From the Vault: Jupiter’s Children

one is just a fascinating, literally otherworldly destination. We can't wait till you get to the end and experience the fiery planes of Io. Welcome to Stuff to Blow your mind. From how Stuff Works dot com. It really is darker out here in the outer Solar System. Your space freighter's one remaining forest dome struggles but barely scrapes along, surviving the plants still put out leaves. It seems only yesterday that you defied orders to jettison the dome and return

to Earth immediately, but instead you absconded. You took the plant life capsule, and you flew away away from the Sun, out into the Outer Solar System. You have only the forest and a pair of robots now to accompany you through this long twilight. You'd hope to pass beyond Jupiter and find refuge within the rings of Saturn, but the great gas giant will not be defied. It's massive gravity tugs at your humble freighter. The red eye of its century spanning storm taunts you as Jupiter drags you into

the orbital realm of its many moons. But still there's hope. Perhaps one of the four Eater moons the Galilean moons will offer some place of refuge. But which of these strange and hostile worlds might serve as a new home for you and this geodesic refugium from Old Earth's lost bio diversity. Hey, welcome to stuff to blow your mind. My name is Robert Lamb and I'm Joe McCormick, and you should imagine yourself in the scenario we just described.

You're in some kind of spacecraft, hopefully one that has some some plants along with it to keep you sustained through the long Outer Solar System journey, and no hostiles you know, more th onboard exactly, and you are caught in the gravitational influence of the planet Jupiter. You didn't mean to end up this way, but hey, you know, Jupiter's gravity is something that's difficult to escape. And now now you're stuck spiraling in towards Jupiter, slowly decaying in

your orbit, getting closer and closer all the time. But one thing you have noticed is that you will get to see a close up view and perhaps, if you're lucky enough, maybe land on Jupiter's four largest moons, known as the Galilean moons. This is the tour we want to take you on today. Indeed, these moons are of

course of immense interest to science. Now, one analogy that I think is interesting to help us understand the way the Jupiter system and its gravitational influence works, is to think of Jupiter kind of like a star within our solar system, like it's its own star, and the planet, the moons that are going around Jupiter a kind of

like planets orbiting this solar system within a solar system. Indeed, because it is a massive planet, it's mass is three hundred and seventeen point eight to eight uh times that of Earth, and uh it's of course a gas giant it's mostly gas. It might have a solid core about the size of Earth at the center, possibly a rocky ice covered core with insane levels of atmospheric pressure and temperatures hotter than the surface of the Sun. And Jupiter

features no fewer than sixty seven lunar objects. That includes fifty confirmed moons and seventeen unconfirmed or provisional moons. Yeah, and these are the ones we know about. Yeah, but yeah, and they've got cool names like Metis and and Drastia. And then of course there's also the There are also three faint gossamer rings around Jupiter as well, certainly not as robust as the Saturn's rings, but they're there nonetheless.

So we should back up and start at the beginning, because we're learning a whole lot more about Jupiter's moons, especially Jupiter's Galilean moons, the ones we're going to focus on today, the four largest moons, But we were learning a lot more about that recently. But we've known about Jupiter since ancient times because you don't need a telescope to see Jupiter. That's right, it's visible from Earth, and so it factors into many ancient systems of astrology by

virtue virtue of that cosmology. The Roman name Jupiter stems from the king of the gods, but the planet to plays a role in many cultural beliefs. In Chinese astrology, for instance, it's the character of Foo uh character of foods tied to Jupiter, and he's the embodiment who is Foo. He's the embodiment of good fortune uh, symbolized in a scholars dress, and he's cradling a child. The three stars that you'll often see. You often see these three statues

of these men in Chinese households, Chinese businesses uh. And they each kind of they each represent a different form of of idealized to success. So one is old and wise one and one is a successful with his family, and the other one is successful with business. I always think it's interesting that we see this cross cultural phenomenon of associating planetary bodies or objects in the sky with gods. Yeah, it's fascinating because you see this in other systems as well.

For instance, the Vedic astrology, Jupiter is everything from the dwarf incarnation of Vishnu to to Ganesha or sometimes Brahma. So it it varies with within that system. But yeah, that Jupiter always seems to have a pretty cushy role within a given a given cultures astrology. Yeah, so we mentioned that ancient cultures knew about Jupiter because you can see it with the naked eye, But one of the things they didn't know was much more about Jupiter other

than it being a point of light. That's right. For instance, when we think of Jupiter, what what do we picture? We picture that big, big gas giant with a big red eye, right, red spot, Yeah, the giant red hurricane on Jupiter's outer surface. Yeah, it's great to focus in on on the red storm because it helps us really

understand Jupiter and our relationship to Jupiter. Because, for one, on one hand, that storm has not been there forever, uh, and it will not be there forever, but it spans centuries, it's been there as long as we've been able to see Jupiter in that kind of detail. Uh. And it in the storm itself is two to three times the size of Earth. Uh. So that helps put again the massive scale of Jupiter. Can you imagine in reference if on Earth we had storms that lasted for I don't know,

hundreds of years. I've I've thought about it, like when you start teasing apart our weather system and you start looking at the different the different systems involved there, and the different factors that end up decreasing a hurricane's power. You know, what if those were not there? What if you had a scenario where the storm was essentially just a permanent part of the planet as a mortal individual would experience it. You know, that would be a great

set up for like a sci fi thriller. Imagine the weather conditions on Earth change that such that tornadoes tend not to dissipate on their own unless you have to. You have to find a way to essentially dissipate tornadoes by force. Yeah, indeed, and that that red storm on Jupiter is dissipating slowly but still there as of this recording. Now, as far as how far away Jupiter is, it's fo four million miles seven million kilometers or five point two

astronomical units uh from the planet Earth. Okay, so we know Jupiter is a gas giant, but you always wonder what's inside a gas giant. I mean, is it all just gas or is there something solid inside there? Well,

we don't know for certain. We Uh, the atmosphere of Jupiter is mostly hydrogen and helium, but it might have a solid core about the size of Earth, and this might be an icy covered core with just really insane levels of atmospheric pressure and temperature is hotter than the surface of the Sun. So it's very much the core and not you know, not the surface of the planet.

But but you know, you can't help it. Imagine, well, what if what if you could what if you could transport yourself down to the physical surface of this gas world. It would of course be just unimaginable with one of the most hostile environments you can even envision in the

Solar System. Yeah, it's pretty rough. And one of the things that's going to come up repeatedly I think today is how Jupiter, though it may look very serene and beautiful to us, is it kind of meets that analogy I worked out at the beginning about it being like a star, because Jupiter is it has massive gravitational influence, it's very electrically active, and it's just it's just full

of radiation. You don't want to go near Jupiter. Yeah, Yeah, to be sucked into Jupiter would be to be sucked into death, really, and that's one of the things we're out lying in the intra material. Yeah, so it's really unfortunate that we're slowly spiraling into Jupiter in today's thought experiment. But but we should at least take the time to appreciate the sites we'll see along the way. That's right.

And uh and and maybe if we're lucky, grasp onto them and uh and seek refuge refuge upon them, because even though they are all very hostile worlds in their own right, uh, there's still a better bargain and they still present a better chance for not only the potential like the real life potential for for human visitation, but in some of these cases we'll discuss the possibility for extraterrestrial life. Yeah, Okay, Now, Jupiter is not entirely unexplored today.

We've actually sent quite a few probes Jupiter's way that have that have orbited Jupiter and made various observations about it and it's major satellites, right, that's right. To date, NASA has sent nine space missions to or buy the gas giant. So we're talking to the the Pioneer Program seventy four, the Voyager Program seventy nine. Ulysses into Cassini in two thousand new horizons in two thousand seven. Also, Galileo is a big one, and that's a through two thousand three Juno.

That one's of course a very current that's two thousands sixteen. And uh, there are various additional missions and schemes for missions in the works. Oh yeah, I know the e s A is working on the Juice Explorer, right, the Jupiter Icy Moon Explorer, which I don't know. I don't know if I agree with the wisdom of calling it Juice. It's it seems just a little too cool, like like it's like the name doesn't need to be that cool because it's going to Jupiter exactly know, it's going to

the moons of Jupiter. That alone is is just mind bending. Yeah, and so hopefully it's going to explore three of the four main moons we're going to talk about today, the icy moons of the icy Galilean moons of Jupiter. And it's launching in two right, Yeah, I believe that's the current plant. And NASA is currently putting together the Europa Multiple flat by mission for the same time period. Alright, So I mentioned earlier thinking about the Jupiter system like

a solar system within a solar system. And if you do that, of course you've lots of bodies out there. We mentioned the sixties seven known satellites of Jupiter, things that are orbiting, but a lot of them are very small. If we do think about Jupiter like a solar system, it has four main planets. That's right, they stand out and the most due they're just their sheer size. And

these are Calisto, Ganymede, Europa, and Io. So you can think of them as it's four scoops on a on a Jovian ice cream cone, and you get the following flavors of scoops. You'll get salty craters, magnets, ice, and of course lava lava. That's a good flavor. Now, Robert, did you know that you seem to be you're a fan of ice cream metaphors? I did. I use them when thinking about planets. I use them when thinking about the brains. Though. Is this a good way of explaining

things to children? Did they just really grasp onto ice cream metaphors? You know? I don't know. I guess it's a good way to explain it to the child within Um, yeah, I mean maybe it comes back to sort of like a Sesame Street mentality. You know, like I grew up watching these visual representations, and it seems like it seems like there were more than one Sesame Street skit that had ice cream in them, So maybe that that ended

up sticking. I guess that does make sense. But it is interesting to think about the flavors of each of these moons because they kind of do each have their own flavor, especially the inner two I think, yes, yeah, each one is is its own weird world with its own properties, its own unique landscape, and that's why we

wanted to take our listeners on a journey through each one. Now, one thing we should mention about all of these worlds that's kind of different than most of the inner planets of the Solar system that we think about that have like a soul, uh you know, a solar rotational day, is that all of these moons are tidally locked with Jupiter. The same side of the Moon always faces in towards Jupiter. Yes, almost like they're completely obedient. They dare not look away

from their their master, right yeah. Or or it's kind of like in in Mario, you know, they're afraid to turn their back on the ghosts because when the ghost comes to get you. So we mentioned that these are referred to as the Galilean moons, and we should probably explain first how they were discovered and why they're called the Galilean moons. Today. The obvious conclusion you might reaches that they're named after Galileo. You know, he's an astronomer,

and if you assume to that, you'd be right. That's where the name comes from. That's right. And I think most of you are probably familiar at least a little bit with Italian astronomer slash heretic Galileo galile He who was born in fifteen sixty four died in sixteen forty two, and he was a true renaissance man, uh in the Renaissance. He was also a physicist and engineer, a philosopher, a mathematician, a true superstar in the history of science and really

in the history of human civilization in general. It's really it's really difficult to to overstate the importance the importance of Galileo. Yeah, I mean often today scientific struggles against ingrained orthodoxy are framed in terms of Galileo's struggle against the the scientific and religious orthodoxy of the day. Both of which opposed him. Yeah, well, our listeners a little more about the controversy surrounding helio centritism. All right, yeah, well,

so you'll probably associate Galileo with helio centrism. The idea that the planets in the Solar System go around the Sun could have also the day in the at the time meant that everything in the universe goes around the Sun. Of course, now we know that's not correct, but we were still very much working our way outward and our understanding of the universe. But it was certainly onto something in the idea that the Earth goes around the Sun and not the other way around the Earth end all

the other bodies in the Solar System. And so Galileo did not come up with the idea of heliocentrism. He didn't invent this. This was a Copernican idea. It was already in circulation, and Galileo was one of the Copernican astronomers of the seventeenth century. However, a version of the geocentric Aristotelian Ptolemaic model was what was dominant in the day,

was what most people believed. And in this model, the Earth is It's not just that the Sun goes around the Earth, and the Moon goes around the Earth and all that. It's that the Earth is literally the center of motion in the universe. So by by a principle that centers on the Earth, the whole universe just goes all goes around us. So we're what everything else is

focused on. And the role of Galileo's discovery is that in observing the sphere of Jupiter's gravitational influence, Galileo provided new evidence against that type of geocentrism that dominated in his day, and one one piece of evidence became apparent in January six when Galileo made his first round of observations through a telescope looking at Jupiter. So Galileo also, like not inventing helio centrism, did not invent the telescope,

but what he did do was improved it. He made a series of improvements to a design of the telescope that allowed him to resolve farther objects than ever before, and by the time Galileo got the magnification power of his telescope cranked up to twenty times, he aimed at the planet Jupiter and he saw something really weird. As we mentioned earlier, you can see Jupiter with the naked eye, right, yes, yeah, And so ancient astronomers had been seeing Jupiter for a

long time. They're already aware of its existence. But what Galileo saw when he focused on Jupiter was interesting. He saw stars. He saw three stars lined up right next to Jupiter, almost as if strung along a spear extending out through Jupiter's equator. So Galileo made a note of this,

and he decided to check back on it later. Now, if those had been stars that were just in the background, you know, if they just happened to line up with Jupiter from the star field beyond the next time you looked at Jupiter, they shouldn't be there, right, because Jupiter should have moved on relative to the background starfield. Right. They shouldn't be following the planet because there would be distant opjecs ex on the planet exactly. But instead the

stars followed Jupiter. Where Jupiter went, the spear of stars followed and they change their positions relative to Jupiter. And so after some observation, Scalio realized that there are actually four stars on this spear, not just three. And the conclusion he realized was that these weren't stars. The star spear was not a star spear, it was a moon spear. These are moons that are orbiting Jupiter the same way Earth's moon orbits the Earth. And so, okay, well, so

Jupiter has moons. What does that mean for the cosmological debate of the day. Well, if there are moons orbiting Jupiter, it disproves the Aristotelian principle that Earth is the universal hub of motion of planetary bodies. Those moons don't orbit the Earth, they orbit something else. And so this gives you a kind of general principle of things orbiting things rather than everything orbiting Earth. And it's clear that there's

more than one center of motion possible. There at least two that now that we know of Jupiter and Earth. And if there are two, you can assume they're probably more than two. And this eventually led to the type of thinking that showed us what was really out there in terms of heliocentrism in the way gravity works. Now, I should also add that the discovery of Jupiter's moons wasn't unique to Galileo, and he wasn't even necessarily the

only or first person to have discovered them. I found accounts that at least one other guy, a German astronomer named Simon Marius, discovered them independently at around the same time. And it's also been suggested that an ancient Chinese astronomer named Gone Day might have discovered one of the moons of Jupiter in the fourth century b c e. When

he said that he saw around Jupiter a small red star. Now, technically, under the right circumstances, the moons of Jupiter should be visible to the naked eye from Earth, and the only thing that really prevents it is that Jupiter is too bright. You look up at Jupiter and it's it's so bright that it drowns out other tiny points of light that are close to it, so you can't usually see them. But if Jupiter weren't there, you should be able to

see these objects. Oh but you know what, I think that sound means that we're coming up on Jupiter's first gal and moon spiraling in from the outside, and that's going to be the moon Callisto. Yes, and I think this is this is a pretty good pit stop to consider. So Callisto is about the size of the planet Mercury. It's the third largest moon in the entire Solar System, and it's the outermost of the four Galileean moons. As we've discussed, uh, it orbits beyond Jupiter's main radiation belts.

So Jupiter is highly radioactive, it's putting out a lot of scary stuff, but Callisto is far enough away that it's relatively safe. That's right. Yeah, we're we're outside of that that death lea, the death zone. Yeah. It's also the most heavily cratered o chick in the Solar system. So that's interesting. Yeah, this is this is really fascinating.

So as we as we as we we get closer and closer, as we're able to observe the surface of Callisto and maybe i know, hopefully even get out even land our vessel and find a semi permanent home on this uh this this strange moon. You would find that the surface, to to walk the surface of Callisto would be to walk a dead landscape of craters and occasional small icy peaks. And this surface, this landscape has not

changed in four billion years. Yeah, that's one of the things that we often associate having heavy cratering with, right, like more cratering. You see the older the surfaces, because what does cratering mean? It's been like that a long time without any kind of repaving. That's right. This is the last time Callisto suffered any extensive resurfacing was four billion years ago. And there are no plate tectonics, there are no volcanoes, a no active geology to alter the landscape.

So it seems like a kind of quiet, serene, dead Yeah. I mean it's like a dinosaur world. Right. It's like the moon itself is only four point five billion years old, and again it hasn't changed in four billion um. It's also the darkest of the four moons that we're discussing here,

in the least dents. So Callisto's composition is about half water ice and half rocky material, and the mean surface temperature of Callisto is negative two and eighteen point forty seven degrees fahrenheit, and the thin atmosphere consists of mostly carbon dioxide. Okay, so it may be very quiet and serene on this on this seemingly dead rock. But should we take away from that that Callisto is definitely not

a place to look for signs of life. Well, I think we've both watched enough science fiction to know that that world that you land on it seems dead is never It's not always really that dead. I have a sidetrack to take here. Do you notice how in science fiction, whenever you land on a planet that does turn out to have hostile aliens on it, you never land where the aliens are doing something. Right, then you always land in somewhere where there's no sign of them, and it's

only after exploring for a while that you run into them. Yeah, it would be it would be interesting to have that story where the ship touches down and all the hideous night creatures are already out, you know, viciously killing the eight creatures that lived there during the day. I like how the the viciously killing motion you made was like lopping with shears. Yeah, Like I'm thinking like two big

old pincher arms that are just for stabbing apes. Um, so we're not thinking about big pincher arms on Callisto. But there might be something to look for here, right, That's right. Surprisingly, for a world that we've described in these terms, you know, it's just being this dead crater landscape. There is some talk of life on or more specifically within Callisto. Specifically the stability of an electric, salty subsurface ocean. So you're probably wondering, well, where do we Where did

we dream up this idea? How do you say? Who says yeah, because you could say you couldn't you say that about any world like, oh, well, maybe there's an ocean beneath mercury. Now, so there's life on the moon. Come on, it's the spiders from that what's that horrible movie? Horrible movie with spiders. Pick one. It's a rich, rich tapestry. Okay, sorry,

who said this about Callisto? Well, this comes from a doctor Krishawn K. Corona of U c l A and his colleagues who examined Galileo's measurements, Not not Galileo the scientists, but Galileo the spacecraft that we mentioned earlier. Uh. They examined galileos measurements of Callisto's magnetic field, and they noticed that the magnetic field fluctuated in time with Jupiter's rotation. Okay,

so what does that mean. It means that Jupiter's powerful magnetic field was creating electrical currents inside of Callisto, and those currents, in turn created a fluctuating magnetic field. Around Callisto. Now for that to happen, you need a conduct her and that thin uh atmosphere crater skate that we've touched on earlier, that's just not gonna cut it. What would work, however, is a salty layer of melted ice down there, a

subsurface ocean electrolytes. Yeah, it's what alien life craves. Yeah, a a a sub world gatorade ocean, if you will, so cautiously, very cautiously, there is the potential for extreme file life within this theorized subsurface ocean. There's liquid water, perhaps salty, there's energy. So we'd be talking micro if we were to you know, consider life using our only model of it, which is Earth life, we'd be talking micro organisms like our keya bacteria, salt loving bacteria. There

wouldn't be any gigantic electronic moon whales. There wouldn't be any uh, there's certainly no you know, mandible ape stab creatures. But of and of course, it would also be very cold, and the ocean would only be heated by radioactive elements. So it's a very very very very hostile environment that we're picturing here. But based on our understanding of life on Earth, it would not be impossible for something to

have evolved and and even thrive there. Still. Yeah, and though we do want to point out that when we think about what hostile to life is, we're thinking about hostile to Earth life, right, And of course the Earth environment might be incredibly hostile to organisms adapted to some other kind of world. So, like you know, on Earth, on Earth we have oxygen and oxygen atmosphere. Oxygen is nice to us because we're adapted to it, but it

could be highly corrosive to some other type of organism. Yeah, indeed, so you know, with all this, it's it's relative based on our human perspective and our our preference for all things that support human life. Now, as far as the exploration goes, we've we've had nothing Callisto specific in the past, but most missions to or by Jupiter involves some level of callisto study. I mean, you're you're you're swinging by, it's in the neighborhood, it's one of the four largest moons.

You're you're gonna get some data off of it. Now,

I know we mentioned earlier the juice. The juice is thinking about studying icy moons of Jupiter and that would include Callisto right indeed, and then as far as considering any kind of far future visitation or specific study there, NASA's two thousand three Human Outer Space Exploration or HOPE project suggested that in a hypothetical five Jovian mission UH, Callisto could serve as a base of operations UH for study of Jupiter UH as well as other know outer

Solar System concerns thanks to its stable geology and low radiation so again, nothing's changing their no earthquakes, there no volcanoes, and you're outside of that death zone for the most part. So it would be a great place to UH to UH to tell operate say a Europa submarine we're going to do rope in a little bit a little bit or or other gallee and noon explorations. It could also

serve as a way station for outward bound vessels. I think that teleoperation idea is very interesting in the future of space exploration because one of the things you often run into and space exploration is well, Okay, when you've got a job that's very dangerous and and requires an extremely hardy explorer, you think, okay, we need a robot, right, But then when you've got a job that requires quick thinking and adaptability, you think you need a human explorer

because I mean, a robot is not going to be able to figure out how to get around a problem very easily if you didn't anticipate it in advance. And a good way I've heard of of bridging this gap

is having teleoperated robots. So instead of putting a human on the surface of Europa, you have a human in some nearby vessel, in a you know, spacecraft orbiting Europa or some or year by on Callisto maybe, and they are essentially by by avatar type of control making a robot do what it needs to do, but also being able to adapt to unexpected conditions and problems. So you send a robot to Europa, and you send maybe like a human brain and a scream canister to Callisto to

remote control the robot in Europe. I feel like after reading about Callisto, though, I kind of felt bad for Callisto reading this proposal, because I'm like, you landed on Callisto. Callisto's cool, Callisto's fascinating. Don't get to Callisto and then dream of Europa. That's kind of inconsiderate. That's like, you're you're hanging out with this friend, don't text that one the other one during the hangout. But I mean, what if this other friend you're texting is just way more

likely to have life on them. It's true, it's true. Okay, I think we're gonna take a break, but when we come back, we're going to get into the three inner Galilean moons where things really start to get interesting. Alright, we're back. We've left Callisto, We've left that dead, cratered world and it's a potential salt ocean hidden beneath its surface. What is our next destination in our journey? While our next destination isn't going to be all that different from

Callisto in many respects. So we we left one cold, icy, rocky world and we're headed to another cold, icy, rocky world. But this one is Ganymede. Now, what the basic stats on Ganymy Ganymede is about in diameter about three thousand, two hundred and seventy three miles across or five thousand, two hundred and sixty eight kilometers. This makes it the largest moon in orbit around Jupiter, and not just there in fact, it's the largest moon in the entire Solar System.

It's bigger than Pluto, bigger than the planet Mercury, but not nearly as massive due to low density composition. So you take an interior cross section of this planet, imagine you could sheer away half of it and look at an interior profile. You've got an iron core kind of like Earth has, but it's also possibly partially molten iron, and that's important for something I'm going to get to

in a second. Then around that iron core you've got a layer of rocky inner mantle that's so like silicate rock standard rock, and then around that is a layer of water ice, probably also some salty liquid water. And then finally on top you've got an ice crust that shows signs of age, craters and scarring. So the molten metal in the iron core is probably why Ganymede has its own magneto sphere like Earth, and and the fact

that it has its own magnetosphere is interesting. A lot of objects in the Solar System don't, but don't have a magnetic shield that extends outward from the planet, which makes possible visitation to those worlds all the more problematic. So I'm thinking this. I mean, we missed Colisto. This one sounds like a good place to touch down. What's it like on the surface. Okay, well, let's take a little tour of the surface of Ganymede. First of all,

you're gonna notice as a thin oxygen atmosphere. But the emphasis is on thin. It's not thick enough that you could breathe it. But there is gonna be a little bit of gas around there. And imagine you step out of the spacecraft, say Anamde, so you're walking on ice. The crust of the planet is ice. It's this dark, endless plane of ice, possibly with some rocky elements here and there, but mostly it's going to be ice. It's like a frozen pond extending over the whole planet. So

bring ice skates. Maybe, Actually I wonder, you know, if so ice is slippery here on Earth, is ice slippery on Ganymede. I have no idea why I would even wonder that. I would have to assume the physics are somewhat similar, but maybe not. I mean, it depends. Yeah, there's it's easy to take for granted something like ice skating, But ice skating it's going to depend on on what the gravity is like on the world, right, Yeah, yeah,

gravity and the surface conditions. Now, one thing actually I think is that ice is less slippery the colder it gets outside, right, like an extremely cold conditions, You're less likely to slip on the ice. I feel like the novel that Forever War went into this a little bit. I believe like there's a section where he was getting into like the physics of being a visitor to an

icy world and how slippery would be. But if then a long time since I've read that left up here from listeners, yeah, I would like to hear if you have ideas about that. But anyway, you're out on this ice crust, and one thing you can notice is that you can, as you travel the surface of Ganymede move from different kinds of landscapes into one another. So Ganymede has interlocking sections of an old face and a young face.

Both are made of ice, but the old face is dark, covered in ancient craters from impacts over billions of years. It's what we talked about earlier. You know, the more craters you see on a surface, typically the older it is because it's been there to absorb blows from the shoe gallery of the Solar System for a longer period of time. Yeah, be aware of those planets where you

don't see craters everywhere because something's happening there. Yeah. The craters on Ganymede I've read, are actually relatively smooth and gentle, and this possibly might be from millions of years of ice settling. So unlike rock where there's a crater, it's a brittle crater with edges, and it remains that way

for a long time. With ice, over a long period of time, even though it's very cold, there is some kind of almost kind of gelatinous quality to the ice over long enough time scales so be kind of like an ice jelly. It's kind of like the way glaciers

can deform over a long period of um. But then there's also a younger ice plaine on the surface of Ganymede, so you can move from one dark, scarred plane to another one, and these these younger ice planes are brighter in color, with fewer craters, and instead of craters, you'd walk through these deep wooves known as sulki. Each each of these it's a sulcus, is this groove running along the surface of the planet. It's like a wrinkle in the face of Ganymede, the sulci of Ganymede. I like it. Yeah,

it's beautiful. And what are those caused by? Well, it's not exactly known, but I think the main idea I've read is that it's caused by internal stresses, entitled forces acting upon the planet, kind of causing wrinkles and perturbations in the crust. Okay, well, what are the natives like here? Well, if there are any, and there actually is a possibility, it's going to be kind of like what we talked

about with callisso a similar kind of situations. Because findings announced by NASA and from the Hubble Space Telescope showed that Ganymede probably has liquid underground oceans sandwich between I see layers, And they figured this out by looking at at the aurora around Ganymede and figured out that you know, to see the to see the charged particle displays that we see around the outside of Ghanamy, we would probably be expected that we would probably expect that to be

caused by liquid oceans under the surface. Uh, and anywhere of course that there's liquid water. We kind of have to wonder is there a possibility, And so that's the idea, and it's another case of subsurface liquid water that may

indeed harbor microbial life. Now, past observations of Ganymede have been done by the some of the same missions we've talked about in the past, the usual suspects here, and of course Ganymede is one of the potential targets of Juice that the juice, so it's we mentioned earlier, but

it's part of the Essays Cosmic Vision program. And the idea is that the probe would launch in two putting it on course to arrive in the Jupiter System around twenty and it would make observations of Jupiter itself but also Europa, Ganymede, and Callisto. And the main focus on Ganymede would be to learn more about its underground oceans and whether they have the potential to sustain life. But in addition to that, there are some Russian science tists

who want to put a lander on Ganymede. Again, this would be to study potential habitable habitability. But this wouldn't just be a fly by. This would be a probe settling down on the surface and uh, and using various tools to figure out what's going on on the surface of Ganymede and and what might be going on under

the surface. In indeed, that's a tantalizing part, right to to not only arrive there but too, but but to but to actually dig down into the surface and see if these oceans are really there and then what it consists up. Yeah, And of course Ganymede is not the only place where scientists want to drill under some ice and look at habitability concerns. In fact, there's an even better spot to study that, and it's the one that's

coming up next on our death spiral into Jupiter. That's right, Europa in Europa is quite a big one in our in our consideration of Jovian moods. Yeah, if you read science fiction, I bet this is the most likely one you've read a story about. And it's often I would say, would you agree that of all the places in the Solar System, it's the one where astrobiologists most often talk

about the possibility of finding life. Yes, this is definitely the one where where that has the most excitement around it. So Robert introduced us to this moon. We're coming up on now right. So while the surface of Europa appears to be a solid sheet of ice, scientists believe this outer shell hides a deep liquid ocean or an ocean of of ice slush underneath, the heated by tidal friction and thermal vents sixty two miles beneath Europa's ice caps.

So Europa boasts a layered structure like Earth that consists of an iron core, a rock mantle around that core, a thick soft ice layer, and a thin crust of impure water ice over again what is probably a global

subsurface water layer. Yeah, and so though Europa is a little bit smaller than Earth's moon, based on the Galileo data, you know, the data from the Galileta robe again not from Galileo galile uh, scientists think that Europa actually has more water on it than Earth does, which is pretty incredible because Earth is often known as the water planet. So if you you are the aliens from signs, it

is even worse to try colonizing Europa than Earth. Now that ocean finding, as with Callisto's suspected subwa subsurface waters, come down to the Galileo spacecraft's measurements, specifically the manner in which Jupiter's magnetic field was disrupted in space around Europa. And the theory is that the field is induced by a large body of electrocly conductive salty fluid beneath the surface. Now, if we're to actually move in a little closer, if

we were to touch down on Europa, what would we find. Well, the surface is apparently a vast landscape of frozen ice and it's criss crossed by long linear fractures and these are caused by tidal flexing, the tidal force caused by Jupiter's gravity. There are very few craters to be seen bloomishing this landscape, as as the surface is actually quite young, only for million years old, which is kind of creepy when you think about it. Yeah, this this ancient planet.

We've never been there and it's got a young surface. Yeah, that's that's the first red red flag for any sci fi visitors. Right now. You'll also spot reddish brown materials and some of the fractures and splotchy deposits, and we're not yet sure what those are exactly. It might be magnesium sulfate, maybe sulfuric acid hydrate. You know, I think I've read that recent research suggested that the dark discolorations on Europea's ice crust could be caused by sea salt,

supposed to radiation. Yet another piece of evidence that the water below the ice crust might be salty. Well, there you go. Now you'll also come across pits and domes in the ice that suggest that it could be slowly turning over or convecting due to heat from the possible oceans below. Or maybe they're just the dome cathedrals and fighting pit of some weird off world elder species right now. Now, wait, a second heat coming from the oceans below. Now that's interesting. Yeah, yeah,

that's because if there's heat, that's one more possibly. Not only do we have a salty ocean, but there's there's heat, there's energy their energy rich, yeah, energy rich, more potential for life. Now there's also the chaos terrain. This is one of my favorite terms in astronomy. Is it astronomy, I don't know, astrogeology, planetology, Yeah, I guess so. Yeah, the chaos terrain. This is a broken, blocky landscape covered in the mysterious reddish material that we mentioned earlier. So

it might be spots of geogeologic activity. It might be places where the ice has collapsed into lakes in the ice. And it's also possible that we're just merely over interpreting h imperfections in the Galileo spacecraft imagery. Oh yes, and is revealed in the in two thousand thirteen Hubble telescope data. Europa is actively venting plumes of water into space. So this means that it is definitely geologically active. So it's

like geyser is shooting off of the Yeah. Yeah, So so we've got that to think of two, like space geysers shooting water into space. So does it have an atmosphere at all? It does. It has a molecular oxygen and O two atmosphere. Hydrogen floats away from the planet because it's too light and collects in a gas torus around the planet. Less impressive than than the one on Io that will discuss, but still pretty pretty interesting nonetheless. And as far as size goes for your Europa, it's

slightly smaller than Earth's moons. So Europa is the smallest of the four Gallean moons. Yes, but size doesn't necessarily matter when it comes to subsurface life, that's right, So if Europa's oceans do exist, and we're pretty sure they do, it's I think most scientists agree that's what's what's going on under there. Then the tides might also create volcanic or hydrothermal activity on the sea floor, supplying nutrients that

could make the ocean sustainable for living things. Yeah. So often when you want to imagine what kind of alien life could exist on place, in places other than Earth, it's a good idea to look at extrema files on Earth. What exists in some of the most difficult conditions on Earth. And one of the things to look out on Earth might be the life that is sustained by hydrothermal vents on the ocean's floor. Yes, we're talking about deep, dark places where really the only font of energy is is

the the the hydrothermal vent. But that is, you know, pumping out some very high temperatures in an otherwise cold and light lift environment. And uh, and there are there are organisms that have evolved to thrive in that environment. But look again, it's go back to what you said earlier. We call them extreme of files. But of course, if that were the only place life could exist on a world, would they really be extreme of aisles. It kind of

depends on how you know where you're approaching it from it. Yeah, that's what they're adapted to. Yeah, I mean, try to put them in a in a lush farm land on Earth and then you would die out. That would be their extreme environment. Yeah. So there's a lot of a lot of hope, a lot of excitement, uh, specifically for Europa because a number of the factors UH in the or in the emergence of life seemed to exist there. Yeah, and because of that, Europa is a prime target for

future exploration and research. So we've mentioned Juice. Juice wants to go to Europa, of course, but what else is going to Europa? Well, NASA is currently putting together the Europa Multiple fly By mission for the same time period. That mission is scheduled launch in arriving at the Jovian System in two seems to be a big year in general. According to a BBC report from actually earlier this month, NASA is eyeing that year as a potential launch date

for a soft landing mission to Europa. All so es A scientists are currently considering these five different concepts um for their own explorations So one is a remote sensing instrument that would go aboard that that American two probe. Another is a small free flying satellite that would detach from this probe. Another is a small satellite that would detach from the lander's mother ship. Another is one or

two instrumented projectiles that would drop from the mother ship projectiles. Yeah, and we'll we'll get to to the projectile aspect here in a second. Also an instrument to ride on the soft lander and uh quote unquote do science at the surface. Um. I love it when landers do science. Yeah, I mean it's one of those things where it's you know that we're in the early enough stages for figuring out exactly what it would do, but then we also know a

number of the science that it would do. But then the one that really is fascinating is the idea of a penetrator hard Lander. So this would a steel missile loaded with sensors that strikes at three hundred miles per second and collects data on the interior. So we're talking some very rugged instruments. They've apparently tested this out a little bit on Earth, uh and found that, yes, that

the instruments do survive such an impact. Well, that's one of the interesting questions is what we would do to get to that subsurface ocean, because so you'd have to if you land on the surface of Europa, if you imagine it has an extremely thick ice crust and the subsurface ocean is underneath that, you'd have to drill down or melt down to get to it. And then once you're down there, how do you get the data back

up to the surface. Right, And and we don't want to discount just the journey to any of these moons in general, because this is not like the friendliest neighborhood to enter into your kind of entering. As we mentioned, you're kind of going into a sub solar system with plenty of objects singing around with rings, etcetera. So it's, uh, there are a number of factors that there are a number of hurdles to even getting to your destination. Now, Robert,

have you seen the science fiction movie Europa Report. I have not. I really liked Europa Report. I I would be interested in hearing what you guys out there think,

our listeners. Have you seen this movie? I thought it was cool and that it was a modest science fiction movie that did it did a lot with a little and one thing I really liked about it is that it was truly a science fiction movie about the exploration of Europa and science fiction, I mean, um, a lot of movies that are called science fiction are really just sort of action fantasy where the instead of having magical weapons, you have technological weapons, but they're still basically the same

the viewer that has no idea what it's just. Instead of having a religious or supernatural explanation for the magic, it is a vaguely science explanation for them magic. Yeah, exactly. And this movie was not like that. I mean that it was a science fiction movie in that the plot

was inherently about science. It had a it has scientific plot and the scientific thrust, and the characters had a scientific mission that was actually grounded in real things we'd want to learn in the real ways we'd go about

trying to learn them. Uh. And so I won't I will try not spoil anything about the movie, but they it's a movie about a manned mission, or I should say a crude mission, a mission with a crew going to the surface of Europa and trying to figure out if there's life in the oceans underneath and so I give it a thumbs up. Does hilarityst No, not really hilarity maybe some I, without spoiling too much, I will say that things don't go exactly to plan. Did it

wouldn't be much of a movie, all right. Well, at this point, let us sadly leave Europa with its mysteries unsolved, and continue on to the innermost of the Galilean moons. Yes, now does time. We're approaching Io. It's spelled two letters io, and that seems to make sense. But because there's a kind of grinding simplicity and beauty and weirdness to this planet, it's it's it's maybe the strangest and most gorgeous of all of them, and of all of them it most

wants to kill you. So IOW is Jupiter's innermost Galileean moon. In terms of diameter, it is slightly, but only slightly larger than Earth's moon. It's almost comparable in size, and its orbit keeps it within four hundred and two kilometers or two hundred sixty two thous miles of Jupiter. That's not not a whole lot farther than the distance between the Earth and its moon, except think about how big Jupiter is yeah. Yeah, so what's yeah, So what's like

on the surface of Io. It's freezing hell and burning hell at the same time, where the ground that you walk on churns up and down like a tsunami as the tides go in and out. On the solid world. Io is a world of extremes. It's uh. It's the most geologically active object in the Solar System, the whole Solar System, including Earth, with more than four hundred active volcanoes that we know about some eruptions. These volcanoes shoot ejective plumes of three hundred kilometers or a hundred and

eighty six miles out into space above the surface. If you see some images of these, it's incredible. It looks like it looks like there's something else going on behind Io that's being obscured by the planet. But no, you that's not what it is. You're just seeing in profile plumes of planet sized proportions exploding off of the surface.

And uh. And so the average temperature on the surface is negative two hundred and two degrees fahrenheit or negative a hundred and thirty degrees celsius, which is far colder than the coldest natural temperature ever recorded on Earth, that is, unless you're standing near one of Io's hundreds of volcanoes while it's erupting, and here the temperatures are more like three thousand degrees fahrenheit or D one thousand sixty nine

degrees celsius. There is an atmosphere, but it's thin and mostly made of the toxic gas sulfur dioxide, which is often associated with volcanic activity even on Earth. So if you know, you get killed by toxic fumes near a volcano or something like that, you may be breathing sulfur dioxide. And speaking of sulfur compounds, the planet is also going to be covered probably in fields of yellow snow. You don't eat the yellow snow in this case, and it's

because it's sulfur dioxide snow. So the planet it has these eruptions where these particles of sulfur dioxide gas come out and go all around the planet. But then because it's so cold, they tend to crystallize and fall down as the sulfur dioxide yellow snow. Uh, So it's just covered in these poisonous golden snow fields. But other than that, it's a good place to visit. No, no, it's also a blasted heath of radiation. So uh, it's the closest

to Jupiter and the most exposed to Jupiter's radiation. And then there's also because Io is connected to Jupiter through a sort of magnetic ring that comes out of Jupiter's magnetosphere, it also creates what's called a plasma torus, which is just this ring of killer charged particles flowing off of Io and into Jupiter. Uh. And it's it's kind of unbelievable. You you wouldn't want to get near it, you wouldn't want to stand in it. You really don't even want

to fly a probe through it. And I mentioned earlier the tidal heaving on Io. So on Io, there there are tides, but there are no oceans. It doesn't have water to have tides. It has tides in the ground itself. Now other planets well too, tides of course, you know, being influenced by the gravity of surrounding bodies. There's there's tidal action acting on Io from Jupiter and from the

other moons that are going around Jupiter. But these incredibly powerful gravitational forces, instead of moving water around on the surface, end up moving the ground up and down hundreds of feet. Now, from what I understand, I think you wouldn't feel this like you know, waves coming up and down really fast or anything like that. But it does. This tidle flexing and stretching of the solid mass of the planet does

lead to incredible friction. I mean, think what would happen if you were constantly flexing a rock in and out to get pretty hot, And this is what happens to the interior of Io, leading it to be this burning hellscape within the freezing hellscape. Another crazy fact about Io Jupiter is going to loom huge in the sky. The NASA JPL website has a really interesting app that I

recommend you try to use it. It's the Solar System Simulator, which lets you simulate looking at one object in the Solar System from another object in the Solar System at any given time. Uh. And I tried this out. I was like, Okay, what does it look like looking at Jupiter from Io right now? And from the surface of Io right now? Jupiter currently takes about it takes up about nineteen point five degrees in the sky, so you know, imagine the degrees from horizon to horizon you've got about

a hundred and eighty degrees. Uh this so this is about twenty degrees. That's like one ninth of the width of the sky. It's crazy to imagine that. I mean, it's it's crazy to imagine even of course, standing on the surface of Io and you're I guess godlikes space

suit that somehow protects you from all of these extreme conditions. Somehow, I think we're not ever going to be walking on I yeah, I mean you would have to be dealing with like a what like a level level one or level two civilization just kardashi yea Cardachan level, like some sort of like crazy sci fi field system like where it wouldn't even be a physical suit as much as like a crazy energy shield that is somehow protecting you unless you're Sean Connery with a shotgun. Right. Oh? Yes, Um,

is it too early to mention Outland? No, it's not so. Before we recorded the episode, we were talking about how Robert just rediscovered that the movie Outland, the starring Sean Connery, which is essentially high Noon in space. Yeah, it's a space western, Uh, nice and gritty. It's it feels like you could take place in the same universe as Alien US, you know, a lesser film, but it has that kind of grimy uh you know Workman's vision of life in

the solar the opposite of Flash Gordon. But it takes place us on Io right again, How realistic is that? Seems not very Yeah, it's been a while since I've seen it, but I do not recall the I do not recall any highly volcanic scenes. I could be wrong on that. I felt feel like they delivered like a

cold or vision of Io. Yeah, but it's it's a great film, very violent, a very very gritty space drugs, space prostitutes, Sean Connie with a shotgun, Peter Boyle and some other actors that would go on to to make a name for themselves, and then the cast as well. Is it kind of like Leviathan in Space? Not really, there's no monster. It's like it's a very human story. It's it's essentially you know, it's it's a mining town Western scenario. But on this Jovian, I guess I was

just going with the mining outpost aspect of Leviathan. Um, do we need to talk about Leviathan on this podcast? We can carry on. Sorry, I've seen that one more recently. Yeah, well it does have a great poster. It does fabulous poster. Okay, So back to Io. Given everything we've said so far freezing hell and burning hell, uh, sulfur dioxide, vicious radiation bath, we shouldn't expect this place to have any life at all, right, it seems a ridiculous proposition. Also, no liquid water on

the surface. It sounds like the last place. No organic molecules ever detected there, I mean, why ferocious radiation, so we can definitely rule out the possibility right, Well, actually not according to everyone. And I wonder if this is just an expert uh an astrobiologists trying to emphasize what possibilities are out there, more thought experiment than anything it

could be. But from two thousand ten, I found an article by Charles Q. Choi that speaks to Dr Dirk Schultz may COOCHU an astro biole an astrobiologist at Washington State University, and UH. Dr Schultz may Cooch said, quote, life on the surface is all but impossible, but if you go down further into the rocks, it could be intriguing. We shouldn't categorize it as dead, right, away just because

it's so extreme. So, based on this guy's comments, this astrobiologist comments, the article went on to sort of explore what life could be like on Io. You know, if we if we look at Europa and Ganymede, which have water ice, we can get a picture closer to what Io might have looked like billions of years ago, closer

to the time of its formation. Radiation from Jupiter probably would have ripped away Io's water within about ten million years or so, but life that evolved on the surface during that period could possibly have retreated underground, surviving in subterranean lava tubes, which could contain moisture and protect the microbial life forms from radiation that's on Io's surface. What what is impossible up above may not be impossible below.

And as we've pointed out before, they're extreme a file organisms on Earth that can survive and thrive in lava tubes and even near active geotherm hotspots like Geyser's. So Schultz make Coach comments that the ultimate chances of finding life on Io seem pretty low, but we shouldn't rule it out. And besides, how amazing would that be to

find life on this sulfurous golden hell. It would really change your idea of what's possible for self replicating organisms in the universe, I think indeed, you know, and it also makes me wander you know, we've we've been discussing some sci fi a little bit here, but you're always encountering that idea of of of either a human or other intelligence civilization seating life in other worlds. And generally

that doesn't take the forum of extreme of files. But but I wonder, like, what could we one day reach the point where a human or human derived civilization would reach a world like like Io. Look at it determined that there's no even there's no life, even extreme a file life. But then custom makes something to survive, and it's like it's in its most tolerable, um A location. I don't know, it's fun to think about. Yeah, well there, I mean, I think you get into, of course, the

the ethics questions about seeding life. You know, you'd have to be sure if that's even possible that there was no life there now and that life wasn't you know, in store for it at some point in the future. Um So, who's to say? But then again, I think that's kind of weird, like I feel this ethical intuition that you shouldn't go about, you know, contaminating other worlds with possible life that could extinguish the life that exists there now. But then again, I really don't feel bad

about using alcohol to kill bacteria. If you're washing your hands before surgery or something like that, you know, it's I don't know, well, you know that bacteria was never going to make it to Aisle anyway, so it's fine. I guess so alien bacteria just has so many more

rights than Earth bacteria. Okay, So future missions to Io one would be the Io volcano observed over one proposed future mission at least we don't know, but uh, the proposed future mission to Io would be this observer, primarily the work of the planetary geologist Alfred McEwan, And this would be a probe that goes into orbit around Jupiter and observes Io close up over the course of at

least nine flyby's over two years. And this would be studying Io's temperature, it's a volcanic activity and its surface composition. And if the proposed mission is accepted, it's going to launch by around one So it seems like in the early twenties, there's going to be a lot of potential

Jupiter missions launching. That has got to be a I mean, we've already discussed the volcanic eruptions that blast out into into space off of Io, so that would see, it would seem like it would be a difficult orbit to maintain, and maybe that's part of the gamble, like how well I mean, I guess the question would be exactly how close is it getting to Io if it's gonna be

orbiting Jupiter. Uh. I think I read something like that the closest point it would ever get to Io would be around two hundred kilometers away, which is I mean, that's pretty past. But the bigger question, I think, much more than the geologic activity, is just the radiation. I mean, even even non organic just our instruments at that point are can be subject to extreme radiation and so it would have to be a hardy kind of probe to survive. If anything were to actually land on Io, it would

have to be a flying fallout shelter. As we've mentioned, the radiations fierce, and it has damaged instruments on probes in the past, right, Yes, I mean that's how that's how potent the radiation of IO is. One last thing I wanted to add about IO coming from the angle of exo theology. Uh, the religion space religion. Oh, this is a this is a topic I love. Yeah, of

course I love it too. And uh, we should add that we keep using the Hell analogy for I just merely for descriptive reasons, to give you an image to map it onto in your brain. But there's actually at least one theologian who exists who believes Hell can be found in the Solar system. Uh. He is a guy named Michael sin teeny and he's a reverend who he self published a book that argues that the Christian Hell

is literally to be found on the planet Venus. And I don't know how many people he's managed to convince of this. This is obviously not a standard Christian belief. This is his idea. Um, but I wonder why not Io instead? I know, seems like an even better candidate. Yeah, I mean, you have it. Fl It flows perfectly with Dante's vision, right because you have both the hot region, the hot regions, the cold regions. It's it's perfect. All

you need is Satan there after his waist. And yeah, and it matches with our journey of descent, right as we've gone closer and closer into the planet. Which reminds me, now that we've reached the end of our journey, we're getting very close to Jupiter itself. Yeah, and our our little terrarium capsule is withering a little bit. It was standing the inner radiation of the Jovian System. I wonder what's going to happen as we descend into the gas.

I don't know. We're descending into a into a massive gas world of storms and poison and uh and eventually a Rocky core. Uh. With the pressure and the it's just insane. I'm pretty sure we'll be obliterated before we reach the Rocky Cory. Oh yes, yes, certainly. I doubt we'll love to reach the Rocky Corps. But maybe there is no Rocky Core. Maybe the Rocky Core is all in your mind. Well, the important thing is that we made it this far. I mean, we were ordered to

jettison the dome a while back. We held on this long. Everything got to survive there just a little bit longer, so we can we can play one last game of checkers or cards with the robots and just go out on a high note. Well. One thing I should have mentioned you as we were going, but I didn't because I was afraid was that at each moon we passed along the way, I jettisoned all a capsule of Earth life, unethically seating these planets and potentially contaminating them for all

future research. But maybe these little life forms will take hold. Yeah. Well, hey, that's better than nothing, right, So let's hope something takes root, all right. So there you have it, an exploration of the Galilean moons, just the four greatest of the Jovian moons in general, but each one a fascinating world. And uh and the cool thing too, is that even over the course of the next year or so, we're hopefully

going to learn more and more about these these places. Yeah, so we want to thank you for joining us on our journey through this solar system. Within a solar system, the the gas Giant and it's wonderful sphere of influence. Indeed, and if you want to see images of some of these moons as well as explore some links out to additional data about them, be sure to check out the landing page for this episode. At stuff to blow your Mind dot com. That's the mothership. That's where we will

find all the podcast episodes. You'll find blog posts, you'll find galleries, lists, videos, links out to our social media accounts such as Facebook and Twitter, where blow the Mind on both of those. We also have Tumbler and Instagram accounts.

If that is your jam, and if you want to get in touch with us with your favorite fact about Jupiter or its moons, or you want to let us know what you think the most interesting object in the Solar System is, or where you think we're most likely to find the life outside of Earth, you can email us at blow the Mind at how stuff works dot com. Well more on this and thousands of other topics. Is it how stuff works dot com blasted three per prop first