Does Mars Have a Liquid Center?

00:00:08
Speaker 1: Hey, Jorgey, I have a food engineering question for you. Food engineering. We're trying to melt ice cream with a particle collider, not yet, but now I'm gonna go try that. Now I'm wondering how they engineer foods with a liquid center inside. Okay, now you're trying to make our candy with liquid inside? Yeah? Or like, how do they make peanut butter vealed pretzels? That's a billion dollars secret. I can't just reveal it. We might get sued. Alright, I guess we should stick to revealing big science secrets. Yeah. I don't think we'll get sued for those. They're usually free and maybe also useless. You said it not mean. Hi. I am more Hammon cartoonists and the creator of PhD comics. Hi. I'm Daniel. I'm a particle physicist, and I do enjoy me a peanut butter field pretzel. Really, why can't you just put the peanut butter on the outside. It's a totally different taste experience, man, I mean this can't be compared. Plus, I admire the engineering. Somehow they baked this pretzel around the peanut butter. It's incredible. You think that's how they do it. They formed the bread around the peanut butter. Actually did some research about this. It was the basis of a big lawsuit. And there's a fancy co extrusion process where they have the pretzel dough around the peanut butter and then they bake it. Co extrusion. Wow, that sounds like a heavy duty physics term. You should google it. They used to find some really fun YouTube videos about the interior of these factories. Pretty fascinating food engineering. And by experiments, you mean you tried it at home a bunch of times, or you ate a bunch of pretzels with peanut butter. I ate a bunch of pretzels. I tried the chocolate covered versions, the non chocolate cover versions. I'm in the name of science. Have you tried coach twinging butter and pretzels? That's the next level heart attack recipe. You should sell that idea to Ben and Jerry's. But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of I Heart Radio in which we extrude ideas about the universe into your head without breaking your skull. Somehow, we wrap your mind around the peanut butter field delicious secrets of the universe. We talk about all of the crazy stuff happening deep out in crazy space, and all the tiny stuff happening in between your toes and the smallest particles. We break down quantum mechanics, We talk about astrophysics and everything in between. Wait, I thought that the science secrets that we reveal our the pretzel part that surrounds the yummy peanut butter inside of our punts. It could be I was thinking of my brain is the peanut butter and my skull is the pretzel. You just ruined that vision of deliciousness for me. Every time you bite into one of those from now on, just think I'm eating Daniel's head, not mom goodness, let's please hitit that out. But anyways, we do like to talk about the universe and all of it's amazing goodness inside and everything that you can quote through it, inside of it, and all the things that you can discover because it's the big cosmos and there are wonderful things out there hiding in plain sight, that's right. And the more we look out into the universe, the more we discover these surprises and the more questions we have about exactly how things work, what layers they're in, and how they're organized and how they got that way, right, because we can see the universe and touch it and probe, but who knows what's line underneath the surface, what is at the core of the universe and how it works. And everything that's out there has a history. The Moon, the Earth, Mars, every planet, every star has a sometimes billion years long history, a crazy story that tells us how it got to be the way it is today. And unraveling that story is like the biggest, most delicious detective mystery in the universe. Figuring out what exactly happened to the object. Can we tell just by looking on the outside or just by looking through a telescope, exactly what the story is of this heavenly body? Yeah, because we want to know, right, the species as human beings, were curious about where things came from and how they got to be the way they got to be, and that's all part of their history, and it's all they're inside of the things for looking at. Yeah, we showed up in this universe basically the last minute, and a lot of stuff happened before we got here. So it's fun to unravel those stories and figure out have things looked this way for a long time? The things used to be really different. Does that mean things are going to change? It's all just part of like becoming conscious beings and exploring the world that we find around us. So today we'll be talking about one of these mysteries. Line underneath the surface of our own neighborhood. It's something that we can see almost every night, but that is kind of hidden from us, right, that's right. We have questions about what's beneath our feet, and we have questions about what's beneath the feet of potential neighbors. You mean the actual neighbors. Like is your neighbor sitting on top of a giant oil well or something? Yeah, maybe there's like a huge peanut butter deposit under my neighbor's house and I could sell that to that factory. Yeah, instead of liquid gold, that's liquid saturated fats. Well, it's peanut butter technically a liquid or is it a solid? I guess it depends if it's smooth or what's the other one crunching? What is the phase diagram of peanut butter? Can it sublimate into a gas? I wonder. I don't know if anybody's ever done that experiment. You mean, like go straight into a gas form of peanut butter, like you can invade peanut butter. Not recommended, folks, not recommended. Our lawyers have not vetted that statement. Please do not vape peanut butter. You could clog through your lungs directly with peanut butter. But if you do vape peanut butter, tell us about it, because we're curious that may will be another billion dollar industry who knows, or a billion dollar lawsuit. We're about to get hit with people who use it to cure their pretzel addiction, and then they'll need some patches, some peanut butter patches. Anyways, Yeah, we'll be tackling one such mystry in our own solar system, so to be on the podcast, we'll be asking the question, does Mars have a solid or liquid core? I guess the question is Mars hardcore or softcore? Is it a hard boiled egg or a soft boiled egg? Exactly? I think it's a super fascinating question, and it's fun for me because I think about like when people were asking this question about the Earth, you know, for a long time, we didn't really know, like, hey, what's the Earth made out of? It's just one big rock? Or is there something crazy going on under our own feet? And now that we have a little bit of a sense of what's going on inside the Earth, we can ask similar questions about other planets, and so it's fascinating to wonder, like, are they different, are they the same? What's going on? I guess just to verify, the Earth has a softcore. Right, The inside of our planet is molten, right, It's like melted rock. Yeah, there's some melted rock and a lot of melted metal, melted iron, liquid nickel, all this kind of stuff flowing underneath our feet. It's part of why we have, for example, a magnetic field. I see now, I guess, is it possible for a planet of our size to have a solid core? Like, wouldn't all that pressure, gravity pressure eventually kind of I don't know, melt the stuff inside. Yeah. The reason that we do have a liquid core is because of all that temperature and pressure, and that comes from both the gravitational pressure and also the decay of the isotopes inside the Earth that helped keep it hot. But it's not going to be that way forever. You know, we got a certain spoonful of Earth, and eventually it's gonna cool off. I think we estimated once on this podcast that it's going to take more than a hundred billion years before the Earth cools, So we got some time, and you know, the Sun is going to go red super giant before that, so it's not going to be our number one problem. But other planets are different sizes and so they will have different cooling off times. It's gonna be a while before we're cool. I can relate to that. Hey, we're gonna be young and hot for a long time. Think about it that way. That sounds very hard corn, all right, But they were asking questions about Mars. Does Mars have a solid or liquid core? And it's kind of a big deal, right because it might tell us whether or not Mars is still you know, sort of young and active, and it might tell us also what our future might be for that's right. And I think it's just a question that people have when they look up into the sky and they wonder, you know, is that planet over there a lot like our planet or is it totally different? And what does that mean about the nature of planets and planets in other solar systems, and it's to me just really connects with this basic, simple initial curiosity we have when we look up at the sky, we wonder what those things are like. Hey, but before we answer this question, we wanted to answer a question from one of our listeners, perhaps our youngest listener. That's right. You may remember last week we talked about Hannah, who was home sick from school. She's two and a half years old. She lives in Australia and she wanted to hear Daniel and Jorge. So I reached out to her dad and asked him, Hey, does Hannah have any questions she wants us to answer while she's homesick? And he asked her what questions she had for day own Jorge, and she said, monkey, wait? Monkey? Is her question? Was her first question or answer to the universe and everything in it? I don't know. It's hard to get in the mind of a two and a half year old sometimes. But then he asked her again, and so here's Hannah's real question. How and how my land home? Why is the Larne shine? Oh that's adorable. It's like a little tiny little nerd. Yeah, and she has the same curiosity. Today we're talking about Mars and what's in it, But you know, she's looking up in the sky and she's wondering, why is that thing up there glowing at me? It has the same root of curiosity. I see you're saying that it taps into that same like looking up at the sky and wondering what's going on out there? Yeah, exactly why is that thing up there doing that thing that it's doing? Well? Really quickly? Then what is the answer for Hannah? Why does the moon shine? Yeah, Hannah, the reason the moon shines, especially at night, is that it's actually reflecting light from the Sun. Even though you can't see the sun at night, the sun can see the moon, and so the Sun's light bounces off the moon and down to your eyeball. So at night you're kind of seeing the sun by seeing it reflect off the moon. So moonlight is all just reflected sunlight. Right. Do you think she's asking about moonshine as well? Why does my dad drink so much moonshine? I don't know. I think that's a question for her dad and his father. There nothing wrong with moonshine, nothing wrong with the little moonshine. All right, well, Hannah, that's to your answer. The moon shines because it bounces light from the sun, so it looks like it glows, but really it's just kind of like a mirror, just reflecting and getting lit up by the sun. That's right, all right, Well back to our question, those marks have a solid or liquid core? This is a pretty interesting question, and we were wondering, as usual, if people out there and new the answer to this billion year question. So thanks to everybody who volunteered to answer this question as usual. If you'd like to participate for future episodes, please write to me two questions at Daniel and Jorge dot com. Think about it first. Second, do you think Mars is solid or liquid on the inside. Here's what people had to say. Yes, they might be a big diamond inside it. Now I think Mars has hot liquid. Yes, it does completely solid, because Mars doesn't have any radioactive isotopes inside the core. Keep it hot and keep it liquid. I'm going to say, yes, Mars has a solid core of iron or nickel or some other heavy element, just like Earth. Yes, Mars has a solid core. It has no obvious plate tectonics going on it obviously had some sort of tectonic activity going on at some time, and the magnetic field is almost non existent. So I think if we were to dig deeper, I think we'd find it does have a solid core. I don't think Mars has a significant magnetic field because solar radiation is a concern for explorers. I would say it cooled down at least a billion years ago to a solid all the way through to its core. Yes, I think it has and used to be more powerful and active. But judging by the strength of the magnetic field and the atmosphere, it weakened in time. Probably that will happen to Earth to I don't know for sure, but kind of this is the way I think it would go. Mars does have a solid core. End of story. I see you remember you saying in an earlier podcast that Mars does not have um an electromagnetic field protecting it because it doesn't have a solid core. So I'm going to say no, all right, some pretty definitive answers here. I feel like people were pretty confident about their answers here. They're like, yes, definitely, this, definitely, that definitely peanut butter, A big hot diamond. I like that one. Why do you think people are so confident this time? I think that a lot of people have heard that Mars is smaller and cooled faster, doesn't have volcanoes on the surface or a magnetic field, and so I think that leads people to suspect that it might just be a big lump of hard rock, unlike the Earth and the story. All right, thanks for joining us, um, But there's more, I see, there's more to the story. There is more to the story, Yes, exactly. I think there's some really interesting nuances here that these listeners will learn. All right, well, let's dig into it. First of all, Daniel, why is this question interesting to you, I guess and to physicists and generally to the public. Why should we care whether Mars is hardcore or soft and squishy on the inside. Yeah, Well, for me, there's sort of two levels there. One is just inherent curiosity, like I have questions, is about what's inside stuff. You know, you ever get a rock and you crack it open, you find a crystal inside. There's like a joy there discovering something you didn't expect, and so you always want to like look inside stuff to see what's there. Maybe there's something hidden, maybe there's a mystery. You know, that's why we explore the universe. We don't just sit back and think about it in our minds the way the Greeks do. So we sort of want to know what's out there because we could be shocked, we could be surprised. Mars couldn't be like hollow on the inside and filled with aliens or something. So we definitely want to go look and see what's inside this stuff. But also I think there's a question about just sort of the nature of planets, Like we have an interest in how many planets are out there, how do they form, what do they look like? Are their potential homes for humanity out there? And to get an answers to that, we really need to know like how planets warm and what they're made out of it that will give us an answer to like what they're like on the surface. So we got to know how the insides work if we want to figure out how the outsides look. Yeah, because you know, it's still kind of a big mystery in astrophysics and in science is how do the Solar System form and out of these planets specifically form in in an early version of the solar system, right, and it's still kind of a big question. We're still running simulations and trying to figure that out. Yeah, we talked about on this podcast we don't even really understand how our solar system came to be, Like we run models about our solar system doesn't really quite make sense, Like why is Mars so small? And why do we have very few planets close to our Sun whereas many other solar systems have lots and lots of planets in between the distance between our Sun and Mercury. So we want to know the answer to that question, like what is the story of our solar system? For me, it drives me crazy to think that there's an exciting, traumatic story something that happened here and we just don't know it. Maybe were coextruded by the great planet factoring the sky, a new creation myth folks born here today on the podcast, co extrusion sounds like a good novel name. Yeah, And you know, there are folks who do that kind of study, like look for other planets and other solar systems. They look for exoplanets, and then there's a whole community people who just study like the planets in our solar system and what's in them. People who dedicate their entire research careers to like this question what's inside Mars, And you're saying that there might be parallels but the Earth as well, Like knowing what happened to Mars might help us understand what's happening here in Earth and let us study things like earthquakes and what we can expect in the future. Absolutely, you never want to just have any equals one, right. You don't want to base all of your conclusions about how planets work from one example. You want to look at a bunch of them. You want to population so you can get a sense for what's typical, and you can also see the future, Like if Mars is smaller and colder than Earth, then in some sense it might be what the future of Earth looks like, you know, in millions and billions of years. But it'd be good to get an understanding of how these processes work because we rely on the Earth to have these layers in order to have our civilization and our society function. So it would be good to know, like the factors that control that, What are the forces at play? Are things rising or sinking or cooling or eating or what's going on inside. So absolutely we want to get a better handle on the interior mechanisms of our planet. And it's all right there, hidden under the surface, bubbling up or maybe just chilling out. Let's get into whether or not Mars has a solid or liquid core and whether we'll ever know. But first let's take a quick we're talking about whether Mars the planet, right, not the Mars bars, because we know those have a newgat center, right, But isnt a liquid or a solid? Oh no, another you have a whole episode on strange matter from in candies. Daniel vapes various candies. That's in my new podcast series, one episode long. You just blew my mind vaping. What does that even mean? Oh my goodness, how could it be possible that nobody's ever tried that before, you know, after raping other stuff, since somebody must have had that idea. Oh man, I think you're in the run business, Daniel. Alright, So we're trying to figure out whether Mars has a solid or liquid core, not just for curiosity about what's going on there, but I might tell about the history of our planet and the whole Solar System. And so Daniel, you actually went out there and talked to an expert on this topic. Right, that's right. I called up a colleague of mine, Katherine Johnson. She's at the University of British Columbia, and I asked her why she was so excited about this particular question. Here's what she had to say. So then it's my pleasure to introduce to the program professor Katherine Johnson. Catherine said hello to our listeners and tell them a little bit about yourself. Hi. So it's pressure to be here. And I'm a faculty member at the University of British Columbia in Vancouver and also a scientist at the Planetary Science Institute a Tucson and I work in geophysics in uh sort of planetary science. So I'm interested in understanding the interior state and evolution of of the planets, moons, and asteroids in our Solar system. And tell me why that's exciting for you. What is it about the interior of Mars, for example, that makes you curious, that makes you wonder what's going on inside there? So you know, one of the reasons that I like to think about other planets is really to try to understand our own planet better. I think you know, for me, that's one of the major motivations to try to understand planets in our own solar system, especially in the inner Solar system right where we have Mercury, Venus, the Earth, Mars, our own Moon, and they're all completely different from each other, even though they started in somewhat similar at least with the exception of the Moon, started in somewhat similar ways. And so a lot of this really has to do with their interiors and how they are interiors of like shaped their histories. All right, Thank you, Katherine. And so you went and chatted with her about this topic, Yeah, I did. We had a really fun conversation after all about it. Learned a lot of gory details of how the project works and the politics of getting her instrument up and on Mars and how that all works. It was a lot of fun. Thanks Catherine very much for educating me about your research. She has an instrument on Mars. She does exactly. She helped design and build this seizedmometer that they have on Mars, which is one of the ways they figure out what's inside. Interesting because that is sort of a way they do it here on Earth. Right, we haven't actually like dug a hole or a little people to the center of the earth. We have just models and kind of sound and sound wave detections on the surface, right, that's right. We have dug in only very shallow holes relatively speaking, into the earth, and so we have not actually probed physically the center of the Earth. But we do have a pretty good picture of what's going on inside the earth because of earthquakes. Every time there's an earthquake, it's like the earth rings sort of like a bell, and the waves they don't just like shake the outer crust, they propagate all the way through the interior. And when waves cross a threshold, like when you go from solid to liquid, or the quit to solid, or one kind of metal or to another, you get reflections. Just like when light hits a piece of glass, most of it goes through, but some of it reflects. So these reflections and the interior of the earth make for really complicated patterns. But if you have a bunch of seized momometers all over the earth that measure the shaking, you can get a really nice picture of exactly how this wave propagated through the earth. And then from that you can back out like, oh, there must have been a layer here, and it must have been a layer there, and you can make really detailed measurements about the composition and the density and the flow of those layers. And so she has some instruments on Mars, and are the earthquakes on Mars as she is, she can measure there are no earthquakes on Mars. There are Mars quakes, Martian quakes. Yeah, they actually only have one sized momometer on Mars, so it's a little trickier, but we'll dig into it in detail in a few minutes, all right. And I like how she talked about how every planet is different and how like the insights tell you a lot about your history. I guess that's true for people to write like you can look at my veins and be like, this guy hit a lot of peanut butter. Unfortunately, sometimes our interiors do reveal our history exactly, and every planet has a very different story. And the thing that always surprises me is to realize that these stories change with time. You know, It's not like Venus has always looking the way it does today and that Mars has always looked the way it does today. You know, right now, the surface of Mars is very cool and inactive. But scientists think that Mars had volcanoes active on its surface up to maybe like a million years ago, which is basically no time at all in the billions of years history of Mars. So like, this is an active story that's still developing. We're in the middle of history. We are history is being made exactly all right, Well, maybe it step us through here. Why do we think Mars might have a solid core? Like where did this idea first come from? And why do we need to assume that? Well, you know, we just didn't know for a long time. I think the popular conception is that Mars has a solid core just because it's smaller and colder. Right, Mars is really weird and small. People might not realized. But it has like a tenth of the mass of the Earth, so it's really a much smaller chunk of stuff than the Earth is. Well, I really a ten I knew it was smaller, but I didn't know it's ten times smaller, lighter. Yeah, it's you know, maybe ten but it's just like not really that much stuff. And people think that it might be Jupiter's fault, you know, Jupiter might have come into the inner solar system earlier on, like millions and billions of years ago, and sort of pushed away a lot of the stuff that might have helped make Mars bigger. That might be one reason why Mars is small. But that's, you know, just a mystery. But in the end, Mars is a smaller chunk of stuff, and a smaller chunk of stuff doesn't have as much gravity, so it doesn't have as much pressure and high temperature stuff and its interior, and it cools faster. So there's this sense that Mars is, like being a smaller rock, has a less chance to have a molten core than Earth does. Like you know, asteroids out there don't have molten corks. They're not big enough to generate that pressure and temperate in their interiors. Oh, I see, So that's where I guess you might first assume that Mars has a solid core, and we also know just have a magnetic field, right, I mean, I guess if I said this, like they took a compass to Mars and it didn't work. Yeah, there's lots of satellites orbiting Mars looking for magnetic fields and they don't have one. But if you look at some of the rocks on Mars, you can see fossil evidence for a magnetic field. That means that we know that Mars used to have a magnetic field. So that sort of adds to the narrative, like maybe Mars when it was young and hot, literally had a flowing interior core that generated this magnetic field. But it's gone now, and so maybe that like locked up and there's no longer any motion in the core. Yeah. I used to be a lot more magnetic when I was younger, and otter too, but no, I'm just cool. Yeah, back when you had a better interior flow. Yeah, back when were his clogged with candy killings? All right, So then where did this idea that it could be liquid? And I mean, it seems pretty reasonable for it to be solid and likely, but what makes this thing it could have a liquid core? Well, you know, we just don't know, And so one question is like, maybe we think it has a solid core, but let's go check. Remember a lot of the amazing discoveries we've made in history come from just sort of checking off things where we didn't expect to find anything interesting. Like let's check to see how quickly galaxies rotate. Oh my, gosh, they're rotating way too fast. That's how we discovered dark matter. Let's check to see what happens when we shoot photons at this metal that seems boring. Oh my gosh, we discover quantum mechanics. So there's lots of wonderful opportunities to discover things when you just sort of do basic checks. So that's number one. I guess you don't want to go around the university just assuming things right. You want to actually make sure. Yeah, that's why we do experiments right, because often the results are a surprise, and those are the most delicious times in science, right when you get a result that surprises you, that doesn't make sense, it conflicts with your idea of the universe, and that's how you learn, right, that's what science is. But then people also realize that we didn't actually have conclusive evidence that Mars had a solid core, that you could build a model of Mars with a liquid core that was still consistent with everything we saw and we knew about Mars. But I guess maybe the question is could it be liquid? I mean, if it doesn't have a magnetic field, wouldn't that, you know, tell us that it has a solid core, not necessarily, because the magnetic field actually requires two different things. It requires some liquid, but it also requires flow, Like that liquid has to be in motion. There needs to be some sort of like circulation of that liquid. Because remember the dynamo effect that gives you a magnetic field doesn't just come from having liquid sitting around. It comes from currents right ionized particles in motion. So it's possible that Mars has a liquid, but that liquid isn't flowing in the right way to give you a magnetic field. Oh, I see. It could just be like liquid center just sitting there. Yeah. Or you could have a liquid layer between two other solid layers and it could just be sort of like too thin to have the right kind of rotating currents. Or it might just be the like the heat difference between that liquid layer and the next layer isn't great enough to get like the convection. You need to have flow, don't. You also need like to have special metals in that you know, liquid layer for you to get the magnetic field, Like is an iron in our molten core a big part of why we have a magnetic field, yeah, exactly, And so you need to be open to those possibilities. We do think, based on density estimates, that there is a big iron nickel core to Mars. So the question is really is some of it liquid or is it all solid? But you're right, you need some metal. If you had just like a core of you know, ceramic or whatever, something that was totally insulating, then you couldn't get a magnetic feel from that has to conduct electricity. So it could have a liquid core. Mars could look sort of small and cold, but it could be inside you know, frosthing or seating or you know, have a soft, squishy center or layer. Absolutely, and that's a really exciting moment in science when you realize, hold on a second, you know, everything we thought was true could be different. This other theories actually totally consistent with everything we know. And that's exciting because it gives you like two possibilities to explore. It gives you an opportunity to be surprised. Then, I guess the big question then is if it could be liquid inside, how could we ever know? I mean, we're sitting here, thousands and thousands of miles away, sending small robots one at a time. How are we going to find out what's inside? Daniel. Yeah, Well, it turns out we have lots of different ways to prove this question, some of which we can do without actually going to the surface of Mars. One of them is really cool is that they measure basically how squishy Mars is. They have a satellite which rotates around Mars and basically it's imaging its surface and making a picture of like the shape of Mars, how spherical is it? Because Mars, like everything else, is getting squeezed by the Sun. Remember we talked about tidal forces, how the gravitational force on an object is stronger on the side that's closer to the Sun than further from the Sun. Or for example, this is why Jupiter's moon Io has hot interior, because it's getting squeezed by these tidal forces. Well, Mars is getting squeezed by the Sun, and it would get squeezed differently if it had a liquid center or some liquid layers than if it was totally solid. Basically would get squished more So by measuring really precisely the shape of Mars as it spins and goes around the Sun, you can get a sense for whether or not it has a liquid layer. You mean, like as it goes around the Sun or as it spins around its axis. Yeah, basically the important thing is which side of it is facing the Sun, because that's the part that's getting sort of pulled towards the Sun really, and as it spins and as it moves around the Sun, a different part of it is facing the Sun, and so it's getting squeezed. So if it was a solid rock, then it wouldn't get really deformed by the gravity of the Sun much as it goes around. But if it was liquid inside, it might you know, kind of wish, kind of like a drop of water in space. Yeah, exactly, That's exactly what happens, and so we can measure that, and that gives us some clue about whether or not there's a liquid or solid layer inside Mars. All right, well, let's get into some of the other ways we can tell if Mars is soft and squishy on the inside or if it's hardcore. So let's get into that. But first let's take another quick break. Alright, is Mars hardcore or is it just a big squishy or person inside. Now, we talked about how we can tell, and we can tell sometimes by the tidal effects of the Sun on its shape. So that's one way, and that's happening to us here on Earth. To Daniel, our Earth is getting squished. Yeah, our Earth gets squished by the Sun and by the moon. Right, the reason that we have tides in our ocean is that the Moon is having exactly that same effect on our liquid exterior, and then the Sun has that effect on our liquid interior because it squeezes the whole planet. All right, Well, what are some of the other ways we could tell if Mars is soft or our inside. Another way they do it is by measuring it's wobble. So Mars is spinning and it's going around the Sun, and they measure its orbit very very precisely. And something with a liquid center will spin a little bit differently than something with a solid center, because the liquid center, for example, might not be keeping up with the rest of the object, right, it might be flowing at a different rate, and that's will affect how Mars sort of wobbles as it goes around the Sun and changes its orbit. Really because of like conservation of angular momentum, or is it just like you know, like moving around a water bottle with water in it. It just creates a lot of kind of inner forces that kind of throw you off. Yeah. Well, there is definitely a different moment of inertia for an object that has liquid inside of it because the distributed differently, like the density is different, right, So you can get a sense for the interior density. But then also, as you say, you're gonna get like flows and it's not necessarily going to catch up to the rest of Mars. And so you can tell sort of like you know, the difference between having a liquid and solid based on how sort of the angle of Mars spin changes as it goes around it. Think of it's sort of like a top. You know, a top that has a liquid center will spin differently than the top that doesn't have a liquid center. Right, Well, a top of the liquid tender would slow down faster, wouldn't it. It depends on if the liquid is initially spinning. I guess. So that another way we can tell we can very carefully kind of study the orbit of Mars. Yeah, but then the most precise way, of course is to get down to the surface and actually measure Mars quakes and use those to get an internal picture of what's going on inside Mars. Oh, I see, like get onto Mars surface and measure how you know, sound ways to travel through the planet precisely. And they did this originally on the Viking Landers. They actually had seized moometers on the first two Viking Landers, but it didn't really work like one of them, it didn't deploy, so it didn't get onto the surface, and the other one only ever heard one Mars quake, but it was before it was actually touching the surface, and so it was this very sort of controversial event in planetary science community. Had Viking heard of Mars quake or not, and so before inside landed on Mars fairly recently, nobody knew if there actually were Mars quakes or if it was just totally quiet thing. I guess, well, maybe first of all, let's take a step back and maybe mentioned briefly how you can use sound waves to tell what the core looks like like the sound waves traveled differently if there was liquid or solid. Yeah, just like we do for the Earth, as we talked about earlier. If there are Mars quakes, then they generate these compression waves, and those compression waves will bounce off of interior layers, and so if there's a interface between the layers, like a solid mantle and then a liquid layer. Then you'll have the sound waves bounce off differently than it's just all solid, just like light going through glass or hitting water. When you transfer from one medium to another or from one density to another, you're gonna get all sorts of complicated reflections. And if you measure the sound waves on the surface, then you can get a picture of that. It can give you a map of the interior of the planet I see, and then from the density map you can maybe infer like, oh, this part is less dense, it must be liquid. But also those transition points are really important. You can tell where the transition points are by telling when the reflection happened in exactly the direction that the wave wind. And we actually have confirmation that there are Mars quakes, like we've seen them or felt them, or do we know for sure? Yeah, we actually do have now. So the inside lander that's sitting on Mars, it has the seized momometer on it. And so the lander landed and then put out this cute little bubble which sits on the surface of Mars, and it's shielded from the sun and from the wind, and it just listens to the surface of Mars. So before they landed, they had all these theories about how you might get Mars quakes even without any tectonic activity. Right, there's no like plates on Mars. You don't have like earthquakes on Mars the same way you have on Earth because you don't have tectonic activity. But they thought that you would still have little Mars quakes. So they landed this thing on Mars and they saw like four hundred and fifty Mars quakes in two thousand nineteen. Wait, what four hundred Mars quakes a year? Yeah, so more than one every day. And these are pretty small. Little quakes are like, you know, things that the sizedmometer could pick up but you wouldn't necessarily notice. Could it be the Mars inside their caves kind partying or something jumping up and down. It's actually really fascinating. In order to understand whether they could be quakes on Mars without tectonic activity, right, without these tectonic plates smashing into each other, they look to see if there are earthquakes on Earth far away from the plate boundaries, and it turns out that there are, So you can get earthquakes even where you don't have plates that can come from like the sun heating up big slabs of rock which then expand, or things happening underneath that affect you know, how the crust is moving. And so from those models, they expected there to be a bunch of Mars quakes, and then they put this thing on Mars and they actually see these quakes. Interesting, like, even if there are no liquid core, and there are in any like big giant plates of rock floating and crashing into each other, you can still get earthquakes just from a rock just sitting there getting keated out by the sun. Yeah, and that's not something that we understand very very well, and so it's something they're curious about. They were really curious when they landed this thing, like what we see with the level of quakes we expected, or where they be a lot more than we expected, will be a lot quieter than we expected. They had some pretty good arguments, but they just weren't sure. You know. That's why we go explore the Solar system. And so we measured four and fifty Mars quakes in and then twenty they stopped because of the pandemic. Also, No, that's just the latest data that they've released, so that's the latest result. But you know, they're still analyzing data. This is an active area research. They're still collecting data, and they're still waiting for a really big quake. So far, they've seen sort of a lot of small quakes, and I think they're a little bit disappointed. They were hoping for like a bunch of big ones, because the big ones are the ones that carry a lot of energy and really help them see the interior. With the smaller quakes, it doesn't penetrate as deeply, so you can't really tell what's going on. So they're sort of hanging out waiting to get lucky. So they have detected Mars quakes, but there aren't big enough for them to sort of be able to see much about the inter core. They're not as big as they hoped, but you know, they are clever scientists, and so they've developed fancy new ideas for how to use these to see the interior here anyway, and it's not as powerful as they would have hoped until they get like a really big one in all of Mars rings like a bell. But they have been able to get a pretty good picture for what's going on all right, well, then that's out there on Mars, and Katherine Johnson is one of the scientists on it. So what did she say that we've found so far? So I asked her to give me the insight on Mars and tell me what's going on in the interior. And here's what she had to say. So, we've had a good idea for quite a while now a decade or so, that the deepest interior of Mars is at least partly fluid, but we haven't been able to confirm it with seismology, and that's something that we're hoping to do with the Insight mission that's currently on Mars. And the other thing that we really haven't known is how big it's core is. This is really important because we don't know exactly how big it is. The trade off is it could be smaller and pure metal or a bit bigger with some light stuff mixed in with it. So it seems like Mars does have liquid in its core. Really they can tell, Yeah, it's at least partly fluid. That's what she said. And all these different methods that we've been using, the Wibble method, the Wobble method, and these seismic methods all sort of tell the same story that there is some liquid in the interior of Mars, interesting like at the core or as a layer, probably as a layer on the outer core, just like with the Earth. You know, in the Earth, as you go into the Earth, you have the mantle and then you have sort of an outer core and inter core, and there you have like increasing temperature and pressure. At first, temperature winds and things are like hot and melty, and then as you get to the very center, pressure winds. Even though things are still really hot, pressure takes over and you have a solid core. So they think that's probably what's happening on Mars. Also, you have this core that's like eight kilometers and radius and the outer layers of it probably liquid, so they feel pretty confident. Then they know the answer. So all of our listeners were, how wrong, or most of them were, as I would have been, But that's pretty surprising. So they found that Mars does have a liquid center, Yeah, exactly. Mars is still hot and young, and I was surprised as well. You know, I also expected Mars to be solid because it seems cold and it's small, and I expected things will have cooled off and for all the reasons we gave before, it seemed like a reasonable guest, but you never know until you actually go out there and measure it. There are surprises out there waiting for us, and so we are still learning a lot about how planets form and how they develop into their middle age. Can you still call it lava or magma or would it be like marthma. I'm not sure what the name of it would be, but this is stuff much much deeper than the outer layers, right, Magma is actually part of the crust that's become liquid because it's become really hot. We're talking about stuff that's below the crust, below the mantle, down into the core itself, like the real interior Mars. This other question of like is there magma still on Mars is another fascinating question because vulcanism on Mars seems to have ended fairly recently, so it could be that inside the crust of Mars there is still some sort of hot mac interesting. That's cool. Maybe when we get there we could use that for energy. Is that possible, Yeah, absolutely, it's possible. You know, I guess it wouldn't be called geo thermal energy and be called like mart show thermal energy, yeah, mio thermal energy. But Mars has a thicker crust we think than the Earth does. We think the crust is like fifty to a hundred kilometers thick, so it's probably colder and thicker. So it might be harder to find a spot where there's still like you know, active magma. We don't even know if there is still. But you know, Mars had is like volcanic history for billions of years, which seems to have ended kind of recently, so it would be a surprise if there was totally cold and quiet in the interior in terms of the crust. So it's just another flavor of peanut butter, maybe crusty, smooth, crunchy and crusty. Mars is very multifacet that it is not just two layers, man, There are layers and layers and layers. Mars was co co co co extruded. All right, Well that's a pretty surprising answer, and thank you to Katherine Johnson for helping us out. And it just goes to show you how many surprises are out there waiting in our own backyard or in our neighbor's backyard, and you just have to go out there and check, or at least, you know, spent a few billion dollars building a little robot doesn't for you? Yeah, exactly, build a big robot and use it to investigate your neighbor's backyard. See how that goes, See how that works out. You might call the solar system police on you use it to steal their peanut Butterfield pretzels or their vapen so you can do some experiments at home. All right, Well, we hope you enjoyed then and came away thinking that maybe the even our own backyard, It's not what it seems sometimes, so keep its gloring, keep asking questions, and thanks for tuning in. See you next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I Heart Radio. For more podcast from my Heart Radio, visit the i heart Radio app, Apple Podcasts, or wherever you listen to your favorite show. This