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Consider the spot where you’re sitting.

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Travel backwards in time

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

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buried under miles of rock,

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or floating through a molten, 
infernal landscape.

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But go back far enough—

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about 4.6 billion years,

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

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orbiting a newborn star.

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

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the mysteries of cosmic dust bunnies.

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Seemingly empty regions 
of space between stars

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actually contain clouds of gas and dust,

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usually blown there by supernovas.

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

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it collapses in on itself.

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

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eventually becoming hot enough to burn 
hydrogen in its core.

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At this point a star is born.

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As fusion begins in the new star,

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

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

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This is a surprisingly windy place;

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

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

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

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at various stages of development

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as dust clumps together
into larger and larger masses.

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

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through what’s called 
the van der Waals force.

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

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

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

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

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the windy atmosphere of a disk should 
constantly break them up

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as they crash into each other.

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

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One theory looks to electrostatic charge 
to answer this.

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Energetic gamma rays, x-rays, 
and UV photons

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knock electrons off of gas 
atoms within the disk,

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creating positive ions 
and negative electrons.

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Electrons run into and stick to dust,

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making it negatively charged.

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Now, when the wind pushes 
clusters together,

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like repels like 
and slows them down as they collide.

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With gentle collisions 
they won’t fragment,

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

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One theory suggests that high energy 
particles

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can knock more electrons off of some 
dust clumps,

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leaving them positively charged.

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Opposites again attract, 
and clusters grow rapidly.

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But before long we reach 
another set of mysteries.

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We know from evidence found in meteorites

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that these fluffy dust bunnies 
eventually get heated, melted

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and then cooled into solid 
pellets called chondrules.

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And we have no idea how 
or why that happens.

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

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The electrostatic forces from before 
are too weak,

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

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Gravity increases proportionally to the 
mass of the objects involved.

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

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using just the force generated 
by your legs.

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So if not gravity, then what?

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Perhaps it’s dust.

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A fluffy dust rim collected around the 
outside of the pellets

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could act like Velcro.

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There’s evidence for this in meteors,

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

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possibly condensed dust.

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Eventually the chondrule pellets get 
cemented together inside larger rocks,

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which at about 1 kilometer across

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are finally large enough to hold 
themselves together through gravity.

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

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including the planets we know today.

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Ultimately, the seeds of 
everything familiar–

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

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and its elemental composition–

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were determined by an uncountably large 
series of random collisions.

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Change the dust cloud just a bit,

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and perhaps the conditions wouldn’t 
have been right

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for the formation of life on our planet.