1
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A dangerous asteroid
is heading towards Earth.

2
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It's the size of
the empire state building,

3
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and it's travelling at
16,000 miles an hour.

4
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It's called Apophis,
after the Egyptian god of chaos.

5
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It will fly close to us in 2029.

6
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It won't hit us... This time,

7
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but when it returns in 2068,

8
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that 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

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in U.S. history.

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Earth is stuck in the crosshairs

13
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of a potential asteroid strike.

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Apophis is one of around 2,000
potentially hazardous asteroids

15
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that present
a real and present danger.

16
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Asteroids have hit us before,
and they will hit us again.

17
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As far as cosmic dangerous go,

18
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they're number one on the list.

19
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This is not a drill.

20
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If we do nothing...

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This is our future.

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<font color="#ffff00">Captions by vitac</font>...
<font color="#00ffff">www.vitac.com</font>

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captions paid for by
discovery communications

24
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December 2018.

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The U.S. military detect
a huge explosion

26
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in the Earth's atmosphere

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high over the Bering sea

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off the coast of Alaska.

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When an explosion of this
magnitude is detected,

30
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everyone's mind
goes to the same thing... nukes.

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But when the real answer
was found and it was determined

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that it didn't even
originate from Earth,

33
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that was even more shock.

34
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The cause of the blast...

35
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an asteroid.

36
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This asteroid was
30 feet across...

37
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something like that...

38
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over a thousand tons,

39
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but it was moving
at 20 miles per second,

40
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over 70,000 miles an hour.

41
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This asteroid was
small, and it exploded

42
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in the atmosphere
over the ocean,

43
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so nobody was hurt.

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But if it had been bigger

45
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or it had come
in over a different place

46
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or it had been moving
a lot faster,

47
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this could have been
a dangerous object.

48
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But the scariest thing about it

49
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is that we didn't see it coming.

50
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So far, we've been lucky.

51
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But near misses happen
all the time.

52
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About once a year,
we get something

53
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the equivalent of a nuclear bomb
going off in our atmosphere.

54
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And while that sounds horrible,

55
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most of these happen
tens of miles up...

56
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Over open ocean, where we go
on completely oblivious.

57
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We may be oblivious to most
of the threats from space,

58
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but they are very real.

59
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We're going to get hit.

60
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Over a certain amount of time,

61
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an asteroid impact
is inevitable.

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It will happen 100%,
absolute certainty.

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NASA considers the threat
from the skies so severe

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it has made protection
from asteroids a top priority.

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These events are not rare.
They happen.

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And of course it's up to us to
make sure that we are detecting

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and characterizing, tracking
all of the near-Earth objects

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that potentially
could be a threat.

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This is not about Hollywood.
It's not about movies.

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This is about ultimately
protecting the only planet

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we know right now to host life,

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and that is the planet Earth.

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To help plan
protecting our home,

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we carry out
Earth defense simulations.

75
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For three days,

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200 scientist at the planetary
defense conference

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battle a simulated
asteroid 20 times larger

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than the Bering sea space rock.

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We practice, "alright,
what if this hits a major city?

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What would we need to do?"

81
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By running
potential impact scenarios,

82
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we can prepare
for a real asteroid strike.

83
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This is like a fire drill
that you would do at school

84
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or at work, where you practice

85
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and think about, okay, what if?

86
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Where are the exits?
How do I get out?

87
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How fast do I get out?

88
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The drill starts
with the discovery

89
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of a simulated
Earthbound asteroid.

90
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So, the first information
is there's a big asteroid

91
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coming towards the Earth.

92
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Then we get a better estimate

93
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of how big it is,
how fast it's going,

94
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and where it's going to hit.

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The asteroid
is heading straight for Earth

96
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with Denver, Colorado,
in its sights.

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The planetary defense scientists

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send up a simulated spacecraft
to smash into the asteroid

99
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and push it off its path.

100
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But it's a big gamble.

101
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You can push it the wrong way.

102
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You can potentially
have unintended consequences.

103
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In the simulation,

104
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the spacecraft
strikes the asteroid...

105
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Deflecting it away from Earth.

106
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But the impact dislodge
is a 200-foot chunk,

107
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which is now heading straight
towards the eastern seaboard.

108
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So there's this one last piece

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that is now
going to hit New York.

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We know that something that size

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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

114
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and you understand eventually

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that New York City
is going to be destroyed...

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And you're having strategies
about how to evacuate people,

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all the timing,
when you're doing the simulation

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you're in your head.

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You're thinking
about these things.

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You're trying to
reason them out,

121
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but can you imagine the feeling
in your gut, in your heart,

122
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if this was real?

123
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If this were real,
the chunk of asteroid

124
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would strike Earth's atmosphere

125
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at 43,000 miles an hour.

126
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As the space rock hurtles
down, it collides

127
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with molecules in the atmosphere
which buffet the falling rock.

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It's kind of like doing
a belly flop into a pool, right?

129
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You're going from
the vacuum of space

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into the dense lower atmosphere
in mere seconds.

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And that's an incredible
amount of pressure

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to put on the object.

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The asteroid slams into the air

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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

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from the heating
of the shockwave,

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the world's most
intense Sonic boom if you will,

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that heats the air
to incandescence

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as the object passes through.

141
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So that's the source
of that 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

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of Chelyabinsk in 2013.

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All of a sudden, there was
a huge fireball

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streaking through the sky,

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and people had no idea
what they were witnessing

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because it looked like the sky
was on fire.

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It was insanity.

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As the asteroid descends,

151
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the compression
of the denser air beneath it

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starts to flatten and even
disrupt the falling rock.

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There's a high pressure
on the front,

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there's no pressure on the back

155
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and it's being super heated.

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And that intense temperature
causes the air to glow,

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which is how we see
this streak of a meteor.

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And it also disintegrates
the asteroid itself.

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It's hard enough
to literally melt rock.

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This can often
lead to them exploding.

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The combination
of heat and pressure invade

162
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the falling asteroid,
causing it to blow up.

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Most asteroids
don't reach the ground

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before they
completely disintegrate

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in a tremendous release
of energy.

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This is what we call
an air burst,

167
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and we learned a lot about these

168
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while we were testing nuclear
weapons after world war ii.

169
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Some of these bombs
were blown up

170
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underground and on the ground,

171
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but they found out when they
blew up bombs above the ground,

172
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it actually did more damage.

173
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It was more widespread damage.

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The explosion of
the Chelyabinsk asteroid

175
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sent out a powerful shockwave
at thousands of miles an hour.

176
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The blast traveled
over 100 miles.

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It damaged 7,000 buildings

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and put 1,500 people
in the hospital.

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All of the injuries
pretty much came from people

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who saw, "oh, what's
that bright flash in the sky?"

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And they came close to a window
to look and see what it was,

182
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and then the pressure wave hit
and blew glass in their face.

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The Chelyabinsk asteroid
was only 65 feet across.

184
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The rock in the
defense simulation

185
00:09:58,620 --> 00:10:00,780
is three times more massive,

186
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and it's heading straight
for New York City.

187
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Imagine what would happen
if an explosion a thousand times

188
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greater than that over Hiroshima
hit New York.

189
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We're talking about an utter
complete destruction of the city

190
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and millions of people.

191
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With so little warning,

192
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the only option would be
to evacuate New York City.

193
00:10:27,180 --> 00:10:29,210
How do we get everybody out
of New York City

194
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within just a few days?

195
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That's where panic sets in.

196
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That's where fear would really
become the dominant emotion.

197
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Anyone left in New York City

198
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would see the bolide
racing in...

199
00:10:45,460 --> 00:10:48,160
...followed
by a blinding light...

200
00:10:48,160 --> 00:10:52,630
As the asteroid explodes
above the city.

201
00:10:52,640 --> 00:10:56,940
The blast would be equivalent
to the largest nuclear weapon

202
00:10:56,940 --> 00:10:59,270
ever detonated on Earth.

203
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Buildings would be
flattened, melted.

204
00:11:01,680 --> 00:11:04,380
There would be fires
for miles around

205
00:11:04,380 --> 00:11:06,710
in the first moments
of the explosion.

206
00:11:06,720 --> 00:11:09,550
A million people
could be killed instantly

207
00:11:09,550 --> 00:11:11,520
and many more would die later
in the rubble,

208
00:11:11,520 --> 00:11:15,560
in the ruins
of what would happen there.

209
00:11:15,560 --> 00:11:19,460
Everything within nine miles
of the blast epicenter

210
00:11:19,460 --> 00:11:21,730
would be completely destroyed.

211
00:11:28,870 --> 00:11:33,770
The intense heat and
pressure would wreck buildings.

212
00:11:33,780 --> 00:11:37,310
It's the worst possible
day for new yorkers,

213
00:11:37,310 --> 00:11:39,610
and not just the city itself.

214
00:11:39,620 --> 00:11:42,780
There's something like
15 million people

215
00:11:42,790 --> 00:11:44,950
living in the New York area.

216
00:11:48,690 --> 00:11:53,730
The shock wave would race
out over 250 square miles.

217
00:11:53,730 --> 00:11:55,700
This would certainly be
the worst disaster

218
00:11:55,700 --> 00:11:57,160
that the U.S.
has ever experienced.

219
00:11:57,170 --> 00:12:00,200
We're talking about millions
and millions of people

220
00:12:00,200 --> 00:12:02,770
displaced,
affected within an instant.

221
00:12:09,410 --> 00:12:13,410
This scenario is
just a simulation... For now.

222
00:12:18,550 --> 00:12:21,960
The asteroid Apophis
is heading our way.

223
00:12:24,630 --> 00:12:26,090
If it hits Earth,

224
00:12:26,100 --> 00:12:28,430
it might not just kill a city.

225
00:12:28,430 --> 00:12:31,230
It could kill a whole region.

226
00:12:31,230 --> 00:12:32,870
I wouldn't exactly
want to be there

227
00:12:32,870 --> 00:12:38,110
when that happens...
want to be very, very far away.

228
00:12:38,110 --> 00:12:43,580
Apophis will skim Earth in 2029.

229
00:12:43,580 --> 00:12:46,710
But its path could change,

230
00:12:46,720 --> 00:12:49,880
possibly turning
a future miss...

231
00:12:49,890 --> 00:12:51,550
Into a direct hit.

232
00:13:10,240 --> 00:13:13,070
April 13, 2029,

233
00:13:13,080 --> 00:13:16,080
a speck of light
races towards the Earth.

234
00:13:16,080 --> 00:13:20,180
It's an 1,100 foot wide asteroid
called Apophis.

235
00:13:20,180 --> 00:13:24,990
We are about to have
an extremely close shave.

236
00:13:26,090 --> 00:13:28,660
It's the closest approach
of any asteroid

237
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that didn't actually hit us
for a long, long time.

238
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It will be 10 times closer
than the moon itself.

239
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It'll be so close that
it will be brighter

240
00:13:38,300 --> 00:13:40,500
than some stars.

241
00:13:40,500 --> 00:13:43,440
The football-stadium
sized Apophis

242
00:13:43,440 --> 00:13:46,310
will race over the Atlantic.

243
00:13:46,310 --> 00:13:48,080
If it were sitting on
the surface of the Earth,

244
00:13:48,080 --> 00:13:50,180
it would weigh
about 50 million tons,

245
00:13:50,180 --> 00:13:51,850
something like that,

246
00:13:51,850 --> 00:13:55,220
and that is not the place
you want it to be.

247
00:13:55,220 --> 00:14:00,190
You want it to be in space
and far away.

248
00:14:00,190 --> 00:14:03,220
When we discovered
Apophis in 2004,

249
00:14:03,230 --> 00:14:06,360
we thought it might be
on a collision course with Earth

250
00:14:06,360 --> 00:14:08,130
with a potential impact

251
00:14:08,130 --> 00:14:12,770
greater than the largest
atomic bomb ever exploded.

252
00:14:12,770 --> 00:14:15,700
The largest nuclear
device, atomic device

253
00:14:15,710 --> 00:14:19,440
ever detonated on our planet was
the Tsar Bomba bomb in Russia,

254
00:14:19,440 --> 00:14:22,440
so something like
55 or 56 megatons.

255
00:14:22,450 --> 00:14:26,780
When Krakatoa exploded in 1883

256
00:14:26,780 --> 00:14:29,020
that was something
like 200 megatons.

257
00:14:29,020 --> 00:14:32,150
Apophis' impact
would be 450 megatons.

258
00:14:32,150 --> 00:14:34,460
If something like that were
to happen over New York City

259
00:14:34,460 --> 00:14:39,690
or Washington D.C.,
you're going to lose the city.

260
00:14:39,700 --> 00:14:42,730
The impact would be
at least 10 times greater

261
00:14:42,730 --> 00:14:45,600
than the simulated
asteroid strike on New York.

262
00:14:52,810 --> 00:14:55,710
Well, when you put it
in those terms,

263
00:14:55,710 --> 00:14:57,780
that's just plain scary.

264
00:14:57,780 --> 00:15:02,020
In a word, an impact
from an Apophis-sized asteroid

265
00:15:02,020 --> 00:15:07,020
would be bad... very, very bad.

266
00:15:07,020 --> 00:15:09,390
Apophis' orbit will cross Earth

267
00:15:09,390 --> 00:15:12,990
every seven years this century.

268
00:15:13,000 --> 00:15:15,200
It won't hit us in 2029,

269
00:15:15,200 --> 00:15:20,370
but this close encounter
could change Apophis' orbit.

270
00:15:20,370 --> 00:15:25,170
When a small asteroid encounters
a bigger body like a planet,

271
00:15:25,170 --> 00:15:28,180
it's like a bunch
of roller derby players.

272
00:15:30,380 --> 00:15:32,010
Most of them
are clumped together,

273
00:15:32,010 --> 00:15:35,820
but maybe there's one just on
their own particular orbit,

274
00:15:35,820 --> 00:15:37,320
and as they circle around,

275
00:15:37,320 --> 00:15:39,290
as they get close
to that larger clump,

276
00:15:39,290 --> 00:15:41,020
there'll be some interactions...

277
00:15:41,020 --> 00:15:42,890
potentially violent
interactions...

278
00:15:42,890 --> 00:15:46,230
that will change
the future trajectory

279
00:15:46,230 --> 00:15:49,160
of that lone
roller derby skater.

280
00:15:49,170 --> 00:15:50,530
And the next time around,

281
00:15:50,530 --> 00:15:54,870
it might be a wide miss
or it might be a head-on impact.

282
00:15:58,980 --> 00:16:01,710
It's the same
in the solar system.

283
00:16:01,710 --> 00:16:04,310
The combined gravity
of the Earth and moon

284
00:16:04,310 --> 00:16:09,020
creates what's called
a gravitational keyhole,

285
00:16:09,020 --> 00:16:12,020
a gravitational sweet spot,

286
00:16:12,020 --> 00:16:15,890
which could change
Apophis' orbit.

287
00:16:15,890 --> 00:16:19,330
That will change the potential
future trajectory of this rock

288
00:16:19,330 --> 00:16:21,830
and might make it
totally harmless

289
00:16:21,830 --> 00:16:24,000
or might increase the chances

290
00:16:24,000 --> 00:16:28,440
of an impact
even further in the future.

291
00:16:28,440 --> 00:16:30,840
Because of the
gravitational keyhole,

292
00:16:30,840 --> 00:16:32,270
there's still a small chance

293
00:16:32,270 --> 00:16:36,680
that Apophis will hit Earth
in 2068.

294
00:16:40,980 --> 00:16:43,920
That is the important
lesson that Apophis taught us...

295
00:16:43,920 --> 00:16:45,490
you can miss the Earth,

296
00:16:45,490 --> 00:16:47,590
but if you pass through
one of these keyholes,

297
00:16:47,590 --> 00:16:51,660
at some time later,
you will hit the Earth.

298
00:16:51,660 --> 00:16:56,560
We now know Apophis
will miss the keyhole in 2029,

299
00:16:56,570 --> 00:16:59,970
but there are other keyholes
and other close passes.

300
00:17:07,410 --> 00:17:11,650
Apophis is not a lone threat.

301
00:17:11,650 --> 00:17:16,250
There are an estimated
832,500 asteroids

302
00:17:16,250 --> 00:17:19,020
orbiting the sun.

303
00:17:19,020 --> 00:17:21,860
Most asteroids live their lives

304
00:17:21,860 --> 00:17:25,760
perfectly peacefully
past the orbit of Mars

305
00:17:25,760 --> 00:17:29,760
or trailing Jupiter
and don't mind anybody else,

306
00:17:29,770 --> 00:17:33,130
don't cause any troubles,
but some asteroids

307
00:17:33,140 --> 00:17:35,670
are on very particular orbits

308
00:17:35,670 --> 00:17:40,270
that cross the orbit
of the Earth.

309
00:17:40,280 --> 00:17:42,710
These asteroids
have left the stable orbit

310
00:17:42,710 --> 00:17:44,240
of the asteroid belt

311
00:17:44,250 --> 00:17:48,450
and moved into orbits
that get near our own.

312
00:17:48,450 --> 00:17:51,790
These asteroids are called
near Earth asteroids

313
00:17:51,790 --> 00:17:54,490
or N.E.A.S for short.

314
00:17:54,490 --> 00:17:56,960
The near Earth asteroid
population is interesting

315
00:17:56,960 --> 00:17:58,830
and potentially dangerous
because they are the ones

316
00:17:58,830 --> 00:18:00,560
that actually cross
the orbit of the Earth.

317
00:18:00,560 --> 00:18:03,330
So they're most likely
to have, at some point

318
00:18:03,330 --> 00:18:06,030
in the future,
an impact with the Earth.

319
00:18:08,000 --> 00:18:12,440
Most N.E.A.S pose
little or no threat to Earth.

320
00:18:12,440 --> 00:18:14,510
But we've detected over 2,000,

321
00:18:14,510 --> 00:18:19,380
including the 1,200 foot Apophis
that do.

322
00:18:19,380 --> 00:18:21,620
These are called P.H.A.S...

323
00:18:21,620 --> 00:18:25,750
potentially hazardous asteroids.

324
00:18:25,750 --> 00:18:27,890
The difference between
a near Earth asteroid

325
00:18:27,890 --> 00:18:33,590
and a potentially hazardous
asteroid is distance and size.

326
00:18:33,600 --> 00:18:35,100
Anything can get near the Earth,

327
00:18:35,100 --> 00:18:37,460
and that could be
20 million miles away,

328
00:18:37,470 --> 00:18:39,900
something like that,
and be a near Earth asteroid,

329
00:18:39,900 --> 00:18:42,800
but a potentially hazardous one
can hit us,

330
00:18:42,810 --> 00:18:45,070
and it's big enough
to do damage.

331
00:18:49,010 --> 00:18:51,350
So something that over
the next hundred years or so

332
00:18:51,350 --> 00:18:54,780
has a chance of hitting us
and doing damage when it does...

333
00:18:54,780 --> 00:18:57,080
that's a potentially
hazardous object.

334
00:18:59,120 --> 00:19:03,290
P.H.A.S are asteroids
that are 460 feet or larger

335
00:19:03,290 --> 00:19:04,990
that could collide with Earth.

336
00:19:07,230 --> 00:19:10,360
Take a 400-foot asteroid...
if it hits,

337
00:19:10,370 --> 00:19:12,330
it would release as much energy

338
00:19:12,330 --> 00:19:15,970
as 3,000
Hiroshima nuclear bombs.

339
00:19:22,110 --> 00:19:23,580
In July of 2018,

340
00:19:23,580 --> 00:19:25,550
NASA published a map

341
00:19:25,550 --> 00:19:29,320
of all the known
N.E.A.S and p.H.A.S.

342
00:19:32,450 --> 00:19:34,620
The animation tracks
their discovery

343
00:19:34,620 --> 00:19:38,030
from 1999 through 2018.

344
00:19:40,060 --> 00:19:41,460
Every time I look
at this animation,

345
00:19:41,460 --> 00:19:43,500
it does make my heart
stop a little bit

346
00:19:43,500 --> 00:19:45,470
because it looks like
we're in the middle of a swarm

347
00:19:45,470 --> 00:19:49,370
of angry bees
circling all around us.

348
00:19:49,370 --> 00:19:51,670
In 1999, we'd identified

349
00:19:51,670 --> 00:19:53,670
under 300 N.E.A.S

350
00:19:53,680 --> 00:19:56,440
scattered through
the inner solar system.

351
00:19:56,450 --> 00:20:00,610
10 years later,
we'd found 500 more.

352
00:20:00,620 --> 00:20:05,950
By 2018, we'd discovered 18,000
near Earth asteroids,

353
00:20:05,960 --> 00:20:10,260
but we estimate
there are millions out there.

354
00:20:10,260 --> 00:20:12,990
It seems like we could
never find all the asteroids.

355
00:20:13,000 --> 00:20:14,290
They just keep coming.

356
00:20:14,300 --> 00:20:17,260
It's like we're fighting
an army of zombies.

357
00:20:17,270 --> 00:20:21,130
Zombies that keep
hurtling our way,

358
00:20:21,140 --> 00:20:26,910
hitting the Earth at up
to 64,000 miles an hour.

359
00:20:26,910 --> 00:20:28,540
That is very, very fast.

360
00:20:28,540 --> 00:20:30,710
That is much faster
than a rifle bullet.

361
00:20:30,710 --> 00:20:33,510
And that's the key
to its destructive power.

362
00:20:36,790 --> 00:20:40,250
When a really fast
and really large asteroid hits,

363
00:20:40,260 --> 00:20:43,960
the impact is off the charts.

364
00:20:43,960 --> 00:20:46,130
The blast is so intense,

365
00:20:46,130 --> 00:20:49,530
it can melt
or even vaporize rock.

366
00:21:04,310 --> 00:21:06,510
January 2019,

367
00:21:06,520 --> 00:21:08,820
a total eclipse of the moon.

368
00:21:08,820 --> 00:21:10,580
Astronomers train
their telescopes

369
00:21:10,590 --> 00:21:12,950
on the darkening lunar surface.

370
00:21:14,760 --> 00:21:17,620
They capture a bright flash

371
00:21:17,630 --> 00:21:21,160
that lasts around a quarter
of a second.

372
00:21:21,160 --> 00:21:23,300
It was recorded. There were
a lot of live webcasts

373
00:21:23,300 --> 00:21:25,630
and things like that going on
at the time,

374
00:21:25,630 --> 00:21:27,700
and you can see
this flash of light.

375
00:21:27,700 --> 00:21:29,340
What the heck was that?

376
00:21:31,270 --> 00:21:35,480
At first, the cause
of the flash was a mystery.

377
00:21:35,480 --> 00:21:39,750
It turns out it was actually
a meteorite hitting

378
00:21:39,750 --> 00:21:42,320
the surface of the moon,
and because it was dark

379
00:21:42,320 --> 00:21:43,680
and because we were all looking
at it,

380
00:21:43,690 --> 00:21:46,820
we could actually see it.

381
00:21:46,820 --> 00:21:49,490
The moon's dark
surface gave us a unique view

382
00:21:49,490 --> 00:21:52,390
of what happens
when an asteroid strikes.

383
00:21:52,390 --> 00:21:53,860
What was so exciting
about being able

384
00:21:53,860 --> 00:21:57,400
to see this impact
on the moon in a dark area

385
00:21:57,400 --> 00:22:00,370
is that we could actually look
at the light that it produced

386
00:22:00,370 --> 00:22:01,970
and then back-calculate

387
00:22:01,970 --> 00:22:04,870
exactly what the size
of the impactor was.

388
00:22:04,870 --> 00:22:07,410
We worked out that
the impacting asteroid

389
00:22:07,410 --> 00:22:09,980
was just 20 inches wide.

390
00:22:09,980 --> 00:22:14,280
The crater it blew out
was 45 feet across.

391
00:22:14,280 --> 00:22:18,990
How can something so small
be so destructive?

392
00:22:18,990 --> 00:22:21,860
The two things that matter
the most are how fast it's going

393
00:22:21,860 --> 00:22:23,260
and how massive is the thing.

394
00:22:23,260 --> 00:22:24,860
The more massive,
the bigger the boom,

395
00:22:24,860 --> 00:22:26,690
the faster the bigger the boom.

396
00:22:26,700 --> 00:22:29,030
Speed and weight
are two very important factors

397
00:22:29,030 --> 00:22:31,800
to assess how much damage
an asteroid will do.

398
00:22:31,800 --> 00:22:34,030
Just like a boxer...
if a tiny person like me

399
00:22:34,040 --> 00:22:35,470
were to swing a punch,

400
00:22:35,470 --> 00:22:39,010
it would do a lot less damage
than a heavyweight champion.

401
00:22:39,010 --> 00:22:40,170
Same thing with asteroids.

402
00:22:40,180 --> 00:22:42,010
The bigger they are,
the bigger the punch.

403
00:22:42,010 --> 00:22:43,840
But the same thing
is fast, right?

404
00:22:43,850 --> 00:22:46,110
If I hit you really slowly,
it's not gonna hurt.

405
00:22:46,120 --> 00:22:48,420
I have to really wind back
and pap.

406
00:22:48,420 --> 00:22:51,590
That's what happens
with an asteroid.

407
00:22:51,590 --> 00:22:53,290
The damage from
an asteroid strike

408
00:22:53,290 --> 00:22:55,620
is determined
by its kinetic energy.

409
00:22:55,620 --> 00:22:57,960
Kinetic energy depends
on two things...

410
00:22:57,960 --> 00:23:00,060
speed and weight.

411
00:23:02,630 --> 00:23:05,900
Of the two, speed matters most.

412
00:23:08,500 --> 00:23:11,270
If you double the mass,
you double the kinetic energy,

413
00:23:11,270 --> 00:23:13,010
but if you double the velocity,

414
00:23:13,010 --> 00:23:15,240
you get four times
the kinetic energy.

415
00:23:15,240 --> 00:23:17,910
Three times the speed,
nine times the impact energy.

416
00:23:17,910 --> 00:23:19,180
10 times as fast,

417
00:23:19,180 --> 00:23:21,480
it has a hundred times
the energy,

418
00:23:21,480 --> 00:23:24,150
so the velocity
is what's really critical here.

419
00:23:26,790 --> 00:23:29,360
The lunar asteroid
weighed only 100 pounds,

420
00:23:29,360 --> 00:23:34,460
but it was traveling
at 38,000 miles an hour.

421
00:23:34,460 --> 00:23:38,730
Carrying a huge kinetic energy,
which gouged out the crater.

422
00:23:40,770 --> 00:23:45,670
It's the same principle
for impacts on Earth.

423
00:23:45,670 --> 00:23:49,310
50,000 years ago,
a 150-foot asteroid

424
00:23:49,310 --> 00:23:51,610
hit what is now Arizona.

425
00:23:53,820 --> 00:23:56,680
The impact blasted out
an impressive hole

426
00:23:56,690 --> 00:23:59,150
now called Barringer crater.

427
00:23:59,150 --> 00:24:01,920
It's about 3/4 of a mile across,

428
00:24:01,920 --> 00:24:03,260
over 500 feet deep.

429
00:24:03,260 --> 00:24:04,860
You could put
the Washington monument

430
00:24:04,860 --> 00:24:06,360
in the bottom of the crater,

431
00:24:06,360 --> 00:24:09,160
and the top of the monument
wouldn't quite clear the rim.

432
00:24:09,160 --> 00:24:11,400
It's a pretty impressive hole
in the ground.

433
00:24:15,340 --> 00:24:18,510
In 2016,
impact specialist Cathy Plesko

434
00:24:18,510 --> 00:24:20,170
visited Barringer crater

435
00:24:20,180 --> 00:24:23,380
to see firsthand
what mass and speed

436
00:24:23,380 --> 00:24:25,350
do to the surface of the Earth.

437
00:24:29,690 --> 00:24:35,220
This is awe-inspiring to stand
on the rim of a crater like this

438
00:24:35,220 --> 00:24:38,660
understanding
just how much energy

439
00:24:38,660 --> 00:24:42,800
it must have taken
to excavate this much rock.

440
00:24:46,170 --> 00:24:51,140
The asteroid came in
at about 27,000 miles an hour.

441
00:24:53,310 --> 00:24:55,010
It comes slamming
into the surface

442
00:24:55,010 --> 00:24:56,510
and just explodes.

443
00:24:56,510 --> 00:24:58,380
Anywhere nearby here

444
00:24:58,380 --> 00:25:00,910
would have seen winds
of thousands of miles an hour

445
00:25:00,920 --> 00:25:02,850
as the shockwave came out.

446
00:25:08,960 --> 00:25:11,490
The immense power
of an asteroid impact

447
00:25:11,490 --> 00:25:13,390
comes from the kinetic energy

448
00:25:13,400 --> 00:25:17,460
being transferred from the space
rock into the surface rock.

449
00:25:19,970 --> 00:25:22,500
It's an extremely
violent process,

450
00:25:22,500 --> 00:25:24,570
and it starts with the moment
of contact

451
00:25:24,570 --> 00:25:28,780
of the projectile
with the surface itself.

452
00:25:28,780 --> 00:25:31,610
It pushes into the crust,

453
00:25:31,610 --> 00:25:35,420
and at first,
it's just almost punching, like,

454
00:25:35,420 --> 00:25:36,850
sticking your thumb into dough.

455
00:25:36,850 --> 00:25:39,420
It's only about
as wide as the object is.

456
00:25:39,420 --> 00:25:41,120
It's going straight down in,

457
00:25:41,120 --> 00:25:45,660
but then it's meeting resistance
from the surface of the Earth.

458
00:25:45,660 --> 00:25:47,790
And so it squishes,
squishes, squishes,

459
00:25:47,800 --> 00:25:51,630
until it runs out of momentum,
but then it's very compressed

460
00:25:51,630 --> 00:25:54,200
and all of that energy is in
a very small space.

461
00:25:54,200 --> 00:25:56,800
As it releases,
it detonates like a bomb.

462
00:25:56,810 --> 00:26:01,810
And that's what makes
the impact crater.

463
00:26:01,810 --> 00:26:04,580
Simulations of
an asteroid strike in the lab

464
00:26:04,580 --> 00:26:07,180
reveal the impact
in slow motion.

465
00:26:10,590 --> 00:26:14,150
As the high speed pellet
hits the surface,

466
00:26:14,160 --> 00:26:19,430
the sand compresses downwards,
then rebounds.

467
00:26:19,430 --> 00:26:21,260
And as that rebound
is occurring,

468
00:26:21,260 --> 00:26:23,630
that's when the material
is being ejected

469
00:26:23,630 --> 00:26:26,730
out of the crater itself.

470
00:26:26,740 --> 00:26:28,700
You'll see the surface
erupting outwards

471
00:26:28,700 --> 00:26:31,910
like the blooming petals
of some big rocky flower

472
00:26:31,910 --> 00:26:34,810
as all this debris goes
spraying out in every direction.

473
00:26:39,850 --> 00:26:42,420
The 150-foot Barringer asteroid

474
00:26:42,420 --> 00:26:46,050
turned the rock to powder.

475
00:26:46,050 --> 00:26:48,190
66 million years ago,

476
00:26:48,190 --> 00:26:50,990
an asteroid
around 200 times larger

477
00:26:50,990 --> 00:26:53,330
and moving
one and a half times faster

478
00:26:53,330 --> 00:26:55,860
than Barringer hit Earth.

479
00:26:55,860 --> 00:26:59,100
This asteroid impact...
called k-pg...

480
00:26:59,100 --> 00:27:00,670
had so much energy,

481
00:27:00,670 --> 00:27:03,540
it turned rock to liquid.

482
00:27:03,540 --> 00:27:05,510
This thing was immense.
It's really hard to wrap

483
00:27:05,510 --> 00:27:08,140
your head around
just how big it is.

484
00:27:08,140 --> 00:27:11,950
When it hits the back end of it,
it is so far back,

485
00:27:11,950 --> 00:27:15,280
that it's where
a modern jetliner would fly.

486
00:27:17,720 --> 00:27:19,720
The k-pg asteroid hit the ground

487
00:27:19,720 --> 00:27:23,920
with a lethal combination
of mass and speed.

488
00:27:23,930 --> 00:27:28,660
A trillion tons traveling
at 45,000 miles an hour.

489
00:27:30,600 --> 00:27:32,570
Some rock is
completely vaporized.

490
00:27:32,570 --> 00:27:34,270
It just becomes a gas.

491
00:27:34,270 --> 00:27:36,600
You have some rock
that is melted.

492
00:27:36,610 --> 00:27:39,840
You have some
that's thrown out into space.

493
00:27:41,680 --> 00:27:44,480
This material goes up
through that and then falls down

494
00:27:44,480 --> 00:27:46,750
and settles down
over a huge area.

495
00:27:46,750 --> 00:27:49,480
That might be dust.
It might be pulverized rock.

496
00:27:49,480 --> 00:27:51,690
It might be vaporized metal.

497
00:27:51,690 --> 00:27:55,020
It's all of this hot material
raining down everywhere.

498
00:27:57,290 --> 00:28:00,290
Some of the rock
exploded skywards,

499
00:28:00,300 --> 00:28:03,830
but rock below the surface
was slammed by a shockwave

500
00:28:03,830 --> 00:28:06,670
that was completely
off the charts.

501
00:28:06,670 --> 00:28:11,270
Rock stopped behaving like rock.

502
00:28:11,270 --> 00:28:14,240
We experience rocks
as solid objects,

503
00:28:14,240 --> 00:28:15,740
but if you hit a rock
hard enough,

504
00:28:15,740 --> 00:28:17,840
it flows like water.

505
00:28:17,850 --> 00:28:20,680
The k-pg asteroid hit so hard,

506
00:28:20,680 --> 00:28:22,580
it pulverized the rock,

507
00:28:22,580 --> 00:28:24,580
turning it into liquid.

508
00:28:24,590 --> 00:28:26,750
Almost like ripples
on a pond moving away

509
00:28:26,760 --> 00:28:29,190
from a stone
that's been dropped in it.

510
00:28:29,190 --> 00:28:30,590
It's almost like a splash

511
00:28:30,590 --> 00:28:32,890
in the solid body
of the Earth itself,

512
00:28:32,890 --> 00:28:35,560
and like water droplets
splashing in water,

513
00:28:35,560 --> 00:28:39,030
you'll see that central peak
will kind of splash up

514
00:28:39,030 --> 00:28:41,740
and rise to a high altitude
and then come back down again.

515
00:28:41,740 --> 00:28:44,540
We think a process very similar
to that probably happened

516
00:28:44,540 --> 00:28:47,440
in the rock itself
at the center of the crater,

517
00:28:47,440 --> 00:28:49,980
rising up
as high as the Himalayas

518
00:28:49,980 --> 00:28:53,080
before relaxing back down
to their current position again.

519
00:28:53,080 --> 00:28:56,620
The material slumps,
and so these ripples

520
00:28:56,620 --> 00:28:58,320
are frozen in the rock,

521
00:28:58,320 --> 00:29:01,190
and there are other fragments
that go away radially,

522
00:29:01,190 --> 00:29:03,560
almost like the spider web
pattern in glass

523
00:29:03,560 --> 00:29:06,990
that you get after
it's shot with a bullet.

524
00:29:07,000 --> 00:29:10,600
The k-pg impact
blew out a crater

525
00:29:10,600 --> 00:29:13,330
111 miles wide.

526
00:29:13,340 --> 00:29:15,800
It is the third largest
confirmed

527
00:29:15,800 --> 00:29:18,240
impact structure on Earth.

528
00:29:20,510 --> 00:29:23,740
A large and fast asteroid
heading our way

529
00:29:23,750 --> 00:29:26,150
is always going to be a problem.

530
00:29:26,150 --> 00:29:28,480
So what do we do?

531
00:29:28,480 --> 00:29:32,050
Wait for oblivion?

532
00:29:32,050 --> 00:29:33,690
Or fight back?

533
00:29:49,870 --> 00:29:52,010
The space
in the inner solar system

534
00:29:52,010 --> 00:29:56,210
seems calm, stable, and empty.

535
00:29:56,210 --> 00:29:59,110
It's not.

536
00:29:59,110 --> 00:30:01,410
There are tens of thousands
of near Earth objects

537
00:30:01,420 --> 00:30:03,050
just whizzing around Earth.

538
00:30:03,050 --> 00:30:05,650
Now, space is big.

539
00:30:05,650 --> 00:30:09,960
They're not gonna hit us
every time they orbit the sun,

540
00:30:09,960 --> 00:30:12,330
but this does set up
the possibility

541
00:30:12,330 --> 00:30:14,560
that, one of these years,

542
00:30:14,560 --> 00:30:17,600
we're gonna end up
at the same spot in space

543
00:30:17,600 --> 00:30:20,570
at the same time
as that asteroid,

544
00:30:20,570 --> 00:30:22,200
and then it's gonna be
an impact.

545
00:30:24,640 --> 00:30:26,270
We're living in a cosmic
shooting gallery.

546
00:30:26,270 --> 00:30:28,270
Asteroids strike the Earth
all the time

547
00:30:28,280 --> 00:30:29,880
through history,

548
00:30:29,880 --> 00:30:31,850
and it's gonna happen again.

549
00:30:31,850 --> 00:30:33,680
Scientists are
developing strategies

550
00:30:33,680 --> 00:30:37,720
to stop an asteroid
from hitting our planet.

551
00:30:37,720 --> 00:30:42,790
Our options... destroy
or deflect the space rock.

552
00:30:42,790 --> 00:30:46,290
But first, we need to detect
any dangerous asteroids

553
00:30:46,290 --> 00:30:48,160
heading our way.

554
00:30:48,160 --> 00:30:49,630
It's a little bit
unnerving to know

555
00:30:49,630 --> 00:30:52,270
that we haven't yet detected
all of the asteroids

556
00:30:52,270 --> 00:30:55,100
that exist that could
possibly cross our path.

557
00:30:55,100 --> 00:30:57,240
We've discovered
a lot of asteroids now,

558
00:30:57,240 --> 00:31:01,110
but we typically discover
the big ones.

559
00:31:01,110 --> 00:31:03,910
But for asteroids
that are below 100 feet,

560
00:31:03,910 --> 00:31:06,780
there's a lot still out there
that we haven't discovered.

561
00:31:06,780 --> 00:31:09,420
And such an asteroid
can do some real damage

562
00:31:09,420 --> 00:31:13,490
if it were to explode
over a populated area.

563
00:31:13,490 --> 00:31:15,290
To prevent such a catastrophe,

564
00:31:15,290 --> 00:31:19,590
we need to find all asteroids
whose orbits cross our own.

565
00:31:19,590 --> 00:31:22,830
Detection is crucial in
our defense against asteroids.

566
00:31:22,830 --> 00:31:25,900
And the reason is the earlier
they're detected,

567
00:31:25,900 --> 00:31:29,870
the easier it is to deflect them
away from hitting the Earth.

568
00:31:29,870 --> 00:31:32,940
You want to do deflection,
the first step is detection.

569
00:31:35,210 --> 00:31:37,740
The problem is,
asteroids are very hard

570
00:31:37,750 --> 00:31:39,580
to detect.

571
00:31:39,580 --> 00:31:42,180
Finding asteroids
and cataloging all their orbits

572
00:31:42,180 --> 00:31:44,180
is really challenging.

573
00:31:44,190 --> 00:31:46,420
They can move quite fast
across the sky,

574
00:31:46,420 --> 00:31:48,320
and they might go away

575
00:31:48,320 --> 00:31:53,130
on the other side of the sun
for years and years and years.

576
00:31:53,130 --> 00:31:56,630
So we can't see them.

577
00:31:56,630 --> 00:31:59,330
And even when they are
on this side of the sun,

578
00:31:59,330 --> 00:32:02,100
they're hard to spot.

579
00:32:02,100 --> 00:32:03,940
But the problem is,
they're very small

580
00:32:03,940 --> 00:32:05,340
and they're very dark,

581
00:32:05,340 --> 00:32:07,510
and when I say very dark,
I mean really dark,

582
00:32:07,510 --> 00:32:08,840
like a lump of coal.

583
00:32:08,840 --> 00:32:11,210
So how do you find
a small, dark rock

584
00:32:11,210 --> 00:32:13,850
just wandering around out there
in the solar system?

585
00:32:18,690 --> 00:32:22,320
The Catalina
sky survey has the answer.

586
00:32:24,660 --> 00:32:28,360
The huge telescope in the
mountains above Tucson, Arizona,

587
00:32:28,360 --> 00:32:33,130
takes a series of images
over a 20-minute period.

588
00:32:33,130 --> 00:32:36,000
It's hunting
for anything that moves

589
00:32:36,000 --> 00:32:39,770
because stars don't move,
but asteroids do.

590
00:32:42,280 --> 00:32:44,410
If it's a really
bright asteroid,

591
00:32:44,410 --> 00:32:46,750
we will see some bright points

592
00:32:46,750 --> 00:32:50,920
of light
tracking across the four images.

593
00:32:50,920 --> 00:32:53,690
Ah, here we go.

594
00:32:53,690 --> 00:32:55,620
This is a real object.

595
00:32:55,620 --> 00:32:58,290
You can see it's moving
across the sky here

596
00:32:58,290 --> 00:33:00,790
from the lower right
to the upper left.

597
00:33:00,800 --> 00:33:04,100
We are very, very excited
to have discovered one tonight

598
00:33:04,100 --> 00:33:08,000
because this is an object
that's approaching near space,

599
00:33:08,000 --> 00:33:10,900
likely in the neighborhood
of Earth.

600
00:33:14,580 --> 00:33:16,810
Catalina has limitations.

601
00:33:16,810 --> 00:33:19,610
It can only see visible light,

602
00:33:19,610 --> 00:33:25,220
so a particularly dim asteroid
could be missed.

603
00:33:25,220 --> 00:33:26,720
Asteroids are very cold.

604
00:33:26,720 --> 00:33:28,650
They're usually quite far away
from the sun,

605
00:33:28,660 --> 00:33:30,090
but amazingly, the best way

606
00:33:30,090 --> 00:33:32,860
we have to find these
is infrared light

607
00:33:32,860 --> 00:33:35,290
because things that are cold
by human scales

608
00:33:35,300 --> 00:33:37,930
can still be very warm
to an infrared telescope.

609
00:33:37,930 --> 00:33:40,700
So even if asteroids are just
a few tens of degrees

610
00:33:40,700 --> 00:33:41,830
above absolute zero,

611
00:33:41,840 --> 00:33:45,540
that's still enough heat
to detect them.

612
00:33:45,540 --> 00:33:48,240
When the infrared
space telescope Neowise

613
00:33:48,240 --> 00:33:51,380
turned its gaze onto asteroids,

614
00:33:51,380 --> 00:33:53,880
it had immediate results.

615
00:33:53,880 --> 00:33:55,380
Neowise has now detected

616
00:33:55,380 --> 00:34:00,250
close to 160,000 new asteroids
and comets in our solar system,

617
00:34:00,260 --> 00:34:02,160
and about 780 of those

618
00:34:02,160 --> 00:34:04,320
are things
that are near the Earth.

619
00:34:04,330 --> 00:34:07,130
10 of those near
objects have been classified

620
00:34:07,130 --> 00:34:12,630
as p.H.A.S...
potentially hazardous asteroids.

621
00:34:12,630 --> 00:34:16,000
Without Neowise,
we would have missed them.

622
00:34:16,000 --> 00:34:17,500
Using an infrared
space telescope

623
00:34:17,510 --> 00:34:22,810
is a way of of better detecting
some of the smaller asteroids

624
00:34:22,810 --> 00:34:26,280
and comets
in the near Earth vicinity.

625
00:34:26,280 --> 00:34:29,080
Detection is
an important first step,

626
00:34:29,080 --> 00:34:30,350
but it only tells us

627
00:34:30,350 --> 00:34:32,990
that there is
another asteroid out there.

628
00:34:32,990 --> 00:34:34,920
Once we've spotted an asteroid,

629
00:34:34,920 --> 00:34:37,790
all we know is that
it's a tiny dot of light.

630
00:34:37,790 --> 00:34:40,230
We don't know anything else
about it.

631
00:34:40,230 --> 00:34:42,160
So when a new asteroid
is discovered,

632
00:34:42,160 --> 00:34:43,430
the most important thing is

633
00:34:43,430 --> 00:34:45,930
to determine its path,
to track it, to figure out

634
00:34:45,930 --> 00:34:47,770
exactly how it's orbiting
around the sun

635
00:34:47,770 --> 00:34:49,540
and how close
it's gonna get to Earth.

636
00:34:49,540 --> 00:34:51,270
For that, we have to know
where they are now...

637
00:34:51,270 --> 00:34:54,940
so its current location...
and measure how fast it's going

638
00:34:54,940 --> 00:34:57,080
and which direction
it's travelling.

639
00:34:57,080 --> 00:34:59,180
All of these things together
are really important

640
00:34:59,180 --> 00:35:01,010
for tracking
where it's gonna be next

641
00:35:01,020 --> 00:35:03,180
and whether or not
they're gonna hit us.

642
00:35:05,390 --> 00:35:06,650
To get this information,

643
00:35:06,650 --> 00:35:09,560
we need something much bigger
and more powerful.

644
00:35:11,930 --> 00:35:14,930
The Arecibo observatory.

645
00:35:14,930 --> 00:35:16,960
Once Catalina
or another telescope

646
00:35:16,970 --> 00:35:20,730
detects a near Earth asteroid
in our cosmic neighborhood,

647
00:35:20,740 --> 00:35:26,070
Arecibo's thousand-foot dish
swings into action.

648
00:35:26,070 --> 00:35:27,840
They discover these asteroids,

649
00:35:27,840 --> 00:35:30,840
and then once we know
where they were,

650
00:35:30,850 --> 00:35:33,550
we can try and point
the radio telescope

651
00:35:33,550 --> 00:35:35,380
and see where they are
at the moment

652
00:35:35,380 --> 00:35:40,590
and measure their exact location
and their trajectory.

653
00:35:40,590 --> 00:35:43,560
Arecibo achieves
this level of precision

654
00:35:43,560 --> 00:35:46,530
by using radio detection
and ranging,

655
00:35:46,530 --> 00:35:49,260
more commonly known as radar.

656
00:35:49,260 --> 00:35:51,960
The planetary radar system
at Arecibo observatory

657
00:35:51,970 --> 00:35:55,070
is the most powerful
radar system in the world.

658
00:35:55,070 --> 00:35:58,070
We focus on
potentially hazardous asteroids,

659
00:35:58,070 --> 00:36:03,410
which are those that have a high
probability of impacting Earth.

660
00:36:03,410 --> 00:36:05,340
Arecibo sends out radio signals

661
00:36:05,350 --> 00:36:07,350
toward the newly
detected asteroid.

662
00:36:07,350 --> 00:36:09,480
It emanates radio signals.

663
00:36:09,480 --> 00:36:14,150
Some of them hit the asteroid
just like a radar gun from a cop

664
00:36:14,160 --> 00:36:16,160
might hit the side of your car.

665
00:36:16,160 --> 00:36:17,390
That's pretty similar,

666
00:36:17,390 --> 00:36:19,230
but instead of doing it
with a radar gun

667
00:36:19,230 --> 00:36:21,960
on the small scale, we're
doing at a really big scale

668
00:36:21,960 --> 00:36:25,130
with one megawatt power
hitting objects that are

669
00:36:25,130 --> 00:36:27,370
tens of lunar distances away.

670
00:36:27,370 --> 00:36:30,900
And then those radio
waves bounce back to Earth

671
00:36:30,910 --> 00:36:35,170
and we detect them again,
and by comparing the differences

672
00:36:35,180 --> 00:36:38,210
between what we sent
and what we received,

673
00:36:38,210 --> 00:36:41,780
we can get a map
of the asteroid itself

674
00:36:41,780 --> 00:36:46,620
and we can get where it's moving
and how fast it's moving.

675
00:36:46,620 --> 00:36:49,660
Speed, size,
and location of strike

676
00:36:49,660 --> 00:36:53,730
determine the outcome
of an asteroid impact.

677
00:36:53,730 --> 00:36:57,200
But the type of asteroid
is another factor.

678
00:36:57,200 --> 00:36:59,970
It can mean the difference
between survival

679
00:36:59,970 --> 00:37:02,700
or complete annihilation.

680
00:37:19,820 --> 00:37:23,460
The Bering sea asteroid
blew up in the atmosphere,

681
00:37:23,460 --> 00:37:27,560
but the Barringer crater
asteroid hit the ground intact

682
00:37:27,560 --> 00:37:29,200
with its full force.

683
00:37:31,530 --> 00:37:35,030
Why do different asteroids
behave differently?

684
00:37:35,040 --> 00:37:38,540
And what will Apophis do
when it heads our way?

685
00:37:40,710 --> 00:37:44,610
Arecibo's radar
may have the answer.

686
00:37:44,610 --> 00:37:47,650
When we bounce radar waves
off of these objects,

687
00:37:47,650 --> 00:37:51,050
we can get effectively imagery
of the surface

688
00:37:51,050 --> 00:37:52,620
of some of these small objects

689
00:37:52,620 --> 00:37:56,420
that we just cannot do
with optical telescopes.

690
00:37:56,420 --> 00:37:59,260
This is
the radar image of Apophis.

691
00:37:59,260 --> 00:38:02,930
It's so far away that all they
could image were a few pixels.

692
00:38:05,770 --> 00:38:08,430
So this is our most recent
radar image

693
00:38:08,440 --> 00:38:11,440
of asteroid Apophis.

694
00:38:11,440 --> 00:38:14,810
And you can see
it's only a few pixels,

695
00:38:14,810 --> 00:38:16,910
but it does give us information

696
00:38:16,910 --> 00:38:20,580
on what it actually is.

697
00:38:20,580 --> 00:38:23,150
These few pixels
are enough to work out

698
00:38:23,150 --> 00:38:26,750
how big Apophis is.

699
00:38:26,750 --> 00:38:29,760
From this image,
we can constrain the size

700
00:38:29,760 --> 00:38:32,060
to be about 1,000 feet,

701
00:38:32,060 --> 00:38:34,690
which is about the same size
as the Arecibo

702
00:38:34,700 --> 00:38:37,100
radio telescope.

703
00:38:37,100 --> 00:38:40,530
All of that from what were
a bunch of pixels.

704
00:38:46,240 --> 00:38:48,410
Knowing the size
and mass of an asteroid

705
00:38:48,410 --> 00:38:53,750
is critical to understanding
what an asteroid is made of.

706
00:38:53,750 --> 00:38:56,520
If we have the size and
the mass, we get the density.

707
00:38:56,520 --> 00:38:58,950
If we have the density,
we know what it's made of.

708
00:38:58,950 --> 00:39:02,960
Rock has some density.
Metal has a different density.

709
00:39:02,960 --> 00:39:06,030
So we can determine
a huge amount about the asteroid

710
00:39:06,030 --> 00:39:08,590
simply by pinging it with radar.

711
00:39:11,570 --> 00:39:13,100
Arecibo's data reveals

712
00:39:13,100 --> 00:39:15,530
that not all asteroids
are alike.

713
00:39:17,540 --> 00:39:19,570
There's not just
one kind of asteroid.

714
00:39:19,570 --> 00:39:21,340
There are actually
several kinds,

715
00:39:21,340 --> 00:39:23,240
and this is important
to understand

716
00:39:23,240 --> 00:39:25,110
because they behave differently.

717
00:39:25,110 --> 00:39:27,180
They behave differently
if they impact us,

718
00:39:27,180 --> 00:39:29,780
and they behave differently
if we're trying to prevent them

719
00:39:29,780 --> 00:39:31,120
from impacting us.

720
00:39:31,120 --> 00:39:34,650
We need to know what these
asteroids are made of

721
00:39:34,660 --> 00:39:36,020
if they're gonna hit the Earth

722
00:39:36,020 --> 00:39:40,330
because that drastically alters
the potential effects.

723
00:39:40,330 --> 00:39:43,460
Asteroids come in different
shapes, different sizes,

724
00:39:43,460 --> 00:39:46,400
and different compositions,
and we think that is

725
00:39:46,400 --> 00:39:49,970
because they are the leftovers
of planet formation.

726
00:39:49,970 --> 00:39:52,840
To understand how
each asteroid formed

727
00:39:52,840 --> 00:39:54,770
and their threat level,
we have to go back

728
00:39:54,780 --> 00:40:00,150
4.6 billion years to the start
of the solar system.

729
00:40:00,150 --> 00:40:02,150
The reason that there are
all these asteroids

730
00:40:02,150 --> 00:40:04,520
floating around
in our solar system today

731
00:40:04,520 --> 00:40:07,390
is just because of the early
violence of the solar system

732
00:40:07,390 --> 00:40:09,020
as it was forming.

733
00:40:11,830 --> 00:40:13,430
At the birth
of the solar system,

734
00:40:13,430 --> 00:40:16,460
the sun ignites,

735
00:40:16,460 --> 00:40:19,470
leaving a disk of gas and dust.

736
00:40:23,000 --> 00:40:27,070
Slowly, over time, planets form.

737
00:40:27,070 --> 00:40:29,710
Lots of planets.

738
00:40:29,710 --> 00:40:33,110
The early solar system
was a messy place.

739
00:40:33,110 --> 00:40:36,480
There were a lot more planets,
a lot more forming planets.

740
00:40:36,480 --> 00:40:38,180
They would crash in
to each other,

741
00:40:38,190 --> 00:40:40,220
they would merge,
they would disintegrate,

742
00:40:40,220 --> 00:40:42,490
they would re-form.

743
00:40:45,230 --> 00:40:48,460
This process of accretion
of building planetary worlds

744
00:40:48,460 --> 00:40:51,860
was not just, you know,
kind of gentle and happy.

745
00:40:51,870 --> 00:40:54,270
It was violent.

746
00:40:54,270 --> 00:40:57,240
It was like a giant
cosmic game of pool...

747
00:40:57,240 --> 00:40:59,910
planet smashing into planet.

748
00:41:03,140 --> 00:41:05,380
The leftovers from this violence

749
00:41:05,380 --> 00:41:09,650
formed a ring of junk
between Mars and Jupiter.

750
00:41:09,650 --> 00:41:12,080
And now we call
that junk asteroids.

751
00:41:12,090 --> 00:41:13,850
They're just basically
rubble left over

752
00:41:13,860 --> 00:41:16,020
from the formation
of the solar system.

753
00:41:20,360 --> 00:41:23,130
Rocky leftovers became c-type

754
00:41:23,130 --> 00:41:26,770
or chondrite asteroids.

755
00:41:26,770 --> 00:41:30,370
They're quite dense, so big ones
can punch through the atmosphere

756
00:41:30,370 --> 00:41:31,970
and hit the ground.

757
00:41:35,340 --> 00:41:40,310
Radar reveals
a rarer type of asteroid.

758
00:41:40,310 --> 00:41:42,920
Some of them really stand out
because their density

759
00:41:42,920 --> 00:41:46,990
is so much higher than the rest
of the other asteroids.

760
00:41:46,990 --> 00:41:50,560
These asteroids
are m-type or metal.

761
00:41:53,190 --> 00:41:55,160
Because their mass is great,

762
00:41:55,160 --> 00:41:59,470
they carry more kinetic energy
during a strike.

763
00:41:59,470 --> 00:42:03,170
By far, the worst one
is this iron meteorite.

764
00:42:03,170 --> 00:42:06,240
This is really heavy,
so the difference...

765
00:42:06,240 --> 00:42:07,710
if you were being hit by this,

766
00:42:07,710 --> 00:42:10,010
it would be the difference
between being hit by a rock

767
00:42:10,010 --> 00:42:14,350
and being hit by a metal hammer.

768
00:42:14,350 --> 00:42:16,350
We think that both the Barringer

769
00:42:16,350 --> 00:42:18,680
and the k-pg dinosaur killer

770
00:42:18,690 --> 00:42:21,120
were caused by metal asteroids.

771
00:42:23,990 --> 00:42:26,660
But there's another more
mysterious type

772
00:42:26,660 --> 00:42:28,360
floating through space.

773
00:42:34,670 --> 00:42:36,640
December 2018,

774
00:42:36,640 --> 00:42:39,870
NASA's spacecraft Osiris-Rex
approached

775
00:42:39,870 --> 00:42:43,680
the near Earth asteroid Bennu.

776
00:42:43,680 --> 00:42:46,710
Over time, it drifted out
of the main asteroid belt,

777
00:42:46,710 --> 00:42:48,880
made its way into
the inner solar system,

778
00:42:48,880 --> 00:42:51,020
until it became
a near Earth asteroid,

779
00:42:51,020 --> 00:42:54,850
accessible for our spacecraft
to go and visit.

780
00:42:54,860 --> 00:42:57,590
Osiris trained
its camera on Bennu.

781
00:43:04,770 --> 00:43:07,370
One of the biggest surprises
on arrival of Bennu

782
00:43:07,370 --> 00:43:11,140
was the large number of
large boulders on its surface.

783
00:43:11,140 --> 00:43:13,610
Bennu is really littered
with huge boulders

784
00:43:13,610 --> 00:43:15,940
and littered
with medium-sized boulders

785
00:43:15,940 --> 00:43:18,180
and littered
with small boulders.

786
00:43:18,180 --> 00:43:20,850
Bennu is not
a solid lump of rock.

787
00:43:20,850 --> 00:43:23,550
It's made up of thousands
of bits of rock

788
00:43:23,550 --> 00:43:27,150
forming what we call
a rubble pile.

789
00:43:27,150 --> 00:43:31,020
These asteroids aren't big,
singular, spherical balls

790
00:43:31,030 --> 00:43:32,160
of rock,

791
00:43:32,160 --> 00:43:34,660
but rather they're literally
piles of rubble.

792
00:43:34,660 --> 00:43:36,400
They're all sorts
of pieces and fragments

793
00:43:36,400 --> 00:43:38,230
from another asteroid
that had previously

794
00:43:38,230 --> 00:43:41,230
been disrupted
that have all come back together

795
00:43:41,240 --> 00:43:44,000
and formed literally a pile
of rocks held together

796
00:43:44,010 --> 00:43:45,570
by their own gravity.

797
00:43:45,570 --> 00:43:48,340
We think rubble piles
formed from collisions

798
00:43:48,340 --> 00:43:53,580
inside the asteroid belt
each impact blasted bits off.

799
00:43:53,580 --> 00:43:56,350
Then, over time,
they came back together

800
00:43:56,350 --> 00:43:59,350
to form a loose pile of rocks.

801
00:43:59,350 --> 00:44:01,750
Imagine taking
a big cosmic dump truck

802
00:44:01,760 --> 00:44:03,690
full of gravel and rubble

803
00:44:03,690 --> 00:44:05,560
and dumping it
out there in the space

804
00:44:05,560 --> 00:44:08,630
and letting gravity
weakly hold it together.

805
00:44:10,800 --> 00:44:13,770
When scientists probe
deeper into Bennu,

806
00:44:13,770 --> 00:44:15,670
they found another surprise.

807
00:44:15,670 --> 00:44:19,670
It's full of holes,
like Swiss cheese.

808
00:44:19,670 --> 00:44:22,210
If you could slice open
one of these asteroids,

809
00:44:22,210 --> 00:44:24,340
you'd see there are
a lot of voids.

810
00:44:24,350 --> 00:44:28,250
In fact, 60% of what we're
looking at is a void space,

811
00:44:28,250 --> 00:44:30,220
so they're actually
really fluffy.

812
00:44:30,220 --> 00:44:31,580
So even though
they're made of rocks,

813
00:44:31,590 --> 00:44:35,120
they're sort of
the lint of rocks.

814
00:44:35,120 --> 00:44:38,060
Bennu helps us
understand Apophis.

815
00:44:38,060 --> 00:44:43,100
Radar data shows that
Apophis is also a rubble pile.

816
00:44:43,100 --> 00:44:44,800
If you look at Apophis,
we really want to know

817
00:44:44,800 --> 00:44:47,100
how its orbit will evolve
in the future.

818
00:44:47,100 --> 00:44:49,440
What we learn at Bennu
about similar-sized

819
00:44:49,440 --> 00:44:51,970
rubble-pile asteroids
might help us understand

820
00:44:51,970 --> 00:44:55,010
the future of an asteroid
like Apophis.

821
00:44:55,010 --> 00:44:57,080
So what would happen
if the rubble pile

822
00:44:57,080 --> 00:44:59,080
called Apophis hits Earth?

823
00:44:59,080 --> 00:45:00,980
You probably don't want
that to hit you still,

824
00:45:00,980 --> 00:45:03,180
but it definitely
makes it a lot weaker

825
00:45:03,180 --> 00:45:05,450
than something like a solid rock

826
00:45:05,450 --> 00:45:10,220
or even more, a chunk
of nickel iron metal.

827
00:45:10,220 --> 00:45:14,060
Does its composition
make it any less of a threat?

828
00:45:14,060 --> 00:45:17,260
A rubble pile like Apophis
is especially unnerving

829
00:45:17,260 --> 00:45:19,930
because we don't know, when it
interacts with the atmosphere,

830
00:45:19,930 --> 00:45:22,000
if it's gonna stay
as one solid piece,

831
00:45:22,000 --> 00:45:24,370
will it break up.

832
00:45:24,370 --> 00:45:27,740
When these rubble piles
start interacting with planets,

833
00:45:27,740 --> 00:45:30,310
if they fly near a planet,
they can get pulled apart

834
00:45:30,310 --> 00:45:32,140
into all of their little pieces.

835
00:45:32,150 --> 00:45:34,710
Or if they enter
the atmosphere of a planet

836
00:45:34,720 --> 00:45:38,320
to impact the surface, they
might slowly get pulled apart

837
00:45:38,320 --> 00:45:40,050
as they enter the atmosphere

838
00:45:40,050 --> 00:45:42,520
and end up being
an array of little impacts

839
00:45:42,520 --> 00:45:44,420
instead of one big
single impact.

840
00:45:53,570 --> 00:45:59,340
But what would happen
if these impacts occur at sea?

841
00:45:59,340 --> 00:46:01,310
Will our oceans save us,

842
00:46:01,310 --> 00:46:05,180
or will a giant Tsunami
wipe us out?

843
00:46:17,390 --> 00:46:19,060
2019,

844
00:46:19,060 --> 00:46:23,630
U.S. researchers
discover deposits of fossils.

845
00:46:23,630 --> 00:46:29,470
They contain both the remains
of land and sea creatures.

846
00:46:29,470 --> 00:46:31,870
You see things that
are all jumbled together,

847
00:46:31,870 --> 00:46:35,240
so you'll have fossils
of sea creatures.

848
00:46:35,240 --> 00:46:39,340
You'll have ocean deposits
that are mixed up

849
00:46:39,350 --> 00:46:42,820
with coastal deposits
and onshore deposits,

850
00:46:42,820 --> 00:46:45,920
and you see those deposits
in places

851
00:46:45,920 --> 00:46:47,290
that are very, very far away

852
00:46:47,290 --> 00:46:49,690
from where you would
expect them to be.

853
00:46:49,690 --> 00:46:51,920
And so this material was
obviously thrown

854
00:46:51,930 --> 00:46:54,890
very far inland.

855
00:46:54,900 --> 00:46:56,260
The jumbled deposits

856
00:46:56,260 --> 00:46:59,670
suggest that the creatures
were killed at the same time

857
00:46:59,670 --> 00:47:02,940
in a huge and violent event,

858
00:47:02,940 --> 00:47:04,570
something powerful enough

859
00:47:04,570 --> 00:47:09,710
to sweep ocean-dwelling
creatures far inland.

860
00:47:09,710 --> 00:47:11,880
A Tsunami.

861
00:47:11,880 --> 00:47:14,050
Tsunamis are usually created

862
00:47:14,050 --> 00:47:17,050
when the ocean floor
moves suddenly.

863
00:47:17,050 --> 00:47:19,890
The ground picks up
the entire ocean

864
00:47:19,890 --> 00:47:21,790
and shakes it up and down,

865
00:47:21,790 --> 00:47:24,060
and it's sort of like
taking a rope and shaking it,

866
00:47:24,060 --> 00:47:26,660
and it moves all across
the ocean floor

867
00:47:26,660 --> 00:47:29,160
and ocean surface
until it reaches land.

868
00:47:29,160 --> 00:47:33,500
The biggest recent Tsunami
was caused by the Earth's crust

869
00:47:33,500 --> 00:47:36,000
at the bottom of the ocean
lifting slightly,

870
00:47:36,000 --> 00:47:39,200
so this means that
that entire length of crust

871
00:47:39,210 --> 00:47:42,370
that lifted displaced
the water above it,

872
00:47:42,380 --> 00:47:45,380
so the waves,
the tsunamis that result,

873
00:47:45,380 --> 00:47:47,510
are really long and wide,

874
00:47:47,510 --> 00:47:49,750
and it can travel
across the ocean

875
00:47:49,750 --> 00:47:54,550
at tremendous speeds
and up on land.

876
00:47:54,560 --> 00:47:57,160
Is this what happened
to the fossilized creatures?

877
00:47:57,160 --> 00:48:01,630
Were they killed
by a huge Tsunami?

878
00:48:01,630 --> 00:48:05,630
Clues come from dating
the preserved remains.

879
00:48:05,630 --> 00:48:09,270
They're 66 million years old.

880
00:48:09,270 --> 00:48:11,840
From the same time
a six-mile-wide asteroid

881
00:48:11,840 --> 00:48:16,380
crashed into the sea off
the Yucatan peninsula in Mexico.

882
00:48:20,150 --> 00:48:22,350
Are the two events connected?

883
00:48:22,350 --> 00:48:26,890
Do ocean-impacting asteroids
trigger tsunamis?

884
00:48:26,890 --> 00:48:28,390
We used to think
that a big asteroid

885
00:48:28,390 --> 00:48:31,960
impacting in the ocean would
drive a tremendous Tsunami,

886
00:48:31,960 --> 00:48:35,760
a huge wall of water
out at very rapid speeds,

887
00:48:35,760 --> 00:48:38,860
which would basically
scour clean everything.

888
00:48:38,870 --> 00:48:41,830
Now new research
from 2018 suggests

889
00:48:41,840 --> 00:48:44,370
a very different scenario.

890
00:48:44,370 --> 00:48:47,970
Scientists use super computers
to model asteroids

891
00:48:47,980 --> 00:48:51,580
hitting the deep ocean
to work out how much of

892
00:48:51,580 --> 00:48:55,880
the asteroid's kinetic energy
is converted into a Tsunami.

893
00:48:58,790 --> 00:49:02,290
In the simulations,
a 1,600-foot asteroid

894
00:49:02,290 --> 00:49:05,420
hits the ocean at
20,000 miles an hour

895
00:49:05,430 --> 00:49:08,990
and dives into the water.

896
00:49:09,000 --> 00:49:12,560
As it goes deeper in,
of course it's meeting a lot

897
00:49:12,570 --> 00:49:15,500
of resistance and it slows down
and it compresses up.

898
00:49:15,500 --> 00:49:18,940
It compresses and compresses
and compresses, and then finally

899
00:49:18,940 --> 00:49:20,610
it runs out of momentum,

900
00:49:20,610 --> 00:49:23,340
and it's at an extremely
high pressure.

901
00:49:24,410 --> 00:49:28,950
The huge pressure
causes the asteroid to vaporize.

902
00:49:28,950 --> 00:49:31,880
Temperatures hotter than
the surface of the sun

903
00:49:31,890 --> 00:49:35,950
turn trillions
of gallons of water into steam.

904
00:49:36,560 --> 00:49:40,160
The blast creates a huge
short lived cavity

905
00:49:40,160 --> 00:49:42,530
in the water's surface

906
00:49:42,530 --> 00:49:44,960
and a splash curtain,
a wall of water,

907
00:49:44,970 --> 00:49:47,870
that leaps up several miles.

908
00:49:47,870 --> 00:49:50,800
This curtain then collapses
and water falls

909
00:49:50,800 --> 00:49:54,240
back into the cavity,
shooting a column of water

910
00:49:54,240 --> 00:49:56,780
five miles up.

911
00:49:56,780 --> 00:49:59,640
This very tall column
can't support its own weight

912
00:49:59,650 --> 00:50:03,020
and collapses back down.

913
00:50:03,020 --> 00:50:05,550
The collapse of
so much water triggers

914
00:50:05,550 --> 00:50:08,690
a wave 1,200 feet high.

915
00:50:08,690 --> 00:50:12,090
Could this become
a huge Tsunami?

916
00:50:16,630 --> 00:50:18,730
If we think about a meteor
striking the ocean,

917
00:50:18,730 --> 00:50:21,030
we want to understand
how far the waves

918
00:50:21,040 --> 00:50:22,600
might propagate from the site.

919
00:50:22,600 --> 00:50:25,840
We could actually just use a
stone and throw it into a pond,

920
00:50:25,840 --> 00:50:27,970
and you might think,
"okay, well, it's a big stone,

921
00:50:27,980 --> 00:50:29,340
it's going to make
a really big splash,

922
00:50:29,340 --> 00:50:31,810
and that's just going to
extend out a long distance."

923
00:50:31,810 --> 00:50:34,980
But it turns out the splash
stays the biggest really close

924
00:50:34,980 --> 00:50:36,110
to where it impacts.

925
00:50:36,120 --> 00:50:37,580
And then the ripples
die down after that.

926
00:50:37,580 --> 00:50:39,280
So let's try that.

927
00:50:40,590 --> 00:50:43,120
Big splash in the middle.

928
00:50:43,120 --> 00:50:44,590
And we see the ripples
going outward,

929
00:50:44,590 --> 00:50:45,960
but they're really
pretty small compared

930
00:50:45,960 --> 00:50:48,290
with that initial big splash.

931
00:50:49,700 --> 00:50:53,770
It's the same with
an ocean impacting asteroid.

932
00:50:53,770 --> 00:50:58,040
The impact creates surface
waves that die away quickly

933
00:50:58,040 --> 00:51:01,610
because only a small amount
of the asteroid's kinetic energy

934
00:51:01,610 --> 00:51:03,310
gets into the water.

935
00:51:03,310 --> 00:51:05,380
It's actually
pretty tough to make

936
00:51:05,380 --> 00:51:06,650
a Tsunami like that.

937
00:51:06,650 --> 00:51:08,950
The energy of the asteroid
doesn't couple well

938
00:51:08,950 --> 00:51:11,480
with the water
to drive this wave.

939
00:51:11,490 --> 00:51:12,980
Instead, most of the energy

940
00:51:12,990 --> 00:51:15,890
goes into vaporizing
the asteroid itself

941
00:51:15,890 --> 00:51:19,090
as well as all of the water
around it.

942
00:51:19,090 --> 00:51:21,860
Only 1% of
the asteroid's kinetic energy

943
00:51:21,860 --> 00:51:24,030
goes into making a wave.

944
00:51:24,030 --> 00:51:28,470
So only low energy waves form,
too weak to become

945
00:51:28,470 --> 00:51:32,870
giant tsunamis
traveling hundreds of miles.

946
00:51:32,870 --> 00:51:35,570
So what caused
the jumbled fossil deposits

947
00:51:35,580 --> 00:51:39,850
found thousands of miles away
from the impact site?

948
00:51:39,850 --> 00:51:41,810
We don't think there
could be that much energy

949
00:51:41,820 --> 00:51:45,780
still transmitted that far away
from the impact site.

950
00:51:45,790 --> 00:51:48,650
Instead, there has to be
a different source of energy

951
00:51:48,660 --> 00:51:50,660
that created different waves

952
00:51:50,660 --> 00:51:53,690
right about the same time
as that impact event.

953
00:51:55,500 --> 00:51:58,830
Research from 2019
may have the answer.

954
00:51:58,830 --> 00:52:02,700
The KPG asteroid struck
on the continental shelf,

955
00:52:02,700 --> 00:52:06,240
the shallow region between land
and deep ocean.

956
00:52:06,240 --> 00:52:10,180
The impact triggered a localized
Tsunami large enough

957
00:52:10,180 --> 00:52:13,110
to kill creatures in the region.

958
00:52:13,110 --> 00:52:16,550
But it also sent a huge
shock wave into the bedrock.

959
00:52:18,420 --> 00:52:20,050
There's going to be
a shock wave driven

960
00:52:20,050 --> 00:52:21,320
through the ground.

961
00:52:21,320 --> 00:52:23,790
That probably would have
killed anything in the area.

962
00:52:23,790 --> 00:52:28,530
If you had a dinosaur
that was standing on

963
00:52:28,530 --> 00:52:33,170
the Gulf coast of what is now
the United States,

964
00:52:33,170 --> 00:52:38,640
that animal would have
experienced a seismic pulse,

965
00:52:38,640 --> 00:52:41,410
an Earthquake that is stronger
than anything

966
00:52:41,410 --> 00:52:43,240
on our current Richter scale.

967
00:52:43,240 --> 00:52:46,440
It would have actually driven
its legs up into its body cavity

968
00:52:46,450 --> 00:52:47,610
killing it instantly.

969
00:52:47,610 --> 00:52:50,520
There's all manner of mayhem
and death

970
00:52:50,520 --> 00:52:51,920
taking place at this time.

971
00:52:51,920 --> 00:52:53,920
There was no escaping
this event.

972
00:52:55,590 --> 00:52:59,290
The initial shock wave
smashed into the ground rock

973
00:52:59,290 --> 00:53:03,060
and traveled through
the Earth's crust.

974
00:53:03,060 --> 00:53:06,700
The impact would have shaken
the crust of the Earth,

975
00:53:06,700 --> 00:53:09,630
which also would have triggered
Earthquakes around the world,

976
00:53:09,640 --> 00:53:13,640
which themselves may have
triggered secondary salamis.

977
00:53:16,710 --> 00:53:19,950
Secondary tsunamis
thousands of miles from

978
00:53:19,950 --> 00:53:24,120
the impact site killed both
land and sea creatures.

979
00:53:24,120 --> 00:53:31,520
The KPG impact went on to wipe
out 70% of all life on Earth.

980
00:53:31,530 --> 00:53:37,160
So how did one asteroid
strike cause a global kill zone?

981
00:53:55,380 --> 00:54:00,420
66 million years ago,
70% of life on Earth died

982
00:54:00,420 --> 00:54:03,660
after the KPG asteroid strike.

983
00:54:07,360 --> 00:54:11,000
How could one space rocket
hitting the sea cause

984
00:54:11,000 --> 00:54:13,100
a global catastrophe?

985
00:54:14,500 --> 00:54:17,270
When you have a big rock
hitting the ocean,

986
00:54:17,270 --> 00:54:19,870
the biggest danger
is not from the waves

987
00:54:19,870 --> 00:54:23,580
but actually from the steam
that it creates.

988
00:54:23,580 --> 00:54:27,650
The impact vaporized
trillions of tons of seawater.

989
00:54:27,650 --> 00:54:30,580
This steam Rose up
into the atmosphere

990
00:54:30,580 --> 00:54:34,250
where it condensed
into water vapor.

991
00:54:34,250 --> 00:54:36,320
Water vapor is a greenhouse gas.

992
00:54:36,320 --> 00:54:39,420
So that's done going up
into the upper atmosphere,

993
00:54:39,430 --> 00:54:42,190
and it's trapping heat,

994
00:54:42,200 --> 00:54:44,430
but at different layers
it's making clouds.

995
00:54:44,430 --> 00:54:47,070
It's just throwing
everything off kilter.

996
00:54:47,070 --> 00:54:49,500
Water is a very effective
greenhouse gas as you

997
00:54:49,500 --> 00:54:53,000
will actually affect some very
significant climate change

998
00:54:53,010 --> 00:54:55,610
very quickly
as a result of that impact.

999
00:54:57,510 --> 00:54:59,710
Within weeks
of the asteroid strike,

1000
00:54:59,710 --> 00:55:04,020
water vapor in the atmosphere
caused temperatures to rise.

1001
00:55:05,120 --> 00:55:07,720
But that was only the start.

1002
00:55:08,890 --> 00:55:13,060
The impact also blew out
10 trillion tons of rock,

1003
00:55:13,060 --> 00:55:15,330
ash, and dust.

1004
00:55:16,700 --> 00:55:20,130
This asteroid is so big,
six miles wide.

1005
00:55:20,130 --> 00:55:21,800
It's punched a hole in the air.

1006
00:55:21,800 --> 00:55:24,500
There's like a column
of low density, a chimney,

1007
00:55:24,500 --> 00:55:27,540
that goes from the ground up to
the top of the atmosphere.

1008
00:55:27,540 --> 00:55:29,870
And that means there's
very little air resistance

1009
00:55:29,880 --> 00:55:31,440
in that tunnel.

1010
00:55:31,450 --> 00:55:34,210
These rocks can actually
blast up into the chimney

1011
00:55:34,210 --> 00:55:36,920
and find it easier
to get up out of the atmosphere.

1012
00:55:36,920 --> 00:55:40,390
It sent that material
flying up halfway

1013
00:55:40,390 --> 00:55:43,760
to the orbit of the moon,
circled around the Earth.

1014
00:55:43,760 --> 00:55:47,860
All this ring of material
falling back on to the Earth.

1015
00:55:47,860 --> 00:55:51,600
And it was like the sky itself
was on fire.

1016
00:55:51,600 --> 00:55:53,570
So not only do you
have rocks falling on you,

1017
00:55:53,570 --> 00:55:56,100
but they're molten,
and these rocks

1018
00:55:56,100 --> 00:56:00,570
will start catching plants
and anything else on fire.

1019
00:56:05,510 --> 00:56:09,350
Soot and ash Rose
into the atmosphere

1020
00:56:09,350 --> 00:56:11,650
blocking out the sun.

1021
00:56:13,620 --> 00:56:16,020
Material was thrown
into the atmosphere,

1022
00:56:16,020 --> 00:56:18,520
plunging the planet
into a nuclear winter.

1023
00:56:18,530 --> 00:56:24,800
It was complete chaos, and it
went dark for two full years.

1024
00:56:24,800 --> 00:56:27,830
Without sunlight,
temperatures dropped.

1025
00:56:29,600 --> 00:56:34,970
Just months after the impact,
the planet cooled by 20 degrees.

1026
00:56:35,740 --> 00:56:38,580
In the immediate area, there's
just tremendous destruction.

1027
00:56:38,580 --> 00:56:40,480
Just everything gets destroyed.

1028
00:56:40,480 --> 00:56:43,050
But over the long term,
you're talking about ash

1029
00:56:43,050 --> 00:56:46,620
kicked up in the atmosphere,
extremely cold weather,

1030
00:56:46,620 --> 00:56:48,890
basically a global ice age.

1031
00:56:50,060 --> 00:56:52,190
The freezing
temperatures killed off

1032
00:56:52,190 --> 00:56:54,160
most plant life.

1033
00:56:54,160 --> 00:56:56,690
Imagine how that
affected life on Earth.

1034
00:56:56,700 --> 00:57:00,700
No plants and the base
of the ecosystem collapses.

1035
00:57:04,400 --> 00:57:07,940
This dark nuclear
winter lasted two years

1036
00:57:07,940 --> 00:57:12,040
and prevented plants
from photosynthesizing.

1037
00:57:12,050 --> 00:57:14,650
So if plants can no longer
use photosynthesis

1038
00:57:14,650 --> 00:57:16,650
to live, they'll die.

1039
00:57:16,650 --> 00:57:19,380
And then with no plants,
then you have no food

1040
00:57:19,390 --> 00:57:21,050
for these larger animals.

1041
00:57:21,050 --> 00:57:23,990
And so anything that eats
those animals will also die.

1042
00:57:23,990 --> 00:57:25,220
If you lose your plants,

1043
00:57:25,230 --> 00:57:28,430
you're going to lose
your large scale life.

1044
00:57:28,430 --> 00:57:31,560
First the plant eating
herbivores died off,

1045
00:57:31,570 --> 00:57:35,400
followed by the meat eating
carnivores.

1046
00:57:35,400 --> 00:57:39,040
Most of the dinosaurs
were just unable to find food

1047
00:57:39,040 --> 00:57:42,040
and to survive through
the cold long night.

1048
00:57:43,810 --> 00:57:46,850
The global devastation
wasn't over yet.

1049
00:57:46,850 --> 00:57:50,220
The rock of the continental
shelf where the asteroid hit

1050
00:57:50,220 --> 00:57:52,820
contained carbon and sulfur.

1051
00:57:54,420 --> 00:57:58,020
These carbonate rocks
were heated and vaporized

1052
00:57:58,020 --> 00:58:00,890
and released carbon dioxide
into the atmosphere.

1053
00:58:00,890 --> 00:58:02,990
Yet another greenhouse gas.

1054
00:58:03,000 --> 00:58:06,000
So you're vaporizing
a lot of sulfur,

1055
00:58:06,000 --> 00:58:08,830
a lot of salts
of different kinds

1056
00:58:08,840 --> 00:58:12,570
that are then lofted up
into the upper atmosphere,

1057
00:58:12,570 --> 00:58:15,340
that then plays havoc
on the climate.

1058
00:58:19,480 --> 00:58:23,280
These greenhouse gases
built up in the atmosphere

1059
00:58:23,280 --> 00:58:25,680
forming a warming blanket.

1060
00:58:28,690 --> 00:58:31,760
Triggering the next phase
of destruction.

1061
00:58:34,590 --> 00:58:37,300
Global warming on steroids.

1062
00:58:39,600 --> 00:58:44,270
Temperatures Rose 10 degrees
above normal.

1063
00:58:44,270 --> 00:58:48,370
Then the oceans warmed, as well.

1064
00:58:48,380 --> 00:58:51,910
Oxygen levels dropped,
and the seas became toxic

1065
00:58:51,910 --> 00:58:55,310
to simple life forms.

1066
00:58:55,320 --> 00:58:58,320
It actually made it impossible
for certain microbes

1067
00:58:58,320 --> 00:59:01,820
to actually live, and they're
the basis of the food system.

1068
00:59:01,820 --> 00:59:05,820
So really it changed what could
actually live in the ocean

1069
00:59:05,830 --> 00:59:09,460
and how much could live there.

1070
00:59:09,460 --> 00:59:11,700
Dead zones appeared
in the oceans

1071
00:59:11,700 --> 00:59:14,600
just as they had on land.

1072
00:59:14,600 --> 00:59:20,470
Nearly three quarters
of all life on Earth died,

1073
00:59:20,470 --> 00:59:23,680
all from one asteroid impact.

1074
00:59:27,780 --> 00:59:29,780
To prevent it
from happening again,

1075
00:59:29,780 --> 00:59:33,650
we need to track all
potentially dangerous asteroids.

1076
00:59:35,820 --> 00:59:37,120
But that isn't easy

1077
00:59:37,120 --> 00:59:40,690
because these space rocks
can change direction.

1078
00:59:57,210 --> 00:59:59,780
Saricicek, Turkey.

1079
00:59:59,780 --> 01:00:03,010
Security cameras record
a flash in the sky.

1080
01:00:04,920 --> 01:00:10,150
The flash... a 3-foot asteroid
exploding in the atmosphere.

1081
01:00:16,100 --> 01:00:18,900
It blew up in
the atmosphere and rained down,

1082
01:00:18,900 --> 01:00:20,160
and people saw that.

1083
01:00:20,170 --> 01:00:21,670
It was very noticeable.

1084
01:00:21,670 --> 01:00:24,240
And they went, and they
collected those meteorites.

1085
01:00:24,240 --> 01:00:28,010
And then they tried to figure
out what they were looking at.

1086
01:00:30,510 --> 01:00:34,150
The debris was sent
for fragment analysis.

1087
01:00:35,450 --> 01:00:38,320
I have a piece of one here.
So first, on the outside,

1088
01:00:38,320 --> 01:00:40,720
you can see it has
a really black fusion crust.

1089
01:00:40,720 --> 01:00:42,620
This is from when it fell
into the Earth's atmosphere,

1090
01:00:42,620 --> 01:00:44,060
so it was melted.

1091
01:00:44,060 --> 01:00:46,390
But when you look on
the inside, it reveals

1092
01:00:46,390 --> 01:00:50,630
this beautiful, very light tone,
fine grained material.

1093
01:00:50,630 --> 01:00:53,530
And so these meteorites
are incredibly distinctive

1094
01:00:53,530 --> 01:00:55,430
and really beautiful.

1095
01:00:55,440 --> 01:00:57,370
The meteorites are rocky.

1096
01:00:57,370 --> 01:01:01,670
They're beautiful color comes
from a mineral called howardite.

1097
01:01:01,680 --> 01:01:06,540
It's rare, and it doesn't
form on Earth.

1098
01:01:06,550 --> 01:01:09,950
Howardite meteorites come from
the asteroid Vesta,

1099
01:01:09,950 --> 01:01:12,720
and we know that because
of the dawn mission

1100
01:01:12,720 --> 01:01:14,850
that actually went to Vesta
and took a look at it

1101
01:01:14,850 --> 01:01:17,920
very carefully, so we know
the composition very well.

1102
01:01:17,920 --> 01:01:20,690
And so now suddenly here
was a new kind of meteorite

1103
01:01:20,690 --> 01:01:26,130
that's in Turkey that matches
the Vesta family of meteorites

1104
01:01:26,970 --> 01:01:30,130
but how can we be sure
that these bits of space rock

1105
01:01:30,140 --> 01:01:35,740
came from Vesta, an asteroid
over 100 million miles away.

1106
01:01:35,740 --> 01:01:38,440
It was a fall meteorite,
and so what that means

1107
01:01:38,450 --> 01:01:41,310
is that someone saw it,
you know, we saw it fall.

1108
01:01:41,310 --> 01:01:43,280
And so we knew its trajectory.

1109
01:01:43,280 --> 01:01:46,050
So we could actually
work backwards to say,

1110
01:01:46,050 --> 01:01:48,850
where did that meteorite
come from?

1111
01:01:48,860 --> 01:01:50,820
Retracing the trajectory of

1112
01:01:50,820 --> 01:01:54,960
the Turkish meteorites took
the scientists all the way back

1113
01:01:54,960 --> 01:01:57,960
to the 328-mile wide Vesta.

1114
01:02:02,100 --> 01:02:04,100
Where they studied
Vesta's surface,

1115
01:02:04,100 --> 01:02:06,640
they found further evidence.

1116
01:02:06,640 --> 01:02:09,740
On the surface of Vesta,
there's actually a very large

1117
01:02:09,740 --> 01:02:13,310
and fresh impact crater
that is around the same age

1118
01:02:13,310 --> 01:02:14,980
of the Turkish meteorite.

1119
01:02:14,980 --> 01:02:17,120
So that really clinched it.

1120
01:02:17,120 --> 01:02:20,820
This thing is definitely
from Vesta, and we proved it.

1121
01:02:20,820 --> 01:02:25,020
So how did bits of
Vesta end up here on Earth?

1122
01:02:25,020 --> 01:02:29,060
22 million years ago,
some very large impactor

1123
01:02:29,060 --> 01:02:32,030
struck Vesta,
made a huge crater,

1124
01:02:32,030 --> 01:02:34,900
and some of the rocks
from that crater actually

1125
01:02:34,900 --> 01:02:40,610
escaped from Vesta's gravity
and were lofted into space.

1126
01:02:40,610 --> 01:02:43,340
Some of these rocks
from Vesta went into orbits

1127
01:02:43,340 --> 01:02:45,910
that intersected with Earth.

1128
01:02:46,450 --> 01:02:51,150
22 million years later,
one blew up over Saricicek.

1129
01:02:54,220 --> 01:02:57,390
This Saricicek meteor shows
that the asteroid belt

1130
01:02:57,390 --> 01:02:59,190
is an unstable environment.

1131
01:03:01,960 --> 01:03:05,360
Asteroids frequently strike
other asteroids.

1132
01:03:08,070 --> 01:03:09,470
That's actually
happening all the time.

1133
01:03:09,470 --> 01:03:11,000
Things are running
into each other

1134
01:03:11,000 --> 01:03:13,140
in our solar system right now.

1135
01:03:13,140 --> 01:03:14,910
And so that makes it
really hard for us

1136
01:03:14,910 --> 01:03:18,040
to track all of those objects
because we don't actually know

1137
01:03:18,040 --> 01:03:20,240
what happens after they collide
with each other.

1138
01:03:20,250 --> 01:03:21,910
Now things are
totally different.

1139
01:03:21,920 --> 01:03:24,580
And that changes
the whole system.

1140
01:03:24,580 --> 01:03:29,150
Each collision
makes more asteroids.

1141
01:03:29,160 --> 01:03:30,820
There's many
different possibilities

1142
01:03:30,820 --> 01:03:33,320
of what could happen
when asteroids collide.

1143
01:03:33,330 --> 01:03:36,230
Imagine a roller derby
situation.

1144
01:03:38,670 --> 01:03:40,700
If you have two
groups of players

1145
01:03:40,700 --> 01:03:42,070
that run into each other,

1146
01:03:42,070 --> 01:03:45,270
that could be like two asteroids
running into each other.

1147
01:03:45,270 --> 01:03:49,270
And one possible outcome
is that one stays intact

1148
01:03:49,280 --> 01:03:51,710
while the other
is completely blown apart.

1149
01:03:54,710 --> 01:03:58,120
That sends fragments flying all
through the main asteroid belt,

1150
01:03:58,120 --> 01:04:00,080
and then there's
a little asteroid fragments

1151
01:04:00,090 --> 01:04:03,150
are on their own independent
orbits around the sun.

1152
01:04:04,390 --> 01:04:06,690
A problem with
asteroid impacts is that

1153
01:04:06,690 --> 01:04:08,690
we're always making
new asteroids.

1154
01:04:08,700 --> 01:04:10,460
There are big asteroids
out there,

1155
01:04:10,460 --> 01:04:11,960
and they get hit
by other asteroids,

1156
01:04:11,970 --> 01:04:13,430
and then you get shrapnel.

1157
01:04:13,430 --> 01:04:16,130
And now you've got not one
big one and one smaller one,

1158
01:04:16,140 --> 01:04:17,870
you've got one big one,
one smaller one,

1159
01:04:17,870 --> 01:04:19,640
and millions of little ones.

1160
01:04:19,640 --> 01:04:22,610
Now, most of these aren't very
big, but some of them might be

1161
01:04:22,610 --> 01:04:25,180
bigger and could be
potentially hazardous.

1162
01:04:26,580 --> 01:04:28,480
As the solar system ages,

1163
01:04:28,480 --> 01:04:31,180
the number of
asteroids increases.

1164
01:04:31,180 --> 01:04:34,390
Each new space rock
travels on a new course

1165
01:04:34,390 --> 01:04:38,020
which could intersect
with Earth.

1166
01:04:38,020 --> 01:04:40,590
So we're constantly producing
new asteroids

1167
01:04:40,590 --> 01:04:42,960
and big collisions
in the main asteroid belt.

1168
01:04:42,960 --> 01:04:44,760
And these are producing
the small asteroids

1169
01:04:44,760 --> 01:04:49,070
that will eventually drift
inward in the solar system.

1170
01:04:49,070 --> 01:04:51,700
Tracking this
constantly evolving population

1171
01:04:51,700 --> 01:04:55,940
of asteroids gives scientists
a huge headache.

1172
01:04:55,940 --> 01:04:58,140
If they break apart,
then that gives you

1173
01:04:58,140 --> 01:05:00,650
even more pieces
of the asteroid to track.

1174
01:05:00,650 --> 01:05:04,050
It's not a simple thing
to track and predict

1175
01:05:04,050 --> 01:05:07,520
the orbits of asteroids
and their movements,

1176
01:05:07,520 --> 01:05:11,690
because one tiny little change

1177
01:05:11,690 --> 01:05:17,760
can have huge dramatic impacts
for its possible future.

1178
01:05:17,760 --> 01:05:19,730
Figuring out exactly
where they're going to go

1179
01:05:19,730 --> 01:05:22,070
and keeping track of how
they interact with each other,

1180
01:05:22,070 --> 01:05:24,400
this is a huge endeavor.

1181
01:05:24,400 --> 01:05:27,140
The sheer volume
of asteroids can affect

1182
01:05:27,140 --> 01:05:29,170
the behavior of other asteroids

1183
01:05:29,180 --> 01:05:32,640
as they gravitationally
interact.

1184
01:05:32,650 --> 01:05:36,480
Think about your roller derby
player skating in circles.

1185
01:05:36,480 --> 01:05:38,280
The path they're going
to follow would evolve

1186
01:05:38,280 --> 01:05:41,150
the more people you plop down
on the track

1187
01:05:41,150 --> 01:05:42,620
they start interacting
with each other,

1188
01:05:42,620 --> 01:05:44,860
and their trajectory
will change.

1189
01:05:46,130 --> 01:05:48,430
The more crowded you make
the solar system,

1190
01:05:48,430 --> 01:05:50,860
the more things are
to change your orbit

1191
01:05:50,860 --> 01:05:53,860
of your individual asteroid.

1192
01:05:55,070 --> 01:05:56,870
It's not like
air traffic control,

1193
01:05:56,870 --> 01:05:58,940
where there's a known
amount of airplanes

1194
01:05:58,940 --> 01:06:00,770
and they all follow a plan.

1195
01:06:02,240 --> 01:06:04,880
This situation is
further complicated because

1196
01:06:04,880 --> 01:06:09,910
asteroid orbits can be affected
by other more subtle forces.

1197
01:06:10,850 --> 01:06:14,650
One of these is called the
Yarkovsky or the Yorp effect.

1198
01:06:14,650 --> 01:06:17,290
Honestly Yorp
is more fun to say.

1199
01:06:17,290 --> 01:06:19,960
The Yorp effect is
caused by sunlight

1200
01:06:19,960 --> 01:06:22,130
hitting an asteroid.

1201
01:06:22,130 --> 01:06:24,660
Light is made up of photons
that are traveling,

1202
01:06:24,660 --> 01:06:27,130
and these photons
actually have momentum.

1203
01:06:27,130 --> 01:06:29,100
So when light shines
on something,

1204
01:06:29,100 --> 01:06:31,100
it actually pushes on it.

1205
01:06:33,040 --> 01:06:35,010
When sunlight hits an asteroid,

1206
01:06:35,010 --> 01:06:38,280
the photons give it
a tiny push...

1207
01:06:39,410 --> 01:06:43,050
...enough to change
the space rock's trajectory.

1208
01:06:48,690 --> 01:06:51,560
When we know an asteroid
is really heading our way,

1209
01:06:51,560 --> 01:06:54,090
it's time to fight back.

1210
01:06:54,090 --> 01:06:56,030
So we've got an asteroid
that's headed at us.

1211
01:06:56,030 --> 01:06:57,130
What do we do?

1212
01:06:57,130 --> 01:06:59,160
Two main possibilities...
we deflect it,

1213
01:06:59,170 --> 01:07:01,130
we nudge it a little bit
so it misses,

1214
01:07:01,130 --> 01:07:03,430
or we blow it up, we destroy it.

1215
01:07:03,440 --> 01:07:05,500
Which of those
do you want to do?

1216
01:07:11,080 --> 01:07:13,640
It's a tough choice.

1217
01:07:13,650 --> 01:07:18,180
Get it wrong, and we could
end up being hit by a swarm

1218
01:07:18,180 --> 01:07:20,820
of radioactive space rocks.

1219
01:07:41,770 --> 01:07:44,580
An asteroid is heading our way,

1220
01:07:44,580 --> 01:07:47,310
and it may hit us in 2068.

1221
01:07:48,180 --> 01:07:50,750
How do we prevent
such a catastrophe

1222
01:07:50,750 --> 01:07:54,590
and stop it
from ever getting close?

1223
01:07:54,590 --> 01:07:56,350
Well, you just don't want
to take get anywhere near us

1224
01:07:56,360 --> 01:07:57,620
in the first place.

1225
01:07:57,620 --> 01:07:58,720
So what do you do?

1226
01:07:58,720 --> 01:08:01,330
Well, you can destroy them,

1227
01:08:01,330 --> 01:08:04,530
or you can push them
out of the way.

1228
01:08:04,530 --> 01:08:06,760
This is something where our
science fiction ideas

1229
01:08:06,770 --> 01:08:08,730
have got it almost
entirely wrong.

1230
01:08:08,730 --> 01:08:13,370
If you're in a bad movie,
a really, really bad movie,

1231
01:08:13,370 --> 01:08:16,040
you can send astronauts
to an asteroid,

1232
01:08:16,040 --> 01:08:17,580
put a nuclear bomb in it,

1233
01:08:17,580 --> 01:08:19,440
and blow it up
into lots of little bits

1234
01:08:19,450 --> 01:08:21,910
that then burn up harmlessly
in our atmosphere.

1235
01:08:21,910 --> 01:08:24,680
Yeah, it doesn't work that way.

1236
01:08:24,680 --> 01:08:26,150
Blowing up an asteroid

1237
01:08:26,150 --> 01:08:28,520
would make the problem
much worse.

1238
01:08:28,520 --> 01:08:31,920
We are no longer dealing with
just one space rock.

1239
01:08:31,920 --> 01:08:34,390
My issue with this is that
you may have turned

1240
01:08:34,390 --> 01:08:36,360
one problem into 50.

1241
01:08:36,360 --> 01:08:38,560
Instead of one
regular sized asteroid,

1242
01:08:38,560 --> 01:08:40,630
now you have a whole bunch
of littler ones,

1243
01:08:40,630 --> 01:08:42,800
and these may still hit
the Earth and cause damage.

1244
01:08:42,800 --> 01:08:45,540
And you know what?
That's not much less fun

1245
01:08:45,540 --> 01:08:47,810
than just having
a single big asteroid.

1246
01:08:47,810 --> 01:08:49,440
Now you've just taken
all that devastation

1247
01:08:49,440 --> 01:08:52,510
and spread it out
for everybody to enjoy.

1248
01:08:52,510 --> 01:08:55,350
The problem with using
a nuclear device is that

1249
01:08:55,350 --> 01:08:59,220
the products that rain down
on Earth are now radioactive.

1250
01:09:07,730 --> 01:09:10,860
If a dangerous
asteroid was on its way,

1251
01:09:10,860 --> 01:09:13,600
blowing it up
would be a last resort.

1252
01:09:14,770 --> 01:09:17,470
A less risky method
is to deflect it off

1253
01:09:17,470 --> 01:09:19,640
its collision course.

1254
01:09:19,640 --> 01:09:21,840
A small nudge early enough

1255
01:09:21,840 --> 01:09:25,510
can change in asteroid's
trajectory away from Earth.

1256
01:09:26,880 --> 01:09:30,280
You don't have to nudge it
very much for it to miss, right?

1257
01:09:30,280 --> 01:09:32,020
So if it's headed
straight at it,

1258
01:09:32,020 --> 01:09:33,320
I just touch it slightly,

1259
01:09:33,320 --> 01:09:36,220
by the time it gets to Earth,
its way off course.

1260
01:09:38,160 --> 01:09:40,760
NASA is investigating
ways to change

1261
01:09:40,760 --> 01:09:46,760
an asteroid's path,
including using a nuclear burst.

1262
01:09:46,770 --> 01:09:51,900
In a nuclear burst, what we do
is we don't actually hit it.

1263
01:09:51,900 --> 01:09:56,270
We come up to it with the device
on a spacecraft,

1264
01:09:56,280 --> 01:09:59,010
and then the device would be
detonated at a certain height

1265
01:09:59,010 --> 01:10:01,350
above the surface.

1266
01:10:01,350 --> 01:10:03,310
That heats up
the surface of the asteroid,

1267
01:10:03,320 --> 01:10:04,820
which vaporizes.

1268
01:10:04,820 --> 01:10:07,520
You get vaporized rock or metal
which blasts off the surface,

1269
01:10:07,520 --> 01:10:09,450
and that's how a rocket works.

1270
01:10:09,460 --> 01:10:11,920
So you blow up a bomb here,
and it winds up

1271
01:10:11,920 --> 01:10:15,630
pushing the asteroid
in the other direction

1272
01:10:15,630 --> 01:10:18,330
to prevent
any potential nuclear fallout,

1273
01:10:18,330 --> 01:10:21,770
NASA would detonate the bomb
a long way from Earth

1274
01:10:23,200 --> 01:10:26,770
any deflection attempt
has to be done years in advance,

1275
01:10:26,770 --> 01:10:28,370
which means it would be done
on the other side

1276
01:10:28,370 --> 01:10:30,310
of the solar system from us

1277
01:10:30,310 --> 01:10:33,080
on the opposite side
of the object's orbit.

1278
01:10:33,080 --> 01:10:35,710
That means that all of
the vapor made during

1279
01:10:35,720 --> 01:10:38,320
the explosion gets blown away
by the solar wind.

1280
01:10:39,890 --> 01:10:43,620
NASA is investigating
other less explosive methods

1281
01:10:43,620 --> 01:10:45,820
of deflecting an asteroid.

1282
01:10:45,830 --> 01:10:49,790
De-star would blast the asteroid
with a laser.

1283
01:10:49,800 --> 01:10:52,760
We hit it with
the laser, material vaporizes

1284
01:10:52,770 --> 01:10:54,900
and flies off the asteroid,

1285
01:10:54,900 --> 01:10:56,800
and because
of Newton's third law,

1286
01:10:56,800 --> 01:10:58,770
which is that for every action
there is an opposite

1287
01:10:58,770 --> 01:11:02,440
an equal reaction, this means
that vaporize material

1288
01:11:02,440 --> 01:11:04,940
moving off in one direction
moves the asteroid

1289
01:11:04,940 --> 01:11:07,240
in the opposite direction.

1290
01:11:08,680 --> 01:11:10,750
Both the laser
and the nuclear burst

1291
01:11:10,750 --> 01:11:13,580
are still just ideas
on the drawing board.

1292
01:11:16,320 --> 01:11:19,360
But one asteroid
deflection mission called

1293
01:11:19,360 --> 01:11:23,560
double asteroid redirection
test, or dart for short,

1294
01:11:23,560 --> 01:11:28,070
is already up and running and
scheduled for launch in 2021.

1295
01:11:29,640 --> 01:11:31,600
Dart is a kinetic impactor

1296
01:11:31,600 --> 01:11:35,110
and will try to knock
an asteroid off course.

1297
01:11:36,610 --> 01:11:38,840
At NASA for the longest
time, all we've been able to do

1298
01:11:38,840 --> 01:11:41,280
is theorize about how
we change their path.

1299
01:11:41,280 --> 01:11:42,380
But now for the first time,

1300
01:11:42,380 --> 01:11:44,880
we're actually gonna
practice in.

1301
01:11:44,880 --> 01:11:47,050
Leading this
groundbreaking mission to bump

1302
01:11:47,050 --> 01:11:51,590
an asteroid off its orbit
is Dr. Andy Chang.

1303
01:11:51,590 --> 01:11:54,890
Dart is the first
planetary defense mission

1304
01:11:54,890 --> 01:11:57,490
that we've ever done,
where we take a spacecraft,

1305
01:11:57,500 --> 01:12:01,670
we fly the spacecraft into
the asteroid to change

1306
01:12:01,670 --> 01:12:04,600
its course and make it
miss the Earth.

1307
01:12:04,600 --> 01:12:07,970
Dart's target
is a 525 foot space rock

1308
01:12:07,970 --> 01:12:12,910
orbiting the large
near Earth asteroid Didymos.

1309
01:12:12,910 --> 01:12:15,150
We pick the near Earth asteroid
Didymos as a target

1310
01:12:15,150 --> 01:12:17,010
for the dart mission because
although it's

1311
01:12:17,020 --> 01:12:19,350
a near Earth asteroid,
it's one that's very safely

1312
01:12:19,350 --> 01:12:20,880
parked away out there in space.

1313
01:12:20,890 --> 01:12:23,120
There's no way we can move
Didymos or its moon

1314
01:12:23,120 --> 01:12:25,760
in any way big enough to cause
a problem for the Earth.

1315
01:12:27,690 --> 01:12:29,890
The diddy-moon asteroid weighs

1316
01:12:29,900 --> 01:12:33,400
around 10 1/2 billion pounds.

1317
01:12:33,400 --> 01:12:36,570
So how do you knock such
a large lump of rock

1318
01:12:36,570 --> 01:12:38,870
off its path?

1319
01:12:53,320 --> 01:12:54,750
We're sending a spacecraft

1320
01:12:54,750 --> 01:12:58,220
to knock the diddy-moon
asteroid off course.

1321
01:12:59,360 --> 01:13:02,960
The asteroid is moving at
over 36,000 miles an hour

1322
01:13:02,960 --> 01:13:06,700
and is around
seven million miles away.

1323
01:13:06,700 --> 01:13:10,170
So how do you move
a 10 and a half billion pound

1324
01:13:10,170 --> 01:13:12,700
space rock?

1325
01:13:12,710 --> 01:13:15,810
You need to hit it really hard
to change its orbit,

1326
01:13:15,810 --> 01:13:19,880
so it's going to be coming in
at a super high velocity

1327
01:13:19,880 --> 01:13:23,180
in order to impart a bunch
of energy momentum to that moon.

1328
01:13:25,020 --> 01:13:26,880
Dart will hit the target

1329
01:13:26,890 --> 01:13:29,590
at around 14,000 miles an hour.

1330
01:13:29,590 --> 01:13:33,690
The speed of the dart impact
will be more than nine times

1331
01:13:33,690 --> 01:13:37,090
the speed of the rifle bullet
from an AK-47.

1332
01:13:39,030 --> 01:13:42,570
The impact will give
the asteroid a small push.

1333
01:13:42,570 --> 01:13:44,870
To work out how big a push,

1334
01:13:44,870 --> 01:13:49,340
we test impacts
with the Ames vertical gun.

1335
01:13:49,340 --> 01:13:51,780
At the NASA Ames
research center in California,

1336
01:13:51,780 --> 01:13:53,410
there's a very special
facility called

1337
01:13:53,410 --> 01:13:55,510
the Ames vertical gun range.

1338
01:13:55,510 --> 01:13:57,750
It's a hyper velocity gas gun
that allows us

1339
01:13:57,750 --> 01:14:01,890
to shoot little metal BBS
at rock targets at speeds

1340
01:14:01,890 --> 01:14:05,960
up to like 13,000, 14,000
miles per hour.

1341
01:14:05,960 --> 01:14:07,890
The gun replicates the impact

1342
01:14:07,890 --> 01:14:09,990
the dart mission will make.

1343
01:14:10,000 --> 01:14:12,530
It reveals that an impact
will blow off

1344
01:14:12,530 --> 01:14:16,500
a small amount of debris
but at extremely high speed,

1345
01:14:16,500 --> 01:14:20,370
enough to give the asteroid
an additional kick.

1346
01:14:20,370 --> 01:14:22,970
The impact will blow off pieces
of the asteroid,

1347
01:14:22,980 --> 01:14:25,310
so the pieces
are thrown off the back.

1348
01:14:25,310 --> 01:14:28,980
And so that that process acts
like a little rocket engine.

1349
01:14:28,980 --> 01:14:31,980
That provides an additional
momentum change,

1350
01:14:31,980 --> 01:14:34,850
momentum push
to the target itself.

1351
01:14:34,850 --> 01:14:37,220
The combined push
from the kinetic impactor

1352
01:14:37,220 --> 01:14:40,290
and the ejected debris is tiny,

1353
01:14:40,290 --> 01:14:43,460
around 0.0009 of
a mile per hour.

1354
01:14:43,460 --> 01:14:47,000
But hopefully it's enough
to change the asteroid's orbit.

1355
01:14:47,000 --> 01:14:50,430
If dart works, we could
then use a similar mission

1356
01:14:50,440 --> 01:14:53,300
to defend Earth
when the time comes.

1357
01:14:54,270 --> 01:14:56,770
This isn't some
small rock prototype

1358
01:14:56,780 --> 01:14:58,280
that we're doing this test on.

1359
01:14:58,280 --> 01:15:01,510
This is a real dress rehearsal
for an asteroid

1360
01:15:01,510 --> 01:15:03,580
that could destroy cities

1361
01:15:03,580 --> 01:15:06,920
or even maybe send
the Earth in chaos.

1362
01:15:06,920 --> 01:15:10,290
The moon of Didymos
is a solid lump of rock.

1363
01:15:10,290 --> 01:15:13,060
Will a kinetic impactor
like dart work

1364
01:15:13,060 --> 01:15:16,160
with a rubble pile asteroid
like Apophis?

1365
01:15:16,160 --> 01:15:18,160
When you shoot a rubble pile
with a projectile,

1366
01:15:18,160 --> 01:15:20,060
it's a little bit more
like trying to punch a sandbag.

1367
01:15:20,070 --> 01:15:22,770
You get a lot more a lot more
the energy is absorbed

1368
01:15:22,770 --> 01:15:25,640
into just moving the sand
around inside the bag

1369
01:15:25,640 --> 01:15:27,770
than ejecting it,
and so rubble piles

1370
01:15:27,770 --> 01:15:30,910
might be a little harder
to move by this method.

1371
01:15:31,910 --> 01:15:34,910
We don't know if we
can deflect a rubble pile

1372
01:15:34,910 --> 01:15:37,010
asteroid like Apophis.

1373
01:15:37,020 --> 01:15:40,120
They remain a clear
and present danger.

1374
01:15:40,990 --> 01:15:43,950
And something
we might not survive.

1375
01:15:47,330 --> 01:15:50,860
But there may be
a space lifeboat.

1376
01:15:55,730 --> 01:16:00,870
In 2018, scientists reexamined
rocks collected by Apollo 14

1377
01:16:00,870 --> 01:16:03,010
astronauts from the moon.

1378
01:16:09,380 --> 01:16:14,180
Buried in the samples was a rock
that shouldn't be there.

1379
01:16:15,490 --> 01:16:18,290
They got something
they didn't expect,

1380
01:16:18,290 --> 01:16:20,660
and that was an Earth rock.

1381
01:16:20,660 --> 01:16:24,700
They actually picked up
a rock from Earth on the moon.

1382
01:16:24,700 --> 01:16:26,360
They didn't bring it with them.

1383
01:16:26,370 --> 01:16:29,400
It's very likely that it was
something that was lofted up

1384
01:16:29,400 --> 01:16:34,140
when something hit Earth,
throw up a bunch of rocks.

1385
01:16:34,140 --> 01:16:36,340
Some of those rocks
fell on to the moon,

1386
01:16:36,340 --> 01:16:39,340
and that's a meteorite
on the moon,

1387
01:16:39,350 --> 01:16:41,580
but it's from Earth.

1388
01:16:45,580 --> 01:16:47,450
Super computer simulations of

1389
01:16:47,450 --> 01:16:52,220
the KPG asteroid strike revealed
how the impact had so much

1390
01:16:52,220 --> 01:16:56,530
energy that it catapulted rocks
out of Earth's atmosphere

1391
01:16:56,530 --> 01:16:58,430
and into space.

1392
01:16:58,430 --> 01:17:00,600
They were then caught
by the moon's gravity

1393
01:17:00,600 --> 01:17:03,730
and pulled down
to the lunar surface.

1394
01:17:03,740 --> 01:17:09,570
We now know the material ejected
into space from asteroid impacts

1395
01:17:09,580 --> 01:17:12,110
can travel to other planets,
as well,

1396
01:17:12,110 --> 01:17:15,810
which would explain
the 100 Mars meteorites

1397
01:17:15,810 --> 01:17:17,450
we've found here on Earth.

1398
01:17:20,090 --> 01:17:22,650
We think that there was probably
the exchange of a huge amount

1399
01:17:22,660 --> 01:17:24,720
of material
between different bodies,

1400
01:17:24,720 --> 01:17:27,520
Earth to the moon
and back again and to Mars.

1401
01:17:30,660 --> 01:17:33,160
With each impact that occurs
in our solar system

1402
01:17:33,170 --> 01:17:36,770
that ejects all types of
material that allows material

1403
01:17:36,770 --> 01:17:40,370
to swap from planet to planet,
moon to planet, moon to moon.

1404
01:17:40,370 --> 01:17:41,870
And so there's all
of this material

1405
01:17:41,870 --> 01:17:44,980
that eventually travels
from place to place.

1406
01:17:44,980 --> 01:17:48,080
Should another giant
asteroid hit our planet,

1407
01:17:48,080 --> 01:17:52,850
this planetary interchange
may give life on Earth

1408
01:17:52,850 --> 01:17:54,820
a lifeline.

1409
01:17:54,820 --> 01:17:57,490
If you think about
such an impact today,

1410
01:17:57,490 --> 01:18:00,690
you know, the chances are high
that a lot of life would be

1411
01:18:00,690 --> 01:18:05,100
wiped out, much of life,
probably all of human life.

1412
01:18:05,100 --> 01:18:08,270
It's certainly possible that
a big enough asteroid strike

1413
01:18:08,270 --> 01:18:10,270
could completely sterilize
the planet.

1414
01:18:10,270 --> 01:18:13,200
Talking about
no life whatsoever.

1415
01:18:13,210 --> 01:18:14,940
Not to put too fine
a point on it,

1416
01:18:14,940 --> 01:18:17,010
but if there's a dinosaur killer
asteroid out there

1417
01:18:17,010 --> 01:18:19,480
and it hits the Earth,
the chance of humanity's

1418
01:18:19,480 --> 01:18:23,550
survival of such a thing
as a species, mm, not great.

1419
01:18:27,290 --> 01:18:29,520
Humans may not survive.

1420
01:18:29,520 --> 01:18:35,130
But some scientists believe
that simple life forms could.

1421
01:18:55,710 --> 01:18:58,580
Asteroids have hit
our planet many times

1422
01:18:58,580 --> 01:19:00,150
in the past.

1423
01:19:01,650 --> 01:19:06,560
One giant strike wiped out
70% of all life on Earth.

1424
01:19:07,490 --> 01:19:12,130
If another huge asteroid
hits us, can life survive?

1425
01:19:17,040 --> 01:19:20,300
If a giant rock hits
the Earth and kills almost

1426
01:19:20,310 --> 01:19:25,980
all life on Earth,
there is a slim line of hope.

1427
01:19:25,980 --> 01:19:29,880
And that's because the dirt,
the rocks on Earth

1428
01:19:29,880 --> 01:19:35,390
are infused with bacterial life,
with microscopic life.

1429
01:19:35,390 --> 01:19:37,920
And in the event
of a giant impact,

1430
01:19:37,920 --> 01:19:42,030
some of these bits of rock
will be ejected into space

1431
01:19:42,030 --> 01:19:43,490
and might float around.

1432
01:19:43,500 --> 01:19:46,360
After an asteroid impact,
whatever ejected

1433
01:19:46,370 --> 01:19:49,230
into the atmosphere
could contain microbial life

1434
01:19:49,230 --> 01:19:51,870
that when it falls back down
on to the ground

1435
01:19:51,870 --> 01:19:54,500
could re-seed the life
on that planet.

1436
01:19:59,440 --> 01:20:02,250
Some bacteria can
survive the harsh conditions

1437
01:20:02,250 --> 01:20:06,950
of space and can cope with
an asteroid strike, reentry,

1438
01:20:06,950 --> 01:20:10,050
and landing back
on Earth's surface.

1439
01:20:19,260 --> 01:20:22,630
I think in terms of life
on planet Earth,

1440
01:20:22,630 --> 01:20:25,340
I think we've learned that we
live on a very resilient planet.

1441
01:20:25,340 --> 01:20:28,240
And I think life in some form,
even if it has to crawl

1442
01:20:28,240 --> 01:20:31,110
its way back
from bacterial stage,

1443
01:20:31,110 --> 01:20:34,880
I think life on this planet is
going to going to eke through.

1444
01:20:36,250 --> 01:20:40,650
Life is pretty good at
figuring out a way of surviving.

1445
01:20:40,650 --> 01:20:43,090
We know that life
first formed on the Earth

1446
01:20:43,090 --> 01:20:45,260
well over 4 billion years ago

1447
01:20:45,260 --> 01:20:48,290
and has never been wiped out
in all of that time.

1448
01:20:48,290 --> 01:20:49,790
There's always been something

1449
01:20:49,800 --> 01:20:52,160
after every major
mass extinction.

1450
01:20:52,160 --> 01:20:57,130
So life will continue.
It just won't necessarily be us.

1451
01:20:58,140 --> 01:21:00,770
An asteroid strike
on another world

1452
01:21:00,770 --> 01:21:04,140
may be how life on Earth
started in the first place.

1453
01:21:04,140 --> 01:21:07,080
There's an interesting
idea that an asteroid strike

1454
01:21:07,080 --> 01:21:10,180
on another planet could have
actually seeded life on Earth.

1455
01:21:10,180 --> 01:21:12,250
And the way this works is,
you have a life

1456
01:21:12,250 --> 01:21:15,820
that's somehow gotten a foothold
on some other planet like Mars,

1457
01:21:15,820 --> 01:21:18,050
a big asteroid strike hits
that planet

1458
01:21:18,060 --> 01:21:21,220
and knocks a piece of it off,
eventually rains down on Earth,

1459
01:21:21,230 --> 01:21:25,130
carrying with it life.

1460
01:21:25,130 --> 01:21:30,470
We may owe the existence of life
here to asteroid impacts.

1461
01:21:32,870 --> 01:21:35,810
That's speculative,
but it's kind of a cool thought.

1462
01:21:38,110 --> 01:21:41,240
Life seeding asteroids
may have hit us in the past,

1463
01:21:41,250 --> 01:21:44,480
and other asteroids
will hit us in the future.

1464
01:21:47,750 --> 01:21:50,020
One of those maybe Apophis,

1465
01:21:50,020 --> 01:21:53,120
arriving in less than
half a century.

1466
01:21:54,490 --> 01:21:57,690
Maybe we'll deflect it.

1467
01:21:57,700 --> 01:22:02,130
Maybe it'll miss us
all on its own.

1468
01:22:02,130 --> 01:22:05,270
Either way, we need
to keep tabs on it.

1469
01:22:06,640 --> 01:22:08,810
The best thing we can
do as a species, and it's funny

1470
01:22:08,810 --> 01:22:10,470
because it almost sounds
like I'm advocating

1471
01:22:10,480 --> 01:22:12,310
for more jobs for astronomers.

1472
01:22:12,310 --> 01:22:14,040
We need to keep looking
at the sky.

1473
01:22:14,050 --> 01:22:16,210
We need look at the sky
longer and deeper,

1474
01:22:16,210 --> 01:22:17,910
with more sensitive instruments

1475
01:22:17,920 --> 01:22:20,580
and get more of a sense
of what out there is around us.

1476
01:22:20,590 --> 01:22:24,750
That's what our species needs
to do to ultimately survive.

1477
01:22:24,760 --> 01:22:26,520
Because now we have the ability

1478
01:22:26,530 --> 01:22:28,830
to see these things
a little bit better,

1479
01:22:28,830 --> 01:22:30,690
we have the ability
to protect ourselves better.

1480
01:22:30,700 --> 01:22:32,630
It doesn't have
to be a surprise.

1481
01:22:32,630 --> 01:22:35,070
You know, the first time we see
a big impact doesn't have to be

1482
01:22:35,070 --> 01:22:37,330
as it's bearing down
destroying our planet.

1483
01:22:37,340 --> 01:22:39,870
We can actually see it
before it gets to us

1484
01:22:39,870 --> 01:22:42,410
and decide
what we want to do about it.

1485
01:22:43,540 --> 01:22:47,840
Earth's history is
littered with asteroid strikes.

1486
01:22:47,850 --> 01:22:51,610
Some wiped out
millions of species.

1487
01:22:51,620 --> 01:22:55,820
Some may have seeded life
in the first place.

1488
01:22:55,820 --> 01:22:58,220
What the future holds
and our relationship

1489
01:22:58,220 --> 01:23:01,960
with these space rocks,
no one knows.

1490
01:23:02,690 --> 01:23:06,460
Even though the chances of
something really large hitting

1491
01:23:06,470 --> 01:23:10,400
the Earth are pretty small,
the consequences are dire.

1492
01:23:10,400 --> 01:23:13,440
It would really destroy
our planet or at least life

1493
01:23:13,440 --> 01:23:15,170
as we understand it.

1494
01:23:15,170 --> 01:23:18,440
And so in many ways,
asteroids are the greatest

1495
01:23:18,440 --> 01:23:20,080
threat that we face.

1496
01:23:20,080 --> 01:23:24,410
Life is fragile, so of course
we live in a larger environment

1497
01:23:24,420 --> 01:23:26,850
where something could come
and hit us at any time.

1498
01:23:26,850 --> 01:23:28,420
That's part of being alive.

1499
01:23:28,420 --> 01:23:30,720
There's no guarantee tomorrow
will happen.

1500
01:23:30,720 --> 01:23:33,360
But what there is
is a high likelihood

1501
01:23:33,360 --> 01:23:35,230
that you'll still be
safe tomorrow.

1502
01:23:37,960 --> 01:23:40,760
Impacts from space are rare,

1503
01:23:40,770 --> 01:23:43,400
but if they do happen,
it's a huge deal.

1504
01:23:43,400 --> 01:23:45,640
And so you've got to put those
two things together.

1505
01:23:45,640 --> 01:23:48,510
That means we got to
pay attention.

1506
01:23:48,510 --> 01:23:51,210
Those impacts have
happened many times in the past,

1507
01:23:51,210 --> 01:23:54,140
and they're going to continue to
happen many times in the future.

1508
01:23:54,150 --> 01:23:57,480
Fortunately it's not probably
in our immediate future.

1509
01:23:57,480 --> 01:24:02,020
Impacts are rare, but the Earth
lives a long time.

1510
01:24:02,020 --> 01:24:04,290
So you're unlikely to get
in a car accident,

1511
01:24:04,290 --> 01:24:07,460
but if you drive enough, you're
going to get in a car accident.

1512
01:24:10,230 --> 01:24:11,800
Over a century time scale,

1513
01:24:11,800 --> 01:24:14,060
yes, we should be concerned
about these.

1514
01:24:14,070 --> 01:24:17,330
But over the daily, weekly,
monthly, even yearly time scale,

1515
01:24:17,340 --> 01:24:19,170
I wouldn't sweat it too much.

1516
01:24:19,170 --> 01:24:21,700
I wouldn't say we should lose
sleep over an asteroid

1517
01:24:21,710 --> 01:24:23,270
or comet striking Earth,

1518
01:24:23,280 --> 01:24:26,280
but the reality is
it will happen again.

1519
01:24:28,880 --> 01:24:31,050
So when you think
about asteroid strikes,

1520
01:24:31,050 --> 01:24:33,020
remember this wonderful
dramatic universe

1521
01:24:33,020 --> 01:24:34,450
you find yourself in.

1522
01:24:34,450 --> 01:24:37,190
We're here because
stars died and exploded.

1523
01:24:37,190 --> 01:24:39,190
Life on Earth wouldn't
be the same

1524
01:24:39,190 --> 01:24:41,220
if we didn't find ourselves
in this dramatic

1525
01:24:41,230 --> 01:24:43,530
and even dangerous environment
in space.

1526
01:24:43,530 --> 01:24:46,230
But this is who we are.
This is nothing new.

1527
01:24:46,230 --> 01:24:49,100
And this will continue
for the future of our planet.