崩塌
When the nebula collapsed around
the sun as the sun was forming,
它产生一种内在的运动
there was an intrinsic motion,
使行星获得了速度
and that gave our planet a velocity.
其实我们一直向着太阳自♥由♥下落
Literally, we are falling freely
toward the sun at all times,
但由于速度太快, 总是不断错过
but we're going so
fast, we keep missing it
于是形成轨道运行
That's what an orbit is.
好比旋转木马
Think of a
merry-go-round.
转得越快就脱离中心越远
The faster it spins, the farther and
farther you're thrown from the centre.
一旦减速就会失去动力掉下来
When it slows down, you lose
momentum and fall back inwards.
这跟行星的情形一样
It's something like that with planets.
形成行星的圆盘是在旋转的
The disk that gave birth
to the planets was spinning,
它剩下的动力令行星一直运行至今
and the momentum left over from that
keeps everything going around to this day.
地球每小时移♥动♥66000哩
Moving at 66,000 miles an hour,
需要一年绕太阳运行一周
the Earth takes one
year to orbit the sun.
离太阳越远, 轨道半径越大
Planets farther from the
sun have bigger orbits,
移♥动♥越慢和时间越长
move slower, and take longer.
土星每29年绕太阳一周
Saturn orbits the sun
once every 29 years.
海王星需要16♥4♥年
Neptune takes 16♥4♥ years.
每个行星都在精确轨道上绕日运行
Each planet stays on a
precise path around the sun.
对我们来说, 这是好事
And for us, that's a good thing.
行星之间距离适当
Our solar system has a somewhat
fortunate spacing of the planets,
轨道几乎都是圆形
with nearly circular orbits...
令到这座纸牌搭的房♥子
which keeps the whole house of cards
不会瓦解, 烟消云散
from falling apart, crumbling,
scattering to the wind.
若我们的太阳系没有…
If our solar system did not have
规则, 稳定, 近乎圆形的轨道
nice, neat, stable,
nearly circular orbits,
地球就不可能存在
the Earth wouldn't be here
我们也不可能坐在这里谈论这些
and we wouldn't be here talking about it
行星在安全稳定的轨道上运行
The planets are on
safe, stable orbits...
但数十亿颗彗星和小行星则不然
but billions of comets
and asteroids are not.
许多会飞快闯入内太阳系
Many come streaking into
the inner solar system.
当这情况出现时, 当心
And when they do, watch out.
现在见到的这个陨石坑是五万年前
The meteor crater which
we see here today...
一个直径150呎的石铁陨石
formed as a result... of a
150'-foot rocky iron object
撞向地球所造成的
coming in and slamming into the Earth
- roughly 50,000 years ago.
有些撞向我们的物体可能大得多
Some of the objects coming
our way can be much bigger.
看一下月球
Look at the moon.
哪里满布巨大的陨石坑
It's covered with large impact craters.
地球也曾多次被撞击
Earth has been hit, too. A lot.
但这些陨石坑已被侵蚀
But the craters have eroded.
我们知道6500万年前一颗小行星
We know that a huge asteroid
smashed into the Earth,
撞落墨西哥海岸对开
off the coast of Mexico,
65 million years ago.
飞行速度高达每小时45000哩
It was going 45,000 miles an hour,
撞击所产生的能量
and when it hit, it released more energy
超过50亿个广岛原♥子♥弹♥
than five billion Hiroshima bombs.
地球上七成生命毁于一旦
It wiped out 70 percent
of life on Earth.
几次这种撞击能毁灭地球一切生命
A few more impacts like that
could destroy all life on Earth.
但信不信由你, 地球有个巨型保镖
But believe it or not,
Earth has a giant bodyguard.
木星除了是一个美丽的星球
Jupiter is more than just... another
pretty face through the telescope.
它对地球上的生命亦至关重要
it's actually really
important for life on Earth.
由于木星的引力巨大无比
Jupiter's gravity is so huge
加上它的位置恰到好处
and it's just in the right
place in the solar system...
所以能够保护地球免遭彗星的撞击
that it protects the Earth from comets
that come from deep in the solar system
它们在太阳的引力下可能撞向地球
and swing by the sun and
could possibly hit the Earth.
木星就像太阳系最大的棒球棒
Jupiter plays the role of the biggest
baseball bat in the solar system.
当这些彗星袭来时
As these comets come by,
大多数都被木星挡出了太阳系
most of them get knocked out
of the solar system by Jupiter.
1994年, 苏梅克列维九号♥彗星
In 1994, Comet Shoemaker-Levy 9
朝着内太阳系冲过来
raced toward the inner solar system.
但它根本过不了木星这一关
But it never got past Jipiter.
天文学家目睹木星将它撕得粉碎
Astronomers watched as
Jupiter tore it to pieces
并把碎片拉到木星表面
and dragged its remains...
down to the planet's surface.
我们看到彗星撞入木星
We have seen comets smash into Jupiter,
产生比地球还大的火球
creating fireballs that
were bigger than the Earth.
这是我们的太阳系中最大型爆♥炸♥
They were the biggest explosions
ever seen in our solar system.
若那颗彗星撞到地球就不堪设想
Had that comet hit us, it
would have resurfaced the planet
地球所有生命都会灭绝
It would have been the
end of life as we know it.
若没有木星, 地球的撞击率
If Jupiter wasn't there, we believe
that the impact rate on the Earth
会比现在多1000倍
would be something like a thousand
times more than we see today.
幸而地球有一个完美的轨道
Lucky for us, Earth
has the perfect orbit.
木星遮挡了小行星和彗星的侵袭
Jupiter protects us from
asteroids and comets.
离太阳够近令我们有液态水
We're close enough to
the sun for liquid water
但不会近到令水被蒸发掉
but not so close that it boils away.
这种组合对生命来说怡到好处
It's just the right
combination for life.
问题是
Question is,
若我们的太阳系能够创造完美条件
if our solar system could
create the perfect conditions,
其它太阳系也能够做到吗?
could other solar systems do it, too?
行星探测器发现一个太阳系
Planet hunters have
spotted a solar system
距离我们20光年
20 light-years away,
有一颗行星大小和位置都恰到好处
and it has a planet just the
right size in just the right place.
世界各地的天文学家
Astronomers around the world
are looking for new planets
正在寻找遥远的太阳系的新行星
in distant solar systems.
迄今为止, 已发现了420多颗
So far, they've
discovered more than 420.
大多数是像木星这样的气体巨行星
Most are huge gas
giants, like Jupiter...
但它们不是离恒星太近就是太远
but they're either very close
to the star or much farther away.
2005年, 天文学家有一个惊人发现
Then, in 2005, astronomers
made an exciting discovery.
就是有一个太阳系也有岩态行星
They detected a solar system
with rocky planets like our own.
这些行星绕着恒星格利泽581运行
These planets orbit a
star called Gliese 581.
恒星格利泽581和它的四颗行星
This star, Gliese 581,
and its four planets
和我们的太阳系相比十分奇异
is, frankly, quite bizarre
relative to our solar system.
这四颗行星都与母恒星十分接近
The four planets we know of all
orbit very close to the host star,
四颗行星跟母恒星的距离
all foir of them orbiting closer than
the planet Mercury, our closest planet,
都比离太阳最近的水星还近
orbits the sun.
格利泽581是一颗小型恒星
But Gliese 581 is a small star.
无论光和热都比不上太阳
It doesn't burn as brightly or
give off as much heat as our sun
所以行星可这样近运行而不会气化
so the planets can orbit much
closer without being vaporised
我们知道有四个行星绕着恒星运行
We know of four planets
going around this star,
而其中几个相当有趣