Planetary Radio • Sep 02, 2020

The Sirens of Mars Call to Us

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Sarah Stewart Johnson

Associate Professor of Planetary Science, Georgetown University

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Mat Kaplan

Senior Communications Adviser and former Host of Planetary Radio for The Planetary Society

Georgetown University planetary scientist Sarah Stewart Johnson has written a beautiful book that chronicles our long quest for life on the Red Planet. That search may finally be reaching a climax with the new Perseverance rover and the beginnings of sample return. A copy of The Sirens of Mars will go to the winner of yet another What’s Up space trivia contest. In a nice coincidence, Bruce Betts will tell us where to find a brilliantly bright Mars in the night sky.

Sirens of Mars
Sirens of Mars Sirens of Mars by Sarah Stewart Johnson book cover.Image: Crown / Penguin Random House
Perseverance on Mars at Sunset
Perseverance on Mars at Sunset This artist's concept shows NASA's Perseverance rover exploring Mars, with the sun low on the horizon.Image: NASA/JPL-Caltech

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Trivia Contest

This week's prizes:

The Sirens of Mars: Searching for Life on Another World

This week's question:

What is the only spacecraft that launched with solar system escape velocity?

To submit your answer:

Complete the contest entry form at or write to us at [email protected] no later than Wednesday, September 9th at 8am Pacific Time. Be sure to include your name and mailing address.

Last week's question:

Assuming a combined Greek and Roman pantheon mythology, within this mythology, which planet (in our solar system) is named after the earliest (oldest) god?


The winner will be revealed next week. 

Question from the 19 August space trivia contest:

As of August, 2020, what is our Mat Kaplan’s single credit in the Internet Movie Database (IMDB)?


As of August, 2020, our Mat Kaplan’s single credit in the Internet Movie Database (IMDB) was for his role in The Fina Medoza Mysteries Podcast as the House Historian.


Mat Kaplan: The sirens of Mars call to us, this week on Planetary Radio. Welcome. I'm Mat Kaplan of The Planetary Society with more of the human adventure across our solar system and beyond. Georgetown University professor and planetary scientist Sarah Stewart Johnson has written a beautiful book she calls The Sirens of Mars: Searching for Life on Another World. We'll spend some time with her in a few moments, and we'll award a copy of the book to the winner of the new space trivia contest Bruce has cooked up for you this week. It's a nice coincidence that Mars is shining bright in the sky right now, and Bruce will tell you where to find it.

Mat Kaplan: Our sympathies and best wishes for a quick recovery go to everyone affected by last week's terrible storms in North America. Before Laura became a hurricane, it was a tropical storm that our own LightSail 2 snapped a picture of. That shot tops the August 28th edition of The Downlink, The Planetary Society's weekly newsletter that you'll find at As spectacular, or even more so, is the shadow of Japan's Hayabusa2 spacecraft against asteroid Ryugu. This was minutes after the probe collected the first of two samples that are now speeding Earthward. The James Webb Space Telescope passed a couple of important tests. We're now just over a year from its planned launch. And China is looking for partners. Russia and the European Space Agency have responded to calls for collaboration on a lunar base that could be visited by humans in the early 2030s. There's much, much more waiting for you in The Downlink, with a new edition every Friday.

Mat Kaplan: Last week, we looked toward the end of the universe with Katie Mack. This time, we join the search for life right next door. Sarah Stewart Johnson has written a wonderful book about humankind's fascination with the red planet for ... Oh, let's say forever, or at least since our ancestors noticed that red star wandering the sky. Speculation about life on Mars also goes back very far, but it's only in the last six decades that we have been visiting. Sarah is in the thick of our quest for Martian biosignatures, signs that life may have existed up there billions of years before it seems to have appeared on Earth. It has been a troubled search, full of wrong turns and disappointments. But now, with the rover called Perseverance and the beginning of sample return, we may be on the edge of a discovery that will shake our own world. All of this is chronicled in The Sirens of Mars: Searching for Life on Another World, published by Crown.

Mat Kaplan: The great writing reminds me of Sasha Sagan's For Small Creatures Such as We, which is a high compliment. Sarah is Associate Professor of Planetary Science at Georgetown University in Washington, D.C., where her lab focuses on how we find and recognize life. She has been part of the teams behind the Spirit, Opportunity, and Curiosity rovers, and is a visiting scientist with the Planetary Environments Lab at NASA Goddard. I talked a few days ago with this former Rhodes scholar and White House Fellow. Sarah, thank you very much for joining us on Planetary Radio, and thank you for this really lovely lyrical book, which I just so much enjoyed reading.

Sarah Stewart Johnson: Oh, thank you, Mat, and thanks so much for having me.

Mat Kaplan: You grabbed me right from the start of this book, not just because I love the story you tell about our search for and our fascination with life on Mars, but because of how well you tell it. In the book's prologue, you talk about a lake in the far reaches of Australia. Here's a quote from that. I'm going to read it.

Mat Kaplan: "In the right place with a good grip, you can pull out a crystal of gypsum, severed like a shark's tooth from the jaw of the Earth. The spear-tipped blades are as large as your hand. When you rinse away the red mud and hold it to the light, it flashes in the sun like a gemstone. Under a microscope, you can see the tiniest of pockets within it, glinting drops of lake water, sheathed in mineral hideaways: life caught in a crystalline dagger."

Mat Kaplan: Life caught in a crystalline dagger; that's how you caught me. It's beautiful. And of course, that's your theme in the book, this ongoing search for life on this other, nearby world that is still far enough away that it's been a very slow process discovering more about it. Before we really get into the book, could you talk a little bit about what you do at Georgetown? Are you in your lab?

Sarah Stewart Johnson: Sure. So I'm a planetary science professor and an astrobiologist. And the focus of our lab is in biosignature detection, so looking for biosignatures or traces of life in planetary environments. So part of what we do is we try to understand how these signatures of life can be preserved over time. We go out to these analog environments, places here on Earth that bear relevant similarities to other planetary environments, like the ancient terrain on Mars. And we really try to learn how to look, and trying to test out different approaches and different techniques. But then a big part of the lab also is analyzing data from current spacecraft and trying to design concepts for future missions, for future instruments.

Mat Kaplan: There's another Sarah who has been on our show, and is in kind of the same line of work, Sarah Hörst at Johns Hopkins. You seem to be in the same business.

Sarah Stewart Johnson: Oh, we are. Sarah's a good friend. Sarah's just fantastic. She's really focused on the outer moons, moons of the outer planets, whereas I'm a little closer to home, focused on Mars. But she's just a terrific scientist and one of my favorite folks to follow on Twitter.

Mat Kaplan: There is of course life as we know it, which is largely what we have been looking for on Mars. But I know that you also are fascinated by the search for life as we don't know it. Is that something that you're also working on?

Sarah Stewart Johnson: Oh, it is, indeed. We're funded by NASA for this project that we've been calling the Laboratory for Agnostic Biosignatures. And that's really what we're after, trying to find signs of life that don't presuppose any particular molecular framework or any specific underlying biochemistry. It's a big challenge because we have developed these incredibly robust ways to look for biosignatures that are associated with life as we know it. We could go out into the extreme environments here on Earth where there's very little life to begin with and use these techniques. We can use them to understand the earliest history of our own planet, looking at how certain types of molecules are preserved over geologic time.

Sarah Stewart Johnson: But what we're doing here is really looking for ways that we could detect things that are just really beyond the confines of our current thinking. So looking for things like chemical complexity or energy transfer or accumulations of elements or isotopes that are really different from what you'd expect from abiotic processes alone. Sometimes, it feels like trying to imagine a color that you've never seen before. But it's one of the most exciting things that my lab is working on right now. I feel like it's a great intellectual challenge, but it's also great fun trying to imagine what other types of life we could be looking for.

Mat Kaplan: It is absolutely fascinating, something that we love to talk about on the show from time to time because it does take us into such uncharted territory. Let me ask you a couple of questions, and these are things that you cover in the book as well about how you got into all of this. And I'm thinking of an experience that you had with your father many years ago that seems to partially explain how your heart as well as your mind were first captured by Mars and the night sky. It was a trip you made out to the desert with your father?

Sarah Stewart Johnson: So that was when I was in my early 20s. My father had always been something of an amateur astronomer, an amateur geologist. He would like to look at the night sky with a [inaudible 00:08:42] ... I mean, he had a pair of binoculars for most of my childhood, and then he got a telescope when I was older. He also liked to drive over by the side of road cuts along highways in the Appalachian Mountains and go look at rocks. But he never really liked flying. And we never traveled far beyond the state line when I was growing up.

Sarah Stewart Johnson: But I was able to convince him, when I was about 21 or 22, to get on an airplane with me and go out to Tucson. We rented a car and we drove up to this little observatory that was called the Vega–Bray Observatory, and we spent a few days there. The greatest thing about this little place, they had telescopes. They were these medium-range telescopes where you could look at a dot in the night sky, you could look at the telescope directly pointed at that dot and you realized, "Oh, wow, that one's got all of these incredible moons and that polar cap. That's what that little white dot at the top of this world. And this one has all of these rings." I mean, it was just an incredible experience. And it's something that I think can sometimes be lost in the age of modern astronomy because for a long time, every practitioner had a direct relationship with the night sky. And now so much of astronomy's done via computer, and you're not sitting out in the middle of the desert. But there was something absolutely incredible about that moment, and I'll never forget it.

Mat Kaplan: You remind me of one of the terrific individuals that you talk about in the book, Galileo, who I knew was the first to see Mars as a sphere, but I did not know that he speculated on whether it might be a world like our own.

Sarah Stewart Johnson: He did. Really, one of the best things about writing the book was getting to dive into some of the history and all of my predecessors, these planetary scientists in one form or another, stretching all the way back to Galileo. And he did speculate that there could be a world there. And he didn't want to pass judgment on what might be existing there, but he did write a letter to a colleague saying that there could be inhabitants. He mentions the possibility, but said he would leave it to others wiser than him.

Mat Kaplan: Yeah. I'm also thinking of an experience that you say in the book made you a planetary scientist. You were in Hawaii. It had to do with both the beauty and the tenacity of life.

Sarah Stewart Johnson: Yes. I had this incredible professor named Ray Arvidson as an undergraduate at Washington University in St. Louis. And he took all of us in a class that he was teaching off to the Big Island of Hawaii on a field trip. There was this moment when we were exploring the summit of Mauna Kea, which is this huge volcano. And you drive up the side of the volcano and you pass the end of the tree line, you pass the last of the scrub, and you even have to stop to acclimatize for a few hours because the oxygen is so thin by the time you get to the very summit. And there are a lot of telescopes up there.

Sarah Stewart Johnson: But we were walking around this terrain, hiking about, and there's just nothing green in sight. It looks almost like a crystallized bruise. It's all shards of black and gray and purple. And I was walking around kicking at some of those volcanic rocks and at one point, one turned over and I saw that there was the smallest little fern that was growing there, just against all odds. It was just the most tenacious, beautiful thing that I had seen. And it just seemed like that fern stood for all of us in this vast emptiness, this huge wasteland. There was just this tiny splash of life. There really was something in that moment that I think made me become a planetary scientist, or just made this idea of searching for life in the universe make sense to me.

Mat Kaplan: It's a striking moment, and obviously one that had great influence over you. Your studies and your work seem to have taken you all over our planet, and to simulations of places that aren't on our planet. I'm thinking now of work that you did years ago with simulated Martian dust at NASA Ames, which is another great passage in the book.

Sarah Stewart Johnson: Yes, yes. That was a great summer. It must have been between my sophomore and junior year in college, and I got to be part of something called NASA's Astrobiology Academy, which was just the best program you can imagine. I was living on the campus of Stanford University in a big house with all these other interns that were interested in astrobiology. And I had a research placement in this giant wind tunnel, the Mars Wind Tunnel, that was at Ames, NASA's Ames Research Center. It was this extraordinarily large cavern. They'd used it originally to test buffeting of rockets. But the whole chamber could be pumped down to different pressures. So, you could pump it down to just six millibars, which is six one-thousandths of our terrestrial atmospheric pressure.

Sarah Stewart Johnson: We would do these experiments simulating how dust would flow through this laminar flow wind tunnel and how it would settle onto the panels of spacecraft. We were trying to figure out what the attenuation in power would be when the Mars Polar Lander reached the planet. It was just this incredible experience to really feel like we had our hands on the controls of this massive machine that could change fundamental things in our physical world.

Sarah Stewart Johnson: And there's a moment I describe in the book where I got to watch this cup of water that we put just on the other side of a thick pane of glass. And one of the graduate students had suggested this would be a fun thing to do. And we watched as the pressure pumped down and down and down. And there was a moment where the water started to bubble and it started to boil. Then all of a sudden, right in the middle, this shock appeared, and it was just impossible. It was impossible. But we were passing through the trickle point, the point at which the temperature and pressure conditions are such that water can exist as a liquid, a gas, and a solid at the same time. But it was just one of these reminders of just how incredibly alien Mars is. As much as it seems familiar, it's the planet that's most like the Earth that we've ever found. Of all the planets we've discovered in the night sky, it's still just indescribably foreign.

Mat Kaplan: Just wonderful. And that dust got into everything, didn't it, as some of it stayed with you?

Sarah Stewart Johnson: I do. I remember thinking as I wrote the book, OSHA probably would not like me talking about how I have all of this dust [inaudible 00:15:51]. Oh my goodness, the fingerprints in the cracks of the seats in the van, and it would fall out from my clothes onto the floorboards of this old house we were all living in on Stanford's campus.

Mat Kaplan: Probably a grain or two of it left in your lungs, which I'm sure will not do any damage, but it's kind of romantic to think so. Kind of like the people I know, the great science fiction writer, Kim Stanley Robinson, who told the story on our show of how he bought a bit of a Mars meteorite, went up on his roof looking at Mars, and ate it so that it would be incorporated into his body.

Sarah Stewart Johnson: There you have it. That's great. That's such a great story.

Mat Kaplan: You divide the book up into three major sections. The titles of each are drawn from Euclid and his geometry, and the scope expands from section to section, like from a point to a line. Is there a metaphor here for our expanding knowledge of Mars?

Sarah Stewart Johnson: I think so. I think so. I write about that a bit in the last chapter of the book. Euclid is somebody that had a lot of influence on me, especially when I was younger. For a while, I sort of toyed with the idea of becoming a mathematician. And I had really found so much beauty and meaning in how Euclid had built this understanding of the world, especially encapsulated in his beautiful book, Euclid's Elements. And it's really spare and poignant, but it just sort of walks us through, beginning at very first principles, to this incredible system, this understanding of how the natural world works with geometry and with number theory.

Sarah Stewart Johnson: I think I just see that all of our fields of science that we have approached as humanity, we've had to start with these very first principles. And we build and we build and we build. And especially that's so clear with Mars. I mean, Mars was a point of light in the night sky. And really, over the last 50 years, since the dawn of the space age, and we've been able to send missions. And starting in 1965 we had our first pictures of that planet and we've had so many blind alleys and twists and turns, and all these things that have resulted in this truer understanding of this distant world. And there just seems to be lots of parallels there, to me.

Mat Kaplan: More of Sarah Stewart Johnson and The Sirens of Mars is coming right after this break.

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Mat Kaplan: I'm so glad you mentioned those first close-up pictures of Mars. The book is a wonderful chronicle of, really, the history of Mars exploration and speculation. And there are these wonderful characters whose life you take us into. One of them is Bob Leighton of the Jet Propulsion Lab. Can you tell us about him and what he accomplished? Because I think we can largely thank him for those images from Mariner 4.

Sarah Stewart Johnson: Absolutely. And I guess it's hard to understand now, but there really was this time where one of the prevailing views was that pictures. Pictures were public relationships. Pictures weren't science.

Mat Kaplan: Right, right.

Sarah Stewart Johnson: And we'd sent the Mariner 2 mission to Venus, no cameras there. And when Mariner 4 came along, there was a period in which it was really unclear that there were going to be pictures at all. There was a lot of focus on different types of measurements about temperature and pressure and those types of things. Bob Leighton was somebody that really, really could appreciate the value of an image and what it really meant to see something. He had grown up in Los Angeles. He had a single mom who worked as a maid in a hotel. And he'd been really scrappy, gotten himself through school. And he'd gotten a job working as a photographic assistant at an advertising company. One day, he made a mistake. He threw away a bunch of negatives, and he got his walking papers. And he decided that he'll go back and just go study physics instead, and we can all thank him for that big mistake because he eventually found his way to Caltech and he stayed there the rest of his career.

Sarah Stewart Johnson: Even as a young professor, he would spend a lot of time up at Mount Wilson, and he would make these beautiful movies of Mars using those great telescopes. He'd have to use them on holidays, times where other people weren't using them. And I think there was a big feeling at the moment that planets, they were too close and too cold. They couldn't really tell us really important things about the nature of the universe. There was a lot of pressure to be looking out further. But he really liked looking at Mars and he made these beautiful color images. Then one of his students had ties to JPL and said, "You've got to propose this instrument," and he did. He proposed this incredible instrument that ended up taking 21 photographs in a few lines, and the 22nd photograph as Mariner 4 swept across the surface of Mars in a fly-by of 1965, in July of that year.

Mat Kaplan: Unfortunately, those pictures caused a great deal of disillusionment, disappointment for Mars scientists. And there seemed to have been more than one period of disillusionment as we have studied the red planet. Not just failed missions, because we've had some of those too, but missions like Mariner 4 that indicated, at least at first glance, that the chance of life on Mars was slim or nil. So another great story you tell along these lines is of one of our three cofounders of The Planetary Society, Carl Sagan, who of course was an early big believer in the importance of images of these places that our robotic ambassadors were visiting, along with Bruce Murray, who was a real fighter for putting cameras on spacecraft; the former director of JPL, of course. But Carl, I guess I'm thinking more in terms of the Viking mission here, which Carl really fought to make sure would be life detection missions, and even wanted to make sure there was a camera that could capture anything crawling across the surface. He took a lot of heat for some of these positions, didn't he?

Sarah Stewart Johnson: Oh, he did. Carl Sagan will always be a hero of mine. I feel like he's just such a broad thinker, such an imaginative thinker. And even going back before Viking, we had these first images and they were covered with craters. And Mars just looked like the lifeless moon. If the planet had that many craters, it couldn't have had plate tectonics, it couldn't have had the kind of fluvial erosion that we have here on Earth. It was just this desolate, barren, empty surface. And The New York Times, after those first images were released, had declared their staggering disappointment that Mars was probably a dead planet.

Sarah Stewart Johnson: Carl Sagan, never one to be dissuaded, he had taken a set of images, not just from Mariner 4, but the following fly-by missions, and he found a parallel set of images that were at the same resolution of the Earth. And he looked at them and he said, "This is astonishing. Here's this world that's completely covered by life, not just life, but intelligent life." And you can't tell at that scale. You could not see these major cities. They're just invisible at that scale. And even when you get to higher resolution looking at some of the images taken the Apollo and the Gemini astronauts, you still couldn't really make sense of it unless you knew what you were looking for, a road or the edge of a tilled field. Those would only make sense if you knew what it is you were trying to see. So, I loved that story.

Sarah Stewart Johnson: And even going into the Viking mission, so there were these life detection experiments that were part of Viking. And Carl Sagan was part of a different team. He was on the imaging team. And he said, "Well, hold on. These cameras are the instrument, just with a single measurement, might be able to detect life." He really pushed to have these cameras that were working and imaging. And even if something walked by and we couldn't see it, he wanted to be able to image the footprints.

Sarah Stewart Johnson: One of my favorite concepts, hypotheses that he had was that we might even find what he called macrobes on Mars, as opposed to microbes. He theorized that because it was so cold and so very dry, that conservation of heat and moisture were going to be critical for organisms in this sort of environment. And as a small cell, you had not so much volume but a lot of surface area. But if you were a very large creature, you would have much less surface area per volume, so it would make it easier for you to conserve heat and moisture. And he said, "Evolution could have favored these very, very large creatures." And this was of course a time where polar bears were out and roaming the tundra, these ecosystems that were really now coming into the popular imagination as habitats. And he said, "We could find these huge petrophages or crystophages that are living there on the surface of the planet. And we shouldn't be too quick to write off these large creatures."

Mat Kaplan: And even though we didn't find them, he sure thought about these things in wonderful, novel ways. And in some ways he wasn't that far off, because you later describe one of the great reversals of this disappointment about the surface when we realized, when we learned, that there was a lot of water on Mars, you just had to look under the surface. You had to dig for it. Like you, I was thrilled when the Phoenix Lander began to scrap away at the surface. Remind us of what it found.

Sarah Stewart Johnson: The Phoenix Lander was a great mission. It was only a few months. It wasn't sort of like Opportunity, that lasted 15 years. But in those few months there, in those cold, polar conditions, Phoenix had a scoop. And once it got under the Martian soil, found this incredibly gleaming white patch. And there was so much excitement. And pretty clearly, we realized that that couldn't be salt. That had to be actual ice and water ice. And the chemical experiments confirmed that. Then we had all kinds of orbital missions as well that have detected subsurface ice. And we've found gullies, we've found all kinds of evidence for thin films of water. So it's not just the ancient water, but there still is a fair amount of water, swimming pools and swimming pools worth of water that's locked into the shallow subsurface and, of course, the polar caps of Mars.

Mat Kaplan: I also want to thank you on behalf of The Planetary Society for mentioning the special cargo that Phoenix brought to the red planet, that mini DVD ... sort of a library of Mars.

Sarah Stewart Johnson: Yes. It was a wonderful effort by The Planetary Society. It is so funny to think of it now, that there was a period when those mini DVDs were all the rage. And of course now they seem very dated. But recorded onto that mini DVD were these ... this tremendous collection, a whole library. And they include early science fiction writers. They go back all the way to Voltaire including a beautiful Micromegas story which I also write about in the book. It has people talking and telling stories, and Arthur C. Clarke next to a waterfall talking about his hopes and his imaginings. And it's just the most marvelous expression of our humanity. And to think that it will be preserved on the surface for millennia to come. It might even outlast our own civilization. It's just a very profound thing to contemplate.

Mat Kaplan: Again, I'm very glad that you mentioned that story by Voltaire, Micromegas, about this gigantic alien, I mean, really gigantic, who visits Earth and is shocked to find life that is unlike any he has ever known. It actually reminds me of the Dr. Seuss book that my grandson most loves for me to read to him, Horton Hears a Who!, because, "A person's a person, no matter how small." Lots of parallels there to the work that you do.

Sarah Stewart Johnson: That's such a great book. I know it well. Yeah, and it's so funny that even Voltaire, hundreds of years ago, was thinking about these same kinds of ideas. In that story, it's this 120,000-foot tall giant that arrives on Earth. And of course, it looks lifeless. Then eventually, he notices there's this speck down below. And he leans in, and it's a ship that he picks up on the edge of his finger and he examines it. And he eventually can hear the voices of these tiny sailors. And it's just such a nice allegory. It really brings to mind this idea of when we go about searching for life, do we have the scale right? Do we have the time scale right? Do we have the size right? Are we looking in the right space to really find it? Or are we just kind of trapped by our own existence and looking for what we know?

Mat Kaplan: Well put, whether you're describing that story or your own work. There are a lot more of these personal stories in the book. We can't go through all of them, of course. But there is one more I think we should talk about because you devote many pages to the story of Maria Zuber, who eventually became a mentor to you.

Sarah Stewart Johnson: Oh, Maria's just one of those extraordinary scientists. I first heard Maria give a talk when I was in college. And I write about that a bit in the book as well, this moment when I realized it was the first woman I'd ever heard give a talk on planetary science. She was describing the just fantastic results that came back from the Mars Global Surveyor mission, and specifically the MOLA instrument, which was measuring topography in exquisite resolution. I just remember looking at those maps as an undergraduate, sitting in this crowded conference room. And it really shone to me, like a church window. And Maria, who seemed so impossibly small by the podium, I mean, she just took us on this tour de force through the new science. And I was just rapt. It was really quite a moment.

Sarah Stewart Johnson: And then years later, I had the opportunity to study with her at MIT. She agreed to take me on as her PhD advisee. She was able to really pull back the curtain and show me what planetary science was like. She was really at the pinnacle of her field. She was the first woman to ever lead a planetary mission by NASA, so she was breaking glass ceilings left and right. She was also just this incredible person. She had grown up in coal country in Pennsylvania, and had lots of siblings, and her own parents really couldn't quite understand why she stayed in school for as long as she did. But she had gone through as the first person in her high school to ever earn a PhD. Then she's now the Vice Provost for Research at MIT. And she's just the most extraordinary woman, not just as a scientist, but as a human being.

Mat Kaplan: So here we are, 2020. We've learned so much about the red planet, going back to the times of Galileo through Schiaparelli and Lowell, and even the early days of Maria Zuber's career, and Carl Sagan. Now we've got three more missions on their way to Mars, including Perseverance, the descendant of Curiosity, but the first to go back to the red planet since Viking that will actually be headed there to actively look for life. This has got to be very exciting for you.

Sarah Stewart Johnson: Indeed, it's like a watershed moment. We had this lull, 20 years after Viking, no Mars missions. Then we started back in the late '90s with this idea that we would follow the water. Then we just kept finding the water and finding the water and finding the water. Then the next step was to look for signs of habitability to really understand the context for life. And with the Curiosity rover mission, we've also definitively found evidence of ancient, habitable environments, places that have the ingredients, the essential elements for life as we know it, as well as the building blocks, those organic molecules from which a house of life can be built. Now we are finally, finally moving back to actively looking for biosignatures. So Perseverance is going to kick off this breathtakingly ambitious campaign to collect samples from Jezero crater, this exquisitely preserved river delta there on the surface of Mars, and then bring them back to Earth for study in different laboratories, to look for evidence of ancient life.

Mat Kaplan: Awfully exciting, which is why we frequently talk about it on Planetary Radio. Let me ask you, both as a scientist and someone who feels what our boss calls the passion, beauty, and joy of all of this, if Perseverance does its job, maybe doesn't even have to wait for sample return but maybe its microscope, after drilling down a little bit, finds something that looks an awful lot like evidence of past life, maybe microbial life on Mars, what will that mean to you and to science and to humanity?

Sarah Stewart Johnson: Well, I have to say, I'm not getting my hopes up too high for the immediate primary mission because one of the things that we could find, I mean, it would be incredible if we looked into some ancient terrain and we found something that looked like a stromatolite from this ancient lake. But even so, I think about here on Earth, we are having huge debates over what is and what isn't life in the ancient rock record. And part of that is we have this overprinting of life and contamination. But we've really wanted to study those samples carefully to really be able to say definitively, "Okay, this was certainly life." It may be in many ways easier to find life on Mars because we aren't messing with the signals in the same way that we are here on Earth. We haven't swallowed so much of the ancient crust. Those rocks have not been metamorphosed.

Sarah Stewart Johnson: But getting back to your original question, if we were to find something that looked like a smoking gun and especially once we had that back in our labs and we were able to confirm with multiple lines of evidence that this really looks like the real thing, I just think it would be one of the greatest discoveries in the history of modern science. We simply have one data point for life. All the life that we know of is exactly the same. It's this DNA-based stuff, carbon-based us. And if we had another data point, especially if it was a separate genesis, I just think that would be transformational. It would really get to so many of the fundamental questions we have about whether biology is just a consequence of energetic systems, and how different biologies might come into being. And I also think it would just be another Copernican revolution in terms of how we see our place in the universe.

Mat Kaplan: Another Copernican revolution. My fingers are crossed. I got just one more question for you before I ask you to read a particularly lovely passage from the last chapter of the book. And this question, really, it's a thread that has run through our conversation, runs through many conversations I have with researchers on this show, how is the story of Mars also a story about Earth?

Sarah Stewart Johnson: I like that question a lot. Science, it's not just about the science. It never is. Our exploration of Mars is about our human relationship to the planet. And we have brought so much passion and ingenuity, drive and just yearning to the search for life that I think is so reflective of who we are as a curious species. And in many ways, that's why I wanted to write the book because I just thought Mars needed a different type of treatment. There were just so many things that were poignant and beautiful and compelling about the endeavor, that I just don't ever think would ever find expression on the pages of scientific journals. And there's just so much about the mystery and the wonder of this quest. And I guess that's what I hope I accomplished with the project.

Mat Kaplan: I can assure you, speaking for myself, you absolutely did. And it is why I recommend this book so highly. Would you please take on reading this little passage that I sent you from the last chapter? Before you do, you're going to have to define one word, an ancient Egyptian term, am I pronouncing this correctly, akhet?

Sarah Stewart Johnson: I think that's right. We're not actually sure how it's pronounced because the vowels have been lost to history. It's just the hieroglyph from which we've reconstructed the word, just with its consonants. But this was one of the seasons, the ancient Egyptians, there would be the flooding, the repeated flooding of the Nile delta. And as the waters would come in, there would be this moment, the end of akhet when the waters would recede and you would finally be able to have solid ground once again.

Sarah Stewart Johnson: The quote, which is from the final chapter of the book, it starts with, "What if life is a consequence of energetic systems? What if the nothing to something has happened time and again, and because of the chinks in our cavern are so small, we don't know it? For me, this is what the search for life amounts to. It is not just the search for the other or for companionship, nor is it just the search for knowledge. It is the search for infinity, the search for evidence that our capacious universe might hold life elsewhere in a different place or at a different time or in a different form. That confirmation would be a rebuke to the cratered image of Mars, the acid waters, the sterile soil. It would stand in contradistinction to the finite life to which we are confined, to the finite planet we inhabit. Finding life, even if it is the smallest microbe, would, for me, be the end of akhet. It would be the first dry mound emerging from the limitless dark water, an actual fact about the actual world, a truth, a beginning. It would be a shimmering hope that life might not be an ephemeral thing, even if we are."

Mat Kaplan: Just beautiful, Sarah. Thank you so much for reading that and for giving us this book, The Sirens of Mars: Searching for Life on Another World, published by Random House, a division of Penguin Random House. And here's a word to the wise: if you stick around for this week's What's Up segment, Bruce and I will mention that you might win a copy of The Sirens of Mars in this week's space trivia contest. Again, Sarah, thank you. Best of continued success as you continue your work there at Georgetown and across the void to Mars. And by the way, congratulations on achieving tenure at Georgetown University.

Sarah Stewart Johnson: Thank you, Mat. Thank you. I really appreciate it. It was such a pleasure to chat today. Thanks so much for having me on the show.

Mat Kaplan: Sarah Stewart Johnson, planetary scientist, seeker of life, and newly published author of The Sirens of Mars, which you'll have a chance to win as we head into What's Up. Time for What's Up on Planetary Radio, starring the chief scientist of The Planetary Society. Welcome, Bruce Betts, who has ... I haven't actually looked myself, but I am told six different listings in the IMDb.

Bruce Betts: Yes, and they're missing a couple from blockbuster movies that I did.

Mat Kaplan: All right. Well, if that's a mystery to you, why I brought this up, it won't be when we get to answering the contest this week, coming up with that. All will become clear as is, I hope, the sky over your head tonight so that you can see the things that Bruce is going to tell us about.

Bruce Betts: Nice. Nice. Well played, sir. Yes, both evening and predawn are glorious, planet-wise. We've got Jupiter and Saturn up in the south in the early evening, Jupiter being the super bright object, Saturn to its left looking yellowish. And also now coming up in the early evening, we've got Mars getting brighter and brighter through early October. And it is brighter than any star in the sky, though still not quite as bright as Jupiter, looking reddish over in the east. And wait, if you look at it on September 5th, the evening of September 5th, the moon will be very close to it. If you happen to be in much of the central portion of South America, the moon will actually go in front of Mars. But if you're not, it won't. But it'll be very close. It'll be within a degree or two moon diameters for pretty much everyone who gets to see it.

Bruce Betts: So, that's September 5th. Then in the predawn, you can't miss Venus. It's going to be getting lower over the coming weeks and months. But it's up there for a while and looking super bright in the east in the predawn. We move on. In this week in space history, I can't believe another year has passed for me to tell you, Mat, hey, Star Trek the original series premiered this week in 1966.

Mat Kaplan: Which is why this is known as Star Trek day. And I think our colleagues at The Society are going to be celebrating that in our social media.

Bruce Betts: Well, we have good friends out of the Star Trek universe.

Mat Kaplan: Yeah, yeah. I think they're going to premiere a very cool video, which I won't talk about, but it's going to be such fun.

Bruce Betts: I would talk about it, but you would probably cut it out, so I will just say it is very, very nice, very cool. And one more this week in space history, 1977, Voyager 1 launched. It's still going, and we'll talk a little bit more about it in just a moment as we get to Random Space Fact.

Mat Kaplan: Oh, don't be sad.

Bruce Betts: I don't know what came over me. It's more of a happy emotion with Voyager. So every year, Voyager 1, as it heads out of the solar system, every year, Voyager 1 travels about six times the Earth to Mars' closest distance.

Mat Kaplan: Just racing on out there. It's amazing.

Bruce Betts: Okay, let's move on to the trivia contest. I said as of now, August 2020, what is our Mat Kaplan's one credit on IMDb, the Internet Movie Database? How'd we do, Mat? Was it weird for you?

Mat Kaplan: It was, yeah, odd. It was decidedly odd. Before we get to the answer, here is all the wrong answers from [Mel Powell 00:45:05] in California. He said, "Before I looked it up" ... He made a list of guesses. One, enterprise relief communications officer in Star Trek VI: Undiscovered Country. Two, M4PO, random background droid at Mos Eisley. Or three, FIDO Number Three, uncredited in Apollo 13.

Bruce Betts: Were you any of those, Mat?

Mat Kaplan: I was one of them. I won't tell you which one.

Bruce Betts: Oh, man. That'll be next trivia contest. All right, keep going.

Mat Kaplan: Here's the response from our Poet Laureate, Dave Fairchild in Kansas: "Back in November of 2019, Mat and Mendoza were paired and worked on a mystery sighting of cats that took Fina quite unawares. In episode six, a catastrophe came, and that's how it all came to be that Mat has his name for a single event you can find in the IMDb."

Mat Kaplan: What the heck is he talking about there? It's the Fina Mendoza Mysteries. Yes, that got me a credit, much to my surprise, as you discovered two weeks ago when you posed this question. My very good friend for a million years, Kitty Felde, author, playwright, actress, host, speaker, she wrote this book for kids, Welcome to Washington, Fina Mendoza. Kitty was also a Washington, D.C. reporter for many years and got to know D.C. very well. And it's about this young girl, Fina Mendoza, who is the daughter of a new congressman. She gets involved in this mystery having to do with a cat in the Capitol building.

Mat Kaplan: It is a book. You can find it at, a little plug there. And it is also, it's listed as either a TV series or a podcast. It's really more of a radio drama, an episodic radio drama. That's how I would describe it. It's great fun, and I do have this little part in it. I think I'm in episode six. So, there you go. That got me into the prized IMDb.

Bruce Betts: Congratulations.

Mat Kaplan: Yeah, thank you. Oh, I should tell you who won.

Bruce Betts: Well, that's why I was leaving some dead space for you to fill that in. Usually, it's kind of a weird little tradition we've got.

Mat Kaplan: It's a given. Leonard [Sojka 00:47:26] is given the prize this time around. Leonard, in the state of Virginia. And he said he actually listened to episode six just to verify that I'm actually there. He made sure it was really me. It is. Leonard, he's a past winner. But it has been, get this, four years since he last won the contest. So congrats, Leonard. You are going to get a copy of The Backyard Astronomer's Field Guide: How to Find the Best Objects the Night Sky Has to Offer, by David Dickinson. It's terrific. It's loose leaf, as I said when we introduced this, so that you can take it outside and the wind probably won't blow the pages over while you're looking up at the night sky. It's an excellent, excellent field guide. I got more stuff, of course.

Mat Kaplan: Here's a little poem from [Marine Benz 00:48:19]. "The rabbit hole was deep this week, a mystery to be solved. Would Fina find the demon cat? Would questions be resolved? The spooky saga continues forth as house historian Mat assists. Capitol Hill produces clues, although the mystery doth persist."

Mat Kaplan: Nick Bell, in Indiana: "While I was unable to find all of your Academy Award performances, I think Brad Pitt was credited with a few of your roles."

Bruce Betts: I've heard if they make a movie about his life, he wants you to play him.

Mat Kaplan: When they see pictures of us ... We're confused all the time. I get it all the time on the street.

Bruce Betts: Yep, you got a face for radio.

Mat Kaplan: Sorry, Brad. A whole bunch of people found the other Matt Kaplan, who is the founder and CEO of what's described as a top-tier entertainment company, but he spells his name wrong. So yeah, that's not me. Mark Dunning says, "Thank you to Planetary Radio Space Policy Edition, and now the Fina Mendoza Mysteries." Now, he says, he has two things about Washington, D.C. that aren't totally, soul-crushingly depressing.

Mat Kaplan: And finally, one more poem from [Jean Lewin 00:49:36] in Washington: "His single credit for all to see listed there on IMDb, Fina Mendoza led to this fame as house historian, his acting name. This accolade does not reflect the true albedo of our respect. And we're all glad his true frontier led to Planetary Radio for all these years."

Bruce Betts: Yay.

Mat Kaplan: I had to get that in. I mean, it uses albedo, so. Thanks, everybody. We're ready for another one.

Bruce Betts: What is the only spacecraft to launch with solar system escape velocity? So in other words, as it left Earth, it had enough velocity to escape the solar system? Go to

Mat Kaplan: So, it didn't have to pick up any more velocity from little fly-bys, right, and bouncing around to the planets?

Bruce Betts: It was not required.

Mat Kaplan: The prize ... Well, first of all, you have until the 9th, that's Wednesday, September 9th, at 8:00 AM Pacific time to get us the answer to this one. And the prize, should you have it right and be chosen by, is the book that we were just talking with Sarah Stewart Johnson about, her book, The Sirens of Mars: Searching for Life on Another World, available from Crown. And it is as good as you heard me saying during that conversation. So, good luck, everybody. And good luck to you, Bruce. Go after that seventh Internet Movie Database entry.

Bruce Betts: Well, you know, they're missing a couple. I'll work on that. All right, everybody, go out there, look up at the night sky, and think about what role Mat Kaplan may have played in The Lord of the Rings. Thank you, and good night.

Mat Kaplan: I don't want to give any hints away. My precious. Actually, I was in a sitcom pilot. But it never went anywhere. It was-

Bruce Betts: What?

Mat Kaplan: Yeah. It's a story for another day. That's Bruce Betts. He's the chief scientist for The Planetary Society, who joins us here and in the IMDb every week for What's Up.

Bruce Betts: I'd watch your sitcom.

Mat Kaplan: No, it kind of sucked.

Mat Kaplan: Planetary Radio is produced by The Planetary Society in Pasadena, California, and it's made possible by its lively members. Live it up with them at Mark Hilverda is our associate producer. Josh Doyle composed our theme, which is arranged and performed by Peter Schlosser. Ad astra.