I love it when a planet comes together - EWTS #007

Joe: Hello and welcome to Enough with the Science, I’m Joe.

Senan: And I’m Senan. This is the show where gas things happen in a gigantic way.

Joe: Well, maybe we should go back before all your gas jokes and your questionable references to Uranus. That is going to be part of today’s program and just to explain, this is Enough with the Science where Senan researches a science topic and talks about it at great length, and I try and dissuade him from talking about it by various means, whatever is necessary, until we run out of wind.

Senan: The topic this week is the outer planets. We better define what that is because there are, of course, further out planets than the outer planets. To make matters more confusing, things we call exoplanets, which are planets that are not in the solar system but are in some other solar system very far away. Thanks to our advanced space telescopes, we have discovered round about 5,000 of those.

Joe: Right. Just to be annoying now, so where does our solar system end?

Senan: That’s a subject of much debate. There’s a thing called the Heliosphere, which is the patch of space that is affected by the solar wind, the particles that stream off the surface of our sun out into space in all directions away from the sun.

Joe: The Voyager probes?

Senan: Voyager, yes. That’s a subject of much debate. A PhD student, I think he was, who was interning with NASA, realised that there was a very fortuitous alignment of planets coming up in a few years time that would allow a thing called gravity assist to be carried out loads of times one after another. Gravity assist basically means, say you are flying your spaceship and you want to go a bit faster without having to start up your engine again or maybe all your fuel is gone. If you can fly past a planet closely enough, the gravity of that planet will pull you in as you approach the planet, and then after you pass the planet by, if you’re going fast enough to pass the planet by, you’ve gained some speed for free.

Joe: Right. So, they basically piggybacked on the gravity of all these planets and whizzed out of the solar system.

Senan: Yeah. So those voyagers whizzed out of the solar system and they will probably be, when humanity and our civilisation is dead and gone in however million years...

Joe: That’s not going to happen, kids. That’s Uncle Senan is just losing his mind here.

Senan: They will be the last artefacts of humanity to survive.

Joe: What was the music? There was music put on them wasn't there?

Senan: There was, yeah. There was music and a load of pictures of people and places.

Joe: Tell me it wasn't U2. Tell me they didn't get U2 on the Voyager.

Senan: I don't think it was U2, no. I think it was probably Debussy or Strauss or Beethoven or one of those lads. Anyway, I'm not going to ruin it for you but their assumption of the person who gave them that present didn't turn out to be true regarding them never being able to reach the edge. Those probes have gone way beyond Pluto. They’re way past all the planets now. And they have sensors on them still working, unbelievably. Like, these things were launched at the beginning of the 70s, like 50 years ago.

Joe: So they're still sending back information?

Senan: They are, yeah. One of them is. I’m not sure if one of them might be dead. Anyway, the sensors were able to somehow detect the nature of the solar radiation particles in space around them. So, it appears like they passed over a border where there was no more influence from the radiation from the sun. That appears to be a kind of nebulous border because they seem to pass in and out of it a couple of times. But anyway, way out there somewhere is our best theory for what the edge of our solar system is when there’s no more influence from the particles that are streaming out of the sun.

Joe: Right, okay.

Senan: A bit further in though, we’ve got something called the Kuiper belt.

Joe: Kuiper.

Senan: Kuiper, yes. Dutch astronomer.

Joe: There we go. That is that. I don't even have to ask anymore. Just look at you and just go... Kuiper?

Senan: So, yeah. It’s like this orbiting halo of debris way, way out at the edge of the solar system. And that’s where Pluto resides. Pluto is one of the bits of debris that is in the Kuiper belt. Probably the biggest one.

Joe: And that’s why it’s not a planet anymore.

Senan: Yeah, you're after hitting on a very controversial subject there because of course Pluto was the ninth planet for a long time. And then about ten years ago astronomers collectively, or a lot of them did anyway, decided that it doesn't really deserve to be called a planet. It’s now designated a dwarf planet.

Joe: Right now, you're going to add... there's some criteria obviously they use for this.

Senan: Yeah, and it's a debate. Not every astronomer still agrees with it today. But I think most of them do at this stage.

Joe: Sure the family of the guy who discovered Pluto was probably against it being renamed or declassified.

Senan: Clyde Tombaugh is the guy you're talking about.

Joe: All right, okay. Well, his family are probably going, "No, you can't reclassify his planet."

Senan: It must affect his royalties.

Joe: How do you get royalties from a planet? I don't know. What's the point of discovering them then?

Senan: That brings to mind a science fiction book I read where somebody was given rights to a distant star assuming that they would never ever reach that star. It was just a theoretical present.

Joe: Usually Christmas. You see it comes up and you can buy a plot on the moon by a square foot of the moon and have your name put on a star and that's yours.

Senan: Anyway, I'm not going to ruin it for you. Pluto, yeah. I don't know how you'd make money off Pluto. However, the Kuiper belt... Pluto is a dwarf planet. The reason it’s a dwarf planet is the modern definition of a planet is something which has cleared its orbit. It dominates its own orbit and has cleared it of other debris. So, for example, apart from the moon, Earth’s orbit, apart from the moon, there isn't any other objects in our orbit that we’re sharing it with.

Joe: That’s good for us.

Senan: Yeah, that's good for us. Look, there's the occasional asteroid that comes close to us. But in general...

Joe: Bruce Willis will take care of that.

Senan: He will. In general, we have Earth has cleared its orbit of other debris. It dominates its orbit even though the moon is a significant body in the same orbit, it’s dominated by the Earth. Earth drags it around after it and so on.

Joe: So once you have cleared your orbit, you get like, there's your passport, you are a planet.

Senan: Yeah, pretty much. And as long as you're orbiting the sun and not orbiting another planet, in which case you're a moon.

Joe: Okay. There we go. Good definition.

Senan: So Pluto is just a member of the Kuiper belt community. There are known to be four other dwarf planets out there as well. So that’s, they're somewhere in between 500 and 3,000 kilometres in width. These are big enough things like.

Joe: They are big, but 500 kilometres... you would imagine a planet is bigger than that. I don't know. In my head.

Senan: But planets come in all kinds of shapes and sizes. I mean, the planet Mercury is smaller than some of the moons of Saturn.

Joe: Okay. But that's an inner planet, we're not talking about Mercury this week.

Senan: So yeah, and apart from like those five dwarf planets, there are believed to be about 100,000 objects out there which are more than 100 kilometres wide. So, there's an awful lot of stuff out there in the Kuiper belt. Now it’s very hard to see. To see these other planets, we’re basically relying on reflected sunlight. So, the sun shines on them even though they're very far away and we see this dot of light in the sky that's moving in a particular pattern and we can infer there's a planet. That’s kind of how Pluto was discovered. And it just happens to be one of the brighter objects. Something called albedo, to use a complicated scientific word. And it just means how bright reflectively it is.

Joe: So it's made of reflecty stuff.

Senan: Like, you know, if you have a white tennis ball and a black tennis ball. The white tennis ball has higher albedo than the black tennis ball.

Joe: So basically Pluto is a high-vis exoplanet... or planet-ette.

Senan: Planeteen. Yeah. So that’s kind of how we saw it. Most of the other objects out there are not that bright so the other things, the other dwarf planets and other large objects in the Kuiper belt, were not discovered for a long time later after Pluto was discovered. But it’s very cold out there. I mean, it’s minus 240 degrees.

Joe: That’s jacket. You want jacket and gloves and a hat weather.

Senan: I think you might even need a sleeping bag or what do they call it... dry robe. You know those. You need a dry robe I think. So, most of them are kind of icy things out there. So you're talking about frozen water, frozen ammonia, frozen methane. Now Pluto as it happens is a rocky planet. It is covered in kind of snowy, frozen icy stuff but there is rock underneath all that. It’s 40 Astronomical Units. Any idea what that might mean?

Joe: 40 Astronomical Units... is that you can buy it? If you have that money, you think about Star Wars credits now.

Senan: So yeah, an Astronomical Unit is not a very big thing at all, but it's also a very big measurement. It’s the average distance from the Earth to the Sun.

Joe: Oh, the average distance.

Senan: Yeah, yeah. Depending on where the Earth is in its orbit around the sun, there's a small bit of variation. So the average distance, about 150 million kilometres or eight light minutes. That’s what we call one Astronomical Unit. Pluto is 40 times further away.

Joe: So that's 320 light minutes.

Senan: 8 fours are 32... Yes. Correct.

Joe: Which is five hours, 20 minutes. So, the sun could be destroyed and Pluto won't know for five hours.

Senan: That’s correct, yeah. The rest of us will know a bit sooner.

Joe: Eight minutes.

Senan: Eight minutes in our case, yeah. Unless you're on Mars or something, might be a bit longer. So yeah, that's Pluto and the Kuiper belt. There’s a heart on it.

Joe: Right. Heart of Darkness? Or Heart of lightness?

Senan: It wears its heart on its sleeve.

Joe: [singing]

Senan: I'm not going to try and sing that song because you don't really think I can sing, do you?

Joe: I couldn't possibly comment.

Senan: Anyway, that's a tune from the 70s. So, if you're of a certain age like I am, you might remember that ditty. But yeah, so there is... It was only in recent years when we got good enough space telescopes to get a really clear picture of Pluto that we discovered there's this massive whitish heart on one side of the planet. It is almost completely covered by this heart shape.

Joe: And can this be seen from Earth or it can only be seen by kind of a probe with an iPhone?

Senan: Can the Hubble Space Telescope see it? I think it probably can see it. But certainly, some of the other probes we have sent out to the outer solar system have gotten good pictures of it. And as a result, we’ve now know this distinctive heart-shaped region is on one side of it. It’s kind of white or, well, kind of off-white ivory kind of colour. But the rest of the planet, why it stands out so much, is the rest of the planet is this reddish colour. Strange. So, there is a kind of a... they think that it snows methane or ammonia or something there and there are chemicals called tholins in it which have some kind of reddish hue. It’s not like bright red but it’s got a reddish kind of colour. Interesting looking planet.

Joe: So the heart is white and around it is red.

Senan: Yeah, most all the rest of it is red, yeah. It’s a bit of a Santy colour scheme.

Joe: I'll be out with the telescope. Out for a look at that.

Senan: Maybe that's where Santy hangs out when he's not around at Christmas time.

Joe: Yeah, let's just assume that.

Senan: Or maybe that's where Coca-Cola is made by that logic.

Joe: [laughter]

Senan: Kuiper belt is coming... Kuiper belt is coming... oh, I started singing, didn't I.

Joe: There we go. We're finished. I warned him.

Senan: So, the rest of the outer planets that we're going to talk about. So we're, by outer planets we mean anything that's further away from the sun than Mars.

Joe: Yeah.

Senan: And that's just an arbitrary thing I picked, place I picked.

Joe: Oh, you picked it.

Senan: Well, oh yeah, I don't think it's official.

Joe: Okay. Well it's official now. We'll make it official.

Senan: We certainly will. Enough with the Science officially designates anything beyond Mars as an outer planet. So it’s... the rest of them. So Pluto is number one, then there's four more. They're all gas giants. And that’s a peculiar kind of planet. So, we're talking about, for starters they're huge, the gas giants. They're much bigger than Earth. But we're talking about a small rocky core surrounded by a huge atmosphere of gas. Much, much deeper atmosphere than Earth's.

Joe: So our core in Earth is molten. So I imagine...

Senan: Well by core, the rocky part of the planet.

Joe: The rocky part of the planet. Is molten?

Senan: Oh, in a gas giant? Yes, well, some of the rocky part of Earth is molten. Like the bit in the middle is molten lava. But the rest of it that we're standing on right now is obviously solid. But it's still part of the rocky part of the planet. That's what I mean. So, you've got this rocky ball in the middle which, thanks to the extreme physics that goes on in gas giants, is probably all lava.

Joe: So it's all... so there's no, there's nowhere to go and stand if you decided to go to one of these planets. Like you couldn't just land a spaceship.

Senan: Well if you had asbestos boots you might be able to stand there for a moment.

Joe: But theoretically if there was a ship that could withstand horrific temperatures and pressures, but there's actually no solid bits. It's all liquidy, gassy, molten-y.

Senan: Yeah, so the interesting thing is we think that surrounding the rocky core, we think that there is what's called metallic hydrogen. So this is... hydrogen is a gas as far as we're concerned. But the atmosphere of these gas giant planets is so deep that the pressure just keeps increasing, increasing. So the thicker your atmosphere is, the more pressure there is down in the depths of it. Just by virtue purely of the weight of all that atmosphere above you.

Joe: Even if it was helium.

Senan: Anything. Any gas, yeah. And in actual fact, hydrogen which is almost as light as helium is one of the main constituents of those gas giants. So the deeper you go down in that, the pressure increases massively. And that has an interesting side effect in that things are being squeezed so much, molecules are being squeezed so much, that heat builds up. So it gets really, really hot and really, really heavy strong pressure the further down you go. And we think that in that environment when you go... pressure increases so much and heat increases so much, that the hydrogen gas becomes metallic. It actually turns into a metal. So we think that surrounding this ball of rock that's in the middle is like a shallow ocean of liquid... of metallic hydrogen.

Joe: It's Terminator stuff. You're going to expect Arnie Schwarzenegger to be coming out of this stuff.

Senan: Yeah, yeah. And one of the side effects of that is... we need to talk about magnetic fields. So Earth as most people will know has a magnetic field and it protects us from a lot of the dangerous radiation that's flowing around in space. But the reason we have a magnetic field is because there's a molten iron core in Earth, in the centre of the Earth. And it's rotating slowly, but that rotation is enough to cause an electric current or a magnetic field to... bit like the way a generator, an electric generator works. But the metallic hydrogen is also rotating in these gas giants. But its ability to generate a magnetic field seems much more potent than the iron core that's in Earth because they all have much stronger magnetic fields than what we do on Earth.

Joe: And just to go back, you were saying that's because of the pressure at the surface that all of this weird science happens.

Senan: Well, the pressure deep down in the atmosphere, yeah, yeah.

Joe: So like compared to Earth, for example. So we have atmospheric pressure.

Senan: Yeah.

Joe: But these guys have... like compared to Earth, are we talking...

Senan: Far thousands... thousands of times the pressure that we have here on Earth.

Joe: So we'd be squished into like...

Senan: Oh yeah, like there's no way you'd survive. If you fell into the clouds, it'd be a competition between the heat and the pressure about which one would kill you first.

Joe: Wow. I don't like those types of competitions. I normally like competitions but no, that one, no. Not so much.

Senan: Oh yeah, not not considered survivable at all to... for a living person. Even like we probably couldn't make a ship strong enough to withstand that.

Joe: So Earth's atmosphere is about 100 miles is it? 100 kilometers?

Senan: 100 kilometres tall roughly yeah, yeah.

Joe: And for some of these guys?

Senan: Good question. It's in the thousands. I can't remember but it's in the... it's in the tens or hundreds of thousands. Like, you know, take for example the real monster out there, Jupiter. I mean that is 1,300 times the size of Earth. In other words, Earth could fit inside of Jupiter 1,300 times. I mean you're talking about much, much bigger. In fact, while we're talking about that monster Jupiter, every other planet in the solar system could fit inside Jupiter. Not the sun, but all the planets could.

Joe: I'm getting the picture that Jupiter is the big boy.

Senan: Absolutely. Monstrous. Monstrous. It's huge. So okay, well right we were at Pluto. What's the next one? Let's run along to the neighbourhood.

Joe: Yeah. So the next one in is Neptune. Neptune is 30 times... 30 Astronomical Units away from the sun. 30 times further away than Earth. 57 times bigger than Earth. And unlike ourselves with our one lonely moon, it has 14 moons. So you can imagine what the tides on Neptune would be like if there was an ocean there.

Joe: Wow. There is a question. Talk about a theoretical question. Imagine what the tides would be like if there was an ocean on Neptune.

Senan: On Neptune.

Joe: Yeah because I mean, you know, our tides are nice and predictable because we have one moon and we can look at the motion of that moon and observe what it does to the sea and then we can make predictions about the tides. Imagine if you were trying to figure out what 14 different moons were doing.

Senan: So, lovely blue colour, Neptune. Deep blue colour because of... there's a lot of methane in its upper atmosphere and methane absorbs every other colour except blue, which we know from a previous episode means it looks blue.

Joe: That makes it easier to see than obviously as well. What is like... because it stands out?

Senan: Neptune... of course it's quite big. So hard to miss.

Joe: Yeah. Okay.

Senan: But yeah, I mean you know there's a nice blue glint in the sky if you point a telescope in the right direction, yeah, yeah. I mean you wouldn't see it with the naked eye. It's not that close. And in fact, none of these that we're talking about today can be seen with the naked eye.

Joe: Right.

Senan: Maybe Jupiter you can... it looks like a star all right but you can't really make out that it's a planet. So I guess we should talk about why do these gas giants even exist in the first place?

Joe: Yes we should. Why do these gas giants exist?

Senan: I mean that was the obvious question. I'm here tapping my foot. He's going to answer that question. He's going to ask that question any minute now.

Joe: Well I mean you're back to fundamentals of the universe. Why does anything exist? So let's we might as well focus on the existential question about gas giants. Why do we need gas giants?

Senan: Why do we need gas giants? So before there was ever any planets or even a sun in our sol... for our solar system became a solar system, there was just this massive cloud of dust and gas. And it was there as a result of a supernova which is an explosion of another star that had reached the end of its life. So when it exploded it spewed all this gas and dust out into this region of space. So gradually over time some of the dust particles began to clump together. And now you've got a little nugget that has its own little bit of gravity. Not much, but the more mass you put together in one place, the more gravity you get. So that nugget began to attract other bits of dust and gas towards it and that's how all the planets got formed. Now the interesting thing is the inner part of the cloud, which we now know as the inner solar system, was where most of the dust was. So that's how that the rocky planets are all in the inside of the solar system. With the exception of Pluto... are all in the inside of the solar system. Whereas the outer part of that cloud was mostly gas. So the gas giants got... although all of those gas giants do have a small rocky planet in the middle of them, that was just the seed, the gravity seed that pulled in the gas.

Joe: So the gas is just held in place by gravity?

Senan: Absolutely yeah, yeah. And I mean our atmosphere is the same. Like gravity of our planet is what keeps our atmosphere glued as it were to the outside of the planet. Other than that our air would just go away and we wouldn't have any, like the moon has no air.

Joe: That's where gas giants came from. And Neptune...

Senan: Yeah, Neptune. So Neptune is the first gas giant coming in from the outside after Pluto. And bonkers winds. It has winds of 2,400 kilometres an hour we estimate. I mean those are unimaginable winds. You can imagine what that wind would do to your clothesline with your washing on it.

Joe: 2,400 kilometres an hour.

Senan: Yeah, yeah.

Joe: I mean that... how...

Senan: I mean 200 kilometres an hour here is a very severe storm.

Joe: Yeah. So multiply that by...

Senan: By ten.

Joe: No, by ten. Or by one point something. Next week we're doing maths. We're going to be talking about maths on next week's program.

Senan: So why why why do you get those winds? Well, the planets are... those gas giants tend to rotate quite quickly so you have a lot of motion induced in the atmosphere by the rotation speed of the planet. You have also got an awful lot of heat which generates like... when you heat a gas it you get convection currents in the gas. So the more heat you have, the more convection you get so that's causes stronger winds. Why is the heat there? Because the atmosphere is so thick, in other words the distance from the top of the atmosphere where space starts all the way down to where the rocky little core in the middle is, is thousands and thousands of kilometres. So that's a really thick atmosphere. So you have a huge amount of pressure in the lower parts of that atmosphere just due to the weight of gas that's above it. And that pressure, that compression of the gas generates heat. It heats it up. So so there's quite a lot of heat. I mean there's really thousands of degrees. Like in close to the centre, the gas that the planet is made of is like 4,000, 5,000 or maybe 10,000 degrees Celsius. Like hotter than the surface of the sun in there.

Joe: So one second pizza.

Senan: One second pizza. [laughter] In and out. Very quickly.

Joe: One fraction of one second pizza I'm thinking.

Senan: So you you also have towards the surface, the viscosity of the gas, the stickiness of the gas is quite low. So all of those things contribute to these really fast winds. I mean some of those planets have storms that have been going on for hundreds of years. Jupiter's famous red spot, for example. Visible with any telescope that can see the planet Jupiter you you'll be able to see this huge red spot on one side of it. That is a storm which is bigger than planet Earth. And it has been going on for at least 300 years.

Joe: Imagine if you'd planned your holidays there. You'd just be... oh no.

Senan: Yeah, I don't think holidays in... actually holidays near Jupiter might be interesting. You'd have lovely view over your head if you could survive all the radiation that's in Jupiter's neck of the woods.

Joe: Another hypothetical. Imagine if you could survive radiation.

Senan: And why is the radiation there? Now it's no harm... seems we've mentioned the fact that these gas giants tend to have very strong radiation. They're called radiation belts around them. And the reason for that is they have this real strong magnetic field. That's because they have the metallic hydrogen core. And those magnetic fields are so strong that they're actually able to trap the radiation particles, the high energy particles that are coming from the sun. So there's pockets of this stuff being trapped in belts around the planet, pockets and belts, I'm getting my analogies mixed up here.

Joe: Trousers. They're wearing trousers. So radiation trousers they've got.

Senan: The point the point is it acts as a trap for radiation, these magnetic fields. And so if you're sending a probe, space probe, little robot up there to investigate you know what the science around Jupiter or Saturn, it's a real challenge to make it capable of withstanding that radiation. That stuff can fry the electronics, the computers to control our little spaceships. So yeah, it's a very challenging environment around them.

Joe: Around all of them.

Senan: Yeah. Oh yeah, I think I think all of them have... now look, Jupiter is enormous. It really is the biggest of all of them by far. And its magnetic field and radiation belts are real bonkers. But yeah, they all have quite strong magnetic fields and radiation around them.

Joe: So we started with Pluto, we came past Neptune.

Senan: Yeah, next we're going to do the next planet without any jokes.

Joe: Before we get on to the anterior next planet...

Senan: Before we get on to the anterior next planet... we need to talk about one really peculiar thing about Neptune. It is theorised that Neptune might have diamond hailstones.

Joe: Right. Now I can see why an entire fleet of ships is being prepared to try and mine these planets.

Senan: Yeah. So the problem is of course in order to get at them you've got to descend into the high pressure zone. Because they think that when the methane in the atmosphere reaches, you know, in the deeper parts of of of the atmosphere, when it reaches the extreme pressures, they think the pressure and the heat is enough to separate out the carbon component and compress that carbon into diamond... because diamonds are made of carbon. Compress that into crystalline carbon which is what diamonds are. And then they would start falling down in the gravity. But chances are before they actually get all the way to the ground as it were, the heat probably destroys them, probably vaporises them again. So there's like a diamond rain cycle going on there.

Joe: It's just this band of diamonds like being created and then falling and being destroyed constantly.

Senan: Yeah, yeah. And you know what else goes with a diamond but rings?

Joe: Nice segue. Finally.

Senan: And Neptune... I know Saturn is the planet that we all consider as the one which has rings. But Neptune actually has has its own rings as well. But they're dark in colour and... I've made a mistake.

Joe: Really? They don't have... Neptune doesn't have any rings?

Senan: It's Uranus. It's Uranus has the rings.

Joe: So Neptune... like we go back. Go back now so Neptune has the diamonds but no rings.

Senan: Yeah. You are definitely going to edit out this bit.

Joe: No, I'm keeping this. This is staying in.

Senan: Anyway, we'll move into the next planet in.

Joe: You're going to actually refer to this as just the next planet. For now... the planet in between Neptune and Saturn. You're not even going to say the name. Everyone knows it.

Senan: So let me get one joke. No. Please let me have one.

Joe: No, you can't have any. No, it's too obvious. It's just too Benny Hill.

Senan: I'm going to say it anyway.

Joe: I'm leaving. I'm leaving.

Senan: Joe. Uranus smells terrible.

Joe: There you go.

Senan: And it's because there's hydrogen sulfide in its atmosphere. But we should probably refer to it by that other slightly different pronunciation, Uranus. Just...

Joe: There you go. Uranus will do.

Senan: That allows me to... allows you to ruin all the jokes I had lined up for for this part of the podcast.

Joe: Absolutely. Thank god.

Senan: Uranus, okay. So 19 times further from the sun than Earth is. 19 Astronomical Units. You could fit 63 Earths inside in it.

Joe: Okay.

Senan: It's pretty big. It has a paltry count of only 27 moons. So again, the theoretical tides would be even worse there. Takes it 84 Earth years to go around the sun. So one one year of Uranus is 84 Earth years. But one day is only 17 hours so it spins quite fast. Especially for a big planet like... so the surface is actually whipping around quite fast. It's bluish but not quite as blue as Neptune. We're not quite sure why Neptune is a stronger blue. I mean the blue is a signature for methane but it may be down to the percentage of of methane that's in the atmosphere but yeah, not quite as strong a blue. And of course the big piece of weirdness about Uranus is that it's sideways. In comparison to every other planet in the solar system.

Joe: Right. What does that mean? Yeah, what does that mean like yeah, exactly.

Senan: So imagine every planet has a pole going through the middle of it like an axis that it spins around. So we we refer to the North Pole and the South Pole because there's like an imaginary pole right through the middle of the planet and it's spinning like a spinning top on that.

Joe: Yeah.

Senan: So our North Pole on Earth points in the same direction as the North Pole of every other planet and the sun. They all point up in the same way that our North Pole points up.

Joe: Right.

Senan: They're all lined up.

Joe: They're all lined up with the center of...

Senan: With the sun effectively. The North Pole of the sun points upwards, we'll call it up in our frame of reference. And so does every other planet except Uranus.

Joe: But okay, wait. So all the planets are... when they're spinning...

Senan: Yeah.

Joe: They are spinning around the same axis.

Senan: They're spinning around an an axis that is parallel to the axis of every other planet.

Joe: Right. So like it's like having spinning tops on a floor.

Senan: Yes, several of them. Yeah, yeah.

Joe: They're all...

Senan: So their up is the same.

Joe: Of all of them.

Senan: Yeah, yeah. And seen as you mentioned a two-dimensional surface like a floor, they're also on the same plane as each other.

Joe: Yeah.

Senan: So literally having them all on the floor is a good analogy for how they really are.

Joe: All the planets.

Senan: Yeah, all the planets. Except Pluto, which is slightly off, but the rest of them are all on the same plane. Or all the same flat... if you if you were to cut a slice across the middle of the solar system all the way across it, that where the planets are, they'd all be on that slice.

Joe: Right.

Senan: Uranus is on its side. So its North Pole is kind of facing east or west as far as we're concerned.

Joe: Right. So like we're all spinning like tops and it's rolling along the floor essentially.

Senan: Essentially, yeah, yeah. Well, it's rolling now the rolling is not causing it to move so the analogy breaks down there. But yeah, it's true, it's funny isn't it? There's all these planets have their own little surprises for us.

Joe: And Pluto. So Pluto's off the plane. Pluto is no longer on the plane with us.

Senan: Pluto's orbit is tilted slightly off the plane. I mean it still orbits the sun although it has a weird oblong orbit. So you know there's times when the distance between Pluto and the sun varies quite a lot depending on where it is in its orbit. So it's not... most of the planets are in circular or nearly circular orbits. But Pluto's is quite oblong and it's off centre. So it's a weird bunny Pluto. Anyway, moving further a little further in, we come to Saturn. Very interesting place. Ten times further from the sun than Earth is. Ten Astronomical Units out. Massive planet. You could fit Earth into it 764 times.

Joe: Wow. That's some real estate.

Senan: Yeah and it's all just gas. Or most of it anyway. The rings of course. Saturn is famous for the rings. And they are quite thin. They're like thin blades made from ice, mostly ice chunks of ice.

Joe: Okay. Now when you say quite thin, you like I mean are you talking...

Senan: No more than maybe 50, 100 kilometres wide which in comparison to the size of the planet is is very thin.

Joe: Yeah. Okay that's quite thin. Yeah.

Senan: So they think it's theory... they seem to be mostly made of ice. And theory is that there was like maybe a shower of comets, so a lot of comets are made from ice, a shower of comets came a bit too close to Saturn's massive gravity and got pulled in. And eventually over time they the spin of the planet meant that they tended to the gravity kind of funnelled them into this flat disc which matches... it's essentially around the equator of Saturn.

Joe: Okay.

Senan: Its where the the rings are. Also we are very lucky to be alive at a time when we can see them. It'll it sound... best estimate is that they're a fleeting phenomenon that might only be visible for 100 million years. Who put only with 100 million years? But the point is that like you know the age the solar system is probably four or five billion years old. So in the context of that, 100 million years is a tiny slice of time and they're gradually falling in to Saturn.

Joe: Oh. Okay. So they're collapsing.

Senan: They'll be gone in a while in you know a while as in 100 million years.

Joe: Short short time.

Senan: Yeah. There's one real mystery about Saturn. It's got a hexagon storm at its North Pole. So if you look at picture, it's pictures are really weird. You should see them. There's like a hexagon with sharply defined hexagonal sides and corners right around the North Pole of Saturn.

Joe: And it's a storm.

Senan: It's a storm, yeah. But it's not like most storms on Earth are circular. Or roughly circular. This thing is hexagonal. For some reason it's taking left turns and left turns and left turns at particular places.

Joe: The indigenous Saturnians must be wondering why we're not getting their... we've been sending them signals. We've been like kind of we've sent them our favourite shape. We're getting nothing. We're getting nothing back.

Senan: I think it must be an alien portal. It's all it could be. Now it's massive also. It's like it's 30,000 kilometres wide so you could drop the Earth into the middle of it no problem. Like it's huge. But it's a real mystery why that's there. We knew about Saturn for a long time before we knew this thing existed. It was only when we got a probe into a position above it a bit that we could get a photograph down towards its its North Pole. We had this really interesting probe actually that was sent to um think it was round about 20 years ago it was launched. But it was sent to examine the science around Saturn and the moons of Saturn because Saturn has 274 moons.

Joe: Right. Okay. Little greedy.

Senan: But Cassini it was called. It was a real groundbreaking mission. They did some great science. The thing was there for about ten years visiting the different moons and then coming close flybys of the planet and in between the rings and everything. Spectacular photographs. And there's a there's one wonderful picture it took where it got on the far side of Saturn from Earth. And you have a picture of Saturn in the foreground and this tiny little blue dot way in the distance.

Joe: Oh, this is the blue dot photograph.

Senan: Yeah, taken by by the Cassini space probe. But one of the most fantastic discoveries it made was one of Saturn's moons is called Enceladus. So Enceladus is smallish moon but it's got a surface that's just a crust of ice. Now by crust I mean like maybe 100 kilometres thick of ice. But underneath that there is a liquid water ocean. So there's the centre of the moon, whatever geological processes are going on in the centre of that moon, there's enough heat being generated by the geology of the moon to keep a big ocean of water from freezing even though the surface is frozen. But the really cute part was Cassini took photographs with the light from the sun behind the the moon and it showed that there was these geysers of water coming out through cracks in the surface and spraying up into space, like way high up into space. So what they did was they got it to fly through... they got this Cassini probe which took quite a bit of maneuvering to line it up in a way that it could fly through these these geysers in space and sample using its scientific instruments sniff what chemicals were in that liquid. Mostly water, but there was quite...

Joe: Did nobody just say is this risky? Is this like kind of we don't know what that is? Is it like kind of Cassini melting acid that has been shot out of this moon?

Senan: Well, I suppose we it was such a weird phenomenon that had not been observed on any other planet or moon anywhere in the solar system to you know it's worth the risk to find out what this stuff is made of. And like essentially they discovered there's loads of organic molecules like organic chemistry diluted or dissolved into that water. Now that doesn't mean that there is definitely life there. Those are by organic chemicals we mean like the building blocks of life, chemicals that could be used to create living creatures or could be the the waste products of living creatures. But it's believed by many scientists to be the best chance of us finding microbial life somewhere else in the solar system in that ocean underneath underneath all that ice on on Enceladus because of the chemicals that were found that were found in the plumes.

Joe: Is Cassini still out there?

Senan: No. So Cassini eventually began to run out of of of whatever it needed to keep itself alive. Battery or fuel or whatever. I think it's probably fuel. But it was there for about ten years so anyway what they did was they really cool they actually crashed it into the Saturn into the atmosphere of Saturn deliberately at a kind of a shallow angle so that it would last for a reasonable amount of time before the pressure and heat and all that got... So they actually got some quite broadcast... it kept broadcasting until it died somewhere in the atmosphere of of Saturn and they got some interesting science back about analysis of the gas. It was really cool that mission. Another real cool part of the Cassini mission, there's another moon of Saturn called Titan. Now it's called that because it's absolutely enormous. It's bigger than Mercury. But Cassini carried a little piggyback robot, another small robot that was hitching a ride on it. And it released that robot near the moon Titan and the robot landed on the surface of Titan. Which is like to me mind-boggling, the idea that we had one robot carrying another robot and just the right time near this moon of Saturn which is a long way from here, it released it and the thing glided down, fell down.

Joe: Oh actually I there was there was parachutes and things. Like it was a pretty complicated device.

Senan: It made a soft landing. Like it took photographs all the way down. It made a soft landing in a dry riverbed. And we know it's a dry riverbed because, the photographs it took before it landed we could see the the shape of the river and the erosion it caused on the landscape. But once it got onto the riverbed we could see rounded boulders which that kind of rounded erosion only happens with flowing water. So like except it's not water in this case it's methane. So it has Titan has an atmosphere, it has methane and ethane rain, it has rivers made of liquid ethane and methane and lakes. Like we can see the photographs that it took on the way down showed us all of that. It's like mind-boggling this is going on on a moon of Saturn.

Joe: And this little robot is dead now obviously.

Senan: Oh yeah since they flew it into... oh the little robot yes that didn't last very long. It didn't have the resources and the atmosphere of Titan is thick misty kind of atmosphere, very little light out there, very little heat. So it just couldn't survive. But yeah some really cool stuff out there around Saturn. So finally we're going to come on to the monster of the solar system.

Joe: Is your favourite planet isn't it?

Senan: This is my favourite planet because it has probably saved us all.

Joe: It's our saviour. They should have named it Bruce Willis.

Senan: Oh Bruce was in that movie... what was the movie? It was about saving the world from an asteroid.

Joe: Armageddon.

Senan: Armageddon. Yeah that was the one yeah. So yeah and so Jupiter is our Bruce Willis and the reason is this is an absolute monster of a planet. It's 1,300 times the size of Earth. In fact you could fit every other planet in the solar system inside Jupiter. Not the sun, the sun is bigger than Jupiter, but all the planets yes. And as a result it's got mind-boggling amounts of gravity at its disposal. So anything that comes anywhere near Jupiter is going to get sucked in or at the very least deflected rapidly. So you can sometimes get asteroids or rocks flying through space that are going so fast that Jupiter even Jupiter's massive gravity wouldn't pull them in but it will deflect them, it will make them change direction. So that is effectively acting as a minesweeper in the outer solar system. So earlier on in the evolution of our solar system there was an awful lot of asteroids rocks flying around at very high speed. And Jupiter has hoovered up most of them. And were was it not for Jupiter, our planet would probably have been bombarded by dinosaur killer asteroids far more often than actually happened. So life might have been wiped out by those things. So Jupiter is yeah definitely my favourite planet.

Joe: Pretty good.

Senan: Do you know it bulges in the middle? It's not perfectly round.

Joe: It's like myself.

Senan: It's the reason is it spins so fast. It has a ten hour day. Can you imagine a planet that size, 1,300 times the size of Earth and it's still able to spin that fast that it has a ten hour day. And it actually bulges a bit in the middle because it's spinning so fast.

Joe: The numbers are just kind of mind-blown really.

Senan: Really oh yeah only unimaginable to us. I mean Earth we consider Earth to be of huge size. Like you know how long would it take you to walk around it for example. But yet it's a baby in comparison to the gas giants.

Joe: Like I think the biggest thing about the gas giants though are is that when I think of a planet there is a physical surface that you can walk on.

Senan: Yeah.

Joe: Whereas with any of these gas giants it's almost impossible to imagine what that might even look like should it exist somewhere. That there's a hard like even though there's a rocky core but it's not rock. It's molten like steam and gas.

Senan: Yeah and probably has a coating of metallic hydrogen around the outside of it.

Joe: Yeah. So it's just it's almost impossible to imagine that these things like their atmospheres are so gigantic but it's all gas until you get to a certain level and then some of them have like diamond rain and then the diamonds explode and then there's like liquid silver stuff that Terminators come out of and then it's like hellish at the bottom and...

Senan: Yeah. That's the thing I mean even the temperature like in close to the centre of them the temperature is much much hotter than the surface of the sun. Like it's unreal.

Joe: Yeah. They're they're scary places. They're not places to go for the weekend really.

Senan: No. And the reality is, based on our observations of exoplanets in other solar systems gas giants seem to be the most common type of planet.

Joe: Right. So we are hopelessly looking for Goldilocks, Goldilocks planet.

Senan: Oh an Earth, an Earth-like planet yeah. There's super-Earths they think where these are planets that are the right distance from their local star that they would have liquid water but much much bigger than Earth so much stronger gravity. So if there is life on them they're they're big boned muscular creatures.

Joe: Or very short.

Senan: Yeah. Two-dimensional creatures.

Joe: So I think with like our big so Jupiter are is our planet saviour.

Senan: Absolutely.

Joe: And we'll have to do the inner planets then next week are we?

Senan: We'll do them sometime. We'll do them sometime. I think maybe the listeners have had enough planets for one month.

Joe: You can never have enough planets. So I think that's enough with the science then for this month.

Senan: Yeah. I'm Senan and hopefully we'll see you again next week.

Joe: I'm Joe. Take it easy.