IRA FLATOW: Time now to turn to the Science Friday Bookclub, The Sirens of Mars. That’s what we’re reading. It’s all about the centuries-long fascination with the red planet and its potential for life. You can learn more about how to join us in reading and discussing this book. Yeah, it’s at our website, sciencefriday.com/bookclub. Joining me now is my favorite Martian producer, Christie Taylor, here with more cool Mars science. Hey, Christie.

CHRISTIE TAYLOR: Hey there, Ira.

IRA FLATOW: Now, last week we talked about clues in Martian meteorites. What’s the update today?

CHRISTIE TAYLOR: Well, we’ve been asking listeners to weigh in on what they thought about life on Mars. This is all in the Science Friday VoxPop app. And there’s Tim from Scottsboro, Alabama. He thinks the planet once definitely had life.

SPEAKER 1: But I think in our present day that it’s just a bleak, lifeless desert.

CHRISTIE TAYLOR: And then we had Kevin in Tulsa, who thinks life might actually still be there.

SPEAKER 2: I think somehow, way in the distant past, Mars was in the Goldilocks zone and had liquid water. I think microscopic life from that time is trapped in the polar ice cap.

CHRISTIE TAYLOR: And that Goldilocks zone he’s referring to, by the way, is the sweet spot around a star where a planet can count on having liquid water.

IRA FLATOW: Not too hot, not too cold, just like the porridge.

CHRISTIE TAYLOR: Just like the porridge.

IRA FLATOW: But what are we talking about when we talk about this word, life? I mean, couldn’t there be other unfamiliar life forms out there? And how would we even know what to look for?

CHRISTIE TAYLOR: That is such a great set of questions, Ira. And there’s actually a whole group of astrobiologists who are asking those same things, too. Mars is actually a lot like ancient Earth. But beyond Mars, there’s some really wild moons and exoplanets that could host some really weird stuff.

So to talk through these questions, I brought in some scientists who are also using their imaginations a lot. And in this case, I’m talking about science fiction. Dr. Moiya McTier is an astronomer and folklorist. And she hosts the Exolore podcast, which is all about inventing fake life on real planets.

And Dr. Mike Wong, a postdoctoral fellow at the Carnegie Institution for Science, he’s got a podcast, too. It’s called Strange New Worlds. And he talks about the science of Star Trek. And I started by asking Mike to talk about his day job, which is looking for traces of life in planetary atmospheres.

MIKE WONG: Oh my goodness, yes, I do. So we are discovering exoplanets by the bucket load these days. These are planets orbiting other stars. And the only conceivable way to try to assess whether there is life on those worlds as of right now, given the technology that we have at the moment, is to try to identify the molecular fingerprints of atmospheric gas molecules that life has breathed out into the atmosphere.

And the way we look at this is basically as the planet orbits its star and passes between its star and us, that starlight will filter through the atmosphere and enter our telescopes. And because of the specific ways in which molecules of gas absorb that light, we can actually get a handle of what’s in that atmosphere. And if we detect certain combinations of molecules that look really intriguing, because they are tied to our theories for what life should do in that planetary context, then maybe we’ll even get a hint that there is a biosphere on that planet.

MOIYA MCTIER: Mike, I know as an astrobiologist, you’re probably spending a lot of time thinking about biosignatures. But I, in my past research endeavors, have also spent some time thinking about technosignatures. So I guess I would push back a little bit saying that we can only detect life by looking for these molecules and other compounds that we think would be formed by biological processes. There are also some technical signals that we might be able to find.

CHRISTIE TAYLOR: OK, but what is a technosignature and what would it look like?

MOIYA MCTIER: Yeah, so similar to biosignatures, where you’re looking for a signal or something that would only or mostly exist in the presence of biological processes, a technosignature is something that we think would happen because of a technological civilization. There have been a few papers coming out over the last decade looking for different types of technosignatures. One that you might be familiar with would be a Dyson sphere. This is a big structure that an alien civilization might build around their star to capture all of its energy.

But you can also imagine smaller-scale things, like there was a paper that came out a few years ago looking for nightlights on planets using something similar to the transmission spectroscopy that Mike was talking about. But instead of looking at the spectra of light, it’s really just looking at the amount of light. If a planet has more light on its dark side than we expect to see, then maybe that’s a hint that there are bright city lights on that planet.

CHRISTIE TAYLOR: Mike, we just went straight for the jugular, technological societies. What’s your take on that?

MIKE WONG: [LAUGHS] Well, I sit here in my closet absolutely corrected. Technological societies is a really interesting point, that maybe we can think of them as a natural emergence in the course of living planet’s history. But it’s also something that has arrived here on Earth relatively late in our planet’s history.

Animal life on Earth has existed only within the last tenth of Earth’s history. And then technological civilization has been around for, depends on who you talk to in terms of anthropology and when they date the beginning of civilization as we define it here on Earth. But it’s definitely less than 1 million years.

This is a blip in Earth’s history. And I think what we might say as astrobiologists is that the idea that we could potentially detect life out there that is simply biological life, maybe even just microbial life, is potentially a lot greater than finding evidence for technological life, because it is easier for that kind of simple life to emerge in multiple places. However, I absolutely agree with Moiya that if we get technological civilizations out there, the signals, those flares that we would see from them as a result of all of their technology would be so much more obvious to our telescopes.

CHRISTIE TAYLOR: I want to take us a step backwards, though, because here we are, we’re talking about highly sophisticated technological societies. Meanwhile on Mars, the rovers are hunting for evidence of basically ancient bacteria. So when we’re talking about the definition of what life could be, I remember way back in high school biology, some of the basic characteristics we were taught about life involve things like reproduction, metabolism.

Life responds to its environment. And NASA’s definition of life is just a self-sustaining chemical system capable of Darwinian evolution. Can definitions like that help us in this search?

MOIYA MCTIER: Hmm, I think yes, by definition they will, because when you’re looking for something, you have to at least have an idea of what you’re hoping to find. But I think it’s also really important to be open to the idea that what you find might not look anything like what you expect, especially when we’re talking about extraterrestrial life that if it exists would be adapted to their own local environment. And based on the amazing diversity of planets that we have found, I think you’re right, Mike, it is up to 5,000 by now. These planets are so different, which means the life on these planets would be so different.

CHRISTIE TAYLOR: Moiya, I know one of the things that you have spent time researching is whether we can tell how bumpy an exoplanet is. That’s the technical term. Why is this important in the search for life?

MOIYA MCTIER: So there there’s some evidence that mountains and other topographical features, like volcanoes and trenches, are a good proxy for how habitable the planet is. These mountains and other features will form through internal mechanisms that are really useful for life. Having plate tectonics, the ability to cycle material in and out of the interior of a planet helps with things like regulating the amount of carbon dioxide in an atmosphere.

Or other molecules, whatever that planet has, this plate tectonic process is really good for cycling. Even having volcanoes is a sign that your planet has internal volcanism. So if your planet is outside of the circumstellar habitable zone, if it’s farther from its star, it might still be OK if it has this internal source of heat.

MIKE WONG: So this reminds me of a paper that just came out recently from my colleague, Stuart Bartlett, who was trying to identify a way to calculate the complexity of a planet, especially an exoplanet that we are just observing as a single pixel and our telescope’s very far away. If you have mountains, if you have a habitable planet with constant tectonic motion, yeah, the complexity of that planet’s surface is going to go up.

And so what Stuart and his colleagues did was they figured out a way to observe the Earth, and also observe Jupiter, another very complex world in our solar system. And what Stuart and his colleagues found was that the Earth is way more complex than Jupiter. Although by eye, I look at Jupiter’s storms, all those beautiful images that the JunoCam is beaming back to us. And I look at those swirls and pinkish and reddish and orangish cloud features. And I’m like, that’s a complex world. But it has nothing on the Earth.

MOIYA MCTIER: I’m not surprised by that, actually, but that sounds like a really cool paper.

MIKE WONG: Yeah.

CHRISTIE TAYLOR: Let’s talk a little bit more about the ways in which life as we don’t know it may or may not manifest. And I want to do that through the lens of science fiction, since that’s a place in our culture where we often let our imaginations run quite wild as far as that question is concerned. You two are both podcast hosts as well as scientists. You think about this a lot. Why is science fiction an important way to conceive of life beyond our understanding?

MIKE WONG: One of my favorite instances of life elsewhere in science fiction is the Borg from Star Trek. So for those listeners who are not familiar, the Borg are basically this collective of cybernetic integrated individuals who are all linked to a hive mind. And I just love them because they show an alternative form of learning, through assimilating other civilizations’ technology and biology and making it a part of their own.

So this is different from what we think of as strictly Darwinian learning, this descent with modification that Darwin described. And it’s actually a little bit more akin to horizontal gene transfer. You basically let others innovate and generate novelty. And then you just steal it from them. I really think that information and information processing and information transfer is at the heart of what it means to be alive.

But anyway, I just love the Borg because they are basically a warning to us about where we might be going as a technological society. And I think it’s worth putting into perspective, again, that our technosphere or our dataome, as some might call it, is a result of 4 billion years of biological evolution. It’s a part of life on Earth, but it’s an emergence on our planet that has never before happened in the history of all of Earth. And so we’ve got to turn to science fiction to try to predict its outcomes.

MOIYA MCTIER: Yeah, that’s a great example, Mike. I love that you brought up the Borg, because I think that one of the purposes of science fiction is to let us humans work through some of our deepest societal issues and things that we have a hard time grappling with here on Earth when we’re talking about human experience. But when you separate it from humanity, when you put it on another planet or with another species, it makes it so much easier to deal with.

MIKE WONG: Yeah, the same is true about astrobiology. When we look for life out there, we are also asking, what even are we that we are looking for something out there that resembles us? When we ask about the origin of life, we’re asking about our own story. When we are asking about the habitability of other worlds, we can’t help but also turn around and look at how we are disrupting the climate and the habitability of our own.

Astrobiology is like science fiction in this way. It is a mirror for ourselves. By thinking about these hard questions out there, we are also thinking about hard questions in here.

CHRISTIE TAYLOR: Moiya, Mike just mentioned the Borg from Star Trek. I on your Exolore podcast, you ask questions like what kind of life could live on a planet that was mostly volcanoes? And I think that one involved shiny turtles with precious metals in their shells. Is that how one might go about imagining life, take a real set of physical conditions and try to imagine what might survive there?

MOIYA MCTIER: That’s my process. I have talked to other world builders. These are people who build imaginary worlds, usually for the purpose of putting a story in those worlds, but not always. And my personal process starts with imagining the intention that you have for your world and then building out the physical environment and then going to biology and then going to culture, because that’s how our world happened.

That’s how worlds in nature are built. And so I feel like it’s just nice to follow that same path. So many world builders have their own processes. But I think it makes sense to start with the environment, because I use my world building as a vehicle for science communication and getting people to better understand the facts that have underpinned our own world here on Earth.

CHRISTIE TAYLOR: Just a quick reminder that this is Science Friday from WNYC Studios, talking about how we imagine life, and I mean alien life that we’ve never seen before. Mike Wong, Moiya McTier, where do you want to go looking for life in our solar system?

MIKE WONG: OK, well with all due respect to Mars, I’m going to go for team Europa here. So just for context, Europa is a moon of Jupiter. And because of the tidal forces that it experiences, its interior gets heated to the extent that there is a global ocean of liquid water hiding underneath of this kilometers-thick ice crust.

And the thing is that water is in contact with rock on the bottom of that ocean. And one of the leading theories for the emergence of life here on Earth situates our emergence at submarine hydrothermal vents. So I really find Europa this great possibility for life on a world that is very differently oriented than the Earth.

We have these oceans in contact with a brilliant atmosphere that feeds us carbon dioxide and everything. Europa has no such thing. But it still could be alive. And it would be really groundbreaking if we did find life there.

CHRISTIE TAYLOR: Moiya?

MOIYA MCTIER: I agree 100%. I think that there’s a long history of people being more obsessed with Mars and its potential for life than we should be. And Mike’s totally right that Europa is more interesting from that perspective.

I love the idea of this world where dimensions don’t work in the same way. So I often have a lot of fun imagining entire worlds built in an ocean. I did an episode where I imagined life on a planet or on a moon like Europa. And because they have that thick ice sheet at the top, what you end up with actually is upside-down ice mountains that dip down into the water. And you also have features at the bottom with the rock.

And so I just love that imagery. We ended up imagining giant matriarchal squid societies. And yeah, so Europa is super cool.

MIKE WONG: Wow. Awesome.

CHRISTIE TAYLOR: That’s excellent. I think the takeaway I’m getting here is that life, it’s complicated.

MIKE WONG: Yeah.

CHRISTIE TAYLOR: Moiya, Mike, thank you so much for your time today.

MOIYA MCTIER: Uh-huh, thanks for your great questions.

MIKE WONG: Yeah, my pleasure.

CHRISTIE TAYLOR: Dr. Mike Wang is a postdoctoral fellow at the Carnegie Institution for Sciences, Earth, and Planets Laboratory, host of the podcast Strange New Worlds. And Dr. Moiya McTier is an astronomer and folklorist. Her podcast is called Exolore.

IRA FLATOW: Thanks so much for this complex conversation, Christie.

CHRISTIE TAYLOR: Thank you, Ira.

IRA FLATOW: And listeners, are you reading The Sirens of Mars with us at the SciFri Book Club? You can hear author and planetary scientist Sarah Stewart Johnson talk about her work, maybe ask her all about it. Just come to our next Zoom call-in event. It’s a behind-the-scenes Q&A that you can join before it airs on the show. Check it out at sciencefriday.com/marsevents.

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