The Planets (2017) s01e03 Episode Script
Giants
'Three, two, one, go.
' In August 1977, two spacecraft called Voyager began an incredible journey.
If they survived the hazards of billions of miles of space, they'd reach worlds so distant and strange, they defied the imagination - the gas giants.
Voyager was heading for four planets that could swallow Earth thousands of times: Jupiter, with its strange bands of cloud and its great red spot, a world crackling with radiation we can hear from Earth.
Beyond Jupiter was Saturn.
How did it alone come to have its array of rings? Stranger still was Uranus.
From the orbiting of its moons, Uranus was known to have been tipped over on its back.
Why should this be? Neptune was barely visible even through powerful telescopes.
What kind of worlds were these? What could they reveal about the solar system, of which Earth is a tiny part? Zero G, I feel fine.
'Capsule is turning around.
'Oh, that view is tremendous.
' In the early 1960s, sending a spacecraft to the giants was unthinkable.
Men had flown just a few miles up in orbit around the Earth.
Unmanned probes ventured further, to the nearest planets, Venus and Mars.
'Signal level's gone down, 'report continuing low signal level.
' Even this was pushing the very limits of science.
'In 1964, the first spacecraft, Mariner 4, flew by Mars.
' 'The spacecraft barely made it.
' Yes, it's there.
'Going to Jupiter -' which is half a billion miles away, Saturn a billion, Uranus two, and Neptune three billion miles away and twelve years in journey - was not even something one could easily imagine.
A solution came from an unlikely source.
A student at NASA's Jet Propulsion Laboratory was asked to calculate trajectories to Jupiter.
'I was a summer student, working on my degree.
'When I was told to look at the outer planets,' it was like a make-work project.
I was kept busy while the important business of getting to Mars was underway.
Flandro discovered something that made a flight to the giants possible.
The first thing is to determine when the planets will be in reachable positions for us.
'I drew maps of where they'd be, 'and in one important drawing, 'I drew their positions versus the date.
' I noticed immediately that the lines for Jupiter, Saturn, Uranus and Neptune all crossed 'in the 1975-76 time period.
'Those planets were on the same side of the sun, 'in the same position at the same time.
' It gave me the idea of one flight to all those planets.
Flandro's discovery was not just a convenient planetary line-up.
Rocket power alone could only propel a spacecraft to Jupiter.
But if a probe approached a planet at the right angle, it'd be caught by the planet's momentum, then pitched in a new direction, at a greater speed.
The trick is you fire your rocket with enough propulsion to get to Jupiter, 5 times the distance of the sun.
Go by Jupiter in the right way, to get a gravitational slingshot effect.
That propels you to Saturn.
If Saturn's in the right place at the right time, it can propel you to Uranus, and from Uranus to Neptune.
That happens about every 175 years.
It happened in terms of launch date in 1977.
A former administrator of NASA, Tom Paine, said the last time this happened, Jefferson was President, and he blew it.
For NASA, this was too good an opportunity to miss.
They announced a mission to the giants called Voyager.
It was a new era for astronomers who'd struggled to understand the hazy views they saw through Earth-based telescopes.
The man leading the imaging team was Brad Smith.
'I had started looking at Jupiter in the late '50s,' but it was difficult to make observations from the ground.
When the opportunity came up to be involved with Voyager, I realised that I could see Jupiter up close; to see detail that we could never see from the ground.
The hopes of astronomers lay in the hands of the engineers, who faced what seemed an impossible task.
'I frequently heard from people I was working with,' "That mission is never going to happen.
It's too complicated.
" 'We had to build a machine that could fly for 10 years, 'which was pushing the limits 'of what we then could do with electronics.
' We had to pass through the asteroid belt.
How can we get this spacecraft through that dangerous area beyond Mars without a collision? That seemed to be a very challenging task.
One of the worries was data transfer.
Even if we could do this flight, could we get useful data? So we worried a lot.
The engineers had a decade to make this mission possible.
Around the world, giant antennae were built - the Deep Space Network - to communicate with probes across billions of miles.
It wasn't known if a spacecraft could survive the asteroid belt, a band of drifting rocks between Mars and Jupiter.
Voyager would have only one chance.
Two less elaborate probes were sent to test the way.
Pioneer 10 and 11 were launched to Jupiter and Saturn.
'Pioneer 10 and 11 were important 'in exploring the outer solar system.
' It was critical they'd lead the way, telling us about the environment and making important discoveries allowing us to come safely behind with the Voyagers.
James Van Allen was a veteran of missions to Mars and Venus.
Now he led a team of scientists on Pioneer.
'Pioneer 10 was the first venture beyond Mars.
' First time we went such enormous distances.
First time we'd cross the asteroid belt between the orbits of Mars and Jupiter.
'It was a hazardous and high-risk mission.
'We had a keen sense of its historic possibilities' in blazing the trail to the outer planets.
'Pioneer 10 successfully got through the asteroid belt.
' We knew it was possible to get to the outer planets safely.
Another key question for Pioneer 10 was how intense was the radiation around Jupiter? Since the '50s, radio emissions from Jupiter had been detected, suggesting intense radiation around the planet.
The man who had to investigate this was Van Allen, who discovered radiation bands around Earth with the first American satellite.
They were later called the Van Allen belts.
We've encountered a high intensity of radiation, one thousand times as intense as could be attributed to cosmic rays as ordinarily understood.
Van Allen predicted greater radiation belts around Jupiter.
But even he did not anticipate what Pioneer found.
'As we went in, the radiation intensity got greater.
' There was a strong apprehension about the survival of the electronic equipment.
'It went to a maximum, and we survived, 'then it went down, so we sighed with relief that we'd made it.
' Jupiter's radiation belts were 10,000 times more intense than Earth's.
Pioneer also encountered a vast magnetic field, stretching 7 million miles out from the planet.
Pioneer 10 discovered that Jupiter's magnetic field is the largest structure in the solar system.
It would appear to be as large as the sun, being five times further away.
But it's invisible, and it can damage electronics.
The Voyager probes had to be redesigned to survive Jupiter's magnetic fields and radiation belts.
'The Pioneer saved our lives.
' Had we flown into that, unknowingly, with Voyager's sophisticated electronics and mechanisms, we'd have died instantly.
We were well into the design of that spacecraft when the Pioneer results came.
We had to redesign a lot.
(Rock and roll music) Final preparations were made for Voyager.
For any curious extraterrestrials, the probes carried a disc showing images from Earth.
This was a moment I had thought about for years.
And there was our spacecraft, going to Jupiter, Saturn, Uranus and Neptune.
A very marvellous feeling.
This was the world where Voyager was heading.
It was 4 centuries since Galileo turned his telescope on Jupiter, and discovered four points of light moving around it.
These were four moons.
The first proof that not everything in the universe revolves around Earth.
For Voyager's chief scientist, the mission promised a new era of discovery.
'We were in the tradition of Galileo,' who saw Jupiter's moons first, and first applied an instrument to increase our ability to observe the universe.
'Voyager is just the latest tool mankind had managed to devise, 'so powerful that we saw things 'nobody had seen before or had imagined we would see.
' The probe was 50 million miles from Jupiter when it sent the views everyone had been waiting for.
'We approached Jupiter with great expectation 'and grandiose theories about what we'd see.
'But Jupiter fooled us all.
' There was bizarre behaviour.
Little clouds moving along, swept up in the red spot, then it would spit them out again.
'Other clouds would roll along, 'coalesce into a single cloud and break apart again.
' Those kinds of details are still not understood.
The first encounter with Jupiter was marvellous, especially the approach shots showing the planet revolving, 'watching the red spot revolving and getting closer, 'till we could see this was the top of a large storm.
'As a child, I'd wondered if that was a storm,' or an island floating in an ocean.
Finally, the answers were there.
Voyager revealed an atmosphere of hydrogen and helium gas, whose clouds were much more dynamic than had been imagined.
Jupiter's winds gust at hundreds of miles an hour.
The red spot alone is three times the size of Earth.
The greatest storm in the solar system.
Voyager hinted at why.
Jupiter gives out twice as much energy as it receives, suggesting its core must be hot.
Scientists believe that at Jupiter's heart the gases are compressed till they become a metallic liquid.
This hot core could be the powerhouse driving the winds, and, like a dynamo, creates the enormous magnetic field.
Voyager then turned its cameras towards Jupiter's moons.
When the encounter took place, Bruce Murray was head of JPL.
'Just before the mission,' the interest was on the planets and bands.
Things you could see through a telescope.
There was hardly any interest in the satellites of the planets, because they at most were little spots.
'I led a one-man crusade 'to have them listed as targets for Voyager.
' Scientists had expected Jupiter's moons to be cold, dead, covered in craters, like our Moon.
They found an array of worlds as different as the planets.
Io, the closest of Jupiter's large moons, was more geologically active than Earth.
Jupiter's gravity stretches and squeezes Io, heating it up, so it stays molten inside.
'Io had eight active volcanoes, 'the most volcanically active body in the solar system.
' That was so unexpected.
It was a shift in our paradigm about the outer solar system, where it's very cold and, we thought, dead.
'It characterised the sense of seeing things 'we hadn't thought about.
'That was very characteristic of the rest of the mission.
' As Io orbits close to Jupiter, it is constantly brushing against its magnetic field.
Io builds up a huge electrical charge, which discharges onto Jupiter in a flow of three million amps, causing storms on the surface of the planet.
'The rest is reddish.
' The moon Europa was different but no less surprising.
It had a surface of water ice, frozen as hard as rock.
Underneath this icy crust, scientists believe there are oceans of warm water.
The moon Ganymede was bigger than the planet Mercury.
Its landscapes of rock and ice reminded Voyager's geologist Laurence Soderblom of Earth.
'Ganymede turned out to be really exciting.
' We found a broken surface, complex patterns.
It's kind of a cross between ice floes in the Arctic and continental drift on Earth.
'Its icy crust has been sheared, twisted, broken, 'something we didn't expect.
' The last major moon, Callisto, was different again.
Like our moon, it was covered with craters.
Its icy crust preserved a record of a violent age, when meteorites crashed into its surface.
What Voyager found at Jupiter's moons transformed the mission.
'The first thing you notice is everything is different.
' The diversity is overwhelming.
This is a discovery, it's Captain Cook.
It's really, in the solar system, seeing new things.
.
.
there's a twin, a pair there, another pair What about the relief from the cracks? To have enough heating 'All the scientists, except me, 'were atmospheric scientists and astronomers.
' It wasn't until we recognised the exotic variety and diversity of the satellites that geologists were added to the Voyager team.
'The satellites became the star 'of the whole Voyager experience.
' Jupiter's moons are a solar system in miniature.
As Jupiter formed, its immense gravity must have attracted a cloud of dust and gas, from which its moons were born, just as the planets around the sun.
Close to Jupiter are dense, active worlds, Io and Europa.
A mirror of the inner rocky planets, Venus, Earth and Mars.
Further out, Ganymede and Callisto are larger, icy worlds, the giants of the Jupiter system.
Voyager's next goal was Saturn.
Saturn was thought to be the last planet in the solar system.
The first to observe the rings, Giovanni Cassini, saw a flat disc with just one gap.
Scientists hoped Voyager would reveal clues to the origin of these rings.
This time, after Voyager's success at Jupiter, the press and the public came to see the first images of everyone's favourite planet.
'We thought we knew it all.
' But again, we were looking at a very complex situation.
'The rings were broken up into mini rings, with gaps, 'there were dynamical phenomena we didn't understand.
' So we very hurriedly reprogrammed Voyager 2, to look closer at the rings.
'When I began my work in 1964,' I had suggested this particular mission could fly between the planet and the rings.
'Fortunately, we didn't do that, 'because the region the spacecraft would have entered 'was filled with more rings.
' The spacecraft would not have survived going through that gap.
The imaging team could barely cope with all the detail Voyager 2 gave.
They saw delicate rings intertwined, and rings held in place by tiny moons called shepherds.
There were strange features called spokes, patches of dust particles slightly above the rings.
These caught the eye of one graduate student.
I started studying the spokes, these ghostly features that were seen to come and go.
'It came to my head to categorise the pictures.
' One pile for those images with a lot of spokes, another for the images that had no spokes at all, and an intermediate category.
'Each image was tagged with a time.
'I did an analysis on the computer of this,' and found the spokes weren't sporadic, they came and went with a certain period.
Carolyn Porco discovered the spokes followed Saturn's magnetic field as it rotated with the planet.
'I made my first scientific discovery.
' Knowing I had found something nobody else in the world knew was such an exhilarating experience.
But where did the rings come from? A possible answer came when Voyager met Saturn's moons, icy worlds scarred by impact craters made by meteorites long ago.
'The Saturnian system was as we'd expected,' small, cold, icy moons, heavily cratered.
But there were real surprises, too.
The innermost large satellite is Mimas.
We found large impacts.
This crater, called Herschel, is a fourth the size of the object - nearly large enough to blast it apart.
There's a similar crater on Tethys, the next moon, a third the size of the object.
In early history, they were blasted by things large enough to have torn them apart.
'If Mimas nearly got bashed up to bits, 'then very likely other satellites did get smashed up.
' Saturn's rings probably came from a satellite that was close into the planet, got smashed up, the collisional shards got strewn out into a planetary ring system.
As Voyager encountered the planet itself, it found Saturn was made of the same gases as Jupiter.
These two are the gas giants of the solar system, dwarfing all the other planets.
Yet Saturn held mysteries of its own.
It's smaller and colder than Jupiter.
It generates less heat within, and receives less energy from the sun.
Yet Voyager recorded faster winds on Saturn than on Jupiter: a thousand miles an hour.
Why this should be was not yet understood.
As Voyager left Saturn, there was one final enigma.
Saturn's largest moon, Titan, is the only moon in the solar system with a thick atmosphere.
Voyager's cameras could not penetrate the orange haze.
I found myself alone in the Voyager imaging area, about ten o'clock in the evening.
Just me and the television monitor.
This monitor had showed us all these tremendous pictures.
Now it was just showing the image of Saturn that Voyager 1 had as it receded from it.
I was mesmerised by this whole thing, 'thinking nobody had seen Saturn from this perspective before, 'because we'd never been on the other side.
' I was so moved by me and Saturn alone in this room, 'I was completely swept away.
' Voyager's next goal was Uranus, a world discovered just 200 years before and still barely seen.
Would this planet, tipped over on its back, resemble its neighbours Jupiter and Saturn? Even travelling at 50,000 miles an hour, it would take Voyager five years to reach Uranus.
The engineers needed every moment to prepare for their most difficult challenge yet.
'Voyager, operating at one billion miles at Saturn, 'had to operate at two billion at Uranus, 'where the sun was very dim.
' We did several things, like longer exposures on the camera.
If it's too long, and you're moving fast, things get smeared.
We had to turn the spacecraft at just the right rate so that it would compensate for its motion.
When Voyager reached Uranus, it found little to photograph.
'We'd been so spoiled by the glamour, colour and intricacies of the atmospheres of Jupiter and Saturn, that Uranus was a let-down, because it was so bland.
'There's more atmosphere and haze above the clouds, 'so it's hard to see the features.
' Even at its closest approach, Voyager revealed little detail in the atmosphere of Uranus.
Uranus is different than Jupiter and Saturn in that it has no internal heat source.
They're radiating more energy than the sun gives, because there's heat inside them.
At Uranus, that heat source had shut down, so the atmosphere was much blander.
Voyager had found a different kind of giant.
A world smaller and colder than Jupiter and Saturn.
It was shrouded in different gases - methane and ammonia - under which scientists believed lay oceans of water and ice.
What exactly is that? Is that in here? Uranus had been a disappointment, but the imaging team found many surprises in its moons.
Most striking of all was the tiny moon Miranda.
'Miranda looks like a jigsaw puzzle, 'with regions looking like giant complex racetracks, 'as if put together by a committee.
' There are pieces that look like they belong to other planets.
One idea was it was busted apart, these coarse pieces stayed intact, then were glued back together, so you get this hodgepodge.
Perhaps it was such a collision, on a grander scale, that knocked Uranus over on its back in the earliest days of the solar system.
From Uranus onwards to Neptune, three billion miles away from Earth.
The probe had to take a precise trajectory over the planet's north pole, to get the best possible view of Neptune and its moon Triton.
'The challenge at Neptune was the most difficult one.
' We had to know within one second when we'd fly over Neptune's north pole.
A major navigational challenge.
We hadn't delivered that accuracy before.
If we were wrong, we had no second chance.
After 12 years in flight, Voyager arrived at Neptune.
Brad Smith's team feared, after bland Uranus, they'd see little when they got to the last giant.
They need not have worried.
.
.
Is that a rugged surface or what? The final encounter I was able to witness here at JPL with my youngest son.
We watched with fascination as the Neptune pictures unfolded.
'Suddenly, things no one had imagined were there.
'Here was a planet vibrant with life, 'it had its own great, dark spot, 'white clouds floating in its atmosphere.
'They unfolded before our eyes.
' Neptune was a great, wonderful surprise for me.
'There was something strange about Neptune.
' The last planet, the sentinel at the outer edge of our solar system, looks like Earth, with its beautiful deep blue colour and its white clouds in the atmosphere.
We had an exciting planet again with Neptune.
'There were fast-moving clouds, moving in different directions, 'some at almost sonic speeds.
'The complexity of the planet's atmosphere 'was far beyond our expectations.
' Neptune turned out to have the strongest winds of all.
In the extremes of the solar system, where the sun barely penetrates, the last giant defied all expectations.
'You'd expect that with less energy from the sun 'to drive the winds, they'd be slower.
' Jupiter's winds were already hundreds of miles per hour.
Rather than slower winds, we found faster ones, over 1,000 miles per hour at Neptune.
'We now understand why.
'Enough energy creates a lot of turbulence, 'and that slows the wind down.
' Neptune had so little energy that the wind got started and would just go and go.
Neptune's atmosphere was more dynamic than Uranus, but made of the same gases and ices.
These two giants were different from their more massive cousins.
Uranus and Neptune are not gas giants but ice giants.
From Earth, nobody had seen a full set of rings at Neptune.
Some scientists believed they'd seen segments of a ring, which they called arcs.
When we got to Neptune, I was leading the group on the imaging team responsible for the rings and the ring arcs.
'Some people on the imaging team doubted their existence, 'they thought we were crazy and wasting spacecraft resources.
' It was gratifying to see that one image, where we finally captured the Neptune ring arcs.
'So it was a tremendous achievement.
' Neptune is indeed surrounded by ring arcs.
How they got there and why the ring is incomplete is not clear.
The impossible mission was almost over.
Neptune's moon Triton was the final encounter.
Triton is a large moon, as big as Pluto.
In orbit around the sun it'd be a planet, but it's in orbit around Neptune.
Unlike the other satellites which orbit in the direction the planet rotates, Triton is going around Neptune backwards.
That meant it was not likely formed around Neptune, but had been captured by it.
Triton is a moon that might have been a planet.
It strayed too close to Neptune and was caught by its gravity.
Triton was one of the strangest worlds encountered.
This is too much.
Too much to believe.
Oh-ho.
God.
Look at the tyre tracks.
(Laughter) Tyre tracks! There you go.
'Triton was unlike any world we'd seen before.
' The coldest surface in the solar system, 40 degrees above absolute zero.
So cold that nitrogen, which forms the atmosphere on Earth, is frozen, solid ice.
Triton's polar caps are frozen nitrogen, not frozen water.
Even so, we found geysers on the surface of Triton.
'Nitrogen geysers, miles high.
'Even at the deepest part of our solar system, 'there is geologic activity - it is everywhere.
' The solar system is alive, evolving.
That's why it's so exciting and there's so much to learn.
Voyager had survived to reach the extremes of the solar system and reveal not just the giants, but whole systems of rings and moons unlike anything imagined.
The planets moved out of their alignment, and Uranus and Neptune drifted out of our reach again.
It's unlikely they'll be visited again in our lifetime.
But Voyager was not the last mission to the gas giants.
In 1994, the probe Galileo went to Jupiter and its moons.
It found Io's surface covered by fresh sulphurous lava.
Europa had looked so smooth, but was covered in great ridges and chasms.
Fresh detail was revealed in Ganymede's alien landscapes.
There was more destruction than had been imagined on Callisto.
In October 1997, a mission called Cassini left for Saturn.
For four years, it'll send high-resolution images of the great planet, its rings and its many satellites.
Head of the imaging team is Carolyn Porco.
We're interested, for scientific purposes, in taking images of Titan and the satellites.
How many images will you need? Four, normally.
Four images? In 30 minutes? OK.
We've designed the camera system specifically, among other things, to see down to Titan's surface, which we weren't able to do on Voyager.
'We'll be able to see things on the scale of office blocks.
'We'll collect data from Cassini for four years, 'so we'll have a chance to monitor changes.
'It'll be a new era.
' But it will never have the same feeling or even .
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historical significance as Voyager had.
'That experience can never be duplicated.
' The next awards are the Exceptional Scientific Achievement Medal.
The first goes to Gary Flandro, for seminal contributions to the design and engineering of missions, including the opportunity for the epic Voyager explorations.
The views we achieved of those planets exceeded expectations, but it was a ghostly feeling of having already been there, flying that mission in my mind in the 1960s.
- It started in that office.
- Is that right? Building 180 is where you worked? Looking out that window through those trees, and said "We can do this.
Four planets in one flight.
" After the planets, Voyager went on to search for the edge of the solar system, where the sun's influence runs out, and interstellar space begins.
'The Voyager mission isn't over.
'We hope we can listen to it for another 20 years 'before we finally lose power on the spacecraft.
' In 2015, Voyager 1 will be 12 billion miles from the Earth, and perhaps in interstellar space.
We listen to the two Voyager spacecraft every day, looking for some signal we're getting close 'to interstellar space.
' The greatest voyager in history is still travelling.
' In August 1977, two spacecraft called Voyager began an incredible journey.
If they survived the hazards of billions of miles of space, they'd reach worlds so distant and strange, they defied the imagination - the gas giants.
Voyager was heading for four planets that could swallow Earth thousands of times: Jupiter, with its strange bands of cloud and its great red spot, a world crackling with radiation we can hear from Earth.
Beyond Jupiter was Saturn.
How did it alone come to have its array of rings? Stranger still was Uranus.
From the orbiting of its moons, Uranus was known to have been tipped over on its back.
Why should this be? Neptune was barely visible even through powerful telescopes.
What kind of worlds were these? What could they reveal about the solar system, of which Earth is a tiny part? Zero G, I feel fine.
'Capsule is turning around.
'Oh, that view is tremendous.
' In the early 1960s, sending a spacecraft to the giants was unthinkable.
Men had flown just a few miles up in orbit around the Earth.
Unmanned probes ventured further, to the nearest planets, Venus and Mars.
'Signal level's gone down, 'report continuing low signal level.
' Even this was pushing the very limits of science.
'In 1964, the first spacecraft, Mariner 4, flew by Mars.
' 'The spacecraft barely made it.
' Yes, it's there.
'Going to Jupiter -' which is half a billion miles away, Saturn a billion, Uranus two, and Neptune three billion miles away and twelve years in journey - was not even something one could easily imagine.
A solution came from an unlikely source.
A student at NASA's Jet Propulsion Laboratory was asked to calculate trajectories to Jupiter.
'I was a summer student, working on my degree.
'When I was told to look at the outer planets,' it was like a make-work project.
I was kept busy while the important business of getting to Mars was underway.
Flandro discovered something that made a flight to the giants possible.
The first thing is to determine when the planets will be in reachable positions for us.
'I drew maps of where they'd be, 'and in one important drawing, 'I drew their positions versus the date.
' I noticed immediately that the lines for Jupiter, Saturn, Uranus and Neptune all crossed 'in the 1975-76 time period.
'Those planets were on the same side of the sun, 'in the same position at the same time.
' It gave me the idea of one flight to all those planets.
Flandro's discovery was not just a convenient planetary line-up.
Rocket power alone could only propel a spacecraft to Jupiter.
But if a probe approached a planet at the right angle, it'd be caught by the planet's momentum, then pitched in a new direction, at a greater speed.
The trick is you fire your rocket with enough propulsion to get to Jupiter, 5 times the distance of the sun.
Go by Jupiter in the right way, to get a gravitational slingshot effect.
That propels you to Saturn.
If Saturn's in the right place at the right time, it can propel you to Uranus, and from Uranus to Neptune.
That happens about every 175 years.
It happened in terms of launch date in 1977.
A former administrator of NASA, Tom Paine, said the last time this happened, Jefferson was President, and he blew it.
For NASA, this was too good an opportunity to miss.
They announced a mission to the giants called Voyager.
It was a new era for astronomers who'd struggled to understand the hazy views they saw through Earth-based telescopes.
The man leading the imaging team was Brad Smith.
'I had started looking at Jupiter in the late '50s,' but it was difficult to make observations from the ground.
When the opportunity came up to be involved with Voyager, I realised that I could see Jupiter up close; to see detail that we could never see from the ground.
The hopes of astronomers lay in the hands of the engineers, who faced what seemed an impossible task.
'I frequently heard from people I was working with,' "That mission is never going to happen.
It's too complicated.
" 'We had to build a machine that could fly for 10 years, 'which was pushing the limits 'of what we then could do with electronics.
' We had to pass through the asteroid belt.
How can we get this spacecraft through that dangerous area beyond Mars without a collision? That seemed to be a very challenging task.
One of the worries was data transfer.
Even if we could do this flight, could we get useful data? So we worried a lot.
The engineers had a decade to make this mission possible.
Around the world, giant antennae were built - the Deep Space Network - to communicate with probes across billions of miles.
It wasn't known if a spacecraft could survive the asteroid belt, a band of drifting rocks between Mars and Jupiter.
Voyager would have only one chance.
Two less elaborate probes were sent to test the way.
Pioneer 10 and 11 were launched to Jupiter and Saturn.
'Pioneer 10 and 11 were important 'in exploring the outer solar system.
' It was critical they'd lead the way, telling us about the environment and making important discoveries allowing us to come safely behind with the Voyagers.
James Van Allen was a veteran of missions to Mars and Venus.
Now he led a team of scientists on Pioneer.
'Pioneer 10 was the first venture beyond Mars.
' First time we went such enormous distances.
First time we'd cross the asteroid belt between the orbits of Mars and Jupiter.
'It was a hazardous and high-risk mission.
'We had a keen sense of its historic possibilities' in blazing the trail to the outer planets.
'Pioneer 10 successfully got through the asteroid belt.
' We knew it was possible to get to the outer planets safely.
Another key question for Pioneer 10 was how intense was the radiation around Jupiter? Since the '50s, radio emissions from Jupiter had been detected, suggesting intense radiation around the planet.
The man who had to investigate this was Van Allen, who discovered radiation bands around Earth with the first American satellite.
They were later called the Van Allen belts.
We've encountered a high intensity of radiation, one thousand times as intense as could be attributed to cosmic rays as ordinarily understood.
Van Allen predicted greater radiation belts around Jupiter.
But even he did not anticipate what Pioneer found.
'As we went in, the radiation intensity got greater.
' There was a strong apprehension about the survival of the electronic equipment.
'It went to a maximum, and we survived, 'then it went down, so we sighed with relief that we'd made it.
' Jupiter's radiation belts were 10,000 times more intense than Earth's.
Pioneer also encountered a vast magnetic field, stretching 7 million miles out from the planet.
Pioneer 10 discovered that Jupiter's magnetic field is the largest structure in the solar system.
It would appear to be as large as the sun, being five times further away.
But it's invisible, and it can damage electronics.
The Voyager probes had to be redesigned to survive Jupiter's magnetic fields and radiation belts.
'The Pioneer saved our lives.
' Had we flown into that, unknowingly, with Voyager's sophisticated electronics and mechanisms, we'd have died instantly.
We were well into the design of that spacecraft when the Pioneer results came.
We had to redesign a lot.
(Rock and roll music) Final preparations were made for Voyager.
For any curious extraterrestrials, the probes carried a disc showing images from Earth.
This was a moment I had thought about for years.
And there was our spacecraft, going to Jupiter, Saturn, Uranus and Neptune.
A very marvellous feeling.
This was the world where Voyager was heading.
It was 4 centuries since Galileo turned his telescope on Jupiter, and discovered four points of light moving around it.
These were four moons.
The first proof that not everything in the universe revolves around Earth.
For Voyager's chief scientist, the mission promised a new era of discovery.
'We were in the tradition of Galileo,' who saw Jupiter's moons first, and first applied an instrument to increase our ability to observe the universe.
'Voyager is just the latest tool mankind had managed to devise, 'so powerful that we saw things 'nobody had seen before or had imagined we would see.
' The probe was 50 million miles from Jupiter when it sent the views everyone had been waiting for.
'We approached Jupiter with great expectation 'and grandiose theories about what we'd see.
'But Jupiter fooled us all.
' There was bizarre behaviour.
Little clouds moving along, swept up in the red spot, then it would spit them out again.
'Other clouds would roll along, 'coalesce into a single cloud and break apart again.
' Those kinds of details are still not understood.
The first encounter with Jupiter was marvellous, especially the approach shots showing the planet revolving, 'watching the red spot revolving and getting closer, 'till we could see this was the top of a large storm.
'As a child, I'd wondered if that was a storm,' or an island floating in an ocean.
Finally, the answers were there.
Voyager revealed an atmosphere of hydrogen and helium gas, whose clouds were much more dynamic than had been imagined.
Jupiter's winds gust at hundreds of miles an hour.
The red spot alone is three times the size of Earth.
The greatest storm in the solar system.
Voyager hinted at why.
Jupiter gives out twice as much energy as it receives, suggesting its core must be hot.
Scientists believe that at Jupiter's heart the gases are compressed till they become a metallic liquid.
This hot core could be the powerhouse driving the winds, and, like a dynamo, creates the enormous magnetic field.
Voyager then turned its cameras towards Jupiter's moons.
When the encounter took place, Bruce Murray was head of JPL.
'Just before the mission,' the interest was on the planets and bands.
Things you could see through a telescope.
There was hardly any interest in the satellites of the planets, because they at most were little spots.
'I led a one-man crusade 'to have them listed as targets for Voyager.
' Scientists had expected Jupiter's moons to be cold, dead, covered in craters, like our Moon.
They found an array of worlds as different as the planets.
Io, the closest of Jupiter's large moons, was more geologically active than Earth.
Jupiter's gravity stretches and squeezes Io, heating it up, so it stays molten inside.
'Io had eight active volcanoes, 'the most volcanically active body in the solar system.
' That was so unexpected.
It was a shift in our paradigm about the outer solar system, where it's very cold and, we thought, dead.
'It characterised the sense of seeing things 'we hadn't thought about.
'That was very characteristic of the rest of the mission.
' As Io orbits close to Jupiter, it is constantly brushing against its magnetic field.
Io builds up a huge electrical charge, which discharges onto Jupiter in a flow of three million amps, causing storms on the surface of the planet.
'The rest is reddish.
' The moon Europa was different but no less surprising.
It had a surface of water ice, frozen as hard as rock.
Underneath this icy crust, scientists believe there are oceans of warm water.
The moon Ganymede was bigger than the planet Mercury.
Its landscapes of rock and ice reminded Voyager's geologist Laurence Soderblom of Earth.
'Ganymede turned out to be really exciting.
' We found a broken surface, complex patterns.
It's kind of a cross between ice floes in the Arctic and continental drift on Earth.
'Its icy crust has been sheared, twisted, broken, 'something we didn't expect.
' The last major moon, Callisto, was different again.
Like our moon, it was covered with craters.
Its icy crust preserved a record of a violent age, when meteorites crashed into its surface.
What Voyager found at Jupiter's moons transformed the mission.
'The first thing you notice is everything is different.
' The diversity is overwhelming.
This is a discovery, it's Captain Cook.
It's really, in the solar system, seeing new things.
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there's a twin, a pair there, another pair What about the relief from the cracks? To have enough heating 'All the scientists, except me, 'were atmospheric scientists and astronomers.
' It wasn't until we recognised the exotic variety and diversity of the satellites that geologists were added to the Voyager team.
'The satellites became the star 'of the whole Voyager experience.
' Jupiter's moons are a solar system in miniature.
As Jupiter formed, its immense gravity must have attracted a cloud of dust and gas, from which its moons were born, just as the planets around the sun.
Close to Jupiter are dense, active worlds, Io and Europa.
A mirror of the inner rocky planets, Venus, Earth and Mars.
Further out, Ganymede and Callisto are larger, icy worlds, the giants of the Jupiter system.
Voyager's next goal was Saturn.
Saturn was thought to be the last planet in the solar system.
The first to observe the rings, Giovanni Cassini, saw a flat disc with just one gap.
Scientists hoped Voyager would reveal clues to the origin of these rings.
This time, after Voyager's success at Jupiter, the press and the public came to see the first images of everyone's favourite planet.
'We thought we knew it all.
' But again, we were looking at a very complex situation.
'The rings were broken up into mini rings, with gaps, 'there were dynamical phenomena we didn't understand.
' So we very hurriedly reprogrammed Voyager 2, to look closer at the rings.
'When I began my work in 1964,' I had suggested this particular mission could fly between the planet and the rings.
'Fortunately, we didn't do that, 'because the region the spacecraft would have entered 'was filled with more rings.
' The spacecraft would not have survived going through that gap.
The imaging team could barely cope with all the detail Voyager 2 gave.
They saw delicate rings intertwined, and rings held in place by tiny moons called shepherds.
There were strange features called spokes, patches of dust particles slightly above the rings.
These caught the eye of one graduate student.
I started studying the spokes, these ghostly features that were seen to come and go.
'It came to my head to categorise the pictures.
' One pile for those images with a lot of spokes, another for the images that had no spokes at all, and an intermediate category.
'Each image was tagged with a time.
'I did an analysis on the computer of this,' and found the spokes weren't sporadic, they came and went with a certain period.
Carolyn Porco discovered the spokes followed Saturn's magnetic field as it rotated with the planet.
'I made my first scientific discovery.
' Knowing I had found something nobody else in the world knew was such an exhilarating experience.
But where did the rings come from? A possible answer came when Voyager met Saturn's moons, icy worlds scarred by impact craters made by meteorites long ago.
'The Saturnian system was as we'd expected,' small, cold, icy moons, heavily cratered.
But there were real surprises, too.
The innermost large satellite is Mimas.
We found large impacts.
This crater, called Herschel, is a fourth the size of the object - nearly large enough to blast it apart.
There's a similar crater on Tethys, the next moon, a third the size of the object.
In early history, they were blasted by things large enough to have torn them apart.
'If Mimas nearly got bashed up to bits, 'then very likely other satellites did get smashed up.
' Saturn's rings probably came from a satellite that was close into the planet, got smashed up, the collisional shards got strewn out into a planetary ring system.
As Voyager encountered the planet itself, it found Saturn was made of the same gases as Jupiter.
These two are the gas giants of the solar system, dwarfing all the other planets.
Yet Saturn held mysteries of its own.
It's smaller and colder than Jupiter.
It generates less heat within, and receives less energy from the sun.
Yet Voyager recorded faster winds on Saturn than on Jupiter: a thousand miles an hour.
Why this should be was not yet understood.
As Voyager left Saturn, there was one final enigma.
Saturn's largest moon, Titan, is the only moon in the solar system with a thick atmosphere.
Voyager's cameras could not penetrate the orange haze.
I found myself alone in the Voyager imaging area, about ten o'clock in the evening.
Just me and the television monitor.
This monitor had showed us all these tremendous pictures.
Now it was just showing the image of Saturn that Voyager 1 had as it receded from it.
I was mesmerised by this whole thing, 'thinking nobody had seen Saturn from this perspective before, 'because we'd never been on the other side.
' I was so moved by me and Saturn alone in this room, 'I was completely swept away.
' Voyager's next goal was Uranus, a world discovered just 200 years before and still barely seen.
Would this planet, tipped over on its back, resemble its neighbours Jupiter and Saturn? Even travelling at 50,000 miles an hour, it would take Voyager five years to reach Uranus.
The engineers needed every moment to prepare for their most difficult challenge yet.
'Voyager, operating at one billion miles at Saturn, 'had to operate at two billion at Uranus, 'where the sun was very dim.
' We did several things, like longer exposures on the camera.
If it's too long, and you're moving fast, things get smeared.
We had to turn the spacecraft at just the right rate so that it would compensate for its motion.
When Voyager reached Uranus, it found little to photograph.
'We'd been so spoiled by the glamour, colour and intricacies of the atmospheres of Jupiter and Saturn, that Uranus was a let-down, because it was so bland.
'There's more atmosphere and haze above the clouds, 'so it's hard to see the features.
' Even at its closest approach, Voyager revealed little detail in the atmosphere of Uranus.
Uranus is different than Jupiter and Saturn in that it has no internal heat source.
They're radiating more energy than the sun gives, because there's heat inside them.
At Uranus, that heat source had shut down, so the atmosphere was much blander.
Voyager had found a different kind of giant.
A world smaller and colder than Jupiter and Saturn.
It was shrouded in different gases - methane and ammonia - under which scientists believed lay oceans of water and ice.
What exactly is that? Is that in here? Uranus had been a disappointment, but the imaging team found many surprises in its moons.
Most striking of all was the tiny moon Miranda.
'Miranda looks like a jigsaw puzzle, 'with regions looking like giant complex racetracks, 'as if put together by a committee.
' There are pieces that look like they belong to other planets.
One idea was it was busted apart, these coarse pieces stayed intact, then were glued back together, so you get this hodgepodge.
Perhaps it was such a collision, on a grander scale, that knocked Uranus over on its back in the earliest days of the solar system.
From Uranus onwards to Neptune, three billion miles away from Earth.
The probe had to take a precise trajectory over the planet's north pole, to get the best possible view of Neptune and its moon Triton.
'The challenge at Neptune was the most difficult one.
' We had to know within one second when we'd fly over Neptune's north pole.
A major navigational challenge.
We hadn't delivered that accuracy before.
If we were wrong, we had no second chance.
After 12 years in flight, Voyager arrived at Neptune.
Brad Smith's team feared, after bland Uranus, they'd see little when they got to the last giant.
They need not have worried.
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Is that a rugged surface or what? The final encounter I was able to witness here at JPL with my youngest son.
We watched with fascination as the Neptune pictures unfolded.
'Suddenly, things no one had imagined were there.
'Here was a planet vibrant with life, 'it had its own great, dark spot, 'white clouds floating in its atmosphere.
'They unfolded before our eyes.
' Neptune was a great, wonderful surprise for me.
'There was something strange about Neptune.
' The last planet, the sentinel at the outer edge of our solar system, looks like Earth, with its beautiful deep blue colour and its white clouds in the atmosphere.
We had an exciting planet again with Neptune.
'There were fast-moving clouds, moving in different directions, 'some at almost sonic speeds.
'The complexity of the planet's atmosphere 'was far beyond our expectations.
' Neptune turned out to have the strongest winds of all.
In the extremes of the solar system, where the sun barely penetrates, the last giant defied all expectations.
'You'd expect that with less energy from the sun 'to drive the winds, they'd be slower.
' Jupiter's winds were already hundreds of miles per hour.
Rather than slower winds, we found faster ones, over 1,000 miles per hour at Neptune.
'We now understand why.
'Enough energy creates a lot of turbulence, 'and that slows the wind down.
' Neptune had so little energy that the wind got started and would just go and go.
Neptune's atmosphere was more dynamic than Uranus, but made of the same gases and ices.
These two giants were different from their more massive cousins.
Uranus and Neptune are not gas giants but ice giants.
From Earth, nobody had seen a full set of rings at Neptune.
Some scientists believed they'd seen segments of a ring, which they called arcs.
When we got to Neptune, I was leading the group on the imaging team responsible for the rings and the ring arcs.
'Some people on the imaging team doubted their existence, 'they thought we were crazy and wasting spacecraft resources.
' It was gratifying to see that one image, where we finally captured the Neptune ring arcs.
'So it was a tremendous achievement.
' Neptune is indeed surrounded by ring arcs.
How they got there and why the ring is incomplete is not clear.
The impossible mission was almost over.
Neptune's moon Triton was the final encounter.
Triton is a large moon, as big as Pluto.
In orbit around the sun it'd be a planet, but it's in orbit around Neptune.
Unlike the other satellites which orbit in the direction the planet rotates, Triton is going around Neptune backwards.
That meant it was not likely formed around Neptune, but had been captured by it.
Triton is a moon that might have been a planet.
It strayed too close to Neptune and was caught by its gravity.
Triton was one of the strangest worlds encountered.
This is too much.
Too much to believe.
Oh-ho.
God.
Look at the tyre tracks.
(Laughter) Tyre tracks! There you go.
'Triton was unlike any world we'd seen before.
' The coldest surface in the solar system, 40 degrees above absolute zero.
So cold that nitrogen, which forms the atmosphere on Earth, is frozen, solid ice.
Triton's polar caps are frozen nitrogen, not frozen water.
Even so, we found geysers on the surface of Triton.
'Nitrogen geysers, miles high.
'Even at the deepest part of our solar system, 'there is geologic activity - it is everywhere.
' The solar system is alive, evolving.
That's why it's so exciting and there's so much to learn.
Voyager had survived to reach the extremes of the solar system and reveal not just the giants, but whole systems of rings and moons unlike anything imagined.
The planets moved out of their alignment, and Uranus and Neptune drifted out of our reach again.
It's unlikely they'll be visited again in our lifetime.
But Voyager was not the last mission to the gas giants.
In 1994, the probe Galileo went to Jupiter and its moons.
It found Io's surface covered by fresh sulphurous lava.
Europa had looked so smooth, but was covered in great ridges and chasms.
Fresh detail was revealed in Ganymede's alien landscapes.
There was more destruction than had been imagined on Callisto.
In October 1997, a mission called Cassini left for Saturn.
For four years, it'll send high-resolution images of the great planet, its rings and its many satellites.
Head of the imaging team is Carolyn Porco.
We're interested, for scientific purposes, in taking images of Titan and the satellites.
How many images will you need? Four, normally.
Four images? In 30 minutes? OK.
We've designed the camera system specifically, among other things, to see down to Titan's surface, which we weren't able to do on Voyager.
'We'll be able to see things on the scale of office blocks.
'We'll collect data from Cassini for four years, 'so we'll have a chance to monitor changes.
'It'll be a new era.
' But it will never have the same feeling or even .
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historical significance as Voyager had.
'That experience can never be duplicated.
' The next awards are the Exceptional Scientific Achievement Medal.
The first goes to Gary Flandro, for seminal contributions to the design and engineering of missions, including the opportunity for the epic Voyager explorations.
The views we achieved of those planets exceeded expectations, but it was a ghostly feeling of having already been there, flying that mission in my mind in the 1960s.
- It started in that office.
- Is that right? Building 180 is where you worked? Looking out that window through those trees, and said "We can do this.
Four planets in one flight.
" After the planets, Voyager went on to search for the edge of the solar system, where the sun's influence runs out, and interstellar space begins.
'The Voyager mission isn't over.
'We hope we can listen to it for another 20 years 'before we finally lose power on the spacecraft.
' In 2015, Voyager 1 will be 12 billion miles from the Earth, and perhaps in interstellar space.
We listen to the two Voyager spacecraft every day, looking for some signal we're getting close 'to interstellar space.
' The greatest voyager in history is still travelling.