0:00:08 > 0:00:12The instinct to explore is one of the qualities that defines us
0:00:12 > 0:00:14as human beings.
0:00:14 > 0:00:17It's propelled us across vast oceans
0:00:17 > 0:00:20and to every corner of every continent.
0:00:21 > 0:00:26But far, far away from these shores, two tiny spacecraft
0:00:26 > 0:00:30are lifting this spirit of exploration to extraordinary levels.
0:00:32 > 0:00:33For three and a half decades,
0:00:33 > 0:00:37they've been investigating the outer reaches of our solar system.
0:00:38 > 0:00:41They are the Voyagers.
0:00:42 > 0:00:47Voyager was the right spacecraft at the right time,
0:00:47 > 0:00:51when a huge amount of stuff was waiting to be discovered
0:00:51 > 0:00:53and Voyager was capable of discovering it.
0:00:53 > 0:00:58Voyager was the seminal mission of the past 50 years.
0:00:58 > 0:01:00It represents the golden age of space exploration.
0:01:00 > 0:01:04The Voyager journey has been driven
0:01:04 > 0:01:08by remarkable human endeavour and achievement.
0:01:08 > 0:01:12They've been a window into worlds almost beyond imagination.
0:01:15 > 0:01:19And they've have helped unlock the secrets of our solar system.
0:01:23 > 0:01:26For many of us, they're probably best known for carrying
0:01:26 > 0:01:28a kind of message in a bottle.
0:01:28 > 0:01:30A record of humanity here on Earth,
0:01:30 > 0:01:34meant for any extraterrestrial civilisation that may find them.
0:01:34 > 0:01:38Each spacecraft carries a golden disc.
0:01:38 > 0:01:42It holds a snapshot of humanity, a dispatch to the stars.
0:01:42 > 0:01:46'Hello from the children of planet Earth.'
0:01:47 > 0:01:51And now the Voyager mission is about to cross the final frontier.
0:01:51 > 0:01:55They are the first objects built by humans
0:01:55 > 0:01:59ever to pass beyond the solar system and into the galaxy beyond.
0:02:01 > 0:02:03This is the tale of the two most intrepid explorers
0:02:03 > 0:02:05in our planet's history.
0:02:07 > 0:02:09This is the Voyager story.
0:02:26 > 0:02:28Right, here we go. 1977,
0:02:28 > 0:02:32a good year for music.
0:02:32 > 0:02:35The question is, what do you start with?
0:02:35 > 0:02:39Do you go with a crowd pleaser or do you go with your favourite track?
0:02:40 > 0:02:42MUSIC: Never Going Back Again by Fleetwood Mac
0:02:45 > 0:02:47Brilliant.
0:02:50 > 0:02:53# She broke down and let me in... #
0:02:53 > 0:02:59It's 1977, and Fleetwood Mac have just released Rumours.
0:02:59 > 0:03:01The world feels like a different place.
0:03:01 > 0:03:03..of the United States...
0:03:03 > 0:03:08Jimmy Carter is the ne, American president.
0:03:08 > 0:03:10and Elvis has just died.
0:03:10 > 0:03:13The cause of death is cardiac arrhythmia.
0:03:14 > 0:03:18And technologically, it's a million miles from today.
0:03:20 > 0:03:25A new company called Apple Computers has just been founded.
0:03:25 > 0:03:29# I was strolling on the moon one day. #
0:03:29 > 0:03:32And it's not long since the final Apollo mission landed on the moon.
0:03:32 > 0:03:34'One of the most proud moments of my life.'
0:03:34 > 0:03:38And this new technological confidence has fuelled
0:03:38 > 0:03:40something else - a renewed interest in science fiction.
0:03:40 > 0:03:45The public has gone crazy for films like Star Wars
0:03:45 > 0:03:47and Close Encounters Of The Third Kind.
0:03:49 > 0:03:54And this combination of breakthrough technology and exciting
0:03:54 > 0:03:59science fiction has helped to inspire a surprising project.
0:04:04 > 0:04:09Because in August 1977, NASA began one of the greatest adventures
0:04:09 > 0:04:11in the history of spaceflight.
0:04:11 > 0:04:15"Three, two, one, zero."
0:04:17 > 0:04:19Here were two unmanned space probes,
0:04:19 > 0:04:24attempting something straight out of an Arthur C Clarke story.
0:04:32 > 0:04:37Their mission - to explore the outer planets of the solar system...
0:04:38 > 0:04:42..Jupiter, Saturn, Uranus and Neptune.
0:04:44 > 0:04:47Their first encounter with Jupiter would be two years
0:04:47 > 0:04:49and half a billion miles away.
0:04:52 > 0:04:55The two spacecraft were now heading on their epic journey.
0:04:57 > 0:05:01But the story of the Voyager mission began almost 20 years earlier.
0:05:09 > 0:05:12To uncover its origins, I've come to California,
0:05:12 > 0:05:14to find out how it all started.
0:05:19 > 0:05:23Today, it's really easy to take the successes of these remarkable
0:05:23 > 0:05:26missions for granted, but in the years preceding Voyager,
0:05:26 > 0:05:30simply getting to the outer planets was thought to be impossible.
0:05:34 > 0:05:39The first object launched into orbit was Sputnik 1.
0:05:42 > 0:05:46And from then on, space scientists became obsessed with journeying
0:05:46 > 0:05:51ever further from Earth, exploring the far reaches of our solar system.
0:05:53 > 0:05:57Yet no spacecraft could get much further than Mars...
0:05:57 > 0:05:59and even that was a struggle.
0:05:59 > 0:06:01The simple fact was we just didn't have a rocket
0:06:01 > 0:06:04that was powerful enough to actually to be able
0:06:04 > 0:06:06to escape the gravitational pull
0:06:06 > 0:06:09of the sun and be able to get to the outer solar system.
0:06:09 > 0:06:13And even if we did, the vast distances involved would mean
0:06:13 > 0:06:18that a trip to Neptune would take half a lifetime - 30 or 40 years.
0:06:18 > 0:06:21The outer planets were simply out of reach.
0:06:26 > 0:06:30But back in 1961, here in California,
0:06:30 > 0:06:35one man thought he might know how to bring these planets into reach.
0:06:35 > 0:06:41He was a brilliant maths graduate, and his name was Michael Minovitch.
0:06:41 > 0:06:44My father taught me how to do arithmetic
0:06:44 > 0:06:47when I was like in 4th or 5th grade.
0:06:47 > 0:06:51And then I learned the language - the secret of science.
0:06:51 > 0:06:54And the secret of science is mathematics.
0:06:57 > 0:07:00At the age of only 25, while he was still studying
0:07:00 > 0:07:04for his PhD at UCLA, Minovitch set himself the challenge
0:07:04 > 0:07:08of solving the most difficult problem in space exploration.
0:07:10 > 0:07:14It was a puzzle that had stumped the world's greatest
0:07:14 > 0:07:17mathematicians for centuries.
0:07:17 > 0:07:19It's called the "three-body problem" -
0:07:19 > 0:07:24body one, body two and body three.
0:07:24 > 0:07:28And it involves the fiendishly complicated task of trying
0:07:28 > 0:07:31to plot the trajectory of a small object,
0:07:31 > 0:07:35ie a spacecraft, as it moves throughout the solar system,
0:07:35 > 0:07:39whilst at the same time being deflected by the gravitational pull
0:07:39 > 0:07:41of two much more massive objects,
0:07:41 > 0:07:44ie the sun and a planet.
0:07:47 > 0:07:49A solution to the three-body problem,
0:07:49 > 0:07:54the ability to predict exactly how a spacecraft passing a planet
0:07:54 > 0:07:58would have its path affected, was still beyond science...
0:07:58 > 0:08:02until, that is, the young Minovitch came along.
0:08:03 > 0:08:06It would have been regarded as impossibility
0:08:06 > 0:08:09prior to what I did in 1961.
0:08:16 > 0:08:19I was gifted being at a university that had
0:08:19 > 0:08:24the 7090 computer, so that was the key.
0:08:24 > 0:08:27UCLA's state-of-the-art IBM computer
0:08:27 > 0:08:29was the fastest on Earth at the time,
0:08:29 > 0:08:33and Minovitch put it to good use.
0:08:33 > 0:08:36He began calculating thousands of alternative directions
0:08:36 > 0:08:42and speeds, in an attempt to home in on the solution.
0:08:42 > 0:08:45It was a long shot - not only for the young student
0:08:45 > 0:08:48but also the university.
0:08:48 > 0:08:53Working on a 7090 was costing 1,000 an hour,
0:08:53 > 0:09:00so they were dumping bushels of money into a fantastic belief
0:09:00 > 0:09:01and what was the belief?
0:09:01 > 0:09:05Belief that a person that hadn't got his PhD
0:09:05 > 0:09:10solved the problem that all the most advanced mathematicians in history
0:09:10 > 0:09:15couldn't solve. That meant pressure on me, and so I thought to myself,
0:09:15 > 0:09:16"How could I...?
0:09:16 > 0:09:20"I can't live with myself, given this gift, knowing that there's
0:09:20 > 0:09:24"a very strong possibility that my trajectories were not correct."
0:09:30 > 0:09:35Minovitch went to the people with the most accurate data on the solar system at the time -
0:09:35 > 0:09:38NASA's Jet Propulsion Laboratory in Pasadena.
0:09:41 > 0:09:45They would decide if he had solved the three-body problem
0:09:45 > 0:09:48or just wasted a lot of the university's money.
0:09:49 > 0:09:54They ran the tests, about four or five different trajectory types,
0:09:54 > 0:09:55different encounters,
0:09:55 > 0:10:00and found every single one converged to the exact solution.
0:10:07 > 0:10:10It was a beautiful moment in mathematics.
0:10:10 > 0:10:14By solving the three-body problem, Minovitch had discovered a way
0:10:14 > 0:10:19to use gravity to propel a spacecraft further and faster than ever before.
0:10:22 > 0:10:24What Minovitch realised was,
0:10:24 > 0:10:27as a spacecraft approaches the planet,
0:10:27 > 0:10:29it gets pulled in by its gravity,
0:10:29 > 0:10:31and as long as it doesn't crash into the planet,
0:10:31 > 0:10:38because the planet is orbiting the sun at tens of thousands of kilometres an hour,
0:10:38 > 0:10:42that spacecraft can take some of that energy and use it to get
0:10:42 > 0:10:48catapulted out at an increased speed further out into the solar system.
0:10:51 > 0:10:53With his new slingshot technique,
0:10:53 > 0:10:56Minovitch had opened a gateway
0:10:56 > 0:10:58to the outer planets, at least theoretically.
0:11:01 > 0:11:04He identified hundreds of possible missions
0:11:04 > 0:11:08to the planets, meticulously drawing them up in his notebooks.
0:11:10 > 0:11:12The concept that I invented,
0:11:12 > 0:11:16and I can show you the printout, if you look here,
0:11:16 > 0:11:18you'll see there was no limit.
0:11:18 > 0:11:21I could have a sequence that was a 100 planets long,
0:11:21 > 0:11:26nonstop, planet to planet to planet, launched from Earth.
0:11:26 > 0:11:29And then you come to Jupiter. Jupiter, you get a nice big bounce
0:11:29 > 0:11:34and you use that to propel yourself to Saturn, and then Saturn is
0:11:34 > 0:11:38a pretty darn big planet, and that will catapult you out to Pluto.
0:11:38 > 0:11:43This concept could be used to explore the whole solar system
0:11:43 > 0:11:46with one launch vehicle at one time
0:11:46 > 0:11:48without any rocket propulsion at all.
0:11:53 > 0:11:55But buried amongst those hundreds of theoretical
0:11:55 > 0:12:00flight paths was one very special trajectory.
0:12:02 > 0:12:06And no-one, not even Minovitch, noticed its significance.
0:12:09 > 0:12:10In the summer of 1965,
0:12:10 > 0:12:15right here at NASA's JPL, another vacation student was hired
0:12:15 > 0:12:18to number-crunch the options for a mission to the outer planets.
0:12:18 > 0:12:20And his name was Gary Flandro.
0:12:22 > 0:12:26I was a summer student working on my degree at the time,
0:12:26 > 0:12:30so when I was given the job of looking at the outer planets,
0:12:30 > 0:12:33I thought that was kind of make-work project -
0:12:33 > 0:12:35I was being kind of kept out of the way.
0:12:38 > 0:12:42Flandro was a young engineer, grounded in the hard realities
0:12:42 > 0:12:46of spaceflight, and he began to look at whether
0:12:46 > 0:12:50a solution to the three-body problem could be put to practical use.
0:12:56 > 0:12:59Obviously, the first thing is to determine
0:12:59 > 0:13:03when the planets are going to be in positions where we could reach them.
0:13:03 > 0:13:08So I drew very careful maps of where the planets would be,
0:13:08 > 0:13:11and one of the most important drawings was one in which
0:13:11 > 0:13:14I drew the positions of the planets versus the date.
0:13:14 > 0:13:19And the thing that caught my attention immediately was
0:13:19 > 0:13:22that the lines for Jupiter, Saturn, Uranus and Neptune
0:13:22 > 0:13:26all crossed in about the 1975-76 time period.
0:13:26 > 0:13:30In other words, those four major planets were on the same side of the sun
0:13:30 > 0:13:33and in the same general position at the same time.
0:13:33 > 0:13:36So it gave me the idea immediately that we could do
0:13:36 > 0:13:38all of those planets with one flight.
0:13:40 > 0:13:44This narrow window - to slingshot from one planet straight
0:13:44 > 0:13:49to the next - would not open again for another 176 years.
0:13:49 > 0:13:52It was too good an opportunity to miss.
0:13:58 > 0:14:01And so was born the idea of a Grand Tour,
0:14:01 > 0:14:04the most ambitious space mission of its time.
0:14:04 > 0:14:08It would send two identical space probes to all four
0:14:08 > 0:14:12of the solar system's outer planets in one relatively short flight.
0:14:13 > 0:14:17Such encounters promised spectacular views of these distant worlds,
0:14:17 > 0:14:20planets we only knew as blurry objects through telescopes.
0:14:22 > 0:14:25The half billion miles to Jupiter would take two years.
0:14:27 > 0:14:29Then another two years to Saturn...
0:14:31 > 0:14:34..five more to Uranus
0:14:34 > 0:14:37and a final three to reach Neptune.
0:14:40 > 0:14:46It meant the Voyagers would need to function for at least 12 years.
0:14:46 > 0:14:50Yet NASA had never built a spacecraft guaranteed to last
0:14:50 > 0:14:52longer than a few months.
0:14:52 > 0:14:55It was their biggest challenge yet.
0:14:58 > 0:14:59Hi, John, how are you?
0:14:59 > 0:15:02Oh, Dallas, I'm fine. Thanks for coming.
0:15:02 > 0:15:06And it was one which fell to a young engineer called John Casani.
0:15:09 > 0:15:13The issue was the time. It takes time to cover that distance.
0:15:13 > 0:15:15You're going a long ways, and that takes time,
0:15:15 > 0:15:18and the time is...can you make all these machines operate
0:15:18 > 0:15:20without human intervention or adjustment?
0:15:20 > 0:15:21Well, I mean...
0:15:21 > 0:15:25At that point in time, that was a mind-blowing thought -
0:15:25 > 0:15:28how you build a spacecraft that can survive failures
0:15:28 > 0:15:31and still keep on chugging?
0:15:31 > 0:15:34Five years of testing and redesigning followed,
0:15:34 > 0:15:38as NASA's engineers grappled with the task of building
0:15:38 > 0:15:41a spacecraft capable of the job.
0:15:41 > 0:15:45And they needed to do it before 1977,
0:15:45 > 0:15:49when the launch window for this Grand Tour would close...
0:15:49 > 0:15:52at least for another 176 years.
0:15:52 > 0:15:56The thing that was scary was that it was going to be based
0:15:56 > 0:16:01on a lot of new technology, so it was a technological leap.
0:16:02 > 0:16:05We thought we could do it - nobody else did.
0:16:08 > 0:16:11They'd cracked the mathematics,
0:16:11 > 0:16:13they were confident tackling the technology,
0:16:13 > 0:16:17but there was one more thing they needed - money.
0:16:17 > 0:16:21NASA still lacked the funding to support the mission beyond Saturn.
0:16:21 > 0:16:25To ensure further funding, the public and Congress would need
0:16:25 > 0:16:29regular reminders of their achievements.
0:16:29 > 0:16:33The Voyagers needed a voice, someone who could turn their saga of
0:16:33 > 0:16:37celestial exploration into something that all Americans could share.
0:16:37 > 0:16:41They turned to a young member of the Voyager team
0:16:41 > 0:16:43with a passion for storytelling -
0:16:43 > 0:16:45his name was Carl Sagan.
0:16:45 > 0:16:47Wouldn't it be lovely
0:16:47 > 0:16:50to make contact with another civilisation
0:16:50 > 0:16:53that has arisen and evolved independently?
0:16:53 > 0:16:57Aware that the Voyagers would head away from us forever,
0:16:57 > 0:17:01Sagan proposed an extraordinary idea.
0:17:01 > 0:17:04On board each spacecraft, he suggested placing
0:17:04 > 0:17:07a message from Earth -
0:17:07 > 0:17:10an idea which would capture public imagination.
0:17:10 > 0:17:15Attached to each spacecraft is a fairly elaborate message
0:17:15 > 0:17:19in the form of a phonograph record and instructions for playing.
0:17:19 > 0:17:21It was a gold-plated copper record -
0:17:21 > 0:17:24a gift of recordings and greetings
0:17:24 > 0:17:29from the inhabitants of this planet to those of some other.
0:17:30 > 0:17:32'Bonjour, tout le monde...'
0:17:32 > 0:17:35GREETINGS IN JAPANESE AND RUSSIAN
0:17:35 > 0:17:38Each disc contained a combination of sounds
0:17:38 > 0:17:41and pictures and above all music -
0:17:41 > 0:17:46from Chuck Berry to Azerbaijani bagpipes and Johann Sebastian Bach.
0:17:48 > 0:17:52Sagan argued that sometime, somewhere,
0:17:52 > 0:17:55another civilisation may find one of the Voyagers.
0:17:55 > 0:17:57The record's purpose was to tell them
0:17:57 > 0:18:01what kind of creatures had sent it.
0:18:01 > 0:18:05How much will they know about us, what we're really like?
0:18:05 > 0:18:11To communicate that, music is a way of expression of human feelings,
0:18:11 > 0:18:14desires, passions, hopes.
0:18:14 > 0:18:16In some sense, all the performers
0:18:16 > 0:18:19and composers on this record will live forever.
0:18:19 > 0:18:22With their golden records on board,
0:18:22 > 0:18:27and the public's imagination fired up, the Grand Tour was underway.
0:18:27 > 0:18:30But no-one could know if the mission was going to deliver results
0:18:30 > 0:18:34until the Voyagers reached their first planet,
0:18:34 > 0:18:38and that would take two long years.
0:18:50 > 0:18:56April 1979, and two years after launch, Mission Control was steering
0:18:56 > 0:18:59the Voyagers towards their first rendezvous.
0:18:59 > 0:19:03It was with the largest planet in our solar system - Jupiter.
0:19:08 > 0:19:11Before Voyager, the best images astronomers had of
0:19:11 > 0:19:15Jupiter and its moons were fuzzy photographs.
0:19:15 > 0:19:18Could the Voyagers change all that?
0:19:18 > 0:19:21I think we all felt that we were in the tradition of Galileo,
0:19:21 > 0:19:24who was the first to see the moons of Jupiter,
0:19:24 > 0:19:27and the first to apply an instrument
0:19:27 > 0:19:30to increase our ability to observe the universe.
0:19:30 > 0:19:35Voyager was just the latest tool which we, as a civilisation,
0:19:35 > 0:19:36had managed to devise.
0:19:36 > 0:19:40And, of course, the tool was so powerful that we saw things
0:19:40 > 0:19:43nobody had seen before and that nobody had imagined we would see.
0:19:44 > 0:19:49For the man who'd first proposed the mission, it was a thrilling moment.
0:19:49 > 0:19:52That first encounter with Jupiter was a marvellous...
0:19:52 > 0:19:56time for me, especially the approach shots showing the planet
0:19:56 > 0:19:59revolving and watching the great red spot revolving getting closer
0:19:59 > 0:20:04and closer till finally we could see that indeed this was
0:20:04 > 0:20:06the top of a large storm.
0:20:06 > 0:20:10As a child, I had studied that and wondered if that was a storm
0:20:10 > 0:20:12or was that an island floating in an ocean -
0:20:12 > 0:20:13it was very difficult to know -
0:20:13 > 0:20:16and, finally, the answers were there before our eyes.
0:20:18 > 0:20:21At the time, Voyager scientist Andy Ingersoll revealed
0:20:21 > 0:20:25these discoveries to a BBC Horizon crew.
0:20:25 > 0:20:29The movie here shows pictures of Jupiter taken every ten hours.
0:20:29 > 0:20:31The shutter was snapped,
0:20:31 > 0:20:33then this is played in a sequence over and over again
0:20:33 > 0:20:36so you can see motion.
0:20:36 > 0:20:39And this rapid mixing makes the existence of permanent
0:20:39 > 0:20:42different-coloured, different chemical features
0:20:42 > 0:20:44even more mysterious.
0:20:48 > 0:20:51See, I'm a weather man, I'm an atmospheric scientist,
0:20:51 > 0:20:55and we knew about the 300-year-old storms, the great red spot,
0:20:55 > 0:20:58because people had been looking at it from Earth,
0:20:58 > 0:21:01and for me the surprise was, when we got up close,
0:21:01 > 0:21:04we saw that the atmosphere was just churning and turbulent,
0:21:04 > 0:21:09and it made this 300-year-old storm all the more mysterious,
0:21:09 > 0:21:14cos how could it go on in the midst of all this turbulence?
0:21:16 > 0:21:19We all approached Jupiter with great expectation
0:21:19 > 0:21:22and we all had our grandiose theories about what we were
0:21:22 > 0:21:25going to see, but, of course, Jupiter fooled us all.
0:21:25 > 0:21:28There was some bizarre behaviour.
0:21:28 > 0:21:31Little clouds moving along and being swept up in the great red spot
0:21:31 > 0:21:33and then being...
0:21:33 > 0:21:34it would spit them out again.
0:21:36 > 0:21:39Other clouds would roll along next to one another,
0:21:39 > 0:21:42coalesce into a single cloud and then break apart again.
0:21:47 > 0:21:52Voyager's pictures suggested that Jupiter's wildly churning atmosphere
0:21:52 > 0:21:56seemed to be driven by heat from deep within the planet.
0:21:57 > 0:21:59Scientists speculated that it came from a hot,
0:21:59 > 0:22:03high-pressure core of metallic hydrogen.
0:22:05 > 0:22:09Such a centre also seemed to be powering an immense magnetic field,
0:22:09 > 0:22:1210,000 times stronger than Earth's,
0:22:12 > 0:22:16and for the Voyagers, that was a problem,
0:22:16 > 0:22:20because this magnetism creates lethal radiation belts,
0:22:20 > 0:22:24which can scramble the computers of any spacecraft that gets too close.
0:22:30 > 0:22:34Yet getting close was exactly what was needed.
0:22:34 > 0:22:38The Voyager team wanted to send Voyager 1 to explore Io,
0:22:38 > 0:22:41one of Jupiter's four largest moons,
0:22:41 > 0:22:44and it was the nearest of all of them to the planet.
0:22:44 > 0:22:47The spacecraft was designed to withstand
0:22:47 > 0:22:52a certain total dose of radiation, and fully 50% of that expected dose
0:22:52 > 0:22:56was going to occur as we approached and flew by Io.
0:23:02 > 0:23:04As Voyager 1 approached,
0:23:04 > 0:23:08it sent back recordings of the radio signal generated by the radiation.
0:23:08 > 0:23:11LOUD, DISTORTED WHISTLES
0:23:13 > 0:23:16These are the real sounds of the onslaught.
0:23:23 > 0:23:27Back at JPL, the Voyager team worried whether it could withstand
0:23:27 > 0:23:32such an assault, and whether the gamble would pay off.
0:23:34 > 0:23:40Voyager navigation engineer Linda Hyder was the first to find out.
0:23:40 > 0:23:44I came in about nine o'clock that morning to the navigation area,
0:23:44 > 0:23:47and the tape with the pictures the spacecraft had taken
0:23:47 > 0:23:49the day before was on my desk.
0:23:49 > 0:23:53I put them on the computer system and I displayed them.
0:23:53 > 0:23:56And I could see that Io, the moon of Io, was a crescent,
0:23:56 > 0:24:00as very often our own moon is a crescent in the night sky,
0:24:00 > 0:24:02and I went and enhanced the brightness,
0:24:02 > 0:24:06and there appeared beside Io an object, a huge object,
0:24:06 > 0:24:09and it completely captured my attention.
0:24:12 > 0:24:15It looked like another moon peeking out from behind Io.
0:24:19 > 0:24:24But there was no other moon and no fault in the camera.
0:24:24 > 0:24:28Linda decided this object had to be part of Io.
0:24:28 > 0:24:32And, in fact, that was very hard to accept,
0:24:32 > 0:24:34because the size of this object was enormous.
0:24:44 > 0:24:46And when I explored it,
0:24:46 > 0:24:49I was able to find that this large, strange object,
0:24:49 > 0:24:54it was exactly coincident and fell over a heart-shaped feature on Io.
0:24:54 > 0:24:59What I had discovered was the huge plume of a volcanic eruption,
0:24:59 > 0:25:04arising 270km over the surface of Io and raining back down onto it.
0:25:08 > 0:25:12So I had discovered the first-ever volcanic eruption ever seen
0:25:12 > 0:25:15on another world besides the Earth.
0:25:21 > 0:25:25The gamble of being exposed to such radiation had paid off.
0:25:25 > 0:25:29Voyager 1 had revealed that Io,
0:25:29 > 0:25:31the closest of Jupiter's large moons,
0:25:31 > 0:25:34was more geologically active than the Earth.
0:25:34 > 0:25:39Jupiter's enormous gravity stretches and squeezes the moon,
0:25:39 > 0:25:43forcing its core to heat up and its interior to stay molten.
0:25:43 > 0:25:47We found that Io had eight active volcanoes on it,
0:25:47 > 0:25:50the most volcanically active body in the solar system,
0:25:50 > 0:25:54and it's just a small moon, and that was so unexpected.
0:25:54 > 0:25:57And it was such a shift in our paradigm
0:25:57 > 0:26:00about what was going on in the outer solar system
0:26:00 > 0:26:03where it's very cold and, presumably, we thought very dead.
0:26:03 > 0:26:07So in that sense, it characterised for us
0:26:07 > 0:26:10the sense of seeing things that we really hadn't thought about,
0:26:10 > 0:26:12and that was in fact very characteristic
0:26:12 > 0:26:14of the rest of the mission.
0:26:19 > 0:26:20And that wasn't all.
0:26:20 > 0:26:24As the Voyagers flew by Jupiter's other moons,
0:26:24 > 0:26:26more discoveries began pouring in.
0:26:26 > 0:26:31These exotic satellite worlds of rock and ice needed
0:26:31 > 0:26:34a new expertise to interpret them.
0:26:34 > 0:26:36The Voyager team had to react quickly,
0:26:36 > 0:26:40bringing on board more planetary geologists.
0:26:40 > 0:26:42There's a twin, a pair there, and then there's...
0:26:42 > 0:26:46What about the relief from the cracks? Shouldn't the cracks...
0:26:46 > 0:26:48In order for there...
0:26:48 > 0:26:50'All of the scientists, with the exception
0:26:50 > 0:26:52'of me, were atmospheric scientists and astronomers.'
0:26:52 > 0:26:57And, in fact, it wasn't until we really recognised the exotic variety
0:26:57 > 0:26:59and diversity of the satellites,
0:26:59 > 0:27:03that geologists were really added to the Voyager team.
0:27:05 > 0:27:06And in fact the satellites, in my view,
0:27:06 > 0:27:09became the star of the whole Voyager experience.
0:27:15 > 0:27:18Voyager's encounter with Jupiter was a triumph,
0:27:18 > 0:27:22and Carl Sagan hosted a televised evening to celebrate.
0:27:23 > 0:27:27It's impossible to look at these pictures with only
0:27:27 > 0:27:31a scientific cast of mind, because they are simply exquisite.
0:27:31 > 0:27:36And this is part of the remarkable historical transition,
0:27:36 > 0:27:39which is happening in the late 20th century in which we are,
0:27:39 > 0:27:43for the first time, learning the realities, not the myths,
0:27:43 > 0:27:47of our little swimming hole in space.
0:27:47 > 0:27:52On a night like tonight, our eyes, our minds, our souls,
0:27:52 > 0:27:55our blood are moving out through the universe.
0:27:56 > 0:27:58We're part of history,
0:27:58 > 0:28:02and that means that we have to replace the old myths with new ones.
0:28:05 > 0:28:09With Jupiter behind them, the two Voyager spacecraft headed
0:28:09 > 0:28:12further out into interplanetary space.
0:28:15 > 0:28:16It would be more than two years
0:28:16 > 0:28:18before they reached the next destination
0:28:18 > 0:28:24on their Grand Tour - the planet Saturn, almost a billion miles away.
0:28:26 > 0:28:29The technology and engineering needed to accomplish
0:28:29 > 0:28:35such long-distance, long-duration spaceflight, was truly remarkable.
0:28:35 > 0:28:39The spacecraft needed to be designed to cope with anything
0:28:39 > 0:28:42their multi-billion-mile journey would throw at them.
0:28:43 > 0:28:46Luckily, you don't need to travel 11 billion miles to
0:28:46 > 0:28:49get up close and personal and really appreciate the
0:28:49 > 0:28:51extraordinary engineering of Voyager,
0:28:51 > 0:28:54because there's another one a little bit closer to home.
0:28:56 > 0:28:59When JPL built the Voyagers,
0:28:59 > 0:29:03they also assembled a couple of extra models from flight spares,
0:29:03 > 0:29:07as an Earth-bound reminder of their visionary 1970s technology.
0:29:22 > 0:29:27Dominating the entire structure is this great communications dish
0:29:27 > 0:29:30that's beaming back to Earth all that data that the Voyager
0:29:30 > 0:29:35spacecrafts collect across billions of miles of empty space.
0:29:35 > 0:29:40Incredibly, the power of this signal was designed to be a mere 20 watts -
0:29:40 > 0:29:43about the same as a fridge light bulb.
0:29:43 > 0:29:45And situated on this arm,
0:29:45 > 0:29:47quite sensibly far away from the spacecraft,
0:29:47 > 0:29:49is Voyager's power supply.
0:29:49 > 0:29:54It's a plutonium-fuelled generator that can power the spacecraft
0:29:54 > 0:29:57in deep space when solar power just isn't an option.
0:29:58 > 0:30:01And over on the other side, sticking out on another boom,
0:30:01 > 0:30:05perhaps most excitingly, this is Voyager's eyes.
0:30:05 > 0:30:07This great collection of cameras that revealed
0:30:07 > 0:30:09new worlds for the first time,
0:30:09 > 0:30:13and let us see the solar system with greater clarity than ever before.
0:30:17 > 0:30:221981, and two years on from the stunning images of Jupiter,
0:30:22 > 0:30:26the public were queuing up to get their first clear views
0:30:26 > 0:30:29of the mysterious ringed planet, Saturn.
0:30:29 > 0:30:32MUSIC: More Than A Feeling by Boston
0:30:37 > 0:30:42The Voyager team had prepared in meticulous detail for the encounter,
0:30:42 > 0:30:46as they knew they had just a tiny window to get it right.
0:30:46 > 0:30:49Each spacecraft would fly by so quickly,
0:30:49 > 0:30:54on such a close approach, there was almost no time to gather data.
0:30:54 > 0:31:00The closest approach fly-by sequences are a matter of hours.
0:31:00 > 0:31:04Really, the tightest closest approach activity is within a 12-hour span.
0:31:08 > 0:31:13In particular, the team needed to decide where to point the cameras.
0:31:13 > 0:31:16The scan platform, which included the cameras
0:31:16 > 0:31:19and spectrometers, am I going to point it at the moon
0:31:19 > 0:31:22and which moon, or am I going to point it at the planet?
0:31:22 > 0:31:24Which way am I going to point it?
0:31:24 > 0:31:28And so you have to argue with your colleagues.
0:31:28 > 0:31:33Blue-ish. Blue-er than grey.
0:31:35 > 0:31:39But it was the rings of Saturn which stole the show.
0:31:39 > 0:31:41We thought we knew it all,
0:31:41 > 0:31:46but, once again, we were looking at a very, very complex situation.
0:31:46 > 0:31:48The rings were broken up into mini-rings.
0:31:48 > 0:31:50There were gaps in there,
0:31:50 > 0:31:54there were all sorts of dynamical phenomena that we didn't understand.
0:32:06 > 0:32:09When I began my work, I had suggested that one thing
0:32:09 > 0:32:12we could do with this particular mission was
0:32:12 > 0:32:15to fly between the planet and the rings,
0:32:15 > 0:32:17and, very fortunately, we didn't do that,
0:32:17 > 0:32:19because, as we approached Saturn,
0:32:19 > 0:32:23we saw that the region there we would have had to flown through with the spacecraft
0:32:23 > 0:32:24was filled with more rings.
0:32:24 > 0:32:28There was no question - that spacecraft would not have survived
0:32:28 > 0:32:30trying to go through that gap.
0:32:32 > 0:32:36The imaging team could barely cope with all the new data.
0:32:40 > 0:32:44What I remember...it wasn't really stressful,
0:32:44 > 0:32:47but it was just chaotic and hectic and exciting.
0:32:47 > 0:32:51Right in the few days around the encounter, trying to keep up
0:32:51 > 0:32:55with the discoveries as they poured in.
0:32:55 > 0:32:57Eventually, no-one got any sleep,
0:32:57 > 0:33:00because we were just overwhelmed with new stuff.
0:33:04 > 0:33:07Voyager revealed delicate rings that were intertwined
0:33:07 > 0:33:13and rings that were held in place by tiny moons they called shepherds.
0:33:13 > 0:33:16There were strange features called spokes,
0:33:16 > 0:33:21patches of dust particles, slightly raised above the rings.
0:33:21 > 0:33:24These caught the eye of one young graduate student in particular.
0:33:27 > 0:33:29I got involved in the study of the spokes,
0:33:29 > 0:33:33which were these ghostly features that were seen to come and go,
0:33:33 > 0:33:37and it just came to my head to kind of categorise the pictures.
0:33:37 > 0:33:40Into one pile, I put all those images that seemed to have
0:33:40 > 0:33:42a lot of spokes in them,
0:33:42 > 0:33:44and into another pile, I put those images
0:33:44 > 0:33:47that seemed to have virtually no spokes at all.
0:33:47 > 0:33:49And I made an intermediate category.
0:33:49 > 0:33:52And, of course, each image was tagged with a time,
0:33:52 > 0:33:56and I basically did an analysis on the computer of this
0:33:56 > 0:34:02and found that the spokes actually weren't just sporadic but, in fact,
0:34:02 > 0:34:04they came and went with a certain period.
0:34:14 > 0:34:18Remarkably, Carolyn Porco had discovered that the spokes
0:34:18 > 0:34:24followed Saturn's magnetic field as it rotated with the planet.
0:34:24 > 0:34:30I made my very first scientific discovery, and just knowing that
0:34:30 > 0:34:33I had found something that nobody else on the face of the planet knew
0:34:33 > 0:34:37at that time was just such an exhilarating experience.
0:34:42 > 0:34:44Well, I think Saturn has not disappointed us.
0:34:44 > 0:34:47I really expected that since we had such a rudimentary
0:34:47 > 0:34:51knowledge of Saturn system that we would be seeing many surprises,
0:34:51 > 0:34:54but, as usual, our imaginations were not nearly up to
0:34:54 > 0:34:56what nature provided.
0:35:00 > 0:35:04Four years since launch, the Voyagers had,
0:35:04 > 0:35:07so far, been a wild success.
0:35:07 > 0:35:11But now came the mission planner's biggest gamble.
0:35:11 > 0:35:15Here at Saturn, the twin spacecraft would part company.
0:35:17 > 0:35:21Voyager 1 would be diverted towards Saturn's largest moon, Titan.
0:35:22 > 0:35:24It was an enticing target.
0:35:26 > 0:35:29It was clear that the composition of Titan's atmosphere
0:35:29 > 0:35:32makes it kind of an analogue with the Earth,
0:35:32 > 0:35:35which is terribly surprising, because no-one expected years ago
0:35:35 > 0:35:38you'd find an analogue of the Earth out at the distance of Saturn.
0:35:40 > 0:35:44With an atmosphere of similar density to Earth's,
0:35:44 > 0:35:47it was believed Titan might even harbour primitive life.
0:35:49 > 0:35:52But the manoeuvre came at great cost.
0:35:52 > 0:35:55To fly past Titan, Voyager 1's Grand Tour
0:35:55 > 0:35:58would have to be sacrificed.
0:35:58 > 0:36:00To visit this intriguing moon,
0:36:00 > 0:36:02it needed to be put on a different path,
0:36:02 > 0:36:07throwing it up at an angle, out of the plane of the solar system.
0:36:07 > 0:36:12Beyond Titan, there would be no more planetary encounters for Voyager 1.
0:36:18 > 0:36:22In the end, the Titan fly-by was a disappointment.
0:36:22 > 0:36:25Voyager 1's cameras couldn't penetrate its atmosphere
0:36:25 > 0:36:28to offer further clues to whether life might lie beneath.
0:36:31 > 0:36:34Titan was the first major setback for the Voyager team.
0:36:40 > 0:36:43It meant Voyager 1 had been sacrificed for very little
0:36:43 > 0:36:46and was now speeding away from the solar system.
0:36:52 > 0:36:54The rest of the Grand Tour would have to rely on
0:36:54 > 0:36:57one single spacecraft -
0:36:57 > 0:36:59Voyager 2.
0:36:59 > 0:37:02Now on its own, it was heading across the solar system
0:37:02 > 0:37:04towards the outermost planets.
0:37:08 > 0:37:12But then, just as it left Saturn, another setback -
0:37:12 > 0:37:16the team noticed Voyager 2's camera platform had started to jam.
0:37:18 > 0:37:21Without the crucial ability to pan its cameras,
0:37:21 > 0:37:25there would be few pictures of the other outer planets.
0:37:25 > 0:37:29It was a potential disaster, and the team struggled to find the cause.
0:37:31 > 0:37:35In the case of the stuck scan platform, the expectation
0:37:35 > 0:37:38was that there was a piece of debris, which is not likely.
0:37:38 > 0:37:42I mean, we're so careful when we put these machines together.
0:37:44 > 0:37:49So then it goes down to, well, maybe it's the lubricant,
0:37:49 > 0:37:52the way the lubricant has distributed itself.
0:37:55 > 0:38:00So how do you fix a spacecraft that's over a billion miles away?
0:38:01 > 0:38:05What we decided to do was to exercise it very carefully,
0:38:05 > 0:38:08moving the gears train back and forth slowly over this spot.
0:38:10 > 0:38:12We could see that we were making progress and we said,
0:38:12 > 0:38:14"OK, this is it. We can work through it".
0:38:16 > 0:38:18But without any target to focus the cameras on,
0:38:18 > 0:38:23they had no way to know if their fix was successful.
0:38:23 > 0:38:28They'd only know that when Voyager 2 reached its next destination -
0:38:28 > 0:38:29Uranus.
0:38:29 > 0:38:32Even travelling at 50,000 miles an hour,
0:38:32 > 0:38:35this encounter was five years away.
0:38:38 > 0:38:42Half a decade of uncertainty and anxiety.
0:38:49 > 0:38:52Well, just about two minutes ago,
0:38:52 > 0:38:56Voyager 2 passed through its closest approach to Uranus.
0:38:56 > 0:38:58APPLAUSE
0:39:04 > 0:39:06Despite their fix to the scan platform,
0:39:06 > 0:39:09with the limited light this far from the sun,
0:39:09 > 0:39:13the Voyager team knew their cameras would struggle.
0:39:13 > 0:39:17Voyager was planned to operate at 1 billion miles at Saturn.
0:39:17 > 0:39:20It was now being asked to operate at 2 billion miles at Uranus,
0:39:20 > 0:39:23where the sun was very dim, and we had to do several things.
0:39:23 > 0:39:26For instance, you have to have much longer exposures on the camera,
0:39:26 > 0:39:27and, if you have too long an exposure,
0:39:27 > 0:39:31the spacecraft's moving very rapidly, things become smeared.
0:39:31 > 0:39:34So we had to learn how to program the spacecraft
0:39:34 > 0:39:36to turn at just the right rate,
0:39:36 > 0:39:40so that it would compensate for the motion of the spacecraft.
0:39:44 > 0:39:49They had to basically reprogram the brains of the spacecraft.
0:39:49 > 0:39:51It didn't have very many brains by today's standards,
0:39:51 > 0:39:54but they had to reprogram it.
0:39:54 > 0:39:56Those were fantastic achievements.
0:39:58 > 0:40:02As the first images of Uranus arrived back on Earth,
0:40:02 > 0:40:08it became clear the engineers' ingenuity had once again paid off.
0:40:08 > 0:40:12But the extraordinary, pin-sharp pictures of this distant planet,
0:40:12 > 0:40:17two billion miles from Earth, revealed tantalisingly little.
0:40:17 > 0:40:22After all the waiting, it was a reminder that with Voyager,
0:40:22 > 0:40:25nothing could be taken for granted.
0:40:25 > 0:40:27Uranus is different than Jupiter and Saturn
0:40:27 > 0:40:30in the sense that it has no internal heat source.
0:40:30 > 0:40:33Both Jupiter and Saturn are radiating more energy
0:40:33 > 0:40:34than they receive from the sun,
0:40:34 > 0:40:37because there's still heat inside those planets.
0:40:37 > 0:40:40For a reason, at Uranus, that heat had been shut down
0:40:40 > 0:40:43and was not driving the atmosphere, so the atmosphere was much blander.
0:40:47 > 0:40:49Check...
0:40:53 > 0:40:57If Uranus itself was something of a disappointment,
0:40:57 > 0:41:00once again, the team found plenty of surprises in its moons.
0:41:02 > 0:41:05Most striking of all was the tiny moon, Miranda.
0:41:08 > 0:41:12Miranda looks like a three-dimensional jigsaw puzzle.
0:41:12 > 0:41:15We see regions looking like giant, complex racetracks,
0:41:15 > 0:41:19almost as if it's put together by a committee.
0:41:19 > 0:41:20There are pieces stuck on the surface
0:41:20 > 0:41:23that look like they belong to different planets,
0:41:23 > 0:41:26and one idea was that it was busted apart
0:41:26 > 0:41:29and these core pieces stayed intact,
0:41:29 > 0:41:32and then they were glued back together,
0:41:32 > 0:41:34and so you get this hodgepodge.
0:41:44 > 0:41:48From Uranus, Voyager 2 faced it's final challenge -
0:41:48 > 0:41:53the journey to Neptune, over a billion miles further out
0:41:53 > 0:41:56and three years more space travel to survive.
0:41:57 > 0:42:00The last major planet in the solar system,
0:42:00 > 0:42:04this most mysterious world had resisted investigation
0:42:04 > 0:42:06from even the most powerful telescopes.
0:42:11 > 0:42:13To maintain its trajectory,
0:42:13 > 0:42:17Voyager 2 needed to make a low pass over Neptune's north pole.
0:42:18 > 0:42:20But this brought its own problems.
0:42:20 > 0:42:23Because of increased speed and approach angle,
0:42:23 > 0:42:27Voyager 2's window of opportunity would be the narrowest yet.
0:42:31 > 0:42:36The challenge at Neptune was the most difficult one we had.
0:42:36 > 0:42:38We had to know, within one second,
0:42:38 > 0:42:41when we were going to fly over the north pole of Neptune.
0:42:41 > 0:42:44That was a major navigational challenge -
0:42:44 > 0:42:47we had never delivered that kind of accuracy before.
0:42:47 > 0:42:49If we were right, it worked.
0:42:49 > 0:42:53If we were wrong, we had no second chance.
0:42:55 > 0:42:59Not only did the team need to position a spacecraft
0:42:59 > 0:43:03to within a second of accuracy, after a flight of 12 years,
0:43:03 > 0:43:07but to ensure scientific success, they also had to forecast
0:43:07 > 0:43:12the weather on a planet three billion miles away from Earth.
0:43:12 > 0:43:17We had to forecast where to point the cameras,
0:43:17 > 0:43:19two weeks in advance,
0:43:19 > 0:43:22where those interesting features were going to be.
0:43:22 > 0:43:25And we said, "Well, they're moving around.
0:43:25 > 0:43:27"There are storms in the atmosphere of Neptune."
0:43:27 > 0:43:29And this was August of 1989,
0:43:29 > 0:43:33and there was a big hurricane off the coast of Florida.
0:43:33 > 0:43:36And weather forecasters here were saying,
0:43:36 > 0:43:39"Well, 12 hours from now, we think it's going to veer right
0:43:39 > 0:43:42"or we think it's going to go left, but we're not sure."
0:43:42 > 0:43:44It may be starting to turn a little bit more towards
0:43:44 > 0:43:45the northwest or west-northwest...
0:43:45 > 0:43:49And, meanwhile, we were confidently issuing weather forecasts
0:43:49 > 0:43:53for Neptune two weeks in advance and telling the engineers,
0:43:53 > 0:43:54"OK, two weeks from now,
0:43:54 > 0:43:57"point your camera there and there will be a storm there."
0:43:57 > 0:44:00And we were right. It was glorious!
0:44:01 > 0:44:04The fly-by was approaching.
0:44:04 > 0:44:08Would the software rewrites and running repairs hold together
0:44:08 > 0:44:12to give humanity its only close encounter with Neptune?
0:44:12 > 0:44:17There was nothing more to do but wait and hope.
0:44:21 > 0:44:25After 12 years of flight, and decades of anticipation,
0:44:25 > 0:44:29the giant blue planet began to loom in Voyager 2's lenses.
0:44:47 > 0:44:51On the 25th August 1989, the spacecraft passed
0:44:51 > 0:44:54within 3,000 miles of Neptune's north pole.
0:45:00 > 0:45:03The craft had survived the three billion mile journey
0:45:03 > 0:45:05to the edge of the solar system.
0:45:05 > 0:45:07APPLAUSE
0:45:07 > 0:45:11The final encounter I was able to witness,
0:45:11 > 0:45:15here at JPL with my youngest son,
0:45:15 > 0:45:19and we watched with fascination as the pictures of Neptune unfolded.
0:45:19 > 0:45:24Suddenly things that no-one had imagined were there.
0:45:24 > 0:45:27Here was a planet that was vibrant with life.
0:45:27 > 0:45:31It had its own great spot, a dark spot in this case,
0:45:31 > 0:45:33white clouds floating in its atmosphere,
0:45:33 > 0:45:36and these things unfolded before our very eyes.
0:45:36 > 0:45:38What a wonderful surprise.
0:45:38 > 0:45:41Neptune, for me, was a great surprise.
0:45:46 > 0:45:50There was something strange and eerie about Neptune,
0:45:50 > 0:45:55because here, the last planet, the sentinel at the outer edge
0:45:55 > 0:45:58of our solar system, looks like Earth,
0:45:58 > 0:46:01with its beautiful deep blue colour
0:46:01 > 0:46:04and its white clouds floating in the atmosphere.
0:46:10 > 0:46:13We were back with a really exciting planet again at Neptune.
0:46:13 > 0:46:15There were fast-moving clouds,
0:46:15 > 0:46:18clouds that moved in different directions,
0:46:18 > 0:46:20some of them almost at sonic speeds.
0:46:20 > 0:46:22The complexity of the planet's atmosphere
0:46:22 > 0:46:25was far beyond our expectations.
0:46:31 > 0:46:34The Grand Tour was almost over,
0:46:34 > 0:46:38but Voyager 2 had one more surprise in store.
0:46:44 > 0:46:46Neptune's moon, Triton.
0:47:00 > 0:47:03This is too much... too much to believe.
0:47:08 > 0:47:11- Look at the tyre tracks. - Yeah.
0:47:11 > 0:47:13Tyre tracks.
0:47:15 > 0:47:19Triton was a world unlike any we had seen before.
0:47:19 > 0:47:21It was the coldest surface we had seen in the solar system,
0:47:21 > 0:47:2440 degrees above absolute zero.
0:47:24 > 0:47:29So cold that nitrogen, which forms most of the atmosphere on Earth,
0:47:29 > 0:47:31is frozen, solid ice,
0:47:31 > 0:47:36and the polar caps on Triton are frozen nitrogen, not frozen water.
0:47:36 > 0:47:41Even so, we found geysers on the surface of Triton,
0:47:41 > 0:47:43nitrogen geysers miles high.
0:47:43 > 0:47:48So even at the very deepest part of our solar system,
0:47:48 > 0:47:49there is geologic activity.
0:47:49 > 0:47:50It is everywhere.
0:47:50 > 0:47:53The solar system is alive, evolving,
0:47:53 > 0:47:55and that's what makes it so exciting,
0:47:55 > 0:47:57and makes it so much to learn.
0:48:01 > 0:48:05Voyager 2 had survived to reach the extremes of the solar system.
0:48:05 > 0:48:09It had revealed not just the planets themselves
0:48:09 > 0:48:14but whole systems of rings and moons unlike anything we'd imagined.
0:48:15 > 0:48:18Suzanne Dodd captured a final image from the flight.
0:48:19 > 0:48:22One of the images I took and helped design
0:48:22 > 0:48:23was the one where you have...
0:48:23 > 0:48:26It's actually one taken when you're going away.
0:48:26 > 0:48:30You have Neptune, the crescent of Neptune,
0:48:30 > 0:48:32and then you have the crescent of Neptune's moon, Triton,
0:48:32 > 0:48:35in the background, and you're taking that as the spacecraft is
0:48:35 > 0:48:38travelling out of the solar system.
0:48:38 > 0:48:42That's the last image that Voyager 2 is going to take,
0:48:42 > 0:48:44and that's the last image that spacecraft is going to
0:48:44 > 0:48:47remember of those planets.
0:48:50 > 0:48:53MUSIC: Hoppipolla by Sigur Ros
0:48:57 > 0:49:02Voyager 2 delivered its final images in 1989.
0:49:04 > 0:49:07More data on the outer planets had been collected by
0:49:07 > 0:49:12the two Voyager spacecraft than in the rest of human history.
0:49:29 > 0:49:31But let's not forget Voyager 1,
0:49:31 > 0:49:34heading out of the plane of the solar system.
0:49:34 > 0:49:38Although it hadn't been able to have any more encounters with planets,
0:49:38 > 0:49:43there was one last, special task its makers asked of it.
0:49:44 > 0:49:49Because it was high above the solar system rather than in its plane,
0:49:49 > 0:49:52Voyager 1 had a view of all the planets
0:49:52 > 0:49:54that its twin could never have.
0:49:55 > 0:49:59Carl Sagan and Carolyn Porco began discussing an idea.
0:50:03 > 0:50:06Voyager was going to be in a location
0:50:06 > 0:50:11that no other spacecraft had been before, equipped with,
0:50:11 > 0:50:14you know, sophisticated instrumentation
0:50:14 > 0:50:17so that it could turn around and take a picture
0:50:17 > 0:50:21of all the planets in the solar system.
0:50:21 > 0:50:24And I thought that this would be a riveting collection of images,
0:50:24 > 0:50:25you know, a first.
0:50:27 > 0:50:31And they said, "Well, there's really no scientific justification
0:50:31 > 0:50:35"for this," and I couldn't argue with that, because there wasn't.
0:50:35 > 0:50:37The planets were going to be just pinpoints,
0:50:37 > 0:50:39they were going to be just pixels.
0:50:39 > 0:50:41They couldn't see it.
0:50:45 > 0:50:51On Valentine's Day 1990, 13 years after leaving Earth,
0:50:51 > 0:50:55Voyager 1 was asked to turn its cameras back towards the planets.
0:50:57 > 0:51:01Now 3.7 billion miles away,
0:51:01 > 0:51:04by the time Voyager's pitifully weak signal reached
0:51:04 > 0:51:06the dishes on Earth,
0:51:06 > 0:51:10it was just a millionth of a billionth of a watt of power.
0:51:10 > 0:51:14It was then boosted and sent on to Pasadena,
0:51:14 > 0:51:18where the image was assembled, here in the Deep Space Control Room.
0:51:21 > 0:51:24A unique family portrait,
0:51:24 > 0:51:27the ultimate snapshot of our solar system.
0:51:33 > 0:51:34And this is it!
0:51:34 > 0:51:36There's actually only six planets visible,
0:51:36 > 0:51:39because Mercury and Mars were obscured by the sun's glare.
0:51:39 > 0:51:42But the picture that captured everybody's imagination
0:51:42 > 0:51:43was that of Earth,
0:51:43 > 0:51:46only a tenth of a pixel in size.
0:51:46 > 0:51:47And here it is blown up.
0:51:51 > 0:51:54Here is the mosaic...
0:51:54 > 0:52:00For Carl Sagan, the symbolic value of the photograph was a gift.
0:52:00 > 0:52:05He held a press conference to publicise it around the world.
0:52:05 > 0:52:09The portrait of the planets has now been taken.
0:52:09 > 0:52:13This looks more than a dot,
0:52:13 > 0:52:16but it is in fact less than a pixel.
0:52:16 > 0:52:21In this colour picture, you can see it is slightly blue,
0:52:21 > 0:52:26and this is where we live, on a blue dot.
0:52:28 > 0:52:30With this final historic image captured,
0:52:30 > 0:52:32and nothing more to photograph,
0:52:32 > 0:52:36Voyager 1's cameras were switched off to save power.
0:52:43 > 0:52:46But that wasn't the end of the mission.
0:52:46 > 0:52:47Over 35 years on,
0:52:47 > 0:52:52as they hurtle away from us at over 10 miles a second,
0:52:52 > 0:52:56their cutting-edge 1970s technology keeps on chugging.
0:53:00 > 0:53:01And remarkably,
0:53:01 > 0:53:05they continue to send back new information about the space
0:53:05 > 0:53:09they're now travelling through, 11 billion miles from Earth.
0:53:13 > 0:53:15Even travelling at the speed of light,
0:53:15 > 0:53:18their messages take quite a while to get home.
0:53:20 > 0:53:23The journey time now is about 15 hours one way
0:53:23 > 0:53:24from Voyager 1 back to Earth,
0:53:24 > 0:53:27so you send a signal up,
0:53:27 > 0:53:30and the next day, you come back and you have some indication
0:53:30 > 0:53:33that the spacecraft heard the signal and responded.
0:53:35 > 0:53:40There are five instruments that are still operating on the spacecraft,
0:53:40 > 0:53:43and we're starting to see the evidence now in the data
0:53:43 > 0:53:45that we are crossing into interstellar space.
0:53:45 > 0:53:48We're seeing things that would lead us to believe
0:53:48 > 0:53:51that we are on that boundary.
0:53:51 > 0:53:55Now, at the end of 2012, our planetary explorers are crossing
0:53:55 > 0:53:59this boundary of the sun's influence.
0:53:59 > 0:54:02They're travelling beyond the limits of our solar wind
0:54:02 > 0:54:04and into the galaxy beyond.
0:54:04 > 0:54:09It's the first time any object built by humans has achieved this.
0:54:09 > 0:54:13A new chapter in human exploration is beginning.
0:54:13 > 0:54:16We have enough power to get us to about ten more years,
0:54:16 > 0:54:20maybe out to 2025, but we will, over the course of those years,
0:54:20 > 0:54:24have to turn off things so that we continue to have enough power
0:54:24 > 0:54:28to run the transmitter to send the data back to Earth.
0:54:34 > 0:54:36The fact that Voyager's still alive
0:54:36 > 0:54:39and there's still a signal from it
0:54:39 > 0:54:44and it's about to leave the solar system, I think that's wonderful.
0:54:44 > 0:54:48That it hasn't just given up or that we haven't given up on it.
0:54:48 > 0:54:54It's a tribute to what Voyager means to us that we've kept it going.
0:54:56 > 0:55:00Really, it's wonderful, as a scientist, to be still exploring,
0:55:00 > 0:55:03still going somewhere no spacecraft has been before.
0:55:04 > 0:55:1035 years on, this one mission has seen the team at JPL age,
0:55:10 > 0:55:13events in their lives running parallel to
0:55:13 > 0:55:15the Voyager's encounters.
0:55:15 > 0:55:19When I started on the Voyager, my two daughters were young.
0:55:19 > 0:55:23By the time they were in college, we already had passed Saturn
0:55:23 > 0:55:25and were on our way to Uranus.
0:55:25 > 0:55:27They got married, and the Voyager just kept going.
0:55:27 > 0:55:30We had grandchildren, and Voyager just kept going,
0:55:30 > 0:55:31and so now our grandchildren are aware
0:55:31 > 0:55:35of what's happening to Voyager, just like our children were.
0:55:35 > 0:55:38Long after all their power has gone,
0:55:38 > 0:55:42the Voyagers will continue to rush away from us.
0:55:42 > 0:55:45One and a half tonnes of 1970s engineering,
0:55:45 > 0:55:49monuments to human endeavour and exploration,
0:55:49 > 0:55:51heading out towards the stars.
0:55:52 > 0:55:56I believe the next encounter with the closest star
0:55:56 > 0:55:59is something like 40,000 years from now.
0:56:06 > 0:56:11The two Voyager spacecraft are the furthest that we've ever sailed,
0:56:11 > 0:56:13but for all their amazing science
0:56:13 > 0:56:17and new worlds that they've found and data that they've collected,
0:56:17 > 0:56:21the Voyager mission is still an incredibly symbolic mission.
0:56:22 > 0:56:25Because those two golden discs are still fixed
0:56:25 > 0:56:28to the sides of each spacecraft.
0:56:28 > 0:56:32And in the benign, empty environment of deep space,
0:56:32 > 0:56:36they will outlive the pyramids, they're likely to outlive us,
0:56:36 > 0:56:41and perhaps even the Earth itself - the only record of our existence.
0:56:43 > 0:56:46'Hello from the children of planet Earth.'
0:56:46 > 0:56:49Yet, despite the ambition,
0:56:49 > 0:56:53given the vastness of space, it's almost inconceivable
0:56:53 > 0:56:59that these two tiny spacecraft will ever be intercepted by other beings.
0:56:59 > 0:57:05It's a little bit like throwing a bottle into the cosmic ocean.
0:57:05 > 0:57:08But Sagan was clever enough to realise this.
0:57:09 > 0:57:12He knew it wasn't what the golden record said to
0:57:12 > 0:57:15other civilisations that mattered -
0:57:15 > 0:57:18more significant was what it said to our own.
0:57:20 > 0:57:23You might think that it is a hopelessly quixotic project
0:57:23 > 0:57:29to launch this message in a bottle into interstellar space
0:57:29 > 0:57:31and expect anyone will find it,
0:57:31 > 0:57:35but there are really two kinds of recipients of the message
0:57:35 > 0:57:37on the Voyager records.
0:57:37 > 0:57:42One is the extraterrestrial audience.
0:57:42 > 0:57:44The other one is the audience down here down on Earth.
0:57:44 > 0:57:49Here is a moment when we have to suddenly think,
0:57:49 > 0:57:51"What is there about our culture
0:57:51 > 0:57:54"that we would want others to know about,
0:57:54 > 0:57:56"that we would be proud of?"
0:57:56 > 0:58:01The record should represent the human species as an entirety.
0:58:04 > 0:58:07The unity of the human species, seen down here,
0:58:07 > 0:58:11is a fact that is essential for the human future.
0:58:20 > 0:58:24MUSIC: Over The Rainbow by Israel Kamakawiwo'ole
0:58:24 > 0:58:28# Oh, someday I'll wish upon a star
0:58:28 > 0:58:34# Wake up where the clouds are far behind
0:58:34 > 0:58:36# Me
0:58:36 > 0:58:39# Where trouble melts like lemon drops
0:58:39 > 0:58:42# High above the chimney top
0:58:42 > 0:58:47# That's where you'll find me
0:58:47 > 0:58:55# Oh, somewhere over the rainbow
0:58:55 > 0:58:57# Way up high... #