Volcanic worlds across the Solar System

Sarah Al-Ahmed: We are chasing eruptions across the Solar 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. You might picture lava rivers and fire when you think of volcanoes, but what if they spewed snow, metal, or even methane? In this special compilation episode, we'll explore volcanic activity around the Solar System from the basalt flows of Venus, to the mysterious heat still rising from distant dwarf planets like Eris and Makemake. Along the way, you'll hear excerpts from my conversations and from those of my predecessor Mat Kaplan, who created Planetary Radio and hosted the show for 20 years. He's now our senior communications advisor at the Planetary Society. Together with planetary volcanologists, geochemists and atmospheric scientists, we'll explore the powerful processes that shape worlds, even when they're frozen or long thought dead. Then our chief scientist, Dr. Bruce Betts will join us for What's Up and a look at recent Juno mission results from its close passes by Jupiter's moon Io. 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. Let's start where volcanism is at its most extreme, on Jupiter's moon Io. Back in February 2003, Mat Kaplan spoke with Dr. Rosaly Lopes, who at the time was a senior research scientist and manager for Planetary Science at NASA's Jet Propulsion Laboratory. She walked us through the relentless volcanic fury of Io, the most geologically active world in our Solar System.

Mat Kaplan: Rosaly, first of all, thanks for being here.

Rosaly Lopes: You're welcome.

Mat Kaplan: Tell us why in roughly 1979, when Voyager made its flyby of the planet Jupiter, this odd moon Io came to be called the Pizza Moon.

Rosaly Lopes: Well, when Voyager first flew by Io, the scientists in the imaging team who were looking at the images of Io were very puzzled. Io seemed just about the strangest object they had ever seen in the Solar System. Io is a moon about the size of our Earth's moon, but its colors are very strange, lots of oranges and yellows and blacks. And one of the scientists said, "It looks like a pepperoni pizza."

Mat Kaplan: And it stuck.

Rosaly Lopes: And it stuck. And one of the surprises was that Io didn't have any impact craters. Now, if you look at the moons of the Solar System, because there are meteorites and asteroids around in the Solar System peppered with craters, and if there are not any craters there, it is because something has obliterated them. Some other process has wiped out those craters. So at first the mystery was, what had caused those craters to disappear that should have been there.

Mat Kaplan: And they quickly came to realize that there were active volcanoes on this little moon, lots of them,

Rosaly Lopes: Yes. In fact, the discovery was made by Linda Morabito, who was a member of the navigation team, and she looked at one of the images of Io taken for navigation purposes because we used the cameras on the spacecraft also to help navigation. And she noticed an umbrella-shaped plume on the side of Io and thought this may be an erupting volcano. When one of the other instruments on that spacecraft, looking at infrared wavelengths detected some heat that coincided with one of the plumes, it became quite clear that active volcanoes were around. And they found about a dozen plumes and about a dozen hot spots, as they called them, the active volcanoes. And it became clear that this moon had active volcanism. And this is so important because Io is the first place outside Earth where we have actually seen active volcanoes.

Mat Kaplan: And I think, you said all the colors of this odd-looking moon. I think it's beautiful. I think it's quite a place, and of course it's changing all the time.

Rosaly Lopes: Yes, Io is a real cartographer's nightmare. People start making maps of Io and then it changes, and it even changed during the two Voyager flybys that were only four months apart, particularly the deposit from one of Io's largest plumes called Pele actually changed in shape, went from being heart-shaped to circular, so there were noticeable changes even in four months.

Mat Kaplan: So we had this tantalizing couple of looks at this amazing little moon, and then the Voyager spacecraft flew on and a lot of years went by, as folks like you, scientists, you in particular as a volcanologist, must have been going crazy waiting for the next visit, which of course was Galileo.

Rosaly Lopes: Yes. And the Galileo launch was delayed and the Galileo mission only finally got off the ground in 1989, and it had a long flyby around the Solar System to get to Jupiter, it had gravity assists at Venus and at Earth, and we finally got to Jupiter in 1995. Got into orbit around Jupiter and then started looking at Io in the middle of 1996, but it was worth the wait. There were a number of surprises, but of course there had been changes as we had expected in the years between Voyager and Galileo. Io had in fact been observed from Earth, from Earth-based telescopes, and the most violent eruptions could be detected from Earth at infrared wavelengths. So we knew that a lot of activity was still going on, and particularly from a volcano called Loki. But in fact where we saw some big surface changes in some places, Loki looked pretty much the same as it had during the time of Voyager. So there were places with a lot of changes on the surface and places where there had been a lot of volcanic activity, but the activity was confined within a big volcanic crater that we call a caldera. So it was also surprising that some places where we expected big changes, we didn't find them.

Mat Kaplan: I love these names by the way, Pele and Loki and another one that's going to come up later in our conversation. Tvashtar, am I pronouncing it correctly?

Rosaly Lopes: Yes, yes. Those are all after Gods and heroes related to fire and volcanoes and thunder. In fact, I suggested the name to the International Astronomical Union. In fact, a couple of names, Tupan and Monan, and they were accepted as names of volcanoes. And these names come from Brazilian native mythology from my native country. And so I was very pleased that those were accepted.

Mat Kaplan: You must be very proud. I would be if I had a volcano out there near Jupiter that I had named. Let's talk about what else Galileo learned. We have these spectacular images which can be seen on The Planetary Society website and also at the JPL site where you work, but there were other instruments on Galileo, some of which created images, some didn't. One that you worked on was this instrument that worked in the infrared rather than the visible range of light or light wavelengths.

Rosaly Lopes: Yes. I worked with NIMS, which is the Near Infrared Mapping Spectrometer, and it turned out to be extremely exciting because in the infrared wavelengths, you can detect heat from the volcanoes. So we were able to discover many new volcanoes on Io active volcanoes, and that was pretty exciting for me. I was always the first person to analyze those infrared images and to detect all those volcanoes. I think I detected over 40 new ones after a while I stopped counting. But just to say, oh, that's another active volcano, another active volcano, and it was really very exciting. And we worked very well with the imaging team because it was a lot harder for them to tell if something was actually active or not. They could only tell it if they had observed Io in eclipse from Jupiter when it was totally dark, and then that one micron, using a one micron filter, they could detect high temperatures, but we could detect lower temperatures and we could detect heat even when Io was in reflected sunlight.

Mat Kaplan: And one micron being reference to filtering the wavelengths of visible light that they could make out?

Rosaly Lopes: That's right, yes.

Mat Kaplan: So really the instruments, even though it does sometimes seem like the visible light images get all the attention, all of the instruments on the spacecraft work together to paint the picture.

Rosaly Lopes: Yes, and in fact, one of the eye of close flybys, it was quite interesting. The imaging team detected a plume and they expected it to be coming from a volcano called Tvashtar, which is a very active volcano, and we had detected a major eruption from there. And then analyzing the images and doing the geometry of the plume, they figured out it didn't quite fit the location of Tvashtar, but it was fairly close and they were making some tentative identifications when I received an infrared image, a new one, it was downlinked and I saw this great thermal emission in the infrared from a new volcano. At least one that we had never seen to be active before. And so I told my colleagues on the imaging team, "I know where your plume's coming from."

Mat Kaplan: Before we leave the topic of that, hot topic of that hot little moon, do we now understand why Io is so beautiful, why it has all those amazing colors you talked about a few minutes ago?

Rosaly Lopes: We think there is a lot of sulfur on Io and that's what it gives these colors, the oranges and the reds, they are different forms of sulfur. We also understand a lot more about Io now than we did at the time of Voyager. We know that there are many more active volcanoes than we knew about from Voyager. We knew of about a dozen after the Voyager flybys, and now we know there are more than 120. So Io is really literally covered with active volcanoes, and we also seen something very interesting on Io. We detected lavas hotter than any lava that we see on Earth today. And these lavas are similar, we think, to lavas we call komatiites, that geologists call komatiites. They are very ancient, primitive lavas on Earth. So in a way, studying Io is like looking at the Earth billions of years ago, and that was unexpected and very interesting for us.

Mat Kaplan: Fascinating, and I think that we also think we understand now why this moon turns out to be so unexpectedly active.

Rosaly Lopes: Yes. Io is located between Jupiter, which has of course a huge gravitational attraction, being a very large planet and other large moons that we call the Galilean satellites, Io, Europa, Ganymede, and Callisto are called Galilean satellites because they were discovered by Galileo with his telescope. And Io is in a very peculiar orbit, so it's being pulled on one side by Jupiter and on the other side by the other moons. You can imagine it in a simple way as a tug of war, and that generates tides on the surface, actually in the crust, which would be like ocean tides, except that the whole crust is suffering them. And that generates friction and heat, and that's what keeps the interior molten. If it wasn't for that peculiar orbit, Io would've cooled a long time ago very much like our own Earth's moon.

Mat Kaplan: Well, I guess we should be glad it hasn't because it certainly would be less interesting.

Rosaly Lopes: Right on.

Mat Kaplan: We mentioned, of course, you can't go to Io, you've done the next best thing, but you have been to many volcanoes here on Earth.

Rosaly Lopes: Yes. I started studying volcanoes in 1979, and I have been to many of the Earth's volcanoes and I particularly like active volcanoes, so I did a lot of my PhD work on Mount Etna in Sicily. I worked at Vesuvius and I've been to Hawaii and a bunch of times in Iceland and Martinique and Montserrat and a number of other volcanoes. And I think active volcanoes are just the most fascinating places on Earth.

Mat Kaplan: Well, you're not alone, obviously a lot of the public feels that way. But I wonder, and you started to talk about this, you talked about those very hot forms of lava that seem to still be active in the volcanoes on Io and how this appears to be much like these ancient lava beds on Earth. Are we learning more? I mean, what has Io told us about volcanic activity here at home?

Rosaly Lopes: Well, when we look at volcanic activity on a different planet, the nice thing is that we can see how volcanic eruptions work under very different environments. For example, here on Earth, you can go to one volcano and then another volcano that has a different composition of the lava, but you can't change things like the gravity or the thickness of the crust, and you can't change the composition of the lava that much. Some of these really hot lavas on Earth have been dead for a long, long time. So when we look at volcanoes on Earth, we try to figure out the physics of volcanic eruptions, and it's actually very useful to be able to look at the eruptions on another planet and test out what we are seeing on Earth and test out some of our theories, how lava flows evolve, how volcanic plumes evolve. And Io is certainly an extreme environment. Also, it has no atmosphere, so it is almost a different discipline of actually looking, for example, at explosive volcanism in a vacuum. It's very, very different. So we call it a natural laboratory. It's like setting up different conditions somewhere else, so that makes it quite fascinating.

Sarah Al-Ahmed: From the lava fountains of Io, we move to a world that was once believed to be geologically dead, Mars. In December 2016, Mat spoke with Dr. Nick Schneider, then an associate professor at the University of Colorado Boulder and part of the MAVEN science team. He described how Mars is towering volcanic peaks, like Olympus Mons, continue to shape the planet's atmosphere and weather.

Nick Schneider: So this video that we've produced takes a handful of MAVEN images as the planet rotates, and now the Mars day is pretty similar to the Earth day, close to 24 hours. Here's the scene. The animation starts with just the hint of those incredible volcanic mountains on Mars, which are tens of kilometers tall.

Mat Kaplan: Like Olympus Mons.

Nick Schneider: Olympus Mons, and there's a set of three right in a row, and as the video progresses, those rotate onto the disk and they each start with the tiniest white dot of cloud, and over the span of seven hours, those clouds grow and grow and grow, so that by the time sunset comes around and we have this image as they're sort of fading into twilight, those tiny dots of clouds have just merged into this cloud bank, which is literally 1000 miles across. Now, this is not a foreign phenomenon. This happens everywhere in-

Mat Kaplan: Oh yeah. I was going to say, I've seen it around Denali in Alaska

Nick Schneider: And we see it in Colorado all the time. First of all, orographic clouds, really common phenomenon. The air has a little bit of moisture in it, and as it passes over a mountaintop, the air gets carried upwards where it's cooler and that's enough to cause condensation and to make a cloud. You might not have looked at clouds in this sense, but anytime you see a cloud over a mountain and you know the wind is blowing, an ice crystal, usually, is forming and is being carried over the top of the mountain or the volcano and then it's being carried downwards and evaporates. Those are just a transient phase in the wind.

Mat Kaplan: And I don't have to go to Alaska. I mean we see the cloud banks up against the mountains right behind us here in the San Gabriels above Pasadena.

Nick Schneider: Right. And in Colorado, we have afternoon thunderstorms, sometimes every day in the summer, and that's the same thing. You get the heat of the day, the buildup, you get this convection that again raises the air to higher altitudes, lower temperatures and the clouds form. And so this combined effect, I see it all the time here on the Earth and there it is happening on Mars. I watched that and home away from home I guess would be the sense that I got.

Mat Kaplan: So I mentioned Olympus Mons, tallest mountain in the game in the Solar System, which literally stands out in the photos that you showed.

Nick Schneider: Isn't that remarkable?

Mat Kaplan: Yeah.

Nick Schneider: So the number I carry in my head is 30 kilometers for the height of Olympus Mons.

Mat Kaplan: Sounds right.

Nick Schneider: And a typical atmospheric scale height is in the neighborhood of 10 kilometers. And that means at the top of Olympus Mons, the math would say you're down by a factor of E cubes. My son could do that in his head. But at any rate, yes, the top of Olympus Mons is sticking up through the atmosphere and because that atmosphere is so strongly scattering, really scattering, same thing that makes our sky blue. In these pictures, Olympus Mons looks black against this fuzzy, hazy planet because we are seeing its dark basalts rock surface hanging out there up above the atmosphere.

Mat Kaplan: Basically in space. This is why the author Kim Stanley Robinson put the planet side of his space elevator on top of Olympus Mons.

Nick Schneider: Of course, of course.

Sarah Al-Ahmed: Not all volcanoes are molten, some erupt with ice, salt and other chemicals. In January 2022, my colleague Rae Paoletta, our director of content and engagement for The Planetary Society, joined Mat to talk about the strange snow-like materials being ejected from some of the coldest corners of our Solar System. Her article called, Meet the Snow Worlds, explored phenomena like Enceladus's cryovolcanic plumes and even heavy metal snow on Venus.

Mat Kaplan: Rae, welcome back to the show. Got any snow outside your window there?

Rae Paoletta: It's melted now, but the few times I've taken my dog out in the last 24 hours, we've been getting some sprinkles, some dusting for sure.

Mat Kaplan: You know, I'm a Southern California boy, born and raised, and so I have to travel to be in the snow, usually not too far, certainly not as far as Mars or Io or any of these other places that you wrote about in this great January 24th article. It's up at planetary.org and it is fascinating to read about that fluffy stuff coming down around the Solar System, though I guess some of it you probably wouldn't want to take a bite out of.

Rae Paoletta: Yeah, I'm thinking that maybe the heavy metal snow on Venus might not be the best place to go skiing.

Mat Kaplan: I was reading about that and with apologies to Frank Zappa, watch out where those canoes blow and don't you eat that multicolored snow?

Rae Paoletta: From the snow canoe if we want to keep the rhyme up too.

Mat Kaplan: Yeah, I'm thinking also of Io, I didn't really expect to read about snow there.

Rae Paoletta: Isn't that wild? What doesn't Io have? I know I say that in the piece, but I think about this all the time. It's got hundreds of volcanoes and then you have this wild snow, that's been detected now many, many times and it's coming from potentially these volcanoes, which just blows my mind because volcanoes are super hot and snow is not, so it really does blow my mind.

Mat Kaplan: So you cover Mars as well, but I want to go back to what you mentioned a moment ago and that was Venus because of the speculation still about volcanoes there, that maybe there's this interesting material or element spewing out that's changing the look of the planet.

Rae Paoletta: It's cool because it is kind of a mystery that goes back all the way to 1989 with Magellan. It picked up that there were some strange unexplained brightness coming off of Venus, and since then, all these different elements have been thrown out, you know what could be causing this? As well as some unexplained dark regions. Some scientists might have thought it was something called tellurium, but now others think that it could be lead sulfide, which is pretty incredible. It is literally heavy metal and Venus does everything pretty heavy metal, so that would be fitting in a metaphorical sense as well.

Mat Kaplan: One more stop, Enceladus. You talked to another friend of the show, I mean you talked to Tanya Harrison too, who's been heard on the show. But Sarah Hörst talked to you about what's going on with those geysers that we've seen up there, and I guess Enceladus likes to spread the snow around.

Rae Paoletta: Oh my gosh, I think this is one of my favorite parts of the whole piece, was learning about this so-called snow cannon from Enceladus. Basically, Enceladus gets this quote unquote "snow", but it's not just enough that Enceladus can get the sprinkling. It's also so powerful that it gets to some of Saturn's other moons as well. So I just love that Enceladus is spreading the wintry vibes all around.

Mat Kaplan: There's more that makes this special. It's the whole look of the piece, which is like nothing that I've seen anyway that we've done on our website, and it includes, well, you talk about these great little animated GIFs.

Rae Paoletta: Yeah, no, I love the pixelated art that we did. It almost looks like a video game and Sam Marcus, the artist who designed this, is so talented. Definitely check out some of his other work. I think we'll be linking to the GIPHY, so that you can share the GIFs all over the internet. I just can't get enough of it. I especially love Enceladus and Io.

Mat Kaplan: They are really, really fun. And we'll put the link up to our GIPHY site as well. Rae, great piece and thanks for coming back on the show to talk about making snow all over the Solar System.

Rae Paoletta: Let it snow. Always a pleasure. Thanks Mat.

Sarah Al-Ahmed: We'll be right back after the short break.

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Sarah Al-Ahmed: Venus may have a hellish surface, but for decades we weren't sure if it was still geologically active. We got more evidence of that in 2023. On our March 29th episode, we featured Dr. Robbie Herrick, who was then a research professor at the University of Alaska Fairbanks and Dr. Scott Hensley, a senior research scientist at NASA's JPL. They just discovered compelling evidence of recent volcanic activity on Venus, using decades old Magellan radar data in a whole new way. Hi, Robbie and Scott.

Robbie Herrick: Thank you for having us.

Scott Hensley: Nice to be here.

Sarah Al-Ahmed: So you've just released a new paper that's about surface changes on Venus and it's gotten a lot of attention among the planetary science community. Even our guest last week, Lindy Elkins-Tanton, who was the PI for the Psyche mission, brought up this research because she was so excited about it. So what has your experience been like since this finding was released to the world?

Robbie Herrick: Sure. I thought it was a pretty important result and that it would get some press. I've kind of been overwhelmed with how widespread the coverage is and trying to soak in my 15 minutes of fame so to speak, and it's been pretty thrilling. I got to do interviews live on TV and radio around the world, and I'm glad that there's renewing some excitement about Venus. Of course, there was a lot of excitement when these upcoming missions were selected a year or so ago as well.

Sarah Al-Ahmed: How about you, Scott? What's the last week been like?

Scott Hensley: It's been very nice to see all the interest in the result, first of all, and that's both from professional colleagues and from the general public alike. It's been really great to hear the excitement overall in the community. It's been really great for me as being a member of both the two of the upcoming Venus missions, to see them being brought back to the forefront again and the excitement about people going back to Venus.

Sarah Al-Ahmed: Why is Venus such a challenging place to research? And why is there so much disagreement and predictions on volcanic activity on this planet?

Robbie Herrick: It's particularly challenging to study from the surface simply because the temperature is, I think around 850 Fahrenheit, 450 C. The former Soviet Union landed a handful of landers which lasted a maximum a couple of hours, and even then it's still quite difficult to do things. And so what that has meant is that the science that has been able to be done from the surface is very limited because of your time limit. And not only is it an issue of the time on your surface, but the nature of the conditions are such that even if you can deal with keeping your instruments cool or functioning, there's also the issue of the power source and that if you're trying to do things right now, we don't have a setup where you could use solar power from the surface. And there's a whole other set of issues trying to use something like nuclear power. And so even if you can get things to survive, you're still going to end up battery-limited on doing things on the surface. From orbit, Synthetic Aperture Radar can see through the clouds without a problem. And so that's a great tool. A whole bunch of other stuff has a lot of problems seeing through the atmosphere. If you look at Venus through a telescope, it looks like a fairly featureless yellow blob, and if you fly right and put yourself right in orbit around it, it will still look like a featureless yellow blob in visible light. And then even in kind of shorter wavelengths and radar, where you can partially see through the clouds, that very dense atmosphere is refracting a lot of the light and dispersing it. And so even though, for instance, there's a window where you can see through the atmosphere and the infrared, that scattering of light by the dense atmosphere makes the resolution that you can get very low. You do have some options for say, floating around in the clouds at maybe 30 or 40 kilometers upwards. Other than having sulfuric acid in the atmosphere, which is not too terribly difficult to deal with, but getting a balloon into the clouds is still a major challenge. So that makes the challenges pretty acute in terms of getting there. What Magellan revealed, in very short terms, is that Venus, and it should be this way, Venus, because it's roughly the same sizes, or it has a similar amount of diversity in terms of the volcanic and tectonic structures that you see, so much more so than say Mars or the moon. So there are true mountain ranges on the surface of Venus. There's a huge variety of volcanic landforms, there's gigantic rift systems, plenty of evidence of things erupting and moving around on the surface. But we don't see things like the organized system of mid-ocean ridges that we have on Earth. There might be a few things that look like arcs of subduction zones. And we also don't see something, like on Earth, where you can take high-standing landforms and piece them back together, like say Africa and South America and get the feeling that you have clear evidence that things have moved hundreds or thousands of kilometers around. So Venus is very complicated, but it doesn't seem to currently have plate tectonics. And so what it has instead, now and in the past, there's been a wide variety of big-picture scenarios that have been put forth to try and explain what we're seeing now. Some of those scenarios involve Venus being remarkably Earth-like through most of its history and then changing dramatically, to the point where there's some people that think Venus had plate tectonics and had a habitable atmosphere until the last billion years ago. But there's other ideas in terms of, one of the issues is that all of the things we associate with plate tectonics are really about a planet that is hotter than outer space cooling off. And so when you come up with these scenarios, there are flavors where Venus is comparably active to Earth now and backwards in time, but it's just doing things differently. And then there's other ideas, where to get similar overall levels of heat coming out on Venus, just like the Earth, what you do is you dramatically fluctuate up and down the volcanic and tectonic activity, so that right now you end up with a Venus that is remarkably less active than Earth. But you balance that by having it way more active at some time in the past and you cycle through that. To bring it back to this particular discovery, there was a lot of evidence that, everybody agreed that future volcanic eruptions are going to occur on Venus and that Venus is volcanically active in some sense, but how often those eruptions take place could be on timescales of every few months, every few years or every 10,000 years. There were ideas that you could make any of those options fit with what we had before. But now of course there's a data set of one, right? So there's the possibility we might've found the only thing that's happened on Venus in the last million years and we just got lucky. But realistically, I think this brings Venus into a comparable level of volcanic activity to at least Earth's big, basaltic shield volcanoes like Iceland, Hawaii, the Canary Islands, that sort of thing.

Sarah Al-Ahmed: You pointed this out, but Venus might've changed dramatically over time. So Scott, why is it that understanding volcanism on Venus can tell us more about how the planet has changed over time? What makes us think that volcanism could have played a serious role in changing Venus from this potentially habitable world into this kind of lead-melting, face-melting, hellscape it is now?

Scott Hensley: First of all, all planets evolve over time and for a planet this size, we always expect volcanism to play a role of one form or another. It's the question of how it's structured. And I think Robbie went into great length in terms of how volcanism may be structured as a function of time. Is it organized around plate tectonics? Is it organized as intense periods of activity followed by very quiescent periods? It's the spatial and temporal organization of the volcanism that's really questioned, not that volcanism would be involved at all. And so what we've seen on the surface of Venus of course, is that it is extremely volcanically, or has been in the past, and influenced a lot of the evolution of the planet. The question is then which one of these theories that has been put forward really best represents how that evolution occurred and in what timeframe it did? Maybe I give a little bit of background. How people determine the ages of surface and when things occurred is crater counting, basically looking at the size and distribution of impact craters on the surface. Unfortunately for Venus, we have what's called basically a uniform distribution. So unlike places on the Moon or Mars, we can't tell relative ages of elements very well on the surface of Venus. So we don't have one of our great key indicators of time or how things evolved in time. So that's one of the things that a lot of these theories still open on the table. And one of the things we might hope with these newer missions, with a better resolution and additional tools that they bring to the table, that we might get some better idea on the relative chronology and that will maybe help us separate some of how Venus evolved over time questions answered.

Sarah Al-Ahmed: And don't you love that, when something just throws you for a loop? That tells us that there's some interesting physics going on there that could tell us a lot about planets in our Solar System but maybe even beyond, exoplanets as well?

Scott Hensley: That's certainly the case, and it's one of the things that excites the community is what are the broader implications. Laboratory we have in our solar system is Venus, the Earth, Mars and the moon. So we definitely have to understand that first before we have a chance of really understanding the broader implication of what's happening with rock body evolution around the galaxy.

Sarah Al-Ahmed: This research just kind of goes to show that past spacecraft, like Magellan, still have a lot to teach us about our Solar System. But as you said, Robbie, trying to find a feature like this on Venus is like looking for a needle in a haystack. So how did you go about narrowing down your search for features like this?

Robbie Herrick: To give you a little bit of background, Magellan passed over every place on the surface surface of Venus during its imaging portion of its mission three times. But while it was doing that, the spacecraft was degrading, so the area that it actually imaged the second time around, it got about 35% of the planet or so, and then about 15% the third time around. And each of those was done with, it wasn't designed to look for changes, it was done with a different imaging geometry. What I did in the search was I kind of had a list compiled from various sources of top 50 prospects for change during the Magellan mission. Just started going through there. In terms of looking for changes with time, some of that repeat imaging is a lot easier to work with than others. And sort of like the old story about the guy searching for his keys under a street lamp because that's where the light was good. I started in this one area that wasn't in my top 50 prospects, but it was the one area on Venus where two images were taken, separated in time with the exact same viewing geometry. And then I moved on from there to the prospects that were in the easier to work with data. Where I actually found something was in this area called Atla Regio, narrowed in on place where there are two of the largest volcano on the planet in terms of height and size. And the number one place where you would expect to find a change is where we found a change. But it wasn't the first place I looked because it was somewhere where the images were particularly challenging to work with in terms of looking for changes. So that's kind of how things went overall. And like any funded scientist, once I found something, I stopped and wrote the paper. So there's a lot of other areas that still could be looked at and maybe have something found.

Sarah Al-Ahmed: But you bring up a really interesting topic, which is that as Magellan was going around this planet, it's taking images, but the viewing angle is very different as it's going around, which complicates this process. And Scott, you were instrumental in taking this data and then figuring out how to glean information about it based on its different angles. So can you tell us a little bit about that process and what you did to make this data make more sense?

Scott Hensley: Robbie sent me the imagery in an email saying, "Look, Scott, I think I found change on the surface of Venus." And I was cautious about that because people had sent me things like this in the past and every single time I was able to prove that there was nothing that changed. It was really just an imaging geometry difference from the way the sensor collected the data. When I looked at Robbie's stuff, I was cautiously optimistic right away that he really found something, but I really wanted to make sure that this couldn't be confused with just, we just looked at this from two different perspectives and it just looked like something changed and something really did not. So what I did is I used some knowledge about how radar really works and one of the images, we could get a pretty good idea of the shape that was on the surface. And we know what vents look like generally, so we could figure out basically what the topographic profile look like. And with those two pieces of information and knowing which direction the radar was looking at the data, it's possible to simulate what the images should look like. And so what we were able to do then is we took the two different imaging geometries plus our assumed shape of the crater, and then we made simulated look images that we could then compare to the real images. And we did lots of different variations of the crater shape until we found things that matched the data. There was another vent that was nearby that we didn't think did change at all, and we could match that up on both images very, very nicely. But there's nothing that we could do that would match up the images the first time and the second time for the vent that changed. Its shape was different. It was no longer round, it was kidney-shaped. The way the backscatter, how bright it looked inside the vent was totally different than the models, so nothing looked right. So that gave us a lot of confidence that indeed the vent had really changed and we really found, or Robbie's keen eye had really detected something that had changed on the surface.

Sarah Al-Ahmed: Finally, we journey to the frozen reaches of the Kuiper Belt, where the icy dwarf planets, Eris and Makemake are quietly rewriting our expectations. In March 2024, I spoke with Dr. Chris Glein, principal scientist at the Southwest Research Institute. His team used the James Webb space Telescope to detect signs of methane and potentially internal heat on these distant worlds, hinting at cryovolcanic activity deep beneath their icy crusts.

Christopher Glein: So from the density you can infer that they're mixtures of water and rock, which is helpful to know, and it turns out that they are mostly rock. And having rock is pretty essential if high-temperature processes or geothermal activity needs to produce methane because there needs to be some source of heat. Like if you look, I study the moons of Jupiter and Saturn a lot, and on those worlds we think that tidal heating is a huge factor. This is like gravitational tugs between the moons and the giant planets. But in the Kuiper Belt and on these particular worlds, you just don't have that kind of energy source. So really having abundant rock is critical. The radioactive elements of uranium or thorium and potassium, one kind of potassium, you have nuclear chemistry and this nuclear chemistry can power geothermal heating deep in the interior.

Sarah Al-Ahmed: That's an interesting point because these bodies are so far away from the sun, which is why we're so surprised by this level of activity. But can we start assuming that potentially these radioactive processes inside of these worlds are going to make way more of them more active than we thought possible?

Christopher Glein: It could. I think Pluto opened that door. And now the door is being open a bit further with these new observations from Eris and Makemake. But yeah, I think we're starting to learn that the observations are showing us that there must be some kind of ways to sustain a certain level of heating to promote chemistry. Now, whether all this chemistry happens today or it's from the deep dark past, we don't know that. We just see the methane on the surface today. So we don't know if methane was cooked up in the interior 4 billion years ago, or if it could still be happening today. That's something that people are going to have to start modeling, and we're going to think about what are the next steps for measurements that we might want to make to try to test these ideas.

Sarah Al-Ahmed: The fact that you bring up tidal heating of Jupiter's moons and things like that sparks an idea for me. Did you in any way analyze the moons of Eris and Makemake?

Christopher Glein: Not yet. So there are data from, Eris has a pretty big moon known as Dysnomia. It's much darker than Eris. It looks like it's dark, but its interior is mostly made of ice. It doesn't appear to have a high density to have much rock in it. So there's some difference between Eris and its Moon that isn't well understood right now, but we do have observations of Eris's moon. So I think in the future there'll be the opportunity to analyze the data and see what can we learn about its moon and what can that help us understand about the history of the Eris-Dysnomia system? Because what we learned from New Horizons, the mission to Pluto, we learned that there's this very intimate relationship between Pluto and its moon, Charon. And the thinking is that Charon and Pluto actually had a collision early on, and that's how Charon became a moon of Pluto, and maybe something similar happened for Eris and its moon.

Sarah Al-Ahmed: You also pointed out earlier that there is a lot of distance between Eris and Makemake, like 50 AU difference. Was there also a difference in the types of methane and the relative abundances of these isotopes? Or were these worlds very similar?

Christopher Glein: They look very similar as far as the isotope chemistry. Within the error bars, so although these are demanding measurements and they're unprecedented, really, there are still error bars associated with these measurements. So within the error bars, we can't really say one way or another if the isotope chemistry is really different, but there are notable differences. So Makemake is closer to the sun than Eris is. That's one thing. And Makemake is also smaller than Eris, which is interesting. So in our paper, we propose that probably Eris may have a more vigorous history because it's larger. So you have this greater internal engine, right? This radioactive decay, the rock to drive the chemistry. You might imagine these processes would be more vigorous on Eris or more recent because you have a greater energy budget. One possibility is that this methane production, chemical cooking, the kitchen of the Kuiper Belt was open, let's say, in early on in the history of Makemake. Maybe it has an ocean today, maybe it doesn't. For Eris, the odds are probably better that it has an ocean and there could still be some active chemistry going on in the subsurface.

Sarah Al-Ahmed: That's it for today's tour of volcanic worlds. Thanks for coming on the journey across our Solar System and Planetary Radio history. Now, let's check in with our chief scientist Dr. Bruce Betts for What's Up. We'll take a look at the latest findings from NASA's Juno mission, which recently completed a series of breathtaking close passes by Jupiter's moon, Io. Hey Bruce.

Bruce Betts: Hello, Sarah.

Sarah Al-Ahmed: Have you ever gone to see a volcano in real life?

Bruce Betts: I've seen many volcano, but I've never seen a volcano while it was erupting.

Sarah Al-Ahmed: Yeah, definitely seen some old volcanoes, but nothing that's active. One of these days, that would be a really cool trip to go see.

Bruce Betts: I would. It's quite spectacular, I hear. Well, assuming you are seeing it in a controlled circumstance and not an uncontrolled, dangerous circumstance.

Sarah Al-Ahmed: Yeah, getting taken out by a pyroclastic flow or something would not be the way I'd want to go out. But you know, we don't get to make these choices, I guess.

Bruce Betts: Well, you can stay away from volcanoes and then you won't have that happen.

Sarah Al-Ahmed: That's true. I'm hoping one of these days I'll get to go see the Keck telescope in Hawaii and maybe while I'm there, I can go on some volcanic geological adventures just to learn more, but-

Bruce Betts: You can check out Kilauea, it's been firing up recently anyway.

Sarah Al-Ahmed: Yeah, but some of the really cool images I've been seeing recently are from the Juno mission. I don't know if everybody out there has been following these adventures of Juno at Io, but those images are absolutely nuts.

Bruce Betts: Io's just nuts in general.

Sarah Al-Ahmed: Right?

Bruce Betts: Since we first started getting indication that there was volcanism and then it's the Pizza Moon. It looks kind of like a weirdo pizza and it's got all this different type of volcanism that makes it all really cool looking. So you've got silicate like on Earth, and you've also got sulfur, and you've got sulfur dioxide being spewed out and coming down as frost. Sulfur's just weird, so it forms different colors depending on temperature and the like. And because there's almost no atmosphere, there's only some atmosphere because these volcanoes keep belching stuff out. Some of these plumes go up 100, 150 kilometers. Kilometers. And some of the stuff gets out into space. And in fact, by chance, we may talk about that in my other when I talk to in a little bit about certain kinds of facts. But for now, what do you want to talk about? Juno and Io. I just got excited about Io. I'm sorry.

Sarah Al-Ahmed: I mean Io is so cool. I've had some really terrifying nightmares about that moon of all the places in space. But as we've been getting more and more of these images, we've been learning more things about these lakes of lava and stuff that are on the surface. So I wanted to ask you a bit about what are some of the more recent things that we've been learning about Io from these observations?

Bruce Betts: I mean, we know that there are lava lakes on Io, but with infrared images coming from the Italian JIRAM, I don't know how it's pronounced, the Jovian InfraRed Auroral Mapper, can do infrared bands that will see these, and they've located more than 40 of these lava lakes on Io and they're huge. You get a lava lake in a caldera or somewhere tied to a volcano on Earth, and it's hundreds of meters wide. These are 10 to 100 kilometers wide. We knew that lakes existed but didn't have as much detail as now. So thanks to Juno, we have various interesting little tidbits, like the lava lakes are usually hotter at the perimeter. They seem to have crusted in the middle. And of course Io's really cold, so things freeze out quickly. But yeah, it's weird. And also, they discovered the massive volcanic hot spot, which seems a little presumptuous to call it that because there are all these volcanoes. I mean Io, most volcanic thing in the Solar System. You got like 400 volcanoes that are active, but this massive hot spot was discovered that's larger than Lake Superior. So basically, they see extreme heat and extreme eruptions spitting out six times the total energy of all Earth's power plants combined when it erupts sometimes.

Sarah Al-Ahmed: Nice.

Bruce Betts: That seems like a lot

Sarah Al-Ahmed: Really though, but we're going to get some cool new observations of it over time. So maybe as we, I know not all of them are as close to this moon, I think some of the more recent flybys have been a bit more distant. But if we can combine all of this over time, I want to know how that hot spot changes.

Bruce Betts: It's a scary place that Io, and it's a scary environment around it, so that's why they only dip the spacecraft close for part of their orbit because of the high particle radiation environment.

Sarah Al-Ahmed: Gosh, it would be so cool to go there, but also super-duper duper dangerous. I don't know why it's the most dangerous places in the Solar System that make me want to go visit.

Bruce Betts: Because of who you are, Sarah.

Sarah Al-Ahmed: It's true.

Bruce Betts: Exciting, crazy. These are the types of adjectives that come to mind.

Sarah Al-Ahmed: Let's go check out a volcano.

Bruce Betts: Adventurous.

Sarah Al-Ahmed: Let's just go to Antarctica.

Bruce Betts: Road trip.

Sarah Al-Ahmed: Road trip.

Bruce Betts: Should we migrate into the random taste fact? Do you like donuts?

Sarah Al-Ahmed: I love donuts.

Bruce Betts: What would you think of a donut the size of the Earth's moon's orbit?

Sarah Al-Ahmed: Oh man. How would you eat that?

Bruce Betts: Well, it's even trickier because I'm referring of course to the Io plasma torus, which is a mathematical term for a donut shape for those more crude than mathematicians. And it's all, it's charged particles, it's plasma, and so it exists in this fourth state of matter, primarily with ions whipping around in Jupiter's magnetic field. So Io is not just a weirdo down at the surface in its volcanism, but it also, when it spews those plumes of material up really high, it ends up having a neutral cloud of material hanging out around the moon part of the atmosphere, but then extended beyond that as well. And you've got these particles that are already in Jupiter's giant magnetosphere, Jupiter's whipping around every 10 hours with the magnetosphere and slams things into other things, and it ionizes things. So you got positive charge stuff and negative charge stuff, and it's all running around all crazy. And it forms this donut shape around Jupiter, a torus. There's even more weird stuff, which I'll just mention. One of the things which is, you also have the Io flux tube, which connects Io to the polar regions of Jupiter with charge particles and running along magnetic field lines. And you can actually see the effects of Io in the aurora of Jupiter. So this is mostly just to say, hey, donuts, tasty. Plasma donuts, huge, less tasty. Now I want donuts.

Sarah Al-Ahmed: This is reminding me of two things. One is the E ring around Saturn that's produced by Enceladus, so frequently these moons are just pumping out whatever it is, whether it's water in the case of Enceladus or in the case of Io, some kind of ridiculous material from the volcanoes. But also, the original images that Juno got of the aurora and how it connected to Io is really spectacular. But those recent images that JWST took of the aurora and Jupiter that came out, I don't know a couple weeks ago, were also just absolutely crazy.

Bruce Betts: Yeah, aurora are weird enough already. And then you get interactions with moons and it gets quite deliciously, enticingly, bizarro.

Sarah Al-Ahmed: All right.

Bruce Betts: I want donuts. That's all I can think about now. I'm sorry. Everybody go out there, look in the night sky and yes, think about donuts. 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 more space science and exploration. If you love the show, you can get Planetary Radio t-shirts at planetary.org/shop, along with lots of other cool spacey merchandise. Help others discover the passion, beauty and joy of space science and exploration by leaving your review and a rating on platforms like Apple Podcasts and Spotify. 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 and our member community app. Planetary Radio is produced by The Planetary Society in Pasadena, California and is made possible by our members from all around the world. You can join us as we marvel together at the strange worlds around us 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.