Original subtitles

We've seen the movie.

A huge asteroid heads towards Earth,

It smashes through the atmosphere

slams into the surface.

Sends up a huge fireball

and a deadly shockwave.

The Earth dies screaming.

But this is not one of those films.

This is how the Earth and humans fight back.

Putting the apocalypse on hold.

Planet Earth.

A cradle of life floating peacefully through space.

Or is it?

Our planet can be one of the most hostile places in the universe.

Think about what natural disasters befall humanity.

Earthquakes, hurricanes, tornadoes,

all of these sorts of things, we can't do anything about those.

But an asteroid?

Hey, this is a huge natural disaster that we can actually prevent.

When people hear the word asteroid the first thing that comes to mind

are the Sci-Fi movies of these very dangerous asteroids coming to hit us.

The story of how the dinosaurs became extinct.

Yes, there are some asteroids out there that are dangerous.

When it comes to finding asteroids in defending the Earth,

Scientists are very solidly the heroes.

Across the world, teams of planetary protectors

are working out ways to cancel the apocalypse.

They're scanning the skies,

doing the math,

designing the tech,

and making the plans that could ensure planetary extinctions from space,

are nothing more than science fiction.

If you're facing an opponent.

You need to know a lot about them in order to defeat them.

Their size, their strength, what they're made of, how they move.

Well, we need to know the same things about these asteroids.

Cause we want to knock them out.

To better understand this opponent,

Cathy Plesko from Los Alamos National Laboratory travels to Arizona.

Around 50 thousand years ago,

this was Ground Zero for an impact

that left a crater over 550 ft deep.

This is Meteor Crater.

This is, awe inspiring to stand on the rim of the crater like this and

see the, the scale of something this large and feeling this small.

Understanding just

how much energy it must have taken to excavate this much rock.

The meteor that carved out the crater landed with the power of a hydrogen bomb.

But the sky rock was just 130 ft across.

Meteor Crater is helping us understand

how speed can turn a small projectile

into a killer.

The asteroid came in at about 27 thousand miles an hour

that is ten times faster than the muzzle velocity of a bullet coming out of a rifle.

It comes slamming into the surface and just explodes

and that explosion then opens up the crater.

The impact shocked the surrounding solid rock into dust

and sent an immense shockwave barreling outwards.

So it's pretty windy here today,

but that's nothing like it would have been

in the shockwave from an impact.

Anywhere near by here would have seen winds

of thousands of miles an hour as the shockwave came out.

Scientists calculate

there's a 20% chance of such a hit on earth every century.

If an asteroid like this struck today,

it could level a city.

But Cathy's research is helping build up our defenses.

So we think that there's a variety of ways that we might

prevent an asteroid from hitting the Earth.

My colleagues and I at Los Alamos

and at Livermore and other places

can use computer models on super computers

to do very careful high-fidelity simulations.

To tell us, what's a good idea.

Maybe what's not a good idea.

And then be able to present to policymakers

okay here's what we can do.

In comparison to what Bruce Willis could do.

The most potent weapon in the planetary protectors arsenal,

a nuclear bomb.

Blowing up an asteroid this way has its drawbacks,

it risks showering the Earth with hundreds of smaller meteors.

But Cathy's team is working on plans that would avoid this risk,

instead, they use a nuclear weapon to deflect an asteroid.

So one of the things I do study is nuclear deflection.

In some cases and in the near-term future

there could be a scenario where we might need to

shove something fairly large out of the way

and those sorts of things, if they're large enough,

we might need to use a nuclear device to do that.

We might launch a nuclear device

detonate it above the surface of the object

changing its velocity a little bit.

Detonating a nuclear device near an asteroid

vaporizes part of its surface

pushing the asteroid off course.

But firing nuclear weapons into space

is no one's first choice.

So there's some pros and cons to using nuclear deflection

there's some situations where it is definitely

an appropriate technology

where it may be the only option at the time.

But we hope in the future,

that will have other methods at our disposal that are not as

challenging, diplomatically or politically.

The race is on, for scientists to find a way to deflect an asteroid

without using nuclear weapons.

We're discovering more and more about the asteroids

we're understanding them

and we're realizing that there really are ways we can mitigate

the destructive effects of an impact on Earth.

This could be the most important scientific endeavor humanity has ever undertaken.

And the best way to cancel the asteroid apocalypse could be to take them out

before they even become a threat.

Our solar system is a dangerous place.

Fast moving asteroids hurtle through space.

And many of these rocks are headed our way.

To counter the asteroid threat

scientists are drawing up battle plans.

The very first step in understanding this hazard

and in preventing this hazard, is to find them.

Not just the big ones that could end our civilization

but even the small that could devastate your city.

High in the mountains at the Catalina Sky survey in Arizona

asteroid Hunter Greg Leonard is leading the search.

We are the eyes for the world

on this night, at this telescope, on the summit of this mountain.

By comparing four images of the same patch of sky

taken over a 20 minute period.

Greg can hunt for elusive asteroids hidden among the stars.

Because in these images, stars don't move.

But asteroids do.

If it's a really bright asteroid,

we will see some bright points of light tracking across the four images.

You have to kiss a lot of frogs before you get a prince or a princess

and this is the case tonight as it is almost every night.

Here we go!

This is a real object.

You can see it's moving

across the sky hear from the lower right to the upper left

we are very, very excited to have discovered one tonight.

Because this is an object that's approaching near Earth space.

Likely in the neighborhood of Earth.

Greg's research reveals

this 100 ft asteroid could get as close as 630 thousand miles to Earth.

That's less than three times the distance to the Moon.

And in the future, this asteroid's orbit

could move closer to Earth.

Even onto a collision course.

If that happens, we need to be ready for it.

The earlier we spot it,

the best chance we have of altering its course.

Space is so big and the Earth is so small

and the asteroid would be starting from so far away,

that if you just deflected it a little bit

gave it a little nudge, a tiny course correction

by the time it got to where the Earth's region is,

it would miss us completely.

To do that, we need to move asteroids off their trajectory.

Think of a golf swing,

hook or shank the ball by just

one degree off of the tee

and you'll miss the green completely.

Now, scale that up to asteroids.

Over time, space rocks can leave their home turf of the asteroid belt

becoming threatening near-earth objects

30 million miles away that could one day hit our planet.

But if planetary protectors can change the course of a dangerous object

by just a tenth of a degree,

they'd miss the Earth completely.

And scientists have come up with a very direct way to do it.

In a football game, if somebody on the defense has

seen the quarterback running into the endzone, what do they do?

Boom, hit him, knock him out of bounds, knock them down, do something like that.

That's what we want to do with asteroids.

So if we send something moving towards an asteroid very quickly to hit it

we call that a kinetic impactor.

Slams into it really hard,

changes not just the velocity of the asteroid but also its trajectory.

Scientists have already intercepted asteroid like objects in space

2005, the Deep Impact Spacecraft arrived at Temple One

a comet half the size of Manhattan.

This spacecraft shot a little probe at the comet.

Like a bullet, it slammed into Temple One

picking up material from the surface.

Research into kinetics impactors continues.

In 2022, a spacecraft called Dart

will slam into an asteroid

at over 13 thousand miles an hour.

That transfer of momentum,

would change the velocity of the asteroid, just a little bit

maybe, a fraction of a mile per hour.

But over maybe a decade

that change in velocity, even though it's very tiny, would add up

to a change in position big enough to completely miss the Earth.

Knocking a giant space rock off course may sound unusual

but astronomers have discovered,

that in space, it's happened a lot.

When you have a lot of traffic driving on the highway

and a lot of lane changing going on.

Sooner or later there's going to be a fender bender

and that happens in our solar system as well.

It's a busy place out there in the asteroid belt

asteroids will run into each other at many miles per second.

Relative speeds. And when that happens, the sparks fly.

If you started with two asteroids and they collided,

suddenly, you'd have ten asteroids.

Those ten asteroids are now going to collide again

and now you have a hundred asteroids.

Those asteroids will collide and now you have

a thousand, a million, a billion, possible impactors for the Earth.

But this war isn't just a numbers game,

because asteroids aren't all built out of the same stuff.

So we're going to need,

different kinds of weapons to take each type out.

Across the world

planetary protectors are developing battle strategies

to save us from a major asteroid impact.

But there's millions of asteroids in the solar system

and each one presents a different type of threat.

Their speed, size and distance from the earth

help dictate the degree of danger.

The more we can really understand about an asteroid,

the better prepared we are to be able to defend against it.

This is definitely a case of 'Know thy enemy'

we need to know something about the properties of these objects

if we have any hope of a moving a threatening one out of our path one day.

But scientists are realizing

that an asteroid's composition could be the deadliest factor.

Knowing what asteroids are made of can help us find chinks in their armor.

Marina Brozovic from the center for near-earth object studies

uses a technology developed during World War II.

Radar.

Planetary radar is really like a big cousin of airport radar and so

the same way like the airport is tracking airplanes we are tracking asteroids.

That are, you know, hundreds of thousands sometimes millions of kilometers away.

Another thing that radars do is

they tell us about how this asteroid looks like.

You to know: What's their size? What's their shape?

What's their chemical composition?

Considering the detail that we see on the surface,

short of sending a spacecraft, you cannot achieve that.

So radar is, in a way, it's own little space mission.

Radar shows that asteroids can be made of rock,

metal,

or a combination of the two.

This is crucial information for calculating how to deal with them.

So metallic asteroids are far more dense

then a normal rocky asteroid.

So an impact from a big iron asteroid could have much more energy

for the same size asteroid that was just rocky.

Just as a metal cannonball

would do more damage than a similar sized rock,

metallic asteroids could be far more deadly than rocky asteroids.

But scientists have now discovered that most asteroids are less like cannonballs

and more like vast cosmic shotgun shells.

Most of the asteroids, they're not a single object,

they're not monolithic but instead, their rubble piles.

So they consist of many smaller rocks and pebbles

and grains and pieces of sand.

And all of this is held very loosely with gravity.

Rubble pile asteroids like the peanut shaped Itokawa

probably formed from violent collisions between asteroids.

Initially, the rocky debris from these collisions scatters like shrapnel.

Then gravity can draw some of the rocks loosely back together again.

The structure of rubble pile asteroids presents

a major challenge to our planetary protectors.

How can our science heroes save us from a pile of rubble?

If the object is a solid mass of metal.

It's going to respond to an impact or an explosion in a far different way

than if it's just a loosely bound rubble pile

barely held together by its own gravity.

Well, they're very, very delicate objects

and so those objects need some special consideration.

We can't just go slamming into them necessarily.

Smashing into a rubble pile asteroid

would be like kicking a pile of leaves.

Thousands of smaller rocks would go hurtling out in every direction.

They'd be undetectable, unpredictable and could continue to head our way.

But we have a plan.

Instead of using violent force,

we could use the gentle tug of gravity.

So instead of this ham-fisted approach of whacking it and then just walking away.

We need something.

We need something more careful, something more precise

and that's where the gravity tractor comes in.

Rubble piles of rock may be small,

but it has gravity.

And if we send up a probe that has the mass of say, a ton.

It has gravity too. Now, not much.

But it's there.

And if you put it near the asteroid,

You can actually use the mutual gravity,

the attraction between them, to tug the asteroid into a safe orbit.

All you have to do is park a spacecraft next to the asteroid,

Hover it there,

don't let the gravity of the asteroid and the spacecraft pull each other together,

and let the gravity of the spacecraft

act as a tow line to pull the asteroid out of the way.

This sounds like science fiction,

but it turns out the physics of this is relatively simple.

And we can do it.

But gravity tractors only work

if we can accurately track the movements of these asteroids.

Problem is, there's a massive complicating factor

at the center of our solar system.

The Sun.

Planetary protectors want to put the apocalypse on hold.

Their mission:

Protect the Earth from these seemingly inevitable asteroid impacts.

But to do that, they need to predict their every move.

In a constantly changing Solar system, that's not easy.

We measure their orbits and we can draw up maps of

all their orbits as we see them today.

But we know that it's not a static population,

that it's dynamic, things are constantly evolving in the asteroid belt.

It's not just about size with asteroids.

You have to understand the density,

the orbit, the speed, in order to really tackle it.

Collisions can set asteroid debris off on new orbits.

But there's another factor at play, the immense gravity of the gas giant, Jupiter.

Jupiter is the most massive planet in the solar system and

it's sitting outside the asteroid belt.

It's gravity can tweak and tug these asteroids

and make their orbits more elliptical.

Sending them in towards the Sun.

Crossing Earth's orbit.

Modeling Jupiter's effect on millions of asteroids is hard enough.

Now add the influence of some of the asteroid belts biggest bruisers.

300 mile wide rocks like Vesta

and Pallas.

A tricky task becomes near impossible.

But gravity isn't the only force creating orbital chaos.

This is the asteroid Bennu.

There's one chance in 2700 it'll hit the Earth.

But Bennu's orbit keeps changing.

In the last 18 years, it shifted over a hundred miles off course

and the culprit could be the Sun.

So what can change the orbit of an asteroid?

It's easy to think of these large rocks

passing by each other tugging on each other gravitationally.

But could the most dramatic changes be due something as gentle as sunlight?

It might feel very subtle, but the sunlight,

on our bodies, exerts a subtle pressure.

The fact that you're hotter on one side than on the other side,

actually exerts a kind of a thrust that can move you around.

Sunlight is made up of tiny packets of energy called photons.

When photons hit an asteroid

they pass on a tiny amount of momentum

and a tiny amount of heat.

Let's actually, you know, let's imagine this situation,

here's our asteroid, in reality, this might be,

10 miles across or a mile across, something like that.

Here's our asteroid, here's the Sun.

This asteroid is orbiting the Sun this way.

This face of the asteroid is being warmed by the heat from the Sun.

Out here on the back side facing the cold vacuum of space it's a lot colder.

In fact, I can even feel it already with my hands.

The warm side that's being illuminated by sunshine

actually re-radiates that heat in the infrared portion of the spectrum.

All of that infrared radiation off the side of the asteroid

acts like a like a little rocket motor in a way.

It actually pushes on the asteroid.

This is known as the Yarkovsky effect,

it's a slow process.

The asteroid is pushed by a force

equal to the weight of a few grapes on Earth.

But as Bennu circles the Sun it heats up on one side

which moves it into a different orbit.

The Yarkovsky effect is actually a bit of a problem.

If there were just gravity acting on these asteroids

then we can predict where all the asteroids and planets will be

and we'd be able to figure out the trajectory of these asteroids

many years in the future.

But with the Yarkovsky effect,

that actually changes it in ways that are difficult to predict.

Because it depends on how dark the asteroid is,

whether it's spinning, what shape it is

and so it makes the orbit of the asteroid much, much more difficult to predict

a long time into the future.

The Yarkovsky effect makes predicting the movement of asteroids like Bennu,

even harder.

But our planetary protectors are an ingenious bunch

and they're attempting to use the Yarkovsky effect

to create a new weapon for their armory.

So the Yarkovsky effect we know can

change asteroid orbits pretty dramatically.

It's an effect that we could use

to move asteroids ourselves.

If we could change the way the asteroid is heated by the Sun.

By changing its color or

changing its shape so that it gets heated in a very specific way,

That we could change its orbit that way.

If scientists could send a satellite to an asteroid,

it could use black or white paint

to increase or decrease the heating effect.

But at the University of Southern California,

a team of scientists are working on a higher tech solution.

They're trying to one-up the Yarkovsky effect

using a space-based laser called D-Star.

Let's say we see an asteroid that's on its way towards the Earth.

We can use space lasers to zap the asteroid.

You vaporize the surface material.

That turns into a gas which expands very quickly

and that acts like a rocket.

And so you can use that to push the asteroid

into a safer path as well.

Space lasers are another powerful weapon

for our planetary protectors fight against asteroids.

They joined gravity tractors,

kinetic impactors

and nuclear weapons in the armory.

But there is one very big problem.

All of the methods of defending against asteroids that we've mentioned

are technologically possible.

The thing that's a little bit nerve-wracking is that

none of them are actually ready to go right now.

So it's not time to cancel the apocalypse yet.

We've made a lot of progress especially in the last few years.

But we're not really there yet.

But we could get to that point within the next maybe 10 or 15 years.

But don't panic just yet.

Turns out the Earth has a built-in defense system

that can burn up asteroids, before they ever hit the ground.

Arizona, June 2nd 2016.

A 5 ft wide rock hurdles towards the Earth.

It's moving at over 40 thousand miles per hour

and as it streaks overhead, it lights up the sky.

In the very early morning hours,

an asteroid came screaming into the Earth's atmosphere

far faster than a rifle bullet.

There was a fireball that lit up the Red Rocks all around us that night.

It was bright enough to burn out cameras on the ground

from NASA that were watching for fireballs.

The asteroid is just seconds away from impact

and major damage seems inevitable.

But the asteroid never makes it to the ground, why?

We do have a natural barrier against at least small asteroid impacts.

And let me give you a hint about what that is.

The air around us seems too tenuous

to actually defend against a threat from space.

But in fact, the atmosphere is sort of the last line of defense against asteroids.

One day our planetary protectors will be ready to save us from asteroid strikes.

Until then, we'll have to rely on the Earth's built in defense system,

the atmosphere.

We know for a fact that our atmosphere acts like a shield.

Because space rocks come the earth every day.

Some of them are tiny, some of them are a bit larger.

But what's happening is that as they enter the atmosphere at high speed

the friction burns them up.

Even though the top layers of the atmosphere are very thin,

compared to the vacuum of space, they're extremely dense.

As rocky asteroids hurtle through the atmosphere,

friction and air pressure can heat them to over 3 thousand degrees Fahrenheit.

The larger the asteroid, the longer it takes to burn up.

And for these larger rocks, the effects can be dramatic.

If there's a rock that's big enough that it doesn't burn out very quickly.

We call that a bolide, and as the bolide falls through the atmosphere,

it creates a spectacular show, called a fireball.

In February 2013, the town of Chelyabinsk in Russia had it's own fireball

when a 60 ft wide space rock barreled through the sky.

This asteroid was bigger than a school bus

and it traveled at 11 miles per second.

It got super hot, broke up into small pieces,

those pieces then rammed through the atmosphere.

When all of that vast energy of motion of this rock

was converted into light and heat, it exploded.

The Chelyabinsk meteor is the largest natural object seen

entering the atmosphere in over a hundred years.

It explodes 12 miles above the Earth's surface

with the power of 30 nuclear bombs.

The blast causes over 15 hundred injuries and damages seven thousand buildings.

But if it wasn't for the protective shielding of our atmosphere,

the results would have been far worse.

The problem is,

the atmosphere can only protect us from rocky and rubble pile asteroids

up to around 100 ft wide.

And there is something else much more dangerous to consider,

metallic asteroids.

If you had a rocky asteroid hitting,

or a rubbly rocky asteroid hitting,

It wouldn't make it to the ground.

An asteroid that's around a 100 ft across

would actually blow up in the sky.

But if a 100 ft metallic asteroid were to hit,

First of all you wouldn't have much warning

it would hit the top of the atmosphere

and then would hit the ground about a second later.

Causing an enormous explosion that would

open up a crater that would be about a mile across.

You'd have a flattened ruin of remnants of buildings.

Millions dead from the shockwave that would be radiating out

and layer of dust falling back down over the next minutes and hours.

The metallic asteroid punches through the atmosphere

because it's too hard for friction and air pressure to break up completely.

So it slams into the ground in a catastrophic explosion.

Metallic asteroids could be our planetary protectors greatest foe.

But turns out the Earth could have another built in defense.

We know an asteroid punched through the atmosphere and killed off the dinosaurs.

But research is showing our planet could have saved them.

The dinosaurs were incredibly unlucky.

Even if the object does make it past our atmosphere

we still have another line of defense.

It's not always what an asteroid is made of that makes the difference.

Sometimes, it's all about where it is.

Our planetary protectors are creating technologies

to divert a potentially catastrophic asteroid.

But until their armory is complete,

the Earth has its own defensive strategy.

One of the things that is sure, is that we will be hit by an asteroid or comet again.

It may not happen for millions of years, but it will happen.

And on that day the thing that will differentiate

between a just being a very bad day and it being a global catastrophe,

is location, location, location.

Some regions of the Earth

could actually reduce the damage done by a killer asteroid.

How do we know that?

Dinosaurs.

65 million years ago, the dinosaurs had a very bad day.

They had the bad luck to be wiped out by an asteroid impact.

We thought we knew the full story.

But researchers have revealed something astonishing.

If the asteroid had hit the earth just minutes later.

Dinosaurs may still roam the planet today, but how?

This object hit right at the Yucatan Peninsula.

It caused an incredible tsunami that flooded North America

but it also threw a lot of sulfates into the air.

The six mile wide asteroid landed in shallow seas

in what is now the Gulf of Mexico.

It vaporized rocks in the sea floor of the continental shelf.

The impact blasted out trillions of tons of gases into the atmosphere.

Triggering catastrophic climate change.

70% of all life on Earth became extinct.

Including the dinosaurs.

The thing that's kind of tragic

is that the Earth had rotated just a little bit more,

when that impact hit, it would have been in deeper ocean.

And there wouldn't have been all that vaporized rock and sulphur.

Our planet spins at a thousand miles an hour.

70% of the earth's surface is covered by ocean.

With a little luck, the dinosaur destroyer could have struck in deeper water.

There's no good place on the earth

to take a five mile wide asteroid strike, there's just no good place.

Some places are worse than others and

the Yucatan Peninsula with that much sulfur was one of the worst possible.

So it's just not going to be a good day.

The asteroid that killed the dinosaurs, allowed us mammals to take over the Earth.

Fortunately, these giant asteroids only strike once every few million years.

But every two thousand years or so,

a rock about the size of a football field hits Earth.

What would happen if one of these smaller,

more common asteroids, were to hit the ocean?

Think of something like the Pacific Ocean,

there's a lot of coastline there.

And so you have many, many people that are at risk.

Most of the Earth's surface is ocean.

So it's a much more likely scenario,

for an asteroid to hit the ocean.

And so the question is, how much of a tsunami risk is there?

Scientist have modeled what would happen.

If an asteroid strikes different places in the ocean.

It was studied in three dimensions

with different types of compositions, different ocean depths,

different entry angles

and found out that the continental shelf actually saves us.

The continental shelf is an underwater landmass that extends

around 50 miles beyond the coast.

So when an asteroid hundreds of feet across

slams into the deep ocean,

the shallow sea created by the continental shelf

could force a tsunami to collapse before it hits land.

It seems, the ocean has our back.

For the deep ocean we think that asteroids smaller than 400 ft across,

which is quite large, are not a tsunami risk

and so we don't need to worry as much as we thought we did, about it.

That shallow part of the water

actually buffers any tsunami wave that might be coming in.

So our planet has defense mechanisms

and our scientists are devising plans that will take the fight to the asteroids.

What they need is time.

Astronomy very well can save the world, because we're on the lookout

for all the asteroids that may someday collide with Earth

and if we find them we could avoid a civilization ending event.

If we have warning time, we then have the advantage of

being able to think about the problem, plan for it

and actually build up the technologies practice the techniques that it's gonna

take to push that asteroid out of the way, time is definitely an ally for us.

We're not ready to cancel the apocalypse just yet.

But with the planetary protection team on the case,

soon, we'll have a fighting chance.

If you want to know what, like an astronomer's sweatiest nightmare is.

It's an asteroid impact. It's kinda personal, right?

This is happening right here on Earth.

It's a challenge to us and that's why we want to prevent them.

The good news is, we actually are on the cusp of being able to deflect them.

We're almost there we just have to push it through.

The planet is incredibly resilient.

Even if one specific species or one specific individual is very fragile,

as a whole, the Earth is actually quite tough.

It really comes back to, as human beings:

What is our will to discover, to explore and understand the solar system?

It becomes very important when you think about asteroids.

We need to keep scanning the skies.

We need to keep being scientists to defend the Earth.

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