The Infinite Monkey Cage - How We Measure the Universe

Episode Date: February 11, 2019

How to Measure the UniverseBrian Cox and Robin Ince are joined on stage by comedian Jo Brand, and physicists Prof Jo Dunkley and Dr Adam Masters to look at how we go about measuring our universe, from measuring the contents of atmospheres of planets and moons at the outer edges of our solar system to looking far back in time to study the very earliest beginnings of the cosmos. Our ability to learn about phenomena and worlds that seem almost impossibly out of reach, now give us an incredible insight into the universe we occupy, and how we got here. Brian and Robin find out about some of the big new missions providing information into our own solar system and beyond, and find out what big questions in cosmology still remain a tantalising challenge?Producer: Alexandra Feachem

In our new podcast, Nature Answers, rural stories from a changing planet, we are traveling with you to Uganda and Ghana to meet the people on the front lines of climate change. We will share stories of how they are thriving using lessons learned from nature. And good news, it is working. Learn more by listening to Nature Answers wherever you get your podcasts. This is the first radio ad you can smell. The new Cinnabon pull apart only at Wendy's. It's ooey gooey and just five bucks with a small coffee all day long. Taxes extra at participating Wendy's until May 5th. Terms and conditions apply. BBC Sounds. Music, radio, podcasts.

Hello. Hello. We used to be the centre of a conveniently small cosmos with a sky made of crystal spheres and only the peculiar path of Mars to worry about. But as usual, science couldn't leave it alone, could it? No. So Galileo stuck his telescope in, spots the moon circling around Jupiter. Typically the next thing you know, we're stuck in the backwater of a galaxy that's among two trillion other galaxies with billions of planets in each and the universe is expanding at 70 kilometres per second per megaparsec.

Did it sometimes make you hunger for a simpler time of inquisitions and where truth was found out through fear and torture. So the moral of the story, as you see it, Robin, is that nature is unnecessarily complicated and it would be better in any case if we knew less. Yep, that's roughly what I'm saying. I want to go back to a time when you could settle neighbourly disputes by suggesting the lady next door was practising witchcraft.

It was a simpler, more aggressively dogmatic time. While Robin remembers his ducking stool with fondness, the rest of us will consider the magnitude and magnificence of the universe as revealed by science. What is the size of the universe and how long has it existed? What is the distance to the planets and the stars and galaxies and what do we know about their histories? How do we measure the universe?

Joining us as we explore the universe, we have a distinguished panel of space explorers, and they are... Hello, I'm Adam Masters. I'm a lecturer in planetary science at Imperial College London, and I think the most exciting discovery about the universe has been that there are oceans of liquid water underneath the icy surfaces of some of Jupiter's and Saturn's moons, and these are really good potential habitats for life.

Hi, my name's Jo Dunkley. I'm a professor of physics at Princeton University and author of a new book, Our Universe. And to me, the most remarkable discovery about our universe is simply how enormous it is. It's big. Hello, my name's Jo Brandt, and I think the most remarkable thing about the universe

is that there are oceans of liquid water... LAUGHTER ..under the surfaces of... Was that Jupiter? Yeah, that's right. Great answer. I didn't get to the end, but whatever you said, anyway. And this is our panel! APPLAUSE And this is our panel. Thank you. Jo, I suppose as the most regular guest on our show,

you probably do have the greatest amount of gravitas when it comes to understanding the universe. So I'll start with you, Jo Brand. How do you think we measure the universe? Is it to do with expanding and contracting stars moving away from you or towards you? Let's find out. Thank you, Jo. Yes, apparently she's nodding.

Adam's going, oh, not sure, because he doesn't know, because he's filling in for me. Jo. Brian, am I right? Let's find out. That's pretty good, actually. Yeah, so it's actually kind of a challenge looking at and measuring the universe

and seeing where everything is, because all we get to do is sit here on Earth and look. I mean, you can send some spacecraft out in the solar system, but we want to measure something much bigger. We'd like to figure out where everything is. You just dismissed Adam's entire career there, by the way. All off the stage here. Apart from this little thing that Adam does we'll come to

that we'll come to that that's right you know all you could do as an astronomer or as a human is sit here on earth and look out and you see the see the stars above us and they're kind of like a just a two-dimensional surface around us but what we want to do is figure out where everything is and how we fit into like a 3d picture of of where everything fits in and also is it moving towards or away from us and where things are and actually measuring the distances to things out in space is one of the hardest things that we have to do in astronomy when when did we first get any idea actually that the stars are very distant or even actually when were we able to measure the

distance of the planets well so the distance of the planets we've been able to see that the planets were moving in the sky so we've known for we knew for like a long long time that they were going around that they were moving through the sky and then we figured out they're going around the sun but actually it was only in the 1790s that people figured out how big the solar system is and it was really cool actually it was through a transit of venus measurements that this inspirational astronomer called edmund halley told future generations of astronomers that if they only could only go and measure a transit of venus when it's going in front of the sun that they could actually figure out the scale of our whole solar system and the way that works is that it's actually...

I use this thing called parallax. So let's say you want to measure the length of your arm, OK? So if you put your arm out in front of you with your finger stretched out, and maybe everyone can do this at home and it is now, OK? Unless you're listening to this whilst driving again. Prince Philip. APPLAUSE Philip. So let's say you want to measure the length of your arm but you can't be bothered to go and measure it.

You close one eye and see where your finger is against the thing behind it. And then close the other eye, if you can, and see if it moves, right? Do you see your finger move? And if you then put it towards you and do the same thing... I'd have measured it by this time, Jo. Because you can't be bothered to measure it.

You'll notice that it moves further if it's closer to your eye, right? So if your arm is shorter, it moves further. And all you need to know is the distance between your two eyes and the amount your finger moves, and you can figure to know is the distance between your two eyes and the amount your finger moves and you can figure out the length of your arm from that just using a triangle trigonometry that you might have learned at school and if anyone any other listeners if you'd like to do that now and then send in your results and we'll be able to work out who's closest because i'm sure there's someone i always go my arms 27 meters long i've definitely done some measurement. I can't be Mr. Tickle. That's right.

So these astronomers, you know, back hundreds of years ago, did the same thing using Venus as your finger and the backdrop, and they used Venus as it passed across the sun. And your two eyes were two different positions on earth. So groups of astronomers would go to different parts of the world and look at Venus transiting the sun from two different places. Halley proposed that, I think, in the 1670s. And it wasn't until 1761 that Venus crossed the face of the sun, which gives you a sense of the length of time, the importance of the measurement.

There's almost a century, wasn't it, they had to wait? And it's so depressing for him. I know! I know how we can work it out. When's the next one? I'll be dead. You know, that kind of... The delayed gratification, you know, both theoretical physics and generally cosmology, there's a certain almost sadness but a beauty to it.

Well, I think it's amazing because we see it actually throughout the history of astronomy and cosmology that he realised that it could be done, but that he wouldn't do it. And so he actually wrote this really inspirational paper that he wrote, exhorting younger people to go and make this measurement. And this is why. So the transit of Venus means Venus going across the sun. That's right.

As opposed to the transit of norman who's our builder and he doesn't have any tools left in it overnight just in case people were wondering so once that information has been gained though that's that done now we don't have to keep waiting for the transit of venus we've got the measuring tools that's the starting point isn't it of then being able to get the rest of of of the view of distance of stars, etc. Is that fair? That's right. So you step out. That's right. And so the next thing is, so once you know the size of the solar system, the next thing out is the stars.

But it turns out you can measure the distance to stars also using parallax. But now, instead of two different positions on Earth being your two eyes, you look at a distant star that you want to measure the distance to. It's your finger again. And you look at the star against the backdrop of much more distant stars. And you close one eye by looking at the star from Earth at one time of the year. And six months later, when the Earth has gone around the sun halfway, then you look again at the star, basically closing your other eye, and you see how far in the backdrop it moves. So now you just have to see what angle the star, basically closing your other eye, and you see how far in the backdrop it moves.

So now you just have to see what angle the star moves against the backdrop of more distant stars, and you can actually find the distance to it. And you could never go there. So this is where you really can't go and measure your arm because you can't actually get to the stars to make that measurement. It's a beautiful idea, isn't it? Because it's very, very simple, but it's basically the only way to do it. I was thinking, actually, you were talking about Venus, that in terms of measurement, we're talking about measuring the universe, measuring or understanding the planets is also extremely recent. I mean, Venus, you know, I remember Patrick Moore, reading that Patrick Moore, even in the 50s or so,

and professional astronomers were imagining Venus might be a cloud-covered world in a tropical paradise. And it's not until we went there to make measurements that we found it was anything but. It's true. I mean, you know, picking up on this theme of having to wait a long time before the opportunity to make a measurement, even within the solar system, if you think about the planets that are the furthest away, so Neptune, Neptune's 30 times further away from the sun than we are. And we're about 150 million kilometers away from the

sun so it's a long way so you know at the moment there's all of these plans to go to Neptune and the earliest we could launch would be 2030 which in my field is pretty soon and so you've then got 15 years at best if you want to orbit to get to your target so you know I'll be retired. So even in planetary science, within the solar system, where things are closer than looking at stars and galaxies and things, we still have a long sort of timescale, and it's really the generation after me that's going to do all the science.

We get nothing for it. Adam, you said you're working on designing those missions to Neptune. So what is that spacecraft? What would you like to know about the outer planets that we don't know now? So, I mean, Neptune and Uranus as well, they're so far away. We've only ever had a snapshot with Voyager 2. So Voyager, as a mission, was two spacecraft, and they took advantage of very favourable celestial conditions, and they went to all the big planets. So everything we know about Uranus and Neptune is from one flyby one flyby can i just ask when something like that when it's being planned what are the kind of things that are being thought through in terms of going this is the right time now to launch and send so if you want to get from a to b where a is surface of the earth at a launch site out to say

neptune then you care about things like where's Jupiter? Because Jupiter is enormous and a bit like if you've got billiard balls on a pool table and they collide and one of them comes off a bit faster. You can use that collision to gain speed. We call it a gravitational assist or gravitational kick. So one of the things you use to dictate your launch year is when's a good time to launch? Swing around the sun a couple of times. Use Venus in a similar way, for example. And then use Jupiter for a huge kick. That's the sort of thing that gets you going really fast. The problem is, the faster you're going,

the more you've got to slow yourself down when you get there. And to do that, you need to fire the engines, and that's sort of one of the most risky and scary times after the launch is when you arrive, when you have to do that dangerous orbit insertion manoeuvre, which Cassini did in 2004. Yes, which is why Cassini was the great mission to Saturn. How big a surprise was that when we got to Saturn

and then Voyager and other spacecraft at Jupiter that we found that the moons themselves were interesting objects? I think it was a huge surprise. So with these sort of missions, you plan things years in advance. So we know for a mission like the Jupiter-IT Moons Explorer that's being built right now, we know where it's going to be in 2031, you know, to the nearest few kilometers. So you plan your mission based on what you expect to be interesting. And arguably one of, well, maybe the biggest discovery in planetary science was the Enceladus discovery of liquid water.

And Cassini was not planned around Enceladus at all. So that tells you how much of a surprise it was. They had to redesign the mission on the fly, orbit by orbit, using a bit of extra fuel to get closer. So, you know, it was a big, big surprise. We didn't plan for it at all. So, Joe, looking at the different kind of the distances we're talking about i mean are the clashes of ideology with you know in in your two areas that you're talking you know you're seeing the magnitude of the universe itself

uh distances galaxies and then also i suppose in some ways is it fair to say that there is in one way what we're really working at in that level of uh investigation i don't talk about is kind of parochial. And do you get caught between those... Classic Inns question. I'm just wondering... Well, basically, yeah, I just wonder, you know, are things that are a long, long way away

better than things that are all close? That's better. No. No, I think you're trying to do different things. I mean, goodness, you should, of course, go and look at the stuff you're trying to do different things that i mean goodness you should you should of course go and look at the stuff you can get to i mean if i could get out and look at stuff that was further away i would but we just can't get to our nearest stars even so we just have to look at them i think i mean i'm interested in finding out what the big picture is but the stuff we can go

see sure we want to go see it um but i do think we're asking different questions about you know if i'm looking out further i'm trying to figure out the properties of the whole of the universe then i have to i have to not worry about the details so much so so we've got out to the nearest stars parallax this simple simple idea with essentially blinking your eyes with a head what 180 million miles in diameter between the eyes but how far can you get out using that technique and then what do we do to get further out yeah so so um if you have a telescope just on earth then you can get a few hundred light years away from us the nearest stars to us a star is four light years away from us. So you can get out beyond the nearest stars and into

our Milky Way galaxy, which is the bigger thing we're part of. And actually, there's been beautiful measurements just this past year from the Gaia satellite, which can do the parallax measurement even better because it's out of Earth's atmosphere. So it can see thousands

of light years. But you're still stuck in our galaxy. Big enough for Robin. Yes. Is that big or little on your scale, Robin, the galaxy? It's kind of middly. So you can get out into our galaxy with parallax, but then you get stuck. And it's simply because the shift in position of the stars

when the Earth goes around the sun is just too small to see. And so to get out further, you have to be able to do something else. And the something else, the next step, was figured out just over 100 years ago by this great astronomer called Henrietta Swan Leavitt. She was actually part of this incredible group of women astronomers that are known as the Harvard Computers. They were employed by this astronomer called Edward Pickering,

who realised that he could hire women at low cost to do great work. So that's what he did. He hired these women to study images of stars and to look for patterns in their behaviour. And she discovered this behaviour of this particular class of stars that let us see much further, and they're called Cepheid stars. And they're stars that change their brightness in time. They pulsate, they kind of shrink and grow in size. And she figured out there was this very specific pattern of these particular stars that the longer they took to vary in brightness the brighter they were

and so the brightest ones might take weeks or months to to pulsate in brightness and the dim ones only days what that says is that if you can just go and measure how quickly these stars are pulsating, you know how intrinsically bright they are. And then you look at how bright they appear to you from here on Earth, and that tells you how far away they are, because then if they're dimmer, they're further away. This was in 1908, and astronomers quickly picked up on this and used it to then figure out how big the whole Milky Way is because they went and looked at these stars far out in our galaxy and they figured it was like 100,000 light years across, pretty big.

But then, even better, Edwin Hubble, an American astronomer, in the 1920s took this pattern and he figured out that actually there were these smudges of light in the sky that previously people had just thought were part of our Milky Way galaxy. And he found these particular pulsating Cepheid stars in these smudges of light and worked out that they were so dim that they had to be just way beyond our Milky Way. And he realised that they were actually galaxies beyond our own. They weren't in the Milky Way. And he realised that they were actually galaxies beyond our own. They weren't in the Milky Way.

And do you actually still get, I know you're scientists and all proper and everything, but every now and again, when you think of the enormity of something which came from what we might say is almost nothing or nothing, do you still have those moments as you're collating those measurements of going, whoa, this is so big, and you have to kind of stop, and there's a little bit of kind of excited nausea? Yes. You feel very small, but you just, as an astronomer, you try not to imagine all of it at once,

because it becomes overwhelming. Do you find that, Adam, when you're... You have the... You know that your spacecraft is out there, and it's such a tiny thing, and if it's in orbit around Saturn, or, you know, in the future, in orbit around Neptune, those distance scales are so vast i mean do you feel that i suppose you feel it in the amount of time you've got to design this spacecraft for the engineering excellence of the thing it's got to work for you said 15 20 years or so yeah i mean i would be lying if 150 million kilometers is something i can really picture. You can't.

So you think about the system on a scale that makes more sense, as though you've made a little model in a box. But, yeah, these sort of time scales, length scales, I've never really got my head around them, to be honest with you, and I think that a lot of other scientists would agree with me. Joe, there's two Joes. We're going to have to work out a system. I've just realised this.

Joe Brown, do you have those moments where the size of the universe becomes too daunting and you just have to stop for a second? Not compared to me, no, not really. No, funnily enough, I don't actually have those moments and I don't know why. I just feel a bit cross, actually, because what was that woman's name?

Henrietta. You've heard of Hubble, you've heard of Hallie. Who's heard of her? And it sounds to me like she actually, she didn't just look and she actually thought and realised a pattern, you know. And I think it's kind of shocking when you go backwards to see how little.

First of all, they were paid much less presumably and they were cheap to hire as you said but actually a lot of them were obviously kind of very bright and really made a contribution and i just i find that sort of i kind of find that upsetting really potentially pickering did publish the paper with her name on it, which was not usual at the time, was it? So they did publish together, Pickering and Leavitt. And I think it said that he was writing on behalf of her, which at the time was making quite unusual, I would have thought. Quite unusual, but at the time as well.

But I totally agree. And the reason they were also looking at the images only is they weren't allowed to use the telescopes only the men could actually operate the telescopes because of course it's really hard um not some freudian thing well they might have thought the women might get overheated by using a phallic symbol every day as of course we would. Well, I was talking... Bizarre. But Brenna Hassett, who runs a thing called Trailblazers, which is kind of celebrating a lot of the, for a long time, forgotten women of things like paleontology and archaeology,

says quite often you find these old papers from the 19th century which say, and thank you very much to my wife for typing this out, which actually means, and thank you very much to my wife for writing half of this, but I'm not going to say that, no way. It makes my moustache droop. I think there's also some efforts to try and so in astronomy recently um the pattern that she figured out um now it's being increasingly referred to as levitt's law and as an astronomy community people are we are trying to to acknowledge that more but it's but it's still true that the you know the history of astronomy and at that time you know she was part of this group of women the harvard computers but

a bunch of the other women in that group also made great discoveries and we haven't really heard of them either um they classified the stars like all the the way in which we understand how all the stars in the sky are different they were classified by these women as well and can i just ask you one more thing i mean as a woman working in that field today do you feel there are sort of any differences still between men and women working in your science well i don't think there's a difference in how clever we are but uh i don't mean that i didn't think are you a bit thick and all the men are very intelligent no i meant in terms of you know women do kind of get patronized in male you know is it still male dominated for it is yeah and well i think women do have a tendency to be patronized in those areas certainly that's what i meant i can tell you're brighter than all of them

um but you know do you do you find it difficult in any spheres of work yeah i do so so there are there aren't enough of us there's a very you know there's maybe 20 percent or fewer women and actually as you get more senior there are even fewer of us um but there are but it's increasing it's increasing so it's going in the right direction it's moving the right direction so i think i feel optimism but i still yeah work to done. So we've got the stars that we can see, that we know the intrinsic brightness of them so we can measure the distance. But that doesn't go in any sense all the way out to the edge of the universe. So what do we do for the final step?

Because we want to get to the size of the universe. That's right. So these Cepheid stars take us out beyond the nearby galaxies around us, and it takes us even out to further galaxies. But yeah, it doesn't take us out to the furthest reaches of the universe. And for that, to get even further, we use supernovae. So these are now not pulsing stars, these are exploding stars. And it's what happens when quite a unique star

called a white dwarf star gets a bit too heavy and then explodes. And our sun will turn into one in about billions of years from now. And they're so bright, the explosions, that they briefly outshine an entire galaxy of billions of stars. So they're so bright that we can then see incredibly far away out to the more distant galaxies. And that takes us out billions of years back in time. So we need, before we move back probably locally to the solar system again, we need the final answer. So we're talking about

measuring the universe. So how big is the universe, the piece of the universe we can see? How big is it? So the observable universe is just the part that we are able to see. And so it's by definition centered on us, because we are just able to look out and we can just see a finite amount. And so why can we only see a finite amount? It's because we actually now think that the universe has a finite age. It's only been around for a certain amount of time, 14 billion years, roughly, more or less. It's only been around for a certain amount of time, 14 billion years roughly, more or less.

And so we can actually only see out as far as light has had time to reach us in that 14 billion years. So you might then naively think that the distance to the edge of the universe is 14 billion light years. It's actually bigger than that because the universe has been growing that whole time. So it's more like between 40 and 50 billion light years out to the edge of the observable universe. Has the universe actually got an edge? No. So you're saying the edge in terms of what we can see. That's right, yeah. So what's over the other side just more of the same?

Probably. It's not like a service station or a... It's one of the big questions, isn't it? Whether it is infinite or not. Would it bother you, actually? Because it's one of those things that when I... People seem to get upset. Sometimes when I talk to them,

I can't comprehend an infinite universe. I'm happy with the finite one that's way bigger than, what, 50 billion light years in every direction. I think an infinite one is quite upsetting.'s something isn't there about infinity that's unsettling in a sense there is and there's also something about the limits of our brains mine more than yours i'd imagine but um trying to visualize something that goes on forever is really hard to do in your head i certainly don't feel particularly comfortable with the infinite universe um the nice thing is that there is a possibility of it being

finite but still without any edges because it's possible it's all wrapped up on itself so in the same way that i've never seen joe brand look as comforted as she does now. I wish I'd brought some benzodiazepines with me. No-one knows what they are. That would be like the surface of the Earth, wouldn't it? That's right. The surface of the Earth is finite, right? So there are no edges to the surface of the Earth, but the surface of the Earth is only two-dimensional.

So we think it's possible that the whole of space is finite in the same way, but now you've got to imagine having the edges wrapped up, but in three dimensions. And our brains can't do that because you see the surface of the earth in three dimensions. And so if you want to visualize three dimensions, you need a four dimensional brain, which I don't have. But it's quite possible that if you... Aye, I have. Imagine if I did, that'd be so brilliant. If that was true, then you could go out any direction in space, so out that way or out that way or out that way,

and you'd end up coming back round where you started. Listeners at home, you may now take your red pill. Adam, is that why you stick to close by, sort of rather reassuring planets? I would do as well, I think. Absolutely, yeah. Career choice. So, Adam, we've talked about the measurements that essentially all we have is light there.

So we've talked about the vast amount that we can do by looking at the light from distant stars and galaxies. But what sort of measurements beyond the cameras, and the cameras are things I think everyone thinks about on space probes, but beyond that, what are the sort of instruments we're putting on space probes, like Cassini at Saturn, Voyager perhaps, and the new probes to Neptune? I mean, you know, we have a whole range of different types of instruments that we have flown and plan to fly and are currently flying on different missions.

First thing to say is actually a lot of really high-profile, very, very exciting and successful missions like the Hubble Space Telescope. That's a mission that bridges the gap between Joe's field, which is much, much bigger, and also solar system science, where Hubble's allowed us to do some really great things, looking at Jupiter's aurora, for example. On a spacecraft, you have your cameras.

They're always on there, especially if it's the first time you go into a system or one of the first few times. You have instruments that measure particles. So you have electrons and ions whizzing around in space around a planet. That's something you want to measure. It can also tell you something about the surfaces of the moons. Sometimes you get particles that come from moons or planets' atmosphere. You don't just care about the visible wavelength.

So you have images in other wavelengths, which is something that astronomers really started, looking at lots of different wavelengths, but we also do it in the solar system. Magnetic fields, I mean, you can get a sense that this is the list that's going to go on and on and on. Dust, radio waves, everything. I think the magnetic fields are interesting, aren't they?

Because a question you mentioned at the start, that the greatest discovery, you think, or one of the greatest discoveries is the discovery of oceans, of liquid water below the surface of moons. Oh, yeah, I said that as well. Yeah, you said it as well. Joe also concurred with that analysis. But we didn't land on those moons.

So how did we know? So the short answer is there was a magnetic field that was measured that was unexpected. So when you fly with a spacecraft that's got a magnetometer, it's a bit like a compass in space. And it tells you which way locally the magnetic field points. So just a three-dimensional compass. So you have an idea of what you expect to measure. You're going to a big planet like Saturn, let's say, which Cassini did. And Saturn, like the Earth, has a big magnetic field,

really like lots of energy in the core, dynamo action, producing a huge magnetic field. So you expect to measure that. So then if you measure something else as well, so if your measurement is different from your prediction, then you've got to explain what causes that difference. And that's where the Enceladus discovery came in. So the magnetometer team, led by Michelle Doherty,

who's also based at Imperial, same as me, they identified a magnetic field signature near Enceladus that just shouldn't have been there. And that's the beginning of then showing that that magnetic signature is because the magnetic field is having to bend around this plume of water that gets ionized in space and presents an obstacle to the field so it's a really powerful effectively remote sensing tool because the magnetic field is a three-dimensional field it's invisible but it

responds to you know is that the only thing it could possibly be then water could it not be something else well since then they've gone and measured that it is actually water so it began with looking at the signature but actually it's a good question because at jupiter thank you adam because at jupiter where we don't necessarily have plumes of water erupting out that cassini was able to fly directly through at jupiter another spacecraft galileo saw a magnetic field that was changing with time that shouldn't have, Galileo, saw a magnetic field that was changing with time that shouldn't have been there. And that's a magnetic field arising in a water ocean

underneath the surface that we've never got anywhere near. But we know it's there because it's the only explanation for why that magnetic field's arising. So we think that similar to when you're at the airport and you go through a metal detector, you've got a system there where electric current flows and it generates what we call induction in anything metallic. Anything conducting in your body is then going to have a magnetic field.

It generates itself. So that's effectively what's happening at these Jovian moons. You've got a big background field that's changing. Electromagnetic induction happens in a water ocean that's a little bit conducting just enough and it gives you this field you didn't expect and that's uh europa that's europa but also ganymede ganymede's another really interesting one those two and possibly also callisto so these are three of the four so-called galilean moons the really big ones

i mean ganymede's about the same size as Mercury. So these are enormous. Planetary-sized. Can I just ask one thing as well? Are there times when, like you said, it couldn't be anything else? But are there times in science where people have thought it couldn't be anything else and it was something else they didn't know about and there's some kind of flaw in the deductions?

And they're not right because there's something that you don't know about and there's some kind of flaw in the deductions and they're and you know then they're not right because there's something that you don't know yet for example absolutely i mean sticking with cassini as a sort of case study um we mentioned that saturn's got a big magnetic field like the earth but the properties of that that magnetic field and we characterized its sort of orientation and how it changes with time is a violation apparently of our basic understanding of how planets generate magnetic fields. So we had

a hypothesis, a prediction and then when you go there you measure a field which doesn't conform to that. And we're still trying to understand exactly why that is. So there's plenty of occasions and that's actually what you want when you launch a mission. You plan to answer a load of different questions, but the biggest discoveries are quite often the unexpected ones.

Can I ask you, because I think a little more than a week before we recorded this, the Saturn news was about the rings of Saturn and finding out about their age compared to Saturn itself. So how has that been discovered? So the only way they were able to make that big discovery about the age of the rings, which is based on the total mass of the rings, which is based on gravity measurements, you needed to get very, very close

to see the difference in the spacecraft velocity compared to what you'd expect. That's how you determine the total mass of the rings. They only were able to do it right at the end of the mission. We had this fantastic grand finale, as they call it, where we had 20-something dives between the rings and the planet, and at the end of it mission. We had this fantastic grand finale, as they call it, where we had 20-something dives between the rings and the planet, and at the end of it, we burned up. And so we're still doing science with that data now. I mean, big science, big discoveries,

and that's going to continue for many years. And we found out the rings are possibly only a few, well, even tens of millions or hundreds of millions of years old. That's right. So the total mass of the rings is a big factor here because the more massive they are, the older we'd think they'd be. So the mass tells you they're younger. But also the brightness of the rings is another clue that came a bit earlier.

Yeah, so the dinosaurs, were they in possession of a telescope, would not maybe have seen Saturn's rings because they might not have been there, which is a remarkable thought, isn't it, about Saturn? What? No, I just like that image. You put a lovely image in people's heads.

Dinosaurs. Of a Tyrannosaurus Rex going, I've made the telescope, but I can't get it to me eye. You know, it's a beautiful thing. Oh, I haven't thought this through at all. I kind of like that idea that it made it. And when I was told Saturn was a very beautiful planet and there were no rings there at all, which is a idea that it made it and when i was told saturn was a very beautiful planet and there were no rings there at all which is a temporal problem as well with that

isn't it yes can i ask you one really really quick thing you know when people name their relatives after a star do they really do that or so like can you look through a telescope because i named one after my mum go oh look joyce brand's looking particularly bright does that actually happen or you or you can't no i knew it didn't there are some rules some people name things after themselves where it is but there are there are some naming conventions yes so that's all a big con isn't it then that star whatever it's called has anyone here done it let's all gang together and get our money back, then.

That's what I like, the speed in which you can turn this show into That's Life. Just one last question, Adam, just one final thing. How do we name those? So there's the thing that New Horizons spacecraft went to after Pluto. Oh, Pluto itself is a good example. So these are objects

that are discovered in modern times that are part of the solar system. What's the naming process? Well, Greek mythology is always our go-to, but we're running out of deities. So now you've got a lot of very unimaginative names. I mean, even missions. So a lot of missions, like Galileo was the Jupiter

mission, which makes sense. But now we're getting to much more boring names. I mean, the next big Jupiter mission at the moment is Jupiter Iiter icy moons explorer you know i'm just checking if there's any mistake much less grand but at least it says what it's going to do can't we name it after anything that's been in a ray harry hausen movie because they're great like you know jason the argonauts stuff let's broaden out in terms of the myths that can be used well i have to say that there's lots of different mission proposals out there. They get proposed all the time, and some of them are pretty crazy.

But what's quite interesting is the discussion about naming the mission is sometimes longer than the discussion about how to get from A to B. And it's always, you know, Delphin was the leader of the dolphins in Greek mythology or something like that, and then there's a big discussion about it. Can you name a mission after my mum's singer? She'd be really disappointed after this show. Right, anyway, so we asked the audience, if you

could live anywhere else in the universe, where would it be and why? And they answered I would live on the moon so I could eat my body weight in cheese every day and remain weightless. A galaxy far, far away cos Princess Leia. Brian Blessed's lungs.

Lovely and spacious, although it's a bit of a dive! Mars. Why? No humans. And, most importantly, no flat earthers. Also, I've seen Matt Damon in The Martian several times. I'll be fine. Wouldn't it be terrible if Thomas, who wrote that, actually got to Mars and looked back and went, oh, bloody hell, it is flat. Anyway, so

Brian Cox's Barber's Where Magic Really Lives. How about this one? The Other Side of the Moon to Surprise the Chinese. That's good, isn't it? That's from Gem. Well done, Gem.

So, anyway, thank you very much to our panel, Adam Masters, Joe Dunkley and Joe Brand. And this is the last episode of Series 19, which will be the last prime-numbered series of The Infinite Monkey Cage until 2021. The prime factors of which are 43 and 47. At which rate, at two series a year, that means that it will broadcast when?

Send your answer by postcard only to the infinite monkey cage beneath the crystal spheres, just above the elephant, but not too close to the turtle's earth. You've not been paying attention, have you? Not really. No one has. They just hear your lyrical voice, and they go, ooh,

it's a lovely sound, I don't know what it means. Goodbye. Turned out nice again. OK, OK, OK. If science podcasts are your thing, but you've run out of monkey cage supplies, or you've just had enough of Brian Cox. How about something a little bit different? The possibilities are infinite, of course, but you could try my Life Scientific podcast. I've spent seven years interviewing some of the finest scientists alive. I've talked to people who've climbed into volcanoes,

analysed the teenage brain, and invented the batteries for your mobile phone. Black holes and bacteria, robotics, genetics, fossils and Formula One. It's all there. The Life Scientific podcast is a collection of in-depth interviews with brilliant men and women whose work is changing our world. That's The Life Scientific, hosted by me, Jim Al-Khalili. You can download it from BBC Sounds. This is the first radio ad you can smell.

The new Cinnabon pull-apart only at Wendy's. It's ooey, gooey and just five bucks for the small coffee all day long. Taxes extra at participating Wendy's until May 5th. Terms and conditions apply. In our new podcast, Nature Answers, rural stories from a changing planet.

We are traveling with you to Uganda and Ghana to meet the people on the front lines of climate change. We will share stories of how they are thriving using lessons learned from nature. And good news, it is working. Learn more by listening to Nature Answers wherever you get your podcasts.