Can we defend the Earth from deadly space rocks?

Published May 17, 2022, 5:00 AM

Daniel and Kelly talk about where space rocks come from, how dangerous they are and what humanity can do about it.

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Hey, Kelly, do you guys get really nice dark skies out there on the science Farm.

Yeah, we totally do. We're far enough away from civilization that we get really awesome dark skies at night.

Oh that's so nice. So what kinds of things do your kids like to see up in the dark skies?

Well, we've got this app and we like to try to figure out where the ISS is, but usually we miss it. And so what we do get lucky and see sometimes that they love is shooting stars, which like, of course, because all kids love seeing shooting stars.

I find that kind of amazing.

What shooting stars?

No, it's amazing to me that kids like shooting stars.

What's not to like?

I don't know the part where you explain to them how each one is like a huge flaming bullet screaming across the cosmos that could land anywhere on Earth, devastating people.

I like to keep the level of existential dread in the family to like a minimum. And so you're officially never invited to come look at the night sky with my family.

Sounds like your family can't handle the truth at least about shooting stars. Hi, I'm Daniel, I'm a particle physicist and a professor at UC Irvine, and every shooting star makes me nervous.

Hello, I'm Kelly Wiedersmith. I'm a parasitologist and adjunct with Rice University, and shooting stars don't make me nervous unless I'm talking to Daniel and he's ruining them for me.

And that's the job of physics, ruining everything since fifteen forty seven.

Right, that's right, that's right.

Well, we joke, but the job of physics is to tell us the truth about the universe, to reveal to us exactly the nature of the cosmos that we live in. And so welcome to the podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio in which we talk about exactly what is out there in the universe, what's going on beyond the borders of our atmosphere, outpast the Solar system, outpassed even the edge of our galaxy into the deepest mysteries of the cosmos. Where did it all come from, how does it all work, what's going to happen? And will we survive it? My usual co host Toorges on a break today. So we are very happy to be chatting with Kelly, who apparently doesn't worry about death from above at all.

Well, you know, I guess I worry about it. No, you're right. I don't think about it too much unless I'm talking to my physicist friends, or unless I'm talking to people who are thinking about trying to mine the asteroids, which requires being able to move them. That makes me nervous. But I can just look up at the night sky and enjoy it and not think too hard about it. On the other hand, I can't look at sushi without overthinking it as a parasitologist. So we all have our blind spots or the spots where we had.

Unless it's really old, sushi's unlikely to blow up in your face or cause a fireball.

Yeah, no, you're You're probably pretty safe from those particulars.

But somehow growing up and being an adult in this universe means understanding just how crazy and dangerous and chaotic the universe is. Just like when you learn that every surface is covered in microbes of some kind. Now we are learning that our spaceship Earth is also constantly bombarded with rocks from space.

So do you remember the first time you looked at a shooting star and thought, uh, oh, that could be bad as opposed to like, were you a child with wonder in your heart, Daniel, or were you born a physicist?

Well, you know, I was a child with wonder in my heart. And then my father told me that those shooting stars are actually rocks from space that are hurtling towards us, burning up in the atmosphere, and sometimes they actually land and explode.

Is there one in particular that you heard about that that made you nervous about this that you remember?

Well, I grew up part of the time in Arizona, so we visited Meteor Crater and so we had a very like visceral example of how rocks from space really can come all the way down to the surface and create huge explosions which leave dense in the Earth's surface for thousands or millions of years.

And do you remember like having a profound moment of oh shoot when you looked at that.

I do, and ever since then, when I look at shooting stars, I'm wondering like, hmmm, who's that one going to hit you? No, it's sort of like we're in a shooting gallery and we're like, ooh, look at all the fancy bullets.

See that's funny. Like I think, for at least the first twenty years of my life, I lived in this amazing state of complete oblivion. And so you know, like, for example, in preparation for this episode, I was looking up some comet impacts that happened in the past, and I don't remember hearing anything about Shoemaker Levee. For example, do you remember when that hit?

I do remember Shoemaker Levee because I was doing one of my first research internships that summer and the guy I worked with had a super high speed camera and a telescope, so we actually hooked up his high speed plasma imaging camera to a Telsco hoping to take pictures of the fireballs when they erupted off of Jupiter. So yeah, I was definitely very aware of that. I was excited. I was like, yeah, let's blow up Jupiter.

And did you get the footage that y'all wanted?

We didn't actually because the night we were observing, Shoemaker Levey hit on the backside of Jupiter, so we didn't actually get to see it.

Ah See, I don't even remember that it hit on the backside.

But it was also a funny lesson in early days of science communication on the NASA website because when Shoemaker Levey came into the Solar System, it got broken up by the tidle forces. So it wasn't just like one big comet. It was this train of comets, like twenty three or twenty four of them, and so of course astronomers named them ABCD, et cetera.

That's so boring.

Yeah, And then when the first one hit Jupiter, they called that the A spot, and then when the second one hit Jupiter, they called that the B spot. And it wasn't until I think they got to F that they realized, Mmm, what are we gonna call where the G one hits? And so on the NASA website there was like pictures of the F spot and then the G impact site and then the H spot.

You gotta think these things through all the way.

Yeah, before you name it aspot, think about what happens. Anyway, this was very visceral to me, and it made me realize like, wow, space really is not empty. Space is filled with stuff. And this is something we've been talking about on the podcast for a while, not just that space has huge rocks that might end human civilization. But space is not empty on lots and lots of levels, you know, from like tiny particles, the solar wind is a huge stream of protons and electrons that are put out by the Sun. It doesn't just make light. And we've talked on the program a lot about neutrinos. The Sun pumps out zillions and zillions of neutrinos. So even from the particle point of view, if you go out into space, you're inundated with radiation. And then take a step up to like micro meteorites, you fly spaceship or spend time on the iss, you have to really worry about your little life bubble getting hold by one of these high speed moving pebbles.

Well yeah, and then you got to worry about the neutrinos too, right. Didn't those cause the Carrington event on Earth? So sometimes those cause problems down on Earth as well.

The solar wind definitely causes problems on Earth. It can fry satellites and in cases of really big coronal mass injections, it can also make like telephone and electrical wires spark here on Earth. It's not due to the neutrinos. Those interact so weakly that they can pass through like a light year of lead without having any effect, but the high energy electrons and protons and photons from one of those events can really cause damage here on Earth. We actually had a whole episode about just what to do if that happens. But space is filled with this stuff, right, It's not like when you go out there, it's just total emptiness. It's not actually that safe out there in space. It's sort of contrary to what I think a lot of people's view of space is in their mind's eye.

But so like when I was younger, I watched a lot of movies, like I watched what was It Armageddon? With Bruce Willis and Ben Affleck, and so I'm pretty sure that any of these space based problems we could probably figure out.

Well. It's interesting also to see how Hollywood reacts to science. You know, when Shoemaker Levee came into the Solar System, it was a wake up call for the human race, for NASA, for scientists, for everybody. Until then, people hadn't really understood the dangers of these comments. You know, it wasn't until like the mid sixties that we understood that the surface of the Moon had craters because there were so many impactors, and it wasn't until a few decades ago that we understood that, you know, the dinosaurs had been wiped out by a large impactor. But it was Shoemaker Levey that made it real, that made people think, oh my gosh, this just happened to our neighbor Jupiter, it could also happen to us. And that's when NASA's like planetary protection program really took off. And that's when Hollywood realized, ooh, here's a whole new topic for a movie. And that's why you got two big movies, What was at Armageddon and Deep Impact that came out like in the same year about the same top because there was this sort of human awakening of the danger.

So based on our timing of awakening to this danger, didn't the hypothesis that an asteroid killed the dinosaurs? Didn't that predate Shoemaker Levee or were we just not quite sure about it at that point?

That predated Shoemaker Levey? But you know that was sixty five million years ago.

Well, I mean our understanding of it as a.

Problem, right exactly, But we understood that it was so long ago. It's probably a really rare event might come every few million years, not something we have to worry about. But Shoemaker levee happening like right now basically means that's not that uncommon. It might be that there are commentary impacts every few decades in the solar system or every hundred years. It's much more immediate than this like ancient thing that happened a long long time ago. And I think that really brought the danger into focus for people.

So if I had to guess, like, so, I know, Hollywood has made it seem like, you know, maybe sometimes we can solve these problems, But based on how humans are dealing with the risk of climate change, I'm going to guess that we're also not doing much to deal with the risk of risk of asteroids. Is that about, right? Are we just sort of crossing our fingers and hoping it'll work out.

I'm guessing you watched Don't Look Up recently and that didn't make you enthusiastic about humanity's ability to confront existential crises.

I'm not sure I was optimistic before, but yeah, you're right, the movie didn't help too much.

Well, there is a lot of conversation about whether that movie is about climate change, or actually about an asteroid impactor, but you might actually be pleased to learn that since that day, humanity really has woken up to the danger and there's a broad and vigorous effort to figure out where these rocks are, how much danger we're in, and try to do something about it.

Oh, let's talk about that. Side note. I think that just yesterday there was news that an asteroid we had discovered two hours earlier that was pretty big was about to hit, which doesn't make me feel like we're as on top of it as maybe i'd like.

Yeah, there are definitely some holes in our protection system, and so we'll dig into in detail, and on today's episode we'll be asking the question can we defend Earth from deadly space rocks? Subtitle? Does Kelly need to tell her kids the truth?

Kelly will not be doing that. The pandemic has been enough of an existential threat. Maybe when they're eighteen.

Are you saying that your kids don't listen to the podcast? Is that what's going on here?

Oh?

H No, they definitely listen to the podcast, but just maybe not this episode.

I'll email your husband'll link to it. Then, So the idea is that waking up to the crazy dangers of our solar system, understanding that space is not empty but filled with death bullets that might impact us. There's not nothing that we can do about it. We can actually wake up as a species and try to confront this danger, and so we thought it'd be fun to explore what we know about these asteroids and commets, how dangerous they actually are, and the status of the Earth Protection System. This is an easy one. It's obviously to send VERSU one that's up there with pen afflect, even if they don't want to go send them up there as well.

There's no correct answer. Just what do you think is the best way? I think it's a laser laser?

Okay, yeah, laser.

The best way to break up an incoming asteroid I think would be too probably not to blow up a nuclear weapon like an armageddon, so not to do it Bruce Wallers style. I would say to send a spaceship that could give it a slight nudge and then it could deviate slightly from its original path and miss the Earth.

I don't think there really is a good way to break up an incoming asteroid, especially as they can really vary on how solid they truly are one big glob of iron and rock or a big old pile of pebbles, And if you don't do it right, all the pieces still hit the Earth, so you still get all of that energy into our atmosphere, which is not a good thing for us. Far better to just find the best way to move it, which also will probably vary based on its makeup.

The best way to break up an incoming asteroid would be to heat it with another one of similar size.

I'm going to take a page out of the Wargames playbook and guess the best way to break up an incoming asteroid is not to do so, because if you do break it up, you have a bunch of fragments, some of which may still hit Earth with enough mass and velocity to be quite dangerous. And I assume that's why you're trying to break one up in the first place.

If you really did have to break one up, though, I would guess the best way would be to drill as deep a hole as you possibly can down to the center anyway, a nuclear weapon or something like that, and.

Blow that sucker up.

The best way I can put it is slowly, because if you blast an asteroid, it can turn into a lot more little pieces, but that can still make significant damage. Now you have ten problems to deal with instead of one. So I don't know if it's like with kind of a laser that isn't too powerful to totally blast it, but kind of too corroded away, so then you can maintain it as one asteroid, but then keep its shape.

Well, if you could fling another asteroid at it and hit it like a billiard ball and send it in another direction, that'd be great.

It's my understanding.

If you just blow it up, then you have a bunch of little pieces raining down on earth that might not be little enough.

I don't think you really want to break it up.

I think you want to.

Push it off course, not break it up.

Then you just get held with a bunch of stuff.

So it seems like a common thread here is that you don't want to blow up asteroids because you're gonna cause more trouble that way. It was interesting to see that so many people that sort of honed in on that theme, And to be honest, I don't know if that's true or not. It maybe it depends on how big your blast is and how far away you are, But it does seem like everybody has some idea of how to tackle this problem in their heads already, and I was happy to see that at least one person had watched the movie that I had watched Is it Armageddon? With Bruce Willis and Ben Affleck? Is that what it was called?

I do remember which is which? Anymore? You're probably right and probably seeing those two movies is what everybody knows about asteroids and commentary impacts. That's probably the amount of research people have done, and so we can thank Hollywood, I guess, for at least educating the public about the dangers and maybe misleading them about the possible solutions.

That's how it always works, isn't it.

I wonder if they had legitimate science advisors on those movies. I know these days they try to reach out to experts in the field to consult, but back in the nineties, I have the feeling they were probably just winging it.

Yeah.

I think there was probably some one in it, and I think even today they don't even always listen to their experts. So you always got to be a little critical when you're watching a movie. Okay, so where are these things coming from? Could they be coming from anywhere in space or do they tend to like start in certain areas and those are like more likely to produce deadly space rocks.

I think something that would surprise people is that most of the deadly space rocks are basically our neighbors. If a rock comes and hits the Earth, it's not likely to be coming from like deep deep space, another solar system, or somewhere else randomly in the galaxy. Instead, it's much more likely to come from somewhere here in our Solar system. And to understand why, you have to go back to the very formation of the Solar system. Remember, before we had our Sun and all of the planets, everything was basically just a huge cloud of gas and dust, rocks, bits left over from other solar systems that had burned and made mistakes and made silly movies and lied to their children about dangers. Hey pretended that Santa Claus and the tooth Fairy existed, all this kind of stuff, And then you know, those solar systems came to an end and their debris was the fodder for our Solar system. So you have this huge cloud of stuff which then gathers together gravitationally. Most of it, of course, is still hydrogen because that's what was created in the Big Bang, and fusion in the heart of stars has turned a little bit into heavier elements, but still hydrogen is the dominant thing in the universe. And so you get the Sun, which has most of the hydrogen in the Solar System, and then the formation of other stuff. You get the planets where you get these like little gravitational seeds that accrete other stuff. But not everything ends up inside a Sun or a planet, and that's why you have, for example, the asteroid Belt, which is a huge collection of rocks basically between Mars and Jupiter that never formed into a planet.

So how many potential Earth killing things are out.

There, it's a great question. We aren't exactly sure because these things are hard to see. I remember, asteroids are dark, they don't glow like a star. So if you're going to see one, you have to see it because light has gone from the Sun hit the asteroid and then bounce back exactly into your telescope. So it's only when this thing happens to reflect light right back to Earth that we can see it. So the good news is that the bigger it is, the easier it is to see. And NASA's been tracking these things for a few decades pretty carefully, and they're pretty sure that they've seen all the really big ones, and then as you go smaller and smaller on the scale, they get less and less certain. But they have these goals to see like ninety percent of all the objects greater than a kilometer or ninety five percent of all the objects greater than five kilometers. But as you said, they're sometimes surprised, like when one of these things came into the skies over Chellieminsk. This was a twenty meter object that came really fast. It was small enough that nobody knew it existed, and it created a huge explosion. Two thousand people were hurt, buildings were shattered. So it's definitely possible that there are ones out there that we have not seen.

The dash Can videos on that thing are crazy. Do we know that that came from the asteroid belt? Like, if something you know makes its way to Earth, can we back calculate where it started from?

Yes, Because of all the dash can videos, we can calculate the trajectory of this thing, and then we know its mass and its velocity and its angle, and so we could figure out where it came from. And so that definitely came from somewhere in the asteroid belt. And there's a huge number of objects out there. There's just way too many to track now at Cheliabinsk, like explosion is never going to end the human race, right. It could kill thousands of people, it would be a terrible disaster, but it's not like a planet killer. You know, it's not going to tear the planet in half, or it's not going to cause the kind of devastation that would wipe out humanity. But still, you know, you definitely don't want to lose two thousand people because you didn't notice something. So you want your planetary defense shield to be pretty robust. The interesting thing about the asteroids is that there's a huge variety of these sizes. Like the asteroid belt itself, half of the mass is in just four objects. Like one of the things in the asteroid belt is a dwarf planet called Series.

I've heard of Series. Are there other dwarf planets in the asteroid belt or is that the only one?

There are four objects that have like half the mass. Series is the biggest one it's like almost a kilometer wide, and then it drops down pretty quickly after that. But even if you add up all of the mass of all the stuff in the asteroid belt, it's not that much. It's only like four percent of the mass of the Moon. Still, though, you don't want to get hit by an object that's like four percent the mass of the Moon.

Yeah, that would be. And so how like do those things tend to stay put or are they getting like kicked out pretty often?

It's a great question because you might wonder, like why are these things there? Why don't they just pull together into like a new planet, right, And so you have to understand all the forces on these things. So number one, the reason that they haven't just formed their own planet, you know, and declared independence from the Solar System or whatever, is that these things are being tortured by Jupiter. Right. Jupiter is such a massive planet. It's so much bigger than everything else that it's gravity really controls that sort of middle Solar System region, and there are tidal forces on these things, you know, anything that gets big enough near Jupiter, Jupiter's gravity pulls on the closer part of it harder than it pulls on the further part of it, which basically pulls it apart. And so Jupiter's forces are constantly disrupting what would otherwise be a nice, steady formation of a new planet in the asteroid belt. So these things have been whizzing around for hundreds of millions of years, maybe billions of years. Sometimes they do bounce into each other and then you know, they careen off into the inner Solar System. They can also just fly around in a nice stable orbit for you know, billions of years and not bother anyone.

And you know, I feel like, now that you and I have recorded a nice number of episodes together, I feel like the answer now just about any astronomy question of why is it like that, the answer is Jupiter. Why is this weird thing happening? Probably Jupiter that's the go to answer.

Jupiter is such a bully in the Solar System because of its gravity. It affects every thing. Right. There may have been like another planet like Neptuna Urinus that was tossed out of the Solar System by Jupiter. It's crazy. And we had that whole fun episode about how Jupiter might have been formed the outer Solar System, migrated in came back out because it was saved by Saturn. Like, the story of our Solar system is really incredible and dynamic. It's not just like a bunch of rocks calmly floating in space the same way forever. You know this chaos, there's intrigue, there's.

Backstabbing, there is it's totally wild.

And especially in the very early part of the history of the Solar System. We think that the asteroid belt used to have a lot more mass to it, but something like ninety nine point nine percent of it was lost in the first hundred million years because things banged into each other and then fell into the Sun or got ejected from the Solar System. So the asteroid belt we have today it's like a shadow of the very early asteroid belt we had in the history of the Solar System.

Which is probably lucky for us. I don't think we would have wanted to have been around when all the chaotic stuff was flying around.

Called the heavy bombardment period of the Solar System. And we think that Earth before its current atmosphere was formed, we just like rain down by these death rocks.

Yeah, I'm glad I missed the death rock period.

It would have been hard to convince your children it wasn't happening if you lived back then.

Yeah, yeah, you know, it's nice to be able to lie to your kids, and you're right, that would have made it harder and maybe not lie, you know, sugar coat the.

Truth there you go, preserve their childhood innocence. Something else that surprised me about the asteroid but we're reading about it, is that it's not just a collection of rocks between Mars and Jupiter. There's two clumps of rocks that are co orbiting with Jupiter. They're like in Jupiter's orbit, but one of them is trailing and one of them is leading Jupiter.

Oh and how much stuff is in that?

Not that much. But because they are astronomers involved, they have silly names. So one group called the Greeks and the other one is called the Trojans, and I guess that's, you know, a play on the fact that we name all of our Solar System planets after Greek gods.

So okay, So I'm working on this book about space settlements, and so whenever I read about the assid Belt, I am reading about people who are interested in mining the asteroids because there's cool stuff in those asteroids. Can you tell us a little bit about what's in those asteroids and like how common the good stuff is.

Yeah, the asteroid belt is made from the same stuff as the rest of the Solar System. It means that there's a lot of carbon, there's a lot of silicon. There's also a lot of metal and so as I'm sure you know, some of those asteroids have like huge nodes of platinum or other rare earth metals that could be pretty useful for a space based industry. Do you find any of those schemes for mining asteroids to be plausible at all? No, that's going to be a short chapter in your next book, right space mining? Will it work? No?

Maybe eventually, and it'll support some settlements, but I'm not seeing a near term potential. But check out my book for more information.

It's only a few pages long.

We find a way to draw it out, that's what authors do you know?

I see it's just like, no, like five pages of nodes.

I don't think my editor would let that slide. There are a narrow you know, maybe taking water from the asteroids and selling it to the iss or to moon settlements. That might be a like you know, in a couple decades feasible, but in the very near term, I don't think it's gonna work out economically.

So very naively, why not if I'm up in space and I need to build something, why shouldn't I just go get iron from some nearby asteroid instead of like lifting it off the surface of the Earth.

Well, so the problem is for starters, you said, if I'm up in space trying to build something, which hasn't happened yet, and so like, I mean, we've gone up to space to assemble things that are pre exists that we built on Earth. You know, like we've assembled the ISS, and there have been some groups like Made in Space that three do some three D printing and stuff in space. But like it's gonna take a while before we can really get these settlements started. There's a lot we don't know about how the human body responds to microgravity or to the spare or radiation in space. And then there's a lot we don't know about how to actually get these asteroids. So you know a lot of them are rubble piles. They're not just like this big dense thing. How do you collect a rubble pile where if you try to land on it. You're just going to sort of smooth it out and push it away, and then how do you extract ore in space? Or are you just going to bring the asteroid and drop it to Earth? Probably not a great idea. There's just a lot of problems that need to get solved before this becomes something that we need and something that we actually can do.

Wow. Way to bring the harsh reality down on my dreams there, Kelly.

Well, you know, I guess we're taking turn.

I was expecting to get a little bit of that, you know, childhood innocence protection you offer your kids, But I guess that's, you know, an umbrella only for your family.

You're a grown adult, Daniel.

I can deal with it. I can deal with it.

Okay. Well, now that I've had an opportunity to crush your dreams, let's take an uplifting break and when we come back, we'll talk about some of the risks that are farther out in the Solar system.

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Okay, I hope you didn't have too many existential crises during the break. But we're back and now let's talk about the Kuiper belts. We talked about the asteroid belts. Risks are looking for us in the Kuiper Belt.

So fortunately I survived that break. No large objects from space crash landed on my house, so I'm still here to talk about future dangers. And some of the most dangerous objects in the Solar System are not in the asteroid belt. Well, they come from further out. So the Kuiper Belt is the source of short period comets ice balls that orbit the Sun with a period of about less than two hundred years or so. And these are basically little things that never formed a planet, but they're much further out. They're like past Neptune. They're between thirty and fifty AU. Remember AU is the distance between the Sun and the Earth, so it's sort of like a second asteroid belt, but it's further out.

And more dangerous.

You're suggesting these things are more dangerous because they come from further out, which makes them harder to spot. Right. Things that are further away are harder to see, so we can't track them as well. And because they come from further out, they're going faster when they do come into the inner Solar system. Imagine like rolling a rock down a hill, it's going to go pretty fast. Instead roll that rock from like the top of a mountain. Then by the time it gets to the bottom, it's going to be going super duper fast. So the Earth moves around the Sun and like thirty kilometers per second, and asteroids typical velocities like forty kilometers per second. Commets can be going much much faster, seventy to one hundred kilometers per second, and that translates into kinetic energy, which means more destruction if they do hit.

Yikes. So I heard you use asteroid in comets. So we've got the asteroid belt which has a lot of asteroids, and so does the Kuiper Belt have more comets, then, yeah.

It's just a name thing. If it comes from the asteroid Belt, we call it an asteroid. If it comes from the Kuiper Belt, we call it a comet. There's also a difference in the makeup because as the Solar System formed, the amount of stuff in various parts of the Solar System was different, and so for example, in the Inner Solar System you don't have as much ice and water. A lot of that was vaporized, whereas in the outer Solar System, before the Sun could vaporize it, it froze into crystals and it could participate in like accretions. So things that like started to gather together gravitationally are also able to gather ice as part of their makeup, which is why the ice giants Neptune and Urineus are out there. In the outer Solar System. You don't get ice giants between Venus and Mercury, for example. So the things in the Kuiper belts are more like snowballs, and the things in the asteroid belt are more like rocks.

Interesting, okay, And then we talked about series the dwarf planet and the asteroid belt, and I know poor Pluto is now merely a dwarf planet. Are there other dwarf planets in the Kuiper belts? Because we have now exhausted my knowledge of dwarf planets.

There are lots of dwarf planets, And that I think is the whole controversy, people realizing, oh, Pluto is not that special. Yes, we love Pluto, it has a heart on it, all that stuff, but it's just one of lots of these objects deep in the Solar System where things didn't form into larger masses. And so I think if we made Pluto a planet, then anytime we found another object that size, and we're going to find a lot that we'd be adding another planet to the Solar System. And that's I think the argument for drawing the line before Pluto. But the point is, as you say, there's a lot of stuff out there, and you might wonder again, like, well, why doesn't this form into big planets, like there's no Jupiter out there in that deep Solar system to prevent these guys from forming. The answer is just mostly time and space. As you get further out from the Sun, the density of stuff drops and the space between it grows because You're just getting more and more space as radius cubed, and so it takes longer for stuff to come together. Gravity is pretty weak, and so this stuff just takes a long time to come together.

Wasn't Deep Impact about something coming from the Kuiper Belt.

This is this Deep Impact the movie from Hollywood, which I think was in response to seeing Shoemaker levee impact Jupiter, and then Hollywood responded by making an actual mission to a comet and calling it Deep Impact, so you know, the whole like Hollywood science cycle there. So this is a super cool mission because it went out and visited a comet and basically punched it in the face to see, like what's going on? Way to go, NASA, And I'm just glad they weren't like aliens hiding inside that comet, you know, observing us being like whoah. I imagine like aliens on a steak out, you know, eating pistachio nuts and then all of a sudden NASA comes out and punches them in the face.

What the heck man? Totally unnecessary.

I know you could have just said hi. Anyway, as far as we know, there weren't any aliens hiding inside the Comet temple one, and when they punched it, they learned a lot about what these things are made out of. Turns out, these things, or at least this one, was a lot more dusty and less icy than they expected. Like the stuff that's on it is not as much ice and sand, more like baby powder. It's like this really really fine dust that this thing is made out of.

Huh, And so does that make it less dangerous for us? What is the implication for me of what you just said, Daniel, That's what I'm wondering.

It's a good question. It doesn't matter that much if it's made out of baby powder or sand. What matters is like how much it's holding together, because when it hits the atmosphere, if it breaks up into thousands and thousands of small pieces, then that kinetic energy is spread over a larger area, so you're less likely to have like one big one that's going to land in the Pacific Ocean and cause a mile high tsunami. Better if it's like a rubble pile that gets spread out by some impactor or something else. It doesn't really matter that much if it's baby powder or sand.

But so that sounds like the exact opposite of what the people who called in said.

Yeah, people were worried about getting these dangerous fragments, but it's actually much much better. Like would you rather be shot by an armor piercing bullet or a shotgun? You know, we have like lots of very small pellets which will embed themselves in your skin, but are less likely to go all the way through. And in the same way, the Earth can't absorb a pretty big hit. That's what shooting stars are, right. We're constantly getting hit by lots and lots of small rocks and they briefly heat up the atmosphere. Much better to be hit by lots and lots of fragments than it is to be hit by one big one.

Okay, that makes sense, all right. So we've got the Asphoid Belt and the Kuiper Belt. That's all the like, you know, human killer locations in the Solar System, right.

Unfortunately, No, there's one more source of death out there in deep space, and that's my favorite part of this y system. Actually, it's the Ort Cloud. This is well beyond the Kuiper Belt. It's another cloud of icy mini planets and objects. This is much much further out In fact, it's so far from the Sun that you can almost think of it as sort of like transitional out into deeper space. This is like two thousand to like one hundred thousand AU, so we're talking about like, you know, one or two light years from the Sun. There's actually two layers of ort cloud. There's like an inner taurus and then an outer sphere that the Sun is just like barely holding on to.

Thanks Sun for holding on to human killers. That sounds really far away. Is there a lot of stuff out there that could get us?

It's very far away. It's like a thousand times further than the Kuiper Belt. But they think that it's got like trillions of objects in it, each of which are bigger than a kilometer, and they're probably billions of things bigger than twenty kilometers. I remember, anything bigger than like five kilometers is basically an extinction event if it hits the Earth. So there's a huge amount of stuff. If you add it all up, it's like five times the mass of the Earth. So it's much much more massive than the asteroid belt or the Kuiper Belt.

So I'm definitely not telling my daughter about these existential risks, and I'm kind of feeling like you shouldn't be telling me about these.

The other scary thing about them is that when they make comets, because you know, like a nearby star comes by and disturbs them and one of them falls into the inner Solar system. Those comets are very, very long period comets. It can be like thousands of years. What that means is that we might not have seen it before. Like some comments we see every seventy seven years or every eighty five years. We know it, we see it, we can track it, we can predict where it's going to go. There could be a comet out there that goes around the Sun every nineteen thousand years and we just haven't been doing astronomy that long, so we've never seen it. And the first time we see it might be when we discover, oh my gosh, this thing is on a collision course Earth.

And how much lead time on something like that would we have.

It depends a lot on how good our telescopes are and how lucky we get, because these things are pretty dark and moving pretty fast, and so it might just be months. If we're lucky, it would be years, but it might just be months.

All right, Well, on that dark note, let's take another break, and when we come back, we'll talk about the possible scale of devastation.

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All right, I hope everybody had a nice break, and we're back to talk about the scale of devastation. So okay, tell us a bit about what we know about how awful these things can.

Be, all right, and I'll try to match your upbeat tone when we're talking about planet wide catastrophes. Yay, yay. Well, we don't know for sure. All we can do is estimate based on what we've seen and the smaller ones, you know, things less than a meter for example, we see this all the time, like every day. Basically, things that are less than a meter hit the top of the atmosphere and make shooting stars. And Kelly tells her kids nice fantasy stories about the universe.

They are pretty.

And then as you get bigger, like if something gets to be about five meters wide, we think one of these things hits the atmosphere about once every five years. So already just five meters wide, you know, the size of an apartment or something. It's getting pretty rare, just every once in five years. The problem is that something that big has a lot of mass, and so it actually delivers an enormous amount of energy to the upper atmosphere, but.

The damage is constrained to the upper atmosphere, because I don't feel like every five years I'm hearing about massive scary asteroid related events.

Yeah, it's mostly constrained to the upper atmosphere, but it releases as much energy as an atomic bomb. The unit here is like the power of the bomb dropped on Hiroshima. So this is like one Hiroshima every five years. Now. Usually this explodes like somewhere over the Pacific, and so it doesn't really matter. It doesn't affect anybody, and.

It doesn't affect the satellites because they're above where the atmosphere is, and so the big boom is below them. Is that right?

Yeah? And then as you get bigger, so if you have one like twenty meters wide, and that's about the size of the one that Hitcheliabinsk, that comes about every fifty years, and that's the power of like thirty hiroshimas. So when that blew up over that city, it was an enormous explosion, like we're talking about equivalent to a nuclear attack.

So far, we've been super lucky that when these things have fallen, they've fallen in relatively like uninhabited areas. So like Chilibinsk, I'll never say it, right, but that was in Siberia, right, and like in a low population area.

Yeah, but yeah, you know not the windows were shattered, two thousand people were hurt. There was an event in earlier part of this century to Tunguska in nineteen oh eight, which flattened hundreds of square miles of forest. If you look up these pictures, it has all these trees just like lying straight down. It's incredible.

That's also Siberia, isn't it.

Yes, exactly, Siberia is big, and so it's going to take a lot of hits.

All right, So how about let's go up level. What happens when you get up to the next level of devastation.

Well, if you go up to like a kilometer, we think these will impact the earth about once every five hundred thousand years, and it's good that they're that rare, because these things contain about as much energy as three million hiroshimas.

Is that an extinction level event? That's crazy?

It might be. It's right on the edge. If you go up to like five thousand meters like five kilometer wide rock, it should come about every twenty million years, and yeah, then we're all toast. If it hits in the water, you're getting like a mile high tsunami and an incredible amount of vapor in the atmosphere, which is gonna cause a runaway greenhouse effect. If it hits on land, you're gonna get super volcanoes, You're gonna get a incredible amount of dust. It's not gonna be fun for anybody.

Is one of those scenarios better than the other? That was probably not? Probably both. You're just dead and that's that.

Are you imagining some scenario where like you have to choose where you're like, Kelly, where do you want this thing to hit? The earth is waiting for you?

Well, you know, as a person who lives on a farm, you encounter a lot of preppers and you find yourself talking about scenarios where like could I survive this, could I survive that? Like under what you know parameter range, do I have a chance? And I think in general Zach and I are probably just gonners because we could never defend ourselves. But you know, I do wonder these things sometimes, but it sounds like probably one way or another, we'd be goners.

Yeah, if it's big enough, you be gone. If it's smaller, you know, like a one kilometer rock, I think you probably prefer it to land in fairly shallow water shallows so you don't get like a mile high tsunami, but some water, so it absorbs a little bit of the impact and doesn't just throw up as much dust into the atmosphere. So if you have to pick, maybe you know, send it to the Mediterranean.

Got it? But I guess you don't usually get to pick so for these extinction level events. So you did mention that whether our ability to know that they're coming depends on things like you know, how big they are and what color you know, if they're dark or easy to see. When we're talking about extinction level events, do we like definitely, can we definitely see those coming? Will we have a heads up?

So there's good news and there's bad news. I'll give you the good news first, and then you can shut your ears for the bad news if you choose. The good news is that we've been working pretty hard on this, and NASA thinks they know where all the planet killers are and that none of them are going to hit the Earth in the next few hundred years. So that's the good news. Because the bigger ones are easy to see. They tend to reflect more light and so be visible in our telescopes. The bad news is that the most dangerous ones are the comets, and those are harder to see because they come from further out. They're less predictable. We might not see one at all before we discover it's on a trajectory for the Earth. Like these asteroids, we get to watch some wizard on the Sun for years and carefully plot their trajectory, which allows us to predict for hundreds of years in the future where they might go commet. It might be the first time we see it is when we discover it's headed towards the Earth.

Oh my gosh. Okay, so say we see it for the first time, what are our options? Has NASA planned for that too? You got to walk back the existential dread.

Now NASA has planned for that and actually spoke to Steve Chelsea at JPL, who's one of the people in charge of this for the planet, and he said, quote, if you're responsible for protecting the Earth from asteroids, there's three things to keep track of, the first one is to find them early, and the other two don't really matter very much.

And you just told me it's hard to find the most dangerous ones early. So I thought you were supposed to be making me feel better and you've done the opposite. Thanks Chelsea.

I'm just glad that the Planet Terry Protection Officer has a sense of humor about it. You know, even if it's some dark humor.

We'll all be chuckling right before our demise.

But it really does matter when you see these things, because the earlier you see them, the easier it is to protect the Earth. If you can just like deflect this thing a tiny bit when it's really still very far away, it'll just miss the Earth. You know. Imagine somebody shooting a bullet at you, but they're shooting it at you from like one thousand miles away. A very tiny breeze sideways will deflect the bullet and it'll miss you, whereas if somebody standing right in front of you and attacking you point blank, then it'd be much much harder to deflect that bullet. So if you see something coming and it's still like a year or ten years away, then the tiniest little push will send it on another pass and it will miss the Earth.

How do you deflect an asteroid?

How do you deflect an asteroid? Exactly? Well, we got ideas and a lot of this is determined by this formula that tells us how much deflection we need, and it's about three and a half senime years per second of velocity divided by the number of years you got. So that means if the thing is ten years away from hitting, you only have to deflect it like three and a half millimeters per second. That's a tiny change in its velocity. But if it's one month away from hitting, then you have to deflect it like thirty centimeters per second, which is a lot more when we're talking about a big, massive rock.

Yeah, and especially since Chiliabinsk was a surprise, I'm guessing that you often don't have years or I guess it just depends.

We hope that we will have years, but yes, you might not and even in the case of the asteroid belt, like they're projections that none of the planet killers are likely to hit the Earth. That assumes that there aren't you know, collisions or surprises there like these things can be very hard to predict far out into the future. The sort of error band grows very quickly because of nonlinearities. This one gets near to that one and tugs on this other one, and then you know, chaos reigns, and all of a sudden, the trajectories have changed. So something we've got to keep a constant eye on to see if things have changed. Might have a lot of warning, you know, the dinosaurs had a lot of warning. They actually reconstructed the likely path of the impactor that wiped out the dinosaurs, and it has this funny loop in it where it looks like it made a near miss past the Earth the first time around, went through this gravitational keyhole and went around the Sun and came back and then slammed into the Earth. And it was so close that they think if you had looked up, you could have seen it from the surface of the Earth.

And they did nothing about it. I don't understand it.

It's their fault. You know, they were busy telling their children it's nothing to worry about, and so you know they weren't prepared.

You know, try to decide where to go with that. Do you want? It's not fair to victim blame, But.

It is possible for us to potentially deflect an asteroid if we have enough time.

So what would that look like? So say we decide we've got some time, we're going to try to deflect this asteroid. How would we do that?

So there's a few really fun ideas. One of them is called gravity deflection, and this is sort of like a gravity tractor. The idea is that gravity pulls on stuff, and so if you could get something else near the asteroid, its gravity would tug on the asteroid. So just like, launch a heavy blob of metal, put it near the asteroid, and its gravity, we'll tug it off course so that it doesn't hit the Earth.

But I mean, that's gonna have to be an incredibly heavy blob of metal, right, Like how big are we talk? Could we? I mean? I guess if you load how many times would you have to load starship to make that happen.

Well, it's a trade off. It either has to be very very heavy, or you need a lot of time. It doesn't have to be that big. If you get this thing up there ten years before it hits the Earth, you could have a several hundred ton object and it could really change the path of this object. But that's the key thing. This gravity tractor is a very very gentle push. It's very expensive and we take a long time to work, so you can need like years of lead time.

So we have gone out to asteroids and comets, so we at least have the technology to like get to these far off places in the Solar System.

But not very quickly is the problem. Like we can send these things out there, but you know they like pass by Venus and do a gravitational slingshot. We're not really in a hurry. We want to get them out there with like minimal cost. When you're in a hurry, it's a very different problem, and you want to minimize the time it takes for your system to get there, and that's not something we're currently great at.

That sounds to me like a pretty clever method which hopefully we could pull off. You know, but like Armageddon showed me that what you really want to do is blow stuff up. So what are what are our options for blowing stuff up?

Well, there are a few options there. One is not to blow it up, but just like knock into it, like shoot a big rocket up at it, you know, ten kilometers per second and bang into it, and that might be enough like momentum to change its course. Again, it depends on how early it is in its trajectory. If it's about to hit next week, that's going to have no useful effect. If you're talking about something that's going to hit in a few years, it could really change the path of the rocket.

Have we ever tried this or tried something like it to sort of get to handle on how it would work.

Yeah, NASA actually launched the double Asteroid Redirection test called DART, which is a kinetic impact or spacecraft. They launched it in November twenty twenty one, and it's going to hit this thing called dimorphous one hundred and eighty meter wide minor planet Moon. It's going to hit in October of twenty twenty two, when this thing is pretty close to the Earth. So we can turn our telescopes and watch and see what happens, and I'll give us a sense for like, well, what happens when you bang basically a big bullet into an asteroid.

Oh, that's awesome. And presumably they were careful enough to do this far enough away that it's not going to cause any problems.

Presumably they know what they're doing.

Well, I don't know. That's a pretty big ifs sometimes, although NASA's got a good track record, so all right, we'll go with it. Are are there any more like sort of futuristic methods? I guess fusion rockets. That's pretty futuristic, right about. How about more futuristic methods.

One of my favorite methods is the laser method. The idea being if you could shine or really power full laser at one side of the rock, it would melt ice and supplimate gases from that side of the rock, basically creating a rocket to push its sideways. So build a huge, powerful laser and just zap the rock.

That's pretty cool. Can you zap the rock with something other than a laser, because you probably need a pretty powerful laser to pull that trick off? Although I guess not if you are. The sooner you catch it, the more time you have, less powerful the laser needs to be.

I'm catching on, you're catching on. But they have a plan to build this system in space and it would rely on ten kilometer wide solar panel system. So now we're doing solar power in space, and the idea is that you could then zap these asteroids and send them off course. Of course, the other worry is, now you're building a huge space laser, and you know, some hackers take control of it and write their name on the Washington Monument or.

Something existential threats about.

But you don't have to build a laser. You could also just take advantage of the fact that the Sun is out there in space and shooting out a huge amount of energy.

Oh okay, and so it's shooting out a bunch of energy, but you know the aspirin has been moved in the commet, or the commet has been moving in this world where the Sun exists, and so you'd have to focus the energy right to get it to move off track.

Yeah, So imagine the way you take a magnifying glass and you use it to like fry a small object. You build a huge lens in space and you focus the Sun's energy on this thing, and that can change its course. Not in the sense you're trying to blow it up again. All you need to do is heat up a little edge of it so it creates a small rocket to push it sideways in it. Then it goes off, of course, and that might sound a little bit impractical. You're going to build this huge space lens and pointed at this thing. One of my favorite ideas involves wrapping half of the asteroid in foil, because you're right that they've already taken into account the fact that the sun is pushing on this thing. But if you change how much energy it absorbs, if you change how much momentum kick the Sun's like gives it by making it more reflective, you're basically turning this thing into a sol or sale and that can send it off course. So just wrap it in an aluminum foil.

Okay, So this is where asteroid mining is going to take off. You know, they're finally going to be able to get the money by saying we're going to save the world, but going to the asteroids to get the aluminum. We'll coat the asteroid that's coming to get us, and then suddenly everybody's going to be totally on board with us, and maybe that will save money because it would be expensive to shift the aluminum up from Earth, and if you could get an asteroid's worth of it. Anyway, we've solved the asteroid mining problem. What about nuclear weapons? Since we're talking about existential threats.

All right, I see that you're desperate to blow this thing up, right, So there's two categories. There's deflected and then there's destroy it and deflect it is better if you can do it early because it requires less explosive and less energy and its cheaper in general. But you're right, if it gets close enough, then you you got to just blow it up. And so people have done actually a bunch of studies of like what's the best strategy. Do you actually want to drill in deep and blow up a nuclear weapon or do you want to blow up the nuclear weapons sort of near it? Because if the thing is like a rubble pile, as you were saying before, blowing up a new uclear weapon in the middle of it might not change its profile that much. Instead, you might want to blow it up on the outside, so it tends to disperse it more so you get more of a shotgun effect on the Earth's atmosphere instead of an impactor.

So there are people whose job it is presumably to model nuclear explosions on asteroids, and like how that's going to impact the direction of the resulting rubble. And I know, if I had life to live over again, that sounds like a really fun job.

Remember that everything we learned in science is the product of somebody being so curious about it that they decided to spend their life asking that particular question and finding the answer. I was reading a thesis last week from JOHNS. Hopkins, a mechanical engineer who spent his thesis studying how to blow up these asteroids and doing hyper realistic simulations of what would happen when you injected a nuclear weapon, how far down it would have to go, and he actually found some surprises. He thinks that the asteroids are probably stronger and tougher than we have thought, and they would require more energy to be shattered. And he was modeling like how the cracks would move along the surface and whether they would make it all the way to the other side, and the effects of gravity of like pulling this thing back together at the same time. It's a really complicated process.

And I'll note that all sounds bad for asteroid mining as well.

There's another thing you can do if the thing is gonna hit and you want to blow it up without using nuclear weapons. This actually reminds me about something you brought up the other day, about one time that we put a bunch of copper rods into space. Some folks have this idea of laying out a series of rods in space in front of the path of the asteroid. And the idea is the asteroid's already moving really really fast. You don't need to shoot it with something else moving fast. You just basically put a bunch of bullets in space in front of it, and from the asteroid's point of view, it's like those bullets are coming at the asteroid. So if you sort of create this spray of rods in space between us and the asteroid, when it passes through, I get shredded and I'll break it up, and then you end up with again a lot of small bits instead of one big one.

Well, I'm personally hoping that this question does not come up in my lifetime. Do we have the option and I think I know the answer to this one. Do we have the option of abandoning ship if something is definitely going to destroy Earth and we can't make it go away because at the beginning of don't look up, some of them are able to abandon ship.

Well, I think Elon Musk probably has those plans, but for the rest of us, we don't really you know, there's no realistic way to get six billion people off the Earth in a short amount of time and let them live in space or colonize Mars like. We are decades or hundreds of years away from being able to do that. So unfortunately, there really isn't an option of abandoning ship. People would like us to have colonies on Mars so that humanity survives if something does impact the Earth, and you know, I see the logic in that argument, but it also means that everybody else who's on Earth is going to die in that scenario, so I think there's a kind of a big hole in that plan.

I also think we're decades or one hundred of years away from the Martians not dying when the Earthlings die, because Martians are going to require resupply trips from Earth for a long time before they're self sustaining and autarcic, so I think they're gunners too. They'll just watch as Earthlings die and then they will slowly fade away. So I think that everybody is poned.

If you will, I totally agree with you. And so what we really need to do is invest a little bit more in telescopes. You'd be surprised at the tiny amount of resources devoted to this. There's like a telescope in New Mexico and one near Tucson, and a couple of very small satellites. But you know, with more satellites and more telescopes, so we could see more of these things, and then we would have more time to respond if we did see one of these guys headed for Earth.

So why do you think we aren't investing more in this? Like it's clearly scary stuff. People can see shooting stars, so they can like it shouldn't be hard to convince them that there's stuff that's bombarding our atmosphere and as it gets bigger, it can cause a problem. Why don't we invest in this?

I think it's for the same reason that people let stuff fall apart on their house. As a civilization, we're moving from crisis to crisis, and if it's not the most important crisis in front of you right now, then it doesn't get attention, and so it's sort of theoretical and maybe's going to happen, but we don't need to deal with it today. Fine, let's deal with it tomorrow. And so far tomorrow hasn't come.

There have certainly been lots of crises in the last couple of years to deal with.

Yeah, we've got plenty on our plate, exactly.

All right, Well, here's hopeing we all decide to invest in science. Though. I'm sure that the money that we spend on those telescopes to protect ourselves would probably also teach us a lot about the world that we live in, So it would be a good investment in lots of ways.

Yay science, Yay science. And for those of you making long term plans, we do know that a rock called Apofis, which is three hundred and seventy meters wide, is due to make a very close pass by the Earth on Friday the thirteenth in April twenty twenty nine, so plan your camping trips.

Maybe by then Ada will be old enough for me to explain what's happening to her. We can check it.

Out as you've seen her happy birthday in the underground bunker you have built that's right.

That's not quite her birthday. But yeah, yeah, yeah, maybe I'm not sure. We'll try to tie that to celebrating a birthday party.

We'll see, all right. Well, thanks everybody for coming along on this ride of curiosity as we learn about the dangers that are out there in space and what science has done and can do to potentially protect us. Thanks very much, Kelly for joining.

Us, Thanks for having me, Thanks for listening.

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Daniel and Jorge Explain the Universe

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