All language subtitles for How the Universe Works s02e07.eng

Asteroids are
the Earth's nemesis.

They've blitzed our world
for billions of years.

This takes a few seconds
to create.

50,000 years ago was a very bad
day for anybody living nearby.

Yet asteroids are
also a valuable resource --

giant boulders
rich with valuable metals,

icy miniature worlds
with more freshwater than Earth.

Ultimately, asteroids
may be a stepping stone

by which we can one day leave
the entire solar system.

Asteroids are planet builders.

Without them,
our world would not be here.

We owe our very existence
to these things.

They are the givers
and takers of life.

== sync, corrected by elderman ==

The night sky is full of stars,

galaxies, planets,
and asteroids.

"Asteroid" actually
means "star-like."

Even in the very best
telescopes,

they look like nothing more than
just points of light in the sky.

They're cosmic boulders,

and there are trillions of them,

from the size of a car to giants
hundreds of miles across.

Together they tell the story
of how we came to be.

The Earth was made by asteroids.

4.5 billion years ago,

the solar system is a vast,
cosmic whirlpool.

Dust sticks together
to create asteroids.

In our own solar system
and in every solar system,

the first objects to form --
the first large rocks --

before planets form,
are essentially asteroids.

There are no planets yet.

Instead, trillions of rocks
and stones

swirl around the newly born Sun.

It would've been
a very strange place,

kind of like a merry-go-round

of all these objects orbiting
around the Sun.

And there are millions
of these asteroids

that are just in different sizes
and different shapes.

These ancient asteroids

will shape the solar system

and build the planet we live on.

Asteroids are so much more
than just rocks in space.

They're the building blocks
of our very own planet.

Billions of small asteroids

must clump together
to make a planet.

But asteroids move at thousands
of miles per hour.

Getting them to stick is hard.

We're here at the stock car race

to see what the early solar
system may have looked like.

High-speed car
collisions cause damage.

Parts smash off.

Asteroid collisions
are the same.

To join together, somehow
they must collide and stick.

Stock cars
show how this happens.

They move fast
but all in the same direction,

just like the asteroids
in the early solar system.

When collisions happen,
they're relatively gentle.

Instead of smashing apart,
they join together.

These are planets in the making.

They're going around
almost at the same speed,

and they begin
to stick together,

and that's how planets
begin to form.

Asteroids gather
into rock piles,

like two cars locked together.

As more asteroids collide,
the rock piles grow.

Building whole planets this way
would take billions of years.

Yet the planets formed
in just a few million years.

How?

When the rock piles
reach mountain size,

gravity speeds up the process.

Gravity started
to become important

when they were about the size
of one of the Rocky Mountains,

like Pikes Peak behind me.

It was when they were
several miles across

that they had enough mass

that their gravity could start
to draw material in.

Now, if the Earth weren't here,

and it were just Pikes Peak
over there a few miles away,

I would very slowly
start to drift toward it,

faster and faster,

accelerating the whole way
until I actually impacted it.

The gravity would draw me in.

It would pull on me

until I actually hit
the mountain itself.

Large asteroids
are mountains in space.

The early solar system
is full of them.

Their gravity pulls
other asteroids toward them.

The larger an asteroid becomes,

the more rocks it pulls in
and the faster it grows.

At that point,
the events happen very quickly.

It would actually draw that
stuff in and grow very rapidly.

One of these early
space mountains keeps on growing

until there are no rocks left
to pull in.

It's no longer an asteroid.

It's a young planet --
the Earth.

All of the planets,
even the Earth,

they owe their existence
to the fact

that there were asteroids
back then.

This is how all
rocky planets form --

asteroids join together
until there are no more left.

Mercury, Venus,

Earth, and Mars

are all overgrown asteroids.

But beyond Mars,
something went wrong.

No rocky planets.

Instead, billions of rocks
and boulders

that never joined together --
the asteroid belt.

Out here,
construction came to a halt

before a rocky planet
could form --

because of Jupiter.

The gas giant had already
formed nearby.

Jupiter is humongous.

It's the 800-pound gorilla.

It dominates everything
gravitationally.

4.5 billion years ago,

Jupiter's gravity causes havoc.

It flings asteroids
in every direction.

Giant boulders scatter
from their regular orbits

onto extreme chaotic paths.

The stock car race ends,
and the demolition derby begins.

Once Jupiter got involved,

the solar system began to look
like a demolition derby --

things colliding
with each other,

going in all sorts
of different directions.

A cosmic pileup --

rocks smash into each other
from every direction,

violent, chaotic collisions.

These rocks
don't clump together.

They shatter...

and create the asteroid belt.

Violent collisions still rock
the asteroid belt today.

In 2010, the Hubble Space
Telescope captured this --

the aftermath
of a hypervelocity collision.

Asteroids can both create
and destroy.

If many of them come together
gently, you get planets.

Too much violence and you get
the asteroid belt --

billions of rocks and boulders,

a graveyard for a planet
that never formed.

The asteroid belt
is a mysterious realm,

full of danger
and full of promise,

a new frontier just waiting
to be explored.

Asteroids are as
diverse as planets or moons.

Some are metallic...

some rocky...

some icy.

Some even have their own moons.

They come in all shapes
and sizes...

From boulders all the way
to miniature worlds.

And they're everywhere.

Distant solar systems have
their own asteroid belts.

The star Epsilon Eridani
is just 10 light-years away.

It has not one
but two asteroid belts.

Another star has a belt
25 times larger

than our own.

If you're actually living on
a planet in that solar system,

the asteroid belt
would look like a --

much brighter
than the Milky Way,

a big streak
across the night sky.

Asteroid belts
are the scraps left over

after plans have formed,

so they tell us a lot
about their solar system.

Our asteroid belt
is full of variety --

millions of strange asteroids,

each with a story to tell.

Yet we have barely
explored it at all.

That's about to change.

The first mission to the
asteroid belt is under way --

the Dawn Probe.

Its goal?

To explore a mysterious,
distant realm.

We're gonna learn more
about the main belt asteroids

from this one mission

than we will have

since we discovered the asteroid
belt in the first place.

In July 2011,

Dawn arrived at its first target

and sent back these pictures.

Vesta is the second-largest
asteroid in the belt.

It almost became a planet.

Then Jupiter's massive gravity
stunted its growth.

Today it's a miniature world.

One of the common misconceptions
about the asteroid belt

is that things are fairly small.

But some of
the largest asteroids

are really more correctly
thought of as minor planets.

They're several hundred
miles across.

Vesta even has a mountain

three times higher than Everest.

Mark Sykes is co-investigator
of the mission.

It's just a real excitement

because you're seeing a new
world for the first time,

and you know just enough
to be dangerous

in trying to explain what it is
that you're seeing.

Vesta is like
a snapshot of the infant Earth

when it was just as wide
as Arizona.

We're seeing perhaps

what an embryonic, early
terrestrial planet like Earth

looked like in the first few
million years of its history.

The Dawn Probe
has already found

that Vesta has an iron core
like the Earth --

evidence that
the Earth's core formed

when the planet was still young.

This stunted world
offers us a window

on the Earth's distant past.

We're seeing things that
we didn't necessarily expect,

but that's what makes it fun.

After Vesta,

the Dawn mission will head

into the asteroid belt's
outer reaches

to explore an icy,
primeval world

four times bigger than Vesta.

There, Dawn aims to settle
another mystery

about the Earth's past --

where did our oceans come from?

The asteroid belt is
ancient, violent, and remote --

hundreds of millions of miles
from Earth.

But not all asteroids
stay in the asteroid belt.

They can roam all over
the solar system.

The Moon's surface records
a violent past --

a massive, cosmic bombardment.

We see evidence every night
when the Moon comes out.

What do we see?

A pockmarked, barren world --

evidence that there was
an intense rain of asteroids

and debris that came
from outer space,

completely disfiguring
the surface of the Moon.

Millions of craters
cover the Moon,

including the largest
in the solar system --

1,500 miles across,

itself scarred by thousands
of smaller craters.

A storm of asteroids
blasted the Moon

4 billion years ago.

And if that happened
to the Moon,

it must also have happened
to Earth.

The Earth is a much bigger,
more massive target in space.

For every one of those craters
you see on the Moon,

you've got to imagine
50 or 60 craters

here on the planet Earth.

The impacts back then
must have been horrendous.

Every few weeks, a gigantic
object hurtling from outer space

gouging out a huge chunk
of the planet Earth.

We call it
the late heavy bombardment.

For 200 million years,
fireballs rained from the sky.

The impacts trigger earthquakes

bigger than any
in recorded history.

10,000-mile-per-hour hurricanes

rip through
Earth's primitive atmosphere.

But asteroids also bring
a new substance to Earth.

Some asteroids contain ice --

frozen water that melts
on impact.

Each asteroid
brings a little more.

But could asteroids
really bring enough water

to cover 2/3 of our planet?

One of the questions we have is
how did water get to the Earth.

Because the original Earth,
we think,

was very hot and very dry.

NASA's Dawn Probe
aims to find out.

The asteroid belt still contains
icy asteroids to this day

in the coldest,
most distant part.

In 2015,

Dawn will arrive at the solar
system's largest asteroid --

Ceres.

Ceres is 1/3 the mass
of the entire asteroid belt

and four times as large
as any other known asteroid.

A lot of it
looks like pure ice.

Ceres has a rocky
interior and ice-rich mantle.

It's far enough away from
the Sun -- it's cold enough --

that it's stable.

Ceres is just 600 miles wide,

yet there may be
more frozen water here

than all the freshwater
on Earth.

The Dawn mission will find out
for sure.

If Ceres really does hold
so much ice,

it could help explain why
the Earth has so much water.

When asteroids bombarded
the Earth 4 billion years ago,

massive icy bodies like Ceres

could've brought vast amounts
of water.

Water itself,
in the form of ice,

came down from the heavens

to create the lush oceans
of the Earth.

And not just the oceans.

Clouds, rivers...

glaciers may all have come
from space.

The Dawn mission
may uncover something

even more significant on Ceres.

It may find an ocean
underneath the ice --

an inner mantle of liquid water,

melted by heat from
the dwarf planet's core.

Life as we know it
depends on water.

Wherever we find water,
we may find the spark of life.

If there is a liquid-water ocean
underneath the surface today,

that begs the question

of whether there could be
life there.

Extraterrestrial life
could've started

in the asteroid belt.

Ceres could be home
to basic life-forms

flourishing
in a subsurface ocean.

If asteroids like Ceres
can support life,

that could reveal how life
started on Earth.

4 billion years ago,

asteroids bombarded
the young Earth.

They brought water,
and they may have brought life.

From the asteroid belt

to Earth's new oceans...

Primitive organisms that thrived

and ultimately evolved into all
the Earth's creatures --

a planet that brims with life.

Our earliest ancestors
may have arrived

from the asteroid belt.

Perhaps these little worlds
could be incubators of life

throughout our solar system,

maybe even in other solar
systems around other stars.

Asteroids may bring life

to worlds throughout
the Universe.

They may also bring death.

Asteroids are crucial
to life in the Universe.

But once life gets started,
asteroids can also end it.

Asteroids really have
two sides to them.

They're sort of creation
and destruction

all wrapped up together.

Planet Earth is right
in the firing line.

We've come to realize
in recent years

that we live in this kind of
a cosmic shooting gallery.

Astronauts
witness this firsthand.

When I flew on Apollo 9 and I
went outside the spacecraft,

it's very likely that I was hit

by, you know,
a very, very small asteroid.

And, you know, it will make
a hole in a space suit.

Most objects in
the Earth's vicinity are tiny,

but they move at thousands
of miles per hour.

So, the suits
are very, very well-built,

the result of which
is they're very heavy.

But, you know, we've never had
one penetrated yet.

The Earth, too,
has built-in protection

from small asteroids --
the atmosphere.

When asteroids hit
the atmosphere, they burn.

I can remember,

one night when we were looking
down at the dark Earth,

and I kept thinking I saw
an occasional flash of light,

but I wasn't sure.

And then suddenly, we're
realizing, of course, you know,

we're looking at shooting stars.

Most people don't
realize that on a given night,

if you lie in the grass
and look up at the night sky,

you'll see shooting stars,
many of them each hour.

Most shooting stars
are the size of grains of sand.

These burn up.

But larger space rocks

can punch right through
to the ground.

Here's the proof --

meteor crater in Arizona,

gouged out by an asteroid

just 150 feet across.

You can see the huge
force that excavated this,

and you can also see
the layers of material

that were turned over
as the crater was excavated,

and so some of these rocks
around here

are kind of upside-down
from where they started.

There have been
millions of impacts like this

in Earth's past.

There will be more.

Imagine a city
where meteor crater is now.

You can see a fireball coming
through the sky very quickly.

You know, this thing is moving
at eight miles a second,

and so it wouldn't take
very long

for it to move across the sky
and strike the ground.

Heat from the fireball
scorches the surface.

But most damage comes
after the impact.

Once it strikes the ground,

this takes a few seconds
to create.

So, a very short time,
very large amount of energy,

and very devastating effects.

The asteroid is obliterated.

A mighty shock wave
generates winds

six times more powerful
than a hurricane.

You have the blast
that comes out,

probably for several miles,

and large debris that would
crush buildings and homes.

If it hit today,

the asteroid from meteor crater
would be a city killer.

But the meteor crater asteroid
was small.

It was likely a fragment
from a much larger asteroid.

Whatever it is that hit in
meteor crater wasn't very big.

It was probably 50 yards across,

so not even as big
as a football field.

There are millions
of much larger asteroids.

These would cause
even more carnage --

country killers and worse.

Asteroids over a half mile wide

could end our civilization --

worldwide killers.

We know because
it happened already.

There are traces everywhere.

There's evidence of giant
impacts all over the world,

and it's right underneath
your feet.

And in fact, in some places,
it's pretty easy to spot.

Like here in Southern Colorado.

So, this layer of light-colored
rock, that's the KT boundary.

And it's called a boundary
because it marks the boundary

between two different
time periods.

Everything that was
put down here

underneath the KT boundary
had dinosaurs in it.

Everything above it --
no dinosaurs.

So it really marks
that point in time

when the dinosaurs went away.

The layer is rich
in an element called iridium.

It's rare on the Earth's surface
but common in asteroids.

So, if a giant asteroid came in,
smacked into the Earth,

blew out dust everywhere,

the iridium inside the asteroid

would've settled down
into a layer all over Earth,

and that's exactly
what we see right here.

The clear fingerprint
of an asteroid.

There must have been
some perfect morning

before the asteroid impact

when the land of the dinosaurs
was still very much

as it had been
for millions of years.

Then there would be something
sighted up in the sky,

something very bright, very hot.

The asteroid
is six miles long,

big enough
to devastate the planet.

The asteroid that came in
and formed this layer here

was very massive
and was moving very fast,

and so when it impacted
the Earth,

that energy was turned into
boom -- a very, very big boom.

It has the force
of 5 billion Hiroshima bombs.

Large pieces of Earth blow out
into space,

then rain back down --
a storm of fireballs.

Wildfires rage across the globe.

In the KT boundary layer
is a layer of soot,

and that's an indication
that there were global fires,

that everything on Earth
was basically on fire

after this happened.

The Earth plunges
into darkness --

an impact winter --

mass extinction.

Basically
you can think of this

as every environmental
catastrophe

all happening at the same time.

It was an incredibly bad day
for planet Earth.

A chilling reminder
of the threat from space.

Asteroids this big
will hit us again.

We will go
the way of the dinosaurs.

We will be survived,

most likely by the bugs,
the cockroaches.

They will be the ones
who will inherit this Earth.

But hopefully that's gonna be
a long time from now.

Is mankind doomed?

Or can we dodge fate?

Asteroids built our world.

They brought water.

They killed the dinosaurs

and made room for new species.

But asteroids are also a threat.

We know absolutely
for certain

that there will be large impacts
in the future,

so it's not a question of "if,"
it's only a question of "when."

Large meteor impacts happen once
every 60 to 100 million years.

We're due for one soon perhaps.

If we want to survive,
we need to prepare.

We must find the asteroids,

determine if they're heading
for Earth,

then stop them.

That's not easy.

But it may be possible.

Happily, there's a difference
between us and dinosaurs.

We have telescopes,

and we can get advance notice
of an impact.

Asteroids are much smaller
than stars and planets.

It's hard to see them coming.

To track asteroids,

you need a giant telescope

like the Arecibo Observatory
in Puerto Rico.

Right now I'm on top of the
largest telescope in the world,

and this place may actually be
our best defense

against getting hit by one
of these near-earth asteroids.

The vast bowl
is 1,000 feet across.

And it's not only the world's
biggest telescope,

it's also the world's
biggest radar dish.

When you think about using radar

to keep track
of all the airplanes

that are up in the sky,

well, this one is so powerful,

it can actually track near-earth
objects millions of miles away.

Unlike a telescope,

radar can directly measure
an object's distance

and reveal exactly where it is.

That's perfect
for tracking asteroids.

In 2004,

astronomers spot
a stadium-sized asteroid

heading toward Earth.

Its name --

"Apophis," after the Egyptian
God of destruction.

The day it might hit us --

April 13, 2029,

Friday the 13th.

Apophis was the first
near-earth object

of the modern era that had
astronomers honestly scared.

There seemed to be
a one in 30 chance

of something catastrophic
happening.

Arecibo springs into action

against the biggest threat
from space ever detected.

Apophis could devastate
entire countries.

But the asteroid's path
is still uncertain.

It might hit,
or it might just miss.

Only Arecibo
can tell us for sure.

The Arecibo telescope

was able to reduce the
uncertainty of Apophis by 98%.

It told us that there was
no chance

this thing would hit us in 2029.

It will be close.

Apophis will pass closer
to the Earth than the Moon,

closer even than some
communications satellites.

We have powerful tools
to detect asteroids.

Someday, we'll find one
that will hit the Earth.

How can we protect ourselves?

The obvious strategy
is to destroy the asteroid

before it destroys us.

But that could be risky.

You don't want to blow it up

because you may end up
breaking it up

into two or three
or five pieces,

which then end up hitting
all around the Earth

and wiping out
many, many people.

Exploding an asteroid
could cause more harm than good.

Better to make it
miss completely.

When an asteroid is headed
for Earth,

their future paths cross.

And they'll both reach
that point at the same time.

Imagine the Earth
is a freight train

and the asteroid is a car,

both heading
for a railroad crossing.

If they reach that crossing
at the same time,

they will collide.

The best way to avoid the impact

is not to swerve away
from the train,

it's to hit the gas
or the brakes.

If you can cross the tracks
before the train gets there

or wait for the train to pass
and then cross them --

that's what we want to do
with asteroids,

just to make sure that
the asteroid and the Earth

aren't at the same place
at the same time.

By simply slowing down the car,
we're gonna miss.

That's the way to avert
a collision.

But asteroids
don't come with brakes.

We need another way
to change their speed.

One approach is to use
the asteroid's gravity.

For a small enough asteroid,

all you need to do is park
a large spacecraft

next to the asteroid.

A spaceship would hover above
the asteroid's surface.

You can thrust
with your spacecraft

to keep it from falling onto
the surface of the asteroid,

and so it's like a little
gravity tractor --

using gravity as the tow line

to move the asteroid
out of the way.

Over time,
the gravity between them

would slow down the asteroid
just enough

for it to miss the Earth.

Asteroids could shape our future
in another way.

We could turn them
from a deadly threat

into a precious resource.

Asteroids are a creative force.

They build planets.

They bring water.

But they're also destructive.

Asteroids are both a boon
and a threat.

Early on, they bring
the materials for life.

Later on, they can destroy life.

Asteroids bring
violence and death.

But life may not always
be in danger.

Ultimately, if life
becomes intelligent enough,

it can send objects out

to deflect or destroy
the impending asteroids.

We now have the
technology to divert asteroids.

That means we can treat them
not as a threat

but an opportunity.

We could mine them.

Many of them are
just ripe for the taking

in these wonderful
mineral resources.

And so the asteroids,
in some ways,

are literally gold mines
in the sky.

They're not just gold mines.

They're zinc mines,

aluminum mines,

platinum mines.

Just one average-sized asteroid

could contain minerals

worth thousands of billions
of dollars.

But first, we have to reach
the asteroids.

On April 15, 2010,

President Obama
announced a new plan.

By 2025,

we expect new spacecraft
designed for long journeys

to allow us to begin the first
ever crewed missions

beyond the Moon into deep space.

We'll start by sending
astronauts to an asteroid

for the first time in history.

Ironically,

the easiest asteroids to reach

are the same ones
that threaten the Earth.

As they pass by,

a spaceship could rendezvous
with the asteroid.

Yet even when asteroids
come so close,

asteroid mining may be too good
to be true.

The reason why we're not
mining the asteroid belt today

and letting the space program
pay for itself

is because of cost.

It takes an enormous amount
of rocket fuel and expertise

to bring back an asteroid
from outer space.

But perhaps we don't need

to bring the minerals back
to Earth.

We could use the resources
of asteroids

to build settlements
out in space.

You don't have to build
a space station.

It's already there.

You don't need shielding

because you can simply drill
right into the soil

and use the rocky material
as shielding

against radiation
and micro-meteorites.

So, in some sense,

think of an asteroid
as a ready-made space station.

Low gravity makes it
easy to come and go.

There's plenty of water,

and all the construction
materials

that colonizers could ever need.

So, one day, when we have
colonies in the asteroid belt,

and we need
to build cities there,

that's where we're gonna
find valuable deposits

of metals
in the asteroid belt itself.

A vast band of cities in space

strung across a billion miles.

And not just cities
but factories

to turn metal from the asteroids
into spaceships.

Perhaps asteroids could actually
provide the metal --

the real structure --
to build our spacecraft.

So somewhere up there,
between Mars and Jupiter,

there may be the makings
of our future spaceships.

Ultimately, asteroids
may be a stepping stone

by which we can, one day,
leave the entire solar system.

Asteroids made the Earth.

Perhaps they even
brought life here.

And in the future,

asteroids could help humans
escape the Earth

and colonize the galaxy.

So, in a way, asteroids
are drawing us out into space,

whether to protect ourselves
or to expand where we live.

Advanced civilizations
all over the Universe

may use asteroids as
stepping stones to the stars.

Mankind may soon enter the age

of asteroids.

== sync, corrected by elderman ==

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