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NASA's plan to save Earth from a giant asteroid - Video học tiếng Anh
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NASA's plan to save Earth from a giant asteroid
NASA's plan to save Earth from a giant asteroid
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Subtitles (168)
0:00
In 1954, Ann Hodges was hit by a meteorite.
0:03
"What time of the day was it?"
0:05
"It was 12:45."
0:06
"12:45."
0:07
"And this comes through the roof and hits you."
0:10
She was napping,
0:11
when the rock crashed through her ceiling
0:13
and bounced off the radio into her stomach.
0:16
Because it was small, her injuries were minor.
0:18
"The first person ever to be hit by a meteorite.
0:19
Imagine that."
0:20
But much bigger objects have collided with Earth.
0:24
65 million years ago,
0:25
a rock ten kilometers wide
0:27
slammed into the Gulf of Mexico.
0:29
An event that likely caused dinosaurs
0:31
to go extinct.
0:33
Elsewhere, mammoth meteorites have been discovered
0:35
everywhere from The US
0:37
to Russia,
0:39
and blasted craters in North America,
0:41
Australia,
0:42
and Africa.
0:43
Falling objects from the sky
0:45
have always fascinated humans,
0:47
but they have also made us fearful,
0:49
making us wonder whether someday
0:50
a giant asteroid
0:52
could come for us.
0:55
"Run!"
0:55
In movies like Deep Impact and Armageddon
0:58
those fears are played out.
0:59
[clock ticking]
1:00
"One minute!"
1:01
And heroes save the day.
1:02
"We all gotta die right?
1:04
I'm the guy who gets to do it saving the world."
1:06
"YEAHHHH!"
1:07
You might think this only happens in Hollywood,
1:11
but that’s not exactly true.
1:14
There is a small chance, a
1:18
of a large asteroid hitting Earth.
1:21
So scientists are getting ready,
1:23
just in case.
1:27
"Asteroids" are hunks of rock
1:28
that weren't big enough to become planets
1:30
when the solar system formed.
1:32
Smaller asteroids are called "meteoroids"
1:34
and when they fall through Earth’s atmosphere
1:36
they become "meteors".
1:37
If they make it to the surface,
1:39
they are called "meteorites".
1:42
Between 1988 and 2017,
1:45
NASA counted over 700 fireballs
1:47
created by objects entering our atmosphere.
1:50
In order to detect asteroids,
1:52
NASA takes multiple pictures of the night sky
1:54
and uses computers to scan for moving objects.
1:58
As Earth orbits,
1:59
scientists make several observations
2:01
from different locations
2:02
to detect how close the asteroids are to Earth.
2:05
Here, the nearest objects are labelled in green.
2:08
At least 16,000 of them
2:10
have been classified as “near-Earth”,
2:12
meaning they orbit within roughly a third
2:14
of the distance from the Sun.
2:16
And based on the object’s speed and brightness,
2:18
scientists can map a trajectory
2:20
to predict whether it will collide with Earth.
2:23
The impact energy of a 10-meter object,
2:25
just a little smaller than a school bus,
2:28
would be 100 kilotons.
2:30
But the larger the object,
2:32
the nastier the impact.
2:34
A meteorite just a little larger
2:36
than The Great Pyramid at Giza,
2:37
at about 150 meters,
2:40
would generate 288 megatons of energy.
2:44
For reference,
2:45
the number of megatons in the payload of the
2:47
Castle Bravo hydrogen bomb
2:49
was only 15.
2:51
But asteroids don’t need to hit Earth to cause damage.
2:55
In 2013, a 17-meter-wide meteor
2:58
exploded over Chelyabinsk, Russia
2:59
before it ever reached the ground
3:03
and the resulting shockwave
3:04
released about 440 kilotons of energy
3:07
that damaged structures and injured over 1,500 people.
3:12
Following that event in Russia,
3:13
US politicians called on NASA
3:15
to ask about the threat of future collisions.
3:18
"I said, 'If we saw one coming toward Omaha,
3:20
what could we they about it?'
3:22
[Scientists] said they could use a laser."
3:25
"First of all, it would not be practical
3:27
to have a laser powerful enough to split it in half."
3:30
Their questions sounded like
3:31
plot lines for a new blockbuster,
3:33
but their ideas weren’t actually that far off.
3:36
"How far inland could a
3:40
reasonably sized asteroid
3:43
make water come in?"
3:45
Scientists have analyzed
3:46
how asteroid impacts would kill people
3:48
and getting hit by the "ejecta",
3:50
meaning space rock and other debris it kicks up,
3:52
is one of the least likely ways to die.
3:55
The most lethal cause is
3:56
violent wind generated by the impact blast,
3:59
followed by scorching heat,
4:00
and massive tsunamis.
4:02
"The odds of a near-Earth object strike
4:05
causing massive casualties
4:07
and destruction of infrastructure
4:09
are very small,
4:10
but the potential consequences are so large
4:13
that it makes sense to take the risk seriously."
4:17
"All agents are go."
4:18
In Armageddon, annihilation is avoided
4:20
by nuking the killer asteroid.
4:22
But in real life, our ability to prevent impact
4:25
depends on how big it is and when we detect it.
4:30
A 140-meter-wide space rock
4:33
is large enough to destroy a city
4:34
and if it were on a path to collide with Earth
4:36
in less than a year,
4:37
the only thing to do would be
4:39
evacuate the impact zone.
4:42
But if we are lucky enough
4:44
to spot an asteroid seven to ten years out,
4:46
NASA would have enough time
4:47
to try deflecting the object,
4:49
which they could do a number of ways.
4:53
First, NASA could launch a spacecraft to
4:55
act as a battering ram
4:58
and if the asteroid is far enough out,
5:00
it would only need to be pushed a few centimeters
5:02
off course to avoid hitting Earth.
5:05
Right now, NASA is in the early stages of "DART":
5:08
The Double Asteroid Redirection Test,
5:10
which will try out this approach
5:12
by trying it on a non-threatening asteroid,
5:14
called “Didymoon”,
5:15
which will pass near Earth in 2022.
5:20
Another method would be using something
5:22
called a "gravity tractor",
5:24
which pulls the asteroid in a new direction
5:26
and points it away from Earth.
5:28
Theoretically, a spacecraft could do this
5:30
by hovering near an object to create
5:32
a slight gravitational attraction
5:34
that could be used to redirect the asteroid.
5:37
The third option would be to go full Hollywood
5:40
and use a nuclear device to vaporize part of the surface.
5:44
"What you can do, in principle,
5:46
if you have a very powerful laser,
5:49
is to cause jets of material heated by the laser
5:54
to fly off of the asteroid
5:57
and that is essentially the equivalent of
5:59
a jet engine pushing the asteroid off course."
6:03
So far, NASA hasn’t found any asteroids
6:06
big enough to threaten Earth,
6:08
but we haven’t been searching that long.
6:10
There is still lots of space to survey
6:12
and the big one might be on its way,
6:14
we just haven't found it yet.
