Is there another planet in the universe like Earth? Is there life elsewhere? And if so, how advanced is it? Join us as Sara Seager — astronomer, planet hunter, MIT professor, and MacArthur Genius Grant recipient — presents a mind-blowing progress report on the rigorous search for Earth’s planetary twin and other life in the universe.
Chapter 1: What is the search for another Earth?
Most astronomers believe that because of the vastness of the universe, the fact that there are trillions and trillions of stars and planets, that there could be life elsewhere. But with so many possibilities for life, how will we find or recognize life on other planets, whether it's microbes, plants, or perhaps even intelligent civilizations?
And how will we know which planets are habitable by us? Hi, everyone. I'm Lynn Thoman, and this is Three Takeaways. On Three Takeaways, I talk with some of the world's best thinkers, business leaders, writers, politicians, newsmakers, and scientists. Each episode ends with three key takeaways to help us understand the world and maybe even ourselves a little better.
Today, I'm excited to be with astronomer and planet hunter Sarah Seeger. When Sarah arrived at Harvard in 1994, the only planets beyond our solar system were Star Trek fiction. No planets outside of our solar system had been discovered. But every star in the sky is a sun. And since our sun has planets, it seemed possible that other suns would also have planets.
Chapter 2: How did Sara Seager get involved in astronomy?
Sarah was a graduate student in astronomy when the first reports of planets outside our solar system, so-called exoplanets, were coming in. Her advisor asked her if she wanted to work on these planets, and she jumped at the chance. She began working with one of the first teams of scientists focused on finding exoplanets, and she has been searching for another Earth ever since.
Sarah is currently a professor at MIT, where she leads the university's research on life beyond Earth. She is a MacArthur Fellow, having won one of the most prestigious grants in science, a MacArthur Foundation so-called genius grant. Sarah is so invested in finding another Earth that she even threw herself a planet hunting birthday party.
She rented out an auditorium at MIT and invited dozens of guests from astronomy and astronomy related fields. And she challenged them to help her come up with a winning strategy to find another Earth. I'm excited to find out how we'll find a planet that is habitable for humanity and how we'll recognize life elsewhere in the universe.
Welcome, Sarah, and thanks so much for joining Three Takeaways today. Thank you very much. Sarah, you fell in love with space and the stars and the planets. What do you love most of all about astronomy and being an astronomer?
Mostly I love the exploration. It's really a journey of exploration, a cross between like being the explorers that first went to the South Pole or the armchair crime solvers, the detectives, you know, it's kind of all of that all mixed together, but in a way that lets us find brand new things that we never imagined possible. And I also really love the night sky.
I really hope that you and the listeners get a chance to go and see the truly dark sky. Have you?
Yes. I wish I knew, though, more about the stars and what I'm looking at.
But sometimes just the beauty of it speaks for itself because it's so mysterious and there are just so many stars out there.
What are a couple of things that would surprise people about space and exoplanets?
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Chapter 3: What surprising facts do we know about exoplanets?
Like here on our planet, we have oxygen. We all humans all need oxygen to survive. Oxygen fills our Earth's atmosphere to 20% by volume. Without plants and photosynthetic bacteria, we would have virtually zero oxygen.
So if there's an intelligent civilization on a planet orbiting a nearby star looking back at us, they'll suspect there's life here, not because they can see animals or not from big things like the Great Wall of China, but from oxygen, a gas that's so reactive, it shouldn't be here at all unless it's continually replenished. And so that's what we're looking for.
And it'll be tricky, very tricky to assign unusual gases to life.
Do you think that there are or have been other advanced civilizations elsewhere in the universe?
We have no real evidence that there has, and people look. We have a whole other category of search for life called technosignatures, signs of a technologically advanced civilization. And we really don't have evidence of any yet. However, to speculate, our universe is so vast. We have 100 billion stars in our Milky Way galaxy. And in our universe, there are hundreds of billions of galaxies.
So there's untold numbers of possibilities. Surely there has to be advanced life somewhere. Our question really is, is it close enough to us that we could someday somehow make contact?
Can you explain how astronomers are essentially time travelers?
Well, light has a finite speed. So when we look at stars, the light from those stars was emitted a while back. So when we look at a star, for example, if a star is 100 light years away, the information we're measuring from that star came from that star 100 years ago. It just took that long to reach us. So we're time travelers in the sense that what we see are things that happened a long time ago.
That to me is so interesting. Sarah, I believe as a non-astronomer, there are essentially two parts of the universe. There is the observable part of the universe and the non-observable part, if you will. What do we know about the observable universe?
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Chapter 4: How do we recognize life on other planets?
How large is the observable universe approximately?
Very large. I think it's like tens of billions of light years across, like almost 100 billion light years. So big.
Your life's work is finding a planet habitable for us, a planet in the so-called Goldilocks zone. What would that look like and how are you hoping to find one?
Well, it turns out that many astronomers have a different version of a habitable planet. And that's because planets and stars come in all sizes and all kinds. So one of the short-term focus for astronomers is finding any kind of planet in any star's habitable zone. And the easiest ones to find right now with the telescopes we have are planets orbiting small stars.
There are stars out there that are half the size of our sun down to one tenth the size of our sun. These are called M dwarf stars. They're small red stars with a lot of magnetic activity. On those planets, there'd be a lot of northern lights. a lot of flares, a lot of star spots. And these planets are quite different from our Earth, actually. I like to call them Earth cousins.
They're not like an Earth twin. They're more like an Earth cousin because the star is so small and doesn't have much energy. And the stars give off flares a lot. And these Earth cousins, because they're so close to the star to get enough energy to be habitable, the habitable zone is quite close to the star because the stars give off very little energy. And one day is the same as one year.
They rotate one time for every time they orbit. Our moon actually does that because we see the same face of the moon at all times. So one of these earth cousins, what it means is that their star, which is their sun, is actually the same place in the sky at all times. So on that planet, you know, you would live where it's always day, or maybe you would live where it's always nighttime.
It's a very different type of world. So today we're studying these earth cousins because we can. They're what nature provided that our telescopes can do. But what I want to do, what I and a growing number of people see as our destiny really is to find the earth twin, not the cousin, it's the twin. That would like be you finding your cousin.
versus, wow, once in a while someone finds out they've got an identical twin. It's like that. We want to do that. And to find the Earth twin, we have to go above the blurring effects of Earth's atmosphere and have a special kind of space telescope, one that has a way to block out the star light entirely so we can find planets directly.
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Chapter 5: Are there advanced civilizations in the universe?
And how do you think personally about finding another Earth?
Well, I feel like it's a very hard challenge. It would be like asking a regular person to just get ready to hike up Mount Everest, and it's going to take a ton of work. We have different ways to find planets, but the problem is our Earth is so small, so less massive, and so dim compared to our sun.
Chapter 6: How do astronomers act as time travelers?
So an Earth twin, it's not that an Earth twin is like the faintest thing that has ever been observed by the Hubble Space Telescope or the James Webb Space Telescope. It's that it's right next to a big, bright, massive star. It's just so overwhelmed in every possible way that any technique we do have has to work way better than you can imagine.
Like for example, let's say you're moving a table into your apartment and you have to make sure it's going to fit through the door and you're going to measure the table with a tape, measuring tape, but you're going to measure it that your table is five feet wide or maybe it's three feet wide, but are you going to measure it's 5.00001 feet?
Like, I don't think your measuring tape goes to that many decimal places. Well, to find another Earth, by going to space and blocking out the starlight so we can see the planet directly, we have to go to 10 decimal places. And so that's extremely hard to do, to block out the glare of the star, hopefully so that only planet light enters the telescope. And we have several ways to do that.
Chapter 7: What do we know about the observable universe?
There's a NASA mission afoot called Habitable Worlds Observatory. And their target launch is the mid 2040s, which is quite far away. And the project is incredibly challenging to have a device that goes inside the telescope and blocks out the light to one part in 10 billion. My favorite one is called Starshade.
Starshade is a giant, specially shaped screen like a huge sunflower that would have its own spacecraft and go to outer space. and work with the space telescope by formation flying and blocking out the starlight so that only planet light enters the telescope.
And some people, myself included, are trying to find a way to start everything before the 2040s to get something happening so we can move this field forward and hammer away at the very nearest sun-like stars to see what's there.
So exciting. Sarah, what are the three takeaways you'd like to leave the audience with today?
The first takeaway is that all stars appear to have planets. So the next time you go out and look up at the night sky and see the stars, you can wonder what kind of planet is around that star. I actually love to imagine there are intelligent beings on planets orbiting other stars, and they look back at our sun, a star to them, and that they're wondering the same thing.
The second takeaway is that solar system copies are rare. Before exoplanets were known, when scientists studied our planetary system, our solar system, they expected that copies of that would be everywhere, that other stars also had terrestrial planets close to the star and giant planets further out.
So imagine our surprise when the first exoplanet found around a sun-like star was the Jupiter mass planet, but not far from its star like Jupiter is, instead way up close. many times closer to its star than Mercury is to our sun. And what it's doing there, no one really knew. So all those planetary systems out there, they have very different configurations.
So far, our planet-finding methods can't really find solar systems, but we found enough planets to know that solar system copies are rare. My third takeaway is one thing I've been lucky to do and I really hope others can as well is to find something you love doing that you're also very good at and that pays the bills and you will find success.
Thank you, Sarah. This has been wonderful. Thank you for your work to find another habitable earth. Wishing you success and soon. Thank you very much. If you're enjoying the podcast, and I really hope you are, please review us on Apple Podcasts or Spotify or wherever you get your podcasts. It really helps get the word out.
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