We love to destroy the universe, and also rebuild it. Today we begin a new series where we destroy and rebuild. Let’s talk about some existential threats we face, and ways we could recover, starting with the sword of Damocles hanging over our head: killer asteroids!
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Pamela: This episode of Astronomy Cast is sponsored by BarkBox. Visit barkbox.com/astro and get a free box with your 6- to 12-month subscription.
Here at Astronomy Cast, we’ve been super-lucky to have sponsors with products we truly love. Each BarkBox comes with four to six different monthly surprises for my dog, Eddie. There are all-natural chews, perfect for an hour-long distraction while we record, and tiny training treats for helping him learn to sit and stay. I can even reorder the things we really like, which means the awesome smelling Booberry treats from Halloween can be purchased again and again.
If you’ve got a dog and you want to spoil them while supporting us, go check out barkbox.com/astro. Your furbuddy will thank you.
Fraser: Astronomy Cast Episode 437: Destroy and Rebuild, Part 1: The Torino Scale
Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know but how we know what we know.
My name is Fraser Cain. I’m the publisher of Universe Today and with me is Dr. Pamela Gay – here we go – the director of Technology and Citizen Science at the Astronomical Society of the Pacific and the director of CosmoQuest.
Hey, Pamela. How are you doin’?
Pamela: I’m doin’ well. How are you doin’, Fraser?
Fraser: Doing great. I still have to read that one very slowly and carefully to get through your new title. Hopefully everyone is caught up to speed now on all the new changes and all the new awesomeness.
Pamela: Yes. And I want to say many thanks to all of you who have donated to us the past two weeks. We’re good to cover our bills this month, which I’m sure Susie and Chad will deeply appreciate. Please keep giving so we can pay them next month too.
We love all of you! You’re fabulous and you keep us going.
Fraser: For those of you who are watching the live stream, you just saw Pamela make a little heart with her hands.
Let’s get on with the show.
So, we love to destroy the universe and also rebuild it. Today we begin a new series where we destroy and rebuild. Let’s talk about some existential threats we face and ways we could recover, starting with the sword of Damocles hanging over our heads: killer asteroids.
I’m going to admit something here, which is that the existential threat of killer asteroids was actually what got me into space journalism in the first place.
Fraser: Yeah, yeah, yeah.
So, what happened was – What was I reading? I was reading Pale Blue Dot, I think, and The Case for Mars back 20 years ago and thinking about the existential threat of asteroids and how, you know, we’ve been hit in the past; it’s just a matter of time before we get hit in the future. And that we need to sort of become a space-faring civilization.
And, as part of that process, I was sort of, like, “Well then, I want to get involved in that” and it’s like, “How am I going to get involved in that? Well, I guess I will use the talents that I have, which is to make things on the internet, and use that to participate in this conversation.”
And it’s been this long, weird ride ever since but here we are, 17 years later – almost 18 years later – still doing the same job. And it’s thanks to my terrified worry about the existential threat of killer asteroids.
Pamela: I can’t judge. I got in because of Battlestar Galactica because, like, characters had names of constellations and I was 6.
Fraser: That’s awesome.
Pamela: Yeah. So, it is an existential crisis that hopefully will drive people to think, to look up, to explore. But, on any one given day, we only have like a 1-in-65-million chance of death by asteroid.
Pamela: So, on any given day, we’re good.
Fraser: Well, the – But it turns out, I’m not the only person on Earth to be concerned about this issue; other people have. In fact, people have been so concerned about it that they created a scale to measure our collective freak-out and how much – You can literally freak out and you’re like, “How worried should I be?” There is a scale. It goes from 0 to 10; feel free to worry that much.
Pamela: And it’s actually very, very similar to the scale used for how much should you worry about a volcano. So, if you know the colors related to one, you probably know the colors related to the other and how much you need to run. And, while there are volcanoes you should run away from, we currently don’t have any asteroids you need to run away from.
Fraser: Right. Okay.
So let’s talk a bit about the scale and devastation that these killer asteroids can provide. And then, sort of talk – And then we’ll talk a bit about, sort of the Torino Scale and how the whole thing was constructed and then how we measure it.
So let’s start with the – Just let’s get a sense of bad days that can be had.
Pamela: So there are actually lots of ways asteroids can destroy our world. And I have to admit, I didn’t fully understand all of the ways by which we could die by asteroid until I went on a dystopian science fiction kick this year. And this got me realizing that there are problems beyond the crater and relating tsunamis that we have to worry about, that aren’t the things they teach you about in your average news article.
So, for instance, if you have a bunch of shrapnel from space – so, say that two asteroids happen to collide in the path of the Earth and the Earth flies through this cloud of shrapnel and there’s a fairly significant differential velocity between shrapnel and Earth – all of that shrapnel is going to enter our atmosphere and have a lot of kinetic energy.
And it could be that all of these bits of former asteroids are small enough that, for the most part, they’re not gonna hit the surface of the planet as anything bigger than maybe rabbit pellets but, as they pass through the atmosphere, they’re going to have all sorts of kinetic energy that they give up to the atmosphere; in the process, heating the atmosphere, which has two bad things.
The lesser bad thing is a hot atmosphere is a bigger atmosphere, which creates greater drag on the things that are in orbit. And if you have things in orbit that can’t get pushed to a bigger orbit, they fall out of orbit – which is bad for the things on orbit.
Fraser: Oh, no! A rain of asteroids hit the Earth and now the Space Station takes more energy to keep it up.
Pamela: Right. But it’s actually way worse for the people below the atmosphere.
Pamela: Because all that –
Fraser: I just like where you started on the scale of consequences of a rain of asteroids hitting the Earth.
Pamela: I just want to make it clear, up front; you’re not safe on the Space Station.
Fraser: Saying, “Budget a little more for station upkeep.” Okay.
Pamela: So, if you’re beneath that asteroid that is currently getting bombarded with shrapnel – and, again, we’re not talking things that are going to create catastrophic craters, we’re talking things that might create rabbit-pellet sized rocks hitting Earth – but there’s a whole lot of mass, with a whole lot of energy, passing through our rotating planet’s atmosphere; giving up its kinetic energy to that atmosphere, where that energy is getting converted to heat.
Now, when you heat up our atmosphere, this is like turning on your oven. Everything gets really hot and if it gets too hot, you die.
Fraser: Okay. Right. A direct impact from a Texas-sized asteroid – of which there’s only one which is Ceres and it’s not going to come anywhere close to us anytime soon but that was an Armageddon reference – but the direct impact from a 1 to 10 kilometer asteroid, that first impact where it smashes into the Earth, is a problem. But the other part of this is that rain that comes back down – the shrapnel goes up into space, rains back down around the Earth, heats up the atmosphere – how bad?
Pamela: So, depending on just how much kinetic energy it has to lose, it could actually kill everything that’s above the surface of the water and the dirt.
One of the interesting articles I read earlier this year – after reading Seveneves and going, “No, that can’t be true!” No, it’s true. One of the interesting articles I read talked about how one of the reasons we probably got so many mammals out of the death of the dinosaurs is, those suckers were smart and they were burrowed under the dirt. And, by being a few centimeters under that insulating soil cover, they didn’t get baked.
Now, even if you don’t die because the atmosphere reached a couple hundred degrees, it’s going to kill a lot of your food sources, kill a lot of the plants that – well, if anyone’s ever had a house plant out there, you know how easy they are to kill in general. Yeah – heating the atmosphere, bad.
Now, once you heat the atmosphere, there are some additional side effects you have to worry about.
Fraser: Such as?
Pamela: What happens to ice when you heat it up?
Fraser: Oh, I see. So the ice melts.
Pamela: All the ice melts.
Fraser: All the ice melts.
Pamela: All the snow melts.
Pamela: All of it.
So, now we’ve taken, like, all of our reserves of fresh water and dumped them into the sea, changing the salinity of the ocean. And when you change the salinity of the ocean, some of the currents that are driven by changes in density between hot and cold salt water no longer have that salt in the water.
Fraser: So you think you’re safe in the water but now the water that you were living in is now poison to you, but also not good enough for the creatures that evolved in rivers, lakes – they don’t care because their water boiled away.
Pamela: We’ve also killed the currents. So, you initially melt all the ice – all the ice, gone. But now you’ve killed the mid-ocean convection current by changing the salinity of the oceans and, when this happens, suddenly you don’t have the warm tropical water getting carried to the polar regions and keeping places like England nice and friendly and temperate. So, you melt all the ice and then it’s happy to come back.
Fraser: You’ve gone to a very dark place, Pamela. I think maybe you need a more positive, hopeful next book to read. You clearly read Seveneves and Lucifer’s Hammer and you went down all this – this dark place – and then you just were, like, “Is this real?” And then you – “Yes.”
Pamela: I live in the United States.
Fraser: I confirm this is –
Pamela: Lucifer’s Hammer is friendly.
Fraser: Right. So – okay.
So that’s the – I mean, that’s the big rock. That’s the life-killer, right? But you get smaller impacts – and we saw it with Chelyabinsk. We’ve seen that the Earth does get smashed on a regular basis with smaller objects; something in the hundred-meter scale, something in the ten-meter scale.
What are the impacts of those smaller objects? They’re not going to set our atmosphere on fire.
Pamela: No. So, if you have one friendly, smaller object coming along, it may poof the atmosphere a little bit.
Fraser: Again with the poof atmosphere.
Pamela: But it’s temporary. This is the kind of thing that actually the LADEE mission did a pretty good job studying with the moon, where we actually had amateur astronomers who studied the moon, looking for bright flashes that were tied to small things hitting the moon – not big things, small things – and so you get a bright flash when that kinetic energy gets turned into other forms of energy.
And so, when that happened, the LADEE mission – which was sensing the moon’s extraordinarily thin, diffused atmosphere – could actually see that atmosphere poof up.
Fraser: But I mean, in terms of, like, impact – you know, we’re looking at things that could take out a region, a city; the impact of, you know, a very – what? – a 5 megaton, 20 megaton nuclear explosion going off in a city. We’re talking, if you are at ground zero when that thing hits, then your city is gone.
Pamela: And I’m kind of okay with being in ground zero, because surviving after it hits is where things get tricky.
So, let’s start with a smaller thing. So let’s imagine: You have a 20?meter asteroid comes along; it hits the atmosphere. This is 376 kilotons of kinetic energy. So this is going to create a giant air burst up in the higher atmosphere. We know what to do with things like this.
You start to get something that is in the 80-meter, 80/90-meter, you’re now looking at more like 30 megatons of energy. But we’re still looking more at an airburst.
Now, once you start getting over 100, then you’re definitely going to hit the Earth and you’re looking at like a 1.2 kilometer crater. Now, as far as we know, these only occur about every 5,000 years – so, any given year, 1-in-5,000 chance – yeah.
Fraser: Alright. So, I want to talk about the actual Torino Scale now. We’ve just – We’ve set people’s brains on fire here. And don’t worry. This story will have a pretty reasonably not-scary ending. So stick with us here.
So, there are different objects of different sizes. There’s a bunch of them out there – it’s not a matter of “if”, it’s a question of “when” – one of these things is going to hit the Earth and cause some damage. But how much damage? How much should we panic? How much should we worry?
And so this is this idea of the Torino Scale, a measurement for how much you should panic.
So, where did this idea of the scale come from?
Pamela: It basically comes from a bunch of scientists – in particular, Binzel, who was at MIT where many good things come from – who were concerned that these kinds of impacts happen. And they held a conference – and it was in Turin, so Torino (Turin). And at the meeting, they sat down and they started to talk out: How do we classify things?
Because scientists like to put things in boxes: We have planets, we have dwarf planets; we have Torino Level 4, we have Torino Level 6. These have very specific scientific meanings so then, when we talk to each other, we know exactly how much to worry, exactly what we’re looking at and how much follow up is needed. Because scientists like to know: Is this something I should be interested in or is this something really boring that I can ignore for the next – well, rest of my life?
Fraser: And so they’ve got this scale. So let’s kind of go through the classifications of the scale to get a sense of where they go.
So let’s start with zero. So I guess – just to set the stage here – each object that is discovered, every asteroid, is given a measurement on the Torino Scale.
Fraser: And zero is fine.
Fraser: Don’t worry about it.
Fraser: So let’s move up through the scale.
Pamela: So, zero, also shown in white – so, quick scanning down a list, you know how much to be afraid – it’s not going to hit. It’s also, perhaps, a small object that’s going to burn up in the atmosphere. So don’t worry about. Be chill. It’s cool. It’s just a rock in space.
Fraser: And again, we’ll count up the number of different objects and the different scales when we get to the end.
So let’s kind of move through and talk about the next level then. So let’s move to the green and then into the yellow.
Pamela: Green is just level 1. This is something that we discover on a regular basis. You’ve probably seen on Twitter: “Asteroid discovered, passing two moon distances away from the Earth.” They’re things that don’t need any attention but are cool to know about. Hey, rock out there, flying by. Take a look. It’s cool.
Fraser: But I guess the point with the 1, right, is that they can’t completely, conclusively rule out that this thing isn’t going to cause some damage in the far, far future.
Fraser: Right? That more observations are required but the expectation is when they do those observations, it’s going to come back to zero.
Pamela: Yes. And so it’s definitely in the category of: This is something that we just discovered. It doesn’t appear to pose an unusual risk but hey, let’s just verify its orbit now and then.
So Ceres, for instance, is a zero. It’s orbiting far, far away. Ceres is never going to hit us. Some of these asteroids that fly by at twice the lunar distance, they might, in the future, come back and whack us later, so let’s just make sure they’re not going to.
Fraser: Alright. Let’s move on to sort of the yellow zone; the ones that merit attention.
Pamela: Yes. And these, we actually get periodically. These are the –
Fraser: Spoiler alert!
So, these are the ones that we look at them and, when we do the initial “what is the error ring around its orbit”, we realize the Earth just might be within that error set. And so we probably want to follow up on this; just make sure we’re not actually, like, gonna to get hit in a bad way. So these are generally, again, routine. Things land in this category when we don’t have really good observations to narrow that orbit down a lot.
So, if you think about it, if you know where an asteroid is – plus or minus a thousand kilometers, plus or minus – Actually, a thousand kilometers is super-good. So, let that one sink into your head. So, if we know where an asteroid is, plus or minus 20 times the distance to the moon, that’s a pretty big error bar. And it’s not that hard for that error bar to include the Earth for a lot of these asteroids that have Earth-crossing orbits, when we look far into the future.
And then, let’s move into the one you should be worried about, which is the threatening zone.
Pamela: Yeah. So this is categories 5, 6 and 7; these are things where critical attention is really needed to make sure it’s not going to hit, because its orbit really is looking like it’s gonna be close and we might want to do some contingency planning.
And then, as the object gets bigger and the uncertainty doesn’t go away and the closeness of the encounter appears to get closer, we get – from the friendly statement of “A close encounter posing a serious but still uncertain threat of regional devastation” for level 5 to, at level 7, “A very close encounter by a large object which, if occurring this century, poses an unprecedented but still uncertain threat of global catastrophe.”
I love the wording of these things, by the way.
Fraser: Yeah. But I guess the point – the distinction here – is that we’re into a place where there is an object that is probably, maybe, going to hit the Earth in the far – in a fairly long period of time. They are the size of, you know – If it’s a 5, it’s small object; it’s going to cause regional issues. If it’s a 7, it’s a much larger object; it’s going to cause potentially worldwide destruction. But the timeframe is long and your opportunity to stop it, redirect it, prevent it or just better study it is still available to you here.
And let’s move up to the red zone.
Pamela: So, the red zone is: Yeah, it’s gonna hit. Which, while making for a fabulous plot for a book or a good movie – or a great way to ruin a movie –
Fraser: We’re still waiting for that good movie but – yeah.
Pamela: Eh. Yeah, Deep Impact tried. It tried.
Fraser: Yeah, it was alright. It was fine.
Pamela: So, with these objects, they’re going to hit. And it starts to become a question of: Is it hitting land or water? Is it hitting a populated area or an unpopulated area? Just how bad is it?
Fraser: I mean, like the 8 – So, the 8 on the scale is, it’s absolutely going to hit us but it’s just going to wreck a little portion of the Earth; maybe it’s just gonna take out a city, cause a tsunami. It’s, for sure, going to hit. It’s gonna really suck. And, you know, you’re looking at the – What do they say? Between the 50 and – once per 50 years and once per 1,000 years.
Fraser: That’s – Right? So, these smaller ones. Sort of like if Tunguska could have been predicted, it probably would have been an 8; maybe a little smaller than an 8. If they saw Tunguska coming in, they would’ve called that an 8. Right?
Pamela: Yeah. I suspect that’s the case.
Fraser: Or Chelyabinsk – Yeah, Chelyabinsk or Tunguska. You know, like a pretty big impact. In the end, it, you know, it didn’t cause as much – I mean, Tunguska would have been an 8; Chelyabinsk maybe not quite an 8. It would’ve been bad.
Pamela: And one of the amazing things is we don’t actually know how frequently these things happen. So our current estimates on how frequently Tunguska or Chelyabinsk or any of these apparently, preferentially hitting Russia events occur, our estimates of frequency are every 50 to 1,000 years.
Fraser: Yeah, yeah.
So – And then, when we go to the 9 and we go to the 10, we’re just – It’s just how much of your planet is absolutely going to get ruined.
Pamela: Yeah. So, if you’ve read the book, Lucifer’s Hammer, here, that was probably a Torino Level 10 event. And this is where the definition runs, “A collision is certain, capable of causing global climatic catastrophe that may threaten the future of civilization as we know it, whether impacting land or ocean. Such events occur, on average, once per hundred thousand years or less.”
And, on the one end of the scale, you probably have, like, a kilometer-sized object that, if it hits Earth, it’s going to heat up the atmosphere and end human civilization; if it hits the water, it’s gonna heat up the atmosphere and end human civilization. It doesn’t matter where it hits, it is the end of your time. And –
Fraser: And that’s the smaller one but we can go all the way up to the 10?kilometer – like, the Chelya – No, the –
Fraser: No, the Chicxulub, right?
Fraser: The one that killed the dinosaurs, right?
Pamela: Chicxulub, yeah.
Fraser: Chicxulub. So you’re looking at something that happens once every 65 million years. So, that’s still a 10. I know you’d think it would go to an 11 or a 12 but, once you hit 10 – for our purposes as humanity and civilization – the story is over.
Pamela: And, I mean, one of the other things that we haven’t even brought up is, if these suckers happen to have fallen apart and you have multiple bits hitting. With these big ones, you end up with a large chunk hitting the Earth somewhere; large chunk of varying degrees of largeness. And when they hit, they’re still hot. And if they hit in water, you have now just taken a really hot stone, essentially, and dumped it in water. And there are cooking techniques where you grab a hot rock out of your fire and you put it in your soup, to cook your soup. Well, we can turn our oceans into a soup that boils off. And that is, again, bad.
Now, we’re sort of nearing the end of today’s episode – in the beginning of a long list of existential episodes, but also some positive ones. But I promised people that we’d give them some good news at the end.
So, we understand the Torino Scale. Every object that exists in the solar system has been given its classification. On the Torino Scale, how many 10s are there out there?
Pamela: Of things on the Torino Scale?
Fraser: Currently on the Torino Scale, how many 10s are there?
Pamela: Well, if you count zero as a place, they’re all at zero.
Pamela: I’m literally looking at –
Fraser: Yeah, there’s nothing.
Pamela: – the NASA website. So, if you go to neo.jpl.nasa.gov/risk, it lists out all of the suckers that we need to maybe worry about and currently, everything is either a small object that’s 50 meters or less or a zero.
Fraser: Right. So, if we went down the list – number of – you know, how many are a 10 on the Torino Scale? Zero. How many are 9? Zero. How many are 8? Zero. 7, 6, 5, 4, 3, 2, 1? Zero.
Zero – there is not a single object today that is anywhere on the Torino Scale. In other words, for all of the objects that astronomers have studied across the entire solar system, every single asteroid – the thousands and hundreds of thousands of objects that we know about – you don’t have to worry at all about any of them, ever.
Fraser: Now, that said, asteroids have climbed the Torino Scale briefly, at various times, when they do get discovered.
Pamela: Right. So the asteroid, Apophis is probably the most famous of all of these. It shares the names with a mythological god and a character from Stargate, who was named after the mythological god.
It looked, for a while, like it might – not on its most near-term pass by the Earth but in a future pass by the Earth – fail to pass. And there’s some things that you don’t want to say, “Thou shalt not pass” to. Asteroids are one of them.
And so there were a whole bunch of movies; there’s a whole bunch of hoopla. Once we refined our understanding of the orbit, it’s fine.
Fraser: Yeah. And so Apophis, for example – when it was first discovered and when it was really studied – astronomers put it up to level 4.
Fraser: Well, it started as 2 and then they pushed it up to 4 – which, for your memory, 4 is “A close encounter meriting attention with a 1 percent or greater chance of collision, capable of regional devastation.”
So, in other words, based on all the calculations, there was a 1 percent chance that this object was going to crash into the Earth, down the road. And then more observations downgraded it again to zero, where it belongs.
And every now and then, a new object is found. It goes to 1, sometimes 2, and then goes back down to zero. And where we stand today, there isn’t a single object that we observe that is any kind of risk to us.
Pamela: But it’s fun to read about the potential risks. So, while you’re out there, everyone stay safe and go find yourself a good dystopian fiction that you can learn science from.
Fraser: Exactly. So, there you go. Good news! There is no threat to any asteroid today and we’ll update you if it ever happens.
And we get, all the time – people are freaked out about various asteroids. They’re worried about – I forget what’s the one now. DF?9 or something like that? There’s a new one that’s making the rounds and people think it’s going to crash into the Earth on February. It will not!
Pamela: No. No, we’re good.
Fraser: Don’t worry.
Pamela: We’re good.
Pamela: You’re fine.
Fraser: We’re fine, yeah.
Pamela: And so, if you want to hear us tell more stories about potential devastation of the planet Earth, because the universe is trying to kill you –
Fraser: And the universe itself.
Fraser: I want to talk about some other existential threats.
Pamela: We’re starting in on a new series.
And you can make sure we can pay our editors to edit this series and our producers to get it all out, pushed to you on the internet, by going to astronomycast.com/donate.
Alright. Thanks, Pamela. We’ll see you next week for another terrifying threat from space.
Pamela: See ya later.
Male Speaker: Thank you for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Fraser Cain and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at firstname.lastname@example.org. Tweet us @astronomycast. Like us on Facebook or circle us on Google Plus.
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Duration: 31 minutes