The universe is enormous and time to observe it is limited. This means planet-hunters have to be extra picky in their search for habitable worlds. Dean chats with Dr. Néstor Espinoza, an astronomer at the Space Telescope Science Institute who has his eye on one specific star system, Trappist-1.
Because this planet is thought to be tidally locked to its star, meaning the same face of the planet is always pointed at the star, there would be a region called the terminator that perpetually divides day and night. If the night side is icy, the day side might give way to liquid water in the area where sufficient starlight hits the surface.
One of the unusual features of TRAPPIST-1 planets is how close they are to each other -- so close that other planets could be visible in the sky from the surface of each one. In this view, the planets in the sky correspond to TRAPPIST1e (top left crescent), d (middle crescent) and c (bright dot to the lower right of the crescents). TRAPPIST-1e would appear about the same size as the moon and TRAPPIST1-c is on the far side of the star. The star itself, an ultra-cool dwarf, would appear about three times larger than our own sun does in Earth's skies.
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Episode Transcript:
Looking Up is transcribed using a combination of AI speech recognition and human editors. It may contain errors. Please check the corresponding audio before quoting in print. This transcript may include additional material from the conversation, not featured in the audio.
Dean Regas: Exoplanets, the planets that astronomers have found far outside our solar system orbiting distant stars. Now, I've seen a lot of them that were discovered by the Kepler spacecraft, with names like Kepler 16b and Kepler 20e, and there's others from the WASP survey and the XXX catalog. But one exoplanet system is called TRAPPIST-1. And I'm thinking, what is that named after? Never heard of a telescope or survey named that. I need to look for clues closer to home… at the bar, because it's named by Belgian beer lovers! Yeah, seriously.
From the studios of Cincinnati Public Radio, I'm your host, Dean Regas. And this is Looking Up, the show that takes you deep into the cosmos, or just to the telescope in your backyard, to learn more about what makes this amazing universe of ours so great. My guest today is Néstor Espinoza, an astronomer at the Space Telescope Science Institute, where he studies exoplanets and their atmospheres.
Yep. TRAPPIST-1. The planetary system was named by Belgian astronomers for their favorite types of beer. But the name TRAPPIST actually comes from the two Belgian-operated telescopes that are studying exoplanets. TRAPPIST stands for Transiting Planets and Planetesimals Small Telescope. That's a pretty big stretch for an acronym. It's such a huge stretch from beer to telescope name that it's actually considered a backronym.
A backronym is when you take an existing word and use it as an acronym for something else on purpose, even if it has nothing to do with anything.
Another, like, spacey example is an exercise machine on the International Space Station called the COLBERT.
[Stephen Colbert]: Greetings, NASA. It's me, Stephen Colbert.
Dean Regas: Yes, this is named for comedian Stephen Colbert and stands for, are you ready? “The Combined Operational Load-Bearing External Resistance Treadmill.”
Okay, so really, I just wanted to share the new vocabulary word I just learned because I'm truly a DEAN: A Device Enhancing Auditory Noise. All right, enough vocabulary. Let's look at the exoplanets of TRAPPIST-1 with a real expert who is no DEAN.
Néstor Espinoza: Hi. My name is Néstor Espinoza. I'm a mission scientist for exoplanet science and an astronomer here at the Space Telescope Science Institute, where I do a lot of exoplanet research but also provide support for NASA's flagship missions, like James Webb and the Hubble Space Telescope, and soon the Roman Space Telescope as well.
Dean Regas: Well, Néstor, thanks so much for joining me today.
Néstor Espinoza: Well, thank you for inviting me. It's an honor to be here.
Dean Regas: I want to dive into TRAPPIST-1. I mean, this is the surprising and exciting star system with multiple planets only 40 light-years away. Tell us about the star there and what we found orbiting it.
Néstor Espinoza: Yeah, this system is as alien as it gets, right? And the star is very, very weird because it's as small as Jupiter. It's much colder than the sun, like, around half its temperature. And it doesn't have one, two or three rocky planets orbiting. It has at least seven rocky exoplanets orbiting the star, and some of them orbit at a distance from the star such that if they had atmospheres like the Earth, they could sustain liquid water. So, it's a very exciting system in many regards. And as you can tell, I'm pretty excited about this system myself.
Dean Regas: Well, I mean, yeah, number one, the star would be considered a red dwarf. Is that the classification? And so, this is like one of the most popular stars in the galaxy. So, if there's planets around this that gets people excited, there could be planets around lots of red dwarf stars.
Néstor Espinoza: Exactly. I think that's a very, very important point when you stop a person randomly on the street and you ask them how do you think the average star looks like? Everyone thinks like, oh, you know, it has to be like the sun, right? But the reality is that, yes, these small stars are cool. They make up the majority of the stars in our galaxy, and if we understand them, we understand the majority of stars out there, which is pretty exciting from the perspective of vacation destinations, perhaps eventually for future explorers out there.
Dean Regas: Oh, yeah. So, are there any planets in particular out of the seven in the TRAPPIST-1 system that you have your eye on?
Néstor Espinoza: Yeah, yeah, there's one in particular that I had my eye on, which is called TRAPPIST-1e. TRAPPIST-1e is very special because it's in this particular zone which is not too cold, not too hot. It's like right in the right distance from the star that if it had an atmosphere, it could sustain liquid water on its surface. And that makes it very exciting. It's what we call the habitable zone of the star. But we don't know if this planet has an atmosphere. But we have observations trying to investigate if it has an atmosphere or not. And we have more coming.
Dean Regas: And is this something that the James Webb Telescope and others can look closer at?
Néstor Espinoza: Yes, that's an excellent question because that's exactly how we're taking a look at this planet. We are targeting this planet with the James Webb Space Telescope, trying to gather enough data such that we can hopefully get an answer to, does this planet have an atmosphere or not? That's the very first step.
Dean Regas: And so let's say perfect situation. You get the data back from the Webb telescope. What do you want to see in the data?
Néstor Espinoza: When you look at the light that is emitted from the planets in our own solar system, one of the very big signatures of this light is a particular feature from a particular molecule. And that molecule is carbon dioxide. So, carbon dioxide is present on Mars, is present on Earth and is present on Venus. And this feature is just huge. This is exactly the signature that we're trying to figure out if it's there in TRAPPIST-1e. This is what we're targeting. And in this ideal scenario, we will hopefully see a huge bump in the data thanks to this CO₂ that is being absorbed in the atmosphere of TRAPPIST-1e.
Dean Regas: So I think the thing that really grabs my geeky attention is that we're looking at a star that's 40 light-years away. So that's trillions, hundreds of trillions of miles away. And we're looking at a little planet that's going around the star, and then we're looking for a thin atmosphere around this tiny planet, around this distant star. I mean, how do you do it? How is this possible?
Néstor Espinoza: Yeah, it does sound pretty magical. But actually, it has a lot of very, very clever science behind it. So, the reality, first of all, to make this very, very explicit and very clear, we are not getting pictures of these planets. So, getting pictures of these planets is very, very hard. Not because necessarily the planets are faint. The problem is that the planets are too close to the star, and it's very hard for us to disentangle that in an image.
So, because we cannot take a picture of this planet, we have to find other ways of looking at them. And the way in which we're doing this study, it's a very, very clever method. So, if you're lucky enough, some planets, while they orbit around their stars, if you follow the brightness of this system, some of these planets will pass in front of the stars. We call that a transit. And you say, ah, that's it. There's a planet passing in front.
But the thing doesn't stop there. When the planet passes in front of the star, something very magical also happens. The starlight that is coming to us and is now blocked by the planet, part of that starlight passes through the planet atmosphere. So, the planet atmosphere kind of interacts with this light.
So we're waiting until the planet passes in front of the star. And if the atmosphere has CO₂, CO₂ will absorb that light. We know the star has this light, but now when we do these observations, it's not there anymore. And that would mean, in this case, that the planet has CO₂.
So we're doing this planet detective game on how much starlight the atmosphere is eating while it transits. And that's how we try to figure out what these planets are made of. This technique, which we call transmission spectroscopy, when it was proposed back in the early 2000s, it was suggested that the people that proposed it thought there was not going to be any instrument being able to do that. But here we are. We have used this technique for many, many planets, like hundreds, I think. And now we're using it to try to figure out if a planet in the habitable zone could have an atmosphere, which is pretty exciting. It's been a long, long journey for this technique to work, and we do know it works, which is fantastic.
Dean Regas: Well, I have to be the downer here, but let's say you don't find what you're looking for. You don't find an atmosphere there in the TRAPPIST-1 system. Where should we go next?
Néstor Espinoza: Yeah, there's many others to look at. And, in fact, this is not the only program that is trying to look for atmospheres around these cool planets that might be habitable. Now, I think maybe what you might be hinting at is, what if we find that these rocky planets around these cool stars, what if we find that none of them have atmospheres? And that's a very real possibility. That could be the case. But that would be an actually exciting answer to this question, too, because it might mean that we live in a very special place, that our star, the sun, is very special, and maybe that our own Earth is a very special planet.
So both answers are actually pretty exciting. I think it's a win-win game.
Dean Regas: Answered like a true scientist. That's perfect. And, you know, we always talk about finding Earth 2.0 out there, but is there like a solar system 2.0 out there, a situation similar to ours with a sunlike star and rocky planets and gaseous planets?
Néstor Espinoza: That's an excellent question. And that's the guiding question to me, is how weird is the solar system right now? We don't know. And, in fact, we're already trying to plan for the next task that could make those observations happen. So, I'm talking about the Habitable Worlds Observatory. That was one of the key recommendations from the Decadal Survey for Astronomy and Astrophysics, was let's really try to take a picture of an Earth-size planet around a sunlike star out there.
And to do that, we really need to develop new technology. But if you ask me, I think that's totally doable. As humans, we're super smart, and we can make that happen. And that's kind of the next goal. So that dream is alive. And that is the guiding principle for a lot of the astronomy community in exoplanet science.
Dean Regas: So I'm going to test your scientific credibility here again with an unscientific question, possibly. With all of these new worlds found and all these Earth-size planets out there and some in the Goldilocks zone, do you think there is life out there somewhere in the universe, another habitable planet.
Néstor Espinoza: Somewhere in the universe? I can almost attest to that, that that has to be possible. And the reasoning is as follows. We know that we have life on this planet. It's at least one planet, one star in this galaxy. There's tens of billions of galaxies out there. One in 10 billion sounds like an extremely sad universe, right? I don't think that's the case.
Also, there have been studies by cosmologists, people that study how the universe evolves, that ask the question, is the current state of the universe the most habitable environment in the following sense? When the universe was created, there was only the very basic hydrogen, helium and maybe some extra molecules. But as stars started to evolve, they started creating new molecules, more complex molecules, like the ones like calcium and all the beautiful ones that make up human beings. So the universe has gone up in complexity in terms of molecules, and we are not at the top of that complexity yet. We're getting there, yet.
So in the future, as the universe evolves, it will get maybe even easier to make planets out there. So we have to think life, too, in time. Are we in the right space of time right now? We arrived as life here, but in the future, other life forms might evolve and might appear on other planets out there too. So it's not only space, it's time as well.
Dean Regas: Wow. That's some deep thoughts. Like the best is yet to come still for us.
Néstor Espinoza: Oh, yeah. Yeah, yeah, for life at least. Maybe not for us. I don't know how we humans will figure this out. Hopefully we figure things out, and we keep evolving for many, many more years to come. But that makes me kind of confident that I think it's unlikely that we're the only life form in the universe. Now, the question that we are trying to answer is, are we the only life form in our galaxy? That's a different question, and that's a much more complicated one.
Dean Regas: Well, Néstor, this has been great fun talking about your research. Best of luck with the search, and hopefully we find some atmospheres or hopefully we don't either way.
Néstor Espinoza: Right. Exactly. Yeah. Again, any of the answers I'm really excited about. So thanks for inviting me. This was very fun. And yeah, I'll keep in touch. Whenever we have new results, I'll be sure to ping you folks to talk more about that.
Dean Regas: Oh, yeah, you got our phone number? Let us know when Earth 2.0 is discovered.
Néstor Espinoza: There you go. I will.
Dean Regas: Okay. My imagination is going big time. I'm dreaming of visiting the TRAPPIST-1 system and, you know, do some planet hopping. And this is where I find my two of many problems that I have with sci-fi plots. If you're going to fly from a planet to a planet, you really need to plan ahead. You can't just, like, fly to Mars from Earth whenever you want.
[Clip from The Expanse]: Planetary defenses have been placed on high alert at UNN. Ships were dispatched from Earth and Luna to reinforce fleets in the belt and outer planets.
Dean Regas: Mars is moving around the sun at a different rate from us, and only once every 26 months is it closer to us. But sci-fi often deals with interplanetary travel like a trip from Cincinnati to Denver. In reality, it would be like if you want to fly to a moving Denver from a moving Cincinnati. Sometimes it's 1,400 miles away, and other times it could be 7,000 miles away.
The other thing with sci-fi is gravity. Isn't it amazing that every planet they visit on Star Wars, Star Trek and others, they land on this planet with the exact surface gravity of Earth. Wow. What luck on the planet, captain.
[Clip from Star Trek]: Density 5.5. Diameter 7,917. Off the equator. Atmosphere 78 percent nitrogen, 21 percent oxygen. Again. Exactly like Earth. Exactly. In some ways different, in others.
Dean Regas: So let's take a real-life example. Let's say you want to visit all the planets in the TRAPPIST-1 system. Forget about the temperature, atmosphere, water or lack of water. Here's what the gravity will feel like, how your weight will change from planet to planet.
So we'll start off on TRAPPIST-1b, the closest planet to its star. Gravity is 110 percent more there than on Earth, so you'd weigh 10 percent more and everything else would feel 10 percent heavier. All right, you might get used to that.
Then hop to the next planet, TRAPPIST-1c, where it would feel very similar, about 109 percent of Earth. And the next one, planet 1d. Your burden will be lightened by this tiny world where gravity is a mere 62 percent of Earth. Awesome. You would feel so light.
Then on planet 1e, you'd bulk up to about 82 percent of Earth before going to 1f, 95 percent of Earth gravity. And then 1g, which is the most Earthlike at 103 percent. Finally, on your seventh stop, planet 1h, the only way 57 percent of what you weigh on Earth.
This is my, like, imaginary itinerary. This is how I would do it. Get the heavy planets out of the way first and then end as a Superman. If I can keep my Earth muscles, I can rule that world.
Looking Up with Dean Regas is a production of Cincinnati Public Radio. Kevin Reynolds and I created the podcast in 2017. Ella Rowen and Carlos Lopez Cornu produce and edit our show and are really into the TRAPPIST-1 diet plan. Want to lose weight? Just fly to a different planet. Jenell Walton is our vice president of content, and Ronny Salerno is our digital platforms manager. Our theme song is “Possible Light” by Ziv Moran. Our social media coordinator is Hannah Pflum, and our cover art is by Nicole Tiffany. I'm Dean Regas. Keep looking up.
