Io and Voyager 2: Lost oceans and found signals

Sarah Al-Ahmed: Exploring the radiant infancy of the Jovian system, 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. This week, we're traveling back in time to the early Solar System to delve into the luminous beginnings of Jupiter and the profound impact it had on one of its most fascinating moons, Io. Carver Bierson, a postdoctoral researcher at Arizona State University joins us to unravel the deep connection between Jupiter's early brightness and the processes that could have turned a once watery Io into a world covered in lakes of lava. But first, we'll hear from two legendary figures of space exploration, Voyager project manager Suzanne Dodd and Voyager project scientist Linda Spilker. They'll share their insights on the remarkable reestablishment of connection with the Voyager 2 spacecraft with our senior communications advisor, Mat Kaplan. And stay tuned for what's up with Bruce Betts, our chief scientist as he answers a question from our Planetary Society member community. If you love Planetary Radio and want to stay informed about the latest space discoveries, make sure you hit that subscribe button on your favorite podcasting platform. By subscribing, you'll never miss an episode filled with new and awe-inspiring ways to know the cosmos and our place within it. You may have heard a sigh of relief from all of us here at The Planetary Society and other space fans around the world on August 2nd. That's when we got word that the Jet Propulsion Lab had reestablished full communications with Voyager 2 way out there in interstellar space. The spacecraft marked its 46th anniversary of its launch just a few weeks later on August 20th, and its twin spacecraft Voyager 1 on September 5th. It's a perfect moment to celebrate. My colleague Mat Kaplan, now senior communications advisor, has been following the Twin Voyager spacecraft since before their launch. He called on Voyager project manager, Suzanne or Suzy Dodd and Voyager project scientist, Linda Spilker to talk about their close call and to reflect on this mission they've been part of for decades. Suzanne starts the tale.

Suzanne Dodd: We did have a scare on Voyager 2. We had an unfortunate mispointing of the Voyager 2 spacecraft that took it off of Earth Point and actually pointed it out more toward the Jupiter orbit. Because of that, we couldn't get commands back down from the spacecraft, and we were also extremely worried that we could not get commands into the spacecraft because we were so far off pointed. And from what we knew about the design of the mission and the design of the telecom system, we thought it would be highly unlikely that we would be able to get commands into Voyager 2. We had onboard software that was going to restart our pointing algorithm the middle of October, but we would've been waiting three months worrying. I would certainly be worrying and fingers crossed and everything until the onboard software should put us back on Earth, but will it really? And we decided we would try to send a command to Voyager 2 to point it back to Earth and we would just send a single command and we would send it with the highest power available to us, which is the S-band, a 100 kilowatt transmitter down in Australia. And if you recall, Voyager 2 is down and out of the plane of the planet, so it can only see the Southern Hemisphere. So our only communication link to Voyager 2 is through the Australian Deep Space Network. And we sent it and it worked and like, oh, I'm so relieved it worked.

Mat Kaplan: But I guess when you're 18 and a half light hours from home or almost 12.5 billion miles, that still made it pretty much a long shot.

Suzanne Dodd: Right, it did make it a long shot for sure.

Linda Spilker: And it was just very reassuring to essentially pick up that heartbeat to know that Voyager 2 was still there, still operating, sending its data back, but we just couldn't get the ones and zeros back. Just that tone that let us know, yes, I'm still here.

Mat Kaplan: So a 100,000 Watts coming from Earth. I've forgotten. Do you remember what the transmitter power is on Voyager 2? I mean, it's double digits, right, at most?

Suzanne Dodd: Yeah, it's about 22 watts.

Mat Kaplan: 22 watts, a dim light bulb, a dim [inaudible 00:04:37] light bulb.

Suzanne Dodd: Yeah, [inaudible 00:04:38] light bulb is the quote that we've use for years. So yeah.

Mat Kaplan: Suzy, I mean, you're not just the Voyager project manager. You could speak with authority about the Deep Space Network because you are also the director of the Interplanetary Network Directorate at JPL, which means you oversee the DSN and other things. So you really had both feet in this effort. Talk again about what a relief it must have been after two anxious weeks.

Suzanne Dodd: It is true. You can never talk about Voyager without talking about how you get those signals back from so far away, which is the Deep Space Network. And you can't talk about this Deep Space Network without people asking, well, how far away can you get signals? And I go, "Well, from interstellar space, from Voyager 1 and Voyager 2." So it's a great synergy for me personally.

Mat Kaplan: I'm also thinking of the reaction around the world because everybody took notice when this problem first surfaced, was announced to the public just as they did, well, just last year I think when Voyager 1 was having some data problems. And I just wonder what both of you think about what this says about how near and dear these twin spacecraft are to so many of us down here on this pale blue dot.

Linda Spilker: It's amazing, Mat, I was walking down the street and one of my neighbors said, "Hey, how's Voyager doing?" So it's clear that there's just this recognition of these two intrepid spacecraft, the furthest away from the Earth in interstellar space and just still that interest in following up on what's happening with them.

Suzanne Dodd: I echo that. I have relatives that live across the country. I have friends that live abroad and they had all heard about Voyager 2's issue and they all wanted to know what the status was and once it was back, it was email high-fives and congratulations. And even letters from the general public. I frequently get letters from the general public and they'll write and send me a note, so happy that you've got Voyager 2 back, such a great mission, one of NASA's finest ever. It really makes you feel proud to be a part of that.

Mat Kaplan: I don't blame you.

Linda Spilker: Absolutely, yeah. And Mat, I would add in all of this interest often someone will say, well, I was in third grade when Voyager flew by Neptune. You get to hear those stories of their personal connection to the mission itself, and that's really a lot of fun. And I echo Susie, I'm really proud to work on Voyager as well.

Mat Kaplan: If I'm right, Voyager 1 is now almost five times as far away as Pluto and considerably further from us than Voyager 2 is. What's the general health of the spacecraft, Susie?

Suzanne Dodd: For senior citizens, they're both pretty healthy. They each have their own ailments, but really in human years, the spacecraft might be more like 100 than 46, double it kind of thing. But they're healthy, they're showing some signs, Voyager 1 in particular, we're watching the thrusters closely now. They're starting to show more thruster firings than we'd like to see, sort of a clogged artery syndrome type thing, not being able to get as much for the pulses and the thrusters. So that's becoming a concern for us.

Linda Spilker: I'd like to add too, on the science side, as we're getting further and further into interstellar space, this will inform any future missions like interstellar probe about what they might want to consider for science instruments and what to expect with the distances. And also there's some interest now from the astrophysics community as well because clearly in studying galactic cosmic rays and studying the part of the bubble that our Solar System is in in the local interstellar cloud, there's some unique information there as well.

Mat Kaplan: You're just providing more proof that even if this mission ends tomorrow, its legacy is safe, and in fact they'll continue on across the light years carrying that gold record that the two of you can see over my shoulder. It is an amazing, amazing accomplishment and I just want to thank both of you for continuing to lead this effort that is literally taking us to the stars.

Suzanne Dodd: Thank you so much for having us, Mat.

Linda Spilker: Yes, thank you very much, Mat.

Mat Kaplan: Go Voyager.

Linda Spilker: Go Voyager.

Sarah Al-Ahmed: You can hear Mat's complete conversation with Susie and Linda on this week's show page at planetary.org/radio, or if you're a Planetary Society member, I'm going to put a link to it in the Planetary Radio space in our member community app. And now for our main topic of the day. In the early chapters of the Solar System, Jupiter was a beacon of light or so research suggests. After its formation, there was a time where it shined up to 104 times brighter than it does today. The illuminating glow of the largest planet in our Solar System profoundly impacted its moons, most notably Io. Today Io is well known for being the most volcanic body in our Solar System. Its surface is covered in volcanoes, but it may have once been a watery world like its neighboring Galilean moons. Even Europa, which we now think has a subsurface ocean, could have been deeply impacted by a young, bright Jupiter. So let's explore the question, could Jupiter's early luminosity have been the force that stripped Io and potentially even Europa of their initial water inventories? Our guest today, Dr. Carver Bierson is a postdoctoral researcher at Arizona State University, a role that finds him deeply involved in the preparatory studies for NASA's upcoming psyche mission. But his expertise doesn't stop at asteroids. He studies the evolution of worlds over time, dissecting the intricate relationships between solid bodies and atmospheres. Beyond his research, he harbors a deep passion for science outreach, nurturing young minds and sharing his contagious enthusiasm for the Solar System through teaching. He's about to give us all one more reason to love Jupiter and its Galilean moons. Carver's team's recent paper called Jupiter's Early Luminosity may have Driven Off Io's Initial Water Inventory was published in the Planetary Science Journal on July 14th, 2023. Hi Carver.

Carver Bierson: Hello.

Sarah Al-Ahmed: Just a few weeks ago I was talking with your colleague Kevin Trinh, on the show. We're talking all about the evolution of Europa over time, and I believe you were also on that paper as well. And during the conversation he brought up this thing that completely blew my mind. He said that Jupiter's early luminosity could have turned Io from a water world into this volcano land, and thank you so much for coming on the show to tell me more.

Carver Bierson: Yeah, really excited to be here.

Sarah Al-Ahmed: The Solar System was a very different place in the beginning when it was forming, and that makes modeling the evolution of these worlds so much more complicated and the Jovian system is just absolutely ridiculous. So when I heard that the luminosity could be as much as a hundred times brighter than it is today early on, that seems like very, very shiny. How did that happen?

Carver Bierson: So the Jovian system, as Jupiter is for me, is a really cool place because Jupiter with its nearby moons is almost like a mini Solar System. We think about the Solar System forming as this disc of gas and dust around the sun. Well, Jupiter had its own disc of gas and dust around Jupiter, and Jupiter was sucking up this gas growing and growing over time until it gets to its giant size we see today and the moons were forming in that disc around Jupiter. And a lot of the details are things that we're still trying to figure out. We don't know exactly how hot the disc was or how long it lasted or how long the moons took to form even. These are all pieces we're still trying to put together, but as Jupiter's sucking in all this material, it's getting all this gravitational potential and it just warms up and warms up and gets brighter and brighter and brighter. So right after it finishes forming, Jupiter is the brightest it will have ever been.

Sarah Al-Ahmed: When in the timeline of the Solar System would it have reached this peak luminosity?

Carver Bierson: Basically right at the start, just a few million years after the first solids condensed in the Solar System. So we're talking right at the beginning. Essentially it's going to be its brightest when that disc of gas and dust around the sun is just being blown away. Sun basically kicks on to the main sequence, blows away all the gas and dust around, and that means Jupiter now has no more gas to suck in in any creaks to get any bigger, and so it is bright and hot from all this new material that's created and will be shining that light directly on the nearby moons.

Sarah Al-Ahmed: This paper suggests that this early luminosity really impacted the formation of these Galilean moons, but the timeline there would really change how this plays out, and we're not a 100% sure how long it took the moons to form. So what do we think was the scenario here time-wise? Were the moons still forming when it was at this peak brightness or were they already beginning their current state?

Carver Bierson: I mean, as you point out, there's a lot of uncertainty here. We're looking in the farthest depths of our Solar System right at the beginning, so we don't have that much information to go on, but what we expect is that once this gas and dust is blown away, you've run out of stuff to build the moons out of now. So the moons have to be done being formed. They are more or less their present sizes that we see today, and we don't know exactly how bright Jupiter was, but from the best guesses we have, we would expect that if you were on Io looking at Jupiter, Jupiter would be giving off as much energy as like the sun does in the Earth's sky today. So you would have temperatures on the surface of Io that are comparable to Earth-like temperatures. So if there was any water around, it would be liquid on the surface and it would be warm.

Sarah Al-Ahmed: That is so amazing because as Io stands today, it's literally the most volcanic body in our Solar System. There are lakes of lava on this moon, so thinking that it could have been a cool vacation spot at one point in the Solar System is just completely nuts to me in the best way.

Carver Bierson: Yes, Io is a wonderful world. So you have these lakes of lava and at the same time it's super cold today too. It's 100 Kelvin, so something like -300 degrees Fahrenheit thereabouts. And there's sulfur ices on the surface 'cause there's so much volcanic outgassing of sulfur dioxide, sulfur oxides. Those turn into ices, essentially freeze onto the cliffs.

Sarah Al-Ahmed: So at this point we're assuming that the moons are already formed, but was there any kind of dust that was still left in the system? Because that could impede the light getting to these moons and probably affect that evolution.

Carver Bierson: At this point, most of that dust is going to have cleared out, and so it's a question of how bright is Jupiter at this point once you've blown off this gas and dust? There's a chance that Jupiter has already cooled off significantly by this point. So again, no one was there, we don't know. So maybe it was bright enough to do this, maybe it wasn't. There's also a chance that Io didn't have any water left already. That's really one of the big mysteries, is when did Io lose its water? Did it ever have it? We see this trend of Io being really rocky close to Jupiter. Europa is mostly rock a little farther away, and then Ganymede and Callisto are half rock, half ice by volume. We're trying to figure out why. One of the interesting things here is that if you take Io and just add a bunch of ice to it, it ends up looking a lot like Ganymede and Callisto. Basically the rocky core of Ganymede and Callisto is basically the same size as Io. I say that these moons are like a mini Solar System, but one of the big differences here is that it's really small compared to our Solar System. So when they formed, it's hard to separate out materials 'cause there was probably a lot of ice being delivered to Io during that formation, but maybe it didn't stick. Maybe during formation things were hot enough to drive off the ice. Or if it was still run after that formation, this luminosity from Jupiter could help drive that off. As that liquid water sits at the surface, it creates an atmosphere and Io just doesn't have that much gravity, and so it can't hang on to that atmosphere very well. So it could be lost over a few million years, maybe 10 million years, right at the start of the Solar System.

Sarah Al-Ahmed: I always assumed that there was some kind of ice line or some distance away from Jupiter at which you could form these more icy moons and that Io was just too close. Is that possible?

Carver Bierson: Yeah. This is something that people have talked about a lot for decades, and actually one of the earliest versions of this ice line hypothesis around Jupiter from back in the late '70s was that it was actually the light and heat from Jupiter that created the ice line, and then eventually that idea fell out of favor as we thought more about this disc and how thick it was, and it probably was blocking that really early heat from Jupiter. But the problem that people kept running into with this ice line hypothesis is that again, the system's so small, so if you're forming icy stuff in the outer part of the disc, and we know you were, 'cause you were forming Ganymede and Callisto, which are very icy, then some of that icy stuff should be falling in towards Jupiter and running into Io along the way. And so you end up delivering a bunch of ice to Io and then you need to get rid of it somehow. And so maybe it's getting rid of while there's still that hot gas and dust around to help melt it and evaporate it off the surface, or maybe it's getting rid of in this period right after, that dust and gas goes away and it's luminosity from Jupiter itself driving it off.

Sarah Al-Ahmed: There's so many things to consider here because if these worlds were covered in ice, they start puffing up and outgassing all of this water, I'm sure there's a point at which the greenhouse effect comes in into play as well and that's got to complicate it even further.

Carver Bierson: Yeah, there's so many additional factors that can come in and stack on top of this. One of the important ones is greenhouse effect, so that water vapor that's going to form the atmosphere is going to want to trap extra heat, and that's essentially extra energy that can go into evaporating more water, putting more of it in the atmosphere so it can get lost even faster. And another interesting wrinkle in this is that we'd expect Io at this point to probably already be entirely locked to Jupiter. So Jupiter is only facing one side of Io all the time. Essentially there's a daytime half of Io and a nighttime half of Io, one side that's always getting cooked and one side that's always cold. And we see this in some exoplanets around other stars as well, and it's a system where we don't really understand the atmospheric dynamics of what that looks like very well 'cause we don't have any examples of that in the modern Solar System today that we can look at and learn from. So we're still trying to understand what would happen? How evenly distributed would the heat be? Could the ocean [inaudible 00:20:37] basically even everything out or not? There's so many excellent questions about these early times and how different things interact with each other.

Sarah Al-Ahmed: Something I was thinking about is the fact that we're kind of assuming that these moons formed where they are currently, but if our Solar System is any indication, things kind of migrate around and make things even more complicated. I don't think that was something that you could take into account in this paper because honestly, how would we even know where the moons were when they formed? That's a really complicated problem.

Carver Bierson: We see the moons are moving today. The tidal heating that's driving Io, the energy for those volcanoes is actually coming from Jupiter's rotation. There's these interactions between the different moons tugging on each other and tugging on Jupiter, and the net effect is that all of these moons are slowly moving away from Jupiter over time, and Jupiter itself is slowing down in its rotation. Same thing is actually happening here at the Earth. The Earth is slowing down in its rotation and our moon is slowly receding away. And so we actually know that Io would've been a little bit closer to Jupiter really early on, which helps. There's more energy coming from Jupiter as you get closer, but we don't know how much closer because we don't know the full history of how long has Io been volcanically active like we see it today? When you have a surface covered with active volcanoes, you erase the past very quickly.

Sarah Al-Ahmed: It's funny to think that this tidal interaction that allows moons like Europa to potentially have subsurface oceans could also be devastating enough to completely destroy an ocean on another world. That's so cool.

Carver Bierson: Yeah. And one of the interesting things is that tidal heating, it provides all of this amazing energy that we see in these active geology at the surface. Tidal heating is a ton of energy in terms of surface features, volcanoes, oceans, things like that, but it's actually not very much energy when we think about atmospheres or surface temperatures. It's a rounding error on those processes. So while tidal heating can drive this amazing volcanic activity, it's not actually enough energy to get rid of a lot of ice over Solar System history. And so this leads us to thinking that I really did, if it accreted this ice, it had to get rid of it really early on. And that's why the Jupiter's early luminosity might be a good way of explaining that.

Sarah Al-Ahmed: It makes total sense to me. If you had something the size of Jupiter blazing like a sun in the sky over Io, there's no way that wouldn't have an impact. And it is shielded by Jupiter's magnetosphere, but it's not like Io has its own little comfy magnetosphere to protect its atmosphere in the case that its water started getting blown off. I'm wondering how long could it potentially have had liquid water on the surface if this was the case?

Carver Bierson: It wouldn't have been very long. The number one thing you need to hang onto an atmosphere is gravity. You have to have the gravity to hold onto the gas molecules or they just fly off into space, and Io is not that big. It's somewhat similar in size to our own moon, so it just doesn't have the gravity to really hang onto an atmosphere, so it wouldn't have been more than a few million years of having water on the surface, and it's just essentially evaporating almost directly into space as you go, and so you're losing it. And maybe it's less than a million years, hundreds of thousands of years, something like that. It would be a very short period of time geologically speaking.

Sarah Al-Ahmed: Well, if anybody has a time machine, that would be a really cool thing to go see.

Carver Bierson: Absolutely.

Sarah Al-Ahmed: As I was reading your paper, there was a lot of indication that it was either Io and Europa had this ice and lost all their water or they retained all their water and it was a very hard either this or that, but almost nothing in between. Why is there such a stark difference in these formation scenarios?

Carver Bierson: A lot of this comes down to the fact that we don't really know how bright Jupiter was and just the behavior of water. So if Jupiter is bright enough to basically start melting the water, once you get it melted, then it starts evaporating and goes in the atmosphere and starts driving all this stuff. But if it's not quite bright enough to melt everything and essentially go from having ice to water, then it's not and you're not going to get much evaporation and you're not going to have much gas in the atmosphere and so everything can stick around. And in some sense, this is why even with this really bright Jupiter idea, Ganymede and Callisto still hang onto their water because they're just a little bit farther away. The amount of energy you receive drops off pretty fast as you go farther away at this inverse square law, and so they stay icy, they stay cold because of that extra little bit of distance.

Sarah Al-Ahmed: We'll be right back with the rest of my interview with Carver Bierson after the short break.

Bill Nye: Greetings, Bill Nye here, CEO of The Planetary Society. Thanks to you, our LightSail program is our greatest shared accomplishment. Our LightSail 2 spacecraft was in space for more than three years from June 2019 to November 2022 and successfully used sunlight to change its orbit around Earth. Because of your support, our members demonstrated that highly maneuverable solar sailing is possible. Now it's time for the next chapter in the LightSail's continuing mission. We need to educate the world about the possibilities of solar sailing by sharing the remarkable story of LightSail with scientists, engineers, and space enthusiasts around the world. We're going to publish a commemorative book for your mission. It will be filled with all the best images captured by LightSail from space, as well as chapters describing the development of the mission, stories from the launch, and its technical results to help ensure that this key technology is adopted by future missions. Along with the book, we will be doing one of the most important tasks of any project. We'll be disseminating our findings in scientific journals, at conferences and other events, and we'll build a master archive of all the mission data. So every bit of information we've collected will be available to engineers, scientists and future missions anywhere. In short, there's still a lot to do with LightSail and that's where you come in. As a member of the LightSail mission team, we need your support to secure LightSail's legacy with all of these projects. Visit planetary.org/legacy to make your gift today. LightSail is your story, your success, your legacy, and it's making a valuable contribution to the future of solar sailing and space exploration. Your donation will help us continue to share the successful story of LightSail. Thank you.

Sarah Al-Ahmed: What I think is really cool about this is that, I mean, it's not surprising because you were also on the paper that Kevin was working on, but that paper suggested that Europa basically got most of its water content from the rocks itself, that the rocks, over time, dehydrated and it formed this ocean. So if that's the case, then it's okay that all the water might've gotten blown off by Jupiter because it still explains why it has an ocean, but Io doesn't, and these papers link together very well.

Carver Bierson: Yeah, it was an interesting thing where we were kind of working on both these things in parallel and realized this connection as we were going of, well, if Europa got its ocean from dehydrating these rocks, from taking water molecules that were in actually the chemical structure of these rocks, heating them up to release that water form the ocean much later on, well, Io heats up a lot faster because it's closer to Jupiter so there's a lot more tidal heating, and so maybe it dehydrates these rocks really early, essentially right as it's forming right during this initial period while Jupiter's still bright. And so you release that really early ocean and you're instantly evaporating it and losing it to space. Where Europa is farther away, it's cooler, there's not as much tidal heating. It just takes longer for everything to get going. And yeah, we're still looking at this mystery of, did Europa's ocean come from the rocks and was it squeezed out that way, or was it delivered by ices coming in and being accreted like probably most of Ganymede and Callisto's oceans come from?

Sarah Al-Ahmed: This raises an interesting scenario in my brain for Io, which is that it perhaps had ice on the surface already that then the luminosity of Jupiter and all these other effects destroyed, but maybe the rocks themselves were already hydrated, so maybe it also then formed a secondary ocean. That's a very complicated scenario. I'm not even sure it's possible, but that's really cool too.

Carver Bierson: Yeah, there may have been lots of different phases of ices being delivered to Io and lost by different processes. Maybe there was a little bit of an ice line and a little bit of Jupiter's luminosity driving stuff off. We come up with all these ideas and we tend to think of them in buckets, but they could have all been acting at the same time and all working with each other. Now the hard part is trying to figure out what actually happened and what observations we can use to try and test this.

Sarah Al-Ahmed: That is a really complicated question because as you said already, Io is a volcanically active moon that keeps resurfacing itself. So what could we do to actually figure out whether or not this was the scenario?

Carver Bierson: One of the things that I'm excited about is we have all of these upcoming missions to the different Jovian moons. We have Europa Clipper that's going to be going to Europa. We have the Juice mission from the European Space Agency that's going to Ganymede and Callisto. And if we could compare the chemistry and the isotopes in the ice, the chemical signature of these ices, we might be able to learn how similar is Europa's water and ice to that of Ganymede and Callisto? Do they look the same, meaning they're probably both accreted from ice in the system? Does Europa's look like it accreted a bunch and then lost some over time or does it look different? Does it look like it there is more of a chemical flavor that was squeezed out of the rocks in the interior? And I think that's probably the best clue that we're going to get as to what the history of Europa's ocean is, and then we can try to use that to infer what happened at Io as well.

Sarah Al-Ahmed: Unfortunately, we don't have any missions that are aimed directly at Io right now, but we've got a lot of great Jupiter missions coming up, and there are plenty of other worlds that also need missions. It's just once more I'm left with this feeling of I wish we had an orbiter around every world in the Solar System because honestly, it's going to be difficult to try to figure out what's going on with Io just inferring from the other moons.

Carver Bierson: Absolutely. There's a lot of scientists who love Iowa and are super excited about it and are always trying to get mission there because it is such an exceptional place. It is the most volcanically active world in our Solar System, and there's so much we could learn about tidal heating itself as a process, how it works and how it changes the inside of a moon and how it changes the chemistry of the rocks over time and how it creates this weird sulfur atmosphere around the moon that freezes and thaws and does all these strange things. Super interesting world, but for the time being, we're going to use these kind of adjacent observations where maybe one of these other missions will point its camera to the side briefly and give us a little bit more information of Io as we go.

Sarah Al-Ahmed: At least we're getting some Juno images of it. That's really cool. Each time we get a new Juno image of that world, I just wish we could get closer.

Carver Bierson: Yes, absolutely.

Sarah Al-Ahmed: And this is actually a really good research topic, not just for understanding our own Solar System, but as you pointed out, there are plenty of other exoplanets out there and exo moons that we need to understand, and I was just talking with someone last week particularly about the fact that most water worlds probably have subsurface oceans and a lot of that has to do with tidal heating. So this is something I really want to know more about because I want to know more about the rest of the universe, and this is the only thing we have to reference really.

Carver Bierson: Yeah, the Jovian moons in particular are just such a wonderful example of the different pads that moons around a giant planet can take. They have so much variety in their internal structures and the amount of tidal heating they have, from tons of tidal heating at Io to essentially none at the far edge in Callisto. So you have this slow gradual change in the amount, and you can see how that has impacted each of these different worlds as they evolve through time. We have Ganymede, which has a magnetic field. It's the only moon in our Solar System we know has its own internal magnetic field that it's creating, and we still don't really understand that. That's why the Juice mission is going to be so exciting to really understand what's making this magnetic field and what is that telling us about its interior.

Sarah Al-Ahmed: That world is so strange. Every time I talk about the magnetic field on Ganymede and how that interacts with Jupiter, it just gets weirder and weirder.

Carver Bierson: Absolutely.

Sarah Al-Ahmed: How did that happen? Why is it the only other place that managed to accomplish that? That's so strange.

Carver Bierson: And the fact that it's so different from its neighbor Callisto, who seems to be basically the same size and made out of basically the same stuff and is right there, but they appear to have taken very different paths and we still don't really understand why or even how different those paths work 'cause We know so little about Ganymede and Callisto.

Sarah Al-Ahmed: We've been talking primarily about the Galilean moons 'cause they're the inner moons of Jupiter and also the biggest ones. But would this early luminosity have impacts on all the other moons that we could potentially study?

Carver Bierson: Yeah, it's really easy to see here in part because Jupiter is the biggest of the giant plants in our Solar System, so it would've been the brightest. Saturn would've been much dimmer than Jupiter. And also Saturn's moons, well, they're a little bit of a mess. You have Titan in the outside and it's probably been doing its thing because it's pretty far away from Saturn, but all the inner moons look to be connected to the rings in one way or another. So whatever created Saturn's rings probably has a lot to do with what created those moons as well. They probably aren't there from the beginning right after Saturn finished forming. There's lots of ideas about some other giant moon around Saturn coming too close and getting ripped apart by Saturn's of gravity to create the rings and then a lot of these smaller moons in the interior forming out of that as well. And as we go up to the ice giants in our Solar System, it's a similar thing. Neptune has Triton, which is orbiting the wrong direction. So any moons that were there before Triton showed up have been kicked out of the system. They're gone. Triton disrupted any original moons that Neptune had. And around Uranus, well, Uranus is tilted on its side 90 degrees towards the sun, and we think that was probably from a giant impact of some sort, or at least whatever process knocked it on its side also yanked all the moons on its side, and so also completely reconfigured that system.

Sarah Al-Ahmed: Which is so weird. How do you knock both the planet and the rings? There's got to be some interesting timing there about when the rings formed versus when the planet formed. We need a mission to Uranus yesterday.

Carver Bierson: Yes, absolutely. And maybe it's all connected to this giant impact, knocks on the side and makes the moons and rings all at once. We don't know. We're still working on that. So many open questions there, but the nice thing about the Jupiter system, the Galilean satellites, is they look like the only ones that were there from right after the planet forms and are still there today for us to see without being disrupted by some big catastrophic event in the system.

Sarah Al-Ahmed: That just speaks to the chaos of the early Solar System that so many of these other bodies have been completely disturbed, and I'm glad that we have Jupiter as a reference point here because otherwise how would we make sense of any of this? Because I mean, in the case of Neptune and Triton, I'm guessing that thing was actually a Kuiper Belt object that got captured or something. It doesn't make any sense.

Carver Bierson: Yeah, it looks like it's the same size as Pluto. It looks like it's made out of all the same stuff as Pluto, and it just got a little bit too close to Neptune so it got pulled in and any moons that were there before it got captured would've been totally disrupted, maybe thrown into Neptune or thrown out of the system entirely as it got captured.

Sarah Al-Ahmed: We don't actually have a mission that's on its way to Io right now, unfortunately, but if we were to design a mission specifically to try to figure out this question, what would it need to measure? Would it even be possible?

Carver Bierson: Yeah. So if we're looking specifically at the water, it's really hard because one way or another, Io lost all of its water so there's nothing left to measure and see what happens there. So I think for trying to understand the story of the water, really going to the other moons is where you want to be and understanding their chemistry and isotopic signatures in the ice of the other moons. But I think sending a mission to Io, there's still so, so much we could learn. For Io, we still don't understand if under that rocky lid that has all the volcanoes, is there a magma ocean under there or is there just a mush with a bunch of little pockets of magma sitting on the surface connected through some sort of channels or pathways more like the Earth? This is a big debate within the community right now and a mission to Io absolutely could resolve that by looking at the gravity of Io and how it's deformed by Jupiter as it orbits. So there's tons of open questions. What's the chemistry of the lavas that are coming out of Io? What is that telling us about how long it's been active, how long it's been volcanic and the way we see it today?

Sarah Al-Ahmed: Could those emissions from volcanoes in any way tell us about the hydration of the rocks?

Carver Bierson: For Io today, because it's so volcanically active, we're pretty sure the interior is really hot to generate all of that magma and rocks that are that hot can't hold on to water molecules. So it's certainly the case that if the rocks at Io were initially hydrated, they were dehydrated long ago. It's been a long time since they had any water molecules tied up in that chemical structure. Now for Europa, Ganymede and Callisto, they could still have hydrated rocks in their interior. They're so much colder, or at least we think that they're much colder in their interior, but Io, we see all the volcanoes. That one has a hot interior, there's tons of magma down there. There's no water hanging out in those chemical structures anymore.

Sarah Al-Ahmed: That's a shame. But still, it would be worth having a mission there just to take pictures of all the space volcanoes.

Carver Bierson: Absolutely.

Sarah Al-Ahmed: I mean, anytime we get even a small glimpse of them, it is completely bonkers.

Carver Bierson: It's always a good day to take closeup images of Io because there's always volcanoes erupting all of the time, and they're huge, sending giant plumes into space. It's a absolutely gorgeous move.

Sarah Al-Ahmed: So as we're trying to figure this out, we have limited data, but are there any other factors that you can include in the models to make them more accurate?

Carver Bierson: The place where we can make them more accurate would be in the atmospheric modeling side of this. What is the detailed impact of these greenhouse effects and clouds that would be forming and how would heat be moving around because Io is tightly locked? What are the circulation patterns in the winds that you would see if there's a ocean on the surface? How is that moving heat from the hot side of Io to the cold side? And what does this mean for how much water is evaporating, how thick your atmosphere is, and how quickly it's being lost to space?

Sarah Al-Ahmed: That tidal locking really makes things more complicated on any planet or moon that we're studying. We need to know more about this, and I wish we had an example of a water world that was tightly locked up. You could just study for a hot second. Maybe with JWST, we can find one. Fingers crossed.

Carver Bierson: Yeah, people have speculated a lot about what an ice world around the M dwarf star would be, for example, what it might look like. Whether you just get a hole in the ice that looks like an eight ball or something like that where you have water facing the star all the time, or whether there's liquid water all around the equator because that warm water gets dragged around by circulation and melts things there. Or if it's really efficient at moving heat around, whether there's no ice at the surface at all, and you can keep basically water everywhere. We don't know. It's really hard to model. We don't have a clear example that we've seen to really test these different models and ideas that we have.

Sarah Al-Ahmed: I was just talking with Lujendra Ojha from Rutgers University last week specifically about these icy exo Earths around these M dwarf stars. There's so much we don't know there, but chances are there are more of those worlds with water in the subsurface than anything like Earth out there with water on the surface, just with land and water like Earth. It's so complicated, and every time I learn more about this, it just makes me so grateful that we live on this rock in particular.

Carver Bierson: Yes, we have nice clement temperatures more or less all of the time, and lots of water around unless you're here in the Phoenix Desert where I am.

Sarah Al-Ahmed: So do you have any upcoming research on this topic that you're planning to do or are you diverting most of your attention to the Psyche mission right now?

Carver Bierson: Right now I'm really focused on the psyche mission. We're getting ready for launch, which is happening in early October, and we are very excited. It's going to be a pretty long cruise to get there. The mission won't get to the Asteroid Psyche until 2029, but then we will be exploring a metal world for the first time.

Sarah Al-Ahmed: One of my coworkers is going to be going to the Psyche launch. It's going to be his first launch ever and I'm so excited for him because what a mission to say your first rocket launch was. That's such a special moment. And Psyche is such a strange world. I'm definitely going to have to have someone else come on the show to talk about that as we approach the launch 'cause we've talked about it in the past, but it's worth revisiting. A metallic asteroid like Psyche is, again, such a weird case that we got to learn more. That one is strange.

Carver Bierson: Psyche, because it's a different kind of world that we've never seen before, we don't really know what to expect, and that's what makes it so exciting. It's a mission of discovery, of going to a new class of objects that we've never seen and we don't know what we're going to find. Maybe there'll be volcanoes of metal that have frozen in time, or what do impact craters look like when they hit a metal surface? These are all things that we just don't know until we get there.

Sarah Al-Ahmed: How do you even model that? Shoot bullets at a sheet of metal and hope it's somehow analogous? Well, the only answers to go there and take pictures?

Carver Bierson: We do have members of the Psyche team shooting things into bits of metal to try and figure out what will happen. So that is being done.

Sarah Al-Ahmed: That makes me so happy to hear. Oh my gosh. Well, I want to wish you so much luck on the upcoming Psyche mission, and if there's anything that comes out of Juice or Europa Clipper, we're going to have to wait quite a while for either of them to get there, but I'm sure it'll tell us a lot about these Galilean moons, and even if it's a decade out, it'd be wonderful to have you come back on the show and tell us all about it.

Carver Bierson: Absolutely. I am eagerly awaiting all of these missions to arrive.

Sarah Al-Ahmed: Well, you've completely blown my mind Carver, and I'm sure a lot of other people out there, so thanks for completely upending my understanding of Io.

Carver Bierson: Yeah, it's a pleasure to be here.

Sarah Al-Ahmed: It's a wonder to me that no matter how much I learn about space, there's always more to study and ponder. I'll literally never think of Io the same way again. Now, let's check in with Bruce Betts, the chief scientist of The Planetary Society for what's up. Hey, Bruce.

Bruce Betts: Hey, Sarah. You've been to subsurface ocean lately?

Sarah Al-Ahmed: Oh, yeah. Yeah. I just took a trip during my three-day weekend to go to the oceans of Enceladus. No, I was playing Starfield.

Bruce Betts: Oh, well, okay. Maybe not.

Sarah Al-Ahmed: Well, a few weeks ago we were having this conversation 'cause I had Kevin Trinh from Arizona State University on to talk about Europa and its development, and he threw out there that there was this paper about Jupiter's early luminosity potentially blowing off the water on Io and its effect on Galilean moons. I brought it up to you. You're like, "Hey, get those people on the show." And I did. So mission accomplished.

Bruce Betts: Hey, nice job.

Sarah Al-Ahmed: But that's just one more reason to think of Jupiter as just totally terrifying. I know I come back to this. My love of space is so linked to my horror because just Jupiter's so big, but the idea of it being so shiny that it could literally blow the ocean off a moon and turn it into a hellscape like Io is so cool and yikes.

Bruce Betts: You're complicated.

Sarah Al-Ahmed: Aren't we all?

Bruce Betts: Yeah, most of us are. The interesting ones are anyway.

Sarah Al-Ahmed: But we got a question this week for you Bruce, from one of our members, Mason Howell from Missouri USA, wanted to know what future missions are you most excited for and how are they going to impact the scientific community?

Bruce Betts: Wow.

Sarah Al-Ahmed: Come on, try to be positive, Bruce. I believe in you.

Bruce Betts: I have a little bit of a reputation apparently. I actually am positive about this so it's actually easy for a change. You didn't ask me whether certain missions would succeed or fail. That's usually where I get in trouble. Missions I'm most excited... I'm excited about all missions. I mean, that sounds ridiculous, but it's actually true. But here, I'll start with a half negative thing. If we ever succeed in doing Mars sample-return, that's super exciting. Dragonfly, I mean, I can't believe it got funded because it will fly-

Sarah Al-Ahmed: Come on.

Bruce Betts: We can fly a drone on Titan, I never would've believed that possible, but apparently they've done a great job proving it so that's awesome. I mean, if that works... Sorry, that's the cautious side of me. That's pretty darn groovy and Titan has a lot of mysteries. So I mean, there's a lot of great stuff, just ongoing Mars missions, but in terms of doing stuff that really might give us results that are wild and new, that's certainly one of them. I feel badly because sure, I'm missing a gazillion missions that are doing great stuff. Obviously we're going back to the moon and I'm sure we can rediscover water on the moon and water on Mars a few times, so that'll be good. What about you, Sarah? What am I forgetting? Oh, we have a whole pile of Venus missions.

Sarah Al-Ahmed: Yeah, the Venus missions. I really do hope that missions like VERITAS and DAVINCI get the funding that they need. And there's so many different space agencies that are going to Venus right now, but I'm looking forward to Europa Clipper. I mean, you already claimed Dragonfly. I feel like that one is my heart song mission right now.

Bruce Betts: I'll trade you. You can have Dragonfly because I worry too much about success. Not because of anything they did, but just because of the nature of the mission, I'll take you up at Clipper because that is the one that I forgot that's very cool. And Juice mostly because it was a great acronym until for some reason ESA said they're not doing it as an acronym, but-

Sarah Al-Ahmed: Really though?

Bruce Betts: It's a mission named Juice. That's enough to make me happy.

Sarah Al-Ahmed: It's the Jupiter Icy Moons Explorer, it has a whole purpose behind the acronym. Are they just like, those moons are juicy, let's go?

Bruce Betts: Yeah, that's exactly what was in the ESA press release.

Sarah Al-Ahmed: If Sarah wrote everyone's press releases...

Bruce Betts: God, it would be so much more entertaining. We wouldn't understand anything probably. No, that's not true. But it would be way more entertaining.

Sarah Al-Ahmed: One can hope.

Bruce Betts: No, I'm sorry. I'm sorry. I'm being too flippant. Both of those missions are great going out there. Feel free to talk more about your Europa desires.

Sarah Al-Ahmed: If we're not going to be sending a mission to Enceladus right this second, I want to know more about Europa. I want to know more about what's going on with these icy covered worlds full of water. Because now that we know that there's probably just a prevalence of them all over our universe, I want to know as much as possible about them, and Europa is a good place to start.

Bruce Betts: You're still hoping some creature breaks through the ice based upon-

Sarah Al-Ahmed: Always. Always.

Bruce Betts: Yeah.

Sarah Al-Ahmed: Out there in the infinite universe, Bruce, it must be true, but in our backyard, I'm guessing it's just some microbes or something.

Bruce Betts: Yeah, odds are if it exists, it's microbes wherever you are because that's what was here for most of the history. I would be remiss in not mentioning, of course, the return of humans to the moon, which is just super exciting and excitingly dangerous and give us new views. And once you decide to fly humans, they'll do a lot of great stuff scientifically while they're on the way. I did want to answer your question what the scientific community will get out of it. The great thing about most of these missions is we don't know. That's why we're flying them. And so we don't know what we're going to learn. We know what we're studying, what we designed, what we might learn, but that's what's great about planetary exploration. Even when you've got orbiters at Mars for 20 years, you can take a look at the data in a different way when you have Apollo samples that people reanalyze 50 years later using new techniques. You can find new things. And when you're looking at I don't know, let's just say hypothetically flying around in an atmosphere of a moon of Saturn that has methane lakes, I mean, who knows what you'll find?

Sarah Al-Ahmed: Who knows?

Bruce Betts: So I was thinking we should probably do a random space fact.

Sarah Al-Ahmed: That's just a validation that you're actually a cute cartoon character.

Bruce Betts: No, I'm not. I'm definitely not. All right, I'm done. All right, so here's your random space fact. And I've toyed around with pieces of this in the long past, but I wanted to summarize. There are 10 chemical elements which are named after heavenly bodies, or at least share the naming. Most of them were actually the object in space was discovered first. There was a whole thing, so if you haven't thought about it, you got your uranium, Neptune and plutonium, but also series and palace. When they were discovered, they led to people naming things, Ceres and palladium. And then it gets a little trickier. Selenium for the Greek word for the moon, Selene. Really obscure ones, which is like phosphorus. I did not know this until I was digging in. Apparently some of the ancient cultures would categorize Venus as two different objects, one in the morning, one in the evening. One of the terms used was phosphorus or related to phosphorus from Greek phosphorus, a name applied to the planet Penis when appearing as a morning star.

Sarah Al-Ahmed: I had no idea. That's really cool.

Bruce Betts: I know. That's why I do these. So there you go.

Sarah Al-Ahmed: Yeah. And of course there's the bonus fact, helium for Helios.

Bruce Betts: Sorry, I meant to mention that.

Sarah Al-Ahmed: But it's not a planet though. The sun is not a planet, so it doesn't count.

Bruce Betts: What? No, and again, I try not to at least fully repeat anything, but one of the really cool facts that I've used and you probably know, is that helium was first discovered on the sun actually quite a number of years before it was ever discovered on Earth. They had spectral lines of the sun that no one recognized, and it took a while. And because of that, they named it... They actually had a real reason for naming that after Helios, the Greek word tied to the sun because they first discovered it on the sun, which was not true. They did not first discover plutonium on Pluto, FYI.

Sarah Al-Ahmed: Where's that mission in our history books? That would be fascinating.

Bruce Betts: We can't discuss that on here.

Sarah Al-Ahmed: Secrets. Yeah, it's pretty funny. I feel like helium had this beautiful, just majestic origin and now we use it to fill party balloons.

Bruce Betts: Dude, party balloons make a lot of people happy.

Sarah Al-Ahmed: This is true. I spent a lot of time with balloons in college, but mostly just sticking them into vats of liquid nitrogen.

Bruce Betts: So here's a story you can keep or throw out. When I was a physics undergrad at Stanford up in the upper division part, they asked for a volunteer to help out with demonstrations for the intro physics. And that's where I learned how to pseudo drink liquid nitrogen, which we do not recommend.

Sarah Al-Ahmed: Here at The Planetary Society, we do not condone drinking liquid nitrogen. Just have to say that.

Bruce Betts: But it looks impressive. And the professor, unbeknownst to me, introduced me as, this is Bruce, he's an undergrad so we actually don't care what happens to him, and he's going to demonstrate because graduate students actually do research for him. All right, there you are.

Sarah Al-Ahmed: Academia. All right, let's close out there.

Bruce Betts: All right, everybody go out there, look up at the night sky and think about what fun things you'd like to do with liquid nitrogen. Thank you. Good night.

Sarah Al-Ahmed: We've reached the end of this week's episode of Planetary Radio, but we'll be back next week with a very special guest, Planetary Society co-founder, Louis Friedman. He'll talk all about his new book, Alone But Not Lonely: Exploring for Extraterrestrial Life. You can help others discover the passion, beauty, and joy of space science and exploration by leaving a review and a rating on platforms like Apple Podcast. Your feedback not only brightens our day, but helps other curious minds find their place in space through Planetary Radio. You can also send us your space thoughts, questions, and poetry at our email at [email protected]. Or if you're a Planetary Society member, leave a comment in the Planetary Radio space in our member community app. Planetary Radio is produced by The Planetary Society in Pasadena, California and is made possible by our luminous members. You can join us as we continue to advocate for more mind-blowing missions to Jupiter and its moons at planetary.org/ join. Mark Hilverda and Rae Paoletta are our associate producers. Andrew Lucas is our audio editor, Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. And until next week, ad astra.