Why were the Voyager missions so important? Where are they now, and where are they going? What is their ultimate fate? And that Golden Record…good idea or bad idea? I discuss these questions and more in today’s Ask a Spaceman!
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Hosted by Paul M. Sutter, astrophysicist at The Ohio State University, Chief Scientist at COSI Science Center, and the one and only Agent to the Stars (http://www.pmsutter.com).
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EPISODE TRANSCRIPTION (AUTO-GENERATED)
You know what time it is. It's time for Ask a Spaceman. I'm your host, Paul Sutter. You've got questions and I've got answers. You know how this show works, but let's travel out there one more time. You go online to Twitter or Facebook, use the hashtag Ask a Spaceman and send some questions and I will find them. You can also follow me directly on Twitter and Facebook. That name is at Paul Matt Sutter. You can also go to the website AskASpaceman.com, AskASpaceman at gmail.com, youtube.com slash Paul M. Sutter. So many ways to get questions, but really just one way to answer them. And that is through this show. We have one simple goal with this show. That is complete knowledge of time and space. And on the road to complete knowledge of time and space, we have today's questions. Rob H. via Facebook asking, what awaits the Voyager mission? Ryan asks via email, what is the sun's motion through the galaxy in the direction of Voyager? Wow. Voyager probes. This is historic. I'm recording this episode, by the way, near the 40th anniversary of their launch.
And it's hard to describe just how groundbreaking. Space-breaking? Yeah. Let's go with space breaking. It's hard to describe just how space breaking the Voyager missions were. And they happened at just the right time. It is such a cosmic coincidence, a lucky break at just the time that we were able to actually develop interstellar spacecraft, right? and launch them outside of the Earth's gravity well, send them into space, pack them with scientific gear that could take pictures, that could carry instruments to detect other things, be able to power it, and be able to communicate back with Earth. I mean, think of all the technologies that are packed into a spacecraft and how... 10 years before, 20 years before, 50 years before, 100 years before. That kind of package wouldn't just be impossible, it'd be inconceivable. Go back to the 1800s and try to explain to someone the concept of an interplanetary spacecraft. That's just not a thing that a 19th century mind could wrap itself around. But we're able to do it very, very quickly in the 50s, 60s, and 70s.
And at just the right time in the 70s and 80s, the outer planets lined up. That only happens about every 200 years. 200 years! So if we missed the window, say they lined up in 1910, we would have to wait another 100 years for this opportunity. The planets were in just the right orbit where you can launch them from Earth and swing from gas giant planet, gas giant planet, using the gravity assist to boost the spacecraft each time and kind of hop around like a monkey on a vine from tree to tree swinging from planet to planet. It didn't just make it easy, it made it possible. Because if the planets were on the opposite side of the solar system, you would get to visit one, maybe two. And, you know, that's an expensive mission no matter what, you know, politics and all that kind of stuff maybe just would have never happened. But we did get lucky and we took advantage of it. NASA took the Mariner design, which was very successful for Mars missions, and did two copies, two different spacecraft.
And those were the days when NASA could build two of everything. And sent them, these were the Voyager missions, Voyager 1, Voyager 2, launched from Earth. on a decades-long mission to explore the outer solar system. Do you remember the excitement from New Horizons when it first returned its images of Pluto? And just the fascination and the sense of adventure and excitement and curiosity and how we're seeing things that no one in human history has seen before. It was kind of like that times 10, right? Yes, we had the Pioneer missions before the Voyagers, but those cameras weren't nearly as good. Those were kind of just like test runs compared to the Voyager. The Voyager missions revolutionized our understanding of the outer worlds and brought... our solar system into the popular imagination. You know how like everywhere, like you can, I can just say Saturn and boom, you think of Saturn. It's because of the Voyager missions that I can say Saturn. And you don't just think of a little dot of light or a little blurry image.
You think of a detailed world with cloud bands in the rings and the moons. You can picture it in your mind because of Voyager. Voyager 1 just hit Jupiter and Saturn, plus visited Titan for a bit. Voyager 2 got to visit all four. To this day, by the way, to this day, Voyager 2 is the only spacecraft to visit Uranus and Neptune. Open up any book on the solar system. Search online, solar system. Go ahead, I dare you. If you look up, what is the picture of Neptune? That picture will be from Voyager 2. That's it. That's it. That's all we got, folks. It's hard to describe the amount of data gathered by those missions. It really opened up this frontier, this outer solar system. What New Horizons is doing now with the realm of Pluto and the Kuiper Belt, Voyager did for the outer planets. 30 and 40 years ago. There's detailed images of the Great Red Spot. There's the volcanic eruptions on Io. There's the cracks on the surface of Europa. There's impact sites on Ganymede. It's just, man. So much to discover and so many questions raised by this mission.
Like, what's going on there? What's over here? Why is this happening here? That all modern missions to the outer planets basically go back to the Voyager mission and say, hey, remember when Voyager detected this or saw this or we got this feature? Yeah, we want to figure that out some more. Voyager was the first one. It was not a short mission. It was launched in 1977, hit Jupiter in 1979, Saturn in 1981. Five years later, Voyager 2 gets to Uranus and finally Neptune in 1989. These spacecraft were built tough. They had to operate in the dead of space off and on for decades. And they spent a day tops at each planet. So cruising through space, doing nothing for years and then oh planet mission everything every all systems online full communication full power collecting data for a day and if it's gone they would loop around the total it spent about a month each spacecraft would spend a month around each system but the flybys of the planets themselves lasted about a day In that month, they would get images and detailed observations of the moons of those planets if there are lucky alignments.
But just think about a day like you've been waiting for years and then it's go time and then it's over in a day. The designers of the Voyager spacecraft knew that they would reach interstellar space. Spoiler alert, by the way. So they included a gigantic antenna dish. 12 foot diameter, that's 3.7 meters. That's a big antenna dish. And you're going to need it if you're going to be beyond the edge of the solar system and still communicate with Earth. And it just amazes me how much science and scientific gear the engineers packed into these spacecraft. Optical cameras, infrared and UV spectrometers, magnetometers, plasma wave antennas, triaxial flux gate magnetometer, which sounds way cooler than it actually is. Try saying it three times fast. Cosmic ray detectors, shields, thrusters, computers, targeting sensors, the works. So much stuff is packed into these spacecraft. And they're equipped to not just take pretty pictures, which are very pretty and also very useful, but really study the physical properties and the environment of these systems.
Remember, this was like a once-in-a-lifetime shot. They had to make it work. They had to make it count. They had to take data, they had to do science, gather as much information as possible. So not just a pretty picture of the atmosphere, but temperature differentials across different latitudes, magnetic field strength and penetration of the magnetic field, the whole deal, the whole deal. But enough of what they did. Where are they now? They're about plus or minus 13 billion miles from the sun. That's 21 billion kilometers. As if that means anything. That's just a large number to most of us. It's hard to picture that. That's 140 times further from the sun than the Earth is. Five times further than Pluto is. They've been trucking for a while. They've been going 30,000 miles per hour for 40 years. Some of the fastest spacecraft ever designed, and they've been cruising nonstop for 40 years. They're at such a distance from the sun that even the giant planets are just bright pixels in a grainy image.
Even here on Earth, if you pull out some backyard binoculars, you can see the disk of Jupiter. You can see the disk of the planet Saturn and its rings. Voyager has a much, much better camera than your backyard binoculars, but it's so far away, it can't even see Jupiter, Saturn, Uranus, and Neptune. One of the last images it took was what's called the family portrait, a series of images capturing each planet. And each planet is just like a little tiny dot. If you get out to the distance of Neptune and Pluto, that's like deep twilight. Like, you know, like say an hour into sunset where the sun has definitely gone down, but there's still some light left. That's what it's like at Neptune and Pluto. This is about 1 25th. of that level of light, that level of illumination. I can only imagine it's incredibly weird and isolating out there because the sun is also very small at these distances. It's just a point of light, just like any other star is a point of light, but it is still uncommonly bright.
It would still be painful to look at. You can definitely pick out the sun from the field of stars. Like, yes, that's the sun, but it's not a disk. It doesn't take up any area on the sky. It's just a thin point, but in an uncommonly bright point of light. And Voyager 1 really is in interstellar space. It reached it on August 25th, 2012. Voyager 2 is on the cusp of interstellar space. It'll reach there in 2019. How do we define interstellar space? You know, there's a few definitions that you could pick. The one NASA chose is a good one and good enough for my purposes. I would count this as truly interstellar space is based on the sun's influence, for lack of a better word. Not gravitational influence, that extends technically to infinity, but pretty far. But rather the bubble influence. It's the place where the solar wind meets the interstellar medium. The sun is constantly ejecting charged particles off the surface. And it floods. These charged particles flood our solar system. When they come to the Earth, they interact with our magnetic field.
They get funneled to the poles. We call them the aurora. But these particles extend way out into space, past the orbit of Neptune and Pluto, the Kuiper Belt, the whole deal. But our solar system is embedded in the galaxy, and the galaxy is filled with its own population of high-energy particles, you know, ejected from other stars, ejected from stars. supernova accelerated by magnetic fields. The whole deal, the whole deal. And there's a certain point where you can tell. It tastes different. Where you're like, nope, nope, this is the sun's. This is the sun's charged particles. And then... Nope, nope, nope. This is the galaxy. It mixes together. Almost as if I were to pass gas. No, in an elevator. I don't like that analogy. Let's say you were to pass gas in an elevator. There's a point where the expanding shell of gas coming out of you just mixes with the general atmosphere. And where there's a certain point, if you get further away, you couldn't even tell the difference. It's kind of like that, but made of charged particles.
There's a certain point where the bubble of our sun's influence just mixes and mingles with the galactic milieu. And we give names. Of course, this is astronomy, so we have to give names to everything. We have the solar wind. Eventually, the solar wind stops. It slows down where it meets the galactic interstellar medium. That's called the termination shock. Then there's a region called the heliosheath. and the heliopause after that, and the bow shock beyond that. And of course, it's not just a spherical bubble around us. Our solar system is moving through the galaxy. So it's compressed on one end and extends out the other. Kind of looks like a tadpole. That's our little region, our little tadpole region. For Voyager 1, there are multiple crossings, multiple crossing events where you could tell the difference between the solar environment and the galactic environment. So that suggests that it appears to fluctuate. It wibbles and wobbles back and forth. And that's new stuff, by the way. Voyager 1 is the only one to do that ever.
So we're basing this totally on its observations and its detections. We had no idea where the termination shock might be. We had no idea how thick the helio sheath might be, where it begins to mix from the solar environment to the galactic environment. This is new stuff. And that's pretty cool. So that's in addition. to the Voyager probes, and especially Voyager 1, opening up our outer solar system, reveals what's going on at the very edge of the sun's influence. It really is an interstellar space. It is beyond the influence of our own sun. It is the furthest human-made artifact. We are still communicating with Voyager 1 very weakly. Its power source is dwindling. Obviously, solar power isn't going to get you very far out here, so it has what's called a radioisotope thermoelectric generator. Pretty straightforward concept. You take a lump of radioactive plutonium, stick it in one end of a piece of metal, a semiconductor, and it will heat up the metal. But because you actually have two pieces of metal glued together, they're slightly different materials.
One will heat up faster than the other. because of the heat from the plutonium. And if you have a metal that's hot on one side and cold on the other, you get a flow of electrons, and a flow of electrons is called electricity. So it's pretty easy, straightforward device. It gives long-lasting power. It's like a nuclear battery. That's a good way to think of it. It doesn't last forever, though. One by one, we've been shutting off its systems. We shut its cameras off pretty early. Those are pretty power hungry. Just have a couple detectors, especially to study this helio sheath and helio pause and the bow shock and the determination for all that good stuff at the mix at the boundary between our solar system and interstellar space and to communicate back with Earth and to run the computers. So it's been on low power mode. We can still communicate with Voyager. And by 2025, there will not be enough power to run the antenna. It's a radio antenna, so it will go silent. It would be so quiet. It can't even contribute to Patreon.
Patreon.com slash PM Sutter is how this show and all my education outreach activities are funded by you, the audience, by my supporters. I can't thank you enough. It is your contributions that keep this show going. So thank you. Patreon.com slash PM Sutter to learn more. But Poitier can't even do it. It can't log in. It can't upload its credit card information to make that monthly donation. And eventually its credit card will expire and then it's bad news. So Voyager 1 is outside our solar system. according to that definition of the boundary between the solar wind and the interstellar medium, between the particles ejected from the sun and the particles that are just in the general galactic mix. There is, however, stuff associated with our solar system that's out there. There's the Oort cloud. The Oort cloud is a thin, diffuse shell of frozen debris that was kicked out when our solar system was formed. This is the home of comets that take tens of thousands or millions of years to complete their orbits.
There'll be these little rocks, frozen rocks, Hanging out in the distant parts of the solar system, they can get perturbed, they can get bothered, and they can fall in and swing in towards the sun. It will take about 300 years before Voyager 1 reaches the inner boundary of that Oort cloud. These are objects living in interstellar space, but still gravitationally bound to our sun. Voyager 1, however, is not gravitationally bound to our sun. It will keep going and going. It will never return. It will eventually pass by another star coming within 1.6 light years of a star called Gliese 445. And you know what? That sounds super far away. But when we're talking interstellar distances and galactic scales, 1.6 light years is pretty close. That will happen, by the way, in 40,000 years. Voyager 2 should reach interstellar space, we think, in about 2019, depending on its exact boundary of the heliopause. It, too, will pass by a star in about 40,000 years. It will come within 1.7 light years of Ross 245.
It will also come within 4.3 light years from Sirius, the brightest star in the sky. That will happen in 296,000 years. And then nothing. That's it. These are galactic scales. These are interstellar scales. And I love introducing the topic of Voyagers. I love talking about the Voyager probes in talks because it really hits home what it means to be interstellar, the true scales of our galaxy. It's like a punch in the gut when you really think about it. It took 40 years for Voyager 1 just to reach the edge of this bubble and see, like, oh, space isn't that big. That's four decades. That's not so bad. Oh, and then to even reach another star, 40,000 years. And then that's it. It's hard to predict, of course, because there is some chaotic motion to star movements. You know, new stars can be born and die. There can be molecular clouds that disrupt. But we're pretty sure it's never going to get that close to any other star ever. Our Milky Way galaxy is made up of hundreds of billions of stars.
And Voyager 1 and Voyager 2 will never encounter another one. Ever. Ever, ever, ever, ever. That's it. Forger one got to be close to our son and get to be close to Glees 445. Forger two will get close to Ross 248 and then kind of sort of close to Sirius. And that's it. The sun is sitting about two-thirds of the way out from the center of the Milky Way galaxy, situated on what we call the Orion Arm, one of the spiral arms of our galaxy. The sun itself has a speed of around 200 kilometers per second, so the speed of the Voyagers is that plus 38,000 miles per hour, which is still 200 kilometers per second, about. The Voyager probes themselves were launched going in front of the sun, so they take the speed of the sun, plus that they're kind of going out ahead of us. They really are voyaging out ahead of us. Going slightly up-ish and slightly down-ish, the interactions they had with the planets sent them on these slightly different trajectories. So they're not gonna keep going straight ahead of us in the galaxy in our direction, in our own orbit around the Milky Way, so they'll go up and down a little bit.
In 200 million years, they will circumnavigate the galaxy once. 200 million years after that, they'll do it again. It's weird to think about if you were attached to the Voyager spacecraft, wouldn't you be dead? But let's assume you were alive. Just the loneliness of being out there. Where slowly year after year our sun gets dimmer and dimmer and dimmer until you can't even tell it apart from the field of stars that surround you. And then dimmer still so you can't even pick it out. You can't even see it. And then dimmer still where you can't even pick it out with a telescope. And you'll pass by some other stars. Some will get brighter. Some will get dimmer. But that's it. You're never falling into another solar system. You're never seriously encountering another object. Nothing bigger than a microscopic grain of dust. A cosmic ray here and there. That's all you'll ever touch. That's all the Voyager spacecraft will ever touch. The story... of the voyager spacecraft isn't quite over even though their mission will end in 2025 no more communication no more data that we can acquire from those spacecraft there is something else on both spacecraft there's uh tucked between the instruments on the side is a small golden disc And we've etched some carvings into those disks.
Diagrams of people. You know, there's the dude waving high and the lady just standing there. Same as the pioneer plaques. The location of our sun relative to nearby known pulsars. And there's some basics about the hydrogen atom and the 21 centimeter emission line. Some basic facts that we think are totally universal. And there's some instructions. There's a little pictogram. And you could, it's hoped, look at this pictogram and realize that they're instructions. And if you follow the instructions, you end up assembling a spinning platform and a little stylus. And then you can take this golden disc, set it into that spinning platform and set the stylus in the grooves that are etched into the disc and start spinning the disc. And the stylus will start vibrating. And then you can interpret those vibrations as sound waves. And you could listen to those sound waves and those sound waves would carry information. There'd be some basic facts again, kind of establish what's going on. And then you would start to hear voices, sounds of nature, you know, crickets chirping in oceans crashing against the shore.
And then you'd hear music. There's a selection of songs placed on these interstellar spacecraft. It's taken from around the world. If I had to judge it, it seems kind of biased towards Western classical music. But there's a lot of cool stuff on there. And apparently, you would be wowed and brought to tears by that selection of music. And... This is like this is considered it was considered an emissary of Earth. Like, OK, definitely this golden record is going to outlive the designers and creators. It was led by a committee led by Carl Sagan, Frank Drake, you know, all the usual suspects. And it will definitely outlive them. And, you know, there's a pretty solid chance it's going to outlive humans as a species. And so like this is it. It's like a time capsule. of our time here on earth and an emissary like here's a little slice of our world a little slice of what we experience and a little slice of of us of our own culture of our own values of of who we are there's lots of recordings of people saying hi in various languages and the the the hope is the romantic hope is that you know someday eon literally eons from now Some civilization might encounter a Voyager spacecraft, recognize the golden record for what it is, follow the instructions, construct a spinning platform, look at the vibrations on the stylus, correctly interpret them as meaningful information, listen to the sounds and be like, oh, wow, okay, cool.
I honestly can't decide. If the Voyager golden records are this bold, noble emissary into the great void, the everlasting record of humane, a small piece, as small as it could be, as it is, it's still a part of us, and it's now permanently a part of us. So even in four billion years when the sun consumes the earth, when it dies, we've still got the Voyager probes out there with a little piece of our culture and who made them. I can't decide if that's cool or kind of silly because we know that those Voyager spacecraft are not going anywhere anytime soon. And the chances of the Voyager spacecraft coming within range of any star system are literally astronomically small, let alone one that is full of intelligent beings that could spot the Voyager spacecraft. They are kind of small after all. Toe it in, do all the stuff, gather meaningful information, and actually listen to the golden records. So it's... It's kind of, in one view, it's kind of self-serving and narcissistic. Like, oh, we need to make our mark on the universe.
So we have to send the golden records out just on the off chance that someone will encounter them. They have to know that we were here. They have to know that we existed. That seems, I don't know, that just strikes me as narcissistic and self-serving. Like, we're not doing it for them, whoever might encounter it, whoever they are. We're doing it for us to make ourselves feel good. But on the other hand, it's kind of noble and beautiful and poetic that we do have this emissary out into the great void. So is it a good idea or a bad idea? Is it silly or noble? I honestly don't know. I go back and forth. And I'd love to hear your thoughts on Twitter and Facebook. Go ahead and shoot me. What do you think? What do you think of the Golden Records? Good idea or silly idea? Let me know and I'd love to have that discussion with you. Thanks so much to my Patreon contributors this month, especially my top ones, Justin G, Matthew K, Kevin O, Justin R, Chris C, and Thanks to all the Patreon contributors, patreon.com slash pmsutter for more info.
And of course, thank you to the people who asked the questions for today's episode. Rob H. on Facebook and Ryan S. via email. Beautiful subject, the Voyager missions. The scientific return is enormous. Thoughts of where they are and where they will be. very sobering and then open up this interesting question on the voyager golden records thank you so much thanks again you can follow me on twitter and facebook directly at paul matt sutter love to hear your thoughts on this episode you can also go to the website ask a spaceman.com send questions to ask a spaceman at gmail.com go to youtube.com slash paul m sutter go to itunes and submit a review that really helps the show's visibility i really appreciate it and i'll see you next time for more complete knowledge of time and space