Cosmic Queries – Life on Exoplanets with Sara Seager

0:00Hey, StarTalkians, Neil here. You're about to listen to an episode specially drawn from our archives to serve your cosmic curiosities. Check it out. Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now. This is StarTalk. I'm your host, Neil deGrasse Tyson, your personal astrophysicist. And this week is a Cosmic Queries edition. The always popular Cosmic Queries. And the topic, the always popular Search for Life in the Universe. And I've got with me is my co-host, Matt Kirshen. Matt! Hey! Hey, Neil. How you doing? I spent all day yesterday trying to memorize the name of your podcast.

0:52It's Probably Science. Did I get it right? It is! I always mangle it. I was going to go for another variant. I stumbled in my efforts there. I found a podcast called Sometimes or Mostly Science. It's a whole other podcast. Oh, we hate them. No, we've got a running rivalry with them. You totally have rivalries. I got to make sure I get your stuff right. It's going to come to violence at some point. Probably violence. So I know a little bit about the search for life, but not as much as our guest today. Our guest today is Sarah Seeger. Sarah, welcome to StarTalk. Thanks for having me today. Yeah, so Sarah, let me get your full title up here.

1:33So you're a professor of aeronautics and astronautics, physics, and planetary science at MIT. Is that, no, they left out a few categories. No, no, no. It's because exoplanets and the search for life is an incredibly interdissimilar topic. Okay. And it draws upon all those different fields. Excellent. But between you and me, can I call you a planetary scientist, right? That's really... Yes, yes. I mean, my home is really in astrophysics. Okay. So you can call me an astrophysicist or a planetary scientist or both. In the club. So I guess the search for life in the universe has to necessarily include the search for exoplanets, right?

2:15Right. They go together. But is that part of our bias? Not necessarily. We do. I mean, we're definitely Terra-centric. we definitely are narrow-minded, but at the same time... Terra-centric, like Earth-centric. Yeah, like Earth-centric. And on Earth, we believe that for the origin of life, we need a place for ingredients to concentrate. And it's hard to imagine ingredients just concentrating in the vastness and that low density of outer space. Okay, so this concentration thing, I think, is under-celebrated out there. I mean, in the public, they have people... We take it for granted that we have rocks and buildings and mountains and people.

2:51and in our greater universe, nothing is together. Mostly, it's mostly empty. And where it's not mostly empty, it's highly rarefied. And so planets are really special places. Is that fair? Very special because they do concentrate complex molecules. They concentrate elements, nutrients, and everything we need. Am I right in thinking they are substantially less special or at least less rare than we thought they were even five, ten years ago? Yes, actually. We are slowly making ourselves less and less precious, less and less special.

3:33No, Sarah, it's okay to know that. You're not just supposed to tell people that. I think that's nice about science. I like the fact that science has sort of switched between going you're incredibly special and you're not special. We do. We love thinking back to the Copernican revolution where before Copernicus, the model of the universe was that our Earth literally was at the center of the universe. All the planets and the sun and the stars apparently all orbited Earth. I think I've heard, is it Andrewian, describe this sequence. Some combination of her and the Carl Sagan camp referred to it as the sequence of great demotions for whatever we imagined ourselves to be.

4:17Plus, there was some rebuttal to that. I forgot the fellow's name, but he wrote, I think, convincingly, that the idea that we are in the center is not necessarily an elevated place if heavens are above us, right? So the center could be the slag heap of where everything collects, and your ultimate goal is to ascend from that to greater places. But in either case, the location was unique, I think. Interesting. I think about it. So in his mind, we're like the plug hole of the universe. We're sort of a drain. So, Sarah, was it natural to transition from exoplanet discovery to the search for life? Or did someone have to sort of nudge you?

5:04Or was it just obvious as the next thing to do? You know, every scientist is different. And I've sort of been the random walk type of scientist. Like work on a problem and see a more interesting problem and then move over slowly. You're like the dog being distracted by the squirrel. You know, squirrel. Yeah. You can't keep it. But when you started out in the late 90s, we didn't know many exoplanets. And even those that we did, it was fun to think of aliens on them. but there was no research program there yet. So it seems to me you were there at the birth of this, if not having birthed it yourself.

5:46Yes, and in fact, but just to go back even further, before my time, perhaps even before yours, but in the decades past, since the - Even before Neil. There is no such thing. No, okay, well, you know, what's interesting is if you look back, like even, you know, just after the time of Sputnik, like in the early 1960s, there's actually a report from a think tank kind of company, and it actually talks about planets and exoplanets and the chance for other Earths. And even in the decades after that, you know, there were always studies on how would we go about finding another Earth. And so when exoplanets was born in the mid-1990s, and yes, I was there, I was a graduate student working on exoplanets at the time, you know, they were hot Jupiters.

6:34They were not suitable for life in any way. But slowly those two things came together. You know, all the past decades of thinking about Earths, then switching gears to the hot giant planets. And so the thought of finding Earths in life, it was kind of always there in the background, even though it might have been a bit of a stretch. And just to be clear, the Jupiters that you're referring to being hot was, it was easier to find really massive planets first compared to low mass planet. So you're going to find a Jupiter first and they're hot because why? Because they're very close to the star. So close to the star that as heated by the star, they're just hot.

7:10Okay. So they're Jupiters, but they didn't look like our Jupiter. So there again, we were not. So we thought we were representative of the universe and we're not. I mean, at least our solar system. Right, right. We always expected to find a Jupiter where our Jupiter is, which is, you know, five times further from our sun than Earth is. And instead, we found Jupiter mass objects within a few day period orbits of the star. So even our bias, which shows up every day in race relations and sexism, it even shows up in astrophysics. It did, yeah. And the funny thing is, is just to take that a level further, when people first found these hot Jupiters so close to the star, we just assumed that they had the same albedo, the same reflectance properties as Jupiter itself.

7:56Jupiter is quite bright. You know, you see it in the sky because it's got icy clouds. And we couldn't see Jupiter in reflected light. And with a little more thought, we realized, wow, these hot Jupiters, they're incredibly dark. They're very absorbing. They have no reflective clouds, most of them. Wow. Okay, so they're not only... So they're big Jupiters that don't look anything like Jupiter. That's what you're saying. Like, I mean, yes and no. They don't appear like their atmospheres aren't like Jupiter, but they're kind of bulk composition. They're mostly made of hydrogen and helium. That part's the same.

8:27So if you come to this as an astrophysicist, planetary scientist, and now you want to think about life, you got to start knocking on the doors of biologists. So when did all that happen? Remarkably, it really, it started happening for me when I had my first staff position. I worked at a place called the Carnegie Institute of Science. And I was in Washington, D.C. And it's quite interdisciplinary there already. and they were already part of working on the somewhat new field back then of astrobiology. So I started interacting with biologists there. And the funny thing was, is I got a postdoc there and I signed him up to work with me.

9:02And it literally took us like nine months before we could even understand each other because our language was so different. Yeah. So you need the coffee lounges, you know, between at the intersections of departments because otherwise we just live in our stovepipes and discoveries go unattended to. It's true, it's true. And later on, I attended an astrobiology conference and I met a remarkable person there who became one of my closest colleagues. And so then through him, him being a biologist, I was able to learn and create more collaborators. And so, I mean, you have a fascinating story. I only recently learned that you've actually collected that together in a kind of a memoir, the smallest lights in the universe.

9:45So congratulations on that memoir, published by Crown in 2020. And because we're all distracted by big explosions and big lights and big things, but maybe the smallest lights in the universe, I guess these are the exoplanets, or it could be metaphor for other things in the book, that it's just call attention to other previously underserved domains of the cosmos. Thanks. Yeah. So let's get straight to this. What is life? You know, in exoplanets, we have a good excuse for completely avoiding that question. And we do, we do. I'll run it by you. I'll run it by you. All right. Because we have telescopes and we can see atmospheres of other planets.

10:31We're hoping with our next generation telescopes to see atmospheres of small rocky planets. And we're going to look for signs of life by way of gases that might be attributed to life that have accumulated in the atmosphere. So we prefer to think about what life does. Life metabolizes. And it may give off gases during that chemical process of metabolism. So we conveniently sweep that under the rug and we just talk about what life does. And you sweep it under the rug because you can't do anything about that question anyway. We can't do anything about it. And it's just a question that no one wants to agree on what the answer is.

11:05So you sweep it under the rug and say, let's observe what life does. So you're the atmospheric gases equivalent to the people who study animal poop, for example. It's things that life does, even if you're not studying the life itself. Is that? That's right. Not to equilibrate your study with the study of feces. And actually, Neil, that has never been done before. So that is brand new. It's a brand new analogy. So you're saying atmospheres on planets are kind of the animal remains of the galaxy. Well, the gaseous effluences, I guess. Yes, actually, that's a great way to look at it. So Sarah, but clearly there are gases out there.

11:53And I want to get to the Q &A because Matt has them lined up and I don't want to lose any time on that. But clearly there's some gases, let's take methane, for example, that we know is the byproduct of life, not all life, of course, but some bacterial life on Earth. We know that. So now let's look to another place, like Saturn's moon Titan. Oh, my gosh, it's completely covered in methane. So it must be teeming with life. But it's not. So where did, how, what, who, yeah, what? Yeah, that's the single most biggest problem, that we need to be able to see other gases in the atmosphere and put the gas in question in context with what else is there.

12:41But even doing that will be, it'll still be hard. It'll be very, like a forensic crime scene, you know? How do we pick out what is really life, what is really not made by life? So the gases you list that are the products of life are necessary but insufficient to prove that there's life. Yes, actually. And that is the sort of, let's call it the dirty secret of the whole field, is that we'll never be able to prove it. So in forensic crime scene terms, you've sort of got to distinguish between blood that was caused by the crime and blood that was just previously existing, sort of decorative blood in that room.

13:16Precisely. Just blood that someone had put there that would just naturally be there on the walls. Yeah, the normal blood that exists in the room. I'm sure Sarah is going to put that analogy in her next research paper. Yeah. Just put just an equation and that's all science is, right? Yeah, but it's in an equation, it's legit. Yeah. And so on our Earth, we have methane produced by life, by bacteria, by cows. But we also have methane coming out of mid-ocean ridges. So in a lot of cases, it is definitely ambiguous. And methane is natural gas that we have in our stoves. And I'm pretty sure what's coming out of your stove is not cow farts.

13:58It's come from another location on Earth. Okay. So, Matt, we have a couple of minutes left in this segment. Let's see if we can squeeze in a question. Okay, great. Well, this one, I love the questions that come from our younger listeners. This one comes from Carrie Jenkins, an eight-year-old fan. Eight! How long do you think it'll take for us to find other life in the universe? Yeah, how close are we, Sarah? How many more years? What do we got here? Well, we actually will have, we like to say we'll have the, I'm not purposely trying to evade all your questions, honestly, but I would like to say that we will have the capability to find signs of life very soon with the launch of the James Webb Space Telescope.

14:38But whether we find life, that really depends on what's out there. You know, if every planet has life, if life is extremely common, life that makes gases. So I, if you want a concrete answer, I could say anywhere between two years and 30 years, let's say. Okay, so this would be the usable life expectancy of the James Webb Space Telescope. Well, I was putting the James Webb, whose nominal life expectancy is five years, maybe 10. I was thinking of future telescopes beyond the James Webb. Okay, and possibly missions to the icy moons of Jupiter, where there might be life beneath the surface or even life beneath the surface of Mars, right?

15:20I mean, why not? Right, right. You're not looking for that life, but you got other people, top people doing that as well. Right. Okay, so we might find life or definitely know there isn't life as we know it in the lifetime of this eight-year-old girl. Well, maybe this eight-year-old girl will carry the torch. If all the searches we're doing now are exhausted, maybe she'll be the one to think of the next new idea. Maybe you all aren't clever enough and we need her to come along and solve all the problems. There you go.

16:04Hi, I'm Ernie Carducci from Columbus, Ohio. I'm here with my son Ernie because we listen to StarTalk every night and support StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.

16:30What more do you have for us? Also, by the way, we should mention that our guest today isn't the only one with a new book out. And you've got a book based on Cosmic Queries that has a chapter that talks about the search for life. Oh, yes, indeed. So thanks for mentioning that because I almost forgot. I probably wouldn't have forgotten by the end. But there's a book called Cosmic Queries. Because this format was so successful, we said we've got to do more than just put it out there as a podcast. So there's a book called Cosmic Queries that takes all the biggest questions, including this one. And much of Sarah's research that informs this field is contained in that chapter.

17:13And so in a celebration of Cosmic Queries as a thing and the search for life as a sub-thing of the bigger thing, we've got Sarah Seeger. So Sarah, thank you again for being on StarTalk and for checking in for this. So Matt, what do you have for us? Well, I've got to do another Cosmic Query question from another young Patreon listener. This comes from Violetta and Violetta's mom, Izzy. Violetta is a 12 and a half year old astrophysicist here in Birmingham, Alabama. 12 and a half. When you're young, those halves are important. And I asked Professor Seeger, I want to know, firstly, what exactly are biosignature gases?

17:54And secondly, what biosignature gases would Earth give off that would be detectable by extraterrestrial life who might be looking for inhabited planets like ours? Perfect question. Yes, Sarah, what do you got? Or would ETs not need to look for our biosignature gases because our existence would be pretty obvious because, duh, space junk. Yes, well, a biosignature gas is a signature of life. It's a gas produced by life that can accumulate in an atmosphere of a planet to a level that we can detect with our telescopes. You know, I love to imagine, you know, there are intelligent aliens on a planet orbiting a nearby star.

18:30and they have the kind of space telescopes we're building or hoping to build, they would look at our Earth and they would definitely see a very strong biosignature gas, and that's oxygen. And oxygen fills our atmosphere to 20 % by volume. But without plants, without photosynthetic bacteria, we would have literally virtually no oxygen. So if all the plant life went away, you know, walked off the Earth today, how long would it take for our oxygen supply to sort of drop to zero. And why would it drop at all? Why wouldn't it just stay there? Well, we also have bacteria that make oxygen. So I'm not sure, you know, what the division between the molecules.

19:10No, no, no. Just take away everything that's making oxygen. Take everything away. And so now we've got 20 % oxygen. What happens to it? Well, what happens to it is oxygen is a highly reactive gas. And it will just react away with other molecules in the atmosphere, with lots of things on the surface, you know, with gases coming out of vents and volcanoes. and that oxygen just won't be there. How much time would that take? Would it happen like next week or in a year? No, no, it wouldn't happen next week. It probably wouldn't happen in a year. It's probably more like thousands of years. Okay, or more.

19:42Okay, so if we kill all the life, the oxygen-deprecation life, we can still live out our lives with oxygen. It's something that generation will suffocate. Yes, probably we could live out our lives. Okay, so what you're saying is even though this 20 % has been stable over the history, mostly stable, it's not actually a stagnant number because we are constantly producing it and constantly removing it and it just happens to be balanced at this number. Is that a fair way to say it? That's a fair way to say it. Okay, okay, cool. All right, all right, Matt, give me another one. All right, this comes from Grumsatuff, one word, I hope I'm pronouncing that even closer correctly.

20:26Whatever you did, it's better than what Chuck does with names. Chuck can't pronounce anything. What is your most optimistic explanation of the Fermi paradox? I like that question. Oh, yeah. I think we all have our favorite answer to that one. Well, tell me what it is first. The Fermi paradox is the idea that if there is intelligent life that can harness energy and get in spacecraft and journey beyond their planet, that they should have colonized the entire galaxy by now. Because once they can get to one planet and colonize that, they can just keep going. And so the Fermi paradox is summed up by the question, where are they?

21:03So what you're saying is in the lifetime of the galaxy, it doesn't really take that much time, if you're intelligent by our measures, to build spacecraft and start traveling to planets, even if you can't travel at the speed of light. Right, right. That over time, you would eventually reach planets and colonize. Okay, so all right. So where are they? Okay, so there's the explanation I think is the real one, and then there's the one that I hope is the real one. Wait, wait, so Matt, her explanation would be, they're already here. Yeah, I like that one. Yeah, that's the funnest answer, but go on. Yeah, sure, we don't need to talk about that.

21:39So, you know, one answer is that it just takes too much energy. Like, we as humans, we know now what it takes to get in a spacecraft and go somewhere. That's a lot of resources. So perhaps they're just not doing that. There's another answer that the intelligent civilization will unfortunately and inevitably self-destruct. They'll destroy their planet. They'll kill each other. They won't ever reach that kind of place. Wouldn't that be the definition of not being intelligent? Yeah, well, it would be. My explanation that I love is, I'll put it to you this way. Just imagine an ant colony in your house, which you might have, or your apartment.

22:21And the ants, they appear kind of, you know, dumb, but they're somewhat clever, right? Because they have a society and you see them doing like a reconnaissance mission. But just to be clear, just to make sure we're all on the same page, by an ant colony, you mean like one of those ant habitat module things where you can see - No, I just mean, it could be that ant colony habitat or it could just be the ants like in your house. Like you might have - Oh, just ants in the house. Okay. Yeah, ants in the house. And I don't know if you've ever had this, but you'll see like a few of them kind of looking around and they might come across like a piece of cat food on your counter or something.

22:55And then shortly thereafter, you have a huge stream of them and they're all coming to get this cat food in like a little river. Well, you can mess them up if you like wipe away their trail for a moment, they kind of get lost. But I want you to imagine, you know, Neil, Matt, having a conversation with those ants. Like tell them about the universe. Tell them about the Hubble Space Telescope and the vastness of the number of stars and galaxies. And tell them about calculus and geography. Yes, yes, yes. So what I love to imagine is that to these intelligent aliens out there, that we are like the ants.

23:28Like, why and how would they contact us? Okay, so Matt, Sarah's bumming us out. First we're insignificant, now we're just plain stupid. Well, also, I think it is worth pointing out, there are different, I mean, like Sarah was alluded to, there are very different types of intelligence. You know, I've been to university, you've both spent a lot more time in academia, that we've all met people who are incredibly smart in specific ways and otherwise idiots. Okay. So, you know, maybe they have the ability to travel across galaxies, but then not the ability to not shoot themselves within a very short amount of time.

24:05And maybe they're us. The official answer to the Fermi paradox, where are they? They think we're idiots. So... Either they think we're idiots or we think they are for having self-destructed before they could get here. Oh, there it is. Touche. Touche. All right. So, Matt, give me some more. So along the lines of interacting with other civilizations, Eric Gross asks, let's say we discover proof of life not in our own solar system, but on some distant celestial body. Would there be any meaningful scientific value of the discovery or opportunity to expand upon the knowledge? It may, of course, have broad societal and emotional effects, but would science practitioners have any real hope of gaining more information about life forms that are at a minimum of 4.3 light years from Earth.

24:48I love that question. And Matt, who asked it? That was Eric Gross. Eric Gross. Okay. Yeah, so Sarah, I love that question because generally when we think of scientific discoveries or advances, we think, okay, in five years or 10 years, engineers will get a hold of it and they'll make some new device and we'll all be living better and differently. And so life's somewhere else that you can't actually have a conversation with. Even if it's intelligent, are you getting secrets from them? I mean, what if you can't, or can you? Are we missing something here? It's such a great question. I mean, we are so wrapped up in the emotion and the excitement of the journey of exploration and of being the first who can try to find out what's out there.

25:29So in a practical sense, not really. I mean, we're not doing this to find anything practical. That said, wouldn't it be amazing if there is life, intelligent life on the nearest star system four light years away, and we could have a very slow conversation. Very slow. But we could imagine. No witty repartee there. Right. Send them a message and, you know, four years later, you'll get their message back and we could exchange ideas about technology. So if we wanted to be practical, like that's probably the most practical avenue. So, but in terms of biology, unless we learn from them through these radio signals what their sort of biochemistry is like, we wouldn't get to compare DNA or if they have DNA at all.

26:10You wouldn't be able to do any sort of in-situ kind of comparisons to advance biology on life, I would guess. Is that correct? Right. No, that's correct. That's correct. Yeah, but I don't want to sound like, who was that philosopher 150 years ago who said, the stars, they're just lights on the sky and we can know, you know, how bright they are in the location, but we will never know what they're made of. Right. And think about this. Like, we're just here now. Imagine 1 ,000 years from now, 10 ,000 years from now. Right. We may have a way to get to this. Imagine if there's intelligent life on that planet and we do a sample return.