 It's one o'clock on Tuesday, April 26th. So you must be watching Science at Soast, streaming live from beautiful downtown Honolulu. I'm your host, Pete McGinnis-Mark, and every week we have one of the graduate students from the School of Ocean, Earth Science and Technology, which is Soast at the University of Hawaii, on the show telling us about some of the exciting research which is being done at the campus. And today I'm really pleased to have Lillian Burkhardt, who is a graduate student from the Earth Sciences Department. And we're going to be talking about tectonics of icy worlds. And I can hardly wait, Lillian, welcome to the show. It's great to have you on. As always, I asked the student, like, where did you come from? What did your degree, your bachelor's degree, what topics was it? So tell us a little bit about yourself. So I'm from Switzerland, but I've been here a while and I did my undergraduate, actually, AUH. And that's how I got into the studies that I'm doing now as a graduate student through my advisor, because she hired me as an undergraduate worker, basically. So I was working on drawing maps for icy moons and then I just continued on. OK, so if you're from Switzerland, I would have thought studying icy worlds would have been better than a home rather than Hawaii. Why do you feel Hawaii is a great place to do this kind of research? Well, we actually have a really good department here that does a wide variety of research. You know, when you think of Hawaii, you always think of the volcanoes and studying these kinds of things or coastal processes or stuff like that. But we actually have a really good program for everything in space. So and I was just lucky to get into it through my advisor because she was working on a NASA project. And so you came to Hawaii, not expecting to be working in this field. It's something which evolved once you got here. Exactly, because I was originally a biology major. And I took Bridget's class as an elective. And then we sort of got talking and I was hired as her worker, but I needed to change majors in order to do that. So I changed my major over, but I was always interested in like the beginning of life and how life emerged. So that's why my advisor and I got talking about all this because she was studying the icy moons and maybe there's, you know, some sort of life there. But some of the worlds we'll be talking about today could be great candidates for extraterrestrial life. But we're talking about tectonics. And I'm not sure if the viewers actually know what that subject is. So give us a very brief introduction. What do we mean by tectonics of icy worlds? Well, I am specifically studying strike slip faults and also the San Andreas fault, which is the most well-known strike slip fault. I think everyone knows that San Andreas fault in California. So the plates move besides each other. And tectonic processes are just surface processes that include all the plates that we have on earth. So you can have subducting plates or, you know, the colliding plates as you have in Tibetan plateau. And it means these things can build mountains. It means these things can build problems, so openings in the earth. And these processes also happen. Probably on other icy, on other planets and other moons in our solar system. So everybody's familiar with earthquakes. It sounds like you study the results of similar quakes, except that the landscape is made out of ice as opposed to solid rock. Yes, you're not a seismologist. So you're not worried about the actual earthquake. You just study the end result. Well, we've talked about the icy moons. Let's take a look at the first slide. And maybe you can just lead us through here, three classic examples. What is it we're looking at, William? So on the left side, we have Titan, which is an icy moon of Saturn. And it's the largest icy moon of Saturn. And in the middle, you see Ganymede, which is actually the largest moon in our solar system. It's comparable in size, probably to Mercury, if you're familiar with that size. And it has a lot of water actually underneath the surface. And then on the left, on the right side, you see Enceladus, which is a very small little moon, also a moon icy moon of Saturn. And you see how the surface is very, very bright and clear. And it's the brightest, actually, I think the brightest object in our solar system as a moon. So the surface is very reflective, like a little snowball. So all of these moons, what they have in common is that they have apparently an icy surface and then a liquid water ocean underneath. And these oceans, we think, maybe there could be some sort of microbial life. So we're very interested in studying these moons and the processes of these moons. And studying tectonic processes is important because these tectonic processes can act as a pathway to get to the ocean or from things to get to the surface from the ocean. So that's why we're studying these things. Now, these three worlds look very different colors. You know, as well, we should point out the slide. They aren't all projected at the same scale, which is why we have the size. So obviously, Ganymede's ten times the diameter of Enceladus. But Titan looks orange and Ganymede has both light gray and dark gray. And as you mentioned, Enceladus is almost white. And yet they're made of the same stuff. Is that true? Well, almost. When you see Titan and you see all the orange haze around it, that's because Titan has a very thick atmosphere. So the visible atmosphere of Titan, the haze that we see is about 600 kilometers thick. So and it's a very thick atmosphere, meaning there's not much sunlight reaching the surface. The problem is also when we look at it from afar, we don't see the surface. Whereas in Ganymede, there's basically no atmosphere and you can see the surface very clear. And you also see that the surface of Ganymede is obviously older than Enceladus's surface. There's less craters on Enceladus for sure. And the surface is very bright and just more. It looks very recent. Right. And the dark patches on Ganymede, presumably older terrain and those little white dots that we can see in the image. That's the set of craters which you're referring to, which take perhaps billions of years, presumably to to form, you know, it's a random event. But yes. All right. So Enceladus is a really young surface and Ganymede is quite old. Let's take a look at the second slide and you can tell us a bit more about Ganymede, because I find that one to be particularly interesting not only because it's the largest moon in the solar system, but because it shows this age variations. It is an interesting slide. What is this which we're looking at here? Yeah, on Ganymede, you can actually see tectonic deformation from afar like this feature here, which is a clear offset feature. It's a right lateral strike slip feature. So you can see the displacement right there with the red arrows. And Dardanus sulcus is that bright streak right there. So that's a younger surface that we see there that has been displaced. So there must be some sort of forces doing this kind of displacement. And we're not really sure what they are, but it's speculated to be tidal forces and tidal deformation of the surface that might have caused this kind of deformation. So this is one of the most interesting features that we see. There's a few of these displacements that are very obvious on Ganymede. Right. And you mentioned that, you know, each of these worlds might have a liquid water ocean at some depth. So perhaps the viewers can imagine, you know, you've got an ice sheet or an iceberg floating on Earth's ocean. And what you've just shown us is more like movement from side to side in that topmost ice crust. Exactly. Do we have any idea how thick the crust might be? Does your studies actually help us with that? Well, sort of, because all the inputs I have into my models come from somewhere else, you know, the bulk density of things and then the calculations that go into it. So we have estimates of the surface of the ice shell thickness and the ocean thicknesses, not entirely sure again about Ganymede. It might be around 100 or 50, 100 kilometers. And then the ocean is about 50 kilometers, I think. On Titan is a little bit different. I think on Titan is the ice is supposedly 100 kilometers thick. And then the ocean 200 kilometers thick. And so for the viewers, this icy crust is tens of miles thick, at least. It's not it's not something like the Arctic sea ice, which we have here on Earth, which might be a few tens of feet or a few meters in thickness. So this is quite quite a rigid icy layer. So the forces you're trying to investigate, they must be quite strong to crack an ice sheet that might be, let's say, 50 miles thick. Yes. So if you want to compare it to Earth, like our lithosphere, you know, it's about 20 something kilometers. And then if you say Titan has an ice sheet of 100 kilometers, that's five times as big, basically. So when if you think about the processes that happen on Earth in the displacement of the plates and what could be happening, of course, it's ice, but it's ice at a very cold temperature. So it reacts like a rock, basically, in the end. But there's other factors that can decrease the sheer strength of that crust, like liquids, for instance, that we have. And the tidal stresses as the the planet or the moon goes around its parent planet. Yes, we'll get in later today to some of these forces. But it's quite remarkable that worlds, which are much smaller than Earth. You can crack a nice wire or crust for much greater thickness. And I think in the slide three, we'll see just your interpretation of some of this movement on Ganymede. This, I think, is one of the illustrations from your thesis or from somebody else's one of your collaborators. Yes. What are the colors indicated? So we were mapping this. This was for a study for the PhD student I used to work for when I was an undergraduate. I drew these maps for the 2018 study was published then. And we drew these in order to see basically the principle of superposition, you know, which one is which feature is on top of the other so we can have relative ages of different units. Of these tectonic deformations. So you see how the green unit, for instance, is cross cutting the blue one. So that means unit five must have been younger than the other one because it's cross cutting. So that's why we were grouping all of these little features together into these bigger groups to actually see relative ages of the surface. And if our technician can go back to slide two bounce between slide two and three, then we get a much much better understanding of what we're doing. If we go back to three, there you go. So this is very instructive and it tells, obviously, that the relative age of features that see that looks a very complicated map that you drew. Yeah. Have you done the whole of Ganymede because that's no politics time? Yeah, because we actually don't have high resolution data of the whole surface of Ganymede. So they're only like, I think, eight or something patches that we have in this higher resolution. And when I say higher resolution, I mean, hundreds of meters down to tens of meters per pixel. So if we would actually have the same data available for earth, you would not even see buildings if you have a resolution of 100 meters per pixel. Pixel is one dot on the image. So we would not see any roads or buildings, but you can see a larger scale mountain ranges, for instance. OK, that's what we're basically mapping. So we don't have a complete surface image. Let's move on to another one. So I know you've got a few slides of Titan. So slide four. We've heard of Titan earlier in this TV series before we've got two views of the same world here. We've seen the left hand one and the right hand image shows. That is the radar coverage that we have. So because of the atmosphere, we can't use, you know, and a good camera to actually see the surface. So we have to use radar that can penetrate the atmosphere and then see the surface with radar imagery. But the problem is also here, as you can see, we don't have a complete coverage of the whole surface. So I think about 70 percent of the surface has been captured with the radar at about five to two kilometer resolution, kind of low. And then you see the other stripes right there. Those are the stripes that are higher resolution and they're about, I think the lowest is three hundred and fifty meters per pixel. So still kind of large. So that's what this is showing. And I believe the coverage is best at the North Pole, which is what we see in slide five. We can go to the high five. Yes, the North Pole, I think, is in that white gap at top left. Yes. So we're missing data there in those white gap. And so if you were to look at parts of Titan to try and find tectonic features, that would be the quality of the data that you have to work with. Yes, preferably better, but we don't have anything better right now. We need another spacecraft going to Titan. Yes, I know there's one going in a few years' time, but that's not a radar system. But slide six shows us a little bit about the kinds of tectonic studies you can do, right? So am I right in thinking the two gray images are actually parts of Titan? Yes, so this is the Western Xanada region. The Xanada region is a bright radar feature. Basically, it's a brighter patch and it's kind of mountainous. Well, a few hundred meters elevation. Titan is not very high in elevation, but there are features there that I saw while I was going through the more higher resolution data. So this is at three hundred fifty one per pixel that kind of look like things that we see on Earth. So on the right side, you have a displacement on the San Andreas fault of a flu wheel feature. This is Wallace Creek and the displacement here, you can see the right lateral displacement. It is about one hundred and thirty meters offset. And when you compare it to Titan, these flu wheel features, they seem to have an offset, both of these, that trend in about the same direction at the same sort of incident angle. And they are offset by about ten kilometers. So there must be some sort of tectonic fabric underneath or whatever that is causing this type of displacement for these flu wheel features that we see. So Earth and the San Andreas fault in California is providing a good analog to tectonics on Titan. But now my Titan actually produced some of this tectonic features. So my study actually looks at the diurnal tidal stresses. If the tidal stresses could be enough to deform the surface as Titan goes around orbit in Saturn. And these types of studies have been done on other icy moons like Europa and Salatus and Ganymede as well. So I just use these types of methods and applied it to Titan. OK. And is that what we're seeing in slide number seven? If we go on to the next slide, here's a really nice cartoon. We recognize Saturn in the in the middle. And this is what we're seeing. Titan has been stretched, does it? Yes. So as it goes around orbit, because the orbit is not entirely circular, it's sort of more elliptical. So it has a deformation as it goes around in orbit. And you can see the closest approach, which is periopsis, closest approach to Saturn. And then the furthest away is up or up. So we use these measurements to calculate the tidal deformation at any point during orbit and also at any point on the surface. OK. So the key idea you have or the community has is that because Titan does not orbit in a circular orbit around Saturn, it's being squeezed like a rubber ball by Saturn's gravity. So that's what's driving the tectonics. Could be driving, yes. Could be driving, yes. Because I'm familiar. I may be some of our viewers are familiar, like with the moons of Jupiter the volcanic activity on the Moon called Io or Europa, where it's being pulled in two different directions by moons on either side of it. But Titan's unusual because there's no other big moon around Saturn as far as I can remember. Yes. And also, Titan is unusual because the orbital eccentricity is quite high. Zero point zero two eight eight, where you compare it to like anime where it's zero point zero zero zero one three or something. So it's, you know, magnitudes larger, actually. Now, you've actually done some computer modeling, which I think slide eight will show some results. And this might need a bit of explanation. So what is it we're looking at? So here we're looking at an output that I have that gives me the the components to calculate the stresses on the surface. So this is the on the first on the top part, you see the closest approach to Saturn. So we're at oppo ops. And then you see the map on the left side. So this is a map view of the surface of Titan. And you see how the surface goes into tension or compression. So here we have, of course, the equator, which is closer to pulled to Saturn. You see how it has higher values there in tension. So there's more tension there. And then you see this is a hundred and forty orbital position. So not quite a box, but close by. So you see how in the equatorial region, it is more in compression and then also in more tension as these stresses to sweep across the surface. As we go through orbit. OK, and to help the viewers, each of those colored diagrams it goes from the North Pole at the top to the South Pole at the bottom. And it wraps all the way around this conference at the moment, right? Exactly. And so the colors correspond to compression and tension on the scale of a and I think the little illustrations of where Titan is with respect to Saturn, the two images on the right hand side give their respective distances. So that and you can run this for the entire orbit of Saturn. Does it produce the kind of tension and compression that you would expect to define, given the landscapes that you look at? Yes, well, one of the main factors that we can put into these calculations that we cannot put into any of the other icy moons is the liquids that are present on the surface because liquids decrease the sheer strength of the cross. So we can actually put in a parameter for poor fluid pressures and that gives us actually enough resistance, less resistance so it can actually lead to fault failure on the surface. OK, so you could essentially do some detective work to try and find what the subsurface composition or structure might be. That must be fascinating to do, right? Yeah, very much so. But does any of it actually work? Have you come up with a real explanation or is this an area of future research for you? The problem, yeah. Well, the problem with modeling is always that you need to have some sort of analog that you see on the surface. Actually, that is like a benchmark for your model. But the problem with Titan is that we don't have that great of a data. So, you know, if we can't compare it like on Ganymede, where we actually have these offsets that we can actually use as a benchmark. Well, we have a few minutes left. So let's really challenge you with one other icy world. We were introduced to Enceladus at the start of the show. Let's look at Enceladus. You said it was like a snowball, but in this image where he's talking on the side with the North Pole on the right and South Pole on the left, they look like great cracks running through it. Am I looking at this correctly? Yeah, it's, you know, it looks like ice sheets. You know, if you look at our polar regions, it looks like just an icy surface. You know, so it's super interesting. But I think that image might be a little bit false color or enhanced colors because the blue is more enhanced right there. OK, well, well, maybe the last slide side 10 will give us a better view, which I think is the South Pole region. Yes. And and and the insert. Enceladus is quite interesting when you look at the the entire world. It looks like there's volcanic eruptions there. Yeah. Am I seeing this correct? Well, maybe volcanic is a strong word. It looks so Enceladus has these openings at the South Pole. Basically, these these faults that spew out you know, water ice, I mean, water. And it has these plumes that come out. So there is active something active going on right there. But these openings could also be temporal, in a sense, with related to tidal stresses and as it goes around Saturn. I think more of geysers like old Facebook than Kilauea erupting or something like that. Yeah. Yeah. OK. Well, I'm afraid we're running out of time. So I thank you again for appearing on the show and fascinating to see some of these icy worlds. I'm sure our viewers aren't that familiar with some of the worlds which have been seen today. I want to wish you good luck. I understand you'll be defending your PhD thesis in a few months time and good luck with your future career. So having in mind the audience, you have been watching Science at Soast. I've been your host, Pete McGinnis-Marc, and my guest today has been Lillian Burka. And I look forward to seeing you again next Tuesday as well. And we will have another guest from the School of Ocean Science and Technology. So until then, goodbye from now and goodbye, Lillian. Thank you.