How big can a comet get?

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Speaker 1: Hey, Katie, how do you like your gelato? Definitely with two scoops of basically any flavor. So it's all about quantity for you, that right, It's all about gelato. What's to complain about? All right? So is that also true for things out in space? Bigger is always better? I mean, the sun is gigantic, and I only have good things to say about that. So you know, all right, you should leave a five star review for our star? What about things like comets? Is bigger always better there? I mean, especially if they're made out of ice cream? So a big old comet streaking above our sky leaving a trail of sprinkles? Who doesn't want that? Well? What if it's sprinkling its way towards the earth like impact style? Well then I can order a triple gelato with no consequences. Hi. I'm Daniel. I'm a particle physicist and a professor at U C Irvine, and I am Katie, and I'm the host of the podcast Creature Feature. And I enjoy ice cream as much as I enjoy physics, which is a lot but not too much moderation in all things? Is that the vibe I'm getting? That's probably right? In both cases, if I have too much physics at once, I also get a brain freeze. Or did you mean like after a nice large meal you need a little bit of physics to sort of like balance out the palette. I mean, I think that's what digestion is, right, Absolutely well, Welcome to the podcast Daniel and Jorge explain the universe in which we try to digest the entire universe. We serve it up on a platter d you and give it to you in tiny little spoonfuls, hoping that helps you understand the mysteries of black holes, the incredible froth and quantum nature of reality, the mysteries, the puzzles, the insides, all of it. We sprinkle delicious treats on top and serve it up to you. It's the Moves Bouge of particle physics. My typical co host and friend, Jorge Champ can't be here today, so as usual we are joined by the wonderful Katie. Katie, thank you very much for joining us again today. Yeah, happy to be here again. Want to point out Jorge and I have never been seen together in the same room. Raises some questions, doesn't it? Does that mean that Jorge transforms into you or you transform into Jorge. At this point, who can say who is who Isn't that the lesson of jack Bile and Hide exactly the quantum mechanical interpretation of modern literature. It's really the jackal Hide wave function, that's right, got to collapse the wave form. Well, we are happy to talk physics with either Katie or Jorge, so thanks for joining us. And while we nibble on our gelato, we ponder the mysteries of the universe, but we also ponder the mysteries of our own neighborhood. You might think that astronomers have our backyard the Solar system, mostly figured out, and that the open questions in physics revolve around things very very far away and far in the future and far back in time. But you might be surprised to learn that our own neighborhood remains something of a mystery to us. Now, that doesn't seem right, because my understanding as we've already got real estate on Mars and have every crevice, every crater of the Moon mapped out, So how can there be any mysteries left here in our solar system? Well, it's probably true that some entrepreneur has planned the first gelato stand on Mars that's pretty close to Earth. And you know, the Solar System is actually really really vast. The Earth is tucked in really tightly, very close to the Sun, but outpassed Jupiter and outpassed the icy planets. There's a lot of mysterious stuff going on. What's the furthest we've ever sent any of our instruments out into space. We haven't gotten past our own Solar System. We have sent some probs really deep into space, just like launch them out there and see how long they last. And the one that's the furthest out the object the humans have built that has gone the deepest into space is Voyager one. But even Voyager one hasn't officially left the Solar System yet. In around three hundred years, it might reach the outskirts of the Solar System, but unfortunately it's power runs out in five so by the time it gets there, it'll just be a dead lump. Well so we so, you know, you'll be fifty gelato by that point. Anyway, I can only hope. So there could be some space gopers in our space backyard and we wouldn't even know it. That's right. There are mysteries right here in our own backyard. There are things we do not understand. One way to explore the mist to send probes deep into the outskirts of the Solar System. But that's pretty slow. You know, it takes years for things to get out there because it's so day far away. You know, it takes months to get to Venus or Mars, but to get out to Pluto can take a decade. To get further out deep into the farthest reaches of the Solar System to explore its fringes takes even longer. But there's another way to study our deep, mysterious backyard, and that's to wait for it to come to us. Because sometimes things out from the outskirts do fall into the Solar System, and these things are called comets. They accelerate to incredible speeds as they whip around the Sun and then go back to where they came from. So how do comets find us? Did they see some kind of flyer way out in space It at the Earth sale about two point five light years away? Is it just random chance? Are they drawn into our Solar system? They hang out there in the deep reaches of the Solar System, and we're not exactly sure what sometimes triggers them to fall in. It might be the passing of a nearby star, or the gravitational tug of the Milky Way, or something else. Entirely, we don't even really understand what's going on out there and what is out there waiting to maybe fall into the Solar System. For those of you who have seen don't look up and worry about things hitting the Earth. You don't have to worry too much about things like asteroids, those rocks that are orbiting the inner Solar system. But comets are much more dangerous because they can be hard to predict, and they're moving much more quickly when they do enter the Solar System. I watched Don't Look Up, and I find it interesting because I think there is a big divide in terms of how realistic people find it in Those who are either climate scientists or even in any related science find it very realistic, whereas other people think, oh, this this is just two on the nose, it's too outrageous. You mean, like the social response to the scientific warning, or you mean the science itself, the social response to the scientific warning that's in the movie. Yeah, that was pretty sobering. Actually, I think that was mostly the point of the movie. The actual science a bit where they're like at the white board figuring out the trajectory of the comment. That was like the first two minutes of the movie. After that, there was a great much science, But that part was pretty accurate. You know though, I heard that they had to find somebody to play a math double for Leonardo DiCaprio. When they zoom in on the whiteboard, that's not actually his hand doing those calculations, which means there's a whole other career. I didn't even realize I was missing out on, you know, Hollywood math double. Who do you think you would be in terms of Hollywood's math double. I'd like to be Jeff Goldblum's math double. I want to do his math. Jeff, if you're listening, please hooking me up. I don't want you to hurt yourself doing maths, so please let me take the fall for you. But speaking of taking the falls, some of these comets that enter the Solar System are pretty small. There's just a few kilometers wide. But there's some been some recent discoveries that are stretching people's brains about how big a comet can be. So you're saying that asteroids are not typically that dangerous whereas comets are. Why is that is that base stun the stuff that they're made out of, or their behaviors. It's mostly based on our ability to see them. Commets orbit in the Inner Solar System, and so we can point our telescopes and we can watch them, and we can see where they're going, and we are not worried about them because we know where basically all the big ones are. They reflect enough sunlight for us to track them and predict their path for a few hundred years. Once it astronomer gets like four or five six measurements of the motion of an object, they can pretty well predict its path. But comets have very long periods. Some of these things have like hundreds or thousands of years long period, which means the first time we see it might be when it's headed towards the Earth, which is why you might not get a whole lot of warning. And they're going much much faster because they're falling in from much further away. And those of you who watch these guys might remember that this happened in This is not just fiction. In comment entered the Solar System and then smacked right into Jupiter. It was spectacular. You could see it with your own telescope in your own backyard, earth size fireballs rising from the surface of Jupiter. It was like astronomical schadenfreud. You know, it's pretty awesome, but we were glad it wasn't hitting us. Those poor Jupidtonians Jupidonians having to have that name. Man, we'll have to ask or hey, what he would prefer as a name of that. It's definitely not jupiter Lyns. That would be pretty awkward Jupeians. Maybe a much bit Cans, my fellow Jupidicns. We can't necessarily know when a comment is coming, but should we really be that worried? Our atmosphere is pretty hot, so it seems like it could melt a comment, right. Our atmosphere is pretty hot, and you can melt a comment if it wasn't too big. But remember the impactory that took out the dinosaurs million years ago was only a few kilometers wide, So anything bigger than that is going to make it to the surface of the Earth and deposit a lot of kinetic energy. And so that's why it's really important to think about questions like, well, how big can a comment get? And so today in the podcast will be asking that exact question, how big can a comment get? Um Empire State building size? That's that's my guest. You just like the mental visual of the Empire state building crashing into the earth. Somebody's got to do that in Hollywood. Maybe blue whale size, because I also like the image of a blue whale crashing in Earth. Man talk about a belly flop, right, a blue whale coming from space and hitting the ocean. Ouch, that sounds like it hurts well as usual. I was curious what people out there in the Internet thought about this question. Have people thought about how big a commt is? Do they have any idea how large these snowballs from the far reaches of space can be? So I asked folks to volunteer to answer random physics questions to contribute to the podcast. And if you would like to participate, lease, don't be shy. You are very very welcome. No expertise is required. Just email me two questions at Daniel and Jorge dot com. So before you listen to these answers, think to yourself, how big do you think a comet can get here's what people had to say, pretty big. But then it starts getting into like whether you classify as common or a planet. I think comments can get as big as some of the largest planets out there. I think if something happens where planet gets out of orbit or start pades away, um, then those planets could then become free. Practically, I never thought that comments could or like pigeonholed into a certain size. I think, you know, it could just be a stray ice ball. But size doesn't really matter for comments. Well, based purely on imagination, I think comments can get as big as our moon. I ventured to guess comments can become as large as they can until they are too large to be called commets. From what I know, commets are this frozen stuff of dust and solids and gases. So it depends on what the commet has in it, because most of the stuff gets melted away as it enters and becomes warmer and hotter. What would prevent a comment from getting too big? I guess the two things that I can think of our If it's too big, it could break up easily, and hence you won't have one comment, you'll have multiple comments, and that's related to the structure of it. The other thing is that if you have something that's very big, it's likely not made out of a large percentage of ice crystals, is probably going to be highly metallic and won't develop the tails of the comments. So that still doesn't answer the question of how big can the comment get. I would guess I don't know, three or four or bus sizes. I don't know. I would imagine it will get as big as it can without the dust squishing it, because aren't commits quite low density. I suppose the gravity might turn it into an asteroid. I'm not sure about what the definitions are there, but I hope that's helped in some way. That's a good question. I imagine they could get bigger than an asteroid, depending on how much gravity maybe they had when they were out far far far in the far reaches of the solar systems or the orc clouds, or wherever they get all their ice from. Like, maybe they're just a particularly big chunk that gathered a whole lot and solidified before it came rushing in towards the center of our solar system. All right, so nobody else that empire states building or whale sized. Well, I am interested in the question of when does it become a planet. Is the only thing separating something like a comet and a planet just its signs? Or is there some other property to a comet that makes it not a planet? Oh man, this is such a tangle of names. The astronomers have made such a mess of what they call things. Is it a centaur, is it a trans Newtonian object? It is a minor planet. There are such ridiculous and sometimes conflicting rules about these things. In this case, you can actually make a nice little line between what's a comet and what's not. What you call a comet is something that has an atmosphere because the Sun is heating it up and it's out gassing. So imagine some icy ball thousands of au away from the Sun. It's just going to be sitting there frozen. But if it falls in towards the Solar System and the Sun starts to heat it up, then some of those ices are going to turn into gas, and they're going to give that comet a little atmosphere, which they call a co and it might even give it a little tail if some of it is blown off behind it. So that's what distinguishes an asteroid from a comet or a planet, or even a minor planet, or a or trans neptunity sorry, trans Neptunian objects, not trans Newtonian. Nobody launched isamutany into outer space yet they should have, though, that would teach him a thing or two about gravity. So if these comets have atmospheres, could this mean that some form of life could conceivably breathe it in or is it just inherently unfriendly towards life? Oh, I was hoping you were going to go there, the biologist, and you can't resist asking that question. Now, of course, we can never say never, because life is weird and could take all sorts of strange forms. But these would be very short lived atmospheres. This is something that doesn't exist when it's out there, deep into space. It only appears when the comet is falling towards the Sun and it's not gravitationally bound like these things are not big enough to have an atmosphere. The reason an asteroid doesn't have an atmosphere is that doesn't have enough gravity to hold onto it. Even the Moon doesn't have enough gravity to hold onto it. If you like pumped an atmosphere onto the moon. We all just drift away in a few dozen years or maybe a hundred. So a commet, it's atmosphere sort of transient. It keeps losing it and then it keeps replenishing it by outgassing it. So it'd be pretty hard situation, I think for life to form. So you'd basically just get a few puffs of atmosphere as life, but you wouldn't have millions of years to evolve. On this comment more of a vape situation. If you're a life form, Yeah, unless you're something really weird form of life, which can like go into stasis for a long long time and then wake up again, like those insects that wake up every seventeen years and like take a few breaths, live a very short life as the common is diving towards the sun, and then go back to sleep. Well, you know, there is a life form already out in space that can go into stays us and can survive the rigors of the vacuum of space at least for short periods of time, and those are tartar grades. So who knows, maybe some of those tartar grades we accidentally dropped on the moon, will someday find their way to sort of ride a comet for a little while. You think maybe they're gonna just like jump off the moon because there's such a little gravity there, land on a comet and ride it around the Solar system. That sounds pretty awesome, like doctor Strange love Tartar Grade, little tiny silver surfers. Well, that sounds like a great science fiction novel. So what we're talking about today are these comets, and these comments are again distinguished from asteroids because they have a coma and they can have a tail. A tail is not actually necessary for it to be a comet. A lot of people think about comments. They think about tails because when you look up in the sky, that's how a comet looks different from just like a star or something else shiny. Technically, though, astronom will call it a comet even if it doesn't yet have a tail, like before it's really fallen into the inner Solar system, it can still just have a coma. The other weird thing about comets is that they don't always just have one tail. They can have two different tails simultaneously, so just kind of a split stream going on or these tails made out of different stuff, so comments on that, like these dirty snowballs, and some of the stuff when he gets heated up, turns into gas and then the sun blows that away. So one of the tails of a comet is a gas tail, and that's pointing away from the sun. A lot of people think like the comets tail is pointing behind it, sort of like a rocket's exhaust or like you know those wiggle motions in a cartoon. That means that something is moving fast, but it's actually pointing away from the sun, like the sun is blowing gas away from it. So that's the gas tail. The other tail is typically made out of dust to like little bits of rock or whatever from the core of a comet, the non ice parts, and those are a little heavier so they don't get blown by the solar wind and they do actually follow more like the trajectory of the comet. So you have one tail that's sort of flying out behind the comet along its path and the other one that's getting blown away by the sun. And these are not always pointed in the same direction. So if you're really lucky, you can see a comet with both of these tails. Simultaneously, it looks pretty spectacular. So for thinking of a comet like a runway model, the gas tail is its hair getting blown out of its face by some conveniently placed fans, and the dust tail is like it's cloak, kind of wafting behind it as it struts down the runway, hopefully not towards Earth exactly. And if you are running with a tail wind right when the comet comes around the Sun and it's now going back into the outer Solar System, then its tail is pointing in the direction it's moving. It's like an anti tail because the Sun is now behind it, and so it's blowing gas in the direction the comet is moving. So the tail isn't always even behind the comet. Sometimes it's ahead of comment. So if we see a giant comet that has a tail pointed in our direction, that does not mean we're not in danger, because it could be coming right this way. That's right. You need me at the white board or somebody else doing those calculations before you know whether or not we should abandon the planet. And these comments come into different groups. Some of them are short period comets which come from the Piper Belt. This is a region of just like icy stuff. Planetism as just past Neptune, you know, past Neptune. This like a whole, big, messy pile of stuff. That's why people argue about whether Pluto should be a planet, because Pluto is the first thing we saw out there that was about that size, and then we discovered, oh my gosh, there's a lot of these like frozen balls out there. There are about Pluto size. We call Pluto a planet, we've got to call them all planets. So like after Neptune, the solar systems basically just a big mess. Sounds like a lot of planetary gate keeping. Just because Pluto's a mess doesn't mean it shouldn't be a planet. It's not just that Pluto is a mess. It's Pluto, and it's like seventeen thousand friends are all a mess, And do you want a solar system with seventeen thousand planets in it? You know, I guess it just depends on way to think of a solar system. But you know, to me, these arguments are just about names gues. It depends on if they're bringing pizza money or if they're just coming there for the free food. That's right. Anybody who brings gelato is welcome. But some of these little icy balls out there and the Kuiper Belt can get nudged and fall into the Solar System. And these are called short period comets, meaning that they take months or years to go around the Solar System. But there's another group, these long period comets that come from another source that much further out passed even the Kuiper Belt way past Pluto, many many, many thousands and millions of kilometers, and that comes from this blob called the Oort Cloud, which is this theoretical cloud of icy many planets. And I say theoretical because we're pretty sure it's there, but we've never actually seen it, so we only know about it's possible existence based on the garbage that it throws our way exactly. We can't otherwise explain where these comments come from. And so based on these comments about fifty years ago, Yon Ord suggested maybe there's this huge group of icy balls out there and just a tiny fraction them are occasionally falling towards the Earth. So I want to talk a lot more about the Ord Cloud and what it contains and the size of the comets that might be lurking in there. But first, let's take a quick break. All right, we're back and we're talking about what's going on in the messy outer reaches of the Solar system. Well passed Pluto, well passed, all of the trans Neptunian objects, well passed everything that might be called a planet, deep deep, deep out there, more like a thousand or two thousand astronaut coomical units past the Sun. There is this graveyard of icy objects which might form future comments. So we only know about this based on this sort of space junk that comes our way. We've never actually seen the cloud itself exactly, and that's because it's so far away. You know. The an astronomical unit is the distance between the Sun and the Earth, and the orc cloud starts like thousands of astronomical units, maybe up to fifty thousand astronomical units from the Sun. We're talking like one to two light years away. And it's really hard to see these objects when they're so far away because they don't reflect a whole lot of sun because not much sun gets there, and they're so small that not much of their light comes back to us. You know, they're not glowing on their own like stars. We can only see them if the light reflects it just the right angle and there's enough of it. So we've never seen it directly. We've only seen the ones that are falling towards the earth, and from that we're trying to guess what's out there. It's like if you couldn't see clouds, but you could measure rain, and you're wondering, like, what's up there in the sky. Maybe there are these huge reservoirs of water floating above us. Or it's like when you can't see a squirrel in a tree, but you know it must be there because you keep getting little pieces of acorn shell showering down on your head. Yeah, exactly. And the range of speculation for like how much stuff is out there is enormous. It could be that there are billions of icy objects out there. It could be that there are trillions of icy objects out there. It all depends on also, like how big they are, Like there could be billions of things like twenty kilometers wide or larger, but if you get too smaller and smaller objects like just kilometer or so, there could be even trillions out there. And it's a lot of stuff that we're talking about. They speculate that if you add up all of this stuff, it's like five to ten times the mass of the Earth. So it's not a small amount of basic material that's orbiting out there in the distance waiting for its trip around the Sun. So how much can we determine just based on the sort of fall off that happens from this proposed or cloud, like do we know the shape of it or can we just kind of basically guess, well, it's there and maybe it's big. A lot of it is guesswork based on modeling. We try to think about how the Solar system formed, how stuff would end up, what's likely to be out there, and that really informs a lot of our understanding of the Solar system for things that we cannot see. And that doesn't mean that it's bolognay, it's not just something we're making up. You know, this is a really valuable part of how we do sciences. We try to tell a complete holistic story of the Solar system and say, if this is true and that is true, what does that mean about the early times or the late times or what's going on. It's really valuable and you know, you can take the measurements that we have and you try to make them consistent with that story. And so they think about this huge cloud out of gas and dust and ice crystals that helped form the Solar System. The reason we talk about ice in the far reaches of the Solar System is because it's cold out there and ice melts, and any water that was closer before the snow line they call it would have been liquid or vapor, and so it wouldn't form these icy objects. So we think, based on these models, that the Orc Cloud has sort of two different shapes. That's like an inner or cloud that's sort of like a doughnut sort of flat, like the rest of the Solar System. And this might be from like a few thousand a U out to like twenty thousand a U. And then there might be like a larger spherical or cloud surrounding the entire Solar System, like a huge ball that goes out to like fifty thousand a U or even further. And that's sort of like at the edge of the interstellar distance. You know, other stars are like a few light years away. So now we're talking about like the very edges of our little corner of space bumping up against other stars, edges of their space, and so may be this sort cloud and these big icy for us to donuts can only exist between solar systems because otherwise they get too warm or they get pulled in and then become a comet that eventually melts or collides with something. Exactly in order to be an ice blob, you have to be far away from the star, and that's why Earth, for example, is not an ice ball. It's just too warm and mercury and venus, and that's why the icy planets are far away from the Sun. And as you say, these things are too far away to get melted. So that's where you go to find gelato on your trip between stars. I'm glad I don't have to walk as far here for gelato, but it would still be worth it. Right, Gelato is just that good. But it's really fascinating to me because it shows you something of the tug of war between solar systems. We tend to think of stars as like totally separate. We have our solar system, they got their solar system, and maybe very rarely two stars will come near each other and there'll be chaos. But in reality, there's like a constant tug of war at the boundaries between the Solar system. Like imagine you're halfway between two stars and you're feeling gentle gravity from both stars, and so you're being tugged one way, tugged another way, And that's these stars are moving relative to each other, that gravity is changing. So maybe you get like bumped from one solar system to another, which means that, like some parts of our Worth Cloud might not be from our Solar system. They might have like started out in another solar system and then got past two hours, maybe several times. Maybe they're like hopscotching from solar system to solar system. Could that be one reason that our solar system is able to host our comfy little planet Earth without having gotten pummeled by too many comments? Could there be a benevolent Solar system out there absorbing or sucking in more comments. I like your optimistic theory of the universe that there's somebody out there looking out for us by eating all the gelato before it falls to Earth to kill us. It could be yeah, you know, maybe not intentionally, but just by here a chance a son out, they're kind of preventing more of these frozen ice balls from colliding with our Solar System, it could be, or it could be even closer to home. A lot of folks think that our gas giants Saturn and Jupiter provides something of a gravitational shield against impactors in the inner Solar System, and that like a lot of the icy balls in the or cloud are there because they got thrown out of the Solar System early on by these gas giants as things were like still coming together, and so now they're like lurking outside waiting for their chance to come back into the light. Well, it seems like for some planets that maybe protecting all life on Earth, we should come up with a more flattering name than gas giants. But you know, I guess that's it's accurate at least. Well, you know, we did name them after the most important gods, you know, like Jupiter and Zeus, so that you know, that's pretty flattering. Right, there's no planet named Zeus. Zeus is the Greek version of Jupiter, isn't it right? Yes, that's right, that's right. I think z would be a much better name for a planet than Jupiter. Right, I'm petitioning that we renamed Jupiter Zeus because then the people who live on it would be called Zeusians. That rolls off the tongue much nicer, and then you can't have that schoolyard chant of girls go to Jupiter to get more stupider. So I'm all for it. Heard that one that's terrible. Well, it goes either way. You can say boys go to Jupiter to get more stupider, girls go to Mars to drive cool cars, or vice versa. But you know, I think we should be breaking those rigid gender roles in terms of planets. Totally agree. And so one question about what's out there in the or cloud is just like how did it get formed and what's its composition? But a big and important question, and one that might really affect our future is how big are the things out there? You know, a lot of the comets that we have seen coming in our Solar System are just a few kilometers wide, and they're big enough to be spectacular. But people wonder, like, are their planet sized objects out there in the or cloud? Could one of them fall into the inner Solar System and like really do some damage. So if there's an ice ball hang out there that is planet sized, would it be considered a planet before it becomes a comet? Or is it just considered some kind of ice ball. I think that the new definition of planet makes it basically impossible because an object has to like clear its own path, that has to basically have its own unique path through the Solar System to be called a planet. But I also think that there are now conflicting definitions of what a planet is. But as soon as it falls in towards the Solar System and develops a coma, then it's a comet, even if it used to be like the Moon sized or Pluto sized, or even I guess Neptune sized, right, Like one of the listeners was guessing planets that lose their orbits could be comets, Like that's really crazy to think about. They would be at least ice planets. So could there be a big ice ball the size of Earth that at some point comes in and smashes into our Solar System? Like? How much sleep should I lose after otarting this podcast? Well, we just don't know, is the thing. It's a mystery to us. One thing we do know is that most of the things that fall in from the or cloud tend to be smaller. But there's now a spectrum and we're seeing larger and larger objects. So the thing that should scare you is that as we keep studying, we keep discovering larger and larger objects of the Orc cloud. We'll talk about one particular monster in a minute. So that should terrify you because it might mean that there are really some huge blobs of ice waiting out there. The thing that should help you fall asleep, though, is that we do know that there's an inverse relationship between how many there are and their size. Like with everything else, there's going to be lots and lots of dust screens, and then it's wund be fewer things the size of snowball, and fewer things the size of a bus, and even fewer things the size of you know, there are ten kilometers across. The interesting thing is we don't know what the maximum is like. There might just be one real monster out there. But how big is the biggest monster? If you can't see it, if we're too far away to be able to see it with any of our monitoring tools from here on Earth or even you know, the ones that we send out on the edges of our solar system, how would you be able to guess the size of the biggest ice ball. Yeah, you would have to use some models. You'd have to understand how all those ice balls formed. Then you'd have to develop a simulation that ran through the formation of the Solar system, and you'd look for models that explain what we do see. You know that look at this relationship between size and frequency and correctly predict that, and then you can extrapolate. You could say, well, as they get bigger, if the rate of their occurrence drops by you know, some factor, then you could follow that line forward and try to predict like how big theoretically an object could be. But this is the kind of thing that we do all the time in astronomy, and then we're surprised, Like we have predictions for how big the largest galactic clusters should be, and then we keep finding bigger ones. Were like, well, I guess something was wrong, but that's just the process of science. And so until we actually see these things, were often not sure about what the upper limits are. So we would have to base it on the sort of our existing models and things we can observe and sort of use that to extrapolate what it is. But do we know theoretically if there is a limit to just physically to an ice ball. How big can an object made with a solid core and then sort of an icy exterior get that we know of. I think there are some theoretical limits you good place, Like we know that you could be as big as Neptune or Uranus because we see those and those are basically the same thing. A huge balls of ice with a rocky core. If it gets much bigger than that Jupiter size, that could still exist. If it gets even bigger than that, if it gets like a hundred times to size of Jubiter, then it would be big enough to ignite fusion in its core and it would start to glow. We would definitely see that. If there was another star out there that was actually emitting light, we would see it. So the orc cloud is dark, and that in itself puts a limit on the biggest thing that could be in there. You can't have a glowing star in the word cloud. So like a hundred jupiters is the biggest anything could be theoretically, But that's really big, like Jupiter itself is three hundred times the mass of the Earth. So that's not a very useful limit. It doesn't really reassure anybody. We wouldn't be less dead if we were hit by a half the size of Jupiter, Comment versus twice the size of Jupiter. Comment would be equally dead in both scenarios, is what you're saying? Yeah, exactly, though the astronomers would be like, oh wow, that's really interesting. We're surprised just before we all get blown up. Hey, well that's worth something. At least the astronomers will get their kicks as we're munch agone gelato. But recently we did spot a pretty big monster object in the Orc Cloud heading towards the Inner Solar System. That kind of surprised astronomers. Nobody had ever seen some this large, and it sort of stretched people's brains about how big one of these I see objects could be. It's not Jupiter size, but it is pretty large. So the object that hit the Earth sixty five billion years ago was about five to six kilometers wide. We think based on reconstructions, how much is that in blue whales? That's not a physical unit I'm familiar with, so I have to type that into Google. Wealth blue whale is maybe about thirty long yea, So we're talking about something that's two hundred blue whales long by volume, that would make it like eight million blue whales. That's a lot of blue whales, exactly eight million blue whales rolled into a six kilometer wide ball impacting the Earth would not be a great situation. But that's basically what happened sixty five million years ago. But two astronomers called Bernadelli and Bernstein recently spotted an object that they think is a hundred to two hundred kilometers across, so like much bigger and the one that hit the Earth and caused an environmental cataclysm that changed the future of the planet. This thing is forty times bigger, so we'll lose forty times the number of dinosaurs this time around. You don't think its scales that way. Don't tell me how to do a math. That's a hefty that's a hefty comment. How far away is it? Just asking for general, generally interested. This thing we think started its journey around forty thousand a US away, so deep deep in the Orc cloud. And last time it was spotted middle of last year, it was about twenty a U away, So that's twenty times the distance from the Sun to the Earth, so still really really far away, and so I want to talk about how we spotted this thing, what its future trajectory is, what we might learn about the deep reaches of the Solar System by studying this massive comment. But first, let's take another quick break and I'm going to take some deep breathing. All right, we're back, and we're talking about a ginormous visitor from the far edges of the Solar system. Comment Bernadeli Bernstein. And I don't know anything about Bernardelli or Bernstein, but I'm imagining this very nice friendship between an Italian guy and the Jewish guy having an ice cream, having a gelato, discovering a giant comment. Yeah, maybe they're having some gelato on their bobka, you know, and they're just like really fusing the cultures together. Yeah, having some halva and some here you go. You know, every culture has its take on ice cream. But now, for the life of me, I can't think what is the Jewish version of ice cream? Do we have our own kind of ice cream? I don't know. That's why I said halva, because that's sort of the creamiest dessert I know of. But yeah, I'm I am not sure. Desert cultures, I guess don't have an everything exactly except for those of us who ended up in Siberia. Yeah, yeah, right, So we are importing gelato from the far regions of the Solar System into our desert culture. Here as comment Bernard Deli Bernstein comes closer to the Sun, is developing a coma. So that's why we don't call this thing a minor planet or a dwarf Planet's officially a comet because it's grown a coma. They can see this thing out gassing and it's like surrounded by this little puff of gas. So again, just generally interested, no big deal. But do we know the direction this giant comment is going in? We do. We've spotted it a few times, We've made a bunch of measurements, and so we can predict its trajectory. It looks like the closest it's gonna come is in twenty thirty one. It's gonna come within around eleven A U. So that's the closest to the Sun it's gonna get, which means we are totally safe. Right, We are at one a U. So this thing is going to be really far away compared to us, and so this comment is going to swoop actually up it's like not following the plane of the ecliptic. It's actually coming like sort of from below the plane. It's going to swoop up between the orbits of Saturn and Uranus, and then it's going to pass above the Solar System. So these commets aren't necessarily limited to the plane of the Solar System because they come from this spherical cloud of objects the outer word cloud. So it probably had its own trajectory and velocity before it started being influenced by our Sun, right, yeah, probably, and it's probably been falling in towards the Sun for a long long time. They estimate that the period of this commet is about three million years. It's gonna take three million years to loop around go back out into the really far reach of the Solar System, where it's going to start moving really really slow. Right, People think about things moving fast when they're far away from the Sun, but the opposite is true when you're really close to the Sun. When you're moving really really fast, like Mercury's orbit is very fast, Pluto plunks along very very slowly because it's far away from the Sun, which means that the Sun's gravity is not very strong, so it doesn't have to be moving very fast to be in an orbit, in the same way a commet. When it zooms towards the center of the Solar system, it's going really fast as it whips around the Sun, and then it slows down as it gets far out. It's sort of like a ball in a well. It zooms down, it's going it's fastest at the bottom, and then when it comes back up and before it turns around, it's like stops. It's the same thing with a commet. And so it takes three million years to do this whole orbit, all the way deep into the or cloud and then back in towards the Sun. But well, we actually get to see it. If it's eleven au away, we will get to see it, but we'll have to use telescopes, so you won't be able to see it with your naked eye. Even though this thing is a monster, right, it's like almost two kilometers across, it's gonna be too far away for us to spot it. The comments that you can see with the naked eye, Gailey's comet and other stuff, that's because they come close enough to the Earth that you can really see them. But you will be able to see this thing with an amateur telescope, and they suspect that it might grow a tail. Right now, it just has a coma, but as it gets closer and closer to the Sun, it's gonna get heated up more and more and it might develop this gas tail or a dust tail. So that would be pretty useful also because studying that tail can help us understand what is out there in the Orc cloud. What can the tail tell us about the Orc cloud? So we don't know what the stuff out there is made out if we think it's like ice and rock, and we really want to build better models of how the solar system forms so we can understand what is out there, and so we can take measurements of what's in this tail even without going out there. Like when an object is just frozen, all you can do is bounce light off of it and measure like how much light reflects. But if you have vapor, if you have gas and light passes through it, then you can tell a lot more about what's in it because you can look at the frequency of light that passes through it, and it will also glow in its own frequencies, just like you can tell what's in the atmosphere of Venus by looking at the frequencies of light that passed through it and the frequencies in which that gas loows, because remember, every kind of gas glows in different frequencies, is like a little fingerprint based on which kinds of photons it likes to absorb in which kinds it likes to give off. So, because the comet is visiting closer to the Sun and some of its icy components are being turned into gas, we can then study that tail and try to understand like, oh, how much methane is there, or how much carbon is there, how much oxygen is there in these frozen objects, and that will really inform the models we build about how the Ord Cloud came to be and where everything is distributed in the Solar system, and it could maybe tell us like how big the largest ice balls might be in the Orc Club exactly. The more data we have about these details, the better we can build our models to really specifically predict what's out there in the Orc Cloud. Because this is the biggest one we've seen, is it likely that it's the biggest thing in the Orc Cloud? Almost certainly? Not right, Probably there are many more of these things waiting out there to fuse different culture together as astronomers from around the world come together to find them. But there are probably much bigger ones that we just have not seen yet. So mark down on your calendars nine years from now, get your telescopes out, and start looking at that comment. Hunh exactly. And another fun way to think about commets is not just the size of their central object, like we're talking about the icy, frozen core, like how much stuff there is to the commet, which is, you know, a useful way to think about it if you're worried about the comets hitting the planet. But there's another way you can measure the size of the comment, and that's by the size of the coma. They make this gaseous envelope that surrounds the commet. As it gets heated up, some of these things get like crazy big, it's ridiculous, it's bonkers. These things are not gravitationally bound. They're just sort of like surrounding the comet. But they can eject so much gas that their commas can be like enormous. There's a comment they found in two thousand seven called commet homes that has a really tiny, small core, but it's coma. Get ready for this because it's gonna sound insane. It's coma is bigger than the sun. Shut the front door of the cellar for the system, and don't let any of these ens. So how can it produce if it's got a small core, how can it produce such a huge cloud of gas? And don't say cuteoba, because I won't believe you. Exactly that's the problem with being flavored ice cream exactly for Jolie gelato, not a good idea. Nobody knows really, and it's a question about like what is this thing made out of and how did it do this? But they saw this comma. It's one point four million kilometers wide. You can actually see it in our skies. It's like a big circular cloud. So we don't really understand it. The core of this thing, common homes is just four kilometers in diameter, and it made this enormous coma. So it could be something about what that common is made out of, or maybe how it was layered. You know, if you get layers in just the right way, you can get like explosive release of energy than like a gradual release. We're just building models and trying to understand it. It's fascinating. And that's why it's so much fun to look up at the night sky, because, as we were saying earlier, there are always surprises. We're gonna make a model of what's in the work clad and what the biggest thing out there is, and then five years later it's gonna say, I got a bigger one for you. How long could something like that last? Like, if you have a small core and it's exuding so much gas in this giant ball, it can't launch that long, right, It's got to be sort of a flash in a pan. Yeah, it can't laughs out long exactly because the Sun is constantly stripping it of this gas. To maintain it has to continuously evaporate or sublimate more and more gas. And actually some of the things in the asteroid belt they think are dead comets. Comets that used to be rocks surrounded by ice that flew around the sun, blew up all of that ice into a coma and are now just totally stripped and are just dead rocks. And so now they're called asteroids because they no longer have a coma. So a comet is like a transitional period in the life of a Solar System object. You can be a comet for a while and then eventually you get downgraded to an asteroid when you've blown all of your gas. I'm trying to imagine what it would be like to sort of pass through that coma of a comet. Would it be like you're in the swirling world of like chunks of ice and gases. Would you immediately be sort of pulverized by these little particles being shooting out from it? What would that experience be like being in the coma of a comet. It's not nearly as dense as our atmosphere. It's very very dilute in comparison, and so it's nothing like being in air, but it is more dense than the rest of space. And so one thing you have to worry about is the velocity. If there are dust greens in this tail or, in this coma that are moving at high speeds, they can carry a lot of kinetic energy and they could, you know, hold your spaceship. We talked about is actually on the podcast recently, about how to protect ships from high speed micro meteorites or death grains. It's a challenge, but we have sent stuff up there. We have sent probes to comets. We had Rosetta, which landed on a comet, and then NASA sent Deep Impact, which actually blasted a crater off of a comet to try to study what it was made out of. So you can send spaceships up to like intercept commets and study them. It's pretty awesome. What did Rosetta and Deep Impact find? Like were they able to get some kind of samples of what the comets were made out of and bring them back to Earth. So there currently aren't any samples from comets that have returned to Earth. But they did send these missions out there and they studied them, and they tried to understand, like, you know, what is the geology of this thing? And the thing that surprises me the most is that looking at the surface of these things, they just sort of look like big rocks. They're sort of familiar, like they look like a big rocky you would see sitting on the ground in Joshua tree or you know, near some are like volcano or something. They're sort of familiar looking objects. They're not otherworldly at all. They have weird shapes and each one tells its history, but we're still sort of studying the data from deep Impact and from Rosetta to understand like the deep geology of what's in those comments. Do those probes remain on the commets forever and just send us back this data. They don't last very long. One of them was orbiting the commet for a while and then sent down a lander, and the lander didn't last for very long. It like took a little bit of data and then sort of died and the orbitter was able to take a picture of it dead on the surface of the commet. So sad, so sad. But yeah, these things don't last very long, all right. So that's a little tour of what's going on out there in the deep edges of the Solar System, including some surprises. There are comments out there that are bigger than a bus, bigger than many school buses, bigger than maybe even millions of blue whales all packed together. And so as usual, the thing that I love is discovering that there are surprises out there in space, not just super far away, but here in our backyard. And that's really fun because it means we can learn the answers. We don't have to rely on aliens coming to visit to tell us the deep secrets of the universe. We could actually send more probes out there and explore the rac cloud, build more space telescopes and get better pictures. These are things that we will know the answers to In a hundred years, astronomers will know so much more about the far reaches of the Solar System, and they'll look back and think of us as living in the dark ages. And I'm just totally happy that there's a big cloud of mysterious giant ice balls of which we do not know the maximum size. I think that's great and perfectly fine. I'll sleep like a baby tonight, have an feather spoonful of gelato, and just enjoy your life. Katie. All right, well, thanks Katie very much for joining us today. Thank you for having me, and thanks to all of you for listening to and in next time, ye thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I Heart Radio. For more podcast for my Heart Radio, visit the I Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows. H