The dust bunnies that built our planet - Lorin Swint Matthews

翻译人员: Jessie zhang 校对人员: Yolanda Zhang

Consider the spot where you’re sitting.

考虑你现在坐的地方，

Travel backwards in time

时光倒流，

and it might’ve been submerged at the bottom of a shallow sea,

它可能被淹没在浅海底部，

buried under miles of rock,

埋在几英里深的岩石下，

or floating through a molten, infernal landscape.

或者漂浮在熔融的景观中。

But go back far enough—

但是回到久远的

about 4.6 billion years,

46亿年前，

and you’d be in the middle of an enormous cloud of dust and gas

你将置身于无边的尘埃 和气体云团中，

orbiting a newborn star.

围绕一个新的星球旋转。

This is the setting for some of the biggest, smallest mysteries of physics:

这是物理学最大，也是最小的谜团：

the mysteries of cosmic dust bunnies.

宇宙尘埃的谜团。

Seemingly empty regions of space between stars

看似空旷的星际空间

actually contain clouds of gas and dust,

实际上存在着气体和尘埃云团，

usually blown there by supernovas.

通常被超新星吹到那里。

When a dense cloud reaches a certain threshold called the Jeans mass,

当云团密度达到临界值， 即金斯质量，

it collapses in on itself.

它自身会坍塌。

The shrinking cloud rotates faster and faster, and heats up,

收缩的云团越转越快，逐渐升温，

eventually becoming hot enough to burn hydrogen in its core.

最后在内核点燃氢气。

At this point a star is born.

一个新的星球在此刻诞生。

As fusion begins in the new star,

随着新的星球开始出现聚变反应，

it sends out jets of gas that blow off the top and bottom of the cloud,

它喷发出的气体 将云团顶部和底部吹散，

leaving behind an orbiting ring of gas and dust called a protoplanetary disk.

留下一个环绕星球旋转的 气体和尘埃环，被称为原行星盘。

This is a surprisingly windy place;

这个地方的风出奇的大；

eddies of gas carry particles apart, and send them smashing into each other.

气流旋涡带动粒子分离， 使它们互相碰撞，

The dust consists of tiny metal fragments, bits of rock, and, further out, ices.

宇宙尘埃由小的金属碎片， 岩石颗粒，以及冰块组成。

We’ve observed thousands of these disks in the sky,

我们可以在天空中观察到 数千个类似的原行星盘，

at various stages of development

它们处于不同的发展阶段，

as dust clumps together into larger and larger masses.

随着尘埃聚集成群，变成更大的云团

Dust grains 100 times smaller than the width of a human hair stick to each other

尘埃颗粒比人类的一根 头发丝还小100倍，

through what’s called the van der Waals force.

它们之间的引力被称为范德华力。

That’s where a cloud of electrons shifts to one side of a molecule,

那里电子云团会转移到分子的一侧，

creating a negative charge on one end, and a positive charge on the other.

使得分子的一端产生正电荷， 一端产生负电荷。

Opposites attract, but van der Waals can only hold tiny things together.

正负相吸，范德华力 将它们吸引在一起。

And there’s a problem: once dust clusters grow to a certain size,

但问题是：一旦尘埃团 增长到一定规模，

the windy atmosphere of a disk should constantly break them up

星盘的多风空气层 总是会把它们打碎，

as they crash into each other.

它们随之相互碰撞。

The question of how they continue to grow is the first mystery of dust bunnies.

宇宙尘埃的一大谜题 就是它们如何继续膨胀。

One theory looks to electrostatic charge to answer this.

静电力理论也许能回答这个问题。

Energetic gamma rays, x-rays, and UV photons

高能伽马射线，X射线，紫外线光子

knock electrons off of gas atoms within the disk,

使星盘中气体原子携带的电子减少，

creating positive ions and negative electrons.

从而制造出正离子和负电子。

Electrons run into and stick to dust,

电子与尘埃的结合

making it negatively charged.

使尘埃携带负电荷，

Now, when the wind pushes clusters together,

当风把尘埃粒子聚在一起，

like repels like and slows them down as they collide.

同性相斥，碰撞也使得 粒子的运动速度降低。

With gentle collisions they won’t fragment,

轻微的碰撞不会使它们碎裂，

but if the repulsion is too strong, they’ll never grow.

但是如果相斥力太强， 它们就没法长大。

One theory suggests that high energy particles

有一种理论说的是，高能量粒子

can knock more electrons off of some dust clumps,

可以使尘埃团的电子减少，

leaving them positively charged.

使得它们携带正电荷。

Opposites again attract, and clusters grow rapidly.

异性相吸，云团迅速增长，

But before long we reach another set of mysteries.

但不久我们就会发现另一组谜团。

We know from evidence found in meteorites

我们从陨石中找到了证据，

that these fluffy dust bunnies eventually get heated, melted

证明这些蓬松的尘埃团 最终被加热，融化，

and then cooled into solid pellets called chondrules.

之后冷却成固体的陨石颗粒。

And we have no idea how or why that happens.

但我们并不知道这一过程 究竟是如何发生的。

Furthermore, once those pellets do form, how do they stick together?

一旦颗粒团形成， 它们又是如何黏在一起的呢？

The electrostatic forces from before are too weak,

之前的静电力很弱，

and small rocks can’t be held together by gravity either.

小的石块不会在引力下结合在一起，

Gravity increases proportionally to the mass of the objects involved.

万有引力随着物体的质量变大 按比例地增加。

That’s why you could effortlessly escape an asteroid the size of a small mountain

这就是为什么仅仅使用脚上的力量， 我们就可以毫不费力地

using just the force generated by your legs.

从一个像小山一样大的小行星中逃逸。

So if not gravity, then what?

那么如果不是引力，又是什么？

Perhaps it’s dust.

可能是尘埃。

A fluffy dust rim collected around the outside of the pellets

在颗粒团的外部收集 的蓬松的灰尘边缘可以

could act like Velcro.

像尼龙搭扣一样运动。

There’s evidence for this in meteors,

在陨石中可以找到相关的证据，

where we find many chondrules surrounded by a thin rim of very fine material–

我们发现陨石颗粒上面有一层 薄薄的，质地细密的矿物质——

possibly condensed dust.

可能是凝结的尘埃。

Eventually the chondrule pellets get cemented together inside larger rocks,

最后陨石颗粒粘合在一起 形成更大的岩石，

which at about 1 kilometer across

直径达1公里，

are finally large enough to hold themselves together through gravity.

最终大到足够在引力下支撑自己。

They continue to collide and grow into larger and larger bodies,

它们继续撞击并增长到更大的体积，

including the planets we know today.

包括我们已知的行星。

Ultimately, the seeds of everything familiar–

最终，所有的事情开始变得熟悉——

the size of our planet, its position within the solar system,

行星的规模，它们在太阳系的位置，

and its elemental composition–

以及它们的元素组成——

were determined by an uncountably large series of random collisions.

是由无数随机的碰撞形成的。

Change the dust cloud just a bit,

稍微改变一下尘埃云，

and perhaps the conditions wouldn’t have been right

也许我们星球上的环境

for the formation of life on our planet.

就不再适合生命的形成。