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Public Radio's Environmental News Magazine (follow us on Google News)

Extended Version: The Sirens of Mars

Published: July 29, 2020

Sarah Stewart Johnson is the author of Sirens of Mars: Searching for Life on Another World. (Photo: Courtesy of Penguin Random House)

(stream/download) as an MP3 file

The search for life elsewhere in the Universe is focused now on Mars, our closest planetary neighbor, with the Perseverance mission planned to launch sometime between the end of July and the middle of August. Astrobiologist Sarah Stewart Johnson is a Georgetown associate professor and NASA scientist who has spent her career searching for answers to these questions. Her book Sirens of Mars: Searching for Life on Another World captures the intersection between planetary science and her life's journey, and she joins Host Steve Curwood to explore the big questions that define space exploration and the human species’ fascination with Mars.

CURWOOD: Hi, I’m Steve Curwood and today on the Living on Earth Podcast we’re talking about going to Mars.
Not people today, but sophisticated robots that are looking for past or present signs of life.
But first, your support helps make it possible to bring you this podcast, so please contribute what you can.
Five dollars or more makes a difference.
You can donate right now at LOE.org and thanks!

CURWOOD: 2020 is the first year in nearly a decade where three different space agencies from around the world are launching missions to visit our nearest planetary neighbor, Mars. The first of these was the Hope Orbiter launched by the United Arab Emirates on July 19. That was followed on July 23, by China's Tianwen-1 mission, which launched a spacecraft carrying an orbiter, a lander and a rover. The last of these missions is America's own Mars 2020 mission, carrying the Perseverance rover, set to launch on July 30. Few people are paying more attention to these missions than astrobiologist Sarah Stewart Johnson. Based at Georgetown University, Professor Johnson works closely with NASA on the design, build and operation of robotic systems being sent to Mars to try to discover life past or present. Over the years, as she's teamed up to work on this epic quest, Sarah Stewart Johnson has also kept a notebook, and lucky for us she has just published her thoughts and experiences in a fascinating book called Sirens of Mars: Searching for Life on Another World. Joining us now is Sarah Stewart Johnson. Sarah, welcome to Living on Earth.

JOHNSON: Thanks, Steve. It's such a pleasure to be here.

CURWOOD: And congratulations on such a well-written book.

JOHNSON: Oh, thank you.

CURWOOD: So, you open up your book with an anecdote about honing your life-finding skills in the wild wastelands around the world. How do you practice that on planet Earth when, well let's face it, Mars is a bit different than here?

JOHNSON: I mean, that is one thing you must always keep in mind about Mars, it is the planet that's most similar to Earth that we know of. But at the same time, it's just indescribably foreign. And you have to make sure that doesn't take you down some blind alley. A lot of what we do in my laboratory is trying to develop tools and techniques to detect traces of life or these bio signatures, and a lot of that work involves developing instrumentation or developing ideas and approaches and going out to places that bear relevant similarities to Mars in terms of their mineralogy, these types of physical factors, and looking in these environments and trying to test these methods to get better and better at what we do before we send something up to Mars.

CURWOOD: So, give me an example of a couple of places which are, well, kind of like Mars, you think. Even though of course, Mars is a different place.

JOHNSON: Well, one place that we've done a fair amount of work is down in Antarctica in the Dry Valleys, which is a really special place. There's been no rain there for 2 million years and it's one of the very driest deserts on Earth. The dry valleys used to be filled with lakes that have now receded to just very, very small ice-covered pockets of water at the very base of the valleys. But there's still paleo-shorelines that go all the way up the hills. And we've been doing a lot of different experiments trying to figure out what traces of life are preserved over millions of years in these environments.

CURWOOD: Have you found any?

JOHNSON: So we did, we found lots of evidence for life and in fact, even some cells that are still eking out an existence despite the harsh conditions.

CURWOOD: 2 million years later, huh?

JOHNSON: Well, some of those are just on thousand-year timescales. But we did look at some deposits as old as 14 million years at a place called Mount Boreas down there in the Antarctic Dry Valleys.

CURWOOD: And there's life you can find there?

JOHNSON: We didn't see active life in those million year old samples, but we did see molecular fossils incredibly well preserved over those timeframes.

CURWOOD: Now, Sirens of Mars weaves together the stories of Mars Exploration with stories from your own life. So tell us, how did you get started in this field originally?

JOHNSON: Well, if I go way back, I guess a lot of it must trace to my father. He was a bit of an amateur astronomer and a bit of an amateur geologist. And he would, you know, show me the different things about space through a big pair of binoculars from our backyard. When I was growing up, he subscribed to astronomy magazine, and he kind of tucked it under his arm, as we'd look and when we'd drive around, he'd drag us out of the car to show us things about the geology and road cuts. And I think at the time, I just thought 'ugh, dad'. But you know, I went off to college when I was 18. And suddenly all of these things came rushing back and I found these were the things that I was very much gravitating toward, and had an extraordinary opportunity my freshman year. I was at Washington University in St. Louis and a planetary science professor named Ray Arvidson let me start working in his laboratory. And he took me out to the Mojave Desert and I mean, I'd rarely crossed the state line at this point, and here I was in the middle of this completely entrancing place. And we were testing prototype Mars rovers, to, you know, eventually go up to Mars. And as part of that trip, I also got to go to NASA's Jet Propulsion Laboratory, which is in a canyon north of Pasadena. It's the epicenter of the robotic space exploration program. And it was just the most exciting thing I'd ever done.

CURWOOD: So once at JPL, you couldn't shake it out of your life, huh?

JOHNSON: I guess that must be true.

CURWOOD: Often, though, let's face it in this culture, young women are encouraged to do science. Who encouraged you initially, do you think?

JOHNSON: Yeah, I mean, my father for sure. I mean, I've been so lucky as I look back that, you know, so many men and women encouraged me along this path. I had the pleasure of doing my PhD with this woman named Maria Zuber at the Massachusetts Institute of Technology. And she was just at the pinnacle of the field, she was the very first woman to ever lead a planetary mission for NASA. And working with her was incredible. She was such an inspiration. And you know, really changed the possibilities in the way I imagined my own career unfolding, because I saw her doing all of these extraordinary things. And whenever I'd question myself or doubt myself, I look around and say, oh, there's not a lot of people here that look like me. I could always look at her and she had sort of broken every barrier. And she was just not only a tremendous, tremendous scientist, but she's such a interesting, fascinating person. And so incredibly supportive. It was terrific. And, you know, and it's so heartening for me to see the field, you know, becoming much more diverse with regard to gender at this stage, you know? Even my laboratory right now, I've got 12 folks working in my group, and they happen to be all women and, and I didn't pick it that way, that wasn't on purpose. You know, I just, I always go about working with the very best students that I can find, but it's just a reflection of how many more people are getting into the field. But you know, one thing we still need to work on, astronomy and planetary science in general is, you know, there are far fewer underrepresented minorities coming into these fields. And that is one thing you just notice so very clearly when you go to scientific conferences, and it's something I feel very strongly about, very important to make sure that we have everybody coming into this field because we need the very best and the very brightest people to answer these really big deep questions.

CURWOOD: Your mentor allowed you to do things you're not supposed to let PhD students do: wander off and just kind of hang out with a research group and then, oh, wander off and do something else for data.

JOHNSON: Maria was very permissive like that, like if Maria saw some red tape, she would just cut right through it. It was really amazing. And I guess I must have been persistent about wanting to do all these things. But it's true. You know, a lot of my PhD I spent either working on missions or off in Antarctica. I took some time and went over to Copenhagen and worked at the Niels Bohr Institute. And I think I just, I followed where the science was the most interesting and where I could kind of be at the epicenter of the questions that I was most interested in. But Maria was great on that front. You know, she just really encouraged me to follow my heart and follow my passions.

CURWOOD: So to what extent do you have a similar dream? What desire do you have to lead a planetary mission to Mars?

JOHNSON: It would be, it would be quite exciting to do that one day, you know, I am just captivated by this idea of are we alone and searching for life in the universe and these big questions, you know, where did we come from? And why is there something and not nothing? Did that something from nothing, did it happen once? Or did it happen time and again? And we're at this moment in human history when we have the tools to answer those questions. And the idea of leading a life detection mission, someday just would be the most thrilling thing ever. I just feel so driven to try to get to answers to those questions. And now we have a way to do that with instruments and with planetary missions.

CURWOOD: Speaking of instrumentation, the first successful flyby of Mars happened in 1965. We're talking about more than 55 years ago. Sarah, give us please a brief history of the missions to Mars that have happened since.

JOHNSON: So this was just a watershed moment. All of a sudden, we just went to Mars. We had our first flyby mission in 1965, the Mariner 4 mission. And this mission was just very small, it was about the power of a pocket calculator. And it was designed to make a number of measurements about the environment. And it also collected 21 photographs of the planet's surface, and each one of those took eight hours to relay back to Earth. And when those images were put together, it was just staggeringly disappointing because one of the things that those images revealed was that the surface of Mars was covered with ancient craters. And this meant number one, Mars had no plate tectonics and number two, there was no fluid erosion of any sort that would have erased those craters. And it meant the surface was ancient and there had been no water there, and it was just pockmarked, like the moon. And we just really were not expecting that. I'm not sure we knew what we were expecting. But it was just this hard moment. And the New York Times even declared that Mars was a dead planet at that point. Fortunately, we didn't cease from exploration, you know, we continued to go back, we sent more flyby missions, two in 1969. 1971, we had Mariner 9, which was the very first mission to go into orbit. And it made a number of tremendous discoveries. But one of them was that the surface of Mars was covered with ancient rivers, and that there were all of these features that had to have been created by water. So even though there was no water today, on the surface in liquid form, even though the pressure was too low, and the temperature was too cold, Mars was a much different place in the ancient past. And then not long after, later in the 1970s, we sent two orbiters, the Viking orbiters, and they each released a lander, the Viking 1 and 2 landers. And they did the very first life detection experiments on the surface of Mars. And, you know, those experiments were ver confounding, the results. At first there was this enormous response from one of the three life detection instruments, to the point where some of the team members called off for champagne and cigars, thinking that they had just made the biggest discovery in the history of modern science. But then those results, they just sort of dropped off unexpectedly. And then there were the controls, which were supposed to be negative had these big results as well in two of the three experiments. And then the real kicker was that there was a chemistry instrument that was looking for the building blocks of life, these carbon containing organic molecules, and there were none whatsoever detected. And this was perplexing because even on the moon even on other planetary bodies, there's a rain of these abiotic organic molecules down from space and there were just none at all, which was a big mystery. But you know, the the broad conclusion of those experiments was that no life was detected the surface was just very bleak, you know, covered in this red dust, that was the consistency of cigarette smoke.

The Mariner 4 spacecraft launched on November 28th in 1964 performed the first successful flyby of Mars. (Photo: NASA, Public Domain)

CURWOOD: Oh, wait, I thought there was supposed to be Martians there. It's certainly not Martians, at least there were canals that they had dug. But these flybys and these early landers don't find any of that. So if there was life on Mars, it sounds like must have happened a long, long, long, long, long, long time ago.

JOHNSON: Yeah. Well, you know, I will say that we took a 20 year break from exploring Mars after those Viking missions. I think part of it was the disappointment, part of it was that there were other targets in the solar system that were becoming increasingly exciting, like the outer planets. Part of that was bad luck, there was a big mission that failed that NASA sent in the early 90s. But once we started back in 1997, NASA has been sending mass missions every 26 months when the planets align on the same side of the sun. And these missions on this rough cadence of every two years have come back with astonishing findings, things that have just brought the planets into Technicolor focus. And even if the surface may not be hospitable anymore, and may not be habitable because of the conditions, down deep in the subsurface, which is one of the most intriguing places to look, I think there's still a very real possibility that we could find simple microbial life. I mean, a lot of our biomass here on Earth is beneath the surface and microbial form. We've barely even scratched the surface when it comes to this kind of exploration. We will have the visit first mission that will drill down to look for biosignatures or traces of life with a European mission that goes in two years, the Rosalind Franklin rover.

CURWOOD: Whoa. So you are swinging for the fences here, you could discover life on another planet in a mission that you lead, it just is really tiny, it's microbial and way, way, way, way down underneath the surface, hmm.

JOHNSON: Maybe not even so far down, you know, even two meters down, you're below a lot of the very damaging cosmic radiation that makes it very hard for molecules to stay together at the surface. But I do feel like there's so many possibilities there ready to be explored.

CURWOOD: So there are four successful rovers that have wound up on Mars. What, Sojourner the Opportunity, Spirit and wait, there's one still going, right? It's called the Curiosity. What were these rovers goals and accomplishments so far, and I guess it doesn't include finding life. But maybe that's a 'not yet'.

A “selfie” from the Curiosity rover, composed of 57 individual images stitched together into a panorama. (Photo: Curiosity, NASA, Public Domain)

JOHNSON: Well, so NASA kind of went back to the drawing board when we began this new era of Mars exploration in the late 90s. It was driven on the one hand by this idea of a better, faster, cheaper, have more missions, have them more often. And then there was also an idea that we should follow the water. Because everywhere we looked on Earth, you know, life could be very, very different in different types of environments. But the one constant seem to be water, at least at some part of its life cycle. And so NASA's new mantra, 'follow the water', kicked into place. And the very first rover that went was only the very small little thing, the Pathfinder rover. It was the size of a suitcase. It landed on July 4, and it was really more of a technological demonstration to show that there was a new type of exploration. You didn't have to just look at what was right in front of your face, you could traverse and you could get to interesting scientific targets. And then the next two rovers, these twin rovers Spirit and Opportunity, followed, landing in early 2004. And these rovers were about the size of a golf cart. And they landed on opposite sides of the planet. They were only built to last 90 days. But Spirit went on for four years, and Opportunity, all the way until 2018. So 14 years, over 5000 days of exploration, it went a total of 28 miles across the surface of Mars. And in that 28 miles, all of those explorations that those two rovers did, we found out some incredibly astonishing things about the planet. And that really motivated this idea of sending a scientific laboratory to the surface, which was the Curiosity rover, also called the Mars Science Laboratory. And that landed in 2012. It was the size of a car, you know, a metric time put down on the surface. Landed in the base of Gale Crater. And inside Gale Crater is a mountain, and it's called Mount Sharp, and it rises higher than Mount Rainier above Seattle. And it records a very big chunk of Martian climate history. And so we can look at the sediments that have been laid down, which are sort of laid down like the pages of a history book and record the environmental conditions. And we've been exploring as we've been ascending that mountain, and we're still doing that today. It's been a just a really exciting campaign and Curiosity has revealed that this is a habitable environment. You know, we've moved beyond 'follow the water' to understanding that all the ingredients necessary for life as we know it are there, or were there in the surface of Mars and that is there was all this ancient water, water that was pH neutral, the kind of water you could drink a glass of, had you been standing on the surface billions of years ago. You know, rushing by in streams, you know, there could have been a big lake that filled Gale Crater, the top of the mountain might have even stood as an island. We've gone back and we found those organic building blocks of life. Those organic molecules have been detected by the Sample Analysis at Mars instrument on the Curiosity rover. And I've been fortunate to work as part of that instrument team. And so we've just done some really astonishing things there with Curiosity. And now it's time to send Perseverance.

CURWOOD: So, what is in Perseverance?

JOHNSON: So Perseverance in some ways, looks just like Curiosity. It's built on the same chassis, which saved a lot of money and a lot of design features. It'll land in the exact same way. Well, a little bit more refined. We're getting much better at targeting little landing ellipses these days. But Perseverance has a different set of instruments. Seven instruments that are really targeted towards spatially resolving and honing in on the best samples to collect. Because what Perseverance is doing is it's kicking off this breathtakingly ambitious campaign to return samples of Mars that are carefully selected to Earth. And it's going to take three missions to do it and a lot of international cooperation. But the idea is that perseverance will collect a few dozen samples about the size of a pin light, leave them in a cache on the surface, then a fetch rover will come along and pick those up and put them into an ascent vehicle. And then another vehicle will come along and collect those out of orbit and bring them back to Earth.

CURWOOD: What's the timing for all of that if you can send missions there every couple of years, we're talking a decade from now, you'll get this stuff back, in round numbers?

JOHNSON: Oh, we're hoping. I would love to see that. There isn't an exact timeline yet. Like it really depends on, you know, of course, budgetary factors and what happens with international cooperation. But a lot of the scientific team is hoping that within a decade, we would actually have these samples back.

CURWOOD: Scientists have made plenty of guesses about the possibility of extraterrestrial life. So, what's your feeling here? This is not a scientific question. This is a feeling question. How alone are we in the universe, do you think? And if we're not, how likely are we to find evidence of life forms, as close to us as Mars?

JOHNSON: That's a great questions, Steve? And I think you're right, as a scientist, it's hard to answer because we, we aren't basing our feelings at this moment in data, right? But I can tell you, I feel incredibly strongly that we must keep looking and I've got a couple of reasons for that. And of course, I would have picked a different career, if I wasn't thinking that this would pay off in the end, but I think I just must underscore just how enormous that payoff would be, the idea of finding life on Mars or at another planetary target, here in our solar system or beyond. So, we only have one data point for life. You know, it's the life as we know it, the life that we have here on Earth. And it's all basically the same. It's this DNA-based, carbon-based life. And it all traces back to a common origin. And as a result, I would argue that biology is largely a descriptive science. We don't have that second data point. We can't make the kind of constitutional, fundamental understanding of biology, we can't make that leap yet because we're limited. You know, we don't know if life is just a consequence of energetic systems. We don't know what paths it would follow. We know that we had all the same sorts of starting ingredients that we had here on Earth, on Mars. And we know that they were there around the time that life was getting started here. And even if life on Mars had been, say, ancestrally, related to life on Earth, there were lots of rocks exchanged between the planets, especially early in their histories around the time life was getting started here, there is a chance that life just got caught from the next planet over. But even that would be remarkable, this idea of playing the tape of evolution over again and seeing what results. This idea of running that great experiment one more time would be revelatory. But I have to say the thing that excites me most is this idea of a separate genesis, a type of life that's completely different from anything that we've ever seen before. And I can tell you this, like if we find it on Mars, then you know, that's just the next planet, that's our near neighbor. It would just have huge implications, it would really imply that the universe would be positively teeming with life.

Curiosity’s view of Mount Sharp in Gale Crater. (Photo: Curiosity Rover, NASA / JPL-Caltech, Public Domain)

CURWOOD: But in that case, if there is a different, unique basis of life, to what extent are you using the correct instruments to look for it?

JOHNSON: Ah, no, that's a great question. And this is something I feel very passionate about. I'm currently leading a big NASA project right now, going after this very question. That's not just looking for life as we know it, but also looking for life as we don't know it, something that we've been calling agnostic biosignatures. And the idea there is to look for signs of life that might not necessarily share the same biochemistry, or the same underlying molecular framework as life here on earth. And there are all kinds of ways that you can do this, you can look for signs of chemical complexity, or unexpected accumulations of elements and isotopes. You could look for chemical disequilibrium, or signs of energy transfer. And so in our team, we're working hard to develop tools and techniques that could really go after this type of life that could be, you know, very different from life here on Earth that could, say, not even be carbon-based, and that we could find ways that we could detect it, not just the sort of traditional tools that we use when we look back and see our early rock record here on Earth.

CURWOOD: Humans have perhaps always been captivated by space. And of course, more recently, space travel. What is it specifically about Mars that calls to us, do you think? The red planet.

JOHNSON: So Mars has been enchanting us, you know, since ancient times, you know, we've looked up into the sky, and even you know, the Babylonians realize that there are these five points of light that were separate from the fixed stars that moved separately and they call them 'wanders'. The root of that came to be the word 'planets'. And of those there was one that not only had this incredibly distinctive red color, but it also had this very bizarre motion, where it would move east, you know, in relation to the fixed star background, night after night after night. But then, once every couple of years, it would backpedal against the Zodiac and move west for 60 to 80 days before resuming its normal course. And it would effectively trace out this loop and sometimes this elongated loop was smaller and some times it was larger. And I love this story: from this, Plato had even concluded that the planets must have souls, for what else could these retrograde expressions be if not, you know, freewill coming to bear. And it's one of these things that Mars as we've gotten to know it better and better, as we've done the hard work of really getting to know the place, we've realized that it is so very similar to our own world, the most similar place that we've ever found. And yet at the same time, it's indescribably foreign. Yet it's different, yet it's every bit as complex as the Earth. But it took this different path, our planetary paths diverged long, long ago. And so I think part of that comes from this idea of what happened, you know, why, why did these planets take these very different paths? I think part of that comes from this just incredibly strong desire to figure out if this place that was so very similar to our own world, could have possibly developed life and if that life might still persist to this day. But I just think it's something that's hardwired into our human minds, this curiosity, this desire to explore and understand the world around us.

The Perseverance rover performs its first driving test on Dec. 17, 2019. The Mars 2020 mission is set to land on Mars in February of 2021. (Photo: NASA / JPL-Caltech, Public Domain)

CURWOOD: So, fascination since the ancient times with Mars. But, you know, 100 years ago, when we were still only able to look and some people took quite interesting measures to try to get a closer look. We didn't have any of the technology that now has gotten us to actually put instruments there, things that can drill, and plans now to have them drill up a little something and send it back. So if you look ahead, say another hundred years, what might we have in the way of technology that could much better inform us?

JOHNSON: So what kind of instrumentation what I love to see? I mean, Steve, I don't know if you watch Star Trek, but there was always this little instrument called a tricorder that you could use to recognize anything. And I mean, that would be my dream from a technological perspective, that you could have some little gizmo and you could find a sample and you could say, well, what is that and is that alive? And is that life? I mean, that would just be extraordinary. And I think about, you know, just the last 50 years of exploration, how the robotic machines that we're creating and sending as rovers and landers and orbiters to the planet's surface would have been just completely unrecognizable to that first batch of Mariner 4 scientists. And then when I go even further back, you know, Mars 100 years ago, back at the time of the canal frenzy, when you know, much of the literate world believe that intelligent life had been discovered on the surface of Mars and in the form of these engineered canals, which are really just kind of a figment of our vision, you know, this this remnant of how we were seeing the planet, it's such a very, very far distance. There are not this network of linear features on the surface, as many telescopic observers were purporting to see. But just back then, you know, even the idea of going to Mars was ludicrous, you know,it was in the realm of science fiction, the idea that we could know more about it than you know, just a few things that we could observe through telescopes at a very great distance. And I think about that a lot in terms of exoplanets today. So these are the planets that are around other stars, other solar systems beyond our own, and they're incredibly far away, Steve, you know, they're light years away. And the universe has a speed limit, and it's incredibly slow, and you can't go faster than 3 times 10 to the eighth meters per second. And it does feel like they're inaccessible, you know, we might know a few things about it. We could maybe intuit a bit of information spectroscopically about the composition of their atmospheres, you know, but the idea of really knowing these places just seems out of reach. But of course, that's exactly how Mars seemed 100 years ago. And so, Lord knows what kinds of miniature spacecraft we might propel that are maybe just a gram in size that we could send off powered by giant lasers pushed off toward these distant stars, distant worlds. I mean, it's just so exciting to kind of think about those possibilities.

Sarah Stewart Johnson is a Georgetown University Associate Professor who has worked with the NASA Science Teams for the Opportunity, Spirit, and Curiosity rovers. (Photo: Brittany Waddell)

CURWOOD: When humans start showing up on Mars, and there are folks who would like to have that happen sooner or later, to what extent do we kind of mess up the experiment there? Not knowing the life forms that we find are things that we brought, as opposed to what were there originally.

JOHNSON: I think that human exploration will happen. I think it will happen at some point. And there is this period of time, where we are still sending these very sophisticated robotic machines before humans arrive. And I think it's a very important one, from the perspective of astrobiology, not to say that the search for life and human exploration can't go hand in hand, but it does get a bit more difficult in some respects. You know, humans are bags of biology and we're sloughing off cells left and right. And it makes it more difficult. At the same time, we have, I believe the tools and the techniques and the technology to make those differentiations. For instance, if we found some cells on Mars, we could just sequence them. And we could look at, you know, their genetic code. And we could say, oh, you know, this is DNA base life. This is very similar to the kinds of common contaminants, or this is similar to the types of bacteria that humans carry in their own bodies. Or we can say, this is a type of life that either diverged billions of years ago that is unlike anything that we've ever seen here on earth. And so I think that we will be able to recognize different life, though it does complicate it in the sense that you know, it might be harder to see the sort of signal to noise if there's a lot of Earth light floating around on the planet's surface.

CURWOOD: So, what do you hope readers will take away from your book Sirens of Mars, writing that in 2020.

JOHNSON: So, you know, the book is not just about the science, it's really about our human relationship with the planet. And when I started writing it, it was just really a bunch of scribbles. Like, I would go to these talks and seminars and I would read these papers. And there would be these things that would strike me as incredibly evocative or poignant, or compelling, the kinds of things that would never find expression in the pages of scientific journals. And those ideas just started to coalesce at some point I just felt that Mars deserved a different type of treatment, you know, something that would really capture the majesty and the wonder of the entire quest. And that's how the book came together. And I really wanted to reach out to readers that weren't just, you know, already in love with science, but including people that didn't necessarily engage with science on a regular basis just to see how exciting and compelling and interesting it could be. But one thing I think would be great for people to take away is that, you know, we're a small species in this vast universe. And our lives are just incredibly short, you know, on the scale of geologic time, and we really just have a moment to be here. And it just makes life so very precious and so very special. And we've really just got to make the very most of this one moment that we each have.

CURWOOD: Sarah Stewart Johnson is an associate professor at Georgetown University and the author of Sirens of Mars: Searching for Life on Another World. Thank you so much for taking the time with us today.

JOHNSON: Steve, thank you. This was such a pleasure to talk with you.

CURWOOD: And I do hope you find what you're looking for.

JOHNSON: Me too.


CURWOOD: Living on Earth is produced by the World Media Foundation. Our crew includes Naomi Arenberg, Bobby Bascomb, Paloma Beltran, Jenni Doering, Jay Feinstein, Anne Flaherty, Don Lyman, Isaac Merson, Aynsley O’Neill, Kori Suzuki, and Jolanda Omari. Jake Rego engineered our show. Alison Lirish Dean composed our themes. You can hear us anytime at L-O-E dot org, Apple Podcasts and Google Podcasts, and like us, please, on our Facebook page - Living on Earth. We tweet from @livingonearth. And you can find us on Instagram at livingonearthradio. I’m Steve Curwood. Thanks for listening!

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