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00:00:00A dangerous asteroid is heading towards Earth.
00:00:06It's the size of the Empire State Building, and it's traveling at 16,000 miles an hour.
00:00:15It's called Apophis, after the Egyptian god of chaos.
00:00:20It will fly close to us in 2029.
00:00:24It won't hit us this time.
00:00:28When it returns in 2068, it could be another story.
00:00:34If it blows up over a city, millions of people will die.
00:00:41This could be the most devastating single event in U.S. history.
00:00:46Earth is stuck in the crosshairs of a potential asteroid strike.
00:00:52Apophis is one of around 2,000 potentially hazardous asteroids.
00:01:00Asteroids have hit us before, and they will hit us again.
00:01:08As far as cosmic dangers go, they're number one on the list.
00:01:13This is not a drill.
00:01:16If we do nothing, this is our future.
00:01:38In December 2018, the U.S. military detects a huge explosion in the Earth's atmosphere,
00:01:46high over the Bering Sea, off the coast of Alaska.
00:01:52When an explosion of this magnitude is detected, everyone's mind goes to the same thing, nukes.
00:01:58But when the real answer was found, and it was determined that it didn't even originate
00:02:03from Earth, that was even more shocking.
00:02:07The cause of the blast was an asteroid.
00:02:11This asteroid was 30 feet across, something like that, over 1,000 tons, but it was moving
00:02:17at 20 miles per second, over 70,000 miles an hour.
00:02:23This asteroid was small, and it exploded in the atmosphere over the ocean, so nobody was
00:02:29hurt.
00:02:30But if it had been bigger, or it had come in over a different place, or it had been
00:02:38moving a lot faster, this could have been a dangerous object.
00:02:41But the scariest thing about it is that we didn't see it coming.
00:02:51We've been lucky so far, but near misses happen all the time.
00:03:00About once a year, we get something the equivalent of a nuclear bomb going off in our atmosphere.
00:03:06And while that sounds horrible, most of these happen tens of miles up, over open ocean,
00:03:15where we go on completely oblivious.
00:03:21We may be oblivious to most of the threats from space, but they are very real.
00:03:27We are going to get hit.
00:03:30Over a certain amount of time, an asteroid impact is inevitable.
00:03:34It will happen, 100% absolute certainty.
00:03:51NASA considers the threat from the sky so severe, it has made protection from asteroids
00:03:59a top priority.
00:04:03These events are not rare.
00:04:05They happen.
00:04:06And of course, it's up to us to make sure that we are detecting and characterizing,
00:04:11tracking all of the near-Earth objects that potentially could be a threat.
00:04:16This is not about Hollywood.
00:04:18It's not about movies.
00:04:19This is about ultimately protecting the only planet we know right now to host life.
00:04:25And that is the planet Earth.
00:04:30To help protect our home, we carry out Earth defense simulations.
00:04:35For three days, 200 scientists at the Planetary Defense Conference battle a simulated asteroid
00:04:4220 times larger than the Bering Sea's space rock.
00:04:48We practice, all right, what if this hits a major city?
00:04:53What would we need to do?
00:04:56By running potential impact scenarios, we can prepare for a real asteroid strike.
00:05:02This is like a fire drill that you would do at school or at work, where you practice and
00:05:06think about, okay, what if, where are the exits?
00:05:08How do I get out?
00:05:10How fast do I get out?
00:05:14The drill starts with the discovery of a simulated Earth-bound asteroid.
00:05:20So the first information is, there's a big asteroid coming towards the Earth.
00:05:24Then we get a better estimate of how big it is, how fast it's going, and where it's going
00:05:28to hit.
00:05:30The asteroid is heading straight for Earth, with Denver, Colorado in its sights.
00:05:37The planetary defense scientists send up a simulated spacecraft to smash into the asteroid
00:05:43and push it off its path.
00:05:45But it's a big gamble.
00:05:48You can push it the wrong way.
00:05:50You can potentially have unintended consequences.
00:05:57In the simulation, the spacecraft strikes the asteroid, deflecting it away from Earth.
00:06:06But the impact dislodges a 200-foot chunk, which is now heading straight towards the
00:06:12eastern seaboard.
00:06:15So there's this one last piece that is now going to hit New York.
00:06:20We know that something that size is going to have citywide consequences.
00:06:27That is huge.
00:06:28That's a horrible impact.
00:06:31When you're actually in the conference room and you understand eventually that New York
00:06:35City is going to be destroyed, and you're having strategies about how to evacuate people,
00:06:40all the timing, when you're doing the simulation, you're in your head.
00:06:44You're thinking about these things.
00:06:45You're trying to reason them out.
00:06:47But can you imagine the feeling in your gut, in your heart, if this was real?
00:06:52If this were real, the chunk of asteroid would strike the Earth's atmosphere at 43,000 miles
00:06:59an hour.
00:07:01As the space rock descends, it collides with molecules in the atmosphere, which buffet
00:07:07the falling rock.
00:07:10It's kind of like doing a belly flop into a pool, right?
00:07:13You're going from the vacuum of space into the dense lower atmosphere in mere seconds.
00:07:19And that's an incredible amount of pressure to put on the object.
00:07:24The asteroid slams into the air ahead of it, compressing it violently.
00:07:29The surface of the asteroid gets hotter and brighter.
00:07:34It's the air itself that's glowing luminously from the heating of the shock wave, the world's
00:07:39most intense sonic boom, if you will, that heats the air to incandescence as the object
00:07:44passes through.
00:07:45So that's the source of that brilliant illumination.
00:07:50This bright burning asteroid is called a bolide.
00:07:54We witnessed one descending over the Russian city of Chelyabinsk in 2013.
00:08:00All of a sudden there was a huge fireball streaking through the sky, and people had
00:08:04no idea what they were witnessing because it looked like the sky was on fire.
00:08:09It was insanity.
00:08:12As the asteroid descends, the compression of the denser air lower down starts to flatten
00:08:18and even disrupt the falling rock.
00:08:21There's a high pressure on the front, there's no pressure on the back, and it's being superheated.
00:08:26And that intense temperature causes the air to glow, which is how we see the streak of
00:08:32a meteor.
00:08:33And it also disintegrates the asteroid itself.
00:08:35It's hot enough to literally melt rock.
00:08:39This can often lead to them exploding.
00:08:42The combination of heat and pressure invade the falling asteroid, causing it to blow up.
00:08:50Most asteroids don't reach the ground before they completely disintegrate in a tremendous
00:08:55release of energy.
00:08:56This is what we call an airburst, and we learned a lot about these while we were testing nuclear
00:09:01weapons after World War II.
00:09:05Some of these bombs were blown up underground and on the ground, but they found out when
00:09:09they blew up bombs above the ground, it actually did more damage.
00:09:13It was more widespread damage.
00:09:16The explosion of the Chelyabinsk asteroid sent out a powerful shockwave at thousands
00:09:22of miles an hour.
00:09:25The blast traveled over 100 miles.
00:09:29It damaged 7,000 buildings and put 1,500 people in the hospital.
00:09:35All of the injuries pretty much came from people who saw, oh, what's that bright flash
00:09:39in the sky?
00:09:40And they came close to a window to look and see what it was, and then the pressure wave
00:09:45hit and blew glass in their face.
00:09:50The Chelyabinsk asteroid was only 65 feet across.
00:09:56The rock in the defense simulation is three times more massive and is now heading for
00:10:02New York City.
00:10:05Imagine what would happen if an explosion 1,000 times greater than that over Hiroshima
00:10:11hit New York.
00:10:13We're talking about an utter, complete destruction of the city and millions of people.
00:10:20With so little warning, the only option would be to evacuate New York City.
00:10:27How do we get everybody out of New York City within just a few days?
00:10:31That's where panic sets in.
00:10:32That's where fear would really become the dominant emotion.
00:10:38Anyone left in New York would see the bolide race in, followed by a blinding light as the
00:10:48asteroid explodes above the city.
00:10:52The blast would be the equivalent to the largest nuclear weapon ever detonated on Earth.
00:10:59Buildings would be flattened, melted, there would be fires for miles around.
00:11:04In the first moments of the explosion, a million people could be killed instantly, and many
00:11:09more would die later in the rubble and the ruins of what would happen there.
00:11:16Anything within nine miles of the blast epicenter would be completely destroyed.
00:11:28The intense heat and pressure would wreck buildings.
00:11:34It's the worst possible day for New Yorkers.
00:11:37And not just the city itself, there's something like 15 million people living in the New York
00:11:43area.
00:11:47The destructive shockwave would race out over 250 square miles.
00:11:54This would certainly be the worst disaster that the U.S. has ever experienced.
00:11:57We're talking about millions and millions of people displaced, affected within an instant.
00:12:09This scenario is just a simulation, for now.
00:12:18The asteroid Apophis is heading our way.
00:12:22If it hits Earth, it might not just kill a city, it could kill a whole region.
00:12:31I wouldn't exactly want to be there when that happens.
00:12:33I want to be very, very far away.
00:12:38Apophis will skim Earth in 2029.
00:12:43But its path will change, possibly turning a future miss into a direct hit.
00:12:59April 13, 2029, a speck of light races towards Earth.
00:13:06It's an 1,100-foot-wide asteroid called Apophis.
00:13:11We are about to have an extremely close shave.
00:13:16It's the closest approach of any asteroid that didn't actually hit us for a long, long
00:13:22time.
00:13:23It will be 10 times closer than the moon itself.
00:13:26It'll be so close, it'll be brighter than some stars.
00:13:30The football stadium-sized Apophis will race over the Atlantic.
00:13:36If it were sitting on the surface of the Earth, it would weigh about 50 million tons,
00:13:40something like that.
00:13:42And that is not the place you want it to be.
00:13:45You want it to be in space and far away.
00:13:50When we discovered Apophis in 2004, we thought it might be on a collision course with Earth,
00:13:56with a potential impact greater than the largest atomic bomb ever exploded.
00:14:03The largest nuclear device, atomic device, ever detonated on our planet was the Tsar
00:14:08Bomba bomb in Russia, so something like 55 or 56 megatons.
00:14:14When Krakatoa exploded in 1883, that was something like 200 megatons.
00:14:19Apophis' impact would be 450 megatons.
00:14:22If something like that were to happen over New York City or Washington, D.C., you're
00:14:26going to lose the city.
00:14:30The impact would be at least 10 times greater than the simulated asteroid strike on New
00:14:35York.
00:14:43When you put it in those terms, that's just plain scary.
00:14:48In a word, an impact from an Apophis-sized asteroid would be bad, very, very bad.
00:14:57Apophis' orbit will cross Earth every seven years this century, but it won't hit us
00:15:03in 2029.
00:15:05But this close encounter will change Apophis' orbit.
00:15:11When a small asteroid encounters a bigger body like a planet, it's like a bunch of
00:15:16roller derby players.
00:15:21Most of them are clumped together, but maybe there's one just on their own particular
00:15:25orbit.
00:15:26And as they circle around, as they get close to that larger clump, there'll be some interactions,
00:15:31potentially violent interactions, that will change the future trajectory of that lone
00:15:37roller derby skater.
00:15:39And the next time around, it might be a wide miss, or it might be a head-on impact.
00:15:49It's the same in the solar system.
00:15:52The combined gravity of the Earth and Moon creates what's called a gravitational keyhole.
00:15:59A gravitational sweet spot, which could change Apophis' orbit.
00:16:06That will change the potential future trajectory of this rock, and might make it totally harmless,
00:16:12or might increase the chances of an impact even further in the future.
00:16:20Because of the gravitational keyhole, there is still a small chance that Apophis will
00:16:25hit Earth in 2068.
00:16:31That is the important lesson that Apophis taught us.
00:16:34You can miss the Earth, but if you pass through one of these keyholes, at some time later,
00:16:39you will hit the Earth.
00:16:42We now know Apophis will miss the keyhole in 2029.
00:16:47But there are other keyholes, and other close passes.
00:16:57Apophis is not a lone threat.
00:17:00There are an estimated 832,557 asteroids orbiting the Sun.
00:17:10Most asteroids live their lives perfectly, peacefully, past the orbit of Mars, or trailing
00:17:16Jupiter, and don't mind anybody else, and don't cause any troubles.
00:17:22But some asteroids are on very particular orbits that cross the orbit of the Earth.
00:17:31These asteroids have left the stable orbit of the asteroid belt, and moved into orbits
00:17:36that get near our own.
00:17:38These asteroids are called Near Earth Asteroids, or NEAs for short.
00:17:45The Near Earth Asteroid population is interesting, and potentially dangerous, because they're
00:17:48the ones that actually cross the orbit of the Earth.
00:17:51So they're most likely to have, at some point in the future, an impact with the Earth.
00:17:58Most NEAs pose little or no threat to Earth.
00:18:02But we've detected over 2,000 that do, including Apophis.
00:18:10These are called PHAs, Potentially Hazardous Asteroids.
00:18:16The difference between a Near Earth Asteroid and a Potentially Hazardous Asteroid is distance
00:18:22and size.
00:18:24Anything can get near the Earth, and that could be 20 million miles away, something
00:18:28like that, and be a Near Earth Asteroid.
00:18:30But a Potentially Hazardous one can hit us, and it's big enough to do damage.
00:18:39So something that, over the next 100 years or so, has a chance of hitting us, and doing
00:18:43damage when it does, that's a Potentially Hazardous Object.
00:18:48PHAs are asteroids 500 foot or larger that could collide with Earth.
00:18:57Take a 400 foot asteroid.
00:19:00If it hits, it would release as much energy as 3,000 Hiroshima nuclear bombs.
00:19:12In July 2018, NASA published a map of all known NEAs and PHAs.
00:19:22The animation tracks their discovery from 1999 through 2018.
00:19:30Every time I look at this animation, it does make my heart stop a little bit, because it
00:19:34looks like we're in the middle of this swarm of angry bees circling all around us.
00:19:38In 1999, we'd identified under 300 NEAs scattered through the inner solar system.
00:19:46Ten years later, we'd discovered 500 more.
00:19:50By 2018, we'd discovered 18,000 Near Earth Asteroids, but we estimate there are millions
00:19:58out there.
00:20:00It seems like we could never find all the asteroids.
00:20:03They just keep coming.
00:20:04It's like we're fighting an army of zombies.
00:20:08Zombies that keep hurtling our way, hitting Earth at up to 64,000 miles an hour.
00:20:17That is very, very fast.
00:20:19That is much faster than a rifle bullet.
00:20:21And that's the key to its destructive power.
00:20:24When a really fast and really large asteroid hits, the impact is off the charts.
00:20:33The blast is so intense, it can melt or even vaporize rock.
00:20:45January 2019, a total eclipse of the moon.
00:20:52Astronomers train their telescopes on the darkening lunar surface.
00:20:56They capture a bright flash that lasts around a quarter of a second.
00:21:02It was recorded.
00:21:03There were a lot of live webcasts and things like that going on at the time.
00:21:07And you can see this flash of light.
00:21:09What the heck was that?
00:21:12At first, the cause of the flash was a mystery.
00:21:17It turns out it was actually a meteorite hitting the surface of the moon.
00:21:22And because it was dark and because we were all looking at it, we could actually see it.
00:21:27The moon's dark surface gave us a unique view into what happens when an asteroid strikes.
00:21:33What was so exciting about being able to see this impact on the moon in a dark area is
00:21:39that we could actually look at the light that it produced and then back-calculate exactly
00:21:44what the size of the impactor was.
00:21:46We worked out that the impacting asteroid was just 20 inches wide.
00:21:51The crater it blew out was 45 feet across.
00:21:55How could something so small be so destructive?
00:22:00The two things that matter the most are how fast it's going and how massive is the thing.
00:22:05The more massive, the bigger the boom.
00:22:06The faster, the bigger the boom.
00:22:08Range and weight are two very important factors to assess how much damage an asteroid will do.
00:22:13Just like a boxer, if a tiny person like me were to swing a punch, it would do a lot less
00:22:17damage than a heavyweight champion.
00:22:20Same thing with asteroids.
00:22:21The bigger they are, the bigger the punch.
00:22:23But the same thing is fast, right?
00:22:25If I hit you really slowly, it's not going to hurt.
00:22:27I have to really wind back and pop.
00:22:30That's what happens with an asteroid.
00:22:33The damage from an asteroid strike is determined by its kinetic energy.
00:22:40Kinetic energy depends on two things, speed and weight.
00:22:45Speed is the most important.
00:22:48If you double the mass, you double the kinetic energy.
00:22:53But if you double the velocity, you get four times the kinetic energy.
00:22:57Three times the speed, nine times the impact energy.
00:22:59Ten times as fast, it has a hundred times the energy.
00:23:03So the velocity is what's really critical here.
00:23:08The lunar asteroid weighed only 100 pounds.
00:23:11But it was traveling at 38,000 miles an hour, carrying a huge kinetic energy which gouged
00:23:19out the crater.
00:23:22It's the same principle for impacts on Earth.
00:23:2650,000 years ago, a 150-foot asteroid hit what is now Arizona.
00:23:33The impact blasted out an impressive hole, now called Beringer Crater.
00:23:41It's about three-quarters of a mile across, over 500 feet deep.
00:23:44You could put the Washington Monument in the bottom of the crater, and the top of the monument
00:23:48wouldn't quite clear the rim.
00:23:50It's a pretty impressive hole in the ground.
00:23:56In 2016, impact specialist Kathy Plesko visited Beringer Crater to see firsthand what mass
00:24:04and speed do to the surface of the Earth.
00:24:11This is awe-inspiring, to stand on the rim of a crater like this, understanding just
00:24:18how much energy it must have taken to excavate this much rock.
00:24:26An asteroid came in at about 27,000 miles an hour.
00:24:35It comes slamming into the surface and just explodes.
00:24:38Anywhere nearby here would have seen winds of thousands of miles an hour as the shock
00:24:43wave came out.
00:24:50The immense power of an asteroid impact comes from the kinetic energy being transferred
00:24:56from the space rock into the surface rock.
00:24:59It's an extremely violent process, and it starts with the moment of contact of the projectile
00:25:07with the surface itself.
00:25:10It pushes into the crust, and at first it's just almost punching, like sticking your thumb
00:25:17into dough.
00:25:18It's only about as wide as the object is.
00:25:21It's going straight down in, but then it's meeting resistance from the surface of the
00:25:26Earth, and so it squishes, squishes, squishes until it runs out of momentum, but then it's
00:25:32very compressed, and all of that energy is in a very small space.
00:25:36As it releases, it detonates like a bomb, and that's what makes the impact crater.
00:25:44Images of an asteroid strike in the lab reveal the impact in slow motion.
00:25:52As the high-speed pellet hits the surface, the sand compresses downwards, then rebounds.
00:26:01As that rebound is occurring, that's when the material is being ejected out of the crater
00:26:06itself.
00:26:08You'll see the surface erupting outwards like the blooming petals of some big rocky flower
00:26:13as all this debris goes spraying out in every direction.
00:26:21The 150-foot Beringer asteroid turned the rock to powder.
00:26:26Sixty-six million years ago, an asteroid around 200 times larger and moving one and a half
00:26:33times faster than Beringer hit Earth.
00:26:37This asteroid, called KPG, had so much energy, it turned rock to liquid.
00:26:45This thing was immense.
00:26:46It's really hard to wrap your head around just how big it is.
00:26:50When it hits the back end of it, it is so far back that it's where a modern jetliner
00:26:55would fly.
00:26:59The KPG asteroid hit the ground with a lethal combination of mass and speed.
00:27:05A trillion tons traveling at 45,000 miles an hour.
00:27:12Some rock is completely vaporized.
00:27:14It just becomes a gas.
00:27:16You have some rock that is melted.
00:27:18You have some that's thrown out into space.
00:27:23This material goes up through that and then falls down and settles down over a huge area.
00:27:28That might be dust.
00:27:29It might be pulverized rock.
00:27:31It might be vaporized metal.
00:27:33It's all of this hot material raining down everywhere.
00:27:39As some rock exploded skywards, rock below the surface was slammed by a shockwave that
00:27:45was completely off the charts.
00:27:48Rock stopped, behaving like rock.
00:27:53We experience rocks as solid objects, but if you hit a rock hard enough, it flows like
00:27:58water.
00:27:59The KPG impact hit so hard, it pulverized the rock and turned it into a liquid.
00:28:06Almost like ripples on a pond moving away from a stone that's been dropped in it.
00:28:10It's almost like a splash in the solid body of the earth itself.
00:28:14And like a water droplet splashing in water, you'll see that that central peak will kind
00:28:19of splash up and rise to a high altitude and then come back down again.
00:28:23We think a process very similar to that probably happened in the rock itself at the center
00:28:28of the crater, rising up as high as the Himalayas before relaxing back down into their current
00:28:33position again.
00:28:34The material slumps, and so these ripples are frozen in the rock.
00:28:40And there are other fragments that go away radially, almost like the spiderweb pattern
00:28:44in glass that you get after it's shot with a bullet.
00:28:49The KPG impact blew out a 111-mile-wide crater.
00:28:57A large and fast asteroid heading our way is always going to be a problem.
00:29:05So what do we do?
00:29:07Wait for oblivion?
00:29:11Or fight back?
00:29:22The space in the inner solar system seems calm, stable, and empty, but it's not.
00:29:32There are tens of thousands of near-Earth objects just whizzing around Earth.
00:29:36Now, space is big.
00:29:38They're not going to hit us every time they orbit the sun, but this does set up the possibility
00:29:45that one of these years, we're going to end up at the same spot in space at the same time
00:29:51as that asteroid, and then it's going to be an impact.
00:29:57We're living in a cosmic shooting gallery.
00:29:59Asteroids strike the Earth all the time through history, and it's going to happen again.
00:30:05Scientists are developing strategies to stop an asteroid hitting our planet.
00:30:10Our options?
00:30:12Destroy or deflect the space rock.
00:30:15But first, we need to detect any dangerous asteroids.
00:30:21It's a little bit unnerving to know that we haven't yet detected all of the asteroids
00:30:25that exist that could possibly cross our path.
00:30:28We've discovered a lot of asteroids now, but we typically discover the big ones.
00:30:34But for asteroids that are below 100 feet, there's a lot still out there that we haven't
00:30:39discovered.
00:30:40And such an asteroid can do some real damage if it were to explode over a populated area.
00:30:45To prevent such a catastrophe, we need to find all asteroids whose orbits cross our
00:30:51own.
00:30:53Detection is crucial in our defense against asteroids.
00:30:56And the reason is, the earlier they're detected, the easier it is to deflect them away from
00:31:01hitting the Earth.
00:31:03You want to do deflection, the first step is detection.
00:31:08The problem is, asteroids are very hard to detect.
00:31:13Detecting asteroids and cataloging all their orbits is really challenging.
00:31:17They can move quite fast across the sky, and they might go away on the other side of the
00:31:22sun for years and years and years.
00:31:26So we can't see them.
00:31:29And even when they are this side of the sun, they're hard to spot.
00:31:34But the problem is, they're very small, and they're very dark.
00:31:38And when I say very dark, I mean really dark like a lump of coal.
00:31:42So how do you find a small, dark rock just wandering around out there in the solar system?
00:31:52The Catalina Sky Survey has the answer.
00:31:57The huge telescope in the mountains above Tucson, Arizona, takes a series of images
00:32:02over a 20-minute period.
00:32:05It's looking for anything that moves, because stars don't move, but asteroids do.
00:32:15If it's a really bright asteroid, we will see some bright points of light tracking across
00:32:21the four images.
00:32:23Ah, here we go.
00:32:27This is a real object.
00:32:28You can see it's moving across the sky here from the lower right to the upper left.
00:32:34We are very, very excited to have discovered one tonight, because this is an object that's
00:32:38approaching nearer space, likely in the neighborhood of Earth.
00:32:48Catalina has limitations.
00:32:50It can only see visible light, so a particularly dim asteroid could be missed.
00:32:58Asteroids are very cold.
00:32:59They're usually quite far away from the sun.
00:33:01But amazingly, the best way we have to find these is infrared light, because things that
00:33:06are cold by human scales can still be very warm to an infrared telescope.
00:33:11So even if asteroids are just a few tens of degrees above absolute zero, that's still
00:33:15enough heat to detect them.
00:33:18When the Infrared Space Telescope, NEOWISE, turned its gaze onto asteroids, it had immediate
00:33:25results.
00:33:27NEOWISE has now detected close to 160,000 new asteroids and comets in our solar system,
00:33:33and about 780 of those are things that are near the Earth.
00:33:37Ten of those near objects have been classified as PHAs, Potentially Hazardous Asteroids.
00:33:45Without NEOWISE, we would have missed them.
00:33:49Using an infrared space telescope is a way of better detecting some of the smaller asteroids
00:33:55and comets in the near-Earth vicinity.
00:33:58Detection is an important first step, but it only tells us there's another asteroid
00:34:04out there.
00:34:06Once we've spotted an asteroid, all we know is that it's a tiny dot of light.
00:34:10We don't know anything else about it.
00:34:13So when a new asteroid is discovered, the most important thing is to determine its path,
00:34:17to track it, to figure out exactly how it's orbiting around the sun and how close it's
00:34:21going to get to Earth.
00:34:22For that, we have to know where they are now, so its current location, and measure
00:34:26how fast it's going and which direction it's traveling.
00:34:30All of these things together are really important for tracking where it's going to be next
00:34:34and whether or not they're going to hit us.
00:34:38To get this information, we need something much bigger and more powerful.
00:34:44The Arecibo Observatory.
00:34:47Once Catalina or another telescope detects a near-Earth asteroid in our cosmic neighborhood,
00:34:53Arecibo's 1,000-foot dish swings into action.
00:34:59They discover these asteroids, and then once we know where they were, we can try and point
00:35:05the radio telescope and see where they are at the moment and measure their exact location
00:35:11and their trajectory.
00:35:12Arecibo achieves this level of precision by using radio detection and ranging, more commonly
00:35:20known as radar.
00:35:22The Planetary Radar System at Arecibo Observatory is the most powerful radar system in the world.
00:35:28We focus on potentially hazardous asteroids, which are those that have a high probability
00:35:33of impacting Earth.
00:35:35Arecibo sends out radio signals towards the newly detected asteroid.
00:35:40It emanates radio signals.
00:35:42Some of them hit the asteroid, just like a radar gun from a cop might hit the side of
00:35:48your car.
00:35:49It's pretty similar, but instead of doing it with a radar gun on a small scale, we're
00:35:53doing it on a really big scale with one megawatt power, hitting objects that are tens of lunar
00:35:58distances away.
00:36:00And then those radio waves bounce back to Earth and we detect them again, and by comparing
00:36:07the differences between what we sent and what we received, we can get a map of the
00:36:14asteroid itself and we can get where it's moving and how fast it's moving.
00:36:20But asteroids may not be the biggest threat from space.
00:36:25November 25, 2018, cameras on board the Solar and Heliospheric Observatory film a large
00:36:34object crashing into the sun.
00:36:38We recorded the impact of an object into the sun at over a million miles per hour.
00:36:45The incredible speed tells us that this was not an asteroid.
00:36:50It was the death plunge of something much more unpredictable and dangerous, a killer
00:36:55object from the outer reaches of the solar system.
00:37:00Comets in some way, you could consider maybe being more dangerous than near-Earth asteroids.
00:37:05When near-Earth asteroids, you could imagine that we would discover all of them.
00:37:09And if we get perfect knowledge of all of their orbits, we can predict into the future
00:37:13where they'll be and when they may or may not have a orbit that crosses the actual Earth
00:37:19and could be an impact.
00:37:21Comets, a large part of that population, we only see once.
00:37:25They come in from way out in the distant part of the solar system, they do one lap around
00:37:29the sun, and they go back out there for millions of years.
00:37:35Comets are dirty snowballs, huge lumps of ice and dust.
00:37:40They come in two flavors.
00:37:43There's something we call short-period comets.
00:37:46These are comets that are kind of constrained to the solar system, the inner solar system,
00:37:50and their orbits are never more than a few hundred years.
00:37:55Short-period comets come from the Kuiper Belt, a region of the solar system beyond
00:37:59the orbit of Neptune.
00:38:03These comets have short orbits on the same plane as Earth.
00:38:13The second type of comet are called long-period comets.
00:38:18They originate in the Oort Cloud, a sphere of icy objects located at the very edges of
00:38:24the solar system.
00:38:28There are thousands and thousands of comets out there in the Oort Cloud.
00:38:31There's just waiting.
00:38:32And so in principle, one of them can get knocked off course and come raining down into the
00:38:36inner solar system.
00:38:42Long-period comets are very large, and they travel very fast.
00:38:48Comets can get really big and they're really heavy, and essentially they're falling to
00:38:53Earth from two billion light-years away.
00:38:56So imagine how fast they're going.
00:39:00We know from studying asteroids that the faster they go, the more kinetic energy they release
00:39:05on impact.
00:39:11Comets travel even faster than asteroids.
00:39:14In general, they're moving 50 percent faster, something like that.
00:39:18But that doubles their impact energy.
00:39:20And that's sort of a best-case scenario.
00:39:22In a worst-case scenario, pound for pound, they could have five or up to almost ten times
00:39:27as much energy as an asteroid impact.
00:39:34The Bering Sea asteroid blew up in the atmosphere, but the Beringer crater asteroid hit the ground
00:39:40intact with its full force.
00:39:46Why do different asteroids behave differently?
00:39:50And what will Apophis do?
00:39:52When it heads our way, Arecibo's radar may have the answer.
00:39:59When we bounce radar waves off of these objects, we can get effectively imagery of the surface
00:40:05of some of these small objects that we just cannot do with optical telescopes.
00:40:10This is the radar image of Apophis.
00:40:13It's so far away that all we could image was a few pixels.
00:40:20So this is our most recent radar image of asteroid Apophis.
00:40:25And you can see it's only a few pixels.
00:40:29But it does give us information on what it actually is.
00:40:35These few pixels are enough to work out how big Apophis is.
00:40:41From this image, we can constrain the size to be about 1,000 feet, which is about the
00:40:47same size as the Arecibo radio telescope.
00:40:51All of that from a weird bunch of pixels.
00:41:00Knowing the size and mass of an asteroid is critical to understanding what an asteroid
00:41:05is made of.
00:41:08If we have the size and the mass, we get the density.
00:41:11If we have the density, we know what it's made of.
00:41:13Rock has some density.
00:41:15Metal has a different density.
00:41:17So we can determine a huge amount about the asteroid simply by pinging it with radar.
00:41:26Arecibo's data reveals that not all asteroids are alike.
00:41:32There's not just one kind of asteroid.
00:41:34There are actually several kinds.
00:41:35And this is important to understand because they behave differently.
00:41:39They behave differently if they impact us, and they behave differently if we're trying
00:41:42to prevent them from impacting us.
00:41:45We need to know what these asteroids are made of if they're going to hit the Earth because
00:41:50that drastically alters the potential effects.
00:41:55Asteroids come in different shapes, different sizes, and different compositions.
00:41:59And we think that is because they are the leftovers of planet formation.
00:42:04To understand how each asteroid formed and its threat level, we have to go back 4.6 billion
00:42:10years to the start of the solar system.
00:42:14The reason that there are all these asteroids floating around in our solar system today
00:42:18is just because of the early violence of the solar system as it was forming.
00:42:25At the birth of the solar system, the sun ignited, leaving a disk of gas and dust.
00:42:38Only over time, planets formed.
00:42:41Many planets.
00:42:44The early solar system was a messy place.
00:42:47There were a lot more planets, a lot more forming planets.
00:42:50They would crash into each other.
00:42:52They would merge.
00:42:53They would disintegrate.
00:42:54They would reform.
00:42:59This process of accretion, of building planetary worlds, was not just, you know, kind of gentle
00:43:05and happy.
00:43:06It was violent.
00:43:09It was like a giant cosmic game of pool.
00:43:15Planets smashing into planet.
00:43:17The leftovers from this violence formed a ring of junk between Mars and Jupiter.
00:43:24And now we call that junk asteroids.
00:43:26They're just basically rubble left over from the formation of the solar system.
00:43:33Many leftovers became C-type, or chondrite asteroids.
00:43:37They are quite dense, so big ones can punch through the atmosphere and hit the ground.
00:43:50Radar reveals a rarer type of asteroid.
00:43:54Some of them really stand out because their density is so much higher than the rest of
00:43:58the other asteroids.
00:44:01These asteroids are M-type, or metal.
00:44:07Because their mass is great, they carry more kinetic energy during a strike.
00:44:13By far the worst one is this iron meteorite.
00:44:17This is really heavy.
00:44:19So the difference, if you were being hit by this, it would be the difference between being
00:44:23hit by a rock and being hit by a metal hammer.
00:44:28We think that both the Beringer and the KPG Dinosaur Killer events were caused by metal
00:44:36asteroids.
00:44:40There is another, more mysterious type floating through space.
00:44:48December 2018, NASA spacecraft OSIRIS-REx approached the near-Earth asteroid Bennu.
00:44:58Over time, it drifted out of the main asteroid belt, made its way into the inner solar system,
00:45:03until it became a near-Earth asteroid accessible for our spacecraft to go and visit.
00:45:09OSIRIS-REx trained its camera on Bennu.
00:45:19One of the biggest surprises on arrival at Bennu was the large number of large boulders
00:45:24on its surface.
00:45:25Bennu is really littered with huge boulders and littered with medium-sized boulders and
00:45:30littered with small boulders.
00:45:32Bennu is not a solid lump of rock.
00:45:35It's made up of thousands of bits of rock, forming what we call a rubble pile.
00:45:41These asteroids aren't big, singular, spherical balls of rock, but rather they're literally
00:45:47piles of rubble.
00:45:48They're all sorts of pieces and fragments from another asteroid that had previously
00:45:52been disrupted that have all come back together and formed literally a pile of rocks held
00:45:58together by their own gravity.
00:46:00We think rubble piles form from collisions inside the asteroid belt.
00:46:05Each impact blasted bits off.
00:46:08Then over time, they came back together to form the loose pile of rocks.
00:46:14Imagine taking a big cosmic dump truck full of gravel and rubble and dumping it out there
00:46:18into space and letting gravity weakly hold it together.
00:46:24When scientists probed deeper into Bennu, they had another surprise.
00:46:29It's full of holes, like Swiss cheese.
00:46:34If you could slice open one of these asteroids, you'd see there are a lot of voids.
00:46:38In fact, 60% of what we're looking at is a void space.
00:46:42So they're actually really fluffy.
00:46:44So even though they're made of rocks, they're sort of the lint of rocks.
00:46:48Bennu helps us understand Apophis.
00:46:52Radar data shows that Apophis is also a rubble pile.
00:46:56If you look at Apophis, we really want to know how its orbit will evolve in the future.
00:47:01What we learn at Bennu about similar sized rubble pile asteroids might help us understand
00:47:06the future of an asteroid like Apophis.
00:47:09So what would happen if rubble pile Apophis hits Earth?
00:47:13You probably don't want that to hit you still, but it definitely makes it a lot weaker than
00:47:17something like a solid rock, or even more, a chunk of nickel iron metal.
00:47:23Does its rubble pile composition make it any less of a threat?
00:47:28A rubble pile like Apophis is especially unnerving because we don't know when it interacts with
00:47:33the atmosphere if it's going to stay as one solid piece.
00:47:36Will it break up?
00:47:38When these rubble piles start interacting with planets, if they fly near a planet, they
00:47:43can get pulled apart into all of their little pieces.
00:47:46Or if they enter the atmosphere of a planet, to impact the surface, they might slowly get
00:47:52pulled apart as they enter the atmosphere and end up being an array of little impacts
00:47:56instead of one big single impact.
00:48:04In 2017, we had another wake-up call.
00:48:08A strange space rock arrived in our neighborhood.
00:48:12Its shape was unlike anything we'd seen before.
00:48:17The thing that made Oumuamua different from anything else we'd ever seen is it seemed
00:48:21to be almost a shard, a sharp piece of metal tumbling through space.
00:48:26Typically things that move around our solar system are somewhat spherical.
00:48:31This in no way was spherical, it was almost cigar-shaped, so it kind of really plugged
00:48:37into all those alien theories, but we were able to confirm that it didn't slow down as
00:48:43it went by the Earth, which was, we figured if it was an alien craft it would probably
00:48:46stop and have a little bit of a look, but it carried on its trajectory.
00:48:50It wasn't a comet or an asteroid from the asteroid belt.
00:48:55It was a space rock from interstellar space.
00:49:01Interstellar asteroids are probably pretty rare, but the thing about them is they're
00:49:03moving really fast, so if they happen to hit us, it's really bad.
00:49:09Oumuamua was traveling over 100 times faster than a fighter jet.
00:49:15And as we know, speed means danger.
00:49:19Had Oumuamua been on an impact trajectory with the Earth, at those kinds of speeds,
00:49:25very much faster than anything in our solar system, those, remember the kinetic energy
00:49:30goes as the square of the impact speed.
00:49:33At those kinds of speeds, imagine it hitting us at 196,000 miles per hour, that carries
00:49:39an incredibly powerful punch.
00:49:42And so, for a given size object, the impact of Oumuamua compared to a regular solar system
00:49:48object would have been absolutely devastating.
00:49:51Oumuamua passed safely through the solar system, but it won't be the last invader from interstellar
00:49:58space.
00:49:59Astronomers estimate that one alien object visits our cosmic neighborhood every year.
00:50:092019, U.S. researchers discover deposits of fossils.
00:50:16They contain both the remnants of land and sea creatures.
00:50:21You see things that are all jumbled together, so you'll have fossils of sea creatures,
00:50:27you'll have ocean deposits that are mixed up with coastal deposits and onshore deposits.
00:50:35And you see those deposits in places that are very, very far away from where you would
00:50:40expect them to be.
00:50:41And so this material was obviously thrown very far inland.
00:50:47The jumbled deposits suggest the creatures were killed at the same time, in a huge and
00:50:53violent event.
00:50:55Something powerful enough to sweep ocean-dwelling creatures far inland.
00:51:01A tsunami.
00:51:03Tsunamis are usually created when the ocean floor suddenly moves.
00:51:09The ground picks up the entire ocean and shakes it up and down, and it's sort of like taking
00:51:14a rope and shaking it.
00:51:16And it moves all across the ocean floor and ocean surface until it reaches land.
00:51:21The biggest recent tsunami was caused by the Earth's crust at the bottom of the ocean
00:51:26lifting slightly.
00:51:28So this means that that entire length of crust that lifted displaced the water above it.
00:51:34So the waves, the tsunamis that result are really long and wide, and it can travel across
00:51:41the ocean at tremendous speeds and up on land.
00:51:44Is this what happened to the fossilized creatures?
00:51:50Were they killed by a huge tsunami?
00:51:53Clues come from dating the preserved remains.
00:51:57They are 66 million years old, from the same time a six-mile-wide asteroid crashed into
00:52:04the sea off the Yucatan Peninsula, Mexico.
00:52:10Are the two events connected?
00:52:14Do ocean-impacting asteroids trigger tsunamis?
00:52:19We used to think that a big asteroid impacting in the ocean would drive a tremendous tsunami,
00:52:24a huge wall of water, out at very rapid speeds, which would basically scour clean everything.
00:52:31Now new research from 2018 suggests a very different scenario.
00:52:37Scientists used supercomputers to model asteroids hitting the deep ocean, to work out how much
00:52:44of the asteroid's kinetic energy is converted into a tsunami wave.
00:52:50In the simulations, a 1600-foot asteroid hits the ocean at 20,000 miles an hour and dives
00:52:58into the water.
00:53:01As it goes deeper in, of course it's meeting a lot of resistance, and it slows down and
00:53:06it compresses up, it compresses and compresses and compresses, and then finally it runs out
00:53:11of momentum, and it's at an extremely high pressure.
00:53:16The huge pressure causes the asteroid to explode and vaporize.
00:53:22Temperatures hotter than the surface of the sun turn trillions of gallons of water into
00:53:27steam.
00:53:29The blast creates a huge short-lived cavity in the water's surface, and a splash curtain,
00:53:36a wall of water that leaps up several miles.
00:53:40This curtain then collapses and water falls back into the cavity, shooting a column of
00:53:45water five miles up.
00:53:49This very tall column can't support its own weight and collapses back down.
00:53:55The collapse of so much water triggers a 1,200-foot-high wave.
00:54:00Could this become a huge tsunami?
00:54:08If we think about a meteor striking the ocean, we want to understand how far the waves might
00:54:13propagate from the site.
00:54:14We could actually just use a stone and throw it into a pond.
00:54:18And you might think, okay, well, it's a big stone, it's going to make a really big splash
00:54:21and that's just going to extend out a long distance.
00:54:24But it turns out the splash stays the biggest, really close to where it impacts, and then
00:54:28the ripples die down after that.
00:54:29So let's try that.
00:54:32Big splash in the middle.
00:54:35And we see the ripples going outward, but they're really pretty small compared with
00:54:38that initial big splash.
00:54:42It's the same with an ocean-impacting asteroid.
00:54:46The impact creates surface waves that die away quickly because only a small amount of
00:54:52the asteroid's kinetic energy gets into the water.
00:54:55It's actually pretty tough to make a tsunami like that.
00:54:58The energy of the asteroid doesn't couple well with the water to drive this wave.
00:55:03Instead, most of the energy goes into vaporizing the asteroid itself, as well as all of the
00:55:09water around it.
00:55:11Only 1% of the asteroid's kinetic energy goes into making a wave.
00:55:17So only low-energy waves form, too weak to become giant tsunamis traveling hundreds of
00:55:23miles.
00:55:25So what caused the jumbled fossil deposits thousands of miles away from the impact site?
00:55:32We don't think there could be that much energy still transmitted that far away from the impact
00:55:36site.
00:55:37Instead, there has to be a different source of energy that created different waves right
00:55:43about the same time as that impact event.
00:55:48Research from 2019 may have the answer.
00:55:51The KPG asteroid struck on the continental shelf, the shallow region between land and
00:55:58deep ocean.
00:55:59The impact triggered a localized tsunami, large enough to kill creatures in the region.
00:56:06But it also sent a huge shockwave into the bedrock.
00:56:10There's going to be a shockwave driven through the ground.
00:56:13That probably would have killed anything in the area.
00:56:16If you had a dinosaur that was standing on the Gulf Coast of what is now the United States,
00:56:25that animal would have experienced a seismic pulse, an earthquake, that is stronger than
00:56:33anything on our current Richter scale.
00:56:35It would have actually driven its legs up into its body cavity, killing it instantly.
00:56:40There's all manner of mayhem and death taking place at this time.
00:56:44There was no escape in this event.
00:56:49The initial shockwave would have traveled through the Earth's crust.
00:56:55The impact would have shaken the crust of the Earth, which also would have triggered
00:57:00earthquakes around the world, which themselves may have triggered secondary tsunamis.
00:57:09Secondary tsunamis, thousands of miles from the impact site, killed both land and sea
00:57:14creatures.
00:57:16The KPG impact went on to wipe out 70% of all life on Earth.
00:57:29How could one space rock hitting the sea cause a global catastrophe?
00:57:36When you have a big rock hitting the ocean, the biggest danger is not from the waves,
00:57:41but actually from the steam that it creates.
00:57:44The impact vaporized trillions of tons of seawater.
00:57:49This steam rose up into the atmosphere, where it condensed into water vapor.
00:57:56Water vapor is a greenhouse gas, so that's then going up into the upper atmosphere and
00:58:02It's trapping heat, but at different layers it's making clouds.
00:58:06It's just throwing everything off kilter.
00:58:09Water is a very effective greenhouse gas, as you will actually affect some very significant
00:58:14climate change very quickly as a result of that impact.
00:58:19Within weeks of the asteroid strike, water vapor in the atmosphere caused temperatures
00:58:24to rise.
00:58:27But that was only the start.
00:58:30The impact also blew out 10 trillion tons of rock, ash, and dust.
00:58:38This asteroid is so big, six miles wide, it's punched a hole in the air.
00:58:43There's like a column of low density, a chimney, that goes from the ground up to the top of
00:58:48the atmosphere.
00:58:49And that means there's very little air resistance in that tunnel.
00:58:53These rocks can actually blast up into the chimney and find it easier to get up out of
00:58:58the atmosphere.
00:58:59It sent that material flying up halfway to the orbit of the moon, circled around the
00:59:05earth, all this ring of material falling back onto the earth, and it was like the sky itself
00:59:11was on fire.
00:59:12So you not only do you have rocks falling on you, but they're molten.
00:59:16And these rocks will start catching plants and anything else on fire.
00:59:27Soot and ash rose up into the atmosphere, blocking the sun.
00:59:36Material was thrown into the atmosphere, plunging the planet into a nuclear winter.
00:59:40It was complete chaos, and it went dark for two full years.
00:59:47Without sunlight, temperatures seesawed.
00:59:51Just months after the impact, the planet cooled by 20 degrees.
00:59:57In the immediate area, there's just tremendous destruction, just everything gets destroyed.
01:00:02But over the long term, you're talking about ash kicked up in the atmosphere, extremely
01:00:06cold weather, basically a global ice age.
01:00:12The freezing temperatures killed off most plant life.
01:00:16Imagine how that affected life on earth.
01:00:18No plants, and the base of the ecosystem collapses.
01:00:25This dark nuclear winter lasted two years and prevented plants from photosynthesizing.
01:00:34So if plants can no longer use photosynthesis to live, they'll die.
01:00:38And then with no plants, then you have no food for these larger animals.
01:00:42And so anything that eats those animals will also die.
01:00:45If you lose your plants, you're going to lose your large-scale life.
01:00:49First, plant-eating herbivores died off, then meat-eating carnivores.
01:00:57Most of the dinosaurs were just unable to find food and to survive through the cold,
01:01:03long night.
01:01:05The global devastation wasn't over yet.
01:01:09The rock of the continental shelf, where the asteroid hit, contained carbon and sulfur.
01:01:16These carbonate rocks were heated and vaporized and released carbon dioxide into the atmosphere,
01:01:22yet another greenhouse gas.
01:01:25So you're vaporizing a lot of sulfur, a lot of salts of different kinds that are then
01:01:31lofted up into the upper atmosphere that then plays havoc on the climate.
01:01:41These greenhouse gases built up in the atmosphere, forming a warming blanket.
01:01:50These gases triggered the next phase of destruction, global warming on steroids.
01:02:01Temperatures rose 10 degrees above normal.
01:02:06Then the oceans warmed as well.
01:02:09Oxygen levels dropped, and the seas became toxic to simple life forms.
01:02:17It actually made it impossible for certain microbes to actually live, and they're the
01:02:21basis of the food system.
01:02:23So really it changed what could actually live in the ocean and how much could live there.
01:02:30Dead zones appeared in the oceans, just as they had on land.
01:02:36Nearly three-quarters of life on Earth died.
01:02:42All from one asteroid impact.
01:02:49To prevent it from happening again, we need to track all potentially dangerous asteroids.
01:02:55But that's not easy, because these floating space rocks can change direction.
01:03:09In Saracic, Turkey, security cameras record a flash in the sky.
01:03:17The flash was from a three-foot asteroid exploding in the atmosphere.
01:03:28It blew up in the atmosphere and rained down.
01:03:31And people saw that.
01:03:32It was very noticeable.
01:03:34And they went and they collected those meteorites.
01:03:36And then they tried to figure out what they were looking at.
01:03:42The debris was sent for fragment analysis.
01:03:47I have a piece of one here.
01:03:49So first, on the outside, you can see it has a really black fusion crust.
01:03:53This is from when it fell into the Earth's atmosphere, so it was melted.
01:03:56But when you look on the inside, it reveals this beautiful, very light-toned, fine-grained
01:04:02material.
01:04:03And so these meteorites are incredibly distinctive and really beautiful.
01:04:07The meteorites are rocky.
01:04:10Their beautiful color comes from a mineral called howardite.
01:04:15It's rare, and it doesn't form on Earth.
01:04:19Howardite meteorites come from the asteroid Vesta, and we know that because of the Dawn
01:04:24mission that actually went to Vesta and took a look at it very carefully.
01:04:27So we know the composition very well.
01:04:30So now suddenly, here was a new kind of meteorite that's in Turkey that matches the Vesta family
01:04:36of meteorites.
01:04:41But how can we be sure that these bits of space rock come from Vesta?
01:04:48It was a fall meteorite, and so what that means is that someone saw it.
01:04:52You know, we saw it fall, and so we knew its trajectory, so we could actually work backwards
01:04:57to say, where did that meteorite come from?
01:05:01Tracing the trajectory of the Turkish meteorite's back took the scientists all the way to the
01:05:07328-mile-wide Vesta.
01:05:13When they studied Vesta's surface, they found further evidence.
01:05:19On the surface of Vesta, there's actually a very large and fresh impact crater that
01:05:23is around the same age of the Turkish meteorite.
01:05:27So that really clinched it.
01:05:29This thing is definitely from Vesta, and we proved it.
01:05:33So how did bits of Vesta end up here on Earth?
01:05:37Twenty-two million years ago, some very large impactor struck Vesta and made a huge crater,
01:05:44and some of the rocks from that crater actually escaped from Vesta's gravity and were lofted
01:05:50into space.
01:05:54Some of these rocks from Vesta went into orbits that intersected with Earth.
01:05:59Twenty-two million years later, one blew up over Serochicek.
01:06:05The Serochicek meteor shows that the asteroid belt is an unstable environment.
01:06:14Asteroids frequently strike other asteroids.
01:06:20That's actually happening all the time.
01:06:22Things are running into each other in our solar system right now, and so that makes
01:06:25it really hard for us to track all of those objects because we don't actually know what
01:06:30happens after they collide with each other.
01:06:32Now things are totally different, and that changes the whole system.
01:06:37Each collision makes more asteroids.
01:06:41There's many different possibilities of what could happen when asteroids collide.
01:06:46Imagine a roller derby situation.
01:06:51If you have two groups of players that run into each other, that could be like two asteroids
01:06:55running into each other.
01:06:57And one possible outcome is that one stays intact while the other is completely blown
01:07:03apart.
01:07:07That sends fragments flying all through the main asteroid belt, and then those little
01:07:11asteroid fragments are on their own independent orbits around the sun.
01:07:16A problem with asteroid impacts is that we're always making new asteroids.
01:07:21There are big asteroids out there, and they get hit by other asteroids, and you get shrapnel.
01:07:25And now you've got not one big one and one smaller one.
01:07:28You've got one big one, one smaller one, and millions of little ones.
01:07:32Now most of these aren't very big, but some of them might be bigger and could be potentially
01:07:36hazardous.
01:07:38As the solar system ages, the number of asteroids increases.
01:07:43Each new space rock travels on a new course, which could intersect with Earth.
01:07:50So we're constantly producing new asteroids and big collisions in the main asteroid belt.
01:07:55And these are producing the small asteroids that will eventually drift inward in the solar
01:07:58system.
01:08:01Tracking this constantly evolving population of asteroids gives scientists a huge headache.
01:08:08If they break apart, then that gives you even more pieces of the asteroid to track.
01:08:13It's not a simple thing to track and predict the orbits of asteroids and their movements.
01:08:20Because one tiny little change can have huge dramatic impacts for its possible future.
01:08:30Figuring out exactly where they're going to go and keeping track of how they interact
01:08:33with each other, this is a huge endeavor.
01:08:37The sheer volume of asteroids can affect the behavior of other asteroids as they gravitationally
01:08:43interact.
01:08:45Think about your roller derby player, skating in circles.
01:08:48The path they're going to follow would evolve the more people you plop down on that track.
01:08:53They start interacting with each other and their trajectory will change.
01:08:57The more crowded you make the solar system, the more things there are to change your orbit
01:09:03of your individual asteroid.
01:09:07It's not like air traffic control where there's a known amount of airplanes and they all follow
01:09:12a plan.
01:09:13This situation is further complicated because asteroid orbits can be affected by other more
01:09:20subtle forces.
01:09:23One of these is called the Yarkovsky or the Yorp effect.
01:09:26Honestly, Yorp is more fun to say.
01:09:29The Yorp effect is caused by sunlight hitting an asteroid.
01:09:34Light is made up of photons that are traveling and these photons actually have momentum.
01:09:39So when light shines on something, it actually pushes on it.
01:09:45When sunlight hits an asteroid, the photons give it a tiny push, enough to change the
01:09:52space rock's trajectory.
01:10:05Asteroids can change course, which makes tracking them hard.
01:10:10Comets stay on course, but they are much harder to track.
01:10:17We track asteroids pretty regularly because they hang out in the inner solar system.
01:10:22We can look for any potential dangerous ones.
01:10:25The comets are a completely different story because they come in from random directions
01:10:30at random times.
01:10:32They are completely unpredictable.
01:10:37Which is why we've only detected a fraction of what's out there.
01:10:42There are millions and tens of millions of them.
01:10:45Guess how many we found?
01:10:476,300.
01:10:48That means that we virtually found zero.
01:10:52The low number is because long-period comets spend much of their orbit over 10 billion
01:10:58miles away, where they are invisible.
01:11:03The trouble with long-period comets is, of course, their periods are very long.
01:11:07And so we only see a small part of their arc.
01:11:10They go very distant into the solar system.
01:11:14And so it just makes them difficult to follow when they get a very long way from the sun.
01:11:18We're not able to track their orbits anymore.
01:11:20And so it becomes a little bit more guesswork.
01:11:24We don't see them until they are already in the inner solar system, inside the orbit of
01:11:28Jupiter.
01:11:29We never really know about them until they've already started their passage from really
01:11:37far away and started their dive into the solar system at really high velocity.
01:11:41We really only discover these comets at the very last minute.
01:11:46You could spot an asteroid 10, 15 years in advance.
01:11:49These comets, that's basically impossible.
01:11:52We may have a couple of years warning for them.
01:12:02When we know an asteroid is really heading our way, it's time to fight back.
01:12:08So we've got an asteroid that's headed at us.
01:12:10What do we do?
01:12:11Two main possibilities.
01:12:12We deflect it, we nudge it a little bit so it misses, or we blow it up, we destroy it.
01:12:18Which of those do you want to do?
01:12:20This is something where our science fiction ideas have gotten almost entirely wrong.
01:12:25If you're in a bad movie, a really, really bad movie, you can send astronauts to an asteroid,
01:12:32put a nuclear bomb in it, and blow it up into lots of little bits that then burn up harmlessly
01:12:36in our atmosphere.
01:12:37Yeah, it doesn't work that way.
01:12:40Blowing up an asteroid would make the problem much worse.
01:12:44You're no longer dealing with just one marauding space rock.
01:12:48My issue with this is that you may have turned one problem into 50.
01:12:52Instead of one regular-sized asteroid, now you have a whole bunch of littler ones, and
01:12:57these may still hit the Earth and cause damage.
01:12:58And you know what?
01:12:59That's not much less fun than just having a single big asteroid.
01:13:04Now you've just taken all that devastation and spread it out for everybody to enjoy.
01:13:08The problem with using a nuclear device is that the products that rain down on Earth
01:13:14are now radioactive.
01:13:22If a dangerous asteroid is on its way, blowing up an asteroid would be a last resort.
01:13:29A less risky method is to deflect it off its collision course.
01:13:34A small nudge early enough can change an asteroid's trajectory away from Earth.
01:13:41You don't have to nudge it very much for it to miss, right?
01:13:46So if it's headed straight at it, I just touch it slightly.
01:13:49By the time it gets to Earth, it's way off course.
01:13:55NASA is investigating several techniques to change an asteroid's path, including a nuclear
01:14:01burst.
01:14:03In a nuclear burst, what we do is we don't actually hit it.
01:14:08We come up to it with the device on a spacecraft, and then the device would be detonated a certain
01:14:14height above the surface.
01:14:17That heats up the surface of the asteroid, which vaporizes.
01:14:20You get vaporized rock or metal, which blasts off the surface, and that's how a rocket works.
01:14:25So you blow up a bomb here, and it winds up pushing the asteroid in the other direction.
01:14:31To prevent any potential nuclear fallout, NASA would detonate the bomb a long way from
01:14:37Earth.
01:14:39Any deflection attempt has to be done years in advance, which means it would be done on
01:14:44the other side of the solar system from us, on the opposite side of the object's orbit.
01:14:49That means that all of the vapor made during the explosion gets blown away by the solar
01:14:54wind.
01:14:55NASA is also investigating other, less explosive methods of deflecting an asteroid.
01:15:02DSTAR would blast the asteroid with a laser.
01:15:06We hit it with the laser, material vaporizes and flies off the asteroid, and because of
01:15:11Newton's third law, which is that for every action there's an opposite and equal reaction,
01:15:16this means that vaporized material moving off in one direction moves the asteroid in
01:15:21the opposite direction.
01:15:25Both the laser and nuclear burst are still just ideas on the drawing board.
01:15:32But one asteroid deflection mission, called Double Asteroid Redirection Test, or DART
01:15:37for short, is already up and running, and scheduled for launch in 2021.
01:15:45DART is a kinetic impactor, and will try to knock the asteroid off course.
01:15:52At NASA, for the longest time, all we've been able to do is theorize about how we change
01:15:56their path.
01:15:57But now, for the first time, we're actually going to practice it.
01:16:01Leading this groundbreaking mission to bump an asteroid off its course is Dr. Andy Chang.
01:16:08DART is the first planetary defense mission that we've ever done, where we take a spacecraft,
01:16:13we fly the spacecraft into the asteroid to change its course and make it miss the Earth.
01:16:21DART's target is a 525-foot space rock orbiting the large near-Earth asteroid Didymos.
01:16:29We picked the near-Earth asteroid Didymos as a target for the DART mission because it's,
01:16:32although it's a near-Earth asteroid, it's one that's very safely parked away out there
01:16:36in space.
01:16:37There's no way we can move Didymos or its moon in any way big enough to cause a problem
01:16:40for the Earth.
01:16:49The Didymoon asteroid is moving at over 36,000 miles an hour and is over 4 million miles
01:16:56away.
01:16:57So how do you move a 10.5 billion pound space rock?
01:17:02You need to hit it really hard to change its orbit.
01:17:07So it's going to be coming in at a super high velocity in order to impart a bunch of energy
01:17:12and momentum to that moon.
01:17:16DART will hit the target at around 14,000 miles an hour.
01:17:20The speed of the DART impact will be more than nine times the speed of the rifle bullet
01:17:26from AK-47.
01:17:30The impact will give the asteroid a small push.
01:17:34To work out how big a push, we test impacts with the Ames Vertical Gun.
01:17:40At the NASA Ames Research Center in California, there's a very special facility called the
01:17:44Ames Vertical Gun Range.
01:17:47It's a hyper-velocity gas gun that allows us to shoot little metal BBs at rock targets
01:17:52at speeds up to like 13,000, 14,000 miles per hour.
01:17:56The gun replicates the impact the DART mission will make.
01:18:00It reveals that an impact will blow off a small amount of debris, but at an extremely
01:18:06high speed, enough to give the asteroid an additional kick.
01:18:11The impact will blow off pieces of the asteroid.
01:18:14The pieces are thrown off the back, and so that process acts like a little rocket engine.
01:18:20That provides an additional momentum change, momentum push to the target itself.
01:18:26The combined push from the kinetic impactor and the ejected debris is tiny, around 9-10-thousandths
01:18:32of a mile per hour, but hopefully it's enough to change the asteroid's orbit.
01:18:39If DART works, we could then use a similar mission to defend Earth when the time comes.
01:18:46This isn't some small rock prototype that we're doing this test on.
01:18:49This is a real dress rehearsal for an asteroid that could destroy cities or even maybe send
01:18:56the Earth in chaos.
01:18:58The moon of Didymus is a solid lump of rock.
01:19:01Will a kinetic impactor like DART work with a rubble pile asteroid like Apophis?
01:19:07When you shoot a rubble pile with a projectile, it's a little bit more like trying to punch
01:19:10a sandbag.
01:19:11You get a lot more of the energy absorbed into just moving the sand around inside the
01:19:16bag than ejecting it.
01:19:18And so rubble piles might be a little harder to move by this method.
01:19:23We don't know if we can deflect a rubble pile asteroid like Apophis.
01:19:28They remain a clear and present danger, and something we might not survive.
01:19:41But there may be a space lifeboat.
01:19:50In 2018, scientists re-examined rocks collected by Apollo 14 astronauts from the moon.
01:20:01Buried in the samples was a rock that shouldn't be there.
01:20:07They got something they didn't expect, and that was an Earth rock.
01:20:12They actually picked up a rock from Earth on the moon.
01:20:16They didn't bring it with them.
01:20:18It's very likely that it was something that was lofted up when something hit Earth, threw
01:20:24up a bunch of rocks.
01:20:25Some of those rocks fell onto the moon.
01:20:27And that's a meteorite on the moon, but it's from Earth.
01:20:37Supercomputer simulations of the KPG asteroid strike reveal how the impact had so much energy
01:20:43that it catapulted rocks out of Earth's atmosphere and into space.
01:20:48They were then caught by the moon's gravity and pulled down to the lunar surface.
01:20:55We now know that material ejected into space from asteroid impacts can travel to other
01:21:01planets as well, which would explain the 100 Mars meteorites we've found here on Earth.
01:21:11We think that there was probably the exchange of a huge amount of material between different
01:21:15bodies, Earth to the moon and back again into Mars.
01:21:22With each impact that occurs in our solar system, that ejects all types of material
01:21:26that allows material to swap from planet to planet, moon to planet, moon to moon.
01:21:31And so there's all of this material that eventually travels from place to place.
01:21:37This planetary interchange may give life on Earth a lifeboat, should another giant
01:21:43asteroid hit our planet.
01:21:46If you think about such an impact today, you know, the chances are high that a lot of life
01:21:51will be wiped out.
01:21:53Much of life, probably all of human life.
01:21:56It's certainly possible that a big enough asteroid strike could completely sterilize
01:22:00a planet.
01:22:01Talking about no life whatsoever.
01:22:04Not to put too fine a point on it, but if there's a dinosaur killer asteroid out there
01:22:08and it hits the Earth, the chance of humanity's survival of such a thing as a species, not
01:22:13great.
01:22:20Humans may not survive, but some scientists believe some simple life forms could.
01:22:28If a giant rock hits the Earth and kills almost all life on Earth, there is a slim
01:22:34line of hope.
01:22:37And that's because the dirt, the rocks on Earth are infused with bacterial life, with
01:22:44microscopic life.
01:22:46And in the event of a giant impact, some of these bits of rock will be ejected into space
01:22:52and might float around.
01:22:54After an asteroid impact, whatever ejected into the atmosphere could contain microbial
01:22:59life that, when it falls back down onto the ground, could reseed the life on that planet.
01:23:08Some bacteria can survive the harsh conditions of space.
01:23:13These creatures can cope with an asteroid strike, re-entry, and landing back on Earth's surface.
01:23:30I think in terms of life on planet Earth, I think we've learned that we live on a very
01:23:35resilient planet.
01:23:36And I think life in some form, even if it has to crawl its way back from bacterial stage,
01:23:42I think life on this planet is going to eke through.
01:23:47Life is pretty good at figuring out a way of surviving.
01:23:51We know that life first formed on the Earth well over four billion years ago and has never
01:23:57been wiped out in all of that time.
01:23:59There's always been something after every major mass extinction.
01:24:03So life will continue.
01:24:04It just won't necessarily be us.
01:24:09An asteroid strike on another world may be how life started on Earth in the first place.
01:24:15There's an interesting idea that an asteroid strike on another planet could have actually
01:24:19seeded life on Earth.
01:24:21And the way this works is, you have life that's somehow gotten a foothold on some other planet
01:24:25like Mars.
01:24:26A big asteroid strike hits that planet and knocks a piece of it off, eventually rains
01:24:31down on Earth, carrying with it life.
01:24:36We may owe the existence of life here to asteroid impacts.
01:24:43That's speculative, but it's kind of a cool thought.
01:24:49Life-seeding asteroids may have hit us in the past, and other asteroids will hit us
01:24:55in the future.
01:24:58One of those may be Apophis, arriving in less than half a century.
01:25:05Maybe we will deflect it.
01:25:08Maybe it will miss us all on its own.
01:25:11Either way, we need to keep tabs on it.
01:25:17The best thing we can do as a species, and it's funny because it almost sounds like I'm
01:25:20advocating for more jobs for astronomers, we need to keep looking at the sky.
01:25:25We need to look at the sky longer and deeper with more sensitive instruments and get more
01:25:29of a sense of what out there is around us.
01:25:31That's what our species needs to do to ultimately survive.
01:25:36Because now we have the ability to see these things a little bit better, we have the ability
01:25:40to protect ourselves better.
01:25:41It doesn't have to be a surprise.
01:25:43You know, the first time we see a big impact doesn't have to be as it's bearing down, destroying
01:25:47our planet.
01:25:48We can actually see it before it gets to us and decide what we want to do about it.
01:25:53Earth's history is littered with asteroid strikes.
01:25:57Some wiped out millions of species.
01:26:01Some may have seeded life in the first place.
01:26:05What the future holds in our relationship with these space rocks, no one knows.
01:26:13Even though the chances of something really large hitting the Earth are pretty small,
01:26:18the consequences are dire.
01:26:20It would really destroy our planet, or at least life as we understand it.
01:26:25And so in many ways, asteroids are the greatest threat that we face.
01:26:30Life is fragile, so of course we live in a larger environment where something could
01:26:35come and hit us at any time.
01:26:37That's part of being alive.
01:26:38There's no guarantee tomorrow will happen.
01:26:40But what there is, is a high likelihood that you'll still be safe tomorrow.
01:26:48Impacts from space are rare.
01:26:51But if they do happen, it's a huge deal.
01:26:53So you've got to put those two things together.
01:26:56That means we've got to pay attention.
01:26:59Those impacts have happened many times in the past, and they're going to continue to
01:27:02happen many times in the future.
01:27:04Fortunately, it's not probably in our immediate future.
01:27:08Impacts are rare, but the Earth lives a long time.
01:27:12So you're unlikely to get in a car accident, but if you drive enough, you're going to get
01:27:15in a car accident.
01:27:20Over a century timescale, yes, we should be concerned about these.
01:27:24But over the daily, weekly, monthly, even yearly timescale, I wouldn't sweat it too
01:27:28much.
01:27:29I wouldn't say we should lose sleep over an asteroid or comet striking Earth, but the
01:27:33reality is, it will happen again.
01:27:36So when you think about asteroid strikes, remember this wonderful, dramatic universe
01:27:43you find yourself in.
01:27:44We're here because stars died and exploded.
01:27:47Life on Earth wouldn't be the same if we didn't find ourselves in this dramatic and even dangerous
01:27:52environment in space.
01:27:53But this is who we are.
01:27:55This is nothing new.
01:27:56And this will continue for the future of our planet.