SPEAKER_00 0:05

Please welcome Helen Chesky.

SPEAKER_01 0:13

It is quite nice to be sitting down to the city. It's good, isn't it? We're standing up.

SPEAKER_00 0:17

Quite like the branding as well, in case you weren't sure where we were. The podium doesn't move, so apologies to those of you over there will try and remember to look to the wings. It's really weird talking to you in an astronomy context.

SPEAKER_01 0:30

Yeah. Let me in.

SPEAKER_00 0:32

Well, mostly I've heard you rant about astronomy because of this phrase that people have that. How does it go? We don't understand, we know less about the sea floor than we do the surface of the moon.

SPEAKER_01 0:43

If you're gonna quote something that is awful, you could at least get the I got it the wrong way around. People say we know more about the moon than we know about the deep ocean. That's the one. And it's rubbish. It's rubbish, it's bad, and it's horrid, and none of you should ever say it ever again. And the reason it's rubbish and bad and horrid, uh, this is the short version of this rant, by the way, it goes on for a while. Is is basically that whenever you say it, it makes the deep ocean and the moon sound comparable. It make we know the moon is terribly nice. It does have seeds. But but it has, it's a it's a barren rock that hasn't changed for two billion years. And the ocean is three-dimensional, it's dynamic, it's changing all the time, it's got life in it, you know, it's got all kinds of interesting things going on. There is so much more to know about the deep ocean than there is about the moon. And so the problem is that every time people make this comparison, they sort of diminishes the ocean. It makes it people sort of know what the moon looks like.

SPEAKER_00 1:34

They're trying to help, right? Yes, but it's not helping.

SPEAKER_01 1:37

It's not helping. And but this is the problem is it it reinforces the idea that the ocean that the deep ocean is just this dark, dead place where nothing happens. And um, and actually, it's also sort of a bit offensive to the thousands of ocean scientists who have been in the ocean, studied the ocean, spent their career. I mean, 12 people have been to the moon. Maybe that's about to go up. But you know, 12 people 50 years ago, lots and lots of people have been not sending people down to the very deepest parts of the ocean is is not something that happens regularly. But we have been there, we have seen it, we've seen so much. So, anyway, rant, that's my rant. Like, I appreciate that. Uh, you know, it's because of a quirk of physics, it's because that you can all start laughing at Helen having a rant now. But it's because that you see we can light travels a long distance, um, and we are visual creatures. So we see the moon, and you can see the surface of the moon, and you can see the whole of the moon, the bit of it that faces us, and you can sort of see what it looks like. But in the ocean, our visual creature nature doesn't work because in the ocean the messenger that works is sound, and it's a lot harder to look with sound over, you can't do this kind of take a big view over the whole ocean because you sort of have to ping down a bit of sound at one point and then move along to the next one and ping down there. And there are some other clever ways of doing it, but it's a lot harder. So, so I think that our it's just this quirk of physics that our visual nature makes us continually underestimating.

SPEAKER_00 3:05

Lots of astronomy is affected like that as well, so we've got this visual bias to things that shine in the optical. By the way, you're talking about seeing with sound, and I see Milt's got his laptop out, so it's possible by the end of the lecture we will see the ocean. Um, but uh, but but let's well let's let's talk. I think that's enough random. Enough random. Um let's talk about uh like Earth as the ocean planet, then. So what do we get from thinking about if I put Earth, not in an astronomical context, but we think of it as a whole planet, and we think about how the ocean affects that. What do we learn by sort of taking a global view of the Earth?

SPEAKER_01 3:38

Well, if anyone was on another planet looking at us, that's what they would see. They would see it's completely dominated by water. And of course, if you go all the way around the back, if you go to Google Earth or something and you pick Hawaii and then you zoom out, basically that entire view of the planet is just ocean. The Pacific Ocean is really, really, really big. Um and but it's not just about it being blue or wet. The reason water matters for our planet is that it's doing things, it's a colossal store of energy. So it's actually not very transparent to light, that's why we can't see the deep sea floor from the surface. Um, but as that as that light gets absorbed, it the light energy becomes heat energy and it heats up the surface of the ocean. And as you will know, if you've ever uh looked at your smart energy meter when you put your kettle on, it takes a lot of energy to heat up water, even a little bit. So it's an enormous store of energy, and it doesn't just hold on to it, it helps distribute it around the planet. And then there's all kinds of other things associated with water just being a very, very weird molecule. So it's a universal solvent, which basically means a lot of things dissolve in it, a lot of different types of molecule, not all of them dissolve as well as each other, but water allows those molecules to meet each other, provides an environment where molecules can meet, chemical reactions can happen, life can get started.

SPEAKER_00 4:57

This is why we talk about water as probably being necessary for life, because it's good at doing this.

SPEAKER_01 5:01

So so these so water gives you both stability because you've got this uh sort of you always need some atmosphere that's got some evaporated water in it, and that's kind of in balance with the bit that's liquid. And what that means is if you give the system a bit of extra energy, a bit extra liquid might evaporate, but you still have an ocean. You you have the stable system where the ocean is buffering temperature and where the energy is all the time. And then the water can very conveniently, I mean, it it wouldn't, it it wouldn't, it's not necessary that it has this combination of properties, but it is also because it's a very polar molecule, which means it's got an obvious, uh it's got obvious positive bits and negative bits, it's very good at dissolving molecules. So there's this combination of things that means the ocean makes Earth very, very stable as a place. And of course, if evolution takes a long time, so you need that stability, but it also provides a chemical environment that allows complex molecules to develop.

SPEAKER_00 5:59

One of the striking things, listening to you you talk there, like that's it seems to me to be the kind of language we use to talk about, I know, the atmosphere of Jupiter. This is a system that wraps around the planet, and you you say the ocean, but you mean sort of the ocean, not the Pacific Ocean, not the ocean in a particular place, but a sort of planetary scale process. So this is really the view from outside, in in some sense, that you know, if we want to understand Earth, this is what I got from your book, we have to understand how the ocean's working before we do anything else.

SPEAKER_01 6:28

And for anything else to happen, everything else will sit basically sits in the ocean's shadow. So if you're looking from the outside and wondering what kind of planet Earth might be, what you would see is the ocean shifting energy and nutrients and and things around. And everything else is just kind of taking the leftovers almost from those processes. And so that, but and then that stability is what gives you the time, the time frame. So I I mean it's interesting. I we don't know if anyone will ever discover a definitive signature of of life on another planet, but it would be apps it would be absolutely astonishing if that discovery did not involve water. Right. And so, in a sense, the more water you've got, the better a chance you've got.

SPEAKER_00 7:09

Yeah, and NASA talk about the um on Mars, for example, the the stated aim of the Mars program is follow the water. Yeah. So find where there was water on Mars, find perhaps where there is water on Mars now, or at least ice. And those are the places, if you want to discover life that you go to for exactly that that that that reason.

SPEAKER_01 7:26

And what I would love, by the way, is for uh Thames Water, for example, to look at how how much NASA values water and think that maybe if maybe that's how valuable water is, um, and then transport, you know, just to think about that occasionally.

SPEAKER_00 7:43

I don't know, NASA discovering water in Oxford would be useful, I think. Uh certainly after the the summer that we've had. Um, but there is this idea, so system science, when we talk about this, the the idea of Gaia and sort of those ideas from from Lovelock and others come to mind. And and that's something that's resonated in astronomy as well. Do you want to connect that perhaps together?

SPEAKER_01 8:02

Yeah, so I mean, for those of you that so James Lovelock was uh first of a commercial scientist, basically, and then he became an independent scientist. He invented a thing called an electric capture detector, which allows you to detect very, very tiny quantities of things like CFCs. That doesn't really matter for this story, but it made him a lot of money. Um, and and that gave him the freedom to then explore these other ideas uh later in his life. But it was actually when he was working at JPL, I think, thinking about looking up at the sky. How would you know if there was life on another planet? What is it that we could see from Earth? And of course, the only thing really that connects us, the biggest thing that connects us to the rest of the universe is light. So this signal would have to be in light. And he started thinking about the chemistry of atmospheres because we we can find out a little bit about the chemistry of atmospheres from the light that comes to us. It's hard, but we're getting better at it. And he started thinking about what molecules you what you might see in an atmosphere if it had life in it. And he realized that life does this really odd thing, which is that it keeps itself away from equilibrium. That if, you know, in the physics we all learned at school, classical physics, you know, balls roll down a hill and then they stay at the sort of equilibrium at the stable point at the bottom.

SPEAKER_00 9:21

Water runs downhill.

SPEAKER_01 9:22

Water runs downhill, right? But life is continually taking energy from the universe and making itself more complicated than it needs to be. It's out of equilibrium, it's away from the stable state. Because nothing would happen if everything was stable.

SPEAKER_00 9:36

It's just stuff like we maintain our body temperatures, right? So we're not in equilibrium with our surroundings.

SPEAKER_01 9:40

But we have to keep taking in energy for our cell processes and we generate some sort of waste entropy in effect. Um, so we are we're out of equilibrium. So Lovelock was thinking about well, well, that maybe that's the signal of life. If that's the thing that life does, if it uh takes the world and shifts it to a non-equilibrium state, maybe that's the signature of life. And so it started him thinking about planets as living systems. And that's what became the beginning of the Gaia hypothesis. But actually, you can see it in one of his early papers in an argument about entropy. So he's thinking, so entropy is this idea that the world always gets more disordered overall, that effectively the amount of energy that comes in from the sun and the amount of energy that goes out are pretty much exactly the same. Climate change is shifting that a bit. But the difference between the energy that comes in and the energy that goes out is that the energy that comes in is very ordered, it's low entropy. Whereas the energy that goes out is exporting entropy.

SPEAKER_00 10:43

And that's that light to heat transformation. So that's why we life doesn't get a free lunch, right? So life doesn't break this principle.

SPEAKER_01 10:50

But we effectively pay in entropy, not in energy, which is a sort of misconception. So um, so he was thinking about living creatures, and he sort of said, well, you know, or well, he said it in a slightly different way, but he's slightly trying to, he said, okay, let's imagine an animal. He didn't say it quite like this, but this was the argument. Let's imagine an animal and it takes in some energy and it builds up a complex body, so that's all right, and it exports some energy to the universe. So then that's a little system, so that's a system of life, that's all right. But then he said, okay, so imagine, I mean, this is my uh interpretation of his argument, it's my uh analogy. Let's imagine that animal is a beaver, right? And a beaver can build a dam. So it can create some order outside of itself. So it's created some order somewhere else. So it's so it you can't put the dotted line just around the beaver because it's created some other. So maybe we have to put the dotted line around the beaver and the dam it's built, but then the dam affects the environment, and so you sort of work out, you keep going outwards. And he realized there's a line in one of his early papers that basically says the only sensible place to put the boundary between life and non-life is round the side of the planets because everything inside the planet is interdependent. So so he said, Well, so that's you can you can sort of see him in this paper working out. That means a planet can be treated like an organism.

SPEAKER_00 12:07

And the crucial insight is it's the planet is then inside the line as well. So it's not just you're counting all the living things, it's the oceans and circulation and the dynamics of the whole system.

SPEAKER_01 12:17

That's right, yeah. And and so, and so that and that's where the Gaia hypothesis comes from. And then, of course, it takes on this life of its own because I mean it was 1965 when he first, I think, started thinking about this. He sort of had lots of iterations into the 70s, but people really picked up on this idea because it's kind of it's you know it's a kind of appealing idea that our planet is alive and maybe it's got opinions about us.

SPEAKER_00 12:38

Um, and all people talk about like there's a there's a jump to the idea that it would then be self-regulating in some way, which is both an environmentally good thing because it's a lovely thing to think about the planet regulating itself, and it's also used as an excuse because we don't have to worry about changing what we're doing because the planet can look after itself and adjust, just as my body adjusts to a cheeseburger like at night.

SPEAKER_01 12:58

You know, there's this sort of sort of sort sort of so this this was part of the so in his early version, I mean the earlier versions, he he said that that was the bit that became controversial among scientists was that there's deliberate self-regulation, that it's not just that this system is, you know, balancing and there's all these feedbacks, it's that it's it's choosing somehow to maintain the conditions for life, to maintain a temperature, to, you know, and there were these various arguments that have advanced. And I think he stepped back from that, but of course, it's such a sticky idea, it never really went away. Um, and and then it leads to this idea of how do we how do we think of ourselves in relation to this planetary organism? And then then it evolved into Earth system science where we don't think it's got a consciousness.

SPEAKER_00 13:41

Right, but is that sort of way of thinking helpful when you're thinking about ocean systems and and so on, or is it a nice metaphor?

SPEAKER_01 13:48

So I think I I mean I don't think the consciousness bit is helpful, but I think the interdependences are really important, and and it's really one of the things that I think has been a feature of probably all of our lives in this room, but has not been a feature in all human civilizations, is to see ourselves as something that sits on top of nature. We walk about on top of this blank slate and we take things from it and put them back. And of course, that's literally not true, right? We are made of that system, and the atoms that make us up will go back into that system and become other things. And so we are this change of view to us being part of that system, but also connected with the ocean, it gives you a different idea about the environment because we are there's no place called away. I mean, maybe space is a way, but if you chug, if you if we threw our pollution into space, what a waste of atoms that would be, right? There's no, we're not getting any more atoms from anywhere. So so it I think it changes how you see us as citizens of this planet. And the ocean is obviously part of that, which is, I mean, I describe it as the beating heart of planet Earth because it it really, you know, you can play your games with which organs do what, right? It doesn't go for very long, but without the ocean, Earth is not Earth. That's very, very clear.

SPEAKER_00 15:01

Yeah, and you should watch all of Helen's lecture's book. Your first Gresham lecture, I remember sitting here and being astounded by some of the visualizations and and data that you had there. But if Earth's the ocean world, to switch tacks slightly, why does it have an ocean? Like, what is it about our planet that gives it its oceaness? What do you need for this great circulating system to exist?

SPEAKER_01 15:22

Well, you need a lot of water. And and uh the the thinking on this seems to shift a bit over time. I think the the balance of probabilities at the moment is it being delivered by icy asteroids at some point. Although no one, no, like it's very hard to be completely sure.

SPEAKER_00 15:37

We can't match, but there's a I I went to a brilliant talk about ancient water that I'd been meaning to ask you about, which I won't do now, sorry. Carry on.

SPEAKER_01 15:44

Well, you might know more about ancient water than me.

SPEAKER_00 15:46

But anyway, that is the idea that there was this bombardment. Yeah.

SPEAKER_01 15:49

Yeah, that's right. So so once and once you've got water, the interesting thing about water is it can exist in three states. You can have solid, liquid, and gas, and they can actually all exist at the same temperature. So if you go to the North Pole, for example, where there's sea ice, you can I I have stood on two-meter thick sea ice at the North Pole, definitely solid. Right next to it is water, definitely liquid, and I am standing in an atmosphere of air, definitely gas. And water, so water exists in all three states together. And then and and then that gives you the flexibility. So the fact that we've got a lot of water, that it's at the surface, um, and that it can exist in these three states, it provides a huge amount of the richness of Earth. And so I think about, you know, we talk about the Goldilocks uh sort of distance from the sun.

SPEAKER_00 16:32

Yeah, so this is yeah, the region around the sun where liquid water could exist. That's right.

SPEAKER_01 16:37

And and I sort of think I think we're framing that slightly wrong actually, because uh because I think the interesting thing about Earth is that it's got enough mixing and complexity and variety to be doing interesting things, but it's not so chaotic that everything is all just mixed up and it's just all this, you know, it's just one big soup of stuff because it's just mixing so fast. So I so I think it I think it's got a little bit more to do with complexity and timescales, but water is certainly very helpful.

SPEAKER_00 17:02

But you also care about the atmosphere as well. So this is my problem with the Goldilocks zone, which is you know, Goldilocks because it's not too hot and not too cold, but just right, um, is that it really matters what your planet is and what atmosphere it has. Because after all, the moon is in the Goldilocks zone. Um if the Earth is, we share an orbit, but the moon doesn't have an ocean, it doesn't have liquid water. So uh my friend Elizabeth Tasker, who works for the Japanese Space Agency, has the Echowatts zone, which is the zone in which Earth could have a suitable atmosphere for water. So if you take a planet with Earth's atmosphere, does it have water?

SPEAKER_01 17:35

So it's this interplay between ocean and I like I like this idea that to do science, what you need to do is just get a big box of planets.

SPEAKER_00 17:41

Yes.

SPEAKER_01 17:42

We'll put one here and we'll put one here and we'll put one here and we'll see what happens.

SPEAKER_00 17:45

Well, we're sort of doing that, right? And and people have thought about other ocean worlds. People, there's a wonderful set of um speculative theory works about how we might do this where people have looked to see whether we determine if you had an alien ocean with a wind and you get a choppy sea, you'd get a glint that would be picked up in polarized light. And so you might be able to detect the glint of light on an alien ocean and thus know that it was there. But in the solar system, of course, we have other oceans. We're pretty sure that um some of the moons of Jupiter, certainly Europa, Ganymede, possibly Callisto, have oceans underneath an icy shell. Saturn's moon and Celadus, which is no bigger than the UK, or rather the British Isles, uh, has an icy core, an ocean, and these fountains of water coming out from the South Pole. So we've got these very alien oceans. In fact, the most common ocean in the solar system is bounded not by an atmosphere but by ice.

SPEAKER_01 18:38

It needs a lid.

SPEAKER_00 18:38

It needs a lid of some sort. So I was going to ask, how similar is the physics, do you think, of those places?

SPEAKER_01 18:44

So the interesting thing about ocean physics we have one data point, obviously, but but it's our the way oceans can be on Earth is limited by a couple of things. Um in today's ocean, it's limited by the shape of the continents, because the ocean can only move within the bounds that the continents give it, so it can't move completely freely. So when you get that picture of the tides being a bulge on either side, I mean, obviously it doesn't do that because there's land in the way, right? So land's making things a bit more complicated. Um, but the other thing that is really important in our ocean, and we've only seen it work on way, is the amount of salt that we have. And most of Earth, uh so that the ocean has layers, and that's dictated by temperature and salinity. And almost everywhere on Earth, although both temperature and salinity matter, it's dominated by temperature. So it's warmer, there's a nice warm layer at the top, it's cooler down below. The salinity might vary a bit, but it's not a big difference. There is an exception in the Arctic Ocean, actually, where the salinity dominates because there's ice and fresh water. So you get a fresher layer at the top, which is cold. Then underneath it, you get a layer that's warmer, but it's saltier, so it's still more dense.

SPEAKER_00 19:52

Okay, so that's just fresh water from melting ice.

SPEAKER_01 19:54

That's right, yeah. So then you have a warmer, saltier layer underneath, and then you have cooler, denser water. So that's an example of salt dominating the layering. And it is possible to imagine on another planet, I mean, it's likely to be saltier. We don't know what salts it might be, that depends on the chemistry, but salts are really heavy, they change the density of water. And so you could have a notion that basically obviously it would work on the same physics, but if it's dominated by salt instead of temperature, you would get different sorts of currents and different sorts of overturning.

SPEAKER_00 20:25

Well, that's interesting because we know that the ocean in Enceladus is salty because we flew a spacecraft through it accidentally, because the Enceladus has these fountains coming from the South Pole, and so it's the second easiest. I nearly said it's the easiest place in the solar system to get a sample of the ocean, but it's definitely the second easiest. Um I will never make that mistake again. Um so so the Cassini spacecraft discovered this, uh, these fountains, partly because they flew through it, and they had a magnetometer on board, and they were able to do some analysis. So we know that it had sodium salts in there. Um we need to send a probe back, there's a long-term European probe to go back and do a proper chemical analysis of this stuff. Cassini, when it was launched, we didn't know this ocean existed, and we didn't know these fountains of water existed, so it wasn't built to take advantage of them. But it's salty, and I've always said that that's exciting because we know there's an ocean floor, right? That's where salt must come from. And so in Enceladus, we know we've got ice, we don't know how thick the ice is, we know it's cracked in one place, and then we've got an ocean that we think was long-lived, and there's this flaw, but that means that it would have got saltier over time, which presumably has changed things.

SPEAKER_01 21:34

And over in Earth has been quite a topic of discussion for a long time because you can imagine ways to put salt in, but not ways to take salt out on in an obvious sort of and it turns out there are ways to balance that equation. Um, but but the I wanted to ask about the movement of water on other planets, because obviously one of the things about liquid is that it's not kind of glued to the planet, right? So if a planet's spinning, the water is not necessarily. Spinning at the same rate as the planets. It's not necessarily moving in the same way. And there are potentially signals of that in, you know, if you're measuring angular momentum and things like that. Has anyone tried that?

SPEAKER_00 22:09

So there's a probe on the way to the Jupiter system now. So we've got Juice, which is a European probe that's good, it's the Jovian icy moon explorer, which somehow becomes Juice. That's going to go and fly by Ganymede and Calissa, sorry, Europa. And then there's an American probe called Europa Clipper that goes into orbit around Europa, and that's going to do this measurement. So to try and look at, they're looking for glitches in the in the rotation, which would be to do with a liquid-solid interface. Right. So so but they can also use gravity to try and work out how deep the ocean is. So we don't know in these cases. For Jupiter's moons, we're pretty sure those places have oceans. We see an icy surface with few craters, so that means it's been resurfaced. So because if you live in the solar system, you gain craters over time. And so we know these are young surfaces. But we don't know how deep the ocean is. So we don't know whether it is a 200-kilometer ice cap or a two-kilometer ice cap. It makes a big difference for how you might explore them in in the future. But it really is, I think it's the biggest change in planet comparative planetology in 20 years is that we've gone from water is important, you need a world like the Earth in the Goldilocks zone or the Echowatts zone or whatever it is, to oceans are everywhere. They're an important part of how planets are made. Even Pluto, for example, people think they might have an internal ocean.

SPEAKER_01 23:30

Would it then get rehabilitated as a planet if it had an ocean? No, not all.

SPEAKER_00 23:34

I love that your your criteria. It can't be that only decent planet.

SPEAKER_01 23:38

Well, I'm just asking if it turned out that, you know, it did have an ocean. But does that doesn't matter? No, we didn't pick up the.

SPEAKER_00 23:43

No, this is a common misconception. Now you get my ramp. So we didn't demote Pluto because it's boring. We demoted it because it's smaller than some of the others, and there are loads of them. But many of them probably have oceans. So this sort of ocean physics matters, I think.

SPEAKER_01 23:59

But the other thing that the influences I'm glad I got you on back there. The other thing that influences how the ocean water moves, the reason this layering thing matters is that if you have an ocean that turns over, that can st can store different things in a deep ocean than it has at the surface, you're sort of limiting the dynamics of what can happen at either side. So in Earth, so it's not it is the case now over most of Earth that the very deep ocean is around four degrees Celsius, and the water, the surface, depending on where you are, is somewhere between 30 and minus two, you know, pick your place. But um uh it does, it seems from evidence on Earth that there were times in the past where the deep ocean was much warmer, it was 15 degrees. And what that implies is that there wasn't an overturning circulation. So the way that um part of the reason that the part of the way that the earth, the earth's ocean moves heat around is that you have, as I said, you know, this warmer uh layer at the top. But if it evaporates and you get a cold, salty bit, that can sink down. And you then get this overturning circulation that can basically hide water away from the surface for centuries, potentially thousands of years. And and that affects, again, it's a stability thing, but it also affects where things can get to on your planet. So if you have an if you find an ocean on the moon or a whatever Pluto is or a planet, um it's not just about the the fact that the ocean is there, the way it's moving and the way it's distributing things around the planet will dictate what you can have there, what kind of chemistry you can have, how stable it is, um, you know, how much it changes over time.

SPEAKER_00 25:38

Does that have implications for life as well? Because I think what what's striking me as we talk, and I'm assuming this isn't an original research thought that we've come up with, but but this is exactly what got an Enceladus, because you have a salty ocean that's evaporating through the South Pole, so you might well have this sort of circulation. So does life, in a very crude sense, does life want this kind of mixing because it it helps things or it is is the instability it brings a problem?

SPEAKER_01 26:02

Then we come back to the equilibrium, right? And that what what life needs to get started with is a disequilibrium. And the hydro hydrothermal vents on Earth are a really good place for that because you've got really hot liquid and you've got a very high concentration of the chemicals that are coming out. So basically you've got a stonking great big gradient in both temperature and chemistry. And that means that if you put yourself as a gatekeeper between those things, then you can extract things from the flow. It's like a toll keeper on a bridge, right? If you park yourself at the connecting point, then you can siphon useful things off because you're, you know, you sort of they're on their way down anyway, but you can use them on the way. So what life does need is uh it's a some the stronger the source of the disequilibrium, the more likely it is to happen, basically. So then it's not just about what's happening at the surface, it's about the surface being different from the depths or potentially the equator being different from the poles, but I think surface to deep is a more likely thing. So you need you need, you basically need a difference. Life thrives on a difference between over here and over here. So you have to generate that if you're going to have life.

SPEAKER_00 27:08

So interesting. So I think that's that's a filter one could apply, I think, when thinking about these oceans in the outer solar system. I think Enceladus, when put like that, even though it's small, really feels different from the others, which are more constant, don't have this loss, at least as far as we know.

SPEAKER_01 27:24

Yeah.

SPEAKER_00 27:24

Uh at the moment.

SPEAKER_01 27:25

But if it's losing, that's interesting, isn't it? Because you're all that also if you have a constant, if you constantly have this flux to the atmosphere, you're definitely losing a lot of stuff.

SPEAKER_00 27:33

Yeah, the beautiful.

SPEAKER_01 27:34

It says there must have been more of it in the past.

SPEAKER_00 27:35

That's right. But the beautiful thing is, this is why I said we think it's long-lived, and it's for a beautiful reason, which is that Saturn, of course, is the planet with rings. And there's an outer ring called the E-ring, which we didn't understand. It doesn't look like the others, it's at a very slight angle, but it's also much um uh much lower density um compared to the other rings. All the rings are made of billions of ice particles, but this one looks different, and it turns out it's fed by the fountains. So we've got this, we can observe from Earth that it's like a waterfall the size of Saturn. That's right, yeah, yeah, exactly. And then you can work out the flux. And assuming that the current flux is But does any of it end up back on the moon? No, it it's once it's escaped, it falls down towards Saturn and it creates this beautiful extra ring, which is kind of fun. So it tells us that this ocean is at least um hundreds of millions of years old.

SPEAKER_01 28:25

So, how big was Enceladus that it's fed this It's a good question.

SPEAKER_00 28:29

I I think there has been some shrinking, and people are looking for that on the surface, so we're not sure we're not sure. I mean Enceladus is amazing, it's the shiniest thing in the solar system. It's got the highest albedo, so it reflects more light than anything else. And we think that's maybe because something's happened to the surface, so maybe some of the water does end up back there, so it may be growing as well. It's a complicated system that we don't understand. So coming back to Earth, though, I think we should finish back uh back on home territory. Um what don't we understand? What are the what are the big questions in in your world on a planetary scale about how the system operates?

SPEAKER_01 29:06

So there's a couple of big questions, I guess. One of them is so and for in both of these cases, we know the outlines, we think, and a lot of it's about filling in the details. One of them is about how energy moves through the ocean. I mean, you know, obviously lots of it arise from the sun and it sort of filters around. But it turns out that the ocean is spinning everywhere, not just the big ocean gyres, but because the planet is spinning, you get lots of these little eddies that are, and if you look in the right kind of way at the velocities of the surface, if you average over the right kind of timescales, the ocean is covered in little spinning things. And you actually see it. So I put um my academic work involves me putting uh buoys. I'm told it's wrong to throw boys off the back of ships, and I learned my oceanography in America, so buoys. Chuck it overboard, put a tracker on it, let it go for five days because I'm not going out swimming in those storms, and then it comes back with data. And you can actually see if you look at the track, um, so it's just been blown by the wind and taken by the currents, and it sort of does this. And it's really disconcerting because why is it just sort of nothing? You can see physics, straight lines, right? Or at least curvy lines and stuff. And actually, what's happening is it's kind of hitching a ride on gyre, so it's generally going that way, but it hitches a little ride on this gyre, and then um it it gets that point, you can actually see it, it's a cycloid. You you if you you can play with one, if you get um a pencil and a circle and you kind of roll the circle along them, like watch where one. If you imagine a wheel rolling around with a point on it, right? That point comes to the floor, the wheel's moving and it comes down.

SPEAKER_00 30:41

You can actually see this. If you look at Jupiter, you see this pattern in the belts of the belts of Jupiter have a skull-up dead. Oh, right, right.

SPEAKER_01 30:48

Yeah, so it's that.

SPEAKER_00 30:49

Yeah, yeah, yeah.

SPEAKER_01 30:50

But basically, you see that it's doing this, and it's because it's kind of it's sort of passing through them, but it's also getting carried by these eddies. So it so you can see it. You can see that there are these spinning things all over the ocean. But anyway, that they are feeding energy downwards. And the other source of energy, it's not a big source of energy on the ocean, on ocean scales, it does seem to matter is tidal energy, which actually matters more in the middle rather than at the surface, it turns out, because um if you have tides pulling water across a mountain ridge, you kind of start these internal waves. So the question is where does the energy get dissipated? So there's this big question about you've got this cascade of energy through the ocean. And it sort of sounds a bit technical, but if you think about energy being the thing you need for anything to happen, then asking how energy flows through the global energy. Where we started when we were talking about the system. Yeah, is actually quite a big question. And then really the big qu the biggest unknown about the ocean is how all the feedbacks work, which is possibly sounds like a slightly boring thing, but it really isn't because you've got this beautiful, intricate system with um dissolved iron and dissolved phosphorus, and you know, con nitrogen compounds and life, and they're all sort of exchanging with each other and exchanging with the atmosphere and exchanging with the ice, and there's this amazing, beautiful system of interactions. Now, at least in the human body, you've got a circularitary system, right? You've kind of got little pipes. You definitely know it's going through the pipes, coming out of some other pipes. But in the ocean, you've just got fluid, and it's moving differently on very small scales and very large scales. So there's a sense in which, if you if you can imagine a, you know, kind of like a microscope where you can focus in different ways. If you look at the ocean and average on very short time scales, you see all these really small sort of spinning motions. If you zoom out, if you average the same water over longer time scales, you see different shapes, you see big ocean currents. Um, and so there's this huge web of interdependencies in how the ocean works. And we are still picking apart exactly how those interdependencies work. And you know, my part of that is to understand how carbon dioxide and oxygen cross the ocean surface and where they go just underneath the surface, whether they stay down or not. And and so there's this web of things that you can look right at, but you can't necessarily see them. And and that, so so it's it's like we can see the body, but it's still slightly like a stick figure, and we want to flesh it out.

SPEAKER_00 33:17

Well, I think you know, this hearing these questions makes the case that there's more going on in the ocean than on the moon. And I think it reminds me a bit of there's a story about the great Cambridge astronomer Fred Hoyle, who stood up to give a lecture about stars, and he started off by saying, stars are fundamentally simple. And this voice from the back of the hall that said, Well, you'd look simple if you were light years away. And I just think listening to you talk about the Earth makes me think of all the times I've sat and heard people talk about distant planets and what we can and can't know about them, and I realize how little we actually know about anything, included including our own earth, which is a suitable point, I think, for us to end on. Thank you all for coming. But mostly I'd like to thank Helen for a fascinating discussion. So please thank me for joining Helen Chester.