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a dangerous asteroid is heading towards
Earth.

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It's the size of the Empire State
Building, and it's traveling at 16 ,000

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miles an hour.

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It's called Apophis, after the Egyptian
god of chaos.

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It will fly close to us in 2029.

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It won't hit us this time.

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But when it returns in 2068, It could be
another story.

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If it blows up over a city, millions of
people will die.

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This could be the most devastating
single event in U .S.

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history.

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Earth is stuck in the crosshairs of a
potential asteroid strike.

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Apophis is one of around 2 ,000
potentially hazardous asteroids.

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Asteroids have hit us before, and they
will hit us again.

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As far as cosmic dangers go, they're
number one on the list.

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This is not a thrill.

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If we do nothing,

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this is our future.

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December 2018,

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the U .S.

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military detects a huge explosion in the
Earth's atmosphere, high over the

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Bering Sea off the coast of Alaska.

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When an explosion of this magnitude is
detected, everyone's mind goes to the

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same thing, nukes.

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But when the real answer was found, and
it was determined that it didn't even

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originate from Earth, that was even more
shocking.

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The cause of the blast was an asteroid.

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This asteroid was 30 feet across,
something like that, over 1 ,000 tons.

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was moving at 20 miles per second, over
70 ,000 miles an hour.

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This asteroid was small, and it exploded
in the atmosphere of the ocean, so

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nobody was hurt.

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But if it had been bigger?

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or it had come in over a different
place, or it had been moving a lot

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this could have been a dangerous object.

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But the scariest thing about it is that
we didn't see it coming.

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We've been lucky so far.

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But near misses happen all the time.

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About once a year, we get something the
equivalent of a nuclear bomb going off

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in our atmosphere. And while that sounds
horrible, most of these happen tens of

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miles over open ocean, where we go on
completely

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oblivious.

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We may be oblivious to most of the
threats from space, but they are very

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We are going to get hit.

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Over a certain amount of time, an
asteroid impact is inevitable. It will

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100 % absolute certainty.

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NASA considers the threat from the sky
so severe it has made protection from

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asteroids a top priority.

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These events are not rare.

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They happen.

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And, of course, it's up to us to make
sure that we are detecting and

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characterizing, tracking all of the near
-Earth objects that potentially could

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be a threat.

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This is not about Hollywood. It's not
about movies. This is about ultimately

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protecting. the only planet we know
right now to host life, and that is the

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planet Earth.

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To help protect our home, we carry out
Earth defense simulations.

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For three days, 200 scientists at the
Planetary Defense Conference battle a

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simulated asteroid 20 times larger than
the Bering Sea space rock.

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We practice, all right, what if this
hits a major city?

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What would we need to do?

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By running potential impact scenarios,
we can prepare for a real asteroid

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strike.

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This is like a fire drill that you would
do at school or at work, where you

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practice and think about, okay, what if?
Where are the exits? How do I get out?

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How fast do I get out?

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The drill starts with the discovery of a
simulated Earth -bound asteroid.

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So the first information is, there's a
big asteroid coming towards the Earth.

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Then we get a better estimate of how big
it is, how fast it's going, and where

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it's going to hit.

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The asteroid is heading straight for
Earth, with Denver, Colorado in its

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The planetary defense scientists send up
a simulated spacecraft to smash into

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the asteroid and push it off its path.
But it's a big gamble.

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You can push it the wrong way. You can
potentially have unintended

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In the simulation, the spacecraft
strikes the asteroid, deflecting it

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away from Earth.

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dislodges a 200 -foot junk, which is now
heading straight towards the eastern

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seaboard.

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So there's this one last piece that is
now going to hit New York.

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We know that something that size is
going to have citywide consequences.

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That is huge. That's a horrible impact.

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When you're actually in the conference
room and you understand eventually that

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New York City is going to be destroyed,
and you're having strategies about how

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to evacuate people, all the timing, when
you're doing the simulation, you're in

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your head, you're thinking about these
things, you're trying to reason them

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But can you imagine the feeling in your
gut, in your heart, if this was real?

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If this were real, the chunk of asteroid
would strike the Earth's atmosphere at

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43 ,000 miles an hour.

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As the space rock descends, it collides
with molecules in the atmosphere, which

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buffets the falling rock.

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It's kind of like doing a belly flop
into a pool, right? You're going from

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vacuum of space into the dense lower
atmosphere in mere seconds.

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And that's an incredible amount of
pressure to put on the object.

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The asteroid flams into the air ahead of
it, compressing it violently.

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the surface of the asteroid gets hotter
and brighter.

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It's actually the air itself that's
glowing luminously from the heating of

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shockwave, the world's most intense
sonic boom, if you will, that heats the

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to incandescence as the object passes
through. So that's the source of that

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brilliant illumination.

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This bright -burning asteroid is called
a bolide.

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We witnessed one descending over the
Russian city of Chelyabinsk in 2013.

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All of a sudden, there was a huge
fireball striking through the sky, and

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had no idea what they were witnessing
because it looked like the sky was on

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fire. It was insanity.

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As the asteroid descends, the
compression of the denser air lower down

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flatten and even disrupt the falling
rock.

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There's a high pressure on the front,
there's no pressure on the back, and

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being superheated. And that intense
temperature causes the air to glow,

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how we see the streak of a meteor.

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And it also disintegrates the asteroid
itself. It's hot enough to literally

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rock. This can often lead to them
exploding.

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The combination of heat and pressure
invade the falling asteroid, causing it

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blow up.

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Most asteroids don't reach the ground
before they completely disintegrate in a

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tremendous release of energy. This is
what we call an airburst, and we learned

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lot about these while we were testing
nuclear weapons after World War II.

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Some of these bombs were blown up
underground and on the ground, but they

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out when they blew up bombs above the
ground, it actually did more damage. It

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was more widespread damage.

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The explosion of the Telebent asteroid
sent out a powerful shockwave at

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thousands of miles an hour.

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The blast traveled over 100 miles.

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It damaged 7 ,000 buildings and put 1
,500 people in the hospital.

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All of the injuries pretty much came
from people who saw, oh, what's that

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flash in the sky?

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And they came close to a window to look
and see what it was, and then the

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pressure wave hit and blew glass in
their face.

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The Chelyabinsk asteroid was only 65
feet across.

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The rock in the defense simulation is
three times more massive and is now

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heading for New York City.

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Imagine what would happen if an
explosion a thousand times greater than

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over Hiroshima hit New York.

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We're talking about an utter, complete
destruction of the city and millions of

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people.

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With so little warning, the only option
would be to evacuate New York City.

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How do we get everybody out of New York
City within just a few days?

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That's where panic sets in. That's where
fear would really become the dominant

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emotion.

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Anyone left in New York would see the
bolide race in,

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followed by a blinding light as the
asteroid

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explodes above the city.

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The blast would be the equivalent to the
largest nuclear weapon ever detonated

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on Earth.

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Buildings would be flattened, melted.
There would be fires for miles around.

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In the first moments of the explosion, A
million people could be killed

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instantly, and many more would die later
in the rubble and the ruins of what

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would happen there.

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Everything within nine miles of the
blast epicenter would be completely

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destroyed.

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The intense heat and pressure would
wreck buildings.

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It's the worst possible day for New
Yorkers.

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And not just the city itself.

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There's something like 15 million people
living in the New York area.

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The destructive shockwave would race out
over 250 square miles.

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This would certainly be the worst
disaster that the U .S. has ever

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We're talking about millions and
millions of people displaced, affected

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an instant.

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This scenario is just a simulation, for
now.

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The asteroid Apophis is heading our way.

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If it hits Earth, it might not just kill
a city. It could kill a whole region.

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I wouldn't exactly want to be there when
that happens.

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I want to be very, very far away.

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Apophis will skim Earth in 2029, but its
path will

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change,

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possibly turning a future myth into a
direct hit.

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April 13, 2029.

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A speck of light races towards Earth.

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It's an 1 ,100 -foot -wide asteroid
called Apophis.

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We are about to have an extremely close
shave.

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It's the closest approach of any
asteroid that didn't actually hit us for

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long, long time. It will be ten times
closer than the moon itself. It will be

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close it will be brighter than some
stars.

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The football stadium -sized Apophis.

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will race over the Atlantic.

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If it were sitting on the surface of the
Earth, it would weigh about 50 million

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tons, something like that.

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And that is not the place you want it to
be. You want it to be in space and far

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away.

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When we discovered Apophis in 2004, we
thought it might be on a collision

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with Earth.

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With a potential impact greater than the
largest atomic bomb ever exploded.

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The largest nuclear device, atomic
device, ever detonated on our planet was

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Tsar Bomba bomb in Russia. It was
something like 55 or 56 megatons.

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When Krakatoa exploded in 1883, that was
something like 200 megatons.

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Apophis impact would be 450 megatons.

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If something like that were to happen
over New York City or Washington, D .C.,

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you're going to lose the city.

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The impact would be at least ten times
greater than the simulated asteroid

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strike on New York.

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When you put it in those terms, that's
just plain scary.

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In a word, an impact from an apophysized
asteroid would be bad.

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Very, very bad.

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Apophis' orbit will cross Earth every
seven years this century, but it won't

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us in 2029.

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But this close encounter will change
Apophis' orbit.

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When a small asteroid encounters a
bigger body like a planet, it's like a

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of roller derby players.

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Most of them are clumped together, but
maybe there's one just on their own

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particular orbit.

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And as they circle around, as they get
close to that larger clump, there'll be

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some interactions, potentially violent
interactions, that will change the

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trajectory of that lone roller derby
skater. And the next time around, it

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be a wide miss, or it might be a head
-on impact.

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00:15:49,100 --> 00:15:51,340
It's the same in the solar system.

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The combined gravity of the Earth and
Moon creates what's called a

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keyhole, a gravitational sweet spot,
which could change Apophis'

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00:16:04,080 --> 00:16:05,130
orbit.

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00:16:05,780 --> 00:16:11,219
That will change the potential future
trajectory of this rock and might make

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totally harmless or might increase the
chances of an impact even further in the

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00:16:16,000 --> 00:16:17,050
future.

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00:16:20,050 --> 00:16:24,949
Because of the gravitational keyhole,
there is still a small chance that

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00:16:24,950 --> 00:16:26,930
will hit Earth in 2068.

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00:16:31,070 --> 00:16:35,969
That is the important lesson that
Apophis taught us. You can miss the

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00:16:35,970 --> 00:16:40,329
if you pass through one of these
keyholes at some time later, you will

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00:16:40,330 --> 00:16:41,380
Earth.

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00:16:41,710 --> 00:16:48,690
We now know Apophis will miss the
keyhole in 2029, but there are other

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00:16:49,160 --> 00:16:50,800
and other close passes.

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00:16:57,000 --> 00:16:59,560
Apophis is not a lone threat.

217
00:16:59,880 --> 00:17:06,618
There are an estimated 832 ,557
asteroids orbiting the

218
00:17:06,619 --> 00:17:07,669
sun.

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00:17:08,980 --> 00:17:13,420
Most asteroids live their lives
perfectly peacefully.

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00:17:14,520 --> 00:17:20,399
past the orbit of Mars or trailing
Jupiter and don't mind anybody else and

221
00:17:20,400 --> 00:17:26,858
cause any troubles. But some asteroids
are on very particular orbits that cross

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00:17:26,859 --> 00:17:28,440
the orbit of the Earth.

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00:17:30,180 --> 00:17:35,439
These asteroids have left the stable
orbit of the asteroid belt and moved

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00:17:35,440 --> 00:17:37,680
orbits that get near our own.

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00:17:37,980 --> 00:17:43,940
These asteroids are called near -Earth
asteroids, or NEAs for short.

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00:17:43,941 --> 00:17:48,259
The near -Earth asteroid population is
interesting and potentially dangerous

227
00:17:48,260 --> 00:17:51,259
because they're the ones that actually
cross the orbit of the Earth. So they're

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00:17:51,260 --> 00:17:55,800
most likely to have, at some point in
the future, an impact with the Earth.

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00:17:57,620 --> 00:18:01,300
Most NEAs pose little or no threat to
Earth.

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00:18:02,040 --> 00:18:07,020
But we've detected over 2 ,000 that do,
including apophis.

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00:18:09,380 --> 00:18:12,020
These are called PHAs.

232
00:18:12,220 --> 00:18:14,320
Potentially hazardous asteroids.

233
00:18:15,620 --> 00:18:19,479
The difference between a near -Earth
asteroid and a potentially hazardous

234
00:18:19,480 --> 00:18:22,680
asteroid is distance and size.

235
00:18:23,640 --> 00:18:27,740
Anything can get near the Earth, and
that could be 20 million miles away,

236
00:18:27,860 --> 00:18:31,379
something like that, and be a near
-Earth asteroid. But a potentially

237
00:18:31,380 --> 00:18:34,680
one can hit us, and it's big enough to
do damage.

238
00:18:35,231 --> 00:18:42,879
So something that over the next hundred
years or so has a chance of hitting us

239
00:18:42,880 --> 00:18:46,860
and doing damage when it does, that's a
potentially hazardous object.

240
00:18:49,500 --> 00:18:54,380
PHAs are asteroids 500 foot or larger
that could collide with Earth.

241
00:18:57,220 --> 00:18:59,320
Take a 400 foot asteroid.

242
00:18:59,620 --> 00:19:05,380
If it hit, it would release as much
energy as 3 ,000 Hiroshima nuclear

243
00:19:12,520 --> 00:19:18,740
In July 2018, NASA published a map of
all known NEAs and PHAs.

244
00:19:21,960 --> 00:19:27,820
The animation tracks their discovery
from 1999 through 2018.

245
00:19:27,821 --> 00:19:33,419
Every time I look at this animation, it
does make my heart stop a little bit

246
00:19:33,420 --> 00:19:37,199
because it looks like we're in the
middle of this swarm of angry bees

247
00:19:37,200 --> 00:19:38,250
all around us.

248
00:19:38,410 --> 00:19:39,530
In 1999,

249
00:19:40,410 --> 00:19:45,390
we'd identified under 300 NEAs scattered
through the inner solar system.

250
00:19:45,770 --> 00:19:49,490
Ten years later, we discovered 500 more.

251
00:19:49,930 --> 00:19:55,030
By 2018, we discovered 18 ,000 near
-Earth asteroids.

252
00:19:55,250 --> 00:19:59,070
But we estimate there are millions out
there.

253
00:19:59,970 --> 00:20:04,190
It seems like we can never find all the
asteroids. They just keep coming.

254
00:20:04,410 --> 00:20:06,640
It's like we're fighting an army of
zombies.

255
00:20:07,820 --> 00:20:14,379
Zombies that keep hurtling our way,
hitting Earth at up to 64 ,000 miles an

256
00:20:14,380 --> 00:20:15,430
hour.

257
00:20:16,740 --> 00:20:21,739
That is very, very fast. That is much
faster than a rifle bullet. And that's

258
00:20:21,740 --> 00:20:23,320
key to its destructive power.

259
00:20:25,640 --> 00:20:32,359
When a really fast and really large
asteroid hits, the impact is off the

260
00:20:32,360 --> 00:20:35,640
chart. The blast is so intense.

261
00:20:36,240 --> 00:20:39,580
It can melt or even vaporize rock.

262
00:20:45,440 --> 00:20:47,100
January 2019.

263
00:20:47,620 --> 00:20:50,140
A total eclipse of the moon.

264
00:20:51,100 --> 00:20:55,360
Astronomers train their telescopes on
the darkening lunar surface.

265
00:20:55,820 --> 00:21:00,920
They capture a bright flash that lasts
around a quarter of a second.

266
00:21:00,921 --> 00:21:06,119
It was recorded. There were a lot of
live webcasts and things like that going

267
00:21:06,120 --> 00:21:06,939
at the time.

268
00:21:06,940 --> 00:21:10,200
And you can see this flash of light.
What the heck was that?

269
00:21:11,900 --> 00:21:15,260
At first, the cause of the flash was a
mystery.

270
00:21:16,840 --> 00:21:22,619
It turns out it was actually a meteorite
hitting the surface of the moon. And

271
00:21:22,620 --> 00:21:25,899
because it was dark, and because we were
all looking at it, we could actually

272
00:21:25,900 --> 00:21:26,679
see it.

273
00:21:26,680 --> 00:21:32,759
The moon's dark surface gave us a unique
view into what happens when an asteroid

274
00:21:32,760 --> 00:21:38,039
strikes. What was so exciting about
being able to see this impact on the

275
00:21:38,040 --> 00:21:42,079
a dark area is that we could actually
look at the light that it produced and

276
00:21:42,080 --> 00:21:45,460
then back calculate exactly what the
size of the impactor was.

277
00:21:45,780 --> 00:21:52,219
We worked out that the impacting
asteroid was just 20 inches wide. The

278
00:21:52,220 --> 00:21:54,960
blew out was 45 feet across.

279
00:21:55,450 --> 00:21:59,410
How could something so small be so
destructive?

280
00:22:00,230 --> 00:22:04,309
The two things that matter the most are
how fast it's going and how massive is

281
00:22:04,310 --> 00:22:07,489
the thing. The more massive, the bigger
the boom, the faster, the bigger the

282
00:22:07,490 --> 00:22:11,949
boom. Speed and weight are two very
important factors to assess how much

283
00:22:11,950 --> 00:22:13,000
an asteroid will do.

284
00:22:13,110 --> 00:22:17,349
Just like a boxer, if a tiny person like
me were to swing a punch, it would do a

285
00:22:17,350 --> 00:22:19,710
lot less damage than a heavyweight
champion.

286
00:22:19,711 --> 00:22:21,629
Same thing with asteroids.

287
00:22:21,630 --> 00:22:23,499
The bigger they are, the bigger the
punch.

288
00:22:23,500 --> 00:22:25,180
But the same thing is fast, right?

289
00:22:25,181 --> 00:22:28,759
If I hit you really slowly, it's not
going to hurt. I have to really wind

290
00:22:28,760 --> 00:22:29,659
and pop.

291
00:22:29,660 --> 00:22:31,520
That's what happens with an asteroid.

292
00:22:33,040 --> 00:22:38,800
The damage from an asteroid strike is
determined by its kinetic energy.

293
00:22:39,580 --> 00:22:43,980
Kinetic energy depends on two things,
speed and weight.

294
00:22:44,680 --> 00:22:47,080
Speed is the most important.

295
00:22:49,840 --> 00:22:53,639
If you double the mass, you double the
kinetic energy. But if you double the

296
00:22:53,640 --> 00:22:56,560
velocity, you get four times the kinetic
energy.

297
00:22:56,800 --> 00:23:01,259
Three times the speed, nine times the
impact energy. Ten times as fast, it has

298
00:23:01,260 --> 00:23:05,380
hundred times the energy. So the
velocity is what's really critical here.

299
00:23:07,760 --> 00:23:14,239
The lunar asteroid weighed only 100
pounds, but it was traveling at 38 ,000

300
00:23:14,240 --> 00:23:15,290
miles an hour.

301
00:23:15,580 --> 00:23:20,140
carrying a huge kinetic energy which
gouged out the crater.

302
00:23:21,500 --> 00:23:24,740
It's the same principle for impacts on
Earth.

303
00:23:25,620 --> 00:23:32,220
50 ,000 years ago, a 150 -foot asteroid
hit what is now Arizona.

304
00:23:32,820 --> 00:23:39,480
The impact blasted out an impressive
hole, now called Beringer Crater.

305
00:23:40,160 --> 00:23:42,540
It's about three -quarters of a mile
across.

306
00:23:42,541 --> 00:23:47,139
Over 500 feet deep, you could put the
Washington Monument in the bottom of the

307
00:23:47,140 --> 00:23:51,059
crater, and the top of the monument
wouldn't quite clear the rim. It's a

308
00:23:51,060 --> 00:23:52,560
impressive hole in the ground.

309
00:23:56,260 --> 00:23:57,540
In 2016,

310
00:23:58,380 --> 00:24:03,979
impact specialist Kathy Plesko visited
Beringer Crater to see firsthand what

311
00:24:03,980 --> 00:24:06,920
mass and speed do to the surface of the
Earth.

312
00:24:10,800 --> 00:24:11,850
The food.

313
00:24:12,270 --> 00:24:17,389
It's awe -inspiring to stand on the rim
of a crater like this, understanding

314
00:24:17,390 --> 00:24:23,810
just how much energy it must have taken
to excavate this much rock.

315
00:24:27,210 --> 00:24:32,470
An asteroid came in at about 27 ,000
miles an hour.

316
00:24:34,330 --> 00:24:37,590
It comes slamming into the surface and
just explodes.

317
00:24:38,010 --> 00:24:42,709
Anywhere nearby here would have seen
winds of thousands of miles an hour as

318
00:24:42,710 --> 00:24:43,890
shockwave came out.

319
00:24:49,990 --> 00:24:55,189
The immense power of an asteroid impact
comes from the kinetic energy being

320
00:24:55,190 --> 00:24:58,730
transferred from the space rock into the
surface rock.

321
00:25:01,230 --> 00:25:06,269
It's an extremely violent process, and
it starts with the moment of contact of

322
00:25:06,270 --> 00:25:08,250
the projectile with the surface itself.

323
00:25:10,010 --> 00:25:16,530
It pushes into the crust, and at first
it's just almost punching,

324
00:25:16,830 --> 00:25:20,750
like sticking your thumb into dough.
It's only about as wide as the object

325
00:25:20,910 --> 00:25:26,169
It's going straight down in, but then
it's meeting resistance from the surface

326
00:25:26,170 --> 00:25:26,999
of the Earth.

327
00:25:27,000 --> 00:25:32,079
And so it squishes, squishes, squishes
until it runs out of momentum, but then

328
00:25:32,080 --> 00:25:35,459
it's very compressed, and all of that
energy is in a very small space.

329
00:25:35,460 --> 00:25:39,919
As it releases, it detonates like a
bomb, and that's what makes the impact

330
00:25:39,920 --> 00:25:40,970
crater.

331
00:25:43,720 --> 00:25:48,960
Simulations of an asteroid strike in the
lab reveal the impact in slow motion.

332
00:25:52,140 --> 00:25:58,329
As the high -speed pellet hits the
surface, The sand compresses downwards,

333
00:25:58,330 --> 00:25:59,380
rebounds.

334
00:26:00,590 --> 00:26:05,589
As that rebound is occurring, that's
when the material is being ejected out

335
00:26:05,590 --> 00:26:06,640
the crater itself.

336
00:26:07,850 --> 00:26:12,149
You'll see the surface erupting outwards
like the blooming petals of some big

337
00:26:12,150 --> 00:26:15,830
rocky flower as all this debris goes
spraying out in every direction.

338
00:26:21,130 --> 00:26:25,290
The 150 -foot Behringer asteroid turned
the rock to powder.

339
00:26:26,430 --> 00:26:33,229
66 million years ago, an asteroid around
200 times larger and moving one and a

340
00:26:33,230 --> 00:26:36,070
half times faster than Behringer hit
Earth.

341
00:26:37,210 --> 00:26:44,210
This asteroid, called KPG, had so much
energy, it turned rock to liquid.

342
00:26:44,610 --> 00:26:48,649
The thing was immense. It's really hard
to wrap your head around just how big it

343
00:26:48,650 --> 00:26:55,119
is. When the back end of it is so far
back that it's where a modern

344
00:26:55,120 --> 00:26:56,300
jetliner would fly.

345
00:26:58,660 --> 00:27:05,479
The KPG asteroid hit the ground with a
lethal combination of mass and speed. A

346
00:27:05,480 --> 00:27:09,940
trillion tons traveling at 45 ,000 miles
an hour.

347
00:27:11,700 --> 00:27:15,220
Some rock is completely vaporized. It
just becomes a gas.

348
00:27:15,770 --> 00:27:17,550
You have some rock that has melted.

349
00:27:17,870 --> 00:27:20,850
You have some that's thrown out into
space.

350
00:27:22,770 --> 00:27:27,129
This material goes up through that and
then falls down and settles down over a

351
00:27:27,130 --> 00:27:31,669
huge area. That might be dust. It might
be pulverized rock. It might be

352
00:27:31,670 --> 00:27:32,720
vaporized metal.

353
00:27:32,990 --> 00:27:35,950
It's all of this hot material raining
down everywhere.

354
00:27:38,310 --> 00:27:41,070
As some rock exploded skyward.

355
00:27:41,550 --> 00:27:47,089
Rock below the surface was slammed by a
shockwave that was completely off the

356
00:27:47,090 --> 00:27:48,140
charts.

357
00:27:48,250 --> 00:27:51,230
Rock stopped, behaving like rock.

358
00:27:52,270 --> 00:27:57,469
We experience rocks as solid objects,
but if you hit a rock hard enough, it

359
00:27:57,470 --> 00:27:58,520
flows like water.

360
00:27:58,750 --> 00:28:05,690
The KPG impact hits so hard, it
pulverized the rock and turned it into a

361
00:28:05,910 --> 00:28:10,269
Almost like ripples on a pond moving
away from a stone that's been dropped in

362
00:28:10,270 --> 00:28:14,340
it. It's almost like a splash in the
solid body of the Earth itself.

363
00:28:14,540 --> 00:28:19,039
And like the water droplets splashing in
water, you'll see that central peak

364
00:28:19,040 --> 00:28:22,559
will kind of splash up and rise to a
high altitude and then come back down

365
00:28:22,560 --> 00:28:26,979
again. We think a process very similar
to that probably happened in the rock

366
00:28:26,980 --> 00:28:31,779
itself at the center of the crater,
rising up as high as the Himalayas

367
00:28:31,780 --> 00:28:34,279
relaxing back down into their current
position again.

368
00:28:34,280 --> 00:28:35,330
The material...

369
00:28:36,560 --> 00:28:41,619
And so these ripples are frozen in the
rock. And there are other fragments that

370
00:28:41,620 --> 00:28:45,999
go away radially, almost like the
spiderweb pattern in glass that you get

371
00:28:46,000 --> 00:28:47,480
it's shot with a bullet.

372
00:28:49,000 --> 00:28:54,180
The KPG impact blew out a 111 -mile
-wide crater.

373
00:28:56,780 --> 00:29:03,640
A large and fast asteroid heading our
way is always going to be a problem.

374
00:29:04,680 --> 00:29:05,940
So what do we do?

375
00:29:06,940 --> 00:29:08,620
Wait for oblivion?

376
00:29:10,920 --> 00:29:12,520
Or fight back?

377
00:29:21,780 --> 00:29:28,400
The space in the inner solar system
seems calm, stable, and empty.

378
00:29:28,720 --> 00:29:30,060
But it's not.

379
00:29:31,820 --> 00:29:35,780
There are tens of thousands of near
-Earth objects just whizzing around

380
00:29:36,000 --> 00:29:37,960
Now, space is big.

381
00:29:38,320 --> 00:29:44,379
They're not going to hit us every time
they orbit the sun. But this does set up

382
00:29:44,380 --> 00:29:49,459
the possibility that one of these years,
we're going to end up at the same spot

383
00:29:49,460 --> 00:29:52,920
in space at the same time as that
asteroid.

384
00:29:53,260 --> 00:29:54,880
And then it's going to be an event.

385
00:29:57,360 --> 00:29:59,530
We're living in a cosmic shooting
gallery.

386
00:29:59,540 --> 00:30:03,459
Asteroids strike the Earth all the time
through history, and it's going to

387
00:30:03,460 --> 00:30:04,510
happen again.

388
00:30:04,660 --> 00:30:09,740
Scientists are developing strategies to
stop an asteroid hitting our planet.

389
00:30:10,180 --> 00:30:14,800
Our options, destroy or deflect the
space rock.

390
00:30:15,120 --> 00:30:19,380
But first, we need to detect any
dangerous asteroids.

391
00:30:20,880 --> 00:30:24,799
It's a little bit unnerving to know that
we haven't yet detected all of the

392
00:30:24,800 --> 00:30:29,039
asteroids that exist that could possibly
cross our path. We've discovered a lot

393
00:30:29,040 --> 00:30:32,340
of asteroids now, but we typically
discover the big ones.

394
00:30:33,720 --> 00:30:38,559
But for asteroids that are below 100
feet, there's a lot still out there that

395
00:30:38,560 --> 00:30:39,579
haven't discovered.

396
00:30:39,580 --> 00:30:43,839
And such an asteroid can do some real
damage if it were to explode over a

397
00:30:43,840 --> 00:30:44,890
populated area.

398
00:30:44,920 --> 00:30:46,760
To prevent such a catastrophe...

399
00:30:47,290 --> 00:30:51,730
We need to find all asteroids whose
orbits cross our own.

400
00:30:52,550 --> 00:30:55,510
Detection is crucial in our defense
against asteroids.

401
00:30:55,750 --> 00:31:00,649
And the reason is, the earlier they're
detected, the easier it is to deflect

402
00:31:00,650 --> 00:31:02,270
them away from hitting the Earth.

403
00:31:02,630 --> 00:31:05,400
You want to do deflection, the first
step is detection.

404
00:31:07,490 --> 00:31:11,470
The problem is, asteroids are very hard
to detect.

405
00:31:12,410 --> 00:31:16,730
Finding asteroids and cataloging all
their orbits is really challenging.

406
00:31:17,100 --> 00:31:21,699
They can move quite fast across the sky,
and they might go away on the other

407
00:31:21,700 --> 00:31:23,930
side of the sun for years and years and
years.

408
00:31:26,140 --> 00:31:27,780
So we can't see them.

409
00:31:28,840 --> 00:31:33,380
And even when they are this side of the
sun, they're hard to spot.

410
00:31:34,820 --> 00:31:37,830
But the problem is they're very small
and they're very dark.

411
00:31:38,020 --> 00:31:41,580
And when I say very dark, I mean really
dark like a lump of coal.

412
00:31:41,800 --> 00:31:45,639
So how do you find a small, dark rock
just wandering around out there in the

413
00:31:45,640 --> 00:31:46,690
solar system?

414
00:31:51,820 --> 00:31:54,600
The Catalina Sky Survey has the answer.

415
00:31:56,280 --> 00:32:01,699
The huge telescope in the mountains
above Tucson, Arizona takes a series of

416
00:32:01,700 --> 00:32:03,900
images over a 20 -minute period.

417
00:32:04,340 --> 00:32:07,640
It's looking for anything that moves.

418
00:32:07,860 --> 00:32:12,260
Because stars don't move, but asteroids
do.

419
00:32:14,700 --> 00:32:20,220
If it's a really bright asteroid, we
will see some bright points of light.

420
00:32:20,720 --> 00:32:22,360
tracking across the four images.

421
00:32:23,680 --> 00:32:25,420
Ah, here we go.

422
00:32:26,360 --> 00:32:27,660
This is a real object.

423
00:32:28,220 --> 00:32:33,079
You can see it's moving across the sky
here from the lower right to the upper

424
00:32:33,080 --> 00:32:37,919
left. We are very, very excited to have
discovered one tonight because this is

425
00:32:37,920 --> 00:32:42,580
an object that's approaching nearer
space, likely in the neighborhood of

426
00:32:47,720 --> 00:32:49,340
Catalina has limitations.

427
00:32:50,030 --> 00:32:52,530
it can only see visible light.

428
00:32:52,770 --> 00:32:55,930
So a particularly dim asteroid could be
missed.

429
00:32:58,310 --> 00:32:59,610
Asteroids are very cold.

430
00:32:59,611 --> 00:33:01,509
They're usually quite far away from the
sun.

431
00:33:01,510 --> 00:33:05,170
But amazingly, the best way we have to
find these is infrared light.

432
00:33:05,570 --> 00:33:09,589
Because things that are cold by human
scale can still be very warm to an

433
00:33:09,590 --> 00:33:10,640
infrared telescope.

434
00:33:10,690 --> 00:33:15,169
So even if asteroids are just a few tens
of degrees above absolute zero, that's

435
00:33:15,170 --> 00:33:16,790
still enough heat to detect them.

436
00:33:18,030 --> 00:33:24,369
When the infrared space telescope
NEOWISE turned its gaze onto asteroids,

437
00:33:24,370 --> 00:33:25,550
immediate results.

438
00:33:26,810 --> 00:33:32,449
NEOWISE has now detected close to 160
,000 new asteroids and comets in our

439
00:33:32,450 --> 00:33:36,270
system, and about 780 of those are
things that are near the Earth.

440
00:33:36,970 --> 00:33:43,589
Ten of those near objects have been
classified as PHAs, potentially

441
00:33:43,590 --> 00:33:46,610
asteroids, without NEOWISE.

442
00:33:47,080 --> 00:33:48,340
we would have missed them.

443
00:33:48,660 --> 00:33:53,499
Using an infrared space telescope is a
way of better detecting some of the

444
00:33:53,500 --> 00:33:57,280
smaller asteroids and comets in the near
-Earth vicinity.

445
00:33:58,080 --> 00:34:04,019
Detection is an important first step,
but it only tells us there's another

446
00:34:04,020 --> 00:34:05,320
asteroid out there.

447
00:34:05,660 --> 00:34:10,520
Once we've spotted an asteroid... All we
know is that it's a tiny dot of light.

448
00:34:10,540 --> 00:34:15,339
We don't know anything else about it. So
when a new asteroid is discovered, the

449
00:34:15,340 --> 00:34:18,979
most important thing is to determine its
path, to track it, to figure out

450
00:34:18,980 --> 00:34:22,019
exactly how it's orbiting around the sun
and how close it's going to get to

451
00:34:22,020 --> 00:34:25,579
Earth. For that, we have to know where
they are now, so its current location,

452
00:34:25,580 --> 00:34:29,500
and measure how fast it's going and
which direction it's traveling.

453
00:34:29,501 --> 00:34:33,419
All of these things together are really
important for tracking where it's going

454
00:34:33,420 --> 00:34:36,010
to be next and whether or not they're
going to hit us.

455
00:34:38,120 --> 00:34:43,739
To get this information, we need
something much bigger and more powerful.

456
00:34:44,120 --> 00:34:46,540
The Arecibo Observatory.

457
00:34:46,840 --> 00:34:52,119
Once Catalina or another telescope
detects a near -Earth asteroid in our

458
00:34:52,120 --> 00:34:57,860
neighborhood, Arecibo's 1 ,000 -foot
dish swings into action.

459
00:34:58,730 --> 00:35:04,349
They discover these asteroids, and then
once we know where they were, we can try

460
00:35:04,350 --> 00:35:09,789
and point the radio telescope and see
where they are at the moment and measure

461
00:35:09,790 --> 00:35:12,170
their exact location and their
trajectory.

462
00:35:12,870 --> 00:35:18,370
Arecibo achieves this level of precision
by using radio detection and ranging,

463
00:35:18,770 --> 00:35:20,270
more commonly known.

464
00:35:21,730 --> 00:35:26,429
The planetary radar system at Arecibo
Observatory is the most powerful radar

465
00:35:26,430 --> 00:35:27,590
system in the world.

466
00:35:27,890 --> 00:35:32,649
We focus on potentially hazardous
asteroids, which are those that have a

467
00:35:32,650 --> 00:35:34,290
probability of impacting Earth.

468
00:35:35,470 --> 00:35:39,930
Arecibo sends out radio signals towards
the newly detected asteroid.

469
00:35:40,310 --> 00:35:42,330
It emanates radio signals.

470
00:35:42,570 --> 00:35:47,689
Some of them hit the asteroid, just like
a radar gun from a cop might hit the

471
00:35:47,690 --> 00:35:48,740
side of your car.

472
00:35:48,960 --> 00:35:53,040
It's pretty similar, but instead of
doing it with a radar gun on a small

473
00:35:53,260 --> 00:35:57,219
we're doing it at a really big scale
with one megawatt power hitting objects

474
00:35:57,220 --> 00:35:59,560
that are tens of them are distances
away.

475
00:36:00,040 --> 00:36:06,239
And then those radio waves bounce back
to Earth and we detect them again. And

476
00:36:06,240 --> 00:36:11,819
comparing the differences between what
we sent and what we received, we can get

477
00:36:11,820 --> 00:36:17,199
a map of the asteroid itself and we can
get where it's moving and how fast it's

478
00:36:17,200 --> 00:36:18,250
moving.

479
00:36:20,300 --> 00:36:24,020
But asteroids may not be the biggest
threat from faith.

480
00:36:25,100 --> 00:36:27,660
November 25, 2018.

481
00:36:28,800 --> 00:36:34,639
Cameras on board the solar and
heliospheric observatory film a large

482
00:36:34,640 --> 00:36:36,160
crashing into the sun.

483
00:36:38,140 --> 00:36:43,019
We recorded the impact of an object into
the sun at over a million miles per

484
00:36:43,020 --> 00:36:44,070
hour.

485
00:36:45,060 --> 00:36:46,740
The incredible speed.

486
00:36:47,040 --> 00:36:49,120
tells us that this was not an asteroid.

487
00:36:49,400 --> 00:36:55,019
It was the death plunge of something
much more unpredictable and dangerous, a

488
00:36:55,020 --> 00:36:58,440
killer object from the outer reaches of
the solar system.

489
00:36:59,560 --> 00:37:03,739
Comets, in some way, you could consider
maybe being more dangerous than near

490
00:37:03,740 --> 00:37:04,790
-Earth asteroids.

491
00:37:04,791 --> 00:37:08,559
With near -Earth asteroids, you could
imagine that we would discover all of

492
00:37:08,560 --> 00:37:12,819
them. And if we get perfect knowledge of
all of their orbits, we can predict

493
00:37:12,820 --> 00:37:16,520
into the future where they'll be and
when they may or may not.

494
00:37:16,810 --> 00:37:20,370
have an orbit that crosses the actual
Earth and could be an impact.

495
00:37:21,350 --> 00:37:24,470
Comets, a large part of that population,
we only see once.

496
00:37:24,471 --> 00:37:28,649
They come in from way out in the distant
part of the solar system, they do one

497
00:37:28,650 --> 00:37:32,130
lap around the sun, and they go back out
there for millions of years.

498
00:37:35,270 --> 00:37:39,590
Comets are dirty snowballs, huge lumps
of ice and dust.

499
00:37:39,970 --> 00:37:42,430
They come in two flavors.

500
00:37:42,431 --> 00:37:45,979
There's something we call short -period
comet.

501
00:37:45,980 --> 00:37:49,999
These are comets that are kind of
constrained to the solar system, the

502
00:37:50,000 --> 00:37:53,550
solar system, and their orbits are never
more than a few hundred years.

503
00:37:54,480 --> 00:37:59,119
Short -period comets come from the
Kuiper Belt, a region of the solar

504
00:37:59,120 --> 00:38:00,880
beyond the orbit of Neptune.

505
00:38:02,380 --> 00:38:06,440
These comets have short orbits on the
same plane as Earth.

506
00:38:12,940 --> 00:38:14,540
The second type of comet.

507
00:38:14,800 --> 00:38:17,180
are called long -period comets.

508
00:38:17,620 --> 00:38:23,279
They originate in the Oort Cloud, a
sphere of icy objects located at the

509
00:38:23,280 --> 00:38:24,880
edges of the solar system.

510
00:38:27,580 --> 00:38:31,619
There are thousands and thousands of
comets out there in the Oort Cloud.

511
00:38:31,620 --> 00:38:32,579
just waiting.

512
00:38:32,580 --> 00:38:35,819
And so, in principle, one of them can
get knocked off course and come raining

513
00:38:35,820 --> 00:38:37,700
down into the inner solar system.

514
00:38:41,770 --> 00:38:47,290
Long period comets are very large, and
they travel very fast.

515
00:38:48,130 --> 00:38:51,130
Comets can get really big, and they're
really heavy.

516
00:38:51,390 --> 00:38:55,510
And essentially, they're falling to
Earth from 2 billion light years away.

517
00:38:55,770 --> 00:38:58,490
So imagine how fast they're going.

518
00:38:59,270 --> 00:39:04,829
We know from studying asteroids that the
faster they go, the more kinetic energy

519
00:39:04,830 --> 00:39:06,070
they release on impact.

520
00:39:10,130 --> 00:39:11,270
Comet travel.

521
00:39:11,550 --> 00:39:13,330
even faster than asteroids.

522
00:39:14,210 --> 00:39:17,450
In general, they're moving 50 % faster,
something like that.

523
00:39:17,650 --> 00:39:21,990
But that doubles their impact energy.
And that's sort of a best -case

524
00:39:22,190 --> 00:39:26,369
In a worst -case scenario, pound for
pound, they could have five or up to

525
00:39:26,370 --> 00:39:29,210
ten times as much energy as an asteroid
impact.

526
00:39:33,550 --> 00:39:37,070
The Bering Sea asteroid blew up in the
atmosphere.

527
00:39:37,800 --> 00:39:42,660
But the Beringer crater asteroid hit the
ground intact with its full force.

528
00:39:45,300 --> 00:39:48,880
Why do different asteroids behave
differently?

529
00:39:49,360 --> 00:39:53,380
And what will Apophis do when it heads
our way?

530
00:39:54,520 --> 00:39:57,400
Arecibo's radar may have the answer.

531
00:39:58,200 --> 00:40:03,239
When we bounce radar waves off of these
objects, we can get... effectively

532
00:40:03,240 --> 00:40:07,919
imagery of the surface of some of these
small objects that we just cannot do

533
00:40:07,920 --> 00:40:09,180
with optical telescopes.

534
00:40:09,740 --> 00:40:12,760
This is the radar image of Apophis.

535
00:40:13,180 --> 00:40:17,880
It's so far away that all we could image
was a few pixels.

536
00:40:19,500 --> 00:40:24,040
So this is our most recent radar image
of asteroid Apophis.

537
00:40:25,120 --> 00:40:31,359
And you can see it's only a few pixels,
but it does give us... information on

538
00:40:31,360 --> 00:40:33,020
what it actually is.

539
00:40:34,320 --> 00:40:38,980
These few pixels are enough to work out
how big a pofis is.

540
00:40:40,520 --> 00:40:46,699
From this image, we can constrain the
size to be about 1 ,000 feet, which is

541
00:40:46,700 --> 00:40:50,480
about the same size as our receiver
radio telescope.

542
00:40:51,000 --> 00:40:53,900
All of that from a weird bunch of
pixels.

543
00:41:00,140 --> 00:41:05,179
Knowing the size and mass of an asteroid
is critical to understanding what an

544
00:41:05,180 --> 00:41:06,600
asteroid is made of.

545
00:41:07,560 --> 00:41:10,300
If we have the size and the mass, we get
the density.

546
00:41:10,520 --> 00:41:12,930
If we have the density, we know what
it's made of.

547
00:41:13,120 --> 00:41:14,800
Rock has some density.

548
00:41:15,180 --> 00:41:16,720
Metal has a different density.

549
00:41:16,920 --> 00:41:21,799
So we can determine a huge amount about
the asteroid simply by pinging it with

550
00:41:21,800 --> 00:41:22,850
radar.

551
00:41:25,620 --> 00:41:29,790
Arecibo's data reveals... that not all
asteroids are alike.

552
00:41:31,390 --> 00:41:35,000
There's not just one kind of asteroid.
There are actually several kinds.

553
00:41:35,250 --> 00:41:38,890
And this is important to understand
because they behave differently.

554
00:41:38,891 --> 00:41:42,629
They behave differently if they impact
us, and they behave differently if we're

555
00:41:42,630 --> 00:41:48,089
trying to prevent them from impacting
us. We need to know what these asteroids

556
00:41:48,090 --> 00:41:52,849
are made of, if they're going to hit the
Earth, because that drastically alters

557
00:41:52,850 --> 00:41:54,130
the potential effects.

558
00:41:54,350 --> 00:41:58,790
Asteroids come in different shapes,
different sizes, and different

559
00:41:59,110 --> 00:42:03,210
And we think that is because they are
the leftovers of planet formation.

560
00:42:03,590 --> 00:42:09,289
To understand how each asteroid formed
and its threat level, we have to go back

561
00:42:09,290 --> 00:42:13,670
4 .6 billion years to the start of the
solar system.

562
00:42:14,030 --> 00:42:18,069
The reason that there are all these
asteroids floating around in our solar

563
00:42:18,070 --> 00:42:22,089
system today is just because of the
early violence of the solar system as it

564
00:42:22,090 --> 00:42:23,140
forming.

565
00:42:25,040 --> 00:42:31,619
At the birth of the solar system, the
sun ignited, leaving a

566
00:42:31,620 --> 00:42:33,480
disk of gas and dust.

567
00:42:37,000 --> 00:42:40,200
Slowly over time, planets formed.

568
00:42:40,940 --> 00:42:42,360
Many planets.

569
00:42:43,660 --> 00:42:49,159
The early solar system was a messy
place. There were a lot more planets, a

570
00:42:49,160 --> 00:42:53,639
more forming planets. They would crash
into each other. They would merge. They

571
00:42:53,640 --> 00:42:55,640
would disintegrate. They would reform.

572
00:42:59,120 --> 00:43:04,780
This process of accretion, of building
planetary worlds, was not just, you

573
00:43:04,840 --> 00:43:07,280
kind of gentle and happy. It was
violent.

574
00:43:09,040 --> 00:43:12,620
It was like a giant cosmic game of pool.

575
00:43:14,199 --> 00:43:16,720
planets smashing into planets.

576
00:43:17,200 --> 00:43:22,960
The leftovers from this violence formed
a ring of junk between Mars and Jupiter.

577
00:43:23,420 --> 00:43:25,840
And now we call that junk asteroids.

578
00:43:26,240 --> 00:43:30,270
They're just basically rubble left over
from the formation of the solar system.

579
00:43:32,140 --> 00:43:36,500
Rocky leftovers became C -type, or
chondrite asteroids.

580
00:43:36,980 --> 00:43:42,260
They are quite dense, so big ones can
punch through the atmosphere.

581
00:43:42,720 --> 00:43:43,800
and hit the ground.

582
00:43:49,660 --> 00:43:52,840
Radar reveals a rarer type of asteroid.

583
00:43:54,100 --> 00:43:58,419
Some of them really stand out because
their density is so much higher than the

584
00:43:58,420 --> 00:43:59,800
rest of the other asteroids.

585
00:44:00,720 --> 00:44:04,000
These asteroids are M -type, or metal.

586
00:44:06,140 --> 00:44:11,140
Because their mass is great, they carry
more kinetic energy.

587
00:44:11,470 --> 00:44:12,520
During a strike.

588
00:44:13,250 --> 00:44:17,310
By far the worst one is this iron
meteorite.

589
00:44:17,530 --> 00:44:18,830
This is really heavy.

590
00:44:18,831 --> 00:44:22,529
So the difference, if you were being hit
by this, would be the difference

591
00:44:22,530 --> 00:44:26,050
between being hit by a rock and being
hit by a metal hammer.

592
00:44:27,750 --> 00:44:34,429
We think that both the Behringer and the
KPG dinosaur killer events were

593
00:44:34,430 --> 00:44:36,570
caused by metal asteroids.

594
00:44:40,080 --> 00:44:44,540
There is another, more mysterious type
floating through space.

595
00:44:47,980 --> 00:44:49,460
December 2018.

596
00:44:50,180 --> 00:44:55,740
NASA spacecraft OSIRIS -REx approached
the near -Earth asteroid Bennu.

597
00:44:57,700 --> 00:45:01,999
Over time, it drifted out of the main
asteroid belt, made its way into the

598
00:45:02,000 --> 00:45:06,319
solar system, until it became a near
-Earth asteroid accessible for our

599
00:45:06,320 --> 00:45:07,760
spacecraft to go in business.

600
00:45:08,960 --> 00:45:12,140
Osiris -Rex trained its camera on Bennu.

601
00:45:18,580 --> 00:45:23,979
One of the biggest surprises on arrival
at Bennu was the large number of large

602
00:45:23,980 --> 00:45:25,180
boulders on its surface.

603
00:45:25,380 --> 00:45:29,719
Bennu is really littered with huge
boulders and littered with medium -sized

604
00:45:29,720 --> 00:45:34,700
boulders and littered with small
boulders. Bennu is not a solid lump of

605
00:45:34,990 --> 00:45:40,590
It's made up of thousands of bits of
rock forming what we call a rubble pile.

606
00:45:40,990 --> 00:45:46,709
These asteroids aren't big, singular,
spherical balls of rock, but rather

607
00:45:46,710 --> 00:45:48,450
they're literally piles of rubble.

608
00:45:48,451 --> 00:45:51,909
They're all sorts of pieces and
fragments from another asteroid that had

609
00:45:51,910 --> 00:45:56,249
previously been disrupted that have all
come back together and formed literally

610
00:45:56,250 --> 00:45:59,150
a pile of rocks held together by their
own gravity.

611
00:45:59,630 --> 00:46:04,370
We think rubble piles form from
collisions inside the asteroid belt.

612
00:46:04,830 --> 00:46:11,109
Each impact blasted bits off. Then over
time, they came back together to form

613
00:46:11,110 --> 00:46:12,770
the loose pile of rocks.

614
00:46:13,230 --> 00:46:18,529
Imagine taking a big cosmic dump truck
full of gravel and rubble and dumping it

615
00:46:18,530 --> 00:46:22,250
out there into space and letting gravity
weakly hold it together.

616
00:46:23,630 --> 00:46:28,670
When scientists probed deeper into
Bennu, they had another surprise.

617
00:46:29,210 --> 00:46:32,790
It's full of holes, like Swiss cheese.

618
00:46:33,610 --> 00:46:37,749
If you could slice open one of these
asteroids, you'd see there are a lot of

619
00:46:37,750 --> 00:46:42,110
voids. In fact, 60 % of what we're
looking at is a void space.

620
00:46:42,350 --> 00:46:44,090
So they're actually really fluffy.

621
00:46:44,330 --> 00:46:47,880
So even though they're made of rocks,
they're sort of the lint of rocks.

622
00:46:48,290 --> 00:46:51,070
Bennu helps us understand a pulpit.

623
00:46:51,730 --> 00:46:56,550
Radar data shows that a pulpit is also a
rubble pile.

624
00:46:56,551 --> 00:47:00,479
If you look at Apophis, we really want
to know how its orbit will evolve in the

625
00:47:00,480 --> 00:47:05,339
future. What we learn at Bennu about
similar -sized rubble pile asteroids

626
00:47:05,340 --> 00:47:08,290
help us understand the future of an
asteroid like Apophis.

627
00:47:08,760 --> 00:47:12,840
So what would happen if rubble pile
Apophis hits Earth?

628
00:47:12,841 --> 00:47:16,979
You probably don't want that to hit you
still, but it definitely makes it a lot

629
00:47:16,980 --> 00:47:22,559
weaker than something like a solid rock
or, even more, a chunk of nickel -iron

630
00:47:22,560 --> 00:47:25,420
metal. Does its rubble pile composition?

631
00:47:25,960 --> 00:47:27,780
make it any less of a threat.

632
00:47:28,180 --> 00:47:32,999
A rubble pile like Apophis is especially
unnerving because we don't know when it

633
00:47:33,000 --> 00:47:36,139
interacts with the atmosphere if it's
going to stay as one solid piece.

634
00:47:36,140 --> 00:47:37,190
Will it break up?

635
00:47:38,380 --> 00:47:42,979
When these rubble piles start
interacting with planets, if they fly

636
00:47:42,980 --> 00:47:46,059
planet, they can get pulled apart into
all of their little pieces.

637
00:47:46,060 --> 00:47:50,899
Or if they enter the atmosphere of a
planet to impact the surface, they might

638
00:47:50,900 --> 00:47:53,620
slowly get pulled apart as they enter
the atmosphere.

639
00:47:54,750 --> 00:47:58,510
and end up being an array of little
impacts instead of one big single

640
00:48:03,590 --> 00:48:07,310
In 2017, we had another wake -up call.

641
00:48:07,650 --> 00:48:11,370
A strange base rock arrived in our
neighborhood.

642
00:48:11,790 --> 00:48:15,590
Its shape was unlike anything we'd seen
before.

643
00:48:16,650 --> 00:48:20,849
The thing that made Oumuamua different
from anything else we'd ever seen is it

644
00:48:20,850 --> 00:48:25,090
seemed to be almost a shard, a sharp
piece of metal tumbling through space.

645
00:48:26,390 --> 00:48:30,350
Typically, things that move around our
solar system are somewhat spherical.

646
00:48:31,470 --> 00:48:35,110
This in no way was spherical. It was
almost cigar -shaped.

647
00:48:35,640 --> 00:48:39,540
So it kind of really plugged into all
those alien theories.

648
00:48:39,940 --> 00:48:43,820
But we were able to confirm that it
didn't flow down as it went by the

649
00:48:43,821 --> 00:48:47,239
which was, we figured if it was an alien
craft, it would probably stop and have

650
00:48:47,240 --> 00:48:49,950
a little bit of a look. But it carried
on its trajectory.

651
00:48:50,380 --> 00:48:54,660
It wasn't a comet or an asteroid from
the asteroid belt.

652
00:48:55,100 --> 00:48:58,560
It was a space rock from interstellar
space.

653
00:48:58,561 --> 00:49:03,619
Interstellar asteroids are probably
pretty rare, but the thing about them is

654
00:49:03,620 --> 00:49:05,020
they're moving really fast.

655
00:49:05,460 --> 00:49:08,500
So if they happen to hit us, it's really
bad.

656
00:49:09,580 --> 00:49:14,560
Oumuamua was traveling over 100 times
faster than a fighter jet.

657
00:49:14,840 --> 00:49:17,920
And as we know, speed means danger.

658
00:49:18,980 --> 00:49:23,599
Had Oumuamua been on an impact
trajectory with the Earth, at those

659
00:49:23,600 --> 00:49:27,480
speeds, very much faster than anything
in our solar system,

660
00:49:28,400 --> 00:49:33,879
remember the kinetic energy goes as the
square of the impact speed. At those

661
00:49:33,880 --> 00:49:34,930
kinds of speeds,

662
00:49:35,760 --> 00:49:40,859
imagine it hitting us at 196 ,000 miles
per hour, that carries an incredibly

663
00:49:40,860 --> 00:49:46,439
powerful punch. And so for a given size
object, the impact of Oumuamua compared

664
00:49:46,440 --> 00:49:50,720
to a... regular solar system objects
would have been absolutely devastating.

665
00:49:51,680 --> 00:49:56,619
Oumuamua passed safely through the solar
system, but it won't be the last

666
00:49:56,620 --> 00:49:58,660
invader from interstellar space.

667
00:49:59,180 --> 00:50:05,079
Astronomers estimate that one alien
object visits our cosmic neighborhood

668
00:50:05,080 --> 00:50:06,130
year.

669
00:50:09,700 --> 00:50:10,750
2019.

670
00:50:11,600 --> 00:50:12,650
U .S.

671
00:50:12,880 --> 00:50:15,240
researchers discovered deposits of
fossils.

672
00:50:15,980 --> 00:50:20,400
They contain both the remnants of land
and sea creatures.

673
00:50:20,920 --> 00:50:26,599
You see things that are all jumbled
together. So you'll have fossils of sea

674
00:50:26,600 --> 00:50:32,779
creatures. You'll have ocean deposits
that are mixed up with coastal deposits

675
00:50:32,780 --> 00:50:38,519
and onshore deposits. And you see those
deposits in places that are very, very

676
00:50:38,520 --> 00:50:42,719
far away from where you would expect
them to be. And so this material was

677
00:50:42,720 --> 00:50:44,840
obviously thrown very far inland.

678
00:50:46,760 --> 00:50:52,639
The jumbled deposits suggest the
creatures were killed at the same time

679
00:50:52,640 --> 00:50:57,799
huge and violent event, something
powerful enough to sweep ocean -dwelling

680
00:50:57,800 --> 00:50:59,840
creatures far inland.

681
00:51:00,940 --> 00:51:02,300
A tsunami.

682
00:51:03,080 --> 00:51:07,920
Tsunamis are usually created when the
ocean floor suddenly moves.

683
00:51:08,420 --> 00:51:14,199
The ground picks up the entire ocean and
shakes it up and down, and it's sort of

684
00:51:14,200 --> 00:51:15,820
like taking a rope and shaking it.

685
00:51:15,900 --> 00:51:20,820
and it moves all across the ocean floor
and ocean surface until it reaches land.

686
00:51:21,020 --> 00:51:26,019
The biggest recent tsunami was caused by
the Earth's crust at the bottom of the

687
00:51:26,020 --> 00:51:31,379
ocean lifting slightly. So this means
that that entire length of crust that

688
00:51:31,380 --> 00:51:37,619
lifted displaced the water above it. So
the waves, the tsunamis that result, are

689
00:51:37,620 --> 00:51:42,919
really long and wide, and it can travel
across the ocean at tremendous speeds

690
00:51:42,920 --> 00:51:44,020
and up on land.

691
00:51:46,350 --> 00:51:49,130
Is this what happened to the fossilized
creatures?

692
00:51:49,530 --> 00:51:52,370
Were they killed by a huge tsunami?

693
00:51:53,030 --> 00:51:55,690
Clues come from dating the preserved
remains.

694
00:51:56,910 --> 00:51:59,850
They are 66 million years old.

695
00:52:00,070 --> 00:52:05,889
From the same time, a six -mile -wide
asteroid crashed into the sea off the

696
00:52:05,890 --> 00:52:07,510
Yucatan Peninsula, Mexico.

697
00:52:11,290 --> 00:52:13,350
Are the two events connected?

698
00:52:14,190 --> 00:52:17,930
Do ocean -impacting asteroids trigger
tsunamis?

699
00:52:18,490 --> 00:52:22,589
We used to think that a big asteroid
impacting in the ocean would drive a

700
00:52:22,590 --> 00:52:28,189
tremendous tsunami, a huge wall of
water, out at very rapid speeds, which

701
00:52:28,190 --> 00:52:29,930
basically scour clean everything.

702
00:52:30,770 --> 00:52:36,110
Now, new research from 2018 suggests a
very different scenario.

703
00:52:36,690 --> 00:52:41,910
Scientists used supercomputers to model
asteroids hitting the deep ocean.

704
00:52:42,480 --> 00:52:47,819
to work out how much of the asteroid's
kinetic energy is converted into a

705
00:52:47,820 --> 00:52:48,870
tsunami wave.

706
00:52:50,200 --> 00:52:56,999
In the simulations, a 1600 -foot
asteroid hits the ocean at 20 ,000 miles

707
00:52:57,000 --> 00:52:59,640
an hour and dives into the water.

708
00:53:01,040 --> 00:53:05,859
As it goes deeper in, of course it's
meeting a lot of resistance, and it

709
00:53:05,860 --> 00:53:10,179
down and it compresses up. It compresses
and compresses and compresses. And then

710
00:53:10,180 --> 00:53:14,940
finally it runs out of momentum, and
it's at an extremely high pressure.

711
00:53:15,880 --> 00:53:21,060
The huge pressure causes the asteroid to
explode and vaporize.

712
00:53:21,880 --> 00:53:26,779
Temperatures hotter than the surface of
the sun turn trillions of gallons of

713
00:53:26,780 --> 00:53:27,960
water into steam.

714
00:53:28,360 --> 00:53:29,520
The blast.

715
00:53:29,820 --> 00:53:36,339
creates a huge short -lived cavity in
the water surface and a splash curtain,

716
00:53:36,340 --> 00:53:39,100
wall of water that leaps up several
miles.

717
00:53:39,540 --> 00:53:45,339
This curtain then collapses and water
falls back into the cavity, shooting a

718
00:53:45,340 --> 00:53:48,220
column of water five miles up.

719
00:53:48,460 --> 00:53:53,840
This very tall column can't support its
own weight and collapses back down.

720
00:53:54,760 --> 00:53:57,060
The collapse of so much water.

721
00:53:57,390 --> 00:53:59,790
triggers a 1 ,200 -foot -high wave.

722
00:54:00,230 --> 00:54:02,970
Could this become a huge tsunami?

723
00:54:08,470 --> 00:54:12,869
If we think about a meteor striking the
ocean, we want to understand how far the

724
00:54:12,870 --> 00:54:16,089
waves might propagate from the site. We
could actually just use a stone and

725
00:54:16,090 --> 00:54:17,390
throw it into a pond.

726
00:54:17,391 --> 00:54:21,089
And you might think, OK, well, it's a
big stone. It's going to make a really

727
00:54:21,090 --> 00:54:23,689
splash, and that's just going to extend
out a long distance.

728
00:54:23,690 --> 00:54:27,299
But it turns out the splash stays... the
biggest, really close to where it

729
00:54:27,300 --> 00:54:30,670
impacts, and then the ripples die down
after that. So let's try that.

730
00:54:32,240 --> 00:54:33,540
Big splash in the middle.

731
00:54:33,541 --> 00:54:38,079
And we see the ripples going outward,
but they're really pretty small compared

732
00:54:38,080 --> 00:54:39,520
with that initial big splash.

733
00:54:41,560 --> 00:54:44,900
It's the same with an ocean -impacting
asteroid.

734
00:54:45,920 --> 00:54:51,519
The impact creates surface waves that
die away quickly because only a small

735
00:54:51,520 --> 00:54:54,600
amount of the asteroid's kinetic energy
gets into the water.

736
00:54:55,160 --> 00:54:59,179
It's actually pretty tough to make a
tsunami like that. The energy of the

737
00:54:59,180 --> 00:55:03,000
asteroid doesn't couple well with the
water to drive this wave.

738
00:55:03,400 --> 00:55:08,779
Instead, most of the energy goes into
vaporizing the asteroid itself, as well

739
00:55:08,780 --> 00:55:10,320
all of the water around it.

740
00:55:11,000 --> 00:55:16,080
Only 1 % of the asteroid's kinetic
energy goes into making a wave.

741
00:55:16,520 --> 00:55:23,079
So only low -energy waves form, too weak
to become giant tsunamis traveling

742
00:55:23,080 --> 00:55:24,280
hundreds of miles.

743
00:55:25,040 --> 00:55:30,339
So what caused the jumbled fossil
deposit thousands of miles away from the

744
00:55:30,340 --> 00:55:31,390
impact site?

745
00:55:31,500 --> 00:55:36,219
We don't think there could be that much
energy still transmitted that far away

746
00:55:36,220 --> 00:55:37,270
from the impact site.

747
00:55:37,780 --> 00:55:42,159
Instead, there has to be a different
source of energy that created different

748
00:55:42,160 --> 00:55:45,180
waves right about the same time as that
impact event.

749
00:55:47,180 --> 00:55:50,320
Research from 2019 may have the answer.

750
00:55:50,910 --> 00:55:56,869
The KPG asteroid struck on the
continental shelf, the shallow region

751
00:55:56,870 --> 00:55:58,690
land and deep ocean.

752
00:55:59,050 --> 00:56:04,709
The impact triggered a localized
tsunami, large enough to kill creatures

753
00:56:04,710 --> 00:56:09,570
region. But it also sent a huge
shockwave into the bedrock.

754
00:56:09,950 --> 00:56:14,289
There's going to be a shockwave driven
through the ground. That probably would

755
00:56:14,290 --> 00:56:20,450
have killed anything in the area. If you
had a dinosaur that was standing on...

756
00:56:20,620 --> 00:56:27,319
The Gulf Coast of what is now the United
States, that animal would have

757
00:56:27,320 --> 00:56:33,879
experienced a seismic pulse, an
earthquake that is stronger than

758
00:56:33,880 --> 00:56:38,159
current Richter scale. It would have
actually driven its legs up into its

759
00:56:38,160 --> 00:56:39,660
cavity, killing it instantly.

760
00:56:39,720 --> 00:56:44,719
There's all manner of mayhem and death
taking place at this time. There was no

761
00:56:44,720 --> 00:56:45,770
escape in this event.

762
00:56:48,880 --> 00:56:52,780
The initial shockwave would have
traveled through the Earth's crust.

763
00:56:54,560 --> 00:56:59,779
The impact would have shaken the crust
of the Earth, which also would have

764
00:56:59,780 --> 00:57:03,819
triggered earthquakes around the world,
which themselves may have triggered

765
00:57:03,820 --> 00:57:05,080
secondary tsunamis.

766
00:57:08,240 --> 00:57:14,039
Secondary tsunamis, thousands of miles
from the impact site, killed both land

767
00:57:14,040 --> 00:57:15,260
and sea creatures.

768
00:57:15,780 --> 00:57:17,700
The KPG impact.

769
00:57:18,000 --> 00:57:22,400
went on to wipe out 70 % of all life on
Earth.

770
00:57:28,580 --> 00:57:34,000
How could one space rock hitting the sea
cause a global catastrophe?

771
00:57:35,760 --> 00:57:40,879
When you have a big rock hitting the
ocean, the biggest danger is not from

772
00:57:40,880 --> 00:57:43,700
waves, but actually from the steam that
it creates.

773
00:57:44,280 --> 00:57:45,330
The impact.

774
00:57:45,760 --> 00:57:48,620
vaporized trillions of tons of seawater.

775
00:57:48,940 --> 00:57:54,800
This steam rose up into the atmosphere
where it condensed into water vapor.

776
00:57:55,460 --> 00:57:57,480
Water vapor is a greenhouse gas.

777
00:57:57,710 --> 00:58:04,149
So that's then going up into the upper
atmosphere, and it's trapping heat, but

778
00:58:04,150 --> 00:58:08,069
at different layers it's making clouds.
It's just throwing everything off

779
00:58:08,070 --> 00:58:12,889
kilter. Water is a very effective
greenhouse gas. You will actually affect

780
00:58:12,890 --> 00:58:16,950
very significant climate change very
quickly as a result of that impact.

781
00:58:19,050 --> 00:58:24,229
Within weeks of the asteroid strike,
water vapor in the atmosphere caused

782
00:58:24,230 --> 00:58:25,470
temperatures to rise.

783
00:58:26,920 --> 00:58:28,700
But that was only the start.

784
00:58:29,500 --> 00:58:35,700
The impact also blew out 10 trillion
tons of rock, ash, and dust.

785
00:58:38,000 --> 00:58:43,440
This asteroid is so big, it's six miles
wide. It's punched a hole in the air.

786
00:58:43,560 --> 00:58:47,699
There's like a column of low density, a
chimney, that goes from the ground up to

787
00:58:47,700 --> 00:58:48,919
the top of the atmosphere.

788
00:58:48,920 --> 00:58:52,340
And that means there's very little air
resistance in that tunnel.

789
00:58:52,970 --> 00:58:57,629
These rocks can actually blast up into
the chimney and find it easier to get up

790
00:58:57,630 --> 00:59:03,149
out of the atmosphere. It sent that
material flying up halfway to the orbit

791
00:59:03,150 --> 00:59:08,769
the moon, circled around the Earth, all
this ring of material falling back onto

792
00:59:08,770 --> 00:59:12,450
the Earth, and it was like the sky
itself was on fire.

793
00:59:13,030 --> 00:59:17,069
So you not only do have rocks falling on
you, but they're molten, and these

794
00:59:17,070 --> 00:59:21,050
rocks will start catching plants and
anything else on fire.

795
00:59:26,920 --> 00:59:31,940
Soot and ash rose up into the
atmosphere, blocking the sun.

796
00:59:35,000 --> 00:59:39,439
Material was thrown into the atmosphere,
plunging the planet into a nuclear

797
00:59:39,440 --> 00:59:44,580
winter. It was complete chaos, and it
went dark for two full years.

798
00:59:46,200 --> 00:59:49,820
Without sunlight, temperatures seesawed.

799
00:59:50,520 --> 00:59:55,680
Just months after the impact, the planet
cooled by 20 degrees.

800
00:59:57,100 --> 01:00:00,230
In the immediate area, there's just
tremendous destruction.

801
01:00:00,231 --> 01:00:01,839
Just everything gets destroyed.

802
01:00:01,840 --> 01:00:06,040
But over the long term, you're talking
about ash kicked up in the atmosphere,

803
01:00:06,320 --> 01:00:09,880
extremely cold weather, basically a
global ice age.

804
01:00:11,480 --> 01:00:14,620
The freezing temperatures killed off
most plant life.

805
01:00:15,700 --> 01:00:17,880
Imagine how that affected life on Earth.

806
01:00:18,160 --> 01:00:21,600
No plants, and the base of the ecosystem
collapses.

807
01:00:24,720 --> 01:00:30,819
This dark nuclear winter lasted two
years and prevented plants from

808
01:00:30,820 --> 01:00:32,100
photosynthesizing.

809
01:00:33,280 --> 01:00:38,499
So if plants can no longer use
photosynthesis to live, they'll die. And

810
01:00:38,500 --> 01:00:42,220
with no plants, then you have no food
for these larger animals.

811
01:00:42,500 --> 01:00:46,720
And so anything that eats those animals
will also die. If you lose your plants,

812
01:00:46,880 --> 01:00:49,110
you're going to lose your large -scale
life.

813
01:00:50,040 --> 01:00:53,100
First, plant -eating herbivores died
off.

814
01:00:53,420 --> 01:00:55,500
than meat -eating carnivores.

815
01:00:56,660 --> 01:01:02,019
Most of the dinosaurs were just unable
to find food and to survive through the

816
01:01:02,020 --> 01:01:03,440
cold, long night.

817
01:01:04,460 --> 01:01:08,040
The global devastation wasn't over yet.

818
01:01:08,340 --> 01:01:14,259
The rock of the continental shelf, where
the asteroid hit, contained carbon and

819
01:01:14,260 --> 01:01:15,310
sulfur.

820
01:01:15,820 --> 01:01:21,759
These carbonate rocks were heated and
vaporized and released carbon dioxide

821
01:01:21,760 --> 01:01:27,039
the atmosphere, yet another greenhouse
gas. So you're vaporizing a lot of

822
01:01:27,040 --> 01:01:33,279
sulfur, a lot of salt of different kinds
that are then lofted up into the upper

823
01:01:33,280 --> 01:01:35,880
atmosphere that then plays havoc on the
climate.

824
01:01:40,840 --> 01:01:44,080
These greenhouse gases built up in the
atmosphere.

825
01:01:44,780 --> 01:01:46,560
forming a warming blanket.

826
01:01:49,600 --> 01:01:53,900
These gases triggered the next phase of
destruction.

827
01:01:55,460 --> 01:01:58,620
Global warming on steroids.

828
01:02:00,880 --> 01:02:04,680
Temperatures rose 10 degrees above
normal.

829
01:02:05,020 --> 01:02:07,820
Then the oceans warmed as well.

830
01:02:08,680 --> 01:02:12,980
Oxygen levels dropped and the seas
became toxic.

831
01:02:13,400 --> 01:02:14,900
To simple life forms.

832
01:02:16,640 --> 01:02:21,559
That actually made it impossible for
certain microbes to actually live. And

833
01:02:21,560 --> 01:02:26,319
they're the basis of the food system. So
really it changed what could actually

834
01:02:26,320 --> 01:02:28,680
live in the ocean and how much could
live there.

835
01:02:30,360 --> 01:02:34,980
Dead zones appeared in the oceans just
as they had on land.

836
01:02:36,100 --> 01:02:39,180
Nearly three quarters of life on Earth
died.

837
01:02:41,840 --> 01:02:44,580
All from what asteroid impact?

838
01:02:48,520 --> 01:02:54,079
To prevent it from happening again, we
need to track all potentially dangerous

839
01:02:54,080 --> 01:03:00,999
asteroids. But that's not easy, because
these floating space rocks can change

840
01:03:01,000 --> 01:03:02,050
direction.

841
01:03:11,220 --> 01:03:14,200
Security cameras record a flash in the
sky.

842
01:03:16,800 --> 01:03:21,520
The flash was from a three -foot
asteroid exploding in the atmosphere.

843
01:03:28,020 --> 01:03:32,699
It blew up in the atmosphere and rained
down. And people saw that. It was very

844
01:03:32,700 --> 01:03:37,399
noticeable. And they went and they
collected those meteorites. And then

845
01:03:37,400 --> 01:03:39,690
tried to figure out what they were
looking at.

846
01:03:42,280 --> 01:03:45,240
The debris was sent for fragment
analysis.

847
01:03:47,300 --> 01:03:48,940
I have a piece of one here.

848
01:03:49,180 --> 01:03:53,199
So first, on the outside, you can see it
has a really black fusion crust. This

849
01:03:53,200 --> 01:03:56,039
is from when it fell into the Earth's
atmosphere, so it was melted.

850
01:03:56,040 --> 01:04:01,240
But when you look on the inside, it
reveals this beautiful, very light

851
01:04:01,300 --> 01:04:02,500
fine -grained material.

852
01:04:02,760 --> 01:04:06,550
And so these meteorites are incredibly
distinctive and really beautiful.

853
01:04:07,080 --> 01:04:08,960
The meteorites are rocky.

854
01:04:09,520 --> 01:04:14,060
Their beautiful color comes from a
mineral called Howardite.

855
01:04:14,440 --> 01:04:17,520
It's rare, and it doesn't form on Earth.

856
01:04:18,860 --> 01:04:23,439
Howardite meteorites come from the
asteroid Vesta, and we know that because

857
01:04:23,440 --> 01:04:27,139
the Dawn mission that actually went to
Vesta and took a look at it very

858
01:04:27,140 --> 01:04:29,620
carefully, so we know the composition
very well.

859
01:04:29,860 --> 01:04:34,359
And so now suddenly here was a new kind
of meteorite that's in Turkey that

860
01:04:34,360 --> 01:04:37,360
matches the Vesta family of meteorites.

861
01:04:41,130 --> 01:04:45,830
But how can we be sure that these bits
of space rock come from Vesta?

862
01:04:47,630 --> 01:04:52,389
It was a fall meteorite, and so what
that means is that someone saw it. You

863
01:04:52,390 --> 01:04:56,949
know, we saw it fall, and so we knew its
trajectory, so we could actually work

864
01:04:56,950 --> 01:05:00,130
backwards to say, where did that
meteorite come from?

865
01:05:01,210 --> 01:05:06,169
Tracing the trajectory of the Turkish
meteorite back took the scientists all

866
01:05:06,170 --> 01:05:09,430
way to the 328 -mile -wide Vesta.

867
01:05:13,040 --> 01:05:17,620
When they studied Vesta's surface, they
found further evidence.

868
01:05:18,540 --> 01:05:23,339
On the surface of Vesta, there's
actually a very large and fresh impact

869
01:05:23,340 --> 01:05:29,099
that is around the same age of the
Turkish meteorite. So that really

870
01:05:29,100 --> 01:05:32,080
it. This thing is definitely from Vesta,
and we proved it.

871
01:05:32,720 --> 01:05:36,620
So how did bits of Vesta end up here on
Earth?

872
01:05:37,070 --> 01:05:43,409
22 million years ago, some very large
impactor struck Vesta and made a huge

873
01:05:43,410 --> 01:05:48,349
crater. And some of the rocks from that
crater actually escaped from Vesta's

874
01:05:48,350 --> 01:05:50,890
gravity and were lofted into space.

875
01:05:53,150 --> 01:05:58,050
Some of these rocks from Vesta went into
orbit that intersected with Earth.

876
01:05:58,510 --> 01:06:03,130
22 million years later, one blew up over
Sarah Chichak.

877
01:06:05,230 --> 01:06:10,930
The Saracicic meteor shows that the
asteroid belt is an unstable

878
01:06:13,610 --> 01:06:17,270
Asteroids frequently strike other
asteroids.

879
01:06:17,271 --> 01:06:23,399
That's actually happening all the time.
Things are running into each other in

880
01:06:23,400 --> 01:06:28,139
our solar system right now. And so that
makes it really hard for us to track all

881
01:06:28,140 --> 01:06:31,899
of those objects because we don't
actually know what happens after they

882
01:06:31,900 --> 01:06:35,079
with each other. Now things are totally
different. That changes the whole

883
01:06:35,080 --> 01:06:36,130
system.

884
01:06:36,660 --> 01:06:39,140
Each collision makes more asteroids.

885
01:06:39,141 --> 01:06:44,679
There's many different possibilities of
what could happen when asteroids

886
01:06:44,680 --> 01:06:47,900
collide. Imagine a roller derby
situation.

887
01:06:50,570 --> 01:06:55,169
You have two groups of players that run
into each other. That could be like two

888
01:06:55,170 --> 01:06:56,910
asteroids running into each other.

889
01:06:57,190 --> 01:07:02,829
And one possible outcome is that one
stays intact while the other is

890
01:07:02,830 --> 01:07:03,880
blown apart.

891
01:07:06,650 --> 01:07:09,900
That sends fragments flying all through
the main asteroid belt.

892
01:07:09,901 --> 01:07:14,029
And then those little asteroid fragments
are on their own independent orbits

893
01:07:14,030 --> 01:07:15,080
around the sun.

894
01:07:16,310 --> 01:07:20,350
A problem with asteroid impacts is that
we're always making new asteroids.

895
01:07:20,351 --> 01:07:24,489
There are big asteroids out there, and
they get hit by other asteroids, and you

896
01:07:24,490 --> 01:07:28,649
get shrapnel. And now you've got not one
big one and one smaller one. You've got

897
01:07:28,650 --> 01:07:31,540
one big one, one smaller one, and
millions of little ones.

898
01:07:31,541 --> 01:07:35,369
Now, most of these aren't very big, but
some of them might be bigger and could

899
01:07:35,370 --> 01:07:36,690
be potentially hazardous.

900
01:07:38,050 --> 01:07:42,410
As the solar system ages, the number of
asteroids increases.

901
01:07:43,250 --> 01:07:44,710
Each new space rock.

902
01:07:44,940 --> 01:07:48,800
travels on a new course, which could
intersect with Earth.

903
01:07:49,820 --> 01:07:54,059
So we're constantly producing new
asteroids and big collisions in the main

904
01:07:54,060 --> 01:07:54,919
asteroid belt.

905
01:07:54,920 --> 01:07:58,419
And these are producing the small
asteroids that will eventually drift

906
01:07:58,420 --> 01:07:59,470
the solar system.

907
01:08:00,700 --> 01:08:06,379
Tracking this constantly evolving
population of asteroids gives scientists

908
01:08:06,380 --> 01:08:07,430
huge headache.

909
01:08:07,880 --> 01:08:12,119
If they break apart, then that gives you
even more pieces of the asteroid to

910
01:08:12,120 --> 01:08:14,340
track. It's not a simple thing.

911
01:08:14,640 --> 01:08:19,160
to track and predict the orbit of
asteroids and their movements.

912
01:08:19,460 --> 01:08:25,759
Because one tiny little change can have
huge dramatic

913
01:08:25,760 --> 01:08:28,920
impacts for its possible future.

914
01:08:28,921 --> 01:08:32,978
Figuring out exactly where they're going
to go and keeping track of how they

915
01:08:32,979 --> 01:08:35,509
interact with each other, this is a huge
endeavor.

916
01:08:36,560 --> 01:08:42,339
The sheer volume of asteroids can affect
the behavior of other asteroids as they

917
01:08:42,340 --> 01:08:43,720
gravitationally interact.

918
01:08:44,620 --> 01:08:48,020
Think about your roller derby player,
skating in circles.

919
01:08:48,021 --> 01:08:52,159
The path they're going to follow will
evolve the more people you plop down on

920
01:08:52,160 --> 01:08:53,039
that track.

921
01:08:53,040 --> 01:08:56,770
They start interacting with each other
and their trajectory will change.

922
01:08:57,979 --> 01:09:02,318
The more crowded you make the solar
system, the more things there are to

923
01:09:02,319 --> 01:09:04,899
your orbit of your individual asteroid.

924
01:09:07,060 --> 01:09:11,339
It's not like air traffic control where
there's a known amount of airplanes and

925
01:09:11,340 --> 01:09:12,420
they all follow a plan.

926
01:09:13,260 --> 01:09:19,299
This situation is further complicated
because asteroid orbits can be affected

927
01:09:19,300 --> 01:09:21,120
other, more subtle forces.

928
01:09:22,640 --> 01:09:26,160
One of these is called the Yarkovsky, or
the Yorp effect.

929
01:09:26,600 --> 01:09:28,700
Honestly, Yorp is more fun to say.

930
01:09:29,260 --> 01:09:33,580
The Yorp effect is caused by sunlight
hitting an asteroid.

931
01:09:34,060 --> 01:09:38,339
Light is made up of photons that are
traveling, and these photons actually

932
01:09:38,340 --> 01:09:42,560
momentum. So when light shines on
something, it actually pushes on it.

933
01:09:44,910 --> 01:09:51,228
When sunlight hits an asteroid, the
photons give it a tiny push, enough

934
01:09:51,229 --> 01:09:54,350
to change the space rock's trajectory.

935
01:10:04,710 --> 01:10:08,710
Asteroids can change course, which makes
tracking them hard.

936
01:10:09,330 --> 01:10:12,890
Comets stay on course, but they are much
harder to track.

937
01:10:16,620 --> 01:10:21,559
We track asteroids pretty regularly
because they hang out in the inner solar

938
01:10:21,560 --> 01:10:24,400
system. We can look for any potential
dangerous ones.

939
01:10:24,600 --> 01:10:29,639
The comets are a completely different
story because they come in from random

940
01:10:29,640 --> 01:10:31,760
directions at random times.

941
01:10:32,000 --> 01:10:34,240
They are completely unpredictable.

942
01:10:36,280 --> 01:10:40,340
Which is why we've only detected a
fraction of what's out there.

943
01:10:42,000 --> 01:10:46,280
There are millions and tens of millions
of them. Guess how many we found?

944
01:10:46,560 --> 01:10:47,900
6 ,300.

945
01:10:48,460 --> 01:10:50,740
That means that we virtually found zero.

946
01:10:51,800 --> 01:10:57,739
The low number is because long -period
comets spend much of their orbit over 10

947
01:10:57,740 --> 01:11:00,560
billion miles away, where they are
invisible.

948
01:11:03,260 --> 01:11:07,290
The trouble with long -period comets is,
of course, their periods are very long.

949
01:11:07,320 --> 01:11:11,879
And so we only see a small part of their
arc. They go very distant into the

950
01:11:11,880 --> 01:11:12,930
solar system.

951
01:11:13,660 --> 01:11:17,799
And so it just makes them difficult to
follow when they get a very long way

952
01:11:17,800 --> 01:11:20,379
the sun. We're not able to track their
orbits anymore.

953
01:11:20,380 --> 01:11:22,700
And so it becomes a little bit more
guesswork.

954
01:11:23,720 --> 01:11:27,919
We don't see them until they're already
in the inner solar system, inside the

955
01:11:27,920 --> 01:11:28,970
orbit of Jupiter.

956
01:11:30,830 --> 01:11:36,869
We never really know about them until
they've already started their passage

957
01:11:36,870 --> 01:11:40,749
really far away and started their dive
into the solar system at really high

958
01:11:40,750 --> 01:11:45,150
velocity. We really only discover these
comets at the very last minute.

959
01:11:46,290 --> 01:11:49,150
You could spot an asteroid 10, 15 years
in advance.

960
01:11:49,410 --> 01:11:51,700
These comets, that's basically
impossible.

961
01:11:51,830 --> 01:11:54,120
We may have a couple of years warning
for them.

962
01:12:01,990 --> 01:12:07,650
When we know an asteroid is really
heading our way, it's time to fight

963
01:12:08,290 --> 01:12:11,180
So we've got an asteroid that's headed
at us. What do we do?

964
01:12:11,370 --> 01:12:12,590
Two main possibilities.

965
01:12:12,850 --> 01:12:17,049
We deflect it, we nudge it a little bit
so it misses, or we blow it up, we

966
01:12:17,050 --> 01:12:19,220
destroy it. Which of those do you want
to do?

967
01:12:19,221 --> 01:12:23,889
This is something where our science
fiction ideas have gotten it almost

968
01:12:23,890 --> 01:12:28,950
wrong. If you're in a bad movie, a
really, really bad movie, movie.

969
01:12:29,170 --> 01:12:34,369
You can send astronauts to an asteroid,
put a nuclear bomb in it, and blow it up

970
01:12:34,370 --> 01:12:37,809
into lots of little bits that then burn
up harmlessly in our atmosphere.

971
01:12:37,810 --> 01:12:39,490
Yeah, it doesn't work that way.

972
01:12:40,110 --> 01:12:43,210
Blowing up an asteroid would make the
problem much worse.

973
01:12:43,470 --> 01:12:47,230
You're no longer dealing with just one
marauding space rock.

974
01:12:47,770 --> 01:12:51,970
My issue with this is that you may have
turned one problem into 50.

975
01:12:51,971 --> 01:12:56,009
Instead of one regular -sized asteroid,
now you have a whole bunch of littler

976
01:12:56,010 --> 01:12:59,569
ones, and these may still hit the Earth
and cause damage. And you know what?

977
01:12:59,570 --> 01:13:03,610
That's not much less fun than just
having a single big asteroid.

978
01:13:03,830 --> 01:13:07,189
Now you've just taken all that
devastation and spread it out for

979
01:13:07,190 --> 01:13:08,240
enjoy.

980
01:13:08,270 --> 01:13:13,029
The problem with using a nuclear device
is that the products that rain down on

981
01:13:13,030 --> 01:13:14,770
Earth are now radioactive.

982
01:13:22,210 --> 01:13:27,909
If a dangerous asteroid is on its way,
blowing up an asteroid would be a last

983
01:13:27,910 --> 01:13:33,710
resort. A less risky method is to
deflect it off its collision course.

984
01:13:34,090 --> 01:13:40,710
A small nudge early enough can change an
asteroid's trajectory away from Earth.

985
01:13:42,530 --> 01:13:47,189
You don't have to nudge it very much for
it to miss, right? So head it straight

986
01:13:47,190 --> 01:13:50,789
at it, just touch it slightly. By the
time it gets to Earth, it's way off

987
01:13:50,790 --> 01:13:51,840
course.

988
01:13:54,800 --> 01:14:00,559
NASA is investigating several techniques
to change an asteroid's path, including

989
01:14:00,560 --> 01:14:02,140
a nuclear burst.

990
01:14:02,760 --> 01:14:09,419
In a nuclear burst, what we do is we
don't actually hit it. We come up to it

991
01:14:09,420 --> 01:14:14,439
with the device on a spacecraft, and
then the device would be detonated at a

992
01:14:14,440 --> 01:14:16,120
certain height above the surface.

993
01:14:17,090 --> 01:14:21,329
That heats up the surface of the
asteroid, which vaporizes. You get

994
01:14:21,330 --> 01:14:25,729
rock or metal, which blasts off the
surface, and that's how a rocket works.

995
01:14:25,730 --> 01:14:29,449
you blow up a bomb here, and it winds up
pushing the asteroid in the other

996
01:14:29,450 --> 01:14:30,500
direction.

997
01:14:31,170 --> 01:14:36,569
To prevent any potential nuclear
fallout, NASA would detonate the bomb a

998
01:14:36,570 --> 01:14:37,620
way from Earth.

999
01:14:39,509 --> 01:14:43,689
Any deflection attempt has to be done
years in advance, which means it would

1000
01:14:43,690 --> 01:14:47,969
done on the other side of the solar
system from us, on the opposite side of

1001
01:14:47,970 --> 01:14:48,889
object's orbit.

1002
01:14:48,890 --> 01:14:53,309
That means that all of the vapor made
during the explosion gets blown away by

1003
01:14:53,310 --> 01:14:54,360
the solar wind.

1004
01:14:55,190 --> 01:15:00,729
NASA is also investigating other less
explosive methods of deflecting an

1005
01:15:00,730 --> 01:15:01,780
asteroid.

1006
01:15:02,210 --> 01:15:05,330
D -STAR would blast the asteroid with a
laser.

1007
01:15:05,770 --> 01:15:10,690
We hit it with the laser, material
vaporizes and flies off the asteroid.

1008
01:15:10,691 --> 01:15:14,449
And because of Newton's third law, which
is that for every action there's an

1009
01:15:14,450 --> 01:15:19,109
opposite and equal reaction, this means
that vaporized material moving off in

1010
01:15:19,110 --> 01:15:22,190
one direction moves the asteroid in the
opposite direction.

1011
01:15:24,430 --> 01:15:29,770
Both the laser and nuclear burst are
still just ideas on the drawing board.

1012
01:15:31,730 --> 01:15:36,740
But one asteroid deflection mission...
called Double Asteroid Redirection Test,

1013
01:15:36,940 --> 01:15:42,840
or DART for short, is already up and
running and scheduled for launch in

1014
01:15:45,140 --> 01:15:50,400
DART is a kinetic impactor and will try
to knock the asteroid off work.

1015
01:15:50,401 --> 01:15:55,959
At NASA, for the longest time, all we've
been able to do is theorize about how

1016
01:15:55,960 --> 01:15:59,039
we changed their path. But now, for the
first time, we're actually going to

1017
01:15:59,040 --> 01:16:00,090
practice it.

1018
01:16:00,429 --> 01:16:05,690
Leading this groundbreaking mission to
bump an asteroid off its course is Dr.

1019
01:16:05,990 --> 01:16:07,040
Andy Chang.

1020
01:16:07,630 --> 01:16:12,809
DART is the first planetary defense
mission that we've ever done, where we

1021
01:16:12,810 --> 01:16:19,049
a spacecraft, we fly the spacecraft into
the asteroid to change its course and

1022
01:16:19,050 --> 01:16:20,130
make it miss the Earth.

1023
01:16:20,970 --> 01:16:27,389
DART's target is a 525 -foot space rod
orbiting the large near -Earth asteroid

1024
01:16:27,390 --> 01:16:31,579
Didymus. We picked the near -Earth
asteroid Didymos as a target for the

1025
01:16:31,580 --> 01:16:34,899
mission because although it's a near
-Earth asteroid, it's one that's very

1026
01:16:34,900 --> 01:16:38,939
safely parked away out there in space.
There's no way we can move Didymos or

1027
01:16:38,940 --> 01:16:41,830
moon in any way big enough to cause a
problem for the Earth.

1028
01:16:49,340 --> 01:16:55,419
The Didymoon asteroid is moving at over
36 ,000 miles an hour and is over 4

1029
01:16:55,420 --> 01:16:56,760
million miles away.

1030
01:16:57,280 --> 01:17:02,020
So how do you move a 10 .5 billion pound
space rock?

1031
01:17:03,560 --> 01:17:06,500
You need to hit it really hard to change
its orbit.

1032
01:17:06,740 --> 01:17:12,119
So it's going to be coming in at a super
high velocity in order to impart a

1033
01:17:12,120 --> 01:17:14,230
bunch of energy and momentum to that
moon.

1034
01:17:15,580 --> 01:17:20,240
DART will hit the target at around 14
,000 miles an hour.

1035
01:17:20,600 --> 01:17:22,200
The speed of the DART impact.

1036
01:17:23,050 --> 01:17:27,930
will be more than nine times the speed
of the rifle bullet from AK -47.

1037
01:17:29,930 --> 01:17:33,430
The impact will give the asteroid a
small push.

1038
01:17:33,670 --> 01:17:39,390
To work out how big a push, we test
impacts with the Ames vertical gun.

1039
01:17:40,360 --> 01:17:44,319
At the NASA Ames Research Center in
California, there's a very special

1040
01:17:44,320 --> 01:17:46,120
called the Ames Vertical Gun Range.

1041
01:17:46,440 --> 01:17:51,339
It's a hypervelocity gas gun that allows
us to shoot little metal BBs at rock

1042
01:17:51,340 --> 01:17:55,920
targets at speeds up to like 13 ,000, 14
,000 miles per hour.

1043
01:17:56,340 --> 01:18:00,020
The gun replicates the impact the DART
mission will make.

1044
01:18:00,260 --> 01:18:05,559
It reveals that an impact will blow off
a small amount of debris, but at an

1045
01:18:05,560 --> 01:18:09,060
extremely high speed, enough to get the
asteroid.

1046
01:18:09,390 --> 01:18:10,810
An additional kick.

1047
01:18:11,250 --> 01:18:15,649
The impact will blow off pieces of the
asteroid. So the pieces are thrown off

1048
01:18:15,650 --> 01:18:19,930
the back. And so that process acts like
a little rocket engine.

1049
01:18:20,150 --> 01:18:24,689
That provides an additional momentum
change, momentum push, to the target

1050
01:18:24,690 --> 01:18:25,740
itself.

1051
01:18:26,210 --> 01:18:30,630
The combined push from the kinetic
impactor and the ejected debris is tiny,

1052
01:18:30,910 --> 01:18:33,990
around 9, 10 thousandths of a mile per
hour.

1053
01:18:34,290 --> 01:18:38,130
But hopefully it's enough to change the
asteroid's orbit.

1054
01:18:38,590 --> 01:18:44,169
If DART works, we could then use a
similar mission to defend Earth when the

1055
01:18:44,170 --> 01:18:45,220
comes.

1056
01:18:45,690 --> 01:18:50,089
This isn't some small rock prototype
that we're doing this test on. This is a

1057
01:18:50,090 --> 01:18:55,849
real dress rehearsal for an asteroid
that could destroy cities or even maybe

1058
01:18:55,850 --> 01:18:56,990
send the Earth in chaos.

1059
01:18:57,790 --> 01:19:01,150
The moon of Didymus is a solid lump of
rock.

1060
01:19:01,370 --> 01:19:06,389
Will a kinetic impactor like DART work
with a rubble pile asteroid like a

1061
01:19:06,390 --> 01:19:10,019
Pophis? When you shoot a rubble pile
with a projectile, it's a little bit

1062
01:19:10,020 --> 01:19:13,999
like trying to punch a sandbag. You get
a lot more of the energy that's absorbed

1063
01:19:14,000 --> 01:19:17,760
into just moving the sand around inside
the bag than ejecting it.

1064
01:19:18,000 --> 01:19:21,310
And so rubble piles might be a little
harder to move by this method.

1065
01:19:23,180 --> 01:19:27,740
We don't know if we can deflect a rubble
pile asteroid like Apophis.

1066
01:19:28,000 --> 01:19:33,640
They remain a clear and present danger
and something we might not buy.

1067
01:19:40,620 --> 01:19:44,160
But there may be a space lifeboat.

1068
01:19:49,500 --> 01:19:56,339
In 2018, scientists re -examined rocks
collected by Apollo 14 astronauts from

1069
01:19:56,340 --> 01:19:57,390
the moon.

1070
01:20:00,900 --> 01:20:04,900
Buried in the samples was a rock that
shouldn't be there.

1071
01:20:06,879 --> 01:20:11,440
They got something they didn't expect,
and that was an Earth rock.

1072
01:20:11,640 --> 01:20:15,600
They actually picked up a rock from
Earth on the moon.

1073
01:20:15,820 --> 01:20:17,320
They didn't bring it with them.

1074
01:20:17,460 --> 01:20:21,399
It's very likely that it was something
that was lofted up. When something hit

1075
01:20:21,400 --> 01:20:22,450
Earth,

1076
01:20:24,180 --> 01:20:29,279
threw up a bunch of rocks, some of those
rocks fell onto the moon. And that's a

1077
01:20:29,280 --> 01:20:31,480
meteorite on the moon, but it's from
Earth.

1078
01:20:36,940 --> 01:20:42,079
Supercomputer simulations of the KPG
asteroid strike reveal how the impact

1079
01:20:42,080 --> 01:20:47,019
so much energy that it catapulted rocks
out of Earth's atmosphere and into

1080
01:20:47,020 --> 01:20:53,019
space. They were then caught by the
moon's gravity and pulled down to the

1081
01:20:53,020 --> 01:20:54,070
surface.

1082
01:20:55,160 --> 01:21:00,679
We now know that material ejected into
space from asteroid impacts can travel

1083
01:21:00,680 --> 01:21:06,959
other planets as well, which would
explain the 100 Mars meteorites. we

1084
01:21:06,960 --> 01:21:08,010
here on Earth.

1085
01:21:08,011 --> 01:21:14,459
We think that there was probably the
exchange of a huge amount of material

1086
01:21:14,460 --> 01:21:18,200
between different bodies, Earth to the
moon and back again into Mars.

1087
01:21:21,620 --> 01:21:25,799
With each impact that occurs in our
solar system, that ejects all types of

1088
01:21:25,800 --> 01:21:30,220
material that allows material to swap
from planet to planet, moon to planet,

1089
01:21:30,560 --> 01:21:34,859
moon to moon. And so there's all of this
material that eventually travels from

1090
01:21:34,860 --> 01:21:35,910
place to place.

1091
01:21:36,589 --> 01:21:42,629
This planetary interchange may give life
on Earth a lifeboat should another

1092
01:21:42,630 --> 01:21:44,590
giant asteroid hit our planet.

1093
01:21:45,590 --> 01:21:51,009
If you think about such an impact today,
you know, the chances are high that a

1094
01:21:51,010 --> 01:21:54,790
lot of life will be wiped out. Much of
life, probably all of human life.

1095
01:21:56,070 --> 01:22:00,249
It's certainly possible that a big
enough asteroid strike can completely

1096
01:22:00,250 --> 01:22:01,350
sterilize a planet.

1097
01:22:01,570 --> 01:22:03,250
Talking about no life whatsoever.

1098
01:22:04,050 --> 01:22:08,109
Not to put too fine a point on it, but
if there's a dinosaur killer asteroid

1099
01:22:08,110 --> 01:22:11,849
there and it hits the Earth, the chance
of humanity's survival of such a thing

1100
01:22:11,850 --> 01:22:14,350
as a species, not great.

1101
01:22:19,250 --> 01:22:24,769
Humans may not survive, but some
scientists believe some simple life

1102
01:22:24,770 --> 01:22:25,820
could.

1103
01:22:27,550 --> 01:22:33,609
If a giant rock hits the Earth and kills
almost all life on Earth... There is a

1104
01:22:33,610 --> 01:22:40,469
slim line of hope. And that's because
the dirt, the rocks on

1105
01:22:40,470 --> 01:22:45,570
Earth are infused with bacterial life,
with microscopic life.

1106
01:22:45,850 --> 01:22:51,749
And in the event of a giant impact, some
of these bits of rock will be ejected

1107
01:22:51,750 --> 01:22:52,699
into space.

1108
01:22:52,700 --> 01:22:57,699
and might float around. After an
asteroid impact, whatever ejected into

1109
01:22:57,700 --> 01:23:01,979
atmosphere could contain microbial life
that, when it falls back down onto the

1110
01:23:01,980 --> 01:23:04,600
ground, could reseed the life on that
planet.

1111
01:23:08,140 --> 01:23:12,600
Some bacteria can survive the harsh
conditions of space.

1112
01:23:13,060 --> 01:23:19,079
These creatures can cope with an
asteroid strike, reentry, and landing

1113
01:23:19,080 --> 01:23:20,130
Earth's surface.

1114
01:23:29,900 --> 01:23:34,559
I think in terms of life on planet
Earth, I think we've learned that we

1115
01:23:34,560 --> 01:23:36,000
a very resilient planet.

1116
01:23:36,240 --> 01:23:39,839
And I think life in some form, even if
it has to crawl its way back from

1117
01:23:39,840 --> 01:23:44,160
bacterial stage, I think life on this
planet is going to eke through.

1118
01:23:47,120 --> 01:23:50,320
Life is pretty good at figuring out a
way of surviving.

1119
01:23:51,320 --> 01:23:53,580
We know that life first formed on the
Earth.

1120
01:23:53,870 --> 01:23:58,910
well over 4 billion years ago, and has
never been wiped out in all of that

1121
01:23:59,070 --> 01:24:02,610
There's always been something after
every major mass extinction.

1122
01:24:02,850 --> 01:24:07,290
So life will continue. It just won't
necessarily be us.

1123
01:24:08,550 --> 01:24:13,669
An asteroid strike on another world may
be how life started on Earth in the

1124
01:24:13,670 --> 01:24:14,669
first place.

1125
01:24:14,670 --> 01:24:19,289
There's an interesting idea that an
asteroid strike on another planet could

1126
01:24:19,290 --> 01:24:23,429
actually seeded life on Earth. And the
way this works is you have life that's

1127
01:24:23,430 --> 01:24:27,789
somehow gotten a foothold on some other
planet like Mars. A big asteroid strike

1128
01:24:27,790 --> 01:24:32,030
hits that planet and knocks a piece of
it off, eventually rains down on Earth,

1129
01:24:32,250 --> 01:24:33,330
carrying with it life.

1130
01:24:35,590 --> 01:24:40,270
We may owe the existence of life here to
asteroid impacts.

1131
01:24:44,090 --> 01:24:46,380
Speculative, but it's kind of a cool
thought.

1132
01:24:48,590 --> 01:24:55,129
Life -seeding asteroids may have hit us
in the past, and other asteroids will

1133
01:24:55,130 --> 01:24:56,180
hit us in the future.

1134
01:24:58,230 --> 01:25:03,710
One of them may be a pulpit, arriving in
less than half a century.

1135
01:25:04,970 --> 01:25:06,750
Maybe we will deflect it.

1136
01:25:08,010 --> 01:25:11,050
Maybe it will miss us all on its own.

1137
01:25:12,130 --> 01:25:15,670
Either way, We need to keep tabs on it.

1138
01:25:15,671 --> 01:25:20,489
The best thing we can do as a species,
and it's funny because it almost sounds

1139
01:25:20,490 --> 01:25:24,109
like I'm advocating for more jobs for
astronomers, we need to keep looking at

1140
01:25:24,110 --> 01:25:24,629
the sky.

1141
01:25:24,630 --> 01:25:28,889
We need to look at the sky longer and
deeper with more sensitive instruments

1142
01:25:28,890 --> 01:25:32,289
get more of a sense of what out there is
around us. That's what our species

1143
01:25:32,290 --> 01:25:34,130
needs to do to ultimately survive.

1144
01:25:35,490 --> 01:25:40,129
Because now we have the ability to see
these things a little bit better, we

1145
01:25:40,130 --> 01:25:43,329
the ability to protect ourselves better.
It doesn't have to be a surprise.

1146
01:25:43,330 --> 01:25:46,509
You know, the first time we see a big
impact doesn't have to be as it's

1147
01:25:46,510 --> 01:25:47,950
down, destroying our planet.

1148
01:25:48,070 --> 01:25:52,209
We can actually see it before it gets to
us and decide what we want to do about

1149
01:25:52,210 --> 01:25:53,260
it.

1150
01:25:53,550 --> 01:25:56,630
Earth's history is littered with
asteroid strikes.

1151
01:25:57,470 --> 01:26:00,130
Some wiped out millions of feces.

1152
01:26:00,990 --> 01:26:04,050
Some may have seeded life in the first
place.

1153
01:26:04,490 --> 01:26:11,150
What the future holds in our
relationship with these space rocks, no

1154
01:26:12,290 --> 01:26:17,109
Even though the chances of something
really large hitting the Earth are

1155
01:26:17,110 --> 01:26:19,910
small, the consequences are dire.

1156
01:26:20,210 --> 01:26:24,510
It would really destroy our planet, or
at least life as we understand it.

1157
01:26:24,910 --> 01:26:29,450
And so in many ways, asteroids are the
greatest threat that we face.

1158
01:26:29,870 --> 01:26:31,250
Life is fragile.

1159
01:26:31,850 --> 01:26:35,669
So, of course, we live in a larger
environment where something could come

1160
01:26:35,670 --> 01:26:36,720
hit us at any time.

1161
01:26:36,850 --> 01:26:38,210
That's part of being alive.

1162
01:26:38,470 --> 01:26:42,669
There's no guarantee tomorrow will
happen. But what there is is a high

1163
01:26:42,670 --> 01:26:45,080
likelihood that you'll still be safe
tomorrow.

1164
01:26:48,150 --> 01:26:50,110
Impacts from space are rare.

1165
01:26:50,610 --> 01:26:54,569
But if they do happen, it's a huge deal.
And so you've got to put those two

1166
01:26:54,570 --> 01:26:55,529
things together.

1167
01:26:55,530 --> 01:26:57,390
That means we've got to pay attention.

1168
01:26:57,391 --> 01:27:01,829
Those impacts have happened many times
in the past, and they're going to

1169
01:27:01,830 --> 01:27:04,060
continue to happen many times in the
future.

1170
01:27:04,330 --> 01:27:07,220
Fortunately, it's not probably in our
immediate future.

1171
01:27:07,650 --> 01:27:10,570
Impacts are rare, but the Earth lives a
long time.

1172
01:27:11,950 --> 01:27:15,449
So you're unlikely to get in a car
accident, but if you drive enough,

1173
01:27:15,450 --> 01:27:16,890
going to get in a car accident.

1174
01:27:20,130 --> 01:27:24,289
Over a century timescale, yes, we should
be concerned about these. But over the

1175
01:27:24,290 --> 01:27:29,419
daily, weekly, monthly, even yearly
timescale... I wouldn't sweat it too

1176
01:27:29,420 --> 01:27:33,559
wouldn't say we should lose sleep over
an asteroid or comet striking Earth, but

1177
01:27:33,560 --> 01:27:35,880
the reality is it will happen again.

1178
01:27:39,450 --> 01:27:43,589
about asteroid strikes remember this
wonderful dramatic universe you find

1179
01:27:43,590 --> 01:27:48,449
yourself in we're here because stars
died and exploded life on earth wouldn't

1180
01:27:48,450 --> 01:27:52,109
the same if we didn't find ourselves in
this dramatic and even dangerous

1181
01:27:52,110 --> 01:27:56,749
environment in space but this is who we
are this is nothing new and this will

1182
01:27:56,750 --> 01:27:58,479
continue for the future of our planet

1183
01:27:58,480 --> 01:28:03,030
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