Original subtitles

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.

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.