The Supermassive Podcast - 29: Gas Giants are Weird

Episode Date: May 31, 2022

From hexagonal shaped storms to spinning sideways, Izzie and Dr Becky are exploring our weird and wonderful Gas Giants. Joining them are Dr Tom Stallard from the University of Leicester and Dr Robert Massey, Deputy Director of the Royal Astronomical Society. Plus editor, Richard Hollingham, takes a trip to the Royal Astronomical Society’s library to see Galileo’s first observations of Saturn’s rings and William Herschel’s notebook from when he discovered Uranus.   See Jupiter's fast rotation (thanks to Dr James O'Donoghue) https://twitter.com/physicsJ/status/1519023430053818368   Thank you to Brilliant for sponsoring this episode.  Head to brilliant.org/supermassive to start free courses in maths, science, and computer science. The first 200 subscribers will get 20% off.   The Year In Space 2023 by The Supermassive Team will be out on Oct 2022. Pre-order here: https://geni.us/jNcrw The Supermassive Podcast is a Boffin Media Production by Izzie Clarke and Richard Hollingham. Edited by Sarah Moore.

a big thank you to brilliant who are sponsoring this episode of the super massive podcast there's no denying that podcasts are a great tool for learning but so are videos you know i love a video and brilliant is an interactive stem learning platform that helps you to truly understand concepts in maths science and computer science by guiding you through engaging hands-on courses so i finally started the everyday math course that has gone up recently and it's incredible the visuals are just great they're really helpful to give you that overview and to learn the basics of lots of different topics as well and yeah so I'm actually finding it really fun that's great that's so good I think that's the good thing is that like it's math

that you're not familiar with but in situations that you are familiar with as well. And have you been using those in-depth explanations that they have as well, just like in case you get stuck, that break it down a bit more? Yeah, they're so helpful just to have that on hand if you're getting a bit, if I say, if you, if I get a bit stuck on something. When.

When I get stuck on something. So if anyone else wants to give this a go, head to brilliant.org slash supermassive to get started for free.org slash supermassive to get started for free. And the first 200 subscribers will get 20% off. Jupiter is really, really big. You could fit 1300 Earths inside it. The rings are only 50 million years old or so, which means they didn't exist when the majority of the dinosaurs were around. Gas giant. It kind of does what it said on the tin.

Hello and welcome to the Supermassive podcast from the Royal Astronomical Society with me, science analyst Izzy Clark and astrophysicist Dr Becky Smethurst. This month is the month I've been waiting for. We are talking about my favourite planet, Saturn. No, hang on, Becky. We've talked about this. Come on. And all of the other gas giants' planets too.

That's Jupiter, Neptune and Uranus. We'll be exploring these giant worlds to find out what they can tell us about our solar system. I'll be chatting with Dr Tom Stallard from the University of Leicester to cover the basics. Plus, our editor Richard Hollingham takes a trip to the Royal Astronomical Society's library to see Galileo's first observations of Saturn's rings and William Herschel's notebook from when he discovered Uranus.

And it's not the Supermassive podcast without Dr Robert Massey, the Deputy Director of the Royal Astronomical Society. So, Robert, gas giants. I mean, it kind of does what it says on the tin, but what are the fundamental features of a gas giant? Definitely a name on the tin one here. They are giant and they are gaseous. So yeah, they're big. And in our solar system, we think of Jupiter and Saturn and mostly made up of hydrogen, helium around much smaller solid cores, like a little nucleus for them.

And then you've got the ice giants, Uranus and Neptune, further out. And to give you a sense of scale, Jupiter really is really, really big. You could fit 1,300 Earths inside it. And they're also the easiest planets. There are lots of gas giants in the universe. They're the easiest ones to find around other stars because they're big, so they've got a lot of mass. They pull on the stars, so they're easier to detect. And also, if they block the light of the stars, they're easier to ones to find around other stars because they're big. So they've got a lot of mass. They pull on the stars so they're easier to detect. And also if they block the light of the stars, they're easier to see that way too. So most of the planets we know about are actually like gas giants.

And there is a really exotic type called hot Jupiters around other stars as well. But nothing like that in our solar system. Cheers, Robert. We'll catch up with you later in the show to take on our listener questions. And a quick reminder our book the year in space 2023 is available for pre-order right now and it has a feature on europe's forthcoming mission to jupiter which is bizarrely named juice i love that name jupiter's icy moons and exploring or something like that read the book you'll find out

okay so gas giants they are big and they are gassy but why are they so big and how is each planet different well it was a question that i put to planetary scientist dr tom stallard from the university of leicester so gas giants are really big because they were able to grab a whole lot more material when they were forming. And interestingly, it's because they formed much faster than places like the Earth. So at the core of every gas giant, we think, is something a bit like the Earth, some rubbly rock and metal. So they made a core that was at least the size of the Earth incredibly quickly. made a core that was at least the size of the Earth incredibly quickly. And so they were bigger centres that were able to grab and sequester all of that gas very quickly in the early formation before it all dissipated. Okay, what gases are we talking about here? We've got four gas giants.

Are they all hydrogen and helium? They all have some hydrogen and helium. All of the planets in the solar system were made out of exactly the same stuff as the sun. What is different about the Earth is that it's been rarefied. And so you have a lot of heavy elements and very, very little light elements. Somewhere like Jupiter or Saturn, they have more heavier elements in them than the sun. Jupiter has maybe two times as much saturn has maybe 10 times as much and then there's a another set of planets which we call the ice giants okay so can i so yes so technically when we talk about gas giants basically up until this point we've been saying that is jupiter saturn neptune uranus. I feel like you're about to tell me that technically that's going to change. It's difficult because who writes the rules of what you call a planet or even what a planet is, right? Yeah.

If you want to start getting a bit more nitpicky, technically, when we talk about gas giants, we talk about Jupiter and Saturn. Those are the planets made purely of gas, of light gases, and then Uranus and Neptune we call ice giants. A gas giant would be one that's made mostly of hydrogen and helium, like Saturn or like Jupiter. And then you look at the density of Uranus or the density of Neptune, and the density is much higher. It's somewhere between Earth and Jupiter. And it's made of, we think, mostly things like methane ice and water ice. Because in the outer solar system, during that early formation period, they were all solids. So they were the same as rock. And so those two worlds, what we

call ice giants, are distinct in a very significant way inside of the planet but actually on the outside of those planets they're very similar because hydrogen is light so it floats to the top and so you have an envelope surrounding the interior that is very similar to Jupiter ah okay okay so let's talk through their key differences. You know, like, what is Jupiter like? So Jupiter's the biggest planet in the solar system by a significant amount. It's three times more massive than Saturn even, but it's vastly smaller than the sun. So it sort of stands alone really as this midpoint between stars and more kind of traditional rocky planets like Mars or Earth. And it's sort of the archetype of what a gas giant could be, I'd say.

So Jupiter is special because it's this vast store of energy. It's got this crushing gravity. It's vastly larger gravity than anywhere else. The magnetic power is much stronger than anywhere else. Its magnetic field is vast. If we could see it, it would be the biggest thing in the night sky from Earth. And all of that is driven through all sorts of powerful exchanges of energy. So these massive storms that are larger than the Earth, the magnetic environment that has aurora that is the brightest in the solar system.

It's the big daddy. it's the thing that controls everything right i just think jupiter is just kind of mad so then we get onto saturn its neighbor the first thing people think of other rings but what else is going on on saturn and and how important are those rings to us it's this really evocative image, the classic picture of a planet almost is Saturn's rings surrounding the planet. But in terms of mass, they're tiny, they're inconsequential. It's some kind of moon that got broken apart probably at some point in the past. What's really interesting in the last maybe two, three years is we've started to realize that probably wasn't something that happened a very long time ago. So it's possible that some dinosaurs, had they had telescopes, would have seen a Saturn without a giant ring system.

And it's been fading away. So in another 300 million years, it's quite possible those rings won't exist in the same way anymore. So in the lifetime of Saturn as a whole, as a planet, it wasn't the ringed planet. It wasn't this this world there's lots of other interesting things about Saturn that make it kind of unique like its magnetic field is perfectly aligned with its rotational pole which is weird and we can't

explain it yeah yeah okay okay so then we get on to Neptune what can you tell me about Neptune so Neptune and Uranus are both really interesting worlds. They're very similar to each other in some ways, we think, but also very different. One of the fundamental differences that we don't understand is when we look at Uranus, it doesn't seem to have any heat coming out of it at all. And when we look at Neptune, it seems like there's a huge amount of heat, much more than Jupiter or Saturn. We don't understand that at all. We want space missions to go back to actually explain or at least understand whether that is even the case. The thing that makes both those worlds really

fascinating for me is the magnetic field, and they have really weird and wonderful magnetic fields. Neptune, we got closer to than Uranus, so we have a better measure of how weird it is. And it's very strange indeed. It probably has four magnetic poles, which means it may have four auroral ovals, which is pretty extreme and weird. Yeah, okay. So in terms of like the makeup of Uranus and Neptune, you know, we've said that they're ice giants.

Do we know what elements they're made up of and what's it like on those worlds? So we've had one spacecraft fly past each and we've had a series of observations from Earth. For spacecraft missions, you can maybe look at the gravity and how the planet pulls a spacecraft as it flies past. And that's all you can do. So our understanding of the interiors are pretty limited and are mostly just people making models of what they think might be the interior. We need space missions to go back and make better measurements to be able to really answer those questions. Yeah and are we going to get those missions? So the current state of play has changed very dramatically in the last month. What happened is the release of a decadal survey by NASA. So once every 10 years, they write up what the scientific community want.

And Uranus was positioned very strongly in that. And so it's very likely we will see a Uranus mission in the next 10 to 20 years, something like that. That means it's going to be much harder to get to Neptune, but there is still potential for two missions I'd like to believe that we could do both but yeah it's very much brand new news to the community so everyone's very excited but no one has an answer yet as to whether that mission is viable or whether that mission is actually going to go ahead thank you to Tom Stallard from the University of leicester so don't get me wrong i love the rocky planet you know but there is birth yeah yeah you know credit to them

but there is just so much mystery around gas giants and they are so different from our world and technically i just look at them and i think well they just do whatever they want they're so bizarre and i think that was confirmed recently there do whatever they want. They're so bizarre. And I think that was confirmed recently. There was this tweet that went viral. From James O'Donoghue. Yeah, exactly. I love the stuff he does. And so it's an animation of all of their planets

and their size, their tilt and their rotation. And then it sort of starts with the rocky planets and zooms out. And when you get to Jupiter, it's just off the scale. It's huge, obviously. And its rotation is so fast like I really want everyone to go and see this because I was shocked at just how fast some of the gas giants it's about nine hours that Jupiter takes to rotate is crazy like okay so my question for you Becky then is what actually dictates their rotational speed and why are they so different?

Yeah, I mean, so rotational speed is a good one because it can actually tell us about a planet's evolutionary history, right? Clues of how it came to be, essentially, sort of like a fossil of what's gone in the past. So we think all the planets formed from an amalgamation of the rubble in the early solar system clumping together. And if you think about it in terms of the fact that rubble is going to be coming from all sorts of different directions as it sort of collides together and that adds more and more spin angular momentum as we call it to the planet that's building up and building up and so you can think about it if all the rubble comes from the same direction it can spin up the planet and if all of it comes from the opposite direction it can spin down the planet or even you know flip the spin to go the other way which we see with the likes of venus right it rotates in the opposite

direction to earth so the sun rises in the west and sets in the east you know on venus and as gravity starts to clump material together in planets it's kind of like a skater pulling in their arms as it clumps together and gets denser the the speed can increase. And so the bigger the planet, the more massive the planet, the more massive that effect is as well, the bigger that effect. So that kind of makes sense thinking that Jupiter is rotating so fast.

It's just because it is so big. But if we think about some of the other gas giants, like Uranus, Uranus spins on its side. Which I love. This is what I mean. They're just doing what they want. They're like, yeah, I'm out of here. Here I come.

I imagine it just sort of like lazily like rolling around on its orbit, This is what I mean. They're just doing what they want. They're like, yeah, I'm out of here. Here I come. I imagine it just sort of like lazily like rolling around on its orbit. Just like, ooh. The other gas giants are like, are you okay over there? Exactly. But again, that's one of those things where we think that encodes a tiny part of Uranus's history. So it could be that it got hit by a very large impact in the same way that we think the Earth did. And that's why it's got its little 23 degree tilt that gives us its seasons. And it might have given us the moon at the same time.

We think Uranus could have been hit by a really large object just after it formed. And that could be why it's on its side. This is what we mean by the planet spin encodes its history. Yeah, I love that. So other than just being very cool, gas giants are helpful when it comes to studying planets outside of our solar system, exoplanets. So only Robert gave a little hint to this earlier, but can you explain why gas giants are so helpful in particular? I think it's because the majority of exoplanets we found are very similar to the gas giants. We

found a lot more exoplanets that we characterize in terms of Jupiter's mass or Neptune's mass. You know, we'll say, oh, that's three times the mass of Jupiter, or it's 10 times the mass of Neptune, whatever it might be, than we do with Earth's mass. You know, we very often will not be saying, oh, we found a planet that's two times the mass of the Earth. You know, we do find them, but they're nowhere near as common as the much bigger ones. And that's mainly because the more massive the planet, the easier it is for us to spot because if it passes in front of a star, it causes a bigger dip in brightness.

It also reflects more star lights. We've got a better chance of taking a direct image of a bigger planet as well. But we can also spot planets that orbit closer into their stars much easier as well because again, they cause a bigger impact. They tend to pass in front of the star more often as well because again they cause a bigger impact they tend to pass in front of the star more often as well so you see them more often so you've got a better

chance of spotting that happening so what we end up with if we combine those two things is we end up with lots and lots of planets that are about the size of Jupiter that orbit really close into their stars that we call hot Jupiters and the question obviously in the ongoing sort of characterization of exoplanets as well is that actually representative of the majority of planets are the majority of planets actually these hot jupiters or are we just only seeing one section of the sort of entire spread of planets that you find but by finding these hot jupiters it raises questions like well how did they get there did they form there or did they form further out where we find our gas giants and then migrate inwards or did our gas giants form closer into the sun and then migrate

outwards you know it helps us you know piece together what's going on in terms of you know planet formation in our system our solar system other star systems and we think the most likely is that gas giants formed further out and migrated inwards right and perhaps that didn't happen in our solar system because we had four of them on the outskirts and sort of they all held each other back especially saturn held jupiter back from migrating inwards as well and so you know by finding all these different kinds of planets and different kinds of systems we essentially always come back to our own solar system and how it formed. Yeah. And there are still so many questions out there about our own solar system. I mean,

go back to some of our other episodes. But, okay, Becky, I'm going to give you this one chance. Why is Saturn your favorite planet? So, so, so many reasons. I joke that I have like a list of reasons. It's like 500 items on. Yeah, it brings out like a scroll that just travels the length of the room. I mean, it looks spectacular for one. You've got to admit,

it's definitely the most blingy of all the planets, right? It has this hexagonal shaped polar vortex storm raging on its North Pole, which is amazing. Like sharp edges and corners in space is not something we see, but everything is round. The rings are only 50 million years old or so, which means they didn't exist when the majority of the dinosaurs were around, which is amazing to me. Also two of its moons, Titan and Enceladus, are some of the most likely places we could find life beyond Earth in the solar system plus as i just said most giant planets migrate inwards to become hot jupiters but we think saturn stopped that happening in the solar

system reigning jupiter back in which you know if saturn didn't exist jupiter would have migrated inwards scattered all the inner planets earth might not even be here if it wasn't saturn right so i think owning our entire existence to a planet if that isn't enough to convince you is he i don't know what it's i mean it's a good argument i'll give you that i'll give you that i just want to give a shout out to neptune because i just feel like it always gets forgotten and it's such an interesting world that we just don't really know that much about and it's just like oh yeah and there's neptune yeah and like yeah so i because neptune has rings too and people often forget that exactly and it also it's the best color i'll give neptune that it definitely wins the best

color there we go we're right there we go we'll celebrate neptune for that behind the scenes at every recording of the supermassive podcast sits our editor richard hollingham and frankly he doesn't get out much so we decided to let him out to do some recording he's been lucky enough to return to the library of the royal astronomical society to talk to librarian sean prosser one of our favorite people and see records of the first observations of saturn's rings and some notebooks charting the discovery of a mysterious new and royal planet. Well, it is a delight to be back in the library at the Royal Astronomical Society in central London, where I am surrounded by floor-to-ceiling books. From the floor to the ceiling here, there are 15 shelves of books.

There's one of those ladders that you can push around to get to the high shelves. And even a spiral staircase up to a gallery shone on the table in front of us. Well, let's start with this one. This looks like a regular old book. It's a sort of faded white cover but this is quite special isn't it it is this is a 1655 edition of a book by Galileo it's his book about sunspots he says in the introduction by the way I was doing some observations of the planet Saturn and I noticed something very interesting about it and I'm just turning to the page and he's not just describing what he has seen he's used

typographical printers devices to show but within the line of text what he's seen so he's saying that you know I observed Saturn and it appeared to have two very large moons flanking at neither side, almost as if the two moons were stuck to the main body of the planet. And then I carried out an observation on a different date and the planet appeared to have ears instead. And he's shown these just by a series of o's stuck together and then there's a tiny little diagram of an eared planet it is really curious isn't it because it's just within the text the same size as the text of this ball with the two ears on it and it just to get that out as quickly as possible i've seen this first i published this first. That was his modus operandi,

and that's what made him so very successful early on in his career. And that's why we all know about Galileo, because he was really good at PR. OK, so let's go on to the next one, and this just looks like a rather nicely bound, leather-bound book. It is a beautifully bound book. It's almost as if it's been covered in William Morris wallpaper and in fact this is a 20th century rebinding of a 1659 book by an astronomer called

Christian Huygens. This was an astronomer who among his many achievements, carried out a really detailed survey of Saturn. And this book is called Systema Saturnium. So the Saturnian system. Yes. People were realising that it was a system. It's a very complex celestial object, unlike anything else in the night sky. And this book is famous for having a plate of engravings of 13 different versions of how Saturn was perceived by a dozen different astronomers dating from Galileo's first observation of Saturn as being a strange eared figure. So these pictures are showing suppose, how telescope technology was advancing in the 17th century.

People were able to resolve the details of this planet better. It starts to look almost like, I don't know, the eye of Sauron. And then towards the end of this series of diagrams, you can see the ring system that Christian Huygens was quite confident about proposing. So they were getting to the stage where they thought, well, this is actually a planet with a ring around it, but they didn't know they were gas giants. No, they didn't.

And in fact, it was widely accepted for the first few hundred years that it was a solid ring. William Herschel was quite certain when he was working on Saturn in the 18th century that it was a bevelled ring. Oh, so really? It was a bevelled ring? Yeah. When did they figure out that it wasn't that? It was in the late 19th century that James Clerk Maxwell wrote a prize essay and used

a mathematical proof to show that the rotation of Saturn and its ring required the ring to be made up of a mass of particles. It could not be solid matter otherwise it wouldn't be able to rotate in the way that it was. Now this idea of them being gaseous, a gas giant, that's not anywhere near till the you know 20th century. Yes it wasn't really until the 30s, the 40s, the 50s that astronomers were able to use spectroscopy to take definitive readings of the spectral lines that would prove that these planets were composed of hydrogen and helium. Now, we come to the Herschels. First of all, we have journal number two, and this was a journal that recorded William Herschel's observations from 1780 to 1781. And he was based in Bath at that time. He was a musician, making his living from teaching and composing and performing. But he was incredibly interested in astronomy to the extent that he actually read books on optics and learned how to make his own telescopes, which became some of the most powerful in the world.

And he was carrying out a really systematic survey of the sky with the help of his sister Caroline. This journal goes through night after night of observations. So this is his observation. So this is like his notebook. And if we flick through this, this is A observation so this is like his notebook and if we flick through this this is a4 size journal number two let's put it onto the safely onto the cushion here so it doesn't get damaged and there's a really interesting observation in this one of what he didn't think he'd found a new planet he thought he'd found a new object. He thought he'd found a new object in the sky. Yes, he had. So, Tuesday,

March 13th. In the quartile near a star in Taurus, the lowest of two is a curious either nebulous star or perhaps a comet. And the second document here, on the face of it a nearly identical notebook and this is Caroline's notebook. This is basically a fair copy that Caroline Herschel created in the second decade of the 19th century at William's request. He was in advanced years at this time he was concerned for his legacy as she was and she went through the laborious work of going through all of his notebooks and copying observations into a series of themed notebooks so this notebook is called number one observations on the georgian planet and its satellites and after all the communication and double checking and measuring the orbit of the comet,

it becomes very clear that this is a planet. It's the first time in the modern era that a human had discovered a new planet in the solar system. Now, this is the gas giant we now know as Uranus. But why was it called the Georgian planet? Well, at this time, the monarch of the realm was King George III. And it seemed politically expedient for William Herschel to name the new planet after the king. And this went down very well. And it eventually turned out that William received a royal pension and became named as the king's astronomer. Yn ystod y bryd, dywedodd William ei fod wedi cael peniodd gwirioneddol a'i fod wedi cael ei enw'n

astronomer duw. Roedd y enw'n eithaf amserol oherwydd, yn y cymuned astronomig rhyngwladol, roedd rhai yn teimlo nad oedd yn dderbynol iawn i fyd-dyn sy'n newid i'r cyrff system bwyd ei enw ar gyfer y Rheolwr Gwlad o un cwntr unig yng Nghymru. Felly, yn hytrach, roedd yn cael ei ddychmygu â'r ddynion clasigol o'r planedau. the head of state of one single country on Earth. So instead, it was proposed to keep with the classical theme of planets. And Uranus in mythology is known as the father of Saturn. So it continues the concept of the family tree of the solar system. Thank you to Sian Prosser chatting there to our editor, Richard Hollingham.

Another bit of history for you here, Izzy, as well. Fun fact, did you know that the term gas giant actually seems to come from a science fiction writer called James Blish in 1951 oh my goodness that's amazing that's so interesting it's so cool isn't it think of like the etymology of these things about where they come from and I love the fact that you know a science fiction writer can dub them like you said before like gas giant it's a term that it does what it says on the tin almost right but we need someone almost outside of the field to dub them that to be like oh oh yeah that is what we should call and becky for you my bit of information is there was a comedian in the i think

it's a 1930s called william hay and on my research for this episode i found out that he was also an astronomer a comedian yeah it's brilliant so hang on hang on was he an astronomer by night and a comedian by day or a comedian by night and an astronomer by night we'll have to go into the society's archives to find out I suppose next trip next episode it's we'll do it we'll do it this is the super massive podcast from the Royal Astronomical Society with me, astrophysicist Dr Becky Smethurst, and with science journalist Izzy Clark. This month, it's all about gas and icy giants,

but I feel like we need to move away from the topic for a moment to talk about something that was very exciting and an image that was released this month and I can already see Becky's like winding up with excitement so on the 12th of May 2022 the Event Horizon Telescope released the first ever image of a supermassive black hole at the center of our own galaxy Becky how excited are you? I'm hugely excited like I couldn't contain it on that Thursday I was absolutely like bouncing like off the walls because I mean this is the thing that we expected back in 2019 do you remember when the event

horizon telescope released the first ever image of any supermassive black hole at the time when we knew that announcement was coming everyone assumed it would be of the supermassive black hole in the center of our galaxy the milky way because it's the nearest one but it turned out to be the one in the center of the galaxy Messier 87, which, you know, from a sort of fun twist of fate is yes, a thousand times further away, but it's also a thousand times bigger. So it's about the same size on the sky. So it's like taking a similar image of it, but it turned out that one was much easier to get at because it's much bigger material is orbiting around it in a matter of weeks so if they observe it over three nights it's a very static image whereas the milky way's black hole much smaller the material

takes less than half an hour to go around oh wow okay if you're imaging the light from this material to get at that sort of big round donut shape you know it's very blurred and also there's a load of dust and material in the way in the milky way when you look towards the center that scatters all that light this radio light that we actually detect so it made processing that image so much more difficult so we had to be really patient and wait for it and I guess if you've never done that before as well you want to know that you're you're getting it right first time as well so I suppose it makes sense to go for the slightly easier to reach object rather than our you know jazzy more difficult problematic and so talk us through this image you know why is it so important and what does it show us

yeah i mean it's massively important again it allows us to test our theories of gravity you know our leading one being einstein's theory of gravity with general relativity but then also you've got these modified theories of gravity as well, that perhaps, you know, you might not need dark matter to explain sort of what we see in the universe. So it's lots and lots of tests and Einstein's theory comes out on top again in terms of what's going on around a black hole. What's really interesting is how similar and yet different the two images are of Messier 87 and the Milky Way's black hole. Yeah, because that's what I wanted to ask you about. You know, you can see similarities, obviously,

but the thing that stood out for me on the image of the supermassive black hole in our galaxy is that, I wouldn't say blobs, but like the focal... Hot spots. Yeah, they are brighter, it seems, in these images. So why is there that difference? Yeah, so the hot spots are caused essentially by little clumps of material that are just denser in this material that's swirling around the black hole. And so if it's denser material, it's giving off more light and you see these bright hotspots. They get brighter as well because they get sort of Doppler beamed towards us by the extreme gravity.

So the material that's coming towards us also looks brighter. But as I said before, the Milky Way's material around the black hole it moves around the black hole once every half an hour or so so if you're observing that for an entire night you're essentially seeing that move and you get a blurred image it's like sort of you know doing a long exposure for movement on a camera and you're seeing all the blur so you see those hot spots a number of times as well in the image so that's one of the major differences so that's why it's a bit more blurry as well i think people were like why is this one blurry it's because it's moving and so that's one of the major differences but the similarities are there right they still look remarkably similar and so the big

thing for that was the fact that despite the fact that these are two very different masses and sizes like a thousand times smaller the milky way's black hole these behave in pretty much the same way so any differences we see in the surroundings like for example the Messier 87 has these huge jets coming out of the regions around the black hole all those differences on the bigger scale are due to the galaxy and not the properties of the black hole which is really really interesting for people who are considering like how do galaxies and black holes co-evolve together which is like what we talked about in the past couple of episodes but then the big thing that

i love with this is that a lot of people assumed we'd be looking at this like edge on so if you think about it as almost like saturn's rings yeah you've got the big blob of the black hole in the middle and then you've got this disc of material swirling around we thought we'd be looking at it like edge on so you'd see the disc very flat because people assumed okay the black hole will be spinning with this material around it in line with the way the galaxy is spinning that's actually not the case for the majority of galaxies we look at they're always misaligned usually and again like with planets and how the spin encodes the history the spin of a black hole encodes the history of what it's been through and the history of what the galaxy's been through so instead of it being at like 90 degrees to us it's actually more like 30 degrees to us the spin of this black hole and you can just about tell that from sort of what we see in the image

because it's always going to look like a ring because of the fact that the light gets bent from around the black hole like even from behind it we see light from behind it but there are like these tiny differences that you can pick out that inclination that like what angle it is to us and so the fact that it's at an angle is like okay well maybe the milky way's black hole has had a merger with another one at some point in its history so maybe the milky way galaxy's had a merger like yeah it's so so cool thinking about the implications of what this all means in terms of our milky way and i think it shows us it's like there's the stuff that we we don't know what we don't know at this point it's just like okay here's some more theories that we now have to

come up with because we found something new what the heck does this mean exactly it's really exciting for me because i've actually been studying this like in the past six months like the angle of a black hole to its galaxy and what that tells you about how it's really exciting for me because I've actually been studying this like in the past six months, like the angle of a black hole to its galaxy and what that tells you about how it's evolved. And then this random result about the Milky Way popped up and I was like, this is so relevant. Nobel Prize coming your way. Maybe not.

I had them out now, didn't you know? That's why. I'm so glad. It's who you know is, it's who you know. Okay, right. So maybe we should get back to gas giants. And as always, some brilliant questions on Twitter. So Robert, can we have your help on this too?

The Bath astronomers want to know, how often does Jupiter throw rocks at us? I do like that question from the Bath astronomers. I like the idea of Zeus, you know, the Greek god, throwing rocks at the solar system. Oh, no, I pictured it as like someone stood outside your bedroom window like chucking rocks that actually smashed the window it's a great image yes it is a good question though because for a long time there was this view that jupiter was protecting us some incoming asteroids and comets because we did historically

see some comets quite a few comets, where their orbit gets diverted as they go past Jupiter and quite a few of them are thrown out of the solar system completely. But you might not unreasonably think, well, if it bends the orbit of these comets and asteroids, then perhaps they could be sending us our way too. And that turns out that it probably is the case. So the last 15 years or so, there's been more work done on that. And I found a recent paper by a guy called Kevin Grazier, who is a planetary scientist who i mean how cool is this he also happens to be a consultant for battle star galactica and pirates of the caribbean you know i'm volunteering tribute

becky you need to get in on this like sorry anyway anyway science consultant that is a good gig right so he's worked on a different idea, and he argues that just as often, Jupiter sends comets and asteroids into the inner solar system, and obviously they sometimes come near the Earth. Now, reading through his paper last night, as far as I can tell, the good news is that even though he found thousands of examples of this in his simulation, running it over 100 million years or so, that's still quite a low risk to the Earth because that's only getting near. So the odds of any of those actually hitting the Earth, the risk is pretty low. But if you mean general direction of the Earth, then yeah, it happens quite a low risk to the Earth because that's only getting near. So the odds of any of those actually hitting the Earth,

the risk is pretty low. But if you mean general direction of the Earth, then yeah, it happens quite a lot. And, you know, that's just what happens. Unfortunately, Jupiter's not quite as nice a figure or planet as we thought it was. So it's not holding a boombox outside our window. No, unfortunately not, Becky.

It doesn't sound like it. No, no, or even gently throwing little bits of gravel at the window. There might be dirty grey rocks. And, Becky, or even gently throwing little bits of gravel at the window. There might be dirty grey rocks. And Becky, they've also asked, what would happen if a large near-Saturn object passed through the plane of the rings? Near-Saturn object, I like that. Like a near-Earth object.

NSO, yeah. It's actually a really interesting question because we have actually observed this happening in real time with the Cassini spacecraft when it was still in operation around Saturn, RIP Cassini, but actually only with asteroids that were, you know, like a few meters across, like tiny, tiny near-Saturn objects rather than any large ones, unfortunately. But what they saw, what happened was that the asteroids actually broke apart as they went through the rings, because if we think about what are the rings made of, they're made up of these tiny dust particles

that are moving at speeds anywhere from like 25, to 50 000 miles an hour in the rings as they orbit saturn so it's like loads of tiny bullets essentially impact with these small lumps of rock and break them apart and then you obviously end up with sort of like imagine dropping like a rock into a pond or something right you get this splash back and so you get the splash back of debris not just from the asteroid but also from the rings. But that's also not going to lose its momentum of the fact that it's orbiting around Saturn. So that debris essentially gets stretched out into these sort of long, thin strands where it's ever so slightly denser. So again, you've got more material reflecting light, so it brighter and so what Cassini saw was these sort of like

streaks of sort of white bright bits on the rings after an asteroid had impacted but again these tiny ones so we can imagine okay well what would happen if it was a larger object or something you know maybe the size of a moon which there are moons in Saturn's rings as well that have sort of carved out a gap as they go so that's not un of. But if we think about it dropping like perpendicular to the rings, I guess we'd see a bit of a similar thing, but on a larger scale, right? You wouldn't actually punch a hole that would stay in the rings, for example.

The rings are very fluid, like all these tiny little particles, they would sort of slowly over time fill the gap back in essentially, because it's very, very fluid. But again, you'd probably get this little debris cloud that would be very, very bright and sort of be a streak on Saturn's rings for a while.

Oh, nice. Okay. And Robert, Peter in South Australia says, just curious, do we know any gas moons anywhere? Is that even possible? Well, as far as I know, Peter, I don't think we know of any at the moment. But it is a great concept. And I was sitting there thinking about, about you know could you have a double gas giant in some exotic planetary system but the formation of that would be complicated you know you tend to get things coming into a single object they would interact a lot in that that whole process of that stellar planetary system being born now there is discussion though as i found an online chat with a guy called jonathan lunine at cornell about this might be possible in

interstellar space. And the reason for that is that you have a very, very low temperature. So the atmosphere of this gas moon would be nice and compact, and it would help it stay stable as long as it was far enough away from the planet it orbited. So at the moment, I don't think we know of any at all, but it is just about possible in that exotic setting. What we do see, of course, is we see some of the moons of Jupiter and Saturn do have atmospheres. And the obvious example is Titan, but it's still mostly solid. It's got a very solid surface underneath, so it isn't really like a gas giant. Okay, well, that clears that one up. And then Becky John on Twitter asks, in the future, will a cooling gas giant's increased density cause it to crystallize?

So in theory, if a gas giant was to cool and shrink then all your liquid hydrogen that you've currently got inside all these thick atmospheres that we see on the outside that could become solid hydrogen and if you did it under the right temperatures and conditions and everything was just perfect goldilocks style then maybe you would get these regular crystal structures forming however that most likely will not happen ever um because the cores of the gas giants are at incredible incredible temperatures so for example jupiter's core is thought to be about 20 000 kelvin so around 20 000 degrees c yeah it's pretty damn hot and so that heat is actually generated due to the amount of gravity you essentially have crushing inwards on the material that you've got there, right?

So as long as you've got all of those layers and that huge amount of material in the gas giants above it, you're always going to get that heat generated in this metallic hydrogen that you've got. And then in that rocky core as well, that's right in the middle. So you're always going to have a hot core giving out heat, causing convection, transferring that around all of the entire sort of atmospheric system and interior of the planet as well and so it probably won't ever cool wasn't there that paper a few years guys i saw something else updating on it where uranus and neptune though in compensation they might have a rain of diamonds in their atmosphere so that's sort of compensation rather than the giant gemstone in the middle not a whole crystal just lots of them yeah but that's part of almost like more like the weather on uranus and neptune

right we talk about like exoplanets that might have like ruby rain as well because of these similar conditions where if you have the elements that you need like for diamond it's just carbon right at very specific pressures and temperatures so if you have those pressures and temperatures present in the atmosphere and you have carbon present in the atmosphere then you can get diamond yeah the rain that falls but i don't think that it would ever you would ever get one giant diamond at the end so there's a bit of interstellar bling but not not quite not yeah take that saturn not just okay so thank you everyone for your questions and if you want to send any questions to us for a future episode, then please do so.

You can email podcast at ras.ac.uk or tweet at Royal Astro Sock. We really love reading them. They're so great. And Robert, okay, so let's do some stargazing or planet gazing. What are the best times in the year to spot the gas giants? Well, Saturn is getting a bit, Becky will be pleased to know, is getting a bit easier to spot now. I've been spotting it.

If you're up and about at three in the morning is about its best now. At the moment, it's pretty low down still in the south-southeast in the constellation of Capricanus, which is always very low from the UK. And it actually gets better from here in a few years' time, you know, seven, eight, nine years' time. It'll be a lot higher in the sky. But there are, you know, other things you do it'd be a lot higher in the sky but um there are you know other things you do if you're traveling to the southern hemisphere then it's

really high up from there they're getting a great view at the moment and either way it's going to be pretty much at its best from august until the end of the year and as for how it looks you know it's a fantastic object um you think of the rings but even with a pair of binoculars you can see it's obviously a planet it's this lovely yellow dot and you can see Titan, the biggest moon, going around it. And even a fairly small telescope shows the ring system. You know, you need to focus it, make sure it's on a steady mount and all of those things. But it does stand out. It's easy to see why it was discovered right back in the middle of the 17th century.

And then Jupiter is better a couple of months after that. It's pretty good from the end of September. Pretty much a lot higher up in the UK as well it's in the constellation of Pisces you know much higher in our sky and it's still good from the southern hemisphere and that'll be good as well until the end of the year and you can easily see its bulging shape as well if you hold up a pair of binoculars ideally on a tripod or at least just rest them on a wall you can see that it's distinctly bulging it's that fast rotation making it bulge out does stand out and you can pick out the four bright moons as well, the Galilean moons.

And both of them are really good. If you ever get access to a larger telescope, a larger, say one run by an astronomical society or a public observatory, then they're phenomenal. I remember looking at Saturn with the large telescope in Greenwich and it's mind-blowing. You see all the features you read about, and it's just absolutely stunning sight. So if you ever get that opportunity, definitely grab it with both hands. And as for the other two, the ice giants, well, they're always tougher. They're a lot harder to see. You can see Uranus just about with the eye, but Neptune you can't. And Uranus, first of all, is best after November. It's in Aries,

so it's very high from where we are, but still hard to pick out. You need a good map. And if you look at it with a pair of binoculars, it will just look like a star, as will Neptune. But if you get a decent enough telescope, then it starts to look like a tiny disk. And the distinctive thing, I think, for both Uranus and Neptune is you can pick out the colour. They do have that greenish-blue tint, and it's quite obvious the bigger the telescope is. And Neptune is good from about September onwards. Again, not bad from the UK in Aquarius. But as I said, they both look like really, really tiny disks. It's amazing at some level that it's credit to the quality of work that people like Herschel did in finding Uranus,

because it's not at all obvious. It must be something about, well, that patiently sitting there with not a very big telescope actually and getting a good enough night that he could see it was a disk and realise that he was looking at, eventually looking at a planet rather than another star. Yeah, absolutely. And I think I remember the first time that I saw Saturn and Jupiter through my telescope. And again, you can see the detail.

And I was just like jumping around the garden, like seeing the rings for the first time will always be a standout memory for me because you see pictures of it in books and through high school, university, all of that. But to see it for yourself, there is nothing like it. So I really would, even if it is just binoculars, I would really encourage people to go out

and try and look at it because it does take your breath away. It's phenomenal. So what about some of the other things in the night sky this month? Yeah, we're in the middle of summer. One thing I should say, by the way, is when you were talking earlier about comedians, we do have a current comedian.

Shout out to John Coleshaw, who's on our books, who is both a comedian, a fellow of the Royal Astronomical Society, and an astronomer. Oh, no way! And a pretty good one. Yeah, he always does the prize giving like every year at the National Astronomy Meeting as well. And he does like impressions of like Patrick Moore and like Brian Cox and stuff as he gives

you the prizes. And like, it's very fun. Oh, that sounds great. That sounds great. So, look, it's warm weather at this time. You're getting warmer anyway, and you get shorter nights, obviously. So, and actually, it doesn't even get properly dark until about mid-July. And if you go really far north in the UK, if go up to shetland you get this simmer dim and you know similar latitudes where the sun is never very far below the horizon so i tend to say

to people this time of year it's a good time to look at the brighter planets and they're not that easy from the uk yet you have to get stay up very late in the night but you do have things to look out for like the moon will be a really beautiful crescent in the first days of june as last month it's still some excellent time to do that moon gazing and you can also look because we've got long days it's a good time to observe the sun as well and it happens that the sun is starting to wake up it's going into the active period of its cycle and there are some really amazing sun spot groups at the moment and if you do look at these i have to stress it's there's a lot of caution needs to be uh done in this you need a certified safe solar filter something you've

bought from a reputable telescope supplier and never look at the sun otherwise and it's the only safe way to do is with one of those safe filters and you'll you'll know if you've got one you know otherwise just please go to a telescope supplier and get it we don't want anybody to risk their eyesight but if you do do all that there are some beautiful groupings at the moment. And the sense of perspective you have on that is not only do they look really intricate, these big dark spots, but each of those tends to be several times

the size of the Earth. So we're talking about gas giants. We shouldn't forget just how big the sun is as well. Now, there are obviously still stars visible. You know, even it gets dark, just not as dark as we're used to in the winter. And if you're going further south, particularly, it's a really nice time to start to look for the the milky way the constellations of Sagittarius and Scorpius that point towards the direction of

the centre of the galaxy where the black hole that we're all so excited about is sighted so a great time to look for those as well. Robert I you know you mentioned this sort of really short nights at the beginning of that and the fact that it never really truly gets dark in Shetland and Northern Scotland. They were told you that I believe that the least likely bit of the entire Harry Potter series is that they do an astronomy exam in the middle of June from Northern Scotland at midnight. And on his constellation chart, Harry marks Orion. Either Harry is a terrible astronomer or Jack Harlow doesn't know anything about astronomy. I think we can conclude he failed.

And it says why you need to be a consultant on Hollywood movies. There we go. But you still have to do the podcast. Yeah, sure. Okay, so I think that is it for this month. Thank you to Brilliant for sponsoring this episode. And we'll be back next month with a look at the rocky planets. Yeah, you know, we can't show favorites. Yeah. Right. Despite the fact that I've said Saturn. Yeah, but we don't. And tweet as if you try some astronomy at home.

It's at Royal Astro Sock on Twitter or email your questions to podcast at ras.ac.uk. And we'll try and cover them in a future episode until then though everybody happy stargazing