The Infinite Monkey Cage - Saturn v Jupiter - Katherine Parkinson, Paul Abel and Michele Dougherty

Episode Date: March 12, 2025

Brian Cox and Robin Ince referee as Saturn and Jupiter square up to each other in a planetary face off. Representing team Saturn is space physicist Professor Michele Dougherty, and in the opposite corner is Dr Paul Abel on Team Jupiter. Katherine Parkinson judges this cosmic contest, casting the final vote to decide who will be awarded the coveted Kuiper Belt. It is not all about looks of course, but it is a significant factor in a first impression. Both Saturn and Jupiter score highly in this department, boasting magnificent icy rings and colourful stripes respectively. But what lies beneath their aesthetically pleasing exteriors? How do the planets compare on the inside? The gas giants have been subjects of investigation for many years, with historic missions like Galileo and Cassini uncovering their secrets. But they aren’t alone, each planet is surrounded by its own mini solar system of moons, which get space scientists just as excited as their parent planets do. Both Jupiter and Saturn have moons which are hot contenders in the search for extra-terrestrial life and our panel discuss the future plans to explore them.Producer: Melanie Brown Exec Producer: Sasha Feachem Researcher: Olivia Jani

BBC Sounds music radio podcast. Hello I'm Brian Cox. I'm Robin Ince and this is the Infinite Monkey Cage. Now as many of you will know there is quite an overlap between the world of both theoretical and particle physics and also world and international wrestling. The Large Hadron Collider was indeed inspired by a bout between Rowdy Roddy Piper and Hulk Hogan where Peter Higgs, a very very keen wrestling fan, saw the tremendous amount of energy that was expounded when the two went

from a double leg takedown into a camel clutch ending up with a pile driver. And it was at that point he thought what if the origin of the masses of the W and Z bosons is electro-weak symmetry breaking in the early universe? Perhaps the universe is meta-stable and we live in a false vacuum state. Take him down, Roddy! Are you okay? I'm fine, I'm wondering what a camel clutch is.

I was so glad it wasn't just me. I had no idea either. The physics actually was remarkably accurate there. What he was saying with the Z boson and the photon are essentially the same, apart from the fact that the Z is very massive and the photon is massless. I suppose by your analogy that means that the Z is Big Daddy and Barry McGuigan is the photon or something? No, no, and I know people are already annoyed by that because that is you not merely mixing your metaphors But also mixing your different sporting splendors there. Right. This is a science show Radio 4 is the last bastion of retium values in an increasingly trivial world

So today I'm going gonna be sensible and tell you we're discussing the gas giant planets, Jupiter and Saturn, and the future plans to explore them. But at the same time, it is very important to remember how much wrestling and science have been combined for literally hundreds of years. Many of you who are also fans of Isaac Newton will remember that one of the most important statements in science is, if I have seen further it is because

I've stood on the shoulders of giant haystacks. In the red corner we have Jupiter, a gas giant, weighing in at 2.5 the mass of all the other planets in the solar system. And in the slightly yellowish, perhaps more kind of puce through a smaller telescope, we have Saturn, King of the Rings! APPLAUSE Jupiter and Saturn are each surrounded by their own mini solar system of moons, fascinating worlds in their own right that are prime candidates for the search for life beyond Earth.

So joining us to decide who leaves with the Kuiper belt are a space physicist, a theoretical physicist and someone who has been at the forefront of information technology and they are. I'm Michelle Doherty I'm a professor at Imperial College in London and a planetary scientist and this place I would like to discover most I'm not going to tell you about right now but we'll find out as the evening progresses. Hello everybody my name is Paul Abel I'm a theoretical physicist at Leicester University. My area of expertise is black hole thermodynamics which has nothing whatsoever to do with what we're talking about tonight but they asked me to do the show and I was bored and said yes. So where would I like to go? Well I would like a planet to be discovered where the population

has managed to unite quantum mechanics and gravity together and they have a working quantum theory of gravity because I think a world like that would be very very different from this one and probably quite unrecognizable the technological advancement would be astonishing so I'd like to see that kind of world discovered or a world where the oceans are made of gin. I'm not going to start, actually. Hello, my name is Katherine Parkinson. I'm from the University of Show Business.

And the planet I would most like to discover is the planet or habitable moon that I imagine ET to have come from. Oh. And this is our panel. APPLAUSE I love that, Catherine, because that immediately made me think also of perhaps my favourite one, which would be that asteroid which the little prince is on,

which has the rose that grows and which he has to protect and is so worried about. But let's get down to the real science of it. Who is your favorite wrestler? No, the... I love Barry McGuigan. I know he wasn't a wrestler. He's a boxer but my dad's from Northern Ireland and we Barry was massive in my house growing up so I'm... I liked your reference to him. Now, because you are the adjudicator. We have this kind of battle between a battle of the planets between Saturn and Jupiter and what is your planetary knowledge generally, your planetary science knowledge? I live near the observatory. Yeah, no, that is it. Right.

That's why we chose you. We literally, we had a big map of where all of the people in entertainment lived and we went, she definitely lives closest to the Greenwich Observatory. No, I am very interested in it. I remember when I was about 10, just wondering why we didn't learn more about the planets at school and haven't seen that change as much as I thought it might with my children. We should start then. So Paul, you're championing Jupiter. Yes. So give us the one minute pitch.

I've got it split into two things. Firstly, its place in history. Jupiter was one of the planets Galileo turned his telescope to. And it has four very large moons and you can see them with the telescope he built himself. And at that moment, Jupiter stopped being a star in the sky and became a world surrounded by moons. And that began the Renaissance with not thinking of the Earth as the centre of the universe anymore because if there's moons orbiting Jupiter and the Earth is important, why aren't they orbiting the Earth? So that's the first point. The second point is, yes, everyone goes on about showing people Saturn through a telescope,

but if you show people Jupiter for the first time, they can see the gorgeous cloud markings changing in ten minutes. It doesn't need a very large telescope. As well as that, you've got the moons of Jupiter that pass in front and cast shadows. It really is almost like being in a spaceship approaching it. Then final point, Jupiter saves our lives by its immense gravitational field sucking out comets and debris and stopping them from colliding with the Earth on a way that will be far more frequent

than we have at the moment. It is worth saying, isn't it, that you see those moons and you can see it's a disk with any telescope. Yeah. So for an amateur astronomer, it's the easiest target. And you can do some very simple things. If you time how quickly the Great Red Spot, which is this vast hurricane in Jupiter's southern hemisphere, you time how long that takes to go around the planet.

You can work out how quickly the wind speeds are on Jupiter. And they're absolutely colossal, much more so than here. All you can do with Saturn is look at the rings, not that I'm biased. That is a... You can do real physics with it. Very strong argument there that without Jupiter, we're all going to die.

So, Michelle, Saturn. argument there that without Jupiter we're all gonna die so Michelle Saturn how can he choose Jupiter over Saturn I mean you look in the night sky and there's this gorgeous planet out there with fantastic rings around it moons as well yeah and if we go back in history I can do that as well Cassini had a look at Saturn through a telescope that he built. And when he first saw it, it looked as if it was a funny shape. It wasn't a round ball, there were these two blobs on either side and they changed shape every time he looked at it. It was only after a period of time that he realized there were these rings and depending on how they were oriented

you could see the rings or you couldn't. So Saturn's much more interesting and it's much further away and it's got these fantastic moons Jupiter has fantastic moons, volcanoes, biggest Texas, what more do you want? So Michelle could you just describe a bit a bit more about the structure of these planets how big are they what is their composition? You sort of look at Saturn or Jupiter in the night sky or in fantastic images that you get from? Different telescopes and it looks like it's a solid surface, but it's not if you tried to stand on it You'd fall all the way through so there's a solid core and then there's liquid above that core and then there's gas and They sent a probe there was a probe that went through the atmosphere of Jupiter and there was a probe that went through the atmosphere of Jupiter

and there was a probe that went through, well, Cassini spacecraft dived into the atmosphere of Saturn and they broke up because of the large density in the atmosphere. There's also that metallic hydrogen, so when you get to Jupiter, you get to pressures where the hydrogen is squashed into a metal and it generates this enormous magnetic field. If you could see Jupiter's magnetic field in the night sky it would be as large as the full moon. It really is one of the most impressive structures. As seen from Earth. Yeah, as seen from Earth, that's right. Yeah, yeah. It's an enormously powerful structure. So if we were to slice through Jupiter, first of all what's its radius, how big

is this thing, and could you describe that cross-section through the planet as you dive down? Yeah for Jupiter you've got the upper atmosphere that we see we think the darker cloud bolts were made of ammonia Hydrosulfide and the brighter zones are higher up ice crystals of various things. So it's ammonia hydrogen sulfide I think there is some still debate even though we've got spacecraft out There's some considerable debate about the chemistry of the stuff we can see, let alone the stuff further down. Anyway, you've got these cloud bands and then you go through a water layer and I think there's supposed to be a methane layer and then under that you've got this hydrogen helium layer and it was thought for a long time that that went down quite a way

before it was all squashed by the pressures and temperatures into this metallic hydrogen helium but the Juno spacecraft that is flying around the poles of Jupiter actually seems that the metallic layer is much closer to the cloud tops than we thought and it's a complete mystery and I've asked several of the very distinguished space scientists in our department and all I get is a baffled look so I don't really know. So can I try and match the story about the metallic layer? Yes, because I was going to just say, because although you're advocating for Saturn in this rather artificial construct,

you are on the Juno mission, aren't you? So the Juno mission that Paul referred to is one of the spacecrafts. No, I'm not, but I'm on another Jupiter mission. So I'm very torn tonight. I'm very torn tonight. I hope none of my juice colleagues listen in to this is that I always think you know spacecraft they're wonderful names usually Cassini and Galileo. Well I blame the European Space Agency. Could you say what juice stands for? So I'll tell a little story before that. So to begin with we were going to have a joint spacecraft mission. NASA was going

to build a spacecraft to go to Europa and Europe were going to have a joint spacecraft mission. NASA was going to build a spacecraft to go to Europa, and Europe was going to build a spacecraft to go to Ganymede. And then NASA said, oh, no, we can't afford to do it. So ESA turned around to us and said, you've got three months to design an ESA-only spacecraft mission. And oh, by the way, you've got to change the name. We didn't have time to think about a name.

So after a long day of planning the new mission, we went and sat in the pub. And I think we were three gin and tonics in. And we came up with a list of names. The first two, I can't actually remember them, but ESA said no, other spacecraft had been called that before. So one of the names which we came up with was Meow. Moon Explorer of Ocean Worlds. One of the names which we came up with was Miao, moon explorer of ocean worlds, which we thought was great, but we didn't think we would be taken seriously.

So number four was Jupiter, icy moon explorer, and you've got to work a bit hard at that, but that's where juice comes from. And Issa said to us, you can't call a spacecraft juice, we're going to have to call it something else after launch. And I said to them after launch, we're going to rename it. Oh no, everyone likes juice. That's where juice came from. Your story made me think of when I started drinking when I was 15.

I was told that when I ordered a gin and tonic, I had to say gin and tonic supersonic. It was just some boys winding me up and I thought that's what you had to say to order a gin and tonic, I had to say gin and tonic supersonic. It was just some boys winding me up. I thought that's what you had to say to order a gin and tonic. I said, can I have a gin and tonic supersonic? It's a good thing you weren't in the meeting where we chose the name. Yeah. Good thing I've done that. Were there any similar wind-ups when dealing with astronomy,

where a new student comes in and you create some form of fabrication which they must discover? I used to, when I was very young and stupid, used to tell them equations were easier to solve if they were written in a color red. Until my head of department said stop doing that. So I changed it to green. So Michelle, so you're gonna deviate from the... for Jupiter? Yes. You're not advocating for Jupiter? No, no, no. You're to deviate from the... for Jupiter? Yes. You're not advocating for Jupiter?

No, no, no, no. You're going to describe this cross-section and this strange metallic hydrogen and what that is? So, Saturn is something similar. We're still not quite sure what the interior looks like, but one of the things we plan to do with Cassini is we were responsible for the magnetometer instrument on Cassini, so that measures the magnetic field. So now we're around Saturn again.

We're orbiting around Saturn. And I said to everyone, one of the strange things about Saturn is all the observations that have been made so far seem to imply that the rotation axis of Saturn and the magnetic axis lie on top of each other. And planetary dynamo theory says that cannot be. And so I kept saying to everyone, oh, if we just get closer, if we spend more time there, we'll find out the answer.

Turns out there isn't any tilt at all. It turns out that Saturn is much more interesting than Jupiter. Jupiter has a similar thing. Oh, yeah, well, but Jupiter doesn't have a secondary dynamo which masks the effect of the internal dynamo. So it's unique in the solar system. You could perhaps unpack that a little. Well, refers to the Earth. So, you know, we stand on the surface of the Earth and we've got a compass needle and a point to the north pole of the magnetic field.

And the magnetic field of the Earth that's generated in the interior of the Earth protects us from the effects of the solar wind. So all these energetic particles coming towards us, we get protected by the magnetic field of the Earth. So Jupiter and Saturn also have these internal planetary fields and Jupiter's field in some ways looks similar to the Earth's because there's this tilt between the rotation axis and the dipole axis. Saturn is unique in the solar system because it has this planetary dynamo in the interior, but there's a dynamo on the, quite close to the surface, which is masking the effect of the internal.

So there's something else creating a magnetic field, so it's not just the single thing in the core. So that means that there are electrical currents flowing in the high atmosphere Presumably so what would that be you said it was there's ammonia up there and then there's So Saturn's absolutely layer is more complex If you look at Santa a telescope the banding is much more subtle and I think it's because there's this petro Chemical smog isn't there, that obscures the atmosphere. So what you're seeing there,

because it's kind of a dull yellow, we call it what Robin referred to in the intro. Yeah, that's why. Because that really is haze. Yeah, it's a petrochemical haze, yeah. Why it's there, not on Jupiter, I don't know. Because if you look at Voyager Day and Cassini images, you can see the banding much more strongly

than through a little bit of a stusco. Just that banding, so Jupiter, the first thing you see when you look at Jupiter through a telescope, or any photograph, are those bands, those clouds, which is unusual because you look at Earth's clouds and they don't go into these perfect stripes around the planet. Right. So why is it stripy? I think it's the wind speeds. So the Great Red Spot storm I mentioned that's been going for 300 years, because you mentioned earlier there's no land, these storms can't

break land and lose their energy and dissipate. So that just doesn't happen. Once they get started on these big planets, they go forever. And for some reason, you've got these parallel winds jet streams that go around the equator and all the way up. And I don't really understand how this works, but you get these gases forming between up. And I don't really understand how this works, but you get these gases forming between those, and that's where the belts and zones come in. They seem to be constrained between these very, very fast jet streams.

Yes. I still don't understand why the red spot is still there. It's nearly gone. When I started drawing it, drawing Jupiter a long time ago, it was much larger, and it's now shrunk, and no one knows really what's going to happen to it, whether it just becomes spherical or whether it'll disappear completely or there might be some sort of global event that happens, because the southern hemisphere of Jupiter is quite different to the northern hemisphere and every now and then the band that's in the south,

the one you can see through your telescope, disappears completely and the great red spot gets really dark and then you get this break out of spots in the southern hemisphere and the band reforms and nobody really understands why this happens. So what was interesting is in the first couple of years of us being at Saturn with Cassini, there was a... Oh the storm, yeah. There was a huge storm that was seen in the northern Hemisphere, and over time it spread itself out, and so there was almost like a great red spot, although it wasn't red.

And then as the planet rotated on its axis, it evolved and it moved around and slowly it dissipated, but it took about a year, I think. It did. The features in that part of Saturn remained disturbed for a couple of years afterwards. Very, very unusual. And it was outside the usual spot cycle. Saturn normally has these big, big storms every 30 years, and this was outside that 30 years. No explanation for it.

It's interesting, Catherine, is it that these, the time scales, we speak of weather on these planets, but as you said, this storm is over 300 years old. It's quite daunting. But it does sort of sound like a bad sort of spot that sort of takes a while to settle and then has some kind of damage around it that takes longer to settle. It's three times the size of the earth wasn't it? It was initially much larger than that, it was about five times the size of the earth. Now it's about a couple of times the size of the earth, it's slowly shrinking. I mean this is a question, even though it might not sound like one, but if there was extraterrestrial life and there was all this helium going on,

would they be in a high voice? LAUGHTER I mean, I'll just say yes so we can move on. LAUGHTER We're not moving on now, Paul., we literally found the peak of this show. I'll be able to remember though, remember Carl Sagan, I think it was in Cosmos, had the idea of these floating organisms. There was a painting done I think, wasn't there, showing these huge jellyfish-type creatures in the atmosphere.

Is there somewhere, so is there a region where you could as Sagan did where you could imagine Some kind of life in those atmospheres and there must be a region. You said there's water vapor there I would imagine it is possible I mean if we look at the solar system and we long ago thought all the things that we thought were normal aren't So I could imagine something, you know, it was a very simple like bacteria just exist in that way Just in terms of the conditions what kind of conditions are we speaking about in the cause of these two planets? Incredibly hot. What are we talking about? Plus 300 degrees Celsius. More than that.

Pressures at the kind of levels where on Earth we couldn't even generate them. Lots of material moving around. Even though we've got all these spacecraft and we can study these planets with telescopes both in space and in our gardens and in between, there's still considerable debate about the interior of these planets. I think that's marvellous because it kind of gives amateur astronomy plenty to do. I know you professionals have got all the kit and the money but whilst you don't know what's inside, we've still got a job to do. The last thing I want to mention is... That really put me in my place.

I'm interested in that Saturn's rings, and Jupiter has rings, but they're eroding. And because they think that they were caused by a moon getting too close, is there the potential for, in a long time ahead, more rings to come? Potentially, yes. And one of the things that's also happening to the rings is they've been covered with water vapour from one of my favourite moons. I don't know if I'm allowed to talk about it yet. Titan? You can move on to the moon. But the rings are being covered all the time with water vapor falling on top of them.

Ring rain. Ring rain. Yeah, yeah, no. She's been looking up scientific books. I can tell. Nobody can forget that phrase. So those rings, so what's our current understanding? They're quite recently formed, I think, aren't they?

That's the current view. Yes, it does. Could you describe the current thinking as to how, as Catherine said, how did they form? Why did they form? Well, my understanding is, and the theory guru over there might tell me it's all wrong, but there were a moon, or maybe two, that got a little bit too close to Saturn, and they were pulled apart by the gravitational force of Saturn, and because of orbital dynamics, all the bits that broke up now force of Saturn. And because of orbital dynamics,

all the bits that broke up now orbit around Saturn. So when you look at the rings, they look as if they're solid, but they aren't. They're made of these countless individual particles, each in their own orbit around Saturn. And there's some beautiful images which show moons right on the edge of the rings. And the moons orbit at the same time as the rings, and they make these beautiful wave right on the edge of the rings and the moons orbit at

the same time of the rings and they make these beautiful wave structures on the rings. That bit where you see these patterns and we are a pattern-seeking creature and you know to look at what would appear to be the patterns in Saturn's rings you know that sense of wonder and awe. I know you have done some research you know when you knew you were coming on the show. Did you find yourself looking at certain things and just going what a strange thing that's not just a mess? Yes, the thing of beauty, this subjectively beautiful thing, has come from sort of trauma, potential trauma. I like that.

Yeah, and the fact that it's so ethereal, temporary. So when do we think they will vanish from beauty? Do we have a... Yeah, they will eventually fade and then that'll be it. They were very short-lived phenomena, I guess, in the age of the solar system. But what I find so interesting is they're really thin. So if we were thinking of it on a scale of Earth and Earth had rings, what kind of...

A meter? Yeah, I mean, they're like sheets of paper. They're really that thing. It's just the ice that makes them so very visible. When Voyager was going to Saturn, they wanted to fly through the Cassini division and Carl Sagan's mother astronomer said, perhaps not a terribly good idea because there might be stuff there we can't see. And as they got close up, there was the Cassini division,

which looks empty from the Earth through Earth-based telescopes, filled with rubble and dark material. The spacecraft had been utterly destroyed. We've had two Cassinis here. So Cassini the astronomer, the spacecraft had been utterly destroyed. We've had two Cassini's here, so Cassini the Astronomer, after which the Cassini spacecraft. But also thinking not to get obsessed with Saturn. I feel that it's already stacked against me. You know that cartoon in children's books when you had Saturn with the ring in the bath,

and it being because it's not as dense as water but I think I always thought it was like a rubber ring that you would have at a swimming pool but is that the case that Saturn is less dense than water? Yeah I think it is. You could find an ocean lard in there. So you could just float Saturn on Saturn. I just cannot get my Thing though, I love the idea that when the ring does finally disappear Saturn just kind of drops but oh god That was what was keeping it up But don't we go to Jupiter? Okay, and so can you give us an overview of the the moons that are there? Well, there's lots of dull ones, but there are four very interesting ones. These are ones you can actually

There's lots of dull ones, but there are four very interesting ones. These are the ones you can actually see. We could have just cut it there. There are loads of dull ones. Thank you. How many dull ones are we talking about? I didn't come down to be here to be insulted. I could have stayed at home on social media. There are the four main moons, which you can actually see.

These are the ones that Galileo saw with his small telescope. Io Europa, Ganymede and Callisto. which you can actually see. These are the ones that Galileo saw with his small telescope. Io Europa, Ganymede and Callisto. Ganymede, largest moon in the solar system. In fact, it's larger than the planet Mercury. So these are actually kind of, if they were orbiting the sun, there would be planets in their own right.

But for me, the most fascinating one, everyone chooses the icy moons because, you know, potential for life. But for me, the most fascinating one is Io because it's so volcanic. It's just a bit larger than our own moon and the largest active volcano on on Io is twice as big as Texas. And the reason it's this hot is because one side of Io is very close to Jupiter and the other side you've got the other satellites pulling. It's like bending a paperclip back and forwards

you get a lot of heat generated and that's what's happening on Io. It's been this tug-of-war which generates all this heat and all this vulcanism. You don't get anything like that on Saturn. It really is a fascinating moon. There is a plan to hopefully send a spacecraft called Io Volcanic Explorer. Yes. No, or Observer. Ivo it's called. That'd be fascinating. We're going to try and propose to do that and but we aren't going to go into orbit We're just going to fly past that's enough. If you need the money, we still have a whip round we can

See Europa you mentioned Europa the Europa is the the target of the Europa Clipper mission for example Which as we record is going to be launched next week. So when we broadcast it's either on the way to Jupiter to be launched next week. So when we broadcast it's either on the way to Jupiter or on the way to the inner solar system. Europa kind of looks like a white billiard ball. It's completely covered in ice and very, very smooth. And for a long time it was suspected that the same mechanism by which Io is so volcanic, that same sort of heat process can melt the interior of Europa. And we think there's this ocean on Europa. Obviously, it's very difficult because we can't see through the ice to determine it. But what people did was they compared the Voyager spacecraft images

with ones taken by Galileo. There were subtle markings and changes on... Again, Galileo, the spacecraft Galileo, not the Galileo. Galileo, the spacecraft, imaged... You're very pedantic today Brian and we were able to they were able to see these changes which suggests there is probably a deep ocean whether there's life in that I don't know certainly if we look at the Earth's deep sea vents there's life down there it's

quite different to what we see so maybe there is I just hope we don't spoil it so the G spacecraft which is in flight which you are a scientist on. Yes, so yes we're going to fly past Europa twice. I think we have 29 flybys of Callisto, which is the one furthest out. We're also going to fly past Ganymede on numerous occasions, but then we're going to go into orbit around Ganymede. And why Ganymede? Because Ganymede is unique in the solar system, because not only do we think it has a liquid water ocean under the surface But it's the only moon in the solar system that has an internal dynamo field so if you stood on the surface of Ganymede and you had a compass needle it would point to the North Pole of the

magnetic field so as Magnetometer person where else in the universe would I want to go to other than Saturn? So this is a world that as Paul said it's the's the biggest moon, it's a planetary-sized moon, and it's got a magnetic field, and it's got a liquid ocean. And if there is organic material on the surface, it will be protected from the impact of the radiation from Jupiter because of the magnetic field. So it's a potential target.

It's a potential target. But Europa, we think the silicate mantle is in contact with the liquid water and so organic material might be able to leak out into the liquid water but we aren't sure about that with Genome. Catherine we're over halfway through the show now so we need to know roughly where you are in terms of Which planet is going to be the victor because as you know the the other one will be destroyed. Oh really I didn't know that I'm sorry. I'm so sorry. I have to admit we were deliberately hazy on that I've got us. I've got a spacecraft going there. Can I change my mind?

Yeah, listen to all these things. What is it that you've heard so far? Is it a sense of beauty, the possibility of life? Is it something different? I mean, I feel like Jupiter wins anyway, in many ways, and that's why, of course. Saturn you'll choose, yes. I'm intrigued by the sort of fluffiness of Saturn, but with this obviously very unfluffy core. And I think it's moons do excite one more, but yeah, at the moment it's Saturn,

just because you know, Jupiter is already the Godfather. So we've had Jupiter's moons, so we've talked about Io, Europa, Ganymede, Callisto, the Galilean satellites. Over to Saturn, you mentioned, Catherine mentioned Titan and you've mentioned obliquely this moon Enceladus. Yes. Could you go through Saturn's inventory of large moons? I lose track of how many moons Saturn has. Every time they look they're more so the last count was about 68. You could see

eight of them with a small telescope. Yes, that's right. It is quite phenomenal. What is the size in which something will become defined as a moon? As long as something is orbiting around a planet you can call it a moon. One of my favorites is Enceladus and that's 500 kilometers in diameter and its surface is covered in water ice. And so it's a bit like Europa if you fly over it, it's white, it reflects back at you. And the reason I'm so partial to Enceladus is that we discovered a water vapor plume coming off from the South Pole of Enceladus. And so that's when there was a focus on Enceladus as a place where life could potentially form because you need

four things, you need four things. You need four ingredients. You need liquid water. You need a heat source. You need organic material. And then you need those first three ingredients to be stable enough over a long enough period of time that something can actually happen.

And for me, I think that's probably one of the most important realizations that planetary scientists have come to. And I don't know, the last 30 years or so, is that if you're looking for liquid water in the solar system, you don't have to focus on the inner solar system. You can look beyond us, but it's just not on the surface, it's underneath the surface.

I think that must be the biggest change in planetary science. Most people thought in the 60s that the moons of Jupiter and Saturn were just like our own moon. I think Carl Sagan had to really press For the moons of Jupiter and Saturn to be surveyed by Voyager because everyone thought they'll just be dead and uninteresting And they turned out to be some of the most interesting places at the solar system both of you in terms of when Trying to get financed for missions. Yeah, there's so much to explore get financed for missions. You know, there's so much to explore. There's a very small pool really of money. If you were going into a meeting to say this is where we should be

going, what are the things that will most excite, whether it's ESA, NASA, whatever it might be? The search for potential habitability is how we sold juice. And I think if we hadn't made the discoveries on Cassini that we did we wouldn't have been able to persuade the European Space Agency to fly juice. So it's a search for life. Paul, I think that's exactly the same. I think that's the thing that seems to drive things these space missions. I would love personally to see a space mission to

Iapetus, the moon of Saturn, which is approximately half the hemisphere is really dark and the other half is really light. And there's that really high ridge that runs around the moon. There is, it's very unusual. I mean, if you watch, you can actually see this satellite in a small telescope where it's on one side of Saturn, but as it moves around the other side, it vanishes because it's dropped in magnitude. It's so faint because the dark hemispheres point towards us and it inspired Arthur

C. Clarke to set 2001 initially on Saturn because that moon was part of the monolith and then they changed it to Jupiter. The Cassini. But they changed it to Jupiter. The astronomer Cassini saw it didn't he and he thought it seemed to be vanishing didn't he said Yeah, just see but it can't be no, that's right. Is it the laws of nature would not allow it to vanish? Yeah, so he correctly some eyes didn't need that. It was half very dark and half reflective. That's right It's Saturn. Yeah, it's a day one hour longer on We don't quite know how long a day on Saturn is. Let's just say yes.

It's about 10 hours, whereas on Jupiter it's just over nine hours. Here's a fun fact, if you start observing Jupiter early in the evening about December and stay up till about five in the morning you can see a whole day on Jupiter. It rotates so quickly. Right Catherine I'm now going to give you one final question to Paul and one question, final question to Michelle just before you make your decisions. Okay hypothetically what would Jupiter smell like? A cross between a gentleman's lavatory and a farm yard. This could really swing it. Michelle?

Just say lavender. Hot chocolate. True. She knows me. So Catherine, your decision then? It's Saturn or is it Jupiter? I mean, what brilliant, fascinating planets, but Jupiter's already massive, so Saturn. I knew I liked you. APPLAUSE Just to finally frame that, because this is an important question because when we talk about future missions

So is there any way really of deciding between these two systems because they're both we shouldn't have to Fascinating we shouldn't have to we should spend our money on the exploration of space It's an important part of understanding who we are and the bigger picture of where we are and there's this really cool mission going to Titan Called dragonfly. Oh, yes, and I was in Washington last week and I saw Dragonfly being built. It's a helicopter and it's gonna be dropped into the atmosphere and they hope like hell the rotors will actually fire as they drop it and it's gonna fly over the methane lakes. And it'd be interesting because when the Sun becomes a red giant the habitability of Titan really increases and if there is any organic material there will the magic that converts

that into self-replicating proteins DNA form there it would be fascinating which is why again it should be a protected environment even though it's four million years billion years in the future as you said before we went out there you'd think okay, there's earth and Mars that's pretty much it right nowhere else and then you find these Worlds like multiple worlds here for in orbit around Jupiter three or four in orbit around Saturn That may have the conditions that could support life. Yeah I was it would be somewhat ironic if that's where life is discovered first, not on an exoplanet, not on Mars, but deep in the moons of one of these gas giants,

because no one would ever have thought of that. And one of the things I meant to mention, and I forgot, is that one of the other reasons we want to focus on Ganymede with Jus, is that we think the internal structure of Ganymede is a water world structure And we think a lot of the exoplanets which are being discovered on water world structures. Isn't that wonderful? It's a planet really and I'm in a sense. Yes. Yes, Brian I'm glad I didn't mention it earlier because it might have you know changed the vote No, I could see I could see where I could see you were biased when you were offering her brownies in the in the green rooms

Oh, I know I think that's amazing which way it was going Paul Paul just before we finish You should show some of your sketches because just I know this is radio This is just but because Paul is one of the last remaining old-fashioned astronomers. It doesn't take pictures No, I don't take pictures and anybody who see me trying to operate word will know why I don't. This shows the surface. You probably can't see it, but we've got the Great Red Spot there and on this particular drawing I measured just how wide the Great Red Spot was just because I was bored and it was cold and we also have the moons of Jupiter there. You can see perhaps their shadows being cast and you can watch because the inner moons move quite quickly over the course of two or three hours,

you can see this change. So it is quite spectacular. And there's still a reason to do this. It connects us with the history of astronomy and science. So I think there's still a reason to do it. Could you hold some of the drawings a little bit close to the microphone so the audience are home for a second?

Um, thank you. They're really, really good circles. Do you use a compass to make it very... They are ellipses. No, that's OK. I'll tell you what, ever since he lost, I don't think you two are going to get on so well now. In terms of in the acting world, if there had been a similar kind of, you know, the competition playwrights, actors, plays, whatever it might be, what is the green room of a theatre equivalent of Jupiter versus Saturn?

Oh, I mean that's really hard, but I suppose you could have a comparison of James Bond's or Benedict Cumberbatch versus Idris Elba. I thought you were going to say Chekhov versus Shakespeare. Oh sorry, can we edit that? Can we edit that? Idris Elba. I mean for me it would be Chekov or Ibsen. I've spent a lot of time, because you were saying about how you came up with juice, I've been working on the cross stick myself, and what I I came up with Jupiter ambulating, moving into planetary explorer,

looking eagerly extraterrestrially, contributing understanding regularly to interested species and then you can call it Jamie Lee Curtis. I wonder why you were so quiet. We should do that, if we did that every episode. It would be wonderful. I can't be saying anything when you've done all those different shows where you wonder around with a parasol and explain some kind of orbit? We asked the audience a question as well and the statement is the planet I would most like to live on is... What have you got there Brian? Mars, because on Mars every day I could work, rest and play. That's been welcome.

Now the exciting thing here is waiting for the D-Reme pun that will probably be in it. Have you got the D-Reme pun? The planet I would most like to live on is Venus. She's got it. Yeah, baby. She's got it. Oh, Bananarama before D-Reme. Very rarely happens there.

Pluto, because I'd like to be irrelevant and forgotten. Pluto, nitrogen glaciers, water mountains and potentially a liquid ocean. So there could be life. There could be life on Pluto. So yeah it's been un-forgotten. So you see you don't have to be a planner to have life on it What's the next one you've got Mars because it's made of chocolate to repeat the joke, right? That's a good joke. I've got that this one's moved on from chocolate Mars cuz that's where all the men are Allison is extremely pragmatic.

It's Venus, because wouldn't have to worry about the heating bill. The Forbidden Planet, because I'm just a rebel and I dream of being told off by Brian. That's not me. That's Debbie. LAUGHTER That's Debbie, although it's still me. Saturn, because rings can only get better. CHEERING AND APPLAUSE

Anyway, thanks very much to our panel, Michelle Doherty, Paul Abel and Katherine Parkinson. CHEERING AND APPLAUSE Parkinson. We are recording this in 2024, you were hearing this in 2025, so at the moment we have no idea what next week is going to be about, or even if there is, next week. So I decided the or even if there is next week So I decided the best way was to find out through scientific methods. So I have consulted Brian's Astrological chart to see what is the most likely subject for next week's show. So Paul, how accurate do you think that will be? I think it will be a hundred and twelve percent point three accurate. You're entirely right according According to his astrological chart, it just says bloody

physics again. So thanks very much for listening. Bye bye. Which might be the best friend while I'm losing my cool In the infinite monkey cage The naughty monkey In the infinite monkey cage Without your trousers In the infinite monkey cage Turned out nice again Best medicine Dissecting funny and fascinating medicine

I think pain management is the best medicine. Bibliotherapy. Therapy by books. Sleep. Yes. Well, spot the comedian. Celebrating medicine's past, present and future. I think transplantation is the best medicine because it can completely change someone's life.

Defibrillation. Oh, defibrillator, okay. Amazing machines, that much is clear. Sorry, clear! That's the new series of Best Medicine from Radio 4 with me, Kiri Pritchett-McLean, available now on BBC Sounds.