Our universe is a wild and wonderful place. Join NASA astronauts, scientists, and engineers on a new adventure each episode — all you need is your curiosity. Our universe is a wild and wonderful place. In this season, we’ll learn about lunar mysteries, break through the sound barrier, and search for life among the stars. First-time space explorers welcome.
Episode Description: Are we alone in the universe? It’s a question studied in science fiction, but also by teams here at NASA. Join us as we search for signs of life outside of Earth with scientists Aki Roberge, Ravi Kopparapu and Shawn Domagal-Goldman.
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Aki Roberge
When I was in undergrad…
[Song: A New Momentum Underscore by Blythe Joustra]
Aki Roberge
People thought planets were really rare beasts, that it took like really particular recipes to make a solar system like ours. Since then, we’ve found that planets are common. They’re not hard to make. In fact, they’re amazingly easy to make.
Aki Roberge
That means there’s a ton of real estate out there that could potentially be earth-like, and on top of which, the chemicals of life are the most common chemicals in the universe.
Aki Roberge
So if you’ve got… the planet is like, I don’t know, your frying pan and you’ve got the recipe, the ingredients for life, too, it seems to me like it’s pretty likely that nature will have put the ingredients in the pan and hopefully actually made, you know, more life out there.
[Theme Song: Curiosity by SYSTEM Sounds]
HOST PADI BOYD: This is NASA’s Curious Universe. Our universe is a wild and wonderful place. I’m your host Padi Boyd and in this podcast, NASA is your tour guide.
HOST PADI BOYD:… Are we alone in the universe?
[[Wind sounds, hollow bell echoing]]
HOST PADI BOYD: We are fascinated by what it would mean to find life on another planet.
[[Begin sounds of life: forest animals, bubbling ocean]]
HOST PADI BOYD: Our Earth is teeming with life: from lush forests with thousands of interconnected species to vast ecosystems in the ocean. From complex microorganisms to cities full of people, our planet is alive with activity.
[[Sound of city, car honking]]
HOST PADI BOYD: But what else could be out there? We haven’t found signs of life anywhere else in our solar system, but that certainly doesn’t mean we aren’t looking. And even further beyond – there are hundreds of billions of galaxies in the observable universe…full of stars, planets, and moons that we’ve only begun to discover.
[Song: Dawn to Dusk II by Groupe]
HOST PADI BOYD: Scientists right here at NASA are combing the universe for signs of life at all stages. And trying to answer the question – are we alone?
Shawn Domagal-Goldman
My name is Shawn Domagal-Goldman. I am a research space scientist at NASA’s Goddard Space Flight Center. And I’m an astrobiologist, which means I think about the ways we can look for signs of life on planets beyond Earth.
Shawn Domagal-Goldman
My day to day work is actually a lot like other people’s day to day work. I spend a lot of time answering emails, I spend a lot of time in meetings. The difference is the subject. For me, the subject of those emails and meetings is all about the search for life. And that makes a lot of those, what sounds like more boring things, a lot more fun.
HOST PADI BOYD: Astrobiology is a fascinating field, where scientists like Shawn are looking for life among the stars. It might sound like a term straight out of science fiction, but it’s a very real department here at NASA, focused on a lot of different areas.
HOST PADI BOYD: Not only are we using tools to search the stars for signs of life, we’re trying to better understand life here on Earth so we can try to find it elsewhere in the universe.
[Song: Curious Anticipation Pulse Underscore by Gordon Havryliv]
HOST PADI BOYD: It’s an interdisciplinary field, combining the study of how life emerged and evolved here on Earth, with designing tools like telescopes, satellites, rockets and rovers we can use to look beyond Earth.
Shawn Domagal-Goldman
It’s also doing the work of philosophical questions like, ‘What is life in the first place?’ if we’re looking for life. We try to stitch all of that together, take everything we’ve learned about life’s history on Earth, and everything we know about what we can build today, so we can do that search on other planets tomorrow. Integrating all of it together to me is really what astrobiology is.
HOST PADI BOYD: So how exactly is NASA looking for these signs of life? Well there are lots of ways, from doing fascinating field work right here on Earth, to sending rovers and planetary sample missions into the our solar system. But to search for signs of life that might be really, REALLY, far away… light years away… you’re gonna need a telescope.
Aki Roberge
Hi, I’m Aki Roberge, and I am an astrophysicist at NASA.
[Song: Disturbing Game Underscore by Skornik Skornik]
Aki Roberge
I work on helping people, engineers and our technologists, develop ideas for future space telescopes, like future super Hubbles that would be able to study exoplanets around other stars. In particular, find out if any of them are actually like the Earth with oceans and atmospheres and maybe even life on them.
HOST PADI BOYD: Aki is helping to plan future telescopes that will scan the universe for signs of life. And while technologists and engineers will be the ones building out the telescope itself, astrophysicists like Aki help start the planning process with questions!
Aki Roberge
To look for life, on planets around other stars, we need to use the tools of astronomy, that means telescopes. And so you start thinking ‘Well, okay, what kind of data do I need to really answer this question?’ And this is where the scientists come in. This is why the missions, they start with the science.
HOST PADI BOYD: NASA missions are currently targeting three primary regions in the search for life: Mars, icy moons that orbit planets in our solar system, and faraway worlds beyond our solar system called exoplanets. While that search may seem complicated, astrobiologists start with what we know, and go from there!
Aki Roberge
It all comes down to what you think life needs. And all the life on this planet anyway, needs liquid water at some point in its lifecycle.
Aki Roberge
Mars, it looks like maybe had liquid water on its surface, actually, it’s pretty certain that it did at some point. It is doesn’t today, but it did once. So it’s a really good place to look and see if life arose there in the past.
HOST PADI BOYD: We use a lot of different tools to look for life on Mars. NASA has sent five robotic vehicles to Mars called rovers, which explore the Red Planet and will one day bring back samples for us to study in the lab.
Aki Roberge
But then again, okay, liquid water, where else in the solar system has got liquid water, ah, you know, those icy moons of the outer solar system that have, you know, ice covered shells over these deep oceans that are heated from the bottom now looks even more promising because that happens on Earth. There’s life at geothermal vents at the bottom of our oceans. Okay, so that’s a good place to look too.
HOST PADI BOYD: These icy ocean moons include Enceladus, which orbits around Saturn, and Europa, one of Jupiter’s 80 moons! Even within our solar system, it’s harder for us to send a rover to these worlds than it is to visit our neighbor Mars.
Aki Roberge
Then, if you want to find environments that are really like the Earth, you have to go outside the solar system. The Earth is unique in the solar system, in that it’s got liquid surface water, and a global biosphere that is so abundant, it’s changing the chemistry of the whole atmosphere. We know there aren’t any other environments in the solar system like that. So if we want to find the ones that are really like the Earth, you have to go, you have to go to other stars.
Aki Roberge
From the information that we have already, it looks like there are more planets than stars in the galaxy. We’ve discovered a lot of exoplanets, but right now, we don’t know a lot about them. We basically know how big they are. And we know how far away from their star they are. But that’s… not a lot more. So we’re really pushing now, first with the James Webb Space Telescope, and then with these future telescopes that I work on, to actually try and do a better job of finding out what the planets are actually like.
HOST PADI BOYD: You might remember this from one of our season three episodes: exoplanets are planets outside our solar system that orbit stars other than our sun.
HOST PADI BOYD: As of 2022, we’ve discovered just over 5,000 unique exoplanets with the help of different telescopes including Hubble, Kepler and TESS, the Transiting Exoplanet Survey Satellite. We also have tons of new information coming to us soon, thanks to our newest tool, the James Webb Space Telescope.
[Song: Fabulist by Levesque]
HOST PADI BOYD: Since these exoplanets are so far away, astrobiologists like Shawn search for clues about their composition, atmosphere, and habitability with data, rather than with detailed pictures.
Shawn Domagal-Goldman
Now we’re not going to get a map of those worlds, not even like an old eight-bit pixelated, blocky map from the video games I played when I grew up. We’re gonna get like literally one dot of light, which isn’t really a lot to go on, if you want to look for a forest or something like that.
HOST PADI BOYD: The information we get back from these powerful telescopes is so limited – it’s often just one pixel of light in an image of the night sky. By looking at that pixel of light as a spectrum of different colors or wavelengths, we can learn more about what the planet is made of and how it operates.
HOST PADI BOYD: When you start pulling that data apart, we can discover fascinating things!
Shawn Domagal-Goldman
Once we do that, we’ll be able to look for sort of the fingerprints that certain gases have and if we find the gases that life makes, like oxygen or methane, then we think we’ve found something.
Shawn Domagal-Goldman
At that point, we’re back into the scientific method, because someone, somewhere is going to say, ‘Well, I know some other way to make oxygen’ or ‘I know some other way to make methane’ or whatever our fingerprint is that we found of life, someone, somewhere will say, ‘I know a way to do that without biology’. But either way, we’ll have at that point hypotheses to test and build another generation of telescopes, or maybe one day we do send something to fly by those worlds.
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Ravi Kopparapu
I’m Ravi Kopparapu. I’m a planetary scientist at NASA Goddard. And I look for alien life on other planets. Whenever someone asks my daughter, she says that my dad finds aliens. And that’s as simple as that.
HOST PADI BOYD: Ravi is also a NASA scientist, intent on finding whatever life could exist in the universe. And he does that a couple of different ways, looking for direct and indirect hints of life!
Ravi Kopparapu
So, many of the searches right now that NASA and other scientists, other institutions are trying to find are some signs of biosignatures. What does that mean? It’s a signature of biology happening on a planet. And so those kinds of signatures are the ones that many of NASA missions and NASA telescopes are going to look for.
HOST PADI BOYD: The best way to find life is to get to know life. Our Earth has housed all kinds of biology for a pretty long time! The world of dinosaurs was so different than the world we live in today.
Sound of forest life and roaring
HOST PADI BOYD: And even now there’s wacky ways of life all over the place!
HOST PADI BOYD: A big part of astrobiology is field research right here on Earth. Astrobiologists look to understand how life works all over the world, from lava tubes of Hawaii, and acid mines in Spain, to deep sea vents in the Caribbean and the frozen lakes of the Antarctic.
HOST PADI BOYD: Thinking back on what our home planet has looked like over the eons, as well as the variety of ways Earth looks now, helps us figure out what we should be searching for on other planets.
Ravi Kopparapu
Earth had several biosignatures over its lifetime. Earth is about four, 4.5 billion years old. And life on Earth thrived for about three, three and a half billion years. Over time, our bio signatures, changed. Right now we think, oh, yeah, you know, if you have oxygen and some sort of a nitrogen atmosphere, it should be fine, that’s life, right? But that’s the current Earth right now. About 2 billion years ago, there was no oxygen. There were a lot of methane-loving organisms.
HOST PADI BOYD: Most of Earth’s history doesn’t include life as we know it today. For a long time, “life on Earth” meant microorganisms. You know, like bacteria and fungi…
HOST PADI BOYD: Intelligent life is a blip on Earth’s timeline, but organisms have lasted much longer, which is why the majority of NASA’s extraterrestrial search is for indicators of bacterial life.
[Song: Take A Chance Underscore by Anderson]
Aki Roberge
It’s important, I guess, to remember that humans, we are not in the majority on this planet. It’s plants, it’s bacteria. They outnumber us by a lot. So that’s the kind of life that we think we can detect from interstellar distances, which is really far away.
Ravi Kopparapu
If you find a planet that has a lot of methane and co2, and water and oxygen and nitrogen and things like that, there is a good sign that that planet may be active in biology, that doesn’t necessarily mean that it is for sure a habitable planet, but it’s a good sign.
Ravi Kopparapu
Beyond that, we also want to find technosignatures. Just like a biosignature is a sign of biology, technosignature is also a sign of technology on a planet. Some of them that we have worked on are pollutants. If a planet has had very Industrialized civilization, just like us, they might be emitting pollutants as a byproduct of their industrialized activity.
HOST PADI BOYD: This is where our hypotheses get really creative. Technosignatures, another very real sci-fi concept in our scientists’ arsenal, are indicators of advanced civilization on a planet. Just like we humans have made our mark on the Earth, so could another species change their planet. And if we can see similar changes on another planet, we can start to wonder if something alive was responsible for them.
[Inception Underscore by Lemay]
HOST PADI BOYD: Based on how Earth functions, we already know of things in our atmosphere that weren’t made naturally.
Ravi Kopparapu
Chlorofluorocarbons, for example, we use that in our refrigerants. Nitrogen dioxide, for example. It comes from the vehicle emissions that we are using fossil fuels, right, we use fossil fuels for almost everything. So if you’re using a fossil fuel, you might be generating nitrogen dioxide, we can use that as a signature.
Ravi Kopparapu
We can use city lights, night-side city lights! If you see a planet in the nightside, you see lots of bright things, that’s a city light.
Ravi Kopparapu
…Radiocommunication!
Ravi Kopparapu
We can look for probes within our solar system that other civilizations have sent to us. Imagine this, NASA is sending Voyager probes, Pioneer probes to outer parts of our solar system, they’ve already crossed our solar system and gone outside. If we can do it, they might also be doing it.
HOST PADI BOYD: The SETI Institute, which stands for Search for ExtraTerrestrial Intelligence, is looking for this kind of advanced life, keeping an eye and an ear out for any sort of communication that might be coming our way from an extraterrestrial neighbor.
HOST PADI BOYD: But what if life elsewhere doesn’t look anything like life here? How could we begin to guess about the processes of life we don’t even know exists? That’s why scientists spend a lot of time thinking about it and they start from what we do know.
Shawn Domagal-Goldman
This is one of the most challenging parts of astrobiology, because we’re talking about aliens, right? Like, alien life should be alien to us. And it should be weird, and it should be different.
[Song: Life Elsewhere Underscore by Bellingham]
Shawn Domagal-Goldman
However, if you go too far, you can look for things that just really aren’t plausible. That is a really hard tension to work out. The way that we practically carry that out, right, is we look for life in the most likely places, in the ways we know how to detect it first. And the thing I remind people when I talk about this is, this is just the first generation of these things we’re going to do. We’re going to look for Earth-like life on Mars and on these icy worlds and on exoplanets. And if we don’t find it, it might be because those places are all dead. It also might be because the life on those places is truly weird. And we have to think more creatively and more alien-like to find them with a second generation of missions.
Shawn Domagal-Goldman
If you told me you lost your keys, I would have a bunch of ideas of where you might look. And it would be based on my own experiences. I would say, look in the coat you wore yesterday, look in the pants you wore yesterday, if your pants have pockets, look in your couch cushions, look in your car, maybe under the car seat or in the cupholder. Maybe look at your door because I’ve been forgetful enough to leave my key and my front door when I’m on my way in. That’s not all the theoretical places your keys could be. But I’d find a lot of keys.
Shawn Domagal-Goldman
You can extrapolate from Earth-based life to start your search. And just don’t call it ‘the end.’ Don’t say that the universe is devoid of life if you don’t find it, just start with what’s familiar. And then if that doesn’t work, maybe focus and hone your search to the specific environment you have not yet found life in. And then the third step is to try to get really creative… but for me, you start with the familiar and then branch out.
Ravi Kopparapu
When NASA is looking for life on other planets, trying to explore the galaxy or looking for planets, science is the spearhead for everything. Science decides if you have the right data, science decides if you have the right conclusion.
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Ravi Kopparapu
If science says that you do not have that, it is not there. And that’s what we keep our heads down and look for when we are looking for life on other planets. Science should be the first and the last thing we have to do before we announce anything to anyone else.
HOST PADI BOYD: Finding evidence of life on Mars, an icy moon, or a far off exoplanet, would be groundbreaking. It’s a discovery that would fundamentally change our understanding of the universe. But it also would take a lot of verification, testing, study, and debate before we knew for certain what we’d found.
HOST PADI BOYD: Imagine you’re the scientist who sees the first sign of life. How would it feel to make such a monumental discovery?
HOST PADI BOYD: If you’re Shawn, the first thing you do is call your mom.
[Song: Starting to Understand Instrumental by Doney Perry]
Shawn Domagal-Goldman
If it’s just me sitting with the data, I’m definitely calling my family members. My mom, my brother, my wife and my daughter, tell them all about it.
Shawn Domagal-Goldman
The next step would be to talk to the colleagues on the team I’m on because this is almost certainly not me, looking at the data. It’s probably like a bunch of us in a control room somewhere, kind of all staring at our screens with our jaws open at what we’re seeing.
Shawn Domagal-Goldman
The next step is we’re probably going to put it through a series of tests to make sure that what we think is biology is actually biology and not some astronomical or geological or chemical process.
Shawn Domagal-Goldman
And then after all that, we’d probably write up a paper. And at that point, people that weren’t on the team are going to take a really critical eye to it, probably many people, and they’re going to try to find flaws in our arguments.
Shawn Domagal-Goldman
And if it gets through them, and it’s accepted, and people let us publish a paper that says, ‘We’re not alone’, that’ll then go out to the public. And it’ll probably happen simultaneous with a press conference. And that moment to me is really special, because it might be the moment that the world finds out that we’re not alone. However, we as scientists won’t know it’s that moment, for years. And the reason we won’t know is even if I was sitting on that stage in that press conference, saying we found evidence that we’re not alone, I would know as a scientist, that statement is only going to be accepted after about 10 to 20 years of argument and debate with the rest of the scientific community.
Shawn Domagal-Goldman
And it’s quite possible we are wrong. But we won’t know whether we’re right or wrong until the scientific method can play out for, really, another generation of scientists. Before we know whether or not that original sign of life that we claimed to have discovered was really evidence that we’re not alone or just some false positive that we thought was biology but was really some other process we didn’t understand.
Aki Roberge
It’s probably not going to be, we took this one piece of data and tada, there it is. It’s probably going to be like, Oh, that’s weird. And then we’ll take another piece of data and it’ll be like, Oh, okay, that’s weird, too. But it makes sense with this other piece of weird/ That’s kind of like howall scientific discovery goes, it’s really rare that it’s just like Eureka, I took this one thing and I know exactly what it means. Vast majority time, That’s not how it works. The real like amazing phrase that scientist says themselves when they’re on the cusp of discovery. It’s not Eureka. It’s actually “That’s weird”.
HOST PADI BOYD: We are at the very beginning of understanding who we are and what our place is in the universe. Shawn, Ravi, Aki, and others are laying the groundwork for future missions that will search for signs of life far beyond our solar system.
HOST PADI BOYD: It is such an exciting time for astrobiology, a time of brainstorming, planning, self-reflection, and study that could one day yield incredible results.
[Song: Unlimited Underscore by Bellingham]
Shawn Domagal-Goldman
The stuff that I want to be a part of, all these missions that are going to look for life, they are going to be happening for the next five to 10 to 20 years. Even a five year old today could be done with college and writing their PhD dissertation on the data from one of these missions looking for life. There’s plenty of time for people to get involved.
Shawn Domagal-Goldman
For me, the dream is, when I retire that I’ll be able to take my grandkids out and point at the night sky, and be like, ‘That star over there. There’s a planet around that star that is inhabited globally, like our planet, like our home. We don’t know what kind of life is there yet. But that’s, that’s your generation’s mission to figure that part out.’
[Song: Curiosity Outro by SYSTEM Sounds]
HOST PADI BOYD: This is NASA’s Curious Universe. This episode was written and produced by Christina Dana. Our executive producer is Katie Atkinson. The Curious Universe team includes Maddie Arnold and Micheala Sosby with support from Caroline Capone and Juliette Gudknecht.
HOST PADI BOYD: Our theme song was composed by Matt Russo and Andrew Santaguida of SYSTEM Sounds.
HOST PADI BOYD: Special thanks to Claire Andreoli, Amber Straughn, Barb Mattson, Tahira Allen, Mike Toillon, and the astrophysics team.
HOST PADI BOYD: If you liked this episode, please let us know by leaving us a review, tweeting about the show @NASA, and sharing NASA’s Curious Universe with a friend. And, remember, you can “follow” NASA’s Curious Universe in your favorite podcast app to get a notification each time we post a new episode.
Ravi Kopparapu
So let’s say you’re invited to a party by someone you don’t know much. The first thing you do is to go to someone you already know. So that you can strike up a conversation and then start introducing yourself maybe, and so on. That’s exactly what we are doing with the search for life. We don’t know what life looks like, we don’t know anyone there. And the first thing we want to look for is Earth-like life.
Producer Christina Dana
Amazing, terrifying and amazing!
Ravi Kopparapu
This is not terrifying at all! I mean, we are finding our neighbors right? So our neighbors are fine, I think.