Sara Seager
Appearances
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
I really hope that you and the listeners get a chance to go and see the truly dark sky. Have you?
3 Takeaways
The Search for Another Earth (#229)
But sometimes just the beauty of it speaks for itself because it's so mysterious and there are just so many stars out there.
3 Takeaways
The Search for Another Earth (#229)
One thing that might surprise people is that our solar system, with planets in our solar system's configuration, that is Mercury, Venus, Earth, Mars close to the star, Jupiter, Saturn, the big planets far from the star, that configuration is rare. Most planetary systems are very different from ours.
3 Takeaways
The Search for Another Earth (#229)
It appears to be that the most common type of planet in our galaxy is one that's between the size of Earth and Neptune, right about in the middle of it. And it has no solar system counterpart. We don't know what they're made of. We don't know how they formed. We don't even know why there's so many of them. But in general, we could say that systems are very different from each other.
3 Takeaways
The Search for Another Earth (#229)
One system could have a Jupiter where an Earth should be. Many systems appear to have planets. Well, many systems do have planets so close to their star, many, many times closer to their star than Mercury is to our sun. And the closer the planet is to the star, the faster it orbits. And some of these planets orbit their star that is their year is less than one Earth day.
3 Takeaways
The Search for Another Earth (#229)
There's literally almost every kind of planet out there that's permitted by the laws of physics. Interesting.
3 Takeaways
The Search for Another Earth (#229)
I think we will be able to recognize life on other planets, but most of the life, well, let's divide the search for life into two categories. One is on planets and moons in our own solar system. In those cases, we hope someday to be able to do sample return from planets, sample return of materials from Mars, sample return of the clouds of Venus.
3 Takeaways
The Search for Another Earth (#229)
We've already brought samples back from other things such as asteroids. We know there's no giant animals or plants on any of those planets. So in that case, we'd be looking for a very small microbial type life. I do think we'd be able to recognize it. On exoplanets, they're so far away. They're trillions and trillions of kilometers or miles or more.
3 Takeaways
The Search for Another Earth (#229)
They're tens to hundreds or more light years away. There, we won't be able to spatially resolve the planet for now. We couldn't even see the level of an animal, even a very big one. So in that case, we're looking for chemistry. We're looking not at what life is, but what life does. So the question is, can we recognize chemicals in a planet atmosphere far away that might be signs of life?
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
And it'll be tricky, very tricky to assign unusual gases to life.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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?
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
We know that our universe formed suddenly in a cosmic Big Bang event because we see the leftovers from that in the form of just uniform background radiation. Like after a fire dies down, you see coals burning out of lower temperature. We actually can almost see back to when the first stars and galaxies were born.
3 Takeaways
The Search for Another Earth (#229)
Only there's a little glitch right now because it appears that stars and galaxies formed sooner than we expected them to. They're very massive galaxies that are kind of bigger than for their age than they should be. We know that there's so many galaxies out there and that every galaxy appears to have a massive black hole at its center.
3 Takeaways
The Search for Another Earth (#229)
We know that even in between galaxies and in between stars, in between galaxies, in between galaxy clusters, it's not totally, totally empty. There's still some little tiny small amount of material everywhere.
3 Takeaways
The Search for Another Earth (#229)
Very large. I think it's like tens of billions of light years across, like almost 100 billion light years. So big.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
The method we talked about when the planet goes in front of the star is That's indirect. We don't see light coming from the planet. We see light the planet's blocking. And this going to space and blocking out the starlight is incredibly hard. It's literally at the edges of what we're able to do, but we think we know how to do it.
3 Takeaways
The Search for Another Earth (#229)
Ultimately, we don't know. People do like to speculate that life there to withstand all that gravity probably has to be closer to the ground with giant legs. This sounds pretty scary, but like a cockroach with elephant legs. Because cockroaches look so light and they have those tiny legs, you'd have to have big legs and be close to the ground, most likely.
3 Takeaways
The Search for Another Earth (#229)
You know, sometimes we don't know. We definitely have speculated about this for fun. But one thing in a massive atmosphere, it might block a lot of the sunlight or at least dim it quite a lot. So we love to imagine birds with big wings that also can capture light. So imagine like a cross between a plant and a bird.
3 Takeaways
The Search for Another Earth (#229)
Maybe to get the light for photosynthesis, perhaps the life has to get really high up. And the only way they can do that is flying.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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?
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.
3 Takeaways
The Search for Another Earth (#229)
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.