All language subtitles for How The Universe Works s08e11 Mysteries of Alien Stars.eng

a dangerous asteroid is heading towards
Earth.

It's the size of the Empire State
Building, and it's traveling 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, It could be
another story.

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

This could be the most devastating
single event in U .S.

history.

Earth is stuck in the crosshairs of a
potential asteroid strike.

Apophis is one of around 2 ,000
potentially hazardous asteroids.

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

As far as cosmic dangers go, they're
number one on the list.

This is not a thrill.

If we do nothing,

this is our future.

December 2018,

the U .S.

military detects 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
shocking.

The cause of the blast was an asteroid.

This asteroid was 30 feet across,
something like that, over 1 ,000 tons.

was moving at 20 miles per second, over
70 ,000 miles an hour.

This asteroid was small, and it exploded
in the atmosphere of 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

this could have been a dangerous object.

But the scariest thing about it is that
we didn't see it coming.

We've been lucky so far.

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 over open ocean, where we go on
completely

oblivious.

We may be oblivious to most of the
threats from space, but they are very

We are going to get hit.

Over a certain amount of time, an
asteroid impact is inevitable. It will

100 % absolute certainty.

NASA considers the threat from the sky
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 protect our home, we carry out
Earth defense simulations.

For three days, 200 scientists at the
Planetary Defense Conference battle a

simulated asteroid 20 times larger than
the Bering Sea space rock.

We practice, all right, what if this
hits a major city?

What would we need to do?

By running potential impact scenarios,
we can prepare for a real asteroid

strike.

This is like a fire drill that you would
do at school or at work, where you

practice and think about, okay, what if?
Where are the exits? How do I get out?

How fast do I get out?

The drill starts with the discovery of a
simulated Earth -bound asteroid.

So the first information is, there's a
big asteroid coming towards the Earth.

Then we get a better estimate of how big
it is, how fast it's going, and where

it's going to hit.

The asteroid is heading straight for
Earth, with Denver, Colorado in its

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

In the simulation, the spacecraft
strikes the asteroid, deflecting it

away from Earth.

dislodges a 200 -foot junk, which is now
heading straight towards the eastern

seaboard.

So there's this one last piece that is
now going to hit New York.

We know that something that size is
going to have citywide consequences.

That is huge. That's a horrible impact.

When you're actually in the conference
room and you understand eventually that

New York City is going to be destroyed,
and you're having strategies about how

to evacuate people, all the timing, when
you're doing the simulation, you're in

your head, you're thinking about these
things, you're trying to reason them

But can you imagine the feeling in your
gut, in your heart, if this was real?

If this were real, the chunk of asteroid
would strike the Earth's atmosphere at

43 ,000 miles an hour.

As the space rock descends, it collides
with molecules in the atmosphere, which

buffets the falling rock.

It's kind of like doing a belly flop
into a pool, right? You're going from

vacuum of space into the dense lower
atmosphere in mere seconds.

And that's an incredible amount of
pressure to put on the object.

The asteroid flams into the air ahead of
it, compressing it violently.

the surface of the asteroid gets hotter
and brighter.

It's actually the air itself that's
glowing luminously from the heating of

shockwave, the world's most intense
sonic boom, if you will, that heats the

to incandescence as the object passes
through. So that's the source of that

brilliant illumination.

This bright -burning asteroid is called
a bolide.

We witnessed one descending over the
Russian city of Chelyabinsk in 2013.

All of a sudden, there was a huge
fireball striking through the sky, and

had no idea what they were witnessing
because it looked like the sky was on

fire. It was insanity.

As the asteroid descends, the
compression of the denser air lower down

flatten and even disrupt the falling
rock.

There's a high pressure on the front,
there's no pressure on the back, and

being superheated. And that intense
temperature causes the air to glow,

how we see the streak of a meteor.

And it also disintegrates the asteroid
itself. It's hot enough to literally

rock. This can often lead to them
exploding.

The combination of heat and pressure
invade the falling asteroid, causing it

blow up.

Most asteroids don't reach the ground
before they completely disintegrate in a

tremendous release of energy. This is
what we call an airburst, and we learned

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

out when they blew up bombs above the
ground, it actually did more damage. It

was more widespread damage.

The explosion of the Telebent 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

flash in the sky?

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

pressure wave hit and blew glass in
their face.

The Chelyabinsk asteroid was only 65
feet across.

The rock in the defense simulation is
three times more massive and is now

heading for New York City.

Imagine what would happen if an
explosion a thousand times greater than

over Hiroshima hit New York.

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

people.

With so little warning, the only option
would be to evacuate New York City.

How do we get everybody out of New York
City within just a few days?

That's where panic sets in. That's where
fear would really become the dominant

emotion.

Anyone left in New York would see the
bolide race in,

followed by a blinding light as the
asteroid

explodes above the city.

The blast would be the equivalent to the
largest nuclear weapon ever detonated

on Earth.

Buildings would be flattened, melted.
There would be fires for miles around.

In the first moments of the explosion, A
million people could be killed

instantly, and many more would die later
in the rubble and the ruins of what

would happen there.

Everything within nine miles of the
blast epicenter would be completely

destroyed.

The intense heat and pressure would
wreck buildings.

It's the worst possible day for New
Yorkers.

And not just the city itself.

There's something like 15 million people
living in the New York area.

The destructive shockwave would race out
over 250 square miles.

This would certainly be the worst
disaster that the U .S. has ever

We're talking about millions and
millions of people displaced, affected

an instant.

This scenario is just a simulation, for
now.

The asteroid Apophis is heading our way.

If it hits Earth, it might not just kill
a city. It could kill a whole region.

I wouldn't exactly want to be there when
that happens.

I want to be very, very far away.

Apophis will skim Earth in 2029, but its
path will

change,

possibly turning a future myth into a
direct hit.

April 13, 2029.

A speck of light races towards 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

long, long time. It will be ten times
closer than the moon itself. It will be

close it will be brighter than some
stars.

The football stadium -sized Apophis.

will race over the Atlantic.

If it were sitting on the surface of the
Earth, it would weigh about 50 million

tons, something like that.

And that is not the place you want it to
be. You want it to be in space and far

away.

When we discovered Apophis in 2004, we
thought it might be on a collision

with Earth.

With a potential impact greater than the
largest atomic bomb ever exploded.

The largest nuclear device, atomic
device, ever detonated on our planet was

Tsar Bomba bomb in Russia. It was
something like 55 or 56 megatons.

When Krakatoa exploded in 1883, that was
something like 200 megatons.

Apophis impact would be 450 megatons.

If something like that were to happen
over New York City or Washington, D .C.,

you're going to lose the city.

The impact would be at least ten times
greater than the simulated asteroid

strike on New York.

When you put it in those terms, that's
just plain scary.

In a word, an impact from an apophysized
asteroid would be bad.

Very, very bad.

Apophis' orbit will cross Earth every
seven years this century, but it won't

us in 2029.

But this close encounter will change
Apophis' orbit.

When a small asteroid encounters a
bigger body like a planet, it's like a

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

trajectory of that lone roller derby
skater. And the next time around, it

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

It's the same in the solar system.

The combined gravity of the Earth and
Moon creates what's called a

keyhole, a gravitational sweet spot,
which could change Apophis'

orbit.

That will change the potential future
trajectory of this rock and might make

totally harmless or might increase the
chances of an impact even further in the

future.

Because of the gravitational keyhole,
there is still a small chance that

will hit Earth in 2068.

That is the important lesson that
Apophis taught us. You can miss the

if you pass through one of these
keyholes at some time later, you will

Earth.

We now know Apophis will miss the
keyhole in 2029, but there are other

and other close passes.

Apophis is not a lone threat.

There are an estimated 832 ,557
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 and

cause any troubles. But some asteroids
are on very particular orbits that cross

the orbit of the Earth.

These asteroids have left the stable
orbit of the asteroid belt and moved

orbits that get near our own.

These asteroids are called near -Earth
asteroids, or NEAs for short.

The near -Earth asteroid population is
interesting and potentially dangerous

because they're the ones that actually
cross the orbit of the Earth. So they're

most likely to have, at some point in
the future, an impact with the Earth.

Most NEAs pose little or no threat to
Earth.

But we've detected over 2 ,000 that do,
including apophis.

These are called PHAs.

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

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.

PHAs are asteroids 500 foot or larger
that could collide with Earth.

Take a 400 foot asteroid.

If it hit, it would release as much
energy as 3 ,000 Hiroshima nuclear

In July 2018, NASA published a map of
all known NEAs and PHAs.

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 this swarm of angry bees

all around us.

In 1999,

we'd identified under 300 NEAs scattered
through the inner solar system.

Ten years later, we discovered 500 more.

By 2018, we discovered 18 ,000 near
-Earth asteroids.

But we estimate there are millions out
there.

It seems like we can never find all the
asteroids. They just keep coming.

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

Zombies that keep hurtling our way,
hitting 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

key to its destructive power.

When a really fast and really large
asteroid hits, the impact is off the

chart. The blast is so intense.

It can melt or even vaporize rock.

January 2019.

A total eclipse of the moon.

Astronomers train their telescopes on
the darkening lunar surface.

They capture a bright flash that lasts
around a quarter of a second.

It was recorded. There were a lot of
live webcasts and things like that going

at the time.

And you can see this flash of light.
What the heck was that?

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

It turns out it was actually a meteorite
hitting the surface of the moon. And

because it was dark, and because we were
all looking at it, we could actually

see it.

The moon's dark surface gave us a unique
view into what happens when an asteroid

strikes. What was so exciting about
being able to see this impact on the

a dark area is that we could actually
look at the light that it produced and

then back calculate exactly what the
size of the impactor was.

We worked out that the impacting
asteroid was just 20 inches wide. The

blew out was 45 feet across.

How could 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

an asteroid will do.

Just like a boxer, if a tiny person like
me were to swing a punch, it would do a

lot less damage than a heavyweight
champion.

Same thing with asteroids.

The bigger they are, the bigger the
punch.

But the same thing is fast, right?

If I hit you really slowly, it's not
going to hurt. I have to really wind

and pop.

That's what happens with an asteroid.

The damage from an asteroid strike is
determined by its kinetic energy.

Kinetic energy depends on two things,
speed and weight.

Speed is the most important.

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. Ten times as fast, it has

hundred times the energy. So the
velocity is what's really critical here.

The lunar asteroid weighed only 100
pounds, but it was traveling at 38 ,000

miles an hour.

carrying a huge kinetic energy which
gouged out the crater.

It's the same principle for impacts on
Earth.

50 ,000 years ago, a 150 -foot asteroid
hit what is now Arizona.

The impact blasted out an impressive
hole, now called Beringer Crater.

It's about three -quarters 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

impressive hole in the ground.

In 2016,

impact specialist Kathy Plesko visited
Beringer Crater to see firsthand what

mass and speed do to the surface of the
Earth.

The food.

It's 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.

An 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

shockwave came out.

The immense power of an asteroid impact
comes from the kinetic energy being

transferred from the space rock into the
surface rock.

It's an extremely violent process, and
it starts with the moment of contact of

the projectile with the surface itself.

It pushes into the crust, and at first
it's just almost punching,

like sticking your thumb into dough.
It's only about as wide as the object

It's going straight down in, but then
it's meeting resistance from the surface

of the Earth.

And so it squishes, squishes, squishes
until it runs out of momentum, but then

it's very compressed, and all of that
energy is in a very small space.

As it releases, it detonates like a
bomb, and that's what makes the impact

crater.

Simulations of an asteroid strike in the
lab reveal the impact in slow motion.

As the high -speed pellet hits the
surface, The sand compresses downwards,

rebounds.

As that rebound is occurring, that's
when the material is being ejected out

the crater itself.

You'll see the surface erupting outwards
like the blooming petals of some big

rocky flower as all this debris goes
spraying out in every direction.

The 150 -foot Behringer 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 Behringer hit
Earth.

This asteroid, called KPG, had so much
energy, it turned rock to liquid.

The thing was immense. It's really hard
to wrap your head around just how big it

is. When the back end of it is so far
back that it's where a modern

jetliner would fly.

The KPG 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 has 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.

As some rock exploded skyward.

Rock below the surface was slammed by a
shockwave that was completely off the

charts.

Rock stopped, behaving like rock.

We experience rocks as solid objects,
but if you hit a rock hard enough, it

flows like water.

The KPG impact hits so hard, it
pulverized the rock and turned it into a

Almost like ripples on a pond moving
away from a stone that's been dropped in

it. It's almost like a splash in the
solid body of the Earth itself.

And like the 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

relaxing back down into their current
position again.

The material...

And so these ripples are frozen in the
rock. And there are other fragments that

go away radially, almost like the
spiderweb pattern in glass that you get

it's shot with a bullet.

The KPG impact blew out a 111 -mile
-wide crater.

A large and fast asteroid heading our
way is always going to be a problem.

So what do we do?

Wait for oblivion?

Or fight back?

The space in the inner solar system
seems calm, stable, and empty.

But it's not.

There are tens of thousands of near
-Earth objects just whizzing around

Now, space is big.

They're not going to hit us every time
they orbit the sun. But this does set up

the possibility that one of these years,
we're going to end up at the same spot

in space at the same time as that
asteroid.

And then it's going to be an event.

We're living in a cosmic shooting
gallery.

Asteroids strike the Earth all the time
through history, and it's going to

happen again.

Scientists are developing strategies to
stop an asteroid hitting our planet.

Our options, destroy or deflect the
space rock.

But first, we need to detect any
dangerous asteroids.

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

haven't discovered.

And such an asteroid can do some real
damage if it were to explode over a

populated area.

To prevent such a catastrophe...

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

Detection is crucial in our defense
against asteroids.

And the reason is, the earlier they're
detected, the easier it is to deflect

them away from hitting the Earth.

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

The problem is, asteroids are very hard
to detect.

Finding asteroids and cataloging all
their orbits is really challenging.

They can move quite fast across the sky,
and they might go away on the other

side of the sun for years and years and
years.

So we can't see them.

And even when they are this side of the
sun, they're hard to spot.

But the problem is they're very small
and they're very dark.

And when I say very dark, I mean really
dark like a lump of coal.

So how do you find a small, dark rock
just wandering around out there in the

solar system?

The Catalina Sky Survey has the answer.

The huge telescope in the mountains
above Tucson, Arizona takes a series of

images over a 20 -minute period.

It's looking for anything that moves.

Because stars don't move, but asteroids
do.

If it's a really bright asteroid, we
will see some bright points of light.

tracking across the four images.

Ah, here we go.

This is a real object.

You can see it's moving across the sky
here from the lower right to the upper

left. We are very, very excited to have
discovered one tonight because this is

an object that's approaching nearer
space, likely in the neighborhood of

Catalina has limitations.

it can only see visible light.

So a particularly dim asteroid could be
missed.

Asteroids are very cold.

They're usually quite far away from the
sun.

But amazingly, the best way we have to
find these is infrared light.

Because things that are cold by human
scale can still be very warm to an

infrared telescope.

So even if asteroids are just a few tens
of degrees above absolute zero, that's

still enough heat to detect them.

When the infrared space telescope
NEOWISE turned its gaze onto asteroids,

immediate results.

NEOWISE has now detected close to 160
,000 new asteroids and comets in our

system, and about 780 of those are
things that are near the Earth.

Ten of those near objects have been
classified as PHAs, potentially

asteroids, without NEOWISE.

we would have missed them.

Using an infrared space telescope is a
way of better detecting some of the

smaller asteroids and comets in the near
-Earth vicinity.

Detection is an important first step,
but it only tells us there's 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 going to 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 traveling.

All of these things together are really
important for tracking where it's going

to be next and whether or not they're
going to hit us.

To get this information, we need
something much bigger and more powerful.

The Arecibo Observatory.

Once Catalina or another telescope
detects a near -Earth asteroid in our

neighborhood, Arecibo's 1 ,000 -foot
dish swings into action.

They discover these asteroids, and then
once we know where they were, we can try

and point the radio telescope and see
where they are at the moment and measure

their exact location and their
trajectory.

Arecibo achieves this level of precision
by using radio detection and ranging,

more commonly known.

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

probability of impacting Earth.

Arecibo sends out radio signals towards
the newly detected asteroid.

It emanates radio signals.

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

side of your car.

It's pretty similar, but instead of
doing it with a radar gun on a small

we're doing it at a really big scale
with one megawatt power hitting objects

that are tens of them are distances
away.

And then those radio waves bounce back
to Earth and we detect them again. And

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.

But asteroids may not be the biggest
threat from faith.

November 25, 2018.

Cameras on board the solar and
heliospheric observatory film a large

crashing into the sun.

We recorded the impact of an object into
the sun at over a million miles per

hour.

The incredible speed.

tells us that this was not an asteroid.

It was the death plunge of something
much more unpredictable and dangerous, a

killer object from the outer reaches of
the solar system.

Comets, in some way, you could consider
maybe being more dangerous than near

-Earth asteroids.

With near -Earth asteroids, you could
imagine that we would discover all of

them. And if we get perfect knowledge of
all of their orbits, we can predict

into the future where they'll be and
when they may or may not.

have an orbit that crosses the actual
Earth and could be an impact.

Comets, a large part of that population,
we only see once.

They come in from way out in the distant
part of the solar system, they do one

lap around the sun, and they go back out
there for millions of years.

Comets are dirty snowballs, huge lumps
of ice and dust.

They come in two flavors.

There's something we call short -period
comet.

These are comets that are kind of
constrained to the solar system, the

solar system, and their orbits are never
more than a few hundred years.

Short -period comets come from the
Kuiper Belt, a region of the solar

beyond the orbit of Neptune.

These comets have short orbits on the
same plane as Earth.

The second type of comet.

are called long -period comets.

They originate in the Oort Cloud, a
sphere of icy objects located at the

edges of the solar system.

There are thousands and thousands of
comets out there in the Oort Cloud.

just waiting.

And so, in principle, one of them can
get knocked off course and come raining

down into the inner solar system.

Long period comets are very large, and
they travel very fast.

Comets can get really big, and they're
really heavy.

And essentially, they're falling to
Earth from 2 billion light years away.

So imagine how fast they're going.

We know from studying asteroids that the
faster they go, the more kinetic energy

they release on impact.

Comet travel.

even faster than asteroids.

In general, they're moving 50 % faster,
something like that.

But that doubles their impact energy.
And that's sort of a best -case

In a worst -case scenario, pound for
pound, they could have five or up to

ten times as much energy as an asteroid
impact.

The Bering Sea asteroid blew up in the
atmosphere.

But the Beringer crater asteroid hit the
ground intact with its full force.

Why do different asteroids behave
differently?

And what will Apophis do when it heads
our way?

Arecibo's radar may have the answer.

When we bounce radar waves off of these
objects, we can get... effectively

imagery of the surface of some of these
small objects that we just cannot do

with optical telescopes.

This is the radar image of Apophis.

It's so far away that all we could image
was a few pixels.

So this is our most recent radar image
of asteroid Apophis.

And you can see it's only a few pixels,
but it does give us... information on

what it actually is.

These few pixels are enough to work out
how big a pofis is.

From this image, we can constrain the
size to be about 1 ,000 feet, which is

about the same size as our receiver
radio telescope.

All of that from a weird bunch of
pixels.

Knowing the size and mass of an asteroid
is critical to understanding what an

asteroid is made of.

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

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

Rock has some density.

Metal has a different density.

So we can determine a huge amount about
the asteroid simply by pinging it with

radar.

Arecibo's data reveals... that not all
asteroids are alike.

There's not just one kind of asteroid.
There are actually several kinds.

And this is important to understand
because they behave differently.

They behave differently if they impact
us, and they behave differently if we're

trying to prevent them from impacting
us. We need to know what these asteroids

are made of, if they're going to hit the
Earth, because that drastically alters

the potential effects.

Asteroids come in different shapes,
different sizes, and different

And we think that is because they are
the leftovers of planet formation.

To understand how each asteroid formed
and its 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

forming.

At the birth of the solar system, the
sun ignited, leaving a

disk of gas and dust.

Slowly over time, planets formed.

Many planets.

The early solar system was a messy
place. There were a lot more planets, a

more forming planets. They would crash
into each other. They would merge. They

would disintegrate. They would reform.

This process of accretion, of building
planetary worlds, was not just, you

kind of gentle and happy. It was
violent.

It was like a giant cosmic game of pool.

planets smashing into planets.

The leftovers from this violence formed
a ring of junk between Mars and Jupiter.

And now we call that junk asteroids.

They're just basically rubble left over
from the formation of the solar system.

Rocky leftovers became C -type, or
chondrite asteroids.

They are quite dense, so big ones can
punch through the atmosphere.

and hit the ground.

Radar reveals a rarer type of asteroid.

Some of them really stand out because
their density is so much higher than the

rest of the other asteroids.

These asteroids are M -type, or metal.

Because their mass is great, they carry
more kinetic energy.

During a strike.

By far the worst one is this iron
meteorite.

This is really heavy.

So the difference, if you were being hit
by this, would be the difference

between being hit by a rock and being
hit by a metal hammer.

We think that both the Behringer and the
KPG dinosaur killer events were

caused by metal asteroids.

There is another, more mysterious type
floating through space.

December 2018.

NASA spacecraft OSIRIS -REx approached
the near -Earth asteroid Bennu.

Over time, it drifted out of the main
asteroid belt, made its way into the

solar system, until it became a near
-Earth asteroid accessible for our

spacecraft to go in business.

Osiris -Rex trained its camera on Bennu.

One of the biggest surprises on arrival
at Bennu was the large number of large

boulders on its surface.

Bennu is really littered with huge
boulders and littered with medium -sized

boulders and littered with small
boulders. Bennu is not a solid lump of

It's made up of thousands of bits of
rock forming what we call a rubble pile.

These asteroids aren't big, singular,
spherical balls of rock, but rather

they're literally piles of rubble.

They're all sorts of pieces and
fragments from another asteroid that had

previously been disrupted that have all
come back together and formed literally

a pile of rocks held together by their
own gravity.

We think rubble piles form from
collisions inside the asteroid belt.

Each impact blasted bits off. Then over
time, they came back together to form

the loose pile of rocks.

Imagine taking a big cosmic dump truck
full of gravel and rubble and dumping it

out there into space and letting gravity
weakly hold it together.

When scientists probed deeper into
Bennu, they had another surprise.

It's full of holes, like Swiss cheese.

If you could slice open one of these
asteroids, you'd see there are a lot of

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

So they're actually really fluffy.

So even though they're made of rocks,
they're sort of the lint of rocks.

Bennu helps us understand a pulpit.

Radar data shows that a pulpit 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

help us understand the future of an
asteroid like Apophis.

So what would happen if rubble pile
Apophis hits Earth?

You probably don't want that to hit you
still, but it definitely makes it a lot

weaker than something like a solid rock
or, even more, a chunk of nickel -iron

metal. Does its rubble pile 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
going to stay as one solid piece.

Will it break up?

When these rubble piles start
interacting with planets, if they fly

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

In 2017, we had another wake -up call.

A strange base rock arrived in our
neighborhood.

Its shape was unlike anything we'd seen
before.

The thing that made Oumuamua different
from anything else we'd ever seen is it

seemed to be almost a shard, a sharp
piece of metal tumbling through space.

Typically, things that move around our
solar system are somewhat spherical.

This in no way was spherical. It was
almost cigar -shaped.

So it kind of really plugged into all
those alien theories.

But we were able to confirm that it
didn't flow down as it went by the

which was, we figured if it was an alien
craft, it would probably stop and have

a little bit of a look. But it carried
on its trajectory.

It wasn't a comet or an asteroid from
the asteroid belt.

It was a space rock from interstellar
space.

Interstellar asteroids are probably
pretty rare, but the thing about them is

they're moving really fast.

So if they happen to hit us, it's really
bad.

Oumuamua was traveling over 100 times
faster than a fighter jet.

And as we know, speed means danger.

Had Oumuamua been on an impact
trajectory with the Earth, at those

speeds, very much faster than anything
in our solar system,

remember the kinetic energy goes as the
square of the impact speed. At those

kinds of speeds,

imagine it hitting us at 196 ,000 miles
per hour, that carries an incredibly

powerful punch. And so for a given size
object, the impact of Oumuamua compared

to a... regular solar system objects
would have been absolutely devastating.

Oumuamua passed safely through the solar
system, but it won't be the last

invader from interstellar space.

Astronomers estimate that one alien
object visits our cosmic neighborhood

year.

2019.

U .S.

researchers discovered deposits of
fossils.

They contain both the remnants of land
and sea creatures.

You see things that are all jumbled
together. So you'll have fossils of sea

creatures. You'll have ocean deposits
that are mixed up with coastal deposits

and onshore deposits. And you see those
deposits in places that are very, very

far away from where you would expect
them to be. And so this material was

obviously thrown very far inland.

The jumbled deposits suggest the
creatures were killed at the same time

huge and violent event, something
powerful enough to sweep ocean -dwelling

creatures far inland.

A tsunami.

Tsunamis are usually created when the
ocean floor suddenly moves.

The ground picks up the entire ocean and
shakes it up and down, and it's sort of

like taking a rope and shaking it.

and it moves all across the ocean floor
and ocean surface until it reaches land.

The biggest recent tsunami was caused by
the Earth's crust at the bottom of the

ocean lifting slightly. So this means
that that entire length of crust that

lifted displaced the water above it. So
the waves, the tsunamis that result, are

really long and wide, and it can travel
across the ocean at tremendous speeds

and up on land.

Is this what happened to the fossilized
creatures?

Were they killed by a huge tsunami?

Clues come from dating the preserved
remains.

They are 66 million years old.

From the same time, a six -mile -wide
asteroid crashed into the sea off the

Yucatan Peninsula, 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

basically scour clean everything.

Now, new research from 2018 suggests a
very different scenario.

Scientists used supercomputers to model
asteroids hitting the deep ocean.

to work out how much of the asteroid's
kinetic energy is converted into a

tsunami wave.

In the simulations, a 1600 -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

down and it compresses up. It compresses
and compresses and compresses. And then

finally it runs out of momentum, and
it's at an extremely high pressure.

The huge pressure causes the asteroid to
explode and 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 surface and a splash curtain,

wall of water that leaps up several
miles.

This curtain then collapses and water
falls back into the cavity, shooting a

column of water five miles up.

This very tall column can't support its
own weight and collapses back down.

The collapse of so much water.

triggers a 1 ,200 -foot -high wave.

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, OK, well, it's a
big stone. It's going to make a really

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

But it turns out the splash stays... the
biggest, really close to where it

impacts, and then the ripples die down
after that. So let's try that.

Big splash in the middle.

And we see the ripples going outward,
but they're really pretty small compared

with that initial big splash.

It's the same with an ocean -impacting
asteroid.

The impact creates surface waves that
die away quickly because only a small

amount of the asteroid's kinetic energy
gets into the water.

It's actually pretty tough to make a
tsunami like that. The energy of the

asteroid doesn't couple well with the
water to drive this wave.

Instead, most of the energy goes into
vaporizing the asteroid itself, as well

all of the water around it.

Only 1 % of the asteroid's kinetic
energy goes into making a wave.

So only low -energy waves form, too weak
to become giant tsunamis traveling

hundreds of miles.

So what caused the jumbled fossil
deposit thousands of miles away from the

impact site?

We don't think there could be that much
energy still transmitted that far away

from the impact site.

Instead, there has to be a different
source of energy that created different

waves right about the same time as that
impact event.

Research from 2019 may have the answer.

The KPG asteroid struck on the
continental shelf, the shallow region

land and deep ocean.

The impact triggered a localized
tsunami, large enough to kill creatures

region. But it also sent a huge
shockwave into the bedrock.

There's going to be a shockwave 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

current Richter scale. It would have
actually driven its legs up into its

cavity, killing it instantly.

There's all manner of mayhem and death
taking place at this time. There was no

escape in this event.

The initial shockwave would have
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 tsunamis.

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.

How could one space rock hitting the sea
cause a global catastrophe?

When you have a big rock hitting the
ocean, the biggest danger is not from

waves, but actually from the steam that
it creates.

The impact.

vaporized trillions of tons of seawater.

This steam rose up into the atmosphere
where it condensed into water vapor.

Water vapor is a greenhouse gas.

So that's then 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. You will actually affect

very significant climate change very
quickly as a result of that impact.

Within weeks of the asteroid strike,
water vapor in the atmosphere caused

temperatures to rise.

But that was only the start.

The impact also blew out 10 trillion
tons of rock, ash, and dust.

This asteroid is so big, it's 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

the moon, circled around the Earth, all
this ring of material falling back onto

the Earth, and it was like the sky
itself was on fire.

So you not only do have rocks falling on
you, but they're molten, and these

rocks will start catching plants and
anything else on fire.

Soot and ash rose up into the
atmosphere, blocking the sun.

Material was thrown into the atmosphere,
plunging the planet into a nuclear

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

Without sunlight, temperatures seesawed.

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

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

Just everything gets destroyed.

But over the long term, you're talking
about ash kicked up in the atmosphere,

extremely cold weather, basically a
global ice age.

The freezing temperatures killed off
most plant life.

Imagine how that affected life on Earth.

No plants, and the base of the ecosystem
collapses.

This dark nuclear winter lasted two
years and prevented plants from

photosynthesizing.

So if plants can no longer use
photosynthesis to live, they'll die. And

with no plants, then you have no food
for these larger animals.

And so anything that eats those animals
will also die. If you lose your plants,

you're going to lose your large -scale
life.

First, plant -eating herbivores died
off.

than meat -eating carnivores.

Most of the dinosaurs were just unable
to find food and to survive through the

cold, long night.

The global devastation wasn't over yet.

The rock of the continental shelf, where
the asteroid hit, contained carbon and

sulfur.

These carbonate rocks were heated and
vaporized and released carbon dioxide

the atmosphere, yet another greenhouse
gas. So you're vaporizing a lot of

sulfur, a lot of salt of different kinds
that are then lofted up into the upper

atmosphere that then plays havoc on the
climate.

These greenhouse gases built up in the
atmosphere.

forming a warming blanket.

These gases triggered 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.

That actually made it impossible for
certain microbes to actually live. And

they're the basis of the food system. So
really it changed what could actually

live in the ocean and how much could
live there.

Dead zones appeared in the oceans just
as they had on land.

Nearly three quarters of life on Earth
died.

All from what asteroid impact?

To prevent it from happening again, we
need to track all potentially dangerous

asteroids. But that's not easy, because
these floating space rocks can change

direction.

Security cameras record a flash in the
sky.

The flash was from a three -foot
asteroid exploding in the atmosphere.

It blew up in the atmosphere and rained
down. And people saw that. It was very

noticeable. And they went and they
collected those meteorites. And then

tried to figure out what they were
looking at.

The debris was sent for fragment
analysis.

I have a piece of one here.

So first, on the outside, you can see it
has a really black fusion crust. This

is from when it fell into the Earth's
atmosphere, so it was melted.

But when you look on the inside, it
reveals this beautiful, very light

fine -grained material.

And so these meteorites are incredibly
distinctive and really beautiful.

The meteorites are rocky.

Their 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

the Dawn mission that actually went to
Vesta and took a look at it very

carefully, so we know the composition
very well.

And so now suddenly here was a new kind
of meteorite that's in Turkey that

matches the Vesta family of meteorites.

But how can we be sure that these bits
of space rock come from Vesta?

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?

Tracing the trajectory of the Turkish
meteorite back took the scientists all

way to the 328 -mile -wide Vesta.

When they studied Vesta's surface, they
found further evidence.

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

that is around the same age of the
Turkish meteorite. So that really

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

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

22 million years ago, some very large
impactor struck Vesta and made a huge

crater. And some of the rocks from that
crater actually escaped from Vesta's

gravity and were lofted into space.

Some of these rocks from Vesta went into
orbit that intersected with Earth.

22 million years later, one blew up over
Sarah Chichak.

The Saracicic meteor shows that the
asteroid belt is an unstable

Asteroids frequently strike other
asteroids.

That's actually happening all the time.
Things are running into each other in

our solar system right now. And so that
makes it really hard for us to track all

of those objects because we don't
actually know what happens after they

with each other. Now things are totally
different. That changes the whole

system.

Each collision makes more asteroids.

There's many different possibilities of
what could happen when asteroids

collide. Imagine a roller derby
situation.

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

blown apart.

That sends fragments flying all through
the main asteroid belt.

And then those 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 you

get shrapnel. And now you've got not one
big one and one smaller one. You've got

one big one, one smaller one, and
millions of little ones.

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

be potentially hazardous.

As the solar system ages, the number of
asteroids increases.

Each new space rock.

travels on a new course, which could
intersect with Earth.

So we're constantly producing new
asteroids and big collisions in the main

asteroid belt.

And these are producing the small
asteroids that will eventually drift

the solar system.

Tracking this constantly evolving
population of asteroids gives scientists

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 orbit of
asteroids and their movements.

Because one tiny little change can have
huge dramatic

impacts for its possible future.

Figuring out exactly where they're going
to go and keeping track of how they

interact with each other, this is a huge
endeavor.

The sheer volume of asteroids can affect
the behavior of other asteroids as they

gravitationally interact.

Think about your roller derby player,
skating in circles.

The path they're going to follow will
evolve the more people you plop down on

that track.

They start interacting with each other
and their trajectory will change.

The more crowded you make the solar
system, the more things there are to

your orbit of your individual asteroid.

It's not like air traffic control where
there's a known amount of airplanes and

they all follow a plan.

This situation is further complicated
because asteroid orbits can be affected

other, more subtle forces.

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

Honestly, Yorp is more fun to say.

The Yorp effect is caused by sunlight
hitting an asteroid.

Light is made up of photons that are
traveling, and these photons actually

momentum. So when light shines on
something, it actually pushes on it.

When sunlight hits an asteroid, the
photons give it a tiny push, enough

to change the space rock's trajectory.

Asteroids can change course, which makes
tracking them hard.

Comets stay on course, but they are much
harder to track.

We track asteroids pretty regularly
because they hang out in the inner solar

system. We can look for any potential
dangerous ones.

The comets are a completely different
story because they come in from random

directions at random times.

They are completely unpredictable.

Which is why we've only detected a
fraction of what's out there.

There are millions and tens of millions
of them. Guess how many we found?

6 ,300.

That means that we virtually found zero.

The low number is because long -period
comets spend much of their orbit over 10

billion miles away, where they are
invisible.

The trouble with long -period comets is,
of course, their periods are very long.

And so we only see a small part of their
arc. They go very distant into the

solar system.

And so it just makes them difficult to
follow when they get a very long way

the sun. We're not able to track their
orbits anymore.

And so it becomes a little bit more
guesswork.

We don't see them until they're already
in the inner solar system, inside the

orbit of Jupiter.

We never really know about them until
they've already started their passage

really far away and started their dive
into the solar system at really high

velocity. We really only discover these
comets at the very last minute.

You could spot an asteroid 10, 15 years
in advance.

These comets, that's basically
impossible.

We may have a couple of years warning
for them.

When we know an asteroid is really
heading our way, it's time to fight

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?

This is something where our science
fiction ideas have gotten it almost

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

You can send astronauts to an asteroid,
put a nuclear bomb in it, and blow it up

into lots of little bits that then burn
up harmlessly in our atmosphere.

Yeah, it doesn't work that way.

Blowing up an asteroid would make the
problem much worse.

You're no longer dealing with just one
marauding 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

enjoy.

The problem with using a nuclear device
is that the products that rain down on

Earth are now radioactive.

If a dangerous asteroid is on its way,
blowing up an asteroid would be a last

resort. A less risky method is to
deflect it off its collision course.

A small nudge early enough can change an
asteroid's trajectory away from Earth.

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

at it, just touch it slightly. By the
time it gets to Earth, it's way off

course.

NASA is investigating several techniques
to change an asteroid's path, including

a nuclear burst.

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

with the device on a spacecraft, and
then the device would be detonated at a

certain height above the surface.

That heats up the surface of the
asteroid, which vaporizes. You get

rock or metal, which blasts off the
surface, and that's how a rocket works.

you blow up a bomb here, and it winds up
pushing the asteroid in the other

direction.

To prevent any potential nuclear
fallout, NASA would detonate the bomb a

way from Earth.

Any deflection attempt has to be done
years in advance, which means it would

done on the other side of the solar
system from us, on the opposite side of

object's orbit.

That means that all of the vapor made
during the explosion gets blown away by

the solar wind.

NASA is also investigating other less
explosive methods of deflecting an

asteroid.

D -STAR would blast the asteroid with a
laser.

We hit it with the laser, material
vaporizes and flies off the asteroid.

And because of Newton's third law, which
is that for every action there's an

opposite and equal reaction, this means
that vaporized material moving off in

one direction moves the asteroid in the
opposite direction.

Both the laser and 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

DART is a kinetic impactor and will try
to knock the asteroid off work.

At NASA, for the longest time, all we've
been able to do is theorize about how

we changed their path. But now, for the
first time, we're actually going to

practice it.

Leading this groundbreaking mission to
bump an asteroid off its course is Dr.

Andy Chang.

DART is the first planetary defense
mission that we've ever done, where we

a spacecraft, we fly the spacecraft into
the asteroid to change its course and

make it miss the Earth.

DART's target is a 525 -foot space rod
orbiting the large near -Earth asteroid

Didymus. We picked the near -Earth
asteroid Didymos as a target for the

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

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

The Didymoon asteroid is moving at over
36 ,000 miles an hour and is over 4

million miles away.

So how do you move a 10 .5 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 and momentum to that
moon.

DART will hit the target at around 14
,000 miles an hour.

The speed of the DART impact.

will be more than nine times the speed
of the rifle bullet from AK -47.

The impact will give the asteroid a
small push.

To work out how big a push, we test
impacts with the Ames vertical gun.

At the NASA Ames Research Center in
California, there's a very special

called the Ames Vertical Gun Range.

It's a hypervelocity gas gun that allows
us to shoot little metal BBs at rock

targets at speeds up to like 13 ,000, 14
,000 miles per hour.

The gun replicates the impact the DART
mission will make.

It reveals that an impact will blow off
a small amount of debris, but at an

extremely high speed, enough to get 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 process acts like
a little rocket engine.

That provides an additional momentum
change, momentum push, to the target

itself.

The combined push from the kinetic
impactor and the ejected debris is tiny,

around 9, 10 thousandths 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

comes.

This isn't some small rock prototype
that we're doing this test on. This is a

real dress rehearsal for an asteroid
that could destroy cities or even maybe

send the Earth in chaos.

The moon of Didymus is a solid lump of
rock.

Will a kinetic impactor like DART work
with a rubble pile asteroid like a

Pophis? When you shoot a rubble pile
with a projectile, it's a little bit

like trying to punch a sandbag. You get
a lot more of the energy that's absorbed

into just moving the sand around inside
the bag than ejecting it.

And so rubble piles might be a little
harder to move by this method.

We don't know if we can deflect a rubble
pile asteroid like Apophis.

They remain a clear and present danger
and something we might not buy.

But there may be a space lifeboat.

In 2018, scientists re -examined 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,

threw up a bunch of rocks, some of those
rocks fell onto the moon. And that's a

meteorite on the moon, but it's from
Earth.

Supercomputer simulations of the KPG
asteroid strike reveal how the impact

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

surface.

We now know that material ejected into
space from asteroid impacts can travel

other planets as well, which would
explain the 100 Mars meteorites. we

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 into 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.

This planetary interchange may give life
on Earth a lifeboat should another

giant asteroid hit our planet.

If you think about such an impact today,
you know, the chances are high that a

lot of life will be wiped out. Much of
life, probably all of human life.

It's certainly possible that a big
enough asteroid strike can completely

sterilize a planet.

Talking about no life whatsoever.

Not to put too fine a point on it, but
if there's a dinosaur killer asteroid

there and it hits the Earth, the chance
of humanity's survival of such a thing

as a species, not great.

Humans may not survive, but some
scientists believe some simple life

could.

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

atmosphere could contain microbial life
that, when it falls back down onto the

ground, could reseed the life on that
planet.

Some bacteria can survive the harsh
conditions of space.

These creatures can cope with an
asteroid strike, reentry, and landing

Earth's surface.

I think in terms of life on planet
Earth, I think we've learned that we

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 eke through.

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

We know that life first formed on the
Earth.

well over 4 billion years ago, and has
never been wiped out in all of that

There's always been something after
every major mass extinction.

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

An asteroid strike on another world may
be how life started on Earth in the

first place.

There's an interesting idea that an
asteroid strike on another planet could

actually seeded life on Earth. And the
way this works is you have 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.

Speculative, but it's kind of a cool
thought.

Life -seeding asteroids may have hit us
in the past, and other asteroids will

hit us in the future.

One of them may be a pulpit, arriving in
less than half a century.

Maybe we will deflect it.

Maybe it will miss us all on its own.

Either way, We need to keep tabs on it.

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

like I'm advocating for more jobs for
astronomers, we need to keep looking at

the sky.

We need to look at the sky longer and
deeper with more sensitive instruments

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

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

down, destroying our planet.

We can actually see it before it gets to
us and decide what we want to do about

it.

Earth's history is littered with
asteroid strikes.

Some wiped out millions of feces.

Some may have seeded life in the first
place.

What the future holds in our
relationship with these space rocks, no

Even though the chances of something
really large hitting the Earth are

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

hit us at any time.

That's part of being alive.

There's no guarantee tomorrow will
happen. But what there is is a high

likelihood that you'll still be safe
tomorrow.

Impacts from space are rare.

But if they do happen, it's a huge deal.
And so you've got to put those two

things together.

That means we've got to pay attention.

Those impacts have happened many times
in the past, and they're going to

continue to happen many times in the
future.

Fortunately, it's not probably in our
immediate future.

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

So you're unlikely to get in a car
accident, but if you drive enough,

going to get in a car accident.

Over a century timescale, yes, we should
be concerned about these. But over the

daily, weekly, monthly, even yearly
timescale... I wouldn't sweat it too

wouldn't say we should lose sleep over
an asteroid or comet striking Earth, but

the reality is it will happen again.

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

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

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