Planetary Radio: Space Exploration, Astronomy and Science - Io and Voyager 2: Lost oceans and found signals

Episode Date: September 13, 2023

This week on Planetary Radio, we're traveling back in time to uncover the luminous infancy of Jupiter and its impact on its enigmatic moon, Io. Carver Bierson, a postdoctoral researcher at Arizona State University, tells the tale of how Jupiter's radiant beginnings might have turned Io from a water-rich moon into a world with lakes of lava. You'll also hear from two legendary figures of space exploration, Voyager project manager Suzanne Dodd and Voyager project scientist Linda Spilker, as they delve into the endeavor to reestablish contact with the iconic Voyager 2 spacecraft with our senior communications advisor, Mat Kaplan. And don't miss "What's Up" with our chief scientist, Bruce Betts, as he answers a question from our Planetary Society member community. Discover more at: https://www.planetary.org/planetary-radio/2023-lost-oceans-and-found-signals See omnystudio.com/listener for privacy information.

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 Beerson, 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, Matt 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 re-established 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 Matt Kaplan, now Senior Communications Advisor, has been following the twin Voyager spacecraft since before their launch. He called on Voyager project manager Suzanne or Susie 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.

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 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 have 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. We would send it with the highest power available to us, which is the S-band 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. But I guess when you're 18 and a half light hours from home or like almost 12 and a half billion miles, that still made it pretty much a long shot. Right. It did make it a long shot for sure. That still made it pretty much a long shot. Right. It did make it a long shot for sure. 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 sort of that tone that let us know, yes, I'm still here. So 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. Yeah, it's about 22 watts. 22 watts. A dim light bulb. A dim, incandescent light bulb. The quote that we've used for years. So yeah. Susie, you're not just the Voyager project manager. You can 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. You know, 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. from Voyager 1 and Voyager 2. So it's a great synergy for me personally.

I'm also thinking of the reaction around the world because everybody took notice when this problem, first surface, 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. It's amazing, Matt. I was walking down the street and one of my neighbors said,

hey, how's Voyager doing? And 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. I echo that. I get, you know, 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 get 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. I don't blame you. Absolutely. Yeah. And Matt, 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. 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? For senior citizens, they're both pretty healthy. They each have their own ailments, but really, in human years, a spacecraft might be more like 100 than 46, you know, double it kind of thing. But they're healthy. They're showing some signs. On Voyager 1 in particular, we're watching the thrusters closely now. starting to show more thruster firings and then we'd like to see sort of a clogged artery syndrome type thing, not being able to get as much for the pulses on the thrusters. So that's becoming

a concern for us. 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, the local interstellar cloud, there's some unique information there as well. You know, 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. Thank you so much for having us, Matt. Yes, thank you very much, Matt. Go Voyager. Go Voyager. You can hear Matt's complete conversation with Susie and Linda on this week's show page at planetary.org slash 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 Beerson, 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 14, 2023. Hi, Carver. Hello. 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. Yeah, really excited to be here. 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 like a hundred times brighter than it is today, early on, a hundred times brighter than it is today, early on. That seems like very, very shiny. How did that happen? Yeah, so the Jovian system as Jupiter's forming 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 the sun. Well, Jupiter had its own disk 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 disk 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 disk 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. When in the timeline of the solar system would it have reached this peak luminosity? 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 disk of gas and dust around the Sun is just being blown away. The 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 and creeps to get any bigger. And so it is bright and hot from all this new material it's created and will be shining that

light directly on the nearby moons. 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 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? 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 has 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. It would be warm. 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. Yes, Io is a wonderful world. It's so amazing. You have these lakes of lava, and at the same time, it's super cold today, too. It's 100 Kelvin, so something like minus 300 degrees Fahrenheit, thereabouts. And there's sulfur ices on the surface because there's so much volcanic outgassing of like sulfur dioxide, sulfur oxides. Those turn into ices essentially

freeze onto the cliffs. 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. 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. 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?

You know, we see this trend of Io being really rocky, close to Jupiter. Europa is mostly rock, a little farther away. And then Gamma and Callisto are like 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 like 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 like separate out materials. 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 around after that formation, this luminosity from Jupiter could help drive that off. As that liquid water sits on 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. 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?

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 disk and how thick it was. And it probably was blocking that really early heat from Jupiter. how thick it was, and it probably was blocking that really early heat from Jupiter. But kind of 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 disk, and we know you were

because 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 it in this period right after that dust and gas goes away. And it's the luminosity from Jupiter itself driving it off. There's so many things to consider here, because if these worlds were covered in ice, they start puffing up and outgassing all this water.

I'm sure there's a point at which the greenhouse effect comes into play as well, and that's got to complicate it even further. 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 tidally 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, 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, because 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 atmosphere basically even everything out or not? There's so many excellent questions about these early times and how different things interact with each other. Yeah, 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. Yeah, 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 have 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. 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. 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 of 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 Io really did, if it accreted at this ice, it had to get rid of it really early on. And that's why Jupiter's early luminosity might be a good way of explaining that. 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. Io 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? It wouldn't have been very long. The number one thing you need to hang on to an atmosphere is gravity. You have to have the gravity to hold on to 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 on to 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 billion years, hundreds of thousands of years, something like that. It would be a very short period of time, geologically speaking. Well, you know, if anybody has a time machine, that would be a really cool thing to go see. Absolutely. As I was reading your paper, there was a lot of indication that it was

like 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? 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, right? 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 Cluster still hang on to 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.

We'll be right back with the rest of my interview with Carver Beerson after this short break. 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.

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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. What I think is really cool about this is that it, 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 maybe might have 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. Yeah, it was an interesting thing where we were kind of working on both these things in parallel and realized this connection as we're 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 bright as it's forming right during this initial

period while Jupiter is 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 like, 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?

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. Yeah. And 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 like trying to figure out what actually happened and what observations we can use to try and test this. 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? 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 kind of chemical signature of these ices, we might be able to learn how similar is Europa's water and ice to that of Ganymede and Clisto. 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 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. 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. Absolutely. There's a lot of scientists who love Io 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, you know, point its camera to the side briefly, give us a little bit more information of Io as we go.

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, it's, I just wish we could get closer, you know? Yes, absolutely. 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 exomoons 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. Yeah, the Jochia moons in particular are just such like a wonderful example of the different paths 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 amounts, and you can see how that is 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 that 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. Get 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. Absolutely. How did that happen? Why is it the only other place that managed to accomplish that? That's so strange. 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 were because we know so little about Ganymede and Callisto. We've been talking primarily about the Galilean moons because 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? Yeah, this is really easy to see here in part because Jupiter is the biggest of the giant planets in our solar system. So it would have been the brightest. Saturn would have 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, you know, 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, you know, 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 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, the outer solar system, it's a similar thing.

You know, 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. 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. Yes, absolutely. And maybe it's all connected of

this giant impact knocks it outside and makes the moons and rings all at once. We don't know. We're still working on that. You know, 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 like 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. 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? I mean, in the case of Neptune

and Triton, like I'm guessing that thing was actually a Kuiper belt object that got captured or something. It doesn't make any sense. Yeah, it looks like, you know, it's the same size as Pluto. It looks like it's made out of the same stuff as Pluto and just got a little bit too close to Neptune. So it got pulled in.

And yeah, any moons that were there before it got captured would have been totally disrupted, maybe thrown into Neptune or thrown out of the system entirely as it got captured. 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? out this question, what would it need to measure? Would it even be possible? 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, like, how long it's been active, how long it's been volcanic in the way we see it today? Could those emissions from volcanoes in any way tell us about the hydration of the rocks? 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, Callisto, they could still have hydrated rocks in their interior because they're so much colder, or at least we think that they're much colder in their interiors. But Io, we see all the volcanoes. That moon has a hot interior. There's tons of magma down there. There's no water hanging out in those chemical structures anymore. That's a shame. But still, it would be worth having a mission there just to take pictures of all the space volcanoes. Absolutely. I mean, anytime we

get even a small glimpse of them, it is completely bonkers. It's always a good day to take close-up images of Io because there's always volcanoes erupting all of the time. And they're huge, sending giant plumes into space. It's an absolutely gorgeous moon. So as we're trying to figure this out, you know, we have limited data, but are there any other factors that you can include in the models to make them more accurate? The place where we can make them more accurate would be in the atmospheric modeling side of this. You know, 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 tidally locked? What are the

circulation patterns in the winds that you would see? If there's an 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? how thick your atmosphere is, and how quickly it's being lost to space. 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 tidally locked up. We could just study for a hot second. Maybe with JWST, we can find one. Fingers crossed. Maybe with JWST we can find one.

Fingers crossed. Yeah, people have speculated a lot about what an ice world around an in-dwarf star would be, for example. And what it might look like. Whether you just get like a hole in the ice that looks like an eight ball or something like that. Or 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 just, 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. I was just talking with Luzendra Oja 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. Yes, we have nice climate temperatures, more or less, all of the time. And lots of water around, unless you're here in the Phoenix desert where I

am. 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? Yeah, 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 will get to the asteroid Psyche until 2029. But then we will be exploring a metal world for the first time. Yeah, one of my co-workers 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. Because 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've got to learn more. That one is strange. Yeah, 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. 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. Right. How do you even model that? Shoot bullets at a sheet of metal and hope it's somehow analogous? What would the only answer is to go there and take pictures. 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. 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. Absolutely. I am eagerly awaiting all of these missions to arrive. 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. Yeah, it's a pleasure to be here. 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. Hey, Sarah. You been to Subsurface Ocean lately? 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. Oh, okay. Maybe in that. Yeah. But a few weeks ago, we were having this conversation because I had Kevin Trin 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.

Hey, nice job. But that's just one more reason to think of Jupiter as just totally terrifying. I know I come back to this. Like my, my love of space is so linked to my, my horror because just Jupiter is 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. You're complicated. Aren't we all? Yeah, most of us are. The interesting ones are anyway. But we got a question this week for you, Bruce, from one of our members. Uh-oh.

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? Wow. Come on, try to be positive, Bruce. I believe in you. 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 about. I'm excited about all missions. I mean, that sounds ridiculous, but it's actually true. But let's – here, I'll start with the 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 we're going to fly a drone on Titan. I never would have believed that possible, but apparently they've done a great job proving it. So that's awesome i mean that if that works

there sorry that's the cautious side of me that that's pretty pretty darn groovy and titan has a lot of uh 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 will might give us results that are wild and new. That's certainly one of them. I feel badly because I'm sure I'm missing a gazillion missions that are doing great stuff. Obviously, we're going back to the moon. 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. Yeah, the Venus missions. I really do hope that missions like Veritas and DaVinci get their 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 dragon fly. I feel like that one is my heart song mission right now. I'll trade you.

You can have dragon fly. Cause I worry too much about, you know, success, not because of anything they did, but just because of the nature of the mission. And I'll take your up a clipper. All right.

That is the one that I forgot. That's very cool. And, and a juice mostly because uh it was a great acronym until for some reason isa said it's they're not doing it as an acronym but really though it's my mission name juice that's enough to make me happy the jupiter icy moons explorer like it has a whole a whole purpose behind the acronym. Are they just like, you know, those moons are juicy. Let's go.

That's exactly what was in the ESA press release. If Sarah wrote everyone's press releases. 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. One can hope. No, I'm sorry. I'm sorry. I'm being too flippant. Both of those missions are great going out there. Feel free 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, you know, I want to know as much as possible about them. And Europa is a good place to start. You're still hoping some creature breaks through the ice based upon it. Always. Always. Yeah. Out there in the infinite universe, Bruce, it must be true. But, you know, in our backyard, I'm guessing it's just some microbes or something. Yeah. Odds are, if it exists, it's microbes wherever you are,

because that's what it was here for most of 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're 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 flying, 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? Who knows? So I was thinking we should probably do a random space fact. You know, that's just a validation that you're actually a cute cartoon character.

No, I'm not. No, I'm definitely not. All right. I'm done. All right. So here's your random space fact. And I I've, I've toyed around with pieces of this in the past, long past. But I wanted to summarize. There are 10 elements, 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,

neptunium, and plutonium, but also ceres and pallas when they were discovered. They led to people naming things cerium 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 Venus when appearing as a morning star. I had no idea. That's really cool. I know that's why I do these. So there you go. Yeah. And of course, there's the bonus fact, helium for Helios. Sorry, I meant to mention that.

But, you know, it's not a planet, though. You know, the sun is not a planet, so it doesn't count. What? No, and I try not to at least fully repeat anything. But one of the really cool facts that I've used and that 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 name reason for naming that after it 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. Where's that mission in our history books? That would be fascinating.

We can't discuss that on there. 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. So, yeah. Dude, party balloons make a lot of people happy. This is true. I spent a lot of time with balloons in college, but mostly just sticking them into vats of liquid nitrogen. 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. Here at the Planetary Society, we do not condone drinking liquid nitrogen. Just had to say that. 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, you know, graduate students actually do research for him. All right. Academia. All right. Let's close out there. 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. 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.

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