In Our Time - Solar Wind

Episode Date: January 23, 2020

Melvyn Bragg and guests discuss the flow of particles from the outer region of the Sun which we observe in the Northern and Southern Lights, interacting with Earth's magnetosphere, and in comet tails that stream away from the Sun regardless of their own direction. One way of defining the boundary of the solar system is where the pressure from the solar wind is balanced by that from the region between the stars, the interstellar medium. Its existence was suggested from the C19th and Eugene Parker developed the theory of it in the 1950s and it has been examined and tested by a series of probes in C20th up to today, with more planned.With Andrew Coates Professor of Physics and Deputy Director in charge of the Solar System at the Mullard Space Science Laboratory, University College LondonHelen Mason OBE Reader in Solar Physics at the Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Fellow at St Edmund's CollegeAndTim Horbury Professor of Physics at Imperial College LondonProducer: Simon Tillotson

BBC Sounds, music, radio, podcasts. Thanks for downloading this episode of In Our Time. There's a reading list to go with it on our website, and you can get news about our programs if you follow us on Twitter at BBC In Our Time. I hope you enjoy the programs. Hello, the solar wind is matter, blown from the sun out into the whole solar system at up to 2 million miles per hour. We notice its impact when Earth's magnetic field diverts it towards our poles

for the northern and southern lights, or when it makes comet tails, or when it damages electrical equipment. It was Eugene Parker in 1957, who theorised that matter was escaping from the sun's atmosphere into space, and ever since we've been sending out probes to learn more about this phenomenon, so fundamental to understanding life and the universe. We admit to discuss solar wind, Helen Mason, OBE, reader in solar physics at the Department of Applied Mathematics and Theoretical Physics, University of Cambridge, fellow at St. Edmunds College,

Tim Horbury, Professor of Physics at Imperial College London, and Andrew Coates, Professor of Physics and Deputy Director in charge of the Solar System at Mullard Space Science Laboratory, University College London. Andrew Coates, I've summarised that very elliptically. Can you tell us more about what the solar wind is? Well, the solar wind is a stream of material coming out of the sun all the time. It's about a million tonnes per second. It's gusty, it changes with time,

but it also comes out of speed, which is between 1 and 2 million miles per hour. Those numbers are very big, but what we can say is how far it's going in a second. So actually, the 1 million miles per hour is equivalent to about 300 miles per second. So, you know, imagine something like 300 miles per second. It gives you an idea of how fast this is.

So it goes out through the solar system, interacts with anything getting its way, like the Earth or other planets or comets and so on. How do you arrive at those numbers? Well, it's by measurements. What sort of measurements? Measurements originally, which were started in the late 50s and early 60s, which actually got the measurements of how fast the solar wind is going.

With the sun itself, we know it's not only emitting heat and light, it's also emitting this stream of material, and that's what was discovered with these measurements in the late 50s and early 60s. In fact, the first measurements were actually Russian measurements, Constantine Gringowels, and then Marshall Gnoykawauer, with the American probes, the Mariner II probe, discovered the solar wind. And so you can measure the speed at which the wind is going. And what you're doing actually is measuring the energy of the particles. And that speed of about 300 miles per second corresponds to about one kilowatt of, you know, in terms of the actual speed.

So this solar wind, I mean, it moves outwards from the sun. It's particles moving outwards from the sun. So the particles form a plasma. Plasma is the fourth state of matter beyond solid liquid and gas. And so we have positive and negative charges moving away from the sun, interacting with anything getting in the way. And the composition of it is made up of, so it's hydrogen, but also more heavy molecules as well

and ions all the way up to iron ions, which is difficult to say, but ions made of iron. This began to be coherent this study and then this man Parker who's still alive in the 1950s. What ideas did scientists have about this phenomenon before Parker? Yes, it started really quite a long time ago in 1859 with Carrington, who noticed some events

the sun which then a day later there was some very large effects on the earth which we seen that was a sort of first what were the events on the sun in it well it was a huge flare so it's what we call now a white light solar flare and so that's a really energetic flare in fact we're lucky that that type of flare hasn't happened since because um or in the recent past because um our technology would be very vulnerable to that happening and also the um the solar wind when it gets to Earth a day or two later can cause effects. But so he noticed this very large flare on the sun, so a sudden increase in brightness and made a note of that.

And then people looking at magnetic observatories, the next day he noticed a change in the Earth's magnetic field, which is to do with a magnetic storm. And so the link started to be made. And then sort of going on from there, Eddington in 1910 suggested that there might be streams of positive, and negative particles, but he hadn't put them together. Sidney Chapman in the 30s suggested a solar wind

and actually both electrons and ions going at the same time. But it wasn't until, well, I mean... Let's get to Parker. Yeah, we get to Parker actually via another observation which was made by Beerman who was looking at comet tales. But then Parker came up with the first theory, really, of the solar wind. So he's able to look at the... the theoretical understanding of the solar wind.

Helen Mason, so what did Eugene Parker propose? Eugene Parker is just an amazing man. I've had a great honor to attend one of his lectures on solar and stellar physics, and he is one of the key people in this field. Amazing. And I think one thing that hasn't perhaps been mentioned yet is comets. And from the tail of the comet, the comet can have two tail. It can have a dust tail and an ionized tail. that's a charged tail

and they go in slightly different directions but what Bierman had noticed was that as the comic went around the sun the tail actually changed direction as if there was a wind blowing out from the sun. So there was some evidence there, indirect evidence, that the solar wind was blowing out.

So Parker proposed he looked at the dynamics or he took a hydrostatic model first of all which is just a static model of a gas but one thing I should mention is that key to all of this is eclipse observations. If you see an eclipse of the sun, what you're actually seeing is the outer atmosphere of the sun, the corona, the crown of light around the sun. And you can actually visibly see this tracing out magnetic fields. It goes out to large distances.

There's huge streamers running out there. And from the observations of eclipses, they were mystified about the light that was coming from this corona. They couldn't, explain it, and it took quite a long time to explain it. And they very careful laboratory work, they were able to determine that this corona is actually a million degrees. Even though the surface of the sun is only 6,000 degrees, this atmosphere, this corona was a million degrees. So it's very, very hot. So knowing it is this hot, Parker was able to assault the, we call it gas dynamics, the balance of pressure in that gas with the interstellar media. And he worked out, basically that the sun was streaming off,

that this solar wind was streaming off, this hot atmosphere. Can I pause again at this word measure? I'm fascinated by when you say measure, most of the listeners like myself will think where you get out a ruler and that sort of thing, but what does measure mean in your words? Measuring the temperature of the sun, it's a concept, yes. In our world, in my world,

we get the light and the radiation that comes from the sun. So when I say measure it, That is a complex concept in a way. It's the way we get information from all the other stars. We're able to see the rainbow colors of the sun, but on top of that we're able to see some very specific spectral lines, we call them. It's like a bar chart on something you have in a supermarket. And it tells you very precisely what the sun is made of, how it's moving.

It gives you a lot of information about it, as it would for many other astrophysical objects. Well, Eugene Parker's ideas in the 1950s, were they taken on or were they resisted? No, they were resisted. Why is that? People are sometimes in science, I'm afraid, they're very slow to change. If they have a particular thing in mind, they are very slow to change. So they couldn't let go of these old concepts, that there was nothing flowing from the sun. They wouldn't believe it.

But his equations, which were relatively straightforward, proved that there were. When he submitted his paper to a very prestigious journal, astrophysical journal as the journal we use, it was reviewed as all papers are by two referees, and it was rejected. It was rejected because they couldn't believe it was just concept. And there was nothing wrong with it. The equations were correct. And the editor called Shandra Saker, another very famous scientist, overruled and published the paper. And it's now a seminal paper in Solar Wind. What do we need to know about the corona? You mentioned the corona.

What more do we need to know about it? I mean, apart from infinitely more, but just for the effect of this programme, what more do we? The corona is a million degrees, as I say, but it has different types of regions. So it has where you see perhaps in a visible image of the sun, you can see sunspots, and underneath those sunspots on top of those, there's the sunspots of where the magnetic field of the sun pokes out from the sun, as it were. and we have called active regions and that's where these flares that Andrew mentioned happen so the magnetic field gets twisted, it erupts through and is twisted up

so we have flares on the sun we have very quiet regions on the sun where the magnetic field is open and the solar wind flows out into the surroundings and we know that that is the source of we have two main components that's a source of fast solar wind and it's steady and it's there and it comes out of these regions where the magnetic field is open.

But also around these active regions, there's a possibility that there's a more intermittent and a more discontinuous region. How does this stuff come out of the sun? Tim Horbury, when gravity you would have thought would have kept it in. Yes, exactly. So if you think about the analogy with the Earth's atmosphere, so the Earth has an atmosphere just like the Sun has an atmosphere,

and the Earth's atmosphere doesn't blow off into space. And really the reason why is that the atmosphere is quite thin, so the atmosphere is quite cold, So it varies with height, it drops off, the pressure drops off with height, but it drops off by something like 100 kilometres. So by that kind of height, the Earth's gravity is about the same as it is at the surface, so it's held down. The sun, as Helen was mentioned, the solar atmosphere is incredibly hot.

It's something like a million Kelvin. And as a result, that scale height of the atmosphere, the height that the plasma can get to is much higher, and it's higher than a radius of the sun. And so the sun's gravity further out is lower. And so the pressure doesn't go to zero, as you go further away, it still has a finite pressure. So it's really that pressure difference of the atmosphere

relative to the interstellar medium, relative to the gas between the stars. That pressure difference is really what drives the solar wind outwards. That's the basic fundamental of the Parker model. Now, the question, of course, then, is why is the corona at a million degrees? And that's the big science question in solar physics in some sense, is how does the sun possibly have an atmosphere? I'm still not quite sure how this beats gravity, though.

Because the So if I have a If the hotter I make the earth's atmosphere The Higher up the particles can get So they have more energy More thermal energy And that fights against gravity essentially

So at the top of Everest There's a much lower pressure There is at the surface If I actually heated the atmosphere up Then the pressure at Everest would be higher And so on the sun It's like heating that atmosphere up to a million degrees And so the particles can get much much higher

They've essentially got enough energy to escape the sun's gravity and to get away into interplanetary space. You were about to say? Yeah. So why are they so hot? So how do you, if you have a visible surface at a few thousand degrees on the sun, that's the yellow surface that we see, the photosphere,

how is it that the atmosphere is at a million degrees? How do you possibly get the heat from something colder to something hotter? So there needs to be a way of getting the energy from the sun into its atmosphere. And that's really done. We've mentioned about the magnetic field before. The sun's got a very strong and tangled magnetic field.

and the sun is essentially boiling around its surface, it's convecting away, and that motion on the surface tangles the magnetic field. And somehow that magnetic energy is getting up into the top of the atmosphere. There are two essential theories why, and actually Eugene Parker has contributed in a key way to both of those theories. Somehow you have to get the energy into the atmosphere. The magnetic field is an important part to play.

We don't normally worry about the magnetic field because most of the world around us is essentially, neutral fluids like the air and water and so on, and neutral fluids don't really feel the magnetic field. But when you make the particles hot enough, you end up plasma, you ionise it, those charged particles feel the magnetic field. So they're sensitive to those variations in the field, and we know the magnetic field can be important. So for example, if you play with two bar magnets, you know you feel a force between them. So you know there's energy in the magnetic field. And so that energy can be carried up into the atmosphere and somehow that energy

is then dumped into the atmosphere. Do we know why the sun's atmosphere is so hot? Well, these are these possibilities, and one of the reasons that we're sending spacecraft close to the sun in the next few years is to try and understand what those mechanisms are. So two key theories. One is that it's waves. So essentially you get variations on the surface of the sun. They propagate as waves into the atmosphere. Those waves break in the atmosphere and they dump heat. And the other is a process called magnetic reconnection. So this is an explosive release of magnetic energy. Helen mentioned solar flares. So Eugene Parker also suggests. suggested that there may be many millions of very, very small flares and they're releasing energy impulsively into the atmosphere all the time and it's that that's heating it up. So one of the big questions in solar physics is to understand which of those mechanisms is working and how we're actually heating the corona. Thank you very much. Andrew Coates again. So this stuff matter particles is heading out into space at millions of miles per hour. What happens when it hits planets?

Well, that depends on the nature of the planet. So the Earth, um, has a magnetic field and so do several others in the planets in the solar system. So Jupiter, Saturn, Mercury, Uranus and Neptune, all of these have magnetic fields. So the magnetic field can deflect the charged particles. So they're sort of protecting what's inside to some extent. So the Earth's atmosphere is protected to some extent from this onslaught of the solar wind by the fact that we have a magnetic field. But then there are objects which don't have a magnetic field. So things like Mars and Venus and comets. We've mentioned comets regarding comet tales

and the initial discoveries of the solar wind. But the unmagnetized objects are not protected magnetically from the solar wind. So the solar wind can get directly at their atmosphere and pull the atmosphere away. So you have this wonderful process called solar wind scavenging, which really takes atmospheres away. So at Mars this has happened, for example.

So we think that about 3.8 billion years ago, Mars used to have an atmosphere, which is about the same as the Earth's atmosphere now. But that has been pulled away over time because Mars lost its magnetic field. So that's pulled away into the solar wind to be lost forever to the planet. It's heavy stuff, isn't it? Yes, I'm game. Okay, Helen. What happens when the solar wind hits the earth? Well, as Andrew said, we're lucky. We're very lucky.

It hasn't stripped away our atmosphere. The Earth has a magnetic field, and that magnetic field protects us from the effects of the solar wind. How does do that? Well, because the solar wind is magnetized, it forms a sort of shock at the front of the earth. and much of the solar wind will scoot around it. So it acts as like a blanket protecting us, a magnetic blanket, protecting us from the main impulses of the solar wind. Now, if the solar wind was steady all the time,

maybe it wouldn't affect us so much, but it's not steady all the time. Sometimes it has bursts. We've talked about solar flares, but sometimes the sun can emit huge explosions. We call those coronal mass ejections, which are key. And they can impinge on our magnetic, field and our protection around us.

And they can hit it like a shock wave, hitting, or a car bumping into something, hits hard. And when it hits hard, the structure of our magnetic protection or field can change a little bit. And this can change such that the process that Tim's mentioned called magnetic reconnection can happen and particles can be accelerated back down. And we're particularly vulnerable in the polar regions. So that's where these particles were. will shoot back down again and cause the beautiful aurora that we see, for example, which are caused by particles energizing the atmosphere, the oxygen and the nitrogen in our atmosphere

and causing the beautiful lights. The idea of flowers was mentioned earlier, which sent trimmers around a lot of people listening to this programme. Next time there's a flower, I mean, we're done, aren't we really? No. Well, you did imply that. Well, I didn't. I'm not sure I implied that. That might have implied there. We're not done. Whatever it was. That was implied.

It is a serious question. It is very high on the UK's risk register. Now, I think it was fourth a while back. I'm not sure how high it is now. It's not going to kill us. But we live in a very technological age. We depend a lot on technology. And these are the solar wind,

these coronal mass ejections and solar flares can impact our Earth, particles can be accelerated very, very high velocities. So they can damage spacecraft, they can affect high-flying aircraft, they can be a problem for astronauts if they're, for example, on the International Space Station. They can even induce large currents in our electricity system and knock out our electricity. And this has happened. This has happened in the past. We mentioned the very early flare. we didn't have so much technology then, so it did have an effect, but this has happened.

So it is a serious concern, and one can mitigate against these concerns if you can have a warning. And now the Met Office is heading not just our weather, it's actually heading in a whole space weather warning system, so that if there is the likelihood of the sun producing some space weather in that way and causing these geomagnetic storms, then we can take some action. Tim Hawbury. What happens to the solar wind when he gets further and further and further away from the sun itself? Right.

So the solar wind blows off from the sun in all directions, essentially flowing radially away from the sun. And it's going, as we've heard it several hundred kilometres a second. So eventually that will interact with the interstellar medium. And it's worth actually thinking about numbers. What is the interstellar medium? So the interstellar medium is the very tenuous gas and plasma between the stars. So it's the leftover stuff that's left after the stars have formed in the galaxy.

So there's not a lot of that. There's just a few particles per cubic centimetre. So that's very rarefied. To give you an idea, if you take a cup of tea and you expand it out to the same kind of density, you'll get a volume about the same size as the moon. So there's almost nothing of it. there's not quite nothing, and that's the difference that makes all of this interaction happen. So the solar wind blows outwards. It blows a bubble in the interstellar medium, which goes out

past Pluto. So it's an enormous volume in space, out to about 100 times the distance of the Earth from the sun. And eventually that collides with the interstellar medium. And at that point, actually, we form a lot of shockwave forms called the termination shock. And gradually that material interacts with the interstellar medium. The sun is actually traveling through the interstellar medium at a number that we know remarkably precisely, about 25 kilometres a second.

So you can think of the sun blowing a bubble and then that bubble itself plowing through the interstellar medium and that has a bow wave in front of it, like the wave of a ship. So it's this very complicated interaction where the plasma blows outwards from the sun, it eventually gets this shock wave as it's plowing through. So if you think about the life of,

let's say a proton in the sun, So it was born, it collapsed into the sun in a nebula 4 billion years ago or something. It's been inside the sun the whole time, very hot barreling around. At some point it pops out into the corona, gets accelerated away into the solar wind. It takes it about a year to get out to the termination shock into the interstellar medium. And after that, these particles drift off into interstellar space and they'll never come back again. So the solar wind that blows outwards, I always feel sorry for these particles because they've had this very exciting life inside the sun. And as soon as they leave, they have this exciting, you know, a few months going through the solar system.

And after that, they're left to just drift through the galaxy for the rest of the life of the universe. So they're still around, but they're just drifting. They're long gone, that's right. So the sun is losing material all the time this way that's blowing past us. But actually, we don't need to worry because it's, although it feels like a lot of million tons a second, it's actually nothing in the grand scheme of things, and the sun will lose less than 1% of its mass over its lifetime. So it's not something that we need to worry about. No, it's still got four billion years to go.

That's right. We've got a while yet, that's right. Andrew, Andrew Coates, there's the slow solar and the wind and the fast solar wind. Are they different in other ways from being fast and slow? Yes, certainly the speed is very different,

so it's about double the speed for the fast solar wind. So it's about 2 million miles an hour rather than 1 million miles an hour. And the fast solar wind, the difference is where it's coming from on the sun. The sun has these things called coroner, holes, which are regions of the atmosphere where you get effectively magnetic field, which is open. And that can go all the way out, all the way to the very edge of the solar system, the helipause,

and then connect and come back in again. So that's open. So those particles find it very easy to move along the magnetic field. And so that fast solar wind is going out in those coronal hole regions. The slow solar wind is coming from more like the equator of the sun. I mean, we don't know the details of exactly how either of those are actually coming out. It's roughly right. The slow solar wind is coming from those equatorial regions

where you have more closed magnetic field configurations on the sun. So you get the fast wind and the slow wind, and the thing which is distinguishing them really is where they come from. You can see differences in the composition, so differences in the amount of helium compared to the amount of hydrogen Most of it is hydrogen, but the amount of helium changes a bit between those. But yes, it's where it came from on the sun, which is causing a difference. Helen Mason, how does the sun's activity vary?

And how does that affect the solar wind? So the sun has an 11-year cycle of activity. At certain stages in its cycle, it has a north pole and a south pole like the Earth's magnetic field has. this actually swaps over. It's actually a 22-year cycle because it goes from north, south, south, south, north, south. So it's actually a 22-year cycle of activity. Now, at the moment, the sun is quite quiet. We have very little... Should we be thankful for that? Yeah, we should at the moment. I don't have to worry about it today anyway. It's quite quiet, although there is a little active region going around and there has been a small amount of activity, so don't get too complacent here. but I mentioned sunspots earlier and sunspots are one sign of activity

and when there's very few sunspots there's very little activity but when there's a lot of sun spots then we can have a lot of activity on the sun a lot of these disturbances a lot of explosions causing these solar flares and this coronal mass ejection there's big ejections of material

this is determined by the magnetic field erupting from the from inside the the sun basically. And it's quite a complicated process, which I have to admit, I don't even fully understand. We're not too sure why it's 11 years. But this cycle has been measured over a long period of time

since the early days when Galilea, for example, studied sunspots. And so we don't know why this happens, but it happens. Well, we know in general terms that how the magnetic field is formed and we know how it erupts through the surface. but what I'm saying is we don't know precisely why it's 11 years. I was about to say, is there any play on this number 11? Does it have any other significance in your systems? It doesn't have any other significance for me.

Other stars, of course, we can measure activity and flares on other stars and other stars have different activity cycles. And this could be related to their rotation rate and other aspects like that. So we can learn something from studying other stars as well. a very complicated field called helioseysmology. Right. Tim, Tim Horbury, have we said enough about the interplay of magnetic lines on the solar wind? No, I think we've heard quite a lot about the magnetic field and it's really central to the behaviour of the solar wind. It's important to realise the difference between the plasmas

that we're talking about and the neutral fluid. So when you take... Plasma which is coming out, which is the... Exactly, that's right. So it's charged... Heated up air, really. That's right. Which is heated up water, which is heated up. solids. Right, that's right. No, exactly. So you take a solid and you turn it into a liquid, then a gas, and then a plasma. And that essentially is so hot that we've ripped the electrons off the atoms. So we're left with separate, positively, negatively charged particles. And when they're charged, they can feel the effect of the magnetic field. And actually, it's the interplay of the magnetic fields with the charged particles that generates all of the complicated behavior that we see. So when

we think about the solar wind, we think about the particles. We should also think about the magnetic field. So for example, when Helen talked about the effects of the Earth in the aurora, that's all about the interaction between the magnetic field that's carried by the solar wind with the Earth's magnetic field. So it's important that we measure it. So when we send spacecraft out into the solar wind, we measure the pastcores in interplanetary space and we also measure the magnetic fields. When we send these spacecrafts out, aren't we worried if they get too near the sun? They might be affected by the sun, like melt. Absolutely. And no, it's a big deal. So one of the spacecraft that's been launched recently

that people have been wanting to launch for a very long time is something called Parker Solar Probe, named after Eugene Parker. And for a long time, since the 1950s, people have wanted to send a spacecraft as close to the sun as we possibly can to measure the solar wind when it's really young, precisely to be able to distinguish these theories

about how it's made. And the reason we haven't done it until it only launched last year, many decades after people wanted to originally do it, is precisely because we had to wait for the technology to catch up. So that's a spacecraft where the front of it gets to something like 1500 degrees.

So it's an enormous engineering achievement to be able to make these kind of measurements. What do you hope to find with all this activity on this exploration, Andrew? Well, we're trying to basically find out how the sun works and how the solar wind is expanding. I mean, that has effects on humankind because, I mean, we mentioned the effects

in the atmosphere on the surface of the Earth and effects on satellites. And we want to understand really, is the science behind a field called space weather. So space weather, as Helen was saying, I mean, the Met Office are now predicting space weather, because the weather in space is very important. I mean, while the Apollo astronauts were on the moon, actually,

there was a very large solar eruption, which luckily was in between two of the Apollo missions. Luckily, they weren't on the moon, actually at the time when that went off. Had they been on the moon, that could have been fatal. And so is that a huge consideration just protecting the vehicles? It's a big consideration. So, for example, I mean, we're sending a spacecraft to Mars this year as well, which is going to be traveling through the interplanatory medium

before it actually gets there. So we've got to be sure that that will survive the radiation in space. So we need to know at any point in space what the radiation conditions are going to be. So, I mean, the solar wind and the energetic particles from the sun are very, important part of what makes up that radiation environment. There's also radiation from the galaxy, which is affected by the solar

wind and by the presence of the solar wind. Because we have the importance of the magnetic field, which has been talked about already, and the orientation of the magnetic field, compared to the Earth's magnetic field, critically affects how that interaction happens. So we have that

magnetic reconnection process, which Tim mentioned earlier. That happens in the Earth's environment as well. So we have you can imagine this a little bit like a banana being peeled as if we have obviously directed magnetic fields upstream of the earth, you suddenly get a connection, a magnetic connection from the stuff outside to the stuff inside and that peels back over the whole earth like a banana.

And then you get reconnection in the tail as well and that's what shoots the particles towards the earth and some of those get trapped also in the radiation belts. So there's the radiation environment is very important. And the radiation belts of the Earth and other planets are also hazardous to spacecraft. And so we need to be able to understand all this to get the, you know, where we can basically fly our spacecraft. Helen Mason, you've worked on many space missions. What have you learned from the early ones?

Oh, I've had a fantastic life in working on space missions. I've worked on Skylab, Solar Maximum Missions, Soho, Hinodi. It's been amazing. These missions are both jointly with NASA and with the European Space Agency, ESA and the UK. From the early ones, well, as we said early on, we weren't quite sure where the solar wind was coming from. But as I said to you, the atmosphere is very hot. We've said the corona is very hot.

And because it's very hot, it emits strongly in x-rays and ultraviolet light. So it shines very brightly in x-rays. Now, the early Skylab instrument had an x-ray instrument and we could see these coronal holes, these regions where the magnetic field. field is open very clearly, and they were able to correlate these directly with the fast solar winds. So some very early results there showing that. I personally worked on solar flares,

active regions, and on the Soho spacecraft, I had the pleasure to work on some corona holes, and we were able to determine the source of the fast solar wind precisely from the measurements that we made, measurements again, that we made with these spectral lines. And we find that if you have like a crazy paving, they were coming from the edges of the crazy paving. We could actually see where the source is. For me, it's very exciting. The sun end is very exciting.

Where the solar wind is coming from, how these explosions take place, why the flares happen, why we get the coronal mass ejections, what triggers them. So that's the aspect that really thrills me. Well, the flares as unpredictable as volcano. Well, like volcanoes, you do get some warning

and we can see the regions getting much more complicated but we are looking for more specific measurements of when it can build up that instability can build up and then can suddenly erupt like a volcano so we're looking for ways to measure that and that's kind of something we're really pursuing. What's the goal of this new, the Parker Space Probe, Tim. Right. So, yeah, so Parker was launched in August 2018. And Helen's talked about measurements that we make remotely with telescopes to look at the atmosphere.

Before you go on, Helen was talking about the very first one, Skylab. And now I've got this one. Is it possible, briskly, to say what development has been in the machine itself, in the spacecraft itself, in those years? Yeah, so the technology's changed enormously. So the early ones, even things like the computer power that's available to us, so that spacecraft are little computers flying in space and so the technology that's available is much better. As I mentioned, it's actually very hard to send a spacecraft very close to the sun precisely, as you say, it gets very hot. So if you think about Parker Solar Probe, it's gone, if you think of the distance from the Earth to the sun as being about a metre,

Parker Solar Probe is going to get to about five centimetres away from the sun. It's enormously close. It's essentially going to fly through the atmosphere of the sun. And so the technology that's been developed to be able to do that is even things like it's powered by solar panels. Those solar panels would melt if you put them out in sunshine at that kind of distance. So it actually cools them with water and it puts them in the shadow when it gets close. It's an enormous technological enterprise. So an enormous amount of work has been done to be able to fly a spacecraft that close.

And the reason that NASA have done that is precisely to look at, to measure the conditions in the sun's corona, to be able to distinguish between these different models for how we heat the corona. We talked about waves versus magnetic reconnection. So Parker Solar Probe's job is to fly screaming through the atmosphere of the sun and to actually measure those processes in place in a way that we've never been able to do before because we can look at them remotely with telescopes like Helen's talking about,

but there's nothing quite the same as actually measuring the particles and the magnetic fields when you're there. So I've talked about the solar panels. What else is new compared to the skyline? What else is exceptionally new is what I'd like to know? Right. So for Parker Solar Probe, it's got a very big heat shield on the front. It essentially hides behind a big heat shield because all the instruments would melt if they actually saw the sunshine. So it's sort of cowering behind this big heat shield.

Another issue is that as it goes really close to the sun, we actually can't communicate with it. So the spacecraft has to be completely autonomous. It has to live by itself for weeks on end without any communications and without any control from the ground. So to be able to make sure you point exactly at the sun. If it points the wrong way, then it'll melt. So it has to keep the heat shield in front. So the technology that's been developed, I believe it's been described as the most autonomous spacecraft ever built.

So it has to live by itself. You let it go, and it has to do its own thing for weeks on end without anyone talking to it. So that's an enormous technological achievement. Andrew, Andrew Coates, there's to be the Solar Orbiter mission as well, perhaps going to be launched next month. Can you tell us about that?

Yes, so this is the new European Space Agency mission, which both Tim and ourselves are involved with. So this is going to be measuring the magnetic field and the solar wind directly. And it will also, so it measures the particles and fields. So it measures the actual solar wind. And then it also has images on board. And what it's trying to do is to make the link

between what we see in the solar wind and what we see on the sun. So that's the first time that really will have been done properly. So it will fly close to the sun. as well, not quite as close as Parker Solar Probe, but they will work very closely together. It flies it inside the orbit of Mercury, so it goes quite a long way in towards the sun, but it will really complement what's being done with Parker Solar Probe. So that combination is amazing. So it will be able to measure the solar wind itself, try and link back to the sun, and then at

the end of the mission, it's going to tip out of the plane of the planets just by 25 degrees, but that allows you to see the poles of the sun for the, really for the first time. So that's the first time that will have been imaged. So there's a huge number of new firsts on this mission. But measuring the particles, the fields, the visible, ultraviolet radiation, all of that coming from the sun. And putting that together into a picture where you can understand how the events on the sun are actually propagating into the solar wind

and creating the effect. That's what we hope to get with... It's extraordinary thing about these complicated craft out in space, behaving very intelligently, not on their own guided by here, but it's... Behaving intelligently because they've been programmed by people to do so, hopefully. I wanted to add something to what Andrew was saying. And there's an instrument, one of my favour, I'm very excited because I've talked to you about the bar charts and the spectra, but there's an instrument with the UK leader at Rutherford Appleton Lab,

which will be looking at the source, we call it the source region of the sun. And one of the things that Andrew mentioned was the materials that come off the sun. Now we know hydrogen, helium, but also there's lots of trace elements there, carbon, oxygen, or sulphur, silicon, very small quantities. But these change in different parts of the sun. And with this particular instrument, we'll be able to link directly what we'll be able to link directly what we see on the sun and what we measure as the

abundance of these elements on the sun with what we sample in the solar wind. So this is a kind of unique feature that we'll be able to directly trace through. Yeah, and actually, I mean, Helen And Andrew mentioned solar orbiter in the kind of involvement in the UK. To be parochial, solar orbiter has a very large United Kingdom involvement.

So here at Imperial College, we built the instrument that will measure the magnetic fields in space. I'm a bit biased about magnetic fields. Andrew's institution built the instrument that's going to measure the particles in the solar wind and then as Helen mentioned also in the UK the instrument was built which is going to measure remotely the temperature of the corona

and even the spacecraft itself was built in the UK so the spacecraft was built into Stevenage and so it's actually a remarkably United Kingdom mission it's a European mission and also with American involvement but the UK community has really played a leading role so we're all very excited for the launch in a couple of weeks wouldn't have been great if it had been called Stevenage

wouldn't it well there's still a chance to rename it not I don't know so these are often so you anticipate great things from these from these two interchange information oh it's really going to revolutionise the field of sort of understanding of how the solar wind is coming away from the sun

and try to understand you know the conditions in which the different planets are and so you know really will help to understand why that corona is so hot and then how the solar wind expands and making that link, seeing the poles for the first time. I think all of that is just amazing with these missions. Yeah, one aspect I'd like to bring out is the fact that we work together, not only teamwork in each of the instruments, in each of the satellites,

but also with our colleagues between different satellites, between different observations. So we're already planning joint observations, for example, with Hinodi, which is a Japanese UK, a NASA instrument. So we like to work. We get the maximum amount of information if we pool together a lot of the observations and also to work with the theoreticians as well, of course, to try and understand those observations.

Well, as we learn more about the sun, Tim, do we find it different from anything else that you see? Yeah, I think it's one thing we haven't sort of mentioned yet is that if you look up in the night sky, you see the stars and so for so long people have wondered what does a start look like and of course it's worth remembering the sun is a star and we know what stars look like we have one in our backyard so by studying the sun that gives us insight into lots of other stars the sun is a type of star there are many others and some of those other stars also have stellar winds which blow in different ways to the sun and so on and also the basic physics processes that we measure around the sun we've mentioned magnetic reconnection waves and so on those processes happen in plasmas across the universe. And so by studying the sun, we understand more about how the universe works.

And also, Andrew mentioned about how the solar wind interacts with the Earth and other planets. That we know happens at exoplanets, planets around other stars. So by measuring the solar wind, we also understand more about how other solar systems work across the galaxy. Yeah, I think it's a really

fundamental thing because our magnetic field has sort of acted as a cradle for life on Earth in some sense. It's protected us from the solar wind, So we haven't stripped the atmosphere, you know, the atmosphere hasn't been stripped away. So really the importance of the magnetic field and those interactions, both in our own solar system and beyond, are vital, I think, for life elsewhere. So we know that life developed on Earth.

It's the only life we know of at the moment in the universe, and that magnetic field may well have caused a cradle for that. Well, thanks very much to Andrew Coates, Tim Horbury, and Helen Mason. Next week, it's Alquin of York, the 8th century Northumbrian, at the heart of the Caralingian Renaissance, who promoted learning for its own sake under the patronage of the Emperor Charlemagne. Thanks for listening.

And the In Our Time podcast gets some extra time now with a few minutes of bonus material from Melvin and his guests. Do you want to go first? No. So I brought show and tell. So I brought along a book. So this is the book, it's called The Solar Wind.

So this is the first Solar Wind conference that was held in the California Institute of Technology in Pasadena in 1964. So just two years after Marshall Norgo about how first measured the solar wind. So this was the first meeting and the first paper, of course, is Marsha's paper describing those first measurement. And actually it's a fascinating record of those early observations. And to me, what's amazing is already in just two years how much progress they had made. And you can see the remarkable speed at which we talked about

Eugene Parker's theories being very contentious. They absolutely were when he first published them in 1957, 1958. By 1964, it was completely accepted. and I think his work was so timely but also it was contentious because we didn't have the measurement and I think as soon as we had the measurement pretty well everybody almost immediately accepted that his theories were right so I think it's a really interesting example

of how a theory is contentious and as soon as it's confirmed by measurement the field shifted. Was there any sense of... I'll just ask one question, was there any sense of the very early days of competition between various countries to. Absolutely, yes. In fact, yes, I was asking, I was wondering, actually if Marsha had referenced

the Russians, because the Russians actually got there first in terms of the solar wind measurement. So in 1959, they had a probe which went to orbit, and they actually found evidence for the solar wind. So Constantine Gringhouse might have been the name that people use rather than Marsha Neuagabal, but, you know, they were going at about the same time, doing the same thing, and it was a huge question at the time as to whether the solar wind was there or not. And I think there was one distinction was that lots of people had an idea that occasionally

there would be puffs of material off the sun. And Parker's theory is that it's a continual flow. And Marsha's instrument actually measured for months on end and said, look, it's not individual puffs, it's a continual flow. And I think that was the big kind of conceptual change. There are interesting times in the solar wind when you lose the solar wind completely.

There was a day when you'd completely lost the solar wind. much more recently than those early measurements. And that causes the Earth's magnetic environment to expand significantly. But there was just one event which has been discussed like that. So the presence of the solar wind is very important. I think we had a paper about that. Yeah, there you go. There's one thing that I would like to mention, which we haven't mentioned.

And I mentioned the eclipse observations, which of course are fundamental and very short. and the eclipse observations give us information about the structure of that solar corona and you asked me about the differences between minimum and maximum and the eclipse looks very different during minimum and maximum. During the minimum we see long streamers at the equatorial regions. During maximum we saw a more homogeneous emission. But we can simulate eclipses with an instrument called a corona. and a very clever instrumental guy called Leo first developed this ability to do this on Earth.

But we have also flown these coronagraphs in space. Early on in Skylab had a coronagraph, but also the Solar Maximum Mission and Soho. But we can see puffs of material coming out from the sun with these coronagraphs. And there are others. And I think this is quite important. for bursts of material, which can be quite problematic, as it were, besides the fast and the slow. There are these sudden shocks of material which can impinge on the earth. And there's another interesting technique which we're going to use in the future

to actually try and image how the solar wind interacts with the earth. So rather than just making measurements at a particular point in the solar wind, we're going to be trying to measure the whole of the earth's environment. So this is a process called charge exchange. What we can do basically is sort of take an X-ray picture of the Earth, and that will tell us where the shape, where the cusps, the magnetic cusps of the Earth are, and where the whole solar wind interaction region is.

So we'll be able to watch that breathing in and out. And that is amazing. That's a European Space Agency and Chinese Space Agency mission going in 2023. So in the future, we're going to be able to sort of see the whole effect of the solar wind on the Earth environment. So that's another exciting mission. soon in the future. Yeah, I think we're really entering a new age of

understanding of the solar wind. We've got a fleet of missions going in the next few years. So Park Solar Probe is already down there, close to the sun. And I say, my one solar orbiter, so if people are going to look out, are listening to this in the near future. It's due to launch on the 6th of February, about 427 in the morning UK time. So stay tuned.

And let's hope it all works, and the rocket works okay, and we get it into space. Fingers crossed. In addition to that, we have a new. new Indian satellite going up called Aditya. It's due up this year. And that will have several instruments to study the sun as well. So truly international effort. Do they divide up the bits they're going to cover these different missions? So there's a central council saying, no, we're doing that bit. You can have the other bit. Not really, but they try to complement each other, I think, in some ways. There's

no good repeating something somebody is already done. So obviously there has to be a novel aspect. Right. Yes, there's a lot of comparisons to down at international conferences. So there's a body called Co-Spar, the Committee on Space Research, which is a UN-based thing. So that has a sort of overview.

But yeah, people try to make it as complementary as possible. So NASA and ESA have certainly done that with Parker Solar Prove and Solar Orbiter. And actually Solar Orbiter was approved first. I remember being on the space science panel at ESA, which approved this back in 2000. So now 20 years later, we're about to launch what is this amazing mission

to make that link between what's happening in the solar wind and what's happening on the surface. So, exciting, but 20 years to get to to get to this point. From what you're saying about cooperation, it seems to me that the competition which you spoke about earlier has disappeared,

has it? Oh, there's still scientific competition, of course. I mean, for example, Parker Solar Probe is there first, you know, before solar orbiter has actually got up there. But the idea has been around for a long time. Yeah, but in terms of the communities, they cooperate very closely together.

So at Imperial College, we built an instrument for Solar Orbiter. And a bunch of people that are on my science team are people in America who built the instruments for Parker Solar Probe. And I'm on their science team as well. So we all collaborate with one community. And so, as Helen mentioned, the only way to make progress is to put all the data together. And actually, what you end up with all these spacecraft is essentially a constellation of spacecraft measuring the entire inner solar system at one time

and putting that together gives you a much better global picture of what the sun is doing. And similar, sorry, I thought you wanted to come in. No, I'm fine, sorry. Similarly, with our solar wind instrument, so Chris Owen is the principal investigator for this, and we've built the electron part of that. But the iron part comes from France, and that's going to be measuring the solar wind ions, and then the composition part is coming from America.

So very much cooperative international collaboration is absolutely the name of the game. Actually, I will come in. I've worked with NASA for most of my working life, and I'm very honored to do so with colleagues in the States. I was part of the Skylab workshop series back in the late 70s, early 80s. And we worked to understand the data from Skylab, but those people that I worked with, I've kept in contact with all my life and still worked with on different projects.

So we work very closely between NASA and ESA and Europe and also with Japan, with the Japanese missions that I've mentioned and now also with India. Yeah, similarly for me. I mean, I've been lucky in my career to be able to work on the solar wind and its interactions with many different objects in the solar system. So starting off with Earth and then with Halley's Comet, the Giotto mission to Hallis Comet,

the Cassini mission to Saturn, the Venus Express mission to Venus. But the thing which brings those together, is the solar wind and that's the the link, the scientific link between these things. So we can see how that solar wind is interacting with all these different objects. And it's been a pleasure to be able to work on that. Did you want to mention Bepi Colombo perhaps? Yeah, Bepi Colombo on the way to Mercury.

So, I mean, that again, you know, and that's very interesting because Mercury is this tiny planet which has a magnetic field. So it's a little bit like the Earth to some extent, except there's no atmosphere. but yes, that's on the way to Mercury that gets there in 2025 and the solar wind interaction there is going to be very important. So there there's a Japanese spacecraft called Mio which is going to be measuring the solar wind in its interaction with Mercury. And the European one, the Mercury planetary orbiter,

will be measuring Mercury itself. And so you can do that wonderful comparison between two spacecraft to another planet. The dynamics of how the spacecraft actually get there is very interesting. Interesting. Parker Solar Probe and Solar Orbiter have both used Venus, but really to slow the satellite up and bring it towards the sun. It's actually quite difficult to get towards the sun. So that they need to use the planets as a sort of catapult or bringing it in.

But Mercury, the Beppe Columbus, taking quite a while to actually get there. But that's because it's got to slow up a little bit to get into the... Yes, it's why there haven't been many missions to Mercury. It's actually really difficult to get to. so I mean first of all, Marin Aten did it and then the NASA Messenger mission but then Beppe Colombo which is joint between the European Space Agency in NASA

absolutely this will be using the slingshot type of idea to slow the spacecraft down eventually get it to go into orbit. I presume this is enormously expensive does anybody up there ever ask you what they're going to get out of it what is going to prove to help I don't know, the economy or whatever

You know, we all go and give talks to schools and all these kind of things quite often. And occasionally people ask, so solar orbit's a total mission cost is probably going to be something like 1.5 billion euros from the beginning to the end. That's quite a lot of money. But that's shared between NASA's putting in quite a lot of money. It's paying for the launch, for example. And that's shared amongst the European, the ESA, European Space Agency member states over 10 or 20 years or something. So I think the European Space Agency Science Program is something like one or two pounds per person per year in the European EU, ESA member states like the European Union.

So in the grand scheme of things, it's expensive, but it's not that expensive. And I think we learn a lot. We've talked about space weather, the important economic impact of these kind of things on the Earth. But also we do astronomy missions, which have exactly no impact on us. You know, measuring black holes or something. It's never going to affect our lives on Earth. I'm interested in that and I think a lot of people are interested in learning about the

universe at a relatively modest cost I think and so I don't really ever experience people pushing back against it from that I mean I think the answer or an answer to this is we're fundamentally interested in our place in the universe you know why is mankind here

why are the planets like they are they're abased by the sun so all of this actually the science is kind of trying to understand why you know ultimately why we are here, you know, and what it's like and what the conditions are like. So it's really understanding humankind's placed in the universe, and that's the way I like to think about it.

Thank you very much. I think the producer's impatient to give you a message. Who would like tea or coffee? Can I have a tea? Thank you. Coffee, please. Tea, please. Tea, please. Tea, please.

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