2Fast 2Curious: Finding the source of the fast solar wind

Sarah Al-Ahmed: What can you learn when you fly too close to the sun? We'll find out this week on Planetary Radio. I'm Sarah Al-Ahmed of The Planetary Society with more of The Human Adventure Across our Solar System and Beyond. Some space mysteries just can't be solved without getting up close and personal with the sun. James Drake from the University of Maryland joins us this week to talk about his team's research into the cause of the fast solar wind. We'll sun dive into the Parker Solar probes newest data as it soars Betts will join us for What's up in the Night Sky and a Parker Solar probe themed question for our space trivia contest. Before we start today's journey into the exciting new results about the solar wind, we have an important announcement to share with all of our listeners, especially those of you who are joining us through our wonderful radio affiliate stations. Starting August 2nd, we will be discontinuing the radio distribution of planetary radio. To be clear, the podcast version will continue as always. This is just for the radio side of the show. It was a difficult decision that we've spent many months deeply researching being the scientifically inclined people that we are. Ultimately, our hypothesis was correct. The many hours it takes to maintain the radio side of the broadcast isn't worth the sacrifices we keep having to make to the popular and more commonly consumed podcast version that the majority of you are listening to right now. So, despite how difficult this is, we're excited about this update. These changes will allow us to do things we've never done before, like share videos of our interviews with guests and build upon the success of our podcast. The good news is this may not even be a big change for some of you, but an improvement. All radio stations airing planetary radio are welcome to air the podcast version which features extended interviews with our guests. It and our entire 20 year back catalog will continue to be available for free to stations everywhere. So, if you're listening to this on the radio, you might want to write your station to ask them to start airing the podcast version, and you can always download planetary radio from our website at planetary.org/radio or find it on any of your favorite podcasting apps. I want to send a huge thank you to our radio affiliates and listeners for helping us share The Human Adventure Across our Solar System and Beyond. I know that I and the show's creator and previous host, Matt Kaplan are so grateful for all of your years of support. All right, now for this week's space news. The oceans of Enceladus may contain the building blocks of life. Analysis of data from NASA's Cassini spacecraft, which studied the Saturn system from 2004 to 2017 has found signs of organic compounds. It found them in the icy particles that were ejected from the moon Enceladus into the planet's E-ring. The compounds detected in include phosphorous, one of the ingredients for amino acids that's never been found in an extraterrestrial ocean, until now. Our CEO Bill Nye spoke to CNN about this discovery and what it means for the search for life. I'll link to that video on the website for this episode of planetary radio at planetary.org/radio. China's lunar exploration program is moving along with an international partnership. Russia, Pakistan, The United Arab Emirates, and the Asia Pacific Space Cooperation Organization have all signed agreements to participate in an international lunar research station. It's a project that aims to build a permanent lunar base in the 2030s with a series of stepping stone missions before the end of the decade. And NASA has selected five experiments for the 2024 total solar eclipse. The eclipse is going to be visible from sites across North America on April 8th, 2024 and it's going to be a great opportunity for millions of people to marvel at the celestial phenomenon. It's also a great opportunity for scientists to study the sun. NASA has announced funding for five projects led by researchers at different academic institutions. They're going to study the sun and its influence on earth with a variety of instruments including HAM radios, cameras, high altitude research planes, all kinds of cool stuff, and all with the help of volunteers. You can learn more about these and other stories in the June 23rd edition of our weekly newsletter, the Downlink. Read it or subscribe to have it sent to your inbox for free every Friday at planetary.org/downlink. I also want to wish everyone a Happy Asteroid Day. Asteroid Day is held each year on June 30th. It's the anniversary of the 1908 Tunguska event. It was one of the most recent and dangerous close encounters our planets had with an asteroid Bruce Betts and I will talk a bit about that later in the show. The Planetary Society is one of the sponsors of Asteroid Day and it's always one of our favorite days of the year. You can learn more about asteroid day events or watch their livestream on their website at asteroidday.org. And now for our main topic today, the fast solar wind. Despite living so close to the sun, there's a lot that we don't understand about it. Studying the complex nature of the atmosphere, magnetic field, and other quirks of an object that intense is not an easy feat, but that's not going to stop us. The mystery we're puzzling over this week is the source of the so-called "fast solar wind" for those new to the term, the solar wind is a stream of charged particles, primarily electrons and protons, that are hurled into space from the upper atmosphere of the sun. Most of the time the wind is a gentle, steady breeze, but sometimes it's more like a storm, a fast solar wind gushing out at high speeds. This fast solar wind is vital to understanding solar storms, space, weather, and how they affect our planet. But the source of the fast solar wind has been a mystery for as long as we've been scientifically studying the star over our heads. Now that's where the Parker Solar probe comes in. Launched by NASA in 2018, The Parker Solar probe is humanity's first ever mission to touch our star. It's ventured closer and closer to the sun's surface, braving intense heat and radiation in order to send back unprecedented high resolution data about the sun and its mysterious corona. And one of the key findings? The potential discovery of the origin of the fast solar wind. Our guest this week is Dr. James Drake, or as many know him Jim. Jim is a distinguished university professor at the University of Maryland's Department of Physics and Institute of Physical Science and Technology. He's been instrumental in analyzing the data sent back by the Parker Solar Probe. Let's learn more. Hi Jim.

James Drake: Hi there, how are you?

Sarah Al-Ahmed: Oh, I'm doing great and thanks for joining me on this. I love talking about planetary stuff, but anytime we can get into the sun and the details there, I'm so excited because, let's be honest, it's the biggest thing in our solar system. It's important.

James Drake: Yeah, and it controls a lot of stuff that's going on in our solar system, so that's also a good reason for talking about it.

Sarah Al-Ahmed: Yeah. And the Parker Solar probe is such an interesting instrument because there are so many mysteries about the sun that we literally can't solve until we're right there. But creating an instrument that can get that close to the sun at all is just a feat all on its own, so I'm continuously in awe of this spacecraft.

James Drake: It is awesome and it's producing some amazing stuff, so hopefully we'll get into that.

Sarah Al-Ahmed: Your team's exciting discovery has to do with the origin of the fast solar wind, but before we get into what your team actually found, what is the fast solar wind and how's that different from the regular solar wind that people are familiar with?

James Drake: There's two types of wind that are coming out from the sun. One is known as the fast solar wind and it has of speed of around 800 kilometers per second. And it comes from what are called coronal holes, which are regions of on the surface of the sun where the magnetic field is pointing in a particular direction. And then the slow solar wind is more like 400 kilometers per second, and that comes from mostly active regions on the sun where there's a lot of magnetic fields releasing energy. The fast solar wind anyhow comes from coronal holes. These are the dark regions you see on the surface of the sun. If you look at it.

Sarah Al-Ahmed: The other solar wind, if people were say, looking through a telescope at the sun, would these be things that come from areas with prominences or coronal mass injections, those kinds of structures?

James Drake: Well, the slow solar wind, at least during the quiet period of the sun, the non-active period, of the sun is mostly from low latitudes around the low latitude region. And then during quiet times of the sun, the two poles of the sun are totally dominated by coronal holes and the fast wind then occupies most of space coming out from the sun during active periods of the sun, everything gets mixed up. It's really complicated and they're fast and slow winds are mixed up as they come out.

Sarah Al-Ahmed: The sun goes through this solar cycle over time. When is it more active? When is it less active? How long does that process take? And what's actually causing that?

James Drake: The sun has a magnetic field and this is produced by what's called the solar dynamo. The outer third of the sun is this region where all the ionized gas and non-ionized gas, neutral gas, are mixing around and they're being stirred around and they're very turbulent. And this outer one third of the sun then twists the magnetic field around and amplifies it. And the consequence, of course is all the magnetic field that rises up and then comes out and helps form the corona and the whole magnetic structure of the sun. This has a cycle every 11 years the overall direction of the magnetic field of the sun flips sides, so this is the classic solar dynamo.

Sarah Al-Ahmed: The sun isn't like a solid ball like here on earth. It's all gas and plasma, so does the sun rotate at the same speed at all latitudes or is there some kind of differential rotation going on there?

James Drake: No, there's definitely a differential rotation and the Parker Solar probe mission was named after Eugene Parker, and he's the one who really set up the physical picture for how the magnetic field is generated. And so the differential rotation of the sun plays a key role. It's rotating faster around the equator than it is at higher latitudes. So that differential rotation is a critical part of the magnetic field generation process.

Sarah Al-Ahmed: I love too that this is a probe that was named for someone who was still alive when it launched. That's such a special thing for someone who has contributed so much to science, get to see a spacecraft named after them. I love that so much.

James Drake: I know Eugene Parker pretty well. In fact, he wrote my recommendation letter for tenure at Maryland. You see these people and you watch their career and how they interact and in many ways he's my model. He just kept working and producing interesting stuff up until practically the day he passed away. One of the big disappointments for me is that this paper we just wrote and came out didn't come before he passed away, because he was the person who had the idea about the solar wind being generated. For him to see this result I think would've been just outstanding, but unfortunately didn't quite happen. But it was closed and the mission was already getting really good data by the time he passed away, so it was still great.

Sarah Al-Ahmed: Why is it so hard for us to study the origin of the fast solar wind from the distance where we are here at Earth? Why did we need a spacecraft to go there to answer this question?

James Drake: Let's go back to the main mission goals of Parker Solar probe. Actually there was two. One is what heats the corona? So we need to probably take a step back on this. The corona is about a hundred times hotter than the actual surface of the sun. The corona is this dilute gas of ionized plasma, which surrounds the sun. It's about a hundred times hotter than the surface. Now, why should the outer surfaces of something be hotter than what's interior? That's really unusual, because the source of energy that heats the sun is deep down inside near the core. And so here we have this corona, which is hot, and that of course, what heats that corona has been one of the major mysteries of the sun for many, many years. One of the goals of Parker solar probe is to try to figure out what heats the Corona. And the of course at the same time it's trying to figure out what actually drives the solar wind. And of course from one AU, that's the distance from the sun to the earth, we look at what's going on. We have spacecraft in the solar wind that that's measuring things, but what we now know, now that we've gone very close to the sun with Parker, and by close to the sun I mean it's now around 10 solar radii from the surface. The earth is about 200 plus solar radii. Now that we've gone from 200 plus solar radii down to around 10, we're seeing all this structure in the solar wind that was all blurred out by the time we got to one AU. And because it all got blurred out, we couldn't tell what was going on. That's just the fact of the matter. As we got inside around 20 solar radio, we started seeing a very different solar wind. It was much more bursty. So, that's the reason we haven't been able to figure all this stuff out before and we didn't know what we were going to see. We didn't know that when we got close to the sun it was going to be this bursty thing with all sorts of weird behavior like the magnetic field, for example. When you get close to the sun, it has all these kinks in it. Instead of just pointing out or pointing in, it twists around and turns and goes back in again and then back out. This is really weird. We had seen a little bit of this at one AU, but when we got close to the sun, we started seeing all this very unusual behavior. Parker solar probe is an exploratory mission in the sense that we didn't really know what we were going to see. And that's of course the exciting aspect of this whole mission.

Sarah Al-Ahmed: Yeah, anytime there's a mystery that you can't really interpret from afar, you have to actually go there and figure it out. It's always way more exciting, but also so much more difficult. And the fact that we had to create a spacecraft capable of getting within that distance of the sun is absolutely startling. And even within the sun's atmosphere, even within the corona say, it's not necessarily easy to see these fine structures. And it's also very dependent too on the solar activity. Right now we're hitting almost solar maximum. The sun is very active. Is that impacting how this probe is doing its work or is that in any way obscuring the data?

James Drake: In the press release on this Stuart Bale who's the principal investigator of the so-called field instruments that measure the magnetic field, for example, on the electric field in the solar wind, he pointed out that in many ways when we first start started getting data on this, it was good that we weren't at solar maximum because that would've been really complicated. So, I think the fact that when we started seeing this stuff, it was still just starting to transition from minimum to max. I think that helped us because things weren't quite as complicated as they're likely to get. Now having said that, one of my main interests as we start really hitting solar maximum and we start seeing some very intense debris from solar flares, I want to see the energetic particle measurements that come from those solar flares because I'm trying to model that. And so I'm really excited about solar max because I want to see all these very energetic events coming out. We should have some very nice measurements of the energetic particle spectra that are produced during the energy release process, so that's going to be really exciting.

Sarah Al-Ahmed: How long do we think the Parker Solar probe is going to last? We only have so many years for solar maximum. Are we going to get enough data to do all that science?

James Drake: Yeah, I think we're going to get enough data to do that. Now, how long is it going to last? That I think depends on a lot of things which could be random. Keep in mind that Parker Solar probe has a heat shield and that heat shield is always pointed towards the sun and it protects the spacecraft and all the instruments. We have to maintain the direction of the spacecraft so that it doesn't just burn up. And so that means the operators have to be really careful about what's going on. And this is not my area of expertise, but any case, we certainly are going to make it through this solar maximum. But how long it's going to last, I don't think we can be sure about that.

Sarah Al-Ahmed: And I don't want to give it away because we do a space trivia contest at the end of each episode. This week, the question has to do with that shield, so I'm not going to go into too many of the details, but I really encourage people to look up YouTube videos about this shield because it is absolutely startling how this thing works. And it is very surprising how effective it is given what it looks like.

James Drake: Yeah, it actually works.

Sarah Al-Ahmed: Your team now has a good idea of what might be causing this fast solar wind. Prior to us actually getting this Parker Solar probe in place to do this science, what were the hypotheses that people thought were causing this fast solar wind?

James Drake: There were two main ideas, lines of research on this topic. I'd say the main major one was that the sun produces these waves called [Althane 00:19:01] waves, which are basically kinks in the magnetic field. And the idea was that these are produced down at the surface of the sun. These waves propagate along just like say for a sound wave in our atmosphere when we speak, that's a wave. It's a compressional wave and allows us to communicate like we're doing now. But anyhow, the idea was that there's all these waves produced down near the surface of the sun and that those waves propagate up into the [inaudible 00:19:32] corona. As they propagate up in the corona, they dissipate their energy and they dump their energy into the corona. And the idea was that that's heating the corona, and that's why the corona is a hundred times hotter than the surface. The idea was it's from these waves. One consequence of these waves is that the temperature of the corona goes up as we just talked about, that produces a pressure. If you have higher temperature, you have higher pressure. And the idea was that that pressure then is what drives all of this ionized gas out from the sun to produce the wind. Okay, so that was one of the main ideas of research and in fact, I would say that that in many ways was the dominant idea. The second idea was that there's a process called magnetic reconnection. We haven't talked about that yet. Probably people pretty much know that there are magnetic fields, bar magnets and everything. And of course the sun has a magnetic field as we talked about because of the dynamo. A magnetic field has a direction. If you take two magnetic field lines and we draw these magnetic fields as lines. It's like a line wandering around with a direction. Imagine that you have these two lines and they're pointing in opposite direction. When they're pointing in opposite direction, they can annihilate each other and then when they annihilate each other, they release the energy that's in that magnetic field. And the process by which this happens is called magnetic reconnection. And it turns out that these bursts occur all over the surface of the sun, and that more and more evidence is emerging that these bursts cover the entire surface. And so this second idea was that it's these bursty releases of magnetic energy that are driving the wind. That's the second idea. And so in other words, it's not the waves themselves which are heating the corona that drive the wind, it's the bursty release of magnetic energy down at the surface, which is actually driving the wind outwards.

Sarah Al-Ahmed: Now we get to the real good part, which is what your team actually discovered, which is that you think which of these two mechanisms is actually creating this fast solar wind. So what did you find?

James Drake: Okay, so this gets back to our earlier discussion, which is as Parker got closer to the sun, we started seeing all this bursty behavior. Number one, the wind gets all these bursts. It's not just a steady wind of 400 kilometers per second or 500 kilometers per second. It's got all these spikes in it. The velocity goes up to 600 kilometers per second and then down to 200 kilometers per second, and then it goes back up again. And then they started seeing, not only was it bursty, but the bursts started occurring in patches. So, you'd see a sudden patch of these strong bursts and then it would die down a little bit. And then another patch of very strong bursts. So this started appearing, I would say around 20 solar radii, when Parker was within 20 solar radii. What the team did was to look at the magnetic field at Parker and try to map that magnetic field down to the surface of the sun and say, "Well, where did those patches come from?" And lo and behold, it turns out that these patches match the periodicity of the magnetic field on the surface of the sun. Then we started realizing that the structure of the magnetic field on the surface seemed to be producing this patch, these patchy bursts of solar wind. And not only that, but when they mapped the magnetic field from Parker down to the sun, they realized that it was mapping into a region which had this magnetic field that was pointing outwards and inwards and outwards and inwards. And we then realized that, "Well, that's a natural place where magnetic reconnection could occur." Seeing these patches was really the key discovery that I think pointed towards magnetic reconnection as being the driver. The other thing that was I think pointed in this direction is that we pretty much know from both observations and our efforts to model magnetic reconnection, that it's a bursty process. And so all these bursts that Parker was seeing are one of the natural consequences that you would expect to be happening if magnetic reconnection were the driver for all these things. So, what we were able to do was look at the data and we were able to figure out what's the strength of the magnetic field down on the surface? How fast is magnetic energy being released down there? And when we calculated how fast it was released, we discovered that the energy release rate was sufficient to actually drive the wind. Because based on previous studies over history, scientists knew how much energy do we have to release to drive the wind? So we have a pretty good idea of what that number is. And lo and behold, when we looked at what was going on, we were able to demonstrate that the energy release rate down on the surface from reconnection seemed to have enough energy to actually drive the wind.

Sarah Al-Ahmed: That's so cool that we can finally answer this question. I know there's more science that still needs to be done, but I feel like we've actually stumbled upon the answer here and that's amazing.

James Drake: Yeah. So keep in mind that this is still a scientific discussion. I think not everybody agrees with all of this stuff. Last week we were at the Solar Wind 16 Conference, and from my perspective, the first day was very remarkable in the sense that there's a whole series of talks that were focused on studying these bursts as they come out from the surface of the sun driven by reconnection. And this included data from, for example, the solar orbiter, which is a European spacecraft. Just beautiful data showing that the entire sun surface of the sun has these bursty outflows. And then we presented the data from Parker, and all of these observations are pointing in the direction of reconnection being driving this stuff. But nevertheless, not everybody agrees. So there's still a lot of support for the wave mechanism for driving the wind.

Sarah Al-Ahmed: More science definitely needs to be done, but I'm assuming your team is going to keep looking into this and if not, your team, everybody else with the Parker Solar probe data is going to continue to try to figure this out. So, we'll get to the bottom of it. I trust it.

James Drake: Yeah, there's a lot more, and especially one of the reasons that this idea of the waves driving the wind has had such a lot of support over the years is because the wind itself... We can measure these waves in the wind. We can measure waves in the wind, and the real question is what's producing those waves? We know there are waves in the wind. In fact, if there weren't waves in the wind as the wind came out from the sun, it would cool down and become very cold. And we don't see that. So, we're pretty sure that the waves in the wind are actually heating the wind as the wind propagates out from the sun. But so we know there are waves, but I think the question that's coming up now is whether those waves are actually produced at the surface of the sun and then go out and drive the wind and heat the plasma and everything. Or is this bursty outflow from the sun produced by magnetic reconnection? It comes out as all these bursts and those bursts themselves carry energy. And so my view, and I think the interesting thing we're going be exploring over the next few years is, does all these bursty outflows actually drive the turbulence that we measure in the solar wind? And that's what I think. One thing we know from the measurements around the earth space environment is that magnetic reconnection is bursty. I'm of the opinion now that it's all these bursts that coming out from the sun. As they come out, they're actually twisting the magnetic field up and that these bursts from reconnection are actually what's driving the turbulence in the solar wind. You know, the data from Parker's going to be coming through for quite a few more years, so I think we're going to sort this out.

Sarah Al-Ahmed: We'll be right back with the rest of my interview with James Drake after the short break.

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Sarah Al-Ahmed: These places where there are so many magnetic field lines close together, creating this magnetic reconnection, are those the coronal holes You mentioned earlier?

James Drake: The simplest picture of a coronal hole is it's a region on the surface in which the magnetic field is predominantly in one direction. However, that's too simplistic because actually, if you go down and you look at the surface of the sun, you can actually measure the magnetic field and it's not all pointing in one direction. Down deep in those coronal holes the magnetic field is not pointing just in one direction. It points up and down, and it's true if you add all up, but it's dominantly in one direction, but if you look at the details, it's not. It's up and down and up and down. It's the reversal of that magnetic field, it's the up and down that's actually releasing magnetic energy and driving the wind. So, coronal holes or more complicated than you might have guessed based on historical ideas.

Sarah Al-Ahmed: Yeah, I've read descriptions of these corona holes up close, as I've been researching for this. Basically like shower heads of these strange magnetic field lines poking in and out at pretty consistent distances from each other. But what is the structure that we're seeing of the magnetic field there?

James Drake: That structure comes about because of the dynamo underneath in the outer reaches of the sun. The dynamo twists everything up that twisting up produces these characteristic scales that produce these localized regions. And so the twisting up of the magnetic field produces, for example, these local downflow regions and upflow regions that carry the magnetic field up to the surface. It's the structure of those flows that control the structure of the magnetic field deep within the coronal holes.

Sarah Al-Ahmed: Parker Solar Probe figured this out by getting close to the sun and passing through these jets of solar material. What instruments on Parker Solar probe are allowing us not just to trace these jets back to these coronal holes, but actually analyze the structure of the magnetic field there?

James Drake: Okay, number one of course is the magnetic field. They're measuring the magnetic field. That's part of the so-called fields instrument group, and Stuart Vale from Berkeley is the principal investigator on that. So, the magnetic field, that's clearly key. And then there's the particle measurements. We actually measure the velocity of all these particles that make up the wind, these ionized particles. So, the wind is a plasma, which is an ionized gas, and so it's made up of all these particles. And Parker Solar Probe then measures the velocity of these particles. Then you add them all up and you find out how fast the wind is as a wind. But it's all made up from individual measurements of particles. And this is the so-called span instrument on Parker solar probe that measures the particle velocities. And then there's another set of instruments called ESIS, and the ESIS instrument measures the more energetic particles. We haven't talked about this, but another reason we're actually convinced that magnetic reconnection is driving this is because the wind that Parker is measuring, it's not just a wind blowing at 400 kilometers per second. It's actually an energetic wind and what I mean by that is that there's a spectrum of particles that carry a lot more energy than this 400 kilometers per second energy we're talking about. There's a whole spectrum of particles that goes up to say 80 kilo electron volts, KEVs. The wind blowing it around 300 to 400 kilometers a second, it corresponds to an energy of about one kilovolt. However, Parker measures this energetic component, which is up to like 70, 80.

Sarah Al-Ahmed: Wow.

James Drake: And we never saw this at one AU, because it all just blurred out. And now this wind, we're realizing this wind is an energetic wind. It's got all these energetic particles in it. That's just a total new discovery. And we never knew that this was going to be the case. At Maryland we've carried out these simulations, which actually reproduced the energetic particle spectrum that was measured by Parker Solar Probe. So if you look at the nature paper, we show side by side the spectrum measured by the step I instrument and the ESIS instruments, they put together a spectrum of the flux of particles versus their energy. And then we did the same thing with the computer simulation and the two just beautifully match. So reconnection itself produces an energetic particle spectrum, which produces an energetic wind. So we now know the solar wind is not just this wind moving at 400 kilometers per second. It's an energetic wind, and that's so cool.

Sarah Al-Ahmed: That really is. And wild that we weren't even expecting to discover that. It just speaks to the power of actually doing this kind of exploration. Anytime we get close enough to an object, whether or not it's the sun or some moon or planet, we're always discovering things that completely threw us for a loop that we did not expect. And I hope it's always that way. I hope we never stop finding things we didn't expect as we're going out there.

James Drake: I tell all my students this when I teach physics, or my graduate students too. And that is you need data. If you don't have data... I'm a theorist, so I can sit down and do all the theory I want and I can go off and be in the totally wrong direction and not know that I'm just off base. We need data, because we never would've figured this out without data. It was just hopeless. So Parker Solar Probe is giving this beautiful data. Of course, we combine that with our theoretical understanding and our modeling expertise, but you have to have data to figure out what's going on in the universe. Otherwise, it's just hopeless. So these missions are extraordinarily important.

Sarah Al-Ahmed: You heard it from him, folks. We need to keep advocating for these missions so we can learn even more things that we totally didn't expect. But I'm sure some people are wondering, this is all awesome to understand, but how is understanding this fast solar wind important for us here on earth? We all generally understand that the solar wind causes beautiful aurora at our planet's poles, and sometimes solar storms can impact our communications or electrical systems and stuff like that, but why do we need to know more about these fast solar winds? Particularly

James Drake: The solar wind produces a bubble in the galaxy. And this bubble is the plasma and the magnetic field that the sun sends out. And it creates a bubble that extends out to maybe 130 astronomical units. An astronomical unit is a distance from the sun to the earth. And the heliosphere, which is the domain of the sun produced by the solar wind, the wind goes out at 400 kilometers per second, approximately, all the way out to about 90 AU. And then there's a so-called termination shock, and then the wind slows down dramatically, and then you go out a little further, and then there's the heliopause. And now the Voyager spacecraft have mapped all this out beautifully. But anyhow, the sun then produces this heliospheric bubble in the galaxy. We're a bubble. And all stars produce these bubbles, because they all have winds just like the sun has a wind. Okay, well, why is this of any significance? Well, the galaxy has a lot of energetic cosmic rays. These things are dangerous. Cosmic rays can injure people. They are energetic particles and they can pass through your body. It's not good. The heliospheric bubble shields the planets in our solar system from the galactic cosmic rays. It's not a complete shield. Some cosmic rays get through, but it does form a shield that the screens out a lot of the energetic cosmic rays. So, from that perspective, these bubbles and understanding them are quite important because this bath of cosmic rays in the galaxy can impact potentially whether a planet can have life on it or not. I think one reason for understanding all this is we want to be able to look at a star and ask, "Okay, what kind of bubble is it producing? Are the planets that are circulating around within the Heliospheric bubble? How good is the bubble from this star in terms of shielding the planets from galactic cosmic rays?" Okay, so that's one reason. And the second reason, of course, you already alluded to, and that is in exploring the driver for the solar wind, and magnetic reconnection for example, we're learning a lot about how the sun releases magnetic energy, and it's the release of magnetic energy, which drives solar flares. It produces these corona mass injections, which hit the magnetic field of the earth and annihilate it. So, these storms around the earth are also produced by magnetic reconnection. We haven't discussed this, but these corona mass injections, what happens is there are a big blob of magnetic field, and they smash against the earth's magnetic field and annihilate it, and that's what produces the aurora. The aurora comes from energetic particles produced by magnetic reconnection between the sun's magnetic fields, the magnetic field in the solar wind smashing against the earth's magnetic field, annihilating, producing the energetic particles that produce the Aurora. Understanding magnetic reconnection is a key to understanding all of the stuff that can happen in the airspace environment and can negatively impact our communication systems. So, all of this stuff builds up our knowledge base so we can say, "Okay, what's going on? Are our satellite communication satellites at risk? Are our astronauts at risk?" Because if they're out in space and there's a huge solar storm that produces a lot of energetic particles, that's a big risk. Especially if you really think we want to get to Mars. Astronauts are going to be in space for a long time, and there's a risk that a big storm comes along producing a lot of energetic particles, and that puts our astronauts at risk. So, we want to understand all this stuff, and we've learned a lot, I think now about the reconnection process from the Parker data. And we're going to learn more during Solar Max, that's for sure.

Sarah Al-Ahmed: Is this understanding going to help us interpret what's going on in the sun just from our readings of the solar wind at Earth? Or is it still just too complex what we're reading here from Earth? We have to see what's going on close to the sun to understand?

James Drake: There's many ways of looking at the sun. For example, there's the radio telescopes that are pointed towards the sun. They're also telling us something about how energetic particles are produced during magnetic reconnection during flares. Parker Solar Probe is one of several different ways in which we gather data. Each of these ways of looking at the data or gathering data tells us different things. I'm a big advocate for saying that we explore, for example, magnetic reconnection in the airspace environment, and we explore it on the sun, and we learn information about each of these different ways of looking at things. And then we try to put it together into a scientific picture about what's going on. Having different measurements is what is really allowing us to make progress. For example, if I hadn't done a lot of work on magnetic reconnection and nerve space environment along with many of my colleagues, I don't think we would've been able to figure out what's going on with this Parker Solar Probe data, because these things are connected.

Sarah Al-Ahmed: I think the only other time that we've actually spoken about magnetic reconnection on the show in prior months was when we were talking about the Juno mission with Scott Bolton. They were seeing these same magnetic reconnection events, but instead of the sun and the earth, they were seeing it between Ganymede and Jupiter. So, understanding these things and how magnetic reconnection works helps us in all contexts whenever we're seeing magnetic fields and even in that situation, it's creating beautiful aurora behind Ganymede. That's so wild.

James Drake: Yep. Yep. This is... Magnetic reconnection is universal. It happens throughout the universe. And if you go now to astrophysical meetings, there's a lot of work going on about magnetic reconnection and the consequences. It really is a universal process.

Sarah Al-Ahmed: Well, thanks for joining me, Jim, and for explaining all this. I know that there's just so many things that you have to take the time to explain to put this picture together, but I think you've laid it all out very well, and I hope other people are excited about these results as we both are, because this is some foundational stuff that we didn't even know. We didn't even have the tools to know or understand until just very recently. And good luck to you and your team as you continue to explore this topic, because who knows what new thing we're going to learn that we did not anticipate.

James Drake: Yeah. Thank you very much for having me on the show.

Sarah Al-Ahmed: I'm continuously amazed by the Parker Solar Probe, but also by humanity in general. For all of our faults, we've got to appreciate the fact that we're the kind of curious and determined creatures that literally created a probe capable of flying into the atmosphere of the sun. Talk about daring mighty things. Now let's check in with Bruce Betts, the Chief Scientist of The Planetary Society for What's up. Hey, Bruce, and Happy early Asteroid Day.

Bruce Betts: Happy Asteroid Day to you as well.

Sarah Al-Ahmed: That is an odd choice of words right? On asteroid day, I usually celebrate it by going outside and just shaking my fists at the sky, like, "Keep going, asteroids back off."

Bruce Betts: Wow. We should list that as one of the deflection methods that we work on. That one's truly terrifying. So anyway, yes, an Asteroid Day is of course, the commemoration of Tunguska impact in 1908, which is on my list that... Well, now I've blown it. Now that's a preview for this weekend's space history. But yeah, leveled 2,000 square kilometers of forest in an airburst of a comet/asteroid.

Sarah Al-Ahmed: It's so terrifying that they really didn't know what was going on there for such a long time. I can't even imagine if that happened today, how terrifying that would be.

Bruce Betts: Oh yeah. There was just... Fortunately it hit in the middle of Siberia, but that's one and a half times the area of the city of LA, which is not a small city.

Sarah Al-Ahmed: Oh, man.

Bruce Betts: So if it hits the wrong place... Now, fortunately, they only hit on average once or twice a millennium of that size, we think. But problem is statistics don't really pay attention from day to day to average, only over long periods of time. Anyway, we're working to prevent it, save the earth from disaster for asteroids. That's one of the things we do with The Planetary Society. You know what another thing we do is in our spare time? We look at the night sky. Yes. That was a beautiful segway, I know. And in the evening, for the next month or so, you're going to watch Venus and Mars go away and leave the evening sky. But for now, they're still up there super bright, Venus. Mars has just gotten dimmer and dimmer as it gets farther from earth. An interesting, fun thing, on July 10th and a little bit the night before that and the night after that, in the evening, you'll see Mars is right near Leo's brightest star, which is Regulus. And Regulus is actually a little brighter than Mars right now. But they'll be hanging out about one lunar diameter apart over in the Western sky, and they're above super bright Venus. And if you're really lucky, you might catch Mercury way down low, but that one's a tough one this time around. In the pre-dawn sky, in the night... In fact, in the middle of the night, we've got Saturn coming up around, well, literally middle of the night now, coming up in the east looking yellowish, and then rising high up in the sky by the pre-dawn. And Jupiter coming up an hour or two before sunrise as well, looking super bright over in the East. So, there are planets, and they will do the thing that those planets do and keep moving earlier towards the evening. Let's move on to this week in space history. 1971, 3 Soviet cosmonauts were lost, died in space, and so we remember them. And that was on the Soyuz 11 mission. Moving on to much, much happier things. 1997, Mars Pathfinder landed on Mars. Got us back into the Mars surface game, which we haven't left since then. In 2005, we had the monster truck rally of planetary encounters when... At least the one before Dart, which was slamming into a comet instead of an asteroid this time with the Deep Impact mission. And so I'd just like to say, "[inaudible 00:47:46]."

Sarah Al-Ahmed: Take that comet.

Bruce Betts: Changed its orbit, not by much, because it was really big, and that wasn't the point of the mission. When the mission was to uncover stuff below the surface of the comet, and they learned things. Let's go on, shall we to... "Random [inaudible 00:48:06]."

Sarah Al-Ahmed: Nice.

Bruce Betts: Have you heard of this thing called the Parker Solar Probe?

Sarah Al-Ahmed: Nah, never heard of it. Nah. I love the Parker Solar probe.

Bruce Betts: I feel like people are going to be... Know a lot about it, and they might know this since I don't know what's been discussed, but it's still really impressive. Parker Solar Probe gets so close to the sun. How close does it get? That the sun's intensity is more than 400 times what it is at Earth.

Sarah Al-Ahmed: No, thank you.

Bruce Betts: That's why they need that spiffy, nifty heat shield, which we might... I don't know. It might discuss a little bit later in just a few moments. It could be.

Sarah Al-Ahmed: Could be. Now all those videos of people like testing the material that they use to make that shield just on YouTube, I cannot recommend enough because it is so weird to see someone just using a blowtorch on one side and then another person's hand just press right up against it without burning them. The technology is amazing.

Bruce Betts: Yeah, no, it's very cool. Trivia. Trivia, I asked you, "Who was the fourth woman to fly in space?" How did we do?

Sarah Al-Ahmed: Everyone got this one, right. Mostly.

Bruce Betts: Good.

Sarah Al-Ahmed: The answer is Judy Resnick, who became the fourth woman to go into space on the maiden voyage of the Space Shuttle Discovery in 1984. And of course, a bunch of people wrote in to also add that she wasn't just the fourth woman to go to space or the second American to go to space, but she was also the first Jewish woman to go to space. So that's awesome. Unfortunately, I guess we're talking about tragedies, this show, but unfortunately, she lost her life along with the other heroes in the Challenger disaster in 1986. She was a pioneer.

Bruce Betts: She was and worth remembering.

Sarah Al-Ahmed: Our winner this week is Stephanie Delgado from Tucson, Arizona, USA, and Stephanie, you're going to be winning a copy of The Sky Is Not The Limit by Jeremie Decalf, which is a beautiful illustrated kids book about the Voyager II mission, which I love, and I'm sad to give away, but you deserve it.

Bruce Betts: It sounds very cool. Congratulations. That's a happy note.

Sarah Al-Ahmed: It is. I feel like this trivia question really got people because they just kept chiming in cool things about Judy Resnick, you know?

Bruce Betts: Yeah, she's impressive.

Sarah Al-Ahmed: Really impressive. I loved this comment too. Cody Rockswood from Seminole, Florida, USA said, "Fun fact: Resnick, which is similar to the Polish Reznick, means one who cuts or a butcher. So she was literally cutting the way for the future female astronauts." And of course, I've got to mention Dave Fairchild, our poet laureate, wrote in this poem, which I thought was very beautiful, "Judith Resnick took a ride, discovery showcased, and so became the fourth in line of women into space. Her name is on an asteroid, a crater on the moon. Like all our fallen astronauts, we lost her much too soon."

Bruce Betts: That's very nice.

Sarah Al-Ahmed: All right. Hopefully we don't have a tragedy stricken Parker Solar Probe trivia question this week. What is our next question, Bruce?

Bruce Betts: No, this is back to our protective heat shield that protects the Parker Solar Probe. Approximately, how thick is the Parker Solar probe's Protective Shield? Go to planetary.org/radio contest.

Sarah Al-Ahmed: Nice. And you have until Wednesday, July 5th at 8:00 AM Pacific time to get us your answer. And since we're coming up on Asteroid Day on June 30th, I've decided to give away some cool asteroid posters. I've got some posters from the Psyche mission. So, this time I'm going to be giving away two Psyche posters.

Bruce Betts: Oh.

Sarah Al-Ahmed: Because I've got a bunch of them and they're really, really cool. So, whoever wins this will get some awesome Psyche posters. But this also brings me around to another topic, which is that earlier in this show, we let our listeners know that we're going to be making some changes to Planetary Radio to hopefully reach new audiences and do all the awesome things that we want to do for this show. And this strategy is going to go hand in hand with our new Planetary Society member community. So, one of the things that we're going to be moving from Planetary Radio into the member community is our space trivia contest. And I know this is a big change for our longtime listeners who have been with us for over 20 years, but we want to give as many planetary society members as possible an easy way to participate in this contest, so even more people can get in on it. I know that this means a lot to people, but we're not going to be killing it forever. We're going to give people a new way to do this so more people have an opportunity. Our last space trivia contest question on this show is going to be on July 12th, and I'm trying to find some really awesome prizes to give away. My one sadness is that I can't give away a bunch of those rubber asteroids because... I haven't been talking about this. We're totally out of those asteroids. There's a reason why I haven't been giving them away. We are out of them. So, unless you have been hoarding asteroids in your house, Bruce...

Bruce Betts: I may or may not have.

Sarah Al-Ahmed: Well, if you find any, let me know. Because we can chuck a bunch of squishy asteroids at people.

Bruce Betts: No. No. Don't hurt them. All right, everybody go out there, look up the night sky and think about helium filled balloons. Thank you, and good night.

Sarah Al-Ahmed: We've reached the end of this week's episode of Planetary Radio, but we'll be back next week with more space science and exploration. Planetary Radio is produced by The Planetary Society in Pasadena, California and is made possible by our Solar Powered members. You can join us as we continue to support the daring missions that teach us more about our place in space at planetary.org/join. Mark Hilverda and Ray Paoletta are our associate producers. Andrew Lucas is our audio editor. Josh Doyle composed our theme, which was arranged and performed by Pieter Schlosser. And until next week, ad astra.