The Supermassive Podcast - 20: Firey Worlds

Episode Date: August 27, 2021

Izzie and Dr Becky are turning up the heat and exploring the fiery worlds in our solar system. From planets close to the Sun to a distant world of volcanoes and lava. Joining them are planetary scientist Professor David Rothery from the Open University and Professor Alfred McEwen from the University of Arizona, who wants to send a mission to Jupiter’s moon Io. Plus Dr Robert Massey takes on your questions and has his monthly guide to stargazing. This is a Boffin Media production by Izzie Clarke and Richard Hollingham.

Izzy, do you want to guess at the melting point of rock? Io has hundreds of volcanoes erupting and it's a smaller world, it's not much bigger than our own moon. Venus is even hotter than Mercury. So can we call it a fiery world? Hello, welcome to the Supermassive Podcast from the Royal Astronomical Society with me, science journalist Izzy Clark and astrophysicist Dr Becky Smethurst. Yeah, this month we're doing what the British summer here has not done With me, science journalist Izzy Clark and astrophysicist Dr. Becky Smethurst. Yeah, this month we're doing what the British summer here has not done and we're turning up the heat, right?

We're exploring the fiery worlds in our solar system from planets close to the sun to distant worlds of fire and lava. And to help us, we'll be joined by planetary scientist Professor David Rothery from the Open University. And we'll hear from Professor Alfred McEwan, who wants to send a mission to Jupiter's moon Io. And you know the drill by now. Dr. Robert Massey, the Deputy Director of the Royal Astronomical Society, is here too. So let's get this straight, Robert. What classifies something, whether that is a planet or an object as fiery? Well I think when you think about this there are a lot of fiery worlds out there and even before the space age you know we would have been aware of the fact that Mercury the closest

planet to the sun was scorched by virtue of being closer to the sun so during the day the temperature goes up to 427 degrees Celsius and at night down to minus 180. So you're simultaneously having a fiery and an icy world. But if you go out to Venus, the next planet further out and the closest one to the Earth, we often think of Mars as being the closest, but it's actually Venus. It's the same size of the Earth, but it has a stupendously thick atmosphere with really high atmospheric pressure at the surface, a big blanket of carbon dioxide. So the surface temperature is even higher than on Mercury, 470 degrees Celsius, hot enough to melt lead. And we think it might even have active volcanoes too. I definitely think that counts as a fiery world. And I also like the idea that we should think about the fire, the lava from

volcanoes defining this as well. So Earth in a a sense, could be considered a bit fiery. Bit fiery she is, just a bit. And then the exotic moons further out, like Io around Jupiter is the classic example, which has far more volcanoes than, well, lots of very active volcanoes anyway, compared with the Earth. And it's stretched by Jupiter's gravity. And that generates the melting inside it. And when it was first seen in the Voyager images, when this stuff was first seen in the Voyager

images, right back in 1979, the classic comment from the researchers was, it looks like a pizza, because it does. So Izzy's partner, I'm sure you would respect this, looking at this beautiful pizza image. And these days, even some advanced amateur astronomers can take pictures of that. You know, they can detect the evidence for volcanism on its surface, which says a lot about how amazing amateur astronomy equipment's become in the last 50 years.

And as it happens later on, I'll mention the fact you can see both, well, all of Venus, Jupiter and Io in the sky this month too. Instantly, Io's become my favourite moon. It looks like a pizza. Yeah, fine, okay. I was already my favourite moon, Izzy.

We can debate what sort of pizza. It was already my favourite. And I love the fact that we're going to remind people, Robert, that we can actually see this in the sky. It's not just, you know, the planets and the stars. We can see some moons as well after our own moon. So thank you so much for that, Robert. We'll be catching up with you later in the show.

Okay, so we have enormous volcanoes in space and we have hot planets because they're close to the sun. But how much do we really know about these fiery worlds? I spoke with Professor David Rothery from the Open University and we started with my favourite pizza moon, Io. Astronomers have revealed that there are more than 150 active volcanoes on this moon and have predicted that there could be up to 400. Io has hundreds of volcanoes erupting and it's a smaller world. It's not much bigger than our own moon. And we didn't really expect small bodies like this to be volcanically active. But when Voyager 1 flew past Io in 1979, it saw eruption plumes in the same

week that a paper came out in Science saying, hey, there should be tidal heating on Io, it's going to be molten inside. So that was a remarkable piece of timing. And Io is erupting because it's orbiting this giant planet Jupiter with a very big gravity well. So that's what I was going to ask. Why is it that Io has so many volcanoes? Okay, if you distort any solid, you heat it up. I like to show this to people in lectures

by taking a metal coat hanger, bending it to and fro a few times, touching it to my lips, or better still, to a volunteer's lips, and you'll get burnt because where you've bent the metal, it's hot. Try this at home, people, but be careful. And the interior of Io is being flexed because it's orbiting this planet with a very strong gravity field, and its orbit has not been allowed to become circular. If Io was the only object orbiting Jupiter, it would have been forced into an exactly circular orbit long ago. But it's a moon called Europa orbiting outside of it, which takes twice as

long to go around Jupiter as Io does. And then there's Ganymede, which takes four times as long to go around. Now, because it's got this periodic tug, regular repeated tug from Europa and Ganymede, which takes four times as long to go around. Now, because it's got this periodic tug, regular repeated tug from Europa and Ganymede, keeping the orbit elliptical, that means its distance from Jupiter is changing all the time. Now, Jupiter's strong gravity is raising tidal bulges on Io, one on the near side, one on the far side. So Io's shape is distorted from being spherical by the tides, the solid body tides. Because the orbit is constrained to stay very slightly elliptical because of the presence of Europa and Ganymede in orbital resonance, Io's distance from Jupiter changes throughout its orbit to heat the interior of Io and that's what's powering the volcano. It's causing partial melting of the rock inside,

which rises towards the surface and erupts volcanically. And so these eruptions, you know, is it the same material that we see on Earth? Is it different? Like, what is actually coming out of all of these volcanoes? OK, a lot of it is quite strongly coloured. So when it was first seen, it was suggested that, well, we're erupting molten sulphur here. But that turns out not to be the case. There are infrared measurements of the temperature of what's being erupted, and it's far too hot to

be molten sulphur. It's molten rock. It's probably something called comartii which is high in magnesium but it is molten silicate rock and there are some very dark fast flowing lava flows on the surface as well as explosive eruptions powered by expansion of sulfur as a vapor and by expansion of sulfur dioxide as a vapor to get explosive eruptions you have to have something that will turn to gas and expand violently enough to fragment the rock and drive it out as ash fragments. Yeah, I mean, it's quite an aggressive moon in terms of all of the processes going on there. And then we have a few other fiery worlds, and that's because they are close to a fireball that is our sun. So I'm thinking of Mercury here. Does that classify as a fiery world, would you say? Well, by day, Mercury is about 430 Celsius. But by night, it's below minus 150 Celsius,

I think. There's no atmosphere to trap the heat, so it cools off very quickly at night. But by day, yes, absolutely baking hot. It isn't volcanically active, which is a shame but there's a very clear record of volcanic history and all you see on Mercury's surface is lava flow after lava flow after lava flow of a whole variety of ages mostly between three and four billion years old but more recent volcanic activity has been explosive. There are holes blasted through these lavas on Mercury by the force of expanding gas, which has thrown out volcanic ash particles to a range of up to 100 kilometres from the vents, powered by expanding volatile gases, which is a surprise. We shouldn't have volatile richness at Mercury. So that perplexes those of us who are studying Mercury.

Where did it form? How did it form to be able to retain all these volatiles and end up close to the sun where these volatiles can escape through volcanic processes? It's a strange old place. And just finally, looking at beyond our solar system, we are looking at more and more exoplanets. Have we seen any form of fiery world beyond our solar system? Do we have the ability to detect that yet? The way we're going to demonstrate active volcanism on an exoplanet is a transiting exoplanet that passes in front of its star. That enables us to analyse its

atmospheric gases. Now, if you had a supervolcano eruption, there you would have an atmosphere loaded with ash, loaded with sulphur dioxide to such an extent, but it would affect the atmospheric signal as it transited across the sun, seen from a distant observing point. So we could detect really big catastrophic eruptions when exoplanets transit their stars.

But we're not going to be detecting infrared radiation from lava flows on exoplanets or anything like that. It's secondary effects via the atmosphere that we'll be able to see. That was David Rothery from the Open University. So, Becky, there was one other planet that we've sort of briefly touched on, but that's Venus. So as Robert mentioned at the beginning, Venus is even hotter than Mercury. So can we call it a fiery world? Well, it's certainly hot. And if we were going to go by the definition of whether it's a hot planet, then yes. It is about 50 degrees hotter than Mercury's surface just because it has a denser atmosphere

and a really strong greenhouse effect, right? Like Venus is sort of like the warning sign to all of us on Earth. So by that definition, yes. But I guess the bigger question is whether it's active volcanically or not, right? So it's not got any plate tectonics like Earth does. There's no like heat transfer to the surface like on earth you know one of the big questions is how venus is actually radiating its heat away but we have seen young volcanoes lava flows and stuff like that all over the surface of venus but there's no evidence for the fact that they're still active and they're still active volcanoes it could be that they're mostly dormant. Although they have just like tantalizing hints that maybe it could be, right? So for example, there was a

detection of an increase in sulfur dioxide in the atmosphere of Venus a few years ago. And that's a classic indicator, right? Of like volcano was here, right? It's the big volcanic gas. So some planetary scientists are pretty convinced that it has to be somewhat active, just again, by this idea of it must be getting rid of its heat somehow, maybe through very low level volcanism. And therefore, you probably would classify it as a fiery world as well as one that is very, very hot. But there's been no direct evidence yet anyway. Okay. And Robert, Venus seems to be on the mind of a lot of astronomers at the moment. I mean, we've had at least three missions announced recently. So what are they hoping to find on Venus? Well, you're absolutely right. And I think that was partly driven by the potential discovery of

phosphine last autumn that we obviously talked about a lot on the podcast as well. And so there are now at least six missions under development. When I was looking at this, I thought, oh, yeah, three or so. And then I thought, OK, six missions being considered and possibly even the seventh. But there's six at least at the moment. And there's a number of partners. So Rocket Lab, a company in New Zealand, they're thinking about a private mission that would maybe launch in 2023, drop balloons into the atmosphere with the explicit idea of checking

to see if there's life in the atmosphere of Venus. The Indian Space Agency, ISRO, has its Shukrayan-1 mission, which will launch a year or two after that. And that will also be looking at the atmosphere and studying the surface as well and looking at how the planet interacts with the sun. There's VERITAS,

which is one of the newly approved missions from NASA, launching in 2028 or so. That'll be looking at the geology of Venus and trying to find out whether there was ever water on the planet. Because one of the ideas is that earlier in the history of the solar system, Venus might have had a much more pleasant surface, that there might have been liquid water and even a large ocean. There certainly isn't anything like that now. The Russians want to launch a probe in 2029 with an orbiter and a lander, which is fantastic. Imagine, there have only been a few landers on Venus because they get down to the surface. The Russians were very good at this, or the Soviet Union actually in the 1970s.

And those landers shut down within about an hour and a half because it's such a ridiculously extreme environment. It's not only incredibly hot, but you've got crushing atmospheric pressure and it rains sulfuric acid. So it's a tough call to get technology to work there. That might have a balloon added in. Then there's DaVinci Plus, another NASA one that might arrive the same year. That'll look at the atmosphere, and that's going to drop a probe through the atmosphere to study the atmosphere and go down to the surface, and also try and understand about whether there was an ocean. And then finally, the European Space Agency has approved the Envision mission, which will get there in about 2034 and do similar things,

look again at the atmosphere, look at activity on the surface. So I'm taking a deep breath after that. There's a lot of Venus missions going on. Yeah, there's just so much to look forward to, isn't there? And I mean, like you said, we haven't had a probe or a lander since like the 80s with the Soviet Union. So you think about all the questions that we just didn't know to ask back then, that we now are so interested in, you know, I'm really excited to see, you know, what sort of technology and everything will make it onto all these probes and landers that we can, you know, ask all these questions that we're dying to know the answer. But six, I mean, six to Venus and poor Neptune and Uranus people can't even get one. I'm like, come on. It always feels like a zero-sum game, doesn't it?

You know, but yeah, we want missions to Neptune as well, obviously. So it's clear there are so many questions we want answered when it comes to these fiery worlds. And our next guest is proposing a mission to Io to discover what is actually going on with all of these volcanoes. Professor Alfred McEwen from the University of Arizona, welcome to the Supermassive podcast. Now you're working on something called the Io Volcano Observer. So what is it about volcanoes on Io that we want to understand? Right. So the Io Volcano Observer or IVO is a mission we did propose in the last round of the NASA Discovery missions and it will be proposed again in some form.

But it's a mission dedicated to studying Io, the extremely volcanically active moon of Jupiter that's tidally heated and has hundreds of actively erupting volcanoes with high temperature silicate eruptions. And we want to know more. What makes Io tick? What does this tell us about Io's interior? What's going on with its unique tectonics and how does that relate to uh to the early earth and other planets yeah i was just about to ask whether those the tectonics could teach us a lot about sort of you know anything like mass extinctions on earth that we might think have been driven by volcanic activity that kind of thing right so they're uh at least four out of five of the phanerozoic or the last 500 million year mass extinctions on earth are very precisely correlated in time with the peak eruption of flood lava, such as in Siberia.

So that's probably not a coincidence. And it's thought that those eruptions change the composition of the atmosphere, which in turn changes the composition of the ocean. But anyhow, these are massive eruptions, very high effusion rates, something we've never seen in person. But that's a good thing. Probably wouldn't survive. Yeah, these are orders of magnitude bigger eruptions than anything we've observed. But they're happening today on Io. And there are some features on Io in particular, right, that have grabbed your attention, piqued your interest? Some of us love all the features on Io, but a couple of favorites, crowd pleasers are Loki Patera. This is a 200 kilometer wide depression that's full of lava and it's been described as a lava lake or even a lava sea

and it has periodic sometimes periodic eruptions which might be due to an overturning crust on a lava lake although loki is the trickster god so we keep reminding ourselves that it may be fooling us but that's one feature we'd really like to understand. It's the most intense hotspot in terms of heat flow on Io. Another one is called Pele, after the Hawaiian goddess of volcanology. And this one has had the biggest plume on Io's equatorial region. There's been others at higher latitudes that are comparable in size. But for the IVO mission, we can make close passes over the equatorial region. So this is one that we could actually fly through and

measure the volcanic gases. And that also has a smaller lava lake with a very high temperature hotspot. So those are two favorites. Oh, wow. And so that's something I wanted to touch on there. So you're proposing this mission. So how would you actually try and investigate a lava sea? You know, no big deal. Right, so studying Io is challenging. First of all, it's at Jupiter. You have to get there. But then it's also well deep inside Jupiter's giant magnetosphere.

And all that stuff erupting from Io, that gets charged up by the magnetosphere. So there is a plasma torus full of energetic electrons. So that stuff wears out your electronics in a hurry. So what we have to do is we're in an elliptical orbit around Jupiter that's inclined such that we fly lickety split from north to south by Io, get our data in a hurry and get out of there as fast as possible. So we have a very specific orbital geometry that's designed to minimize the total ionizing dose, we call it. And so then we have to have, how do we get the measurements with such a fast flyby and with advances in instrumentation, we can actually do surprisingly well. Yeah. So is that looking at probes or like what sort of the, what are some of the equipment that

you're hoping to send and to measure? This is quite a hostile environment. Yes. So we are especially interested in what's happening inside Io. Observing the active volcanism is pretty easy. We'll take pictures. We have thermal camera. We can measure the temperatures. And we have to do all that fast, but we can do that. And of course, we have time approaching and departing to get more global view. And so all that is relatively easy. You have to build and test the instruments and all that. But understanding what's inside of Io, that's the hard part. So we have several tools at our disposal.

One is gravity science. So it's not a special instrument. It's just precisely tracking the spacecraft as it flies by Io. In particular, we want to measure the tidal signature. So Io orbits Jupiter every 42 hours. the tidal signature. So Io orbits Jupiter every 42 hours, and the surface rises and sinks by as much as 100 meters every day from the extremely strong gravitational tides. It's in an elliptical orbit around Jupiter, forced by Europa and Ganymede, in fact, with the resonance that they're in. 100 meters is incredible, because if you think about Earth tides is only a couple of meters if we're lucky and that's on the ocean and yet we're talking about rock here. And so it's 100 meters if Io has a magma ocean where the lithosphere is

detached. If Io is more solid with just interstitial liquid then it's more like 30 meters which is still pretty high. Still. So that's one of the things we can measure with the gravity signature is, is it big or small? That means does it have a magma ocean or does it not? Another way is with a magnetometer. So a magma is electrically conducting. And I mentioned that Jupiter has this giant magnetosphere. It's also tilted.

So from Io's point of view, it is sweeping north-south over Io. So this is a giant electromagnetic probing experiment for Io's interior that we get for free. We just have to bring a magnetometer to measure how the magnetic fields vary as Jupiter's magnetosphere goes up and down, which depends on the interior conductivity, which again depends on how much magma there is inside Io. So that's a second method. A third method is to measure the composition of lavas coming out of Io. We have a mass spectrometer on the spacecraft that can tell us exactly the elemental composition of everything coming out of Io's plumes. So what is the status of the IVO mission?

So at the moment, we did extremely well in our last round of discovery. We were one of the finalists. We did a phase A study, it's called. But ultimately, the other ones did well too. And there were four of them. And so NASA could only select two and they selected two Venus missions and that's great because Venus is also deserving of further exploration and it's also very relevant to understanding Earth and so I can't complain about the Venus missions but

you know we can try again. I think this is interesting because it's not something that we talk about all that much but the fact that scientists like yourself will have to put in the research and proposals for missions. And obviously, Io is so interesting. Everything that we've discussed already is just like, yes, let's go. Let's find out more. So what is that next step? It depends on when NASA releases an announcement of opportunity for a new mission, either New Frontiers or Discovery. Right now, we anticipate something like 2023 for that, which means we really need to get going.

They'll announce it well in advance, and we really need to get going in 2022. So that's only next year. There are other missions going to the Jupiter system that can get some remote observations, so that's good. The Europeans are interested in Io as well, but Europe could have a standalone mission at some point in the future or make some extra contribution to a NASA mission, such as we'd really love to have a probe. We release and impacts into Io with a seismometer because the seismic signal from Io has got to be spectacular, and it only needs to survive in one Ionian day, 42 hours,

to get the total signature of that. And it can have a heat flow probe as well for conducted heat flow. So we have lots of ideas. What really happens remains to be seen. We wish you the best of luck. I'm sure all the listeners will agree with that. And thank you so much for joining us as well. That was Professor Alfred McEwan from the University of Arizona. This is the Supermassive podcast from the Royal Astronomical Society with me, astrophysicist Dr Becky Smethurst and science journalist Izzy Clark. This month we're exploring the hottest worlds in our solar system

and we're not the only one with questions. We've got a whole pile of questions from listeners so thanks as ever for sending them in. Robert Lewis on Twitter asks, Am I right in saying that the majority of exoplanets that we have discovered are hot Jupiters? What is special about our solar system that means we don't have actual Jupiter and Saturn closer to the sun?

So perhaps let's start with what is a hot Jupiter? Well, a hot Jupiter is exactly what it implies. It's a big, massive planet close into its star. And a good example is one of the very first one that was discovered. Actually, there was a weird pulsar planet discovered a couple of years before that. But 51 Pegasi b, the defining exoplanet discovery in 1995, co-discovered by Didier Queloz, is actually in the UK, in the University of Cambridge. And he worked with Michel Mayor, they found this object, it goes around its star every 4.2 days. Now, if you think about something

like Mercury, it takes 88 days to go around the sun, our sun. And so the fast orbit is because it's much, much closer, it's just 8 million kilometres from the star's surface, or about six times closer in the Mercury. So it gets heated to at least a thousand degrees Celsius. And that's before you consider any atmospheric effects or anything else. This is the kind of heat you have if you're that close to the star. So that is certainly hot Jupiter. And it turns out, think about Lewis's question, a lot of the planets we found are like that, but that's partly because they're easier to detect. I'm not sure, by the way, if it's still true the majority. It certainly was the case initially. But it's partly because they're easier to detect. I'm not sure, by the way, if it's still true. The majority certainly was the case initially.

But it's partly because they're easier to see because if you detect them because they move in front of the star, what's called a transit where they block out a bit of the light, then a big planet that's doing that very often, it's more likely you're going to be able to detect that. And also if they're Jupiter-sized, they've got a big gravitational pull. And also, if they're Jupiter-sized, they've got a big gravitational pull. One of the other methods of detecting a planet is that the planet goes around the star and pulls it back and forth. And we measure that by looking at the change in the wavelength of the light, the Doppler shift. It goes back and forth as the planet goes around. So bigger planets, that's easier to see. And that's why certainly a lot of the earliest discoveries were like this and why it's much, much harder to find things like Earth-like worlds, because Earth as a smaller gravitational pool is likely to be further away

if you want it in a place where it might be habitable. So that's a lot of the effect. Now, the final thing he did ask about why we don't have that scenario in our solar system. That's a really interesting question. There is a lot of argument. The planets like these hot Jupiters we think migrated in, that they started out further out and then they interacted with either other planets in their system or with the kind of residual planetary

disks that these things form from and ended up much closer to their star. So why that didn't happen in the solar system is a really intriguing question. Maybe the solar system is slightly special that we don't have that kind of setup. And it's the sort of thing to really explore with an exoplanetary specialist as there is a lot of argument about this and whether or not, you know, some people also say these planets might have formed much closer into their star, but the favored view I think is that they formed further out and were likely to migrate in. Yeah, I heard that it was because of the interaction of Jupiter and Saturn. Like this is the leading hypothesis, right? That if hadn't existed then jupiter would have

migrated inwards completely unchecked but saturn essentially pulled it back again into its current orbit and so i mean you could say if you wanted to that saturn is the whole reason that earth is still here and that is reason number 732 why saturn is my favorite planet or are we saying that Saturn is just holding Jupiter back? No. No. I didn't say that. Well, Lewis, I hope that answered your question. Becky Francois asks, is there a limit to the amount of heat a rocky planet can withstand, whether it be from tidal friction, greenhouse atmosphere or proximity?

Yeah, this was a great question. I actually had to look this one up because I didn't know. And I started with what the hottest rocky exoplanet is that we know of. It's Kepler-70b. Well, there is a bit of concession about whether it does exist or not, but we're pretty sure it does. It orbits around its star in five hours and 45 minutes. Wow, okay. So it has an estimated surface temperature of 7,000 Kelvin.

Oh my gosh. And we know it's rocky because it's only about half the size of the Earth as well. So we think it's actually very likely that it's like a core remnant of something that was once a gas giant that's essentially had its atmosphere boiled off, perhaps if its star went

through a red giant phase or something like that and swelled up but at 7 000 kelvin right i mean even if it is a core you've not got solid rock anymore you've got something that's completely and utterly liquid you've got magma you've got lava right because izzy do you want to guess at the melting point of rock i mean i wouldn't know robert you want to guess at the melting point of rock? I mean, I wouldn't know. Robert, do you want to guess a number around about what it is? Well, I admit I did check some of this out, but it depends what the rock's made of, doesn't it? But I think some of it melts at about 1,000 degrees and then some of it melts at 2,000.

Yeah, so it's somewhere between about 900 and about 1,600 Kelvin. So it's pretty high. So you're definitely in the realm of completely melted rock right so at these extreme temperatures of 7 000 kelvin you actually have to start thinking about evaporation of rock of liquid rock which is incredible to think about right it's hot enough that there's enough energy for the rock to overcome the gravitational energy binding the planet together like that's how hot we're talking so i actually found a paper way back from 2013 that was called catastrophic evaporation of rocky planets which

is one of the greatest titles of a paper i've ever seen in my entire life and they modeled this happening with a planet that was just a little bit heavier than Mercury. It's about 10%-ish of the mass of the Earth. And with a temperature of only 2,000 Kelvin, not 7,000 Kelvin. And they worked out that it would take just less than about 10 billion years for that rocky planet to fully evaporate. Now, obviously, Kepler-70b is about half the mass of earth and it's about 7 000 kelvin so it would probably take a little bit longer than 10 billion years despite that larger temperature um and i mean 10 billion years you're getting towards sort

of current age of the universe right of 14 billion years so it's much more likely that like a star would die off and disperse all of the materials before a rocky planet could fully evaporate due to proximity i didn't really look into greenhouse gases but obviously if you're that close to a star you're obviously going to be undergoing tidal friction as well francoise so i mean i think that question is yes theoretically if you gave it long enough and you put it close enough, you could have an evaporating rock planet. I sort of think about this hot

blob going around the star or something with some wonderful long trail. I imagine it a little bit like, you know the videos of water on the International Space Station? Yeah, yeah, yeah. That's what I'm picturing, just like wobbling around in stuff oh my gosh well i mean thanks

for the deep dive becky that's great you're welcome i had a great fun prepping that one all right robert next question is for you from john white who asks would it be possible for a rocky planet in a close orbit to have one half molten and one half with a solid surface because it's tidally locked so let's start with what does it mean if something is tidally locked well tidally locked is the best example of something being tidally locked is our own moon it means that the where one body is orbiting another that they it always keeps the same face to it so it's still rotating round but it's doing that over the length of its orbit. So the moon does spin.

It's just that it takes as long to spin as it does to go around the Earth. So we always see the same face. And that does happen with a lot of systems. I think Pluto and Charon, the moon of Pluto, do that. Some of the moons of the giant planets do it as well. So it's not an unusual thing. And the sun has that effect, I believe, to a lesser extent on Mercury as well. There's partial effects going on there.

We definitely are going to be seeing that with some planets around other stars. So that's what John's referring to there. Now, as for, I was just thinking about Becky's answer, but as for what it would mean if one side was molten and the other wasn't, I think it probably depends a lot on the type of planet. If it had, and whether or not that atmosphere would survive, if it was hot enough for it to be cooked like that, I guess we could assume it's so hot there's probably very little of an original atmosphere left that you're talking about material gassing off the surface. If it's fairly small, I find it hard to believe believe a lot that heat wouldn't be being transferred round. But it is a really intriguing thought, the idea that you might go round to the night side

and there would be this super cold place, like on Mercury, despite the rock facing its star being superheated. And I think you probably need to ask a sort of geologist about how efficiently that heat would transfer through the system. Maybe as well if it didn't.

Again, I don't know whether this would apply or not, but whether it had a molten interior or not like the Earth does, because that would presumably efficiently transfer some of the heat as well. So it's a very intriguing science fiction idea, I think. The idea that you build some sort of base in the twilight area where it's just about a clement temperature. Of course, there's little details like actually getting to the star in this planet in the first place, but, you know, nice idea. And there are examples thinking about, you know, Becky's description. There is the idea that some of the hot Jupiter planets, if they're around long enough, might have their atmosphere stripped

away completely and be left in that sort of situation hot Jupiter planets, if they're around long enough, might have their atmosphere stripped away completely and be left in that sort of situation. So they start off as a very hot Jupiter-type planet and end up as a hot rocky one. But yeah, it's an intriguing thing to look for, just about that planet that's just on the threshold like that. Yeah, and I swear, from some of the questions we get in from listeners, we're basically building a back catalogue for sci-fi book ideas.

I'm just like, yep, making a note of that one. I think we both support and ruin sci-fi sometimes, don't we? Oops. Okay, well, thanks for clearing that one up. And so, Becky, one more question for you. Will the James Webb Space Telescope or one of the proposed future space telescopes

allow us to detect volcanic activity on exoplanets i mean yeah we really hope so anyways what people have got their fingers crossed for so we're talking before about how volcanism gives off you know a lot of telltale gases right we've already spoken about sulfur dioxide which reacts with water in atmospheres to give you sulfuric acid which is not great But you've also got carbon dioxide and methane as well that's produced by volcanic activity. And all of these gases leave an imprint on the starlight that passes through the atmosphere of the planet, you know, while it passes in front of its star. And a lot of those imprints are in the infrared part of the spectrum where the James Webb Space Telescope is sensitive as well. James Webb is also big enough to be able to

collect enough of that light and isolate it from the overall starlight as well, the little bit that's just passed through the atmosphere. So technically, yes, but then you've got to think of sort of like whether any volcanic eruption has spewed out enough gas for it to leave a big enough signal on the light for us to be able to detect it. So we have the capability to do it, but I guess it comes down a little bit to a numbers game as well. Like, is the eruption strong enough? Is the planet passing in front of its star from our perspective at the right time, just after the eruption, for us to see that before it breaks down into things like sulfuric acid so bit of a game of chance but we're very hopeful that we will spot this and this is one of the main goals of the sort

of the james webb space telescope sort of exoplanet science as well yeah i cannot wait for james webb space telescope i just want it ready no offense hubble but you know come on hubble's back though which is good but yeah james webb is supposed to be october i think it's been pushed to december now because of the issues with the um the arianne rocket that it was going to be launched on um but i'm fingers crossed it's definitely going to happen in 2021 um and i can't decide whether i'd love to be one of the people that's at the launch site who've been working on this for the past 20 years of their life or if i'd want to be as far away from as possible i was going to add is there there are a couple of other exoplanet missions that would be trying

to do this kind of thing too, whether or not they're able to, but you know, like CHEOPS is already operating, trying to look at atmospheres of exoplanets. And there's the PLATO mission, which will be looking for rocky planets. I don't know, probably does come to notice exactly what Becky's describing about how big a signature it is, but part of their job is to try and look at the atmospheres of these things for the

first time which is which is an amazing thing is it I mean imagine the idea we didn't even I'm old enough I don't I remember when I'm not even sure if you two

are old enough that you remember when there were no exoplanets but I definitely am well I don't remember but I know that it was something like Jurassic

Park was released in 1993 no exoplanets Toy Story 1995 one exoplanet and that's But I know that it was something like Jurassic Park was released in 1993. No exoplanets. Toy Story, 1995, one exoplanet. And that's the marker I use in my head. It's like, well, pre-Jurassic Park, no. Pre-Jurassic Toy Story, yes. Of course that's your scale.

Of course that's your scale. All right, well, actually some really brilliant questions this month. So thanks, everyone. And if you want to send in a question, do so please we love them so you can email podcast at ras.ac.uk or tweet at royal astro sock so robert what are some of the things that we can see in the night sky this month it's funny this is a great time actually to be out looking at the night sky because the weather you know isn't too cold typically although i admit august has been a slightly disappointing month so far in terms of temperatures understated of the year but i'm waiting for the clear night to see the persons and it never came i think i got lucky we were camping in dorseter last week and we actually had a really dark sky there a fabulous view and it was fairly

clear and i had a lot of sunny weather as well probably something about the coast but what i was really struck by the beautiful thing you do, you get in that setting. Even in the UK, you can go out and you can see the Milky Way stretched across the sky. Absolutely fantastic. I didn't have any cameras with me or anything like that. I just soaked it in and watched the Percy and Meech's shower at the same time. But it's still a really good time to be looking at that because the advantage is that although it's moving more into the evening sky and won't be there all night as it was the skies are a bit darker so we have properly dark night skies in august particularly and the further on the month you go the better uh and into september and the

dust lanes all the wonderful details stand out so what i would really encourage people to do if you're going on a holiday like that you know staycations everybody's sitting there thinking oh you know just about managed to do some camping or something like that but if you get even one or two clear nights take a pair of binoculars with you and soak up the view and you can see quite a lot of little things you can see this wonderful asterism i love i mean look it up on some charts called the coat hanger which is between the stars vega and alto about halfway between the two in the triangle uh and the wild duck cluster another beautiful little little sprinkling of stars lower down. And if you have a small telescope, even better.

I mean, I don't know if taking that to a campsite is more complicated, but if you do have one, then you can see just a whole load of things in that central plane of our galaxy. It's a fantastic time to look at it. But pertinent to today's stuff, Venus is also getting a bit easier to spot as well, and it will improve as the year goes on it's been not been very easy so far it's been very very low down but as we move into september it should get it's a bit better place it'll be a bit higher in the sky after sunset over in the northwest and

then moving around to the west as the position of the sunset changes as the year goes on and on the 10th of september you've got the crescent moon near it another always a fantastic photo op it's just yes exactly we're not going to say what becky've got the crescent moon near it. Always a fantastic photo op. We're not going to say what Becky's definition of crescent moon is. But she might. Fantastic photo op. And also we have got both Saturn and Jupiter low down in the south

as well. They're not going to get that high this year. They're just still stuck down in the lower part of the ecliptic. But if you have part of the zodiac, the constellation of Zem, if you have a nice clear southern horizon, they're very very easy to spot if you have a clear sky and jupiter stands out because there's a it's much brighter than any star but secondly there's just nothing else around it you can't mistake it um so get a pair of binoculars and look at that if you don't have a telescope and you can see the four little points of light that galileo discovered as

recognized as moons the jupiter and that will include io the closest one into jupiter and you can see the four little points of light that Galileo discovered as recognised as moons to Jupiter and that will include Io, the closest one into Jupiter and you have to watch it over a few nights because obviously it depends on exactly where they are. The closest one is Io and if you look at that little tiny point of light you can just imagine the pizza moon and those maybe 400 volcanoes. And another really interesting thing that perhaps you guys can explain is the fact that we've been able to see behind a black hole recently what is going on there i always say there was this new study do you remember the um interstellar the film where they they beautifully rendered that black hole and it and it has this accretion disc around it right which is the material that's spiraling around the black hole that eventually become part of it

and in the film the light from that is bent around the black hole so you almost see this ring of light around the black hole and it's light that comes from behind it so i'm saying basically this new study is like a little tick next to that interstellar rendering of a black hole and people always get confused this idea of behind a black hole because they think of a black hole as a hole but it's not right they were once 3d objects you know and we consider the event horizon as a three-dimensional sphere so what this is like saying is say i got in a little spacecraft i'm imagining that yeah trundled off to behind the moon and i just like off i go right behind the moon playing a game of hide and seek right you can't see me because i'm behind the moon imagine if i took a torch and was sort

of just like flashing light periodically and the moon's gravity was strong enough so that the path of that light was no longer straight it got curved around so you could still see it on earth this is essentially what they've detected they've detected light from the part of the accretion disc that from our perspective you know say if you imagine it like the rings of saturn is behind the black hole that's been bent by the huge gravity around it so that we can actually see it and they can actually tell where it comes from because that accretion disc is moving so depending where it comes from and how close it goes to the black hole it gets a different doppler shift as well a gravitational red shift or a different uh red shift so it's really cool they've seen it in x-rays

which also makes it sound extra cool like x-rays shifted to see behind a black hole right and it was just a really cool study that came out and it and basically it um confirmed something that einstein's theory of general relativity predicted you know way back 100 years ago when you hear when you hear stuff like that you just think god space is so cool like you're just like why why do you think i became an astrophysicist busy i'm just like yeah man okay i can get behind that it's so good right well i think that's it for this month we've covered the fiery worlds so next month it's all about the icy ones.

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