 So I'm Jeff Bonning, and I am a PhD candidate at the Research School of Earth Sciences at ANU. So most of the time what I like to study are the chondrites, and these really primitive meteorites, and they're the building blocks of the planets. Particularly for me, I love the carbonaceous chondrites, which are really our only pieces of the outer solar system that we have that we can actually look at. But a while ago, over the last year, it was the century, the 100th anniversary of, or since it was the 90th anniversary of the discovery of Pluto. And so we were asked to talk about Pluto. So I developed this talk that I'd like to share with you all now, which is just the geology of Pluto. That's what we're going to go over today. So it's really fun, and Pluto, as we'll see, is a really exciting, really bizarre world. Sometimes you want to do it with other planets like Mars, you can make analogies to things, you can talk about, oh, you know, this is, you know, we've got the atmosphere, we've got a rocky crust, maybe there was an ocean, there's ice caps. But with Pluto, things are so different, the chemistry is so different, that it's really hard to draw those analogies. So we'll look at, especially one called the Sputnik Planum, and we'll go over all that. So start off with, let's go here, so here's a little overview of what we're going over. To start with, I'm going to be talking about our intrepid little robot explorer, New Horizons, the spacecraft that actually went to Pluto. Before New Horizons got there in 2015, Pluto was a blurry haze in the Hubble telescope. We could barely see anything, but now we've got all these beautiful high resolution images next to New Horizons. Then we'll go over a little bit of the basics of Pluto, so Pluto one-on-one, just things about how big it's blue, how far away. And then we'll look at a bit of the geography and look at some of the specific features, which you can see right here in that map just there. And then we'll talk briefly about the moons, and then very quickly we'll look at the follow-up to the Pluto mission itself, which was New Horizons, because it's going extremely fast, it's at escape velocity, one of the few spacecraft to do that. It's on its way out of the solar system right now after it's fly by Pluto. And on the way out, it's stopped by a little tiny, tiny world called Arapa. That's the most primitive object we've ever seen, basically a clump of nebula as a world, so we're going to look at that at the very end too. And then we'll talk about the other fact that it's an interstellar space, and time for questions at the end. So New Horizons, yeah, so New Horizons launched in 2006, and you can see it's gone right out here, up and intercepted the Pluto system in 2015. Now we said a Pluto system here, because Pluto, even though it's not technically a planet, we call it a dwarf planet, is actually a binary planetary system, because the center of mass of it and its moon, like Charon, or Charon, if you were to balance them on a stick is actually not inside either of them, so we call it a double binary planetary system, or a double planet system, even though they're both dwarf planets. And then, yeah, so New Horizons is often, like these kbos, what we call the Kuiper Belt object, so really icy things. So we talk about the asteroid belt and the interstellar system between Mars and Jupiter, but you go further on that there is a lot more stuff out there that we are going to just begin to discover and understand. So New Horizons was basically a spacecraft, it's basically a camera and a spectrometer, those are its main instruments are taking pretty pictures and looking at what the things in those pictures are made of. So a spectrometer for those who don't know about them, a spectrometer is an instrument that we use to it splits up the light coming into it, and using that we can see so it splits it up into different colors. And then looking at the intensity of different colors, we can use that to figure out what things are made of, especially by comparing things to things in the lab. So that's how we figure out, so when I talk about chemical information and chemical composition stuff in this, what we're talking about is information that came through the spectrometer. Yeah, oh, and one thing you might notice about New Horizons here is a lot of our solar system exploration craft that you might have seen. A lot of them have solar panels, but this one doesn't because it's going so far away, it cannot rely on that. So it's actually relying on a nuclear generator, a small one. So it's basically just a bunch of radio isotopes in there emitting heat and it's getting power from that. One of the first strange things about Pluto is it's really eccentric, and by that we need really oval orbit. So most of the planets have very circular orbits, it's got a much more oval shaped one. It's also inclined, so most of the planets are in a single plane in the solar system. But Pluto is on this really, really high orbit kind of. And that's the case with a lot of things out there, they're smaller and they are much further away, so they're less tightly bound in some ways to the sun. So as I said, it's 30 to 50 times farther away than the Earth is from the sun. And at that point, the sun is still the brightest object in the sky, but it's only a point of light. So you couldn't actually resolve it right on Earth, right? The sun is about the size of the moon in terms of angular size, you can look at them like this. Out there, it's a point of light and it is 250 times farther than the full moon. So I don't know exactly what that is to look like, but it might hurt your eyes to look at it. And out there, of course, it is extremely cold, minus 229 degrees Celsius being typical. But there are a lot of variations. Because of this, so Pluto is extremely tilted. So not only is it itself inclined, eccentric, Pluto itself is at a really strange angle to its orbit. So we're at about a 25 degree, 24 degree angle roughly to our orbit and the Earth spins something like, I can't really do that with my hands very well, something like that on its orbit. To give us the seasons, Pluto is like this and it's doing something like this. It's doing these huge oscillations. And what that means is that it's summers and winters last an extremely long time. Yeah, so on Earth, you know, if you're at the South Pole or any either of the poles, the day times in the summer are six months long. And the winters, the nights in the winter are also six months long. On Pluto, that's true, but they last almost a century. So extremely long periods of day and night. And because of that really eccentric orbit, if a summer happens when Pluto is close to the sun, so the pole pointing towards that, if that lines up, that's what we call these extreme seasons on Pluto. Pluto has extreme seasons that happen as well as the seasons themselves when that eccentricity lines up. So then you've got, and those happen every 800,000 years. There's been a large cycle there that changes the temperature of the poles dramatically. So Pluto is very small. Here on the facts here, 0.2% the mass of the Earth and its surface gravity is less than 10%. So you could kind of walk around, you know, it's not too dissimilar from the moon or so, but wouldn't be easy. And it's about the size of Russia or a little bit over two times the size of Australia. So if you've walked across Australia, you can probably walk across this. And just as a comparison in the composition, so whereas we've got a rocky, I mean an inner metallic core inside the Earth. So these two bits are metallic. The core of Pluto is rocky. And instead of a rocky mantle like we have, so we've got, this is where a really dense, hot, kind of plastically deforming a really kind of gooey rock is the mantle. Instead of that, it's got water ice acting as its mantle. And above that it's got nitrogen. And this is again, I want to use the analogy that nitrogen is like the water on the Earth, but it's not exactly because it's still a solid most of the time. So it's not exactly like water on the Earth, but it does form this outer layer. Nitrogen is what dominates that bit. And it's also got an atmosphere. So that's something that we kind of knew about from Hubble, but it's not until we got out with new horizons. And we actually see how complex and thick that atmosphere is. So you can see it here. We've got these haze layers. So these are layers of actual haze in the atmosphere. And that haze is made of organic compounds. It's a little bit of methane on Mars. And that's part of the atmosphere and the solar radiation hits that methane. It reacts with itself. So that methane reacts and you form more complex organic chemicals. And as that continues, those organic compounds from the methane starts to get bigger and bigger and bigger and bigger until they slowly rain out of the atmosphere. So there's a really steady accumulation of rain or haze on the surface of Pluto. You can see it again here. It's actually blue. And that's the nitrogen. It's actually blue for the same reason that the Earth's atmosphere is blue. This is the nitrogen in the atmosphere. Now as I was saying before, this is one of the first things that shocked us. This is one of the nice beautiful pictures of Pluto. It's an extremely diverse surface. That was one of the first things that struck the scientists working on the mission. It's not just some dead body. One of the first things we can see is that you've got these really, really cratered ancient terrains like this down here. And then you've also got these really fresh-looking terrains like this. This is something I'm just here. And then you've got kind of intermediate-looking terrains, things that are a bit older but not quite ancient. So there's actually resurfacing going on on Pluto. Pluto is an active world. Mars, for example, can compare to Mars. And Mars is pretty much an extinct world. It's a dead world. I think the surface itself isn't turning over anymore. Pluto, this is clearly still happening. And just to remind you, there's going to be question time at the end. So don't forget to ask any questions if I've just glazed over something and you're like, hang on, what was that? Please ask me. So yeah, so with these organics here, so we're talking about that haze, right? In the atmosphere, and that slowly accumulates. And what that means is that we've got kind of an indicator for the surface age on Pluto. So you can see these redder terrains, the more red the terrain is, the more ancient it is generally. So we've got these really ancient red terrains, fresh white surface on Sputnik Planum, and something kind of intermediate over here. This is over, I think, Tartarus dorsus. So this intermediate age, a little bit red, a little bit cratered, but not quite as red and cratered as this over here. So this is our overview of the geography. This is our geography of Pluto session. And so we have Sputnik Planum in that middle here. This is this footprint shaped one. And Cthulhu Regio here. And this is one of the most ancient terrains that we've found out on. So this is what we call the encounter hemisphere. This is the bit that New Horizons got close to as it flew by. As it flew around the other way, we did get to see the far side. We didn't get to see the other side, but we didn't get to see as well. But we did see that this Cthulhu Regio type of equate band extends all the way around the equator. So you can imagine this thing standing all the way around. And then we're going to start looking at, first we're going to go over the compositions. So nitrogen, like I said, dominates the surface of Pluto. It's the most abundant chemical there. Now most of it is ice, most of it solid, and most of that ice is in that Sputnik Planum. So that's why you kind of want to use the analogy sometimes that nitrogens like the water on Earth. And so nitrogen is kind of like the water and it flows into this plane. So it does flow into it. And it's also the dominant gas in the atmosphere. So again, you want to use the analogy to water, but this plane, as we're going to see, isn't quite analogous to an ocean. It's very solid. It's very different to an ocean. Methane is also a feature here. So we've got that's also mostly as ice and also as a gas in the atmosphere and maybe even sometimes as clouds. So we've seen some tenuous kind of look things that look like clouds there and also in Hubble images, things that kind of look like clouds that might be the methane. Also carbon monoxide, but that's mostly sunk into that Sputnik Planum there. And water, as we know, water is what the bulk of Pluto is or bulk of the mantle of it, but that's only exposed at the equator, this high altitude equatorial region. So that's where we get the water actually being exposed because the nitrogen isn't actually stable there. So you can see it actually not, you see there's no nitrogen there. Just a little overview of some of the geography and the names that we've got on Pluto. So what's kind of fun about it is that it's got three main things that it's drawing on. It's got things that are often underworld deities. So Pluto itself, of course, is one of the three Roman deities of the underworld. But then we've drawn on a number of others, as well as fictional ones. So we've got Cthulhu Ritio here, the Balrog Macula, as well as some others. I mean, it eventually not as familiar with the Krunala Vokup Kameg. And then other things that are named after are explorers and that's a mixture of human and robotic explorers. So we've got Viking, which was a Martian rover. Hyabusa, which was a Japanese spacecraft that went to the first asteroid. And then we've also got the Aladrissi Montes here. So Aladrissi was an Arab explorer that went into Europe and backed all that. So now we're going to zoom in on the Sputnik planet here and see it in a little bit more detail. So again, you want to kind of call it an ocean, but it's solid, but it's still doing convection. It's a very strange thing. So yeah, it's got these cells. So we've got this cellular terrain. And so the middle bit is where the hot material, like convection, if you're not familiar with the term, is what happens in your petal when you're boiling your water or when you're cooking a stew maybe. And you've got hot stuff rising up in the middle and then pushing out to the side and then sinking down at the edges. And that's exactly what we've got going on these cells. So we've got things push up and rise up in the middle and then sink down at these edges. So those are our convection cells. And we can see that these things are quite young because there's no craters on them. We don't see almost any craters on the Sputnik planet. So we expect that these things are surfacing pretty fast in a geological time scale, which means maybe they're 100,000, they take 100,000 years, maybe a million years to turn over. We've also got the edges of Sputnik planet. We've got these mountain-sized icebergs made of water ice. So there's glaciers actually on the edges. So the nitrogen flows into Sputnik planet. So glaciers form at maybe higher altitudes. They flow into Sputnik planet. And as they do that, they break off the water ice that forms the basement rock and these things end up floating out into Sputnik planet. And you can see a little bit better on the past one here. So these things like this. And these are giant icebergs, but they're the size of mountains on Earth. So these things can be up to five kilometers tall. There's gigantic floating mountains. We can also see dunes on top of our convection cells. So that again is evidence that the atmosphere can become quite thick on Pluto. And so that's something else. Remember that nitrogen is acting as the atmosphere. It's acting as one of the things that's moving around on the surface. So it condenses out of the atmosphere like water does on Earth. It can condense out as an ice or it can be a gas. And on Pluto during those really intense summers, so much of the nitrogen is possible that it becomes a gas that the pressure at the surface becomes way greater. So you might actually have liquid nitrogen flowing on the surface of Pluto and wind able to actually blow grains of ice across these dunes, across these convection cells forming these dunes. So during those intense summers, you have the pressure of the atmosphere increase enormously. And the opposite is true during the winter. The atmosphere most of the atmosphere condenses out and you're in basically a vacuum again. And it just kind of forms a snow. Then during the springtime when things are heating up, you've got these sublimation pits. So these things are hundreds of meters across. And a sublimation is not a process that happens much on the Earth. But it's where a solid goes straight to a gas without going through a liquid state. Now most of the time we're used to seeing ice melt in spring. But in the rest of the solar system, especially where pressures are lower on Neptune. I'm sorry, Neptune. Well, on Neptune, Neptune Triton has it. Pluto and Mars as well. Things go from solid to gas pretty regularly. So this is what these pits are. You have a whole piece of the ground evaporating. And next we are going to look briefly at Tartarus dorsi here, which is what we call the bladed terrain. So you can't quite see the bladed texture here. I'm going to zoom in on that now. And so these things are ridges. And they can be kilometers tall. And they're basically oriented north south. So it's called bladed terrain. The description that's from some of the scientists that worked on this is that if you've got all of the knives in your drawer and just kind of stack them up this way and just did it like that. So this is these alleys in between the knives, alleys in between the knives, and then these just sharp clips of methane. And so this is a really bizarre terrain that doesn't really have an analogy on the Earth. And the best thinking about it is that during those extreme summers and extreme winters, the nitrogen evaporates from one of the poles, the nitrogen and the methane evaporate from the current summer pole and migrate to the colder winter pole. And while it's doing that, they're forced up the high altitude equator. So the equator is quite a high altitude. And just like snow on Earth. So when, you know, if you've got moist air being forced up a mountain, you get rainfall and you also get snow. Kind of coming out of the gas. Same thing happens here. As these nitrogen and methane winds blow from the summer pole to the winter pole, the methane crystallizes out and forms these massive ridges. And then the nitrogen winds are kind of blowing through the channels between those huge ridges. So it's a really bizarre terrain that we don't have a huge amount of analogies for on the Earth. And yes, the next we're going to look at the Cthulhu region here. So this is our most ancient terrain. So just that comparison, we've got almost no crater on Sputnik Planum and we've got this very heavily cratered Cthulhu region. Yes, lots of craters there, which tells us it's very old. It's been around to experience a lot of impacts. And because it's at that high altitude, that nitrogen isn't actually stable there. So we get, we see the water ice, that bedrock exposed, the water ice is exposed here. And because it's so ancient that water ice is then coated with what we call tholins. And those are the organics that we were talking about. Those things that rain out of the atmosphere from the methane getting complex. And then once they're all on the surface, they become even more complex still by solar radiation. So you get these really thick kind of on Earth, if you were to melt it, maybe it would look like a tar. But out here it's a kind of, it would be like a solid substance. Yeah, so we've got this really red layer of these organic compounds. And then this white bits, this is not water ice snow, obviously. This is methane snow forming on those. So it's a little bit maybe like those Tartarus dorsi where the winds kind of blow over here and precipitate out on the, on the mountain tops. And again, just remember, if you have questions, please let me know. And I'm rushing through everything here. So let me know. So one of the other things that we see in Virgil fausae, in Cthulhu Virgia, sorry, is the Virgil fausae. So that's this crack you can see here. And so this is a sign of something like tectonism. And this layer is actually a liquid layer in between. So we have that icy shell beneath water ice, nitrogen ice on the outside. But in between those two, there might be a liquid layer inside. And in fact, most of that water layer might be liquid. And so this crack, for one thing is evidence of it because it means that it's kind of shifting around and as that solid nitrogen and water ice layer on the outside shifts around, it might crack a bit. And the other thing that we have to do around that crack, you see a lot more water than you do elsewhere. So it looks like, so we call it cryo-volcanism. It's just cold, volcano. Because it's cold water being squirted out of this crack where that liquid ocean beneath might have just pushed that water out. And part of the way that it stays that cold is all those organic compounds actually form a bit of an antifreeze in there, which unfortunately puts a bit of a damper on the idea of astrobiology. Not to say that it's impossible. It's just that any organic chemistry that we know would find it very hard to live in a liquid water ocean with that much antifreeze kind of substance. It's that kind of, yeah, with that chemistry. So a brief look at the moons now. So we've got Charin and then these other little moons. We've got Styx, Nyx, Kerberos and Hydra. Now Charin itself is a really similar composition to Pluto and it looks like it also had a liquid layer inside at one point, but that froze over. And when it froze over, what you can see is this crack here. So what, if you've never tried putting a water bottle in your fridge or in your freezer side and if you screwed the lid on too tight and that water can't go anywhere and the pressure can't go anywhere as it expands your water bottle might crack. That's basically what happened to Charin. The whole planet basically just rifted around the middle of the planet that expanded and cracked the surface. And you also have this weird layer of this weird immaculate, mordor immaculate on Charin, which seems to be some of the thulins coming. So there might be, what it might be is that between these two planets they're over to each other. Charin might be stealing some of that methane atmosphere. So there might be some of Pluto's tenuous atmosphere kind of trailing over to Charin and depositing on there. And as they deposit, they form those thulins again. So once that methane's on there. And then this is our final view. So this was our final view of Pluto as New Horizons flew past around. So we got the encounter hemisphere, just everything that we've seen so far. Oh, sorry, I should have said, I don't have to mention these guys. So these are just tiny little worlds. So these didn't really get to differentiate. And so they might have, they still argued about whether they accreted along with these other two. So you have a disk of ice as Pluto and Charin are forming around each other. These little moons might have formed from that disk or they might be captures from other coin-propelled objects. They might have just pulled them in and attracted them to it. So this here is the other hemisphere of Pluto that we didn't get to look closely at. But what you can see is that dark equatorial band again, that Cthulhu regia. So that is where that very ancient high altitude terrain goes fully around the planet. And New Horizons as we showed before kept going. It would be extremely hard to stop. So once New Horizons was going at those speeds to get out here, to get to Pluto in a reasonable timeframe, it's very hard to stop. It would have had to carry a lot more fuel to slow itself down. So it just didn't fly by. It flew past and went to this guy. So they didn't actually know exactly where they were going up there and figured that they being NASA and the New Horizons team figured that they could deflect it to one that they selected later. And they ended up with Arakoth. Now it was originally called Ultima Thule which was the most distant place known in Greek mythology. But unfortunately that name is also used by Neo-Nazis as the Arian homeland and the NASA scientists decided that was not a good name to keep Arakoth which is a Powhatan word from North America. So that was where the original settlers in Virginia landed. So that's one of their thunder deities. So it was discovered in 2014 Arakoth. So yeah, so one for one thing was discovered after New Horizons actually launched. And it is the most primitive object we've ever seen up close. So this is, if you were to imagine what happened, what would come out of a nebula. Let me see the beautiful, I should say, if you were to take a bunch of the ice and dust and just kind of push it together like a snowball, this is effectively what that would look like. This is a nebular solid basically. It's never been heated. It is in the same orbit that it was in four and a half billion years ago when the solar system formed. It's barely moved. So really the asteroids in the solar system as a counter example they have moved around. So this is really where they originally formed. Everything's been mixed up. But out here, things stayed really still and quiet and stable. So this is exactly where it was. So you can see it's another kind of a double planet. But what happened here is these two tiny bodies, I should say, it's about 39 kilometers long slowly, slowly orbited each other slowly, slowly, slowly until they just kind of bumped into each other and stuff. So you can see it's all mixed up. If you were to go there, you could grab a fistful of this and you would have basically pristine inter-star dust, the stuff between stars. When you look at the dark band of the galaxy, when you look up in Milky Way, that dark band is the dust between stars and you would basically be getting a sample of that in this kind of object. And as I said before, yeah, new horizons on the way out. So new horizons are the fifth spacecraft to achieve escape velocity from the solar system. So it is one of our fifth interstellar probe. So it's on the way out. Which is very exciting. So I don't know how long it will last after it actually. Any questions about it? Yes, I've got one question already. If you have questions, yeah, just please keep sending them in. We've got someone who's forwarding them on to me. Now the first question was on Pluto that getting more craters than other places. And as far as we have any reason to believe, no. It's not that it is the same on most bodies. We kind of expect that the the impactors come at all directions, come from all directions and on Earth, that's far as we can tell, that's exactly what happens here too. Things impact the surface from all directions and all angles . What the different ages, what the different amount of cratering tells you is much more so about the freshness of the surface. So a surface that hasn't been changed at all gets a lot more craters on it. So as another example, Australia is a bit more of a crater confident than some other fresher younger places. So if you were to take that out of the average size of Indonesia, there is then Australia, which is 3 billion years old, some parts of it. So it's got more craters on it. And likewise here, it's got very ancient terrain, very fresh and young terrain. Second question, does accretion require heat? How do those two lumps of ice get stuck together? It's never melted enough to create some kind of adhesion. So the adhesion on bodies like this is just gravity. It's very weak. They're not very big bodies. The gravity isn't very strong. And you can see that, well, there's actually a little bit of crater there. But a significant impact would break them apart possibly very easily and quickly. But it's just a very slow gravitational kind of settling on to each other. But then that gravity wasn't enough to deform their original shape into a ball, or a planet. The heat doesn't come to the heat integration on larger bodies is often because these things are kind of flying in hot and bringing a lot of energy with them. Whereas this was a very cold collision to start with. Accretion doesn't require heat is the answer to that, but it definitely can involve a lot of heat as it did with the Earth. And that's a big part of the impact. And especially because we were in the inner solvable system where things were being mixed up. So we've got all those Jupiter and Saturn moving around which moved all the planetary building blocks around and threw a bunch of these asteroids at the Earth and created these violent impacts which melted the surface, melted anything that was here. Or here's a very slow, slow question. What is the size of Pluto compared to the Earth? Now I've got that back here. It's all. There you go. It's about 2.2% the mass. And so you can see the surface area would also be quite small. So it's very small. It's actually smaller than the Moon. Yeah, it's smaller than the Earth's Moon, significantly smaller than the Earth's Moon. That's all the questions that I've got coming in so far. Oh, here's another one. How can such a small body hold on to an atmosphere? That's a good question. Sorry, the others are good questions too. That's a very perceptive one because when you go to places like Mars, it's lost a lot of an atmosphere. So how can this tiny body have anything on it? That nitrogen is found here. Yeah. Because it's so cold, the nitrogen, even though it is a gas, is just not kind of vibrating enough to bounce out of the atmosphere. Out there, even though it's barely being held on. It's just simply because it's so cold. And actually that haze, Pluto, one thing that was kind of confusing from Hubble and the measurements that were made from Earth, was that Pluto is actually colder than you would expect. So if you were to, you know, just imagine how cold an airless body is at different distances from the Sun, you can kind of estimate their temperatures based on just how much light is coming onto them. But Pluto is colder than you would expect for a body without an atmosphere. And part of the reason is because of that methane haze. So because it's atmosphere, it's atmosphere actually affects to cool it down because the methane in that haze reflects more light. So another question is how far away is Voyager 1 from Earth now? Answer that one. I don't actually know. I don't have the answer to that. I can look that up and I can Google that in just a second, but I don't actually know the answer to that one. How many moons does Pluto have? And how many is it? Five? Yeah, nailed it. So we got, yeah, Karen's it's major one. Although I could say maybe we should actually kind of say four moons around the Earth. Four moons around a double planetary system. So we can put on Karen's not really technically a moon because it's the center of mass of these bodies is outside of Pluto, which makes it a double planet system, not a planet moon system like the Earth. So four little moons, possibly more smaller ones. New Horizons did look for more, but it didn't see any. But that doesn't mean that there aren't any. It flew by very fast. So it didn't get to spend a long time out there looking for more. Yeah. Any other questions? That's all we've got right now. Any other questions about Pluto? I hope I didn't speak too fast. I hope you could all hear me. It's my first time doing this over Zoom. I'll talk about this. I'm going to get to see the audience's face and see how they're responding. Okay. So I got another question. How do you know the center of mass is in the middle of Pluto and Karen? By, as by knowing their mass, they're individual masses. Sorry, partly by knowing their densities. But we can, we can estimate the based on their composition and how fast they're spinning around each other. So we know that they're made of ice, a lot of rock. And by knowing how fast they're spinning around each other, we can estimate their respective masses from the amount of angular momentum they've got. And yeah, once, once you know those respective masses, then it's just a matter of, kind of balancing those, just taking the distance between those. And it's almost like, you know, in the model, you're kind of really just, if you're trying to, if you're trying to imagine it, you just have a stick between the two and you're trying to kind of put your finger on and balance in the middle of it. And on the earth, in the earth moon system, that balancing point is inside the earth. If you do that calculation, whereas with Pluto and Karen, it's on the outside of Pluto. Who discovered Pluto? Oh, gosh, I should know this one, as we talked about it. Was it Clyde Tombaugh? Is that was, so this feels like, who wants to be in a million area? I know I'm on the hot seat. Sorry guys, I can't Google this. You just saw that. Okay, so it's Clyde Tombaugh. And an extra fun fact was that it was named by a schoolgirl who just kind of wrote into them from what I understand. And I just had been reading about mythology in a book and it was like, Pluto would be a good name for that in terms of the thought of the underworld in this dark, cold place. So as a child, it actually ended. It was in the 19th. Yeah, 19th. Any more questions? So we've got no more questions coming in. So I'm going to wrap up. Thank you all for coming. Hope you enjoyed it. Hope it made sense. Yeah. Thanks. Stay safe, everyone.