How the Universe Works (2010–…): Season 8, Episode 1 - Asteroid Apocalypse: The New Threat - full transcript
If a massive asteroid collides with Earth, it could end life on the planet as one knows it.
Narrator: 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.
Narrator: 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.
Narrator: This is not a drill.
If we do nothing...
This is our future.
♪
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.
Narrator:
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.
Narrator: 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.
♪
Narrator:
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.
Narrator:
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.
[ Dog barking in distance ]
♪
[ Rumbling, car alarm blaring ]
♪
Narrator:
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?"
Narrator: 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?
Narrator: 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.
Narrator: 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.
Narrator:
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.
Thaller: 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?
Narrator: 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.
Narrator:
The asteroid slams into the air
ahead of it,
compressing it violently.
The surface of the asteroid
gets hotter and brighter.
Durda:
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.
Narrator: 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.
Narrator: As the asteroid
descends,
the compression
of the denser air beneath it
starts to flatten and even
disrupt the falling rock.
Oluseyi: There's a high pressure
on the front,
there's no pressure on the back
and it's being super heated.
Sutter:
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.
Narrator: The combination
of heat and pressure invade
the falling asteroid,
causing it to blow up.
[ Explosion ]
Most asteroids
don't reach the ground
before they
completely disintegrate
in a tremendous release
of energy.
Plait: 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.
Narrator: 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.
Narrator:
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.
Narrator:
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.
Narrator: 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.
Plait: 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.
Narrator:
Everything within nine miles
of the blast epicenter
would be completely destroyed.
♪
The intense heat and
pressure would wreck buildings.
Sutter: 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.
Narrator:
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.
♪
Narrator: 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.
Narrator: Apophis will skim
earth in 2029.
But its path could change,
possibly turning
a future miss...
Into a direct hit.
♪
♪
Narrator: 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.
Narrator: The football-stadium
sized apophis
will race over the Atlantic.
Plait: 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.
Narrator: 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.
Durda: 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.
Narrator: The impact would be
at least 10 times greater
than the simulated
asteroid strike on New York.
♪
Sutter: 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.
Narrator: 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.
Narrator: 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.
Narrator: Because of the
gravitational keyhole,
there's still a small chance
that apophis will hit earth
in 2068.
Plait: 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.
Narrator: 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.
Narrator: 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.
Walsh: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
♪
Narrator: 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?
Narrator: 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.
Narrator: 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.
Narrator: 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.
Bullock:
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.
Narrator: 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.
Narrator: 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.
Durda: 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.
Narrator: 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.
♪
Narrator: 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.
Plesko:
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.
Narrator: 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.
♪
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Durda: 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.
Plesko: 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.
Narrator: 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?
♪
Narrator: 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.
Narrator: 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.
Stricker: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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?
Narrator: 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.
Man: 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.
Narrator: Catalina
has limitations.
It can only see visible light,
so a particularly dim asteroid
could be missed.
Thaller:
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.
Narrator: When the infrared
space telescope neowise
turned its gaze
onto asteroids,
it had immediate results.
Thaller:
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.
Narrator: 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.
Narrator: 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.
Narrator:
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.
Narrator: 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.
Narrator: Arecibo sends out
radio signals
toward the newly
detected asteroid.
Sutter:
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.
Zambrano-marin:
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.
Sutter: 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.
Narrator: 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.
♪
Narrator:
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.
Narrator: 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.
Narrator: These few pixels
are enough to work out
how big apophis is.
Virkki: 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.
♪
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Sutter: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Walsh: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Durda: 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.
Narrator: 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.
Narrator: 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.
Narrator: So what would happen
if the rubble pile
called apophis hits earth?
Durda: 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.
Narrator: 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.
♪
Narrator: But what would happen
if these impacts occur at sea?
Will our oceans save us,
or will a giant Tsunami
wipe us out?
Narrator: 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.
Narrator: 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.
Narrator: 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 yucatán 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.
Narrator: 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.
Narrator: 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.
Plesko: This very tall column
can't support its own weight
and collapses back down.
Narrator: 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.
Narrator: 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.
Plait: 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.
Narrator: 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?
Radebaugh: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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?
♪
♪
Narrator: 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?
Lanza: 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.
Narrator: 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.
Narrator: 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.
Lanza: 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.
♪
Narrator: 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.
Narrator: 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.
Narrator: The freezing
temperatures killed off
most plant life.
Oluseyi: Imagine how that
affected life on earth.
No plants and the base
of the ecosystem collapses.
Narrator: 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.
Narrator: 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.
Narrator: The global devastation
wasn't over yet.
The rock of the continental
shelf where the asteroid hit
contained carbon and sulfur.
Lanza: 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.
Narrator: 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.
Narrator: 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.
♪
Narrator: Saricicek, Turkey.
Security cameras record
a flash in the sky.
The flash -- a 3-foot asteroid
exploding in the atmosphere.
♪
Lanza: 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.
Narrator: 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.
Narrator:
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
narrator: 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?
Narrator: 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.
Narrator: 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.
Narrator: 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.
Lanza: 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.
Narrator: Each collision
makes more asteroids.
Oluseyi: 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.
Narrator:
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.
Narrator: 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.
Bullock: Figuring out exactly
where they're going to go
and keeping track of how
they interact with each other,
this is a huge endeavor.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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?
♪
Narrator: It's a tough choice.
Get it wrong, and we could
end up being hit by a swarm
of radioactive space rocks.
♪
♪
Narrator:
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.
Narrator:
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.
Stricker: The problem with using
a nuclear device is that
the products that rain down
on earth are now radioactive.
♪
Narrator: 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.
Narrator: 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.
Plait: 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
narrator: To prevent
any potential nuclear fallout,
NASA would detonate the bomb
a long way from earth
plesko: 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.
Narrator: NASA is investigating
other less explosive methods
of deflecting an asteroid.
De-star would blast the asteroid
with a laser.
Oluseyi: 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.
Narrator: 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.
Thaller: 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.
Narrator: Leading this
groundbreaking mission to bump
an asteroid off its orbit
is Dr. Andy Chang.
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.
Narrator: 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.
Narrator: 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?
♪
Narrator:
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.
Narrator:
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.
Narrator: The impact will give
the asteroid a small push.
To work out how big a push,
we test impacts
with the ames vertical gun.
Durda: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: Should another giant
asteroid hit our planet,
this planetary interchange
may give life on earth
a lifeline.
Lanza: 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.
Narrator:
Humans may not survive.
But some scientists believe
that simple life forms could.
♪
♪
Narrator: 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?
♪
Sutter: 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.
♪
Narrator: 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.
Plait: 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.
Narrator: An asteroid strike
on another world
may be how life on earth
started in the first place.
Bullock: 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.
Narrator: 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.
Thaller: 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.
Narrator: 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.
Bullock: 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.
Durda: 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.
Plait: 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.
Thaller: 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.
♪
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.
Narrator: 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.
Narrator: This is not a drill.
If we do nothing...
This is our future.
♪
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.
Narrator:
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.
Narrator: 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.
♪
Narrator:
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.
Narrator:
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.
[ Dog barking in distance ]
♪
[ Rumbling, car alarm blaring ]
♪
Narrator:
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?"
Narrator: 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?
Narrator: 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.
Narrator: 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.
Narrator:
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.
Thaller: 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?
Narrator: 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.
Narrator:
The asteroid slams into the air
ahead of it,
compressing it violently.
The surface of the asteroid
gets hotter and brighter.
Durda:
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.
Narrator: 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.
Narrator: As the asteroid
descends,
the compression
of the denser air beneath it
starts to flatten and even
disrupt the falling rock.
Oluseyi: There's a high pressure
on the front,
there's no pressure on the back
and it's being super heated.
Sutter:
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.
Narrator: The combination
of heat and pressure invade
the falling asteroid,
causing it to blow up.
[ Explosion ]
Most asteroids
don't reach the ground
before they
completely disintegrate
in a tremendous release
of energy.
Plait: 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.
Narrator: 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.
Narrator:
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.
Narrator:
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.
Narrator: 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.
Plait: 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.
Narrator:
Everything within nine miles
of the blast epicenter
would be completely destroyed.
♪
The intense heat and
pressure would wreck buildings.
Sutter: 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.
Narrator:
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.
♪
Narrator: 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.
Narrator: Apophis will skim
earth in 2029.
But its path could change,
possibly turning
a future miss...
Into a direct hit.
♪
♪
Narrator: 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.
Narrator: The football-stadium
sized apophis
will race over the Atlantic.
Plait: 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.
Narrator: 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.
Durda: 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.
Narrator: The impact would be
at least 10 times greater
than the simulated
asteroid strike on New York.
♪
Sutter: 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.
Narrator: 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.
Narrator: 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.
Narrator: Because of the
gravitational keyhole,
there's still a small chance
that apophis will hit earth
in 2068.
Plait: 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.
Narrator: 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.
Narrator: 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.
Walsh: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
♪
Narrator: 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?
Narrator: 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.
Narrator: 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.
Narrator: 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.
Bullock:
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.
Narrator: 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.
Narrator: 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.
Durda: 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.
Narrator: 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.
♪
Narrator: 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.
Plesko:
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.
Narrator: 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.
♪
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Durda: 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.
Plesko: 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.
Narrator: 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?
♪
Narrator: 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.
Narrator: 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.
Stricker: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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?
Narrator: 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.
Man: 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.
Narrator: Catalina
has limitations.
It can only see visible light,
so a particularly dim asteroid
could be missed.
Thaller:
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.
Narrator: When the infrared
space telescope neowise
turned its gaze
onto asteroids,
it had immediate results.
Thaller:
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.
Narrator: 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.
Narrator: 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.
Narrator:
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.
Narrator: 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.
Narrator: Arecibo sends out
radio signals
toward the newly
detected asteroid.
Sutter:
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.
Zambrano-marin:
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.
Sutter: 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.
Narrator: 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.
♪
Narrator:
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.
Narrator: 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.
Narrator: These few pixels
are enough to work out
how big apophis is.
Virkki: 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.
♪
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Sutter: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Walsh: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Durda: 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.
Narrator: 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.
Narrator: 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.
Narrator: So what would happen
if the rubble pile
called apophis hits earth?
Durda: 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.
Narrator: 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.
♪
Narrator: But what would happen
if these impacts occur at sea?
Will our oceans save us,
or will a giant Tsunami
wipe us out?
Narrator: 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.
Narrator: 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.
Narrator: 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 yucatán 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.
Narrator: 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.
Narrator: 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.
Plesko: This very tall column
can't support its own weight
and collapses back down.
Narrator: 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.
Narrator: 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.
Plait: 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.
Narrator: 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?
Radebaugh: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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?
♪
♪
Narrator: 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?
Lanza: 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.
Narrator: 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.
Narrator: 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.
Lanza: 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.
♪
Narrator: 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.
Narrator: 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.
Narrator: The freezing
temperatures killed off
most plant life.
Oluseyi: Imagine how that
affected life on earth.
No plants and the base
of the ecosystem collapses.
Narrator: 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.
Narrator: 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.
Narrator: The global devastation
wasn't over yet.
The rock of the continental
shelf where the asteroid hit
contained carbon and sulfur.
Lanza: 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.
Narrator: 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.
Narrator: 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.
♪
Narrator: Saricicek, Turkey.
Security cameras record
a flash in the sky.
The flash -- a 3-foot asteroid
exploding in the atmosphere.
♪
Lanza: 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.
Narrator: 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.
Narrator:
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
narrator: 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?
Narrator: 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.
Narrator: 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.
Narrator: 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.
Lanza: 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.
Narrator: Each collision
makes more asteroids.
Oluseyi: 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.
Narrator:
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.
Narrator: 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.
Bullock: Figuring out exactly
where they're going to go
and keeping track of how
they interact with each other,
this is a huge endeavor.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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?
♪
Narrator: It's a tough choice.
Get it wrong, and we could
end up being hit by a swarm
of radioactive space rocks.
♪
♪
Narrator:
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.
Narrator:
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.
Stricker: The problem with using
a nuclear device is that
the products that rain down
on earth are now radioactive.
♪
Narrator: 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.
Narrator: 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.
Plait: 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
narrator: To prevent
any potential nuclear fallout,
NASA would detonate the bomb
a long way from earth
plesko: 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.
Narrator: NASA is investigating
other less explosive methods
of deflecting an asteroid.
De-star would blast the asteroid
with a laser.
Oluseyi: 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.
Narrator: 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.
Thaller: 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.
Narrator: Leading this
groundbreaking mission to bump
an asteroid off its orbit
is Dr. Andy Chang.
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.
Narrator: 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.
Narrator: 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?
♪
Narrator:
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.
Narrator:
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.
Narrator: The impact will give
the asteroid a small push.
To work out how big a push,
we test impacts
with the ames vertical gun.
Durda: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: 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.
Narrator: Should another giant
asteroid hit our planet,
this planetary interchange
may give life on earth
a lifeline.
Lanza: 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.
Narrator:
Humans may not survive.
But some scientists believe
that simple life forms could.
♪
♪
Narrator: 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?
♪
Sutter: 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.
♪
Narrator: 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.
Plait: 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.
Narrator: An asteroid strike
on another world
may be how life on earth
started in the first place.
Bullock: 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.
Narrator: 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.
Thaller: 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.
Narrator: 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.
Bullock: 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.
Durda: 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.
Plait: 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.
Thaller: 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.
♪