IRA FLATOW: It’s one of the biggest fundamental questions– is there life elsewhere in the universe? That question, it opens up a whole string of others, like, how do we look for it? Will we know it if we see it? Will we be able to make sense of what we’re seeing? And how many of what we consider the basic rules of life here on Earth are really just suggestions? Maybe they don’t work so well someplace else.

Well, my next guest tackles these questions and a whole lot more through the lens of both science and science fiction. And we want to hear your thoughts as well. What would most intrigue you about finding a new kind of life? What questions do you have? You make the call, but you have to make the call. Our number is 844-724-8255, 844-SCI-TALK. Or tweet us @SciFri.

Jaime Green is a science writer and author of the book, The Possibility of Life– Science, Imagination, and our Quest for Kinship in the Cosmos, out next week from Hanover Square Press. She joins me from the Studios of Connecticut Public, in Hartford.

Welcome to Science Friday.

JAIME GREEN: Hi. Thank you so much for having me.

IRA FLATOW: Nice to have you. I just want to tell our listeners that the SciFri Book Club, yes, we’ll be reading this book together in May. And you can read along with us next month. More information at sciencefriday.com/bookclub.

Let’s get right into this. Let’s start with the basics. How do we define life? Because it doesn’t sound, from reading your excellent book, that we really quite have the answer to that.

JAIME GREEN: No, we absolutely don’t. And there’s actually a school of thought that looking for a definition of life is a totally misguided project. Carl Sagan wrote this essay in the ’70s about all the possible definitions for life that we have. And for every single one, you can find exceptions. If you say that life consumes fuel to self-sustain itself through energy, well, so does a fire.

And the reason that definitions like that fail is because life isn’t a linguistic term that we invented that we can define. It’s a fundamental property of the universe. And so there are actually some researchers who say that we need to have a theory of life, like a physics of life, the same way that Newton and Einstein gave us a theory of gravity. In order to recognize and find life, we need a physics of life to do that, too.

IRA FLATOW: Well, it’s interesting you bring up Newton and Einstein because there was a progression there, right? Where would you say we are in a physics of life in that progression? Would we be at Newton versus getting up to Einstein at this point?

JAIME GREEN: Oh, no, we’re not even at Newton. We don’t have the right terms. I’ve heard it explained, in terms of chemistry, that we’re still in alchemy. We’re mixing stuff up and trying to figure it out. But we haven’t come up with even figuring out what are the fundamental terms, the same way that for physics Newton figured out that it was mass and position in time and speed. And everything comes back to that.

We don’t have that for life. We don’t know if it’s complexity or energy or inertia or information or something else.

IRA FLATOW: Because we did try to make it in glass jars once, didn’t we? And we still probably try to do that.

JAIME GREEN: Yeah. I think you’re referring to the Miller-Urey experiment to try to figure out the origin of life and try to figure out, was it plausible? And the study of the origin of life has largely continued to follow that path. You take some plausible building blocks, put them in a situation that you hope mimics the conditions on the early Earth, and see if you can figure out what comes first. And what do you have to put in a bottle and shake around in order to get RNA?

Because the one thing we do know for sure is, at some point, once, at least, on Earth, something that wasn’t alive turned into something that’s alive.

IRA FLATOW: And by doing this, you’re sort of limiting yourself to what you’ll find in the cosmos, aren’t you?

JAIME GREEN: Well, yeah. I mean, if you don’t limit yourself, we’ve got all of chemistry and the entirety of the cosmos to look at. So of course, we do have to put some constraints on it. And it makes sense to start with what’s familiar. Because we haven’t nearly exhausted that search. We haven’t even scratched the surface.

But there is a question in the study of the origin of life, just like there is in the search for life beyond Earth, are we being to Earth-centric? Or do we have this one example of how it worked, and we know it worked, and Earth is full of life, so why not at least start with something Similar?

IRA FLATOW: Yeah. Because there have been biologists who talked about, if we would start evolution all over again, right, from the beginning, it wouldn’t turn out to be us again?

JAIME GREEN: Yeah, that’s a really big open question that also informs how we imagine life on other planets. Like, if– and this is a huge if– let’s say life on another world has similar categories to plants and animals, which is by no means guaranteed, then the question to ask is, would those organisms come up with similar solutions to the problems that their environments throw at them as happens on Earth and we see on Earth?

And this is convergent evolution, where different animals independently come up with the same solutions. The body shape of a dolphin and a shark, totally independent. The eyes of humans and octopuses are very anatomically similar, but evolved totally independently.

The big question is, is convergent evolution the rule or is it just a couple of cool examples that we can find in an otherwise random world?

IRA FLATOW: Right. If you’re not sure what you’re going to find out there in terms of the chemistry, the biology, it makes sense then to just look for evidence that it exists, right, so you don’t have to know the exact chemistry?

JAIME GREEN: Yeah. And that’s actually one of the arguments that some researchers use to advocate looking for technology first. Because looking for life’s chemistry, it’s very small. It’s hard to see. It’s hard to know if the oxygen and water vapor that we might detect in an exoplanet’s atmosphere comes from life or comes from just whatever geochemistry is going on on that planet.

But if we found a satellite, if we found a radio transmission with a clear pattern in it– like, technology could be much more obvious. The way one scientist put it to me was, not all life is elephants. But if you found an elephant, you would know that you had found life. So you might as well look for the big stuff, the obvious stuff, and start there.

IRA FLATOW: So you’re looking for some signature?

JAIME GREEN: Exactly.

IRA FLATOW: That life existed and created something, left it behind?

JAIME GREEN: Right. Left it behind or is possibly still using it. But what’s nice is it doesn’t matter. And we don’t need to know how they used it, what it was for, what it meant to them. It’s just like, if we see some solar panels, like, nature doesn’t make solar panels.

IRA FLATOW: Right. Not yet. Let’s go to the phones because a lot of people want to talk about this, of course. Sima, in Spokane, welcome to Science Friday. Hi there. Sima, are you there?

SIMA: Hello.

IRA FLATOW: Yes.

SIMA: I am. I am. Yes, thank you for taking my call.

IRA FLATOW: Go ahead.

SIMA: My question is, if life on Earth is based on carbon, would life elsewhere– could it possibly be based on something else beyond carbon? And would that be classified as life?

IRA FLATOW: Hmm. Good question. I’m going to put that to Jaime. Because in your book you use a lot of science fiction. And a lot of science fiction films and movies have talked about not a carbon based but some other form, right?

JAIME GREEN: Yeah. It’s usually silicon. And the reason is that carbon is really good for life because it has four binding sites on the atom. And so it can make long, complex molecules. It likes to make repeating chains of carbon. And silicon also has four binding sites on the atom. It just is a bigger atom. There’s one extra shell of electrons on the inside.

So that does mean that there are some differences, but it’s the first-go to as a carbon replacement. And so one example that I write about in my book is there’s an episode of Star Trek, of the original series, where there’s a mining colony, and miners are mysteriously dying. And the Enterprise’s sensors aren’t detecting any life signs. They’re like, there’s no one down there.

And then they realize that their detection system is calibrated for carbon-based life forms. And this is a silicon-based creature, it turns out, acting defensively. It’s got eggs and stuff. And so it’s, essentially, made of rock. And so when it gets hurt and the doctor has to take care of it, he basically spackles it with concrete.

IRA FLATOW: That’s scary.

JAIME GREEN: As for whether that’s plausible, there are some challenges. Silicon really likes binding with oxygen– that’s sand and rocks and things like that– which are solid and inert at Earth’s temperatures. But it’s possible that, at higher temperatures, it could be an even better foundation for biochemistry than carbon.

IRA FLATOW: So does that mean we must use our tools, we must create a detector, for silicon-based life also if we’re looking for life?

JAIME GREEN: No. Because we can’t look for everything all at once. Just like telescopes have a limited bandwidth– the JWST is looking at infrared– that’s what it’s doing– similarly– and it’s analogous, it’s not exactly about telescopes– but you have to narrow down your search. You can’t just look at the sky and say, OK, who’s there? You have to decide if you’re looking for technosignatures or biosignatures, if you’re looking for radio waves or lasers, or different kinds of biochemistry. So you’ve got to start somewhere.

IRA FLATOW: Well, where we usually start, and NASA has always started, has been follow the water, right?

JAIME GREEN: Yeah.

IRA FLATOW: Because we assume all life must have water.

JAIME GREEN: We don’t actually assume that all life must have water. But, again, we know that the only life we know of does require water. And water is also a pretty special compound. It’s a fantastic solvent, which is really important for our chemistry. It also is lighter when it freezes. So ice floats, which is extremely rare that a solid would be less dense than its liquid. Which means that fish can survive the winter.

And we also know that water is all over the galaxy. It’s not hard to figure out many different ways for rocky planets like Earth to get water. So it seems like a reasonable assumption. Again, like carbon, we’re not saying that all life definitely requires water, definitely requires carbon. But it’s sort of like with convergent evolution. It’s like, is this just what life on Earth happens to use? Or does life on Earth use these materials because they are the absolutely best suited materials to life?

IRA FLATOW: Let’s go to the phones. More imagination there than I’ve got questions for. So let’s go to Thomas, in Denver. Hi, Thomas. Welcome to Science Friday.

THOMAS: Hey. Thanks for having me.

IRA FLATOW: Hi. Go ahead.

THOMAS: So my question was actually– it connects to the idea that you were talking about water being a precursor for life. Because I was wondering, when we think about life, maybe we should expand our definitions to consider patterns in the world. Because in a lot of planets– gas giants– they cannot support physical life like we are, rocky planets, typically, which support physical life.

But the idea that every celestial body has energy fields, an electromagnetic field, a gravitational field, I just thought about the idea that maybe life could be a pattern. The idea that there are patterns formed. And that sort of leads to the fractal of life. But the idea that a patterns in an electromagnetic system or in a gravity system could be considered sort of a form of life in a way.

IRA FLATOW: Let me ask Jaime. Jaime?

JAIME GREEN: Yeah. I mean, that really illustrates the connection, that life is just one manifestation of physics. And that from the Big Bang, there have been small variations in the universe, that it’s not uniform, it’s not even. And through the movement of time, information accumulates. I talked to one researcher, who says that a molecule is a record of all of the events that led up to its creation. And similarly, life is the same.

And the way that she differentiates life is that life crosses a certain complexity threshold, that it requires information. It requires instructions in order to be built. And it requires a memory. And for us, our DNA is that memory. It’s where all of the instructions for how to remember, how to build a body and to live, come from.

And so then, when you start expanding farther out and looking for more expansive definitions of life– for more expansive theories of life, I should say– you have to decide, is there a line between alive and not alive? Or are we just another manifestation of the universe seeking increasing complexity, holding off entropy for a little bit longer with the use of energy?

It also evokes for me– a few of the science fiction books that I write about in my book– one of them is Stanislaw Lem’s Solaris, which has been made into a few movies also– where the alien entity is something like a planet-spanning ocean. It’s not made of water, but they call it an ocean. And it’s completely impenetrable, completely incomprehensible, but it’s trying to communicate with the humans somehow. And they really don’t even know how conscious or self-aware it might be. And we could have similar questions about complex structures in the cosmos.

It also makes me wonder, does a structure in the cosmos need to be alive in order for us to appreciate its complexity and its long life? Are galaxies meaningful only if we think of them as alive? Or can they be their own beautiful, powerful, strange thing?

IRA FLATOW: Let’s talk a bit about habitability. In other words, can a planet hold life? And is the planet the right size? Is it the right distance from its star or have liquid water? But I was fascinated by what you talked about in your book, about how important the planet having a moon around it, and all the things a moon adds to the survivability and the planet itself. Talk about that.

JAIME GREEN: Yeah. This is another one of those tricky things that we run into when we only have one example to extrapolate from. Because we can see all the ways that the moon is important to life on Earth. And then we start wondering, is that important for all life?

So our moon is, proportionally to the Earth, very big for a moon. And that’s because it was formed in this special way, where, late in the formation of the solar system, a Mars-sized body smashed into the Earth, shooting lots and lots of material into orbit. Which a lot of it coalesced as the moon.

What that impact did, scientists think, was to thin the Earth’s crust. A lot of the crust went up in the explosion and became moon. Which we only were able to verify when the Apollo missions brought moon rocks back to Earth and they could be analyzed. And it’s possible that that thinning of the crust is why we have plate tectonics. And plate tectonics turns out to be vital for regulating the levels of carbon in the atmosphere.

Carbon gets trapped in seabed sediments, which get subsumed back into the mantle of the Earth. Volcanoes release carbon. And it’s this whole feedback cycle that may be what keeps Earth from turning into a snowball or, barring human intervention, getting too hot for life.

The moon also gives us tides. And life began in the oceans and came onto land much later. And it’s possible that having tidal zones, where it was sometimes wet, sometimes dry, facilitated that transition.

The moon also keeps the tilt of the Earth’s axis very consistent. Mars’s axis kind of wobbles up and down. And Uranus orbits completely on its side. One astronomer likened it to a rotisserie chicken, which I thought was so– it’s like, yes, now I can picture that.

But Earth’s tilt is pretty steady, and the moon helps it stay that way. And that tilt is what gives us the seasons. If there was no tilt, there would be no seasons. If there was an extreme tilt, the seasons would be much more extreme and it would be a lot harder to live on the planet.

IRA FLATOW: Let’s go to Lucy, on the phones in Ohio. Hi, Lucy. Welcome to Science Friday.

LUCY: Hi, Ira. Thanks for taking my call. I really appreciate this discussion. It’s fascinating. Thinking that it’s not so much a semantic or philosophical or even biological question, I don’t think we can get around the ethical or moral aspect of, if we found life on other planets if we can’t seem to respect or recognize life here.

And in fact, you talked about Star Trek a couple of times today on the show. And I’ve watched many episodes of the original series. And one of the things that I always took away is that, in order for humans to respect life anywhere, we have to live by a moral compass.

So I don’t think we could be trusted with the information if we did find it. I think it’s still a fascinating question and may be important for our own edification, but I don’t know that we can be trusted. Thank you.

IRA FLATOW: Wait, wait. Can you stay for a second?

LUCY: Sure.

IRA FLATOW: If you say, can we be trusted, what do you mean by that?

LUCY: Well, look around you at what’s happening to the way we treat each other and animals on this planet and the environment. I just don’t believe we’ve demonstrated that we can be accountable or humane or compassionate towards any life except our own.

IRA FLATOW: OK. Jamie, what do you think about that?

JAIME GREEN: That’s a question that comes up a lot. At astrobiology and SETI conferences, there will often be on a panel an anthropologist or a dolphin researcher who points out this exact thing. That we are very bad at recognizing intelligence in other creatures on Earth, even if we look not too far back in human history, even among other human beings, and that we need to be very cautious. And we don’t have a great track record with this.

Ira, your question about, what are we worried about happening? What trust do we not have in ourselves with the situation where an alien’s well-being is going to be in our hands?

If we find microbes on another planet in the solar system, it’s very important that we are mindful of contamination for scientific reasons and for ethical reasons. This came up when it was thought that there had been phosphine detected in the atmosphere of Venus, which was a potential biosignature. That didn’t pan out. But some people were like, cool, we’ve got to send probes to Venus. We’ve got to find what’s there.

But even microbes on another planet, do they have a right to their lives? Do they have a right to not be tampered with? Do they have a right for us not to interfere with their environment?

And Star Trek does offer guidance in terms of the Prime Directive, in terms of how to interact with other intelligent species. But also one of the wonderful things about that show is it proposes an entire worldview that is caring.

And the Earth in that case is post-scarcity, post-poverty, post-war, pretty socialist. There is a very deep ethic running through all of it. It’s not even just the Prime Directive. You have a lot of ethical decisions to make when you are directly interacting with another species or even potentially sending them messages.

IRA FLATOW: Lucy, thank you for that question. I hope that answered it.

LUCY: Thank you, both.

IRA FLATOW: What I find interesting about our discussion here and about what Lucy raised and your references– your references about how to treat other life– it takes it all from science fiction. We have to depend on Star Trek to bring it up, to talk about it. Why are we not thinking on our own about these things?

JAIME GREEN: It is also something that’s discussed in scientific communities using other animals as reference points and also figuring out what the protocol could be if there was detection of an alien signal– if a signal was received. Because there are many governments on Earth, and there are entities with radio telescopes, who could send a message with, like, who’s in charge? Who decides how to act as a single unified diplomatic entity?

So these are conversations that happen in science. But the reason that science fiction is so important is that science fiction is where very creative, insightful writers and storytellers are imagining out the implications. They’re imagining out the possibilities. If this, then what? If we make this choice, what would happen?

Sometimes that’s imbued with cynicism. Sometimes it’s imbued with hope. But that means that the entire genre represents a suite of possibilities, like really robust thought experiments, that have a very important part to play in all of this thinking.

IRA FLATOW: Do you think if we found extraterrestrial life– let’s say there was bacteria on Mars– that the polarization of our community, of the way the United States is so polarized, each one might use it for its own propaganda purposes?

JAIME GREEN: Oh, absolutely. I mean, I think absolutely, if they cared enough. It’s a really interesting question to me whether the discovery of non-intelligent, simple life on another world would feel revolutionary on Earth. I think there are a lot of people out there who probably think that we’ve found life on other planets, whether it’s on Mars or through JWST, on exoplanets.

Because something else that I learned while researching this book that I thought was fascinating was that, for most of modern human history, from the Renaissance to– I don’t know– the 1900s, or maybe even the Viking missions to Mars in the 1970s, people thought that there was life on other worlds. Once Galileo discovered that the planets were spheres, were worlds, people started imagining life on them immediately. And the line between fiction and scientific speculation was much fuzzier then.

And even in the 1900s, people thought they saw canals– people lived their lives thinking there was a civilization on Mars. And it did not make Earth any more peaceful.

IRA FLATOW: This is Science Friday, from WNYC Studios. Talking about life in outer space with Jaime Green, author of The Possibility of Life– Science, Imagination, and our Quest for Kinship in the Cosmos.

I want to go to the phones for a question that kept popping up. Let me go. Somebody else is asking it now also. Let’s go to Frank, in Pittsburgh. Hi, Frank. Welcome to Science Friday.

FRANK: Hi, Ira. Great to be on. Ira, I’d like to hear your guest’s comments on the Fermi paradox, which says that the probability is there’s a lot of life out there. And if that’s so, where are they? Does she think that perhaps there’s something inherent in biological life that makes it destroy itself? Maybe the natural selection competitive thing. Or maybe it takes too much energy to get off planet and very few can do it. I’d like to hear her comments on that.

IRA FLATOW: Yeah.

JAIME GREEN: I think that there are lots of ways to explain why we wouldn’t see other life. If life is cheap and happens on lots of planets, it’s very possible that civilizations are living their lives on their planets and have not come to visit us.

There could be an alien base inside the clouds of Jupiter and we wouldn’t know. There is so much of even just our solar system that is unexplored. There could be stuff in the asteroid belt. Who knows? There could be alien probes and satellites there.

But for me, it’s not the fact that we haven’t encountered alien life that makes me feel a little pessimistic about the odds. For me, it seems like life on Earth arose very easily. Life on Earth arose just about as soon as conditions allowed, as far as we can tell. And that was simple single-celled life, like bacteria or archaea, single cells that don’t have any complex structure even within the cells, let alone evolving into multicellular organisms.

And then it took 2 billion years– billion with a B– for complex life to arise. And that is eukaryotic cells, which are cells with a nucleus, with complex structures, with organelles– you might remember them from 10th grade biology.

IRA FLATOW: Sure.

JAIME GREEN: And that 2-billion-year wait suggests to me, as much as I want the universe to be lousy with life, that that step might have been hard. It might have been lucky. It might be rare. And that happened because one single-celled organism gobbled up the other. And the one that got subsumed went on to basically become our minor mitochondria, which are the powerhouse of the cell. They’re how we get our energy.

And that energy may have been required for the development of internal structures, the development of multicellularity, the development of everything you see with the naked eye. And that makes me wonder if simple life– and bacteria are great, nothing against– I mean, some of them are– and they are incredibly innovative chemically, but they’re not structurally innovative. They don’t build structures of themselves very much. They don’t evolve into multicellularity.

That kind of life could be very common. But I worry that– and I don’t think about this in terms of the Fermi paradox usually because there are plenty of other reasons to explain why we wouldn’t have had visitors– but it’s that step in our history that gives me the most pause.

IRA FLATOW: Thinking that maybe we think it’s more common than it really is. Jaime, it’s a wonderful book. Jaime Green, science writer, author of the book, The Possibility of Life– Science, Imagination, and our Quest for Kinship in the Cosmos, out next week, from Hanover Square Press. Thank you so much for talking with us today. Because it’s a fantastic book and sums up all kinds of thoughts.

JAIME GREEN: Thank you so much, Ira.

IRA FLATOW: You’re welcome. And a note, the SciFri Book Club is reading The Possibility Of Life next month. You can find out more, including how to win a copy, on our website, sciencefriday.com/bookclub.

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