After NASA's recent milestone of over 6000 exoplanets tracked, Dean Regas has one big question. Is anyone living on them? On this episode, Dean chats with Dr. Malena Rice, a planetary astrophysicist and assistant professor in the Yale Department of Astronomy, to find out.
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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:
Astronomers recently announced that they have cracked the 6,000 mark when it comes to exoplanets.
Thousands of exoplanets have been discovered…
6000 exoplanets…
It was not just one discovery, but thousands…
…Exoplanets were unlike anything ever seen…
Dean Regas:
That means they have confirmed the discovery of at least 6,000 planets that orbit around a star other than our sun.
Think about that. We have eight planets in our solar system—eight possible worlds to explore in our neighborhood. Now we have more than 6,000 other worlds that are light-years away. And the number is growing every day.
We are discovering more exo-planets than ever before…
Dean Regas:
Is this the hottest field in astronomy? There are just so many planet possibilities.
…Earth, the only home for life?
Dean Regas:
From the studios of 91ÖĆƬł§, 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 Dr. Malena Rice, a planetary astrophysicist and assistant professor in the Yale Department of Astronomy.
Now, one reason why I’m so excited about exoplanets is for a nerdy reason: finding them takes some serious skill.
We’re looking for extremely faint objects—the planets—that are near an extremely bright object—their star—and we’re looking for them from trillions of miles away.
Even with current telescope technology, limitations still exist. Such as the inability to directly image Earth-like exoplanets, because they are too faint and typically too close to their host stars.
Dean Regas:
For example, Earth is about 1.3 million times smaller than the sun. If an alien were looking at the solar system from a distant exoplanet, how would they ever see little old us?
The best method astronomers have found so far is called the transit method. We can’t see the light of a tiny planet by itself, but we can detect dips in the star’s light. So when a planet passes between us and its star, it creates a mini eclipse—a transit—and when it does so regularly, our detectors on Earth can spot it.
To study worlds where direct imaging is not feasible, scientists use other methods, like noting the light from a star that has passed through an exoplanet’s atmosphere. Also known as transit spectroscopy.
Dean Regas:
We can figure out the relative size of the planet, whether it’s rocky or gaseous, the distance to its star, the exoplanet’s orbital period (the time it takes to go around the star), and estimate its temperature.
This was the plan for NASA’s Kepler Space Telescope—to look for exoplanets transiting their stars. And it worked like a charm, finding not only large planets about the size of Jupiter but also smaller worlds, about the size of Earth. All it had to do was look at 150,000 stars at the same time for a long time.
Since then, other exoplanet surveys are underway, including one called WASP and another called TESS. The more stars we survey, the more exoplanets we find. Although this is just getting started, astronomers estimate one in five stars in our galaxy have at least one exoplanet. That’s 40 to 80 billion planets!
And I know what you’re thinking: one of them has to have life, right? Ooh, I’ve got an expert here to ask that very thing.
Dr. Malena Rice: Hi, my name is Malena Rice. I am a planetary astrophysicist and an assistant professor based at Yale University, and my expertise is in exoplanets and planetary science. I'm interested in planets around stars in the sky, as well as the ones in our solar system.
Dean Regas: Well, Malena, thanks so much for joining me today.
Dr. Malena Rice: Thanks for having me.
Dean Regas: How did you become a planetary astrophysicist?
Dr. Malena Rice: So I was actually pre-med when I was an undergrad, and I started taking a biology class and I just asked too many questions, I think was the issue. I just wasn’t satisfied until I really got to the root of what was really going on, and that ended up sort of pushing me toward physics.
And I had this really, really amazing teacher, Alex Ko, at Berkeley when I was an undergrad. He has inspired many into space, including myself. I feel very lucky to have been able to learn from him, and it really initiated this chapter of my life — if not, you know, the entirety of the rest of my life, potentially.
Dean Regas: Well, and then you were awarded this fellowship called 51 Pegasi b. Tell us about that star system and the fellowship that took its name from it.
Dr. Malena Rice: Yeah, 51 Pegasi b was the first exoplanet that was confirmed around a star that was similar to the sun. And the really amazing thing about 51 Pegasi b is that it was this whopping, enormous signal when they found it because it's this crazy planet that people didn’t expect to exist.
So, it’s called a hot Jupiter — it’s an enormous planet that is just right next to its star, and it’s sort of whipping around its star. It takes about four days to go through a year on this planet. So that was also this incredible discovery that ended up leading to the namesake of this postdoc fellowship that I was a part of, which is this really incredible community that is an interdisciplinary planetary science and exoplanet community.
It’s scientists all around the country who are doing lots of different aspects of planetary science and exoplanet research and coming together at least once a year or so to just build together and think about what we can do at the intersections of our fields as well.
Dean Regas: Well, you mentioned that the 51 Pegasi b is kind of a hot Jupiter, but how do you categorize or break these exoplanets up into categories? How do you do that?
Dr. Malena Rice: Yeah, we have largely used the names of our solar system planets as just an anchor. So we try to think about: Is it similar to the size of Neptune? Is it similar to the size of Jupiter? Is it more like an Earth-like rocky planet?
And then there’s, of course, the ever-descriptive “hot.” That’s temperature — it’s really hot right next to the star — or cold. We’ve got our cold Jupiters that are very far from the star. So it’s pretty intuitive when it comes down to it, which is good. It’s always good to have names where you know exactly what you’re talking about when you hear it.
Dean Regas: Exoplanet research, to me, I believe it’s the most exciting field in astronomy right now. I mean, is it me, or are astronomers finding way more planets around other stars than even the most optimistic person could have predicted?
Dr. Malena Rice: Yeah, we are finding a pretty huge number of planets, and the reason that we’re finding so many is actually because planets that are very different from the solar system are really common, which is totally fascinating and not something that we had really expected.
Dean Regas: Well, that’s what I was wondering — we’ve found all these strange worlds, so it leads me to think, are we normal? Are we the weirdos, or is it too early to tell all this?
Dr. Malena Rice: Yeah, I would say it is in ways too early to tell, and in other ways it really kind of depends on how you define us being weird and how similar a system has to be to ours to consider it weird or not. So if you think that something like the solar system needs to have a Jupiter — it’s gotta be a giant planet on a wide orbit — we already know actually that that is not that common. So if you look at all the sun-like stars, only about 10% of them actually have a Jupiter that looks kind of like ours.
If you’re thinking, does it have an Earth-like planet that could have water on it? We really don’t know. That is really kind of a shot in the dark at this point, and there are lots of tricky ways that you can try to extend our statistical models into that space. But really the answer is that we need to actually build new observatories that are going to be sensitive to that kind of planet, and we just don’t really have that right now.
So in that sense, we could be uncommon along some axes, but there are other axes along which we really just don’t have a good handle on it. And maybe the question is like, what is defined as a weird system? And I think that’s a really fun question as well — starting to refine, like, what do we actually mean when we say we’re looking for solar system analogs or we’re looking for life? Like, what are all the ways that that could look?
Dean Regas: With so many exoplanets out there, what’s your favorite exoplanetary system? You know, places that have more than one planet orbiting their star?
Dr. Malena Rice: Hmm. My favorite planetary system is probably WASP-94. These all have these crazy, sort of telephone number kinds of names, but WASP is the name of a survey — the Wide Angle Survey for Planets, I think, hopefully I got that right. And there’s a hot Jupiter around each of the stars. So it has two stars that are about the same size, and they each have a super, super hot close-orbiting Jupiter-sized planet around them.
Hot Jupiters are not that common — we only see them maybe 1% of the time. If you just pick a random star, there’s about a 1% chance that it’ll have a hot Jupiter. And this system is a binary star system, so there are two stars orbiting each other, and they both have a hot Jupiter. And so the reason that I’m really fascinated by this system is because it gives us maybe this indication that perhaps if you have two stars that form in the same environment — that are made of the same materials they were born with — you might actually end up with similar planets.
I think that’s actually a really profound realization — if that is the case, that if you put in the same ingredients, you get the same things out. It’s not just random. There’s a lot of beautiful structure to the universe. And actually probing that is a lot of the fun of astronomy. You know, how random is it? If I just roll the dice, do I get the solar system? Do I get something totally different? Can I tell what I’m going to get based on where I start? How much does the butterfly effect play a role?
That’s a lot of what I’ve been excited about recently — trying to figure out what is it that actually tells us what we end up with. If we know where we start from, do you always get the same planetary system or not?
Dean Regas: Well, that’s really cool. I haven’t heard about that one. There are so many, I can’t keep up with them. And there’s so much data coming in too. I mean, we’ve got the surveys like WASP that are doing their thing. We still have the Kepler mission — am I wrong in saying we’re still going through the data from the Kepler mission — and now we have the TESS spacecraft? So you’re part of the TESS Users Committee. What are you hoping to find and share with the public?
Dr. Malena Rice: Yeah, so Kepler is still — well, we’re still using Kepler data. Kepler isn’t continuing to observe, but there is just a gold mine of information within that dataset. So people are going back and reprocessing everything. Kepler was amazing for figuring out statistics like what is a normal planetary system? That’s really where Kepler shines — it’s able to tell us how common certain kinds of planets are.
And then TESS is this next step of saying, OK, well, Kepler just stared at this little patch of the sky for a really long time. But what TESS is doing is it’s looking all around the sky at all the brightest stars, and the brightest stars are the ones that are closest to us. So those are the ones where you can actually start to learn more. You’ve got more light, you’ve got a stronger signal.
If you want to learn more about those planets — say you want to get atmospheric observations or start actually getting a bit more information about compositions and things beyond just the fact that the planet exists — it helps for the planets to be nearby and to have a stronger signal for that. TESS is going around and finding all of those planets.
So that’s really exciting. That’s pretty amazing for actually learning more about those systems. Some of what I do with TESS is looking at the planets that have been discovered and working out which way the planets orbit relative to the way their stars spin. I’ve been really excited about this because there are all these super weird planets that orbit backward — their stars spinning one way and they go the other way. That is so weird, and that is not something that happens in the solar system. I am fascinated by what could possibly be causing that.
I’ve also been using TESS to look for outer solar system objects. There’s this idea that there could be a ninth planet lurking in the distant solar system, and that’s one of the things that I’ve been interested in using TESS for. Because you just have tons of data, and you can use it to look for exoplanets or you can use it to look at our solar system. There’s just so much to be discovered in both of those realms.
Dean Regas: Well, looking farther ahead, you’re also part of NASA’s Habitable Worlds Observatory, and I haven’t heard much about this project — I think because maybe it’s so far in the future — but what’s the goal and timeline for Habitable Worlds?
Dr. Malena Rice: Yeah, Habitable Worlds is really exciting, and it’s this idea that we’re going to build the next NASA flagship mission. So Hubble was a flagship mission, the James Webb Space Telescope was a flagship mission, and this Habitable Worlds Observatory — it would be the next one. It would be launched sometime in the 2040s, so still a little ways out because it takes a while to build a space mission and make sure everything’s operating properly.
The idea of this mission would be that it’s going to take images of a large array of nearby star systems, and the goal is to find at least 25 Earth-like exoplanets and check whether they have signatures of life. It’s going to image these planets and actually get spectra — break up the light from the planets into constituent colors — and use that to figure out what could be within the atmospheres of these planets. Is there water? Is there methane? Are there different signatures that could be useful to differentiate between either a lifeless planet or one that maybe looks a little bit more like our own?
This is really tricky because even if you’re looking at Earth analogs, Earth has actually looked quite different in terms of its atmosphere over different points in its life. There’s also this question of, you know, as a function of time, what does a life-bearing planet look like? So there’s a lot of work being done, both on the theory side — trying to figure out what does it actually mean to look for life, what are the different ways that it can manifest, how could we actually see that from many light-years away — as well as how can we build an observatory that’s actually going to be able to check all of this, and then how do we build a spacecraft that’s going to be able to do it all?
It’s really exciting. I am so delighted to be able to contribute to that kind of project.
Dean Regas: Big question. I’m excited to hear an expert answer this — with all of these worlds out there, all these exoplanets, you know what question I’m going to bring: Do you think life is out there?
Dr. Malena Rice: Yeah. I’m going to sound so political in this answer, but this is my genuine answer — I really, as a scientist, try not to decide that I think something is true if I don’t have sufficient evidence to believe that it’s true. I really think that that’s important as a scientist because you want to make sure that you’re not biasing yourself into claiming things also. So I would love for Earth to not be the only thing with life. It would be so cool to have life elsewhere.
And if you just think about the statistics of all the things out there, and if you think, oh, well, what are the odds that Earth is totally unique and there’s no life elsewhere? It seems inevitable — but we don’t actually have concrete confirmations that it has to be the case. And so I struggle to say that there needs to be life out there just because I want it, you know? And so because I want it, I feel that I have to hold myself back and say, no, no, we’re going to hold it in. Until we find something that really convinces us, we’re not going to go out and claim that we’ve seen it or that it has to be there. We’re going to wait, be patient, and follow the evidence.
So that’s my scientist answer. I would love for it to be there, and my intuition may or may not agree with my scientist answer.
Dean Regas: Sounded like a perfect answer to me. I think that’s the way to approach it. Well, Valle, this has been so fun. Thanks so much for chatting with us about our solar system and solar systems beyond.
Dr. Malena Rice: Thanks so much for having me. This has been so much fun. Really appreciate it.
Dean Regas: One of the most intriguing exoplanet systems is around a tiny red dwarf star called TRAPPIST-1. Not too long ago, astronomers were surprised to find exoplanets around red dwarf stars since they didn’t have as much material around them. But good news: red dwarfs can have planets—and that’s doubly good because red dwarf stars are the most numerous type of star in our neighborhood.
Now, TRAPPIST-1 doesn’t have just one planet but has seven known planets. Most, if not all, are small and rocky like Earth. Several of these planets lie in the Goldilocks zone—not too hot and not too cold—where liquid water could exist. And TRAPPIST-1 is relatively close to us, at only 40 light-years away.
And here’s the brand-new part: the James Webb Space Telescope is now taking a closer look at these worlds—specifically, the fourth and fifth planets out from the star. Can Webb see an atmosphere enshrouding one of these planets? Can it detect individual elements like nitrogen, carbon, and oxygen—or even water? Scientists think it can, if those elements are there. Stay tuned, and I’ll report back when Earth 2.0 is found!
Looking Up with Dean Regas is a production of 91ÖĆƬł§. Kevin Reynolds and I created the podcast in 2017. Ella Rowen and Carlos Lopez Cornu produce and edit our show and greatly prefer Earth 1.0 to any exoplanet I talk about. Yeah, it’s rough out there in space.
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 McFarland, and our cover art is by Nicole Tiffany.
I’m Dean Regas—keep looking up!
