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00:00In August 1977, two spacecraft called Voyager began an incredible journey.
00:30If they survived the hazards that lay across billions of miles of space, they would reach
00:42worlds so distant and strange they defied the imagination.
00:49The gas giants.
01:00The gas giants.
01:12Voyager was heading for four vast planets
01:40that could swallow Earth thousands of times.
01:44Jupiter, with its strange bands of cloud
01:47and its great red spot,
01:50a world crackling with radiation
01:51that can be heard from Earth.
01:59Beyond Jupiter was Saturn.
02:02How did this planet alone
02:03come to have its spectacular array of rings?
02:08Stranger still was Uranus.
02:11It was known from the way its moons were orbiting
02:13that Uranus had been tipped over on its back.
02:17Why should this be?
02:23Neptune was barely visible
02:25even through the most powerful telescopes.
02:29What kind of worlds were these?
02:32And what could they reveal about the solar system
02:34of which Earth is such a tiny part?
02:38Roger, zero G, and I feel fine.
02:40Capsule is turning around.
02:43Oh, that view is tremendous.
02:46In the early 1960s,
02:49sending a spacecraft all the way to the giants
02:51was unthinkable.
02:54Men had flown just a few hundred miles up
02:57in orbit around the Earth.
02:58Unmanned probes ventured further,
03:03but only to the nearest planets,
03:05Venus and Mars.
03:06Signal level has gone way down.
03:08Report continuing low signal level.
03:11Even this was pushing the very limits of science.
03:15In 1964, the first spacecraft, Mariner 4, flew by Mars.
03:27There she goes.
03:28The spacecraft just barely made it there.
03:31Yes, it's there.
03:32And so the concept of going to Jupiter,
03:34which was almost a half a billion miles away,
03:37Saturn, almost a billion,
03:39Uranus, almost two,
03:40and Neptune, almost three billion miles away,
03:43and all 12 years in journey,
03:45was not even something one could very easily imagine.
03:54A solution came from a most unlikely source.
03:57A young student at NASA's Jet Propulsion Laboratory
04:03was asked to calculate trajectories
04:06for a flight to Jupiter.
04:08I was a summer student working on my degree at the time,
04:12so when I was given the job of looking at the outer planets,
04:16I thought that was kind of a make-work project.
04:20I was being kind of kept out of the way
04:21while the really important business
04:23of getting to Mars was underway.
04:25Flandreau discovered something
04:28that made the dream of a flight to the giants
04:30a real possibility.
04:37Obviously, the first thing is to determine
04:39when the planets are going to be in positions
04:43where we could reach them.
04:44So I drew very careful maps
04:46of where the planets would be,
04:48and one of the most important drawings
04:50was one in which I drew the positions of the planets
04:53versus the date.
04:55And the thing that caught my attention immediately was
04:58that the lines for Jupiter, Saturn, Uranus, and Neptune
05:02all crossed in about the 1975-76 time period.
05:06In other words, those four major planets
05:09were on the same side of the sun
05:10and in the same general position at the same time.
05:13So it gave me the idea immediately
05:15that we could do all of those planets with one flight.
05:19Flandreau's discovery was more than just a convenient planetary line-up.
05:27Rocket power alone could propel a spacecraft
05:30no further than Jupiter.
05:33But scientists knew that if a probe approached a planet
05:35at the right angle,
05:37it would be caught by the planet's momentum,
05:40then pitched in a new direction
05:42at a greater speed.
05:49The trick you use here is you fire your rocket
05:53with enough propulsion to get to Jupiter,
05:55which is, after all, a long ways away.
05:57It's five times the distance of the sun.
06:00Go by Jupiter in just the right way
06:03that you get a gravitational slingshot effect.
06:07That propels you to Saturn.
06:10Same trick.
06:11If Saturn's in the right place at the right time,
06:14which can propel you to Uranus
06:15if Uranus is in the right place at the right time,
06:17and on to Neptune, same deal.
06:19That happens about every 175 years.
06:23And it happened in terms of launch date in 1977.
06:27And in fact, a former administrator of NASA, Tom Payne,
06:31used to make the joke that the last time this happened,
06:34Thomas Jefferson was president, and he blew it.
06:45For NASA, this was too good an opportunity to miss.
06:49They announced a mission to the giants called Voyager.
06:55It marked a new era for astronomers
06:57who had struggled to understand the hazy views
06:59as they could see through Earth-based telescopes.
07:05The man chosen to lead the imaging team was Brad Smith.
07:09I had started looking at Jupiter seriously
07:11back in the late 50s,
07:13but we were frustrated by the difficulty
07:16of making such observations from the ground.
07:19And so when the opportunity came up
07:22to be involved with Voyager,
07:23I realized that for the first time
07:25I was going to have that opportunity
07:27to see Jupiter up close,
07:29to see detail that we never could possibly see from the ground.
07:35The hopes of astronomers
07:36now lay in the hands of the mission engineers
07:38who faced what seemed an impossible task.
07:45A comment that I frequently heard
07:48from those I was working with was,
07:50that mission is never going to happen.
07:52It's just too complicated.
07:55We had to build a machine that could fly
07:57for perhaps 10 years without failing,
07:59and that was really pushing the limits
08:01of what we thought we could do
08:02with electronics at that time.
08:04We had to pass through the asteroid belt on the way.
08:08How can we get this large spacecraft
08:10through that very dangerous area
08:12beyond Mars without a collision?
08:15That seemed to be a very, very, very challenging task.
08:19One of the big worries was data transfer.
08:23Even if you could do this flight,
08:24could we get any useful data back to the Earth?
08:27So there's a great deal of worry about that.
08:34The engineers had a decade
08:36to make the Voyager mission possible.
08:39Around the world, giant antennae were built,
08:42the Deep Space Network,
08:44to communicate with probes across billions of miles.
08:49But it still wasn't known
08:50if a spacecraft could survive hazards
08:52like the asteroid belt,
08:54a band of drifting rocks between Mars and Jupiter.
08:57Voyager would have only one chance,
09:00so two less elaborate probes
09:03were sent ahead to test the way.
09:09Pioneer 10 and 11 were launched to Jupiter and Saturn.
09:14Pioneer 10 and 11 were a very important part
09:16of the strategy of exploring the outer solar system.
09:18It was critical to have the pioneers lead the way,
09:21telling us about the environment
09:24and making some very important discoveries,
09:26which would then allow us, with the Voyagers,
09:28to come safely behind.
09:31James Van Allen was a veteran of missions to Mars and Venus.
09:35Now he led a team of scientists on Pioneer.
09:39Pioneer 10 was the first venture beyond Mars,
09:44first time we were going into such enormous distances,
09:47first time we were about to cross the asteroid belt,
09:50which lies between the orbits of Mars and Jupiter.
09:53So it was a very hazardous and high-risk mission,
09:57and we had a keen sense of its historic possibilities
10:01in blazing the trail to the outer planets.
10:12Pioneer 10 successfully got through the asteroid belt,
10:15and it was still performing beautifully.
10:16And so we now knew that, in fact,
10:19it was possible to get to the outer planets safely.
10:22Another key question which Pioneer 10 had to address
10:24was how intense was the radiation environment around Jupiter.
10:30Since the 50s, radio emissions had been detected
10:33coming from Jupiter,
10:35suggesting there might be intense radiation around the planet.
10:43The man whose task was to investigate this
10:45was James Van Allen.
10:47Who had discovered bands of radiation around Earth
10:50with the very first American satellite.
10:54They were later called the Van Allen belts.
10:58We have encountered a very high intensity of radiation,
11:01which is of the order of 1,000 times as intense
11:04as could be attributed to cosmic rays
11:06as ordinarily understood.
11:09Van Allen predicted greater radiation belts around Jupiter.
11:13But even he did not anticipate what Pioneer found.
11:19As we went in, the radiation intensity got greater and greater
11:22and greater and greater and greater and greater and greater.
11:24And it was a very strong apprehension
11:27about the survival of the electronic equipment in the spacecraft.
11:31But it went up to a maximum,
11:33it kept going up and up,
11:34and we did survive,
11:35and then it started back going down again.
11:36So we, of course, breathed a sigh of relief
11:38that we had finally made it.
11:42The radiation belts at Jupiter
11:43turned out to be 10,000 times more intense than Earth's.
11:48And Pioneer also encountered a vast magnetic field
11:51stretching 7 million miles out from the planet.
11:54One thing that Pioneer 10 discovered
11:57was that Jupiter's magnetic field
12:00is the largest structure in the solar system.
12:02If you could see it from Earth in the sky,
12:05it would appear to be as large as the sun,
12:07even though it's five times further away.
12:09But, of course, it's invisible,
12:10and this is very damaging to spacecraft
12:12and can damage electronics.
12:15The Voyager probes had to be hurriedly redesigned
12:18to survive the intense magnetic field
12:20and radiation belts of Jupiter.
12:22The Pioneer saved our lives.
12:27Had we flown into that unknowingly
12:29with the more sophisticated electronics
12:32and the more sophisticated mechanisms
12:34that we had on Voyager,
12:35we would have died right on the spot.
12:37We were well into the design of that spacecraft
12:41when the Pioneer results came in,
12:43and we had to do a lot of redesign.
12:49As the launch date drew near,
12:51their final preparations were made for Voyager.
12:54For any curious extraterrestrials they might meet,
12:57the probes carried a disc showing where they had come from
13:00and a collection of images from Earth.
13:02This was a moment that I had imagined and thought about for years,
13:18and there it was happening.
13:31Here was our spacecraft on the way to Jupiter and Saturn and Uranus and Neptune.
13:35A very marvellous feeling, indeed.
13:37It was nearly four centuries since Galileo turned the first telescope on Jupiter
13:50and discovered four points of light moving around the planet.
13:54These were four moons,
13:57the first proof that not everything in the universe revolves around the Earth.
14:02For Voyager's chief scientist,
14:06the mission promised a new era of discovery.
14:09I think we all felt that we were in the tradition of Galileo,
14:14who was the first to see the moons of Jupiter,
14:17and the first to apply an instrument
14:20to increase our ability to observe the universe.
14:24Voyager was just the latest tool
14:27which we as a civilization had managed to devise,
14:30and, of course, the tool was so powerful
14:32that we saw things nobody had seen before
14:34and that nobody had imagined we would see.
14:41The probe was still 50 million miles from Jupiter
14:44when it sent back the views everyone had been waiting for.
15:00We all approached Jupiter with great expectation,
15:04and we all had our grandiose theories about what we were going to see,
15:08but, of course, Jupiter fooled us all.
15:11There was some bizarre behaviour,
15:13little clouds moving along and being swept up in the great red spot
15:17and then being, they would spit them out again.
15:21Other clouds roll along next to one another,
15:24coalesce into a single cloud, and then break apart again.
15:30Those kinds of details are not understood,
15:34not even now, not 20 years later.
15:44The first encounter with Jupiter was a marvellous time for me,
15:49especially the approach shots showing the planet revolving
15:53and watching the great red spot revolving,
15:55getting closer and closer till finally we could see
15:58that indeed this was the top of a large storm.
16:02As a child, I'd studied that and wondered if that was a storm
16:05or was that an island floating in an ocean.
16:08It was very difficult to know,
16:10and finally the answers were there before our eyes.
16:12Voyager revealed an atmosphere of hydrogen and helium gas,
16:24whose clouds were much more dynamic than had been imagined.
16:29Jupiter's winds gust at hundreds of miles an hour,
16:32and the red spot alone is three times the size of the Earth,
16:36the greatest storm in the solar system.
16:38Voyager hinted at why this should be.
16:44It found that Jupiter gives out twice as much energy
16:47as it receives from the Sun,
16:49suggesting that its core must be hot.
16:53Scientists now believe that at the heart of this massive planet,
16:56the gases are compressed until they become a metallic liquid.
16:59This hot, churning core could be the powerhouse that drives Jupiter's winds,
17:06and like a dynamo,
17:07creates the enormous magnetic field around the planet.
17:19Voyager then turned its cameras towards Jupiter's moons.
17:22At the time of the encounter,
17:28Bruce Murray was head of JPL.
17:31Just before the mission,
17:35the interest was on the planet, on those bands,
17:38the things that you could see through a telescope.
17:39There was hardly any interest at all in the satellites of the planets,
17:45because they at most were little spots,
17:47something we couldn't even see, of course.
17:49And I had to lead a one-man crusade
17:52to even have them listed as targets for Voyager when it went there.
17:56Scientists had expected the moons of Jupiter to be cold,
18:04dead, and covered in craters like our own moon.
18:08What they found was an array of worlds
18:11as different and surprising as the planets themselves.
18:15Io, the closest of Jupiter's large moons,
18:19turned out to be more geologically active than Earth.
18:23Jupiter's enormous gravity stretches and squeezes Io,
18:26heating it up, so it stays molten inside.
18:30We found that Io had eight active volcanoes on it,
18:33the most volcanically active body in the solar system,
18:36and it's just a small moon.
18:38And that was so unexpected.
18:41And it was such a shift in our paradigm
18:44about what was going on in the outer solar system,
18:47where it's very cold and presumably, we thought, very dead.
18:50So in that sense, it characterized for us
18:53the sense of seeing things that we really hadn't thought about,
18:57and that was, in fact, very characteristic of the rest of the mission.
19:02As Io orbits close to Jupiter,
19:05it is constantly brushing against the planet's magnetic field.
19:10The little moon builds up a huge electrical charge,
19:13which discharges onto Jupiter
19:16in a continuous flow of three million amps,
19:19causing storms on the surface of the planet.
19:29The rest of it's red.
19:31The rest of it's red.
19:33The next moon, Europa,
19:35was very different, but no less surprising.
19:38It had a surface of water ice,
19:41frozen as hard as rock.
19:42Underneath this icy crust,
19:50scientists believe there are oceans of warm water.
19:53further out,
20:09the moon Ganymede was bigger than the planet Mercury.
20:12It's landscapes of rock and ice
20:29reminded Voyager's geologist,
20:31Laurence Soderblom,
20:33of Earth.
20:34Ganymede turned out to be really exciting.
20:37We found a broken surface,
20:40complex patterns.
20:42It's kind of a cross between
20:44ice flows in the Arctic
20:46and continental drift on the Earth.
20:49And so its icy crust has been sheared,
20:51twisted, broken,
20:53something we didn't expect.
20:54The last major moon, Callisto,
21:00was different again.
21:02Like our own moon,
21:03it was covered with craters.
21:06Its cold, icy crust
21:07preserved a record of a violent age
21:09when meteorites crashed into its surface.
21:12What Voyager found at Jupiter's moons
21:21transformed the rest of the mission.
21:25The first thing that strikes one is,
21:28my lord, everything is different.
21:30And so the diversity is overwhelming
21:32because this is a mission discovery.
21:33This is Captain Cook.
21:35This is really in the solar system,
21:37seeing really new things.
21:38The isle in Europa,
21:39there's a twin, a pair there,
21:41and then there's a pair out again,
21:42means cluster.
21:42What about the relief
21:43from the cracks?
21:44Shouldn't there cracks
21:44that kneel and flow also?
21:46In order for there to be enough heating...
21:47All of the scientists,
21:49with exception to me,
21:50were atmospheric scientists
21:51and astronomers.
21:52And in fact,
21:53it wasn't until we really recognized
21:55the exotic variety and diversity
21:58of the satellites
21:59that geologists were really added
22:01to the Voyager team.
22:03Just rotate it out a little bit.
22:04And in fact,
22:05the satellites, in my view,
22:06became the star
22:07of the whole Voyager experience.
22:12Jupiter's moons are a solar system
22:21in miniature.
22:24As Jupiter formed,
22:25its immense gravity
22:26must have attracted
22:27a cloud of dust and gas,
22:29from which its moons were born,
22:32just as the planets around the sun.
22:36Close to Jupiter
22:37are small, dense, active worlds,
22:40Io and Europa,
22:42a mirror of the inner rocky planets
22:44Venus, Earth and Mars.
22:51Further out,
22:52Ganymede and Callisto
22:53are larger, icy worlds,
22:56the giants of the Jupiter system.
22:58Voyager's next goal
23:07was Saturn.
23:13For early astronomers,
23:15Saturn was the last planet
23:16in the solar system.
23:19The first to observe the rings,
23:21Giovanni Cassini,
23:23saw a flat disk
23:24with just one gap.
23:26Scientists hoped Voyager
23:32would reveal clues
23:33to the origin
23:34of these mysterious rings.
23:44And this time,
23:46after Voyager's success
23:47at Jupiter,
23:48the press and the public
23:50were queuing up
23:51for a glimpse
23:51of the first images
23:52of everyone's favourite planet.
23:56This film was pronounced
24:02in Wedding.
24:05It was a book
24:06called Pric St.
24:07The Institute
24:08metade
24:08with the highest
24:09many years
24:09of the energy
24:10of this year,
24:10magnetic fascination
24:11could do not
24:12the ceilrirvel.
24:13While the marist
24:14was handed
24:15out to飾
24:15and having
24:15the musical
24:16of the media
24:17and he would
24:17give a 74
24:17can of it
24:19to get a América
24:20andama.
24:21It was a gard
24:25We thought we knew it all, but once again, we were looking at a very, very complex situation.
24:37The rings were broken up into mini-rings. There were gaps in there.
24:42There were all sorts of dynamical phenomena that we didn't understand.
24:46So we very, very hurriedly reprogrammed Borgia II to take a much closer look at the rings.
25:03When I began my work in about 1964, I had suggested that one thing we could do with this particular mission was to fly between the planet and the rings.
25:13And very fortunately, we didn't do that, because as we approached Saturn, we saw that the region there that we would have to have flown through with the spacecraft was filled with more rings.
25:23There was no question that spacecraft would not have survived trying to go through that gap.
25:31The imaging team could barely cope with all the new detail revealed by Voyager 2.
25:40They saw delicate rings that were intertwined.
25:43And rings that were held in place by tiny moons called shepherds.
25:51There were strange features called spokes, patches of dust particles slightly raised above the rings.
25:59These caught the eye of one young graduate student.
26:02I got involved in the study of spokes, which were these ghostly features that were seen to come and go.
26:11And it just came to my head to just kind of categorize the pictures.
26:15Into one pile, I put all those images that seemed to have a lot of spokes in them.
26:19And into another pile, I put those images that seemed to have virtually no spokes at all.
26:24And I made an intermediate category.
26:26And, of course, each image was tagged with a time.
26:30And I basically just did an analysis on the computer of this and found that the spokes actually weren't just sporadic, but, in fact, they came and they went with a certain period.
26:41In fact, I was just a very strict moment.
26:49.
26:51Carolyn Porco discovered that the spokes followed Saturn's magnetic field as it rotated with the planet.
26:58i made my very first scientific discovery and just knowing that i had found something that
27:08nobody else on the face of the planet knew at that time was just such an exhilarating experience
27:15but where did the rings come from a possible answer came to light when voyager encountered
27:32saturn's moons a collection of icy worlds scarred by great impact craters made by meteorites long ago
27:39saturnian system was more like what we had actually expected small cold icy moons which are
27:46heavily cratered set of objects but there were some real surprises there as well
27:51the the innermost of the large satellites is mimas we found large impacts this crater called herschel
28:00is a fourth the size of the object nearly large enough to blast it apart we find a similar impact
28:07crater on tethys the next moon out one roughly a third the size of the object so it's clear that
28:13in their early history they were being blasted by things that were large enough to have torn them apart
28:21if mimas nearly got bashed up to bits then it's very likely there were other satellites that did
28:27get smashed up to bits and the rings of saturn probably came from a satellite that was close
28:34into this the planet got smashed up the debris of the collisional shards got strewn out into a planetary
28:43marine system
28:52so
28:55so
28:57so
29:03so
29:05so
29:07so
29:11As Voyager encountered the planet itself,
29:24it found that Saturn was made of the same gases as Jupiter.
29:29These two worlds are the great gas giants of the solar system,
29:34dwarfing all the other planets.
29:35Yet Saturn held mysteries of its own.
29:43Saturn is smaller and colder than Jupiter.
29:46It generates less heat within and receives less energy from the Sun.
29:51Yet Voyager recorded even faster winds on Saturn than on Jupiter,
29:56a thousand miles an hour.
29:58Why this should be was not yet understood.
30:01And as Voyager left Saturn, there was one final enigma.
30:10Saturn's largest moon, Titan,
30:12is the only moon in the solar system with a thick atmosphere.
30:16Voyager's cameras could not penetrate the orange haze
30:19to see what lay beneath.
30:21I found myself alone in the Voyager imaging area late in the evening,
30:35about 10 o'clock in the evening.
30:37And it was just me and the television monitor.
30:40And this was the monitor that had showed us all these tremendous pictures
30:43that people were gathered around.
30:44And now it was just showing the image of Saturn
30:48that Voyager 1 had as it receded from the planet.
30:52And I was mesmerized by this whole thing,
30:56thinking about how humankind had never seen Saturn from this perspective before,
30:59because we had never been on the other side of Saturn before.
31:03And I was so moved by me and Saturn alone in this room
31:08that I was completely swept away by the whole thing.
31:11Voyager's next goal was Uranus,
31:24a world discovered just 200 years before and still barely seen.
31:31Would this strange planet, tipped over on its back,
31:35resemble its great neighbours Jupiter and Saturn?
31:41Even travelling at over 50,000 miles an hour,
31:49it would take some five years for Voyager to reach Uranus.
31:58The engineers needed every moment
32:00to prepare for their most difficult challenge yet.
32:03Voyager was planned to operate at 1 billion miles at Saturn.
32:07It was now being asked to operate at 2 billion miles at Uranus,
32:10where the sun was very dim.
32:12We had to do several things.
32:14For instance, you have to have much longer exposures on the camera.
32:16And if you have too long an exposure,
32:18the spacecraft's moving very rapidly,
32:20things become smeared.
32:22So we had to learn how to program the spacecraft
32:24to turn at just the right rate
32:26so that it would compensate for the motion of the spacecraft.
32:35But when Voyager reached Uranus,
32:38its cameras found little to photograph.
32:40We had been so spoiled by the glamour
32:45and the colour and the intricacies
32:47of what we saw in the atmospheres of Jupiter and Saturn
32:50that Uranus was a little bit of a letdown
32:53because it was so bland.
32:56There's more atmosphere and more haze above the clouds,
32:59and so it's hard to see the features.
33:04Even at its closest approach,
33:06Voyager revealed little detail in the atmosphere of Uranus.
33:09Uranus is different than Jupiter in the center
33:13in the sense that it has no internal heat source.
33:16Both Jupiter and Saturn are radiating more energy
33:19than they receive from the sun
33:20because there's still heat inside those planets.
33:22For some reason at Uranus,
33:24that heat source had been shut down
33:25and was not driving the atmosphere.
33:28So the atmosphere was much blander.
33:33Voyager had found a very different kind of giant,
33:36a world many times smaller and colder
33:38than Jupiter and Saturn.
33:40Check some, what's your race?
33:41Check.
33:42It was shrouded in different gases,
33:44mostly methane and ammonia,
33:46under which scientists believe
33:48there might lie oceans of water and ice.
33:51What exactly is that stuff?
33:55Is that in here, do you think?
33:58If Uranus had been something of a disappointment,
34:01the imaging team found plenty of surprises
34:03in the planet's moons.
34:04Great.
34:14Most striking of all was the tiny moon Miranda.
34:21Miranda looks like a three-dimensional jigsaw puzzle
34:24in which we see regions looking like giant, complex racetracks,
34:29almost as if it's put together by a committee.
34:31There are pieces stuck on the surface
34:33that look like they belong to different planets.
34:36And one idea was that it was busted apart
34:38and that these coarse pieces stayed intact
34:43and then they were glued back together.
34:45And so you get this hodgepodge.
34:47The Hodgepodge
35:17Perhaps it was just such a collision on a much grander scale that knocked Uranus itself
35:43over on its back in the earliest days of the solar system.
35:58From Uranus onwards to Neptune, some 3 billion miles away from Earth, the probe would have
36:05to take a very precise trajectory over the north pole of the planet to get the best possible
36:10view of Neptune and its large moon, Triton.
36:14The challenge at Neptune was the most difficult one we'd had.
36:18We had to know within one second when we were going to fly over the north pole of Neptune.
36:24That was a major navigational challenge.
36:27We had never delivered that kind of accuracy before.
36:30And if we were right, it worked, and if we were wrong, we had no second chance.
36:34After 12 years in flight, Voyager arrived at Neptune.
36:42Brad Smith and his team feared after the bland face of Uranus that they would see little when
36:47they got to the last giant.
36:50They need not have worried.
36:52At quid of them, they were shot, I thought they had no bekannt on their faces.
37:19The final encounter I was able to witness here at JPL with my youngest son, and we watched
37:30with fascination as the pictures of Neptune unfolded, suddenly things that no one had
37:36imagined were there.
37:38Here was a planet that was vibrant with life.
37:41It had its own great spot, a dark spot in this case, white clouds floating in its atmosphere,
37:48and these things unfolded before our very eyes, and what a wonderful surprise.
37:53Neptune for me was a great surprise.
37:57There was something strange and eerie about Neptune because here, the last planet, you
38:06know, the sentinel at the outer edge of our solar system looks like Earth with its beautiful
38:14deep blue color and its white clouds floating in the atmosphere.
38:21We were back with a really exciting planet again with Neptune.
38:28There were fast-moving clouds, clouds that moved in different directions, some of them almost
38:32at sonic speeds.
38:34The complexity of the planet's atmosphere was far beyond our expectations.
38:45Neptune turned out to have the strongest winds of all.
38:50Here in the furthest extremes of the solar system, where the sun barely penetrates, the
38:55last giant defied all expectations.
38:59You might expect that the further you got from the sun, where there was less energy to drive
39:04the winds, the winds would be slower.
39:07The winds on Jupiter were already hundreds of miles per hour.
39:10It turned out, rather than seeing slower winds, we found faster winds.
39:14We found winds over a thousand miles per hour at Neptune.
39:18We now understand why that's the case, and that is, if you have enough energy, it creates
39:22a lot of turbulence, and that slows the wind down.
39:26Neptune, there was so little energy, that the wind basically got started and would just
39:31go and go and go.
39:34Neptune's atmosphere was much more dynamic than Uranus, but it was made of the same gases
39:39and ices.
39:42The last two giants were very different from their more massive cousins.
39:47Uranus and Neptune are not gas giants, but ice giants.
39:51The rest of it's red.
40:00From Earth, nobody had seen a full set of rings at Neptune, but some scientists believed
40:06they had seen incomplete segments of a ring, which they called arcs.
40:10By the time we got to Neptune, I was leading the small group of individuals on the imaging
40:18team who were responsible for the rings and the ring arcs.
40:23In fact, there were some people on the Voyager imaging team who just completely doubted the
40:27existence of these things.
40:28They thought we were crazy.
40:30They thought we were wasting precious spacecraft resources.
40:34And so it was very gratifying to finally see that one image come down where we captured, finally
40:39caught them in the act, the Neptune ring arcs.
40:43So it was a tremendous achievement.
40:48Neptune is indeed surrounded by ring arcs.
40:53How they got there, and why the ring is incomplete, is not yet understood.
41:15The impossible mission was almost over.
41:19Neptune's moon Triton was the final encounter.
41:31Triton is a large moon.
41:34It's about the same size as the planet Pluto, actually.
41:36So if it were out in orbit around the sun, we would call it a planet.
41:40But it's in orbit around Neptune.
41:42But unlike all the other satellites, which orbit in the same direction as the planet rotates,
41:48Triton is in a retrograde orbit.
41:50It's going around Neptune backwards, which told us it was not likely formed around Neptune,
41:56but had been captured by Neptune.
42:02Triton is a moon that might have been a planet.
42:06But it strayed too close to Neptune, and was caught by its gravity.
42:18Triton turned out to be one of the strangest worlds encountered.
42:25Triton was a world unlike any we had seen before.
42:33It was the coldest surface we'd seen in the solar system, 40 degrees above absolute zero.
42:39So cold that nitrogen, which forms most of the atmosphere on Earth, is frozen solid ice.
42:45And the polar caps on Triton are frozen nitrogen, not frozen water.
42:51Even so, we found geysers on the surface of Triton.
43:09Nitrogen geysers miles high.
43:11So even in the very deepest part of our solar system, there is geologic activity.
43:17It is everywhere.
43:18The solar system is alive, evolving, and that's what makes it so exciting and makes it so much to learn.
43:26Voyager had survived to reach the extremes of the solar system, and reveal not just the giants themselves,
43:37but whole systems of rings and moons unlike anything imagined.
43:43As the planets moved out of their alignment, Uranus and Neptune once again drifted out of our reach.
43:50It's unlikely that they'll be visited again in our lifetime.
43:54But Voyager was not the last mission to the gas giants.
44:09In 1994, a probe named Galileo returned to Jupiter and its moons.
44:15It found that Io's surface had been covered by fresh eruptions of sulfurous lava.
44:21Europa, which had looked so smooth, turned out to be covered in great ridges and chasms.
44:38Fresh detail was revealed in Ganymede's alien landscapes.
44:46And there was more destruction than had been imagined on Callisto.
45:03In October 1997, a mission called Cassini set off for Saturn.
45:08It will spend four years sending back high-resolution images of the great planet, its rings, and its many satellites.
45:27Head of the imaging team is Carolyn Porker.
45:31We are interested, for scientific purposes, in taking images of Titan and all the satellites too.
45:37So, how many images do you think you'll need in that block?
45:40Four is what we normally talk about.
45:42Four images? In 30 minutes? Okay.
45:46We have designed the camera system specifically, among many other things.
45:52We've designed it to see down to the surface of Titan, which of course is something we weren't able to do on Voyager.
45:59And we'll be able to see things that are on the scale of office blocks.
46:04We'll be collecting data from Cassini at least for a period of four years,
46:08so we'll have a chance to monitor changes and, you know, it'll be a new era.
46:13But it will never have the same feeling or even significance, historical significance as Voyager had,
46:23because that experience can never be duplicated.
46:27The next awards are the Exceptional Scientific Achievement Medal.
46:32The first award goes to Gary Flandro for seminal contributions to the design and engineering of missions,
46:39including the grand tour opportunity for the epic Voyager explorations.
46:47The views that we achieved there of each of those outer planets far exceeded any expectations,
46:52but it was a ghostly feeling of having already been there, myself flying that mission in my mind in the 1960s.
47:01The work all started right up in that office.
47:03Is that right?
47:04That's where it was.
47:05Building 180 is where you were.
47:06Sat out and looking out that window through those trees and up towards the sun,
47:10and I said, we could do this.
47:12Four planets in one plane.
47:16With the planets behind it, Voyager carried on to search for the very edge of the solar system,
47:22where the sun's influence runs out and interstellar space begins.
47:27The Voyager mission is not over.
47:37We hope we can continue listening to it for at least another 20 years,
47:41before we finally lose power on the spacecraft.
47:44In 2015, Voyager 1 will be 130 times as far from the sun as the Earth,
47:50about 12 billion miles from the Earth,
47:53and perhaps in interstellar space for the first time.
47:56So we listen to the two Voyager spacecraft every day,
47:59looking for some signal that we're getting close to interstellar space.
48:04The greatest Voyager in history is still travelling.
48:16The Voyager spacecraft's mission is still travelling.
48:18The Voyager spacecraft andaho
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