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00:00Voyager, the most ambitious space mission in history.
00:06The two Voyager spacecraft are iconic.
00:09Iconic.
00:10Iconic.
00:11They're the first probes to truly explore half the planets in our solar system.
00:17Jupiter, Saturn, Uranus, and Neptune.
00:20These went from dots of light in the sky to real worlds.
00:25The Voyager missions have ventured far beyond where other probes have explored.
00:31They are the most distant emissary representatives of the human species.
00:37They're the first spacecraft to taste interstellar space.
00:41Exploring further than any human-made spacecraft has gone before.
00:55Voyager 1 and 2
01:01These are the logs of the starships Voyager 1 and 2.
01:05They have crossed the final frontier and are now in interstellar space.
01:12Almost a decade ago, Voyager 1 achieved something that had never been achieved before.
01:17It left our solar system.
01:19When Voyager crossed into interstellar space, humans became an interstellar species.
01:2814 billion miles from Earth, their radio signals, traveling at the speed of light, still take 21 hours to reach us.
01:39The Voyagers are so far out that when they look back toward the sun, it's just a pinprick of light.
01:44And they would need an exceptionally powerful telescope just to see the Earth.
01:49Their original four-year mission has been extended to 44 and counting.
01:55From their current distant vantage point, they look back on the strange new worlds and bold new science they discovered.
02:07August 20, 1977
02:11We have ignition and we have liftoff.
02:15The mission begins when Voyager 2 blasts off.
02:20Followed two weeks later by its twin, Voyager 1, which will take a shorter and faster route.
02:28Their destination? Jupiter and then Saturn.
02:32When the time comes that that mission is actually ready to go to the launch pad,
02:38it's a funny mixture of joy and bittersweet loss.
02:43They become like your children, and that launch is like the birth of a baby.
02:48I was standing there watching it climb up into the sky, and we were cheering, we were so happy.
02:53Voyager was on its way.
02:58Though funded to just explore the two gas giants, mission planners have a much bigger journey in mind.
03:06To send the Voyager spacecraft on a grand tour of the solar system
03:12to the outermost planets, Uranus and Neptune, worlds that have never been explored.
03:21To visit each planet, the probes must stick to a strict schedule, with only a quick flyby of each world.
03:29Once reaching Jupiter, they must use every second to complete close-up studies of the planet and its largest moons.
03:38One of the biggest challenges with flyby spacecraft is it may have taken years to get there,
03:44but the actual time that you're close to the planet is remarkably short.
03:49The Jupiter close-up data occurred during just three days.
03:55February, 1979. Voyager 1 begins beaming pictures back to Earth. It's an anxious wait.
04:04This is pre-Internet, and so when you look at the data coming in, it's coming in line by line, pixel by pixel.
04:11It was such an exciting time, it was hard to know when to sleep.
04:15I brought my sleeping bag into my office so I wouldn't miss a single exciting picture.
04:22Both Voyagers reveal an unbelievably dynamic world.
04:29Scientists were able to take a sequence of images of Jupiter that they could put together like a flip book to get a sense of motion, and it was just astounding.
04:38Now we can see things moving within the atmosphere of Jupiter in a way that we had no sense of before.
04:46Together, the spacecraft take over 33,000 images of the gas giant.
04:52These pictures reshape our understanding of Jupiter, especially its largest moons, Ganymede, Callisto, Europa, and Io.
05:09We saw all sorts of different kinds of landscapes on them, and each one had its own individual type of personality.
05:17Of all the moons around Jupiter, and there are a lot, Io was the one that shocked everybody.
05:24We got back this very unusual picture. We saw this bright feature on the dark limb of Io, and we wondered, what could it be?
05:33At first they thought that arc might be another moon behind Io, but the geometry was wrong. There were no moons there.
05:40Well, they figured out that these were volcanic plumes.
05:44And that bright feature on the dark limb was a volcano erupting on Io.
05:50Voyager 1 records ash and lava blasting 190 miles into space, eight times higher than the largest eruptions on Earth.
06:00This is the first time we'd ever seen another volcanically active world anywhere in the solar system, right?
06:06It really transformed our ideas, our concept of what a moon could be.
06:10But astronomers were also baffled.
06:14When scientists first saw these images of Io, they had to ask the question, how is this looking?
06:20And they were surprised to find that it was actually a moon.
06:24And they were surprised to find that it was actually a moon.
06:29When scientists first saw these images of Io, they had to ask the question, how is this little moon still so hot?
06:36On Earth, we know it's a big planet, it's volcanically active because of plate tectonics, and there's this ancient heat system inside the planet.
06:45When you look at a little moon like Io, you expect, ah, it's going to be dead, right?
06:49But instead, it's the most volcanically active body in the solar system.
06:55Io's volcanism is powered by tidal heating.
07:00As it orbits Jupiter, it gets stretched and compressed by the gravity of Jupiter and the other moons as they all pass by it.
07:09The compression and expansion generates heat, melting Io's interior, a planetary process never before witnessed.
07:19At Jupiter, the Voyagers discover three new moons and a ring system invisible from Earth.
07:28Not to be outdone, the planet itself has a few surprises.
07:34The probes turn to the gas giant's most famous feature, the Great Red Spot.
07:42Jupiter's Red Spot is a feature that has existed in its atmosphere since we began looking at Jupiter.
07:49It's incredible. What it turns out to be is a storm that has lasted centuries.
07:55The Voyagers reveal a maelstrom of gas, swirling counterclockwise between two bands of high-speed winds.
08:04The Red Spot has been kept in a single place because it's sort of sandwiched between these two bands of atmosphere.
08:10Like a whirlpool, an eddy, and two currents that are moving next to each other.
08:14That may have helped promote its stability over all these centuries.
08:18But Voyager's close-up shots show a far more complex structure than we expected.
08:25It turns out the Great Red Spot is not a single vortex. It's more complicated than that, which you might expect from a storm bigger than the Earth.
08:34Voyager actually took close-up images of it and saw several smaller vortices spinning around inside of it.
08:40These small vortices are ten times larger than any hurricane on Earth.
08:46But the Voyagers can't detect how they interact with the spot.
08:51It'll take a new generation of space probes to solve that mystery.
08:56So after Voyager had flew past, there were lots of questions that went unanswered.
09:00And Jupiter is a long way from the Earth, and really the only way to answer some of them was to go back.
09:06Thirty-seven years after the Voyager flybys, the Juno probe arrives at Jupiter.
09:12The Juno spacecraft has a microwave radiometer.
09:15That instrument is able to detect the microwave radiation coming from very deep inside Jupiter.
09:21And from that we're able to determine things like its deep composition and its deep temperature.
09:27Juno finds the Great Red Spot stretches at least 200 miles below the surface.
09:34And in 2021, a team combines Juno data with Hubble and ground-based telescopes to finally discover what powers the gargantuan storm.
09:46These small storms that are coming in are rotating very quickly.
09:50All of that feeds the Great Red Spot and keeps it spinning, gives it that spinning energy that it needs to survive.
09:58The Voyager probes are ready for their next destination, Saturn.
10:03But to get there, they must first fly dangerously close to Jupiter.
10:20The next stop on the Voyager probe's grand tour of the solar system is Saturn.
10:27But the ringed planet is over 450 million miles away from Jupiter.
10:33To get there, the Voyagers will need to perform a maneuver known as a gravitational slingshot,
10:41which will catapult them from one planet to the next.
10:46We allowed the large gravity of Jupiter to actually capture the spacecraft and start accelerating it toward that massive planet.
10:54But we did it at just the right angle, so we would move around it and then continue away from the planet.
11:00Jupiter itself is barreling around the sun at very fast velocities.
11:05As you pull away from Jupiter, you keep some of that velocity with you.
11:10If it's successful, the slingshot will knock years off the Voyager's journey.
11:15If things go wrong, it's game over.
11:19To do a gravitational slingshot, you need to do three things.
11:22You need to have really good calculations, excellent planning, and perfect timing.
11:28Mission controllers achieve all three, and the maneuver works.
11:33Voyagers 1 and 2 speed up by 22,500 miles an hour and race toward Saturn.
11:411980. Right on schedule, Voyager 1 arrives at the ringed planet.
11:47Its sensors probe Saturn's atmosphere and discover it's mainly hydrogen and helium.
11:55Saturn has nearly a hundred times the mass of Jupiter,
12:00Saturn has nearly a hundred times the mass of the Earth,
12:03but it has so much more volume that when you look at its density, it's actually less dense than water.
12:10There's a very old joke in astronomy that if you put Saturn in a bathtub, it would float, but it would leave a ring.
12:19The most striking discovery emerges from the data nine years after Voyager's flybys,
12:25a bizarre cloud formation at the North Pole.
12:30A giant hexagon over the North Pole with sides 9,000 miles long and it's 18,000 miles across.
12:38Yeah, that's bizarre.
12:42You don't often think about very stable geometric shapes like a hexagon.
12:46That feels like it shouldn't happen, right?
12:49You don't get hexagon-shaped clouds on the Earth.
12:53What could possibly create a hexagon more than twice the size of Earth?
12:59Voyager discovered the hexagon, but we didn't have enough information to truly understand it.
13:06Jump forward 24 years after Voyager and another probe arrives at Saturn, Cassini.
13:14The main difference between the Cassini mission and the Voyager missions,
13:17besides Cassini having more cutting-edge equipment on it, is that it was an orbiter.
13:21It orbited Saturn for 13 years. The Voyager missions just flew past it.
13:28Cassini watches the pole for several years, capturing thousands of images of the hexagon.
13:37The beauty of the Cassini mission is that it showed us what the hexagon looked like years later after Voyager.
13:42It didn't necessarily solve the problem of why this thing exists,
13:46but it gave scientists a lot of ammunition to figure it out.
13:50Finally, in 2020, a team solves the mystery.
13:56Many cyclones surround a large jet stream at the planet's north pole.
14:02Where the two weather systems meet, a hexagon cloud forms.
14:07Something we don't see here on Earth.
14:11The trouble with Earth is it has a lot going on.
14:13We have oceans, we have mountains. All of that disrupts the atmosphere.
14:18On Saturn, there isn't any of that.
14:21So you're able to have these very stable air flows.
14:25It just wouldn't be possible on the Earth.
14:27Nature's pretty wonderful.
14:31Next, the Voyagers turn their gaze to Saturn's rings.
14:37Their images are game-changers.
14:41One of my colleagues in my undergraduate planetary astronomy class was a computer whiz,
14:47and he managed to hack into the NASA feed that was going out.
14:51We all piled into his dorm room, the professors, the students,
14:55seeing images coming from the Saturn flyby.
14:59We thought that Saturn had just a handful of wide, flat rings.
15:05Voyager's images reveal thousands of separate rings orbiting the planet.
15:11But there's an even bigger surprise, an impossible ring.
15:17When the F ring of Saturn, a close-up image appeared on the screen,
15:23and instead of being sort of a single ring,
15:25it looked like multiple rings that were braided together.
15:30And my professor, Irwin Shapiro, famous planetary astronomer professor, said,
15:36that's not possible.
15:40Scientists pore over the images to figure out what's causing the bizarre structure.
15:46Our basic understanding of rings back then
15:49was that they were collections of little particles
15:52that were all just following the same orbit.
15:55You'd expect that system to have settled out into, you know,
15:58all the traffic on the highway driving in the same direction,
16:01parallel lanes, all nice and neat.
16:03You don't expect these weird, dynamic interactions that are going on.
16:09Then, scientists find two clues to explain the interactions.
16:14And one of the things that was discovered was two satellites
16:17that orbit inside and outside of the F ring, Prometheus and Pandora.
16:24It pointed to the idea that the moons and the rings were constantly interacting,
16:28but it didn't really tell us how.
16:32Voyager's discovery of the moons doesn't solve the mystery of the braided F ring,
16:37but it does tell the Cassini probe, 25 years later, where to look.
16:43Cassini watches the tiny moons,
16:46looping and twisting around each other as they orbit the planet.
16:51When you have two little moons sort of co-orbiting with the ring,
16:55there's a complex gravitational dance that happens
16:59with the inner moon wanting to speed up particles,
17:02the outer moon wanting to slow them down,
17:05and that interesting gravitational dance is what actually helps confine the ring
17:09into the narrow structure that we actually see.
17:14By seeing these moons either side,
17:16there was an idea that they could be shepherding,
17:19they could be holding the ring in place.
17:23Saturn's many moons and complicated rings are like a mini solar system.
17:31Now, the two Voyager spacecraft separate to carry out two individual missions.
17:37Voyager 1 heads off to explore the edge of the solar system,
17:42and Voyager 2 flies into the freezing cold of Saturn's shadow.
17:51For over two hours, the giant planet blocks all contact with the space probe.
17:59After a tense wait, Voyager 2 emerges.
18:04But something's wrong with the spacecraft.
18:07Picture after picture of dark sky came back,
18:10and we realized something had either happened to the cameras
18:13or something had happened to the scan platform.
18:17The scan platform, the vital rotating joint that points the probe's instruments, isn't working.
18:23But how can scientists fix a probe two billion miles from Earth?
18:33August, 1981.
18:37Pioneering space probe Voyager 2 is in trouble.
18:42Passing behind Saturn, one of its key components, the scan platform, jams.
18:49The scan platform is kind of like your head and neck.
18:52Imagine the cameras as your eyes,
18:54and if you want to turn to look at something, you turn your head,
18:57and your neck has to move.
18:59When Voyager 2 passed behind Saturn, it plowed through the rings at 29,000 miles an hour.
19:05Maybe a chunk of ice damaged the platform,
19:08or maybe the maneuver gave the probe whiplash.
19:13We had been so ambitious in looking at the moons and the rings and Saturn
19:18that we had literally squeezed the lubricant out of the bearings of the scan platform,
19:23and it got stuck.
19:25The broken scan platform could be fatal for the rest of the mission.
19:30And so we worried, could we fix it?
19:32We had Uranus and Neptune ahead of us with Voyager 2.
19:35We wanted to be able to fix the scan platform.
19:39To fix it, the engineers employ some space physiotherapy.
19:45We slowly commanded it from Earth and got it to move a little bit at a time
19:49until finally we could get the probe to move.
19:52With Voyager operational again, NASA agreed to fund the next stage of the mission.
19:58I'm eternally grateful that NASA did decide to complete the Grand Tour.
20:03It was tremendous relief to know we had a healthy spacecraft, Voyager 2,
20:08to go on to Uranus and Neptune.
20:121986.
20:14The first of a new generation of astronauts.
20:17Uranus and Neptune.
20:201986.
20:22Boosted by a slingshot from Saturn, Voyager 2 arrives at Uranus.
20:29After nine years in space, the probe is now in uncharted territory.
20:36Ahead of Voyager's encounter, Uranus was really difficult to know much about.
20:41We knew what its colour was, but it didn't have any obvious features from the Earth.
20:46It looked sort of like a generic green blob.
20:49We did know a couple things.
20:51Uranus has rings and sits on its side.
20:55Unlike most of the other planets, whose spin axes are oriented more or less perpendicular to their orbital plane,
21:02Uranus is tipped over on its side.
21:05It rolls around the sun like a barrel at times.
21:08There are other times where the sun is shining right down the equator.
21:11It's very unusual.
21:13In a flyby lasting just five and a half hours,
21:16Voyager 2 discovers 11 new moons and two more ghostly rings circling Uranus.
21:24But Voyager 2's strangest discovery is the planet's freakish magnetic field.
21:31Voyager carried a magnetic boom that told us about the magnetic field of the planet,
21:35and that turned out to be really interesting.
21:39The strength and direction of Uranus' magnetic field turns out to be unlike any other planet's.
21:46The Earth has a magnetic field, and it's pretty complicated how it behaves,
21:50but you can think of it as if there's a giant bar magnet inside the planet.
21:55There's a north magnetic pole and a south magnetic pole, and magnetic field lines around them.
22:00On Earth, that bar magnet lines up close to our planet's spin axis.
22:06The Voyager probes found the same at Saturn and Jupiter.
22:11But Uranus' magnetosphere is different.
22:15The north and south axis of the magnetic field is tilted by almost 60 degrees
22:20relative to the spin axis of Uranus. That's strange.
22:24If you imagine transforming the Earth's magnetic field to be like the Uranus one,
22:29you'd have the magnetic north pole down near Miami someplace.
22:32It's way out there in left field.
22:35And the magnetic field isn't just tilted.
22:38It's off center, the center of the magnetic field you'd think would be at the center of the planet.
22:43It's actually offset by 5,000 miles, which is a lot.
22:47We think it may be generated in the mantle of Uranus where there is molten water, not molten iron.
22:54Extreme heat and pressure breaks water molecules apart
22:58and rearranges them into a molten crystal structure,
23:02an exotic state called super-ionic ice.
23:06When we talk about ice, like super-ionic ice inside a giant planet,
23:11we're not talking about ice cubes.
23:14Water has lots of different ways of being, and some of them are really strange.
23:19The half-liquid, half-solid ice swirls around in the outer layer of the planet,
23:25moving like liquid metal.
23:28Because the ice conducts electricity, this produces the offset magnetic field around Uranus.
23:36Voyager 2 also uncovered a gigantic magnetic glitch,
23:42but it remained hidden in the data until scientists discovered it in 2020.
23:48What they found was a blip, a strengthening of the magnetic field,
23:52and it was about a million miles behind Uranus, and whatever was causing this was quite large.
23:58It's a giant magnetic bubble, 250,000 miles across, floating in space.
24:06This type of magnetic bubble is called a plasmoid,
24:09and it happens when the magnetic field lines get pinched off,
24:12and it can create sort of a self-contained shell.
24:15This means that the magnetic field around Uranus is dynamic
24:19and can fracture and interact with the solar wind in very interesting ways.
24:23This can also have some of the atmosphere of Uranus in it,
24:26so it's literally leaking gas into space. Uranus is belching.
24:32It'll take another mission to Uranus to truly understand this strange world.
24:38For now, Voyager 2 is the only spacecraft to ever visit,
24:43and what awaits the probe next could be Voyager's greatest discovery yet.
25:001989. Voyager 2 makes one last flyby.
25:05Neptune is the final stop on the planet-hopping tour of the outer solar system.
25:10It's a once-in-a-lifetime opportunity to study the blue ice giant up close.
25:16We had these hints from our ground-based telescope that there was activity in the atmosphere.
25:23But what its nature was, what was it like?
25:28There absolutely was nothing we had to prepare us for what we were going to see.
25:36Voyager 2 spots four new rings and six more moons.
25:41It detects hydrogen, helium and methane in Neptune's atmosphere.
25:47And it records the fastest winds in the solar system,
25:51pushing white clouds across the planet at up to 1,500 miles an hour.
25:57And at their center, a colossal dark storm.
26:04There was a dark spot, a big dark spot on the disk of Neptune.
26:10We hadn't seen anything like that from the ground.
26:13It was like, what is that?
26:16We called it the Great Dark Spot because that's all we could think of at the time.
26:21Five years later, when astronomers look for the Great Dark Spot with the Hubble Space Telescope,
26:27they get a surprise.
26:30I was in a look at how it had changed with time and, you know, where was it located, things like that.
26:36And I remember I got my first images back from Hubble.
26:40No Great Dark Spot. It was gone.
26:44It simply wasn't there.
26:46Like, what happened?
26:49How is this even possible?
26:51The Great Red Spot on Jupiter has lasted for hundreds of years.
26:55It was only five years and this huge feature was simply gone.
27:02Since Voyager 2, we have seen seven different dark spots on Neptune's surface,
27:08none lasting more than a few years.
27:12As to why that is and what's driving that,
27:16those are still mysteries that we haven't fully solved.
27:22Before leaving the Neptune system, Voyager 2 turns its gaze to Neptune's largest moon, Triton.
27:30It was sort of a bit like Voyager's last hurrah,
27:33sort of one of the last things it showed us and it was just phenomenal.
27:39Voyager 2's instruments reveal a frozen world.
27:43At 391 degrees below zero, Triton is one of the coldest objects in the solar system.
27:51Here was a very intriguing world.
27:54We saw these dark streaks on the surface and realized that they were actually sticking up above the surface.
28:00What they were seeing was an active cryovolcano jetting,
28:06a jet of black material something like eight miles up above the surface of Triton
28:13and then the atmosphere of Triton was shearing it out into a large cloud pattern.
28:19That was one of our first indications of geyser-like activity on a planet other than the Earth.
28:24It was almost pandemonium, really, trying to figure out how do you generate this kind of activity
28:29on a moon that should be cryogenically frozen solid.
28:32Where is the energy source for this?
28:35In 2019, scientists finally identify frozen nitrogen and carbon monoxide in the streaks.
28:44We think now what actually is going on there is the action of sunlight
28:48shining into some of the darker deposits on the surface of the moon.
28:52Just a little bit of a temperature change can take the nitrogen and liberate it off the surface.
29:01In their grand tour of the solar system, the Voyager probes produce an astounding number of discoveries.
29:10Volcanoes on Io and geysers on Triton and little weavy features in the rings of Saturn,
29:16it all turned out to be far, far more interesting and alive and dynamic than we ever imagined.
29:24While Voyager 2 leaves the planets behind, its twin, Voyager 1, heads to the edge of the solar system,
29:33but not before taking one last snapshot of home, a family portrait.
29:39This idea by Carl Sagan to take this family portrait is just magnificent
29:44and the scientific need for it may have been limited, but the appeal to our sense of beauty, staggering.
29:53This shot isn't in pursuit of a new discovery, it's about finding a new perspective.
30:00This family portrait is a series of 60 images put together into a mosaic
30:05and in it you can see the sun and six planets, Venus, Earth, Jupiter, Saturn, Uranus and Neptune.
30:12As we were studying the images, we noticed along one of these sunbeams,
30:16there was the Earth, that pale blue dot, which contains every single person.
30:23We realized just how tiny our planet is and how very special.
30:29It's one of the most amazing and beautiful things I've ever seen.
30:35February 1990, the cameras power down for the last time, but this mission isn't over.
30:42The Voyager probes are about to reach the edge of the solar system, a region no spacecraft has been to before.
31:01Far from the sun, at the very edge of the solar system, lies a vast expanse where no human-made object has ever entered.
31:12Until the Voyagers.
31:15This is like early explorers leaving sight of land. They are just surrounded by a vast ocean of night.
31:22And they are all alone.
31:24It's sort of like the boat going from the bay out into the open ocean.
31:29It's a whole different environment.
31:33The Voyager probes are about to leave the calm of the solar system and enter the stormy waters of the galaxy.
31:41They start to exit the heliosphere, a protective bubble around the whole solar system,
31:47and cross into a combat zone that hosts a cosmic battle between the sun and interstellar space.
31:56Inside the heliosphere, waves of particles from the sun, called the solar wind, push outward.
32:03Outside, an ocean of gas and particles pushes back.
32:09As the solar wind is expanding away from the sun, it's pushing against this thin stuff between the stars, the interstellar medium.
32:16That's the last influence that the sun has in the bubble surrounding it.
32:22Once you cross that, you are in interstellar space.
32:28The heliosphere's front line protects us from one of the galaxy's deadliest weapons,
32:34high energy particles called cosmic rays.
32:38Cosmic rays are like tiny bullets, and they travel at close to the speed of light.
32:44December 2004.
32:46Voyager 1 detects a sudden drop in the solar wind,
32:50evidence that the space probe is nearing the heart of the battlefield,
32:55a region known as the termination shock.
33:00The termination shock is the region where the solar wind starts to meet resistance,
33:06starts to run into something, and that causes it to slow down.
33:12Voyager 1 picks up surges from both opposing forces.
33:16Blasts of cosmic rays followed by waves of the solar wind.
33:22The instruments on board Voyager didn't just suddenly change from sun space to galaxy space.
33:29It actually kind of went back and forth several times as it was measuring the energies of the particles at that region.
33:37This suggests that the edge of the heliosphere is not a single battlefront, but rather a complex region of skirmishes.
33:45A sea of gigantic magnetic bubbles created by the sun's magnetic field.
33:52The sun's magnetic field rotates with the sun physically, but this far out, billions of miles from the sun,
33:59those magnetic field lines get dragged by particles, and there's a lot of different effects on them,
34:03and they can get tangled up and loose.
34:05This creates bubbles, and some of these bubbles are a hundred million miles across.
34:11The magnetic bubble boundary is not watertight.
34:14Some cosmic rays blast through.
34:18This heliosphere is much more foamy than we had thought.
34:22There are gaps in our defenses where deadly cosmic rays can find their way through into the inner solar system.
34:30The foamy defensive line blocks 90% of cosmic rays, but allows 10% through.
34:38As Voyager 1 passes through the battlefield, it detects fewer and fewer solar particles.
34:44Eventually, they're only cosmic rays and interstellar space.
34:50In 2012, the probe becomes humankind's first object to leave the solar system, followed in 2018 by Voyager 2.
35:02It's been 50 years since the first satellites poked their way out of the Earth's atmosphere.
35:08And now both Voyager spacecraft have poked their heads out of the sun's atmosphere,
35:14are outside the solar system and exploring the galaxy.
35:20The Voyagers cross the final frontier and sail the ocean between the stars.
35:26They don't see their first discovery. They hear it.
35:32In space, no one can hear you scream. There's no actual sound waves moving around.
35:37But there are waves of plasma, of electrons.
35:41So as Voyager passes through this, we can translate these changes in the plasma density to sound waves.
35:50This is the sound of interstellar space.
35:56Poetically, I kind of like to think of it as the song the galaxy is singing, welcoming Voyager to interstellar space.
36:04Some of these sounds may even come from distant supernovas.
36:08Think about that, a star dying tens of thousands of light years away.
36:13And here's an echo of it, here.
36:20The sounds of deep space tell us more about our part of the galaxy.
36:25As Voyager travels through the interstellar medium, we can use these sounds to map out its local environment.
36:33And since 2017, we've been mapping how these sounds get higher and lower and higher, louder and softer.
36:41And it's telling us that the interstellar medium is not uniform at all.
36:46Built to last five years, Voyager 1 and 2 are now more than 40 years old.
36:52Only one final mission remains, perhaps the most important mission, to let the rest of the galaxy know we're here.
37:12The Voyager spacecraft are now outside the solar system.
37:16Our sun is just the brightest star among many.
37:20How much longer can the probes keep going?
37:24The limiting factor on the mission has turned out to be power.
37:28And every year there are four watts less power to run each of the Voyager spacecraft.
37:34There are no service stations out there. There's no way to, you know, repair things that go wrong.
37:39And it's really remarkable the fact that they're still out there in the cryogenic cold, you know, operating.
37:44They're still working. They're still alive.
37:47In just five years, there may be too little power to transmit signals to Earth.
37:52After a final message home, the Voyagers will fall silent forever.
37:58This part of the Voyager mission, flying in interstellar space, is the long goodbye.
38:07They're going to become our messages in a bottle.
38:10A little bit of humanity, you know, representing us when we're long gone.
38:15The two probes could survive for billions of years.
38:19They could be not only, you know, interstellar Voyagers,
38:22they could turn into intergalactic Voyagers ultimately.
38:26Maybe the Voyagers won't just drift forever.
38:31Maybe they'll be found.
38:35There was kind of a wonderful little jaunt of imagination
38:38that maybe some alien civilization with incredibly powerful telescopes
38:42might notice that there's a little artificial object flying through space and be curious about it.
38:47Strapped to each Voyager is an aluminum case.
38:51On the outer side is a map of how to find Earth with directions from different pulsars.
38:58So why use pulsars to direct aliens to our location?
39:02These are the dead cores of stars after a supernova explosion.
39:06Well, amazingly, pulsars all spin at slightly different rates.
39:10So if you can actually triangulate your location based on the rates of different pulsars in the sky,
39:16you can actually have sort of a galactic GPS system.
39:19You can show the aliens where we are with incredible accuracy.
39:23Inside each case, a gold-plated copper disk.
39:28Looking back on it, it's really kind of this wonderful part of humanity.
39:32We sent aliens out there, you know, unimaginably technologically advanced aliens.
39:36We sent them basically a vinyl record.
39:39The golden disks are literally disks.
39:42They actually are records with grooves.
39:45You can play them. You can jam out to them.
39:47It's got a soundtrack of our species.
39:53The records have tracks by Beethoven, Blind Willie Nelson, and Chuck Berry.
39:59The sound of surf, of thunder, of birdsong, and a human heartbeat.
40:06So, will aliens ever find the records and give them a spin?
40:11The golden record is a lovely idea, especially to energize and excite the public about this.
40:17Will it ever be found?
40:19There's a reason we call it space.
40:24A tiny, cold spacecraft is a difficult target to find.
40:29Any species capable of detecting them would have a better chance of spotting our planet.
40:35But the Voyagers will long outlive Earth.
40:39It's possible that they will find it millions or even billions of years in the future,
40:43long after we're gone, where there really aren't humans anymore.
40:47Or is there even a possibility that when we start traveling to the stars in the far future, we'll find them?
40:53Awaiting discovery, or doomed to drift alone,
40:58Voyager probes have already inspired one civilization, ours.
41:03Calling these Voyager, it's perfect, because that's what they are doing.
41:08They are voyaging out to the outer solar system and beyond,
41:11and showing that there is no end to our desire to explore.
41:18They've shown us countless wonders of the solar system, and a glimpse of what lies beyond.
41:25We, as a species, can build ships that not only sail the oceans of our Earth,
41:32but that can sail outwards to the other planets in our system, and reveal new worlds.
41:39They are the greatest space mission ever.
41:43The legacy of Voyager is our remnant.
41:46It is our memory. It is a sampling of humanity that is out there now among the stars.
41:54And if they last until the death of the universe, as the final stars fade and everything goes dark,
42:02they will be humanity's final statement.
42:06We were here.