How the Universe Works - S06E09 - War on Asteroids
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00:00We've seen the film.
00:06A huge asteroid heads towards Earth.
00:10It plunges through the atmosphere and slams into our planet's surface, sending up a huge
00:15fireball and a deadly shockwave.
00:21Humanity dies screaming.
00:26But this is not one of those films.
00:31This is how we and the Earth can fight back.
00:37Putting the apocalypse on hold.
00:56Planet Earth.
01:03A cradle of life floating peacefully through space.
01:09Or is it?
01:11Our planet can be one of the most hostile places in the universe.
01:18Think about what natural disasters befall humanity.
01:21Earthquakes, hurricanes, tornadoes, all of these sorts of things.
01:26We can't do anything about those.
01:27But an asteroid, hey, this is a huge natural disaster that we can actually prevent.
01:35When people hear the word asteroid, the first thing that comes to mind are these sci-fi
01:38movies of these very dangerous asteroids coming to hit us, the story of how the dinosaurs
01:43became extinct.
01:44Yes, there are some asteroids out there that are dangerous.
01:48When it comes to finding asteroids and defending the Earth, scientists are very solidly the
01:53heroes.
01:56Across the world, teams of planetary protectors are working out ways to halt an apocalypse.
02:04They're scanning the skies, doing the calculations, designing the technology, and making the plans
02:16that could ensure planetary extinctions from space are nothing more than science fiction.
02:23If you're facing an opponent, you need to know a lot about them in order to defeat them.
02:31Their size, their strength, what they're made of, how they move.
02:34Well, we need to know the same things about these asteroids, because we want to knock
02:38them out.
02:45Nancy Plesko from Los Alamos National Laboratory is in Arizona.
02:53Around 50,000 years ago, this was the site of an impact that left a crater over 170 metres
03:00deep.
03:06This is Meteor Crater.
03:12This is awe-inspiring, to stand on the rim of a crater like this and see the scale of
03:20something this large and feeling this small, understanding just how much energy it must
03:29have taken to excavate this much rock.
03:36The meteor that carved out the crater landed with the power of a hydrogen bomb.
03:48Yet it was just 40 metres across.
03:53Meteor Crater is helping us understand how speed can turn a small projectile into a killer.
04:01An asteroid came in at about 27,000 miles an hour.
04:08That is ten times faster than the muzzle velocity of a bullet coming out of a rifle.
04:15It comes slamming into the surface and just explodes.
04:20And that explosion then opens up the crater.
04:28The force of the impact turned the surrounding solid rock to dust and sent an immense shock
04:35wave barrelling outwards.
04:38It's pretty windy here today, but that's nothing like it would have been in the shock wave
04:42from an impact.
04:43Anywhere nearby here would have seen winds of thousands of miles an hour as the shock
04:48wave came out.
04:54Scientists calculate there's a 20% chance of a similar strike on Earth every century.
05:01If an asteroid like this struck today, it could destroy a city.
05:08But Cathy's research is helping build up our defences.
05:14So we think that there's a variety of ways that we might prevent an asteroid from hitting
05:17the Earth.
05:19My colleagues and I at Los Alamos and at Livermore and at other places can use computer models
05:24on supercomputers to do very careful, high fidelity simulations to tell us what's a good
05:30idea, maybe what's not a good idea, and then be able to present to policy makers, OK, here's
05:36what we can do in comparison to what Bruce Willis could do.
05:45The most potent weapon that planetary protectors can currently utilise is a nuclear bomb.
05:53However, using one to blow up an asteroid has its drawbacks.
05:59It risks showering the Earth with hundreds of smaller meteors.
06:03But Cathy's team is working on plans that would avoid this risk.
06:09They'd use a nuclear weapon to deflect an asteroid instead.
06:15So one of the things I do study is nuclear deflection.
06:19In some cases, and in the near term future, there could be a scenario where we might need
06:25to shove something fairly large out of the way.
06:29And those sorts of things, if they're large enough, we might need to use a nuclear device
06:35to do that.
06:36We might launch a nuclear device, detonate it above the surface of the object, changing
06:42its velocity a little bit.
06:46Launching a nuclear device near an asteroid vaporises part of its surface, pushing the
06:52asteroid off course.
06:57But firing nuclear weapons into space is no-one's first option of choice.
07:04So there are some pros and cons to using nuclear deflection.
07:06There are some situations where it is definitely an appropriate technology, where it may be
07:11the only option at the time.
07:14We hope in the future that we'll have other methods at our disposal that are not as challenging
07:22diplomatically or politically.
07:27And scientists are currently on the hunt to find a way to deflect an asteroid without
07:32using nuclear weapons.
07:37We're discovering more and more about the asteroids.
07:39We're understanding them.
07:40And we're realising that there really are ways we can mitigate the destructive effects
07:44of an impact on Earth.
07:47This could be the most important scientific endeavour humanity has ever undertaken.
07:53And the best way to cancel the asteroid apocalypse could be to destroy them before they even
08:00become a threat.
08:17Our solar system is a dangerous place.
08:22Fast-moving asteroids hurtle through space.
08:29And many of these rocks are headed our way.
08:35To counter the asteroid threat, scientists are drawing up battle plans.
08:45The very first step in understanding this hazard and in preventing this hazard is to
08:50find them.
08:52Not just the big ones that can end our civilisation, but even the small ones that can devastate
08:55your city.
08:58However, just finding these asteroids won't be enough.
09:04We need to find them early in order to have time to deflect them.
09:10The problem is that asteroids are smaller and darker than things such as planets.
09:15And in the vast darkness of space, that makes them much harder to find.
09:22Astronomers are pretty good at playing hide-and-seek in their own way.
09:26Imagine you're flying over the Sahara and you're looking for a pebble that's the same
09:30colour as the desert.
09:31That's what looking for asteroids is like in the solar system.
09:37Astronomers believe there are more than a million asteroids a kilometre wide within
09:40our solar system.
09:43And that there could be millions or even billions more that are smaller.
09:49There's an uncountably large amount of asteroids in our solar system.
09:53We're constantly looking and it's hard to find them all because they're tiny dots in
09:58a very dark background of space.
10:08High in the mountains at the Catalina Sky Survey in Arizona, asteroid hunter Greg Leonard
10:14is leading the search.
10:17They are the eyes for the world on this night at this telescope on the summit of this mountain.
10:26By comparing four images of the same patch of sky taken over a 20-minute period, Greg
10:32can hunt for elusive asteroids hidden among the stars.
10:38That's because in these images the stars don't move, but the asteroids do.
10:45If it's a really bright asteroid, we will see some bright points of light tracking across
10:51the four images.
10:59You have to kiss a lot of frogs before you get a prince or a princess and this is the
11:02case tonight as it is almost every night.
11:06Ah, here we go.
11:10This is a real object.
11:12You can see it's moving across the sky here from the lower right to the upper left.
11:17We are very, very excited to have discovered one tonight because this is an object that's
11:22approaching nearer space, likely in the neighbourhood of Earth.
11:30Greg's research revealed this 30-metre asteroid could get as close as 1.01 million kilometres
11:35to Earth.
11:38That's less than three times the distance to the Moon.
11:43Yet in the future, this asteroid's orbit could move closer to Earth and even onto a collision
11:49course.
11:52If that happens, we need to be prepared.
11:57And the earlier we spot it, the better our chance of altering its course.
12:03Space is so big and the Earth is so small and the asteroid would be starting from so
12:07far away that if you just deflected it a little bit, gave it a little nudge, a tiny
12:11course correction, by the time it got to where the Earth's region is, it would miss us completely.
12:19To do that, we need to move asteroids off their trajectory.
12:27Think of a golf swing.
12:30Hook or fade the ball by just one degree off the tee and you'll miss the green completely.
12:38Now scale that up to asteroids.
12:42Over time, these space rocks can leave their home in the asteroid belt, becoming threatening
12:48near-Earth objects 50 million kilometres away that could one day hit our planet.
12:55But if planetary protectors can change the course of a dangerous object by just a tenth
12:59of a degree, it would miss the Earth completely.
13:05And scientists have developed a very direct way to do it.
13:12In a football game, if somebody on the defence is seeing the quarterback running into the
13:16end zone, what do they do?
13:17Boom, hit him, knock him out of bounds, knock him down, do something like that.
13:22That's what we want to do with asteroids.
13:25So if we send something moving towards an asteroid very quickly to hit it, we call that
13:29a kinetic impactor, slams into it really hard, changes not just the velocity of the asteroid
13:34but also its trajectory.
13:42Scientists have already intercepted asteroid-like objects in space.
13:50In 2005, the Deep Impact spacecraft arrived at Temple 1, a 14 by 4 kilometre comet.
14:02This spacecraft shot a little probe at the comet, which slammed into Temple 1, kicking
14:12up material from the surface.
14:18Research is continuing into kinetic impactors.
14:21In 2022, a spacecraft called DART will slam into an asteroid at over 21,000 kilometres
14:30per hour.
14:34That transfer of momentum would change the velocity of the asteroid just a little bit,
14:40maybe a fraction of a mile per hour, but over maybe a decade.
14:46That change in velocity, even though it's very tiny, would add up to a change in position
14:51big enough to completely miss the Earth.
14:59Knocking a giant space rock off course might sound unusual.
15:06But astronomers have discovered that in space, it's occurred a lot.
15:13When you have a lot of traffic driving down the highway and a lot of lane changing going
15:16on, sooner or later there's going to be a fender bender, and that happens in our solar
15:20system as well.
15:21It's a busy place out there in the asteroid belt.
15:25Asteroids will run into each other at many miles per second relative speeds.
15:30And when that happens, the sparks fly.
15:36If you started with two asteroids and they collided, suddenly you'd have ten asteroids.
15:42Those ten asteroids are now going to collide again, and now you have a hundred asteroids.
15:47Those asteroids will collide, and now you have a thousand, a million, a billion possible
15:51impactors for the Earth.
15:54But this isn't just a numbers game.
15:57Even though any one of the millions of asteroids could result in a major impact, they're not
16:05identical.
16:08This means each one presents a different type of threat.
16:13Its speed, size, and distance from the Earth help dictate the degree of danger.
16:20The more we can really understand about an asteroid, the better prepared we are to be
16:24able to defend against it.
16:28This is definitely a case of know thy enemy.
16:29You know, we need to know something about the properties of these objects if we have
16:33any hope of moving a threatening one out of our path one day.
16:40But scientists are realizing that an asteroid's composition could be the deadliest factor.
16:50Knowing what asteroids are made of can help us find chinks in their armor.
16:57To do so, Marina Brozovic from the Center for Near-Earth Object Studies uses a technology
17:03developed during World War II, radar.
17:11Planetary radar is really like a big cousin of airport radar, and so the same way like
17:16the airport radar is tracking the airplanes, we are tracking asteroids that are, you know,
17:21hundreds of thousands, sometimes even millions of kilometers away.
17:25Another thing that radars do is they tell us about how this asteroid looks like.
17:31You want to know what's their size, what's their shape, what's their chemical composition.
17:37Considering the detail that we see on the surface, short of sending a spacecraft, you
17:40cannot achieve that.
17:42So radar is, in a way, its own little space mission.
17:47Radar shows that asteroids can be made of rock, metal, and a combination of the two.
17:57And this is crucial information for calculating how to deal with them.
18:04So metallic asteroids are far more dense than a normal rocky asteroid.
18:09So an impact from a big iron asteroid could have much more energy for the same size asteroid
18:15that was just rocky.
18:18Just as a metal cannonball would do more damage than a similar sized rock, metallic asteroids
18:24could be far more deadly than rocky asteroids.
18:30But scientists have now discovered that most asteroids are less like cannonballs and more
18:35like vast cosmic shotgun shells.
18:40Most of the asteroids, they're not single object, they're not monolithic, but instead
18:43they're rubble piles.
18:45So they consist of many smaller rocks and pebbles and grains and pieces of sand.
18:51And all this is held very loosely with gravity.
18:55Rubble pile asteroids, such as the peanut-shaped Itokawa, probably formed from violent collisions
19:02between asteroids.
19:05Initially, the rocky debris from these collisions scattered like shrapnel.
19:13Then gravity pulled some of the rocks loosely back together again.
19:19This loose pile of rocks can actually reshape, shed mass, build satellites, and form these
19:25interesting shapes that we see among a lot of these asteroids.
19:31They may sound odd, but these loosely bound space rocks form a crucial part of our research.
19:42So what we've learned about the asteroid population is that once you move in size to
19:46asteroids that are maybe 10 miles across, we think that almost all of those asteroids
19:51are actually re-accumulated debris from huge collisions early in the history of the asteroid
19:57belt.
20:00The structure of rubble pile asteroids presents a major challenge to our planetary protectors.
20:08How can they safeguard us from a pile of rubble?
20:13If the object is a solid mass of metal, it's going to respond to an impact or an explosion
20:18in a far different way than if it's just a loosely bound rubble pile barely held together
20:23by its own gravity.
20:24They're very, very delicate objects.
20:27And so those objects need some special consideration.
20:31We can't just go slamming into them necessarily.
20:37Smashing into a rubble pile asteroid would be like kicking a pile of sand.
20:43Thousands of smaller rocks would go hurtling out in every direction.
20:48They'd be undetectable, unpredictable, and could continue to head our way.
20:56But we have a plan.
20:59Instead of using violent force, we could use the gentle tug of gravity.
21:09So instead of this ham-fisted approach of whacking it and then just walking away, we
21:12need something more careful, something more precise.
21:16And that's where the gravity tractor comes in.
21:23Rubble piles of rock may be small, but it has gravity.
21:27If we send up a probe that has the mass of, say, a ton, it has gravity too.
21:31Now, not much, but it's there.
21:34And if you put it near the asteroid, you can actually use the mutual gravity, the attraction
21:39between them, to tug the asteroid into a safe orbit.
21:45All you have to do is park a spacecraft next to the asteroid, hover it there, don't let
21:50the gravity of the asteroid and the spacecraft pull each other together, and let the gravity
21:54of the spacecraft act as a tow line to pull the asteroid out of the way.
22:02This sounds like science fiction, but it turns out the physics of this is relatively simple,
22:07and we can do it.
22:13But gravity tractors will only work if we can accurately track the movements of these
22:17asteroids.
22:21The problem is, there's a massive, complicating factor at the centre of our solar system.
22:29The sun.
22:50Astronomical planetary protectors want to stop an apocalypse.
22:57Their mission is to protect the Earth from these seemingly inevitable asteroid impacts.
23:05But to do that, they need to predict their every move.
23:10And in a constantly changing solar system, that's not easy.
23:16We measure their orbits and we can draw maps of all their orbits as we see them today,
23:22but we know that it's not a static population, that it's dynamic.
23:26Things are constantly evolving in the asteroid belt.
23:30It's not just about size with asteroids.
23:33You have to understand the density, the orbit, the speed, in order to really tackle it.
23:41Collisions can set asteroid debris off on new orbits.
23:45However, there's another influencing factor at play.
23:50The immense gravity of the gas giant, Jupiter.
23:55Jupiter is the most massive planet in the solar system, and it's sitting outside the
23:58asteroid belt.
23:59Its gravity can tweak and tug these asteroids and make their orbits more elliptical, sending
24:04them in towards the sun, crossing Earth's orbit.
24:10Tackling Jupiter's effect on millions of asteroids is hard enough.
24:17Then add the influence of some of the asteroid belt's largest objects, 530-kilometre-wide
24:23rocks such as Vesta and Pallas.
24:28A tricky task becomes near impossible.
24:36But gravity isn't the only force creating orbital chaos.
24:45This is the asteroid Bennu.
24:48There's one chance in 2,700 it'll hit the Earth.
24:53But Bennu's orbit keeps changing.
24:57In the last 18 years, it's shifted over 160 kilometres off course, and the culprit
25:05could be the sun.
25:09So what can change the orbit of an asteroid?
25:11It's easy to think of these large rocks passing by each other, tugging on each other gravitationally.
25:16But could the most dramatic changes be due to something as gentle as sunlight?
25:21It might feel very subtle, but the sunlight on our bodies exerts a subtle pressure.
25:26The fact that you're hotter on one side than on the other side actually exerts a kind of
25:32a thrust that can move you around.
25:36Sunlight is made up of tiny packets of energy called photons.
25:41When photons hit an asteroid, they pass on a tiny amount of momentum and a tiny amount
25:47of heat.
25:50Let's actually, you know, let's imagine this situation.
25:52Here's our asteroid.
25:53You know, in reality, this might be, you know, 10 miles across or a mile across, something
25:57like that.
25:58Here's our asteroid.
25:59Here's the sun.
26:00This asteroid is orbiting the sun this way.
26:03This face of the asteroid is being warmed by the heat from the sun.
26:07Out here on the backside, facing the cold vacuum of space, it's a lot colder.
26:11In fact, I can even feel it already with my hands.
26:15The warm side that's being illuminated by sunshine actually re-radiates that heat in
26:20the infrared portion of the spectrum.
26:22All of that infrared radiation off the side of the asteroid acts like a little rocket
26:26motor in a way.
26:27It actually pushes on the asteroid.
26:32This is known as the Yarkovsky effect.
26:36It's a slow process.
26:39The asteroid is pushed by a force equal to the weight of a few grapes on Earth.
26:46But as Bennu circles the sun, it heats up on one side, which moves it into a different
26:52orbit.
26:58The Yarkovsky effect is actually a bit of a problem.
27:00If there were just gravity acting on these asteroids, then we could predict where all
27:04the asteroids and planets will be, and we'd be able to figure out the trajectory of these
27:08asteroids many years in the future.
27:10But with the Yarkovsky effect, that actually changes it in ways that are difficult to predict
27:15because it depends on how dark the asteroid is, whether it's spinning, what shape it is.
27:20And so it makes the orbit of the asteroid much, much more difficult to predict a long
27:24time into the future.
27:29The Yarkovsky effect makes predicting the movement of asteroids such as Bennu even harder.
27:35But our planetary protectors are ingenious, and they're attempting to use the Yarkovsky
27:41effect to create a new weapon for their armory.
27:46So the Yarkovsky effect we know can change asteroids' orbits pretty dramatically.
27:52It's an effect that we could use to move asteroids ourselves.
27:56If we could change the way the asteroid is heated by the sun, by changing its color or
28:02changing its shape so that it gets heated in a very specific way, we could change its
28:06orbit that way.
28:10If scientists could send a satellite to an asteroid, it could use black or white paint
28:16to increase or decrease the heating effect.
28:21But at the University of Southern California, a team of scientists are working on a higher
28:25tech solution.
28:29They're trying to better the Yarkovsky effect using a space-based laser called DSTAR.
28:36Let's say we see an asteroid that's on its way towards the Earth.
28:40We can use space lasers to zap the asteroid.
28:43You vaporize the surface material.
28:45That turns it into a gas which expands very quickly, and that acts like a rocket.
28:50And so you can use that to push the asteroid into a safer path as well.
28:58Space lasers are another powerful weapon for our planetary protectors' fight against asteroids.
29:05They join gravity tractors, kinetic impactors, and nuclear weapons in the armory.
29:16But there is one very big problem.
29:20All of the methods of defending against asteroids that we've mentioned are technologically possible.
29:25The thing that's a little bit nerve-wracking is that none of them are actually ready to
29:28go right now.
29:32So it's not time to cancel the apocalypse yet.
29:35We've made a lot of progress, especially in the last few years, but we're not really
29:38there yet.
29:39But we could get to that point within the next maybe 10 or 15 years.
29:46But don't panic just yet.
29:50It transpires that the Earth has its own defense system that can burn up asteroids before they
29:57ever hit the ground.
30:04Arizona, June the 2nd, 2016.
30:09A one-and-a-half-meter-wide rock hurtled towards the Earth.
30:15It was moving at over 60,000 kilometers per hour.
30:19And as it streaked overhead, it lit up the sky.
30:27In the very early morning hours, an asteroid came screaming into the Earth's atmosphere
30:32far faster than a rifle bullet.
30:34There was a fireball that lit up the red rocks all around us at night.
30:39It was bright enough to burn out cameras on the ground from NASA that were watching for
30:42fireballs.
30:45The asteroid was just seconds away from impact, and major damage seemed inevitable.
30:51Dude, did you see that?
30:55But the asteroid never hit the ground.
30:58Why?
31:01We do have a natural barrier against at least small asteroid impacts.
31:06And let me give you a hint about what that is.
31:14The air around us seems too tenuous to actually defend against a threat from space.
31:18But in fact, the atmosphere is sort of the last line of defense against asteroids.
31:25One day, our planetary protectors will be ready to save us from asteroid strikes.
31:31Until then, we have to rely on the Earth's built-in defense system, the atmosphere.
31:40We know for a fact that our atmosphere acts like a shield, because space rocks come to
31:45Earth every day.
31:48Some of them are tiny, some of them are a bit larger, but what's happening is that as
31:51they enter the atmosphere at high speed, the friction burns them up.
31:57Even though the top layers of the atmosphere are very thin, compared to the vacuum of space,
32:03they're extremely dense.
32:07As rocky asteroids hurtle through the atmosphere, friction and air pressure can heat them to
32:12over 1,600 degrees Celsius.
32:18The larger the asteroid, the longer it takes to burn up.
32:22And for these larger rocks, the effects can be dramatic.
32:27If there's a rock that's big enough that it doesn't burn up very quickly, we call that
32:31a bolide.
32:32And as the bolide falls through the atmosphere, it creates a spectacular show called a fireball.
32:40In February 2013, the town of Chelyabinsk in Russia had its own fireball.
32:47An 18-metre wide space rock barrelled through the sky.
32:54This asteroid was bigger than a bus, and it travelled at 18 kilometres per second.
33:02It got super hot, broke up into small pieces.
33:06Those pieces then ran through the atmosphere.
33:09When all of that vast energy of motion of this rock was converted into light and heat,
33:14it exploded.
33:18The Chelyabinsk meteor is the largest natural object seen entering the atmosphere in over
33:23100 years.
33:30It exploded 19 kilometres above the Earth's surface, with the power of 30 nuclear bombs.
33:38The blast caused over 1,500 injuries and damaged 7,000 buildings.
33:47But if it wasn't for the protective shielding of our atmosphere, the results would have
33:51been far worse.
33:56The problem is, the atmosphere can only protect us from rocky and rubble-pile asteroids up
34:01to about 50 metres wide.
34:06There is also something much more dangerous to consider.
34:10The metallic asteroids.
34:13If you had a rocky asteroid hitting, or a rubbly rocky asteroid hitting, it wouldn't
34:18make it to the ground.
34:19An asteroid that's around 100 feet across would actually blow up in the sky.
34:24If a 100-foot metallic asteroid were to hit, first of all, you wouldn't have much warning.
34:30It would hit the top of the atmosphere, and then it would hit the ground about a second
34:34later.
34:35Causing an enormous explosion that would open up a crater that would be about a mile across.
34:42You'd have a flattened ruin of remnants of buildings, millions dead from the shockwave
34:50that would be radiating out.
34:53And a layer of dust falling back down over the next minutes and hours.
35:00A metallic asteroid would punch through the atmosphere, because it's too hard for friction
35:05and air pressure to break it up completely.
35:09So it would slam into the ground in a catastrophic explosion.
35:15Metallic asteroids could be our planetary protector's greatest foe.
35:24But it transpires that the Earth could have another built-in defence.
35:31We know an asteroid punched through the atmosphere and killed off the dinosaurs.
35:37But research is showing our planet could have saved them.
35:42The dinosaurs were incredibly unlucky.
35:44Even if the object does make it past our atmosphere, we still have another line of defence.
35:51It's not always what an asteroid is made of that makes the difference.
35:57Sometimes, it's all about where it hits.
36:00Our planetary protectors are creating technologies to divert a potentially catastrophic asteroid.
36:31But until their armoury is complete, the Earth has its own defensive strategy.
36:40One of the things that is sure is that we will be hit by an asteroid or comet again.
36:45It may not happen for millions of years, but it will happen.
36:48And on that day, the thing that will differentiate between it just being a very bad day and it being a global catastrophe
36:54is location, location, location.
37:00Some regions of the Earth could actually reduce the damage caused by a killer asteroid.
37:06How do we know?
37:09Dinosaurs.
37:1165 million years ago, the dinosaurs had a very bad day.
37:16They had the bad luck to be wiped out by an asteroid impact.
37:24We thought we knew the full story.
37:28But researchers have revealed something astonishing.
37:33If the asteroid had hit the Earth just minutes later, dinosaurs may still be roaming the planet today.
37:43But how?
37:45This object hit right at the Yucatan Peninsula.
37:48It was an incredible tsunami that flooded North America, but it also threw a lot of sulfates into the air.
37:57The 9km wide asteroid landed in shallow seas in what is now the Gulf of Mexico.
38:07It vaporised rocks in the seafloor of the continental shelf.
38:12The impact blasted out trillions of tonnes of gases into the atmosphere,
38:17triggering catastrophic climate change.
38:2170% of all life on Earth became extinct, including the dinosaurs.
38:29The thing that's kind of tragic is that if the Earth had rotated just a little bit more when that impact hit,
38:35it would have been in deeper ocean and there wouldn't have been all that vaporised rock and sulphur.
38:44Our planet spins at 1,600km per hour.
38:4970% of the Earth's surface is covered by ocean.
38:55With a little luck, the dinosaur destroyer could have struck in deeper water.
39:02There's no good place on the Earth to take a 5 mile wide asteroid strike.
39:06There's just no good place.
39:08Some places are worse than others, and the Yucatan Peninsula, with that much sulphur, was one of the worst possible.
39:15So it's just not going to be a good day.
39:21The asteroid that killed the dinosaurs allowed us mammals to take over the Earth.
39:28Fortunately, these giant asteroids only strike once every few million years.
39:36But every 2,000 years or so, a rock about the size of a football field hits Earth.
39:45What would happen if one of these smaller, more common asteroids were to hit the ocean?
39:51If you think of something like the Pacific Ocean, there's a lot of coastline there.
39:54And so you have many, many people that are at risk.
39:57Most of the Earth's surface is ocean.
40:00So it's a much more likely scenario for an asteroid to hit the ocean.
40:04And so the question is, how much of a tsunami risk is there?
40:11Scientists have modelled what would happen if an asteroid strikes different points in the ocean.
40:19It was studied in three dimensions with different types of compositions, different ocean depths, different entry angles.
40:26And found out that the continental shelf actually saves us.
40:34The continental shelf is an underwater landmass that extends around 80 kilometres beyond the coast.
40:43So if an asteroid hundreds of metres across slammed into the deep ocean,
40:48the shallow sea created by the continental shelf could force a tsunami to collapse before it hit land.
40:55It seems the ocean could be a natural protector.
41:00For the deep ocean, we think that asteroids smaller than 400 feet across, which is quite large, are not a tsunami risk.
41:08And so we don't need to worry as much as we thought we did about it.
41:13That shallow part of the water actually buffers any tsunami wave that might be coming in.
41:24Nina Lanza demonstrates.
41:26So let's imagine that this rock here is our asteroid. It's heading for Earth.
41:32It's probably going to hit the ocean.
41:35When it hits, it's going to make a huge, big wave.
41:45But as the wave travels outward, it's going to get smaller and smaller.
41:48And so by the time that wave hit the shore, it was no bigger than these smaller waves lapping at my feet.
41:57If an asteroid were to strike the ocean, it's going to wreak some havoc.
42:01But the tsunami from this type of event is probably not as bad as you might imagine.
42:15So our planet has defence mechanisms.
42:18And our scientists are devising plans aiming to combat the dangerous asteroids.
42:27However, what they need is time.
42:32Astronomy very well can save the world because we're on the lookout for all the asteroids that may someday collide with Earth.
42:39And if we find them, we can avoid a civilization-ending event.
42:44If we have warning time, we then have the advantage of being able to think about the problem, plan for it,
42:50and actually build up the technologies, practice the techniques it's going to take to push that asteroid out of the way.
42:55Time is definitely an ally for us.
42:59We're not ready to cancel the apocalypse just yet.
43:03But with the planetary protection team on the case,
43:07soon we'll have a fighting chance.
43:12If you want to know what an astronomer's sweatiest nightmare is, it's an asteroid impact.
43:18It's kind of personal, right?
43:21This is happening right here on Earth.
43:24It's a challenge to us, and that's why we want to prevent it.
43:29The good news is, we actually are on the cusp of being able to deflect them.
43:34We're almost there, we just have to push it through.
43:40The planet is incredibly resilient.
43:42Even if one specific species or one specific individual is very fragile,
43:46as a whole, the Earth is actually quite tough.
43:51It really comes back to, as human beings, what is our will to discover, to explore and understand the solar system.
43:58It becomes very important when you think about asteroids.
44:01We need to keep scanning the skies.
44:03We need to keep being scientists to defend the Earth.