Killer Asteroid: Defending Earth
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?
Category
📺
TVTranscript
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.