All language subtitles for S06E09_War_on_Asteroids

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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