All language subtitles for The universe S06E03 How the Solar System was Made

Male narrator: In the beginning,
there was darkness,

and then, bang,

giving birth to an endless
expanding existence

of time, space, and matter.

Every day, new discoveries
are unlocking the mysterious,

the mind-blowing,
the deadly secrets

of a place we call
The Universe.

The solar system.

How did it emerge from the
oblivion of interstellar chaos?

- We are made
of gas and dust.

Narrator:
Today the Sun and planets

hold fascinating clues
to their origins

in a haze of particles
so small,

they're virtually invisible.

- The evidence of our past
is all around us.

Narrator:
But are the titanic forces

that created
our solar system

common throughout
the universe?

Or are we unique?

- Our solar system seems to be
one of the oddballs.

Narrator: The universe
may have countless strategies

for crafting
stars and planets,

but only one could determine
how the solar system was made.

It begins at a point in time
nearly 4.6 billion years ago.

A giant cloud of gas and dust
floats eerily

through a remote arm
of the Milky Way,

chilled to more than
400 degrees below zero.

- When it's sitting there
all alone,

nothing much is happening
in a molecular cloud.

The temperatures are very low.

The particles are moving around
very, very slowly.

It's just sitting there.

But if you have a nearby
supernova, an exploding star,

it can send a shock wave through
this molecular cloud...

Triggering
its gravitational collapse.

Narrator: That collapse
is the first step

in a long process

that brings the place
we now call the solar system

into existence.

Our mission now
will be to follow a timeline

of the first
700 million years,

the epoch in which
the solar system

formed and stabilized.

We start by looking at the Sun
and its planets

as they are today.

- The evidence of our past
is all around us.

The four planets in the inner
part of the solar system

are made of rock and metal,

and the four planets

in the outer part
of the solar system

are these giant balls of gas.

So clearly, different processes
were at play,

and that tells us something
about how we got here.

Narrator: We learn the story,

as scientists presently believe
it happened,

from time zero,

the very beginning
of our solar system.

The supernova explosion not only
seeds the giant gas cloud

with heavy elements like iron
and uranium;

the jolt of the explosion
gives the cloud a push

into the future,
as wave fronts

compress the cloud's gases
into a critical mass.

- That mass begins to collapse
under the force of gravity,

and then it's unstoppable.

It's rapid.

It's irreversible.

Narrator:
It's like a roller coaster

reaching the top of its track

and speeding down
the other side.

The collapsing cloud destined
to become our solar system

becomes a virtual theme park
of chaotic motion.

- An amusement park
like Knott's Berry Farm

is a great place
for people to come

and experience
the kind of motion

that happens
in the early solar system.

There's gravity.

There's collisions, momentum,
forces.

All of those interactions
that took place

in the early solar system
can be found here

on all the different kinds
of rides.

Narrator:
Those interactions intensify

in the rapidly collapsing
cloud,

where gas and dust contracts
into dense pockets.

Each will become
the nursery of a star.

- When the giant
molecular cloud

was triggered and started
to collapse,

a lot of other pro to stars
and a lot of other solar systems

were formed at the same time.

So our Sun actually has a lot
of brother and sister stars

that formed right around
the same time as the Sun.

Narrator: The first stages
of our solar system's creation

are hardly unique.

Today we witness
the same thing happening

in the Orion
constellation,

where a giant molecular cloud
stretches

hundreds of light-years
across.

In some places,
collapsing pockets

are now forming
clusters of young stars,

which light up
the surrounding gas.

The circus of motions
in the amusement park

aptly parallels
the movements of space matter

that comes together
to make the solar system.

[laughter and screaming]

The most basic of these motions
is circular,

like a celestial carousel.

As the pre-solar cloud
collapses,

we begin to notice
its rotation,

a spin that has actually
been there from the beginning.

- The entire galaxy rotates.

Everything in the galaxy
rotates.

Everything is rotating with
respect to everything else.

And so rotation
is part and parcel

to the physics
of stellar collapse.

Narrator: What happens next
resembles a spinning ice-skater.

When she draws in her arms,
she spins faster.

As gravity draws in
the cloud's gas,

the cloud not only
spins faster;

it inevitably flattens
into a disc.

We can see a similar process
at work on Earth,

in places like Joe Cariati's
glassblowing workshop

in California,

where astronomer Laura Danly
is observing the action.

Joe begins with a round blob
of red-hot molten glass.

- We basically just are taking
a solid mass that was round

and spinning it.

- It flattens because
it's much easier for the fluid,

the fluid
of this liquid glass,

to collapse in the same axis,
along the axis of spinning,

rather than try
to fight the spin

or fight the angular momentum
and move closer.

And just like
in our solar system,

if there were planets
forming in there,

they'd all be
in the same plane.

- Mm-hmm.

- It's just like the disc
of our solar system.

Now, it looks kind of
elliptical.

It's not circular.

We think of our own solar system
as being circular.

But I think you told me
it had to do

with there being more mass
on one side.

- Indeed.

- So maybe it's kind of like
an analog

of a binary star forming,

where you've got maybe
extra mass on one side

that's also going to form
into a star

or brown dwarf or maybe a—

Just a very massive
Jupiter-like planet.

It's so tempting
to touch it,

but I imagine
it's a bad idea.

- Oh, no, we can't do that.
Yeah.

- [laughing]
- We can't do that.

Narrator: 100,000 years
after it began,

the cloud that will become
our solar system

has almost entirely collapsed,

and its center is glowing
with the radiance

of an emerging pro to star.

- A pro to star,
as the very earliest stages

of becoming a star,

is when the star is still
collapsing down,

and the energy that
it's radiating out

is coming from that
gravitational collapse.

It's still getting hotter
because it's getting smaller.

It's not doing
the nuclear reactions

like a star will be doing

when it's in its main phase
of being a star.

Narrator:
The emerging pro to star

begins gobbling up
the disc of gas and dust

that makes up what's called
the solar nebula.

So much of it will end up
in the Sun

that what's left over for
the planets, moons, asteroids,

and even our own bodies
IS SO meager,

it's almost
a cosmic afterthought.

- We happen to live
on a planet,

so the stuff that went into
making the planet

is very important to us.

But it was just a tiny part
of the whole mix.

This parking lot is a good way
of showing how tiny.

When you look at
the solar system today,

the Sun is 99.85%
of the total mass.

So compared with the 500 cars
in this parking lot,

my car is just about
all that's left over

for all the planets,
asteroids, and moons.

And as for the Earth itself,
well, that might be comparable

to this spare tire,
nothing bigger.

Narrator: At 1 million years
after time zero,

the solar system's method
for sorting out

its planet-building material
is clear.

They're separated by
the different temperatures

in the disc.

Close to the pro to sun,

temperatures above 2,000 degrees
vaporize everything.

But about 5 million miles out
lies the rock line,

where it's cool enough

for metals and minerals
to turn solid.

Much farther out
lies the snow line,

where it's as much
as 375 degrees below 0,

cold enough for water, methane,
and ammonia

to freeze into ices.

- The early solar system
is a little bit

like making cotton candy.

And to show us
how cotton candy is made,

we have Kathy Woo here
to make us a delicious treat.

- First we take
the sugar crystals,

and we pour that into
the heating element.

- The heating element
in this case

is here in the center.

In the case of the solar system,
of course,

it's that very hot Sun
in the middle

that's melting things
that are too close to it.

[whirring]

And as that, uh—
that hot Sun heats up,

it starts to melt the stuff
that's close to it.

Whoa, there it comes.

This is now the solar nebula
you can see flying around here.

On the inside, you actually
don't see anything.

The inside, it's all molten.

And as it gets
to the cooler outside,

the solar nebula
starts to condense.

And you can see it starting
to solidify all over the outside

of the solar system,
where it's cold.

You get a line of gaseous stuff
on the inside

and the solid stuff
on the outside.

This is also
a very good analogy

for what those early
pro to planets are like.

They start to accrete
by all sticking together,

very much like
this cotton candy does,

and make larger and larger
things

coming from these tiny little
pieces of crystal

that are the sugar
that's in the cotton candy.

Thank you.

- You're welcome.

- The solar system
is delicious.

Narrator: The particles
sticking together

are microscopic
at this point,

far smaller than
the melting sugar crystals.

And as cotton candy illustrates
how these solids accrete

in the solar system,

another amusement park
attraction

shows what makes them grow.

Bumper cars wouldn't be much fun
without collisions.

And in the solar system,
without collisions,

there would be no growth,
no accretion.

[rider screams]

- The accretion collisions
that were happening

in the early solar system
are of the kind

that allow objects
to stick together

through various kinds

of essentially
friction-type processes,

where you have things
getting stuck together

just due to mechanical
interaction.

Narrator: In the inner
solar system,

the process is time-consuming,

as tiny cosmic dust balls
form slowly,

stuck together
only by random collisions

in their orbits
around the early Sun.

But in the outer solar system,

the story is dramatically
different.

The giant planets are about
to burst into existence

in a cosmic blink of an eye.

Beginning as
a cloud of gas and dust,

the making of our solar system
will take 700 million years.

Now, just 2 million years
after its birth,

the young system
takes its first steps

in creating
a family of planets

that one day will be as diverse
as Jupiter, Saturn...

or the Earth.

For now, though,
they are chunks of matter

continuing their
roller-coaster ride

in the turbulence
of the solar nebula.

The thick, rotating disc,
made mostly of hydrogen gas,

is embedded with solids.

The inner zone is filled
with small chunks of rock,

but outside the boundary
known as the snow line,

there are also ices of methane,
ammonia, and water,

which dominate the outer disc,
and for good reason.

- They're all hydrogen compounds
of one form or another,

and hydrogen is
the most abundant element

in that region of
the solar system at that point.

That abundant hydrogen
is combining with elements

such as oxygen
to form the water

or carbon
to form the methane

or nitrogen
to form the ammonia

and giving us those compounds,

which are then freezing out.

Narrator: Continual collisions
amid the turbulence

make tiny specks of dust and ice
stick together

through friction
and static electricity

until they're large enough
for gravity to take over.

Eventually, they become
planetesimals.

- Planetesimals were
the original building blocks

of our solar system.

They're incredibly small,

only about half a mile
to a mile across.

But there were countless numbers
in the early solar system.

It was simply littered
with them.

Narrator: These 1/2 mile
planetesimals

will eventually form
full-scale planets

but of distinctly different
sizes.

That's what Ryan Chan
of San Mateo, California,

wanted to ask The Universe
by writing:

- Ryan, the inner planets are
smaller than the outer planets

because the inner planets
didn't have much material

from which to be made,

just metals and rocks
and things like that.

The outer planets, after forming
an Earth-like core,

were able to attract ices
of water, ammonia,

methane, and carbon dioxide.

That made them get bigger,

and then they gravitationally
attracted gases,

becoming much, much bigger.

Narrator: 3 million years
after time zero,

planetesimals are merging
into bigger objects

called planet embryos
or pro to planets.

- Pro to planets are built up
of planetesimals,

so they're larger,
about the size of our Moon.

Narrator:
Just beyond the snow line,

where ice is most abundant,

the teeming mob
of pro to planets

collide and fuse
in a frenzy of planet-building.

Within just 3 million years,

these collisions give birth
to a frozen young planet

destined to become the monster
of the solar system:

the infant Jupiter.

- Before it became
a giant planet,

Jupiter was sort of
like a super-Earth,

maybe 10 or 15 Earth masses.

Narrator. The early Jupiter
is made of rock and ice

and continues to grow.

At a crucial moment,
one last pro to planet

slams into its surface.

[rumbling and whooshing]

It's another roller-coaster-like
tipping point

in the making
of the solar system.

The added mass sends Jupiter
over the edge

to become
a gravitational bully.

- After it reached
a certain critical mass,

Jupiter's gravity was able to
very quickly draw in material,

sort of a runaway effect that
made it very large very fast.

Narrator: Like a cosmic
vacuum cleaner,

Jupiter sweeps up virtually
all the gas in its orbital path,

growing to 90%
of its present size

in just 100,000 years.

Saturn, Neptune, and Uranus
in turn follow Jupiter

in devouring enough gas
to become gas giants.

The dramatic sweep
of one or more planets

clearing a lane through a disc
around a star

is thought to be common
in the universe,

a fact borne out in recent
telescope discoveries.

- We see this process happening
in other solar systems

being formed as well.

We're finally at the point

where we can image other discs
around stars

and the gaps that are being
created by the large planets

that are orbiting them.

Narrator: In early 2011,

astronomers using
the Subaru Telescope in Hawaii

released a photograph of a star
450 light-years from Earth.

An advanced optical mask allowed
them to block out the light

of the star itself, revealing
the first direct image

of a disc with zones cleared out
by orbiting planets.

- That's a really amazing
high-resolution image

that shows a disc of gas
and dust around a star,

and the inner parts
have been carved out

by one or more planets
that have accreted material

and also flung other material
away.

Narrator: 3 million years
along the timeline,

Jupiter and Saturn
are now the titans

of the solar system.

The two giant planets
will eventually contain 92%

of all the non-solar mass
in the entire system.

10 million years
into its life,

the young solar system
is virtually out of gas.

In this case, the gas
is the hydrogen and helium

that fueled Jupiter and Saturn's
swift growth.

- The forming star
had this huge solar wind

that was clearing material
out of the solar system.

Jupiter and Saturn
were fortunate enough

to pick up most of this material
in their orbits,

which is why
they're so large.

Uranus and Neptune
were a bit later to the game

and were unable to pick up
as much material,

which is why they're smaller
than Jupiter and Saturn.

Narrator: During the time
before the dust and gas

were blown away,
the forming solar system

was largely hidden from
the rest of the universe.

Even as dust and gas
were forming planets,

the disc remained thick enough
to block light

from the pro to sun
at the center.

- At a distance of several
Earth distances from the Sun,

for example, looking back
towards the Sun

in the earliest phases
of the solar system,

we wouldn't be able
to see the Sun.

We wouldn't be able to see
the visible light.

Narrator: What would
the early solar system

have looked like
to alien astronomers

gazing at us
from even greater distances?

The Hubble Space Telescope
shows us with photos

of pro to planetary discs
in a star-forming region

1,350 light-years
from Earth.

- We can see them
at a variety of angles,

tilts relative
to our line of sight.

For example,
if they are face-on,

we can see a central star
surrounded by a disc.

But when we look at these
objects edge-on,

the gas and dust that is between
our line of sight

and the central star

blocks the light of the star.

Narrator: But now,
10 million years after

the solar system
began to form,

with the dust and gas
virtually gone,

the Sun-to-be shines brilliantly
through space.

It has yet to go through

the process of becoming
a true star,

and at this point, it would seem
strange to modern eyes.

- The spectrum of light
was very different.

So it was putting out
a lot of energy,

just as it does today,

but it was actually much redder
in its spectrum.

So that early solar system

would have been
a very different color

from what we see today.

Narrator: The pro to star,
orange-yellow in appearance,

is a seething cauldron.

In some systems, the cores
of contracting clouds

never glow
with anything more

than the dim light
of dull brown dwarfs.

Our early Sun now nears
a critical point.

Will its internal furnace
sputter and fail,

or will it breach
the nuclear threshold

and shine across the galaxy

with all the brilliance
of a true star?

We're now at
the most critical point

in the making
of our solar system.

At 50 million years old,

the pro to sun
and its forming planets

are barely 1%
of their present age.

In many systems,
the central star

doesn't have enough mass
to fully ignite.

But our Sun is about to overcome
that fate.

It has reached the critical
threshold of heat and pressure

where nuclear fusion
can begin in its core.

[rumbling]

Using the same awesome energy
that powers the hydrogen bomb,

our Sun bursts into life as
a fully-formed newborn star.

- At about 50 million years into
the life of the solar system

since it first began forming,

the Sun goes into
a different phase,

burning hydrogen,
actually doing nuclear fusion.

At that point, the Sun becomes
what we think of as now

a fully-fledged star.

Narrator: Nuclear fusion
will carry the Sun

into the distant future.

It will burn long enough

to support the evolution
of life on Earth,

shining unceasingly
for about 10 billion years.

Unlike the newly nuclear Sun,

the rest of the solar system
is far from mature.

40 million years earlier,
the frozen gas giants

outside the snow line
ceased to grow

and achieved
an icy stability.

But in the hot
inner solar system,

where gas is rare
but rocks abound,

chaos still reigns.

- By the time that the Sun
has become a full-fledged star,

the planets in the inner part
of the solar system

are still trying to grow.

There are small little
pro to planets

that are building together,

colliding,
getting larger and larger,

eventually to become
those four big planets

that we have
in the inner solar system.

Narrator: But just inside
the orbit of Jupiter

lies a narrow region where
the smaller planetesimals rule

and pro to planets are rare.

This is the asteroid belt,

where Jupiter stirs things up

to prevent any planets
from forming.

- Jupiter
is the largest planet,

and so its gravitational
influence is the greatest

in the solar system.

There was a point in the early
solar system where Jupiter

was passing through
what's now the asteroid belt,

pumping up the velocities
of the planetesimals there,

causing them to collide
in a destructive manner.

They blew apart.

We're gonna try to get a feel
for what a destructive collision

is like in the asteroid belt.

But we can't use real rocks
because they're too hard

and the velocities available
to us are too slow,

so what we're going to do is use
these special lightweight rocks,

which were made for us
by Ryan Johnson,

a special effects artist.

Ryan, can you tell us about
these special lightweight

simulated asteroids?

- Sure.

So these props that
we've developed here

are a foamed plaster-type
material that we use

to simulate real rocks in movies
and films and things like that.

Whenever we want something to
break that looks like it's hard,

this stuff breaks really easy,
and it crumbles.

So what we've done is,
we've taken this same material,

and we've developed
a much larger one

we're gonna use
to simulate an asteroid.

So we've got two of these,

and we'll smash 'em together
really hard,

and that'll hopefully simulate
the collision of an asteroid.

- So what sort of speed
do you think

we need to smash them together
so they'll break?

- We just need to drop one
on top of another

from a reasonable height,
and, uh...

Something like that.

- Okay, let's try it.

Let's drop the plumb.

Narrator: The distance
of the drop is about 18 feet,

which will give
the falling asteroid

a speed of 37 miles per hour.

- Little bit more.

Perfect.

Perfect, right there.

Okay, Ryan,
we're ready for the drop.

- Okay, it's pretty windy,

but we'll see how we do.

- All right!

That is excellent.

- Oh, great.

- I would say
that's a success.

- Oh, thanks.

Yeah, that looks good.
- Yep.

- It's amazing, how much
it's, like, really spread out.

- Right,
so in the asteroid belt,

all these pieces would gravitate
back together

and form a rubble pile,

what we would call an asteroid
today.

- So if they're starting
to come together all the time,

isn't that the same process
that actually forms a planet?

Why wouldn't the planet form
in that case?

- Well, no, because then
this thing gets hit again

and again and again.

So these things keep getting
pulverized by impacts,

and you're just left with
little individual rubble piles,

rather than
a complete planet.

- Does this reasonably replicate
what you think possibly

an asteroid collision
would be?

- This is a pretty good analogy,
in fact,

because you get large pieces;
you get dust.

And so what we think
are asteroids

are basically rubble piles
composed of these

large pieces put together,
covered then in dust.

And, uh, and so, yeah,
I think you did a good job.

This looks like a—like a—
the beginnings of an asteroid.

- Great.
Well, I'm glad it worked.

- Right.

Narrator: The asteroid belt
isn't the only region

in the emerging solar system
where planets fail to form.

At the outer fringes
of the solar system,

another ring of small objects
orbits in frozen silence...

the Kuiper belt.

- The Kuiper belt is a region
at and beyond the orbit

of Neptune that has a whole
bunch of rocky and icy objects

pretty far apart
from one another.

Now, they were never able
to coalesce to form a planet

because there's just not enough
of them close enough together.

Narrator: 50 million years
after the solar system was born,

both the Kuiper
and the asteroid belts

have 100 times more objects
in them than they do today.

These objects will play
a monumentally destructive

but vital role
in the final evolution

of the rocky inner planets,
including the Earth.

The inner planets take as much
as ten times longer to form

than the giant planets
outside the snow line.

After 75 million years,
the process is near completion.

About 93 million miles
from the young Sun,

the pro to-Earth
has reached planet size

in a relatively stable orbit.

But it has a cosmic stalker.

- It's actually believed
that the Earth was,

in its early phase, accompanied
by another planet,

a pro to planet called Theia,

which was actually in
a similar orbit to Earth,

essentially following
roughly the same path.

Narrator: For millions of years,
the sister planets

chase each other around the Sun
in a dangerous duet.

But a clash is coming that
will have immense consequences

for the fate of the Earth.

The making of our solar system
has gone on for 80 million years

since the collapse
of the giant gas cloud

that started the process.

The inner planets
have largely taken shape.

But now the Earth, which will
one day harbor life,

faces the potential of
an early and cataclysmic death.

For millions of years,

Earth has been followed
by the pro to planet Theia.

The two bodies travel
in essentially the same orbit,

gradually coming closer
and closer.

Now, for Earth and Theia,
it's crunch time.

[rumbling and crackling]

- The Earth-Theia collision

early in the history
of the solar system

must have been
a spectacular event.

A Mars-sized object came in
and hit Earth's side,

splattering part of the crust
and mantle

of both objects into space,

forming a ring of debris
from which the Moon then formed.

Narrator. Having survived
the cataclysm and gained a Moon,

the Earth settles in
as one of the stable planets

of the inner solar system.

The drama now moves back
to the gas giants,

whose shifting orbits threaten
to tear the solar system apart.

At 500 million years old,

all of the solar system's
planets have been formed.

But surrounded by debris
in the planetary disc,

they are on the move.

- As waves of density
are formed in the disc,

the planets are almost
surfing on the waves

of material
in the disc itself.

You're really
shuffling the deck completely

from where planets are formed
to where we finally see them.

Narrator:
In the early solar system,

the three outermost planets,
as a group,

are closer to the Sun
than they are today.

And Neptune's original orbit
is inside that of Uranus,

the reverse
of their current position.

In addition, the asteroid
and Kuiper belts

each have 100 times more
material than they do today.

The small bodies of both belts
are constantly flung around

by the giant planets
and their intense gravity.

As massive as they are,
the big planets react

every time they toss
a planetesimal somewhere else.

The reactions may be small,

but they add up to make
the orbits of the giant planets

migrate to new positions.

- Early on,
the outer planets

tended to move around
quite a bit.

They migrated.

Now, Saturn, Uranus,
and Neptune

sent planetesimals
in toward the Sun.

That means they had to generally
move outwards,

whereas Jupiter flung
planetesimals out

to very great distances,

even ejected them
from the solar system,

and that means that Jupiter
had to move in.

Narrator: What determines these
in and out movements?

They result
from a law of physics

that says energy
is never lost.

- When a planet ejects
a planetesimal,

the planet itself
has to move in a little bit,

and that's simple conservation
of energy.

It's giving a lot of energy
to the planetesimal,

dumping it way out there.

That means it, the planet,
has to move in.

It loses energy.

If an orbiting object
loses energy,

it's not moving as quickly.

That means it drops
to a lower orbit.

Narrator: The amusement park
again illustrates

the forces at work-

in this case,
the slingshot effect.

It's a gravitational boost

that large planets
can give small objects.

In the 1970s,
scientists exploited it

to accelerate
the Voyager spacecraft

as it swung from planet
to planet

in the outer solar system.

Here on Earth, we can think
of the slingshot

as a roller coaster
over the edge.

- The Boomerang roller coaster
ride that we have here

is a nice example
of the processes

that are involved
in the slingshot effect.

The gravity here that
makes this work here on Earth

is using Earth's gravity.

It pulls down on the cart,
pulls it down the slope,

and then the cart
goes back up the slope

due to the momentum it gained
from coming down the slope.

What if we were to add Jupiter
to the system?

Now, Jupiter's gravity
will still pull the object in,

but Jupiter swings it
around the planet,

and it goes around Jupiter.

And the motion of Jupiter
gives it an extra kick

so that it gets more momentum
than it came in with

and gets shooting back up
the slope and out into space.

Narrator: Millions of small
gravitational tugs

have made subtle changes
to the planetary orbits

for more than
half a billion years.

Earth and the other
young planets

may settle into conditions
conducive to early life.

If so, it's about to be
wiped out

as the gas giants
Jupiter and Saturn

reach a remarkable tipping point
called a resonance.

- As soon as Jupiter and Saturn
hit the resonance,

it was catastrophic.

The entire solar system flew
apart in just a million years,

which is a tiny amount
of time,

compared to the age
of the solar system.

Narrator: The resonance means

that every time Saturn
orbits the Sun once,

Jupiter will go around twice.

The result: Jupiter and Saturn
come very close to each other

in the same part of
the solar system on a regular,

ongoing basis, creating
an immense gravity pump.

- It's like pumping
a kid on a swing.

If you hit the kid on the swing
at just the right time,

you can get the motion to go
higher and higher and higher.

Narrator: The most dramatic
effect is on

the two outermost
giant planets.

- As all of the planets
were orbiting

around the solar system,

having gravitational
interactions with each other,

one of the most amazing things
that happened

is that Uranus and Neptune
actually switched places.

So now Neptune
is farther away than Uranus.

Narrator: The resonance
is a cataclysm

whose effects
sweep through the system

at astounding speed,
not only shifting orbits,

but clearing out most
of the system's small objects.

- Jupiter alone is quite
a gravitational bully

and gradually depleted
the asteroid belt.

But the Jupiter-Saturn resonance
caused a catastrophic depletion

of both the asteroid belt
and the Kuiper belt.

Narrator: 99% of the bodies

in the asteroid and Kuiper belts
are cleared.

While most of them are thrown
out of the system,

some of them plunge inward.

Drawn by the gravity
of the Sun,

they rip through space
toward the inner solar system.

How will the inner planets,

including the Earth,
escape the onslaught?

The making
of our solar system

reaches a violent climax
700 million years

after the pre-solar cloud
first began to collapse.

And Earth
is in the firing line.

The gravitational chaos
of Jupiter and Saturn

is battering the inner solar
system's planets and moons

in an event now known
as the Late Heavy Bombardment.

- A lot of the material
in the outer solar system,

these comets, fell in towards
the inner solar system,

where they collided with
the inner planets and the moon,

creating the craters
that we see today.

Narrator:
Some researchers believe

collisions may have
repeatedly sterilized the Earth,

and that if life had formed,
it was wiped out...

and had to start anew.

But the impact of objects
from space,

along with their violence,

may have also brought
a benefit.

- The Earth might not have
all the water it does today

had it not been bombarded
by material

from the outer solar system.

Some have speculated that much
of the water we have on Earth

is actually
a result of impacts

from the Late Heavy Bombardment
period.

Narrator. Today,
4.6 billion years

after the solar system's
birth,

the ongoing, if remote, danger
of a massive asteroid strike

means the story
is not over.

More important, though,

are the hundreds
of tiny asteroids

hitting the planet
as meteorites.

Studying them tells us

if the making
of the solar system

really happened when and how
we think it did.

- I'm holding a sample
of the Allende meteorite.

The Allende meteorite
is a fragment of rock

that fell in Mexico, near
the village of Allende, in 1969.

One of the components
of the meteorite

are these calcium-,
aluminum-rich inclusions,

these white objects
that you can see on the surface.

These are the oldest known
materials in the solar system,

and we know this by age
dating with radiogenic isotopes.

Narrator: In his
high-tech lab at UCLA,

cosmochemist Ed Young
and his colleagues

carefully examine tiny samples
of ancient meteorites.

- There's a big white fragment
in the middle

which we want to cut out.

Narrator: The lab's precision
lasers aim at the fragments,

blasting out holes
no wider than a human hair.

Sophisticated analysis
measures radioactive elements,

which serve as atomic clocks.

In early 2011,
cosmochemists

in a similar lab at
Arizona State University

dated part of
a North African meteorite

to an incredibly accurate
4.5682 billion years old,

the oldest material
ever found on Earth,

older than the planet itself.

In August 2011,
the Dawn spacecraft arrived

in the asteroid belt,
source of most meteorites.

Close-up pictures of Vesta,
the second largest asteroid,

open a new epoch in telling
the solar system's story.

- One of the exciting things
about the Dawn mission

is that we're gonna get
our first glimpse

into something that was
essentially a mini-planet

that was formed right at the
beginning of the solar system.

Narrator: Since its birth

early in the solar system's
history,

Vesta has been undisturbed
by weather

or many of the geologic forces

that have changed the planets
over time.

- Just like some of the larger
planets, it has volcanoes.

It has a core.

But unlike
these larger planets,

not much else
has happened to it

in the past
4 1/2 billion years.

So we essentially
get a window back

into that very earliest history
of the solar system.

Narrator: Dawn will orbit Vesta
for a year

before going on
to spend another year

orbiting the largest asteroid,
Ceres.

Meanwhile, NASA's Juno probe
has just begun its voyage

to Jupiter, where it will visit
the giant planet

to determine if it really does
have a solid core

and formed early and quickly,
as scientists now believe.

Even more crucial
are other stars

with their own solar systems,
whose formation

sheds essential light
on our own.

- The most important reason

for understanding how
the solar system was made

was to find out whether or not
we're normal.

When you look out and look at
other solar systems being made

with our telescopes today,

for example in Orion
and other places,

we want to answer
the question,

"How normal
is this solar system?"

Narrator: Launched in 2009,

the Kepler mission
is now running full-blast

and has identified
1,200 possible planets

around other stars.

Some systems
have Jupiter-sized planets

close to their suns
or in lopsided orbits.

Others have only small planets

crowded closely in the hot zone
of their stars.

Our solar system, however,

has its planets
in near-circular orbits,

spread out in a stable
arrangement

that seems almost
too perfect.

- One of the great surprises
of the last decade,

as we started to discover
other planetary systems,

was the fact that
our solar system

seems to be
one of the oddballs,

mostly because our own
solar system is so regular.

- Is the solar system
made by processes

that we can observe
going on today,

or are we somehow special?

This goes to the point of
whether or not life is special.

Narrator: And that question

is perhaps the most important
one of all,

as the life story of the Sun
and its planets

essentially becomes
the life story of life itself,

humanity on Earth,
and our ultimate place,

alone or among many in...

The Universe.