#66 Saturn’s largest moon Titan is an incredible place, but could anything live there? Canadian Astrobiologist Dr Catherine Neish led a study on Titan’s habitability. She joins us for a fascinating chat about what she found.

Titan. The largest moon in the Saturnian system has been a candidate as a habitable world ever since NASA’s Cassini mission sent back the first radar images of its surface in 2004. Astrobiologist Dr. Catherine Neish of Western University in Canada has spent years studying Titan, and has just published a study on the habitability of Titan. Catherine joins us to step through the findings, what is needed for life? Is there enough of it on Titan? And does it all come together?

Read Ralph Lorez's paper Titan Under a Red Giant Sun: Anew Kind of Habitable Moon

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Transcript

Andrew Prestage: 0:10

This is Cosmic Coffee Time, the place where we take a look at what's happening somewhere in the universe in about the time it takes to have a coffee. It's cosmology in a cup. I'm Andrew Prestage and I'm a space fan, so join me for a coffee and see where in the universe we're going this time. I was reading the space news a little while back and saw that a new study had been published on the habitability of Saturn's largest moon, titan, and it immediately caught my attention. The study was led by Dr Catherine Neish, associate Professor and Astrobiologist at the University of Western Ontario in Canada.

Andrew Prestage: 0:51

Catherine has spent years studying Titan and very generously agreed to have a chat with me and tell me all about the amazing work that she and her team did and that, even with a whole lot of water and a whole lot of carbon, titan can still give you some really surprising outcomes. Catherine Neish, welcome to Cosmic Coffee Time. Tell us a little of the Catherine Neish story. Where did you grow up and what was your pathway to becoming an astrobiologist? It's such an interesting field.

Dr. Catherine Neish: 1:26

Yeah, thanks, Andrew, glad to be here. So I'm a Canadian so happy to be here with my fellow member of the Commonwealth. I grew up all over Canada, from the East Coast over to the West Coast and everything in between, so I'm a bit of a rambler, I guess you could say. I've lived all over the place. And yeah, I was just fascinated with space as a child. I loved all the sci-fi shows. I watched Star Trek as a kid and that really inspired me. I read all the sci-fi books by Arthur C Clarke and I just found it fascinating.

Dr. Catherine Neish: 2:10

So when I was high school I really started to look more into pursuing astronomy as a career. And in particular when I was in grade 10, I did a science fair project of all things, to design a space station and entered it into a NASA contest and got a prize. And so I was able to go out to NASA Ames in the summer of 1997, which, for the space historians out there might remember, that's when Pathfinder landed on Mars. So everyone was very excited about that and so I was really caught by this space bug. And then I entered another contest in my senior year of high school through the Canadian Space Agency and ended up going to Houston for the summer. I stayed with an astronaut, Chris Hadfield, and his family for a month and got to meet all sorts of astronauts and explore Johnson Space Center. We saw Columbia land in mission control. It was an absolutely stunning experience. I still can't believe it happened. And so, of course, I was hooked.

Dr. Catherine Neish: 3:06

And so I went to university, you know, the next year, and focused on astronomy and got lots of opportunities to try out research in different areas. And I don't know. I was just always fascinated by this idea of is there life out there in the universe and can we detect it? And so, as I was doing my astronomy degree, I realized the stars are really far away and we would never know any detailed information about them.

Dr. Catherine Neish: 3:37

I'm still somewhat skeptical that we can actually detect life on exoplanets, and exoplanets at the time, back in the early 2000s, was a very, very new field. So I decided to switch gears and focus on the planets in our own solar system, which I knew we were already visiting with rovers and landers, and I thought that would be the best place to look for life. So when I entered grad school, that was my focus. I did a degree in planetary science at the University of Arizona, and I was fortunate to arrive at Arizona at the same time that Cassini mission arrived at Saturn in July of 2004. And so we were just immediately inundated with data coming back from Titan and Saturn and its moons, and I just fell in love with Titan and decided to study that. And here I am, 20 years later, still studying Titan.

Andrew Prestage: 4:29

And what is it about astrobiology that we find so fascinating? We're so interested in the possibility of life beyond Earth. We have SETI, the search for extraterrestrial intelligence. We want to know, like, as you said, exoplanets. We want to know if they're in the Goldilocks zone and, you know, if they could be suitable for life. And those planetary missions the Mars missions and other planetary missions they all seem to have an aspect of search for ancient life or some sort of habitability element to them. Is this something that's innate to the human condition? To know that we're not alone?

Dr. Catherine Neish: 5:05

Yeah, maybe, maybe that's it. Maybe we're lonely by nature and we want to feel like we're not so alone, because, when you really think about it, space is enormous. Right, it can be kind of scary to think about how big space is and how lonely we are here on earth without any neighbors, but part of it is also. I think we only have one example of life. All life on earth is related to one another. We all share the same structure, and so everything we know about life comes from this one data point. But if this was any other field, you'd never be able to publish anything with one data point, right? You need multiple data points to really understand how something works, and so for me, that's a real reason I study astrobiology. I'd love to find other life forms that had different origins, different evolutionary paths to really understand how life works, because, like I said, we only have one example to base our knowledge on so far.

Andrew Prestage: 6:03

You recently had a study published in the journal Astrobiology. You led a study into the habitability of Saturn's largest moon, Titan. What are some of the characteristics of Titan? What makes it a candidate for habitability?

Dr. Catherine Neish: 6:18

So, as I mentioned with Cassini, I got really drawn in by Titan. It wasn't a moon I knew much about Honestly, it wasn't a moon anyone knew much about at the time. Cassini really opened her eyes to what Titan was, but it really I think could be argued to be the most potentially habitable world in the solar system. And that's because for life to exist, you need three main things you need a solvent like water, you need some essential elements, primarily carbon, we think is really key to life, and then an energy source. And a lot of places in the solar system have, you know, one or two of these things, but not all three.

Dr. Catherine Neish: 6:59

And I think Titan is really unusual in that it has a large amount of all three of these elements. It's a body made of ice with a subsurface ocean of liquid water. It's got an atmosphere filled with carbon and nitrogen which rain down onto the surface in the form of aerosols, and then it's got energy. It's a large moon. There's radioactive heating inside, there's sunlight coming in, affecting the atmosphere, and a lot of other moons can't say that. It's the only moon with a substantial atmosphere, a carbon-rich atmosphere, which is incredibly unusual.

Andrew Prestage: 7:33

And it's fascinating. I mean, you mentioned the ice shell and that subsurface ocean. It's fascinating to me that we can know, or at least make an accurate calculation of the depth of that ice shell and ocean. How can we know this?

Dr. Catherine Neish: 7:48

And I don't think we know it too well. We have some estimates from Cassini. We can look at the wobble of Titan in its orbit. But basically, yeah, we can kind of look at the geophysical parameters that were measured by Cassini to get an idea of what its interior structure is like, and so we don't have a great idea of how thick the shell is, but we think it's somewhere on the order of 100 kilometers, so it's a pretty thick shell. Definitely, I think more data would be helpful there. If we were to send another mission to the Sternian system, we could get more constraints on the thickness of the ice shell. But we think it's relatively thick.

Andrew Prestage: 8:30

Are there other moons in the outer solar system that also have oceans, and how do they compare with Titan?

Dr. Catherine Neish: 8:36

Right, yeah, so Titan is one of many what we call ocean worlds, and so we started to discover these as we sent more missions to the outer solar system, with Galileo to the Jupiter system and Cassini to the Saturn system. One of the most famous ones you've probably heard of is Europa, which is one of the large moons of Jupiter. Europa is neat because it has a very thin ice shell. Again, we don't know exactly how thin. There's huge debates on the thickness of the ice shell in the scientific community, but this is something a new mission called Europa Clipper will help us answer just how thick that ice shell is. Almost certainly, though, it's thinner than Titan's. And then there's Ganymede, which is Europa's neighbor, which is the largest moon in the solar system. It also very likely has a subsurface ocean, probably about the same distance down as Titan. They're about the same size.

Andrew Prestage: 9:29

And your study of Titan was all about habitability. What was the primary measure of your investigation?

Dr. Catherine Neish: 9:36

So, again, what do you need for habitability? You need water Okay, we've got that in the ocean. We need energy Okay, it's warm enough, probably, for chemical reactions to happen down there. The one missing piece was carbon. Right, how do we get the carbon into the ocean? And there's kind of like two pathways you can think of. You can either have it come up from the interior, so Titan has this sort of hydrated silicate interior, and so maybe some carbon left over from the solar system formation is still in that interior and it could come up into the ocean. But I was looking at it from the other direction. How much carbon could we get coming down from the surface into the ocean? And Titan is covered in organic molecules.

Dr. Catherine Neish: 10:18

We focus on two main compounds haze particles that are formed in Titan's atmosphere, and I can't give you a more precise chemical formula than that. Think of it as any way you can piece carbon, hydrogen and nitrogen together. It's probably in this haze particle, hydrogen and nitrogen together. It's probably in this haze particle. When we make them in the lab, we call them tholins. This was a term that was originally dubbed by Carl Sagan from the Greek word for muddy, because they look like kind of mud when you make them in the lab.

Dr. Catherine Neish: 10:44

And then the other molecule we looked at is hydrogen cyanide, which again is a poisonous compound right, not something you'd want to encounter in your everyday life on earth but there's been lots of experiments that show that if you mix it with water, it can create a lot of the molecules that we think are important to the origin of life, like amino acids, which make up proteins. And so when you mix these two compounds with water either HCN or haze particles you can form, like I said, biological molecules like amino acids. So then we thought okay, well, how much glycine could you produce in these reactions? And glycine is the simplest amino acid, and experiments have shown that you can get reasonable amounts of glycine when you mix these compounds with water. So that's what we focused on in this study.

Andrew Prestage: 11:34

And there was a part of your study that fascinated me, and I'm not sure I understood this correctly, but you calculated that there would be a 25 meter depth of organic material on average over the entire surface of Titan.

Dr. Catherine Neish: 11:57

Is that more than Earth has In terms of organic material? It depends how you define soil. If you consider soil to be an organic compound, then possibly that's a great question. I've never thought of that before, but certainly in terms of just raw organic compounds, it's just raining out of the sky on Titan, which is not true on Earth, thankfully. I mean, we don't want cyanide raining from the sky necessarily.

Andrew Prestage: 12:20

With all of that organic material on the surface, how does it get to the sub-ice shell ocean? If we're talking about 100 kilometers or more of solid ice standing in the way, that's not a small obstacle. I've seen a couple of episodes of Ice Road Truckers a Canadian TV show and the ice on those frozen lakes a few meters thick. That can support 40 ton trucks driving across those frozen lakes in the Canadian winter. That's how strong ice is. So how does this organic material overcome 100 kilometre thick ice and how much of that organic material could possibly be transferred to the ocean?

Dr. Catherine Neish: 13:00

Right. So we looked in particular, at impact craters for this transport mechanism. So impact craters are formed when a comet hits the surface of Titan, explodes, forms a big hole in the ground and also melts the surface. Now, on Titan, the surface is made of ice, so when you melt the surface, you get water and, as everyone knows, water is denser than ice. Right, you put ice cubes in your glass of water. They're going to float, and so we were working from the principle that this water that forms in the bottom of these impact craters could then possibly sink through the ice crust, maybe all the way to the ocean interface. There's been some modeling work that suggests this is difficult but possible to do on icy worlds like Europa and Titan.

Andrew Prestage: 13:48

You referenced some studies on the change in frequency of impacts over the life of the solar system. Does that rate matter? Does habitability require a degree of replenishment of that organic material?

Dr. Catherine Neish: 14:01

Probably yes, and this is something we looked at. So, let's say, in the early solar system, titan developed life and it formed in its ocean and it stayed there, right. But after a while, if there's no influx of more carbon material, you're going to starve, right, all your little critters are going to starve. So you need a constant influx of material, either from the surface or the subsurface to feed yourself. And so, yes, the flux of impact craters would definitely impact the amount of material you're able to bring down into the ocean, and we found that, even on the best circumstances we could think of, it was only about like one elephant's worth of material that we'd be bringing down to the ocean. So probably not enough to feed these critters on a long-term basis. Again, unless there's something coming up from the interior and I have a colleague who's working on that half of the problem as well.

Andrew Prestage: 14:58

And what sort of creatures would live in an environment like Titan's ocean, encased in a hundred kilometer thick shell of ice? Could they be like the extremophiles that we see in the depths of our own oceans, or could they be unlike anything we could even imagine?

Dr. Catherine Neish: 15:19

Yeah, it could be either. We just don't know Certainly we do, as you say, we see examples of these critters on earth at the bottom of the ocean, you don't need light to survive. As surface dwellers we rely a lot on light. Through photosynthesis, it grows plants. We eat them. That's great for us, but you don't need light in order to survive. There's other they're called metabolisms. That's how you generate energy in an organism and there's ways to do that without any light at all, just through chemical processes and so on

Andrew Prestage: 16:25

And I sometimes talk to another guest about the organic material that's found in meteorites and asteroid samples and I always ask him if they've figured out how non-living matter comes to life. That's what I want to know. We haven't figured it out yet. And so, Catherine, if it's not a naive question, even if you've got all the ingredients there, how does non-living matter come to life?

Dr. Catherine Neish: 16:49

That's the $20 million question right? I think you'd definitely win a Nobel Prize if you could figure that out. I think we've certainly gotten close, though. It's pretty easy to make the building blocks of life within the lab. You can just mix some simple ingredients together and form amino acids. That seems relatively easy. People have made cells in the lab. People have started to construct RNA in the lab. So we're getting there, people are making good progress, and so we might be able to do that one day. I kind of think we're going to make life in the lab before we find it elsewhere in the solar system, if I'm being honest, because I see more progress being made from that end of things. But as of right now, we don't know. We don't know. We've never seen something non-living come to life, and how would you even know when something non-living turns into something living? It's a really muddy sort of question. You have to start by asking this very philosophical question of what is life to begin with right, which is not an easy question to answer.

Andrew Prestage: 17:54

If that one elephant's worth of glycine is not enough to make Titan habitable, could there be pockets of concentration that do meet that threshold for habitability?

Dr. Catherine Neish: 18:04

Yes, and so here's where the caveat comes in. If all of that glycine remains concentrated near the ice-ocean interface, I think in that situation that's more encouraging for life, because now things are all concentrated, there's an interface to work with, and it seems like in the origin of life and the maintenance of life having interfaces can be really, really useful. So if all that material can stay, you know, focused and concentrated near that interface, then I think we have a better chance of having a habitable ocean. But if you, if you spread it out throughout the entire ocean, the concentrations are just so low, I don't think any interesting chemistry would happen then.

Andrew Prestage: 18:45

And I have to mention one of your references Miyakawa and others in 2002. This was a real wow moment for me an experiment that was relevant to your study, where a sample was prepared and then frozen at minus 78 degrees centigrade for 27 years. Now, that's commitment to research. I want to know more about this, and was it their intention to store that sample for 27 years, or was it salvaged from another forgotten or abandoned experiment in the past?

Dr. Catherine Neish: 19:21

I love that study. I must admit I have not read it in a few years, but if I had to guess, so you'll notice one of the authors on that study is Stanley Miller, who invented the very famous Miller-Urey experiment in the 50s. So he was the first to try these experiments where you would take simple elements you know, add energy in an early Earth-like environment and made amino acids. It's in science. It kind of kickstarted this whole cottage industry of these reactions that you know even I followed up with 50 years later during my PhD, and so if I had to guess, it was from one of Miller's early experiments. And then he just left it in the freezer Most labs have these minus 80 freezers sitting around for storing samples and maybe he just like left it in there and forgot about it, I don't know. And then they were like, hey, we've had this sample sitting in here for 30 years, we should analyze it. Happy accident. So yeah, I love that study because it's very rare that we have such long timescales to look at these reactions.

Andrew Prestage: 20:23

And looking to the future now, Catherine, do you think life on these moons of the outer solar system could be more likely in the later stages of our solar system? As the sun expands? There seems to be plenty of water, as you've mentioned, and carbon, but if heat is one of the missing elements, would that expansion of the sun, would that provide the heat that those bodies need?

Dr. Catherine Neish: 20:46

Oh, absolutely. I think Titan's going to become a habitable world once the sun goes into its red giant phase. Now it won't last very long because eventually the sun will die, but for those you know a hundred million years, I think the living is going to be pretty good on Titan. Yeah, One of my colleagues actually wrote a whole paper about this, If you or any of your listeners want to check it out a guy by the name of Ralph Lorenz.

Andrew Prestage: 21:13

And one final question for you, Catherine. My first question for you was about why we find habitability so fascinating and, with Titan looking like it's not habitable at the moment. Is this a bad news story? And I know in science there's no good or bad news, but only results. Would it have been more interesting or more exciting if Titan was more habitable, or is this a good opportunity to demonstrate that in science, the results are the results and our preferences have nothing to do with it?

Dr. Catherine Neish: 21:44

Yeah, that's a good point. I think, going into this, I was expecting it to be better than we ended up with, or more habitable, I will say. Because Titan has so much carbon on it, surely some of it must make it into the ocean, and that would make it habitable. This is unlike any other icy world. No other icy world is just covered in, as I said, 25 meters of organic molecules right, this is an insane amount of organics. Surely some of them are going into the ocean. So I was pretty surprised at how few of them ended up there.

Dr. Catherine Neish: 22:17

And I feel like you know. So I'm a big fan of the X-Files and I'm like Fox Mulder. I want to believe, but every time I, you know, do these studies, I just find the answers that are disappointing, and I've kind of turned into this pessimistic astrobiologist where I really want there to be life out there, but I think it's a lot harder than people think it is, and so maybe Earth is really special in that way and we're not going to find life all over the universe. It's going to be in these very specific pockets that have just the right ingredients, and I would love to find those places, but the universe is just so big. I think it's going to be really tricky to find life out there.

Andrew Prestage: 23:01

You're right, earth is very special, and what a great point to end on. Catherine Neish, it's been a real treat to talk with you, congratulations on a really significant study. I found it super compelling and thanks for joining us on Cosmic Coffee Time.

Dr. Catherine Neish: 23:15

Great to be here. I love talking about Titan. Thanks for having me.

Andrew Prestage: 23:19

Catherine's study was published in the journal Astrobiology and if you Google Titan habitability, you can also find summaries. Remember, if there's something in the universe that you want us to take a closer look at, send us an email at cosmiccoffeetime at gmailcom. Thanks for joining me. I'm Andrew Prestige and I'll see you again soon for another Cosmic Coffee Time.