When natural disasters threaten, we turn to science and technology to warn us… to seek shelter or get out of the way. But can they face the ultimate threat: speeding projectiles from the depths of space? Cutting-edge space missions are underway to deflect and destroy space objects that threaten to rock our world. Can they save the planet from a killer asteroid?
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00:00When powerful storms approach, or floodwaters rise, when a volcano threatens to blow, we
00:23turn to science and technology to warn us, to seek shelter, or get out of the way.
00:32But can they face down the ultimate danger, a speeding projectile from the depths of space?
00:47Can new generation space missions neutralize the threat, and save the planet from a killer
00:55asteroid?
01:12Welcome to the New Age of Planetary Defense, and liftoff of the Falcon 9 and DART, on NASA's
01:26first planetary defense test to intentionally crash into an asteroid.
01:33DART, the Double Asteroid Redirection Test, is a 610-kilogram spacecraft on a unique test
01:43mission, to crash into an asteroid and knock it off course.
01:52Its target, an asteroid about the size of two soccer fields, called Dimorphos.
02:01Astronauts have compared DART to a golf cart ramming into the Great Pyramid of Egypt.
02:08In this test mission, they expect to change the orbit of Dimorphos by only a fraction
02:13of one percent.
02:16But if an incoming asteroid is far enough away, that could be enough to deflect it away
02:22from Earth and avoid a catastrophic impact.
02:27There are two things that make the impact hazard unique.
02:30First, it is in fact the biggest natural hazard we know of.
02:35Impact by an asteroid a mile or more in diameter could destroy a billion people, far beyond
02:42any other potential natural hazard.
02:45The good side is, it is the one hazard that we think we could eliminate entirely.
02:51You could never stop an earthquake or a volcanic eruption, but if we had warning of an asteroid
02:56headed our way, then at least in principle, we have the technology to change its orbit,
03:01deflect it, and have it miss entirely.
03:06And yet, we may not always have enough warning time.
03:20February 15, 2013.
03:23The town of Chelyabinsk in southern Russia is just waking up.
03:30Many old citizens are headed to work.
03:34Neither they, nor anyone else on planet Earth, are expecting a visitor.
03:41Now approaching, from outer space, a 20 meter wide asteroid explodes above the city at
04:09an altitude of almost 30 kilometers.
04:13It releases the equivalent of 500 kilotons of TNT, or 20 to 30 Hiroshima bombs.
04:21Over a thousand people are injured, most from falling debris and flying glass.
04:28Eerily, within 24 hours, another, even larger asteroid whizzes by Earth at a distance of
04:3728,000 kilometers.
04:40That's within the orbit of our weather satellites.
04:45An asteroid is a leftover building block from the formation of the solar system.
04:50And a few of them share the inner solar system with the Earth, and will ultimately impact
04:57the Earth, or Mars, or Venus, or the Sun.
05:01Disasters that could impact the Earth are the greatest natural hazard we face, but the
05:07impacts are extremely rare.
05:10They are the extreme example of a disaster of low probability, but high consequence.
05:22Projectiles like these have been hitting our planet since the dawn of humanity, challenging
05:27us to explain.
05:30What are they?
05:31Where do they come from?
05:34Who sent them?
05:38Ancient observers turned to myth and legend for answers, describing them as omens, signs
05:46that something good or ill was happening in human affairs.
05:59In the spring of 44 BC, following the murder of Julius Caesar, the appearance of a comet
06:06was promoted as a sign of his ascent to godhood.
06:16We now know the annual Perseid meteor shower happens when Earth hits debris from the Swift-tuttle
06:23comet.
06:26In ancient Rome, it was linked to Cleopatra's death, and to the rescue of the princess Andromeda
06:36by the warrior Perseus.
06:40Later on, scientists and philosophers who sought to refine their concepts of the universe
06:46struggled to explain these celestial objects.
06:55They saw the universe as a precision instrument, a cosmic clock designed by the ultimate watchmaker,
07:03God.
07:07They described a universe that moves in never-ending cycles.
07:14Planets circle the sun.
07:21The stars arc across the night sky.
07:27The seasons ebb and flow, all in beautiful harmony.
07:34This cosmic timepiece was a testament to the perfection of creation.
07:47In time, the idea of an intelligent designer gave way to the workings of natural laws.
08:00Our sun, we now believe, was born in the core of a vast cloud of dust and gas some five
08:06billion years ago.
08:15Within this solar disk, tiny particles glommed together to form pebbles and rocks.
08:24Drawn by their mutual gravity, they merged into boulders and eventually small bodies
08:29called planetesimals.
08:34Such objects drew in gas and ice crystals to grow into the giants.
08:41Jupiter, Saturn, Neptune, and Uranus.
08:53The gravity of these gas giants caused countless icy bodies that enveloped the solar system
08:59to fly toward the sun, where they became comets.
09:07In the warm inner regions, rocky objects swarmed about.
09:12Some came together, merging or shattering in violent collisions, eventually growing
09:19into the rocky planets we know today.
09:24The collisions didn't end there.
09:32This is an elevation map of planet Mars.
09:36Heading north, we move over a vast lowland region, shown in blue.
09:42It's thought to be a scar left by a monumental impact early in its history that may have
09:47destroyed Mars' life-bearing chances.
09:55Planet Venus.
09:56A giant impact is one explanation for its extremely slow rotation in the opposite direction
10:03of all the other planets.
10:21Early in the history of our planet, a collision brought Earth perilously close to total destruction.
10:33A Mars-sized body crossed its path, slamming into it.
10:44The oblique angle of impact left Earth in one piece.
10:54Current theory holds that massive amounts of debris launched into orbit gradually came
10:59together to form the moon.
11:17Over time, the presence of the moon would stabilize Earth's rotation, while driving
11:22tides that helped pave the way for the emergence of life.
11:32That was only one in a long salvo of impacts.
11:39Remember again that the asteroids are those remnants from which the planets formed.
11:43And while the planets were forming, during that time, there were millions of times more
11:47asteroids than we see today.
11:50And they were raining down on our planet, and growing our planet, in fact.
11:54All you have to do is look up at our moon today, and the cratered face of the moon,
11:57the very features that make the man on the moon, they are a tableau of those large, very
12:03much more numerous impacts that occurred 4.5 billion years ago when the planets were forming.
12:10Craters that pock the lunar surface show the pounding that Earth must also have endured
12:14through its history.
12:21The solar system is still stocked with countless rocky objects, like those that pummeled the
12:26moon and Earth.
12:33Over the eons, objects large and small have continued to strike the Earth.
12:41Most impact craters have long since eroded away.
12:46Others were obliterated by the rise of mountain ranges, or by the reshuffling of continents.
13:00Some 200 left marks we can still see and ponder.
13:06Meteor Crater is one of the most striking.
13:11It dates back to a day some 50,000 years ago, when the core of a busted-up asteroid slammed
13:17into what's now Arizona.
13:25Scientists believe the culprit was a nickel-iron mass 30 to 50 meters wide that weighed in
13:31at 300,000 tons.
13:37It left a hole 180 meters deep and just over a kilometer wide.
13:51This is the Pingouinluat Crater in Quebec, formed 1.3 million years ago.
13:58The impactor unleashed the energy of over 8,000 atomic bombs and left a crater 3.5 kilometers
14:06wide.
14:18The Manicouagan Crater, known as the Eye of Quebec, was blasted out by a 5-kilometer asteroid
14:24214 million years ago.
14:29It may have been part of a chain of impacts that struck in France, Ukraine and North Dakota.
14:41It's reminiscent of a string of fragments from the Shoemaker-Levy comet that struck
14:46Jupiter in 1994.
15:00The largest known impact crater can be found in South Africa.
15:05At 2 billion years old, the Vredefort Crater was created by an asteroid up to 25 kilometers
15:12wide.
15:13What you see here is the inner crater.
15:16It's set within a larger crater 300 kilometers across.
15:23It was part of a rare class of extra-large impactors capable of wreaking havoc all around
15:29the globe.
15:37Just recently, scientists discovered what appears to be an impact basin on the east
15:42coast of Antarctica.
15:58They proposed that shock waves from the impact set off the eruption of a giant volcanic hotspot
16:05on the planet's opposite side.
16:16Called the Siberian Traps, this volcanic eruption was responsible for the greatest mass extinction
16:23on record.
16:27Marking the end of the Permian Period 260 million years ago, the devastation claimed
16:3390% of all species on the Earth.
16:46Then there's the Chicxulub Crater straddling Mexico's Yucatan Peninsula.
16:53It was created 65 million years ago by an impactor at least 10 kilometers wide.
17:00The debris thrown into the upper atmosphere would have enveloped the planet, blocking
17:05the sun.
17:08I think the two most significant impacts that we've seen in Earth's history were the moon
17:12forming impact itself.
17:14And then the impact 65 million years ago, a much smaller scale impact, but very significant
17:19from a human point of view, because that was the impact that wiped the world clear of the
17:24dinosaurs and 75% of all the other species of plants and animals on the planet at the
17:28time and cleared the way for mammals to rise to prominence and for our own origin.
17:37Coincidentally, a few million years later, another large asteroid blew a hole in Greenland.
17:46It's currently hidden beneath the Greenland ice sheet.
17:50The Hiawatha Crater is the most recently discovered large crater.
17:57Impacts like these were more numerous in the distant past.
18:03Over time, an estimated 99% of their total mass was pulverized in collisions, swept up
18:10in rising planets, or flung out of the solar system altogether.
18:16We often see the asteroid belt depicted as this dense stream of rocks right up against
18:23each other, tumbling around in very close proximity to each other.
18:28And it's true that there are a lot of objects out there in this region between Mars and
18:32Jupiter, but they're not dense packed the way you often see them depicted.
18:35In fact, if you were sitting on or standing on any random asteroid out there in the main
18:39belt between Mars and Jupiter, you would never even, by your naked eye, be able to see the
18:44nearest asteroid to you.
18:45They just wouldn't appear that way.
18:50Here is a map of all known asteroids up to the year 2018.
18:56The asteroid belt, shown in orange, is the largest concentration.
19:03To us, the most dangerous are the near-Earth asteroids, those shown in blue.
19:11They come within 1.3 times the distance between Earth and the Sun.
19:21In the last few decades, efforts to count and track them have led to a new sense of
19:26awareness that Earth may still be vulnerable.
19:31Today, the world's population is just under 8 billion people, and could reach 11 billion
19:39by the end of the century.
19:42With so many of us now crowded into cities and coastlines, we struggle to shield ourselves
19:48from a range of natural disasters.
19:54Extreme weather, sparked by a warming climate, rising sea levels and floods, wildfires that
20:09now erupt with unknown fury.
20:16Then there's the ever-present reality of war, with the threat of mass destruction and the
20:25displacement of millions of people.
20:30Can we address the ultimate threat?
20:35The one from space.
20:391998.
20:42Hollywood released two blockbuster movies, Armageddon, a comet is hurtling toward Earth.
20:56Astronaut heroes race out to blow it up and save the planet.
21:09Then, Deep Impact.
21:13This time, Earth doesn't get off so easy.
21:27That same year, 1998, in response to growing popular and scientific awareness of the asteroid
21:40threat, NASA began a long-term effort to discover and track them.
21:47Only in Hollywood do asteroids capriciously change orbit and suddenly head for the Earth.
21:53The fact is they know Newton's laws and they follow them just fine.
21:57So when we do discover an asteroid, if we get good data, we can predict its orbit for
22:02decades or even centuries in the future.
22:09Asteroid hunters have found around 30,000 objects, with 3,000 new ones identified each
22:15year.
22:20That includes an estimated 90% of the most dangerous, like the 10-kilometer rock that
22:28struck 65 million years ago.
22:34Our chance of being hit by one of these dinosaur killers is estimated at once every 100 million
22:40years.
22:45The chance of being hit by a 1-kilometer asteroid rises to once every 700,000 years.
22:55Moving down in size, 300-meter rocks should hit every 70,000 years, bringing continental
23:03scale devastation.
23:08Even still, 140-meter objects hit every 20,000 years, and 40-meter objects, like the one
23:16that punched a hole in Arizona, every 300 years.
23:22A 40-meter object passes within the moon's orbit several times a year.
23:28The next size down, around 10 meters across, zips by about once a week.
23:39Scientists are seeking not only to identify these objects, but to clarify their trajectories
23:45and the chances they'll one day crash into Earth.
23:53Meanwhile, there are those that seem to come out of nowhere, like the one that hit Chelyabinsk
24:00in Russia.
24:03To scientists, it was more than just an ominous threat.
24:08Three and a half hours after it exploded, the polar-orbiting Suomi satellite began tracking
24:14the plume of dust and smoke.
24:20In an effort to learn more about the asteroid's physical properties, scientists followed the
24:25plume as it spread out in upper-level winds, forming a complete global belt.
24:38They further modeled the breakup of the asteroid, hoping to one day predict the atmospheric
24:43effects of incoming objects.
24:48The Chelyabinsk asteroid was reminiscent of the most famous asteroid impact in modern
24:53times.
24:56The Tunguska asteroid exploded over Siberia in 1908, leveling 2,000 square kilometers,
25:07including some 80 million trees.
25:11It took over a century for scientists to identify fragments of this impactor, and to
25:18conclude that it was probably a comet.
25:23Ultimately, the best way to learn what these wayward bodies are made of, and how their
25:29orbits can change over time, is to pay one a visit.
25:37NASA launched the Dawn mission in 2007.
25:43Propelled by an ion-thrust rocket engine, Dawn entered the asteroid belt in 2011.
25:51Its targets?
25:52A large, rocky body named Vesta, and the crown jewel of the asteroid belt, an ice-bound dwarf
26:00planet called Ceres.
26:04Together, they comprise over one-half of the total mass of the asteroid belt.
26:12Today, Vesta is pocked with craters, dark spots, and streaks, scars left by collisions
26:22with other asteroids.
26:26Some gully-like features may be the unlikely erosion marks left by flowing water.
26:35Vesta appears to have been whittled down by collisions.
26:39In fact, scientists have concluded that many of the asteroids that have flown by Earth
26:44were once part of Vesta.
26:49Not long after scientists began tracking and cataloging near-Earth asteroids, a team from
26:54the U.S. Air Force and the Massachusetts Institute of Technology discovered one that
27:00is now considered the greatest threat to Earth.
27:06The asteroid Bennu, represented in this NASA visualization, was named for a mythological
27:12Egyptian god.
27:14It was likely born in a collision of small planets in the inner part of the asteroid
27:19belt.
27:22With a diameter of some 500 meters, Bennu would inflict catastrophic damage if it hit
27:28Earth.
27:30And there is uncertainty about its path, which shifts over time due to the gravitational
27:35pull of planets, as well as the subtle pushing from solar radiation.
27:44The uncertainty of Bennu's path is one reason NASA sent a probe out to study it.
28:00In September 2016, the OSIRIS-REx spacecraft began a journey lasting two years and three
28:07months, covering a distance of about two billion kilometers.
28:19Within just a few days of its arrival, OSIRIS-REx was hit with a blast of particles flying off
28:26the asteroid.
28:31The blast did no harm, but it showed that Bennu is part of a rare class of active asteroids
28:38that regularly shed mass into interplanetary space.
28:46The spacecraft would spend almost two years circling Bennu while sending back images and
28:51mapping its surface.
28:55To the surprise of scientists on Earth, the asteroid is strewn with boulders.
29:01Over 200 of them are larger than 10 meters in diameter.
29:08The asteroid is essentially a loose pile of rocks and dirt held together by its collective
29:14gravity field.
29:16Sixty percent of its volume is actually empty space.
29:25After a survey of potential landing spots, on May 10, 2021, the spacecraft maneuvered
29:31down to a tiny area devoid of large rocks.
29:40An onboard camera captured the descent.
29:48A device at the end of a long arm hit the surface, blasting dirt and small rocks into
29:54a collection device.
30:05The spacecraft hit its thrusters.
30:08To back out of the cloud of dust created by the blast, and to move away from the asteroid.
30:18After orbiting the asteroid, it began the long return flight to Earth.
30:29OSIRIS-REx will drop the sample container into the atmosphere for retrieval.
30:38Data from the mission has already allowed scientists to recalculate Bennu's trajectory.
30:45Fortunately, in its next pass by Earth, nearly two centuries from now, the chance of impact
30:51is set at just one in 1,750.
30:58OSIRIS-REx will go on to shed light on the path of yet another near-Earth asteroid.
31:05In the year 2029, 99942 Apophis, a slightly smaller asteroid, will pass within 32,000
31:13kilometers of Earth.
31:18Here is its path, compared to a sample of man-made satellites orbiting Earth.
31:25Once OSIRIS-REx drops off its Bennu samples, it will then swing back out to meet up with
31:32Apophis, just weeks before it races by Earth.
31:38It will spend the next 18 months orbiting the asteroid, mapping its surface, and studying
31:44the effects of Earth's gravity.
31:50With most large, highly destructive asteroids now identified, astronomers have begun to
31:56shift their search to smaller objects down around 50 meters across.
32:03Only 25% of them are currently known.
32:10What if one of these city killers took aim at Los Angeles, New York, London, or any of
32:30the world's great cities?
32:33Mass generated by the impact could claim 50,000 lives within seconds.
32:42Is such a destructive impact inevitable?
32:47There is a chance that someday we'll detect a giant boulder careening through space, large
32:53enough to survive the plunge into our atmosphere.
32:59How will we respond?
33:03Public awareness is our first line of defense.
33:07If you know it's coming, you might be able to get out of the way.
33:13That's why every June, the founders of World Asteroid Day implore citizens to pay attention
33:19and make planetary defense a priority.
33:29NASA, for one, has set up a new Planetary Defense Coordination Office to manage the
33:35expanding asteroid database and disseminate information to the public.
33:41In the U.S., the Federal Emergency Management Agency, FEMA, has begun to develop evacuation
33:47and public alert procedures.
33:51The next line of defense is detection.
33:55To avoid getting blindsided, we must monitor the sky for anything that moves.
34:04NASA has erected the Deep Space Network to communicate with spacecraft.
34:09That includes planetary radar to scan our solar neighborhood for Earth-bound objects.
34:18The agency runs the NEOWISE space mission to hunt for asteroids, as well as the SCOUT
34:26project, including a software system that projects their pathways.
34:32Atlas telescopes are scanning northern and southern skies.
34:39The new Vera Rubin Observatory will monitor a wide swath of the night sky, looking for
34:44stars exploding in distant space or asteroids and comets racing through the solar system.
34:53The most scientifically interesting results of the last few years are a much more sophisticated
34:58understanding of orbits and how they change.
35:02A recognition, for instance, of what the astronomers call a keyhole, which means that there are
35:07some very sensitive points in an orbit.
35:10If it goes right precisely here, it'll come back and get you.
35:14If it misses by even a mile, it won't.
35:17And so we are understanding some of the details and subtleties of orbits.
35:22Obviously, it's not just a matter of discovering these objects with a survey, but making accurate
35:27predictions of their future path.
35:29And liftoff of the Falcon 9 at dark.
35:35Our third line of defense, intercept and neutralize the threat.
35:43Planetary defense is no longer just the subject of disaster movies.
35:49For a moment in September 2022, citizens of planet Earth turned their attention to an
35:54interplanetary spectacle.
35:59DART, the Double Asteroid Redirection Test, was sent on a 10-month journey powered by
36:09a small ion thrust engine fueled by solar energy.
36:19Racing in at almost 24,000 kilometers per hour, the DART spacecraft homes in on the
36:24binary asteroids Didymus and Dimorphos, 11 million kilometers from Earth.
36:32Ten days from the impact, the DART spacecraft releases a small secondary unit called Leach
36:37Cube to record the action.
36:44Live streaming to Earth, DART's camera sends back one image per second.
36:52T minus one hour.
36:54The asteroids are but a pixel of light.
37:02T minus 20 minutes.
37:05Details appear on the larger asteroid Didymus.
37:10The smaller target, Dimorphos, is behind it.
37:27approach, DART autonomously steers in the direction of Dimorphos.
37:53Two minutes to go.
37:55DART passes Didymus.
38:00Details on Dimorphos now become distinct.
38:03You can see that it's a rubble pile asteroid, similar to Bennu.
38:23Here is the last image, taken two seconds before impact.
38:27The rock in the center is close to five and a half meters wide.
38:36From Earth, the ATLAS telescope catches a cloud of rock and dust flying off the asteroid.
38:45Meanwhile, Leach Cube, the Hubble Space Telescope, and the James Webb Space Telescope each record
39:00the blast.
39:03A week later, in the wake of the impact, the SOAR telescope in the Andes Mountains catches
39:09a 10,000-kilometer comet tail of dust and rocks accelerating away from the asteroid.
39:18Scientists expected the impact might shorten the asteroid's almost 12-hour orbit by at
39:23least 73 seconds.
39:26DART, the tiny interplanetary battering ram, managed to cut it by 32 minutes.
39:37With enough warning time, we can defend against small-sized asteroids like Dimorphos.
39:45Will this work with an asteroid three times larger, such as Bennu?
39:54And what'll we do if the asteroid appears suddenly, with little warning?
40:03One answer, follow the script of Armageddon or deep impact, and nuke it.
40:17A group of scientists at the Los Alamos National Laboratory tried to find out how feasible
40:23this is by simulating a nuclear strike in a powerful supercomputer.
40:32Their study target?
40:33A 330-meter-wide, potentially hazardous, near-Earth asteroid called Itokawa.
40:40A Japanese mission found that it, too, is a conglomerate of dense rocks.
40:46On its surface, scientists planted a virtual one-megaton nuclear bomb, six times more powerful
40:53than Hiroshima.
41:00In the first 30 milliseconds, a shockwave races through the rocks.
41:14Most of the fragments are too small to survive the plunge through Earth's atmosphere.
41:19However, the explosion risks showering the planet in deadly radiation.
41:27A recently published plan offers another solution.
41:32Sometime in the future, a large asteroid is spotted on a beeline for Earth.
41:37A robotic probe is sent out to survey it.
41:41Seeing through the dirt and gravel that lines its surface, the probe reports that it's a
41:47collection of boulders, some larger than a house.
41:54We turn to our last line of defense, a last-ditch effort to save civilization.
42:10Like an iron dome for planet Earth, we've stationed a robotic asteroid hunter on the
42:16surface of the moon.
42:33As the asteroid bears down on Earth, astronomers use radar to track it.
42:40At a critical moment, they activate the system.
43:05It doesn't take much power to escape the moon's gravity.
43:11With its near-Earth mission, the spacecraft can travel light on fuel, but heavy on firepower.
43:23After decades of experiments in tracking and maneuvering in space, planetary defense finally
43:29has its first test.
43:36The asteroid is still half an Earth away.
43:40The spacecraft is actively tracking it, computing its speed and trajectory.
43:49The target is approaching at over 1,000 kilometers per hour.
43:58Earth impact is all but certain.
44:08In this new age of planetary defense, nuclear bombs have been ruled out.
44:14But a single conventional explosive is not enough to destroy an asteroid.
44:21So instead, the spacecraft packs an arsenal.
44:30It fires a series of projectiles to meet the asteroid and soften it up.
44:45One charge penetrates.
44:47Another explodes.
44:51Then, the final impact.
45:21Observing from Earth, scientists and the public, with their fate hanging in the balance, can
45:39only wait and hope.
45:44With any luck, those fragments that hit Earth are small enough to burn up in the atmosphere.
46:06Will we live another day?
46:12To strive.
46:18Create.
46:27To wonder.
46:34And survive.
47:05to wonder.
47:13And survive.
47:21to wonder.
47:27And survive.
47:33To wonder.
47:39And survive.
47:45To wonder.
47:51And survive.