A dangerous asteroid is heading towards Earth.
It's the size of the empire state building,
and it's travelling at 16,000 miles an hour.
It's called Apophis, after the Egyptian god of chaos.
It will fly close to us in 2029.
It won't hit us... This time,
but when it returns in 2068,
that could be another story.
If it blows up over a city, millions of people will die.
This could be the most devastating single event
in U.S. history.
Earth is stuck in the crosshairs
of a potential asteroid strike.
Apophis is one of around 2,000 potentially hazardous asteroids
that present a real and present danger.
Asteroids have hit us before, and they will hit us again.
As far as cosmic dangerous go,
they're number one on the list.
This is not a drill.
If we do nothing...
This is our future.
Captions by vitac... www.vitac.com
captions paid for by discovery communications
December 2018.
The U.S. military detect a huge explosion
in the Earth's atmosphere
high over the Bering sea
off the coast of Alaska.
When an explosion of this magnitude is detected,
everyone's mind goes to the same thing... nukes.
But when the real answer was found and it was determined
that it didn't even originate from Earth,
that was even more shock.
The cause of the blast...
an asteroid.
This asteroid was 30 feet across...
something like that...
over a thousand tons,
but it was moving at 20 miles per second,
over 70,000 miles an hour.
This asteroid was small, and it exploded
in the atmosphere over the ocean,
so nobody was hurt.
But if it had been bigger
or it had come in over a different place
or it had been moving a lot faster,
this could have been a dangerous object.
But the scariest thing about it
is that we didn't see it coming.
So far, we've been lucky.
But near misses happen all the time.
About once a year, we get something
the equivalent of a nuclear bomb going off in our atmosphere.
And while that sounds horrible,
most of these happen tens of miles up...
Over open ocean, where we go on completely oblivious.
We may be oblivious to most of the threats from space,
but they are very real.
We're going to get hit.
Over a certain amount of time,
an asteroid impact is inevitable.
It will happen 100%, absolute certainty.
NASA considers the threat from the skies so severe
it has made protection from asteroids a top priority.
These events are not rare. They happen.
And of course it's up to us to make sure that we are detecting
and characterizing, tracking all of the near-Earth objects
that potentially could be a threat.
This is not about Hollywood. It's not about movies.
This is about ultimately protecting the only planet
we know right now to host life,
and that is the planet Earth.
To help plan protecting our home,
we carry out Earth defense simulations.
For three days,
200 scientist at the planetary defense conference
battle a simulated asteroid 20 times larger
than the Bering sea space rock.
We practice, "alright, what if this hits a major city?
What would we need to do?"
By running potential impact scenarios,
we can prepare for a real asteroid strike.
This is like a fire drill that you would do at school
or at work, where you practice
and think about, okay, what if?
Where are the exits? How do I get out?
How fast do I get out?
The drill starts with the discovery
of a simulated Earthbound asteroid.
So, the first information is there's a big asteroid
coming towards the Earth.
Then we get a better estimate
of how big it is, how fast it's going,
and where it's going to hit.
The asteroid is heading straight for Earth
with Denver, Colorado, in its sights.
The planetary defense scientists
send up a simulated spacecraft to smash into the asteroid
and push it off its path.
But it's a big gamble.
You can push it the wrong way.
You can potentially have unintended consequences.
In the simulation,
the spacecraft strikes the asteroid...
Deflecting it away from Earth.
But the impact dislodge is a 200-foot chunk,
which is now heading straight towards the eastern seaboard.
So there's this one last piece
that is now going to hit New York.
We know that something that size
is going to have citywide consequences.
That is huge. That's a horrible impact.
When you're actually in the conference room
and you understand eventually
that New York City is going to be destroyed...
And you're having strategies about how to evacuate people,
all the timing, when you're doing the simulation
you're in your head.
You're thinking about these things.
You're trying to reason them out,
but can you imagine the feeling in your gut, in your heart,
if this was real?
If this were real, the chunk of asteroid
would strike Earth's atmosphere
at 43,000 miles an hour.
As the space rock hurtles down, it collides
with molecules in the atmosphere which buffet the falling rock.
It's kind of like doing a belly flop into a pool, right?
You're going from the vacuum of space
into the dense lower atmosphere in mere seconds.
And that's an incredible amount of pressure
to put on the object.
The asteroid slams into the air
ahead of it, compressing it violently.
The surface of the asteroid gets hotter and brighter.
It's actually the air itself that's glowing luminously
from the heating of the shockwave,
the world's most intense Sonic boom if you will,
that heats the air to incandescence
as the object passes through.
So that's the source of that brilliant illumination.
This bright, burning asteroid is called a bolide.
We witnessed one descending over the Russian city
of Chelyabinsk in 2013.
All of a sudden, there was a huge fireball
streaking through the sky,
and people had no idea what they were witnessing
because it looked like the sky was on fire.
It was insanity.
As the asteroid descends,
the compression of the denser air beneath it
starts to flatten and even disrupt the falling rock.
There's a high pressure on the front,
there's no pressure on the back
and it's being super heated.
And that intense temperature causes the air to glow,
which is how we see this streak of a meteor.
And it also disintegrates the asteroid itself.
It's hard enough to literally melt rock.
This can often lead to them exploding.
The combination of heat and pressure invade
the falling asteroid, causing it to blow up.
Most asteroids don't reach the ground
before they completely disintegrate
in a tremendous release of energy.
This is what we call an air burst,
and we learned a lot about these
while we were testing nuclear weapons after world war ii.
Some of these bombs were blown up
underground and on the ground,
but they found out when they blew up bombs above the ground,
it actually did more damage.
It was more widespread damage.
The explosion of the Chelyabinsk asteroid
sent out a powerful shockwave at thousands of miles an hour.
The blast traveled over 100 miles.
It damaged 7,000 buildings
and put 1,500 people in the hospital.
All of the injuries pretty much came from people
who saw, "oh, what's that bright flash in the sky?"
And they came close to a window to look and see what it was,
and then the pressure wave hit and blew glass in their face.
The Chelyabinsk asteroid was only 65 feet across.
The rock in the defense simulation
is three times more massive,
and it's heading straight for New York City.
Imagine what would happen if an explosion a thousand times
greater than that over Hiroshima hit New York.
We're talking about an utter complete destruction of the city
and millions of people.
With so little warning,
the only option would be to evacuate New York City.
How do we get everybody out of New York City
within just a few days?
That's where panic sets in.
That's where fear would really become the dominant emotion.
Anyone left in New York City
would see the bolide racing in...
...followed by a blinding light...
As the asteroid explodes above the city.
The blast would be equivalent to the largest nuclear weapon
ever detonated on Earth.
Buildings would be flattened, melted.
There would be fires for miles around
in the first moments of the explosion.
A million people could be killed instantly
and many more would die later in the rubble,
in the ruins of what would happen there.
Everything within nine miles of the blast epicenter
would be completely destroyed.
The intense heat and pressure would wreck buildings.
It's the worst possible day for new yorkers,
and not just the city itself.
There's something like 15 million people
living in the New York area.
The shock wave would race out over 250 square miles.
This would certainly be the worst disaster
that the U.S. has ever experienced.
We're talking about millions and millions of people
displaced, affected within an instant.
This scenario is just a simulation... For now.
The asteroid Apophis is heading our way.
If it hits Earth,
it might not just kill a city.
It could kill a whole region.
I wouldn't exactly want to be there
when that happens... want to be very, very far away.
Apophis will skim Earth in 2029.
But its path could change,
possibly turning a future miss...
Into a direct hit.
April 13, 2029,
a speck of light races towards the Earth.
It's an 1,100 foot wide asteroid called Apophis.
We are about to have an extremely close shave.
It's the closest approach of any asteroid
that didn't actually hit us for a long, long time.
It will be 10 times closer than the moon itself.
It'll be so close that it will be brighter
than some stars.
The football-stadium sized Apophis
will race over the Atlantic.
If it were sitting on the surface of the Earth,
it would weigh about 50 million tons,
something like that,
and that is not the place you want it to be.
You want it to be in space and far away.
When we discovered Apophis in 2004,
we thought it might be on a collision course with Earth
with a potential impact
greater than the largest atomic bomb ever exploded.
The largest nuclear device, atomic device
ever detonated on our planet was the Tsar Bomba bomb in Russia,
so something like 55 or 56 megatons.
When Krakatoa exploded in 1883
that was something like 200 megatons.
Apophis' impact would be 450 megatons.
If something like that were to happen over New York City
or Washington D.C., you're going to lose the city.
The impact would be at least 10 times greater
than the simulated asteroid strike on New York.
Well, when you put it in those terms,
that's just plain scary.
In a word, an impact from an Apophis-sized asteroid
would be bad... very, very bad.
Apophis' orbit will cross Earth
every seven years this century.
It won't hit us in 2029,
but this close encounter could change Apophis' orbit.
When a small asteroid encounters a bigger body like a planet,
it's like a bunch of roller derby players.
Most of them are clumped together,
but maybe there's one just on their own particular orbit,
and as they circle around,
as they get close to that larger clump,
there'll be some interactions...
potentially violent interactions...
that will change the future trajectory
of that lone roller derby skater.
And the next time around,
it might be a wide miss or it might be a head-on impact.
It's the same in the solar system.
The combined gravity of the Earth and moon
creates what's called a gravitational keyhole,
a gravitational sweet spot,
which could change Apophis' orbit.
That will change the potential future trajectory of this rock
and might make it totally harmless
or might increase the chances
of an impact even further in the future.
Because of the gravitational keyhole,
there's still a small chance
that Apophis will hit Earth in 2068.
That is the important lesson that Apophis taught us...
you can miss the Earth,
but if you pass through one of these keyholes,
at some time later, you will hit the Earth.
We now know Apophis will miss the keyhole in 2029,
but there are other keyholes and other close passes.
Apophis is not a lone threat.
There are an estimated 832,500 asteroids
orbiting the sun.
Most asteroids live their lives
perfectly peacefully past the orbit of Mars
or trailing Jupiter and don't mind anybody else,
don't cause any troubles, but some asteroids
are on very particular orbits
that cross the orbit of the Earth.
These asteroids have left the stable orbit
of the asteroid belt
and moved into orbits that get near our own.
These asteroids are called near Earth asteroids
or N.E.A.S for short.
The near Earth asteroid population is interesting
and potentially dangerous because they are the ones
that actually cross the orbit of the Earth.
So they're most likely to have, at some point
in the future, an impact with the Earth.
Most N.E.A.S pose little or no threat to Earth.
But we've detected over 2,000,
including the 1,200 foot Apophis that do.
These are called P.H.A.S...
potentially hazardous asteroids.
The difference between a near Earth asteroid
and a potentially hazardous asteroid is distance and size.
Anything can get near the Earth,
and that could be 20 million miles away,
something like that, and be a near Earth asteroid,
but a potentially hazardous one can hit us,
and it's big enough to do damage.
So something that over the next hundred years or so
has a chance of hitting us and doing damage when it does...
that's a potentially hazardous object.
P.H.A.S are asteroids that are 460 feet or larger
that could collide with Earth.
Take a 400-foot asteroid... if it hits,
it would release as much energy
as 3,000 Hiroshima nuclear bombs.
In July of 2018,
NASA published a map
of all the known N.E.A.S and p.H.A.S.
The animation tracks their discovery
from 1999 through 2018.
Every time I look at this animation,
it does make my heart stop a little bit
because it looks like we're in the middle of a swarm
of angry bees circling all around us.
In 1999, we'd identified
under 300 N.E.A.S
scattered through the inner solar system.
10 years later, we'd found 500 more.
By 2018, we'd discovered 18,000 near Earth asteroids,
but we estimate there are millions out there.
It seems like we could never find all the asteroids.
They just keep coming.
It's like we're fighting an army of zombies.
Zombies that keep hurtling our way,
hitting the Earth at up to 64,000 miles an hour.
That is very, very fast.
That is much faster than a rifle bullet.
And that's the key to its destructive power.
When a really fast and really large asteroid hits,
the impact is off the charts.
The blast is so intense,
it can melt or even vaporize rock.
January 2019,
a total eclipse of the moon.
Astronomers train their telescopes
on the darkening lunar surface.
They capture a bright flash
that lasts around a quarter of a second.
It was recorded. There were a lot of live webcasts
and things like that going on at the time,
and you can see this flash of light.
What the heck was that?
At first, the cause of the flash was a mystery.
It turns out it was actually a meteorite hitting
the surface of the moon, and because it was dark
and because we were all looking at it,
we could actually see it.
The moon's dark surface gave us a unique view
of what happens when an asteroid strikes.
What was so exciting about being able
to see this impact on the moon in a dark area
is that we could actually look at the light that it produced
and then back-calculate
exactly what the size of the impactor was.
We worked out that the impacting asteroid
was just 20 inches wide.
The crater it blew out was 45 feet across.
How can something so small be so destructive?
The two things that matter the most are how fast it's going
and how massive is the thing.
The more massive, the bigger the boom,
the faster the bigger the boom.
Speed and weight are two very important factors
to assess how much damage an asteroid will do.
Just like a boxer... if a tiny person like me
were to swing a punch,
it would do a lot less damage than a heavyweight champion.
Same thing with asteroids.
The bigger they are, the bigger the punch.
But the same thing is fast, right?
If I hit you really slowly, it's not gonna hurt.
I have to really wind back and pap.
That's what happens with an asteroid.
The damage from an asteroid strike
is determined by its kinetic energy.
Kinetic energy depends on two things...
speed and weight.
Of the two, speed matters most.
If you double the mass, you double the kinetic energy,
but if you double the velocity,
you get four times the kinetic energy.
Three times the speed, nine times the impact energy.
10 times as fast,
it has a hundred times the energy,
so the velocity is what's really critical here.
The lunar asteroid weighed only 100 pounds,
but it was traveling at 38,000 miles an hour.
Carrying a huge kinetic energy, which gouged out the crater.
It's the same principle for impacts on Earth.
50,000 years ago, a 150-foot asteroid
hit what is now Arizona.
The impact blasted out an impressive hole
now called Barringer crater.
It's about 3/4 of a mile across,
over 500 feet deep.
You could put the Washington monument
in the bottom of the crater,
and the top of the monument wouldn't quite clear the rim.
It's a pretty impressive hole in the ground.
In 2016, impact specialist Cathy Plesko
visited Barringer crater
to see firsthand what mass and speed
do to the surface of the Earth.
This is awe-inspiring to stand on the rim of a crater like this
understanding just how much energy
it must have taken to excavate this much rock.
The asteroid came in at about 27,000 miles an hour.
It comes slamming into the surface
and just explodes.
Anywhere nearby here
would have seen winds of thousands of miles an hour
as the shockwave came out.
The immense power of an asteroid impact
comes from the kinetic energy
being transferred from the space rock into the surface rock.
It's an extremely violent process,
and it starts with the moment of contact
of the projectile with the surface itself.
It pushes into the crust,
and at first, it's just almost punching, like,
sticking your thumb into dough.
It's only about as wide as the object is.
It's going straight down in,
but then it's meeting resistance from the surface of the Earth.
And so it squishes, squishes, squishes,
until it runs out of momentum, but then it's very compressed
and all of that energy is in a very small space.
As it releases, it detonates like a bomb.
And that's what makes the impact crater.
Simulations of an asteroid strike in the lab
reveal the impact in slow motion.
As the high speed pellet hits the surface,
the sand compresses downwards, then rebounds.
And as that rebound is occurring,
that's when the material is being ejected
out of the crater itself.
You'll see the surface erupting outwards
like the blooming petals of some big rocky flower
as all this debris goes spraying out in every direction.
The 150-foot Barringer asteroid
turned the rock to powder.
66 million years ago,
an asteroid around 200 times larger
and moving one and a half times faster
than Barringer hit Earth.
This asteroid impact... called k-pg...
had so much energy,
it turned rock to liquid.
This thing was immense. It's really hard to wrap
your head around just how big it is.
When it hits the back end of it, it is so far back,
that it's where a modern jetliner would fly.
The k-pg asteroid hit the ground
with a lethal combination of mass and speed.
A trillion tons traveling at 45,000 miles an hour.
Some rock is completely vaporized.
It just becomes a gas.
You have some rock that is melted.
You have some that's thrown out into space.
This material goes up through that and then falls down
and settles down over a huge area.
That might be dust. It might be pulverized rock.
It might be vaporized metal.
It's all of this hot material raining down everywhere.
Some of the rock exploded skywards,
but rock below the surface was slammed by a shockwave
that was completely off the charts.
Rock stopped behaving like rock.
We experience rocks as solid objects,
but if you hit a rock hard enough,
it flows like water.
The k-pg asteroid hit so hard,
it pulverized the rock,
turning it into liquid.
Almost like ripples on a pond moving away
from a stone that's been dropped in it.
It's almost like a splash
in the solid body of the Earth itself,
and like water droplets splashing in water,
you'll see that central peak will kind of splash up
and rise to a high altitude and then come back down again.
We think a process very similar to that probably happened
in the rock itself at the center of the crater,
rising up as high as the Himalayas
before relaxing back down to their current position again.
The material slumps, and so these ripples
are frozen in the rock,
and there are other fragments that go away radially,
almost like the spider web pattern in glass
that you get after it's shot with a bullet.
The k-pg impact blew out a crater
111 miles wide.
It is the third largest confirmed
impact structure on Earth.
A large and fast asteroid heading our way
is always going to be a problem.
So what do we do?
Wait for oblivion?
Or fight back?
The space in the inner solar system
seems calm, stable, and empty.
It's not.
There are tens of thousands of near Earth objects
just whizzing around Earth.
Now, space is big.
They're not gonna hit us every time they orbit the sun,
but this does set up the possibility
that, one of these years,
we're gonna end up at the same spot in space
at the same time as that asteroid,
and then it's gonna be an impact.
We're living in a cosmic shooting gallery.
Asteroids strike the Earth all the time
through history,
and it's gonna happen again.
Scientists are developing strategies
to stop an asteroid from hitting our planet.
Our options... destroy or deflect the space rock.
But first, we need to detect any dangerous asteroids
heading our way.
It's a little bit unnerving to know
that we haven't yet detected all of the asteroids
that exist that could possibly cross our path.
We've discovered a lot of asteroids now,
but we typically discover the big ones.
But for asteroids that are below 100 feet,
there's a lot still out there that we haven't discovered.
And such an asteroid can do some real damage
if it were to explode over a populated area.
To prevent such a catastrophe,
we need to find all asteroids whose orbits cross our own.
Detection is crucial in our defense against asteroids.
And the reason is the earlier they're detected,
the easier it is to deflect them away from hitting the Earth.
You want to do deflection, the first step is detection.
The problem is, asteroids are very hard
to detect.
Finding asteroids and cataloging all their orbits
is really challenging.
They can move quite fast across the sky,
and they might go away
on the other side of the sun for years and years and years.
So we can't see them.
And even when they are on this side of the sun,
they're hard to spot.
But the problem is, they're very small
and they're very dark,
and when I say very dark, I mean really dark,
like a lump of coal.
So how do you find a small, dark rock
just wandering around out there in the solar system?
The Catalina sky survey has the answer.
The huge telescope in the mountains above Tucson, Arizona,
takes a series of images over a 20-minute period.
It's hunting for anything that moves
because stars don't move, but asteroids do.
If it's a really bright asteroid,
we will see some bright points
of light tracking across the four images.
Ah, here we go.
This is a real object.
You can see it's moving across the sky here
from the lower right to the upper left.
We are very, very excited to have discovered one tonight
because this is an object that's approaching near space,
likely in the neighborhood of Earth.
Catalina has limitations.
It can only see visible light,
so a particularly dim asteroid could be missed.
Asteroids are very cold.
They're usually quite far away from the sun,
but amazingly, the best way
we have to find these is infrared light
because things that are cold by human scales
can still be very warm to an infrared telescope.
So even if asteroids are just a few tens of degrees
above absolute zero,
that's still enough heat to detect them.
When the infrared space telescope Neowise
turned its gaze onto asteroids,
it had immediate results.
Neowise has now detected
close to 160,000 new asteroids and comets in our solar system,
and about 780 of those
are things that are near the Earth.
10 of those near objects have been classified
as p.H.A.S... potentially hazardous asteroids.
Without Neowise, we would have missed them.
Using an infrared space telescope
is a way of of better detecting some of the smaller asteroids
and comets in the near Earth vicinity.
Detection is an important first step,
but it only tells us
that there is another asteroid out there.
Once we've spotted an asteroid,
all we know is that it's a tiny dot of light.
We don't know anything else about it.
So when a new asteroid is discovered,
the most important thing is
to determine its path, to track it, to figure out
exactly how it's orbiting around the sun
and how close it's gonna get to Earth.
For that, we have to know where they are now...
so its current location... and measure how fast it's going
and which direction it's travelling.
All of these things together are really important
for tracking where it's gonna be next
and whether or not they're gonna hit us.
To get this information,
we need something much bigger and more powerful.
The Arecibo observatory.
Once Catalina or another telescope
detects a near Earth asteroid in our cosmic neighborhood,
Arecibo's thousand-foot dish swings into action.
They discover these asteroids,
and then once we know where they were,
we can try and point the radio telescope
and see where they are at the moment
and measure their exact location and their trajectory.
Arecibo achieves this level of precision
by using radio detection and ranging,
more commonly known as radar.
The planetary radar system at Arecibo observatory
is the most powerful radar system in the world.
We focus on potentially hazardous asteroids,
which are those that have a high probability of impacting Earth.
Arecibo sends out radio signals
toward the newly detected asteroid.
It emanates radio signals.
Some of them hit the asteroid just like a radar gun from a cop
might hit the side of your car.
That's pretty similar,
but instead of doing it with a radar gun
on the small scale, we're doing at a really big scale
with one megawatt power hitting objects that are
tens of lunar distances away.
And then those radio waves bounce back to Earth
and we detect them again, and by comparing the differences
between what we sent and what we received,
we can get a map of the asteroid itself
and we can get where it's moving and how fast it's moving.
Speed, size, and location of strike
determine the outcome of an asteroid impact.
But the type of asteroid is another factor.
It can mean the difference between survival
or complete annihilation.
The Bering sea asteroid blew up in the atmosphere,
but the Barringer crater asteroid hit the ground intact
with its full force.
Why do different asteroids behave differently?
And what will Apophis do when it heads our way?
Arecibo's radar may have the answer.
When we bounce radar waves off of these objects,
we can get effectively imagery of the surface
of some of these small objects
that we just cannot do with optical telescopes.
This is the radar image of Apophis.
It's so far away that all they could image were a few pixels.
So this is our most recent radar image
of asteroid Apophis.
And you can see it's only a few pixels,
but it does give us information
on what it actually is.
These few pixels are enough to work out
how big Apophis is.
From this image, we can constrain the size
to be about 1,000 feet,
which is about the same size as the Arecibo
radio telescope.
All of that from what were a bunch of pixels.
Knowing the size and mass of an asteroid
is critical to understanding what an asteroid is made of.
If we have the size and the mass, we get the density.
If we have the density, we know what it's made of.
Rock has some density. Metal has a different density.
So we can determine a huge amount about the asteroid
simply by pinging it with radar.
Arecibo's data reveals
that not all asteroids are alike.
There's not just one kind of asteroid.
There are actually several kinds,
and this is important to understand
because they behave differently.
They behave differently if they impact us,
and they behave differently if we're trying to prevent them
from impacting us.
We need to know what these asteroids are made of
if they're gonna hit the Earth
because that drastically alters the potential effects.
Asteroids come in different shapes, different sizes,
and different compositions, and we think that is
because they are the leftovers of planet formation.
To understand how each asteroid formed
and their threat level, we have to go back
4.6 billion years to the start of the solar system.
The reason that there are all these asteroids
floating around in our solar system today
is just because of the early violence of the solar system
as it was forming.
At the birth of the solar system,
the sun ignites,
leaving a disk of gas and dust.
Slowly, over time, planets form.
Lots of planets.
The early solar system was a messy place.
There were a lot more planets, a lot more forming planets.
They would crash in to each other,
they would merge, they would disintegrate,
they would re-form.
This process of accretion of building planetary worlds
was not just, you know, kind of gentle and happy.
It was violent.
It was like a giant cosmic game of pool...
planet smashing into planet.
The leftovers from this violence
formed a ring of junk between Mars and Jupiter.
And now we call that junk asteroids.
They're just basically rubble left over
from the formation of the solar system.
Rocky leftovers became c-type
or chondrite asteroids.
They're quite dense, so big ones can punch through the atmosphere
and hit the ground.
Radar reveals a rarer type of asteroid.
Some of them really stand out because their density
is so much higher than the rest of the other asteroids.
These asteroids are m-type or metal.
Because their mass is great,
they carry more kinetic energy during a strike.
By far, the worst one is this iron meteorite.
This is really heavy, so the difference...
if you were being hit by this,
it would be the difference between being hit by a rock
and being hit by a metal hammer.
We think that both the Barringer
and the k-pg dinosaur killer
were caused by metal asteroids.
But there's another more mysterious type
floating through space.
December 2018,
NASA's spacecraft Osiris-Rex approached
the near Earth asteroid Bennu.
Over time, it drifted out of the main asteroid belt,
made its way into the inner solar system,
until it became a near Earth asteroid,
accessible for our spacecraft to go and visit.
Osiris trained its camera on Bennu.
One of the biggest surprises on arrival of Bennu
was the large number of large boulders on its surface.
Bennu is really littered with huge boulders
and littered with medium-sized boulders
and littered with small boulders.
Bennu is not a solid lump of rock.
It's made up of thousands of bits of rock
forming what we call a rubble pile.
These asteroids aren't big, singular, spherical balls
of rock,
but rather they're literally piles of rubble.
They're all sorts of pieces and fragments
from another asteroid that had previously
been disrupted that have all come back together
and formed literally a pile of rocks held together
by their own gravity.
We think rubble piles formed from collisions
inside the asteroid belt each impact blasted bits off.
Then, over time, they came back together
to form a loose pile of rocks.
Imagine taking a big cosmic dump truck
full of gravel and rubble
and dumping it out there in the space
and letting gravity weakly hold it together.
When scientists probe deeper into Bennu,
they found another surprise.
It's full of holes, like Swiss cheese.
If you could slice open one of these asteroids,
you'd see there are a lot of voids.
In fact, 60% of what we're looking at is a void space,
so they're actually really fluffy.
So even though they're made of rocks,
they're sort of the lint of rocks.
Bennu helps us understand Apophis.
Radar data shows that Apophis is also a rubble pile.
If you look at Apophis, we really want to know
how its orbit will evolve in the future.
What we learn at Bennu about similar-sized
rubble-pile asteroids might help us understand
the future of an asteroid like Apophis.
So what would happen if the rubble pile
called Apophis hits Earth?
You probably don't want that to hit you still,
but it definitely makes it a lot weaker
than something like a solid rock
or even more, a chunk of nickel iron metal.
Does its composition make it any less of a threat?
A rubble pile like Apophis is especially unnerving
because we don't know, when it interacts with the atmosphere,
if it's gonna stay as one solid piece,
will it break up.
When these rubble piles start interacting with planets,
if they fly near a planet, they can get pulled apart
into all of their little pieces.
Or if they enter the atmosphere of a planet
to impact the surface, they might slowly get pulled apart
as they enter the atmosphere
and end up being an array of little impacts
instead of one big single impact.
But what would happen if these impacts occur at sea?
Will our oceans save us,
or will a giant Tsunami wipe us out?
2019,
U.S. researchers discover deposits of fossils.
They contain both the remains of land and sea creatures.
You see things that are all jumbled together,
so you'll have fossils of sea creatures.
You'll have ocean deposits that are mixed up
with coastal deposits and onshore deposits,
and you see those deposits in places
that are very, very far away
from where you would expect them to be.
And so this material was obviously thrown
very far inland.
The jumbled deposits
suggest that the creatures were killed at the same time
in a huge and violent event,
something powerful enough
to sweep ocean-dwelling creatures far inland.
A Tsunami.
Tsunamis are usually created
when the ocean floor moves suddenly.
The ground picks up the entire ocean
and shakes it up and down,
and it's sort of like taking a rope and shaking it,
and it moves all across the ocean floor
and ocean surface until it reaches land.
The biggest recent Tsunami was caused by the Earth's crust
at the bottom of the ocean lifting slightly,
so this means that that entire length of crust
that lifted displaced the water above it,
so the waves, the tsunamis that result,
are really long and wide,
and it can travel across the ocean
at tremendous speeds and up on land.
Is this what happened to the fossilized creatures?
Were they killed by a huge Tsunami?
Clues come from dating the preserved remains.
They're 66 million years old.
From the same time a six-mile-wide asteroid
crashed into the sea off the Yucatan peninsula in Mexico.
Are the two events connected?
Do ocean-impacting asteroids trigger tsunamis?
We used to think that a big asteroid
impacting in the ocean would drive a tremendous Tsunami,
a huge wall of water out at very rapid speeds,
which would basically scour clean everything.
Now new research from 2018 suggests
a very different scenario.
Scientists use super computers to model asteroids
hitting the deep ocean to work out how much of
the asteroid's kinetic energy is converted into a Tsunami.
In the simulations, a 1,600-foot asteroid
hits the ocean at 20,000 miles an hour
and dives into the water.
As it goes deeper in, of course it's meeting a lot
of resistance and it slows down and it compresses up.
It compresses and compresses and compresses, and then finally
it runs out of momentum,
and it's at an extremely high pressure.
The huge pressure causes the asteroid to vaporize.
Temperatures hotter than the surface of the sun
turn trillions of gallons of water into steam.
The blast creates a huge short lived cavity
in the water's surface
and a splash curtain, a wall of water,
that leaps up several miles.
This curtain then collapses and water falls
back into the cavity, shooting a column of water
five miles up.
This very tall column can't support its own weight
and collapses back down.
The collapse of so much water triggers
a wave 1,200 feet high.
Could this become a huge Tsunami?
If we think about a meteor striking the ocean,
we want to understand how far the waves
might propagate from the site.
We could actually just use a stone and throw it into a pond,
and you might think, "okay, well, it's a big stone,
it's going to make a really big splash,
and that's just going to extend out a long distance."
But it turns out the splash stays the biggest really close
to where it impacts.
And then the ripples die down after that.
So let's try that.
Big splash in the middle.
And we see the ripples going outward,
but they're really pretty small compared
with that initial big splash.
It's the same with an ocean impacting asteroid.
The impact creates surface waves that die away quickly
because only a small amount of the asteroid's kinetic energy
gets into the water.
It's actually pretty tough to make
a Tsunami like that.
The energy of the asteroid doesn't couple well
with the water to drive this wave.
Instead, most of the energy
goes into vaporizing the asteroid itself
as well as all of the water around it.
Only 1% of the asteroid's kinetic energy
goes into making a wave.
So only low energy waves form, too weak to become
giant tsunamis traveling hundreds of miles.
So what caused the jumbled fossil deposits
found thousands of miles away from the impact site?
We don't think there could be that much energy
still transmitted that far away from the impact site.
Instead, there has to be a different source of energy
that created different waves
right about the same time as that impact event.
Research from 2019 may have the answer.
The KPG asteroid struck on the continental shelf,
the shallow region between land and deep ocean.
The impact triggered a localized Tsunami large enough
to kill creatures in the region.
But it also sent a huge shock wave into the bedrock.
There's going to be a shock wave driven
through the ground.
That probably would have killed anything in the area.
If you had a dinosaur that was standing on
the Gulf coast of what is now the United States,
that animal would have experienced a seismic pulse,
an Earthquake that is stronger than anything
on our current Richter scale.
It would have actually driven its legs up into its body cavity
killing it instantly.
There's all manner of mayhem and death
taking place at this time.
There was no escaping this event.
The initial shock wave smashed into the ground rock
and traveled through the Earth's crust.
The impact would have shaken the crust of the Earth,
which also would have triggered Earthquakes around the world,
which themselves may have triggered secondary salamis.
Secondary tsunamis thousands of miles from
the impact site killed both land and sea creatures.
The KPG impact went on to wipe out 70% of all life on Earth.
So how did one asteroid strike cause a global kill zone?
66 million years ago, 70% of life on Earth died
after the KPG asteroid strike.
How could one space rocket hitting the sea cause
a global catastrophe?
When you have a big rock hitting the ocean,
the biggest danger is not from the waves
but actually from the steam that it creates.
The impact vaporized trillions of tons of seawater.
This steam Rose up into the atmosphere
where it condensed into water vapor.
Water vapor is a greenhouse gas.
So that's done going up into the upper atmosphere,
and it's trapping heat,
but at different layers it's making clouds.
It's just throwing everything off kilter.
Water is a very effective greenhouse gas as you
will actually affect some very significant climate change
very quickly as a result of that impact.
Within weeks of the asteroid strike,
water vapor in the atmosphere caused temperatures to rise.
But that was only the start.
The impact also blew out 10 trillion tons of rock,
ash, and dust.
This asteroid is so big, six miles wide.
It's punched a hole in the air.
There's like a column of low density, a chimney,
that goes from the ground up to the top of the atmosphere.
And that means there's very little air resistance
in that tunnel.
These rocks can actually blast up into the chimney
and find it easier to get up out of the atmosphere.
It sent that material flying up halfway
to the orbit of the moon, circled around the Earth.
All this ring of material falling back on to the Earth.
And it was like the sky itself was on fire.
So not only do you have rocks falling on you,
but they're molten, and these rocks
will start catching plants and anything else on fire.
Soot and ash Rose into the atmosphere
blocking out the sun.
Material was thrown into the atmosphere,
plunging the planet into a nuclear winter.
It was complete chaos, and it went dark for two full years.
Without sunlight, temperatures dropped.
Just months after the impact, the planet cooled by 20 degrees.
In the immediate area, there's just tremendous destruction.
Just everything gets destroyed.
But over the long term, you're talking about ash
kicked up in the atmosphere, extremely cold weather,
basically a global ice age.
The freezing temperatures killed off
most plant life.
Imagine how that affected life on Earth.
No plants and the base of the ecosystem collapses.
This dark nuclear winter lasted two years
and prevented plants from photosynthesizing.
So if plants can no longer use photosynthesis
to live, they'll die.
And then with no plants, then you have no food
for these larger animals.
And so anything that eats those animals will also die.
If you lose your plants,
you're going to lose your large scale life.
First the plant eating herbivores died off,
followed by the meat eating carnivores.
Most of the dinosaurs were just unable to find food
and to survive through the cold long night.
The global devastation wasn't over yet.
The rock of the continental shelf where the asteroid hit
contained carbon and sulfur.
These carbonate rocks were heated and vaporized
and released carbon dioxide into the atmosphere.
Yet another greenhouse gas.
So you're vaporizing a lot of sulfur,
a lot of salts of different kinds
that are then lofted up into the upper atmosphere,
that then plays havoc on the climate.
These greenhouse gases built up in the atmosphere
forming a warming blanket.
Triggering the next phase of destruction.
Global warming on steroids.
Temperatures Rose 10 degrees above normal.
Then the oceans warmed, as well.
Oxygen levels dropped, and the seas became toxic
to simple life forms.
It actually made it impossible for certain microbes
to actually live, and they're the basis of the food system.
So really it changed what could actually live in the ocean
and how much could live there.
Dead zones appeared in the oceans
just as they had on land.
Nearly three quarters of all life on Earth died,
all from one asteroid impact.
To prevent it from happening again,
we need to track all potentially dangerous asteroids.
But that isn't easy
because these space rocks can change direction.
Saricicek, Turkey.
Security cameras record a flash in the sky.
The flash... a 3-foot asteroid exploding in the atmosphere.
It blew up in the atmosphere and rained down,
and people saw that.
It was very noticeable.
And they went, and they collected those meteorites.
And then they tried to figure out what they were looking at.
The debris was sent for fragment analysis.
I have a piece of one here. So first, on the outside,
you can see it has a really black fusion crust.
This is from when it fell into the Earth's atmosphere,
so it was melted.
But when you look on the inside, it reveals
this beautiful, very light tone, fine grained material.
And so these meteorites are incredibly distinctive
and really beautiful.
The meteorites are rocky.
They're beautiful color comes from a mineral called howardite.
It's rare, and it doesn't form on Earth.
Howardite meteorites come from the asteroid Vesta,
and we know that because of the dawn mission
that actually went to Vesta and took a look at it
very carefully, so we know the composition very well.
And so now suddenly here was a new kind of meteorite
that's in Turkey that matches the Vesta family of meteorites
but how can we be sure that these bits of space rock
came from Vesta, an asteroid over 100 million miles away.
It was a fall meteorite, and so what that means
is that someone saw it, you know, we saw it fall.
And so we knew its trajectory.
So we could actually work backwards to say,
where did that meteorite come from?
Retracing the trajectory of
the Turkish meteorites took the scientists all the way back
to the 328-mile wide Vesta.
Where they studied Vesta's surface,
they found further evidence.
On the surface of Vesta, there's actually a very large
and fresh impact crater that is around the same age
of the Turkish meteorite.
So that really clinched it.
This thing is definitely from Vesta, and we proved it.
So how did bits of Vesta end up here on Earth?
22 million years ago, some very large impactor
struck Vesta, made a huge crater,
and some of the rocks from that crater actually
escaped from Vesta's gravity and were lofted into space.
Some of these rocks from Vesta went into orbits
that intersected with Earth.
22 million years later, one blew up over Saricicek.
This Saricicek meteor shows that the asteroid belt
is an unstable environment.
Asteroids frequently strike other asteroids.
That's actually happening all the time.
Things are running into each other
in our solar system right now.
And so that makes it really hard for us
to track all of those objects because we don't actually know
what happens after they collide with each other.
Now things are totally different.
And that changes the whole system.
Each collision makes more asteroids.
There's many different possibilities
of what could happen when asteroids collide.
Imagine a roller derby situation.
If you have two groups of players
that run into each other,
that could be like two asteroids running into each other.
And one possible outcome is that one stays intact
while the other is completely blown apart.
That sends fragments flying all through the main asteroid belt,
and then there's a little asteroid fragments
are on their own independent orbits around the sun.
A problem with asteroid impacts is that
we're always making new asteroids.
There are big asteroids out there,
and they get hit by other asteroids,
and then you get shrapnel.
And now you've got not one big one and one smaller one,
you've got one big one, one smaller one,
and millions of little ones.
Now, most of these aren't very big, but some of them might be
bigger and could be potentially hazardous.
As the solar system ages,
the number of asteroids increases.
Each new space rock travels on a new course
which could intersect with Earth.
So we're constantly producing new asteroids
and big collisions in the main asteroid belt.
And these are producing the small asteroids
that will eventually drift inward in the solar system.
Tracking this constantly evolving population
of asteroids gives scientists a huge headache.
If they break apart, then that gives you
even more pieces of the asteroid to track.
It's not a simple thing to track and predict
the orbits of asteroids and their movements,
because one tiny little change
can have huge dramatic impacts for its possible future.
Figuring out exactly where they're going to go
and keeping track of how they interact with each other,
this is a huge endeavor.
The sheer volume of asteroids can affect
the behavior of other asteroids
as they gravitationally interact.
Think about your roller derby player skating in circles.
The path they're going to follow would evolve
the more people you plop down on the track
they start interacting with each other,
and their trajectory will change.
The more crowded you make the solar system,
the more things are to change your orbit
of your individual asteroid.
It's not like air traffic control,
where there's a known amount of airplanes
and they all follow a plan.
This situation is further complicated because
asteroid orbits can be affected by other more subtle forces.
One of these is called the Yarkovsky or the Yorp effect.
Honestly Yorp is more fun to say.
The Yorp effect is caused by sunlight
hitting an asteroid.
Light is made up of photons that are traveling,
and these photons actually have momentum.
So when light shines on something,
it actually pushes on it.
When sunlight hits an asteroid,
the photons give it a tiny push...
...enough to change the space rock's trajectory.
When we know an asteroid is really heading our way,
it's time to fight back.
So we've got an asteroid that's headed at us.
What do we do?
Two main possibilities... we deflect it,
we nudge it a little bit so it misses,
or we blow it up, we destroy it.
Which of those do you want to do?
It's a tough choice.
Get it wrong, and we could end up being hit by a swarm
of radioactive space rocks.
An asteroid is heading our way,
and it may hit us in 2068.
How do we prevent such a catastrophe
and stop it from ever getting close?
Well, you just don't want to take get anywhere near us
in the first place.
So what do you do?
Well, you can destroy them,
or you can push them out of the way.
This is something where our science fiction ideas
have got it almost entirely wrong.
If you're in a bad movie, a really, really bad movie,
you can send astronauts to an asteroid,
put a nuclear bomb in it,
and blow it up into lots of little bits
that then burn up harmlessly in our atmosphere.
Yeah, it doesn't work that way.
Blowing up an asteroid
would make the problem much worse.
We are no longer dealing with just one space rock.
My issue with this is that you may have turned
one problem into 50.
Instead of one regular sized asteroid,
now you have a whole bunch of littler ones,
and these may still hit the Earth and cause damage.
And you know what? That's not much less fun
than just having a single big asteroid.
Now you've just taken all that devastation
and spread it out for everybody to enjoy.
The problem with using a nuclear device is that
the products that rain down on Earth are now radioactive.
If a dangerous asteroid was on its way,
blowing it up would be a last resort.
A less risky method is to deflect it off
its collision course.
A small nudge early enough
can change in asteroid's trajectory away from Earth.
You don't have to nudge it very much for it to miss, right?
So if it's headed straight at it,
I just touch it slightly,
by the time it gets to Earth, its way off course.
NASA is investigating ways to change
an asteroid's path, including using a nuclear burst.
In a nuclear burst, what we do is we don't actually hit it.
We come up to it with the device on a spacecraft,
and then the device would be detonated at a certain height
above the surface.
That heats up the surface of the asteroid,
which vaporizes.
You get vaporized rock or metal which blasts off the surface,
and that's how a rocket works.
So you blow up a bomb here, and it winds up
pushing the asteroid in the other direction
to prevent any potential nuclear fallout,
NASA would detonate the bomb a long way from Earth
any deflection attempt has to be done years in advance,
which means it would be done on the other side
of the solar system from us
on the opposite side of the object's orbit.
That means that all of the vapor made during
the explosion gets blown away by the solar wind.
NASA is investigating other less explosive methods
of deflecting an asteroid.
De-star would blast the asteroid with a laser.
We hit it with the laser, material vaporizes
and flies off the asteroid,
and because of Newton's third law,
which is that for every action there is an opposite
an equal reaction, this means that vaporize material
moving off in one direction moves the asteroid
in the opposite direction.
Both the laser and the nuclear burst
are still just ideas on the drawing board.
But one asteroid deflection mission called
double asteroid redirection test, or dart for short,
is already up and running and scheduled for launch in 2021.
Dart is a kinetic impactor
and will try to knock an asteroid off course.
At NASA for the longest time, all we've been able to do
is theorize about how we change their path.
But now for the first time,
we're actually gonna practice in.
Leading this groundbreaking mission to bump
an asteroid off its orbit is Dr. Andy Chang.
Dart is the first planetary defense mission
that we've ever done, where we take a spacecraft,
we fly the spacecraft into the asteroid to change
its course and make it miss the Earth.
Dart's target is a 525 foot space rock
orbiting the large near Earth asteroid Didymos.
We pick the near Earth asteroid Didymos as a target
for the dart mission because although it's
a near Earth asteroid, it's one that's very safely
parked away out there in space.
There's no way we can move Didymos or its moon
in any way big enough to cause a problem for the Earth.
The diddy-moon asteroid weighs
around 10 1/2 billion pounds.
So how do you knock such a large lump of rock
off its path?
We're sending a spacecraft
to knock the diddy-moon asteroid off course.
The asteroid is moving at over 36,000 miles an hour
and is around seven million miles away.
So how do you move a 10 and a half billion pound
space rock?
You need to hit it really hard to change its orbit,
so it's going to be coming in at a super high velocity
in order to impart a bunch of energy momentum to that moon.
Dart will hit the target
at around 14,000 miles an hour.
The speed of the dart impact will be more than nine times
the speed of the rifle bullet from an AK-47.
The impact will give the asteroid a small push.
To work out how big a push,
we test impacts with the Ames vertical gun.
At the NASA Ames research center in California,
there's a very special facility called
the Ames vertical gun range.
It's a hyper velocity gas gun that allows us
to shoot little metal BBS at rock targets at speeds
up to like 13,000, 14,000 miles per hour.
The gun replicates the impact
the dart mission will make.
It reveals that an impact will blow off
a small amount of debris but at extremely high speed,
enough to give the asteroid an additional kick.
The impact will blow off pieces of the asteroid,
so the pieces are thrown off the back.
And so that that process acts like a little rocket engine.
That provides an additional momentum change,
momentum push to the target itself.
The combined push from the kinetic impactor
and the ejected debris is tiny,
around 0.0009 of a mile per hour.
But hopefully it's enough to change the asteroid's orbit.
If dart works, we could then use a similar mission
to defend Earth when the time comes.
This isn't some small rock prototype
that we're doing this test on.
This is a real dress rehearsal for an asteroid
that could destroy cities
or even maybe send the Earth in chaos.
The moon of Didymos is a solid lump of rock.
Will a kinetic impactor like dart work
with a rubble pile asteroid like Apophis?
When you shoot a rubble pile with a projectile,
it's a little bit more like trying to punch a sandbag.
You get a lot more a lot more the energy is absorbed
into just moving the sand around inside the bag
than ejecting it, and so rubble piles
might be a little harder to move by this method.
We don't know if we can deflect a rubble pile
asteroid like Apophis.
They remain a clear and present danger.
And something we might not survive.
But there may be a space lifeboat.
In 2018, scientists reexamined rocks collected by Apollo 14
astronauts from the moon.
Buried in the samples was a rock that shouldn't be there.
They got something they didn't expect,
and that was an Earth rock.
They actually picked up a rock from Earth on the moon.
They didn't bring it with them.
It's very likely that it was something that was lofted up
when something hit Earth, throw up a bunch of rocks.
Some of those rocks fell on to the moon,
and that's a meteorite on the moon,
but it's from Earth.
Super computer simulations of
the KPG asteroid strike revealed how the impact had so much
energy that it catapulted rocks out of Earth's atmosphere
and into space.
They were then caught by the moon's gravity
and pulled down to the lunar surface.
We now know the material ejected into space from asteroid impacts
can travel to other planets, as well,
which would explain the 100 Mars meteorites
we've found here on Earth.
We think that there was probably the exchange of a huge amount
of material between different bodies,
Earth to the moon and back again and to Mars.
With each impact that occurs in our solar system
that ejects all types of material that allows material
to swap from planet to planet, moon to planet, moon to moon.
And so there's all of this material
that eventually travels from place to place.
Should another giant asteroid hit our planet,
this planetary interchange may give life on Earth
a lifeline.
If you think about such an impact today,
you know, the chances are high that a lot of life would be
wiped out, much of life, probably all of human life.
It's certainly possible that a big enough asteroid strike
could completely sterilize the planet.
Talking about no life whatsoever.
Not to put too fine a point on it,
but if there's a dinosaur killer asteroid out there
and it hits the Earth, the chance of humanity's
survival of such a thing as a species, mm, not great.
Humans may not survive.
But some scientists believe that simple life forms could.
Asteroids have hit our planet many times
in the past.
One giant strike wiped out 70% of all life on Earth.
If another huge asteroid hits us, can life survive?
If a giant rock hits the Earth and kills almost
all life on Earth, there is a slim line of hope.
And that's because the dirt, the rocks on Earth
are infused with bacterial life, with microscopic life.
And in the event of a giant impact,
some of these bits of rock will be ejected into space
and might float around.
After an asteroid impact, whatever ejected
into the atmosphere could contain microbial life
that when it falls back down on to the ground
could re-seed the life on that planet.
Some bacteria can survive the harsh conditions
of space and can cope with an asteroid strike, reentry,
and landing back on Earth's surface.
I think in terms of life on planet Earth,
I think we've learned that we live on a very resilient planet.
And I think life in some form, even if it has to crawl
its way back from bacterial stage,
I think life on this planet is going to going to eke through.
Life is pretty good at figuring out a way of surviving.
We know that life first formed on the Earth
well over 4 billion years ago
and has never been wiped out in all of that time.
There's always been something
after every major mass extinction.
So life will continue. It just won't necessarily be us.
An asteroid strike on another world
may be how life on Earth started in the first place.
There's an interesting idea that an asteroid strike
on another planet could have actually seeded life on Earth.
And the way this works is, you have a life
that's somehow gotten a foothold on some other planet like Mars,
a big asteroid strike hits that planet
and knocks a piece of it off, eventually rains down on Earth,
carrying with it life.
We may owe the existence of life here to asteroid impacts.
That's speculative, but it's kind of a cool thought.
Life seeding asteroids may have hit us in the past,
and other asteroids will hit us in the future.
One of those maybe Apophis,
arriving in less than half a century.
Maybe we'll deflect it.
Maybe it'll miss us all on its own.
Either way, we need to keep tabs on it.
The best thing we can do as a species, and it's funny
because it almost sounds like I'm advocating
for more jobs for astronomers.
We need to keep looking at the sky.
We need look at the sky longer and deeper,
with more sensitive instruments
and get more of a sense of what out there is around us.
That's what our species needs to do to ultimately survive.
Because now we have the ability
to see these things a little bit better,
we have the ability to protect ourselves better.
It doesn't have to be a surprise.
You know, the first time we see a big impact doesn't have to be
as it's bearing down destroying our planet.
We can actually see it before it gets to us
and decide what we want to do about it.
Earth's history is littered with asteroid strikes.
Some wiped out millions of species.
Some may have seeded life in the first place.
What the future holds and our relationship
with these space rocks, no one knows.
Even though the chances of something really large hitting
the Earth are pretty small, the consequences are dire.
It would really destroy our planet or at least life
as we understand it.
And so in many ways, asteroids are the greatest
threat that we face.
Life is fragile, so of course we live in a larger environment
where something could come and hit us at any time.
That's part of being alive.
There's no guarantee tomorrow will happen.
But what there is is a high likelihood
that you'll still be safe tomorrow.
Impacts from space are rare,
but if they do happen, it's a huge deal.
And so you've got to put those two things together.
That means we got to pay attention.
Those impacts have happened many times in the past,
and they're going to continue to happen many times in the future.
Fortunately it's not probably in our immediate future.
Impacts are rare, but the Earth lives a long time.
So you're unlikely to get in a car accident,
but if you drive enough, you're going to get in a car accident.
Over a century time scale,
yes, we should be concerned about these.
But over the daily, weekly, monthly, even yearly time scale,
I wouldn't sweat it too much.
I wouldn't say we should lose sleep over an asteroid
or comet striking Earth,
but the reality is it will happen again.
So when you think about asteroid strikes,
remember this wonderful dramatic universe
you find yourself in.
We're here because stars died and exploded.
Life on Earth wouldn't be the same
if we didn't find ourselves in this dramatic
and even dangerous environment in space.
But this is who we are. This is nothing new.
And this will continue for the future of our planet.