The Supermassive Podcast - 30: Rocky Planets Rock

Episode Date: July 1, 2022

Izzie and Dr Becky are flying closer to home to look at the Rocky Planets; Mercury, Venus, Earth and Mars. How are they different? How are they similar? And can understanding their past tell us anything about Earth’s future? Plus, Dr Robert Massey has his stargazing tips for summer. With special thanks to Dr Suzie Imber from the University of Leicester, and Sian Prosser from the Royal Astronomical Society. 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.   Our book, The Year In Space 2023, will be out in Oct 2022. Pre-order here: https://geni.us/jNcrw We'll be LIVE at Standon Calling, Friday 22nd July 2022 at 2pm. Find out more: https://standon-calling.com/ The Supermassive Podcast is a Boffin Media Production by Izzie Clarke and Richard Hollingham. 

Thank you to Brilliant for sponsoring this episode of the Supermassive Podcast. Brilliant is an interactive STEM learning platform that helps you to truly understand concepts, maths, science and computer science by guiding you through really engaging, hands-on courses. Yeah, they're really brilliant to look at. I've still been cracking on with my everyday math course and slowly, surely getting through it. it but honestly the way that they look it's so it's just so easy to follow it's so clear isn't it yeah and it makes it just interesting as well yeah how have you been finding the interactivity because some of the some of the

little widgets they have are great to help you understand like how stuff relates to each other and changes yeah no it's so good and what I find even really helpful if there's something that I don't get then they have a tool just to be like excuse me can I have some help give me more explanation please yeah so it's really helpful yeah that is great because like it means like you never get stuck you're not just sort of like marching through a topic you're really getting to grips with the concepts that like underpin a topic and if you do that you know you learn by doing it and you you have a much better chance of remembering something later down the line yeah it's exactly that so if that sounds interesting to you then head to brilliant.org

slash supermassive to get started for free and the first 200 subscribers will get 20 off come on space what's going on you know i don't worry about space plagues coming back from Mars. I worry a lot more about us going there and trashing that environment. And what can studying these rocky planets tell us? Can't forget the moons of the solar system. They're all rocky planets, if you will. Hello and welcome to the Supermassive podcast from the Royal Astronomical Society. With me, science journalist Izzy Clark and astrophysicist Dr Becky Smethurst. This month we're sticking a little bit closer to home to look at the rocky planets. That's Mercury, Venus, Earth and Mars.

How come they're so different to the gas giants from last month's episode? And can understanding their past tell us anything about earth's future i'll be chatting with dr suzy imber from the university of leicester to cover the basics plus i went back to the royal astronomical society's library oh yes to explore some of the earliest features on mercury ever to be recorded um and it must have been so cool yeah it's great that's coming up later in the show and it's not the super massive podcast without dr robert massey the deputy director of the royal astronomical society robert i think it's kind of similar to the gas giants rocky planets it does what it says on the tin they're made of rock but how similar are they really to each other

well they're definitely similar and different aren't they but they are absolutely all mostly made of rock if you stood on mercury venus earth and mars you'd have wildly different experiences you know mercury you're either cooked by the sun or absolutely frigid incredibly cold on its night side venus has a super thick carbon dioxide atmosphere rain sulfuric acid and if you were on the surface, you'd get baked and crushed at the same time. And Mars, you know, the one we love the most, is still quite a bit colder than the Earth.

Its atmosphere is still toxic and incredibly thin. So really they're very, very different places. I love that. Crushed and cooked at the same time. What a lovely... It's like a recipe. Astronomy cooking, which actually I really want to do a book on astronomy cooking sometime. That's a wholly different matter. I did that once.

I transformed a Mary Berry's Victoria sponge cake recipe into astronomical units. And how did that work out? It was a little bit strange, but I quite liked it. What is it, like a Hubble barn of baking powder? That was quite fun. Yeah. Sorry. Cheers, Robert.

We'll catch up with you later in the show to help me take on some listener questions. And do you know what? I'm actually pretty excited for this topic because I've literally been writing all about exploring Mars for our upcoming book, The Year in Space 2023.

So, I mean, if you want Mars facts, I've got them for you. That was a seamless plug. Yeah, thank you. Available to pre-order now. Thank you. got them for you um but that was that was a seamless plug yeah thank you uh available to pre-order now um thank you okay so looking at the structure of rocky planets there are certainly similarities traveling from the center to the surface we know that earth has a core largely made of metal followed by a rocky mantle and then a crust, and the rocky planets follow suit. This is what we call

differentiated, that the heaviest elements, the metals, sink to the middle and the lighter elements are found further out. But as Robert was saying, Earth, Mars, Mercury and Venus are also very different. But how different are they? It's a question that I put to Dr Susie Imber, Associate Professor of Space Physics at the University of Leicester. Even the interior structure is not the same at each planet. Actually, there are some really interesting differences. So for example, we've got Mercury. Mercury has a massive core, mainly iron core in the middle, and it extends to 80% of Mercury's radius, and the Earth's core extends to about half of the Earth's

radius. So Mercury is mainly core, it's mainly made of this big lump of metal. And that's really interesting because it's quite hard to explain. And because it has impacts for how the planet and its magnetic field interact with the broader environment. So actually it matters the amount of metal and where that metal is relative to the surface. And then how does that core then change for Venus and Mars? Do we know if it's molten? Can we get that level of detail from these other planets? The thing about understanding the interior of a planet is it's just a really hard measurement to make. And how do we know what the inside of a planet looks like in terms of whether it's liquid or solid and whether that core is liquid or solid? And so just to sort of put that in context, the Earth has this solid inner core and a liquid outer core. And having this structure is actually really

important for generating a magnetic field. And that has implications for things like habitability and being able to hold on to your atmosphere and oceans and that kind of thing. So thinking about Mars then, what do we know about Mars? Well, our sort of naive idea might have been that it was just solid inside because it's cold and it's further from the sun. But actually, recent measurements by a Martian lander called InSight and maybe three years of data has been taken and it has a seismometer so as mars cools and shrinks we get these sort of tremors in the crust and we can measure those as similar to earthquakes we call them marsquakes and we can also see through impacts of asteroids as well they also cause waves

to travel through the through the planet and so we can use the seismology technique to tell us a little bit about the inside and and results that were published about a year ago now showed us that certainly the inside of Mars is liquid, whether that entire core is liquid or whether there's a solid bit right in the middle, we don't yet know. Okay, okay and do we even know where to begin with Venus? Have we tried looking at that? It's a really good question, You know, Venus is extremely hot. So our expectation there is that we've got this sort of thick blanket around the planet of this very thick atmosphere. And that's actually also preventing it from cooling down. Another key cooling mechanism is things like plate tectonics. Venus doesn't have that either and neither does Mars. So there's a really interesting interplay between a lot of different features on the different planets.

Another way that we can look at the interior of the planets is we can measure something called the libration. You can think of it as if you had a raw egg and a boiled egg, and you spun both of them, the hard boiled egg would just spin like a solid object, and the other one would wobble slightly because it's got liquid inside. And so we can look at that little wobble of the different planets. And that can also tell us a little bit about whether the interior is molten or solid so we can pick up little hints here and there um the final point to note i guess on this topic is that in order to generate a magnetic field as i mentioned you need to have a we think a solid inner core and a liquid outer core and some mechanism of cooling to allow convection in

that outer metallic core and the convection of the metallic material plus the spinning planet then leads to a magnetic field being generated so just whether we observe a global magnetic field or not can tell us that something is working or not working in this domain you know so if we don't see a magnetic field maybe the interior is, maybe the interior is completely liquid, and we don't get that convection, maybe the planet isn't spinning fast enough, but it helps us to understand a bit more. Yeah, absolutely. And so let's look at the planets themselves. Like, okay, so we know Mercury, 80% core, that's a bit mad. What other features are there on Mercury? You know, what can you tell

me about that planet i should say this 80 core is interesting because there are some theories that suggest that perhaps it got struck repeatedly in its early life and that caused the outer section that mantle that rocky section to get blasted off leaving it with a larger core than you'd expect that's another theory so okay that's quite an interesting one too um but yeah mercury's a really interesting planet it's it's very close to the sun it has a very weak magnetic field of its own and so it experiences extreme driving from from the solar wind extreme space weather events happen at mercury far more so than than what we see at the earth for example it really helps us to understand our own system and people might think space weather is not that important but actually it can be really important a big space weather event would cause incredible

damage to some of the systems that we rely on most so things like our power grids our communication systems our satellite systems etc so you can imagine that actually a big event is something we really want to know about and understand yeah okay and then we go next planet along and we get venus it's known for being quite a hostile planet yes for sure so yeah venus is about the same size as the earth actually um but it has a really really thick dense toxic atmosphere i'm toxic to humans i mean atmosphere yeah um so that means the temperature is extremely high at the surface of venus it makes it very inhospitable place um that combined with the constituents of the atmosphere and the general environment mean it's very difficult to land a lander that's going to last any length of time

on venus we have done it but we haven't had anything that's managed to survive particularly long so it makes it quite challenging and that combined with the really thick clouds mean that it's difficult to to look at the surface and to understand the surface but but we do know that it's highly volcanic Venus and of course that helps to explain this really thick dense atmosphere because you have high levels of volcanism and so that you can imagine that as a production mechanism for that thick atmosphere and then we get to Earth has it always looked like the planet that we know today? Definitely not. No. You know, when Earth formed back in the Hadean and Archean eras, four billion years ago or so, it did not look like the habitable world that we see today.

And in fact, if we think about the history of life on Earth, we look around us and we see this rich abundance and diversity of life, of flora and fauna as well, of course. And we think about the dinosaurs and we think of them as sort of ancient history. But in the history of the Earth, that's simply not the case. This is relatively recent history in the history of the Earth. The Earth went billions of years with really sort of no life and really no advanced life existing. So life has sort of sprung and flourished in very recent uh past when you think about about the earth's history and that's quite interesting too to think about the fact that

actually conditions had to change on on the earth's surface to such a point where life could flourish and then as soon as life took hold and particularly multicellular life took hold it then flourished and everything accelerated and we ended up with the huge diversity we see today yeah and what can studying these rocky planets tell us you know I mean do they tell us anything about our future are we looking at maybe Mars or Venus and being like could that be us one day well you know I think that's a really good question actually because again you know we have one habitable planet that we live on and the balance is delicate and we know we're pushing that balance at the moment so i'm not i'm not saying that we're going to end up in a situation like venus this runaway greenhouse effect where we live in this terrible world but what i will say is that it's interesting to look

at different examples of how planetary systems have evolved or planets have evolved and why they look the way they look today and try to sort of understand that physics and the interaction because again it's really really complex to understand all these different factors influence the development of the atmosphere, the temperature, you know, whether it's habitable or not. So comparative planetary physics is actually a huge area. And as we explore these worlds more, I think we'll do more of this comparative work as we get more data. And that will tell us a lot about the Earth. So that's the first thing. But but I think the second thing is that i mentioned exoplanets earlier so looking

for planets orbiting other stars elsewhere in the universe and we've identified thousands of these exoplanets using instrumentation and there are some really exciting missions coming up which will be looking for more of these different types of planets orbiting other stars. But we can really say, I think at this point, that there are probably billions or trillions of planets, probably most stars have a planet orbiting them. So I think actually, this is where planetary science, which is what I do, and astronomy kind of have this interesting intersection where the astronomers are brilliant at analysing other stars. And what we do for a living is look at planets. And so we're now sort of looking at the intersection between these two disciplines a little bit more and applying our knowledge to

understand them better. That was Susie Imbert from the University of Leicester. So that is a whistle-stop tour of the rocky planets but Becky aside from the four inner planets are there any other rocky worlds elsewhere in our solar system that kind of look similar to the ones that Susie described? Yeah, I mean, I think about many of the dwarf planets really are rocky planets, essentially very similar to Mercury in the sense that, you know, they've achieved what we call hydrostatic equilibrium. enough mass built up, the gravity is strong enough to actually round, say, a lumpy potato-shaped asteroid-style thing into something that is actually nice and spherical that we would sort of call a planet. But obviously, we know there's many lots of different definitions of a planet, which is why things like Pluto and Charon classed as dwarf planets. I think people often refer to them as dwarf planet and moon, but I feel like always with pluto and sharon binary dwarf planet might be a better description because the center of mass is is you know nowhere

it's not actually inside of pluto it's between them so the two almost orbit each other if you will but they look like you know dwarf like rocky planets don't they very similar to to mercury i guess in that respect but then you've also got things like series in the asteroid belt yeah you know the biggest object in the asteroid belt between Mars and Jupiter. That looks very similar to Mercury in the fact that it's just a rocky pockmarked face. And then obviously, you know, similarly, you've got that sort of collection, like a second asteroid belt almost beyond the orbit of Neptune as well. So, yeah, you've got Pluto and Charon, but you've also got Eris and Hamea and Makemake

and stuff like that, which will all be rocky planets, dwarf planets, I guess. But then you can't forget the moons of the solar system as well. Well, that's what I was going to say. Like, come on, let's look at Jupiter and its hundreds and hundreds of moons. Surely, surely. You know, even just the four big ones, right, of Jupiter, Ganymede, Callisto, Io, Europa, they're all rocky planets, if you will. And there was a paper that came out a couple months ago that argued that we really should include these in the definition of what a planet is, because, you know, what definition do you want to come up with?

The fact that they're rocky, they've got a thick atmosphere, you know, there's so much activity going on in them, whether that's volcanic or whatever it might be, that they really are worlds in their own right. And then it's not just around jupiter either you know you've got titan around sun that's got incredibly thick atmosphere and we're planning to send the dragonfly mission to that to explore it this little sort of drone you know they'll just sort of hop around love the space drones i love space drones um but then also you know triton neptune's moon as well that really has a look of Mercury about it when you see it. So even our own moon too. I've seen the moon looks a bit like Mercury.

So, you know, there's loads of these things, these objects that are similar in the solar system. And I think it goes back to what Susie was saying, is that it's important to understand what's going on in our own solar system because as we're doing more exoplanet research, it's good to know what's in your own backyard before you start going further yeah it's good to have a base right it's sort of like a control um which you can always compare to yeah doesn't mean we're the norm but it's still it's still good it's still some information you're like what what's going come on space what's going on so there's a lot of talk about future missions to venus i think the

three planned so far so why so many what what's the rush i mean it feels like it's like the 19th not that i lived through the 1970s but it feels like it's the 1970s what i would imagine to be the 1970s yeah um so yeah i mean i mean back in the 1970s there were so many missions that were sent i think people were hoping that it would be very similar to Earth. It's a very similar size to Earth in that respect. And it obviously has this atmosphere. And so people were like, is it a sister planet? And then they got there and went, oh, no, this is terrible.

You know, obviously just with probes and everything. And they got baked and crushed so beautifully before. And so people realized that actually this wasn't the sort of second earth that people were hoping for you know it's very unlikely that life ever lived there at least life as we know it and so the focus really shifted to mars then for basically all the decades since and the idea that on the surface at least it looks a little bit more what we're familiar with you know sort of the desert landscape almost, if you will. But now, I mean, back in 2021,

there was that claim of phosphine in Venus's atmosphere. Do you remember, Izzy? So it's like ammonia in the fact that ammonia is NH3, but phosphine is pH3. And we don't know of any way that phosphine is naturally made in like a chemical or geological process the only way it's made on earth is in industry or by you know sort of micro bacteria essentially microorganisms and so i was saying there's any industry going on for venus it's very likely there's some unknown

chemical process that's going on but obviously people really latched onto this idea of you know microorganisms in the atmosphere of venus perhaps now there was another study that same year that used the same data but analyzed it a different way and said actually we don't find any evidence of phosphine in the in venus's atmosphere just uh last week the american astronomical society was on and jane greaves who was the lead author of the paper that first claimed phosphine in venus gave a talk yeah we had her on the show. Yeah, we did, didn't we?

Yeah. So she gave a talk at that conference and said, hey, we've got some more data. We've analyzed it in a different way and we still find evidence of phosphine on Venus. So I think there's a real hype about this result. You know, people want to know if there really is phosphine there by sending a probe to look at the atmosphere, that kind of thing. But also I think it's just, it's made Venus a bit more of a mystery again, that people people just want to crack that mystery and so i think that's why there's just so many more missions just to come in i also love the idea that um uh you know there's some of these wacky things like floating balloons in the atmosphere again and all that kind of thing absolutely fantastic you know the idea that you drift around not far from the level where

the phosphine and the the mooted bacteria or microorganisms might be. It just seems fabulous, doesn't it? This thing being controlled from the Earth, scooping samples and having a look. Yeah, we need to go quite down to baked and crushed level. We can do it from a safe distance. Yeah, exactly, yes. From a safe distance, yeah.

But at the same time, we can use all the lessons learned from going to Mars, you know, to send these missions to Venus now too. It adds to the excitement in terms of exploring other planets. You know, previously we've been looking at Mars a lot. You know, we've got NASA's rovers, Curiosity, Perseverance. InSight as well. Mars quakes. InSight as well. Our space drone friend, Ingenuity. And, you know, there are even plans underway for a sample return mission.

So looking forward, what do you both think about getting humans there? Do you think we will get humans there? I think we could. I don't think there's ever a question about whether we could. We could definitely push technology forward. We could do it. I think the question is whether we should. Like for me, is there any point to sending a human to Mars

except for, like, puff up our own egos that we could do it, right? Well done, us. For me, you need a scientific, yeah, pat on the back. For me, you'd need like a scientific reason to go. Like with all this talk about going back to the moon, I'm like, what's the point, right? We need a reason to go back other than the fact that we just want to go back, right?

There's so much that probes and robots and all this kind of stuff can do now on their own that is much more cost effective it's it's a lot less risky than sending a load of humans as well into space and so for me i almost think it's like it's a bit of an interesting philosophical question and also a little bit of like a legal discussion too as well around this like do we have a right to go this whole question of who owns space and do we have a right almost to pollute mars by sending humans i mean do we have a right to pollute mars by sending all this tech at the minute as well with probes and robots a

really cool discussion but i think humans there is a bigger risk of i think that's yeah yeah exactly with the moon it's not having an issue because it's so just completely barren. There's no atmosphere, whatever. But with Mars, there is an atmosphere. There is obviously something there. You know, what are we going to do with all the astronaut? Debris. A poop. I was going to say debris. Debris is a better word.

And if you want to answer that question, is there life on Mars, then taking people there is almost the worst thing to do because you bring all these bacteria with you. You cannot sterilize people, not without killing them anyway. So the idea that, you know, we go and walk around the surface and we're actually able to do that sort of sampling. Well, yes, it sounds very appealing. But yeah, I mean, protecting the environment of Mars,

if there is simple life there from us, would be a real challenge. It's not, you know, I don't worry about space plagues coming back from Mars. I worry a lot more about us going there and trashing that environment. And quite apart from that, when you look at the timescales, the two years it takes to go there and back, the risks on route,

you know, the fact that you're absolutely beyond hope of rescue, even more than the moon. These are still huge challenges. And for all the talk of it, I mean, you know, NASA's talked about going there. I think NASA's talked about going to Mars in the next 20 years for about the last 40 years.

And each time the deadline just gets pushed back and back. And you can see why, because it's not just that it's massively consuming of resources and everything else, but keeping people safe. And it leads back to something that's been in the news quite recently is that I can't remember if it was probably can't and yeah as you said I think someone described it to me as Mars is almost the most pristine experiment that we've got at this moment and we're sort of going in with grubby hands like boop so we'll see we'll see what happens there yeah we'll see throughout the superive podcast, I think we've talked about Mars, Venus and Earth quite a lot. So I think it's time that we give Mercury a shout. I was also jealous of Richard getting to go

to the Royal Astronomical Society last month. So I caught up with librarian Sian Prosser to see what was lurking in the archive about Mercury. What we have open here is a book that was published in 1816. Wow, okay. It's a book on the planet Mercury that was written by Johann Hieronymus Schroeter. Now, when Richard last came to the library, he was talking all about Herschel. Schroeter has been described as the German Herschel.

He trained as a law student. He was really interested in music and actually became very involved in astronomy. He was very inspired by the work of William Herschel and the rest of the Herschel family and published a number of findings of the surface features of planets like Mercury with the excellent telescope that he was using and there were some really intricate diagrams in this book showing surface features of Mercury. So it's a small little A5 book I'd say it's really I mean you can tell it's lived a life there are are pencil marks in it. It's a dark brown, you know, sepia, sort of tea-stained pages. And there's a fold-out on it, an A4 fold-out here,

with lots of different images and sketches of, well, I'm assuming this is Mercury, but can you confirm what we're looking at here, Sian? Well, we have 16 circular diagrams laid out on the page and they're all numbered. Some of them have been engraved with sort of stippling patterns. Some of them have letters and numbers and lines in them. So basically, this is a visual version of the observations that Schroeter was carrying out, where he was showing to his fellow astronomers what he thought he could see through his eyepiece. Now, we know that during this period, and even today, we are so lucky to have access to telescope technology, but there's still a little bit of subjectivity involved,

and there especially was at this time. And some of these features may have been visible to other astronomers. Sometimes people over-interpreted what they could see, but certainly there are some really fine details of features, which I actually think are not so very far away to what we've been able to see in the most recent space images of Mercury. Just to describe these images, as Sian said, it's four by four. So we've got 16 images of Mercury in total.

And it's almost like looking at all these different, how do you say it, like pockmarks almost. There's a cluster on the 16th image. how do you say it, like pockmarks almost. There's a cluster on the 16th image, there's a cluster that sort of runs through the middle of it. And say, if we look at figure eight, it runs down from top to bottom. So how important was it to be able to study Mercury at this time? You know, how much did we know about Mercury at the time? Well, it was obviously known that Mercury was the closest planet to the sun. What was really of interest to a lot of people making observations of solar system planets was, you know, were there any other planets out there? In the early to mid 19th century, there was a lot of excitement about the possibility of a another unknown planet

between the sun and mercury which was given the uh the working title vulcan and we had astronomers like schroeder making many observations of sunspots and another of his close contemporaries um schwaber was tasked with looking out for the planet vulcan and basically carried out sunspot observations every sunny day for decades he never discovered that planet which we know very well does not exist but as a result we have the most fantastic sunspot observation records in our archives, which are still of interest to solar physicists and historians of astronomy today. Oh, wow. And the science fiction fans out there as well, probably. And so can we move on to some of these other books that we've got here?

So which one do you want to start with? Let's start with this larger book, which is the Rudolfine Tables by Johann Kepler. They show the positions of planets at a given point in time. Johann Kepler, and these were invaluable to astronomers, but also people in other walks of life. For example, for centuries, the church had depended on the positions of the planets to determine the calendar year and at what point festivals and religious periods like Easter should be marked.

But all of these observations were based on a geocentric notion. was working with Tycho Brahe in the late 16th, early 17th century to work with the heliocentric theory that had been put forward by Copernicus and make the observed data fit this theory by coming up with his planetary law of ellipses. And this allowed him to take Tycho's data and make this into the most advanced and accurate set of tables, which was finally published in 1627, decades after Tycho Breyer died at the turn of the century and entrusted his that he was able to predict a very rare event called a transit of Mercury across the solar disk to within five hours. That had never been done before and it had never been observed before until Pierre Gassendi used the tables,

used the information put out by Kepler as a kind of warning or admonition to astronomers to look out for this celestial event. He was the one person who not only observed it, but recorded it and published it. And that is what we have in the book next to the Rodolphine Tables. So looking at the Rodolphine Tables, I mean, it's a much bigger book. It's what, almost just bigger than A4, but it's got a lovely colourful front. And it just shows how important this is because, as you say, this is that transition of when we're looking at the bigger solar system.

Earth is not in the centre of that. We've got the sun at the centre of that. And Johannes Kepler created these important tables to show all of that. There's a wonderful drawing in the front of it. It almost looks like a bandstand with lots of sort of celestial figures there's um sort of maps along the bottom um figurines at the top at each of the corners of the bandstand someone's holding a telescope this is what i love about these books they are obviously so key to calculations, but they are works of art.

There is so much art that goes into these books. Yes, this is a very carefully designed frontispiece for this book, which is explaining that this isn't just the summation of Kepler's life work, but showing the debt that he owes to the astronomers who went before him. I love that. That's amazing. So obviously this was, as you say, the foundations for then another very important moment in astronomical history. So can we look at this third and final book, please? This book is called Mercurius in Sole Visus.

And I'm just going to really paraphrase that as Mercury across the face of the sun. Basically, that is what's happening with a transit. It's a planet moving across the solar disk that you can observe. It was written by Pierre Cassendi, a French philosopher, a priest, scientist, astronomer, mathematician. And he had access to the work of Johannes Kepler and was aware of the prediction of this celestial event and was in a position to carry out the observation. five-hour period in 1631 when it was possible to project the image onto a white piece of paper or vellum or whatever you had at that time and see a dark spot moving over several hours across the surface of the sun. Here's the diagram so we've got a big circle as you would imagine and then we've got a line going straight through the center and then two other lines that sort of cut through so what are these what are these lines showing us sean the line below is showing the path of mercury and again

it's a dotted line but with some larger bullet points, I suppose you could call them, showing positions of Mercury at various stages during that five-hour transit. Oh, wow. There they are. So they're sort of in that bottom right corner, aren't they? There's four of them. So is this the first ever observation of a transit? As far as we know, it's the first documented one. And how important would that have been for the time? Obviously, he's proved that Kepler was right all along. Yes, it's an important vindication for that years-long project. It would have given astronomers more confidence than they already had in this newly updated set of tables. But of course, this was just one stage in the, you know, the long tradition of these important reference works of catalogs and atlases that astronomers rely on.

And they've gone on to be updated until, you know, just in the last 20 years, we've had the Hippocampus mission. And now we have the Gaia mission surveying the Milky Way from a space satellite, space telescope. Yeah, I see it all as part of the continuation of that work from Kepler and from beyond and from before Kepler. Thank you to Sian Prosser. Izzy, I just have to know, did you finally swing along the library ladder beauty and the beast style oh it's so tempting every single time i go in i really want to but i can confirm that i did not no i need to find out like who do we talk to about this like robert do you do you know a guy robert is it you do we need to talk to you can we it's a good question it's never crossed my desk but yeah i'll think about it maybe we

need to do it secretly but sean if you're listening this conversation is not happening i love the fact like i don't know if you're gonna leave this in izzy at all but i love the idea that when the royal astronomical society opened their doors to women many years ago it would lead to this moment of being like please can we slide along the library and feel like Belle, like a princess, please? Oh, my God. Oh, my God. That needs to go into our history.

Yeah, yeah, yeah. Definitely. This is the Supermassive podcast from the Royal Astronomical Society with me, astrophysicist Dr. Becky Sfeatherst, and with science journalist Izzy Clark. This month, it is all about rocky planets and we're going to get to everyone's questions in a moment, but we have an exciting announcement.

The Supermassive podcast is going to a festival. Yeah, break out your wellies and your tents. We're going to be at Stand and Calling in Hertfordshire on Friday the 22nd of July, bringing you a live recording of the podcast. We'll finally stop hiding behind our microphones and screens and see people and each other in real life for the first time in about, what, two years? I was thinking this.

I was like, how is it that we recorded three episodes in person, pandemic, haven't seen each other in person since it's it's kind of mad so yeah tickets are actually still available it would be lovely for us to have an audience at our live podcast recording so i'll pop a link in the episode description so it would be great to see some of you there yeah come say hi let's get on to some questions. Robert, Lucy San on Twitter asks this. How massive can terrestrial planets get? Is there a limit that if you add more mass, then they become gas giants? Well, I have to say, Lucy San, this one really caught my attention

because I haven't really thought about it. And then I started looking around and I thought, OK, the Earth obviously is the sort of big terrestrial planet in our solar system. It's quite super in its own way. But if you look elsewhere, there are a lot of super Earths that are somewhat bigger. And even mega Earths, which are maybe tens of times more massive than the Earth, but are still rocky. So you've got worlds like Kepler-277b, which might be 87 times as massive as the Earth. And by the way, it's another uninhabitable place, obviously. You'd weigh 10 times as massive as the earth and by the way it's another uninhabitable

place obviously you'd weigh 10 times as much as you do on earth and its surface temperature is 650 degrees c so pretty unpleasant um but the biggest one is is a really exotic world a pulsar planet so that's a planet that formed in the aftermath of a supernova explosion you've got this this pulsar this debris uh remnant from a supernova in the've got this this pulsar this debris uh for remnant from a supernova in the center and then the planet forms out of that and it's got a maths it's thought of a massive 330 times the earth and it's made of this dense crystalline carbon that is much denser than diamond just imagine so i think the answer is there's there's a really high limit you know it must be really high i mean 330 earths you know this is this is uh more than way more than the mass of saturn um and planets and what are becoming gas giants for

different reasons you've got these nuclei of rocky material when the planetary system forms and if it's surrounded by enough hydrogen helium then the gravity of that pulls in together and makes a gas giant but no i mean huge limits on on rocky planets so yeah again more food for thought for uh any science fiction writers listening there i think yeah but so but how common are those do we see a lot of pulsar planets or is that just like a look at this crazy thing that happened yeah they're pretty rare um i know that might be down to the way that we're detecting them but the interesting thing is that the very first planet to be found outside the solar system was a pulsar planet back in 1993, using this complex method of looking at the timing of the pulses. So we've known about them for a long time, but there still

aren't that many, and there's still a tiny minority compared with the number of other sorts of planets we find through missions like Kepler and telescopes on Earth. Part of that, I suppose, also is that pulsars are a pretty small type of star. But yes, even within that category, there aren't very many pulsar planets. I think it's still single figures as far as I'm aware. Somebody might tweet us and contradict that, but they're definitely rare. Okay. Becky, Cookies of Space want to know, why do some exoplanets orbit so close to their star and how can they orbit in less than five days and not be ripped apart by their star's gravitational pull

like TRAPPIST-BC and D, for example? Yeah, I mean, I think the answer to that is that some of them, as in why are they so close to their stars, is that some of them formed there and some of them migrated there like you know i think from we think anyway you know by studying more systems more exoplanet systems like that where we've got a lot of planets close into the star whether that might be hot jupiter's so jupiter's size planets but obviously close into they're much hotter or whether they're terrestrial planets like in the trappist one system um that cookies in space was cookies of space

sorry who not cookies in space cookies of space cookies made from space anyway i was talking about um and with we can study them by looking at what we call proto-planetary disks so planetary systems forming around new stars they're very dusty because dust obviously is just small grains of particles that will obviously clump together and eventually make something like a protoplanet or a planet. So we have to use infrared and radio telescopes to see through all this dust. So JWST for the win there. We're hoping that's something that JWST,

the JST Space Telescope, will be doing to watch it happening, see how they're forming and see what's happening to these protoplanets. And TRAPPIST, the TRAPPIST system is a really interesting one. It's seven planets. so it's obviously very similar to the solar system, but they all fit within the orbit of Mercury. So it's very, very different. And one of the reasons they don't get ripped apart is the star

in that system is a lot smaller than our sun. So it's about 10% of the size of the sun. It's what we call a red dwarf star. So even though they're very close, some of these planets are still in the habitable zone where it would be not too hot and not too cold for life to form as well even though they're you know within the orbit of mercury and the reason they don't get ripped apart is because they're still orbiting beyond what's known as the rosh limit so the rosh limit is the region around a star or any object where the tidal forces on another object close to it so the tidal forces being the

difference in gravity on the side that's closest to the star and the side that's furthest away from the star those tidal forces would essentially be strong enough to overcome the force binding all the rocks together in that right okay and the planet would then break apart so this is essentially why saturn has rings because some object that wasn't very dense got a little bit too close to Saturn. And it got torn apart by Saturn's gravity. And it's condensed into this ring around Saturn, like this disk, essentially. Now, that is not going to happen in the Trappist system. Because I actually calculated for you, Izzy and Cookies of Space.

I actually calculated the Roche limit of the Trappist system for you izzy and cookies of space i actually calculated the rosh limit of the trap thank you thank you so you have to do it for like specifically for a star on a specific planet because it depends on the density of that planet if it was a different density it would change but for trappist-1b which is the closest planet into the star trappist-1 the rosh limit is 250 000 kilometers okay ish but trappist-1b orbits Roche limit is 250,000 kilometers. Okay. Ish. But TRAPPIST-1b orbits at a distance of 2.3 million kilometers. Oh, okay. Away from the star.

Okay. So it's way further out than this Roche limit. There's still tidal forces on that planet for sure, in the same way that we have tidal forces on the Earth-Moon system and it gives us our tides. You know, there's still going to be a lot of tidal forces on that planet. It's still going to be quite stressed. But at the same time, it's not strong enough to tear it asunder.

Yeah, yeah, yeah. Okay, well, that is a very thorough explanation. Thank you, Becky. So Robert Juan Mariano asks, in what way can a star's relative metallicities affect the formation and composition of the terrestrial planets around it? Okay, well, thanks, Juan. Now, I, again, did some looking around to answer this question.

It's slightly more complicated than I thought. So the most recent paper I found on it was one by a team, basically the US astronomers, JPL, Harvard, Chicago, and Missouri astronomers, and they published a paper last year. And they say, yes, you know, the star, the metallicity of the star kind of reflects its surroundings which is what you'd expect so the disc around it has more metals if the star does and astronomers by the way think of metals as everything apart from hydrogen helium

you know it's just that yeah even helium you know sometimes even helium yeah the metallic gas the stuff the stuff that's uh made you know manufactured in stars and then distributed to make planets so and it looks as though giant planets are more likely to form if you have more metallic stars probably presumably because there's more rocky cores to make them and smaller planets seem to have higher masses as you get more metals but aren't necessarily more common so it's slightly it's slightly up for debate and it's one of those examples of where everyone seems to mostly agree that we just need more data and more telescopes and more observatories to study it and then the question will be easier to answer

which is sort of what astronomers always say when they're not quite sure okay i'm becky manuel rodriguez asks were there less or more terrestrial planets way in the past than today that is a really interesting question and i think it depends on what manuel's asking there is he asking that like more terrestrial planets in the solar system in the past so in the past four and a half billion years of the solar system's life or in the history of the universe of all planet systems forming around stars right they're two very different questions so i think if it means in the solar system my guess would be that there would be definitely more terrestrial planets since we actually lose a huge number of objects when a planet systems forms because they interact with each other.

They get flung out into interstellar space. And I think you lose more than you have by the end. So in that respect, there was probably more. Whether that ratio of terrestrial, like rocky planets to gas giants would change in that interaction, I'm not sure. Maybe gas giants being heavier would always stay in the solar system and the smaller things that are more likely rocky would get flung out so i'd

say yes that ratio might change in the past history of the solar system but if you're talking about the history of the universe i'd probably say there was less rocky planets a long long time ago you know if you've got planets forming around first or second generation stars 13 billion years ago in the universe's history right there's not been enough stars living dying going supernova polluting this pure pristine hydrogen gas after the big bang with all of these metals like robert was just talking about to increase that metalicity to give you the materials you need to make rocky planets right so earlier on i imagine there was probably as an earlier on in the universe's history as planet systems were

forming i imagine there was a lot more gas giants that were formed just because those were the ingredients that were there around stars to then form these planets okay well thanks everyone and if you've got a question for the team then do get get in touch. You can email at podcast.ras.ac.uk or tweet at Royal Astro Sog and we'll get to it. And so, Robert,'re hearing us in late june then you have a chance to see if you're in the right part of the world all four or all three rather of the observable uh rocky planets in the solar system you can see you can actually in the early morning see and by early morning i mean like 3 30 in the morning and even earlier so it's definitely like even i won't get it yeah yeah so you can see stretching out from the sun mercury venus mars and also jupiter and saturn in the right order from the sun so it's a really really interesting thing to see in itself but having said that if you're in the uk then it's

actually really hard to spot mercury is very very low down very difficult further south though the southern united states southern europe and definitely the southern hemisphere this is a really good time to look at them all so if you you want to look at, say, Venus, which is really dazzlingly obvious as ever, then, you know, if you pick up a pair of binoculars and it's closer to the Earth, you can sometimes see the phase. Right now, it's actually moving away. So it's getting further away. A small telescope, though, would show it as looking a bit like a gibbous moon. And if you're really a real expert, some amateur astronomers are able to see things like dusky markings in the atmosphere but they're very very subtle indeed with the eye and then mars the one that you know we always like to look at

but it's actually also one of the most frustrating things to see through a telescope is still still fairly small to the eye at the moment or through a telescope but it is going to get much closer in the next few months it's coming to what we call opposition so the end of the year will be one of the best times for about the next 10 years to see it in December it'll be really high in the sky in the northern hemisphere and it'll be really bright and if you have a telescope you should be able to see a few dark markings and what you're seeing there essentially is the kind of windswept rock the dust covers and uncovers it and you see this sometimes changing pattern that changes over time and as for mercury well that's that's a real struggle for us in the uk at the moment but it is

going to be good in the morning sky in the first half of october if you can wait till then and through a telescope it just looks like a tiny tiny world so you see this beautiful little uh usually half illuminated disc because it's it's pretty much the only time you can see it when it's far enough away from the sun but all of these things you can see with the eye if you just get the right time of year and with Mercury and Venus you can see their shape and their phase change as they move around the sun so yeah I mean that that planet parade in the morning sky I should say I I saw it by accident I woke up at 3 30 because my wife woke up and the cat was bouncing around on the bed and I and my wife said have a look out the up and the cat was bouncing around on the bed. And we got out.

And my wife said, have a look out at the sky. And I thought, you know, looked out at the sky and I thought, oh, well, there's Venus and Mars and Jupiter and the moon. This is amazing. So I put it on my WhatsApp group and all the neighbors got excited in the area. And then I tried to look at it again this morning and it was cloudy. But never mind. I think it's good over the next few weeks, as I said, depending on when you listen. I think that's the best thing to do, isn't it?

Like if you wake up in the middle of the night because you need the loo or the cat woke you up or whatever it is, just nab outside the curtains and just see what's going on. Exactly. And what else should we be looking out for in case our cats wake us up in the middle of the night? Anything else? Yeah, cats, spouses, children, all of these things. Yeah, exactly. Yeah, cats, spouses, children, all of these things. Yeah, exactly.

Well, first of all, I've got to give a shout out to Jowl P2P, who says they really enjoy the podcast and sent us a beautiful image of the Galaxy M51. And, you know, another great example of astrophotography. And we love seeing things like that. But apart from the planets, as the nights get a bit longer, it's a really good time to see the Milky Way and the summer constellations, you know, particularly towards the latter part of July

and into August. And you see the three stars, the summer triangle. But just enjoy the view see the Milky Way in the summer constellations, you know, particularly towards the latter part of July and into August, and you see the three stars, the summer triangle, but just enjoy the view of the Milky Way. The moon's not in the sky. And if you're heading south, if you're going to the Mediterranean or further south, then take a pair of binoculars with you. And if the moon's not around and you're somewhere slightly dark, just enjoy the view, just sweep around with the binoculars and look at that really rich part of the sky the inside view of our galaxy and then finally the other exotic thing to look slightly unusual thing to look for is something called noctilucent clouds and this this is a rare upper atmosphere phenomenon they're about 60 000 meters high so they're much much higher than other clouds they're up in the

mesosphere i think it is one of the regions of the upper atmosphere. And they shine very brightly over the northern horizon every so often. So even when it's fairly dark, you have this beautiful pattern of glowing clouds. So a lot of astrophotographers are quite interested

in taking pictures of those too. And we think they form around maybe dust from meteors or volcanoes or a bit more sadly, possibly pollutants that make it their way up there too. But I do recommend them actually.

They're quite, they're very, very odd things to see because, you know, we're generally just not out and about at that time of night. So another early morning job, I'm afraid. They are quite mesmerising. I saw that Steve Brown, who's an amateur astronomer who we've actually had on the podcast before, he'd done a time-lapse of these noctilucent clouds.

Honestly, so stunning. It's incredible incredible and so with that i think that's it for this month thank you to brilliant for sponsoring this episode we'll be back next month with a special update on the james webb space telescope we can confirm that the first images are expected on tuesday the 12th of july 2022 i've got it in my diary i'm so excited no but seriously it's it's during the national astronomy meeting which is like the biggest conference in the uk like we've not all been together in three years it's going to be the best atmosphere when those are released it's going to be it's going to

be amazing i feel like it's going to be party week for all of the astronomers like at this one conference it i mean it was normal that anyway but yeah this is gonna turn it up to 11 i think anyway tweet as if you try some astronomy at home we had that brilliant picture from ja of m51 which we'll put on our social so that you can see it as well thanks for sending that in it's at royal astro sock on twitter or you can email your questions to podcast ras.ac.uk and we'll try and cover them in a future episode but until next time everyone happy stargazing