Looking for life in the clouds of Venus

[MUSIC PLAYING] IRA FLATOW: Hi, Ira here. And you’re listening to Science Friday. Dr. Sara Seager has made a career out of looking for signs of life in outer space, searching for exoplanets thousands of light years away. But now Dr. Seager has come home, sort of. She has turned her attention to our neighbor, the planet Venus.

At first, it would seem like an unlikely place to look for life. Its surface temperature is hot enough to melt lead. It has a smothering carbon dioxide atmosphere, all topped off with sulfuric acid clouds. But Dr. Seager thinks it might be possible for some form of life to survive there not on the planet’s surface, but up in those clouds.

Dr. Sara Seager is an astrophysicist, planetary scientist at MIT and part of a team leading a proposed series of missions to Venus to sample those clouds for evidence of life. Welcome back to Science Friday.

SARA SEAGER: Thanks, Ira.

IRA FLATOW: When I list the conditions on Venus, life doesn’t seem likely. The idea that life might exist in the clouds there, where does that come from, and why are you hopeful about that?

SARA SEAGER: Well, first, Ira, the way you listed what it’s like in Venus atmosphere, it doesn’t sound too friendly to me either, so yes. Well, when we think about what life requires, if we want to truly boil down to the fundamentals, there’s just a few things. One is temperature, the right temperature for covalent bonds, so complex molecules of the kind life needs to use can form.

The second is energy. And of course, there’s energy from the sun on Venus. And the third is a liquid environment, liquid so that chemical reactions can happen.

So if you just boil it down to that, Venus does have what we require. And although the surface, as you pointed out, is so hot, hot enough to melt lead, just like here on Earth, if you hike up a mountain or go in an airplane, it gets colder and colder as you go above the surface. And the cloud layers with the liquid are the right temperature for life. And this is why over half a century ago, Carl Sagan first put out the idea, based on these fundamentals, that perhaps there could be life in the clouds of Venus.

IRA FLATOW: How would that life form be? Would it be the kind of life we have here on Earth?

SARA SEAGER: Well, at the very basics, first of all, if there is any life in Venus clouds, it’s incredibly primitive. We don’t have evidence for it, not yet anyway. But think about the most primitive type of single-cell type of life possible. So first of all, it would be like that.

Secondly, is it like Earth life? No, because our Earth life cannot survive in sulfuric acid. Specifically, our DNA is rapidly destroyed. So if there is life there, it’s going to be incredibly primitive in the cloud particles, and it has to have a different biological makeup than Earth life.

IRA FLATOW: Now, how would you know that, that life exists there?

SARA SEAGER: Well, we don’t know if life exists there. And this is the billion-dollar question that everyone has of, how do we know if there’s life anywhere? And at the moment, what scientists are doing is they draw a dividing line in chemistry. And on one side of the line are the kinds of basic molecules that nature provides, like from photochemistry or from volcanoes or minerals or just chemicals that are just present.

And on the other side of that line are incredibly complex molecules, so complex that we think only life could make the molecules. And therefore one of the main ideas is if we can find complex molecules, we can infer the presence of life. The only problem is, where do you draw that line? And also, that line keeps changing.

IRA FLATOW: Is it possible to experiment, to create the kind of life you might see in those clouds?

SARA SEAGER: Well, I would say yes and no. I mean, if you think about it, people are trying to create life on Earth in the lab, like life that may have arisen here on Earth first, early on in water. And scientists still haven’t been successful at that, although they’ve been successful in many separate areas in the formation and origin of life. So we can repeat those same experiments.

Like for example, here on Earth in the laboratory, people take lipids, fats with heads, like polar head groups, and they put those in water to try to form little compartments, vesicles. We can’t say primitive cell membrane, but that’s to get the idea, little tiny spherical vesicles, because all of our life has compartments. So we can copy some of those ideas, and we can try to find materials that are stable in concentrated sulfuric acid, what the Venus clouds are made of. And we have done that.

IRA FLATOW: Tell me about that. What do you mean have done that?

SARA SEAGER: Well, in this case, I’d like to give credit to Daniel Duzdevich, who was the lead author on this work, part of Jack Szostak’s group. And they took some lipids with polar heads. So these are simple chains of carbon atoms and about 10 or 12 long. And you put them in water, and they point their polar head outward.

And their tails don’t like water. They’re hydrophobic. And those point inwards. And so then the geometry self arranges to a little spherical vesicle. And my team at MIT has repeated this experiment with using different lipids also. Well, some of these lipids are stable in concentrated sulfuric acid. And they also join together and make these little, tiny vesicles, which you subsequently look at them under the microscope and you see these little spheres.

IRA FLATOW: So you’ve had to start up basically your own biology or biochemistry research group to look at this.

SARA SEAGER: Yes, I definitely have because people traditionally are so– maybe naturally so, but they’re so biased against the even hint of an idea that there could be life in concentrated sulfuric acid. People are very, very resistant to this.

IRA FLATOW: Well, tell me how life could survive in concentrated sulfuric acid?

SARA SEAGER: Well, we certainly don’t have all the answers. So we’re starting from something way simpler than life itself and just the biomolecular building blocks. So for example, we took our 20 biogenic amino acids, and we have put those in concentrated sulfuric acid. And we found, with one exception, that all of them are stable. Some of them are chemically modified, but the rest are stable.

And that’s the kind of thing if we talk about it in a scientific community, people will be like, well, that’s interesting. That is astonishing. But how is that helpful? We need to think about amino acids joined together to form peptides. Then we can study peptides in concentrated sulfuric acid. And that’s an ongoing project right now, where we’re definitely finding that although some of them break down, we are definitely finding variants that are stable.

IRA FLATOW: Mm-hmm. What about the information-carrying parts of life, the molecules like DNA or RNA, would they survive in those clouds?

SARA SEAGER: Our DNA and RNA cannot survive in the clouds. There’s this really well-known experiment. People can Google it, sugar in concentrated sulfuric acid. If you put sugar in concentrated sulfuric acid, wow, it turns black. It gets really hot. And then this kind of snake of dried-out carbon starts growing above the edges of the container that you mixed everything in. So our DNA has sugar. Our DNA cannot survive.

But what I set out to do with my team is to come up with a DNA-like molecule. So not our DNA, but swapping out parts because I want to convince you, Ira, and the listeners and everybody that there may not be this kind of swapped-out DNA, but it could be another kind, just to prove that complex information-carrying molecules could be stable in concentrated sulfuric acid. Well, I’m really pleased to tell you that we have a milestone in this direction. And thanks to my colleague Janusz Porowski, we have come up with a molecule that already existed.

It’s not called DNA. It’s called PNA, which stands for Peptide Nucleic Acid. And it’s a synthetic molecule people use here on Earth. And PNA, we have shown that a single strand of PNA is stable at room temperature in concentrated sulfuric acid, actually up to about 50 degrees Celsius.

IRA FLATOW: Is this the kind of thing you would be looking for in the clouds?

SARA SEAGER: Well, it’s tricky, right? Because if there are aliens out there and they want to find life on Earth, what are they going to look for? There are so many variants that could be possible. And because we don’t how our DNA originated, we don’t which exact DNA-like molecule could be there. So the whole question of what to look for becomes really tricky.

IRA FLATOW: We need to take a quick break, but we’ll be back with more conversation with Sara Seager in just a minute.

Just to let you know, we’re wrapping up Science Friday’s fiscal year on June 30, and that means we need to raise $100,000 to close out our budget. The world needs science journalism more than ever, and we are here to deliver it. We know you’re here for it, too.

You’ve heard me say this before, but it really is true. Science Friday can only continue with your support. So please go to sciencefriday.com/donate to make a donation. Any amount you can chip in will help us get to our $100,000 finish line. Again, that’s sciencefriday.com/donate. And thanks.

So you’re proposing to go to the clouds of Venus, a mission to Venus, called the Morning Star Mission. And to do what?

SARA SEAGER: Well, we have a international consortium that I started and lead, and we call ourselves the Morning Star. Missions to Venus– “Missions,” plural. And we envision a series of small, focused missions, each building on the one before it, to search for signs of life and eventually life itself. So it won’t be like initially we get there and say, we found life. It’s kind of a very long journey because we aim to find evidence for organic molecules. Then, next we aim to find very specific, complex organic molecules we’re looking for. And if we get far enough along, the end goal, the end goal in the future, is a sample return so that we can bring some of the clouds back to Earth to look at them with our incredibly sophisticated techniques here on Earth.

IRA FLATOW: So tell me how far along you are. What are the steps? Where do you find yourself now?

SARA SEAGER: Well, now we have a series of planned missions. And the first mission is called the Rocket Lab Mission to Venus. And we work in partnership with Rocket Lab. Right now, I have been responsible for the science team and the instrument. And our instrument is built. In parallel to this, Rocket Lab has built our entry vehicle. It’s like a little capsule that will be dropped off in the Venus atmosphere.

And this capsule– this is like a small, cheap mission. It’s our first mission, largely privately funded, that will go to Venus. And this capsule will be dropped off in the atmosphere and will slow down due to its own drag and last for about five minutes in the clouds. And this capsule has a very special heat shield on it, supplied to us by NASA Ames, so that the capsule will not get destroyed as it races through the top part of the Venus atmosphere.

In addition to that, there’s a pressure vessel that is built that would go on the inside. So that’s how far along we are. There’s a lot of plans. A lot of other smaller things are getting in shape so that we’ll be able to launch this first mission to Venus.

IRA FLATOW: So you have the instrument. You have the capsule. You need the rocket now to get to Venus. How soon might that rocket be available?

SARA SEAGER: Well, I just want you to Rocket Lab has been an incredible partner, and they’ve done an absolutely fantastic job. And when we first teamed up a bunch of years ago, we were slated to go on the Electron. That is Rocket Lab’s amazingly reliable small-capacity rocket. But for a variety of reasons, Rocket Lab has put us on the Neutron, their much higher-capability rocket.

And the neutron– you can read all about it in the news– it is getting built right now. So we’re waiting till the Neutron rocket is ready. And the Venus launch windows happen about every 18 months. So we and Rocket Lab is aiming to get the next window after Neutron is ready.

IRA FLATOW: And that might be between now and 18 months from now?

SARA SEAGER: I would say so because one of the windows is the summer, and then the next window is about 18 months.

IRA FLATOW: Mm-hmm. And the longterm goal of the flight, the big picture is to continue steps toward bringing a sample return from the clouds, correct?

SARA SEAGER: Yes, Ira. And how amazing would that be if I bump into you again at an event, and I’m like, Ira, here’s a little gift–

IRA FLATOW: [LAUGHS]

SARA SEAGER: –a little tiny sample of liquid clouds from Venus?

IRA FLATOW: Yeah. And you’re pretty confident this is going to happen.

SARA SEAGER: Well, have to understand that scientists like me have to be confident. Why would I wake up every day really early in the morning and get to work on this if I didn’t believe it was possible?

IRA FLATOW: But how do other scientists look at this? Do they think this is a pipe dream for you?

SARA SEAGER: Other scientists do not think there’s a possibility of life on Venus, and I do have a way to explain it to you. It’s been an incredible journey. Well, every milestone we do in the lab– and some of this is my own team, some is with partners from other labs. The organic chemists out there and the people who review our papers, like let’s say, an editor at a high-profile journal, they will legit believe our result. They’ll say, well, this result, it looks good. But even if it is true, this work is going to just dead end.

So initially, they would say, well, amino acids, you’ve shown those are stable. But it doesn’t matter because peptides won’t be stable No, then we can say peptides are stable. Some peptides are stable. And they’ll say, well, that doesn’t really matter because you have to show they fold.

And there’ll come a time, and maybe we can show that. And people will keep complaining about the next thing that will dead end. But I’ll tell you what, I already lived through all this before for exoplanets. I lived through a time when people kept telling us the field was going to dead end.

But if you work in the field and you’re deep in the trenches, and you see all the possibilities flourish, then you know it’s possible. I can’t guarantee that the biomolecule complexity won’t dead end in sulfuric acid. But everything so far shows it’s a go, and we’re going to keep following this and keep on doing it.

IRA FLATOW: What we hear most of the time from scientists is that people will ask them– and I’ve asked this question over and over again– what practical value does any of this have for us? And how do you answer that?

SARA SEAGER: Yes, well, I’ve given this a lot of thought, actually. And I’m about to make a big move from my current job at MIT in the USA to Canada, to the University of Toronto. And Canada is really, really pushing people and encouraging everyone to think about that question.

So one thing is that when we want to go to Venus to search for very specific organic molecules, complex organics, but a long list of them because we don’t what we’re looking for, there are a number of miniature molecular sensors being developed in this area. We’re developing one in my lab. Other ones, like carbon nanotubes, are out there.

And we’re taking all of these, and we’re trying to accelerate their development and usage in terms of their robustness in the field. And a more complicated thing to explain is selectivity. How do you found the molecule that you’re targeting? And these have a lot of different uses. They can be used for chemical threat detection. They may have uses in agriculture and medicine and a lot of areas.

So it is kind of rare, but it happens that in space science we invent something or we build things, like medical imaging. Even GPS came out of people experimenting with rockets. But I do see a way, a path, to making that more purposeful. These crazy questions we’re asking in the search for life and the origin of life on Earth, in exoplanets, in space science, we really have to push the envelope because we’re going to extreme environments. We need more decimal places than we traditionally use here on Earth. So there is room for pushing the envelope in astrobiology and in science, but purposely finding and exploiting and executing the impactful relevance we could have in society.

IRA FLATOW: We’ve been talking for years. You’ve made such a reputation in exoplanets. This almost seems like a career shift for you, Sara. Do you view it that way, why you’re changing directions? I’m not saying it’s less of a thing that you’re working on, but I’m just wondering personally, why the change in direction?

SARA SEAGER: Yes, well, I have two reasons. One is a more thoughtful reason, and one is the reality. So the thoughtful reason’s that I love doing new things, I’m really comfortable pushing the envelope, inventing new things, starting new fields. And my original field of exoplanets, and specifically exoplanet atmospheres, got very mature. And there’s a lot of amazing young people, and even now, people not so young doing a fantastic job there. And I try to not do things that other people can also do. So that’s one reason.

I do still work on exoplanets, but something happened, something pretty serious actually, which gave me pause. And that is that myself, and now a growing number of others, my heart, my whole heart is in wanting to find signs of life on other planets. But we had a little glitch. And this glitch is how sure can we be that we have found signs of life by way of a gas in atmosphere that doesn’t belong? Here on Earth we have oxygen, which fills our atmosphere to 20% by volume.

But without life, without plants and photosynthetic bacteria, we would have no oxygen. And astronomers first thought of this 100 years ago, that maybe we should look for oxygen on other planets. And they did. They looked on Venus, and they looked in other places. And today we’re there. We have the James Webb Space Telescope. The field that I founded, exoplanet atmospheres, is booming now. And there’s thousands of people working on it.

And just to make a very long story short, I was here at MIT making a list of all possible molecules that could be considered a sign of life, a biosignature gas on an exoplanet. And one of the molecules that jumped out as my favorite, is called phosphine. It’s a phosphorus atom tied to three hydrogen atoms, something that on Earth pretty much only exists because of life, us humans making it as pesticides or bacteria in oxygen-free environments.

Well, another astronomer across the globe, Professor Jane Greaves, was also working on phosphine. Very unusual for two astronomers to be thinking about this molecule. And she was purposely trying to find signs of life on Venus by looking for this molecule, which has a signature at radio wavelengths where she’s an expert.

Someone connected our two teams. And together, with a large team led by Professor Jane Greaves– you may remember this. You may have talked about it on your show. But it was a report about five years ago of the detection of phosphine gas in the Venus atmosphere, which couldn’t be produced by lightning, volcanoes, meteorites, or any way with known chemistry, thus leaving the possibility for life in the clouds. Do you remember that?

IRA FLATOW: I do remember that. I remember, though there was pushback against that discovery.

SARA SEAGER: Lots of pushback. And this ended up very controversial for a number of good reasons. The data’s all public. Number one reason, is the signal real? People analyze the data. Many groups did not recover the signal, although some groups did recover it.

Second reason is if the signal’s real, is it attributed to the right gas, phosphine, or could it be another gas? Let’s assume for a moment those are true, that the signal is real and that it is phosphine gas. Then the question where all the money is, question number three is, is this gas made by life, or is it made by some other chemical process?

And I’ll tell you what, those three questions, people strongly disagree on all three of those points. So let’s now switch back to exoplanets. If we’re going to fight over this about Venus, how much harder is it going to be for exoplanets? Exoplanets are very far away. They’re not even a point of light, really. We see them crossing the face of the parent star, and we have to really, really dig deep in our data analysis methods. And we see a bunch of spectral features.

And same thing, any sign of life is probably going to be a tiny signal. And we’ll be asking ourselves, is the signal real? And then we’ll be arguing about that. And then we will ask, is it attributed to the right gas that we think it is, or could it be one of many other gases?

And even if we as astronomers all agree on those first two, how will we know whether it’s made by life or whether it is coming out of the interior of the planet? Because we have no idea what’s coming out of the interior. The point is that Venus is right next door. We have sent spacecraft to Venus. We can send more spacecraft to Venus. We have telescopes that can observe it in great detail. But exoplanets, we have almost no information about them. And it makes that problem many, many millions of times harder.

IRA FLATOW: Mm-hmm. So do you think that what you discover on Venus might influence how we think about exoplanets?

SARA SEAGER: I think so, and I think it has already. Because– and by the way, Ira, I’m still working on exoplanets. I’m working really hard to understand all the kinds of planets out there and all the kinds of false positives that might get confused with future potential signs of life. But it does in two ways. One is there’s efforts to try to find an Earth twin eventually. But will they be Earth twins? Or could Venus twins be the most common thing out there? We don’t know yet.

Secondly, if we have two planets, Earth and Venus, that are similar in mass and size and interior composition, yet have such different outcomes at their surface, that begs the question, surely there are more planets that are even just as different from Earth and Venus as Venus and Earth are from each other. So yes, Venus and studying it definitely affects our perspective on exoplanets.

IRA FLATOW: Mm-hmm What would it take, then, to convince you and your peers that yes, there is life on an exoplanet?

SARA SEAGER: Well, the reason I mentioned sample return from solar system planets was, I think, at least in our solar system, it’s going to take us having a sample where we either see little things moving around, or we are able to analyze the complex molecules in a complex tapestry that would make up any kind of cell wall. For exoplanets, I am still enthused about finding signs of life. But instead of our generation finding a definitive sign, I do think we’ll find lots of things that we could attribute to life, but just not very certain about. And all of these potential biosignature gases will be candidates that will help fuel the next generation of telescopes.

And what is that next generation? I certainly have my favorite. And it’s going to sound way out there, maybe as crazy as finding signs of life in the Venus atmosphere. But my favorite is called the solar gravitational lens telescope. The idea is to send a telescope to 500 times the Earth-Sun distance. And when we figure out how to do that, that alone would take 20 years to get there, and use our sun as a gravitational lens.

Because mass bends space. And we’d have to also block out our sun. But if we chose the right exoplanet system and lined it up perfectly, we could see that background exoplanet magnified in light to 100 billion times. And we could instead put 1,000 by 1,000 pixels across that planet. So to be convinced, we’re going to have to go to the next paradigm of telescopes.

IRA FLATOW: So that telescope would turn its gaze back on our sun, which would be blocked out. But we would see the gravitational lensing of the sun to use it as a telescope.

SARA SEAGER: Yes, we would be using– essentially, the sun would be our lens. It would be a gravitational lens magnifying a background chosen planet of interest.

IRA FLATOW: You really like to think big ideas, don’t you?

SARA SEAGER: I do. I do really like big ideas. I love the impossible.

IRA FLATOW: And you’re so excited about this Venus mission.

SARA SEAGER: Well, I am. And you know when you get so-called bee in your bonnet or you get obsessed with something and really fixated on things? That’s almost the definition of being a scientist. And sometimes you can’t explain why. You don’t ask a child, why did you learn how to walk? They just do.

And so sometimes in science, we get fixated on something. It’s part obsession, part inner voice, part trusting your own judgment. And part of it is just the sheer thrill of the journey of exploration.

IRA FLATOW: So if you’re a betting woman– are you a betting woman?

SARA SEAGER: I’m definitely a betting woman.

IRA FLATOW: All right. Give me some odds here.

SARA SEAGER: OK, well, my odds for life on Venus are 50/50.

IRA FLATOW: Really? That high?

SARA SEAGER: Mm-hmm. Yeah, 50/50, and it depends if you’re a glass-half-full or glass-half-empty kind of person, but yes.

IRA FLATOW: Mm-hmm. Well, we’re all excited for your adventure here. And we’re keeping our fingers crossed and good luck.

SARA SEAGER: Thank you. Thanks a lot, Ira.

IRA FLATOW: You’re welcome. Dr. Sara Seager, astrophysicist and professor of physics and planetary science at MIT. Thank you for taking time to be with us today. This episode was produced by Charles Bergquist. And if you appreciate exploring new worlds, please rate and review us wherever you get your podcasts. Thanks for listening. I’m Ira Flatow.

[MUSIC FADING OUT]

Copyright © 2026 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/