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形成月球的大碰撞 – 译学馆
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形成月球的大碰撞

Collision That Formed The Moon

地球自转轴的角度
The tilt of our planet’s rotational axis
目前约为23º
is about 23 degrees currently.
也正是这种倾斜带了四季变化
And it’s that tilt that gives us our overall seasonal pattern.
这说明了如果我们没有月球
It turns out that if we didn’t have our Moon,
或者我们有月球
or if we had a Moon,
但是比现在的月球要小
but it was just smaller than our current Moon,
那它与太阳系中其他行星之间的相互影响
that interactions with the other planets in the solar system
会让地球的自转轴角度
would cause Earth’s rotational axis to vary
以每百万年几十度的速度发生改变
by many tens of degrees on timescales of millions of years.
这会对全球气候产生深远影响
This would have profound impact on the overall climate of the Earth.
当自转倾斜角度大幅改变的时候
And while the Earth with such a wildly changing tilt
地球可能仍然宜居
might still have been habitable.
但那时的气候肯定和现在的气候
It would certainly have been an entirely different climate
截然不同
on a different Earth than we have today.
因此 月球的形成
And so in this way, the formation of our Moon
以及月球的质量
and the formation of our Moon, of just the mass of our Moon
会对地球自转
has had a very important impact on
产生重大影响
the evolution of the Earth’s spin state,
进而对长期的气候变化产生重大影响
and with it, the evolution of our long-term climate.
阿波罗登月计划中
There’s a fundamental connection
带回的月球岩石样本
between our studies of the origin of the Moon
和月球起源的研究
and the physical samples that were brought back by the Apollo mission,
有着根本性的联系
the actual rocks from the Moon.
我们对这些岩石进行初次研究时
When those rocks were first studied,
便获得了几项重大发现
we learned several very significant things.
首先我们发现这些岩石的组成
One we learned that compositionally those rocks are extraordinarily similar
和地球表层岩石的组成非常相似
to the upper layers of the Earth.
以氧元素为例
If you look at an element like oxygen,
月岩上氧的不同同位素的分布
its distribution of different isotopes of oxygen
和地球岩石上的分布本质上相同
is essentially identical in the Moon and the Earth,
但却和火星和小行星带的陨石大不同
whereas it’s very different in meteorites from Mars or the asteroid belt.
另外我们还发现
Another clue, another constraint we learned from the Apollo samples
阿波罗飞船带回的月球岩石
is that the Moon rocks appeared very dry,
比地球岩石更干燥
compared to Earth rocks,
就像被高温炙烤过
almost as if they had been heated to a high temperature
所以月岩中易被高温蒸发的元素
and that they had lost the elements
已经不见了
that tend to vaporize easily upon heating.
这些发现告诉我们
And that suggested to us that
月球形成的过程必定经过高温炙烤
the process that formed the Moon must be a high-energy event.
因此我们猜想月球是在
So we think the Moon formed,
正在形成中的地球和某个巨大物体
when the Earth was struck by
发生碰撞时形成的
a very large object as the Earth was forming.
所以本来是要形成一个独立的行星的
So this would have been a separately formed planet
并且还要和地球以及其它形成中的行星
that was vying for dominance in the inner Solar System
竞争在太阳系中的一席之地
along with the Earth and other growing planets.
但它与地球发生了碰撞
But it collided with the Earth,
并最终被地球俘获
and ultimately was absorbed by the Earth
于是便形成了月球
and gave birth to our Moon.
我们通常称这颗撞击地球的
So in terms of the impactor which we often call Theia,
行星为忒伊亚原行星
we think that based on its mass
在撞击地球前
that it would have been as big as the planet Mars,
它和火星差不多大
before it collided with the Earth, it would have had an iron core
有着和地球相似的铁核和硅酸盐地幔
and a silicate mantle like the Earth,
质量约为地球的10%
and it would have had about 10% of the mass of the Earth.
我们认为最初太阳系内
We think initially the inner Solar System
原本可能有20颗小行星
had maybe 20 small planets.
随后由于行星间的相互撞击
And it was through collisions between these planets
最终只剩下4颗类地行星
that we eventually ended up with our final four terrestrial planets.
我们认为正是在和地球的最后
And the last of these big collisions on the Earth
一次大碰撞中形成了月球
was the one we think formed the Moon.
我们关注这个和火星一般大的撞击物的原因是
The reason that we focus on a Mars-sized impactor is that
正是由于这样的大小才能让地球发生自转
that is the impactor size that if you hit the Earth
假设一个火星大小的行星以一定的速度和角度
with a Mars-sized impactor at an off-center angle,
撞向地球
at the expected speed,
会使地球产生周期为5个小时的自转
you’ll start the Earth spinning with about a five-hour day.
这样的自转速度很快
Now, that’s a very rapid spin rate,
但事实证明 在如今地球与月球
but it turns out that is what is needed
相距这么远的情况下 保证一天有24小时
to agree with our current 24-hour day,
这样的速度是有必要的
with the Moon at its current distance.
月球正在逐渐远离地球
The Moon is moving away from the Earth.
因此我们可知月球在形成之初时
So we know when the Moon first formed,
与地球相距比较近
it was much closer to the Earth
地球自转速度也比较快
and the Earth was spinning much faster.
70年代中期 月球形成于
So the idea that the Moon formed by this giant collision with the Earth
地球大碰撞的假说被首次提出
was first proposed in the mid-70s.
当时 我们没法验证这个假说
And yet, we couldn’t test the idea initially.
对于小规模的碰撞
For smaller scale collisions,
我们可以在实验室里进行演示
you can perform experiments in the laboratory.
但实验室的设备环境却无法还原
But you can’t perform an experiment of what happens,
两颗行星之间的碰撞
when two planets collide in any laboratory setting.
为了验证假说 我们要建立一个计算模型
To do this, you need to build a computational model
来模拟行星和它们之间的碰撞
to simulate the planets and their response to the collision.
我们把计算机模拟当作一个虚拟实验室
We can use our computer simulations as an essence, a virtual laboratory,
来检验撞击物的大小 速度和角度
to test how the outcome depends on things like
会对实验结果产生怎样的影响
the size of the impactor, the impact speed and angle,
然后用这些实验结果
and use the overall results
来计算形成月球的可能性
to assess the likelihood of forming a Moon like ours.
因此我们对地球最后一次大碰撞进行模拟
So we’re simulating this final large collision with the Earth.
如果当时地球上有个人 那么从他的角度
From the perspective of someone on the Earth at the time,
他会看见一个比现在天上的满月还要大的
what you would have seen is an enormous object approaching the Earth,
庞然大物直冲向地球
many many many times larger than the full Moon in the sky.
它会斜着撞向地球
It would have hit the Earth at an oblique angle.
几个小时内
On a timescale of a few hours,
碰撞产生的强大冲击波
an enormous shock wave from the impact
将会传遍整个地球表面
would have propagated around the entire surface of the Earth.
蒸发汽化的岩石从初始撞击点
The vaporized rock from the initial impact point
喷射而出
would have been ejected out,
它将会环绕整个地球
and it would have flowed around the entire Earth.
并形成一层厚厚的大气层
And the Earth would find itself enveloped by a thick atmosphere,
但还不是我们现在的大气层
but not like an atmosphere we know today.
这是一层由岩石蒸汽构成的大气层
This would have been an atmosphere of vaporized rock,
温度超过5000度
with a temperature of more than 5,000 degrees.
撞击产生的巨大动能
The momentum, the force of this collision, is
足以让地球迅速转动
enough to start the Earth rotating very rapidly.
因此撞击后仅几小时
And so only hours after this impact,
地球发生快速自转
the Earth has a rapid rotation rate.
现在我们认为约一百年后
Now we think on a much longer timescale of about a hundred years,
呈盘状的岩石蒸汽层温度下降 蒸汽凝结
that disk will cool, the vapor will condense.
在岩石蒸汽层外 通过层内的岩石不断碰撞
And out of that disk, through collisions within the disk,
月球逐渐形成
the Moon would have grown in accumulatively.
虽说我们自认为我们为月球的形成
So although we think we have a good idea about
提出了一个不错的假说
how the Moon formed,
但具体细节仍受到争议
the exact details of this event are still being debated.
很大程度上
And this is in large part, a testament
对数十年前被带回到地球的月岩的研究
to how those samples that were returned decades ago,
仍然在促使我们开展积极的科学辩论
are still driving active science debate,
随着研究的不断开展 这些岩石样品
as ongoing analysis provides us with more clues from those samples
将会为地月系统的形成提供更多线索
on how the Earth-Moon system formed.
月球形成可视化电影即将在球幕天文节目上映
Moon formation visualization from the upcoming Fulldome Planetarium show
《地球的诞生》
“BIRTH OF PLANET EARTH”
科学模拟数值来自
Scientific Numerical Simulation
科学模拟数值来自
Scientific Numerical Simulation
由NASA太阳系探索虚拟研究所赞助
Funded by NASA, Solar System Exploration Research Virtual Institute
音乐
music
素材
Footage
部分赞助
Funded in part by

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译制信息
视频概述

月球成因

听录译者

jm

翻译译者

Claudia

审核员

审核员YZ

视频来源

https://www.youtube.com/watch?v=o2lRpiediP8

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