Sara Seager: How Close Are We To Finding Life On Another Planet? In our galaxy alone, there are hundreds of billions of planets. And Sara Seager is looking for the perfect one, a "Goldilocks" planet— neither too hot nor too cold— that could support life.
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Sara Seager: How Close Are We To Finding Life On Another Planet?

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Sara Seager: How Close Are We To Finding Life On Another Planet?

Sara Seager: How Close Are We To Finding Life On Another Planet?

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  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
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SARA SEAGER: Well, I always loved the stars. I remember clearly when I was about 10 years old, for the first time I went camping.


This is astrophysicist Sara Seager.

SEAGER: And one - for whatever reason in the middle of the night, I stepped out of the tent, and I looked up and, wow. I saw so many stars. It just took my breath away.


SEAGER: And all I could think about was, wow. Like, what is this? You know, what's out there? And I also thought, like, why didn't anyone ever tell me about this, you know? I think for most people, maybe it's not a big deal or really relevant, but I just was so shocked. It was like seeing a beautiful piece of artwork or hearing music for the first time.


SEAGER: Like, I just never knew it was out there.


RAZ: Sara is now one of the leading astrophysicists in the world, and she has one main goal in mind.

SEAGER: My life's obsession for planets is to find another planet like Earth, one with water and continents and with signs of life in the atmosphere.

RAZ: Which could be possible one day because just in the past 10 years, scientists like Sara have made incredible discoveries about planets outside our solar system. And up until relatively recently, we only knew of the existence of a small handful of these exoplanets. But today, scientists like Sara Seager have identified thousands.


RAZ: So help me understand this. We are on planet Earth, the pale blue dot, in a - let's just call our solar system a neighborhood, like, our block in our galaxy. Then, like, what's beyond there? What do we know about what's beyond that?

SEAGER: Right. Well, just to build our solar system would be like a very, very busy neighborhood block. In addition to the planets, we have the asteroid belt, and even beyond our last eighth planet, we have the Kuiper Belt, which Pluto is a part of. But beyond that, there's not really a whole lot, actually.

It's trillions of miles to the nearest star, so it's quite empty, actually. Stars are really quite spread out in our block of the galaxy. But what's amazing is that our galaxy is filled with hundreds of billions of stars, many of them like our own sun.

RAZ: Hundreds of billions of suns in our own galaxy.

SEAGER: It's amazing, yes.

RAZ: There are hundreds of billions of solar systems in our own galaxy.

SEAGER: I mean, that's what we're thinking because we have evidence that most stars have planets. And so, yes, we're thinking that each of those stars, each of those suns, has many planets.

RAZ: So if our solar system has eight planets - right? - we have to assume that there are at least maybe hundreds of billions of other planets in our galaxy.

SEAGER: Billions and billions of planets, that's right.

RAZ: And that's just one galaxy in the universe of galaxies.

SEAGER: Right. I mean, we think that our universe has billions and billions of galaxies, hundreds of billions of galaxies.

RAZ: And Sara thinks that on one of those billions of planets, in one of those billions of billions of galaxies, some form of life has to exist. It's just a matter of finding the right exoplanet. And as Sara Seager explained from the TED stage, we've already ruled out quite a few.


SEAGER: Are we alone? Is there life out there? Who is out there? You know, this question has been around for thousands of years since at least the time of the Greek philosophers. But I'm here to tell you just how close we're getting to finding out the answer to this question. It's the first time in human history that this really is within reach for us.

And I have a couple of favorite exoplanets to tell you about. This one is Kepler-10b. It's a hot, hot planet. It orbits over 50 times closer to its star than our Earth does to our sun. And actually, it's so hot, we can't visit any of these planets, but if we could, we would melt long before we got there. We think the surface is hot enough to melt rock and has liquid lava lakes.

Gliese 1214 b - this planet, we know the mass and the size, and it has a fairly low density. It's somewhat warm. We actually don't know really anything about this planet, but one possibility is that it's a water world, like a scaled-up version of one of Jupiter's icy moons that might be 50 percent water by mass. And in this case, it would have a thick seam atmosphere overlaying an ocean, not of liquid water but of a exotic form of water, a superfluid - not quite a gas, not quite a liquid. And under that wouldn't be rock but a form of high pressure ice.

So out of all these planets out there - and the variety is just simply astonishing - we mostly want to find the planets that are Goldilocks planets we call them - not too big, not too small, not too hot, not too cold, but just right for life.


RAZ: So when you - I mean, in your sort of search for the perfect Earth-like planet, we've gotten pretty close, right? We are aware of several planets now that are in that Goldilocks zone, that are just the right distance from their star to be habitable, aren't we?

SEAGER: Well, we're so close yet so far because, really, the planets are so different from what we might imagine. We actually don't know anything about them other than their size or their mass and their distance. Let's think about our Earth for a moment here. And people are worried about our Earth warming by adding parts per million of carbon dioxide, right?

So on our planet, we talk about this thing called the Keeling Curve and, you know, how we're adding greenhouse gases in tiny quantities. Imagine for a moment that a planet like our Earth doesn't have just parts per million more carbon dioxide but has hundred times more or thousand times more carbon dioxide. Wow. I mean, that planet all of a sudden would be so hot.

We can imagine planets that would be in the so-called habitable zone, but because of their atmosphere, which acts like a giant blanket, the planet might be literally suffocating at the surface and too hot for life. So we actually have a ways to go. We know that there are lots of planets in their star's habitable zones that gives us confidence, but we still need a lot more information.

RAZ: But what would happen if we did find another Earth? Like, what would that actually mean?

SEAGER: (Laughter) The funny thing is we're so fixated on just trying to find the planet, believe it or not, we haven't given too much thought about what we'd do next.

RAZ: What we'd do, yeah.

SEAGER: So - well, we would do a lot of things probably. The first thing we would do, though, as scientists, we feel a heavy burden of proof. So the types of things that we spend a lot of time working on and debating is what is an Earth? You know, how will we find it? What is the observational evidence that we could shout out to the world, yay, we found it finally?

But everyone would do lots of things. SETI - Search for Extraterrestrial Intelligence - will listen in on that planet and try to see if there's actually anything going on there in the radio, any alien civilization trying to send us a signal. I think the people trying to send probes at fast speeds will accelerate their activities. So I think that finding an Earth would galvanize many, many different groups of people.

RAZ: Yeah. I mean, do you ever - are there ever moments where you get discouraged, or are you just - is the idea of finding this so - is it such a motivator that it doesn't, you know, it doesn't matter if it never happens?

SEAGER: OK. I'm convinced it will happen someday. There has to be a planet like Earth out there. There are untold numbers of sun-like stars, and it's really - that Earth is just out there waiting to be found. I don't know if we'll find it soon. I don't know what the landscape is, and politics, and money and in technology development. So we'll just have to wait and see. I mean, it's going to happen. It's got to be out there somewhere.

RAZ: Sara Seager. She's an astrophysicist and professor at MIT. You can see her full talk at You can also see some cool images of travel posters to exoplanets that Sara showed in her talk at our Facebook page.


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