Hello, and welcome to SETI Live. I'm your host, Beth Johnson, Communications Specialist here at the SETI Institute. Thank you, everybody, for joining us today. Welcome to our viewers from around the world. Please let us know where you're watching from, and also welcome in to our listeners on the podcast version of SETI Live, available on most podcast platforms.
Joining me today is Dr. Ian Palmerlow from Purdue University, who is the lead author of a fascinating new study published in Nature Astronomy, exploring the icy crust of Ceres and what it tells us about a very small but complex world. Now, before we jump in, just a quick reminder, if you have questions during the live stream, drop them in the chat. We'll be taking your questions toward the end of the show. All right, let's get started. Welcome in, Ian. Thank you for joining me today.
Thank you for having me. So Ceres is the largest object in the asteroid belt. It was originally classified as planet and it was classified as asteroid. Now it's a dwarf planet, but it's the only one so far to be visited by a spacecraft, which was NASA's Dawn mission. And thanks to Dawn, we've learned so many new things about Ceres, but there were some questions that kind of remained basically about the interior of this dwarf planet.
The data that we got and the condition of the craters suggests that there's a lot of ice underneath, but those craters also haven't relaxed or smoothed out if the crust were soft and warm. So this is where your work comes in. So I'm really excited to talk about this. Let's just kind of kick it off. What interested you in Ceres? What drew you to this mystery and the questions about its interior?
Yeah, so Ceres, you did a great rundown of a lot of things about Ceres, but the NASA Dawn mission that visited Ceres gave us a lot of lines of evidence that suggested that the crust is pretty ice rich, except for the craters that you mentioned.
The heavily cratered terrain does not indicate as much ice within the crust, because otherwise the craters would smooth out, relax, as you say, a good way a good analogy for that is if you had like a tub of yogurt and you took a ladle and scooped it out over time the yogurt would kind of smooth out to a an even surface an even flat surface ice would do the same thing on ceres uh but since the craters are not smoothing out to that surface um it was a little unknown about what the
actual composition of the crust would be So what led to all of this uncertainty about the amount of ice underneath Ceres surface? I was kind of surprised to find that we're including this in sort of the list of icy worlds. So how did we get there? Yeah, so there's a lot of data from the Dawn mission did suggest that Ceres has some ice in the crust. Features like landslides, domes, the way the craters form when an impactor hits, that all indicates ice within the crust.
And then gravity data, which can tell us about the density of the crust, that yielded a number very close to the density of ice. But the way that craters deform, as I said, like they're not acting like yogurt. They're not moving. They're not flowing as ice would kind of limited what we thought the amount of ice in the crust could be to about thirty or forty percent volumetrically.
So when you talk about moving, we're really kind of thinking of those sort of similar to, say, glaciers on Earth where they do have the exhibit movement. There is some flow there. It's not just stationary ice.
um so how what what became the missing piece of the puzzle you talk about in the paper impurities in the ice and what led you to that yeah um so ice by itself a pure ice would move very uh quickly over geologic time um like as you mentioned glaciers on earth flow uh on historical time so um We knew initially from the DAWN data, as soon as we got that back, that there's going to be some amount of impurities within the crust of Ceres.
It cannot be a hundred percent ice, otherwise it would move way too fast. And we're not seeing it move that way. So the impurities was something we knew about, but there was this new laboratory study that came out suggesting that just a little bit of impurities, about like six percent mixed into your ice, will drastically slow down the flow of the ice and make it much more rigid. Okay, that leads me into a term that probably a lot of our audience has not heard.
I've barely used it myself, and that's rheology. This is specifically talking about the rheology of ice. What is it and why does it matter for planetary science? Yeah, so the rheology of ice or any solid object kind of describes how it flows like a fluid over geologic time. So if it has a more rigid rheology, then the material will behave more like a solid that you would think of not moving, like rocks are very rigid and have a stiff rheology.
Ice is a much more kind of malleable solid over geologic time and can flow much more readily. So the rheology of ice, as we thought, it was very weak and it should not be able to retain these craters, they should shallow out. With this new laboratory study, it suggested that with just a little bit of impurities mixed into your ice, it will change the rheology to make it much more rock-like, more rigid, stiff, and not behave as glaciers on Earth that we see today.
I don't want to get too much into the details of this, but how do the impurities change the way ice deforms? Yeah, good question.
So, this laboratory study, which is Chi et al. , what they found was that if you add just like about six percent impurities into the ice then that like dusty impurity will if my hands are both grains of ice normally they'll slide against each other and it'll help move and make the rheology of the ice very weak but if there's some dust in between the grains of ice they can't slide against each other and that will slow down the movement of the ice and make the rheology much stiffer
Okay, that makes absolute sense. So did you test different compositions and temperature profiles in this laboratory work? Yes. So I didn't do the laboratory study. That was a different group. I just did the simulations and took the rheology that they found.
And I... mostly tested different compositions of Ceres crust because we wanted to test, you know, how icy could Ceres crust be with this new rigid ice rheology while still maintaining the cratered landscape that we see that, you know, it was initially thought a really icy crust couldn't maintain. So we tested a lot of different compositions, but we found that the composition that slows down the ice's movement and is best able to retain the craters is a crust that is gradational.
So it gets less icy as you go down with depth. Okay, that seems a little unexpected. So how surprising was that, that this ice is tapering off at depth?
yeah um so when we normally think about crusts of planets or just solids in general we tend to think of them as like a uniform composition the whole way through the depth um and across it that it's the same material um but it might be a little bit more complicated than that so uh It was not super surprising that we found this in our results because it was actually suggested by some of the gravity data from the Dawn mission that, as I said, gravity data helps you understand the density of
the crustal layer. That's something that you can use gravity data to understand more about. And what one of the papers from the Ascendant Dawn mission found is that the crust of Ceres, as you go deeper with depth, the density should increase is what they found. So if you have ice being replaced with impurities like clays, silicates, denser stuff than ice, then that actually matches up with that gravity data pretty well. Okay, that makes sense. So... What does it mean?
That's kind of from the headlines and everything. They sort of imply that series froze from the top down. So from the outside in. So what does that mean? How does that actually work? Yeah, so if the results in this paper are indicative of what Ceres crust actually looks like, then Ceres could have been very, early Ceres, four and a half billion years ago, could have looked very similar to potentially Europa or Enceladus with a really watery ocean.
And It would have frozen from the top down because the very surface of that ocean would have been exposed to the harsh, cold space around it. And so that would have led to it freezing on the outside first. And the interior of a planet is where most of the heat that it generates come from. So the core of Earth generates a lot of our heat, our geothermal heat. Same with on Ceres. So it was warmer at the interior, colder at the top.
So as this ice started cooling off and radiating heat into space more and more, the crust would have frozen from this ocean from the top slowly downward. So you mentioned Europa and Enceladus, two of our favorite targets here at the Study Institute because of their subsurface oceans. Does this mean that Ceres was once habitable? Could it have sustained life on this, you know, or at least supported liquid ocean?
Yeah, I think most people that study Ceres would agree that there was some form of ocean on Ceres at one point, though If most other people before these results, with the crustal composition of like thirty to forty percent ice, that ocean would have been really muddy and salty and possibly less habitable than an ocean that's more similar to Europa's or Enceladus', since it has a lot less of that salt and dirt in it.
so as as far as like the chemistry habitability I can't speak too much for that but um since I know europa and enceladus are high astrobiological um of high astrological intent of interest sorry um it's possible that series could have been more habitable Okay, I want to talk to you some more about the impurities, the salts, the clays, that kind of thing. But I'm going to welcome in people because we are getting some answers here. So let's see, I have someone watching from Tripoli.
Wow. Sweden, Texas, and England. So thank you so much for joining us today. Greatly appreciated, everybody. Again, we are talking about Ceres and basically some of the ancient formation of Ceres and why it looks the way it does now, courtesy of the Dawn mission and all of the data we collected there. So, okay, Ian, what role does this mean that these salts and clays played in the geological evolution of Ceres?
So, you know, you've talked a little bit about the content of them, but how did this work?
Yeah, so as Ceres formed in the early solar system, it was likely a bunch of different mixtures of little planetesimals and asteroids of rock and ice coming together, and as they come together to form the larger dwarf planet that is today Ceres, there would have been a lot of melting of the ice, and the rock and ice would have kind of been this chaotic mixture together and the little fine particles of dust or soluble salts or carbonates could have been suspended or dissolved in
the ocean that would have formed as all of these things are coming together. And as the ocean freezes top down, as the ice freezes, it can trap those salts that will come out of the ocean and Also, any of the dust particles that are trapped within the ice as it freezes, that can lead to the impurities between the ice grains and slowing down the flow of the ice after it's formed. And I just kind of want to sort of throw this out there.
When we talk about these craters and everything, are we talking... like heavy bombardment craters, or are we talking craters that are more recent? So the way that this process of the craters shallowing out, it takes a very long time because even, unless it was ice, which takes very little time like glaciers, but in pure ice or rocks, it takes a very long time for this process to actually occur.
So we were looking at... craters that are billions of years old, so potentially from a heavy bombardment era. The surface age of Ceres has been estimated to be like two to three billion years old, though that is with just crater counting and not with actual isotope dating methods. So that is all kind of an estimate. So very old craters, a very old surface. Ceres has been bombarded with impactors its whole life. OK, that makes sense.
In my head, I'm now comparing Ceres to the moon and the craters on the moon. And then I'm also comparing it to Enceladus in Europa and the more smooth areas on those. the solar system is way more complicated than, than I think people realize when you initially like learn about, it's like, okay, planets, here's our planets, here's how they work. And then every time I learn more, I realize, no, it's far more complicated.
Yes. So in the case of this, so if I, if I have this right, the basically you have all of this data collected by the, the Dawn mission, and then it has been analyzed and laboratory testing has been done to sort of to figure out what we were looking at. And now you're running simulations to match up some of these discrepancies. So how do your simulations match up with the data that was observed when it comes to the gravity data or the surface features? Yeah, good question.
So the surface features on Ceres, like the morphology of craters, how they look when they actually hit the surface, and landslides and domes, these kind of surface features, also like the spectrographical, like the composition of the regolith of Ceres or the dirt, the outer layer, that all kind of points to ice being within the subsurface, being within the crust.
And so having a pretty ice rich crust and what our results have shown is that Ceres could have like, ninety percent ice in the very near subsurface and as you go down deeper with depth, you lose that ice content. Our proposed crustal structure does make sense for those icy surface features because we allow a lot of ice in the near subsurface where the surface features are happening. And as far as the gravity data, we picked the gradational trend from really icy to less icy.
That slope that we chose down with depth, we chose it such that it would match the gravity data proposed by the Dawn team. So it matches the gravity data really well, and it allows for a lot of subsurface ice. There's a lot of focus on one small world that has gone through a lot of nomenclature. What can we do? How does this apply to other icy bodies in our solar system?
Not just say like Europa Enceladus where we're talking about known subsurface oceans, but how about like Ganymede or even Pluto? How does this all apply to those?
yeah so my simulations here might be a little bit more specific to ceres um and that's because a lot of the other moons that you listed off pluto ganymede europa and celadus those all have ice shells that are like we we're pretty sure are like a hundred percent ice um and as I said that if it's a hundred percent ice if it is pure ice it is going to deform very differently to ice-like series, where if you just have a little bit of that impurity mixed in, then it changes how the
crust will move and flow as the fluid over geologic time. Maybe it could be applied to a body like Callisto, which is another moon of Jupiter. Some people think that it's not fully, it hasn't fully separated all of the ice and the rock. So it's possible that this new rheology that the laboratory study, Geodolip, found could be applied to Callisto. But it's for the other like really ice rich, exciting moons, it might not be as applicable. Interesting. Okay. I just want to pause for one second.
A couple more people joining in from Colombia. Buenos tardes. Buenas tardes. And hello, Ron in Louisiana on the Bayou. Thank you. Ron is one of our regular viewers. Thank you so much for joining us as always. And also a shout out to Thomas Hill on Facebook for the stars. So thank you so much. That's always appreciated. All right. So The solar system is more complex than we originally thought and seems to get more complex every day.
What does this study tell us about the potential diversity of these ocean worlds, these icy planets that are in our solar system, and maybe even the possibility of discovering that more of our moons or asteroids are like this?
Yeah, I think it could help to open up the door for more ocean worlds, because some of the ocean worlds that we really think about, like Europa and Ganymede and Enceladus, they are heated by their primary, by Saturn or by Jupiter, whereas Ceres is all alone in the asteroid belt. It has no primary.
It's orbiting around other than the sun so it doesn't really get that heating that Enceladus and Europa gets but if the results in this paper are indicative of what Ceres is actually like then it's possible that a lot of these very small icy bodies that don't get any heating from their planets or don't have a planet to help heat them they could also have been once ocean worlds that have since frozen out and could be relic ocean worlds Oh, I like this term, relic ocean worlds.
Okay, so as far as Dawn goes, is there anything in this Dawn mission data that we haven't fully mined yet for answers? It feels like we've mined a lot of it for answers. Yeah, well, there's always more that people can do with surface data and spectrographic data. Plenty of stuff. Something that I'm a little bit more interested in is looking at the gravity data again, because the way the gravity data works, you have to assume that you have a layer of uniform composition.
and I'd like to know what happens when we look at the gravity data assuming this gradational crust that was proposed in this paper. How would that change things? That might be something that someone could look at that I'd be very interested in. Interesting. So I think that kind of brings us to sort of the talking about you a little bit more here. So what What got you into studying Ceres? How did you end up finding this as being where you wanted to be at?
Again, the solar system is very complicated. Planetary science has a lot of different areas to offer. How did you end up with Ceres? Well, I think Ceres is very interesting from a planetary science perspective because it is the nearest icy body. And it's an icy body because some people think it doesn't have that much ice. It could have some more ice, but it's the closest and most accessible icy body to Earth.
uh and that's because you don't have to worry about jupiter or saturn um or getting not only getting out to that distance but also um the radiation dealing with jupiter is a big thing um dealing with uh going to europa um from a personal standpoint I was interested in series because I just like looking at how fluid flows um so when I discovered that Ceres has a crust that, you know, at first we thought if it is a really ice rich crust, it should flow really readily.
And then when the Dawn team, the Dawn mission got there, the team realized that it's not flowing like ice. So like what actually is the composition of this material? Because it doesn't flow like we expected it to. So I think the fluid flow thing aspect of this work really was interesting for me. That's a really different way. I don't know. It certainly wouldn't have been a way that I got into it, but that is really neat that you did, and I like that.
For the future, what has this study sort of opened up for you question-wise? What direction do you want to go in now?
um yeah so I think looking at as I said the gravity data under the assumption of a gradational crust instead of a uniform crust I think that would be a really interesting thing to look at um but uh looking at other icy bodies I might get I might be more interested uh turning out towards the outer solar system where those icy bodies that we mentioned before, like Europa, Ganymede, Enceladus, Pluto, that have like the pure ice crusts, the pure ice shells that are more, they can flow more readily
and can behave a little bit more fluid-like. I'll be interested in doing, looking at objects like those as well. And I'm definitely looking forward to seeing what you find next. All of these solar system discoveries are always so interesting to me. For some of the students that might be watching, what skills and experiences helped you work on a study like this? How did you get to this point? So I got my undergrad degree in both geology and mathematics.
So the math really helped creating the simulations because the simulations that I made, it's basically a lot of matrix math. So understanding linear algebra and differential equations was very helpful. Luckily, I didn't have to do much of that by hand. The computer did most of that for me. But, you know, understanding how it works, very important. And then I really enjoyed tying in my geology experience and knowledge to the results.
And after the simulations gave us some results, figuring out what the implications of those are was really helpful with the geology degree. I appreciate that. I did it. I did a little differently. I got physics with a math and astronomy minors. That was my undergrad. And then my grad work was in geology. So I flipped and did them the other direction. But I do remember my geology advisor looking at me after my first semester.
And he's like, this is normally when I would tell you to go take some more math classes. But there's really nothing left for you to take. Yeah. And I love linear algebra. I'm probably weird that way, but I just love the graphical layout of it and just the... the puzzle solving to it. I think for me, it feels kind of like a logic puzzle. You know, you're trying to figure out how things fit together. So I really like that. And I'm fascinated.
I'm now going to dig even more into your paper and start looking at some of what you've done. I do kind of wonder, did you specifically take any coding classes or was this sort of stuff that you've learned on the fly? So I did take a class that was specific to the method that I used in the simulation. It's called the finite element method.
So I did take a class on that at Purdue University, though I was already well into doing this project and onto starting my second one, which is also looking at finite element stuff on a series. But yeah. The software that I use has a lot of different documentation that I was able to read and understand. So there was a good amount of learning on my own, but I had plenty of online resources that helped tremendously in addition to the class that I took at Purdue. Fantastic.
As always, read the documentation, everybody. It's there for a reason, and it's very useful. So we do have some audience questions. I do want to welcome some people who are watching, again, from Texas and from Cleveland. So thank you for joining us. It looks like there's some basic questions about Ceres that I think people would like to understand. So do we know if Ceres is extrasolar or not? Is this something that formed here in our solar system or did it come from someplace else?
Yeah, so one of the, theories of how Ceres got to the asteroid belt while being this icy body. Because normally things within the asteroid belt, Mars, Earth, Venus, Mercury, are not really icy. One of the theories is that it has migrated from the Kuiper belt and come in from further out beyond the orbit of Neptune into where it is now. How that happens is with orbital dynamics stuff that I'm not as familiar with. I just know that it has been theorized that it's migrated in.
So there's a possibility that it's a relocated Kuiper Belt object? Yes. It is still within the solar system, to answer the question directly. But yeah, it might have come in from way, way out in the solar system. That's one of those things that I think was sort of surprising in the last few, well, the last decade and a half or so that, you know, our solar system has not always been the way that it is now. That has really kind of come about. So I, that's an interesting thing.
I don't think, I was not aware of that. So thank you. Thank you, Thomas, for asking the question. Thank you. The next question, what is the atmosphere of Ceres like? Does it have an atmosphere? Does it have an exosphere? What's the situation? No, it's considered an airless body, so it doesn't really have an atmosphere. Individual particles can bounce around like in an exosphere, but generally it's pretty small, so it can't retain an atmosphere super easily.
Yeah. On a scale, just because I can never remember, where is Ceres on the side scale? Is it bigger or smaller than Pluto? No. I believe it's smaller than Pluto. It is in diameter. It's nine hundred and forty kilometers or miles. That's five hundred and eighty four miles. So if you drew a circle around Texas, Ceres could fit in that circle. Oh, wow. OK. That is pretty small. All right. Huh. I think even my mind kind of stuttered a little there. All right.
Thomas Hill, thank you again for the stars for a second round of them. Very appreciated. One last audience question here. And I think this is kind of a good question to sort of get into our wrap up. Are there any icy bodies in our solar system you think are underrated that you would like to see studied more? Yes. Um, go with, I'm going to go with like all of the bones of Neptune and Uranus right there. That's where I'm going to go, but you go ahead. Yes, I agree with you there.
I think the moons of Uranus are definitely underrated and hopefully we get a flagship mission that will go to the Uranian system. But personally, I think that Callisto does not get as much attention as its Galilean siblings. And that's because it doesn't get any heating from Jupiter like the other Galilean moons do. But it's really big. It's as big as Titan. It's as big as Ganymede. It's bigger than Mercury. So I think it should get more attention. But it's a little hard to get out there.
So we don't have an awesome amount of data. That's really interesting. I didn't even think about that. But yeah, I mean, we talk about Europa. We talk about Io. I am an Io stan. This is my necklace today. I am absolutely about Io. I love that little world. volcanoes. I love volcanoes on earth. I love volcanoes in the solar system. So, uh, and Ganymede, of course, you know, big, big moon has its own, uh, magnetic field, which is the only thing that's not a planet that, that has that.
So it's, you know, there's lots of things, but you're right. Callisto gets no love in all of that. And I think Callisto is considered, you know, another one of those possible like subsurface ocean icy worlds. So yeah. Yeah. Wow. Okay. Well, there we go. We need a mission to Uranus to go do what Cassini did and what Galileo did. Let's do these things. And we also need something to go really focus on Callisto. Yeah. I am for this. All right. Final.
I was going to say, hopefully, JUICE, the ESA mission, and Europa Clipper both are going to do some flybys of Callisto. So we'll still get some new data in the coming decade. That's true. And I, I mean, we did get a little, uh, from Juno. So, um, but I don't think, I don't think there was, it didn't line up as, uh, uh, quite as well as it did for other worlds. So, um, so final question for you, if you had, you know, you're in an elevator, you're going to your room.
If you have seconds to explain your findings to someone who has never heard of series, what would you say? I would say that I do computer simulations of the topography of this world, this dwarf planet series, to try to tell what the composition of it is, because if the composition is really icy, then it's going to move really fast. And we can tell that from things like craters. Or if it's not that icy, then it shouldn't move as fast.
But I'm investigating new rheologies that describe how ice could move in certain circumstances. And hopefully, we find that Ceres could be very, this world could be very ice rich in its crust. Perfect. Thank you so much, Ian, for joining us today. That answer was great. And now you have your elevator pitch. So everybody, thank you for watching. If you enjoyed this conversation, please make sure you like it. Share it with your fellow space nerds.
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