NASA's Curious Universe - What Webb Is Teaching Us About Our Solar System

Episode Date: September 23, 2025

NASA’s James Webb Space Telescope is hard at work answering our biggest questions about the birth of our universe and faraway galaxies. But some astronomers are pointing its powerful eyes much closer to home. In this episode, Caltech astronomer Katherine de Kleer explains how Webb is rewriting our understanding of objects within our solar system–from space rocks in the asteroid belt to the icy and volcanic moons of Jupiter and Saturn.

You're listening to NASA's Curious Universe. I'm your host, Jacob Pinter. NASA's James Webb Space Telescope is allowing us to look further into the depths of space and further back in time than ever before. The largest, most powerful telescope ever sent away from our planet. It's helping us answer big questions about black holes, galaxies, even the birth of our universe. We want to look back and see some of the very first stars and galaxies that were born in the early. universe, what we call cosmic dawn.

Now, this is all stuff that you definitely cannot see with your naked eye. But some scientists are pointing web in a different direction, a little closer to home, and objects within our solar system. Think about Jupiter, which you definitely can see from here on Earth with a regular store-bought telescope, and even with your naked eye sometimes. So to hear what scientists are learning from web, I called up Catherine DeClear. He's an astronomer at Caltech who focuses on our solar system. When she was a student, Catherine wasn't sold on studying planets right away.

Like any good budding astronomer, she was born into galaxies and stars at first, until she had the chance to use the Keck Observatory in Hawaii to look at our solar system's gas giants. And my PhD advisor said, why don't we just quickly look over at I.O. Jupiter's Moon and just kind of see what it's up to. And so we pointed the telescope at Io, and we took this image, and the image that came up on the screen was a picture of this moon with all these little bright spots on it.

And all those bright spots are heat coming off of individual volcanoes on Io. And from night to night, I learned you could see how much heat is coming off of which volcanoes and how that's changing over time, and you can track its eruptions. And I did. not realize until that moment that you could ask the same sorts of questions that you would ask

about Earth, about other objects in the solar system, that you could learn about their atmospheric dynamics, you could study their volcanism, and when I realized that that was possible with telescopes, I was sold. When Webb launched, Catherine was super excited. It took scientists decades to design, build, and launch the telescope. This kind of thing doesn't happen very often. Whenever a new, NASA of flagship telescope launches, it's a big deal for astronomers. It is your opportunity to make some big advance, not just some little incremental improvement on our understanding, but take a real step forward in terms of what we know about the

solar system or the universe. And so I think astronomers are always kind of thinking about what is going to be the big advance in my field that's going to come out of this telescope. Now, there are a lot of telescopes right here on Earth in observatories around the world. And you might be wondering, what makes Webb so special? Why do you need a fancy space telescope to look at stuff that is pretty close to us, relatively speaking? Catherine says it's a fair question. For much of astrophysics, part of what gives the James Webb Space Telescope its edge is that it can look at really, really, really faint things. That's because Webb can see beyond visible light into the infrared end of the spectrum.

That lets its spot dimmer, more distant objects than most telescopes can. But solar system objects tend to be extremely bright. You know, you can look up in the sky and see plenty of them at night if you know where to look. And on top of that, the James Webb Space Telescope, as you may have guessed from the name, is in space. So one of the biggest advantages we get for bright solar system objects from James Webb is that it allows us to observe without the Earth's atmosphere in the way. Looking up through Earth's atmosphere muddies the view for ground-based telescopes. You just can't see all the details Catherine needs to without going up into space. For example, Catherine is looking for signs of water on asteroids and moons.

That particular region of the spectrum happens to be blocked by unsurprisingly water in Earth's atmosphere as well as some carbon dioxide. But with James Webb, we don't have that in the way. And so we can get access to this information that we couldn't. see before. But there's a catch for solar system astronomers like Catherine. Space telescopes are designed first and foremost to look deep into space at those faint objects she mentioned. It is a fairly universal phenomenon with new telescopes that they're basically, they're never

designed primarily with solar system objects in mind. And actually, James Webb did better than most observatories in terms of incorporating solar system scientists from the beginning to make sure these very unusual things that we need were taken into account. So let's talk about those unusual things. For one, close-up objects like planets appear to move much faster relative to Webb's position in space than faraway galaxies. You can get a taste of this in a car driving down the highway.

When you're going fast and you look out toward the horizon, it's easy to keep track of one tree that's way out there. But if you shift your vision and look at the side of the road, it seems like everything is just whipping by. So, to get a good look at everything whipping by, Webb has to really rev up its tracking speed. And that's not the only issue. Some nearby objects are just too bright for Webb to look at. In some modes, the telescope's detector will get completely blinded by the light. To work out the bugs, Catherine got the opportunity to test the telescope before almost anybody else,

to make sure it was ready for prime time for solar system astronomers. So she aimed it at Jupiter. And it was sort of a full circle moment. The part of it that I was kind of in charge of was, in fact, the observations of Io, the volcanic moon I mentioned. And what did you see? And what did it feel like to use this new toy for the first time? Yeah, I was thrilled. So when they start doing the scheduling, you know, first they have these different windows when it might be scheduled.

and they'll tell you it could be on August 12th or maybe it'll be on August 14th or maybe it'll be on August 16th and you're kind of waiting there. And then it gets actually scheduled and, you know, I had it on my calendar and I, you know, I think I was at a party and I was telling people James Webb is observing I.O. for me right this second. Were they impressed? Oh, yeah, absolutely. And then what did you see? So for solar system objects, because we've also sent spacecraft to some of them, it won't be the first time we've observed that object from above Earth's atmosphere, at least for the major planets and moons. But James Webb has access to certain wavelengths where spacecraft instruments have never covered. So specifically for the case of I-O and the Jupiter system, this kind of short end of the mid-infrared range was not covered by any of the missions that had gone by or two.

the Jupiter system. And so we got this kind of little missing piece of the spectrum of IOS surface and saw these big absorption features from the sulfur dioxide frost that coats IOS surface. And we knew that the sulfur dioxide was there, but we hadn't seen these particular big features before. And they are potentially giving us information on the texture of the surface frost as well as maybe even will tell us whether there is a thin frost layer overlying a lava flow, for example, compared to just a thick frost layer that goes down for meters. Since then, Catherine has used Webb to explore all over the solar system. So I had tons of questions for her, but I started off by asking her to give me kind of a tour

of our solar system through Webb's eyes, starting with asteroids. So to start with, the asteroids are, we think of them as these leftover objects from the period of planet formation. And I think on many fronts, James Webb is answering questions about the time of formation, right? The earliest universe, also the early phases of forming solar systems around other stars. It can also tell us about the early stages of our own solar system, even though that happened, you know, four and a half billion years ago. because we can study the remnants from that period. So we find those remnants all across the solar system. The icy outer solar system ones are called the Kuiper Belt objects,

but the inner rocky ones are the asteroids. And the majority of the asteroids reside in the main asteroid belt, which is between Mars and Jupiter. And it's this collection of rocky objects that are basically material that condensed out of the disk that, the planets formed out of and have survived somewhat intact. I won't say fully intact because most of them are actually fragments. But they haven't evolved, you know, to form atmospheres and oceans and all these things

that would have totally erased the kind of initial conditions, right? So they're kind of chemically intact, let's say. The solar system objects formed in one particular distance from the sun, one particular place, or orbit. And then the solar system went through this crazy dynamical time where the planets were all moving from the orbits they started at to the orbits they're at today. And during that process, all these little objects that condensed out of our protoplanetary disk, we call them planetesimals, they got thrown around all over the place. And now many of the ones from the icy outer reaches of the solar system got thrown inwards, for example. And now we find them in the Astroids

and in some other places. And they can tell us about what kind of chemistry was going on as the planets were forming. They can tell us about the building blocks of Earth and other planets. And they can also tell us about this process of the planets moving and throwing all these little things around. We can kind of get insight into how that process took place based on where all these little objects are today compared to where they formed. You were talking earlier about how the James Webb Space Telescope is kind of uniquely positioned to tell us what objects in the solar system are made of. So when you point James Webb at an asteroid, are there like details in the makeup of these asteroids that you're seeing, that are new details or that you're seeing in a different way than you have before? Yeah.

So in the mid-infrared in particular, we get information on the minerals that make up the surfaces of these asteroids. and that's information that we haven't had at this level of detail. So, for example, most of these asteroids are actually made up of minerals that are broadly termed silicates. So this is material like a lava flow or like Earth's mantle. It is dominated by a mineral called olivine, which as a gemstone is called Peridote and also makes up Earth's mantle. So that's kind of the dominant mineral that we see.

but it comes in all these different forms. And James Webb actually lets us tell which form we're seeing, which can tell you how close to the sun this mineral originated from. Wow. It's interesting to think about this mineral that's so common on Earth, you know, in the mantle below the surface, and then seeing it on these little rocks floating out in the rest of the solar system too, right? Yeah, it's amazing how kind of universal certain types of chemistry are.

And kind of by a similar token, scientists are using James Webb to study protoplanetary disks that eventually become basically solar systems like ours, right? And in some cases, are finding similar materials there that you find leftover from the formation of the solar system. That's exactly right. And I think that because of what James Webb and other telescopes are telling us about, protoplanetary disks as well as our solar system that this kind of scientific area of understanding how planets form is one of the most exciting and fast-moving areas right now. And so you mentioned James Webb is looking at these protoplanetary disks. They are also looking at the heat coming off of those disks, just like we're looking at

the heat coming off of asteroids. And they are looking for the exact same signatures that we're looking at. looking for on asteroids. So you have these disks that are basically, it's the same material as the asteroids just four plus billion years ago. And you're looking at the mineral olivine and most of those as well. And you're looking at the exact same signatures. And so I think it's pretty cool that you can basically do the same science on a 100 kilometer

object in the asteroid belt as you're doing on an entire forming solar system. As we tour the solar system, let's take a look at Jupiter's four closest moons, which are called the Galilean moons. I think that a lot of people give them short shrift because they are moons and not planets, but there's just a lot going on. You know, there's volcanoes and thick sheets of ice and in some cases liquid water deep underneath the surface. So what do you want to know about these moons of Jupiter and what are you finding? finding out. You're absolutely right that the moons are just these fascinating worlds in their own right. And I think that certainly the solar system science community has fully come around to that idea.

You know, if you look back at the spacecraft missions, the kind of previous generations of spacecraft missions, they were largely targeting the planets. But now the next generation of missions is very specifically targeting the moons. We have Europa Clipper going to Europa. And lift off. Lift off. A falcon heavy with Europa Clipper, unveiling the mysteries of an enormous ocean

lurking beneath the icy crust of Jupiter's moon, Europa. Europe has the juice mission that is going to the Galayan moons, and this kind of reflects this recognition that the moons are just these fascinating worlds in their own right and in many ways are more Earth-like than the planets, certainly more so than the giant planets. We want to understand, you know, how they formed, what they're made of.

A central question that people are interested in is whether they're habitable. So the outer three of the Galilean moons, Europa, Ganymede and Callisto, are all thought to have oceans underneath thick ice shells, and those oceans are perhaps thought to have the, conditions that is needed for life. If we're sending probes there specifically, I guess what is Webb's role in working with those probes?

Like, what can Webb do that those spacecraft won't be able to do, or how can Webb kind of fill in the gaps in what they're seeing? Yeah, that's a great question. And it is kind of a central question in solar system astronomy. One is that simply knowing that something is there well in advance of the spacecraft's arrival helps the spacecraft team better design their experiments when they get there. So it's very useful to know, for example, that these objects have atmospheres and what those atmospheres are made of because then the mission, you know, has the whole time that the spacecraft

is flying out there to think about how they're going to capitalize on that information to learn more. The other angle of this is that these objects are constantly changing. This is especially true for something like Io that has active volcanoes, but we also see this in the gas that's surrounding moons like Europa, Ganymede, and Callisto. So that the gas is kind of patchy and it looks like it's kind of in a different place every time you see it. And spacecraft can only capture images that it kind of, of at very set times and only for the duration of the mission. And often, you know, the spacecraft is only there during one season, for example, for the object. And so you need observations from

Webb and other telescopes to really understand the context of what you're seeing and whether it reflects the moon's behavior all the time or whether it's just a function of this particular season, for example. This is going to sound a little corny maybe, but, you know, know, I couldn't help thinking that the Galilean moons are named that because they were described by Galileo hundreds of years ago. And so they're like the original thing that we looked at through a telescope, right? And now when you, you know, when you study them with something like the James Webb Space Telescope, that is, you know, kind of in the same lineage, but it's so much more powerful, I don't know, do you ever kind of think back on like that legacy of the many, many

telescopes that have looked at these moons before and how you're sort of building on everything that we've learned along the way? Yeah, absolutely. I would say that that is certainly something that I think about that we've been looking at these objects for 400 years now. And it's just amazing to compare, you know, what Galileo learned about these moons compared to what we can see with telescopes today. So in addition to the moons of Jupiter, James Webb has made some pretty exciting observations on the moons of Saturn, and in particular Enceladus and Titan.

And one of the things that's really cool about Enceladus is that it has these jets of water and other things coming out of its South Pole. Those were discovered by the Cassini spacecraft. And the James Webb Space Telescope looked at Enceladus and its plumes. and I highly recommend that you look up the image because it's measuring specifically water vapor in the plumes and you can see that the water vapor extends to just extends away from Enceladus to many, many times the size of Enceladus itself. Imagine like if some supercharged version of Old Faithful on Earth where you could measure the water out to, you know, the distance of many Earth. out into space, right? It's like at that scale. And, you know, we knew from Cassini that that water was coming out, but it hadn't been mapped out to those distances before the James Webb observations. As we're, you know, winding down our tour here of the solar system, are there any other stops we should make points of interest for you or things that you've just got your eye on?

So one of the things that Webb is particularly good at for the solar system is mapping where we see water and carbon dioxide. So those are central, what we call volatile compounds that are essential for habitability, but also just for the evolution of a planet. And those are the things that we really can't see from Earth because Earth has water and carbon dioxide in its atmosphere. and those are absorbing light, you know, at the wavelengths where we'd be looking for it on other planets. So one of the big things that Webb has revealed is just the distribution of water and carbon dioxide across the solar system. And it has, in fact, discovered a carbon dioxide atmosphere at Ganymede and has been able to map the carbon dioxide atmosphere at Calisto, which has been known from spacecraft but hasn't been mapped before.

So we can actually see how those atmospheres are distributed across the moons. I did a similar interview with an exoplanet scientist not long ago. And like anytime he finds carbon dioxide, you know, out there on an exoplanet somewhere, he's so excited. Like, I guess like as you learn more about the solar system, Do you ever get with the exoplanet researchers and kind of swap notes and say, like, hey, this is what I'm finding. Maybe this can help you. Is there anything out there that you see that maybe can help me studying our solar system?

Yeah, I think that people studying exoplanets look quite a bit at solar system planets to kind of predict the type of signatures that they should see at exoplanets. You know, if they're looking for a exo-Urinus or an exo-Neptune, what would that look like? And they look to the solar system for that. I think conversely, you know, we only have our solar system. We only have this specific set of planets and moons. It's just one example of the many ways that things can be that a solar system could have evolved into. And we don't really have the context, you know, for understanding. is our solar system unique or weird or is it actually just normal?

And the information that we get on exoplanets just allows us to really put into context our own host planet and informs how we think about the history of our solar system as well. By now, I think a lot of people have heard at the James Webb Space Telescope. A lot of us have seen the pretty pictures that come out of it. But at a high level, what do you want people to understand about the science that's coming out of this telescope? Trying to understand what's happening in our universe, in our galaxy, or just in our solar system, requires all these different pieces of information that we get with different telescopes. And in particular, because they see light at all these different wavelengths, radio telescopes, telescopes that operate it at visible wavelengths, and Jabe's Web and the infrared. and that our picture of much of the universe, including our solar system, has been incomplete because we haven't had access to these infrared wavelengths.

And it's kind of like adding one more perspective that just gives us a more complete and true picture of what the universe around us is doing. If we could like magically send you to one place in the solar system safely and non-painfully and all that, and you know, you'd be able to see it for yourself and do some kind of science yourself there, where would you want to go? Ah, that is an easy question. I would go to I.O. You can't do the same sort of study on I.O. that I'm doing on the asteroids because I.O. is so. so bright. It's putting out all of this heat from its volcanoes and it's saturating the James Webb detectors at exactly the wavelengths that you would need to get the composition of its lava flows. So I would love to go there and take some samples of a whole lot of different lava flows because we know from Earth that lava flows have a lot of variability and composition and that tells you about the local geology, etc. And, you know, I, you know, I,

I'd bring a geochemistry lab out there with me and put it on IOS surface and hope it doesn't get covered in a lava flow. And then I would study what all these materials are made of. You just bring a bag full of lava back to a lab here, I guess. Yeah, I don't know what's more feasible bringing a lab there or bringing surface samples back here. But that's where I would go and visit. It's just be such a fun and exciting place, too. Well, Catherine, thank you so much. This was a lot of fun.

Yeah, and thank you. Catherine DeClear is an assistant professor of planetary science and astronomy at Caltech. If you liked this episode, you will love NASA's documentary Cosmic Dawn, all about the James Webb Space Telescope. You'll go behind the scenes with people who made the telescope possible, including John Mather. He's the Nobel Prize-winning NASA scientist who first proposed. the Webb Telescope. I knew when I got into the mission that it was going to be exciting. I said, this is the coolest thing I've ever heard of.

This is what I want to work on. And I do not care how hard it is or how long it's going to take. I just want to work on it and make it happen. You can learn more about John Mather and experience the untold stories of the engineers, scientists, and even truck drivers who brought the telescope to life in the film Cosmic Dawn. Just go to NASA.gov slash Cosmic Dawn. And one more thing. NASA is tracking a comet called 3-Ey Atlas, which is an extremely rare opportunity to study an object that came from outside our solar system.

Scientists are using web to learn more about it. You can find more information and all the latest news from the James Webb Space Telescope at nassah.gov slash webb. This is NASA's Curious Universe. This episode was written and produced by Christian Elliott. Our executive producer is Katie Connance. My co-host is Patty Boyd. Christopher Kim designed our show art. Our theme song was composed by Matt Russo and Andrew Santagwita of System Sounds.

Special thanks to the Academic Media Technologies team at Caltech. As always, if you enjoyed this episode of NASA's Curious Universe, let us know. Leave us a review, send a link to a friend. And remember, you can follow NASA's Curious Universe in your favorite podcast app to get a notification each time we post a new episode. This is an official NASA podcast