Planetary Radio • Feb 01, 2023

JWST confirms its first exoplanet

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Jacob Lustig-Yaeger

Astronomer and Astrobiologist, Exoplanet Post Doctoral Fellow at Johns Hopkins University Applied Physics Laboratory

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Bill Nye

Chief Executive Officer for The Planetary Society

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Jason Davis

Senior Editor for The Planetary Society

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Sarah Al-Ahmed

Planetary Radio Host and Producer for The Planetary Society

The James Webb Space Telescope has confirmed the discovery of its first exoplanet. Jacob Lustig-Yaeger, one of the leads on the team that made the detection, joins us to discuss the details. We share info on the Juno mission to Jupiter's next flybys of Io, let you know how to spot the "green comet" visiting our part of the Solar System, and provide insights on the night sky in What's Up.

Exoplanet LHS 475 b
LHS 475 b Illustration This illustration shows the first exoplanet confirmed by JWST, LHS 475 b. The exoplanet is located 41 light-years away in the Octans constellation. This rocky world is approximately 99% the diameter of Earth.Image: NASA, ESA, CSA, Leah Hustak (STScI)
Light curve from LHS 475 b
LHS 475 b Light Curve This graphic shows the light curve from NASA's JWST's Near-Infrared Spectrograph (NIRSpec) observations on August 31, 2022. It shows the change in brightness over time from the LHS 475 star system as the Earth-sized rocky exoplanet LHS 475 b passes between Earth and its star. This detection was the first of two observations that allowed researchers to confirm LHS 475 b as the first exoplanet detected by JWST.Image: NASA, ESA, CSA, Leah Hustak (STScI)
Exoplanet LHS 475 b transmission spectrum
LHS 475 b Spectrum This graphic shows the spectrum of exoplanet LHS 475 b on August 31, 2022, the first exoplanet detection confirmed by JWST. From this limited data, we can tell that the planet's spectrum is not consistent with a pure methane atmosphere but leaves open the possibility of a pure carbon dioxide atmosphere or no atmosphere at all. Future observations will be needed to definitively state if LHS 475 b has an atmosphere.Image: NASA, ESA, CSA, Leah Hustak (STScI)

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Sarah Al-Ahmed: The New Age of Planet Hunting with JWST begins, this week on Planetary Radio. I'm Sarah Al-Ahmed of The Planetary Society, with more of the human adventure across our solar system and beyond. The James Webb Space Telescope has found its first exoplanet. Jacob Lustig-Yaeger, one of the leads on the team that confirmed the new world, joins us to discuss the groundbreaking discovery, and what it means for the future of exoplanet hunting. We'll share a short report on the Juno mission's planned flybys of Jupiter's volcanic moon Io, and our CEO Bill Nye the Science Guy will pop in to tell you how to spot the green comet that's visiting our part of the solar system. We'll close out our show with Dr. Bruce Betts, as he brings you up to speed on what's going on in the night sky, and what's up. Now we turn to this week's space mission briefings. In April, the European Space Agency's Jupiter Icy Moons Explorer, or JUICE Mission, will finally embark on its journey to the Jovian system. It will study Jupiter's potentially ocean bearing moons, Ganymede, Europa, and Callisto. The mission is all set to be shipped to its launch facility in French Guiana. It's going to take about eight years for it to reach Jupiter, but we know that the data will be worth the wait. The Lucy Spacecraft, which NASA launched in October of 2021 on a mission to study Jupiter's Trojan Asteroids, is still facing issues with one of its two solar arrays. The mission team says that the spacecraft is still functioning well enough to do its job, but their attempts to fix the array have been unsuccessful so far. Don't worry though, the team's efforts to correct the deployment will pick back up when Lucy moves back towards the sun on its trajectory toward Jupiter later this year. We'd also like to send a huge congratulations to the team behind NASA's Ingenuity Mars Helicopter. The small experimental drone spacecraft has successfully completed its 40th flight on Mars. The little copter has accompanied the Perseverance Rover on its journey across the Martian surface for almost two years now. That's so much longer than it was expected to work, and that team should be so proud. You can learn more about these and other stories in our January 27th edition of The Downlink. That's The Planetary Society's weekly newsletter. Read it online, or get it sent to your inbox for free every Friday at In our most recent show, we shared some of the amazing things that NASA's Juno Spacecraft has been learning about Jupiter's moons. Our guest teased that the spacecraft has some upcoming flybys of Io, the most volcanic body that we've ever discovered in our solar system. The data and images from those flybys are going to blow us all away. The Planetary Society's senior editor, Jason Davis, has just published an article on this subject, and he's here to tell us more. Hi Jason, thanks for joining me.

Jason Davis: Hey Sarah, thanks so much for having me.

Sarah Al-Ahmed: Yeah, so last week I had Scott Bolton, the principal investigator of Juno's mission to Jupiter, here to talk about all of the amazing moon science that they've been doing over around Jupiter, but it's perfect timing. You just came out with a new article about Juno's flybys of Io. You want to tell us a little bit about what Juno has in store for us?

Jason Davis: Yeah, so exciting that in Juno's extended mission, it's getting a look at some of the Galilean moons. We've already seen Ganymede and Europa, and now it's time for Io. So cool. Throughout this year, the spacecraft's going to be getting closer and closer on its long orbits of Jupiter, until finally it does a really nice close flyby on December 30th. So mark your calendars, nearly a year from now, and then another one on February 3rd of next year.

Sarah Al-Ahmed: That's awesome. I'm so looking forward to those images from Juno cam. Anytime we get a glimpse of that moon, it is so just beautiful and absolutely terrifying, but just getting a closer look at it for the first time in ages is going to be amazing.

Jason Davis: Yeah, yeah. Juno cam is so neat to remember that this was an add-on instrument at the last minute before Juno launched. It wasn't actually a science instrument, but I believe it was Scott Bolton who you just mentioned who said, "We cannot go to Jupiter without a camera," and they managed to get this little camera on there, and it's just delivered these amazing pictures of Jupiter, and now some of these moons, and can't wait to see what Io looks like through its lens.

Sarah Al-Ahmed: Yeah, even from a distance, just the images of the volcanoes exploding, and when I spoke to Scott Bolton last week, he was talking about how there's just straight up lakes of lava on that moon, so it's going to be really interesting to learn more. I know that when they're going to be making these close passes, they're going to be using an interesting tactic to try to use those passes to learn more about the internal workings of that moon. Can you tell me more?

Jason Davis: One of the big questions about Io is how does it actually work? We know that it gets squeezed on by Jupiter and Europa and Ganymede, but we don't know exactly how the heat is generated inside the moon, and how that heat transforms the magma deep inside it into these lava pools that spill out onto the surface, and shoot into space. So scientists are really keen to try to figure out exactly how that works and model it. So one way we can do that is just watching how Io's gravity affects the spacecraft. It'll transmit a signal to Earth, and as Io's gravity unevenly tugs on it, that signal will shift a little bit, and we can actually see then, or try to determine what's going on inside the moon.

Sarah Al-Ahmed: Are they going to have to turn the spacecraft in order to send that signal back, and is that going to impact what images we get of the moon when it flies by?

Jason Davis: It'll only do this, as far as I know, on those two really close flybys, and they will have to orient the spacecraft in a very specific way to do that, and that'll put Juno cam as playing second fiddle, not in the best position for pictures. But after it does its flyby and Juno is receding into the distance, Juno cam should still be there and manage to get a really cool half lit photo of Io on the side that faces Jupiter. So that'll be a cool, really neat perspective on the moon that we don't see that often. Yeah, it'll be exciting to see what happens.

Sarah Al-Ahmed: That's really cool. Is there anything you're super excited about personally to learn about Io?

Jason Davis: Yeah, I'm really hoping that we'll be able to see some changes on the surface, and that's the goal as they fly by the moon again and again, they can see like what's actually happening. Are we seeing lava spilling onto the surface? Will we see a volcano erupting up into space, which we have captured before with other missions. Just the chance that we might see this jaw dropping picture of a volcano doing something really cool is definitely what I'm looking forward to the most.

Sarah Al-Ahmed: Same. That's going to be amazing. Well, thanks for joining me, Jason. These flybys are going to teach us just so much about the geology and just the geophysics of this volcanic moon, and I'm really excited to learn what it's going to teach us about Jupiter. So I hope everyone checks out Jason's article. I'm going to put it up on the page for this planetary radio episode at, so you can get all the information that you want about Juno's new flybys of Io. Now, before we get into our main subject for today, we'd like to take a moment to share more about how you can spot a beautiful green comet that's swinging close by Earth this week. Here's the planetary society's CEO, Bill Nye, with the details.

Bill Nye: Right now a comet from the outer edges of our solar system is passing close to Earth for the first time in 50,000 years. Here's how to see it. Comet 2022 E3 (ZTF), sometimes referred to as the green comet, will be closest to Earth on February 1st and around that time if you are somewhere with a dark sky, it may be visible to the naked eye, or better yet, use binoculars. It will most likely look like a faint smudge in the sky rather than a bright object. But with a telescope, you might see its tail and its greenish color. To find the comet, look in the northern skies soon after sunset. And remember, even though it may look like a dim smudge in the sky, this particular comet takes about 50,000 years to orbit the sun, so literally no one has seen it since the Stone Age. The green comet, watch for it.

Sarah Al-Ahmed: Well, you heard him, folks. Grab your binoculars if you've got them, and let us know if you spot that comet. You could write us at [email protected]. Now it's time to get into our main topic for today, planet hunting. It wasn't so long ago that finding exoplanets orbiting distant stars was really difficult, but with advances in technology, new space telescopes, and a new generation of people with a passion for finding worlds, humanity can be proud to report that we've discovered more than 5000 exoplanets beyond our solar system. Now, NASA's James Webb Space Telescope, or JWST, has officially joined the planet finding effort, and has discovered its first world. JWST is a new, infrared space telescope that was decades in the making. It's revolutionary in so many ways, and has already taught us a lot about distant galaxies and the early universe, but part of what makes it so powerful in our quest to learn more about the cosmos is JWST's ability to not only find exoplanets, but analyze the atmospheres of these distant worlds and tell us more about their composition. Our guest today is Jacob Lustig-Yaeger. He's an astronomer, astrobiologist and exoplanet hunting post-doctoral fellow at the Johns Hopkins University Applied Physics Laboratory in Maryland, USA. He and his colleague Kevin Stevenson lead the team that recently announced the discovery of the first confirmed exoplanet with JWST, a world named LHS 475 b. It orbits a red dwarf star 41 light years away in the constellation of Octans, and excitingly, it's almost exactly the same size as Earth. Of course, it's a very different world from ours, but still. Their team first observed the exoplanet on August 31st, 2022, and it's just one exoplanet in a series of Earth-sized worlds. Their team is planning to study. They're using a method called transmission spectroscopy to teach us more about the atmospheres of worlds that are similar to the size of ours. When distant exoplanets pass between us and their stars, we can study the light that passes through the air shrouding those worlds and learn more about their atmospheric composition. JWST is the only telescope capable of accomplishing this feat for rocky Earth-sized worlds, so this moment marks a whole new age of exoplanet detection and study. Welcome to Planetary Radio, Jacob.

Jacob Lustig-Yaeger: It's good to be here. Thanks for having me.

Sarah Al-Ahmed: I want to say congratulations to you and your team for detecting the first planet with the James Webb Space Telescope. I mean, it's a whole new age of exoplanetary discovery, and your team is going to be in the history books.

Jacob Lustig-Yaeger: Yeah, thank you. Thank you. The rate of exoplanet detection is really increasing these days, with over 5000 discovered, so it's an exciting time to be studying exoplanets.

Sarah Al-Ahmed: Oh, for sure. I mean, I got really interested in astronomy as a very young child, I think it was right after the second exoplanet was discovered, and now there's thousands of them. It's a good time to be in this field.

Jacob Lustig-Yaeger: Yeah, definitely.

Sarah Al-Ahmed: I watched your press conference at the 241st American Astronomical Society meeting in January, and that had to be so exciting to finally get up there and share this discovery with the astronomical community. I mean, after so many years of dedicating your life to exoplanet discovery, what did that feel like?

Jacob Lustig-Yaeger: It was really cool. JWST has been in science operation mode since July, taking data diligently, and we've had these data on our hands since early September, and worked really hard to put this out and get the materials ready for the AAS conference. So it was really nice to be able to share that, both with the press and with the astronomical and astrophysical community.

Sarah Al-Ahmed: Did you have to keep any of it secret for a little while there, as you were generating graphics?

Jacob Lustig-Yaeger: A little bit, but early versions of our work was shown to some of our colleagues at a meeting at Space Telescope Science Institute in Baltimore, in early December. So it was trickling out there, but certainly we did the coordinated press releases and that caught a lot of attention.

Sarah Al-Ahmed: And just to give a little bit of your backstory in this, you've been studying exoplanets since your undergraduate time at UC Santa Cruz, and then you just kept on going when you went to get your PhD at the University of Washington. Now you're hanging out at the Johns Hopkins Applied Physics Lab doing your postdoc work, and I have to ask, what started this journey? Why are you so in love with exoplanets and why particularly Earth-like exoplanets?

Jacob Lustig-Yaeger: At UC Santa Cruz, I went in there undeclared, not really sure what I wanted to major in. I knew I liked math, I knew I wanted to go into some area of science, was thinking about cognitive science, and chemistry, and physics, definitely. And then I decided on a physics bachelor's path, and at a certain point, I think in a junior year, needed some upper division electives to satisfy credits. And a friend of mine said, "Hey, this exoplanet class taught by Jonathan Fortney looks great. You should take this with me since you like astrophysics." And I was like, "I like astrophysics. Yeah, I guess you're right. You're right." Sometimes your friends know you better than you know yourself at times. And that class was an introduction for me to exoplanets. Jonathan talked about this app called Exoplanets, I think I still have it on my phone, where you can follow new discoveries and I just sort of fell in love thought, wow, this field is up and coming. There's guaranteed to be amazing discoveries over the next, any number of years, five years, 10 years. This field will continue to grow. So it set me on a path to doing research with that professor, Jonathan Fortney. And then he helped me apply to grad school, where I got into the University of Washington in Seattle, and moved up there to start doing research with my PhD advisor, Victoria Meadows, who is now also an astrobiologist. And astrobiology is the fascinating study of the origin, evolution and extent of life in the universe, and it's an incredibly interdisciplinary field, bringing together these chemists, and computer scientists, and astronomers, and physicists, to answer these fundamental questions about life in the universe. And that's the connection to Earth-like planets that you were talking about, where the search for life is this fundamental, long-term question that exoplanet scientists get to try to answer, using the study of exoplanets. And as an astrobiologist and with the focus on the search for life, that is really thought to be something that needs to be conducted on Earth-sized planets, following the way we think life developed here on Earth, and what life requires to exist, takes us to these small rocky planets.

Sarah Al-Ahmed: Yeah, it's going to be interesting when, in the far future when we've established that these rocky planets have life on them, to try to explore what other worlds might have life as well. But start with what you know, and then build on that. So you're part of the team that confirmed the detection of this planet called LHS 475 b, but this is just the first step in a broader program for the James Webb Space Telescope to try to hunt for these Earth-sized worlds and study their atmospheres. And in order to do this, your team looked through data from the transiting exoplanet survey satellite that hunts for planets. You had all kinds of options. Why was this the planet that your team decided to go for, out of all the different worlds you could have explored?

Jacob Lustig-Yaeger: Yeah, that's a great question. And I will say that it's one of five planets that we have in our cycle one program to search for atmospheres on small rocky planets. And so it made the cut in terms of a handful of planets that we're interested in. And so this planet is... It was hinted at, it was a planet candidate prior to our observations, indicated by the TESS satellite, like you said. And so we had a sense for when we would need to observe the star to see it transit, and to be able to confirm its detection. And the planet itself we knew would be around 600 degrees, and that's much warmer than the Earth. It's not in the habitable zone. Part of the motivation for this planet is that we are trying to understand the limits of which planets have atmospheres and which don't, and what processes drive atmospheres to be lost from Earth-sized planets, so that we can put together these physical processes and make better predictions ahead of time when we detect planets about which ones we think might have atmospheres. And then also to just further our general understanding of atmospheric science and exoplanet science through the whole population of planets and whether or not they have atmospheres. So this is a good candidate for that, because it's not by any means the hottest exoplanet we've ever seen. It's less than 1000 Kelvin, which winds up putting it in a warm regime. Astronomers are fast and loose with our terminology sometimes, calling things hot and warm and cold relative to perceptions that we might have, not necessarily the extremes. And so this planet is on that boundary we think, between very well could have an atmosphere. It's only a little bit hotter than Venus, and Venus has a very thick atmosphere. And it's not so hot that we really think the star would strip away the atmosphere.

Sarah Al-Ahmed: So there's a good chance there. Well, we'll get into those details on the atmosphere in a little bit, but I wanted to ask just for the people who aren't super familiar with planet hunting, how can you use a telescope like the James Webb Space Telescope to find planets, and why is it so particularly tricky to find a world of this size, that's so small?

Jacob Lustig-Yaeger: The trick to finding exoplanets with current astronomical telescopes and techniques is to indirectly detect their presence. And the most common technique to indirectly detect exoplanets these days is to see them pass in front of their star, and block a tiny amount of light. And so that method is called the transit technique, because the planet is seen transiting across the face of the star. So it's like if you're sitting on a sunny day, and maybe a cloud passes in front of the sun, you can tell that there's less light, or sometimes even an airplane will pass in front of the sun, and you just see a quick blip and a drop of light. And then you look up and you see, oh, a plane just flew in front of the sun. But here, we're looking at planets many light years away on their orbits around their star, and they have to be aligned in such a way from our point of view and their orbital plane to pass in front of their star. And that's not a guarantee. So there's just a small probability that any given exoplanet in orbit around its star will transit. Despite that caveat, we're finding thousands of exoplanets using this method. And so it's really exciting, and the transiting exoplanet survey satellite, TESS, is so good at doing this initial search to find planets, because it has a broad field of view and it stares at many stars for many days in a row, looking for these planet transits. And so it covers a large portion of the sky and can just conduct this broad survey. Whereas JWST is more, you can think of it like it zooms in a little bit. It's able to do these deep dives into specific narrow corners of the sky, whether that's looking at some of the most ancient light in the universe, or looking at some of the closest stars to try to find molecules in those planet atmospheres as they pass in front of the star.

Sarah Al-Ahmed: And you did say with TESS it has the ability to look at so many stars for so many worlds at a time, but I would think what's really impressive here is that you not only managed to take one detection on this planet, but with just two transits, you were able to learn all kinds of things about this planet. And luckily enough, it's close enough to its star that it orbits quickly enough that you saw it during those two transits. And they were only four days apart, right?

Jacob Lustig-Yaeger: That's right. Yeah. So we were able to catch two independent transits four days apart. It's on a two-day orbital period. So there was one opportunity in those four days where we didn't catch it, but that is okay. And the two observations with JWST were so consistent with one another, and that's one of the amazing things about working with JWST data is just how reproducible the observations are. If you go back and observe the same thing twice, it's extremely stable, and there aren't these systematic errors that sometimes crop up when telescopes are changing temperatures, which can happen if they orbit the Earth and pass into the shadow of the Earth and then back into the sun. That can change aspects of the telescope's operations, and whether you're getting the exact same data. Scientists have to correct for stuff like that, and it gets complicated, but with JWST, the data is extremely clean the second we download it. Of course, we still have to process it, and run models to get to our final result, but ultimately seeing those two transits was the first step in confirming the detection of this planet.

Sarah Al-Ahmed: Yeah. And because that data is so clear, I'm sure your error bars on this are way more narrow. You actually can really get in there and try to figure out details, like, is that an atmosphere? Maybe I'm just still tripping out over this, but the fact that we can even do that kind of science at all at this point just underscores how amazing this new instrument is. How many years have you been looking forward to using this telescope to do this?

Jacob Lustig-Yaeger: Many years. Of course. I'm still an early career scientist, so there are some folks who have been around since the early stages of planning for JWST when there were only a handful of effects of exoplanets that had been discovered. But I did calculations in grad school predicting the capability of JWST, and thinking, okay, well this should be capable of sensing the atmospheres of small, Earth-sized planets around the very smallest of stars. And just to see that it is meeting those requirements right now, and even exceeding pre-launch expectations in some senses, that is an extremely good sign for amazing science to come. And I think that's one of the major takeaways from our work here, is the forward looking perspective that these data are so good. It's expected to be taking data for now well over 10 years, maybe it can last 20 years. That just will bode really well for amazing discoveries.

Sarah Al-Ahmed: Oh, fingers crossed. It's learning so much about exoplanets, but there are a million other things that we want this telescope to teach us about our universe, and the longer we can keep it up there and working the better, because I will be so sad if it ever stops working. I'm still trying to grapple with the fact that someday Hubble will stop working. I'm not emotionally prepared.

Jacob Lustig-Yaeger: Yeah.

Sarah Al-Ahmed: But there are a slew of instruments aboard JWST, and you specifically used the near infrared spectrograph in order to take these readings. Can you tell us a little bit about what that instrument does and why it's so useful for studying atmospheres?

Jacob Lustig-Yaeger: Yeah, so JWST has all these different instruments and different modes for each instrument. It's like looking at this giant menu, and being excited about all the different options. And it just blows out of the water the options that were available for exoplanet science with the Hubble Space Telescope, which is still a very capable space telescope 30 years later. And so we chose the near-spec instrument partially because of the wavelength range that it covers in the electromagnetic spectrum. We knew that we wanted to target molecular absorption features in a potential atmosphere of this planet. And fortunately from laboratory studies here on Earth of molecules, we know exactly what wavelengths each molecule absorbs. And so we specifically were targeting wavelengths where we'd be sensitive to methane and carbon dioxide, two very common molecules in the solar system, that are the two forms of carbon. If you have carbon, you're likely to have it in methane or carbon dioxide. Of course, there's many other molecules out there, those are just extremely common, and they're both covered in this wavelength range that we targeted. Also, the stars tend to be quite bright in the near infrared where near-spec covers. And so brighter star leads to brighter backlighting when the planet passes in front and blocks the light, so we were going to get better quality data than say, choosing longer wavelength observations. And then finally, the near-spec instrument has the highest sensitivity than all other instruments, or at least in the near infrared wavelength range. So a few different lines of reasoning came together for that choice.

Sarah Al-Ahmed: It all makes sense. It's fortuitous that in this case, the star very bright in the telescope, but also a smaller star. It's a red dwarf star, correct?

Jacob Lustig-Yaeger: That's right, yeah. And for people following along with the specific details, this is an M 3.5, it's a main sequence M dwarf, it's about 3300 degrees Kelvin, so a little over half the temperature of the sun.

Sarah Al-Ahmed: And back in my day, but when I first started doing exoplanet detection in college, I remember it being we could only find things maybe Jupiter sized, because we needed them to create such a contrast against the star. But in this case, you're using smaller stars, looking for smaller planets with a telescope capable of actually picking up these differences. I'm wondering if you did have a star in the system that was a sun-like star instead, would you still be able to pick up an Earth-sized world with this telescope?

Jacob Lustig-Yaeger: It would be much more difficult. Like you mentioned, the contrast between an Earth-sized planet transiting, blocking the light from a small star, is much higher than a much larger star. So I think we'd be able to detect the planet's transit to much lower significance, but any hope for searching for the atmosphere, which is just a really small effect on top of an already small effect, is hopeless. And so that's why we're looking at these smallest of stars, which presents other challenges in that these are very different from the sun, and challenge our understanding of what the planets might be like. But at the same time, it's where we can look right now for atmospheres, and any discoveries will expand our knowledge since we don't know anything about rocky planets and their atmospheres for these small class of stars.

Sarah Al-Ahmed: Hold that thought. We'll be right back with the rest of my interview with Jacob Lustig-Yaeger after this short message from George Takei.

George Takei: Hello, I'm George Takei, and as you know, I'm very proud of my association with Star Trek. Star Trek was a show that looked to the future with optimism, boldly going where no one had gone before. I want you to know about a very special organization called The Planetary Society. They are working to make the future that Star Trek represents a reality. When you become a member of The Planetary Society, you join their mission to increase discoveries in our solar system, to elevate the search for life outside our planet, and decrease the risk of Earth being hit by an asteroid. Co-founded by Carl Sagan, and led today by CEO Bill Nye, The Planetary Society exists for those who believe in space exploration to take action together. So join The Planetary Society and boldly go together, to build our future.

Sarah Al-Ahmed: We've gone over some of the details on this planet, but let's just do a full rundown. What do we know about this world so far from these two transits?

Jacob Lustig-Yaeger: Right. So prior to observations, the radius of the planet that TESS was reporting was really, really uncertain. It was possible that it was Earth-sized, but it could have been smaller than Mars, and it could have been nearly almost twice the size of Earth, just a huge range of sizes. And because we're looking at the planet transit, it tends to be extremely sensitive to the radius of the planet. That's the key thing that we're observing with really high precision. And so the first thing we were able to update is the planet radius, which we found delightfully is 0.99 Earth radii. So it's exactly the same size as Earth. So that is just a serendipitous thing. An interesting thing is that we don't actually know the mass right now. The types of measurements that are required to measure the mass have not been made yet, and so we took a look at the population of M dwarf Earth-sized planets that had measured masses and radii, and we were able to estimate what the mass of this planet might be if it shares many characteristics with that population of M dwarf rocky planets, in which case they tend to be slightly under dense relative to the Earth. So we think its mass will be maybe around 90% that of Earth, but there's a broad range of uncertainty on that. So it could have more iron in its interior than Earth, and end up being heavier than Earth's mass, or it might have a larger water fraction than Earth. That could lead to it being less dense than Earth.

Sarah Al-Ahmed: I've got to ask, because 99% is really close to 100%, and how does that compare to all of the other Earth-sized exoplanets that we've found so far? I don't know if I've heard of one that's 99% the radius of Earth. That's wild.

Jacob Lustig-Yaeger: I don't know. I haven't heard of one off the top of my head that is as close to being Earth-sized. And of course, I've got to say again that it's much hotter than the Earth. It is very different from Earth in probably every other way, but it just happens to be Earth-sized, and that's a very cool characteristic to share.

Sarah Al-Ahmed: There are all kinds of things that could play into that temperature there, and I've got some questions about that. But I mean the primary reason is probably just that it is so close to its star, and it's not really in the habitable zone, right? It's a little too close to its star for that to be true.

Jacob Lustig-Yaeger: Yeah, it receives about 20 times the amount of light from its star than Earth receives from the sun. So that puts it well interior to the habitable zone, and hotter than Venus actually, at least without knowledge of any atmospheres in either case, because Venus is a very interesting case in terms of an atmosphere.

Sarah Al-Ahmed: Yeah. And you guys did try to figure out whether or not this thing has an atmosphere, but you weren't exactly able to answer that question just yet. So what do we know about this planet's atmosphere if it does exist?

Jacob Lustig-Yaeger: We were able to take our extremely precise measurements, and they ruled out really extended atmospheres that are composed of hydrogen and helium. Those tend to be the easiest for astronomers to rule out first, because these type of atmospheres that are similar maybe to Jupiter or Saturn's atmosphere, in that they're composed of really light molecules with smaller amounts of other gases like methane, carbon dioxide, carbon monoxide, water. But when you have light molecules in an atmosphere, it tends to make that atmosphere weigh less and it can extend more out. And since, again, we're measuring the radius of the planet here, and we're looking for the signs of molecules, and the way they make the radius of the planet larger at specific wavelengths where the atmosphere absorbs light. And this is the method of transmission spectroscopy that we're using here, and hydrogen dominated atmospheres would've shown up in our data. At night and day we would've seen massive spectroscopic features from hydrogen and helium causing the atmospheres to be extended. And we didn't see that at all. We measured an incredibly precise, very flat line. And so we can throw out all the possibilities that involved hydrogen and helium in this atmosphere. Now, we are able to weekly disfavor a model that has, say, a pure methane atmosphere. Methane is much heavier than hydrogen and helium, but a lot lighter than some of the other molecules that we considered. And that tends to have a bit more of an extended atmosphere as well. And I already mentioned that we targeted this wavelength range specifically to be sensitive to methane and carbon dioxide. And so we don't see a methane feature in our spectrum, and so that leads us to disfavor that pure methane model. But it could still have an atmosphere where the bulk of it isn't made of methane, but it still has some methane in it. And then the most difficult thing is that if we take a look at a pure carbon dioxide atmosphere, similar to that of Mars or Venus, we also get a spectrum that would be a flat line just like we measured. So we don't have the precision from these two observations to distinguish between a pure flat line, that would be the result of a completely airless world with no atmosphere, and a Mars-like or Venus-like atmosphere with 100% carbon dioxide. And so it's going to require further observations to distinguish between those two cases. But I think while there are other atmospheric possibilities besides a pure carbon dioxide, it provides a really good goalpost to aim for, because it is a difficult measurement to make because carbon dioxide is one of the heavier molecules we'd expect to be there. It leads to the atmosphere being very compact, and even though it has extremely strong and well-known spectroscopic features, the compact nature of those carbon dioxide atmospheres just presents a challenge that will just require more data.

Sarah Al-Ahmed: Yeah. And that brings me around to the temperature of the planet, because I always think of atmospheres as planetary jackets. They hold in some of that heat. And I'm wondering if that might give us some clues here, because if the planet has absolutely no atmosphere, we can think of that scenario, its surface temperature is going to be mostly dependent on its star and how close it is, and how wide across this planet is. But in the case that there's an atmosphere, I mean maybe it's holding onto extra heat that could give us a clue, right?

Jacob Lustig-Yaeger: Yeah. And that can go both ways, because with Venus and Earth, that's certainly the case where the atmosphere causes the greenhouse effect that allows it to blanket in and trap heat, and makes the surface temperature much, much higher than you would expect for an airless body. But on the other hand, these really close in planets around M dwarfs are thought to be tidally locked and synchronously rotating, so that they have a permanent day side that always faces the star, and a permanent night side that never faces the star, which is a really interesting scenario for a planet and really gets our sci-fi minds thinking here. And these planets might be quite a bit different, and many people study the atmospheric dynamics in such an atmosphere, where you're looking at what direction the winds go, and how might clouds form on the day side, do those clouds transfer to the night side, what's going on? And so in these tidally locked synchronously rotating atmospheres, the models suggest that they have extremely high winds that transport heat from the day side to the night side. And that acts to cool the planet relative to what you might see for an airless body, at least on that day side. So we tend to be slightly sensitive with a different type of observation. When you watch the planet pass behind the star, a secondary eclipse, you can actually make a measurement of that day side temperature. And so these types of recirculation might cool the planet relative to a constantly heated day side, where you'd expect this really hot, rocky surface, that is just instantly radiating that heat back to us, and able to be observed. So it's a bit more complicated than just the greenhouse effect, but there's really a path forward for learning more about this planet using JWST, I think

Sarah Al-Ahmed: I do have a question about what temperature we would actually be measuring in the scenario that it has an atmosphere. Because with a lot of atmospheres, the temperature varies with its density and its composition, and its altitude in general. I mean even on Earth there's a layer of atmosphere way up there that's hotter than the layers underneath. So what temperature would we be measuring here in the case of an atmosphere? Is it an average across the entire atmosphere?

Jacob Lustig-Yaeger: Yeah, I mean that's such a good question, and the detailed answer has a lot of nuances, and requires modeling. But the key is with an atmosphere, you're measuring a different temperature as a function of wavelength because different wavelengths of light are able to probe different depths into the atmosphere, or really the region from which light emerges is dependent on the actual temperature structure of the atmosphere, like you were saying, how the temperature varies with altitude, and the way that the gases within the atmosphere interact with light. And so those two effects combine in a complicated way that requires numerical modeling and computer simulations to do in detail. But it is exciting, because the spectrum of a planet's thermally emitted light doesn't just tell us about the molecules that are there and how much of them there might be, but it tells us about the actual temperature structure of the atmosphere, which is something that JWST is really capable of doing for larger planets. And so I'm really looking forward to my colleagues' results coming forward in the next, I don't know, year, couple years studying the temperature structures of all of these hot Jupiter planets and super Earths, because it'll be these altitude dependent studies of these really hot planets. And so we're not quite there for Earth size planets, I think either it will take a large amount of time with JWST or even future observations to be sensitive to the thermal emission from them. Because Earth-sized planets are small, and particularly if we want to be studying those that are in the habitable zone, they're just cold, relatively cold, and colder things emit less thermal light.

Sarah Al-Ahmed: Yeah, it is, it's a complicated situation.

Jacob Lustig-Yaeger: It is.

Sarah Al-Ahmed: You're going to be observing this object more in the future. I know there's at least one planned observation sometime this next summer. Do we think that that's going to be the end of the research on this planet with JWST, or is it see how much information you get, gauge whether or not you get the answers you want, and then follow up in the future if you need to?

Jacob Lustig-Yaeger: We're definitely excited about the follow-up observation, the observation that we already have planned as part of this program, in July. And that will add to our current study. We'll revisit the target with all three observations, and update our results at that point. But I think there are huge opportunities to continue using JWST to observe this target. I tend to think that the thermal emission route from the day side is a critical way to get a sense for whether that suggests that the planet has no atmosphere, or a thick atmosphere. And if it has, if those measurements are to hint that it does have an atmosphere, then I think it would be a really strong motivator for observing more transits to try to go after the more compact carbon dioxide atmospheres, because the thermal emission could give us a sense that there's an atmosphere to continue observing. But if it's an airless body, and the thermal measurements show that, then I think it might be the end of JWST observing this target, just because there are so many more targets. And it gets to the core goal of just figuring out whether these small rocky worlds around these small M dwarf stars even have atmospheres. It's a win-win, whether or not they do or don't. If they do have an atmosphere, of course there are more follow-up opportunities to learn more, but if they don't, they go into the bin of those that don't have an atmosphere that, together with that whole population, will allow us to hone our understanding of planetary science.

Sarah Al-Ahmed: Yeah. Because there's a good chance that stars of this type, with planets at that distance, just maybe the star blows the atmosphere straight off of them. So knowing more about this group will be useful in the future, but I know that part of what you guys are trying to figure out with this thing is whether or not it has clouds in the atmosphere. That could give us an indication that it's more Venus-like, with more carbon dioxide. That's just blowing my mind a little bit. I know we've detected clouds on other planets, mostly bigger puffier planets, but with a planet like this that's orbiting its star so quickly, and as you said, might be tidally locked and having these raging winds whipping around it, how would we detect clouds on something like that?

Jacob Lustig-Yaeger: It's a tricky thing to do. There is a history of clouds obscuring what we're seeing in exoplanet atmospheres, and it goes back to the hot Jupiters and super Earths. Basically, a cloud deck has the effect of limiting our sensitivity to absorption features from molecules in the atmosphere. With gas giant planets where there's no question whether or not they have an atmosphere, they must have an atmosphere to be as large as they are, when we see very small absorption features from molecules, it implies right then and there that there is a cloud deck blocking our view to the lower atmosphere. And of course, from our knowledge of the solar system, we can look right at Venus and say, well, Venus's atmosphere, it's incredibly difficult to see the surface. It stumped scientists for hundreds of years, and it required very particular observations to understand the lower atmosphere of Venus. And so there's that solar system example of not being able to see the lower decks of an atmosphere. And we are really going to face that with exoplanets, particularly rocky planets. We can't take for granted that they have an atmosphere. There are a lot of reasons why they might not, and we just don't know. Certainly our observations are a candidate for clouds explaining why we didn't see anything. Of course, it could just be a thin atmosphere like Mars as well. And it's so difficult to see are we blocked because we're just seeing the rocky surface, or are we blocked by a cloud? And that's where these thermal measurements, when the planet is in that secondary eclipse, is the optimal path for disentangling those two effects. Because the clouds are highly reflective, and that's another aspect of them that tends to cool the planet. Planets maintain the balance of energy between the light the star shines on them, and how much of that light they're able to hold within them and allow to heat up. In a very high, we call it high albedo body, but a very reflective planet, perhaps because it has clouds, is able to reflect all that light back to space and only be minimally heated up. And so that stands in huge contrast to a planet that has no atmosphere, and might have a rocky surface like Mercury or the Moon, that are really dark. These rocky surfaces tend to be dark, and so they absorb heat really well. And so again, this is a key path, I think, to answering these next level questions about this target. And I think that's probably the way to go, and the way our group hopes to continue studying this planet with JWST.

Sarah Al-Ahmed: And I think you said this earlier, but it's just one of, what, five planets that you guys are planning to explore. So when are we going to be hearing more about these other worlds you're going to be looking at?

Jacob Lustig-Yaeger: Yeah, so we actually got data in December. On Christmas, actually, we got our second planet in transit, and then a couple days later it transited again. So we have two observations of a second target we're looking at, and so we're working on analyzing those data. It's way too early to say. We have that target coming down the pike. And then another target, two targets being observed, late February and early March. And then a final target, Trappist-1h actually, one of the interesting Trappist-1 planets, will be part of our program, observed, I think one observation this summer, and then two more in the winter. So it's the next year, we'll have JWST periodically looking at the planets from our program. It's not just our program. There's tons of exoplanet science going on with JWST, and many colleagues of ours having other programs going on, other exciting rocky planets, the other Trappist-1 planets, so I think it's going to be a really exciting continuation of this first year of JWST data, and then lots more exciting stuff to come.

Sarah Al-Ahmed: Oh yeah, I'm so glad that you bring up the Trappist-1 system, because I know that you've done some work on this in the past before JWST ever launched. This system, seven Earth-sized planets, many of which are in the habitable zone. This is just the holy grail of planetary searching astronomy right here. There might be so many things in that one system, and it makes me really happy to know that you're going to get to do some of that work, knowing that you've already put in so much effort into learning about that system. So that brightens my day to hear. I'm so glad.

Jacob Lustig-Yaeger: Yeah, it's a fantastic system. I think it's probably my favorite, although it's probably worth reconsidering what my favorite system is now that we've played a role in confirming the discovery of LHS 475 b. But the Trappist-1 system is just undeniably compelling, with those seven known relatively Earth-sized planets. Two of them are well interior of the habitable zone at hot, one of them is on the border of the habitable zone, one is definitely outside the habitable zone, too cold. So within one planetary system, all of the planets are spanning the breadth of this classical habitable zone that we've created from models of the solar system, and extended those really cleverly using sophisticated techniques to other stars. But it's really this opportunity to test that, whether that habitable zone is in existence there. Can we find evidence that these planets have conditions that could be favorable to the origin of life? And they're an opportunity to search for bio signatures with JWST, but we're asking a lot of this one system because it's also a really, really small star. It's Jupiter sized, and it's an active star, it's flaring and it presents some challenges both to the existence of atmospheres on these planets, and the long-term potential habitability on the planets in the habitable zone. Trappist-1h, I'm thrilled to have it as part of our program, because like I said, we're trying to understand the boundaries of which planets have atmospheres and which planets don't. And this is a particularly cold planet, one of the smallest, coldest planets that's known, and to be able to search for its atmosphere provides really a nice contrast to these warmer planets that are going first in our program. And so it is just comforting to me that we have these warm planets, and we have a cold planet in there too, to just spice things up.

Sarah Al-Ahmed: Yeah. Just a wide range of things to explore. I mean, it's a whole galaxy of planets out there to start looking at, and we're only just beginning, and I'm so thrilled that we're in this new age. But it does make me think. We've been waiting for this new telescope for ages, and we can finally begin to do this research. But what do you think that we are finally going to need to really definitively look at worlds and say that is a twin of Earth? Because we're getting close, but we might need a little bit more, or maybe more telescopes just dedicated to this question.

Jacob Lustig-Yaeger: Yeah, I think that's the key there is JWST is going to allow us to embark on this path and study Earth-sized planets. But when it comes to planets in the habitable zone, we're probably going to be able to get a sense for molecules in the atmospheres of a few habitable zone planets around these very, very small stars. But JWST is going to tell us what atmospheres are like around Earth-sized planets and larger planets, but particularly Earth-sized planets around these small stars. And we still want to know about other types of stars. There might be aspects of these small stars, like the proximity of the planets to them, their flaring, that make a search for life challenging, or the existence of life hard in these systems. And it's important that we're able to, in the future, also be able to study more sun-like stars. And so I do think NASA has now embarking on a plan to develop this Habitable World's telescope that has been discussed recently, and was prioritized by the 2020 decadal survey, this 10 year study that the community of astronomers does to figure out a consensus path for the next decade. And there's considerable effort behind this next generation telescope that will build on the successes of JWST. It will be designed to have this hexagonal pattern of segmented mirrors. It'll be designed from the ground up to study the atmospheres of Earth-like planets in the habitable zone of sun-like stars. And it will just take things to the next level, and is, I think, what we'll need to conduct a rigorous study in the search for life on these habitable worlds, and to not put all our eggs in the M dwarf basket, as it were. Because these systems are challenging, not just to study and interpret, but to imagine long-term habitability.

Sarah Al-Ahmed: And it might be a long time before that telescope is done. I think we all learned that lesson waiting for the James Webb Space Telescope to happen, but I think this telescope has proven, if anything, that it was worth the wait, and so will this new generation of telescopes. So I'm so excited. We're just right on the cusp of so many amazing discoveries.

Jacob Lustig-Yaeger: Yep. I'm excited too.

Sarah Al-Ahmed: Well, all kinds of new planet finding to do and look forward to out there, Jacob, and I really want to thank you for joining us today. And please, send our congratulations to the rest of your team for this discovery. It's got to be just such a great feeling.

Jacob Lustig-Yaeger: Well, thank you so much for having me. It's been a pleasure.

Sarah Al-Ahmed: Sometimes when I'm looking at the sky, I think about all of those distant worlds, places no living creature has seen, and how beautiful it is that here we are peering out into the universe with curiosity and optimism, wishing to know those places and searching for the familiar among the stars. Who knows what we'll discover next as JWST continues to look deeper into space than ever before. With that thought, here's The Planetary Society's Chief Scientist, Dr. Bruce Betts, to share what's up in the night sky. I am back once more with the brilliant Bruce Betts. You like the alliteration, Bruce?

Bruce Betts: I do. I'm with the stupendous Sarah.

Sarah Al-Ahmed: That counts. That works.

Bruce Betts: All right, I'll work on that.

Sarah Al-Ahmed: Well, bright and brainy Bruce, bringer of banter, what's up?

Bruce Betts: Oh my gosh, I'm caught so off guard, let's get into what's up in the night sky. How about that? We've got that comet, comet ZTF C/2022B3 that is tough to see if it's even possible to see with the naked eye, but maybe from a dark site and certainly with some binoculars or a telescope, you can see it at least as a fuzzy blob. And that is hanging out in the north, so it's actually good for the Northern Hemisphere right now. It's terrible for the Southern Hemisphere, but will cross farther south in the next couple weeks. So I suggest you find a finder chart online. We've got a nice article on our website about the comet. It is beautiful and green and the like, if you take long exposure pictures with a big telescope, and so there are great pictures of it, but...

Sarah Al-Ahmed: Yeah, already I've seen some amazing images from some of my friends. I'm so excited.

Bruce Betts: Yeah, no, it's very cool. There are some time lapses where you can see the gases coming off, the dust coming off. We've also got our friends, the planets, Venus now hanging out with us for a few months over in the west, anytime after sunset in the early evening. And above super bright Venus is really bright Jupiter, growing closer and closer together over the next month, until they're very close together on March 1st. If you follow a line from Venus to Jupiter across the sky, you'll reach Mars, looking reddish and it's good stuff. All right, we move on to this week in space history. It was 1971 when Apollo 14 landed humans on the moon, and some people view most significantly, when Alan Shepherd hit golf balls on the moon.

Sarah Al-Ahmed: When I was a kid, I thought that was something that was just from cartoons. And when I finally saw images of that, I laughed really hard.

Bruce Betts: Yeah, no, it's quite funny. We move on to random space fact. Speaking of, which we're not, well, we actually are with golf balls. One of the unusual things to have flown in space was the baseball home plate from Shea Stadium of the New York Mets. It flew on a space shuttle STS120 in 2009, just as the Mets moved from Shea Stadium to their new stadium where it's now on display. To fit in the shuttle locker where they carried such items, home plates, Mike Massimino, the astronaut, had to remove the outer black edges of it, and then they were put back together when they got back to Earth. If you are a Yankees fan, don't worry, in 2008 dirt from the pitcher's mound of Yankee Stadium was flown on the space shuttle.

Sarah Al-Ahmed: That's funny. I bet you could write an entire book about all the strange things that have gone to space.

Bruce Betts: Let us move on to the trivia contest, and I asked you, whose voice was the first to be broadcast from space? How did we do?

Sarah Al-Ahmed: We got a lot of answers for this one. Most of them were right. Some people did get confused on this one and thought we were asking them for who the first person in space to send a message was. But the answer was actually US President Dwight Eisenhower, who on December 19th, 1958 sent a Christmas message that was broadcast by the signal communication orbiting relay satellite, or SCOR.

Bruce Betts: SCOR!

Sarah Al-Ahmed: SCOR! And it was a really lovely message, just about the United States wishing everyone peace on Earth and goodwill. So that was nice.

Bruce Betts: Yeah. Well, way to go, Ike.

Sarah Al-Ahmed: And our winner this week is Judy Engelsberg from Mount Laurel, New Jersey. And Judy, you will be receiving a beautiful 2023 International Space Station calendar. So maybe somewhere on there will be pictures of weird objects people have sent to space. No, I checked through it. It doesn't have any of that stuff. It's just beautiful ISS pictures. But we did get a lot of messages from listeners on this one, particularly about the SCOR satellite. This one cracked me up. So one of our previous winners of the trivia contest, Eric O'Day from Winchester, Massachusetts, wrote, "Some of these old satellites looked cool, but SCOR? It looked like the back of someone's refrigerator fell off. No style at all."

Bruce Betts: Well, that's a funny image. I'll have to look it up now.

Sarah Al-Ahmed: No, I did. I looked it up, and he's right. And we also got this great topical limerick from Jonathan Gorback from North Virginia, USA, who wrote, "From a relay above in the night, came a voice that was measured and bright. "Warm solicitations, to all of Earth's nations." Score one for President Dwight."

Bruce Betts: Oh, nice. Very nice.

Sarah Al-Ahmed: That's nice.

Bruce Betts: Got anything more, or shall I move on?

Sarah Al-Ahmed: Yeah, I did want to share one more message, which really put a smile on my face. Joe Shoe from Copperas Cove, Texas, wrote in, "I'm an exchange student from Taiwan. My host parents and I like space. We usually listen to your podcast together when we're in the car, and we really enjoy it. Though I can't understand much, I still like it." So thank you so much. And that makes me really happy to hear, because my family used to host exchange students when I was a kid, and there's just so much that we can learn and share with each other, whether or not it's about space, or different cultures and languages, or just about each other in general. So I wanted to say thank you, Joe, for listening to the show, and I hope you have a really great time while you're visiting Texas.

Bruce Betts: All right, you ready to move on?

Sarah Al-Ahmed: Yeah, let's do this.

Bruce Betts: All right. In our friend comet ZTF C/2022B3, what does ZTF stand for?

Sarah Al-Ahmed: Ooh.

Bruce Betts: Go to

Sarah Al-Ahmed: Nice. And we'll be selecting just one winner for this one, but they'll be receiving a copy of a book called The Year in Space by the Royal Astronomical Society's Supermassive Podcast, another great space podcast out there. It highlights all of the really exciting things that happened last year in space, including what happened with the James Webb Space Telescope. So if anybody wants to enter, you have until Wednesday, February 8th at 8:00 AM Pacific time to get us your answer, and you'll want to go to

Bruce Betts: All right everybody, go out there, look up at the night sky, and think about the optimum design for a can to maximize the volume while minimizing the surface area. Thank you, and goodnight.

Sarah Al-Ahmed: Thanks for joining us this week on Planetary Radio, as we continue to marvel at our place in space. Come back next week for a dose of new Martian discoveries, with Mars expert Tanya Harrison. Planetary Radio is produced by The Planetary Society in Pasadena, California and is made possible by our stellar members. You can join us as we continue to explore worlds and search for life at Mark Hilverda and Ray Paoletta are our associate producers. Andrew Lucas is our audio editor. Josh Doyle composed our theme, which was arranged and performed by Pieter Schlosser. And until next week, ad astra.