Did Jupiter once have a different orbit?

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Speaker 1: Hey, Kelly, how do you feel about moving? It always seems like it's going to be exciting, but it's always a drag. No. Right, It's like there's always one more box of stuff, and by mathematical induction, that means we all have infinite totally checks out. I mean I have like infinite back pain from my last move. Sometimes I wish I had a mobile home so that I wouldn't have to pack everything up every time. That is a genius solution. I mean, you move more stuff, but you do less work because you take your whole house with you exactly. I wonder if it's scales. I'm thinking like mobile neighborhoods, mobile cities, maybe like mobile planets. Earth is just one big mobile home. Man, I didn't realize we lived in a cosmic trailer park. I'm Daniel, I'm a particle physicist, and I once moved across the Atlantic eleven times in four years. Seriously, seriously. This was when I was a junior professor and just getting started at the Large Hadron Collider and teaching on the West coast of the United States. So we actually had a house in France and a house in California, and we had to go back and forth and back and forth, and back and forth and back and forth and back and forth. It almost drove my family crazy. Oh my gosh, did you have kids at that point? We had two young children, one of the whom was born in Switzerland. Oh my goodness. I know. It's amazing I'm not divorced. It is. It is. I shouldn't have said it is so quickly, but well, I'm Kelly Wiener Smith and I'm a parasitologist, and it's amazing that I'm not divorced. Also because I moved my husband four times during my PhD to different states. But you know, I used to think that was bad. And now I'm going to go downstairs and tell Zack later how easy he has it. So thank you for that. That's good. That's my goal is to make other marriages look good. We appreciate it. Well. Welcome to the podcast Daniel and Jorge Explain the Universe, in which we talk about all the crazy and amazing things that we find out there in the universe, moving here and there, taking our brains from the tiniest little particles down to the quantum realm to the vast planets of the outer Solar system and all the way to super clusters. Our goal is to embrace everything we know and that we don't know and explain all of it to you. And as you might have guests today on the program, Jorge is not here, so we have our fabulous guest host, Kelly Weener Smith joining us to talk about all these things and ask good questions. Hey, Daniel, I'm excited to be back. I had fun lost time. Awesome, great, well, thanks very much for joining us. So we started off joking about moving houses and moving planets. But this is something I think is actually really interesting, is thinking about how the planets in our solar system got where they are and whether or not they have ever moved. I personally love this question because it's one of those questions that, like the fact that we have anything that even vaguely resembles an answer, makes me sort of proud to be a human. Like, how can we even think about these sorts of questions and collect data to answer these questions. It just seems so mind blowing to begin with the fact that we have any answers, even preliminary answers, blows my mind. Well, I think it's super fascinating that we even know to ask these questions, right, Like, you look at the Solar system and we have the planets, and they don't seem to be changing from year to year. We have thousands of years of astronomical records and so it seems sort of stable. So it's sort of absurd even to ask, like, could the planets have ever been in another configuration? Could the solar system have looked different? It's like very natural to think, oh, things are going around the Sun. They've been going around the Sun. Of course they were always in the same orientation. But something that's happened over the last just couple of decades is that we've had a chance to glimpse other solar systems. For thousands of years, we've only ever seen ours. We had like one example. Now we're seeing lots and lots of other solar systems, and this gives us a clue that solar systems can look different and that there might be a lot of activity, that they're actually quite volatile. That is super exciting. So for our sample size for these like how many solar systems can we see in enough detail where we can like count all of the planets and get a bit of a sense for what those planets are, like, are we talking hundreds, thousands, millions? How big is our data set here? It's exciting because it's growing so rapidly, Like the first exoplanets were discovered just a few decades ago, and now we have thousands, not yet millions. Someday astronomers will get to play with the datas that have millions of solar systems and ask really detailed questions. But we have thousands of solar systems that we can look at and we see weird stuff in those solar systems that we don't see in our solar system and that makes us wonder, like, wait a second, are those solar systems weird? Or is our Solar system weird? I need to know the answer, And so today on the podcast will be asking the question has our Solar system look different? In particular, did Jupiter ones have a different orbit? And that's a pretty huge question, right because Jupiter is like the biggest planet out there, so where it goes has a big impact. From one point of view, you could imagine it's basically the only planet other than the Sun. Jupiter has like of all the mass in the Solar system. Everything else is basically a detail compared to Jupiter. So yeah, it's a big deal. If Jupiter had been in a different place, everything would be different, and so as usual, I was curious whether people had this in their minds, like, have people imagine the possibility that Jupiter could be in a different place? Is that something people have thought about, have heard about? So I went out there to the wilds of the Internet and I asked people, Hey, do you know the answer to this tough physics question that astronomers are struggling over. Use no preparation, no googling allowed, Just tell me off the top of your head. Here's what people had to say. I guess No, there were impacts off I guess asteroids and or comets, and I may be even bigger objects in the past. So I think the orbit of Jupiter was a different one two beion years ago. No, I think it was, but I think it used to be a lot closer and then it moved out through collisions and the collisions, I think Jupiter used to be in a different orbit. I know Uranus rotates about its access in a way that sideways compared to the other planets. Well, I'm not sure if what I think happened, is that Uranus and Jupiter collies at some point. I suspect that Jupiter has been in its current orbit for quite some time, speaking on you know, the scale of the formation of our Solar system, but I would not at all be surprised if it had moved around somewhat during the early formation period of our solar system. Would say, yes, well, nothing is permanent, so I guess it's at the origin it was part of the the Sun or giant cloud of gas. But to me, well, it's quite stable orbits, and I don't see why each change, except for minor changes such as a collision with that other objects. But I would say yes, no, no, Um. Jupiter at some point was sitting towards the Sun, but it's kinda got locked in by Saturn, probably interaction with settled um, something like that. I don't know, you caught me. I'll guard here. I don't think that Jupiter has always been in its current orbit. I think it formed much closer to the Sun, and as it migrated out into the Solar System, it cleared a lot of the debris and comets and asteroids and dust and everything out of its way um and made things a little bit more stable here in the inner Solar system, so life could form. But I don't think that it started out where it currently is. Somebody say no, but I guess, being it's so big, it could well have picked up a lot of stuff through its time, and as it um, you know, it picks up more stuff gets impacted, and I guess it's gravitational forces would interact with other planets and stuff around, so therefore it get knocked off and moved off its little but quite regularly. Maybe, I think almost certainly no. UM. I think the current model of how those those system was formed UM actually relies on Jupiter migrating inward closer to the Sun and then further away. I believe Jupiter has moved from its original orbit. I think the original orbit was closer to the Sun. All right, Wow, those are some great answers from our listeners. When you heard that this was even a question that people were thinking about, did you have a like, oh my gosh moment or did it just seem like an obvious question for you to be asking. I had an oh my gosh moment and a hope because I thought, oh, that would be super cool if Jupiter wasn't always in its current orbit. Because one of the fun things for me in science is revealing surprises. Right If you ask a question and then the answer is yeah, it's kind of boring Jupiter has always been there. That's not nearly as fun as Oh my gosh, it turns out there's a crazy history here and we have revealed it. Like you were saying earlier, it's incredible that we could, like by gathering small lose left by these crazy cosmic events, actually reconstruct something that happened billions of years ago. It's like solving a billion year old murder mystery. As a biologist, every once in a while we will have discussions about like what makes humans different than other animals, And you know, clearly being able to think about questions like this is one of those things that like, certainly we're the only species who's wondering that on our planet exactly. So it's super fun. And I was really hoping that the answer would be something crazy. So it's pretty interesting to learn about. And I've also really been enjoying following this Excel planet discovery seeing these other solar systems, these other like potential homes for aliens where life could be really different because the planets are so different from ours. You know, we're sort of like trapped in this colloquial way of thinking that our kinds of planets are the kinds of planets you have, like small rocky planets and the inner Solar system and big gas giants and the outside and now it's possible to imagine other kinds of areas. So is our configuration a typical configuration. It turns out it's not. When we look at other solar systems, we see something really weird. First of all, we see that most solar systems have a lot more planets very close to their star, Like between Mercury and the Sun there's basically nothing, But in other solar systems there are lots of planets packed in there. And in particular, we find these things called hot jupiters. Not hot because they're like you know, big on Instagram or they're really curvy, hot because they're really close to the Sun. Like, we find these planets in other solar systems that are really big, like Jupiter size and gas planets, but they orbit the star in just like hours or days, and like a fraction of the distance between the Sun and mercury. So that's a really weird phenomenon to see. Shouldn't they like suck each other into each other pretty quickly? What's the good physics word for that? How do they stay separated if they're both huge and attracting each other and are so close now, suck each other in is exactly they're all right physics word to use, And that's exactly the question people are asking. They're like, hold on a second, how do you get such a big planet so close to the Sun? Can it last very long? Are we seeing something just before it dies? Or can that be a stable configuration? And the models suggests that they can't have been born that close to the Sun and they can't last there very long. And that's the clue that got everybody talking and thinking about whether planets are moving, because they suspect that these hot jupiters form further out and then get sucked in, and so we're witnessing sort of like the end of the life cycle of these planets before they either get torn apart or pulled in. And that's a clue that, like solar systems are volatile, there is stuff going on. It's not just everybody sedately driving in their lane for billions of years? Is Jupiter going to get sucked into our Sun? Not before the Sun explodes? Right? Are you worried about Jupiter? Have you invested in real estate on Jupiter? Well, you know, I was thinking about it. We've been reading about space settlements, but no, obviously not nobody's gonna go live on Jupiter. But maybe it's moons. I went to read I fantastic series and science fiction novels about a civilization in the upper clouds of Jupiter. I think it was called Bio of a Space Tyrant Man. I loved those books when I was a teenager. It was so like fantastically imagined. So I hope that one day humans do get to live on Jupiter, and I hope that we get to keep Jupiter because I like it. I mean, Jupiter is pretty. For all the press that like Mars gets recently, Jupiter is a gorgeous planet. So maybe we should start by thinking about our solar system and understanding of what we know about Jupiter, like where it was made, how it got formed, and that can give us a clue for like why people think there might have been crazy stuff going on in our solar system. At the very beginning of time. Alright, so tell me about how Jupiter got to be where it is. Yes, so we think Jupiter is probably born out in the outer Solar system. There's this point in the Solar system called the ice line, where beyond that it's cold enough for ice to form and to stay melted and basically be like a rock that you can use and building planetary cores. And it's about like three and a half AU. Will remember a U isn't one astronomical units the distance between the Sun and the Earth, So three and a half times the radius of the Earth. Beyond that is the ice line, or some people call it the snow line, and out there it's easier to make big planets because there's ice available to add to your core. So we think that the way the Solar system started obviously, have a big blob of gas and dust and some shock wave comes through it and you get the spark that begins the formation of the whole Solar system, which basically means the Sun. But the Sun has gathered together a huge amount of gas and it has around it a big swirling disk, and that's the disc that's going to provide the material that forms all of the planets now out past the snow line, there's also ice in there. So the ice and the rock and the dust gathered together to make these protoplanetary cores. They start pulling themselves together and that sort of seeds the planets. And so we ended up with what four planets out past the ice line? Is that pretty common? Like that number and like the size of our planets does that match up with what we see in other solar systems. We don't know the answer to that yet, we haven't seen enough. But also remember that we can see a bunch of solar systems, but we're not that great at seeing all of them. And there's certain kinds of solar systems that are easier to see. Like it's easier to see big planets that are closer to their Sun because they block more of the Sun's light. The way we see these exoplanets is that they block the light of their Sun or they tug gravitationally on the Sun. So big planets are easier to see. Close up planets are easier to see, so far out planets harder to spot. Far out small planets harder to spot. Does that mean that like super slow moving things we probably don't have good data on yet because we wouldn't have had a chance to see them pass in front of the sun or tug it as it moves around to the side. That's exactly right, Yeah, we have to watch these things cross their sun, and so basically it's best if you can see and pass a few times so you can see like a regular interval, so the equivalent of several of their years. But if their years take like, you know, a hundred earth years to go around, then we're not going to have had time to see it. So slow moving things, small things, things far from their son are harder to see. So that's a long way of saying we don't have an unbiased picture of what's going on in these other solar systems. And we have to try to play this game of wondering, like, well, if we see only one of them, do we imagine that there are a thousand? Or if we only see two of those, do we imagine there are a hundred. We have to estimate like how good we are seeing them, so we can like invert that and imagine what's actually there that we're missing. But there's a lot that we're missing. Still interesting Yeah, it's really fascinating. And so that's why we focus on our solar system because it's here, it's relevant, and it's one that we can study in great detail. But those other solar systems do give us a lot of clues. Back to jo Butter, we think that it must have had to form and the outer Solar System because that's basically the only place to make these big gas giants. I mean, you need now of ice and enough rock to pull together to make this big core to grab a bunch of gas. Remember, everything in the Solar system is competing with the Sun. In the inner Solar system, is not that much gas left because the Sun has slurped it all up. So to make a gas giant, really have to be far enough away from the Sun to get any of the gas, and you have to be past the snow line, so you can have ice accumulated in your core and get big enough that you can grab some of the gas before all spirals into the Sun. Anyway, Okay, so Jupiter was formed in the outer Solar System and it's still in the outer Solar system. So after the break, let's talk about why we think it moved. Okay, so Jupiter is where we would expect it to be, given how we expect that it formed, So why would we suspect that it had moved at any point. Yeah, it seems at first like it might be a simple story. Right, Jupiter had to form somewhere in the neighborhood where it is today, and so the simplest explanation is, well, maybe it just formed there and stayed there. Why do we imagine it ever took a tour in the inner Solar System? And the reason is that the inner Solar System looks weird, like we can't explain the Inner Solar System in that picture. Our models of how the Solar System came together. We run a bunch of like simulations and try to explain how we got Venus and Earth and Mars. None of the models that we run actually match up with what we see. How are they different? Well, in particular, Mars is really weird, Like Mars is a nice little planet, but it's really small, Like Mars is like ten percent of the mass of the Earth. That's a really small planet. And in all our models of the Solar System, Mars should be a lot bigger, like as you get further out from the Sun, there's more material available because the Sun hasn't stolen at all, and so you expect a planet forming around there to be like about the size of the Earth or even bigger. You know, as you go to the outer Solar System, things get bigger, right, So why is Mars so tiny? Why is it so little? So as you get farther out in the Solar System, things should get bigger. But Jupiter is the biggest and it's not the most far out, So why is Saturn smaller than Jupiter? Then? Oh, yeah, that's a great question. There's a whole other fun story about a sounder Jupiter, maybe switching locations and the whole dance of Uranus and Neptune that they might have done. But you're right, there's a balance there because you want to be far enough away from the Sun so it doesn't steal all the material, but as you get even further away from the Sun you run out of material also, right, Obviously there aren't like super giant planets twice as far away as Jupiter, and so this is something of like a peak location there. Jupiter is probably sitting right there in the spot where you can make the biggest planet. But the question remains like why is Mars so a little what happened to make Mars so tiny? And it's not just Mars? Like the asteroid belt is also kind of weird, like we don't really understand how it formed the way it did. Again, we run these model let's start from just the gas cloud, and you don't get an asteroid belt that looks the way it does. Specifically, our asteroid belt is weird because it has both like rocky objects that seems like they came from the inner Solar System. Plus they have a bunch of icy objects, the kinds of things you would find like in the Kuiper Belt or deeper further out in the Solar system. So there're these like pieces of evidence you were talking earlier about like how could we possibly find clues about things that happened so long ago? Like these are the things that have puzzled scientists for a long time. So is the asteroid belt inside the ice line or on the Jupiter side of the ice line? Yeah, the asteroid belt is really weird. Actually part of his inside the ice line, the part that's like closer to Mars, remember it sits between Mars and Jupiter. But it also extends kind of far out, and part of it actually is in orbit with Jupiter. Like it's not all between Mars and Jupiter. There's these big blobs of asteroids that are in Jupiter's orbit just sort of like rotated away from them, like you know, thirty degrees around the thirty degrees the other direction, and stuff is sort of like sloshing back and forth. So some of it's definitely out there past the ice line and can stay frozen, and some of it's a little bit closer. Interest. Yeah, and so we have these mysteries, and I love that. This is like the way we do science. You know, we say, well, we think we understand how the solar system works, but let's double check. Let's run a bunch of models and see if what we get matches up with what we actually expected. And when you see those weird deviations, when you see something that doesn't make sense, that's when you know you might have found something. So it's like when your model doesn't work is a potential discovery moment. It isn't that how we figured out how humans figured out that was it? Neptune was out there, something was not working mathematically, so there had to be another planet out there exactly. Yeah, there's all these times when something hasn't quite worked, just like you're saying, the orbits of the planets don't quite make sense, and that's been a clue. Is to like a huge discovery, but always makes me think about like all the other times when your model doesn't work and it just because like you have a bug where you did something stupid, you know, and you can't be like, oh my gosh, maybe I've discovered something fantastic. Sort of frustrating part of science. Yeah, usually for me, it's just a bug, but I'll keep all me out hope. We have that experience all the time. It's a large hage on collider because we're always on the lookout for something unexplained, something new, something weird, some new particle that we've just created, or mini black hole or something, and it might be evidenced by some deviation in the data compared to what we expect. But we see that all the time, especially young students make mistakes and they see something weird, like oh my gosh, did I discover something like yeah, well, you discovered that you don't know how to run this program correctly. You discovered that you're missing a bracket. But yeah, exactly, you discovered that bugs are easy to insert in programs, but you also you don't want to squash their enthusiasm. Right, It's wonderful to see this in young scientists, to imagine that they could be the ones making some discovering this could be a historic moment. So I like to tell them stories like this, because it does act really happens sometimes, Right, Sometimes we run these models and we see something weird and it means something real about the universe. Awesome. We can all keep our fingers across the will have those amazing moments where it's not you not being smart enough, it's actually the universe revealing herself to you. And so we're trying to understand, like how our solar system got to be weird the way it is. Why don't we have a bunch of other planets close to the star? Why is mar so small? Why is the asteroid belt the way it is? This weird mix of rocky and icy objects. So we've taken clues from these other solar systems that have big planets really close to their stars. One idea initially was like maybe Jupiters formed close to the Sun. And then like drifted out and along the way sort of messed up things in the Solar system. But you just told us that it needed to be out there where there's ice in order to form. Could it have possibly formed near the Earth? So people spend a while trying to cook up these models and wondering like maybe there's a way to have a hot jupiter that survives, or maybe there's a way to form a planet really close to the star. Maybe there are other methods. So you know, this idea of how you form a jupiter is sort of one model, but there are other models. There's like, you know, gravitational instabilities that maybe stuff smashed together to make like an unusually large object, which then like gathered together a bunch of stuff. And people have been working on these things and trying to put them together, and you know, this is the kind of creativity that's inspired by basically a mystery. But it doesn't seem to really be working, Like there's just not enough gas and not enough mass close to the star, and also it's just too warm, Like a lot of this stuff, if you did happen to form a big object, would get blown apart by the sun. The Sun just like boil the gas off of that planet. And it also probably just like holding apart by the tidal forces. Remember that the Sun has a lot of gravity and it tugs on everything. But if you're a really big object, it's going to tug on the part of you that's closer to the star more than it tugs on the part of you that's far from the star. And that's effectively the same thing as trying to pull you apart. And that's why, for example, you get close to a black hole, you won't survive, because you'll get pulled apart by the relative difference in the gravity at your feet and at your head. It's called spaghettification, one of the best physics words out there. And so now imagine like making a big gas giant. You've accomplished the impossible. You've formed a gas giant close to your star. What's going to happen The star pretty quickly is going to spaghettify Jupiter. And like, that's a lot of spaghetti. I'm there for that. I love spaghetti. So are people still work on that question or have scientists pretty much decided like, okay, this is not the answer. There's always somebody is still working on that question. Right. There are people out there who think that it might have been possible to make a Jupiter close to the star, and they're working on their models, and in that line of thinking, they're hoping that you've made this jupiter close to the star and that it's somehow we don't know how, then drifted out to the outer Solar System and in doing so has perturbed the asteroid belt and in doing so has like stolen a lot of the material that might have made Mars. But I don't think that it's a mainstream idea. I mean, there's always somebody out there, you know, smoking a banana, appeals and thinking about it. And I encourage that, and that kind of creativity is wonderful, and you know, diversity of ideas is also very very important for the scientific method. But I don't think the leading idea is that you form a hot jupiter close to the Sun and that it then drifts out into the outer Solar system. Okay, so it started in the outer Solar System and then it went on a cool vacation towards the Sun and decided it preferred skiing. Yeah, And so we don't think that this idea of it's starting an inner solar system and moving out makes much sense. And another clue is that when we look at these other solar systems, the ones that have hot jupiters, and we wonder, like, how are they made and how could that survive? There's some evidence that we're looking at our really young solar systems, solo systems that haven't been around for very long. And so one explanation for how hot jupiters even exist is that they're transient, that they're gonna be absorbed by the star that we're seeing them before they get spaghettified and sucked in and basically just become part of the star. Because we don't tend to see hot jupiters in older solar systems. Ah, so it started in the outer solar system, it got sucked in, and we are seeing it at a point where it is sort of in the process of soon to be absorbed by the sun. Is that right? That's the leading explanation for why we are seeing hot jupiters in other solar systems. But you know, of course that doesn't answer the question of our solar system because we don't have a hot Jupiter, right, But we still have to explain what happened in the inner Solar System. So we have Jupiter starting in the outer Solar System, we think that makes more sense. We don't have it currently in the Inner Solar System. So then there's this question of like, well, how could it have perturbed things in the inner Solar System? You know, it's sort of like got an alibi. It's like I was born here and I'm still here. Why are you looking at me? Right? Okay, So the progress we've made so far are is that there's an explanation that we don't think is right. So let's try another explanation and see if we can maybe solve some of the problems with what's happening with Mars and the asteroid belt after we take a break. Okay, So we feel pretty confident that Jupiter started in the outer Solar System and it didn't start in the Inner Solar System and then move out. So if it started in the outer Solar System and it's still there, now, does that mean at some point Jupiter sort of toyed with the idea of a summer vacation and then decided it preferred the cold and went back to go skiing. Did it come to the Sun and then leave. I know, this is that moment in the Murder mystery where you're like, this person was home all evening. Hold on a second to actually have a way to account for all their whereabouts. Could they have snuck out and committed the murder and then come back in time? How fast are those trains? We can't leave Jupiter in the outer Solar System for its whole history. But now we have a crazier idea, which is maybe Jupiter did trend into the inner Solar System just like all those other hot jupiters were seeing in other solar systems, but that it stopped and it turned around and it went back out to the outer Solar system. So this is called the Grand Tach hypothesis. Seeing Jupiter's like a sailboat that like sailed into the inner Solar System and then sailed back out. This is blowing my mind. So let's break it into two parts. I guess, So, how did it get pulled in? Just through the typical gravity pulled it in? Yeah, so you have to cast your mind back to the very very early days of the Solar system. Solar system we think is about four or five billion years old and we're talking about things that happened in the first few million years. You shouldn't be imagining a bunch of planets around the star. You should be imagining a star and then a huge disc of gas and dust, and then inside that gas and dusk, we're forming planets. But they're not like clear, they're not like totally separated. If you were doing astronomy back then, you would have a really hard time seeing any planets because there's so much gas and dust everywhere. So the beginning of the story in the first few million years is that, like proto Jupiter has formed, but it's not as far out as it is now. It's only like three and a half au like right there on the snow line. As we were saying earlier, like the peak place to make a gas giant is just pass where things freeze, so you can gather ice and rocks and dust, but not so far out that things are getting dilute. So Jubiter forms there and then it drifts into the inner Solar system. As you're asking, like what makes that happen, it's it just the Sun's gravity, and you know anything can orbit stable. The Sun obviously has a lot of gravity, but The reason, like the Earth is not falling into the Sun right now is that we have a lot of speed. We're in a stable orbit. So we think Jupiter probably wasn't a stable orbit. But remember it wasn't on its own. It's still surrounded by a lot of gas and us that hasn't gotten pulled into any planet. So the idea is that it interacted with that gas and dust, which basically slowed it down and started falling in towards the Sun. That must have been very scary for Jupiter. I know, it's like this inextricable fall, right, you know that you're like rolling in towards this huge burning ball of plasma and there's basically nothing you can do about it. So very dramatic moment. And these gases eventually, you know, spiraled in and they fell into the Sun, and Jupiter was spiraling and also and so the idea is that it passed through the inner Solar System and along the way it gobbled up a lot of material which eventually would have otherwise led to a larger Mars. How far in did it go? Did it get like Earth close or just Mars close, not quite Earth close. We think that it came into like about one and a half a you. And that's why we still have Earth as a pretty reasonable size, because Jupiter came in and it either like gobbled up the material to make ours or scattered it and threw it into the sun. But these things in the inner Solar system were a bit more protected. Okay, so part of Jupiter should have been in Mars. It's like those twins, you know, where like one of them eat the other one and you still have like a jaw or whatever inside the body of the adult. Those are the craziest stories. I don't think they're actually eating the other one, but yes, I know where you're going with that. Well, you don't believe in the evil twin theory that twins can eat each other in the roomb. I was reading about this the other day, and I think it's they like absorb eating suggests a bit more intention that I think is actually happening in there. You know, I'm going to use that next time I eat my kids cookies. I'm like, I didn't eat your cookies, I just absorbed them. And Kelly the biologist, she tells me that's different. And then your children remind you that you are not a fetus. You're a grown man. You can make decisions, and so you know, let them know that they can call me if they need back up. All right, I'll give them your number. Anyways, So Jupiter's out there like unintentionally absorbing the materials that Mars would have needed to get larger and scattering a bunch of other stuff, and so it came into about one and a half a U. And that actually explains a lot about what's going on in our inner Solar system. That's why there are no like other rocky planets after Mars. We think there might have also been other planets out there that were forming that Jupiter just like nudged into the Sun. So why did it nudge them into the Sun as opposed to pulling it into Jupiter. Yeah, we don't know. It could have been either fate, right, this is very chaotic, and so it depends exactly on how big they were and how they were aligned, and so the fate of these planets could be like fall into the Sun or get absorbed by Jupiter, or even get tossed out of the Solar system entirely. Like Jupiter is a big bully, right, It's so much bigger than Earth and Mars, and it comes in and it doesn't take very much to really disrupt the inner Solar System. Okay, so how does this describe what happened or does this help explain what happened with the asteroid belt. Yeah, so it actually all really fits together beautifully, because to explain the after oid belt, you need Jupiter to get back out to where it was. Right. The asteroid belt has rocky stuff in it from the inner Solar System, but also I see stuff from the outer Solar System, and so if you could somehow turn Jupiter around, right, we've seen all these other solar systems. Also that these big gas giants sometimes fall slowly in towards the star, and we think that in most cases probably they just end up inside the star. They didn't happen in our case. So we need Jupiter move somehow to the outer Solar System, and in doing so we think that it will have disrupted the asteroid belt and also disrupted the Kuiper Belt, like pulled some of those objects towards the inner Solar System, so that the asteroid belt then has like a weird mixture of these like further out objects and these inner objects. And that's why we see these like icy objects and rocky objects in our asteroid belt. If we can get Jupiter to go in and then come back out, that's fascinating. So now, how you told us that Jupiter probably slowed down own and that's what caused it to get pulled in. So for Jupiter to go back out again, what is required for that? Doesn't have to start speeding up and then also kind of get nudged. Why did it leave? Well, Jupiter, we think probably was saved by its friend Saturn, because Saturn has the same fate, right, Saturn, also a big gas giant, also probably surrounded by big swarming clouds of gas, getting slowed down drifting in towards the Inner Solar System. To imagine Jupiter like the big brother and then Saturn like the younger sister or the younger brother, following in behind it, having sort of the same fate and seeing what's happening to Jupiter. But the calculations suggests that it's possible that as these two things get close to the Inner Solar System that they then start tugging on each other, and that their gravitational interaction makes this weird resonance where they're pushing on each other and they're passing around the Sun. They're tugging on each other in the same way. So they do this like weird dance. Like imagine two people spinning and both letting go and they flown out of the inner Solar System. I know, it's crazy. It's like Saturn like dove in after Jupiter and saved them both. Right, they could have ended very badly. Yeah, there's got to be a buddy comedy that could be written about this or something that's wild exactly. And so that's maybe the story that Jupiter started in the outer Solar system, got tugged in as it's got slowed down by all this gas, and then got saved by Saturn. And that would explain why Mars is so small, and it would explain why the asteroid belt has the weird composition that it does have. And so is that the only explanation we have for how Jupiter got thrown back out again? Or is that just the top explanation right now? That's the top explanation. And we don't think that it's very likely. I mean we think that in most cases, when you have a big gas giant that falls towards your star, it ends in the way you would expect that it falls towards the star and gets gobbled up, And so most solar systems that have basically a Jupiter, we think that it doesn't last for very long. So that means our solar system is probably weird, right, that we're unusual for keeping this big gas giant and having it back in the outer Solar system in a stable way after all the gas and dust have cleared out. Now Jupiter can go back out to the past the ice line and hang out for billions of years. That would suggest that the reason we're weird is because we also have a Saturn. So do other solar systems without hot jupiters also have a Saturn equivalent? Yeah, great question. I don't think we know the answer to that, because these planets are much harder to spot, right, We're talking about things five six seven a U that only passed their son every few years. Right, Like, if you were observing our Solar system from really far away, Jupiter and Sounder would not be that easy to spot because while they're pretty big, they're also really far away from the Sun and it takes them years and years to orbit, so you would have to be watching our solar system for a long time with a really good telescope before you discovered Jupiter and Saturn. So that's not something that we're really sort of good at knowing about other solar systems. Yet so far, we mostly know what's going on in the inner Solar system for big, fast moving planets around their star. So astronomers have like incredible job security because we're gonna need to watch for hundreds of years to get these data and tuarly the government's going to pay for all of it, exactly. Yeah, And it's incredible what we have learned so far. You know, we've learned so much about how our solar system is weird to compare to the other solar systems that's out there, and that's sort of like cool, like, hey, our solar system is awesome and special. It's also a little bit disheartening because if you believe in aliens, or you want to believe in aliens, and you want to think that there are lots of opportunities for life out there, it makes the story a little bit harder because to have a solar system like ours and a planet like ours, you need this sort of special thing to happen, this dance of the two gas giants to clear out the inner Solar System and then also save themselves and being the outer Solar system. You know, we think that Jupiter probably protect the Earth from a lot of sort of incoming bombardment because it's so big. It's like hoovering up all the comets and other stuff. So it's a special configuration we have. You've kind of bummed me out. You know. At the beginning of this conversation, when we were talking about how big our data set is, I was thinking, all right, that's got to be good for the Drake equation. You know, we're like adding all of these possible solar systems that might have earthlike planets. But now what you're telling me is probably a lot of the ones that are out there don't have earthlike planets. And now I'm kind of bummed, yeah, a little bit. And we've been excited to find what we thought were earthlike planets in these other solar systems, ones about the right radius, about the right distance from the star. But what we don't know is if they really have the right composition to be an Earth. You know, it might be that Jupiter came through the Inner Solar System and it cleared out a lot of gas, etcetera, etcetera, And so we ended up with a planet just the right combination of stuff to have life. If Jupiter hadn't come through the Inner Solar System, Earth might have been a little bit bigger and then might have been more gas, So we might have ended up with a very different composition. You can imagine like a super Earth that's like choked in hydrogen instead of having the atmosphere that we have you other way, like Venus is just like choked in CEO two. It's very oppressive. And so it might be a lot of the planets we're seeing in these other Solar systems are not actually sort of habitable in the way that we would hope for. They're not really copies of Earth. They might have the right size roughly and being roughly the right position, but that doesn't mean to have the same conditions as Earth. Man, we're lucky. Oh we're special. We're special. I'm gonna go with lucky. But maybe life is better if you go with special. So did Jupiter go like back to where it came from or did it end up a little closer a little farther out than where it was before. It ended up a little farther out. It like it wanted to go out. In the excerpts, you know, it was born in the suburbs, and it came to the inner city, and then it decided in its retirement it wanted to live further out. So it started out at three and a half a U. Came in and probably about one and a half and now it's comfortably out around five point two a U. I can totally understand how Jupiter feels. I was born in the suburbs and then I moved to a big city and now I live out in the country where nobody else is. So I feel your Jupiter. Well, it thanks a lot to feel Jupiter. And the story doesn't end there. What we talked about is like the first few million years of the Solar System. But there's still a lot of interesting planetary dynamics that need to be explained. Like we think that maybe Uranus and Neptune switched places at some point, and that Jupiter and Saturn may not have sort of ended up where they are now, that it may have taken a little while, and they may have also done some later migrations we're talking like five hundred million years after the start of the Solar system, So we like to think about the Solar system is sort of like it is what it is, and it's been what it's been. But if you did it like in time lapse over like hundreds of millions of years, it would seem pretty chaotic. It would seem like, wow, there's really something happening there. So that this idea of Jupiter moving in and out, is this like totally accepted by the mainstream or is this just sort of a theory that some people ascribe to. How broadly is this idea accepted? Yeah, it's somewhere in between. The astronomers I spoke to think it's like probably the most plausible explanation. But you know, there's a lot of details still to get right, and our models are just going to keep getting better and better, and then we could ask more and more detailed questions. And right now the models explain Mars, but as we make those models better, we can ask more specific questions about like why does Mars have the composition that it does and why does it get exactly this small and not larger? And maybe as we do those studies we'll find discrepancies and things that don't work, and then we'll need to modify this model. Or maybe there's some other crazy part of this story that we haven't even thought of yet that could be revealed by some little detail that some student uncovers. So, given the gaps in our data sets, which are caused by things that are hard to remove, like really really slow moving planets, what do you think the chance is that by the time you and I are, you know, retiring, that will be able to say, like, definitely, that's what Jupiter. You know, maybe we'll never be able to say definitely, but we feel super confident that that's what Jupiter did. Is this a problem that could get solved soon or are we looking at decades and decades before we can really get a good answer. Well, that depends, Kelly, how long until you plan to retire. I'm not sure I'm ever going to retire. But you know, the the average age of a woman in the US when they die is what seven seventy seven something like that, So that time scale, I think that our understanding of our solar system and other solar systems is going to be continually revolutionized, basically every ten years for the next hundred years, because we are just at the very beginning of understanding how these things work, because we have just started to look and to see these other planets, and we're going to find lots more surprises once we developed telescopes that are better at these things. Was James web launches and t to us more about cold planets. James Webb's an infrared telescope that can see things that are not just quite as hot, that can see like cold disks of protoplanetary formation and actually maybe individual planets that glow in the infrared. So we have a lot more information coming, and if the universe holds true to its reputation, it will be filled with surprises that upend our ideas. So probably by the time we retire, people will look back at these ideas as quaint and goofy, and then we'll have a much more interesting idea, probably filled with dramatic events we haven't even considered. You know, it's a really fascinating time to be alive with the kind of data that we're able to collect right now, It really is. It's a kind of time that makes me just want to like live another ten years because the things we're learning are just blowing our minds. You know. It makes me wonder, like, what would a children's book about the Solar system say in a hundred years, right, Like, I would love, I would kill to travel forward in time and steal children's books about science. Well, this suggests that biology needs more funding because we need people to be working on the problem of immortality. Don't give me that. On my campus, we have like ten times as many biologists as businists already. Alright, alright, fair enough, but I love biologists literally, I mean, I'm married to one. So I'm definitely pro biology. More funding for all the sciences so we can unravel these amazing mysteries of the universe. There you go, agreed. Alright, something we can agree on. So thank you everybody for joining us on this tour of the early days of our solar system, the dramatic story of Jupiter's visit to the inner Solar System and how it might explain everything that we're seeing, all the mysteries about the size of Mars and the composition of the asteroid belt. Thank you very much for sharing your curiosity with us. And thank you again to Kelly, our wonderful guest host for joining us on today's episode, Thanks for having me on the show, and thanks for listening everyone. It was a lot of fun, alright, tune in next time. Yeah, thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I Heart Radio. Or more podcast from my heart Radio, visit the I heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows. H