Voyager 2 is in interstellar space

Hi everyone, welcome to a new episode of Space Cowboys. Hi everyone from MeToo. Yes, Herbert, hi. Hi Thijs. Hi, and with a very special guest today. Tell me. Ed Stone from JPL. One of... Ed Stone? The big names in interplanetary science, let's call it that. And we're going to talk about the Voyager missions. One of my big passions. Both of them. And both of them, yeah. Good. For a very long time I thought there was only one Voyager, but of course there's not. And which one was it? One or two? Well, I think there was always Voyager 1, but there are of course two Voyager missions. And they both left in the summer of 1977. How old were you back then? I did not exist. My molecules were spread through the universe. Right, I knew it. Yes, yes. I was 19. You were 19? Do you vividly remember? Yes. Do you remember? I do. Yeah? Yeah, yeah, yeah. Maybe not so much the launch as the results. Yeah? The first pictures coming in? I was so excited by the photographs. Mainly of Uranus and Neptune. Oh yeah, of course. Because those were mysteries before. Yeah, just like... The only time I ever experienced anything similar was with New Horizons and Pluto. Yeah. Which was... I remember for me it was the feeling of just seeing these little dots, seeing that... Becoming a world. What used to be a dot, yeah. Yeah. Turned into something. Very special. Yeah. And the funny thing is, Voyager 2 was launched first, visiting Jupiter, Saturn, Uranus and Neptune. Yeah. A couple of weeks later, Voyager 1 was launched, also visiting Jupiter and Saturn, and its moon, Titan, of course. Yep. And then they went on to venture out towards the edge of our solar system. Now, I wanted to... And beyond. And beyond. Now, I wanted to say that they left it, and that's what I always tell people, like, oh yeah, the Voyager has left the solar system. But... They left the heliosphere, of course. Yeah. The bubble around our sun that keeps interstellar particles out. That's all a matter of definition. It's a matter of definition. We talked about that. Yeah. To add, of course. Yeah. Voyager 1 reached interstellar space in 2012, and Voyager 2 has kind of just left our sun bubble last November. And I'm so happy to introduce our guest today. He is the former head of the Jet Propulsion Laboratory, JPL, currently a professor of physics at Caltech, and of course, the project scientist. Yeah. And of course, the project scientist. The project scientist for the Voyager missions. Ed Stone, welcome to Space Cowboys. Glad to be with you. Yeah, wonderful. From California. So this show is called Space Cowboys, but I was thinking that maybe that term is... That you deserve that term a little bit more than we do. You got to watch firsthand what these probes were sending back to us from the far reaches of our solar system. How was it to sort of have that firsthand experience of these pictures coming back? It's really been an experience of a lifetime, that's for sure. And it's been a great experience. We explored and discovered things we had no idea were out there to be discovered. So it's been a wonderful journey so far, and we have more to go. Yeah. How much do you love looking at the data that comes back, even now, nowadays? Not pictures, but just data. How is that for you? Well, it's telling us what this bubble is like and how big it is. The sun creates a bubble around itself with its million mile per hour solar wind. And we're... And we are all inside the bubble. And now we have two spacecraft which have left the bubble and are in the local interstellar space. And they're a billion years of journey now in the galaxy. Yeah. And just for people who don't understand that bubble, right, can you just take us through it? So how come there's a bubble coming from our sun, and what is that interstellar wind coming towards us? The sun has an atmosphere, of course. And what was discovered many years ago now is that that atmosphere is speeding away from the sun at 400 kilometers per second. And it's heated by the sun. That's what causes it to expand supersonically, basically. And that supersonic wind creates a huge plasma bubble surrounding the sun. And until 2012, we didn't know exactly how big the bubble was. And that's when Voyager 1 finally left it and entered interstellar space. Yeah. Outside, the wind comes from the explosion of other stars that happened 5, 10, 15 million years ago. And that interstellar wind deforms the bubble into a comet-shaped object. That is, there's a nose and a tail. And why is that? Yes, I'm sorry? Why is that? Why is it that shape? It's that shape because the interstellar wind blows some of the heliosphere back. Just as in the solar system, you know, a comet will have a long tail, because the solar wind does that to the comet. And in interstellar space, the interstellar wind does the same thing to the heliosphere. And then, can you say in general where this interstellar wind is coming from? Or is it coming somehow from all directions? It's really coming from a particular direction. In fact, if you were looking up at the sky at night and looking toward the galactic center, you'd be looking directly into the wind. The wind isn't coming from the center of the galaxy, of course. It's really local. But the direction is that, as you would be facing the wind, if you look toward the galactic center. So that's kind of a coincidence. Yes, it is. But there's really a direction you could travel in space and have headwind, and another direction where you could travel and have tailwind. That's exactly right. And the wind was created by these supernovae, and they were all together in one side of the sun when they exploded. And so that's where the wind is coming from. That's great to hear, because it's really new to me. Yeah, exactly. And that's what Voyager does, right? It gives us suddenly this vista. Your colleague, Nikki Fox, she called this the start of a new era of heliospheric science. And so why did she say that? This is for the first time we have in situ data. All we knew about the heliosphere before was by observing it from where we are, deep inside the heliosphere, looking out. And so we really now have for the first time two probes actually out where the wind is, measuring the properties of the wind. Yeah. And of course Voyager 1 and Voyager 2, they're the same machine, right? Are they identical? They are identical, except one of the instruments is not working on Voyager 1. So we have five instruments working on Voyager 2, and four operating on Voyager 1 now. And it's a plasma science experiment, right, that's not working on Voyager 1, but it is on Voyager 2. Yes, that's correct. So you're getting new data in. Yes, yes we are. We're learning more about how the interstellar wind interacts with the solar wind. Do you have a sneak peek of some of the results? Like, are you already finding stuff out that the world needs to know? Well, what we have learned, for instance, from Voyager 1, is that there are cosmic rays outside. These are atoms which have been accelerated near the speed of light, and some of them can get in, deep inside the heliosphere. But many, most in fact, cannot. And we now know that the heliospheric bubble basically serves as a radiation barrier, so that more than 70% of what's outside cannot get in to 1 AU. So this is part of our radiation defense. So that means Voyagers, both Voyagers are getting an even worse bombardment of radiation, than they even did. How do they survive? Do you expect them to live shorter because of it? Well, there will be a radiation effect long term, but it turns out most of the radiation they got was at Jupiter, because of Jupiter's immense magnetic field and very intense radiation. So that was a very rapid aging process, and the one they're experiencing now is much slower. Really? Okay, that's good. Yeah. I want to sort of rewind things, to the start of these missions, and also where you were. Where were you, to start off with that? Where were you when these missions started? Well, they really got started in 1965, when a graduate student working at JPL discovered that if you launched a spacecraft in 1977, plus or minus a year, that spacecraft could fly by all four of the giant outer planets. They were all, if you like, sort of lined up, so that you could do that. And that's an opportunity that happens only every 176 years. So that was really the start. And that was very early in the space age, and it wasn't clear when could build a spacecraft that could last long enough to get to Neptune. This was before the moon landing. I mean, this is like early space race. Yes, that's right. Yeah. And so you started as a graduate student, and during the launch, where were you at that moment? Well, I was, by the time, actually I was a graduate student when the space age began, so I was already at Caltech developing instruments for a spacecraft when I was asked to be the chief scientist or project scientist for this new mission. That was 1972, when I became the chief scientist, and I'm still the chief scientist today. That's a good career. Just to make sure I understand this correctly, this graduate student who discovered the lineup of the planets, was that actually you? No, no, no. It was not? No. Okay. What was the name of this person? Gary Flandro. Okay. Did he go on to become a famous astronomer himself as well? He was, actually he was in aerodynamics and space instrumentation, so he's an engineer. Okay. But he was working at JPL looking for these opportunities to fly by other planets and found that you could fly by four of them if you launched in this magical period. And for this, I mean, this was really once in, more than one lifetime discovery, right? Yes, it is. 175 years. 75, yeah. So did he get a prize for this or something? He got a medal. He got a medal. Okay. That's good. That counts. That's good enough. That counts. And so what were the expectations? Because as you said, you didn't even know if the spacecraft were going to survive, maybe. What were your expectations when you started this as a scientist? Well, we expected, there would be a lot of discoveries, but we really didn't anticipate how diverse the things in the solar system are. For instance, when Voyager was launched, the only known active volcanoes in the solar system were here on Earth. And then we flew by a moon, just a moon of Jupiter, where there's 10 times more volcanic activity than on the Earth. And so suddenly we realized that the solar system was much more diverse than we had imagined. And time after time, we discovered things that we thought we understood, but we really didn't know that they were there. Was that the first major discovery that it made, those volcanoes? I would say it was typical of the really dramatic discoveries, yes, the first one. And the last one was when we flew by Triton, which is a small moon of Neptune, about the size of Pluto. And it's only about 40 degrees above absolute zero. Even that. Even nitrogen is frozen at those temperatures. Yet we've discovered active geysers erupting from the polar caps. Wow, on Triton. How could you imagine that? That's just incredible. It turned out that our solar system was in a way, way more alive than we thought it was, maybe. That's a very good way of putting it. Yes, it's a very dynamic place. Yeah, nothing but surprises, actually, right? I mean, every moon of Jupiter, Saturn, Neptune, all those ones. Yeah. I was actually surprised by this picture of Voyager, I think Voyager 1, I'm not sure, just leaving Earth and the Moon and even snapping a picture of the Earth and the Moon together. Maybe Pioneer had already done that, but I thought it was kind of cool that Voyager sort of took a last picture of the Earth and the Moon as it was leaving. Yes, that was the first such image, where the Earth and the Moon were in the same frame. Exactly. Exactly. And that's where it started, right after it left. Did it get slingshots in any way, like before it went on to Jupiter, or was it just straight there? It was straight there for Earth. Yeah, exactly, yeah. So how was the Jupiter approach? How did that go? How many years after its launch was that, do you remember? Well, that was 1970, sorry, pardon me, 1979. Two years later, yeah. Two years later. Pardon me just a moment. No worries. Okay. Yep. And so tell us about that approach. How did it go? Well, first of all, we discovered, we were of course interested in what the Great Red Spot was, and we now know it's a huge hurricane-like storm system, but we also discovered it's just the largest of literally dozens of storms which are on the order of the size of the Earth. So that atmosphere was much more dynamic than we had imagined, even given the fact we knew it had high-speed winds. But there were lots and lots of dynamic, lots of dynamic things. Lots of vortices, lots of hurricane-like structures in the atmosphere of Jupiter. That was one. Another big surprise was the moon Europa, which is the same size as Io, but it doesn't have volcanoes. It has an icy crust, and when we saw it up close, we realized that it looked like an ice pack on a liquid water ocean, which in fact the subsequent Galileo mission really proved that that's the case. There is a liquid water ocean. There is a liquid water ocean on Europa. And again, when Voyager was launched, the only liquid water oceans we knew of were here on Earth. And here's just a moon, which has such a liquid water ocean beneath its icy crust. It's crazy. And you could see already that it has sort of like a young surface. Could you already see it on the Voyager pictures, that it lacked craters and such? Yes, yes. Voyager showed that we couldn't find any impact craters. We found lots and lots of cracks. We didn't find any mountain ranges or anything like that. It was just like ice on Europa. It was just like a kind of liquid water ocean. And the pictures being sent back, it was some sort of TV camera almost, right? Yes. Can you tell us about the camera? What kind of camera was it? It's a Vieticon camera, which is a tube. That's what used to be used before CCDs were invented. And so this was a small tube, maybe about an inch in diameter or so, something of that order, and an 800 by 800 pixel image. Ha ha. So it was a digital image, just like you get images in your digital TV these days. Really? A digital image? We had digital images back from Voyager. What? Really? I didn't even know. I thought it was some sort of analog weird signal. Oh, really? So ones and zeros beamed back? Yes, ones and zeros. Through the deep space network that was already up then? Yes, that's correct. And at what data speed did the data come home? We got... At Jupiter we had a data speed of about 115 kilobits per second. Wow. By the time we got to Neptune we had to... Much further away and much weaker signal, we had to use all of the deep space network antennas we could, plus a very large array of 27 antennas, plus another 64-meter antenna in Australia to get the data back, because it's so far away. But still 115 K bits. Yeah. That's faster than the Internet in the 90s. That's right. Yes. That's not that bad for Voyager in the 70s. No, that's right. Well, there you go. This is JPL. NASA, of course, is always, you know, of course, famed for... You could have beamed video of really decent quality back then. Yeah, even decent Skype connection live from Jupiter, yeah. Yeah, we could make the first movies, and we did make movies, showing this fascinating system of atmospheric storms. Of course you did, yeah, yeah. Oh, yeah, of course. Yeah, beautiful. But that was by putting photographs one after the other, right? Right. Yeah, yeah, yeah. And so were all the instruments on both Voyagers, were they up by the time they reached Jupiter? Were they still all working, or were there any setbacks? Yes. Yeah? They were all working, and we did the first and the only instrument we lost was the plasma, which we lost after the...just at the end of the Saturn encounter. Oh, really? Okay. And what was the cause of that? We don't know. Okay. It was never determined why. What we knew happened is that the high voltage, the high voltage, high voltage that you have to have to make the measurement just stopped switching on and off. Oh, yeah. I just kind of want to know for myself. So Voyager 1 and Voyager 2 are literally 100% identical. There's no difference between the machines themselves. I think that's correct. There may be some subtle differences, but not really. They're all the same instruments, right? Because they were back. The reason we had two was to be sure at least one could...in fact, Mission Success, was at least one spacecraft reaching Saturn. Yeah. And returning data on Titan and the rings. That's right, because... And that was Mission Success. Everything else is a bonus. One of them was meant to fly past Uranus and Neptune, and it did. And the other one went past Saturn and then went nowhere, up to the edge. Went up. Okay, yeah. Yeah, it went toward interstellar space. That's right. When we finished the Voyager 2, we finished the Voyager 2 encounter at Saturn. We knew that...the Voyager 1 encounter at Saturn. We knew that we'd done a Saturn science so we could leave Voyager 2 in the plane of the planets, the ecliptic plane, and head on to Uranus and Neptune, which is what we did. Yeah. And why was it that Voyager 2...was it Voyager 2 that was sent up? Right? I sometimes still mix them up. Voyager 1 went on to Neptune and... No, Voyager 1 was flipped. It went off-plane. Yeah. Up out of the plane of the planets, and there were no more planets that it could...that it flew close to, and it just was headed toward interstellar space. That was in 1980 when it flew by Saturn. So from 1980 until 2012 was how long it took for leaving Saturn to get to the interstellar space. And was that because...I believe I read somewhere that there was an idea to maybe send it on to Pluto, but then it wouldn't be able to see Titan. So that's why it went past Titan, and that's why it went up towards interstellar space. I read that somewhere. That's right. The Saturn's ring plane was inclined, and so that meant that since Titan is in the ring plane, we had to have an inclined orbit in order to study Titan. And we wanted to do that because we wanted to know what kind of an atmosphere was there, and that was another major discovery. Yeah. Yeah. We found that there's liquid. There's liquid. There's liquid natural gas raining down on the surface of that planet, of that little moon. There's beaches there. It's a planet-sized moon, by the way. It's almost as big as that planet Mercury. Yeah, really. I think Carolyn Porco calls it seas of paint thinner. Beaches with paint thinner right at your feet. Yeah. But, Ed, tell me, what was actually the design lifetime of both these probes? Did you ever think that they would live this long? Well, you know, when the Volta was built, they were built in the early 20th century. Well, you know, when Voyager was launched, the space age itself was 20 years old. Yeah. So there's no way that we could tell how long that anything could last 20 years since that was just the age of the space age when we were launched. Let alone twice that. This is a grand experiment. We did it step by step, and both are still working today, although they do have their limitations. We are running out of power. Sure. We have to look carefully at how cold they're getting and so on. That's the new instrument. That's the new engineering challenge we have. But after all, it's been over 40 years on the journey so far. Yeah. But what was your intention? What did you say to one another? Okay, if it lives this long, we'll be reasonably happy. What was this long in that case? Well, mission success was defined that at least one reaching Saturn. So we satisfied that mission success in 1980. That's very modest. Then we said the next step was we have to have a successful mission. We had a successful flyby of Uranus. That happened in 1986. Then we started what we call the Voyager-Neptune interstellar mission. That was 1989 when we did the Neptune part, leaving only now the current mission, which is the Voyager interstellar mission. So this was a stepwise expansion of our objective, not stretching too far each time, just so that we could have a plan for each of these encounters and then what followed on with the interstellar space. Amazing. So the only reason why certain instruments were shut off at a certain point was only to save energy then. Once we finished taking all the images, we finished flying by all the planets, we turned off all of the planetary instruments, including the imaging system. That saved power. But the amount of power we had at that time was not a problem. We can't save it. It's a radioactive decay. Oh, yeah. Of course. But it did mean that we could save space in our computers. The computer memory on Voyager is about 100,000 times less than you have in your smartphone. And so we wanted to use all those memory bits there were for the interstellar mission. So we shut down, reprogrammed the computers to focus on interstellar space rather than on planetary space. Ah, that's the reason. And continue to have been running those programs now ever since. Yeah. So to be precise, how many kilobytes do you have? To be precise, how many kilobytes or megabytes do the Voyager probes have? Each, we have three computers that run the spacecraft. Each of those has about 4,000 words of memory. 4,000 words? 4,000 words. 12-bit words, roughly. I can't even imagine such a tiny piece of memory. Yeah, what do you do with it? Yeah, exactly. You program every bit very carefully. Yeah, of course. I guess you do. Yeah. So you have plutonium reactors, right? No, not a reactor. Oh, how do you call it? It's a natural radioactive decay of plutonium-238. It just decays away with an 88-year half-life. And when it decays, it gets hot. And so you bolt thermocouples to the heat source and make electricity. It's a very robust, simple, no moving parts, but it does decay away. That's where the energy comes from, is the heat. And so the heat which we use to make electricity means that we have less heat each year. We now have to turn off each year something that takes four watts, because that's how much we lose, how much less power we have year after year. Four watts. And so eventually we'll have to turn off the spacecraft. Right now it's around 23 watts? Is that how much? That's the transmitter is 23 watts, but it takes about 70 watts of power to get 23 watts to Earth. Ah, okay. That does all of this to get to Earth. That's just to transmit 23 watts. Yeah. So that's about 70 watts, you know, a big old light bulb. That's what the entire Voyager runs on. You lose about four watts a year right now. Four watts a year. Whoa. Okay, so it's a countdown. And I guess this decay and the heat it generates also serves to keep the spacecraft itself at a certain temperature, because otherwise it would stop functioning, right? That's correct. So the thrusters, we have to keep the thrusters above a few degrees centigrade, because that's where the hydrazine fuel freezes. So as the spacecraft gets colder, with time we have to make sure we find a way to keep the thrusters warm enough so that the hydrazine will continue to be usable. Okay, so you still do attitude control as well? Oh, yes. The spacecraft always points at Earth. That's the way you get the data. Yeah, of course. It's always pointed at the Earth. But the limiting factor is power from the plutonium source and not the fuel supply. That's correct. We have plenty of fuel. We just have to make sure we keep the thrusters warm enough and that we have enough power to run everything. Wow. Amazing once more. Amazing, amazing once more. Beautiful. So you keep on steering that thing. How far away are they, 17 light hours-ish? That's right. Yeah, that's about right. Okay. And they beam back. So you said they beam back their signal with… 23 watts of the freaking light bulb. Yeah, it's a light bulb in your fridge-ish. That's right. I don't even get this. And then 17 light hours away with three antennas, right? One in Australia, one in Spain, and one close to you in California? Yeah, that's right. Now we're using the largest antennas, which are 70-meter antennas. Or we can use a… We can… A Ray-2 has 34-meter antennas. So it takes either one antenna or two 34-meter antennas to collect the data now, because it is so faint. But is it… How faint is it exactly? How much noise is in the background, so to speak? Well, we still have very good signal-to-noise. So we're running at 160 bits per second. So the bits are rather long. And that's the way you compensate for the distance. You just stretch out the amount of time you take. That's the amount of time it takes to transmit either a zero or a one. But it's the same speed, if I remember correctly, that you just explained was beamed from Jupiter. Yeah. And since there's more power, the signal is stronger, we can keep the bits shorter. You don't have to… You need to keep the bit on long enough so that you know it's a one and not a zero. Yeah, yeah. And the further away you get, the longer you have to wait before you transmit another bit. So we can transmit about 160 bits per second now. 160 bits per second. Oh, bits. Yeah, not kilobits. Right. Okay, it's a factor of thousands. Yeah, a factor of thousands. I missed that. Okay, I apologize. And so it comes in the form of a wave, I guess, like a radio signal. But it also becomes almost like Morse code in this way, if it's only 160 bits. Yeah, interesting. So… At a certain point, it goes out of… Well, beyond Neptune. And Forager 1 goes up, right? Yeah. And takes this family portrait, of course, of the entire solar system. Can you take us back to that moment? Why the family portrait? Well, we realized this was the first opportunity where we had a camera beyond all the planets. And so when… This was actually on Voyager 1, which… And so it was in February 14th of 1990 that we took the photograph, a series actually of images, because the whole planetary system won't fit on one frame. So we had a whole set of frames, so that when we, if you like, pasted them together, they would show the planets arrayed in the solar system. The first time that we could do that. And so we thought that was another milestone in human exploration. Yeah. Was that actually Carl Sagan's idea, or is that just urban… Well, he was certainly an important factor in making it happen, because it meant we had to continue the mission operations for another year to do it. And keep all the instruments on. And so there was a commitment of funding that was required, as well as keeping the staff on board, so we could take one last set of images. Process them and so on. Really? For those pictures? And that's what we did the first six months of 1990. Really? So only… So for… Specifically for those pictures? Those are some expensive pictures. Yeah, but really cool pictures. Oh yeah. Not just any pictures. Worth every dollar. Yeah. And so… And of course the pale blue dot was in there. Yes. Yeah. And how did that come to be? How did… Because there's this weird light coming from the side. Oh, that's a scattered light. Yeah. That's… What is that? Well, it's just scattered light. You know, the camera was never designed to look that close to the sun. And so what happens is you get a glare, if you like. Okay, so it's sunlight, right? It was… The light in the beam is from the sun. It's just scattered into that stream. Just happened to capture the Earth in that beam. It's an accident again. But I do think we ought to explain, maybe some listeners don't know the pale blue dot. Yeah. Yeah. Carl Sagan had the idea to have Voyager look back to Earth. Yeah. The whole… Like Ed just said, the whole solar system. So it's a whole… Well, that's not the pale blue dot. It's a whole stretch. Yeah. The pale blue dot was… So they took a picture of Earth. Ed, if I'm making any mistake, then please correct me. Yeah. But so then they took a picture of Earth and Earth in the family portrait is the pale blue dot, right? Is that so? Yeah, that's correct. I didn't know that. Yeah. Yeah. I learned another thing. Yeah. Okay. We learned a lot today. Beautiful. So we had… We took separate images. There was an image that had Jupiter in it. Then we had to turn the camera a bit and take a picture with Saturn in it. And then we would move it a bit and take a picture of it with each of the planets. The only one, as I recall, we couldn't do that was… We couldn't do Mars because I think it was too close to the sun. And we couldn't do Mercury because it was too close to the sun. Okay. So it was sort of a panoramic picture. Yeah. It was a panoramic picture. Moving the camera and gluing it together. So the family portrait doesn't include Mercury and Mars. They've been expelled from the family, the black sheep of the family. I never knew. I never knew they weren't in there. So how do you… Is it all programming? Is it constantly coding the voyages or is there some sort of old interface there at JPL that… People still push like the same old buttons? How does it look like? How do you control those two spacecraft? We can control by sending commands to the spacecraft and changing the program on the spacecraft to do something different than it had been planned to do. And so we occasionally, a few times a year, we'll send up a new set of instructions to do something a little bit differently or to do something that hadn't been done before, for instance. We can do that. We send up commands, digital commands. Ones and zeros again. And change the program in the spacecraft so that when the time comes it does something different. Sure. But what I'd like to know, and this may be a very stupid question, do you still use, at Mission Control, the stuff that you used back then or has this all been updated hardware-wise? All the ground-based hardware has been upgraded. In fact, we had one computer which was completely… completely out of date that we kept on through Neptune. That was one which had to do with sequencing of things and we didn't want to have to qualify the program on a new computer. So we managed to keep that ancient computer running until we finished all the imaging. And then we shut it off and there are no programs left anywhere to display those… to interpret those bits and zeros that make images. Yeah. Because I figure it can be harder to use. Yeah. It can be harder to use modern equipment to control an ancient piece of hardware like Voyager in some cases than to use the ancient stuff. Well, no, that's actually… turns out all we need to do to actually control it is to set up commands… send up commands which change the 4000… some part of the 4000 words of memory. Okay. Yeah. And it's actually easier to do that with modern equipment. Yeah. So you can send it up because you're just trying… you're just changing the computer, which is a very tiny computer compared to our capability on Earth. Yes. And you need to edit some commands and you can do that on any computer because it's basically all just text. That's right. It's all just ones and zeros. Yeah. Yeah. Yeah. Yeah. Right. Just sending just plain old ASCII text up or something. Or it's computer code. Or machine language or whatever. Machine language. Yeah. It's probably machine language, right? Machine language. Right. Yeah. Yeah. Very cool. So I sort of want to look ahead to the future. So you already said that Voyager… both Voyagers are now in… what's the name of the mission? The Heliospheric mission? The Voyager Interstellar Mission. The Voyager Interstellar Mission. So that's the currently active mission. I would like to take a step back, if you don't mind. Oh, okay. Then we'll talk about the future in a second. Because we have… when we started this podcast, I said something like, it's all a matter of time. And I'd like to run through the definitions. We have the solar system. Okay, good. Yeah. We have the Heliosphere. Good. We have stuff like the Kuiper Belt and the Oort Cloud. I'd like to know… when I was a kid, I learned about the planets. And there was Pluto was the last one. And beyond Pluto, there was nothing. Nothing… Yeah, that's how I was taught as well. …worth knowing. I mean… Yeah. So to me, the solar system ends with Pluto. That's all. Yeah. So nowadays, it's different. But Ed, can you tell me, if we move beyond Pluto, what boundary do we get first, like the Heliosphere or the Oort Cloud? Or tell me, what's the order of things, please? Yeah, great. Good question. Well, the first thing, the first boundary that you cross, and it's really the only clear boundary, is the heliopause itself. This is where the solar wind and the interstellar wind meet. Okay. And that's the boundary. And beyond that, what's beyond that is the Kuiper Belt, which extends… see, the heliopause is… actually, the Kuiper Belt is actually… much of it is inside the Heliosphere. Mm-hmm. The Kuiper Belt is inside the Heliosphere. That's right. And that's where comets live, okay? Yeah. And then the comets, the long-period comets, come from the Oort Cloud. And it will take us about 300 years to get to the inner edge of the Oort Cloud. You mean… Yeah. You mean about 30,000 years to get to the outer edge of the Oort Cloud. That's fly time of Voyager, is that right? I'm sorry? You say 300 years. That's fly time of Voyager. Yes, that's Voyager. How long it'll be for Voyager. Okay, yeah. That's too bad, because, well, it won't… they won't last that long. You won't see that, no. But 300 to 30,000 years. Yep. That's… so the Oort Cloud is gigantic. Huge. Huge. Giant. Yes. And I mean, you know, we're talking a little bit about the Sun, but when you get… if you think of it, if you get as close to another star as you are to the Sun, you're right between them, at that point, those comets can be around either planet, but as you continue on, the comets will be around that next star. Yeah. Because that gravity field will be stronger. So both stars, Oort Clouds, meet. They kiss, so to speak. Yeah. Yeah. Yeah. Okay. And so there's hardly anything between Pluto and the heliopause. And the heliopause being the edge of the… of the… of the… Well, the hyperbelt is in that region between… Okay. …Punto and the heliopause. Okay. So where, in your opinion, does the solar system end? Well, the solar system doesn't have a clear end. There's a balance point somewhere between the Sun and the nearest star, halfway between… roughly halfway, depends on how the… what the masses are of the two stars. So there's a gradual transition where eventually… Yeah. …you're orbiting the other star. You're closer to the other star than you are to the Sun. Yeah. Yeah. So you would… if I can… if I interpret this correctly, you would define each star's territory, each star's solar system as the edge of its Oort Cloud. Yes, that's right. Yeah. Yeah. Okay. So all these solar systems actually also kiss. Yeah. Yeah. The thing is, Ed, I have a… I have a tattoo of Voyager. Because… Yes. Yes. Yes. Yes. And I love your project very much. And in bars, I always keep on telling people, like, oh yeah, it's the only man-made object that left the solar system. Actually, Ed, we should send you a photo. Maybe we will. Yeah, I'll send you a picture of it. And it's nicely done. Like I really love the artist who made it. I can testify that. Yeah. And… but I always keep on telling this wrong in bars then, I guess. Like I keep on saying, like, oh yeah, it left the solar system. But I have to change my story, I guess. 30,000 years, Thijs. Yeah. Yeah. The reason I got it, though, is because it's this… it keeps on exploring. It keeps on finding new things. So I thought that was very inspiring. So that's why that story still holds, right? Yeah. That's wonderful. But… yeah. But I wonder how we'll talk about it in 10 years, because we're not really sure if we still get data in about 10 years from Voyager, right? That's right. That's right. How do you see it? How will the next 10 years or 20 years go? Well, we still have… we still… we still have… we still have… we still have… we still have lots to learn about this interaction between the interstellar wind and the solar wind, and we will do what we can for the next 5 to 10 years to make… take the best advantage of this unique opportunity. It'll be decades before another spacecraft is where Voyager… where the Voyagers are today. Mm-hmm. True. Which instruments are still on? On Voyager 2, we have a plasma instrument measuring the wind. We have a plasma wave instrument which measures the radi… the oscillations in that wind. We have a low energy charged particle instrument which measures things that have been accelerated up to, say, 5% the speed of light. Then we have the cosmic ray instrument which measures the particles which have gotten accelerated up to almost the speed of light, called cosmic rays coming from those supernova explosions. And the… so we have… that's… yeah. Okay. And that's… we have the plasma instrument which measures the wind. Mm-hmm. Yeah. On Voyager… that's on Voyager 2, not on Voyager 1. And so then how will you determine… On the magnetic field, yes. We have a magnetic… we also measure the magnetic field. Ah, okay. Yeah. Inside the bubble, the magnetic field came from the Sun. Outside the magnetic field is from the galaxy. Right. Insane. Is there any… is there any to speak of? Yeah. I'm sorry? Is there any magnetic field to speak of? Oh, yes. Yes. Yes, it's significant. The magnetic field inside an interstellar space is a bit stronger than the field inside our bubble. What? How? Okay. Well, the field inside our bubble comes from the Sun. It's a long way out there. So the field gets very weak. And then the galaxy is bigger? The galaxy is bigger and the field is actually a bit stronger. Ah. Crazy. But aren't they in some sort of balance right at that point? Right now? Well, yeah. There is a balance. And the point is it's not the magnetic field which balances. It's the total pressure which includes the… the… The… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… the… The wind itself, the plasma. I see. So there's pressure from the plasma, just the wind pressure, and there's pressure from the magnetic field. Which is… which is the… the first instrument you have to start shutting off, you think? We haven't decided that yet, but we have three instruments which have heaters. The first thing we'll be turning off are the heaters. And then we'll turn off a heater that will give us an additional year. Then we'll turn off the next heater that gives us another year. Third heater turn… we turn off gives us another year. And then we have to start turning off one of the instruments, four… four watts each. Wow. That's… is that a sad thing to do for you? Well, it's been a great journey. I don't… I don't think… Yeah. It's been a… really quite a joy. But still… Sure. I'm sure. Do you have… do you have any guidance on what… like what is your… what are the rules of which ones you want to shut off? Well, we… that really depends on what the… what the situation is. What the situation looks like in terms of instrument health at the time we have to do this, and also the question of what science is remaining that can be… where… if we have to prioritize the science. And so the two energetic particle instruments, we'll probably… we would shut off one of those in order to… because we have only one… I think that's what would be one of the… one of the first things we'll turn off is one of the charged particle instruments. Okay. And so that… which is the one that you want to keep on? Yeah. And so that's the one that you want to keep on for the longest as possible? Well, that… well, they really depend on what… you know, what's working… Except the transmitter, of course. …and what science is telling us. Yeah, okay. Yeah. Sure. This is all exploration, so we will make best use of the… make the best decision we can at the time we have to make them. Yeah. Yeah. Great. We… you know what we haven't talked about yet? And this… it's kind of funny because everybody always talks about it right away. It's the Golden Record. The Golden Record. How… how long… so the Golden Record, for the people who don't know, but I… I'm sure… Yeah. …for the people who don't know, but I assume that our listeners kind of know, a golden… Otherwise, Google it. Otherwise, Google it. On YouTube, you can listen to all the sounds, you can see all the pictures. That's right. So, a plate, of course, which is almost like a time capsule of… of humanity in the 70s. I love… I love the picture of the… the children holding their… their hand on the earth. It's such a… it's such a… I don't know. Do you know who came up with these pictures? Yes. I'm not sure. I don't know exactly who came up with which picture, but there's a book out called Murmurs of Earth, which Carl Sagan and the team wrote about how they chose what music is on the record, what pictures are on the record, what greetings are on the record. Yeah. It's so good. You know what I love? I love the idea that all those pictures were analogically coded. Yeah. Yeah. Isn't that right, Ed? I'm sorry, say that again? The pictures are coded in an analog signal. Yes. That's correct. This is a grooved record, and so it's encoded just… it's not coded. It's just a record like the old-fashioned grooved music records, but instead of making music with the groove, you make the sweep of the electron beam on a cathode ray tube like the old-fashioned televisions did. And that's a crazy idea to me. And somehow the recipe for decoding it is also on the record. Yeah. Yeah. And the recording of it is also on the record, right? Yes, that's right. That's… yep. And there's a video, I think, either by Motherboard or The Verge from a few months ago, I think two, three months ago, where they try to decode it as if they're aliens. Like is this actually something that we can… Can this be done? Yeah. Of course, there's a lot of sort of like things that you have to keep in mind that it has to do with… especially the timing is really hard to get right, I believe, right? Yeah. Yeah. Yeah. Yeah. Yeah. So how long will these records last? Well, what you see when you look at what's called the golden record is actually a dust cover. The record, the groove record itself, is behind the dust cover to protect it. The estimates are that dust cover should last at least a billion years in terms of preventing dust from obliterating the grooves in the record. And the record is two-sided, so the backside of the record will last much, much longer. Wow. Yeah. So… Billions of years. And it will just keep on going around the center of the Milky Way. Yes. Just like us. Yep. Like endlessly until… well, so it will outlive the sun then if it's a billion years. Or is it? Not quite. Not quite. The sun will still be there, but the Earth will probably not be habitable by then. That's… Yeah. That's right. We'll see about that. Yeah. Yeah. But you now can foresee when the last… Yeah. When the last instrument of Voyager will be turned off, right? Yes. So, that's in about four years. Did I get that? No, in about… in 2026, Ed, is that around? Something like that. That's right. Yeah. Okay. About seven years. Yeah. Okay. So, what will you do next? What's your new career going to be, Ed? Yeah. Well, yeah, I've already… we've already started on that. We have an instrument on the Parker Solar Probe, which was launched last August. Yeah. And now it already had one solar flyby and has 24 flybys of the sun in a stepwise fashion getting closer and closer to the sun to explore where all the wind began that created the heliosphere, if you'll allow me. Yeah, great. So, you're looking the other way now. The sun is the source. Yeah. You're looking the other way now. This is the inner frontier. This is the inner frontier of the heliosphere. Yeah. Yeah. Yeah. heliospheric science like you that was something that you sort of got into because of voyager then i'm sorry what's the question so suddenly you do heliospheric science um even though voyager was just a well not just was voyager was a a quest for exploration to see what's out there and then it's turned into a a very legit new form of science of studying the uh the heliosphere that's correct yeah so now we're now we're studying the inner frontier of that heliosphere yeah perfect near the sun within 10 solar radii uh in its last encounters it's very very close very close yeah hasn't burned up yet the parker solar probe no and um and so uh we talked earlier on this show about uh maybe missions to neptune and uh and uranus hang on about it oh sorry just one more question about parker and and voyager um how does does this work for you time wise how much of your time does one take up and how much the other well it it varies um and whether we have an event or whether whether we have in other words when we cross the heliopause that's clearly an event so that takes more time uh but then during the regular steady cruise it takes less time so it varies and the parker solar probe of course is a very good example of that and i think it's really clear to us that crawling from but it's a pretty interesting!" going back we it's strange we will probably do that but also the the planet pace is how thin the galaxy is uh it's still not have deep报ing concentration but how do you get are being, well, every five years, of course, I guess, and some events along the way. Yeah. Yeah. And so maybe a mission to Uranus or Neptune to go check out for a second time what's there. How do you feel about that? Well, there will be another. Every 10 years there's a survey that the National Academy of Sciences runs with the community to determine what the next steps are. And there are always lots of good ideas about what to do next. And the next decadal survey will get started in a few years. And right now the next step in the outer planets is a mission to Europa. Of course. Beautiful. To try to fly by very close to Europa and really determine what this world is like and whether there are any places where their liquid water is coming to the surface and could might be... or some other way to analyze what that ocean might be like beneath that icy crust. Wouldn't you love for a probe to land there? Oh, eventually. But the radiation environment in Europa is incredibly intense. Oh, right. And so you'd want to bury something. And you'd like to find a place where you don't have to bury too deeply. So... So the main thing right now is the next mission will be one of mapping. That is looking on the surface where there's current activity of any sort. I mean, there are some indications there may have been some plumes at one point in some of the data we have. And so I think that Europa mission is going to be a very important one. Okay. And not Enceladus instead of Europa. Well, Europa sort of got in the head of the pack and the priorities because we... We've been studying Europa now since Voyager and the Galileo mission is to actually prove that there's a liquid water ocean. So it really became the next priority. But I think eventually there will be missions to Enceladus. There'll be missions to Titan. There are obviously going to be more missions to Mars. This whole issue of search for life is, I think, a very powerful one. Yeah. Because Enceladus, of course, Cassini already flew through the plume. So they... Yes. We have already found organic material even, I think, in that plume. Yeah. Yeah. Well, we're going to see. We're going to see. And so no... I hope so. So you're not rooting for anyone for a mission to Uranus or Neptune? No, I'm not. I'm going to let the community... I'll just watch the community. You've already been there. You've already been there. Exactly. Does it feel that way, by the way? Do you feel as though you've been there? Well, certainly. You feel like you've been there. You're seeing things that nobody's seen before. Yeah. And that's certainly the case for Mars, where you're actually seeing it down on the surface just as though you were standing there. That's right. Incredible. Incredible, right? Yeah. Very incredible. Well, thank you for talking to us, but also thank you for being on that mission. It's an inspiration, I think, for the whole world. Absolutely. Yeah. So thank you very much. It's been great talking with you. Yeah, the same. Same. And good luck. Thank you. With all the new endeavors and your study of the inner heliosphere as well. Right. All right. Thank you so much, Ed. Thanks, Ed. You're welcome. Thank you. Bye-bye. And thanks to all our listeners as well. Yeah, all of them. Yes. For staying tuned. You can listen to the show on Spotify, on iTunes, or anywhere where podcasts live. But also don't forget to subscribe on YouTube because there's also a video, of course. And you can support us via Patreon. And you can support the show, of course. Patreon.com. On Patreon. Space Cowboys. Thank you so much. Bye-bye. Bye. Touchdown. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye. Bye.