All language subtitles for how.the.universe.works.s08e01.asteroid.apocalypse.the.new.threat.480p.web.x264

A dangerous asteroid
is heading towards Earth.

It's the size of
the empire state building,

and it's travelling at
16,000 miles an hour.

It's called Apophis,
after the Egyptian god of chaos.

It will fly close to us in 2029.

It won't hit us... This time,

but when it returns in 2068,

that could be another story.

If it blows up over a city,
millions of people will die.

This could be the most
devastating single event

in U.S. history.

Earth is stuck in the crosshairs

of a potential asteroid strike.

Apophis is one of around 2,000
potentially hazardous asteroids

that present
a real and present danger.

Asteroids have hit us before,
and they will hit us again.

As far as cosmic dangerous go,

they're number one on the list.

This is not a drill.

If we do nothing...

This is our future.

Captions by vitac...
www.vitac.com

captions paid for by
discovery communications

December 2018.

The U.S. military detect
a huge explosion

in the Earth's atmosphere

high over the Bering sea

off the coast of Alaska.

When an explosion of this
magnitude is detected,

everyone's mind
goes to the same thing... nukes.

But when the real answer
was found and it was determined

that it didn't even
originate from Earth,

that was even more shock.

The cause of the blast...

an asteroid.

This asteroid was
30 feet across...

something like that...

over a thousand tons,

but it was moving
at 20 miles per second,

over 70,000 miles an hour.

This asteroid was
small, and it exploded

in the atmosphere
over the ocean,

so nobody was hurt.

But if it had been bigger

or it had come
in over a different place

or it had been moving
a lot faster,

this could have been
a dangerous object.

But the scariest thing about it

is that we didn't see it coming.

So far, we've been lucky.

But near misses happen
all the time.

About once a year,
we get something

the equivalent of a nuclear bomb
going off in our atmosphere.

And while that sounds horrible,

most of these happen
tens of miles up...

Over open ocean, where we go
on completely oblivious.

We may be oblivious to most
of the threats from space,

but they are very real.

We're going to get hit.

Over a certain amount of time,

an asteroid impact
is inevitable.

It will happen 100%,
absolute certainty.

NASA considers the threat
from the skies so severe

it has made protection
from asteroids a top priority.

These events are not rare.
They happen.

And of course it's up to us to
make sure that we are detecting

and characterizing, tracking
all of the near-Earth objects

that potentially
could be a threat.

This is not about Hollywood.
It's not about movies.

This is about ultimately
protecting the only planet

we know right now to host life,

and that is the planet Earth.

To help plan
protecting our home,

we carry out
Earth defense simulations.

For three days,

200 scientist at the planetary
defense conference

battle a simulated
asteroid 20 times larger

than the Bering sea space rock.

We practice, "alright,
what if this hits a major city?

What would we need to do?"

By running
potential impact scenarios,

we can prepare
for a real asteroid strike.

This is like a fire drill
that you would do at school

or at work, where you practice

and think about, okay, what if?

Where are the exits?
How do I get out?

How fast do I get out?

The drill starts
with the discovery

of a simulated
Earthbound asteroid.

So, the first information
is there's a big asteroid

coming towards the Earth.

Then we get a better estimate

of how big it is,
how fast it's going,

and where it's going to hit.

The asteroid
is heading straight for Earth

with Denver, Colorado,
in its sights.

The planetary defense scientists

send up a simulated spacecraft
to smash into the asteroid

and push it off its path.

But it's a big gamble.

You can push it the wrong way.

You can potentially
have unintended consequences.

In the simulation,

the spacecraft
strikes the asteroid...

Deflecting it away from Earth.

But the impact dislodge
is a 200-foot chunk,

which is now heading straight
towards the eastern seaboard.

So there's this one last piece

that is now
going to hit New York.

We know that something that size

is going to have
citywide consequences.

That is huge.
That's a horrible impact.

When you're actually
in the conference room

and you understand eventually

that New York City
is going to be destroyed...

And you're having strategies
about how to evacuate people,

all the timing,
when you're doing the simulation

you're in your head.

You're thinking
about these things.

You're trying to
reason them out,

but can you imagine the feeling
in your gut, in your heart,

if this was real?

If this were real,
the chunk of asteroid

would strike Earth's atmosphere

at 43,000 miles an hour.

As the space rock hurtles
down, it collides

with molecules in the atmosphere
which buffet the falling rock.

It's kind of like doing
a belly flop into a pool, right?

You're going from
the vacuum of space

into the dense lower atmosphere
in mere seconds.

And that's an incredible
amount of pressure

to put on the object.

The asteroid slams into the air

ahead of it,
compressing it violently.

The surface of the asteroid
gets hotter and brighter.

It's actually the air itself
that's glowing luminously

from the heating
of the shockwave,

the world's most
intense Sonic boom if you will,

that heats the air
to incandescence

as the object passes through.

So that's the source
of that brilliant illumination.

This bright, burning
asteroid is called a bolide.

We witnessed one descending
over the Russian city

of Chelyabinsk in 2013.

All of a sudden, there was
a huge fireball

streaking through the sky,

and people had no idea
what they were witnessing

because it looked like the sky
was on fire.

It was insanity.

As the asteroid descends,

the compression
of the denser air beneath it

starts to flatten and even
disrupt the falling rock.

There's a high pressure
on the front,

there's no pressure on the back

and it's being super heated.

And that intense temperature
causes the air to glow,

which is how we see
this streak of a meteor.

And it also disintegrates
the asteroid itself.

It's hard enough
to literally melt rock.

This can often
lead to them exploding.

The combination
of heat and pressure invade

the falling asteroid,
causing it to blow up.

Most asteroids
don't reach the ground

before they
completely disintegrate

in a tremendous release
of energy.

This is what we call
an air burst,

and we learned a lot about these

while we were testing nuclear
weapons after world war ii.

Some of these bombs
were blown up

underground and on the ground,

but they found out when they
blew up bombs above the ground,

it actually did more damage.

It was more widespread damage.

The explosion of
the Chelyabinsk asteroid

sent out a powerful shockwave
at thousands of miles an hour.

The blast traveled
over 100 miles.

It damaged 7,000 buildings

and put 1,500 people
in the hospital.

All of the injuries
pretty much came from people

who saw, "oh, what's
that bright flash in the sky?"

And they came close to a window
to look and see what it was,

and then the pressure wave hit
and blew glass in their face.

The Chelyabinsk asteroid
was only 65 feet across.

The rock in the
defense simulation

is three times more massive,

and it's heading straight
for New York City.

Imagine what would happen
if an explosion a thousand times

greater than that over Hiroshima
hit New York.

We're talking about an utter
complete destruction of the city

and millions of people.

With so little warning,

the only option would be
to evacuate New York City.

How do we get everybody out
of New York City

within just a few days?

That's where panic sets in.

That's where fear would really
become the dominant emotion.

Anyone left in New York City

would see the bolide
racing in...

...followed
by a blinding light...

As the asteroid explodes
above the city.

The blast would be equivalent
to the largest nuclear weapon

ever detonated on Earth.

Buildings would be
flattened, melted.

There would be fires
for miles around

in the first moments
of the explosion.

A million people
could be killed instantly

and many more would die later
in the rubble,

in the ruins
of what would happen there.

Everything within nine miles
of the blast epicenter

would be completely destroyed.

The intense heat and
pressure would wreck buildings.

It's the worst possible
day for new yorkers,

and not just the city itself.

There's something like
15 million people

living in the New York area.

The shock wave would race
out over 250 square miles.

This would certainly be
the worst disaster

that the U.S.
has ever experienced.

We're talking about millions
and millions of people

displaced,
affected within an instant.

This scenario is
just a simulation... For now.

The asteroid Apophis
is heading our way.

If it hits Earth,

it might not just kill a city.

It could kill a whole region.

I wouldn't exactly
want to be there

when that happens...
want to be very, very far away.

Apophis will skim Earth in 2029.

But its path could change,

possibly turning
a future miss...

Into a direct hit.

April 13, 2029,

a speck of light
races towards the Earth.

It's an 1,100 foot wide asteroid
called Apophis.

We are about to have
an extremely close shave.

It's the closest approach
of any asteroid

that didn't actually hit us
for a long, long time.

It will be 10 times closer
than the moon itself.

It'll be so close that
it will be brighter

than some stars.

The football-stadium
sized Apophis

will race over the Atlantic.

If it were sitting on
the surface of the Earth,

it would weigh
about 50 million tons,

something like that,

and that is not the place
you want it to be.

You want it to be in space
and far away.

When we discovered
Apophis in 2004,

we thought it might be
on a collision course with Earth

with a potential impact

greater than the largest
atomic bomb ever exploded.

The largest nuclear
device, atomic device

ever detonated on our planet was
the Tsar Bomba bomb in Russia,

so something like
55 or 56 megatons.

When Krakatoa exploded in 1883

that was something
like 200 megatons.

Apophis' impact
would be 450 megatons.

If something like that were
to happen over New York City

or Washington D.C.,
you're going to lose the city.

The impact would be
at least 10 times greater

than the simulated
asteroid strike on New York.

Well, when you put it
in those terms,

that's just plain scary.

In a word, an impact
from an Apophis-sized asteroid

would be bad... very, very bad.

Apophis' orbit will cross Earth

every seven years this century.

It won't hit us in 2029,

but this close encounter
could change Apophis' orbit.

When a small asteroid encounters
a bigger body like a planet,

it's like a bunch
of roller derby players.

Most of them
are clumped together,

but maybe there's one just on
their own particular orbit,

and as they circle around,

as they get close
to that larger clump,

there'll be some interactions...

potentially violent
interactions...

that will change
the future trajectory

of that lone
roller derby skater.

And the next time around,

it might be a wide miss
or it might be a head-on impact.

It's the same
in the solar system.

The combined gravity
of the Earth and moon

creates what's called
a gravitational keyhole,

a gravitational sweet spot,

which could change
Apophis' orbit.

That will change the potential
future trajectory of this rock

and might make it
totally harmless

or might increase the chances

of an impact
even further in the future.

Because of the
gravitational keyhole,

there's still a small chance

that Apophis will hit Earth
in 2068.

That is the important
lesson that Apophis taught us...

you can miss the Earth,

but if you pass through
one of these keyholes,

at some time later,
you will hit the Earth.

We now know Apophis
will miss the keyhole in 2029,

but there are other keyholes
and other close passes.

Apophis is not a lone threat.

There are an estimated
832,500 asteroids

orbiting the sun.

Most asteroids live their lives

perfectly peacefully
past the orbit of Mars

or trailing Jupiter
and don't mind anybody else,

don't cause any troubles,
but some asteroids

are on very particular orbits

that cross the orbit
of the Earth.

These asteroids
have left the stable orbit

of the asteroid belt

and moved into orbits
that get near our own.

These asteroids are called
near Earth asteroids

or N.E.A.S for short.

The near Earth asteroid
population is interesting

and potentially dangerous
because they are the ones

that actually cross
the orbit of the Earth.

So they're most likely
to have, at some point

in the future,
an impact with the Earth.

Most N.E.A.S pose
little or no threat to Earth.

But we've detected over 2,000,

including the 1,200 foot Apophis
that do.

These are called P.H.A.S...

potentially hazardous asteroids.

The difference between
a near Earth asteroid

and a potentially hazardous
asteroid is distance and size.

Anything can get near the Earth,

and that could be
20 million miles away,

something like that,
and be a near Earth asteroid,

but a potentially hazardous one
can hit us,

and it's big enough
to do damage.

So something that over
the next hundred years or so

has a chance of hitting us
and doing damage when it does...

that's a potentially
hazardous object.

P.H.A.S are asteroids
that are 460 feet or larger

that could collide with Earth.

Take a 400-foot asteroid...
if it hits,

it would release as much energy

as 3,000
Hiroshima nuclear bombs.

In July of 2018,

NASA published a map

of all the known
N.E.A.S and p.H.A.S.

The animation tracks
their discovery

from 1999 through 2018.

Every time I look
at this animation,

it does make my heart
stop a little bit

because it looks like
we're in the middle of a swarm

of angry bees
circling all around us.

In 1999, we'd identified

under 300 N.E.A.S

scattered through
the inner solar system.

10 years later,
we'd found 500 more.

By 2018, we'd discovered 18,000
near Earth asteroids,

but we estimate
there are millions out there.

It seems like we could
never find all the asteroids.

They just keep coming.

It's like we're fighting
an army of zombies.

Zombies that keep
hurtling our way,

hitting the Earth at up
to 64,000 miles an hour.

That is very, very fast.

That is much faster
than a rifle bullet.

And that's the key
to its destructive power.

When a really fast
and really large asteroid hits,

the impact is off the charts.

The blast is so intense,

it can melt
or even vaporize rock.

January 2019,

a total eclipse of the moon.

Astronomers train
their telescopes

on the darkening lunar surface.

They capture a bright flash

that lasts around a quarter
of a second.

It was recorded. There were
a lot of live webcasts

and things like that going on
at the time,

and you can see
this flash of light.

What the heck was that?

At first, the cause
of the flash was a mystery.

It turns out it was actually
a meteorite hitting

the surface of the moon,
and because it was dark

and because we were all looking
at it,

we could actually see it.

The moon's dark
surface gave us a unique view

of what happens
when an asteroid strikes.

What was so exciting
about being able

to see this impact
on the moon in a dark area

is that we could actually look
at the light that it produced

and then back-calculate

exactly what the size
of the impactor was.

We worked out that
the impacting asteroid

was just 20 inches wide.

The crater it blew out
was 45 feet across.

How can something so small
be so destructive?

The two things that matter
the most are how fast it's going

and how massive is the thing.

The more massive,
the bigger the boom,

the faster the bigger the boom.

Speed and weight
are two very important factors

to assess how much damage
an asteroid will do.

Just like a boxer...
if a tiny person like me

were to swing a punch,

it would do a lot less damage
than a heavyweight champion.

Same thing with asteroids.

The bigger they are,
the bigger the punch.

But the same thing
is fast, right?

If I hit you really slowly,
it's not gonna hurt.

I have to really wind back
and pap.

That's what happens
with an asteroid.

The damage from
an asteroid strike

is determined
by its kinetic energy.

Kinetic energy depends
on two things...

speed and weight.

Of the two, speed matters most.

If you double the mass,
you double the kinetic energy,

but if you double the velocity,

you get four times
the kinetic energy.

Three times the speed,
nine times the impact energy.

10 times as fast,

it has a hundred times
the energy,

so the velocity
is what's really critical here.

The lunar asteroid
weighed only 100 pounds,

but it was traveling
at 38,000 miles an hour.

Carrying a huge kinetic energy,
which gouged out the crater.

It's the same principle
for impacts on Earth.

50,000 years ago,
a 150-foot asteroid

hit what is now Arizona.

The impact blasted out
an impressive hole

now called Barringer crater.

It's about 3/4 of a mile across,

over 500 feet deep.

You could put
the Washington monument

in the bottom of the crater,

and the top of the monument
wouldn't quite clear the rim.

It's a pretty impressive hole
in the ground.

In 2016,
impact specialist Cathy Plesko

visited Barringer crater

to see firsthand
what mass and speed

do to the surface of the Earth.

This is awe-inspiring to stand
on the rim of a crater like this

understanding
just how much energy

it must have taken
to excavate this much rock.

The asteroid came in
at about 27,000 miles an hour.

It comes slamming
into the surface

and just explodes.

Anywhere nearby here

would have seen winds
of thousands of miles an hour

as the shockwave came out.

The immense power
of an asteroid impact

comes from the kinetic energy

being transferred from the space
rock into the surface rock.

It's an extremely
violent process,

and it starts with the moment
of contact

of the projectile
with the surface itself.

It pushes into the crust,

and at first,
it's just almost punching, like,

sticking your thumb into dough.

It's only about
as wide as the object is.

It's going straight down in,

but then it's meeting resistance
from the surface of the Earth.

And so it squishes,
squishes, squishes,

until it runs out of momentum,
but then it's very compressed

and all of that energy is in
a very small space.

As it releases,
it detonates like a bomb.

And that's what makes
the impact crater.

Simulations of
an asteroid strike in the lab

reveal the impact
in slow motion.

As the high speed pellet
hits the surface,

the sand compresses downwards,
then rebounds.

And as that rebound
is occurring,

that's when the material
is being ejected

out of the crater itself.

You'll see the surface
erupting outwards

like the blooming petals
of some big rocky flower

as all this debris goes
spraying out in every direction.

The 150-foot Barringer asteroid

turned the rock to powder.

66 million years ago,

an asteroid
around 200 times larger

and moving
one and a half times faster

than Barringer hit Earth.

This asteroid impact...
called k-pg...

had so much energy,

it turned rock to liquid.

This thing was immense.
It's really hard to wrap

your head around
just how big it is.

When it hits the back end of it,
it is so far back,

that it's where
a modern jetliner would fly.

The k-pg asteroid hit the ground

with a lethal combination
of mass and speed.

A trillion tons traveling
at 45,000 miles an hour.

Some rock is
completely vaporized.

It just becomes a gas.

You have some rock
that is melted.

You have some
that's thrown out into space.

This material goes up
through that and then falls down

and settles down
over a huge area.

That might be dust.
It might be pulverized rock.

It might be vaporized metal.

It's all of this hot material
raining down everywhere.

Some of the rock
exploded skywards,

but rock below the surface
was slammed by a shockwave

that was completely
off the charts.

Rock stopped behaving like rock.

We experience rocks
as solid objects,

but if you hit a rock
hard enough,

it flows like water.

The k-pg asteroid hit so hard,

it pulverized the rock,

turning it into liquid.

Almost like ripples
on a pond moving away

from a stone
that's been dropped in it.

It's almost like a splash

in the solid body
of the Earth itself,

and like water droplets
splashing in water,

you'll see that central peak
will kind of splash up

and rise to a high altitude
and then come back down again.

We think a process very similar
to that probably happened

in the rock itself
at the center of the crater,

rising up
as high as the Himalayas

before relaxing back down
to their current position again.

The material slumps,
and so these ripples

are frozen in the rock,

and there are other fragments
that go away radially,

almost like the spider web
pattern in glass

that you get after
it's shot with a bullet.

The k-pg impact
blew out a crater

111 miles wide.

It is the third largest
confirmed

impact structure on Earth.

A large and fast asteroid
heading our way

is always going to be a problem.

So what do we do?

Wait for oblivion?

Or fight back?

The space
in the inner solar system

seems calm, stable, and empty.

It's not.

There are tens of thousands
of near Earth objects

just whizzing around Earth.

Now, space is big.

They're not gonna hit us
every time they orbit the sun,

but this does set up
the possibility

that, one of these years,

we're gonna end up
at the same spot in space

at the same time
as that asteroid,

and then it's gonna be
an impact.

We're living in a cosmic
shooting gallery.

Asteroids strike the Earth
all the time

through history,

and it's gonna happen again.

Scientists are
developing strategies

to stop an asteroid
from hitting our planet.

Our options... destroy
or deflect the space rock.

But first, we need to detect
any dangerous asteroids

heading our way.

It's a little bit
unnerving to know

that we haven't yet detected
all of the asteroids

that exist that could
possibly cross our path.

We've discovered
a lot of asteroids now,

but we typically discover
the big ones.

But for asteroids
that are below 100 feet,

there's a lot still out there
that we haven't discovered.

And such an asteroid
can do some real damage

if it were to explode
over a populated area.

To prevent such a catastrophe,

we need to find all asteroids
whose orbits cross our own.

Detection is crucial in
our defense against asteroids.

And the reason is the earlier
they're detected,

the easier it is to deflect them
away from hitting the Earth.

You want to do deflection,
the first step is detection.

The problem is,
asteroids are very hard

to detect.

Finding asteroids
and cataloging all their orbits

is really challenging.

They can move quite fast
across the sky,

and they might go away

on the other side of the sun
for years and years and years.

So we can't see them.

And even when they are
on this side of the sun,

they're hard to spot.

But the problem is,
they're very small

and they're very dark,

and when I say very dark,
I mean really dark,

like a lump of coal.

So how do you find
a small, dark rock

just wandering around out there
in the solar system?

The Catalina
sky survey has the answer.

The huge telescope in the
mountains above Tucson, Arizona,

takes a series of images
over a 20-minute period.

It's hunting
for anything that moves

because 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.

Ah, here we go.

This is a real object.

You can see it's moving
across the sky here

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 space,

likely in the neighborhood
of Earth.

Catalina has limitations.

It can only see visible light,

so a particularly dim asteroid
could be missed.

Asteroids are very cold.

They're usually quite far away
from the sun,

but amazingly, the best way

we have to find these
is infrared light

because things that are cold
by human scales

can still be very warm
to an infrared telescope.

So even if asteroids are just
a few tens of degrees

above absolute zero,

that's still enough heat
to detect them.

When the infrared
space telescope Neowise

turned its gaze onto asteroids,

it had immediate results.

Neowise has now detected

close to 160,000 new asteroids
and comets in our solar system,

and about 780 of those

are things
that are near the Earth.

10 of those near
objects have been classified

as p.H.A.S...
potentially hazardous asteroids.

Without Neowise,
we would have missed them.

Using an infrared
space telescope

is a way of of better detecting
some of the smaller asteroids

and comets
in the near Earth vicinity.

Detection is
an important first step,

but it only tells us

that there is
another asteroid out there.

Once we've spotted an asteroid,

all we know is that
it's a tiny dot of light.

We don't know anything else
about it.

So when a new asteroid
is discovered,

the most important thing is

to determine its path,
to track it, to figure out

exactly how it's orbiting
around the sun

and how close
it's gonna get to Earth.

For that, we have to know
where they are now...

so its current location...
and measure how fast it's going

and which direction
it's travelling.

All of these things together
are really important

for tracking
where it's gonna be next

and whether or not
they're gonna hit us.

To get this information,

we need something much bigger
and more powerful.

The Arecibo observatory.

Once Catalina
or another telescope

detects a near Earth asteroid
in our cosmic neighborhood,

Arecibo's thousand-foot dish
swings into action.

They discover these asteroids,

and then once we know
where they were,

we can try and point
the radio telescope

and see where they are
at the moment

and measure their exact location
and their trajectory.

Arecibo achieves
this level of precision

by using radio detection
and ranging,

more commonly known as radar.

The planetary radar system
at Arecibo observatory

is the most powerful
radar system in the world.

We focus on
potentially hazardous asteroids,

which are those that have a high
probability of impacting Earth.

Arecibo sends out radio signals

toward the newly
detected asteroid.

It emanates radio signals.

Some of them hit the asteroid
just like a radar gun from a cop

might hit the side of your car.

That's pretty similar,

but instead of doing it
with a radar gun

on the small scale, we're
doing at a really big scale

with one megawatt power
hitting objects that are

tens of lunar distances away.

And then those radio
waves bounce back to Earth

and we detect them again,
and by comparing the differences

between what we sent
and what we received,

we can get a map
of the asteroid itself

and we can get where it's moving
and how fast it's moving.

Speed, size,
and location of strike

determine the outcome
of an asteroid impact.

But the type of asteroid
is another factor.

It can mean the difference
between survival

or complete annihilation.

The Bering sea asteroid
blew up in the atmosphere,

but the Barringer crater
asteroid hit the ground intact

with its full force.

Why do different asteroids
behave differently?

And what will Apophis do
when it heads our way?

Arecibo's radar
may have the answer.

When we bounce radar waves
off of these objects,

we can get effectively imagery
of the surface

of some of these small objects

that we just cannot do
with optical telescopes.

This is
the radar image of Apophis.

It's so far away that all they
could image were a few pixels.

So this is our most recent
radar image

of asteroid Apophis.

And you can see
it's only a few pixels,

but it does give us information

on what it actually is.

These few pixels
are enough to work out

how big Apophis is.

From this image,
we can constrain the size

to be about 1,000 feet,

which is about the same size
as the Arecibo

radio telescope.

All of that from what were
a bunch of pixels.

Knowing the size
and mass of an asteroid

is critical to understanding
what an asteroid is made of.

If we have the size and
the mass, we get the density.

If we have the density,
we know what it's made of.

Rock has some density.
Metal has a different density.

So we can determine
a huge amount about the asteroid

simply by pinging it with radar.

Arecibo's data reveals

that not all asteroids
are alike.

There's not just
one kind of asteroid.

There are actually
several kinds,

and this is important
to understand

because they behave differently.

They behave differently
if they impact us,

and they behave differently
if we're trying to prevent them

from impacting us.

We need to know what these
asteroids are made of

if they're gonna hit the Earth

because that drastically alters
the potential effects.

Asteroids come in different
shapes, different sizes,

and different compositions,
and we think that is

because they are the leftovers
of planet formation.

To understand how
each asteroid formed

and their threat level,
we have to go back

4.6 billion years to the start
of the solar system.

The reason that there are
all these asteroids

floating around
in our solar system today

is just because of the early
violence of the solar system

as it was forming.

At the birth
of the solar system,

the sun ignites,

leaving a disk of gas and dust.

Slowly, over time, planets form.

Lots of planets.

The early solar system
was a messy place.

There were a lot more planets,
a lot more forming planets.

They would crash in
to each other,

they would merge,
they would disintegrate,

they would re-form.

This process of accretion
of building planetary worlds

was not just, you know,
kind of gentle and happy.

It was violent.

It was like a giant
cosmic game of pool...

planet smashing into planet.

The leftovers from this violence

formed a ring of junk
between Mars and Jupiter.

And now we call
that junk asteroids.

They're just basically
rubble left over

from the formation
of the solar system.

Rocky leftovers became c-type

or chondrite asteroids.

They're quite dense, so big ones
can punch through the atmosphere

and hit the ground.

Radar reveals
a rarer type of asteroid.

Some of them really stand out
because their density

is so much higher than the rest
of the other asteroids.

These asteroids
are m-type or metal.

Because their mass is great,

they carry more kinetic energy
during a strike.

By far, the worst one
is this iron meteorite.

This is really heavy,
so the difference...

if you were being hit by this,

it would be the difference
between being hit by a rock

and being hit by a metal hammer.

We think that both the Barringer

and the k-pg dinosaur killer

were caused by metal asteroids.

But there's another more
mysterious type

floating through space.

December 2018,

NASA's spacecraft Osiris-Rex
approached

the near Earth asteroid Bennu.

Over time, it drifted out
of the main asteroid belt,

made its way into
the inner solar system,

until it became
a near Earth asteroid,

accessible for our spacecraft
to go and visit.

Osiris trained
its camera on Bennu.

One of the biggest surprises
on arrival of Bennu

was the large number of
large boulders on its surface.

Bennu is really littered
with huge boulders

and littered
with medium-sized boulders

and littered
with small boulders.

Bennu is not
a solid lump of rock.

It's made up of thousands
of bits of rock

forming what we call
a rubble pile.

These asteroids aren't big,
singular, spherical balls

of rock,

but rather they're literally
piles of rubble.

They're all sorts
of pieces and fragments

from another asteroid
that had previously

been disrupted
that have all come back together

and formed literally a pile
of rocks held together

by their own gravity.

We think rubble piles
formed from collisions

inside the asteroid belt
each impact blasted bits off.

Then, over time,
they came back together

to form a loose pile of rocks.

Imagine taking
a big cosmic dump truck

full of gravel and rubble

and dumping it
out there in the space

and letting gravity
weakly hold it together.

When scientists probe
deeper into Bennu,

they found another surprise.

It's full of holes,
like Swiss cheese.

If you could slice open
one of these asteroids,

you'd see there are
a lot of voids.

In fact, 60% of what we're
looking at is a void space,

so they're actually
really fluffy.

So even though
they're made of rocks,

they're sort of
the lint of rocks.

Bennu helps us
understand Apophis.

Radar data shows that
Apophis is also a rubble pile.

If you look at Apophis,
we really want to know

how its orbit will evolve
in the future.

What we learn at Bennu
about similar-sized

rubble-pile asteroids
might help us understand

the future of an asteroid
like Apophis.

So what would happen
if the rubble pile

called Apophis hits Earth?

You probably don't want
that to hit you still,

but it definitely
makes it a lot weaker

than something like a solid rock

or even more, a chunk
of nickel iron metal.

Does its composition
make it any less of a threat?

A rubble pile like Apophis
is especially unnerving

because we don't know, when it
interacts with the atmosphere,

if it's gonna stay
as one solid piece,

will it break up.

When these rubble piles
start interacting with planets,

if they fly near a planet,
they can get pulled apart

into all of their little pieces.

Or if they enter
the atmosphere of a planet

to impact the surface, they
might slowly get pulled apart

as they enter the atmosphere

and end up being
an array of little impacts

instead of one big
single impact.

But what would happen
if these impacts occur at sea?

Will our oceans save us,

or will a giant Tsunami
wipe us out?

2019,

U.S. researchers
discover deposits of fossils.

They contain both the remains
of land and sea creatures.

You see things that
are all jumbled together,

so you'll have fossils
of sea creatures.

You'll have ocean deposits
that are mixed up

with coastal deposits
and onshore deposits,

and you see those deposits
in places

that are very, very far away

from where you would
expect them to be.

And so this material was
obviously thrown

very far inland.

The jumbled deposits

suggest that the creatures
were killed at the same time

in a huge and violent event,

something powerful enough

to sweep ocean-dwelling
creatures far inland.

A Tsunami.

Tsunamis are usually created

when the ocean floor
moves suddenly.

The ground picks up
the entire ocean

and shakes it up and down,

and it's sort of like
taking a rope and shaking it,

and it moves all across
the ocean floor

and ocean surface
until it reaches land.

The biggest recent Tsunami
was caused by the Earth's crust

at the bottom of the ocean
lifting slightly,

so this means that
that entire length of crust

that lifted displaced
the water above it,

so the waves,
the tsunamis that result,

are really long and wide,

and it can travel
across the ocean

at tremendous speeds
and up on land.

Is this what happened
to the fossilized creatures?

Were they killed
by a huge Tsunami?

Clues come from dating
the preserved remains.

They're 66 million years old.

From the same time
a six-mile-wide asteroid

crashed into the sea off
the Yucatan peninsula in Mexico.

Are the two events connected?

Do ocean-impacting asteroids
trigger tsunamis?

We used to think
that a big asteroid

impacting in the ocean would
drive a tremendous Tsunami,

a huge wall of water
out at very rapid speeds,

which would basically
scour clean everything.

Now new research
from 2018 suggests

a very different scenario.

Scientists use super computers
to model asteroids

hitting the deep ocean
to work out how much of

the asteroid's kinetic energy
is converted into a Tsunami.

In the simulations,
a 1,600-foot asteroid

hits the ocean at
20,000 miles an hour

and dives into the water.

As it goes deeper in,
of course it's meeting a lot

of resistance and it slows down
and it compresses up.

It compresses and compresses
and compresses, and then finally

it runs out of momentum,

and it's at an extremely
high pressure.

The huge pressure
causes the asteroid to vaporize.

Temperatures hotter than
the surface of the sun

turn trillions
of gallons of water into steam.

The blast creates a huge
short lived cavity

in the water's surface

and a splash curtain,
a wall of water,

that leaps up several miles.

This curtain then collapses
and water falls

back into the cavity,
shooting a column of water

five miles up.

This very tall column
can't support its own weight

and collapses back down.

The collapse of
so much water triggers

a wave 1,200 feet high.

Could this become
a huge Tsunami?

If we think about a meteor
striking the ocean,

we want to understand
how far the waves

might propagate from the site.

We could actually just use a
stone and throw it into a pond,

and you might think,
"okay, well, it's a big stone,

it's going to make
a really big splash,

and that's just going to
extend out a long distance."

But it turns out the splash
stays the biggest really close

to where it impacts.

And then the ripples
die down after that.

So let's try that.

Big splash in the middle.

And we see the ripples
going outward,

but they're really
pretty small compared

with that initial big splash.

It's the same with
an ocean impacting asteroid.

The impact creates surface
waves that die away quickly

because only a small amount
of the asteroid's kinetic energy

gets into the water.

It's actually
pretty tough to make

a Tsunami like that.

The energy of the asteroid
doesn't couple well

with the water
to drive this wave.

Instead, most of the energy

goes into vaporizing
the asteroid itself

as well as all of the water
around it.

Only 1% of
the asteroid's kinetic energy

goes into making a wave.

So only low energy waves form,
too weak to become

giant tsunamis
traveling hundreds of miles.

So what caused
the jumbled fossil deposits

found thousands of miles away
from the impact site?

We don't think there
could be that much energy

still transmitted that far away
from the impact site.

Instead, there has to be
a different source of energy

that created different waves

right about the same time
as that impact event.

Research from 2019
may have the answer.

The KPG asteroid struck
on the continental shelf,

the shallow region between land
and deep ocean.

The impact triggered a localized
Tsunami large enough

to kill creatures in the region.

But it also sent a huge
shock wave into the bedrock.

There's going to be
a shock wave driven

through the ground.

That probably would have
killed anything in the area.

If you had a dinosaur
that was standing on

the Gulf coast of what is now
the United States,

that animal would have
experienced a seismic pulse,

an Earthquake that is stronger
than anything

on our current Richter scale.

It would have actually driven
its legs up into its body cavity

killing it instantly.

There's all manner of mayhem
and death

taking place at this time.

There was no escaping
this event.

The initial shock wave
smashed into the ground rock

and traveled through
the Earth's crust.

The impact would have shaken
the crust of the Earth,

which also would have triggered
Earthquakes around the world,

which themselves may have
triggered secondary salamis.

Secondary tsunamis
thousands of miles from

the impact site killed both
land and sea creatures.

The KPG impact went on to wipe
out 70% of all life on Earth.

So how did one asteroid
strike cause a global kill zone?

66 million years ago,
70% of life on Earth died

after the KPG asteroid strike.

How could one space rocket
hitting the sea cause

a global catastrophe?

When you have a big rock
hitting the ocean,

the biggest danger
is not from the waves

but actually from the steam
that it creates.

The impact vaporized
trillions of tons of seawater.

This steam Rose up
into the atmosphere

where it condensed
into water vapor.

Water vapor is a greenhouse gas.

So that's done going up
into the upper atmosphere,

and it's trapping heat,

but at different layers
it's making clouds.

It's just throwing
everything off kilter.

Water is a very effective
greenhouse gas as you

will actually affect some very
significant climate change

very quickly
as a result of that impact.

Within weeks
of the asteroid strike,

water vapor in the atmosphere
caused temperatures to rise.

But that was only the start.

The impact also blew out
10 trillion tons of rock,

ash, and dust.

This asteroid is so big,
six miles wide.

It's punched a hole in the air.

There's like a column
of low density, a chimney,

that goes from the ground up to
the top of the atmosphere.

And that means there's
very little air resistance

in that tunnel.

These rocks can actually
blast up into the chimney

and find it easier
to get up out of the atmosphere.

It sent that material
flying up halfway

to the orbit of the moon,
circled around the Earth.

All this ring of material
falling back on to the Earth.

And it was like the sky itself
was on fire.

So not only do you
have rocks falling on you,

but they're molten,
and these rocks

will start catching plants
and anything else on fire.

Soot and ash Rose
into the atmosphere

blocking out the sun.

Material was thrown
into the atmosphere,

plunging the planet
into a nuclear winter.

It was complete chaos, and it
went dark for two full years.

Without sunlight,
temperatures dropped.

Just months after the impact,
the planet cooled by 20 degrees.

In the immediate area, there's
just tremendous destruction.

Just everything gets destroyed.

But over the long term,
you're talking about ash

kicked up in the atmosphere,
extremely cold weather,

basically a global ice age.

The freezing
temperatures killed off

most plant life.

Imagine how that
affected life on Earth.

No plants and the base
of the ecosystem collapses.

This dark nuclear
winter lasted two years

and prevented plants
from photosynthesizing.

So if plants can no longer
use photosynthesis

to live, they'll die.

And then with no plants,
then you have no food

for these larger animals.

And so anything that eats
those animals will also die.

If you lose your plants,

you're going to lose
your large scale life.

First the plant eating
herbivores died off,

followed by the meat eating
carnivores.

Most of the dinosaurs
were just unable to find food

and to survive through
the cold long night.

The global devastation
wasn't over yet.

The rock of the continental
shelf where the asteroid hit

contained carbon and sulfur.

These carbonate rocks
were heated and vaporized

and released carbon dioxide
into the atmosphere.

Yet another greenhouse gas.

So you're vaporizing
a lot of sulfur,

a lot of salts
of different kinds

that are then lofted up
into the upper atmosphere,

that then plays havoc
on the climate.

These greenhouse gases
built up in the atmosphere

forming a warming blanket.

Triggering the next phase
of destruction.

Global warming on steroids.

Temperatures Rose 10 degrees
above normal.

Then the oceans warmed, as well.

Oxygen levels dropped,
and the seas became toxic

to simple life forms.

It actually made it impossible
for certain microbes

to actually live, and they're
the basis of the food system.

So really it changed what could
actually live in the ocean

and how much could live there.

Dead zones appeared
in the oceans

just as they had on land.

Nearly three quarters
of all life on Earth died,

all from one asteroid impact.

To prevent it
from happening again,

we need to track all
potentially dangerous asteroids.

But that isn't easy

because these space rocks
can change direction.

Saricicek, Turkey.

Security cameras record
a flash in the sky.

The flash... a 3-foot asteroid
exploding in the atmosphere.

It blew up in
the atmosphere and rained down,

and people saw that.

It was very noticeable.

And they went, and they
collected those meteorites.

And then they tried to figure
out what they were looking at.

The debris was sent
for fragment analysis.

I have a piece of one here.
So first, on the outside,

you can see it has
a really black fusion crust.

This is from when it fell
into the Earth's atmosphere,

so it was melted.

But when you look on
the inside, it reveals

this beautiful, very light tone,
fine grained material.

And so these meteorites
are incredibly distinctive

and really beautiful.

The meteorites are rocky.

They're beautiful color comes
from a mineral called howardite.

It's rare, and it doesn't
form on Earth.

Howardite meteorites come from
the asteroid Vesta,

and we know that because
of the dawn mission

that actually went to Vesta
and took a look at it

very carefully, so we know
the composition very well.

And so now suddenly here
was a new kind of meteorite

that's in Turkey that matches
the Vesta family of meteorites

but how can we be sure
that these bits of space rock

came from Vesta, an asteroid
over 100 million miles away.

It was a fall meteorite,
and so what that means

is that someone saw it,
you know, we saw it fall.

And so we knew its trajectory.

So we could actually
work backwards to say,

where did that meteorite
come from?

Retracing the trajectory of

the Turkish meteorites took
the scientists all the way back

to the 328-mile wide Vesta.

Where they studied
Vesta's surface,

they found further evidence.

On the surface of Vesta,
there's actually a very large

and fresh impact crater
that is around the same age

of the Turkish meteorite.

So that really clinched it.

This thing is definitely
from Vesta, and we proved it.

So how did bits of
Vesta end up here on Earth?

22 million years ago,
some very large impactor

struck Vesta,
made a huge crater,

and some of the rocks
from that crater actually

escaped from Vesta's gravity
and were lofted into space.

Some of these rocks
from Vesta went into orbits

that intersected with Earth.

22 million years later,
one blew up over Saricicek.

This Saricicek meteor shows
that the asteroid belt

is an unstable environment.

Asteroids frequently strike
other asteroids.

That's actually
happening all the time.

Things are running
into each other

in our solar system right now.

And so that makes it
really hard for us

to track all of those objects
because we don't actually know

what happens after they collide
with each other.

Now things are
totally different.

And that changes
the whole system.

Each collision
makes more asteroids.

There's many
different possibilities

of what could happen
when asteroids collide.

Imagine a roller derby
situation.

If you have two
groups of players

that run into each other,

that could be like two asteroids
running into each other.

And one possible outcome
is that one stays intact

while the other
is completely blown apart.

That sends fragments flying all
through the main asteroid belt,

and then there's
a little asteroid fragments

are on their own independent
orbits around the sun.

A problem with
asteroid impacts is that

we're always making
new asteroids.

There are big asteroids
out there,

and they get hit
by other asteroids,

and then you get shrapnel.

And now you've got not one
big one and one smaller one,

you've got one big one,
one smaller one,

and millions of little ones.

Now, most of these aren't very
big, but some of them might be

bigger and could be
potentially hazardous.

As the solar system ages,

the number of
asteroids increases.

Each new space rock
travels on a new course

which could intersect
with Earth.

So we're constantly producing
new asteroids

and big collisions
in the main asteroid belt.

And these are producing
the small asteroids

that will eventually drift
inward in the solar system.

Tracking this
constantly evolving population

of asteroids gives scientists
a huge headache.

If they break apart,
then that gives you

even more pieces
of the asteroid to track.

It's not a simple thing
to track and predict

the orbits of asteroids
and their movements,

because one tiny little change

can have huge dramatic impacts
for its possible future.

Figuring out exactly
where they're going to go

and keeping track of how
they interact with each other,

this is a huge endeavor.

The sheer volume
of asteroids can affect

the behavior of other asteroids

as they gravitationally
interact.

Think about your roller derby
player skating in circles.

The path they're going
to follow would evolve

the more people you plop down
on the track

they start interacting
with each other,

and their trajectory
will change.

The more crowded you make
the solar system,

the more things are
to change your orbit

of your individual asteroid.

It's not like
air traffic control,

where there's a known
amount of airplanes

and they all follow a plan.

This situation is
further complicated because

asteroid orbits can be affected
by other more subtle forces.

One of these is called the
Yarkovsky or the Yorp effect.

Honestly Yorp
is more fun to say.

The Yorp effect is
caused by sunlight

hitting an asteroid.

Light is made up of photons
that are traveling,

and these photons
actually have momentum.

So when light shines
on something,

it actually pushes on it.

When sunlight hits an asteroid,

the photons give it
a tiny push...

...enough to change
the space rock's trajectory.

When we know an asteroid
is really heading our way,

it's time to fight back.

So we've got an asteroid
that's headed at us.

What do we do?

Two main possibilities...
we deflect it,

we nudge it a little bit
so it misses,

or we blow it up, we destroy it.

Which of those
do you want to do?

It's a tough choice.

Get it wrong, and we could
end up being hit by a swarm

of radioactive space rocks.

An asteroid is heading our way,

and it may hit us in 2068.

How do we prevent
such a catastrophe

and stop it
from ever getting close?

Well, you just don't want
to take get anywhere near us

in the first place.

So what do you do?

Well, you can destroy them,

or you can push them
out of the way.

This is something where our
science fiction ideas

have got it almost
entirely wrong.

If you're in a bad movie,
a really, really bad movie,

you can send astronauts
to an asteroid,

put a nuclear bomb in it,

and blow it up
into lots of little bits

that then burn up harmlessly
in our atmosphere.

Yeah, it doesn't work that way.

Blowing up an asteroid

would make the problem
much worse.

We are no longer dealing with
just one space rock.

My issue with this is that
you may have turned

one problem into 50.

Instead of one
regular sized asteroid,

now you have a whole bunch
of littler ones,

and these may still hit
the Earth and cause damage.

And you know what?
That's not much less fun

than just having
a single big asteroid.

Now you've just taken
all that devastation

and spread it out
for everybody to enjoy.

The problem with using
a nuclear device is that

the products that rain down
on Earth are now radioactive.

If a dangerous
asteroid was on its way,

blowing it up
would be a last resort.

A less risky method
is to deflect it off

its collision course.

A small nudge early enough

can change in asteroid's
trajectory away from Earth.

You don't have to nudge it
very much for it to miss, right?

So if it's headed
straight at it,

I just touch it slightly,

by the time it gets to Earth,
its way off course.

NASA is investigating
ways to change

an asteroid's path,
including using a nuclear burst.

In a nuclear burst, what we do
is we don't actually hit it.

We come up to it with the device
on a spacecraft,

and then the device would be
detonated at a certain height

above the surface.

That heats up
the surface of the asteroid,

which vaporizes.

You get vaporized rock or metal
which blasts off the surface,

and that's how a rocket works.

So you blow up a bomb here,
and it winds up

pushing the asteroid
in the other direction

to prevent
any potential nuclear fallout,

NASA would detonate the bomb
a long way from Earth

any deflection attempt
has to be done years in advance,

which means it would be done
on the other side

of the solar system from us

on the opposite side
of the object's orbit.

That means that all of
the vapor made during

the explosion gets blown away
by the solar wind.

NASA is investigating
other less explosive methods

of deflecting an asteroid.

De-star would blast the asteroid
with a laser.

We hit it with
the laser, material vaporizes

and flies off the asteroid,

and because
of Newton's third law,

which is that for every action
there is an opposite

an equal reaction, this means
that vaporize material

moving off in one direction
moves the asteroid

in the opposite direction.

Both the laser
and the nuclear burst

are still just ideas
on the drawing board.

But one asteroid
deflection mission called

double asteroid redirection
test, or dart for short,

is already up and running and
scheduled for launch in 2021.

Dart is a kinetic impactor

and will try to knock
an asteroid off course.

At NASA for the longest
time, all we've been able to do

is theorize about how
we change their path.

But now for the first time,

we're actually gonna
practice in.

Leading this
groundbreaking mission to bump

an asteroid off its orbit
is Dr. Andy Chang.

Dart is the first
planetary defense mission

that we've ever done,
where we take a spacecraft,

we fly the spacecraft into
the asteroid to change

its course and make it
miss the Earth.

Dart's target
is a 525 foot space rock

orbiting the large
near Earth asteroid Didymos.

We pick the near Earth asteroid
Didymos as a target

for the dart mission because
although it's

a near Earth asteroid,
it's one that's very safely

parked away out there in space.

There's no way we can move
Didymos or its moon

in any way big enough to cause
a problem for the Earth.

The diddy-moon asteroid weighs

around 10 1/2 billion pounds.

So how do you knock such
a large lump of rock

off its path?

We're sending a spacecraft

to knock the diddy-moon
asteroid off course.

The asteroid is moving at
over 36,000 miles an hour

and is around
seven million miles away.

So how do you move
a 10 and a half billion pound

space rock?

You need to hit it really hard
to change its orbit,

so it's going to be coming in
at a super high velocity

in order to impart a bunch
of energy momentum to that moon.

Dart will hit the target

at around 14,000 miles an hour.

The speed of the dart impact
will be more than nine times

the speed of the rifle bullet
from an AK-47.

The impact will give
the asteroid a small push.

To work out how big a push,

we test impacts
with the Ames vertical gun.

At the NASA Ames
research center in California,

there's a very special
facility called

the Ames vertical gun range.

It's a hyper velocity gas gun
that allows us

to shoot little metal BBS
at rock targets at speeds

up to like 13,000, 14,000
miles per hour.

The gun replicates the impact

the dart mission will make.

It reveals that an impact
will blow off

a small amount of debris
but at extremely high speed,

enough to give the asteroid
an additional kick.

The impact will blow off pieces
of the asteroid,

so the pieces
are thrown off the back.

And so that that process acts
like a little rocket engine.

That provides an additional
momentum change,

momentum push
to the target itself.

The combined push
from the kinetic impactor

and the ejected debris is tiny,

around 0.0009 of
a mile per hour.

But hopefully it's enough
to change the asteroid's orbit.

If dart works, we could
then use a similar mission

to defend Earth
when the time comes.

This isn't some
small rock prototype

that we're doing this test on.

This is a real dress rehearsal
for an asteroid

that could destroy cities

or even maybe send
the Earth in chaos.

The moon of Didymos
is a solid lump of rock.

Will a kinetic impactor
like dart work

with a rubble pile asteroid
like Apophis?

When you shoot a rubble pile
with a projectile,

it's a little bit more
like trying to punch a sandbag.

You get a lot more a lot more
the energy is absorbed

into just moving the sand
around inside the bag

than ejecting it,
and so rubble piles

might be a little harder
to move by this method.

We don't know if we
can deflect a rubble pile

asteroid like Apophis.

They remain a clear
and present danger.

And something
we might not survive.

But there may be
a space lifeboat.

In 2018, scientists reexamined
rocks collected by Apollo 14

astronauts from the moon.

Buried in the samples was a rock
that shouldn't be there.

They got something
they didn't expect,

and that was an Earth rock.

They actually picked up
a rock from Earth on the moon.

They didn't bring it with them.

It's very likely that it was
something that was lofted up

when something hit Earth,
throw up a bunch of rocks.

Some of those rocks
fell on to the moon,

and that's a meteorite
on the moon,

but it's from Earth.

Super computer simulations of

the KPG asteroid strike revealed
how the impact had so much

energy that it catapulted rocks
out of Earth's atmosphere

and into space.

They were then caught
by the moon's gravity

and pulled down
to the lunar surface.

We now know the material ejected
into space from asteroid impacts

can travel to other planets,
as well,

which would explain
the 100 Mars meteorites

we've found here on Earth.

We think that there was probably
the exchange of a huge amount

of material
between different bodies,

Earth to the moon
and back again and to Mars.

With each impact that occurs
in our solar system

that ejects all types of
material that allows material

to swap from planet to planet,
moon to planet, moon to moon.

And so there's all
of this material

that eventually travels
from place to place.

Should another giant
asteroid hit our planet,

this planetary interchange
may give life on Earth

a lifeline.

If you think about
such an impact today,

you know, the chances are high
that a lot of life would be

wiped out, much of life,
probably all of human life.

It's certainly possible that
a big enough asteroid strike

could completely sterilize
the planet.

Talking about
no life whatsoever.

Not to put too fine
a point on it,

but if there's a dinosaur killer
asteroid out there

and it hits the Earth,
the chance of humanity's

survival of such a thing
as a species, mm, not great.

Humans may not survive.

But some scientists believe
that simple life forms could.

Asteroids have hit
our planet many times

in the past.

One giant strike wiped out
70% of all life on Earth.

If another huge asteroid
hits us, can life survive?

If a giant rock hits
the Earth and kills almost

all life on Earth,
there is a slim line of hope.

And that's because the dirt,
the rocks on Earth

are infused with bacterial life,
with microscopic life.

And in the event
of a giant impact,

some of these bits of rock
will be ejected into space

and might float around.

After an asteroid impact,
whatever ejected

into the atmosphere
could contain microbial life

that when it falls back down
on to the ground

could re-seed the life
on that planet.

Some bacteria can
survive the harsh conditions

of space and can cope with
an asteroid strike, reentry,

and landing back
on Earth's surface.

I think in terms of life
on planet Earth,

I think we've learned that we
live on a very resilient planet.

And I think life in some form,
even if it has to crawl

its way back
from bacterial stage,

I think life on this planet is
going to going to eke through.

Life is pretty good at
figuring out a way of surviving.

We know that life
first formed on the Earth

well over 4 billion years ago

and has never been wiped out
in all of that time.

There's always been something

after every major
mass extinction.

So life will continue.
It just won't necessarily be us.

An asteroid strike
on another world

may be how life on Earth
started in the first place.

There's an interesting
idea that an asteroid strike

on another planet could have
actually seeded life on Earth.

And the way this works is,
you have a life

that's somehow gotten a foothold
on some other planet like Mars,

a big asteroid strike hits
that planet

and knocks a piece of it off,
eventually rains down on Earth,

carrying with it life.

We may owe the existence of life
here to asteroid impacts.

That's speculative,
but it's kind of a cool thought.

Life seeding asteroids
may have hit us in the past,

and other asteroids
will hit us in the future.

One of those maybe Apophis,

arriving in less than
half a century.

Maybe we'll deflect it.

Maybe it'll miss us
all on its own.

Either way, we need
to keep tabs on it.

The best thing we can
do as a species, and it's funny

because it almost sounds
like I'm advocating

for more jobs for astronomers.

We need to keep looking
at the sky.

We need look at the sky
longer and deeper,

with more sensitive instruments

and get more of a sense
of what out there is around us.

That's what our species needs
to do to ultimately survive.

Because now we have the ability

to see these things
a little bit better,

we have the ability
to protect ourselves better.

It doesn't have
to be a surprise.

You know, the first time we see
a big impact doesn't have to be

as it's bearing down
destroying our planet.

We can actually see it
before it gets to us

and decide
what we want to do about it.

Earth's history is
littered with asteroid strikes.

Some wiped out
millions of species.

Some may have seeded life
in the first place.

What the future holds
and our relationship

with these space rocks,
no one knows.

Even though the chances of
something really large hitting

the Earth are pretty small,
the consequences are dire.

It would really destroy
our planet or at least life

as we understand it.

And so in many ways,
asteroids are the greatest

threat that we face.

Life is fragile, so of course
we live in a larger environment

where something could come
and hit us at any time.

That's part of being alive.

There's no guarantee tomorrow
will happen.

But what there is
is a high likelihood

that you'll still be
safe tomorrow.

Impacts from space are rare,

but if they do happen,
it's a huge deal.

And so you've got to put those
two things together.

That means we got to
pay attention.

Those impacts have
happened many times in the past,

and they're going to continue to
happen many times in the future.

Fortunately it's not probably
in our immediate future.

Impacts are rare, but the Earth
lives a long time.

So you're unlikely to get
in a car accident,

but if you drive enough, you're
going to get in a car accident.

Over a century time scale,

yes, we should be concerned
about these.

But over the daily, weekly,
monthly, even yearly time scale,

I wouldn't sweat it too much.

I wouldn't say we should lose
sleep over an asteroid

or comet striking Earth,

but the reality is
it will happen again.

So when you think
about asteroid strikes,

remember this wonderful
dramatic universe

you find yourself in.

We're here because
stars died and exploded.

Life on Earth wouldn't
be the same

if we didn't find ourselves
in this dramatic

and even dangerous environment
in space.

But this is who we are.
This is nothing new.

And this will continue
for the future of our planet.