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00:00This video was sponsored by KiwiCo. More about them at the end of the show.
00:15On February 15, 2013, over Chelyabinsk, Russia, an asteroid heavier than the Eiffel Tower slammed into the atmosphere.
00:24And then 30 kilometers above the ground, it exploded.
00:29This violent event was brighter than the sun, but so high up that it was silent for a full 90 seconds after the blast, which only made the devastation worse.
00:42So you see all these videos of people looking, what was that? They see the smoke trail in the sky. Oh, that's amazing.
00:49And then, you know, just when you think nothing's going to happen, the shockwave hits and it blows out the windows.
00:55A thousand people got glass in their face, in their eyes, because they're looking through the windows.
01:00The shockwave damaged thousands of buildings and injured 1,500 people.
01:08What makes the Chelyabinsk incident kind of embarrassing is that the very same day, scientists had predicted that an asteroid would make a close flyby of Earth.
01:19And they were right.
01:2016 hours after Chelyabinsk, a similar sized asteroid, known as Duende, came within 27,000 kilometers of Earth's surface.
01:29That's closer than satellites in geosynchronous orbit.
01:33But while they correctly predicted this close approach, they completely missed the unrelated asteroid that exploded over Russia.
01:41And the truth is, this happens all the time.
01:44We're really not that good at detecting asteroids before they hit us.
01:49Since 1988, over 1,200 asteroids bigger than a meter have collided with the Earth.
01:55And of those, we detected only five before they hit.
02:00Never with more than a day of warning.
02:03With all our technology and all the telescopes across the Earth, not to mention the ones in space, why do we struggle to detect dangerous asteroids before they strike?
02:14What are the chances that a big asteroid will hit, wiping out most, if not all, life on Earth?
02:21And if we saw one coming, what could we do about it?
02:25Asteroids are the leftover debris from when our solar system formed.
02:41Four and a half billion years ago, rocks and dust clumped together into molten protoplanets.
02:49Inside, heavy elements, metals like iron, nickel and iridium, sank into the core, leaving lighter silicate minerals on the surface.
03:00Some of these protoplanets grew into the planets we know today.
03:05But many more collided with each other, breaking into pieces.
03:10These pieces continued orbiting the Sun and smashing into each other and breaking into even smaller fragments.
03:24These became the asteroids.
03:27Which is why some of them are rocky, loose conglomerates of gravel-sized rocks called rubble piles.
03:35And others, from the cores of planetesimals, are mostly metal.
03:40So this is an iron meteorite.
03:45And essentially it's a piece of a core of a small planetary body, like basically a small planet,
03:51that formed four and a half billion years ago, differentiated so the core material fell out.
03:58And then this thing was smashed apart by a collision with another asteroid.
04:03But it's the oldest thing you'll ever see.
04:07Most of the asteroids have stable orbits between Mars and Jupiter, in the main asteroid belt.
04:14But some have made their way closer to Earth.
04:18And these are known as near-Earth objects.
04:21They are of greatest interest to us because of the threat they pose.
04:26In his last book, Stephen Hawking considered an asteroid impact to be the greatest threat to life on Earth.
04:34But finding asteroids is difficult for several reasons.
04:39Most are spotted by ground-based telescopes.
04:42So what you do is you take a sequence of pictures, one, two, three, one, two, three, four,
04:46and you look for essentially a moving dot.
04:49And it's moving because it's orbiting around the sun,
04:52whereas the stuff far away, the stars and galaxies, are not.
04:56But you have to look carefully.
04:58Asteroids are not very big.
05:00They range from meters up to kilometers in size.
05:04And in the vast expanse of space, rocks like that just don't stand out.
05:09And even the small ones can be damaging.
05:12The Chelyabinsk meteor was only around 20 meters in diameter.
05:16Roughly the width of two school buses.
05:19Plus, asteroids are rough and dark.
05:22They only reflect around 15% of the light that hits them.
05:27So our best chance to see them is when they're fully illuminated by the sun.
05:32And that's why over 85% of the near-Earth asteroids we've detected were found in the 45 degrees of sky directly opposite the sun.
05:42This is called the opposition effect.
05:44And it means there are likely more near-Earth and potentially hazardous asteroids that haven't been detected yet.
05:52Any asteroid approaching from the direction of the sun just can't be seen.
05:58This is exactly what happened with Chelyabinsk.
06:01So far, we have detected and catalogued a million asteroids.
06:08The vast majority of which are in the main asteroid belt.
06:12But 24,000 are near-Earth objects.
06:16Ones that we need to keep a particularly close eye on.
06:20Because even once you've detected an asteroid, it's hard to tell if it will hit the Earth.
06:25So if you just discover an object and you only have data from a few days, then you can't really tell where it's going to go because you're trying to take this little arc of motion and predict it far into the future.
06:36So what you need is observations over years and years, but even if you have perfect observations of an asteroid, there's kind of a fundamental limit to how far in the future you can predict.
06:47And that's because of a couple of effects.
06:50But one is that, you know, they're not just orbiting the sun with no other influence.
06:54All of the planets have gravity, and all of the planets are pulling on near-Earth asteroids and can change the orbit significantly.
07:03So there is something called dynamical chaos, which basically means after a certain amount of time, you don't know where the asteroid is going to be.
07:11And in practice, what that means is we can't do any work more than a hundred years in the future.
07:17So the maximum time you can predict with any accuracy at all where a body will be is about a hundred years.
07:24And this is pretty important because we know with certainty, if one does hit, the results will be dramatic.
07:34This is Barringer Crater in Arizona.
07:37It's named after mining engineer Daniel Barringer, who was the first to suggest it was formed by a meteorite impact.
07:44The prevailing view, even up until the 1950s, was that it was created by volcanic activity.
07:50But Barringer was convinced it was the site of an iron meteorite impact.
07:56So in 1903, he staked a mining claim and began drilling for the metallic meteorite, which he believed to be worth more than a billion 1903 dollars.
08:08Yeah, so people are motivated by money, right? So they thought, hey, we can get some iron for free, basically.
08:13So they started to drill in the bottom of the crater and found nothing.
08:17And then they started to do other exploratory drills, and this went on for years and decades.
08:23They started to drill sideways. Somebody said, you know, maybe it came in from an angle, which it did.
08:27And maybe the iron is not under the middle, but maybe it's over there under the wall.
08:32So he was doing drilling. If you go there, you can see the drills now.
08:35He was drilling around the wall. He found nothing.
08:38So what they didn't realize is, when you have an impact at high speed,
08:42it's not like you're throwing a stone into a brick wall, you know, and it makes a hole and sticks in there, or just bounces off.
08:50It's explosive. It's like totally explosive. So the kinetic energy of the projectile comes in maybe 30 kilometers per second.
08:57The kinetic energy of the projectile is big enough to completely vaporize the projectile.
09:02It turns it into a gas. And that gas is super hot and super high pressure.
09:06And it explodes, and it blows out the crater. So the projectile doesn't really exist after the impact.
09:12I mean, little pieces can survive. But this 50-meter body was basically obliterated.
09:18So he was looking for something that did not exist.
09:22He spent 27 years mining the crater, drilling down to a depth of over 400 meters.
09:29But what he was searching for had vaporized on impact 50,000 years earlier.
09:36The 50-meter asteroid, not that much bigger than Chelyabinsk, released the energy equivalent of 10 megatons of TNT.
09:45That's over 600 times the energy of the Hiroshima bomb.
09:50So the thing that most closely resembles a meteorite impact is a very large nuclear explosion.
09:57This is the actual size of the T-Rex skull.
10:10And I thought, this is such a cool thing, I've got to have it.
10:13So I bought the T-Rex.
10:16The dinosaurs were wiped out by a 10-kilometer-sized asteroid that hit about 65 million years ago.
10:23So above a critical size, which is probably a couple of kilometers,
10:28an impactor delivers so much energy that it has a global effect.
10:39So essentially it launches a whole bunch of debris into suborbital trajectories.
10:44So the ejector goes around the Earth, falls back into the Earth all over,
10:49even on the other side of the planet from where the impact occurred.
10:52And what that means is the whole sky lights up with wall-to-wall meteors.
10:59So you can imagine the sky turning from, you know, a nice blue day like today
11:05into essentially a red-hot glow, like being inside a toaster oven.
11:10So the first effect of this impact, apart from the initial blast near where the actual impact occurred,
11:17the first effect is the sky turns into a great source of heat.
11:22And it cooks everything on the ground.
11:24So these guys were basically cooked.
11:26Cooked alive.
11:27Cooked alive as they were walking around.
11:30The only animals that had a chance were the ones living in tunnels under the ground or maybe in the water.
11:37They were able to come back and take over without having to deal with the dinosaurs as a major obstacle.
11:44What are our chances that Earth gets hit by another 10-kilometer or bigger asteroid?
11:51In your lifetime, assume you live to be 100 years old, you have a 10-kilometer impactor like the KT extinction event
11:59every 100 million years or something like that.
12:02So the probability of getting it in one year is 1 in 100 million.
12:06So you have 1 in a million chance of dying from a 10-kilometer impactor.
12:10But because we know that there are no 10-kilometer impactors with a path that intersects the Earth for the next 100 years,
12:19your chance of dying from that is actually zero.
12:22So work done already has reduced that down from 1 in a million to nothing.
12:27So the good news is, there won't be another dinosaur-style extinction event in our lifetimes.
12:33But there are exponentially more asteroids of smaller sizes.
12:38For every 10-kilometer asteroid, there are roughly 1,000 1-kilometer asteroids.
12:44And they're still capable of doing a lot of damage.
12:48One or two kilometers is capable of causing local but massive damage.
12:55So that means, you know, instead of wiping out the entire world,
12:59you would wipe out the equivalent of some European country like France or Germany,
13:05to mention two of my favorites.
13:07So you would obliterate those countries with the impact of a 1- or 2-kilometer-sized body.
13:13Do we know about all the 1- to 2-kilometer bodies that could hit us?
13:18We think that we know 90-something percent, maybe 98 percent of those bodies have been identified,
13:25and we have their orbits, and we can make reasonable predictions for the next 10 years
13:30or something about where they'll be.
13:32And we seem to be okay at the moment.
13:35But, you know, what about the ones that are just a little bit less than a kilometer?
13:39What about the ones that are 800 meters?
13:41That's still pretty savage if it hits.
13:44And this is possibly where the greatest threat of asteroids remains.
13:49A few hundred meters is large enough to obliterate a large city,
13:53but small enough that we haven't detected them all yet.
13:57We're missing a lot of 100-meter-sized projectiles.
14:00And those guys are big enough to cause substantial damage on the Earth, depending on where they hit.
14:06So it could destroy a city?
14:07Yeah, it would knock down the buildings in the city.
14:10It would cause citywide fire.
14:12And if it hit the ground, it would throw up ejecta that would come back down and rain on the ground.
14:19It would be high-speed ejecta that would obliterate a 100-kilometer zone around it.
14:24And this could happen tomorrow?
14:28Well, it could, yeah.
14:31If we saw a big one coming, what's our best bet for, I mean, could we do anything about it?
14:38What would we do about it?
14:39Is there anything we can do to actively...
14:41No.
14:42There's nothing we can do.
14:44I was on a committee that looked at that, okay, like 10 years ago.
14:47What could we do?
14:48One option would be to try to bomb it.
14:51It's a standard thing.
14:52We don't know how that would work out.
14:54Even when you got it there, and even if you could explode it on the surface or in the surface,
14:59it's not clear what you would do.
15:01Because typically what happens is you blow up a body and the fragments move out, they expand out,
15:07but not very quickly, and then gravity pulls them back together again.
15:10So it would reform as a rubble pile if it was not already a rubble pile to begin with,
15:15which it probably would be because of past impacts.
15:18So blowing up a rubble pile is something that we don't really know about.
15:22Another idea is you could attach, you could be all gentle, and attach a rocket to the asteroid
15:27and just try to push it aside.
15:28Let's nudge it aside.
15:29Instead of trying to blow it up, let's just push it gently aside,
15:32so that it deflects it and it doesn't hit the Earth.
15:35The trouble is, when you work out the numbers, none of the rockets that we have can push it around enough.
15:40you would have to keep the rockets attached to the surface, which we don't know how to do.
15:44Remember, it's a rotating body for centuries to have a significant effect on the motion of the asteroid.
15:49So forget bombs, forget attaching rockets.
15:53Ablating the surface, basically you boil the surface with a laser.
15:57We don't have any lasers powerful enough and probably can't make lasers powerful enough.
16:02To do that from the Earth, we would have to take the lasers to the object, which is even more difficult.
16:07The idea that you could wrap an asteroid in cooking foil, aluminum cooking foil is another nice one.
16:12It may be a good one, the best one, but it still doesn't really work because we don't know how to do that.
16:17We don't have a way to launch enough cooking foil to wrap up an asteroid and change its radiative properties,
16:24which would itself move the asteroid around.
16:26So the truth is, to be honest, we do not have a way now to deflect a kilometer-sized asteroid at all.
16:35That could destroy a country?
16:37Yeah, we just don't have a way.
16:38And 10 kilometers?
16:3910 kilometers is absolutely a thousand times more hopeless.
16:43So when we discussed this, you know, we had all these grand ideas, we could do this and this, and none of them worked.
16:50We came down to the most basic idea, well, maybe if we could figure out where the asteroid is going to hit,
16:54like which city is it going to explode over, we could evacuate that city.
16:59And then we looked at the history of city evacuations, and we looked at cases, you know, where, for example,
17:05you have like a week's warning where some hurricane system is going to come in and flood a city,
17:11and evacuation just doesn't work either.
17:14And the reason is very, very simple.
17:16Like going into a city, there are not that many freeways.
17:19If you have millions of people trying to get on a freeway, the first time a car breaks down, you block that freeway.
17:26So instantly you have millions of people trying to get out of the target zone,
17:30and they won't be able to because all of the roads will be instantly blocked.
17:35So, again, even that, even evacuation of a city is probably the most hopeful thing that we could try to do.
17:42Even that's really, really difficult because of the large numbers of people involved.
17:47What I think all reasonable people would conclude is, let's do the thing that we can do first.
17:54So let's look for them. Let's do the surveys. Let's build the telescopes. Let's put this telescope in space.
17:59That will be a major contribution to understanding the threat from the asteroids.
18:04And then, when we find a particular object that looks especially dangerous, then we can focus on it.
18:11We can focus everything we have on it, and we can begin to think seriously and with real motivation about ways to deflect it.
18:20Now, if you're concerned about the world ending in an asteroid impact, let me set your mind at ease.
18:27There are many other potential global catastrophes summarized in this map of doom made by my friend Dom over at Domain of Science.
18:36So, if you want to see which of these horrible scenarios is likeliest to be our downfall, well go check out the video on his channel.
18:47My oldest now knows how to do the sponsor message. Do you want to say it? This episode...
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