The Supermassive Podcast - 8: Journey to the Centre of the Earth

Episode Date: August 28, 2020

Izzie Clarke and Dr Becky Smethurst explore the importance of Earth's core and magnetic field. Plus, the team finds out about the astronomer who sailed the seas in the name of science and Robert Massey joins to chat about all things stargazing. With special thanks to Dr Rebekah Higgitt from National Museums Scotland. You can see the National Maritime Museum's collections of Halley's charts here: https://collections.rmg.co.uk/collections/objects/540213.html The Supermassive Podcast is a Boffin Media Production by Izzie Clarke and Richard Hollingham

Becky, how do you think you'd feel if someone was like, you're a captain of a ship, off you go. Jupiter's magnetic field is one of those unexplained mysteries. Did either of you have any luck seeing the Perseus meteor shower in August? I can't say the word anomaly. Anomaly. We've got our magnetic field, but there's also something called the magnetosphere. If I need the loo at 5am, I'm like, oh, where's Orion?

Did we ever get to the centre of Earth? Earth. I'm like, oh, where's Orion? How did we ever get to the centre of Earth? Hello, welcome to the Supermassive podcast from the Royal Astronomical Society with me, astrophysicist Dr Becky Southerst, and science journalist Izzy Clark. Izzy, what's new this week for you? Literally nothing. Yeah, that sounds about right. Such an exciting life we do. indeed. So shall we get into it then? You know distracted with science. Yeah absolutely. This month we're making our way

down to the earth's core and exploring the importance of our magnetic field. Plus astronomer Robert Massey will be telling us what to keep an eye out for in the night skies this month. Hi Robert. There is some jargon that's often thrown about with this topic. So we've got our magnetic field, but there's also something called the magnetosphere. So can you tell me what's the difference between the two? Yeah, I mean, the magnetic field is the magnetic field generated by the Earth when we're talking about this topic. And the magnetosphere is the region that extends out into space so you have to imagine these magnetic fields they're not they're not discrete we think of them as like lines you know if you think of bar magnets and iron filings you

throw on a magnet school and so on but actually extends way out into space and the magnetosphere is the region that the earth's magnetic field influences so quite a long way actually i think hundreds of times the radius of the earth away from the Sun and about 10 times the radius of the Earth towards the Sun. So it's a really, really big region of space. Does that even encompass the Moon, Robert? I'm trying to work out those numbers in my head at the minute. It's certainly on the side away from the Sun, it does. So the Moon is very much moving within the Earth's magnetosphere.

And if you think of other planets like Jupiter and so on, they're absolutely vast. I think Jupiter's magnetosphere even extends as far as Saturn. So these are really, really enormous regions of space and you know that's why there's I know we covered this in a different episode but it's why things like space weather are so important because you're talking about the area that all the satellites move in as well yeah I like how you said it's you know on the side that's not facing the sun I guess I like to picture it as sort of like a comet in that same regard as sort of this big magnetic tail just sort of streaking out.

I think that's exactly what it looks like. Well, it doesn't look like anything because we can't see it in a sense. But it is this thing that's stretching out the wind from the sun, which is itself carrying a magnetic field because it's moving electric particles, pushes on ours and blows it back. And that's where you get this wonderful effect. And it is related. I mean, that solar wind is what drives comet tails as well so there is a there is a connection to that and it's not surprising i guess that they have that similar shape so yeah magnetosphere anyway is much much bigger than than what you think of as the sort of region affecting compasses on the

surface of the earth cheers robert well we'll catch up with you later in the show for some stargazing as well this month so let's journey to the centre of our planet. If we start on the surface and work inwards, we've got the rocky outer layers like the Earth's crust and then the mantle below that. But go further and we get into the Earth's core. I spoke with Dr. Will Brown from the British Geological Survey, who started by explaining the core is made up of two layers. We have the outer core which is actually liquid it's mostly iron and it's hot enough to be fluid and actually really really quite runny kind of like the consistency of water almost and then below that we get to the solid part of the inner core which is much hotter again but it's actually so the pressure is so high at the centre

of the earth that it actually becomes solid at that point. Just how hot is the core of our planet? And it's probably not an ideal place that we would ever visit. No, journey to the centre of the Earth is not a good idea at all, despite the many very terrible films you might find about it. Yeah, it's very hot at the centre of the Earth. The deeper you go, the hotter it gets. The outer core is a little bit cooler than the inner core, but we're talking a range of temperatures for something like 3,000 to 7,000 degrees Celsius, maybe something like that, getting hotter as you go deeper. Maybe around 5,000 or 6,000, 7,000 for the inner core. to check. We have to kind of infer this remotely. It's actually surprisingly hard to look at the inside of Earth. We can do quite a good job for other planets because we can look away at them and actually tell a reasonable amount about other places from a distance that's quite hard to do when you're sat on the surface. So looking at our core, that generates our magnetic field. So how does it do that exactly? It does that by a process called the geodynamo.

So a dynamo is where you have a mixture of changing electric and magnetic fields and it becomes a system where you keep regenerating the energy from one field to the other. And so we have something in the Earth's core where we have a huge amount of electrically conducting liquid iron sloshing around and it's convecting really turbulently and flowing around and that's generated by the heat of the planet cooling down so let's say the center of the earth is very hot that heat wants to escape outwards and it churns up the outer core and with all this moving flowing electrically conducting liquid iron you get moving electrical currents and these generate changing magnetic fields and this generates a feedback loop as those magnetic fields generate more electrical fields and and so on and so on.

Okay so it's pretty self-sustaining by the sounds of it then? So it is self-sustaining, it will slowly bleed away energy over a very long time but it's been there as far as we're aware for most if not all of earth's history we have a record of the magnetic field going back at least three and a half billion years and the earth is a bit over four and a half billion years so it's been there for a very long time and will be there for a very long time to come so how do you know that we know this from paleomagnetism so pale paleo, we're looking back into the distant history of the earth. If we look at rocks that were created from places like volcanoes,

so we have lava being erupted onto the surface and that rock cools and solidifies when it's exposed to the colder air. And rocks are made up of minerals and minerals are collections of elements. And so a lot of rocks have quite a lot of things like iron in them, and iron and various other metals can be magnetic. These magnetic minerals in rocks are capable of acting like tiny compass needles. And so when a hot lava cools down and solidifies, all these little tiny metallic particles point in the direction of the magnetic field that's present at the time and so if we take a rock that was erupted a million years ago and we look at the direction of the magnetic field that was present when that rock cooled down we can use it as a measurement of what the field was doing at the time that rock formed and so as long as we've

got rocks we can date what the magnetic field was doing at that time. Could it ever be a case that, you know, one moment that our magnetic field is too strong or too weak? Is that ever a possibility or potentially even a problem? Potentially. So we have a kind of history from looking at measurements of rocks from throughout Earth's existence. We have an idea of how strong the Earth's magnetic field has been through, I say, the last several billion years. And it's been stronger at some times and weaker at other times. It's never disappeared. What it has done is reversed its polarity. So that means that the North and South magnetic poles have switched from being which hemisphere they're in. So you might have a North pole in the North hemisphere that might switch to a North pole

in the South hemisphere. I love this. I just think it's so bizarre. And when you say to people like, yeah, well, the magnetic poles can flip. They're just like, why? Why do they do that? Do we know why? It's a really good question. And it's not one that has a definitive answer. We know that the Earth does it. It's really normal for the Earth. It's not very normal for us. But it's happened dozens, hundreds of times through Earth's history, not regularly. So the problem is that it happens completely randomly, as far as we can tell in the historical record. So you get reversals that happen maybe every 100,000 years, but then you might have none that happen for 50 million years. So it's a very random occurrence. The last time it happened was about 780,000 years ago.

So that was before the time of modern humans, but that's not before the time of things that are very close to modern humans. So, you know, primates and early humans were likely around at that time. Say if that happened any time soon, like we rely on a lot of technology, which in itself is very reliant on the magnetic field and just how we operate. So what issues could that cause if we were to see that as if 2020 hasn't been, you know, challenging enough? It's not the year to bring this conversation up. Yeah, sorry guys. No, it's true. So we're not aware of really the impact it would have necessarily on our technology. And

that's the real big question right now. We're aware that these reversals have happened a lot, and they don't seem to be correlated to major climate changes or extinction events and things like that in Earth's past. They seem to be entirely independent of those. So that's good to know that life has survived through these things. But then people haven't been relying on the internet. And so it's possible that if the magnetic field gets weaker before a reversal or turns off for a time, then we might have less protection from the solar wind coming from the sun that might disrupt some of these technologies for a time. So we don't think the magnetic field will disappear completely during a reversal, but we think it might get weaker for perhaps a few thousand years

or tens of thousands of years, which is a long time for humans. It's been reported quite a lot recently that the Earth's magnetic field is getting weaker. So it's decaying about 10% over the last 100 years or so, 150 years. So while it is getting weaker, and quite quickly, if we look back at the historical record, the field is quite strong right now. So actually, even if with it decaying, it's still quite strong historically. And the rate at which it's changing is really not that unusual. It's done this plenty of times in the past. So the Earth seems to be happy doing what it always does. It's just the first time we've really been here to see it in detail. I should have never asked that question. That was Dr. Will Brown from the British Geological Survey.

Paleomagnetism is my new favorite word ever. I was so glad that he defined it. I was like, I'm going to need you to step in on that one. Okay, so Becky, that's our magnetic field covered. So let's talk about Mars. What happened there? Because we think Mars had a magnetic field, but it doesn't anymore. Like, how can that just disappear? Yeah, so Mars doesn't have a a magnetic field, but it doesn't anymore. Like, how can that just disappear?

Yeah, so Mars doesn't have a global magnetic field anymore. It doesn't have anything that's generating the magnetic field in its core like the Earth does. But it does sort of have that magnetosphere anyway, because of sort of the interaction with the solar wind and its atmosphere. So thankfully, that means that Mars does get aurora still which is nice if you're a martian astronaut maybe you'll still have some really nice views of the aurora but the reason we think that the global magnetic field of mars is now sort of disappeared if you will is that the internal core of mars has actually been able to cool and solidify right and so because

you don't have this you know know, moving liquid that Will was talking about before, you no longer have the dynamo and therefore you don't have a magnetic field either. So this has a really big consequence for Mars, obviously, because its atmosphere now is so much thinner and we think it's because it doesn't have magnetic fields. Magnetic field acts as this sort of shield and bubble against the solar wind and the high radiation from the sun. And slowly as that sort of dynamo has shut off the atmosphere has been stripped away and this is another reason why we think that you know asking whether life used to exist on Mars is not an unreasonable question to ask because the atmosphere we think used to be a lot thicker when the dynamo was switched on and

Mars had a magnetic field. So how do we actually know all of this though? Yeah so it's again what Will was talking about you look at the composition of the rocks on Mars and you can see from sort of how the molecules that are metallic are lined up you know when the dynamo was actually sort of up and running sort of maybe about you know four billion years or so ago and when all of a sudden these molecules didn't line up with any magnetic field anymore is when we can figure out when the dynamo switched off we think it was maybe about three and a half billion years ago but it's difficult to pin down obviously because we don't have a lot of martian rock samples and hopefully we'll be able to do this with the newly launched mars rover perseverance or percy as the astro community has dubbed it which is my favorite thing ever

i love the names that they give to like the rovers and stuff but what about the rest of the solar system do any other planets have a magnetic field yeah definitely so we see aurora on all of the gas giants as well which i think is a spectacular thing to see it's sort of aurora on jupiter or on saturn that kind of thing and that all is generated by the magnetic field so we know they have magnetic fields jupiter's magnetic field is sort of one of those unexplained mysteries still it's aurora very only really seen in the uv they're very very high energy which means it has a very very high level magnetic field i'm not entirely sure how that's generated because obviously we don't know that much about the interiors of the gas giants just sort of their densities and we infer stuff from

there so it's still one of those unexplained sort of mysteries in the solar systems in our back garden of the universe but um people are working on it you know people who really sort of buck the trend of astronomers uh not caring about magnetic fields okay and so this might seem a little left field but if we can send like the parker solar probe solar orbiter to the sun could we ever get something to the center of earth so i knew this question was coming and like this threw me like the first time that you asked me this right i was like what on earth where is the connection there between the sun and like the center of the earth and like the technology to do both things and i realized it is the temperature isn't it right because Will said center of the earth is like

about 5,000 centigrade sort of on average and that's sort of the temperature that we think the sun is as well so I guess that's where this sort of idea comes from and I think what you've got to understand is that you know they're two completely different technologies right so whereas when we send something like the park solar probe or solar orbiter to the sun when we're talking about the temperature there we're talking about the energy of the molecules and the particles being released in the sun and like what the equivalent temperature is that they have from that energy that they have which is literally just like how fast are they really going right so all you have to do to shield the probes that you send into space like that is is that you just to put a big

sun shield and a big sort of like radiation shield on them and then they won't heat up in the same way if you're drilling down to the center of the earth with literally a drill made out of metal right even the sort of metal with the highest of melting points you're still completely submersing that in in something that is a thousand plus degrees and so that will melt because there will be sort of direct energy transfer there so that's why i think people might be curious as to what how come we can send space probes that survive such equivalent temperatures but we can't necessarily make something that drills down into that temperature before it just really starts to struggle. So we've really missed not being able to explore the Royal Astronomical Society's archives

in person and we're not able to get into the library yet but we have got some science history for you. So as in the case with a lot of science, we take for granted that we didn't always know the structure of the Earth. Now, Edmund Halley of, you know, comet fame, had his ideas on the internal structure of our planet and undertook a voyage to map the variation of the compass around the world. To tell us more about this is historian of science, Dr. Rebecca Higgett from the National Museums, Scotland. First of all, Rebecca, can you set the scene for us? Like, who was Halley? Halley is known, as you say, best for his work on comets. So he's known as an

astronomer. He became Astronomer Royal toward the end of his life. And he also had been Civilian Professor of Astronomy at Oxford. But he began much earlier than that. He was known to people in the Royal Society. He was known to the Astronomer Royal from a really young age because he was quite fortunate. He was well connected. His father was quite wealthy, lived in London, and he was educated at St Paul's and then Oxford. So he clearly got good connections early on and was present at the very founding moments of the Royal Observatory in Greenwich, although he didn't come to work there himself until

much later. He worked with Flamsteed in trying to understand the stars of the southern skies. So he came up with a project and they worked together on the project to go to St Helena Island in the Atlantic to observe both the transit of Mercury and also the southern stars. So that was a kind of balance to obsessions happening in Greenwich in the northern hemisphere. And that was, you know, just in his 20s. So he began early. Blimey, that's impressive. Yeah, he'd have been on the 30s or 30s. Yeah, for sure.

He sounds like one of those. Super achiever. So how did he think the Earth was structured and what was he going by? Essentially, Halley is coming into a long tradition of discussion and also data gathering. And he is trying to do both. He's trying to fix them together, although it proves a very difficult thing to do. But he drew on data that other people had collected. a model for how the Earth's geomagnetism was arranged, which he thought could perhaps explain the variation and the observations being seen all over the world. And his idea was that the Earth had magnetic poles sort of on its outer surface, as it were, but then inside that, so it was hollow, and then there were other shells inside that also had magnetic poles and that they moved at different rates or

angles to each other and caused this differentiation and variation that was observed. So it wasn't exactly a mathematical model. It wasn't predictive. It didn't really set it up, but he felt it was a possible explanation. So did he go ahead and try and prove this then, even though it wasn't a mathematical model? Did he collect evidence for it? He did collect evidence. So he inherited, in fact, an awful lot of data around 1680. That was when a man called Peter Perkins, who was a master of mathematics at the Royal Hospital School in Christ Hospital in London, died and Halley acquired those papers. And Perkins had been collecting data from mariners for a long time. So he had data right from the end of the 16th century, right through to 1680 from him. And then Halley proposed a voyage, initially very ambitious,

this was being discussed in the Royal Society, and that this might, you know, be a sort of full round the world kind of trip. In the end, it was a couple of voyages in the 1690s that were focused on the Atlantic and tried to fill in a lot of the gaps in the knowledge around there. So he went on two voyages, collecting data really from sort of around the edges of the basin and particular islands, places again like St Helena that were useful to stop at and easy to get to. So he wasn't exactly sweeping the whole thing, but he was collecting data, extrapolating patterns from that not to sort of fit his model but you know a sort of educated Occam's razor kind of guess to make it it work

and it was pretty good I think considering what he was doing and the levels of accuracy of position fixing that they had at the time it strikes me as being a bit odd if you give an astronomer like okay off you go here's a ship go around the world like Becky how do you think you'd feel if someone was like you're a captain of a ship off you go like great I'd just be like I'm not in any astronomy I'm going straight to the Caribbean you know it doesn't really sort of tie together um no it's remarkable and it's remarkable that the admiralty um gave him a command of these voyages I mean this is incredibly unusual that you get a civilian like that being in charge of a naval vessel and naval officers and being allowed to tell them what to do.

He clearly had gained practical experience at sea, and he was at sea at this period a fair amount. He was also doing surveys around the Thames and so on. He presumably had taken it upon himself to get practical experience of observing at sea when he went to St. Helena. Obviously, that Atlantic voyage he did when he was young. He also then travelled to Danzig to meet Hevelius to Paris. So he he was at sea a fair amount and presumably could convince people that he could make these observations. And I know that the people who have looked at the accuracy of the observations he could make it see he was he was quite good at doing it he clearly had the theory whether or not he had the personality to lead something like this is is a different matter and we know that there was trouble on the first voyage he found that his orders were not being obeyed by one of his lieutenants whose name was Edward

Harrison who objected to some orders that were being given essentially set the ship sailing off in a different direction from the one that had been ordered. So it didn't necessarily go smoothly. And he was court-martialed when he came back to Britain. Halley was exceedingly upset and cross about it that his command had been disobeyed. And Harrison was actually treated quite leniently,

given what he'd done. He'd obviously brought the other officers and crew with him they they did follow him rather than Hallie so it's possible that he did have the sort of the favor of the crew on his side and clearly you know some people within the Admiralty felt that it was understandable that they had decided not to follow the orders of someone who was not kind of one of their own this is so drama filled I did not not expect this. This is like, you know, it's like reality TV 200 years ago, isn't it? So please tell me that there exists some sort of record of this like mutiny on the high seas, right? They must have documented their journey. Absolutely. Yeah, there are logs, there are records of the court martial and so on. And

actually, wonderfully, there's a blog available. so anyone can go and look at a lot of these documents transcribed called Halley's Log. And of course, we also have the papers that Halley wrote for the Royal Society of Philosophical Transactions and the wonderful charts that he produced really quickly, actually, after he came back from those voyages on the Atlantic that brought together all of his observations with all of the historical data that he'd brought together as well. And in these really attractive maps, there are copies of them at the National Maritime

Museum that can be seen on their collections online that show the sort of equal points of data across the world. He knew this data wouldn't be for all time, that it would need to be updated, but it was a beautiful presentation of what he'd found out so far. Thanks so much, Rebecca, for talking us through that and great to have you back on the podcast. This is the Supermassive Podcast from the Royal Astronomical Society with astrophysicist Dr. Becky Smethurst, that's me, and with science journalist Izzy Clark. This month, we're traveling to the center of the earth to explore geomagnetism. And Becky will be taking on your questions on the subject in just a moment. But first, and Robert, can I bring you in on this? Did either of you have any luck seeing

the Perseus meteor shower in August? Yeah, a few. I mean, would I say it was spectacular? Well, that would be pushing it, you know, even with the best efforts of hyping in the world. But I did see a few. I dutifully went out in my back garden. The weather was looking a bit iffy. I was up late enough, saw a few just before midnight. I thought, you know, I've done my perceived watch for the year given that it was raining the next day.

So I was happy enough. I didn't feel that we'd misled the public. You know, I'm sure enough people did see them across the room. We got no angry emails. Not yet. I mean, you know, i'll wait and see what happens now i've said this on the podcast no you don't worry i saw some guys so i was uh i was with some friends by the beach socially distanced of course and uh i sort of managed to trick them all

by being like let's go watch the sunset and then what happens after the sunset we stuck around for a bit longer and we uh we ended up soaring a few a few uh meteors which was really nice oh that's so nice London was so rubbish like every time I tried to go around I was just like oh no lots of clouds like no no chance at all but actually for the first time in my life because I set up my telescope I was able to see Jupiter and it's all expanding structure and uh saturn and the ring around it and i was like oh my god i was literally running around my house like everyone you need to come and see this like come on come on get out in the garden yeah there is something really special about seeing saturn for the first time especially like the moon for the first time through a telescope is is a little bit like but like seeing the rings like especially if you've only ever seen them like through binoculars when

they just look like sort of ears poking out like seeing the rings is just oh it's spectacular it was so so good so so good and we should also it's worth saying the Perseids are not over you know it is still August time so you know if you see a meteor in the next couple weeks it probably is very likely to be a Perseid meteor there's just obviously not going to be as many as there was at the peak back in mid-August. I'll cross my fingers then. So we've obviously been covering geophysics for the past two episodes and we've had lots of questions in. So Becky, I hope you can take some of these on. So let's start with this one from Siobhan Hagee and Curious Stargazer, who want to know, why do the poles on planets and stars move and flip over time

okay so there's two questions there right so first of all is move um and so we have sort of a couple of things to think about right the idea that a geomagnetic pole moves this is the idea that you know we're always talking about before the geomagnetic pole doesn't line up with what we call geographic like north pole for example and over the past hundred years we've seen you know the geomagnetic pole move from sort of in Canada to right almost close to the north pole as well and so the reason we think they move is because the dynamo is just constantly changing right it's not something that is a solid object or anything like that it's it's self-sustaining as well so it's constantly moving and that's why we think that this magnetic pole is also moving as for the flip well we're not

entirely sure still but we can work out sort of um the fact that you know it is flipping and we know how often it flips and that's what sort of can eventually hopefully give us clues to figure out why it's doing this from the paleomagnetism that we worked out before. Okay, cool. That's that one sorted. Matthew Edmonds on Instagram asks, what is causing the South Atlantic anomaly? So first up, what is that? Yeah, so the South Atlantic anomaly is, I apparently can't say the word anomaly. Anomaly. So the South Atlantic anomaly is an area of weakness in the earth's magnetic field, right? It's in the Atlantic, it's between sort of south america and africa on the other side and it's about half to a third of the sort of typical average magnetic field strength of the

earth and we think it's actually caused by the fact that this geomagnetic north doesn't line up with sort of the north pole right because not everything is perfectly aligned and so everything's sort of off kilter a little bit so there's some areas where stuff is slightly weaker. But the cool thing is, is actually this could be one of the clues that sort of lets us know if one of these flips is actually going to happen of sort of flipping the North and the South Pole of the Earth's magnetic field, because it could be weakening. And if it's weakening, then that's what we think happens on the Sun when the Sun's magnetic field flips is that it weakens and weakens and weakens. And if it's weakening, then that's what we think happens on the sun when the sun's magnetic field flips is that it weakens and weakens and weakens. And then when it rebuilds in strength, the North and South poles are flipped. So perhaps this could be sort of like an early

warning system that this flipping is actually going to occur. And it's a big deal actually, because, you know, the fact that there is this weakness is an issue because it means that more particles, more of these high energy cosmic rays and particles from the sun actually make it further into the atmosphere and sometimes even to the surface of Earth as well. So for example, satellites going over that region, over sort of South America and Africa, they tend to be bombarded more

with these high energy particles, especially from the sun. And so that can actually sort of fry the electronics on board as well. So it's a big issue for sort of communications. Maybe if you've got any ships sort of in that region on the ocean as well they have to be careful too especially if it's getting weaker but luckily you know ESA and NASA are monitoring this anomaly you know so you know don't lose any sleep over it. Okay because that's interesting because G.

Burghardt actually had a similar question which was is that area more exposed than others to solar winds? Yeah exactly because the magnetic field is this sort of little protective bubble for us all from the solar winds and so the fact that it is weaker does mean more particles are let in and so even the ISS actually has to be careful sort of when it goes over this region as well I think it doesn't have sort of the same impact to the ISS as to satellites because it's obviously a lot more shielded because you've got astronauts on board, but they still have to be aware of it. And sometimes they need to reset things sort of once a month or so. So, you know, everyone's aware of it. That's the main thing.

This final one links back to July's episode and planet formation. So you know the drill, if you haven't heard that one, go back and listen it um but gary sharma has emailed in to ask why are hydrogen and helium so rare on the terrestrial planets in our solar system and then looking at the distribution of elements in our solar system why are some elements more abundant than others yeah great question gary we didn't actually cover this in the last episode did we so no the distribution of elements in the solar system actually reveals a lot about how the solar system formed so the terrestrial planets are denser they're made of heavy materials like metals and those materials will have actually sort of sunk to the center of the system under gravity you know the sun's very very strong gravity whereas the lighter gases like hydrogen helium you know they've stayed sort of on the outskirts of the solar system rather than

sinking to the center and so you know you can imagine in the sort of proto-solar system when planets are forming the gas giants that we ended up with much further out you know Jupiter, Saturn, Neptune, Uranus they're actually also in much colder places in the solar system as well there's not much heat from the sun and so that allows the gas to stay very cold if gas is very cold doesn't have a lot of energy and so it can't counteract gravity as much so any of the sort of planets planetesimals that were forming back in the solar system then will have been able to attract that gas and also because it was cold enough beyond what we call the frost line the gas will have actually been able to condense onto those planets and form an atmosphere too whereas even if that gas was present in the inner solar system where the terrestrial planets are, it probably would have

had a lot of energy because it was a lot warmer. And so it wouldn't have condensed into the atmospheres either, because as soon as you give hydrogen a lot of energy, it's a very light gas. You need a very big planet to hold onto that. So it's a nice little clue actually to how our solar system formed the distribution of hydrogen and helium. Oh, great questions this month. Thanks for sorting that, Becky. So if you want to send in a question for a future episode, then you can email podcast at ras.ac.uk or tweet at Royal Astro Sock. And next time we're going to be talking about missions and space exploration.

So get in on that. 10-year-old Becky's favourite topic. Karin Izzy's favourite topic. So, Robert, what are some of the things that we can look out for this month? His favourite topic. Karin Izzy's favourite topic. So, Robert, what are some of the things that we can look out for this month? Well, this month we're moving into the autumn, as is very obvious in the changing weather, and it's cooling down a little bit. But the good news, if you like looking at the sky, of course, is that the nights are getting longer.

So that gives us a bit more of an opportunity to see things. And particularly if you live in the north of Britain, up in northern Scotland, you get the longer nights are very very significant so I thought it would be appropriate actually to to flag up the fact that as you move into the autumn and winter you have a better chance of seeing things like the northern lights the aurora which connects nicely to what we've been talking about today now we are at solar minimum so there aren't very many spots on the sun and not much activity but it is ramping up very very slowly and what that means on the sun and not much activity, but it is ramping up very, very slowly. And what that means is the sun gets a bit more active. We get a bigger chance of seeing displays of Northern Lights. So if you live up in the north of the UK, do let us know if you're lucky enough

to see some of those. I should stress as well, it's the kind of thing that it's best to look when the moon isn't in the sky. So in September, you know, that means around the middle of the month when you've got a nice new moon and it's nicely dark. As well as that, and looking for the northern lights is very much a matter of luck, it's time, I guess, to start familiarizing yourself with the autumn constellations. The most obvious one is a giant square in the sky, an asterism, strictly speaking, rather than a formal constellation called the Square of Pegasus. And as you get towards the late evening at this time of year,

it's really, really dominant high in the south. And if you live in a city, it's a very obvious square. And if you live in a light polluted sky, it looks as though there's no stars at all in it. It's quite a fairly faint region of the sky, but it's a good signpost. And if you pick up a pair of binoculars or you've got a small telescope,

you can see lots of galaxies in that region because it's relatively dark away from the Milky Way. So you don't get the light of the Milky Way interfering with them in the same way. And in that region as well, one classic object, which I think people like to have seen, even if the view isn't necessarily spectacular, but it's quite easy to spot, and that's the Andromeda Galaxy. So it's quite famous.

If you've heard of any galaxies at all, you've probably heard of that one. It's about two and a half million light years away from the Earth. And it has the distance record. If you go to a dark sky and there's no moon and you can see it, you're seeing two and a half million light years with your eye alone. So it's the furthest object you can see with the eye. So if people ever ask, you know, how far can you see? Well, that's the answer.

Two and a half million light years. So I think any optician can be quite satisfied with that result um but if you want to get a really good view of it then pick up a pair of binoculars you know get a small telescope a nice wide field one i must you have to remind me as you about the type of telescope you've got but small telescopes can be really nice and there are really beautiful images of it made by amateur astronomers as well and i'm sure we'll see plenty of those on Twitter as we mention this. So those are a few things I'd be looking out for as we enter the autumn sky. I mean, you know, the stars of some of the Summer Triangle and so on are still around too. But as you look over towards that darker bit of the sky, these are some of the things to look for.

Yeah, I love this time when like the Summer Triangle is still visible in the evening, but then constellations like Orion arising in the morning. If you're up very late absolutely yeah but it's like so nice isn't it because you can sort of get the best of both worlds at the minute because orion's one of my favorite constellations but i only ever see it you know the winter but if i get up you know if i need the need the loo at 5 a.m i'm like oh where's orion well the morning the morning sky has got venus very very dominant. Mars is coming along in October. We'll have to talk about that with space exploration because it's such a nice connection.

So we're entering that darker spell when Jupiter and Saturn will be harder to spot. The other planets will really be nice. Well, thanks, Robert. And that's it for this month. Next time, as we've said, we're going to be talking about missions and space exploration. So I actually cannot wait.

There is actually so much to talk about. There really exploration so I actually cannot wait there is actually so much to talk about there really is so much for us to cover so if you've got any suggestions of the things you want us to cover maybe it's robotics or space probes or satellite technology just let us know it's at royal astrosoc on twitter or email podcast at ris.ac.uk and we'll hopefully get it covered until then though happy stargazing