About science; About solar winds

This is about science produced by the California Institute of Technology and originally broadcast by station KPCC in Pasadena California. The programs are made available to this station by now if no educational radio. This program is about solar whims with host Dr. Albert here and his guest Dr. Marcia Neugebauer of Caltex Jet Propulsion Laboratory. Here now is Dr. heads. All the early volume of space in between the planets in our solar system is an extremely empty vacuum compared to the atmosphere we're familiar with here on the surface of the earth. Nevertheless it's not completely empty constantly streaming through what are the particles that boil off from the surface of the sun. This is done if you use cloud of particles has been given the name of the solar wind. And here to tell us about it is Mrs. Marshall not about of Caltex Jet Propulsion Laboratory. Marcia Perhaps you want to start out by defining a little better than I have. What is the solar wind. Well the solar wind is a name given to the atmosphere of the sun

which is dreaming outwards through the interplay Terry space continuously. It's not really boiling off. Leaves the sun even faster than that. A better analogy might be with a rocket engine jet propulsion. Where's the jet force because a slight pressure of such is on comet tails or as in something even stronger than that. Now that the sun's atmosphere the sun's corona is so hot that the gases is just like a rocket engine the gas expands outward supersonic planes. The analogy to Iraq it's not as well as about 5 solar radiant from the center of the sun where the earth is it two hundred fifteen so my radio so I most of in a planetary space is going supersonic clay. I see so that the sun itself as I could frame a rocket engine and then the outer corona has a knock on them beyond that there's a super sonic stream out.

Yes but the sun doesn't get propelled by and I don't have first of all uniform in all directions it's a very small but it's uniform in all directions and also. The M.O. isn't that great the sun doesn't get rapidly a lot lighter because of this gas it's customary shooting out. It's probably lust don't leave about 1 percent of its total mess during its whole lifetime due to the solar wind and by the solar wind how fast when you say supersonic way how fast is it that it's moving when it gets out. Never We are arrays I assume it can just keep going out into space or doesn't stop anywhere just continue well. It may stop a man OK. Well at least it was far away by the time it gets out of the earth and still moving out of the fairly high clip. Yes it's going about a few hundred kilometers a second few hundred kilometers means that it takes two to four days to get from the sun to the orbit of the year. When it gets close to arguing about

how far it goes before it starts going slower it slows down again and it. Some estimates say this happened five astronomical units and some people are saying at a thousand. As you know nobody's ever observed this to you know I thought that an arm of the unit would take it far beyond the solar system. But right we're still going along that fast what what forces would slow it down other than just gravity. Which is rather see last year lated. Mechanism is that the. Ions in the solar wind collide. Collide with the interstellar gas and exchange their charge with Interstellar. And this was act actually slow down the particle just to enjoy it. You would get a fast neutral particle the slow ion on it so it would bounce something else away. Yes the momentum would continue to go back to magnetic field will get

back pressure on the solar wind too. So it's like blasting a rocket engine into something where there's already a little bit but very little and that's why it's going so so fast. There's a little back pressure and what is the density of the particles in the solar wind. Now where on an average day it's something like 5 ion pairs pretty cubic centimeters I am pairs because I did say earlier that the solar wind is a completely ionized gas. It's mainly hydrogen but it is so hot that the. Proton and electron have become separated completely ionized the density is about 5. Proton electron pairs for a cubic centimeter. That's how does that compare with the density of air here the surface of the earth. It's about one ten billion billion. Factor of 10 to the 19th less. So it's a very hard vacuum. It's better than any vacuum we know how to make and the surface of the earth by many writers is a magnificent thing they're out.

How do we know how what kind of observations have ever led us to discover that there was such things and so that your rarefied wind. Well first it was inferred that some thing had to occasionally travel from the sun to the earth. Because. It was noticed early in this century that following a solar flare on the Sun two days later there would be all sorts of noise in the earth magnetic field compass needles would bounce up and down and be what's called a do you magnetic storm. It could not have been light from the sun which caused this to happen because it would get here in a few minutes. It had to be particles which were traveling at about a thousand kilometers a second. Then back out in the 1950s. Professor Bearman the Max Planck Institute in Germany. Decided that this flow of particles from the sun was probably

continuous instead of just a now and again thing falling flares. You base this conclusion by observing that. A certain kind of comet tail is always pointed almost directly away from the sun. I see instead of being a curved tail too and drawing another kind of thing. Yes some comets actually have two tails. The one kind is the dust tail which the solar wind does not interact with much of the others. The tail of ionized gas which a solar wind pushes Iran to this point almost right away from the sun it can push it around because the solar winds ionized too is probably the direct interaction mechanism what links the two people. This theory isn't completely worked out yet but it almost certainly has something to do with the magnetic field carried by the stellar wind is when the solar wind is a very. High rise gas with a very high. Electrical kind of activity. When it leaves the sun part of the sun's magnetic field is trapped in this

gas and can't get out of it. And part of the sun's magnetic field is. Carried out into space by the solar wind. And this so when this or when that hits a comet both the particles themselves and this tracked magnetic field. On a comet tail. So with this observation he concluded that there was a solar wind around not just in Florida where the results were but all the time until you know he's noticed when he did find the tail of a comet of this type it was a steady phenomenon as of now the sun didn't come and go. That's correct. And since then we have also observed the solar wind from space vehicles just within the last few years. What kind what artificial satellite do would you have to something you never get further from the earth and that the solar wind cannot penetrate close to the earth because of the Earth's magnetic field this is a hole in itself. This

interaction you mean acts like medically alertness if they were in our solar wind the Earth's magnetic field you left the Earth would just gradually get weaker and weaker and weaker but you could always if you had very very good instrument you could theoretically always measure it. But turns out that the. So a win pushes this in and the sunward side of the year which is the years back towards the earth. Confines it to a cavity which has been named the magneto sphere geomagnetic cavity. She too is a definite boundary between the earth's magnetic field which stops someplace out in space and the magnetic field is coming along with the solar wind and runs into it. That that's right in this cavity that the magneto sphere might first and think it was a ball but turns out that it it's teardrop shaped. People don't really know how long the tail what's called your magnetic tail or the end on

the tear errors. It may go on for many hundreds of thousands of miles we just have never made measurements yet that far from the earth that were conclusive. But at least on the side of the earth toward the sun it's pushed in toward how far out is it from the earth this boundary of the Earth's field and we can say about 10 or to radio which would be about sixty three thousand kilometers 40000 miles out you know and the does it stay there pretty definitely Or does a wobble back and forth. Well I guess I was a scale. It stays pretty much cooked. But as a satellite some sell it to very high Apogees when they go very far from the earth earth interplanetary probes as they leave the earth. They will go through this surface and often they go through it several times and one trip away from the earth. They go through it. Then the surface will catch up with them again suddenly

they find themselves inside the years field for a little while and then will be back and interplanetary space. So it has some sort of motion. Which isn't very well understood yet just what the causes of these motions are what the size of them are. But you have to get outside of this wobbly an invisible wall. The earth's magnetic field to measure the sun's. Actually have to get it even farther than that because there's another complication outside. Of what's called the magneto cause this end of the Earth's magnetic field. There is what's called the earth's bow shock which is a shock wave which is set up in this stream just like in a supersonic aircraft. There's a shock set up ahead of its wings that steers the glowing air around it. The Earth's due your magnetic field in the dimming that field has a shock front ahead of it. And this is typically. Three your fourth

radio in front of the magneto prize again so it's maybe 14 Earth radio away. So you have to get even beyond that before you can see the undisturbed interplanetary. Well then I suppose a probe like the one that went to Venus certainly well outside of this and then you know toward the sun it was possible to make find ways of nice clear measurements of solar wind to get any measurements from. Yes in fact this was one of the. First experiments that. Made fairly detailed measurements that were clearly far enough away from yours not to be affected by this was a mariner to have. How close did it get to the sun measurement and how long did it. Well it's still flying but we can't use for how long it worked for about four months from the end of August 1962 until the end of December that year. We got useful data during

that whole period of almost the whole period of four months. It got it operated about two weeks after it passed beingness and they got in to about point seven seven tenths of an astronomical unit. So that we could see how the solar wind varied over that distance. And that's about where Venus is about seven years it got only slightly inside Minas of intensest for we are what sort of instruments can you use on a spacecraft to measure this extremely rare applied stream particles. Well there are several kinds of happy news they all have several properties in common the particles in the solar wind have so little energy that you can't use ordinary detectors like Geiger counters or things like that because the particles don't have enough energy to get through the window. The geiger counter. So you have to do something that's just completely open to space. And all detector so far have used some form of electrostatic analysis that has pushed the particles around

with an electric field in a certain way and then. I certainly want with a certain range of energies will get through your detector an electric field will push all the others particles out of the way. Then you measure how many particles are each energy. Theoretically you could also do a magnetic analysis by pushing the particles around with magnetic fields. But then but then you have to measure the particles themselves or some extremely sensitive detector on the hand. How do you actually count a particle to measure an electric current. Yes we actually have a collector to measure the total number of particles which enter this collector per unit of time one of the big challenges at making the current detector Tramadol has to measure. Micro micro amperes are hundreds of a micro micro ampere So they're very small and paired which you get in a light bulb.

So the instrument then takes this these charged particles and distorts them or changes their path of the electric field and the ones that manage to negotiate the change paths get collected and I measured it I started to say that we could also do this with a magnetic field. But people haven't done this yet for positive ions because it would take a very large magnetic field. That because they're so heavy. Yes they have high momentum for this the last of me. And you want to also measure what is the magnetic field in this plasma that what is in my neck you know has been carried out from the sun by the solar wind. You don't want to send a sensitive time or rather to measure the magnetic field of your plasma detector Masowe you have so if it was set up such a big magnetic field you'd swap the measurements of the other. That's right so so far. People have used magnetic analysis for electrons but it's been like just that except for Boston heavier positive ions. What about the numbers you got from these measurements of the numbers

you've given us before about speeds and densities. The ones you measured on merit to pair with theory and other measurements would sort it in other words. Did you get a consistent experimental picture from basically from the solar wind measurements on to. Well explain as far as comparing one experiment against the other. All the differences you can say well this if you observe any differences you can say something has changed back on the sun you can always blame anything on the sun rather than blame it on your instrument. And things haven't changed that much during 1062 we saw. The losses which ranged from. Close to 300 kilometers a second to maybe up to almost 800 kilometers a second. While on the EMP satellite which was a year and a half later when the sun was close to solar minimum they saw slightly lower velocities as of last

days sometimes close to 200 kilometers a second and the average is probably less than 400. The solar minimum is a time when the sun spots are the least active and when there are the fewest sunspots and then there's a sort of maximum who years later. Yes this is a sun spot cycle 11 year that 11 years on it and the solar minimum which just last year would. So yes I see that you were. So this amounted to when just before this or that it was still was I was still fairly active. So your measurements on of particle speeds were a little higher than this so and they have observed what and without is a particle. They were comparable. They didn't change very much. Now as far as comparing the observed observations with theory people can. Have made theories which can explain the density in the velocity of the solar wind fairly well I can explain in detail why some days it's higher than other days but the

average theory does pretty well. The thing about the observed property of the solar wind that's a little hard to explain theoretically is the temperature. They observe solar wind is a little too hot to be explained by just a hot sun conducting its heat away through the solar wind conducting convecting. We have to invoke another mechanism of heating this gas between the sun and the earth. And probably what is happening is that this gas is so rarefied that one particle seldom collide with another. In terms of mean free path the mean free path for a particle particle collision is. Approximately twice the distance from the earth to the sun. I see so it could go a couple weeks without hitting on a particle on average. That's right. However the particles will collide with the magnetic with magnetic

irregularities in the magnetic field lines have a little bump in them. A particle can collide with this and come away from this collision with more energy than it went in with more or less bending and the kinetics of the interaction. So the magnetic field irregularities in the magnetic field can heat the plasma or cool irregularities will probably tend to heat it. Why is it one way. Well you generate it. Back up a little bit is all a solar wind isn't travelling at the same speed. Ok what a fast bunch of particles catches up with a slower bunch of particles ahead of a magnetic disturbances or generated energy is transformed in a flowing motion into magnetic field irregularities the wheel gets by being in mixed around. This. Then we'll transfer some of this extra energy will eventually be transferred into the random motions of the

particles. It's a matter of entropy in the long run. But once it's under the random motions of the particles and serene The path is very long and we would you know bump around an equalizer. Well these magnetic irregularities are all moving in the same direction. Now that when you get into a fine theory of it there's in plasma theory you can show that. You cannot have a very an isotropic motion if you are in the system of the gas its moving away from the site you're traveling with the solar wind. The random motions of the particles would be random they wouldn't be going more to the left than to the right and more ahead than back and because their instabilities was a core plasma instabilities which will take over if you ever get too lopsided distribution of particle motions the fields in the particles which interact in a certain way and again be straightening all out interaction with it

through the magnetic field of the next article. That's right it's always a particle field interaction and the whole works are so very conductive and Israel is an integral part of it. What effect does all of this have on the behavior of the sun. The magnetic field of the sun is being as you say carried away along with a small amount of the material from the surface of the sun and supplying energy to drive this whole mass eventually that energy has to come from the sun. How does a how does a wind react back on the sun. Well it probably. Doesn't react in in a gross way it doesn't change its mess much. The whole life of the Son is probably only creased by 1 percent. The energy loss isn't very great. It's much much less than the energy lost by sunlight about a tenth of a percent is lost as energy is lost in the solar wind as in.

Sunlight the effects it might have. It's possible that the solar wind slows down the sun. It may carry away a very appreciable amount of angular momentum principally due to the magnetic field and it certainly distorts the magnetic field shape of the sun the sun does not have the same magnetic field shape that it would have if the solar wind were not going away. People have seen structures of the solar corona seemed to be sort of drawn out into space and this is probably ionized gas to following the radio field when it's closed. It's not a nice dipole you know as the Earth's magnetic field. No it's much distorted from that so this would be the major effect of the field back in the sun as the angle if I can I get a momentum and feel distort lauds effect of the field and the angle Romanum change isn't very well known but there are some theories that have which still look reasonable which say that this is power been important and that one of what effect does it have on the earth outside of the

bow shock against the magneto sphere. Well several. Of the particles in the radiation belts may or may not have come from the solar wind. There's two schools of thought on this. Perhaps the outer belt particles originally came from the solar wind crossed that I'd meet us here and then became slowly accelerated into other the energies that we see the particles in the radiation belts more energy than particles in the solar wind they could've originated there. Yes it's hard for them to get in but there are some takes elaborate theories to get them through the day. That's why you have this you are right about the frictional effects and wave motions and things like that. Aside from the radiation belts the solar winds probably at least indirectly responsible for your are the Northern Lights indirectly get people the particles we see in the Aurora are more energetic than

what you see in the cell and some people are saying that perhaps the particles in the Aurore come from the solar wind to the zones by coming up through the tile. Then that made us fear up to do your magnet on the stair drop tail you were talking about a little while before all the way out there if you have thousand miles away from the earth or someone with you aren't that lucky are a thousand miles away from the Earth here's a solar wind particles come back with a teardrop all the way back to the earth and that's now entered to make the run. So that's when you very. Fascinating. Well what about simply the disturbing distortions of our magnetic field. Certainly when the solar wind changes. If suddenly the solar wind is stronger if there's more particles traveling faster the magnetosphere will be compressed the Earth's field will extend less far. Out into space. This motion will cause comparable motions down in the earth's surface the compression will cause a higher field to be observed at the Earth's surface because you're taking the same number of fuel lines and packing them in closer to you.

Now the trap radiation which is in the magnetic field cracked and I didna could also be affected. That's your ideal gets hard those are accelerated. They may or may not be. Probably some are dumped into the years that Miss fear this time would not cause any Aurora. That yes the Aurora occur right at the edge of the radiation belts. That's a question whether these particles. I used to have been tracked or if they are accelerated right on this boundary and I'm sure that's been tied down. I see no clear indication then between the crap particles on the road that need a fashion what is there and is there some sort of indication of that when there is a variation in the solar wind I so much that happens when there's a solar flare. But then there's a very good doesn't have to be a solar flare. There these very strange regions on the Sun which are called M regions people have been watching this for. Years in the geomagnetic data to magnetic storm in the face of the sun may be

black that might not even be any sunspots but nevertheless there's a magnetic storm. Yes I better call this origin of these particles on the sun in every region and am reading yes. Can you put it down to a region on the sun and away you just by saying the particles must have left the sun so many days ago. So they probably came from a certain part as Einstein that was even a center then how long does it take the sun to go around once on its axis relative to the earth its 27 days I say because the Earth is moving too. But so so that you could follow a particular region on the sun as it went around once or requires of the uses em region storms or notice to recur every 27 days sometimes a given region of the sun would result in a do you magnetic storm 40 50 times in a row. This is use the same region with nothing obvious and the sun would cause a magnetic storm in years. And is this because of a solar wind effect.

It's only because of particles. Yes yes it is and what about sunspots are they connected with the solar wind. Well we haven't really observed a really big flares yet like you see it solar maximum but almost certainly that higher velocity and perhaps also denser and probably also hotter solar wind comes from the region of the solar flare than from the ordinary surface of the sun. Probably it still does exist. Connection same cellar window only more so more sound. I see so that there are the M regions in the solar flares and both of them have an effect on the solar wind which then affects the magnetic field of the Sonnets angular momentum and the Make Me Feel So on the surface of the earth in a very indirect curious electrical manner. Marcia thank you very much for joining us tonight and telling us about the solar wind. This was about science with host Dr. Albert Hibbs and his guest

Dr. Marcia Neugebauer. Dr. Noah Bauer is a physicist at the Jet Propulsion Laboratory of the California Institute of Technology. Join us again for our next program when two more members of the Cal Tech faculty will discuss a subject of interest. About science is produced by the California Institute of Technology and is originally broadcast by station KPCC in Pasadena California. The programs are made available to this station by national educational radio. This is that I have no education no radio network.