Planetary Radio • Sep 20, 2023

Alone but not lonely with Louis Friedman

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Louis D. Friedman

Co-Founder and Executive Director Emeritus for The Planetary Society

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Sarah Al-Ahmed

Planetary Radio Host and Producer for The Planetary Society

Louis Friedman, one of the three co-founders of The Planetary Society, joins Planetary Radio to discuss his new book, "Alone but Not Lonely: Exploring for Extraterrestrial Life." The book takes us on a realistic but hopeful reflection on the search for life, from habitable worlds to the technologies that might allow us to explore exoplanets without leaving our stellar backyard. Then stick around for What's Up with Bruce Betts, chief scientist of The Planetary Society, as we get his hot take on life in the universe.

Alone but Not Lonely book cover
Alone but Not Lonely book cover Alone but Not Lonely: Exploring for Extraterrestrial Life by Planetary Society co-founder Louis Friedman was published in 2023. The book explores the search for life off of Earth, intelligent extraterrestrials, and the technologies that could let us study life on distant worlds.Image: Louis Friedman / The University of Arizona Press


Sarah Al-Ahmed: Seeking Life Among the Stars, this week on Planetary Radio. I'm Sarah Al-Ahmed of The Planetary Society with more of the human adventure across our solar system and beyond. Welcome to a very special episode of Planetary Radio. I've had the pleasure of speaking to so many amazing people from across the space community, but this conversation is one that I think I'll always remember. Louis Friedman, one of the three co-founders of The Planetary Society, joins us today to talk about his new book, Alone But Not Lonely: Exploring for Extra Terrestrial Life. Then I'll check in with Bruce Betts, the chief scientist of The Planetary Society, for what's up. We'll get his hot take on what he thinks about life in the universe. If you love Planetary Radio, and want to stay informed about the latest space discoveries, make sure you hit that subscribe button on your favorite podcasting platform. By subscribing, you'll never miss an episode filled with new and awe-inspiring ways to know the cosmos and are placed within it. One of the most profound questions that has haunted and inspired humanity throughout the ages is whether or not we're alone in this vast and seemingly boundless universe. Is there life out there among the stars? Many look to the sky, and dream of encountering intelligent extraterrestrials, but it wouldn't take contact with beings from beyond to change how we think about life in the universe. Even detecting microbes on a distant world or elsewhere in our Solar System would profoundly impact how we feel about life and our place in space. This mystery ignited the minds of the three co-founders of The Planetary Society, Carl Sagan, Bruce Murray, and our guest today, Louis Friedman also called Lou. That along with the exploration of worlds and the quest protect our planet from impacts are the core enterprises that our organization was created to support over four decades ago. When Lou helped co-found The Planetary Society, he brought a bunch of experience to the position as executive director, including 10 years at the Jet Propulsion Laboratory, and five at AVCO Space Systems Division. He's worked on so many different projects, and used his expertise to help guide our organization. Today, Lou joins us to discuss his new book Alone But Not Lonely: Exploring for Extraterrestrial Life. It takes us on a realistic but hopeful reflection on the search for life from habitable worlds to the technologies that might allow us to explore exoplanets without leaving our stiller backyard. The book also has a beautiful foreword by Mae Jemison, the first African-American woman to go to space, which is worth a read all by itself. As you listen to our discussion, you may hear Lou's two dogs excitedly chiming in. It appears that even our animal companions want to know if there are new friends to make out there in space. Let's learn more. Hi, Lou.

Louis Friedman: Hi. Good to be here.

Sarah Al-Ahmed: I generally don't fan girl about people, but forgive me for saying it. It is a true honor to meet one of the founders of The Planetary Society.

Louis Friedman: Well, thank you.

Sarah Al-Ahmed: Thank you so much for coming on the show for this book and for everything really. From solar sailing to creating the world's most influential space advocacy organization, you've had a huge impact.

Louis Friedman: Well, thank you again. I hope so, and it's certainly been my joy and honor to have done that or to be part of it. Of course, I did it with many, many people.

Sarah Al-Ahmed: It's true. It's a collaborative effort, and thankfully the community is growing all the time, especially when it comes to the search for extraterrestrial intelligence, and exploring exoplanets. So, it's a perfect opportune moment to talk about this book. In a world where there are so many people who are expounding on the idea of the search for extraterrestrial intelligence, and having many books on the subject, why did you feel so compelled to write this book?

Louis Friedman: Well, there is... First of all, it's an interesting subject, and as Carl Sagan used to say, if you're not interested in the questions of our relationship to the universe and life in the universe, you must be made of wood. So, it's an interesting subject, and therefore that's the heart of it, but I'm bringing something new to it, which is a viewpoint that exploring for extraterrestrial life has a new technique of doing it in a way that we'll be able to discover life on many worlds, maybe hundreds of millions of worlds, and open up a whole new field, which I call in the book comparative astrobiology, just the way comparative planetology was opened up in our exploration of the planets. I'm hoping to bring that new perspective, a new way of exploring for extraterrestrial life into a wider audience, and introduce it to people. I also am trying to change some of the older thinking about extraterrestrial life. You even used the words, when you introduced the subject, extraterrestrial intelligence, which is what somebody always jumps to when you bring up the question of extraterrestrial life, because we're interested in ourselves. Well, I have a viewpoint which is that that's a minor part and probably even maybe just an accident of evolution, and that the more interesting exploration of extraterrestrial life won't be this search for extraterrestrial intelligence, which I think is pretty much doomed, but the discovering of different kinds of life on many worlds.

Sarah Al-Ahmed: I think you take a really unique and measured approach to thinking about the search for life, because so many of us want to know whether or not we're alone in the universe, but as you point out, we might need to temper our expectations here when it comes to intelligent life, because it might be very rare. Why do you think it might be such a rare occurrence?

Louis Friedman: Well, one thing I need to overcome, and I've not been successful in doing it, and I'll try it out, and the audience for this book and maybe the audience for this show is if we are alone in the universe, is that a negative result? Are we all disappointed in that? Well, everybody initially jumps at that. I mean, that sound... I mean, alone is a statement of some negativism. I don't feel it's a negative statement, because I think there's so much exploration to do, and there's an old saying that actually you've not been able to attribute to any one person. It's been so widely quoted, which is we are either alone in the universe, or we are not. Either answer is profound. If we are alone in the universe, that just makes what we do here on this planet, and what we do with ourselves, and what we think about our life that much more special. If we are in a universe that teams with life, it's a life that's so distant from us that it changes our outlook, but it doesn't change our daily activity. So, I think the answer is that if we are alone in the universe, it's not a negative feeling. It's something that we can still build on and explore in many ways.

Sarah Al-Ahmed: Which is encapsulated really well in the title of this book. We're alone, but we're not lonely, and it's a hard thing for me to grapple with. I expect statistically-

Louis Friedman: You want us not to be alone.

Sarah Al-Ahmed: I do. It's honestly one of the driving motivations of my life, because when I was a child, it was that question of whether or not there was intelligent life out there that drove me to literally become an astrophysicist to eventually work at The Planetary Society. This is one of those fundamental questions.

Louis Friedman: Let me assure you that if you get into the spirit of the book, and stick with it to the end, you'll be very excited about astrobiology and exploring for extraterrestrial life, because that's where I, at least, want to... This is where I hope I'm going to leave my readers. But let me bring up two timescales, which I make a big deal about in this book. One is the timescale of distance. Universe is big. It's huge. It's empty. Basically, the universe is empty space with a few little blips of things here and there, and the distances are enormous. The distance to the nearest star or the nearest exoplanet, either way you want to think about it, is 250,000 astronomical units. We, the species of earth, humans have gone as far as 150 astronomical units. It's as if we set our goals on Paris, and we got as far as Orange County. I mean, it's not very far, and that's the nearest star. The interesting habitable planets are not at the nearest star. They're probably 10 times to 50 times to 100 times further. So if we want to look for habitable planets in our galaxy or in our universe, we can't even get there. They're distances that are way out of reach, and there's a chapter in the book called The Bridge Too Far, the idea of getting there by interstellar travel, the best interstellar travel that's ever been... The only practical interstellar travel that's ever been thought of gets to the nearest star in 100 years, in 150 years by exploding nuclear fusion every few seconds for that entire 150 years that is taking up thousands and thousands and thousands of hydrogen bombs, and exploding them. It's totally impractical. There is one scheme now being worked on with laser sailing that will send one kilogram in 100 years at 20% the speed of light to the nearest stars. That's one kilogram. That's something I can hold in my hand. It's not going to send a person, and it's only to the nearest star, not the most interesting one, not the most interesting exoplanets. So, that's one timescale to think about. The other timescale to think about is time. The earth has existed 4.3 billion years, and of that, life got started rather quickly. A few hundred million years, life appeared on earth. We don't know whether it originated on earth, or whether it was brought to earth in some meteorites or asteroid bombardment or something like that. But one way or the other, it got here quickly. So, probably that's the rule in the universe that if a planet is going to get life, it probably would be able to start quickly. It was very inhospitable conditions 4.4 billion years ago when life got started here on earth, but then it did nothing for 2 billion years. It stayed a single cell organism for half of our history, and did nothing. It didn't evolve to anything beyond one cell. Then something happened two billion years ago, and it got started to evolve into multicellular organisms, and it found niches on the land that it could start to evolve into more complex molecules and eventually into living beings that were macroscopic instead of microscopic, and ultimately into mammals and into the whole evolutionary tree that we are familiar with here on earth. That took the remainder of the two billion years. But even out of that time, humans only appeared. Hominids only appeared less than a million years ago, and humans only appeared less than a couple of hundred thousand years ago. Technology only appeared 600 years ago. It's a conclusion I get rid. So, we've had a billion species on earth, and all this time of evolution and all these experiments that have been conducted, and mutations that have gone on, and only one of those billion species made it up with the ability to technically show themselves to the universe. That's daunting, at least for me. I think it's a good argument that perhaps the evolution to being able to show yourself to the universe, to being intelligent species, that may be an accident. Intelligence may be an accident. There's no proof that it's good for survival. Species that have survived have been fine without intelligence, and they've survived for millions of years, much longer than we can expect the human species to survive. Our total lifetime is probably 200,000 years ago we started, and be lucky if we last another 10,000 years before we evolve to whatever is the next stage. I'm daunted by both the scales of time and the scales of distance to conclude that intelligence is probably rare and maybe accidental in the universe. But on the other hand, we certainly found billions of planets now exist, or we believe billions of planets exist, habitable planets exist, so there's a good chance there's going to be life in lots of places. That's the dog I warned you about.

Sarah Al-Ahmed: Another example of life on earth. It is an interesting point because it makes me feel very proud of humanity that we've managed to accomplish so much with such a limited amount of time with our technology. Already, we've discovered over 5,500 exoplanets, and literally when I was born, we hadn't even discovered a single one yet. So, we've made some great strides here, but it does indicate that it might be extremely rare in the universe. Even if it wasn't, the distances are so vast. There are so many things to consider here.

Louis Friedman: Yes, and it is a dichotomy, because we have all this experience, and we haven't found any evidence of extraterrestrial life. We still have to remember that extraterrestrial life is still a subject without subject matter, despite the hundreds of years of looking for it, and some intense 50 years of using lots of technology to look for it. Despite our vast exploration of the universe, we still have no evidence of extraterrestrial life. We have lots of evidence that the stuff for it might be out there, but we have to be careful. We haven't found it yet.

Sarah Al-Ahmed: We do have methods that can allow us to at least make guesstimates at the amount of creatures that might be out there. A tool that people frequently use is the Drake equation, which you outlined very well in your book. But for people who are just learning about the search for extraterrestrial intelligence, what is the Drake equation?

Louis Friedman: Drake equation, and by the way, it's named for a very good friend of The Planetary Society, our former advisor, Frank Drake, who was a pioneer in radio astronomy, and conducted some of the first radio searches for extraterrestrial intelligence. He was a director of the Arecibo Observatory, and a close colleague of Carl Sagans at Cornell University as well. His equation basically tried to put in a simple form estimating the probabilities of the factors that go into thinking about extraterrestrial life, the probability of star formation, the probability that stars might have planets, the probability that some of those planets might be in a habitable zone where they could develop temperate conditions of temperature, and for the formation of water, probability that on those planets, life could get started and then ultimately the probability that life could evolve into intelligence. Then ultimately beyond that, you had the last factor, which a lot of attention has been devoted to called the lifetime of intelligent civilizations that you could form an intelligent civilization, but if it was short-lived, there might not be many of them out there. So, all of these factors go into estimating the probability of extraterrestrial intelligence, and if you go through those factors, and do estimates, we can do some of those factors now. Very good. The ones from astronomy, we can do very good. We have now good estimates on star formation rates, on planetary formation around stars, around the possibility of habitable planets. Even in our own solar system, we have a number of targets of astrobiological interest, so we can do well in astronomy and planetary science. We can't quite do as well in the biology factors in the probability that we can say about evolution, because we only have one example, us. So, there's only been one example of the evolution to intelligence, and I hypothesized earlier it could be an accident, in which case the probability is very, very small. In the book, I try to take these numbers, and play with them, and I give a range for what are good guesses based on literature. Then I try to give my own personal guess. What do you know? When I do my own personal guess, the answer comes out to one. We're it. Even in the book, I make it very clear. I might be wrong. I have no special knowledge that says that I can estimate those factors any better than anyone else.

Sarah Al-Ahmed: I was actually really grateful that you took the time in the book to put in your own guesstimates for the terms in the Drake equation, because I feel like so many people are reticent to do that. They don't want to be called out for getting anything wrong, but it's helpful to know that potentially, we really are the only intelligent, technologically advanced species in our galaxy. It would be a little stunning, and I'm trying to still not be sad about it. I'm trying to allow it to make me just more grateful for us and for earth and our ability to even look out and wonder at all. It could make us very, very special.

Louis Friedman: Well, I emphasize... Now, here's a nice thing. I can write these things, and I can deal with these subjects. I have a certain amount of familiarity with it, so maybe my opinion is worth something, but I could be wrong. The nice thing is probably no one's going to prove me wrong in my lifetime. In fact, in the book, there's an introduction or a forward by Mae Jemison who has a very different view about interstellar travel than I do. We discuss it a lot, and she discusses it in the book, but we both agree on one thing. If she's right or I'm right, neither one of us is going to be proved right or wrong in our lifetimes, because the pace of that is just too long.

Sarah Al-Ahmed: Something I think about a lot too with the Drake equation is that for me at least, the greatest limiting factor is this uncertainty and how long humanity will stick around. I love that you began one of the chapters with this idea of maybe intelligence doesn't necessarily help us survive. I think a lot of people think of intelligence as the ultimate pinnacle adaptation, but you think about it like no dolphin ever caused climate change. Try to imagine explaining to your dog the 40-hour workweek or health insurance premiums. Our intelligence is great, and it allows us to explore the universe in ways that other creatures can't, but it might not be the greatest adaptation ever.

Louis Friedman: Well, it's a profound point that you raised, because our intelligence makes us uniquely aware of the universe. We're the only species that is really aware of the universe, and the only species that has produced something that we can show the universe. We have a technology that we can actually send things out there, and show ourselves to the universe. That's profound. But in that same 600 years of technology development, out of the four-million-year history of earth, we've developed various existential threats like you mentioned climate change. We can mention nuclear winter. We can mention pandemics. There's a number of existential threats that we have developed in a very short time. We're developing one right now called artificial intelligence, which no one knows exactly where that's leading. That may be the future of our evolution. So, the idea that we can, in a very short time, gain this knowledge about the universe, and then threaten our very existence with it is again profound. It's why I love this subject so much, because even I have these opinions which make you say are negative about being alone in the universe or reaching other stars. It doesn't matter so much yet whether my opinion is right or wrong. It allows me to think about these really profound questions, and maybe contribute a little to them.

Sarah Al-Ahmed: I love that you bring AI up in this context, because there's a lot of questions around artificial intelligence that you dance around in the book. Could AI be considered life? What even is life, and is AI going to be the tool along with robotics that actually allows us not necessarily to take ourselves to the stars, but to explore space from home through their experiences? Especially at a time now where AI is exploding, I love those questions.

Louis Friedman: I confess that after I finished this book, I got more interested in AI. It's possible that the search for extra terrestrial intelligence, and the search for extra terrestrial life as we explore other worlds, what we see out there may give us hints. If we found, for example, remnants of a living species but no living species, we find no organic life whatsoever, but we find Teco signature's still present, or we find an artificial intelligence, some self-replicating robots roaming the universe. If we ever found that, that would be a clue as to where we're evolving to perhaps. So, it may be that the search for terrestrial and life may actually be a test about the future of human evolution.

Sarah Al-Ahmed: I've heard these ideas before that maybe intelligent life is rare, but they spread AI and technology throughout the universe, and maybe they're just not messing with us because we're not at that phase yet.

Louis Friedman: It might be. I mean, you can always... There's lots of conjectures you can have. One of the things that turned me off to SETI as a scientific discipline was the lack of... I'm not saying it right. I was going to say the lack of a hypothesis to be tested. That's not quite correct. There's too many hypotheses to test. There's no way to winnow it down. When The Planetary Society first got into SETI back in 19... I guess it was '83. It was with Professor Paul Horowitz at Harvard University, and he had come up with a... He working with Carl Sagan actually had come up with a technique for searching based on the idea that there might be magic frequencies for interstellar communications, that certain frequencies were the right places to search. I thought that was very helpful and that at least could be tested. Unfortunately, Paul Horowitz within a year after coming up with that notion had to put it aside, because he also figured out that interstellar scintillations rendered the idea of any specific frequency being a good one irrelevant. So, the search then became we have to look everywhere at every frequency, and that to me is no different than walking out into a field, and trying to look for alien artifacts.

Sarah Al-Ahmed: We'll be right back with the rest of my interview with Lou Friedman after the short break.

Bill Nye: Greetings, Bill Nye here, CEO of The Planetary Society. Thanks to you, our LightSail program is our greatest shared accomplishment. Our LightSail two spacecraft was in space for more than three years, from June 2019 to November 2022, and successfully used sunlight to change its orbit around Earth. Because of your support, our members demonstrated that highly maneuverable solar sailing is possible. Now, it's time for the next chapter In the LightSail's continuing mission. We need to educate the world about the possibilities of solar sailing by sharing the remarkable story of LightSail with scientists, engineers, and space enthusiasts around the world. We're going to publish a commemorative book for your mission. It will be filled with all the best images captured by LightSail from space, as well as chapters describing the development of the mission, stories from the launch, and its technical results to help ensure that this key technology is adopted by future missions. Along with the book, we will be doing one of the most important tasks of any project. We'll be disseminating our findings in scientific journals at conferences and other events, and we'll build a master archive of all the mission data. So, every bit of information we've collected will be available to engineers, scientists, and future missions anywhere. In short, there's still a lot to do with LightSail, and that's where you come in. As a member of the LightSail Mission team, we need your support to secure LightSail's legacy with all of these projects. Visit to make your gift today. LightSail is your story, your success, your legacy, and it's making a valuable contribution to the future of solar sailing and space exploration. Your donation will help us continue to share the successful story of LightSail. Thank you.

Sarah Al-Ahmed: We finally have the James Webb Space Telescope out there. It's finally analyzing the atmospheres of worlds, but this is just the beginning, and you proposed some really cool technologies in this book that could help take us to the whole next step with this. Not to get super into the weeds on it, but you proposed potentially using the sun to help us look at these other worlds rather than building the biggest telescope ever. Could you explain a little bit about solar gravitational lenses?

Louis Friedman: Sure. No matter what, no matter what we do, we're limited in earth-based telescopes looking at planets around other stars. We can't see any planet that would occupy more than one pixel, in fact, a fraction of a pixel, a pixel in any telescope. To build a telescope that would be able to actually see a planet larger than one pixel, we would have to build a telescope that would be almost 100 kilometers in diameter, 100 kilometers, not meters, not feet, not inches, 100 kilometers in diameter. Impossible. Then of course... So, the web, as good as it is, and very large arrays as good as they are, and the now plans for the extremely large telescope that will hopefully be available in the 2030s, or the 30-meter telescope that they're trying to build in Hawaii, they'll be terrific, but they still will not get any planet that will be larger than a fraction of a pixel. However, nature has a telescope for us, and that's the solar gravity lens. Going back to thinking about light and Einstein's theory of relativity, one of the first experiments to prove Einstein's theory of relativity right was the bending of light when it passed the sun. It was observed during a solar eclipse, and that discovery was made. Everybody realized that he was right. Space time is curved. It's warped, and even light doesn't travel in straight lines. It'll get bent by the effect of gravity. So, when light from a distant star or a distant planet goes by the sun, it gets bent slightly. So if you think of a planet far behind the sun, and the light passing the sun, if it's past the sun on one side, it'll get bent down. If it passes the sun on the other side, it'll get bent up, and eventually, those two lines will intersect, and that's called the focus so that there's a natural thing called the solar gravity lens focus. If you work out the numbers, it comes out to that focal. The first focal point is 600 astronomical, 547 astronomical units from the sun. So if we could send a spacecraft out to 547 astronomical units, we would be at the focus of light from a distance star or a distant planet, but it's not just a focal point. Light gets bent at different distances, and as it gets a little further away from the sun, the bending isn't as much. So, it's really a focal line that starts at 547 au, and goes out to infinity actually. But for hundreds of astronomical units, if we had a spacecraft with a modest telescope, even less than a one-meter telescope, we could get a hundred billion times magnification, 10 to the 11th, a hundred billion times magnification of that exoplanet's light. That gives us a chance to actually resolve features on that exoplanet. That would be kilometer scale in dimension that we could see continents. We could see oceans. We could see forests if they existed. If there was technology there, we could see their buildings or their roads. That's the only way. There's no other way we can ever resolve an exoplanet at kilometer scale resolution. That to me was the new discovery that motivated much of what I wanted to write about in the book, because all we have to do... We don't have to get to interstellar distances. All we have to do is get to 600 astronomical units. That's a lot easier than 250,000 astronomical units, and of course, it's a big but. We have only gotten a quarter of that distance with the voyagers after 35 years of flight, and it's still very daunting. Getting out to that kind of distance is still beyond missions of today's decade. We're not going to do it in this decade. We could do it in the next decade. What was nice is that we found a low cost way of doing it with the solar sail flying close to the sun, picking up enormous speed, and going out to those distances at say 20 or 30 astronomical units per year. Then in 20 or 30 years, it would get far enough to fly down the focal line with a telescope and image of exoplanets. Because we could do this with small spacecraft, we could do it for many different exoplanets. We could have many different small spacecraft going to the focal lines of different exoplanets, the ones we thought were the most habitable, and maybe that way, we will build up the discovery of extraterrestrial life.

Sarah Al-Ahmed: I don't know if you can see this, but I'm actually wearing my LightSail two necklace right now, because this spacecraft we all worked on together. 50,000 people around the world came together to crowdfund the first fully crowdfunded spacecraft to test this out. I know that the Japanese space agency got there first with their IKAROS mission, proved solar sailing works, but it just feels like we accomplished something together that could make a profound impact on not just exploring other worlds through this solar gravitational lens technology, but maybe even send a few little solar sails out to other star systems. It feels like that's a much more feasible way to do it than to try to send humans in generational ships.

Louis Friedman: There are several accomplishments at The Planetary Society that stand out in my mind, but certainly, getting the LightSail started and built is one of them.

Sarah Al-Ahmed: As part of my onboarding at The Planetary Society, I Actually got your other book, Starsailing: Solar Sails and Interstellar Travel. So if anybody wants any bonus reading content after that, I really recommend that book, because it'll totally broaden your mind about the ways that we can get out there into space.

Louis Friedman: Thank you.

Sarah Al-Ahmed: I did want to ask though, when we're talking about the search for life out there, we usually focus on planets. Even when we're calculating the Drake equation, people are usually thinking about earth-like exoplanets, but as we've established in our solar system, there are many moons out there orbiting larger planets that have subsurface oceans. So, how might that change our calculations of the potential for intelligent life?

Louis Friedman: That's a very good point, Sarah. I'm glad you brought it up, because so much of the literature of search for extraterrestrial life talks about the habitable zone, this magic zone, the Goldilocks region and the solar system where if we're in a little closer to the star or the sun, it's going to be too hot, and you have Venus-like conditions, and not be able to form life, or if you're a little further away, it'll be too cold, and the planets will not have any liquid volatiles that can be conducive to life. So, the notion was that it was a narrow band, and earth fit in that narrow band of the habitable zone. Even in the current literature, something called the Habital Exoplanet catalog of NASA, they make a big deal about talking about the habitable zone, and ranking the planets that are in it by basis of temperature and distance from the sun or their star, but it's really an antiquated idea. As you point out, most of the objects of astrobiological interest in our solar system are not in the habitable zone of our sun. They're out there at Jupiter or at Saturn, or maybe even beyond because we found other ways that the interior of the planet can be warm from the dynamics of their motion around their planet. These moons like Europa, Enceladus, and even Titan, and even Ganymede might be places where there could be niches that have liquid water, and maybe could have organics that could somehow interact, and life could get started. Now, that's a big leap. I'm not really think that's a high probability that we're easily going to find life on moons around other planets, but they're certainly of interest to the biologists in that regard. It leads us to the conclusion, as these exoplanets get discovered, that basically on the average, every star has a planet, and on the average, every star system will have a habitable planet, at least one, maybe many, that potentially habitable in the sense that Europa is potentially habitable, or Enceladus is potentially habitable. If you put those numbers in the Drake equations, basically, some of those probabilities come out to pretty close to one for the probability of finding planets that are potentially habitable and that where life can get going. Astronomers are very excited about extraterrestrial intelligence even or extraterrestrial life, because these numbers are so optimistic. There are so many planets, and there are so many of them that are potentially habitable. There's probably billions of potentially habitable planets even in our galaxy. Got to have one of them has life, right? Got to have one as intelligent. Then you have to talk to the biologists, and they say, "Wait a minute. Calm down. Those numbers may be wonderful for you astronomers. But again, look at the experience on Earth. Only one species has made it, and it's been a very short time." We don't know what that condition is for that evolution to make that leap into intelligence. The book, by the way, has a chapter of an old debate between Carl Sagan and Earnest Mayer, who was an eminent biologist of his time in which they debated the probabilities for extraterrestrial intelligence with Sagan being very positive, and Mayer being very negative.

Sarah Al-Ahmed: There are some really wonderful appendices in this book to add a lot of flare to it. It's funny because I've been having a lot of conversations recently about the potential for life in subsurface oceans, and I've come around to this understanding that even if there is life in those oceans, it might be potentially even more challenging for them to develop technology the way that we have. That might also be my human-centric brain, but it's not like they'll have the lightning to teach them how to make fire and electricity, and trying to launch into space when you have to fill your spaceship with water in order to breathe might be a real challenge. How do you get your telescopes out there when you're under a sheath of ice? That's such a challenge. So even then, it probably makes sense to focus on the rocky terrestrial planets with potentially lakes and oceans.

Louis Friedman: Well, the dolphins and whales haven't done it yet. That's true. They've been here a lot longer. But again, I just caution even you, and you feel... Excuses my pedantic approach here. Don't focus on intelligence. Focus on life. It's a subject that is going to have literally billions of possibilities, and we know nothing about it now. We don't know any other form of life. All we know is that the conditions for it are terrific out there, and there'll be so much to be learned. When we discover extraterrestrial life on exoplanets or if we're lucky under ice at Europa or in the plumes of Enceladus, and we descend into that, it's going to change our thinking. It's going to be like the Copernican revolution was to... It won't change. The stock market probably won't go up, but the whole notion of how we think about ourselves in the universe will change. That's the exciting subject, and that's why I really want to emphasize that exploring for extraterrestrial life, which has billions of venues, and billions of ways of doing it is very exciting, and it's a very optimistic future. Don't focus on intelligence and technology. That is too anthropomorphic.

Sarah Al-Ahmed: There's, at least in my estimation, a good chance that there's microbial life, at least in so many of these locations. The conditions for life with all the elements and the heating conditions are just all over the place. I guess my truest sadness is not necessarily that we won't find intelligent creatures in my life, but that I really want to find any kind of life in my lifetime, and we're all just going to have to hope, but this isn't just about us. This is about the legacy of all those that came before and all of the people that are going to come after that'll be part of the story, because we're just starting. It's wonderful to be part of the generation that begins that hunt. But someday, as you point out in the book, there might be people out there exploring other worlds in VR, and cataloging different types of astrobiology. That's a future I want to build, even if I can't see it.

Louis Friedman: But you have a chance, you have a better chance than me. You have a chance, because these things are moving fast, and even the solar gravity lens mission that I talked about is not being achievable today. It could be started the next decade, and it could be bringing results back in your lifetime. So, maybe you will see the surface of another planet and the things that might be living there. So, don't give up your hope for that.

Sarah Al-Ahmed: I hope so. Plus, there are so many amazing missions that are coming up right now. We've got Europa Clipper to go hang out around Europa, and see what's going on there, but the one I'm really, really hoping gets the funding that it needs is the Mars sample return mission, because we've taken such amazing steps to begin to explore whether or not there was life on Mars in the past, but there's a lot that we can't do with just rovers on another world. We need to get those samples back to earth to really test this hypothesis.

Louis Friedman: Well, I'm very hopeful about Mars sample return in the sense that... Actually, you may not know this, but when I was... Before The Planetary Society, my last job at JPL was head of the Mars program. I led the Mars sample return studies that we were doing then. We had hoped to be flying missions, that mission in the 1980s, and of course that didn't come to pass. So, I feel very close affinity to Mars sample return. I wonder now, given what the difficulties in getting this mission going, and the extraordinary performance of the rovers and our new instruments that we have, whether or not we would be better off exploring many parts of Mars within situ observations, and not going to the expense of bringing the samples back. I could make the argument both ways now, and I'm anxious to see how NASA copes with the difficulty now, because they're having difficulty, and they asset vehicle that they're proposing bag. There's probably going to be more delays on that mission. So, it's a tough question. You get to the practical issues of budget and everything. I wish we had more Mars in situ observations going on as well.

Sarah Al-Ahmed: Yeah, just replicate that Viking land, or experiment as many times as possible. Just send rovers and helicopters everywhere. As we speak, we're just a few days out from our Planetary Society Day of Action. So people right now, we're already gathering to go talk to Congress next week to advocate for this mission's funding and for so many other missions like the VERITAS mission to Venus. There's a lot that needs our advocacy right now, but that's actually a great sign, because it means that there's just so many more missions out there that are about to go explore. It's a wonder that we've reached this point. It wasn't that long ago that humans learned how to make airplanes, let alone fly to other worlds, and pick up samples. It's hard to wrap your brain around. Something else I'm excited that you talked about in the book was this potential for exploring samples from other star systems through interstellar objects. We've only found two of them so far, but it's really cool that our technology to try to find asteroids and comets really to protect our world has resulted in this side effect of potentially someday allowing us to analyze samples from another star system.

Louis Friedman: Now, we actually do that already in a microscopic way, because stardust, that is in the form of cosmic ray particles and other particles hit our atmosphere all the time, and we have these high altitude balloons and airplane flights which have actually sampled that stardust. So in a sense, we already sample interstellar dust, but the idea of being able to sample it from an interstellar surface, an object that came from another solar system would be exciting. This technique that I mentioned that we've been studying with colleagues at JPL and Aerospace Corporation for the last several years of flying a solar sail near the sun, and then flying outward at high speed, we could actually park the solar sail in a low solar orbit, wait for an interstellar object to be discovered, and then quickly rendezvous with it. No other technique could give you that kind of flexibility for matching the speed, and catching up with one. The two that were observed came through the solar system so fast. We were unprepared to do it. If even we were prepared, we couldn't have caught up to them, but going through a technique like that to have an object ready to go catch it would be exciting. If we could do that, it would be a low cost way of interstellar travel. We could even hop on it, and take ourselves to another star. I don't mean ourselves as our bodies, but I meant maybe our artifacts or our transponders or whatever instruments we could carry.

Sarah Al-Ahmed: I'm just left with this feeling that even though these questions are big, even though we might not have the answers in our lifetime, we're right on the edge of something so important. I'm sure that there are kids out there right now who are just about to discover their love of this, and dedicate their whole lives to exploring these worlds, and perhaps someday they're going to look back on this time, and think how cute and innocent it was that we didn't even know how not alone we are.

Louis Friedman: You pointed out that when you were born, there wasn't any exoplanets discovered. When I was born, there was no space travel. All planets were dots of light, and we had never visited anywhere beyond the earth, and never gotten off the earth. So, these things happen, and they change our view very quickly from the very first planetary encounters with Mars and Venus very, very quickly. That is in a matter of a decade or two, developed a field called comparative planetology, which were words that we didn't know about before then, and began comparing what goes on at Venus and Mars with Earth, and learning about the processes that go on at Earth. They taught us much about what happens when a planet has a carbon dioxide atmosphere, and it blankets the whole planet, and keeps the warmth in, and has a runaway greenhouse effect, or when ozone hits the planetary surface, and the toxic effect is on the surface, and dries out everything on the surface. These things weren't known about until we... They're processes that go on earth, but they weren't known about until we started looking at Mars and Venus. I'll tell you one little anecdote that sticks in my mind from another early day of The Planetary Society. We were advocating Venus radar mapping mission for seeing the surface of Venus, and the Wall Street Journal made fun of me, in particular, in an article and of the whole effort. It said something like, "The Planetary Society, an organization which thinks that going to Venus will help us understand earthquakes, ha, ha, ha, ha," their readers said. Well, you know what, it does. It taught us much about tectonic activity and the nature of planetary formation, and allowed us to understand much about not just earthquakes, but of climate in general on earth, and the forces that control our environment. But to them, it was very funny, and it turned out to be just the natural way we do things now to learn about our environment.

Sarah Al-Ahmed: Right. Who's laughing now? All of those synthetic aperture radar instruments out there are teaching us so many amazing things about Venus and other worlds. Thanks for taking all of that heat so that nowadays, we can just look back on it, and be like, "How funny is it that they didn't think that was worthwhile, because it was so worthwhile?" Well, I think that this book actually gives us a much healthier way of thinking about the search for life in the universe, at least for me to temper our understanding of it, but also to understand just how precious and special we are again here on this pale blue dot. I always come back to that thought. I think people will come out of reading this book with a really good understanding of the search, and a really hopeful outlook for what's in our future.

Louis Friedman: Well, thank you for your interest. I hope you're right. It's part of everything I tried to do when we forming The Planetary Society with Carl Sagan and Bruce Murray. I remember one meeting when Carl and Bruce looked at each other, and they said, "You know what we're really doing when we search for extraterrestrial life, we're looking for ourselves," and that's really true. This was a discussion we were having in, I don't know what, 1981 or something like that, right at the very earliest days of both search for extraterrestrial intelligence before exoplanets were even discovered, but they got it. They got it right in the sense that we're really looking for ourselves, trying to understand our relationship between our life here on earth and our evolution as a species and the universe, and all the factors that go into the forces that are around us, whether they be of our environment, whether they be of the natural laws of the physics and the solar system, or the cosmological factors that are going on in the universe.

Sarah Al-Ahmed: This has been a pleasure getting to meet you, and to talk about this book. Thanks, Lou. It's both frustrating and really cool that we live in a time where we don't know the answers to these questions. It feels like we're on the precipice of something genuinely profound. It may take a while before we have definite answers to our questions about life in the universe, but that's okay. We'll learn more about space and ourselves along the way. Lou Friedman's new book, Alone But Not Lonely: Exploring for Extraterrestrial Life, is now available in print and audiobook. While you're on a book bender, you can also look for Lou's other books, Planetary Adventures from Moscow to Mars, Starsailing: Solar Sails and Interstellar Travel, and Human Space Flight from Mars to the Stars. Now, let's check in with Bruce Betts, the chief scientist of The Planetary Society for WhatsApp. Hey, Bruce.

Bruce Betts: Hey, Sarah.

Sarah Al-Ahmed: I just talked to Lou Friedman for the first time. That was a thing.

Bruce Betts: Like first time ever, or first time on the radio?

Sarah Al-Ahmed: First time ever, first time ever talking to any of The Planetary Society co-founders.

Bruce Betts: I hope you had a good time, and that Lou's doing well.

Sarah Al-Ahmed: Yeah, something I really liked, which is something that happens in our conversations often was Lou's dogs just popping in there to say hello. They wanted to be a part of that conversation big time.

Bruce Betts: My impression is they're passionate about life in the universe and ponderings of it.

Sarah Al-Ahmed: Honestly, as we take to the stars, if we ever do, I really hope that we bring our puppies and kitties with us. I bet the cats would deal better on spacecraft than the dogs would, but as soon as they landed on some world, they'd be real happy generations later. But you haven't had a chance to read Lou's new book obviously. It's only just now out on Kindle and things like that, but there's something I've been mulling over in the aftermath of reading that book, which is that I'm not sure if I should be sad about the conclusion that perhaps we're the only intelligent species in our galaxy, or if sad is too uncomplex a word to describe what that is. What are your feelings about life and our galaxy?

Bruce Betts: I have no feelings.

Sarah Al-Ahmed: Well, we know that, Bruce, but I'm asking about your opinion.

Bruce Betts: Oh, like my thoughts? Okay. Well, first of all, it's hard to believe, and I didn't read Lou's book. It's hard to imagine that there's not a more life out there. I take it he was talking intelligent life.

Sarah Al-Ahmed: Oh yeah, there's definitely... There's probably life out there, statistically a [inaudible 00:54:51] conclusions.

Bruce Betts: We don't know.

Sarah Al-Ahmed: We don't know. We haven't encountered it yet, but the likelihood of encountering intelligent species that we can communicate with.

Bruce Betts: I wouldn't go with sad. I'd go with, "Hey, we're special," and if they're out there, then hey, that's cool. If they're not around, then we don't have to worry about them eating us.

Sarah Al-Ahmed: The book actually mentions that too, because sci-fi is so committed to this idea that they're going to come here and conquer earth for, I don't know what, our sandwiches or something.

Bruce Betts: Ooh, could be.

Sarah Al-Ahmed: Where else in the universe are you going to get a sandwich is all I'm saying.

Bruce Betts: Oh, no, you can worry about that. Trust me. Let's look on the dark side.

Sarah Al-Ahmed: All right.

Bruce Betts: Odds are statistically, they're more advanced than we are if they're already intelligent. We've only been technologically capable for a couple hundred years. Why they would come here, and how they would get across the vast expanses of space is why I'm not too concerned. But whether their motivations are noble or nefarious, hopefully distance means we don't have to worry about it.

Sarah Al-Ahmed: So, what's our random space fact this week?

Bruce Betts: Random space fact. Wow, you hurt my brain so much. I need to remember. Oh, hey, this is truly a random space fact. I was looking up a couple things, and I happened to find a coincidence. Hey, large dog.

Sarah Al-Ahmed: See? The dogs are strong.

Bruce Betts: Sorry, he's just thumping. They are. Hey, Max, did you know that the pressure at the center of the earth is about the same, very approximately, as the pressure in Jupiter at which metallic hydrogen starts forming?

Sarah Al-Ahmed: Seriously?

Bruce Betts: Seriously, three to four million atmospheres is where it is. So again, it's sloppy, but it turns out metallic hydrogen, weird stuff.

Sarah Al-Ahmed: I hope that we can confirm that's down inside Jupiter someday, because that is so weird. Really though, if you're listening to this, and you have no idea what liquid metallic hydrogen is, please Google it because wow.

Bruce Betts: Metal.

Sarah Al-Ahmed: Metal.

Bruce Betts: I mean, it's hard to... With that much hydrogen and just the phase diagram of hydrogen, and the fact that you start stripping electrons off, and it becomes crazy metal, it seems incredibly likely that it's down there, and it's got one hell of a magnetic field from something running around conducting. All right, everybody, go up there, and look up in the night sky, and think about nose bumping your neighbor. Thank you and good night.

Sarah Al-Ahmed: We've reached the end of this week's episode of Planetary Radio, but we'll be back next week with my adventures at the 2023 NASA Innovative Advanced Concept Symposium or NIAC. You can help others discover the passion, beauty, and joy of space, science and exploration by leaving a review and a rating on platforms like Apple or Google Podcast. Your feedback not only brightens our day, but also helps other curious minds find their place in space through Planetary Radio. You can also send us your space, thoughts, questions, and poetry at our email at [email protected], or if you're a Planetary Society member, leave a comment in the Planetary radio space in our member community app. Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible by our wonder-filled members. You can join us as we work together to advance space, science, and exploration at Mark Hilverda and Rae Paoletta are our associate producers. Andrew Lucas is our audio editor. Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. Until next week, ad astra.