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Season 4, Episode 23: The Bright Spot of the Asteroid Belt

Season 4Episode 23Dec 18, 2020

Between the orbits of Mars and Jupiter is a mysterious dwarf planet called Ceres. Its surface is dark and muddy, but has hundreds of patches of bright material.

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Between the orbits of Mars and Jupiter is a mysterious dwarf planet called Ceres. Its surface is dark and muddy, but has hundreds of patches of bright material. The salt-covered dome and other bright features in Occator Crater are so reflective that they looked like flashlights in distant images. NASA’s Dawn spacecraft got a close look, and pointed scientists to the idea that liquid brine has come up from the interior of Ceres, forming the Occator dome and other bright features. Ceres’ crust also contains a significant amount of ice. Astrobiologist Britney Schmidt discusses the implications, as well as her fieldwork in Antarctica.

Jim Green:In the asteroid belt is a huge dwarf planet. It’s called Ceres. Does it have an ocean underneath its icy crust?

Jim Green: Hi, I’m Jim Green, chief scientist at NASA, and this is Gravity Assist. On this season of Gravity Assist we’re looking for life beyond Earth.

Jim Green:I’m here with Dr. Britney Schmidt, who is an astrobiologist and an associate professor in the Earth and Atmospheric Sciences department at Georgia Institute of Technology in Atlanta. Britney, welcome to Gravity Assist.

Britney Schmidt: Thanks very much. Excited to be here.

Jim Green:You know, I think your favorite objects are cold, or you know, very cold.

Jim Green:Why are you so interested in ice? What about it really gets you going?

Britney Schmidt: Well, for me, I got really interested in ice because I was thinking about water. Right? One of the first things you learn about life on our planet is that life needs water to exist. And if you look across the solar system, the most common form of water is ice. And most of the water in the solar system is hidden by that ice. And so, I got interested in ice and everything it tells us from its chemistry, to how it forms, to its crystalline structure, to the geology, to the processes that it creates. And so now even to how it interacts with the ocean has been a big focus. So it’s, it’s the most common need for life to have that water. And so, ice in the solar system is, is one of the questions that we have to, have to answer.

Jim Green:You know, Ceres, is one of those coolest planetary bodies that many people might not have heard about. It’s, you know, it’s the largest body in the asteroid belt. It’s rounded by its own gravity.

Jim Green:So, where is Ceres in our solar system? And how big is it?

Britney Schmidt: So Ceres is in the main asteroid belt, just about smack dab in the middle of it, it is at kind of halfway between the orbits of Mars and Jupiter. And the kind of neat thing about it is actually how big it is, you know, when you think of asteroids, you might think of something small, maybe something the size of your house, but actually Ceres is about the size of the state of Texas. So it’s absolutely gigantic.

Jim Green:So, what makes it so special?

Britney Schmidt: It’s the innermost icy world, and a miniature version of maybe what some of the other planets looked like early on. It’s one of the only planets that’s really made of this kind of frozen ground on the, on the outside. So I kind of like to call it a permafrost planet, if you will. So if you think about the Arctic on the Earth, where the ground is frozen, year round, it’s the same thing on Ceres. It’s kind of this frozen mud up on top. So that’s kind of special. And it’s really a weird object in that way. It has something in common with Mars has something in common with the Earth and with places like Europa and Enceladus in the outer solar syste. But we call it a dwarf planet, it basically means that it is round, as you say, and so it has self-gravity, it’s done some really interesting things that planets do. So when you picture an asteroid being like kind of a twisted hunk of metal or rock, then you’re really missing the picture with Ceres, which is a big sphere, made of this kind of ice-rich, rocky material.

Jim Green:Well, you know, NASA’s Dawn spacecraft first visited Vesta, also a very large asteroid that that is smaller than Ceres, and then left Vesta and went out to Ceres. It spent more than three years orbiting that dwarf planet and took spectacular images and other measurements. Tell us a little bit about what we learned from Dawn.

Britney Schmidt:Dawn was a fantastic mission. It was the first planetary spacecraft to go into orbit around one body, leave it, and go to the next. So that was pretty exciting. And Vesta, that mission was spectacular. But with Ceres we really saw something special. And as you’re zooming in on a planet getting closer and closer, those first images where it becomes more than a point of light, it starts to become a real place, I remember those first images because we could start to see every rotation, this kind of brightness that would kind of show up, and then as we zoomed and we got closer and closer, you could see it looked like a flashlight and some of the images coming from this crater. And as we got closer, we could see that what it was is that though Ceres is very, very dark, there’s also these really bright deposits in this crater called Occator Crater. And those bright deposits were reflecting a huge amount of light back at us.

Britney Schmidt: And when we got up close, what we could see is that these are definitely salts. And so salts are created in the interaction between water and rock. It happens on the Earth, it happens on other planets. And so what we think is that that is briny material, material from deeper inside Ceres that has come up.

Jim Green:Well, as you say, liquid water, in fact, must have some aspect to do with these, these briny salty deposits. So, do we think that Ceres has an ocean inside it or liquid water at some layer?

Britney Schmidt:It looks like there probably is. The gravity data is consistent with that. It’s very, very round, which is really hard for, for solid materials to do that very well. So, liquids, but ice is another good way to make something kind of round. It can relax over time. So there is some evidence to suggest that deep down there might be some liquid layers. There’s certainly evidence to suggest there might be brine pockets or former brine pockets, so a little bit of heat from an impact or something could really warm those up. So, it’s one of those questions that we, we think there’s really good evidence for it. But it’s not clear whether that’s constantly liquid now or was recently liquid in the past.

Jim Green: Here on Earth, everywhere we go, where there’s liquid water, we find life. And so, if Ceres even has liquid water, is there a possibility that life may exist there?

Britney Schmidt:So, Ceres is a little bit different than a place like, you know, like, like the Earth, or places like Europa, or maybe even Enceladus, where we think there’s an ongoing source of energy. So, on Earth, it’s leftover heat from when the planet formed. And so things like hydrothermal vents and plate tectonics mean that you keep cycles of chemical energy alive, that that allows life to persist. And so that’s really important on our planet. One of the reasons that we’re interested in like the ocean worlds in the outer solar system, is that this could be going on on those. Europa is a great example, a moon of Jupiter that we think could have seafloor activity, it could have… it’s got a really young ice shell, so it’s reworking itself all the time. So that tells us that there’s energy right now.

Britney Schmidt: With Ceres, it’s not really the same deal. It has many of the same ingredients, and maybe 4 billion years ago was really cooking, literally cooking the rock in the water together and making energy and maybe making prebiotic materials. We just don’t think it probably went all the way.

Britney Schmidt: And one of the neat things about it is that even if life never got started on Ceres, one of the hardest things to do on the Earth is to understand what the geochemistry was like before life got here. Life is really messy. It kind of messes everything up. It gets its fingers literally in everything. And so it makes it hard to understand what the geochemistry looked like when water and rock were kind of the only games going on this planet.

Britney Schmidt: So, studying places like Ceres, even if they don’t have bugs crawling around right now means that it’s a really neat opportunity to understand planets as they form or as they existed just before life took hold.

Jim Green:Well, it’s so different, as you say, from all the other asteroids. Where do you think it was created? And how did it get where it is today?

Britney Schmidt:It’s actually one of the biggest questions that we have. There are things about it that make Ceres seem like maybe it came from the outer solar system, but we know that there’s ice and water and a bunch of it in the inner solar system too.

Britney Schmidt: So it’s actually, Ceres is cold enough to hang on to the ice for a really long time, but warm enough that it’s not actually stable, really on the surface. So the surface of Ceres is kind of this muddy rock ice mixture. And that’s special because it means it has a geology style that is really different from a lot of other planets. It means that ice is kind of stable towards, towards the poles, but not, not right at the surface at the equator. And so that kind of governs what we see on the surface. And so this kind of interplay of how hot the surface gets and where they’re, you know, cold traps or colder areas, has played a lot, or it has really played out on the surface of Ceres. And that’s why we see what we see today.

Jim Green:Yeah, indeed, in fact, the high-resolution imaging that Dawn did in many areas, but the Occator region in particular, really allows us to think about the future of going back to Ceres, not orbiting again, but getting down to the surface. So what are some of the ideas about future missions going to Ceres?

Britney Schmidt: There is a study that’s being looked at in the Decadal Survey, there’s been a few mission concepts floated even proposed. And in fact, people have even suggested maybe we could return a sample from Ceres, to do some of this work in the lab.

Jim Green:Well, you know, you’ve done some really fascinating fieldwork here on Earth to look for formations that resemble structures on Ceres as well as Jupiter’s moon Europa, what have you found out from what we call these Earth analogs?

Britney Schmidt: Yeah, so one of my research group’s favorite things to do is to go to the places on Earth that allow us to study those processes that are happening here that are the same on other planets. So, you don’t have the exact match. You know, nothing here is the surface of Ceres or the surface of Europa, but there are places that remind us of that, and that teach us about the same kind of physics and, and geology that we need to understand and this idea about subsurface water and subsurface ice. As I mentioned, permafrost is one of the really key ideas here is that we have environments on the Earth where water and ice interact in really special ways and have cool geologic processes.

Britney Schmidt: And I’ll mention two of them. One is ice-rich landslides. Across the solar system, they look really different. And they are formed a little bit differently. They just have different properties than other landslides. And we see them across the surface of Ceres. But we also see them on Earth, and Mars and even on Pluto’s moon Charon. So we’ve seen similar ice rich landslides across the, across the solar system. So we could go study places, even in Colorado, to look for examples of Ceres.

Britney Schmidt: But my favorite one are called pingos. And pingo is just a great word in general, but it basically means it’s an ice cored mountain. And the way it is happen is just like we think maybe you know a giant impact into Ceres heats up the surface and creates pools of water in the subsurface. The surface is very cold, the water is down below. And as that refreezes, it actually exerts pressure and it causes the water to move around.

Britney Schmidt: As that refreezes, it can actually refreeze onto each other. So the water wants to freeze onto ice, wants to freeze onto more ice wants to freeze onto more ice. And what you do is you’re actually slowly grow these mountains. And on Earth, the tallest mountains are around, you know, 50 meters or so tall, so pretty tall, and they’re filled entirely with ice. So, you’d be in the Arctic hiking along you’d see these little domes they look a little bit like a kind of like a fatter, rounder, volcanic dome. And it’s rocks on top, maybe you’d see you know grass and stuff. Obviously we don’t see grass growing on Ceres. But if you were to walk up to that and dig a hole, then you’d find out that the entire mountain below that permafrost layer is made entirely of ice. And so our group has been doing some work now. We’re about to go actually out on our first pingo field season hopefully in the spring, COVID-19 allowing. So ice mountains, hiking around with a bunch of geophysical equipment, cannot wait.

Jim Green:It sounds fantastic. But you’ve also been working on a robot that explores icy waters. And I think you call it Icefin. Can you tell us a little bit about that?

Britney Schmidt:Yeah, so this whole idea of how ice and water work in cryospheres, right, the frozen parts of planets, it’s a process that we don’t understand even all that well on our own planet. I guess the that my favorite thing to tell people is you know, if you look at Mars and most of the pictures of Mars, they remind me at least of like Tucson, where I grew up, you know, rocks and stuff. And you can imagine what your mission would look like if you went to Mars if you’ve lived in Tucson, or you’ve lived in many places in the US to be honest. But if you think about what a mission to Europa would look like, especially the parts that we want to get to the ocean down below, there’s really no option but to go down and get underneath the ice.

Britney Schmidt:And so we’ve been doing work with Icefin, which is an underwater robot that we built using NASA’s funds, but is now working for NASA and NSF to try to understand ice shelves on the Earth, which are these big, thick sheets of ice that are floating out over, over the ocean. And so we actually drill holes in the ice, and put this robot down underneath. And it’s teaching us not only how our own climate works, but also how we might one day explore places like Europa where we’re going to need autonomous navigation and, and different types of science sensors. And we’re going to need to understand what those exchange between the ice and the ocean, all that really works, like how that happens. And so we’ve been using Icefin to do that. So it’s kind of like practicing for Europa, but it’s also doing really important fundamental climate science here on the Earth.

Jim Green:Well, for you to be able to do that. I’m sure you’ve had to go down to Antarctica on a number of occasions. So can you tell us what one of your more interesting or favorite experiences in the Antarctic is all about?

Britney Schmidt:Yeah, so this last season was so in 2019, was my seventh trip to Antarctica. And it really was lucky. It was a fantastic experience. So, we actually made a second copy of Icefin, and we continued our NASA work and then part of our NSF work, we went out to this really special place called Thwaites Glacier.

Britney Schmidt: And what we did there was to work with our British Antarctic Survey colleagues and some other folks from the US to put a hole through 600 meters of ice and put Icefin down. And we swam almost 2 kilometers back to the point where the ice and the sea floor actually touch. And it’s a really important place. It’s where all the melting of these fast-changing glaciers starts. And it’s something we’d never seen until January of 2020. So it was the most amazing experience to be someplace that maybe 10 people have been before them to see something that no one had ever seen before, to be piloting our pseudo-Europa robot back to the grounding zone of this glacier. It was just, just amazing experience. Living out on the ice, we were out there for five weeks, living out of tents and, you know, winds and storms and then warm days and beautiful days, all intermixed, just an amazing experience.

Britney Schmidt:So it’s, I don’t know, it’s like the little piece of feeling like you’re a part of the whole system, and still trying to figure it out that is really just so special. And for me, it’s because, you know, we built the robot ourselves. And it was working with students and postdocs, and like our staff very, very closely, all a really young team to do that. And so it just feels like this amazing, you know, experience to really be actively living your science and to live in this very crazy distant place, that’s a part of our own planet, a little bit of planetary exploration in your backyard.

Jim Green:Well, Britney, you know, I always like to ask my guests to tell me, what was the event or person place or thing that got them so excited about being the scientist they have become today. And I call that event a gravity assist. So, Britney, what was your gravity assist?

Britney Schmidt:Yeah, so my gravity assist was actually when I was an undergrad. So, you know, I always pretty much liked everything. I just liked being in school. And like many people, when you’re first heading into college, it’s kind of a rough time. And, I felt kind of lost. To be honest, I was doing fine in my classes, but I really didn’t think I’d found what I wanted to do. And I happened to take a really amazing class from, from Robert — or Bob as I know him — Brown at the University of Arizona. And it was a big, general education class. And I teach a class like that now partially why I do it was that this class really meant something to me and having this professor who was he had a spectrometer that was on the Cassini spacecraft that was flying in the middle of space. And yet he was spending his, you know, his office hours, with me answering all the questions that I had about how planets worked and finding me books.

Britney Schmidt:And eventually, you know, he sat me down and said, ‘Britney, you ask more questions than any grad student I know. I think this is what you should be thinking about.’ So we sat down with the class course catalog, and he helped me pick out with the classes I was going to take the next semester to try it out. He was like, you’ve tried everything else out theater and English and everything else. Why don’t you try this? And so I took a math class, I took an astronomy class and I worked in Bob’s ice lab. And so Bob taught me that ice was fascinating. When he first proposed that I work with him freezing ice, I asked him if he instead had any paint drying available. And instead it’s become like what I do for my living, right? He, he did that. And he took a chance on me. And he spent time with me at a time that I really needed it. And it turned out to be what I love to do, and I’m good at. And I think that’s a really important kind of an assist.

Jim Green:Britney, thanks so much for joining me and discussing these fantastic topics.

Britney Schmidt:Thanks very much for having me. It was my pleasure.

Jim Green:Well, join me next time as we continue our journey to look for life beyond Earth. I’m Jim Green, and this is your Gravity Assist.


Lead producer: Elizabeth Landau

Audio engineer: Manny Cooper