Planetary Radio • Jan 25, 2023

Juno Journeys to Jupiter’s Moons

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Scott Bolton

Juno Principal Investigator and Associate Vice President of the Southwest Research Institute’s Science and Engineering Division

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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

Dive into the latest discoveries about Jupiter’s moons Ganymede, Europa, and Io with Scott Bolton, the principal investigator for NASA’s Juno mission. We share analysis of the data collected by the spacecraft and look forward to upcoming exploratory missions to Jupiter’s moons from ESA and NASA. Stick around for this week’s What’s Up and our space trivia contest.

Ganymede from Juno 2021
Ganymede from Juno 2021 An image of Ganymede obtained by the JunoCam imager during Juno’s June 7, 2021, flyby of Jupiter's icy moon.Image: NASA/JPL-Caltech/SwRI/MSSS

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Juno Europa flyby composite
Juno Europa flyby composite This view of Europa is a composite image of 3 datasets collected by the Juno spacecraft during its perijove 45 flyby.Image: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill
Infrared view of Io by Juno
Infrared view of Io by Juno In its extended mission phase NASA's Juno spacecraft captured this infrared view of Jupiter's volcanic moon Io. Juno was about 80,000 kilometers (50,000 miles) away. This infrared image was derived from data collected by the Jovian Infrared Auroral Mapper (JIRAM) instrument aboard Juno. In this image, the brighter the color the higher the temperature recorded by JIRAM.Image: NASA / JPL-Caltech / SwRI / ASI / INAF / JIRAM

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Trivia Contest

This Week’s Question:

What is the only mission to fly by Jupiter then go inwards (rather than outwards) in the Solar System?

This Week’s Prize:

A Planetary Society Kick Asteroid r-r-r-rubber asteroid!

To submit your answer:

Complete the contest entry form at or write to us at [email protected] no later than Wednesday, February 1 at 8am Pacific Time. Be sure to include your name and mailing address.

Last week's question:

Whose voice was the first to be broadcast from space?


The winner will be revealed next week.

Question from the January 11, 2023 space trivia contest:

Where in the Solar System is Doom Mons, named after Mount Doom in the Lord of the Rings?


Doom Mons, named after Mount Doom in the Lord of the Rings, is located on Titan, a moon of Saturn.


Sarah Al-Ahmed: Unlocking the secrets of Jupiter's mysterious moons with Juno. 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. NASA's Juno spacecraft has taught us a lot about Jupiter, but what about the moons that orbit it? We delve deeper into the fascinating new discoveries about Ganymede, Europa and Io with Scott Bolton, the Principal Investigator of NASA's Juno mission to Jupiter. Then we'll kick it over to Dr. Bruce Betts, the Chief Scientist of The Planetary Society for what's up and your weekly guide to the night sky. Now on to some of this week's space mission briefings. The Indian Space Research Organization announced last week that the launch of their Shukrayaan 1 Venus Orbiter might be delayed. The mission aims to study the Venetian atmosphere, geology, and potentially look for signs of life. Shukrayaan was originally planned to launch in 2024, but it hasn't yet received official approval from the Indian government. This could push the launch back until 2031. In the United States, SpaceX has reported that it's getting closer to its first orbital launch of the Starship, a reusable, super heavy lift launch vehicle. They're preparing for a final series of tests before an orbital launch attempt in the coming weeks. The company currently does not have a launch license from the US' Federal Aviation Administration for the vehicle. And it should be noted that SpaceX has a history of being a little inaccurate with their predictions regarding the readiness of Starship for launch. But even so, it's very exciting. And for those of you who love staring up at the moon, the National Science Foundation's Green Bank Telescope in West Virginia, USA has captured the most detailed images of the moon ever taken from earth, using a new prototype radar system. The system captured high resolution images showing the beautiful details of Tycho crater, a large impact in the moon's Southern Hemisphere. This system will be used to detect distant asteroids that could potentially pose a threat to Earth, but in the meantime, its pretty pictures are definitely worth a peak. We share more information about these stories and the beautiful new images of the moon in our January 20th edition of the Downlink, The Planetary Society's Weekly newsletter. You can get it sent to your inbox for free every Friday or read it online at All right, now get ready for some Jovian moon science because we are about to get into it. In 2011, NASA launched its Juno spacecraft to Jupiter as part of NASA's New Frontiers Program. The mission was equipped with a slew of scientific instruments designed to study the Solar System's largest planet. It arrived at Jupiter in 2016 and since then it's been busy studying Jupiter's atmosphere, magnetic field, and gravity among other things. Juno's primary mission was a wild success, but it wrapped up in July, of 2021. The spacecraft is now on an extended mission, not just studying the planet, but taking a closer look at its moons. The new data and images from the Jovian system have revealed many amazing new things about three of Jupiter's moons, Ganymede, Europa and Io. Juno flew by Ganymede in 2021. It's not only the largest moon of Jupiter, but the largest moon in our Solar System. It's also the only moon known to have a global magnetic field. And like so many moons of interest, it may have a subsurface ocean. From there, Juno's orbits brought her progressively closer to Europa, another moon of Jupiter with a potential liquid water ocean under its icy crust. Juno's breathtaking views of Europa in 2022 are just one more reminder of why that world is of such interest in the search for life. The last moon we'll explore today is Io the most volcanically active body that has ever been discovered. Juno is already taken outstanding data on Io, but it's just the start as the spacecraft will have a lot of future opportunities to explore that eruptive moon closer and closer. Together, these moons represent an opportunity not only to study other worlds and search for life, but to learn more about the ways that gas giants like Jupiter and their moons interact and impact one another. It's also an excellent example of the creative ways that teams can repurpose spacecraft instruments to learn even more than we expected. With upcoming missions like the European Space Agency's Jupiter Icy Moons Explorer or JUICE and NASA's Europa Clipper mission, we're about to learn so much more about these worlds than we ever did before. Our guests today is Scott Bolton, a planetary scientist and the Principal Investigator for NASA's Juno mission to Jupiter. Bolton has worked on missions to explore the Solar System for decades, including Magellan, Voyager, Galileo, Cassini, and now Juno. You may notice a clicking sound in Scott's audio. We're sorry we couldn't remove it, but we don't think it'll get in the way of all the great things you'll hear from him. Thanks for joining me, Scott, and welcome back to Planetary Radio.

Scott Bolton: Thanks for having me. I'm very excited to share the exciting news of Juno with you.

Sarah Al-Ahmed: I wanted to congratulate you on the success of Juno's extended mission. These last two years have been absolutely wild.

Scott Bolton: Yeah, it's been amazing for me and the whole team. I mean, I think when we were first creating the mission and kind of envisioning the whole mission once we got to Jupiter, I don't think we thought that far ahead and said, "Okay, in the extended mission we will adapt our orbit and we'll get close flybys of the satellites and we'll go right into the rings." I mean, it's so amazing to think back to the days when we were first creating this and then where we are today. I'd like to think I have a great imagination, but I don't think I imagined enough.

Sarah Al-Ahmed: Well, it's really impressive how you've kind of repurposed this spacecraft that was meant to study Jupiter exclusively and then just the creative way that you've used these different instruments to now look at its moons. And I wanted to say I watched your press conference that you gave in December at the American Geophysical Union.

Scott Bolton: Yeah, it was an exciting time. And what's really beautiful about the whole thing is we're still studying Jupiter. So even though we've added these other targets, really important targets like the moons and the rings, we're still studying the aurora, we're still studying the interior in the atmosphere of Jupiter. I mean, we're getting closer and closer to the Northern Hemisphere and the poles and there's so many interesting things that we've discovered about the Northern Hemisphere and the polar regions with these giant polar cyclones. Now we're able to do it all. And so I feel like we've really become a system-wide explorer.

Sarah Al-Ahmed: Absolutely, and those pictures that JunoCam got of the storms around the North Pole of Jupiter are just absolutely wild. And I was thinking about this the other day that I wanted to thank you personally for the role that you played in getting JunoCam on that spacecraft because I know the initial plans for this mission didn't necessarily include that camera. And I think there's so much value for the public and for science to have a camera like that on board. So thank you.

Scott Bolton: Well, it wasn't just me but my whole team. We couldn't imagine going to Jupiter without a camera and the call in the Announcement of Opportunity and sort of the study by the Decadal Survey committees did not include a camera, but we stuck one on anyway just because we were like, "Well, we want to see what the polls look like and I'm sure everybody else does too. Let's find a way to do that." And so we were persistent and I'm really glad. And in fact we got an amazing camera from Malin Space Science Systems. It's not the normal kind of camera on a space mission, but it's actually got us a framing that's more like your smartphone. And I believe that we accidentally stumbled into something that was really great because it gives you the context and allows you to appreciate the images so much better than some of the more advanced cameras that go on Cassini and Galileo and other missions. So I think we should include one of these kind of cameras on every mission.

Sarah Al-Ahmed: I was going to ask too, could you explain a little bit about how the spacecraft's orbit has allowed us to take these kind of progressive flybys of Ganymede and then Europa and then Io because there's like an order to it and it's very particular to how the spacecraft is moving around Jupiter.

Scott Bolton: That's right. And it's really Jupiter doing the work. It has such an amazing gravity field. So first Jupiter's oblate, so it's not perfectly spherical. So the higher order terms in its gravity field sort of twist our orbit around. And so we're in an elliptical orbit and the closest approach to Jupiter started off near the equator and Jupiter's higher order terms kind of twist our orbit. So that perijove or the place where we go closest approach to Jupiter, it starts moving north about a degree on every orbit. And I spent a lot of time trying to stop that, but we didn't have enough propellant and a big enough rocket. We're just mere mortals and Jupiter is this giant God, and so it actually controls us and twists us around. And what became obvious was partway through the mission was that was a blessing in disguise. And in fact Jupiter knew better than we did. It was doing exactly what we needed so that we could advance our exploration and sort of look from different perspectives. And so it's helped us throughout the primary mission and in the extended mission. But that twisting of the orbit, literally we move the perijove further and further north. So that allows us to get closer to those polar cyclones, which is very helpful. But it also, the place that we cross Jupiter's equator coming in starts moving closer and closer to Jupiter just naturally just because I'm taking this ellipse and twisting it. So that allows us... It's something that we feared because we're moving in toward the satellites. We spent the whole time trying to stay away from them and we don't want to go through the higher radiation, but now it's inevitable. And so the first one that we went by really close was Ganymede and then Europa. And as the orbit gets twisted, each time we go around, we get closer and closer. So we went from Ganymede to Europa and next stop is Io, and then we even get even closer. It's just amazing.

Sarah Al-Ahmed: It really is. And just another example of the clever way that you can take a situation and use it to do more science.

Scott Bolton: Yeah, you have to look for those opportunities and think outside the box. The bad part is we're getting higher and higher radiation, but the bulk of our radiation actually doesn't happen near the satellites. It happens very close to Jupiter. We've always gone about 5,000 kilometers above the cloud tops at closest approach, and that pretty much stays the same. What's different is where we're crossing Jupiter's equatorial plane that's moving in. Of course when you get near Io, you've got the whole Io Torus and all those volcanoes going off. And so it's a pretty hazardous place. I mean, we're excited to go there, but most of the missions that go to Jupiter avoid that place.

Sarah Al-Ahmed: Yeah, with good reason. But if it pays off and we get just really amazing images and data from Io up close, I think it'll be worth it. And we've got the ultimate fade of the spacecraft anyway in a few years. It's going to run out of fuel, so might as well dive right into danger.

Scott Bolton: Yeah, that's how we all feel about it. And the other thing is we're not the average spacecraft, so we're built an armored tank because we had to go into Jupiter's radiation belts anyway, and our instruments are designed to withstand that kind of punishment, I will say, and hazardous environment. So we'll get very unique and we already have been getting very unique measurements, and so we're lucky we really built it like an armored tank and the shields are holding.

Sarah Al-Ahmed: Now I'm just envisioning this space tank flying around Jupiter, but let's just dive into this. Let's start with Ganymede, you know the biggest moon in the Solar System, and when Juno has taken images of this place, it's really revealed a whole new level of detail that we never saw with the mission, like say Galileo. And I'm wondering kind of what was the reaction from your team when you first got those images of Ganymede back? That must have been amazing.

Scott Bolton: We were totally flabbergasted. It was a very emotional and exciting time. And of course we only got a few. One of the things about our orbit is we're moving fast and we're spinning right twice per minute, so you can only take so many images before you fly right past the place. But we came in and we got some fantastic images with JunoCam and then we have a special camera that's really a navigation tool, and that's low light, looks at stars to navigate, but we use it for science. And so we actually took a picture of the night side lit up by Jupiter shine and we got lucky and saw some really interesting places. And then we have all these, of course, we have the infrared and then the ultraviolet. And then we have a special tool that's the microwave that was designed and actually invented for Juno, but it was designed so that we could see through the cloud tops and the atmosphere of Jupiter and see down inside into the atmosphere structure below where the sunlight reaches. But when you take an instrument like that and you point it at an icy body, you see into the ice. So we're getting the first maps of what the ice looks like below the top level of the surface. So the whole thing's a windfall. I mean, we were just really excited and we knew that we had these new advanced instruments and when we pointed them at the satellite, we'd get a lot of great stuff. But I don't think we understood how important and how great it really would be because nobody had ever looked with this microwave instrument at an icy body. We kind of had an idea what we'd see, but we didn't even know what we were going to see at Jupiter with it when we first did it, we invented it, it's new. But I think it's really exciting when you do that. And of course we have a great set of instruments for what we call fields and particles to study the magnetosphere. And Ganymede's got its own magnetic field, so we were coming in and getting great measurements of that as well. So it was a real windfall. We were really excited.

Sarah Al-Ahmed: Oh yeah, all of these interesting things that you've learned just reiterate how important it is to study these moons and I think what's really cool about the microwave instrument, as you were saying, it allows us to appear beneath the ice, but a lot of these moons have potential subsurface oceans and that can tell us so much about not just how the terrain interacts with the inside, but about their potential habitability underneath. What are we learning about the internal workings of Ganymede and how the surface interacts with the subsurface?

Scott Bolton: Well, Ganymede has this dark and bright terrains in that it has these places where there's these fresh craters that look like they just blew fresh snow all over the place and fresh ice and clean. The dark ones are warmer and the bright ones are a little bit colder, and scientists have thought for a while that the dark terrain was maybe older and the bright terrain was younger. And when we look at it, we're looking below the top level surface and we can see how deep those differences go, they're not just skin deep. And we can also see evidence of fracturing or reflections coming from below. It's really amazing to compare the different terrain types and see how deep the fracturing goes, and we can even make an estimate of how thick the conductive ice shell is. And of course, Ganymede's ocean is thought to be pretty deep. I don't even think that even with our longest wavelength that we get all the way down to the liquid, but we are getting where the conductive ice shell probably goes through and make an estimate of that based on the thermal gradient. And so it's really exciting to be able to do this new kind of science and set the stage, even contribute a unique data set that can then be combined with NASA's Clipper Mission and the ESA JUICE Mission, which are going to study these moons much more closely, but they don't have our instrumentation, so you actually get a whole nother level. When they get there, I'm sure that we'll go back and we'll combine the data sets and see what else we can learn.

Sarah Al-Ahmed: I know too, that part of what Juno has been seeing on the surface, these linear features that kind of look like they might be shaped by tectonics. And I know everyone on earth loves those videos of how the tectonic plates on earth move around and how earth changes over time. Do we know enough about these kind of tectonic features that might tell us about how Ganymede is changing over time?

Scott Bolton: I don't think so. I mean, what we're seeing is, you see these linear features and the place is kind of cracked up, right?

Sarah Al-Ahmed: Yeah.

Scott Bolton: Literally it has these fractures in it. We're getting some evidence of how deep those go and how severe they might be, even how they might be oriented and what's causing them. But what's really happening is there's all these stresses from gravitational pull and pushes from Jupiter. And Europa and Io are suffering the same kind of thing. It's basically tidal forces that are squeezing these places. And so you're seeing the effects of this and of course how you convey that into plate tectonics where you have, like we think happens on the earth where you have these different layers moving over each other. I don't think we're far enough along, but I think that maybe after JUICE gets there and you really start to map out these things, we just had one flyby. I mean, I would've loved to have been able to say, "Okay, let's stop here and hang out for a couple years and then move on to Europa." But Jupiter allows us to see it, but it also dictates how often you can see it close up. And so we don't even fire our rocket engines to really dictate this, Jupiter's doing all the work for us.

Sarah Al-Ahmed: I know you mentioned this earlier that Ganymede is one of those rare bodies in the Solar System that has its own kind of global magnetic field, but it's so close to Jupiter that these magnetic fields are constantly interacting and Juno has taught us a whole lot about how these things interact over time. Can you tell us a little bit more about that?

Scott Bolton: Yeah, in fact, we were really fortunate. When we went by, we were going by at a fairly unique trajectory compared to what Galileo had done, and that's partly because we're just in this orbit that's heavily inclined. We're in a polar orbit around Jupiter coming in from a different side, sort of a different perspective, and we fly through and we have a very elaborate and very capable fields and particles suite of instruments. So what we saw was a snapping of the magnetic field. So what happens at the earth, and we see this with the solar wind is our magnetic field lines kind of connect and reconnect back up. As we rotate around, we are taking our magnetic field and we're moving it within the solar wind, and sometimes the field lines snap and then they'll reorient and they'll get connected, and that has a big effect on our electrical storms and aurora and things like that. And Ganymede has its own magnetic field sitting inside Jupiter's field, right? It's not necessarily the solar wind, but it's in a background field that's very strong scientists and theorize that maybe this reconnection might be happening there and it should be. We actually saw the reconnection happen. And so we saw an evidence of this snapping of the field. It's almost like creating magnetic fireworks because when this kind of thing happens, when the magnetic field lines break and then reconnect, you get a lot of particle energy that's accelerated very quickly. And while we haven't been able to completely tie that into the aurora as far as location, we've learned a lot about it and it's probably, is linked to the aurora that's on Ganymede itself. So Ganymede has its own aurora, just like the earth has its own magnetic field, and now we know it has its own connection and reconnection. And we're still learning about that on earth with missions that are studying these phenomena. And so of course the fundamental tool of science is comparative study. So now we have this other body to look at reconnection with a little moon inside of Jupiter's magnetic field, and it's just exciting to watch these magical magnetic fireworks go off.

Sarah Al-Ahmed: Right. I'm so glad you brought that up because I was going to ask, Ganymede is one of those tidally locked moons and they're going to be these places where hypothetically if you could stand on the surface, you might be more likely to see the aurora. And I'm just thinking forward to the far future where that is a prime vacation spot.

Scott Bolton: Yeah, I think so. I mean, I was on Galileo and when we first looked at Ganymede, I thought, "Let's go skiing. I mean that's a icy body. It's got probably a lot of cool ski resorts." And I think you're right, I could mix in the aurora viewing. It would be pretty cold. It's a cold place though.

Sarah Al-Ahmed: For sure.

Scott Bolton: You're going to have to dress really warm.

Sarah Al-Ahmed: Well, we'll just wait for the fashion designer that can create the Ganymede coat so we can actually survive out there.

Scott Bolton: Right.

Sarah Al-Ahmed: I was also going to ask kind of about what happens when those magnetic field lines reconnect. I know that we've seen evidence of kind of ultraviolet light bursts and I'm wondering how energetic those bursts are. Would you be able to say, see them from the surface if you had UV goggles or is it more something you'd only see in the results on the aurora?

Scott Bolton: I think you'd mostly see it in the results on the aurora. I mean, you get this reconnection and then that accelerates particles and then they get sent in and hit Ganymede or the tenuous atmosphere there. And that's what would create the aurora. You might be able to see some stuff, but I don't know if it would get high enough energy and have enough of it for you to be able to sit there with some goggles on the edge of Juno's spacecraft and some nice comfortable seat and look with the ultraviolet eyes and see all of it light up. But I mean it depends on how sensitive you are.

Sarah Al-Ahmed: Maybe future humans will genetically engineer their eyeballs to be able to see these things. But I'm sure we could talk about Ganymede for this entire interview, and I almost want to, but I want to make sure that we move on to Europa and Io because Europa is one of those moons that just absolutely captures the imagination with its possibilities and the search for life and just how beautiful it is in general. And I know that you use that same microwave instrument that you use to look at Ganymede to look at Europa, and there was a very similar situation where the surface terrain kind of connects with what's going on underneath, but the microwave readings from that world are very different from what we're seeing from Ganymede, right?

Scott Bolton: Absolutely. I mean, that tells us that the ice shells are very different from each other, but we kind of knew that scientists have theorized that the liquid ocean at Europa is probably shallower than Ganymede. And I think we see some evidence that that's probably true. We may even be able to estimate that. It's kind of early for me to throw out the numbers for you, but I think that we're seeing down into the liquid or getting close. One of the startling things was you didn't see as much variety. So Ganymede has this dark and bright terrain, and we saw very different signatures in the microwave from that as we went into the ice. And on Europa, we don't see quite as much variety. There is this little bit of variety that might be connected to what's called chaos terrain versus the normal smooth terrain. And chaos is just where a lot of ridges and things are happening. Something's happening there or has happened, and that might be a little bit different, but it looks very similar to the other one. But it is a little bit different, whereas Ganymede a much bigger variety. But the exciting thing about Europa is, as you say, there is a potential for habitability. I think both of them have that potential, but Europa, of course, the ocean is thought to be salty and it's thought to be maybe 20 to 50 kilometers thick. Our microwaves probably seeing down that deep. So we're trying to do all of the analysis to understand whether we're really seeing into the liquid and how deep it might be. Is it variable across the surface? And it's also intrinsically exciting to many of us because of Arthur C. Clarke's story, right?

Sarah Al-Ahmed: Mm-hmm. Yeah.

Scott Bolton: And he somehow had a vision and knew Europa was special even back then in the '60s.

Sarah Al-Ahmed: That's so cool. And I know that there was a particular bit of data in the microwave that was like... It was the microwave light that I think it was around 1.2 gigahertz or something where that temperature variation seemed to not stop but be less pronounced. And as you said, I mean that could be an indication that we are actually seeing that place where the ice crust actually meets that subsurface ocean, right?

Scott Bolton: That is a possibility. We see a much more uniform ice shell at that frequency. And so, one idea of that is that liquid would make it very uniform because liquid would serve almost like a mirror to the microwave. So if I get to the liquid, it's going to look all the same temperature. So we were looking for that. It takes a lot of time because at that frequency and the one that we have that's longer, that sees even deeper, you're seeing a lot of reflection from Jupiter's radiation belts, something called synchrotron emission. And so you have to carefully remove that first. Luckily we have our own observations of that because the same microwave instrument sees that as we approach and leave Europa and we're spinning, so we get a look at that. And so we're trying to calibrate that out and make sure that we understand exactly what that is. But that's the plan is to look and see if that's an indication that you're getting near the liquid or already at it. And again, there'll be a conductive and a convective ice shell maybe, and then you get to the liquid. So there's a lot of things that are at play here. You may not be all the way into the liquid, but you're probably getting pretty close. And how deep we're seeing, we have to model and analyze too, because it depends on how pure the ice is. There's a lot of factors that would dictate how deep the microwaves penetrate down or are seeing. And part of that is how pure is the ice. If it's really pure, you see deeper. If it has impurities such as salts and other things, you'll change that. One of the things we desperately need is better lab measurements. So I mean, we need to make a lab and point microwaves at a bunch of different kinds of ice and look at what happens. And we know a little bit of that because we study the Earth's glaciers, but of course, Europa and Ganymede are different. And I didn't fold that into Juno's plan because in the beginning I was only looking at the atmosphere. So we spent all our lab work understanding Jupiter. Now I need to go and make another effort to go figure that out with lab work for the microwave at these icy bodies. But it has a lot of potential. And then we'll couple in with the radar instruments on JUICE and Clipper.

Sarah Al-Ahmed: Yeah, I was going to say, this information is going to be really useful for the Europa Clipper mission. Just trying to figure out how deep that ice shelf goes and where the best places to try to fly by and get some samples are going to be, I'm sure Galileo ages ago when he was looking up at the sky, would be absolutely flabbergasted by what we're doing now.

Scott Bolton: Absolutely. But he started the whole thing and certainly changed our perspective, helping us understand that we weren't the center of everything, but it's really exciting to be taking these next steps. And again, we had the same fortune when we went by Europa. We got great images for JunoCam, but we also used this cellar reference unit, this star camera to take a look at the night side, right? We had very high resolution looking again with Jupiter shine of the dark part of Europa, and with very high resolution, we got a nice image of maybe one of these chaos terrains. We're not really sure. We're still trying to figure out exactly what we're seeing, but you see some really interesting features on that.

Sarah Al-Ahmed: We've got more updates on Jupiter's moons to come in the rest of my interview with Scott Bolton after this short message from The Planetary Society's Public Education Specialist and Canadian Space Advisor, Kate Howells.

Kate Howells: Hi, this is Kate from The Planetary Society. How does space spark your creativity? We want to hear from you whether you make cosmic art, take photos through a telescope, write haikus about the planets or invent space games for your family, really any creative activity that space related, we invite you to share it with us. You can add your work to our collection by emailing it to us at [email protected]. That's [email protected]. Thanks.

Sarah Al-Ahmed: Yeah, this is a great example of something where we create an instrument for one purpose. We change its purpose to do something else. And now I feel like we should be putting these very light sensitive instruments on almost every spacecraft because that ability to look at the night side of worlds is just invaluable.

Scott Bolton: Well, the beautiful thing is they're on every spacecraft, every spacecraft uses stars to navigate. And so every mission has had one of these, but I think we were the first to say, "Let's use it as a science instrument." And we also use it to try to monitor the radiation. We try to exploit every angle we can, every subsystem in every way that we can possibly do it. And I hope that that is an inspiration for other missions to reach down and say, "What else can you do besides what you were originally planning?"

Sarah Al-Ahmed: And who knows? I can't wait to hear about some other mission that decides to repurpose this kind of camera for this instead of just staring at starlight. I want to move on to Io now because it's weird, but this is one of my favorite moons in the entire Solar System just because of how absolutely terrifying it seems to be. I mean the most volcanic body in the entire Solar System. I have to get a closer look at this and Juno's about to show us so much more, and I cannot tell you how excited I am.

Scott Bolton: Yeah, it's very exciting for us too. We're already getting incredible stuff because we go over at a distance, but we have a phenomenal infrared camera that was contributed by the Italian Space Agency, and it's sitting there monitoring the volcanoes at pretty high resolution. And so every couple of months we see another image and we get to see how the volcanoes change. And not only that, but we're looking at the pole, the North Pole, which hasn't been seen that much, but you see a lot of the body, and we're watching this. And of course one of the big questions is, how do these volcanoes affect Jupiter and its giant magnetosphere? You have this monster planet with even a more monster magnetic field, and here's this little moon pumping out volcanic material all over and it's driving the entire system. I mean, this little engine is bumping around Jupiter, this giant, right? And so we're probably going to have one of the first really thorough experiments where we can look at the effects of Io's volcanoes and how they're varying and understand how it affects Jupiter's aurora, Jupiter's magnetosphere, the whole Io Torus, which is just filled with this volcanic material whizzing around because it gets picked up by the magnetic field. And of course, Jupiter's magnetic field is spinning with Jupiter every 10 hours. And so it actually slams into Io. Io spits out material, it gets charged, and then it bangs on the backside, and it's just amazing. This is like a little engine going on. It's actually a big engine. We're sitting there, we're already getting phenomenal images of Io and we just got some on this last orbit. They're just starting to come out now. I think the visible one was released but we're pretty far away, 60, 70,000 kilometers, and so it's not real high resolution. But the infrared camera has really high resolution already at this point, and we're sitting there looking at 20 kilometers or less resolution, so you can really pick out the volcanoes and even start to see their shape. And then we're just going to get closer each orbit, we get a little bit closer until next year around this time actually, we'll fly by at 1500 kilometers distance twice. That one we get to do twice.

Sarah Al-Ahmed: That's so exciting. I cannot wait. Looking at the images that we've seen so far, it's almost like... I mean, I don't want to jump the gun here, but it almost looks like there's pools of lava on that world. Is that possible?

Scott Bolton: Absolutely. There's pools and lakes of lava and you can start to see their shape now in some of these infrared images that we're getting. And you can also see that they're varying, right? Some are hotter at one time, and then they cool off, and another one gets hotter. And so it's a really amazing place. I was just started at JPL when we had just gone by the Jupiter fly by with Voyager, and in fact, I got there just in time to see Saturn. But I remember the images of Io being one of my favorite images. And while it was really famous when we saw this plume coming up, and Candi Hansen who's on our team kind of did the analysis and said, "Look, here's a volcano." And there were some other people that were involved in that discovery as well, but it was the basic image of Io. I remember getting copies of that and sending it to all my relatives and friends and saying, "Look, it looks like a pizza."

Sarah Al-Ahmed: Yeah.

Scott Bolton: And I said, "This is just volcanoes." And it was amazing.

Sarah Al-Ahmed: I think I made that exact same joke about that image, but I was much younger when I first saw the images of Io. I actually think somewhere here in this room, I have my childhood books with the first pictures of Io in there. And I remember saying, "It looks like a pizza." And then learning that it was just covered in volcanoes. To this day, I still have weird dreams and nightmares about the idea of standing on the surface of that moon, which is volcanoes exploding in the distance. It's terrifying, but awesome.

Scott Bolton: Yeah, it must be an amazing place to go visit if you were a geologist. I mean, I've very fearfully, tried to get close in Hawaii. When I would go on vacation, I would try to walk up or take a helicopter ride and see what the volcanoes were. And you see there's a lot of energy involved, and it's hard to imagine that this lava is so hot, it would kill you if it just touched you and that it's ripping apart the earth and it's dripping into the ocean, and that's just one volcano. Maybe you're lucky on Hawaii, there's a couple, but they're usually not active at the same time. But imagine this little moon having hundreds of them all over the place, all popping off all the time. It must be just an amazing place to visit, if you had the right gear.

Sarah Al-Ahmed: Right? I know too, that you said this earlier, but Juno has kind of allowed us to get a view of the polls on Io that we never accomplished before. And what we're finding is that it's actually kind of more volcanic activity near the polar regions, and why do we think that is?

Scott Bolton: We're still trying to figure that out, but there are some ideas that maybe the heat flow comes out of the poles and you get more activity, but there could be other reasons. It may also indicate that the magma ocean is truly a global ocean, or maybe there's more of it in the poles. We see the south, but we haven't been able to see it as well. But we started off earlier in the mission where we were looking at the first image. We were maybe a distance of 400,000, 500,000 miles away. Now we're getting a 10th of that 50,000 kilometers or something like that, and we're just going to keep getting closer. And so you keep seeing higher and higher resolution. But yeah, so that was the first real shot that we had on the polls. And in fact, it showed us the first time we really looked at the polls of Ganymede and Europa as well. It was the first time we saw the poll of Jupiter, and it was covered in polar cyclones. So the polls always hold out some surprise, some potential surprise that then you have to go back and develop new theories to try to explain.

Sarah Al-Ahmed: And I remember those images kind of earlier on in the Juno mission. It wasn't even directly over the poll of Jupiter, but looking at the aurora there and seeing how Io was kind of dragging this beautiful aurora, just personally dragging it around the pole of Jupiter. It's absolutely mind blowing what we're getting out of this spacecraft.

Scott Bolton: Yeah, we are very, very lucky. We count our blessings every day. I mean, the team is really excited. Going into the extended mission and then still being able to do all these new discoveries. It's really a treat. I think we're getting more than our fair share of excitement out of this mission because of the fact that the new territories and new ability to discover just keeps happening because you're getting new perspectives all the time. A lot of times missions are extended, but you're kind of doing a little bit of more of the same thing, but in more detail. This is really new territory.

Sarah Al-Ahmed: And it's laying the groundwork for a whole new set of missions that are going to be delving even deeper into the moon, specifically. You've already said that some of the instruments on Juno are better for one thing than even the upcoming ESA JUICE mission or Europa Clipper can do. But what are the things that these upcoming missions are going to be able to accomplish that we can't do with Juno?

Scott Bolton: Oh, quite a bit. I mean, we have unique instruments, but they do as well, and theirs are even more advanced than ours because they came later. And so you make advances in technology every year, really. On both of those missions, they have radar instruments that were designed to look into the ice. We didn't have that. We're using a radiometer, but it turns out that it may be equally valuable and certainly valuable to complement their perspective. But they will see something new because they're actually actively sending a signal down and watching it bounce off, and they know exactly what they're sending down, and they can send their signal down at different angles and watch how it bounces. Ours is passive, right? We're just watching these moons or Jupiter's atmosphere glow, basically, it's giving off radio emission from deep, and we're interpreting how deep we're seeing. We're not sending any signal down, we're just listening. It's really what's called black body radiation.

Sarah Al-Ahmed: Mm-hmm.

Scott Bolton: And then they also, each one has very special cameras, right? We have this JunoCam, which is really not designed to look at satellites. It wasn't even designed to interrogate who's atmospheres as much as it has been able to do. It's not even a framing camera, right, we're spinning. So we build up the color things with these slices on the CCD, and we have a field of view that's quite large because we were going over the pole and we wanted to get a picture of the whole North Pole of Jupiter at once because we weren't going to have a chance to make a mosaic. Both Clipper and JUICE have very advanced cameras that are an advanced version of what Cassini or Voyager had, so they're going to be able to do very narrow angle and wide angle imaging and get very high resolution. That'll compliment what we've been able to do. They have instruments that are mass spectrometers that go in and are designed to be able to measure the composition. We have some of that, but our composition is charge particles. They actually can do some of the neutral ones. There's a big difference between our instrumentation and theirs. Theirs is tuned to do satellite science. Ours was tuned for Jupiter. We're applying it to the satellites, but we weren't designed to go do that, or I would've thrown on these other instruments. But we also have some things that they don't have besides... We have a very extensive fields of particles payload because we were there to study Jupiter's magnetosphere and aurora and the satellites don't require that. Most of those instruments, they have some fields of particles, but not quite as complete a package is what we have. So I think the missions compliment each other in a really nice way. And of course, I give talks to their teams and they're excited to hear what we're learning and maybe we can affect our planning and we can give them some insights that will help them in their exploration as well.

Sarah Al-Ahmed: It's always a beautiful thing when missions can cooperate like this, and this is a rare opportunity to have so many missions around a world like Jupiter.

Scott Bolton: One of the amazing things about Juno is, like you said, this microwave instrument. I believe that's going to become a primary tool of planetary science. We kind of put it on and invented it for Juno, but now it's not only important to go study Saturn, Uranus, and Neptune with this instrument. But we're learning that you should look at all the satellites with it, all the ocean worlds. And I'm already looking at what would be the next generation of that. Right now that we've flown it, how could you make it better? What could you do that would change it? And I think that you can mix it with other capabilities and actually it'll be really, really important to look at say Triton with it.

Sarah Al-Ahmed: I was just going to say, of all the moons I would love to look at with one of those things, Triton would probably be it. I have one last completely silly question for you before I leave you, but years and years ago, I was giving a field trip to a group of maybe 60 10-year-olds at Griffith Observatory, and I was talking about the Juno mission and everything that it was teaching us about Jupiter. And I pointed out that on board there are three spacecraft grade aluminum, Lego mini figures on board. And one of the students asked me, when the Juno mission ends and dive straight into Jupiter, how deep are those Lego figurines going to get before they get burnt and squished and melted? And I really didn't know the answer, so I'm going to kick this one to you. How deep do you think those Lego mini figurines are going to get?

Scott Bolton: Probably not very deep. It gets very hot in Jupiter as you go down. It's getting warmer, but those figurines, Lego made those to some specifications that I designed, and they're basically the same thing as spacecraft grade aluminum. They're special metal, and the bulk of our instruments and boxes that hold the instruments are made out of the exact same thing. So those Lego mini figures will last as long as and probably melt around the same time as the rest of the bulk of the spacecraft.

Sarah Al-Ahmed: Mm-hmm.

Scott Bolton: Now, what's going to happen as we go into Jupiter is we have giant solar arrays. So those are wings, right? So when we start hitting an atmosphere, those are going to get thrown off right away. You're going to lose control of the spacecraft. Those things are going to fly around like a kite in a horrible storm. And so then it'll start coming in and it'll burn up just as your student suggested, and it'll start to melt and it'll melt with the rest of that spacecraft. They're not going to last any longer and they're not going to melt earlier.

Sarah Al-Ahmed: Wow, that's good. And thankfully, we've got, what? About three years to think on this before Juno actually makes the great dive into Jupiter. Is that right?

Scott Bolton: Well, actually, we don't have one planned, and it may be quite a bit longer. It used to be a plan to dispose of the spacecraft for planetary protection regions at the end of the primary mission. But then when we went into the extended mission, once we passed Europa, there's no risk that we can get back and crash into it. The same reason we can't get back for scientific reasons, we can't get back there by accident either. And so we've shown that to international committees and NASA and said, "What we propose is just let it die naturally." But I can't predict exactly when the spacecraft would fall into Jupiter. The final decisions of all of that have not been done yet, but they're being studied. So we'll run out of fuel or radiation will kill us or something, but then we'll just keep going around Jupiter until we finally just fall in.

Sarah Al-Ahmed: Yeah, see that that's a little easier on the heart, I feel. Like I don't know if I can go through a Juno grand finale like I did with Cassini. That was a hard day.

Scott Bolton: Yeah, it was depressing when I was there for Cassini's and I felt bad about it because it still could have done some science. Even though when it went in, it was going to do some unique science, right? So Cassini had one of these neutral mass spectrometers on board. So when it went in, it kind of measured the upper atmosphere of Saturn, which was very powerful and useful. But nevertheless, after you've worked on something for a really long time, you hate to see it take a dive, a suicide dive.

Sarah Al-Ahmed: But in the end, these missions have taught us just an incredible amount about these worlds, and everything comes to an end ultimately. And we'll always be able to look back at the amazing images and all of the data that Juno has shared with us and remember it just the way that we did with Cassini. It'll be okay, but I will be sad when Juno ends because this mission has just been absolutely revelatory.

Scott Bolton: Yep. It's a little bit like a relative or a good friend in that when it ends, you grieve a little. It's like part of your family. But you're right, it's part of life, right?

Sarah Al-Ahmed: Right.

Scott Bolton: We were, I think, fortunate to have the mission and be able to experience it in our lifetime. We're in a very unique time in history where we're all lucky to be alive at this era of exploration and starting to see other worlds as we've never been able to see them before, start to realize that maybe we're not alone, that there's other planets and planetary systems out there, and we're starting to see those. And so it's a very exciting time to be on the earth living as we really change our whole perspective. It's a little like a renaissance. It must have been like that at the time of Galileo.

Sarah Al-Ahmed: It does feel very lucky to be alive during this time of exploration. And I'm sure that one of these days people are going to look back on this and envy this age of exploration and discovery and all the things that we didn't know yet.

Scott Bolton: Exactly.

Sarah Al-Ahmed: Yeah. Well, I wanted to thank you for joining me for this conversation, and hopefully in the future when the Juno mission does end, I can invite you back on, or even before that when we learn all these new amazing things about Io. Thanks so much, Scott. It's wonderful having Scott Bolton back on Planetary Radio, I feel like I could talk to that guy for hours. But now it's time for us to turn to the Chief Scientist of The Planetary Society. Dr. Bruce Betts for what's up. I am joined once more by Bruce Betts. What's up, Bruce?

Bruce Betts: Hey, super spectacular, wonderful radio host, Sarah.

Sarah Al-Ahmed: Oh, what did I do to deserve that?

Bruce Betts: You said some nice things about me in previous episodes, so. Let's just... What's up? [inaudible 00:47:48] All those things. What's not up much longer is Saturn, Saturn's going away for a little while. It always comes back though, don't worry. But if you look low in the West, actually not even that low nowadays, you can see super bright Venus shortly after sunset. And Saturn's still hanging out below it, but again, it's going to be really tough. Super bright Venus, and then you go up in the sky and you'll see really bright Jupiter both brighter than the brightest star in the sky. Keep going across the sky. You'll find this reddish, orangeish looking kind of bright star that's actually Mars. And near it is a not quite so bright reddish star that actually is a star, it's Aldebaran in Taurus. So those are all up. I also, when I was staring at the winter constellations that are so lovely. So I encourage you to check out Orion and all of its friends. If you follow Orion's belt off to the left, if you've got Orion oriented upright, you will find the brightest star on the sky, not to be confused with the brighter planets. And that is Sirius, the Dog Star. And if you have a clear enough sky, you can look for the outline of a stick figure dog, which almost kind of exists, which is the constellation Canis Major, the Greatest Dog,

Sarah Al-Ahmed: The Greatest Dog. I know too, that some people it's a little early for this, but some people are beginning to get images of that new Comet 2022 E3 (ZTF). So it's a-

Bruce Betts: Well done, you didn't even read that off of anything.

Sarah Al-Ahmed: I know, it's in there now.

Bruce Betts: You're going to need binoculars through a telescope, but you can check it out, at least, with a telescope at this point. It may or may not become visible from a dark side shortly with just your eyes, but I think it's unlikely. But they're comets. They're the cats of the sky, you can't predict them.

Sarah Al-Ahmed: No, I'm just imagining someone try to herd comets like you herd cats.

Bruce Betts: Doesn't work, I'm telling you. Actually, the only thing you can predict pretty well is their orbit. Okay, let's go on to this week in space history. This is the darkest week in the US space program. Basically all three of the fatal accidents involving space flight occurred during this week or close to it. Apollo 1 fire in '67, the Challenger disaster in '86 and the Columbia disaster 20 years ago now in 2003. So we remember all of them and all of the other people contributing in their brave ways to space exploration. And on a happier note, we also had Explorer 1 this week in 1958, the US' first satellite successfully in orbit and Opportunity landed on Mars in 2004. I move on, shall I?

Sarah Al-Ahmed: Yes.

Bruce Betts: All right to [inaudible 00:50:33].

Sarah Al-Ahmed: That was a good one.

Bruce Betts: Well, thank you. Thank you very much. I hear you've been talking about Jovian moons.

Sarah Al-Ahmed: I have. Yeah, that was really cool. We're learning some awesome stuff there.

Bruce Betts: Did you know if you put the three icy Galilean satellites, so all but Io. The icy ones, if you put them next to each other as never happens, that would be about the width of the earth, about the diameter of the Earth.

Sarah Al-Ahmed: I didn't know that, but that would be a cool graphic just to show.

Bruce Betts: I've got it in my head if you need it. All right, we move on to trivia. I asked you, where in the Solar System is Doom Mons named after Mount Doom in the Lord of the Rings? How'd we do?

Sarah Al-Ahmed: We did really well. Clearly we have a lot of overlap between space fans and people who love Lord of the Rings because we got a lot of answers to this one.

Bruce Betts: Oh, good.

Sarah Al-Ahmed: And the answer of course is Saturn's Moon Titan. And Doom Mons isn't the only mountain on that moon that's named for Tolkien's books. There are a lot, including some of my personal favorites, Angmar Montes, Erebor Montes, and of course the coolest one, Misty Montes named for the Misty Mountains.

Bruce Betts: Anyway, let us move on-

Sarah Al-Ahmed: Let us move on.

Bruce Betts: To finding out who won.

Sarah Al-Ahmed: Yeah. Well, we have two winners this time and the prize are these beautiful Artemis pins that Bruce and I procured on our adventures to Kennedy Space Center. So our first winner is Asan Beglu from Richmond Hill, Ontario, Canada. And our second winner is Eric Oday from Winchester, Massachusetts, USA who said, "What a place for a vacation surfing on the Kraken Sea and skiing on Mount Doom." Hope there's no actual Kraken in there.

Bruce Betts: Well, we're looking, but I can't discuss it with you.

Sarah Al-Ahmed: Mm-hmm. And I also really liked this comment that we got from Louis Igo from Sauk Center, Minnesota USA, who clearly likes my choice of using dice instead of random number generator to find the winner for this because they wrote in, "Go polyhedrons of randomness." But anyway, all right. So what's this week's trivia question?

Bruce Betts: All right, so what is the only mission to fly by Jupiter then go inwards rather than outwards in the Solar System? Go to and you could win rubber asteroid.

Sarah Al-Ahmed: Classic rubber asteroid. If anybody would like to win a rubber asteroid, you can enter our trivia contest at and you have until Wednesday, February the 1st at 8:00 AM Pacific time to get us your answer.

Bruce Betts: All right, everybody go out there, look up the night sky and think about squishy asteroids. Thank you and goodnight.

Sarah Al-Ahmed: Well, that's all for this week's episode of Planetary Radio, but we'll be back next week with Jacob Lustig-Yaeger, a member of the team that announced the discovery of the first exoplanet confirmed with the James Webb Space Telescope. Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible by our amazing members. You can join us as we continue to explore the mysterious worlds of our Solar System at Mark Hilverda and Rae 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.