Description
Astrobiology has seen a series of revolutions over the past three decades that have completely reinvigorated the field. Scientists who were curious about life and biological organisms across the universe once had to handle the so-called giggle factor: the idea that they were kooky crazies searching for UFOs and little green men. With a dramatic improvement to the quality of our instruments and a torrent of new and better data, that giggle factor is now no laughing matter: we increasingly have the means to make progress here like never before.
My guest today is Adam Frank, the author of The Little Book of Aliens and a professor of astrophysicis who is focused on improving our ability to identify biosignatures and technosignatures of life throughout the cosmos. He’s just one contributor to a growing community of scientists reinventing our approach to the search for life, a vitality that is leading to the potential first dedicated satellite focused on the search, the Habitable Worlds Observatory.
Alongside host Danny Crichton and Lux’s scientist in residence Sam Arbesman, we talk about the trilogy of revolutions that have brought new vigor to astrobiology, how artificial intelligence is upending the search for life, and what we can also learn about Earth and our climate in searching space for the answers of life.
Transcript
Danny Crichton:
Just to give the conversation away, We mentioned the Drake equation, which to me in some ways was this completely theoretical off-the-shelf notion from Drake who was like, "How many alien species could there be?" And there's some factors you can vent, you can think in your head as a thought experiment. There's some triggers, how many planets are there, how many of them might have the ability to support life. He puts us all together into a formula that in some ways you could imagine was never going to be empirical approval in any way, shape, or form, but my understanding from your book and the work that you've done, we've actually made a lot of progress over the decades from a total theory pie in the sky science fiction. And we always like this term at Lux Capital of, "From science fiction to science fact." But we've actually taken some of the big fiction in this world and made it a little bit more factual over the years. So I'm curious, when you think about the evolution of the field and the work that you've done, what's changed? What's the vanguard today in 2024?
Adam Frank:
I like to think, when it comes to what's changed with astrobiology, I like to think of the three revolutions in astrobiology. The first one is the most important one, which is the discovery of exoplanets. When I was a graduate student back in the 80s or late 80s and 90s, early 90s, no one knew whether there were any planets orbiting any stars other than the eight we had orbiting the sun. And if you look at the history, there are a number of prominent astronomers who ended their careers by claiming to have found an exoplanet and then holding onto that even while it was clear that they were wrong. And then in 1995, and I remember this day, the first exoplanet is discovered, is announced. And it was weird. That was important, right? It was a Jupiter sized world that was on this super tight orbit around a star, like a four-day orbit. It was closer to its star than Mercury is to the Sun.
So from that point, from 1995 on, you see slowly the number of exoplanets increasing until then you get the Kepler satellite and then suddenly, boom, you're starting to get thousands discovered wholesale. And now we know that every star in the sky has planets. So right there, suddenly, since we believe that planets are necessary for life, suddenly the odds just exploded that you could get life in the universe. Second revolution is the solar system. We visited... We have now sent probes to pretty much every planet and every kind of body in the solar system, which means we understand the history of planets so much more, in so much more detail when it comes to their climate and their evolution and how planets evolve, whether they have plate tectonics, whether they have magnetic fields. We've had boots on the ground or wheels on the ground, landing pads on the ground on all these different worlds, which have really given us an understanding of the diversity of planetary environments.
And the third revolution is Earth's own history. We have basically peeled back, there's still lots of questions, but we've peeled back the entire history of the Earth, in particular the 3.8 or so billion year history of life and the Earth, the coupled evolution of life and the planet. And what that has shown us is that Earth has been many worlds across its history. It's been a water world, a jungle world, an ice world. And many times some of the most important transitions in the functioning of the planet came because of life, because life changed it. So the Earth didn't just evolve by itself. The biosphere and what we call the geospheres, the atmosphere, the cryosphere, the hydrosphere, the lithosphere, those have been evolving together. So what that tells you, if Earth is a good guide, is that life hijacks a planet and completely alters its evolution. So the whole game has changed. And that's what the point of the book is, is that astrobiology, which used to be there was no astrobiology. NASA called it exobiology for a while. There really was never a lot of funding for it.
It was not a principal concern for astronomers. Now it is, in some sense, it's the most exciting field. And you can tell that because the next giant telescope we're building, the successor to the James Webb Space Telescope, has a name. It's going to take 20 years, but it has a name. It's called the Habitable Worlds Observatory. And that tells you right there what the principal, this is the flagship telescope we're building. The principal concern of that telescope, it'll do other things, but the principal concern is going to be to find life.
Samuel Arbesman:
The fact that there's now this interest in intelligent life. And is some of it this almost a branding exercise of talking about technosignatures versus SETI or things like that? Do you have a sense of what precipitated making that more acceptable or was it the thing of, "Okay, we're already doing astrobiology, so this is therefore the logical next step is to move from dumb life to intelligent life"?
Adam Frank:
I think for people in the field, I'm still relatively new to the field. My career was not in SETI, I didn't work in SETI. And the classic radio SETI, the things like the pioneers and heroes of the field like Frank Drake and Carl Sagan and more recently Steel [inaudible 00:05:15] amazing hero, they were still using what I would call classic SETI where you're using radio telescopes. And often in that classic search you were looking for beacons. The idea was somebody was setting up a beacon, purposely sending you a message. I always found that... To me, that's one of the reasons I didn't go and didn't spend a lot of time in SETI because it was too much of, "Well, they know that we know that they know that we know." So that's classic SETI. What really changed, I think, over the last, since the exoplanet revolution is now you know exactly where to look. Frank Drake didn't know where to look. He just pointed the telescope at a Sun-like star.
Now we know exactly which stars not only have planets, but have habitable zone planets, have planets in the right place for life to form, meaning that if you poured a cup of water out on the ground, it would stay liquid. It wouldn't boil away and it wouldn't freeze. And so that means the way we're searching for life, whether it's dumb or smart, life has changed utterly. It's this thing called atmospheric characterization, which I can talk about. But I think that is really... What people normally think about when they think about SETI is they're thinking about something that still, there's still lots of great work to be done on it, it's gone beyond just looking for beacons so you can use machine learning to look for non-natural signals. So that's great, but it's just that the field has expanded so much beyond that. That's only one tool in the toolbox. Some people still love using the term SETI. I use technosignatures because I actually do think SETI still carries, the term SETI carries a lot of baggage that we don't need anymore. And really, even the idea of intelligence. What's intelligence?
The classic study had this... I was very much... When it started, 1960s, white guy, kind of science fiction, a certain kind of science fiction view of what a civilization is and how it progresses. And now we've had to really... That's the mission, is to broaden past that 1960s European vision of what a civilization is because we have no idea what a civilization looks like other than it uses energy to do work. So I think that's why for me, SETI, and I'm cool if people want to use it, but I think the real thing is technosignatures. What we're looking for are signatures of technology, right? Not intelligence, technology. That's what we're... We're not going to find a poem. What we're going to do is we're going to find evidence of using energy to do work for the purpose of a civilization.
Samuel Arbesman:
So related to that though, there's a lot of different ways civilizations can do their things and I feel like there's historically been a lot of times in astronomy where people have discovered certain objects or phenomena and thought, "Okay, maybe this is due to intelligent life." So I believe pulsars are one example of that. Then we learn, "Okay, actually it's a natural phenomenon." Obviously in the course of doing that, we've learned a lot about the universe but how do you think about, what is the threshold for evidence for these kind of technosignatures?
Adam Frank:
What's interesting is the whole field, biosignatures and technosignatures, has gone through this maturation. That's what's really fascinating. Once there's funding, means so that you can have a community of people who are talking to each other, having a long conversation. Somebody proposes a biosignature, technosignature, and then somebody writes a paper which criticizes that, and then that criticism gets criticized so that you evolve towards something. The problem with the history of the field, particularly SETI, is that since there was never any support for it or never a lot of support for it, somebody would write a paper like, "Oh, we should be looking at neutron stars. Aliens are going to modify neutron stars." And that paper never... It just sat there forever and nobody ever got a chance to really work on it. Now what's happening is the field is maturing and we're able to address the question of false positives. How would you know whether or not the thing you think is a biosignature or a technosignature is actually something that was produced in a way that had nothing to do with life or nothing to do with intelligence?
So that is a fascinating part of the field now. And a lot of cases it's going to rely on Bayesian methods. So this idea of understanding what your priors are like, "Oh, here's some evidence," but how does this evidence update what I already thought was going to be a technosignature? And part of that means context, right? As Sara Walker likes to say, who's, I think she's one of the great physicists thinking about life in general right now, a molecule is not a biosignature or a technosignature. One single thing does not constitute like, "Oh, we found it." So for example, let me give you an example. We wrote a paper, our group wrote a paper where we proposed, we looked at chlorofluorocarbons as a technosignature. We now have the capacity... Even JWST might be able to do, JWST might be able to do this. We can look into an alien atmosphere, look at the light that passes from the star through the atmosphere, reaches us, and there'll be a spectral imprint. If chlorofluorocarbons are there, we'll be able to tell. We'll be able to see the fingerprint, the spectral fingerprint of that.
Now, as far as we know, chlorofluorocarbons cannot be produced any way by nature. You have to have industrial processes to make them. So on one hand, it's like, that's it. If you find a chlorofluorocarbons, you found a technosignature. Okay, wait, we shouldn't be so... A molecule is not a technosignature. Now you got to look at, let's look at the other things that are happening on that planet. What's its atmosphere like? What's the state of it, its temperature, its pressure? What else can we tell about the atmosphere? Does the planet seem to have water on it? So it's going to be... In order to really know, we're going to have to put together all the other things we know about the planet in order to really, really be confident. So we'll make the detection, we'll be super excited, and then we're going to keep raising the level of our confidence by looking at other aspects of it as well.
Danny Crichton:
We're talking about the frontiers. So we've had a massive explosion of new exoplanets. We have these new instruments like the James Webb to give us a lot more data to use. We're also getting a lot more just from Earth, as you said in your different revolutions where we're understanding more of the evolution, how life affects the planet itself. I'm curious, a lot of our shows focus on AI, and so using all this data, dumping it into an LLM, a large language model, and processing what we're seeing. When I hear you talk about Technosignatures and you're like, "Look, we've got millions of exoplanets. We have these spectral imprints that you're pulling in from single one of them," what I go through my head is like, this is just pattern recognition. I hear Bayesian or almost probabilistic graph models.
Adam Frank:
Right.
Danny Crichton:
Is AI in any way influencing this field given the data that's coming out from all these different instruments?
Adam Frank:
Oh God, absolutely. If you look at the Kepler data, one of the reasons why Kepler has discovered so many exoplanets is they have a pipeline. The Kepler satellite mission finds exoplanets by looking for what are called transits, which are like little mini eclipses. If the alignment of the orbit is right, then once every orbit, the planet passes between us and its host star. And when it passes in front, the light dims a little bit. And there's a very characteristic way in which it makes a U shape in the brightness. If you're looking at the brightness over time, the planet, the star is bright, and then it dims a little bit in this U shaped way and then comes back. And so there's a lot of information in the shape of that U. So the Kepler, in order, because it has sort through so many, has an automated pipeline. And then also every now and then, it finds things it didn't understand and then it vomits it up and says, "Hey, human being, you figure this out."
And that's how we discovered what's called Boyajian's Star, which had this really weird non-periodic strange signal, which some people took to being alien megastructures. So it looked like something was just... A bunch of stuff was just passing, giant stuff was just passing in front of the star and then nothing, and then three of them going by and nothing. And that was a really interesting moment because when they were analyzing it, one of the possibilities they had to consider that it was alien megastructures. Who doesn't like to say the word alien meegastructure? So anyway, so it turns out, sorry, it's not alien megastructures, it's comets. But the important thing is that in all of these domains, we're going to have to search through so much data that AI is going to be an... And machine learning is going to be a really, really important component of this.
Danny Crichton:
And the follow-up question to that is obviously we're searching for stuff that we think exists. So you were getting this in one of your earlier answers, which we have carbon-based life forms. We're looking for certain signatures, we're expecting a certain level of culture. We're not going to find a poem, but we're going to find certain technologies. It could be radio frequencies that aren't naturally occurring but would only occur if you had electronics or transistors or specific inventions along the course. How easy is it to be open to new forms of life? So we see what is available on our own planet, what we've discovered throughout the solar system. But being extremely open-ended, what are the constraints? Can we actually come up with physical rules, like life cannot exist if it has certain chemicals? I'm curious, how do you keep that openness alive in these searches because we have our priors but then there's just this open-ended, like maybe it is an alien megastructure or maybe it's something else. How do you balance that with the rigors of science and not curatorial of entering everything is possible and there's no rigor to it whatsoever?
Adam Frank:
That's the joy of this field. Again, after years of not even being able to talk about it, now, I think one of the most important things we can do is begin to systematize the process, to begin to really understand what we know and what we don't know. And if we want to go beyond Earth's history, how do we do it in a way that like when you were a kid and they had the gutters that would come up so the ball didn't roll in, that way, we need to have our bowling gutters up. And there's a bunch of different ways they can do this. The first thing is just this systemization of just saying, okay, let's run through all the ideas and let's see where we can begin to have consistency checks for it. But I think one, when it comes to just life in general, not just technosignatures, what's really interesting now is to think about life as not just what happened on Earth, but in general, what is life, what does life do? What is the physics of life that might leave signatures?
So one of the thing is, so I'm working on this, we have a Templeton grant, big Templeton grant, to look at life as a system that uses information. The interesting thing about life is that it's the only physical system that uses information. A rock, you can describe a rock or a star. You can describe the nuclear reaction network in a star in terms of information but you don't to. You don't really gain anything. Whereas life is the one system that actually uses information, meaning it stores, it copies, it transports, and it processes information. So we have a big grant right now that's trying to look, understanding what that means, particularly about semantics. Because as you know, Shannon information, all of our stuff is built on Shannon or syntactic information. And syntactic information is just surprise. It's just, "Oh, I have 89 Es and now I got an A and I'm surprised," and that carries information. But really... Truly information, all information is really semantic information. It carries meaning for somebody, right? Because you can't have surprise unless you have a detector for detecting that string.
So already the system has to have organized itself to have a detector for the thing it wants to be surprised by. So there is no purely syntactic information. So information is always... Information only matters when there's already a detector set up by the thing that's trying to stay alive, to use that information to stay alive for. So what that means is that if you have these kinds of definitions, these information-based, network-based, far from equilibrium thermodynamic system-based definitions of life, now you may have things that it doesn't matter about Earth life. It doesn't matter about carbon or water. You may be able to find ways of looking for life in terms of its information, its networked information use where it's drawing energy from some source to maintain its far from equilibrium state and therefore creating dissipation. So these are all these other physics information network theory based ways of looking for life that really are agnostic about what exact form it takes, whether it has two legs, two arms and a head. So I find some of that stuff as a physicist, a theoretical physicist, the most fascinating ways of looking for it.
So just to be explicit, maybe we're going to look at an atmosphere and we're going to be able to look not just for one spectral line due to a molecule, but we're going to look for three or four molecules and we're going to look at how much there is of each one of those. We're going to try and reconstruct the chemical network of reactions between those. And from that, we might be able to be like, "Oh, okay, this kind of chemical network would never be randomly assembled. This is something that has to come either from biology with its purpose-driven, its viability-driven impetus or technology where there's not only viability, not only does it need to stay alive, there's an actual goal in mind. So that may be the way that we go past getting fooled.
Danny Crichton:
Going back to your book, I'm curious, obviously there's just surprise galore across this entire field. There's always new learning. It is one of those fields because it's so open-ended, because it's unconstrained, it's a search problem. But I'm curious if there are particular surprises that you've come up with in your career and in this field that just really shocked you in terms of its value or what its value has been for the science.
Adam Frank:
Yeah, again and again. Look, the first and most important one was that we're weird. The solar system is not the average. By any stretch of the imagination, is not the average solar system. This idea we learn in school, there's the inner solar system with its tidy little rocky planets and then there's the outer solar system with its big gas giants. No, you have lots of worlds where you've got gas giants close to the star, very close to the star, the most common type of planet in the universe, we don't even have in our solar system. It's either what we call super-Earths or sub-Neptunes. These are planets between one Earth mass and one Uranus mass. That's because in the solar system, so that's one Earth mass and Uranus is like 14 or so, 14, 17, Uranus and Neptune, 14, 17. So in our solar system, there's nothing in between that. It's exactly in that valley, that desert, that's where all the other planets are, most of the other planets. So right there, there's an incredible surprise.
We are the weirdos. And then recently, just like this last year, what are called Hycean worlds, the JWST was able to find by characterizing the atmosphere, by telling what was in the atmosphere of this planet, I think it's K2-18 b, that this was likely what's called a Hycean world, hydrogen ocean world, that had only been proposed maybe two years ago. And what's amazing about it, it is a giant world. It's like eight times the size of Earth. And it's got a huge hydrogen atmosphere. Our atmosphere is this little onion skin. This would be a huge atmosphere. And that hydrogen atmosphere warms the planet up so that there's a liquid... It looks like there's a good odds there's a giant liquid ocean on it, warm. And so a great place for life to form. And so this is an entirely new class of habitable zone world. The habitable zone, which is where the zone where you can have liquid water on the surface of a planet, goes back to 1958, that idea was proposed. So it's always been for rocky worlds... And it's the basis of so much of our science.
And here we just discovered this entirely new class of habitable world look nothing like the ones we thought about. And because hydrogen is so good as a blanket for warming things up, its habitable zone is way different than the habitable zone you'd come up with for Earth-like planets. So all the time, every day there are new stunning discoveries that are really force you to change your thinking about what you think is possible.
Danny Crichton:
We have this huge explosion. We've seen more habitable zones, we see super-Earths. We're learning kind of our little place in the world. But this brings up this question of the Fermi paradox, which you cover in the book quite a lot, which is this mismatch between the fact that we now know there are thousands plus exoplanets all around the Milky Way and all the galaxies, et cetera, we're finding that many of them could potentially host life because they're in habitable zones, that they have signatures, technosignatures or biosignatures that could potentially host life, and yet we haven't found it yet. And this paradox between there's so much probability that one of these should host it and yet we lack the conclusive evidence that one exists, how do we address that in 2024 given all the information we've gotten over the last two decades?
Adam Frank:
Yeah. As I like to say, there is no Fermi paradox, at least the kind of one that people often think about. So when Fermi proposed... And it was literally like a joke over lunch, but the traditional Fermi paradox or what I call the direct Fermi paradox goes like this. Look, if there is another civilization which can travel between the stars, develops the will and the technology to travel between the stars even slower than the speed of light, then on a timescale much shorter than the age of the galaxy, it could hop between stars and set up colonies and spread across the entire galaxy. So that Fermi paradox is the question is why aren't they here now, right? That is a very different question from we've looked and we haven't found out there. So let's put the direct Fermi paradox to the side for a second and talk about the one that most people think about, which is you're talking about the indirect Fermi paradox. We've been looking for 50 years and we haven't found anything. No, we haven't, because there's never been any money to look, right?
People have this idea that every night astronomers take their telescopes and they point them to the stars and they search for alien signals. And the fact is that there's never been any funding to do that. So Jason Wright, one of my colleagues based on a suggestion by Jill Tarter, did this great project. It was actually was a student project, where they took all the SETI searches that have ever been done and they added them all up and they tried to figure out how much of the parameter space that had actually been looked at. So if you think of the sky as an ocean that we have to search and we're looking for fish, how much SETI searching have we done? And it turns out we've looked at a hot tub. You think of the entire ocean. And what we've done so far is we've looked at a hot tub's worth of water. We haven't found any fish in that hot tub. Should we now say, "Well, that's it. There's no fish in the ocean." So there's just no Fermi paradox, not the indirect one. Now the direct one, why aren't they here now?
If you're a UFO person, you're like, "Well, they are here now." I'm not really bothered by that one as much because there's a zillion ways out of it. Interstellar travel may be very, very difficult, and it may be so difficult that people just don't want to do it very much. And not only that, we wrote a long paper on this. We did computer simulations of the Milky Way, and we did find, yes, the settlement front expands across the galaxy very quickly but civilizations don't last forever. Based on Earth history, they don't last forever, which means if somebody arrived 2 billion years ago, why not 2 billion years ago? And they lasted for like 10,000 years, which would be a long time by what we know, there'd be no record of them? This is a paper I wrote with Gavin Schmidt about the Silurian hypothesis. After a million, 2 million years, the Earth's surface is completely reworked via various kinds of processes. There would be zero evidence except maybe in Strata, isotopic records in Strata.
So there's no way to know whether they visited a... Because Earth's history is pretty long. So unless they literally visited 20 seconds ago, you wouldn't really know about it. So I just, I'm not really, I don't find... There's so many ways around the real Fermi paradox, the direct Fermi paradox, that I'm not bothered by that. And there is no other Fermi paradox. And the thing is, finally, this is the whole point of the book, is that finally we can look. Finally, we have the ways to look and there's going to be the funding to look. So yeah.
Danny Crichton:
Then let's dive into that. This is a great topic. So 2024, we opened up the what's called Pandora's box or whatever you want to call it.
Samuel Arbesman:
That depends.
Danny Crichton:
We're really opening it all up, we're making a ton of discoveries. What are frontiers here? What kind of sciences are coming to the table? What kind of communities are joining around this effort? What governments are putting the money here? Where are the hubs of it? Where is the vitality of the field today in 2024?
Adam Frank:
In 2020, every 10 years, the entire world astronomy community gets together and produces these things called the decadal reports, where everybody gets together and decides what are the most pressing issues, where should the money be spent for the next generation of instruments, because science requires a lot of planning. You can't just... And this is the thing people don't understand about it, you can't cut the budget on US science for three years in a row and expect like, "Oh, don't worry. We'll put it back later on." You've got to be thinking two decades ahead. But the important thing about that was one of the primary problems, the astronomers identified the most important problem, or at least one of the most important problems, to be the search for life. So that means, and that's where this, that's why the Habitable World's Observatory was chosen as NASA's next big flagship project. So there is lots of effort going on, everything from using ground-based telescopes now to search the skies for biosignatures, there is the JWST, which is just at the hairy edge, the JWST, you could potentially, if we're lucky, find a biosignature or a technosignature.
There's lots of funding for thinking about developing new theoretical models for under... That's what we're getting paid to do. Our job is to come up with a library of technosignatures that could... We're not going to search, but we're going to give the observers the tools that they need to the library of, here's the things you should look for. And then also, part of this community is this, where you're getting biologists involved. Because with Mars, going to Mars, going to Titan, there's all these... There's the ocean moons of Jupiter and Saturn. There's places in the solar system where we could really be looking for microbial life or even something more interesting like in those subsurface oceans of the big moons of Jupiter and Saturn. So it's an interdisciplinary, transdisciplinary field that now is very, very vibrant with real new technologies being developed, real technological technology-driven experimental programs being carried out right now. So my thing was, I said in the book, is that in the next 10, 20, or 30 years, I would say, I feel very confident that we're going to have actual data relevant to this question.
I can't tell you what it's going to say but after... Because these people have been arguing about this for 2,500 years. You can see the Greeks, the ancient Greeks, yelling at each other about whether or not there's other life in the universe. And after 2,500 years of yelling at each other over their opinions, man, or occasionally setting each other on fire over them, Giordano Bruno, we're finally going to have facts, actual data. And this is the most important question in human history. There's nothing, I think, more important than culturally, are we alone? Are we an accident? Are we the only time this has happened, life, in the entire universe? So yeah, there are so many frontiers and they're being pushed hard by so many people. It's really exciting.
Danny Crichton:
That's incredible. Adam Frank, the author of The Little Book of Aliens, thank you so much for joining us.
Adam Frank:
It was a great pleasure. I really enjoyed this conversation.
Samuel Arbesman:
Thank you.