NASA's Curious Universe - Curious Universe: Let’s Go Planet-Hunting!

Episode Date: July 12, 2021

What do we know about the planets outside our solar system? NASA planet hunters Jessie Christiansen and Knicole Colon take us beyond...into the exciting world of exoplanets.  

One of the really fun things about hunting for exoplanets is all the surprises. Before we found any worlds around other stars, we only knew our solar system. So when we came up with ideas of what other solar systems would look like, they very closely resembled ours. All of our theoretical models for how planets formed were designed to recreate the solar system. If your model created something completely different, then you threw it away because it didn't create the solar system when we knew the solar system existed. existed. But when we went out there, we have found anything but we have found all of these other configurations of planets, big planets right next to their star, chains of small planets all packed really closely together, systems where they're all misaligned with each other. So it's been

really, really exciting to just kind of see how much more imaginative nature is than we are. We think almost every star in the galaxy has at least one planet around it. which is incredible because there are 100 billion stars in our galaxy. Just imagine how many worlds that is out there and how much potential that is. This is NASA's curious universe. Our universe is a wild and wonderful place. I'm Patty Boyd and in this podcast, NASA is your tour guide. Today we're taking you outside our solar system and into the planets that lie beyond.

Exoplanets. There are eight planets in our solar system, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. But in the last few decades, scientists have discovered thousands of planets outside our solar system. We call them exoplanets, and evidence suggests that there might be hundreds of millions of them in the Milky Way. So far, planet hunters have discovered and named over 4,000 worlds. within our galaxy. When I'm not hosting this podcast, this is what I study the most, exoplanets and stellar astrophysics. It's amazing to get to explore these faraway planets. Just a generation ago, we didn't even know if there were planets around other stars, and now we know that exoplanets

are everywhere, and the types of exoplanets that we find are dizzying. And we can learn a little bit more about the Earth and our solar system by studying the variety of other planets out there and comparing them to our own. And the planets we're finding are really far away. Space is really big, and I think when I get to tell people that we've found new planets, they're always disappointed by the answer of how far away they are. This is Jesse Christensen, an astrophysicist with the California Institute of Technology. On average, the exoplanets we've found are hundreds or thousands of light years away. The problem is a light year is really, really big. much farther than we could ever imagine traveling.

It's hard to imagine how far away that is. Even with the most powerful telescopes, only a handful of exoplanets, around 20, have been imaged directly. And even those we only see as dim points of light. So how do we know all those others are out there? One of the ways we find planets is called the transit method. Now that relies on the fact that some planets

are lined up just right so that from our point of view, as they're orbiting their star, they pass in front of the star, they eclipse their star and block some of the light. Now, from our distance, we can't actually see that eclipse, but what we can do is measure the brightness of the star over and over again and wait for it to dim just a little bit and then go back up. So it's these tiny little dimmings in the brightness of stars that we're looking for in these data. Exoplanet research is still relatively young. The first one was officially discovered in 1992.

But for millennia, humans have looked to the skies and wondered what else is out there. Ancient philosophers pondered the existence of other worlds. But we are the first generation that can start to answer some of these questions with data. When I work at NASA, I specifically work on several different species. space missions, making sure that they're providing and taking the best data that they can for everybody to investigate and explore. This is Nicole Colon, a research astrophysicist. Her team also uses the transit method to track down exoplanets transiting their stars.

But sometimes stars have more than one planet orbiting around them, which can make things a little bit tricky. A lot of stars have more than one planet. That's what we would think, as we know from our own solar system. That means that we get a lot of overlapping signals when we're looking to study the individual planets. Scientists take those overlapping signals and carefully untangle them to reveal multiple worlds.

One of Nicole's specialties is using that data to determine the compositions of those far-flung planets. We've also been able to study atmospheres of exoplanets. We have been finding water vapor in a lot of their atmospheres, which is expected and exciting because water is everywhere. But we're starting to find other things like helium vapor and different molecules that was a little bit of a surprise and not originally predicted until we started looking more at the chemistry of the atmosphere and what's really going on. In fact, we've already begun exploring what some exoplanets are made of. Luckily, when we can observe, for example, a planet that transits or passes in front of its star, if that planet has an atmosphere, we can actually see what starlight gets blocked or, like, filtered out by that atmosphere. By seeing what's missing, we can say, oh, you know, that planet has water in its atmosphere and that water is blocking starlight from reaching our telescope.

In the future, we'll be able to look for additional molecules like methane and carbon dioxide as well. With thousands of known exoplanets out there and more coming all the time, it's important to keep track of them all. Jesse works at the NASA Exoplanet Archive, which organizes and maintains information about the properties of known exoplanets. So the ancient Greeks, when they were naming our planets, they went for the gods and, you know, the big movers and shakers of the Greek for. philosophical world. Nowadays, we do it much more boringly, unfortunately. We have found over 4,000 exoplanets so far, and they're almost all named in a very particular way. We take the name of the star that the planet is orbiting, and the name of the star is usually pretty boring itself, like HD-189733. Then the first planet in the system, we attach a little B to the name,

so HD-189-733B. The second planet in that system, is HD 189733C. The third planet in the system, I'm sure you see the pattern, HD 189773D. So they're all terrible, terrible names. I'm so sorry on behalf of astronomers everywhere that we give planets such boring names. One of the benefits of gathering all of this information

in one place is that scientists can find new and engaging ways to explore it. What you're hearing now isn't just a pretty song. It's data that's that you're just a pretty song. that captures the discovery of exoplanets. This is a data sonification where planetary information has been translated into sound. Here, each note represents a newly discovered exoplanet. The tone of each note reflects the planet's orbital period,

with longer orbits reflected by lower tones. The music's increasing complexity reflects the rapidly changing pace of exoplanet discovery between 1992, 1992 and 2019. As you can hear, the discoveries came very slowly at first. Then there's a great rush of music reflecting the avalanche of discoveries made by NASA's Kepler mission. This was a huge leap in our catalog. Even today, Kepler's discoveries constitute more than half of all the exoplanets we know of. I have actually contributed to the discovery of several exoplanets.

I don't know the number offhand. I wish I did. I should look into that. Again, this is astrophysicist Nicole Cologne. I have helped discover new exoplanets and of all kinds, ranging from small, rocky exoplanets that are about the size of Earth to these super giant planets that are like Jupiter. So it's pretty incredible being able to discover new planets.

I used to remember a time when I could tell you something about every single exoplanet that we know. Now it was 4,000. I'm like, oh, wait, which one is that again? So things have been changing, but for the better. I do have a lot of favorites. There is one that stands out in terms of what my favorite exoplanet is. And it is actually one I helped discover. So that's partly why it's one of my favorites.

but it's a planet called Kelt 11B. Kelt was the survey that discovered it. First of all, it orbits around its star in less than five days, so it's very close to its star, compared to the Earth orbiting around the sun every 365 days. But it's also larger than Jupiter is, so it's a very giant planet. But then its mass is so low that when you look at it, all together, this planet has a density that is basically the same as styrofoam.

And so if you imagine how, you know, fluffy and light styrofoam is, right? You could just throw it around like it's nothing. We'd probably just float right off or crush the whole thing. I don't know. One of the two. So that intrigued me so much that I actually have worked on projects to study the atmosphere of the planet to find out more. I've used NASA's Hubble telescope to search for water vapor in the planet's atmosphere because that can tell us a little bit about where or how the planet formed

by knowing how much water it contains. What we found was that the amount of water in its atmosphere is so small that it actually cannot be explained by current theories of planet forming. I'm hoping one day to use future telescopes as well to just really shed some light on, okay, how does such a puffy planet exist? A lot of the exoplanets we're discovering seem sort of wacky by Earthling standards, like Nicole's styrofoam planet.

Can you imagine trying to walk around on a planet you might crush? But every once in a while, the data lines up in such a way that we think a planet might fall into the habitable zone. This is a range of distances from a star where a planet's surface might be able to contain liquid water on its surface, a requirement for life as we know it on Earth. Astrophysicist Jesse Christensen has paid special attention to one particular planet that might just be in a habitable zone. The exoplanet I would most want to visit is Kepler 452B. So this is the one planet that Kepler found, which might be a rocky planet.

planet in the habitable zone, meaning it's the right temperature for liquid water, of a star like the sun. The problem is the data are just a little bit noisy and we can't tell from the data we have whether it's real or not. What I really want to do is just go there and look and be like, does this planet exist? Answering that question would be the top of my mind. We do know its size. It's a little bit bigger than the Earth. It's 1.5 to 1.6 times the radius of the Earth. So if it's real, and you could step out on its surface, it likely has a quite high surface gravity. When we walk here on Earth, we feel the Earth pulled down on us and we feel that weight. Now, I'm sure you've seen images or videos from the Moon of the astronauts like kind of bounding on the Moon

because the gravity on the Moon is much lower, so you actually just feel lighter and you can move much more easily. On Kepler 452b, the gravity would be higher because the planet is much bigger and therefore has much more roeer. underneath your feet pulling on you. So it might be very difficult to walk. You might feel like walking through quicksand or something. In 2017, NASA announced the discovery of seven rocky Earth-sized planets in the habitable zone of a single star called Trappist One. All seven planets in the Trappist system have the potential for supporting water on their surface.

But with a much smaller star and an entirely different planetary system, even Even these exoplanets aren't quite like our home here on Earth. While it's exciting to find planets that might be similar in some ways to our own, we're still very far away from being able to send probes to explore them directly. When I tell people that we have found Earth-like planets around other stars, I always see this light in their eyes, right? Like they see it. Like maybe there's some kind of escape plan.

Like maybe there's hope that humanity will, like, go out and colonize the galaxy. There's Earth-like planets everywhere. And I always try to squash that a little bit because in our solar system, we have four rocky planets. Only one of them is habitable. We have this window on this one planet around this one star that's habitable. So what I don't want is for people to hear this message, there are Earth-like planets everywhere in the galaxy, and be like, okay, cool, we can just trash ours because we've got all these other options. We don't have any other options, not even in our solar system.

This is it. Earth is it. We have to take care of the one Earth that we have. One of the wonderful things about studying these faraway worlds is seeing how different they can be from our home on Earth or the familiar planets in our solar system. There are so many combinations of size, atmosphere, chemical composition, and distance from their stars that result in thousands of different places, each with its own unique characteristics. It's really interesting seeing exactly what all these exoplanets have shown us. Finding different molecules that we might not expect to see in this atmosphere, it does bring you back home when you say, okay, are they weird or are we weird?

Are we just the anomaly? What does that actually mean then when it comes down to kind of NASA's end goal and really, you know, my end goal? I think almost every astronomer who studies exoplanets, It's their end goal of knowing if some kind of life might exist out there in the galaxy, what does it mean that exoplanets are so different than on Earth? There's a lot of NASA missions that will help answer that question. Scientists currently use information from ground telescopes and space telescopes to gather data on exoplanets. But there are a lot of exciting plans to expand the search. Tests, the transiting exoplanet survey satellite, launched in 2018,

and has already confirmed over a hundred new planets around bright, relatively nearby stars. And later this year, scientists across the globe will come together to witness the launch of the James Webb Space Telescope, which will allow us to gather even more information about these faraway worlds. You know, there are so many exoplanets that we know of so far, thousands, but there is still so much left to discover, and we're expecting. to discover in the next few years, decades, tens of thousands of more exoplanets. Pretty soon we're going to be able to more definitively say how many there are because we have new NASA missions coming online that are just going to keep finding thousands of exoplanets

to help us even better understand how common they are. Just really help us get to where we want to go, which is understanding our place and the universe. 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, Kate Steiner, and Michaela Sosby, with support from Emma Edmund and Priya Matal. Our theme song and the sonification you heard in this episode were composed by Matt Russo and Andrew Santa Guida of System Sounds. Special thanks to Claire Andrioli, Rylund Heggy, Barb Madsen, Frank Reddy, Amber Strawn, and the astrophysics team.

If you liked this episode, please let us know by leaving us a review, tweeting about the show at NASA, and sharing NASA's curious universe with a friend. Learn more about exoplanets by visiting exoplanets.nets.nassar.gov. Still curious about NASA? You can send us questions about this episode or a previous one, and we'll try to track down the answers. You can email a voice recording or send a written note to NASA-curious Universe at mail.nassah.gov. Go to NASA.gov slash curious universe for more information. Now I am recording on my end. Oh my goodness. Just now as soon as that happened, my cat is going to start crying at the door.