As the two Voyager spacecraft reach interstellar space, experts explore their astonishing discoveries and how their extended operation has transformed into the ultimate mission.
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LearningTranscript
00:01Voyager, the most ambitious space mission in history.
00:05The 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.
00:24The Voyager missions have ventured far beyond where other probes have explored.
00:30They 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.
01:00These 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.
01:18When 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.
01:38The Voyagers are so far out that when they look back toward the sun, it's just a pinprick of light.
01:43And they would need an exceptionally powerful telescope just to see the Earth.
01:48Their 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.
02:03The 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.
02:31When 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.
02:45And that launch is like the birth of a baby.
02:48I was standing there watching it climb up into the sky.
02:51And we were cheering. We were so happy.
02:54Voyager was on its way.
02:57Though funded to just explore the two gas giants,
03:01mission planners have a much bigger journey in mind.
03:05To send the Voyager spacecraft on a grand tour of the solar system.
03:11To the outermost planets, Uranus and Neptune.
03:16Worlds that have never been explored.
03:19To 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.
03:36One 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.
03:54February 1979, Voyager 1 begins beaming pictures back to Earth.
04:01It's an anxious wait.
04:03This is pre-internet.
04:05And 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.
04:12It was hard to know when to sleep.
04:14I brought my sleeping bag into my office, so I wouldn't miss a single exciting picture.
04:20Both Voyagers reveal an unbelievably dynamic world.
04:30Scientists were able to take a sequence of images of Jupiter that they could put together like a flipbook to get a sense of motion.
04:37And it was just astounding.
04:39Now we can see things moving within the atmosphere of Jupiter in a way that we had no sense of before.
04:45Together, the spacecraft take over 33,000 images of the gas giant.
04:55These pictures reshape our understanding of Jupiter, especially its largest moons.
05:03Ganymede, Callisto, Europa, and Io.
05:10We saw all sorts of different kinds of landscapes on them, and each one had its own individual type of personality.
05:20Of all the moons around Jupiter, and there are a lot, Io was the one that shocked everybody.
05:27We got back this very unusual picture.
05:30We saw this bright feature on the dark limb of Io.
05:34And we wondered, what could it be?
05:36At first, they thought that arc might be another moon behind Io, but the geometry was wrong.
05:43There were no moons there.
05:45Well, they figured out that these were volcanic plumes.
05:49And that bright feature on the dark limb was a volcano erupting on Io.
05:54Voyager 1 records ash and lava blasting 190 miles into space.
06:09Eight times higher than the largest eruptions on Earth.
06:13This is the first time we'd ever seen another volcanically active world anywhere in the solar system, right?
06:19It really transformed our ideas, our concept of what a moon could be.
06:26But astronomers were also baffled.
06:30When 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.
06:39It's volcanically active because of plate tectonics.
06:42And 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?
06:50But instead, it's the most volcanically active body in the solar system.
06:56Io'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.
07:07The compression and expansion generates heat, melting Io's interior, a planetary process never before witnessed.
07:21At 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.
07:32The probes turn to the gas giant's most famous feature, the Great Red Spot.
07:43Jupiter's Red Spot is a feature that has existed in its atmosphere since we began looking at Jupiter.
07:49It's incredible.
07:50What it turns out to be is a storm that has lasted centuries.
07:54The 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.
08:17But 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.
08:29It'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.
09:02And really, the only way to answer some of them was to go back.
09:04Thirty-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.
09:56The Voyager probes are ready for their next destination, Saturn.
10:03But to get there, they must first fly dangerously close to Jupiter.
10:08The next stop on the Voyager probes' grand tour of the solar system is Saturn.
10:25But the ringed planet is over 450 million miles away from Jupiter.
10:30To get there, the Voyagers will need to perform a maneuver known as a gravitational slingshot,
10:38which will catapult them from one planet to the next.
10:43We 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.
11:11If it's successful, the slingshot will knock years off the Voyager's journey.
11:16If things go wrong, it's game over.
11:20To do a gravitational slingshot, you need to do three things.
11:23You need to have really good calculations, excellent planning, and perfect timing.
11:29Mission controllers achieve all three, and the maneuver works.
11:35Voyagers 1 and 2 speed up by 22,500 miles an hour and race towards Saturn.
11:441980. Right on schedule, Voyager 1 arrives at the ringed planet.
11:50Its sensors probe Saturn's atmosphere and discover it's mainly hydrogen and helium.
11:58Saturn has nearly 100 times the mass of the Earth,
12:01but it has so much more volume that when you look at its density,
12:05it's actually less dense than water.
12:08There's a very old joke in astronomy that if you put Saturn in a bathtub,
12:12it would float, but it would leave a ring.
12:17The most striking discovery emerges from the data nine years after Voyager's flybys,
12:23a bizarre cloud formation at the North Pole.
12:26A giant hexagon over the North Pole with sides 9,000 miles long,
12:33and it's 18,000 miles across.
12:36Yeah, that's bizarre.
12:39You don't often think about very stable geometric shapes like a hexagon.
12:44That feels like it shouldn't happen, right?
12:47You don't get hexagon-shaped clouds on the Earth.
12:49What could possibly create a hexagon more than twice the size of Earth?
12:56Voyager discovered the hexagon,
12:58but we didn't have enough information to truly understand it.
13:03Jump forward 24 years after Voyager,
13:06and another probe arrives at Saturn, Cassini.
13:11The main difference between the Cassini mission and the Voyager missions,
13:14besides Cassini having more cutting-edge equipment on it,
13:17is that it was an orbiter.
13:19It orbited Saturn for 13 years.
13:22The Voyager missions just flew past it.
13:26Cassini watches the pole for several years,
13:29capturing thousands of images of the hexagon.
13:34The beauty of the Cassini mission
13:36is that it showed us what the hexagon looked like years later after Voyager.
13:40It didn't necessarily solve the problem of why this thing exists,
13:44but it gave scientists a lot of ammunition to figure it out.
13:46Finally, in 2020, a team solves the mystery.
13:54Many cyclones surround a large jet stream at the planet's North Pole.
13:59Where the two weather systems meet, a hexagon cloud forms.
14:05Something we don't see here on Earth.
14:09The trouble with Earth is it has a lot going on.
14:11We have oceans, we have mountains.
14:13All of that disrupts the atmosphere.
14:16On Saturn, there isn't any of that.
14:19So you're able to have these very stable air flows.
14:23It just wouldn't be possible on the Earth.
14:26Nature's pretty wonderful.
14:29Next, the Voyagers turned their gaze to Saturn's rings.
14:33One of my colleagues in my undergraduate planetary astronomy class was a computer whiz,
14:45and he managed to hack into the NASA feed that was going out.
14:49We all piled into his dorm room, the professors, the students, seeing images coming from the Saturn flyby.
14:57We thought that Saturn had just a handful of wide, flat rings.
15:03Voyager's images reveal thousands of separate rings orbiting the planet.
15:08But there's an even bigger surprise, an impossible ring.
15:15When the F ring of Saturn, a close-up image appeared on the screen.
15:21And instead of being sort of a single ring, it looked like multiple rings that were braided together.
15:27And my professor, Erwin Shapiro, famous planetary astronomer professor, said,
15:33that's not possible.
15:38Scientists pore over the images to figure out what's causing the bizarre structure.
15:44Our basic understanding of rings back then was that they were collections of little particles
15:50that were all just following the same orbit.
15:52You would expect that system to have settled out into, you know, all the traffic on the highway,
15:57driving in the same direction, parallel lanes, all nice and neat.
16:01And you don't expect these weird, dynamic interactions that are going on.
16:07Then, scientists find two clues to explain the interactions.
16:12And one of the things that was discovered was two satellites that orbit inside and outside of the F ring,
16:18Prometheus and Pandora.
16:20It pointed to the idea that the moons and the rings were constantly interacting,
16:27but it didn't really tell us how.
16:30Voyager's discovery of the moons doesn't solve the mystery of the braided F ring,
16:35but it does tell the Cassini probe, 25 years later, where to look.
16:41Cassini watches the tiny moons, looping and twisting around each other as they orbit the planet.
16:47When you have two little moons sort of co-orbiting with the ring,
16:53there's a complex gravitational dance that happens with the inner moon wanting to speed up particles,
17:00the outer moon wanting to slow them down.
17:03And that interesting gravitational dance is what actually helps confine the ring into the narrow structure that we actually see.
17:09By seeing these moons either side, there was an idea that they could be shepherding,
17:17they could be holding the ring in place.
17:21Saturn's many moons and complicated rings are like a mini solar system.
17:26Now, the two Voyager spacecraft separate to carry out two individual missions.
17:35Voyager 1 heads off to explore the edge of the solar system,
17:39and Voyager 2 flies into the freezing cold of Saturn's shadow.
17:45For over two hours, the giant planet blocks all contact with the space probe.
17:57After a tense wait, Voyager 2 emerges.
18:02But something's wrong with the spacecraft.
18:05Picture after picture of dark sky came back,
18:08and we realized something had either happened to the cameras
18:11or something had happened to the scan platform.
18:15The scan platform, the vital rotating joint that points the probe's instruments, isn't working.
18:21But how can scientists fix a probe two billion miles from Earth?
18:34August 1981.
18:36Pioneering 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,
19:02it plowed through the rings at 29,000 miles an hour.
19:06Maybe a chunk of ice damaged the platform.
19:09Or maybe the maneuver gave the probe whiplash.
19:14We 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,
19:24and it got stuck.
19:26The broken scan platform could be fatal for the rest of the mission.
19:30And so we worried, could we fix it?
19:33We had Uranus and Neptune ahead of us with Voyager 2.
19:36We 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 those beautiful outbound pictures of Saturn that you see.
19:54With Voyager operational again, NASA agreed to fund the next stage of the mission.
20:01I'm eternally grateful that NASA did decide to complete the grand tour.
20:06There was tremendous relief to know we had a healthy spacecraft, Voyager 2,
20:12to go on to Uranus and Neptune.
20:161986.
20:18Boosted by a slingshot from Saturn, Voyager 2 arrives at Uranus.
20:25After nine years in space, the probe is now in uncharted territory.
20:30Ahead of Voyager's encounter, Uranus was really difficult to know much about.
20:37We knew what its color was, but it didn't have any obvious features from the Earth.
20:42It looked sort of like a generic green blob.
20:45We did know a couple things.
20:47Uranus has rings and sits on its side.
20:51Unlike most of the other planets,
20:53whose spin axes are oriented more or less perpendicular to their orbital plane,
20:58Uranus is tipped over on its side.
21:01It rolls around the sun like a barrel at times.
21:04There are other times where the sun is shining right down the equator.
21:08It's very unusual.
21:10In a flyby lasting just five and a half hours,
21:13Voyager 2 discovers 11 new moons
21:16and two more ghostly rings circling Uranus.
21:20But Voyager 2's strangest discovery
21:23is the planet's freakish magnetic field.
21:26Voyager carried a magnetic boom
21:29that told us about the magnetic field of the planet,
21:32and that turned out to be really interesting.
21:35The strength and direction of Uranus' magnetic field
21:39turns out to be unlike any other planets.
21:43The Earth has a magnetic field,
21:44and it's pretty complicated how it behaves,
21:46but you can think of it
21:47as if there's a giant bar magnet inside the planet.
21:51There's a north magnetic pole and a south magnetic pole
21:53and magnetic field lines around them.
21:56On Earth, that bar magnet lines up close
22:00to our planet's spin axis.
22:02The Voyager probes found the same at Saturn and Jupiter.
22:07But Uranus' magnetosphere is different.
22:10The north and south axis of the magnetic field
22:13is tilted by almost 60 degrees
22:15relative to the spin axis of Uranus.
22:18That's strange.
22:20If you imagine transforming the Earth's magnetic field
22:23to be like the Uranus one,
22:25you'd have the magnetic north pole down near Miami someplace.
22:28It's way out there in left field.
22:31And the magnetic field isn't just tilted.
22:33It's off-center.
22:36The center of the magnetic field
22:37you'd think would be at the center of the planet.
22:39It's actually offset by 5,000 miles, which is a lot.
22:44We think it may be generated in the mantle of Uranus
22:46where there is molten water, not molten iron.
22:51Extreme heat and pressure breaks water molecules apart
22:54and rearranges them into a molten crystal structure,
22:59an exotic state called superionic ice.
23:02When we talk about ice, like superionic ice,
23:06inside a giant planet,
23:08we're not talking about ice cubes.
23:10Water has lots of different ways of being,
23:13and some of them are really strange.
23:16The half-liquid, half-solid ice
23:18swirls around in the outer layer of the planet,
23:22moving like liquid metal.
23:24Because the ice conducts electricity,
23:26this produces the offset magnetic field around Uranus.
23:32Voyager 2 also uncovered a gigantic magnetic glitch,
23:37but it remained hidden in the data
23:39until scientists discovered it in 2020.
23:43What they found was a blip,
23:46a strengthening of the magnetic field,
23:48and it was about a million miles behind Uranus,
23:51and whatever was causing this was quite large.
23:53It's a giant magnetic bubble,
23:57250,000 miles across,
24:00floating in space.
24:02This type of magnetic bubble is called a plasmoid,
24:05and it happens when the magnetic field lines get pinched off,
24:07and it can create sort of a self-contained shell.
24:10This means that the magnetic field around Uranus
24:13is dynamic and can fracture
24:16and interact with the solar wind in very interesting ways.
24:19This can also have some of the atmosphere of Uranus in it,
24:22so it's literally leaking gas into space.
24:26Uranus is belching.
24:28It'll take another mission to Uranus
24:30to truly understand this strange world.
24:34For now, Voyager 2 is the only spacecraft to ever visit,
24:39and what awaits the probe next
24:41could be Voyager's greatest discovery yet.
24:541989.
24:56Voyager 2 makes one last flyby.
24:58Neptune is the final stop
25:01on the planet-hopping tour of the outer solar system.
25:05It's a once-in-a-lifetime opportunity
25:06to study the blue ice giant up close.
25:11We had these hints from our ground-based telescope
25:14that there was activity in the atmosphere,
25:17but what its nature was, what was it like,
25:22there absolutely was nothing we had to prepare us for
25:27what we were going to see.
25:30Voyager 2 spots four new rings
25:33and six more moons.
25:36It detects hydrogen, helium, and methane
25:39in Neptune's atmosphere.
25:41And it records the fastest winds in the solar system,
25:46pushing white clouds across the planet
25:48at up to 1,500 miles an hour.
25:50And at their center, a colossal dark storm.
25:57There was a dark spot, a big, dark spot on the disk of Neptune.
26:04We hadn't seen anything like that from the ground.
26:07It was like, what is that?
26:09We called it the Great Dark Spot
26:11because that's all we could think of at the time.
26:14Five years later, when astronomers look for the Great Dark Spot
26:19with the Hubble Space Telescope,
26:21they get a surprise.
26:24I was in a look at how it had changed with time
26:27and, you know, where was it located, things like that.
26:30And I remember I got my first images back from Hubble.
26:34No great dark spot.
26:36It was gone.
26:38It simply wasn't there.
26:41Like, what happened?
26:43How is this even possible?
26:44The Great Red Spot on Jupiter has lasted for hundreds of years.
26:49This is only five years,
26:50and this huge feature was simply gone.
26:56Since Voyager 2,
26:58we have seen seven different dark spots on Neptune's surface,
27:03none lasting more than a few years.
27:05As to why that is and what's driving that,
27:10those are still mysteries that we haven't fully solved.
27:15Before leaving the Neptune system,
27:18Voyager 2 turns its gaze to Neptune's largest moon, Triton.
27:24It was sort of a bit like Voyager's last hurrah,
27:27sort of one of the last things it showed us,
27:29and it was just phenomenal.
27:31Voyager 2's instruments reveal a frozen world.
27:37At 391 degrees below zero,
27:40Triton is one of the coldest objects in the solar system.
27:45Here was a very intriguing world.
27:48We saw these dark streaks on the surface
27:50and realized that they were actually sticking up above the surface.
27:54What they were seeing was an active cryovolcano jetting,
28:00a jet of black material,
28:02something like eight miles up above the surface of Triton.
28:07And then the atmosphere of Triton was shearing it out into a large cloud pattern.
28:13That was one of our first indications of geyser-like activity on a planet other than the Earth.
28:18It was almost pandemonium, really,
28:21trying to figure out how do you generate this kind of activity
28:23on a moon that should be cryogenically frozen solid.
28:27Where is the energy source for this?
28:29In 2019, scientists finally identify
28:32frozen nitrogen and carbon monoxide in the streaks.
28:37We think now what actually is going on there
28:40is that the action of sunlight
28:42shining into some of the darker deposits on the surface of the moon.
28:46Just a little bit of a temperature change
28:48can take the nitrogen and liberate it off the surface.
28:55In their grand tour of the solar system,
28:58the Voyager probes produce an astounding number of discoveries.
29:02Volcanoes on Io and geysers on Triton
29:07and little weavy features in the rings of Saturn.
29:10It all turned out to be far, far more interesting
29:13and alive and dynamic than we ever imagined.
29:18While Voyager 2 leaves the planets behind,
29:22its twin, Voyager 1, heads to the edge of the solar system.
29:26But not before taking one last snapshot of home,
29:31a family portrait.
29:33This idea by Carl Sagan to take this family portrait
29:36is just magnificent.
29:39And the scientific need for it may have been limited,
29:41but the appeal to our sense of beauty, staggering.
29:47This shot isn't in pursuit of a new discovery.
29:51It's about finding a new perspective.
29:53This family portrait is a series of 60 images
29:58put together into a mosaic.
30:00And in it you can see the sun and six planets,
30:03Venus, Earth, Jupiter, Saturn, Uranus, and Neptune.
30:07As we were studying the images,
30:08we noticed along one of these sunbeams,
30:10there was the Earth, that pale blue dot,
30:14which contains every single person.
30:17We realized just how tiny our planet is
30:21and how very special.
30:24It's one of the most amazing and beautiful things
30:27I've ever seen.
30:29February 1990.
30:31The cameras power down for the last time.
30:34But this mission isn't over.
30:37The Voyager probes are about to reach
30:39the edge of the solar system,
30:42a region no spacecraft has been to before.
30:46Far from the sun,
30:55at the very edge of the solar system,
30:57lies a vast expanse
30:59where no human-made object
31:02has ever entered
31:03until the Voyagers.
31:07This is like early explorers
31:09leaving sight of land.
31:11They are just surrounded
31:12by a vast ocean of night.
31:14and they are all alone.
31:17It's sort of like the boat
31:18going from the bay
31:19out into the open ocean.
31:21It's a whole different environment.
31:25The Voyager probes are about to leave
31:27the calm of the solar system
31:29and enter the stormy waters of the galaxy.
31:32They start to exit the heliosphere,
31:36a protective bubble
31:37around the whole solar system,
31:39and cross into a combat zone
31:41that hosts a cosmic battle
31:43between the sun
31:44and interstellar space.
31:48Inside the heliosphere,
31:50waves of particles from the sun,
31:53called the solar wind,
31:54push outward.
31:55outside,
31:57an ocean of gas
31:58and particles
31:59pushes back.
32:01As the solar wind
32:02is expanding away from the sun,
32:04it's pushing against
32:05this thin stuff
32:06between the stars,
32:07the interstellar medium.
32:09That's the last influence
32:11that the sun has
32:13in the bubble surrounding it.
32:15Once you cross that,
32:16you are
32:17in interstellar space.
32:19The heliosphere's front line
32:22protects us
32:23from one of the galaxy's
32:25deadliest weapons,
32:26high-energy particles
32:28called cosmic rays.
32:31Cosmic rays are like tiny bullets,
32:33and they travel at close
32:35to the speed of light.
32:36December 2004.
32:39Voyager 1 detects
32:40a sudden drop
32:41in the solar wind,
32:43evidence that the space probe
32:45is nearing the heart
32:46of the battlefield,
32:47a region known
32:49as the termination shock.
32:52The termination shock
32:54is the region
32:56where the solar wind
32:57starts to meet resistance,
32:59starts to run into something,
33:01and that causes it
33:02to slow down.
33:05Voyager 1 picks up surges
33:06from both opposing forces,
33:09blasts of cosmic rays
33:10followed by waves
33:12of the solar wind.
33:14The instruments
33:15on board Voyager
33:16didn't just suddenly change
33:18from sun space
33:20to galaxy space.
33:22It actually kind of
33:23went back and forth
33:24several times
33:24as it was measuring
33:25the energies
33:25of the particles
33:26at that region.
33:29This suggests
33:30that the edge
33:31of the heliosphere
33:32is not a single battlefront,
33:34but rather
33:35a complex region
33:36of skirmishes,
33:38a sea of gigantic
33:40magnetic bubbles
33:41created by the sun's
33:43magnetic field.
33:43The sun's magnetic field
33:46rotates with the sun
33:48physically,
33:48but this far out,
33:50billions of miles
33:50from the sun,
33:51those magnetic field lines
33:53get dragged by particles,
33:54and there's a lot
33:55of different effects
33:55on them,
33:56and they can get
33:56tangled up and loose.
33:58This creates bubbles,
33:59and some of these bubbles
34:00are 100 million miles across.
34:03The magnetic bubble boundary
34:05is not watertight.
34:07Some cosmic rays
34:08blast through.
34:09This heliosphere
34:11is much more foamy
34:13than we had thought.
34:14There are gaps
34:15in our defenses
34:16where deadly cosmic rays
34:18can find their way through
34:19into the inner solar system.
34:22The foamy,
34:23defensive line
34:24blocks 90%
34:25of cosmic rays,
34:27but allows 10% through.
34:30As Voyager 1
34:31passes through
34:32the battlefield,
34:33it detects fewer
34:34and fewer solar particles.
34:37Eventually,
34:38their only cosmic rays
34:39is an interstellar space.
34:42In 2012,
34:43the probe becomes
34:44humankind's first object
34:46to leave the solar system,
34:49followed in 2018
34:51by Voyager 2.
34:54It's been 50 years
34:55since the first satellites
34:57poked their way
34:58out of the Earth's atmosphere,
35:00and now both Voyager spacecraft
35:03have poked their heads
35:04out of the sun's atmosphere,
35:06are outside the solar system,
35:08and exploring the galaxy.
35:12The Voyagers cross
35:14the final frontier
35:14and sail the ocean
35:17between the stars.
35:18They don't see
35:20their first discovery.
35:21They hear it.
35:22In space,
35:25no one can hear you scream.
35:27There's no actual
35:27sound waves moving around,
35:30but there are waves
35:31of plasma,
35:32of electrons.
35:34So as Voyager
35:35passes through this,
35:36we can translate
35:38these changes
35:38in the plasma density
35:39to sound waves.
35:43This is the sound
35:44of interstellar space.
35:46Poetically,
35:50I kind of like
35:50to think of it
35:51as the song
35:51the galaxy is singing
35:53welcoming Voyager
35:54to interstellar space.
35:56Some of these sounds
35:57may even come
35:58from distant supernomas.
36:01Think about that,
36:02a star dying
36:03tens of thousands
36:05of light years away,
36:06and here's an echo
36:07of it here.
36:12The sounds of deep space
36:14tell us more
36:15about our part
36:16of the galaxy.
36:17As Voyager travels
36:19through the interstellar medium,
36:21we can use these sounds
36:24to map out
36:25its local environment
36:26and since 2017,
36:27we've been mapping
36:28how these sounds
36:30get higher and lower
36:31and higher,
36:32louder and softer,
36:33and it's telling us
36:35that the interstellar medium
36:36is not uniform at all.
36:39Built to last five years,
36:41Voyager 1 and 2
36:42are now more
36:43than 40 years old.
36:45Only one final mission
36:47remains,
36:48perhaps the most
36:49important mission,
36:51to let the rest
36:51of the galaxy know
36:52we're here.
37:03The Voyager spacecraft
37:04are now outside
37:06the solar system.
37:08Our sun
37:08is just the brightest star
37:10among many.
37:11How much longer
37:12can the probes
37:13keep going?
37:15The limiting factor
37:16on the mission
37:17has turned out
37:17to be power.
37:19And every year,
37:20there are four watts
37:21less power
37:22to run each
37:23of the Voyager spacecraft.
37:25There are no service
37:26stations out there.
37:26There's no way
37:27to, you know,
37:28repair things that go wrong.
37:30And it's really remarkable,
37:31the fact that they're
37:32still out there
37:32in a cryogenic cold,
37:34you know, operating.
37:35They're still working.
37:36They're still alive.
37:37In just five years,
37:39there may be
37:39too little power
37:40to transmit signals
37:42to Earth.
37:43After a final message home,
37:45the Voyagers
37:45will fall silent
37:47forever.
37:49This part of
37:49the Voyager mission,
37:51flying in interstellar space,
37:53is the long goodbye.
37:57They're going to become
37:58our messages in a bottle.
38:01A little bit of humanity,
38:02you know,
38:03representing us
38:04when we're long gone.
38:05The two probes
38:06could survive
38:07for billions of years.
38:10They could be
38:11not only, you know,
38:12interstellar Voyagers,
38:13they could turn into
38:13intergalactic Voyagers,
38:15ultimately.
38:17Maybe the Voyagers
38:18won't just drift forever.
38:21Maybe they'll be found.
38:25There was kind of
38:26a wonderful little
38:27jaunt of imagination
38:28that maybe
38:29some alien civilization
38:30with incredibly powerful
38:32telescopes
38:32might notice
38:33that there's a little
38:34artificial object
38:35flying through space
38:35and be curious about it.
38:38Strapped to each Voyager
38:39is an aluminum case.
38:42On the outer side
38:43is a map
38:44of how to find Earth
38:45with directions
38:46from different pulsars.
38:47So why use pulsars
38:50to direct aliens
38:51to our location?
38:53These are the dead cores
38:54of stars
38:55after a supernova explosion.
38:57Well, amazingly,
38:58pulsars all spin
38:59at slightly different rates.
39:01So if you can actually
39:02triangulate your location
39:03based on the rates
39:05of different pulsars
39:06in the sky,
39:06you can actually have
39:07sort of a galactic GPS system.
39:10You can show the aliens
39:11where we are
39:11with incredible accuracy.
39:13Inside each case,
39:16a gold-plated copper disc.
39:19Looking back on it,
39:20it's really kind of
39:20this wonderful part
39:21of humanity.
39:22We sent aliens out there,
39:24you know,
39:24unimaginably
39:25technologically advanced aliens.
39:27We sent them
39:28basically a vinyl record.
39:30Yeah, the golden discs
39:31are literally discs.
39:33They actually are records
39:35with grooves.
39:35You can play them.
39:36You can jam out to them.
39:38It's got a soundtrack
39:39of our species.
39:43The records have tracks
39:45by Beethoven,
39:47Blind Willie Nelson,
39:48and Chuck Berry.
39:50The sound of surf,
39:51of thunder,
39:52of birdsong,
39:54and a human heartbeat.
39:56So, will aliens
39:58ever find the records
39:59and give them a spin?
40:01The golden record
40:02is a lovely idea,
40:04especially to energize
40:05and excite the public
40:06about this.
40:07Will it ever be found?
40:09There's a reason
40:10we call it space.
40:13A tiny, cold spacecraft
40:16is a difficult target
40:18to find.
40:19Any species capable
40:21of detecting them
40:22would have a better chance
40:23of spotting our planet.
40:25But the voyagers
40:26will long outlive Earth.
40:29It's possible
40:30that they will find it
40:31millions or even billions
40:32of years in the future,
40:33long after we're gone,
40:35where there really
40:35aren't humans anymore.
40:37Or is there even
40:38a possibility
40:39that when we start
40:40traveling to the stars
40:41in the far future,
40:42we'll find them?
40:43A waiting discovery
40:45or doomed
40:47to drift alone,
40:48the voyager probes
40:49have already inspired
40:50one civilization,
40:52ours.
40:54Calling these voyager,
40:55it's perfect
40:57because that's what
40:58they are doing.
40:58They are voyaging out
40:59to the outer solar system
41:01and beyond
41:02and showing that
41:03there is no end
41:04to our desire
41:05to explore.
41:06They've shown us
41:09countless wonders
41:10of the solar system
41:11and a glimpse
41:12of what lies beyond.
41:15We as a species
41:17can build ships
41:19that not only
41:21sail the oceans
41:21of our Earth,
41:22but that can sail
41:24outwards
41:24to the other planets
41:26in our system
41:27and reveal new worlds.
41:29They are the greatest
41:31space mission ever.
41:33The legacy of Voyager
41:34is our remnant.
41:37It is our memory.
41:38It is a sampling
41:40of humanity
41:41that is out there now
41:43among the stars.
41:45And if they last
41:46until the death
41:47of the universe,
41:48as the final stars fade
41:50and everything goes dark,
41:53they will be humanity's
41:55final statement.
41:56We were here.