宇宙（2007）

The Universe S05E06

Part 2 April 22, 2021, 1:50 p.m.

Only occasionally do they hit.
只有偶然情况下才能击中
But unlike the shooting gallery where the bullets,
然而不同于射击场无论是子弹
or in this case, flashes of light
还是这样的一束光
always travel in straight lines,
都是沿直线运动的
asteroids and comets curve toward their targets.
小行星和彗星却是以弧线运动到目标的
Jupiter tends to draw in the asteroids and comets
木星通过其地心引力将小行星和彗星
through its gravity.
吸引过来
So, it's kind of like,
就好比
if I start with my aim way over there,
我原本的射击目标是在那里
Jupiter pulls the barrel of the rifle toward it,
木星吸引枪杆使之朝向它
giving me a direct hit.
让我直接命中
Since earth is much less massive than Jupiter,
由于地球比木星小很多
its lower gravity doesn't draw in as many asteroids
由其引力吸引的小行星数量较少
and the moon, with only a fraction of earth's gravity
月球的引力只相当于地球引力的一小部分
attracts even fewer.
所吸引的小行星少之又少
But as the moon's crater pocked surface illustrates,
但是月球表面的许多月坑显示
infrequent asteroid impacts over a long period of time
长时间的非经常性小行星的撞击
still means plenty of destruction.
依然意味着巨大的破坏性
Jupiter's ability to pull in comets and asteroids
木星吸引彗星和小行星的能力
has been on display a lot recently.
近年来不断显现
In 1994,
1994年
the Shoemaker-Levy 9 comet fragments pounded Jupiter.
苏梅克-列维9号♥彗星的碎片击中木星
Scientists thought this kind of large impact
科学家以为这种大型撞击
was a rare event,
相当罕见
something to be seen once every few hundred years.
实属百年一遇
But then, another comet or asteroid hit
但是很快另一颗彗星或小行星
in July 2009.
于2009年七月再次撞击
It created a large dark spot
这次撞击导致产生了一块大黑斑
and a fireball as large as the earth.
和相当于地球大小的火球
Seeing two different sets of impactors hitting Jupiter
两个不同的木星撞击者
only 15 years apart gives some indication that
撞击时间只间隔了15年
the solar system might even be busier than we thought.
这说明太阳系可能比我们想象的还要活跃
Then, in June 2010, a third object hit Jupiter,
2010年六月一名业余天文爱好者拍到
with an amateur astronomer
第三颗物体
capturing the moment of impact.
撞击木星时的画面
Would this force scientists
这会不会迫使科学家们
to change their estimates and acknowledge
改变现有的学术定论
that Jupiter is hit by large objects
认为木星被大型物体撞击的频率
much more often than every few hundred years?
远多于百年一次呢
I think that there's not necessarily many more
我认为这其实跟我们原有的观点
than we thought before,
并无多少不同
and that's because,
因为
the object that hit in 2009 was smaller
2009年撞击的物体
than comet Shoemaker-Levy 9.
体积小于苏梅克-列维9号♥彗星
And there are many, many more small objects flying
并且那些运行着的小型个体的数量
around there than there are large objects.
远远多于大型个体
But information about any type of impact,
但是不论是关于大型还是小型的
large or small,
撞击信息
is always helpful.
总归是有用处的
To understand the impact hazard on earth,
若要了解威胁地球的撞击
we need to understand
我们必须得了解
the asteroid population, their orbit.
小行星的数量与其运行轨道
So, every piece of information,
因此每一条信息都是至关重要的
even if it's understanding how often they hit Jupiter
包括去了解撞击木星的时间跨度
or out in the Jupiter region,
或者是其他天体
contributes to our understanding of
对于我们掌握太阳系小型物体的
the overall population of objects in the solar system
整体数量和判断
and how concerned we need to be about earth impact.
我们对撞击地球的关注度也至关重要
The major source of that population
小行星数量的主要来源
is the main asteroid belt between Mars and Jupiter.
是火星和木星之间的小行星带
That's where the strong gravitational pull of Jupiter
在此区域内木星的引力
has kept millions of smaller rocks
阻止了上百万的小型石块
from becoming another planet.
形成新的行星
But that's not the whole story.
但是一切并非到此为止
So we think of asteroids as those things
那么我们认为小行星就是来自
that just live in the belt between Mars and Jupiter,
火星和木星之间小行星带的物体
because that's historically where most of them
因为它们中的大部分
were found at first.
最初都在那里被发现
But in fact, there are asteroids
但是事实上有这么一些小行星
that travel way out past Jupiter.
与木星毫并不相干
There are asteroids that come close to the sun,
有些与太阳近在咫尺
asteroids that come close to earth.
还有些与地球近在咫尺
The largest asteroid is 600-mile-wide Ceres,
最大的一颗便是宽600公里的谷神星
which would stretch from Washington D.C. to Chicago.
相当于从华盛顿到芝加哥的距离
It's so large that it makes up
它大到足以
about 1/3 of the total mass in the asteroid belt.
占据小行星带的1/3体积
An impact from something like that
如若此等物体来袭
would be very bad news
对地球上的生物而言
for every living creature on earth.
必是灭顶之灾
It's about 100 times bigger than
它的破坏力将是
the impactor that caused the Chicxulub impact,
奇求鲁布陨石撞击的一百倍
which resulted in the extinction of
而正是此者导致地球上
70% of the species on earth and dinosaurs.
70%的物种消失和恐龙灭绝
So, right off the bat, it seems like a bad thing.
因此乍看之下似乎很糟糕的样子
But it's a really, really bad thing.
但是事实上要更加糟糕
It would be a disaster far beyond biblical proportions.
它是远糟于圣经故事中的灾难的浩劫
It would create a crater
它将会导致
nearly as big as the United States.
一个差不多和美国一样大的坑痕
But while it was doing that,
与此同时
it would spew out molten material around the globe,
还会喷发蔓延全球的熔岩
create supersonic winds around the globe.
和满世界的超音风暴
It would be ugly.
不堪入目
Luckily, Ceres is in a stable orbit around the sun,
幸运的是谷神星围绕着太阳运转稳定
and large asteroids are easy to spot and track.
而大型小行星又很容易定位和跟踪
We'd probably have decades of warning,
如果一颗宽度大于一公里的小行星
if an asteroid larger than a mile wide
可能撞击地球的话
had a chance of hitting earth.
我们将有几十年的警告期
But the smaller ones present a tougher challenge,
但是从最近的信息看来
as the latest information shows.
小型个体才是更大的挑战
There's far more small ones than large ones.
小型行星的数量远多于大型行星
So, if you say the objects that are
因此假若要列举
one kilometer or 2/3 of a mile in diameter or larger,
直径大于等于一千米或者六七百米的小行星
we think there's about940 of those,
我们认为大概有940个
and we've discovered 86% of the population.
并且已经发现了其中的86%
If you move to smaller objects,
若把视线转向较小的小行星
say 100 meters and larger,
比如说是直径100米以上的
we think there's about 50,000 of those
我们认为大概有五万个
and we've discovered 10%.
并且已经发现其中的10%
And if you move to smaller still objects,
若看更小的小行星
30 meter and larger-sized objects,
30米左右的
we think there's about two million of those objects
我们认为大概有两百万个
and we've discovered much less than 1%.
而我们已经发现的还不到1%
Better telescopes coming online over the next decade
未来十年会出现更好的望远镜
will allow astronomers to identify
将为天文学家发现
many more asteroids of all sizes.
更多的小行星提供可能
But a 30 meter or 100-foot-wide asteroid on
但是一颗宽为30米或者100英尺的小行星
a collision course with earth might not be discovered
可能在临近撞击地球之前
until just before it hits.
才会被发现
Something that size
尽管尺寸不大
could still pack a devastating punch.
却仍可能是致命一击
The earth is covered with evidence of past collisions
地球上布满了过去小行星
with asteroids.
撞击的证据
And today's scientists are working feverishly
如今科学家们废寝忘食的工作
to figure out what's coming next.
希望能预测出将来的发展
They know that enormous space rocks have wiped out
他们知道过去无数的太空来客
most life on the planet in the past.
已经洗劫了地球的大部分生命
The good news is that they don't hit very often.
好消息是它们来得并不频繁
It's measured in many millions
百万甚至数千百万年
or tens of millions of years.
才会来袭
And they're big enough that through our observations
而且它们的大块头