The sun is the life-force of our solar system.
The Earth is wholly dependent on its energy.
Their fates are entwined forever.
But in the future the sun will change.
One day its benevolent influence
will turn against the planets it has nurtured.
The astronauts who went to the Moon
thought they would be the first in a long line.
But there have been no more.
The last man to set foot on another world was Gene Cernan.
'The Moon is bland, it's grey in shades.'
And other than the colour you brought
the only colour is the Earth,
the blue oceans,
'white snow and clouds.
'Earth is three-dimensional
'and it moves through this blackness
'with logic, with purpose and with beauty
'beyond comprehension.
'For the first time,
'you're beginning to see the Earth as a planet.
'You never saw it that way before.
'It's spiritually different to see the Earth evolve,
'to see something very strange and yet very familiar,'
and it's something I didn't expect to see -
as you head to the Moon -
'that Earth grows smaller very very quickly,
'until you can literally block out all humanity,
'your identity with reality,
'with something no bigger than your thumb.'
Since the Moon missions, no one has been far enough away
to capture views of our planet from a greater distance...
until Voyager.
The Voyager spacecraft were launched in 1977.
They are now leaving our solar system for interstellar space.
On their way, they have sent back photographs
of the planets in beautiful detail.
(Cheering)
But one more picture just had to be taken,
a final gift from the probe's revelatory journey.
The idea occurred to me
that Voyager was gonna be
in a location no spacecraft had been before,
equipped with sophisticated instrumentation,
so that it could turn around and take a picture
of all the planets in the solar system.
I thought this would be
a riveting collection of images.
Voyager scientist Carl Sagan had long campaigned
for the spacecraft to be turned around.
But the risk of sun damage was seen as too great.
At first, Carolyn Porco met with the same response.
And they said there's no scientific justification,
and I couldn't argue, because there wasn't.
The planets were gonna be pinpoints,
'just pixels.
'They couldn't see it.'
But as Voyager's mission ended,
there was nothing to lose,
and on Valentine's Day 1990,
13 years after leaving Earth,
Voyager turned its cameras
back towards the now distant planets.
The spacecraft was 3.7 billion miles away.
Each signal took five and a half hours to reach Earth.
No single image could capture the entire solar system,
and the mosaic of pictures stretched six metres.
The planets could barely be made out.
Mars and Pluto were too small to record,
and Mercury was lost in the glare of the sun.
'And I took my hand,'
and swiped the glossy print,
trying to remove the dust off it.
And one of those specks of dust was the image of Earth.
It was that small.
These were not tremendously beautiful, glorious images.
That wasn't the point.
'The portrait of the planets'
that has now been taken,
is, it seems to me,
in the same tradition
as the extraordinary colour photographs of the Earth
taken by the Apollo astronauts
'on their way to the Moon.
'This looks like more than a dot,
'but it is less than a pixel.'
In this colour picture
you can see that it is slightly blue,
and this is where we live -
on a blue dot.
I talk about standing on the Moon looking at Earth,
and describing it as humanity,
my identity with humanity.
Think about moving outside of our solar system,
and seeing it as Voyager saw it!
'But that's what we've now done.'
'We came to know the solar system,
'to know its history.'
We came to know how it's configured,
and we're starting to piece together
how it possibly came about,
because of the Voyager mission.
Voyager gave us a perspective we didn't have before.
But what Voyager showed was just one moment in time -
a snapshot.
The planets will change and evolve in different ways
before the end of their lifetime.
One thing we are certain will change is Saturn.
'In a hundred million years the rings won't be there.
'They will be worn away
'by the bombardment of meteorites,'
little bit by little bit.
That material ends up lost to the Saturn system,
or spiralling in and being consumed by Saturn.
'The solar system will be completely reconfigured.
'You wouldn't recognise it.'
In one billion years, at Neptune,
the moon Triton will spiral inwards towards its planet,
gradually encroaching, until the moon is ripped apart.
Out of this destruction
will come something even more spectacular.
'Close in to Neptune is a collection of satellites,'
and if you bashed them all up at the same time
the material would form a ring system
that would look like Saturn's rings.
So we might,
'while losing Saturn's rings,
'we might have, in the future,
'another beautiful ring system around Neptune.
'Which wouldn't be too bad a swap.'
Whatever the solar system will look like,
the most important question
is what will happen to the sun,
the heart of it all?
The sun's fate will determine ours,
but how will it change?
The answers lie in the moon rocks
gathered by the Apollo astronauts.
'You're about full. Got some left?
'Get some small ones.'
'That's a big one.' 'Don't fill it too full.'
'We took some rocks in the spacecraft with us,
'and when we examined them with our bare hands
'the dust would penetrate into the pores of our skin
'and beneath our nails -'
just way down in.
It was weeks, when I got back,
before that lunar dust ever grew out,
and was depenetrated from my skin.
For billions of years,
constantly bombarded by solar particles,
the Moon has been a diary of our sun.
Its rocks act like a sponge,
quietly absorbing the particles,
and so keeping a record of the sun's activity.
The Apollo astronauts removed the rocks
buried beneath the lunar dust,
and brought them home.
The rocks show
how the sun's energies have fluctuated over time.
It has been much more active in the past.
The sun is ageing,
and we, too, are part of that ageing process.
'Thinking about the sun and the solar system,'
and wondering what's their long-term future,
I think is a sobering process,
because we tend to think of the Earth as...forever.
"The eternal sea," we call it.
But when we start looking at the planets,
we realise they're not eternal.
The Earth is halfway through its expected lifetime.
We're living on a middle-aged planet.
The Earth is middle-aged because the sun is middle-aged.
As the sun gets older
it will start to work against us.
Since its creation,
it has been getting 10% hotter every billion years.
In one billion years, it will be so hot
that it will begin to destroy life on Earth.
Plants and animals will find it hard to cope
with falling levels of carbon dioxide.
Our time on Earth could be limited.
'If we come back in a billion years,'
it's still where you can find liquid water.
Earth is still the planet of choice.
Maybe two or three billion years,
it's starting to become a hothouse.
'The oceans might start warming up and evaporating,
'creating a runaway greenhouse, like Venus,
'a very thick atmosphere trapping a lot of heat.
'As the sun gets brighter,'
the Earth might eventually vaporise,
so we can see the Earth becomes less desirable
as a place to live.
'There will reach a point
'where Earth is no longer habitable.
'So we have to find another place to live.'
'3...2...1.
'We have lift-off
'of NASA's Mars Climate orbiter,
'continuing to explore the mysteries of the Red Planet.'
We've imagined life on Mars, yet we didn't find any.
And it was more puzzling,
because there was everything life would need.
But the key ingredient for life on Mars,
liquid water,
is missing.
We now know that water once flowed in abundance.
The many channels in its surface
were created by seas and rivers.
But as the planet cooled over millions of years,
water turned to ice and became trapped below the surface.
'If there is water in the polar caps,
'and as the sun brightens'
and the temperature of Mars gets above the melting point,
the polar caps will turn into oceans.
'Mars will again have a water-rich environment.
'That could release large amounts of CO2 very quickly,
'once it crossed the freezing point.
'Mars may have its second reawakening,
'and could be suitable for life.
'That would occur
'when the sun was 2-3 times brighter
'than it is today.'
Springs will emerge
through the pores of the dusty planet.
The parched surface will again be awash
with the possibility of life.
And as the water vapour rises,
the planet will rebuild its atmosphere,
and again be shrouded in white cloud,
like the Earth.
'As the sun brightens, it could be too much of a good thing.'
It could go from being too cold to being too hot.
'Mars is not a long-term place for home,'
but there's no place that's gonna be suitable forever.
It's just a question of how long.
Earth, we've been lucky, we've had several billion years.
Mars may have half a billion.
But a place for half a billion years is a good place.
As the sun warms,
the moons of the distant planets will perhaps
be the best hope for life in the future solar system.
Jupiter's moon Europa is already the most likely haven.
Far below its inhospitable layers of ice,
some form of primitive life
may even now exist.
Dr David Black is chairman of the NASA Origins programme,
a programme designed to search for signs of life in space.
The moon Europa is very very intriguing.
It appears it's an ice-covered planet,
but features on the surface
suggest that there's a liquid ocean below that.
How extensive, we don't know.
We'll try and explore that.
'We know that deep in our own ocean,
'where there's no sunlight,
'we've seen life near deep sea vents, the "smokers".
'It's possible there's an analogous situation on Europa.
'There may be primitive life.'
In the future,
Europa will warm up
and start to melt.
But it could become a water world,
a place too challenging to inhabit.
'I'm not sure it's a vacation spot in the future,'
but we might see very primitive life,
another place in the solar system.
The Cassini-Huygens mission left Earth in October 1997,
on a seven-year journey to Saturn
and its moon Titan.
As the sun heats up,
this little moon will come into its own.
'It's the only other planetary object
'that looks like our Earth.'
It's the only other object we know of
that has an atmosphere of nitrogen.
Also, we know there is an organic chemistry
taking place inside this atmosphere,
and we have all those molecules we find on Earth.
The only thing lacking is temperature
and a little bit of oxygen.
The beach here is where the probe will land,
and the question is...
In Paris, Athena Coustenis and Chris McKay
are studying some of the latest telescope images of Titan.
It's very cold, but it has all the ingredients.
In some sense, it's like a frozen pie.
'When the sun brightens it would warm up,
'and have a nice water-rich environment,
'with a nitrogen atmosphere.
'And we know that there's rich organic chemistry
'in Titan's atmosphere, and that organic chemistry'
could be the seeds for life.
If life from Earth doesn't migrate to Titan,
Titan could initiate life,
when the sun becomes bright enough to cook that pie.
Titan is covered entirely by a thick cloud deck,
'and you cannot look down to the surface.
'For years we have been trying
'to glimpse the surface of Titan,
'and nothing would come out.'
The tiny Huygens probe
will parachute through the thick Titan atmosphere,
and descend to the surface below.
'To me, the most interesting question'
is "What is the nature of the surface?"
What is that material?
Is it liquid hydrocarbons that have accumulated
over billions of years, a sea of natural gas?
Is it solid ice or solid CO2?
Or something we're not expecting?
No matter how Earth-like it becomes,
eventually even the sanctuary of Titan
will not be enough.
Like the Earth,
it too will finally become uninhabitable.
Ultimately,
there is no hope for survival within our solar system.
The sun is on a path to destruction,
and nothing can stop it.
This future was first discovered by Father Angelo Secchi,
a Vatican astronomer.
In 1868 he peered through his telescope, as he had before.
He gazed up at a dying star far above.
It was Gamma Canis Veniticchi,
400 light years away.
He was using a new technique to analyse starlight -
spectroscopy.
Light was split using a prism,
and the chemical composition of the star could be determined
from the patterns of colour and shadow.
Secchi had recorded blue and yellow stars,
but that night he added a new star,
a red star.
'Secchi started to classify and give names.'
The red star he called "superba"
the arrogant star,
because its spectrum was very very different.
'The real reason is it was cooler, big and luminous.
'What we now know as a red giant star.'
This was one of the most significant Secchi discoveries.
But its secrets were not revealed for 50 years.
Cambridge astrophysicist Douglas Gough
is a leading solar scientist.
He was inspired to work on stars
after studying under Sir Fred Hoyle,
one of the century's greatest cosmological thinkers.
'Fred Hoyle is a leader of the revolution in astronomy.
'His views are often controversial,
'as he strives to understand the origin of our universe.
'Internationally famous,
'he commutes regularly between Cambridge and California.'
Fred Hoyle, who coined the phrase "Big Bang",
realised what was going to happen to our sun.
'He had a really broad vision
'of how everything in physics fitted together,
'and I found that very inspiring.'
He picked out the most important things
that needed to be understood to get it right,
and then pursued them.
During World War Two, Fred Hoyle developed theories
on the evolution of stars
and on the destiny of one star in particular - ours.
It was known red giants existed,
but one of the things that Fred contributed to
was understanding that these are
towards the end of the life of a star.
'There were no computers,
'and so he really had to use his brain and think.
'He started to understand why stars became red giants.'
Our sun was always destined to become a red giant.
Created in a blinding flash,
every star has a finite supply of fuel.
Fred Hoyle realised a red giant is a star
choking on the dregs of its fuel.
He realised that this defined the sun's future.
'Stars are like people.'
They're born, they live, and they die.
A star dies by becoming a red giant.
The sun will swell after another 5 billion years -
nothing that I'm going to worry about.
It will swell up
to perhaps where the Earth is in its orbit.
When the sun becomes a red giant it puffs up,
becomes very distended, whereas the core shrinks,
and it's tiny, like a pea in a swimming pool -
a red swimming pool, because the star is red.
'And it gets very turbulent, lots of motion,
'and the sun will expand 50-100 times its current size.
'The sun will engulf'
Mercury and Venus probably.
It probably won't get to the Earth.
We're not 100% sure.
But it will get a good fraction of the way.
'It will fill the sky.
'This enormous red object in the sky.'
The burning of hydrogen in the sun's core
will eventually end.
But hydrogen in its outer layers, beyond the core,
will cause a final burst of energy
out into the solar system.
As the sun expands, the Earth will start to vaporise.
Its surface will disappear in the intense heat.
'It'll be like a cube of ice in a glass of boiling water.
The outside will start to melt, as the ice would,
'but the inside may survive.
'It depends on how big the sun gets.'
'Maybe it won't engulf Earth,
but nonetheless we will be fried for sure.
So we better hightail it out of here before then.
As the giant red sun gradually cools,
the matter it has shrugged off into space
will leave behind its tiny core -
a white dwarf star.
Ultimately, it will fade into darkness...
and our solar system will fade with it.
'What planets are left'
will still be orbiting around it,
and they will be orbiting something
which is just as heavy,
but which is very small and very dim.
'Everything will be black and cold,
'and it'll be night all the time.'
'As our sun dies, there's gonna be
'other stars and suns that are born.
'I would expect by then'
we will have moved far enough into the future
to hitch a ride on another star,
and find another planet.
'When we go to a dark place anywhere here on Earth,
'we look up, we say, "Look at all the stars!
'"I didn't know there were that many!"'
You realise how many suns, planets and stars are out there
that we know so little about, and we can't see.
A handful of sand contains one million grains.
One thousand handfuls make one billion.
There are 100 billion stars in our galaxy,
and there are at least 50 billion galaxies
in the universe.
There are more stars in the universe
than there are grains of sand on Earth.
'One thing we've learned is almost all young stars'
have discs associated with them.
We believe these are the things out of which planets form.
How many of these discs of dust form planets is unknown.
But astronomers are setting out to hunt for planets
around distant stars.
The detection of planets around other stars is difficult
because the first idea is only to look to see planets,
and this is not so efficient,
because the contrast of light
between the star and the planet is huge.
It's about one billion.
So it's absolutely impossible to...
at least at the present time,
to directly detect and take a picture of a planet.
Planet hunters Michel Mayor and Didier Queloz
have been trying to spot unusual objects around stars.
Every few months, they drive from their base in Geneva
to an observatory
in St Michelle, Haute Provence.
With no chance of seeing a planet directly from Earth,
they developed a way of looking for planets indirectly,
by looking at the motion of stars.
A wobble in the star would indicate a planet,
its gravity tugging against the star's orbit.
The planet is turning around the star.
The star itself is turning a little bit,
'and if the planet is doing a very big orbit,
'the motion of the star will be extremely small.
'So the idea is to look for this wobble.'
In December 1994, they discovered a star
whose wobble could only be caused by a planet.
But it was stranger than anything they had imagined,
and was orbiting the star very quickly,
in a matter of days.
'We detect something crazy -'
a planet the size of Jupiter,
but which had a period of less than five days.
It means very close to the star,
and nobody was expecting this, even us.
They were cautious about revealing their discovery.
It was not the first time such a claim had been made.
There were half a dozen claims
of the detection of the first planet.
All turned out to be bunk.
And various people contributed to the debunking,
but because of this rather sordid history
of planet detections that proved to be false,
there was an extraordinary burden
'on the Swiss team to be extra careful.'
Before they could double-check, the star, 51 Pegasus,
disappeared below the horizon.
They had to wait six months to observe it again.
'We had to be sure that this was real,'
and we had to be convinced
that the only explanation was a planet.
The Swiss team had discovered
the first world outside our solar system.
But such a fast orbit
could be observed by another team.
They had to keep their planet secret until they were ready.
We were joking on this secret,
and my son - he was 17 years old at the time -
say, "I know the number,"
because he was measuring with us during the night.
He was clever enough to see
that every night we were measuring the same star,
and we have a long discussion with Didier,
if we have to kill him to keep the secret or not!
Others had been looking
since the early 1980s without success.
In San Francisco, Geoff Marcy was planet hunting.
When the discovery of 51 Pegasus was announced,
he took a closer look at his piles of data,
and realised he had treasures hidden within them.
'We were developing our technique
'for looking for wobbles of stars
'and not actually analysing our data.
'We only found out'
a couple of months later
that among the 107 stars we had been monitoring,
two of them leapt out immediately as having planets,
and in successive months four more stars leapt out.
So by April of '96 we had discovered six planets
around other stars in rapid succession.
Geoff Marcy's team alone have now discovered
12 possible planets.
The pace of discovery is frenetic.
We're discovering about a planet a month.
I expect that to continue,
'and I think in the next few years we'll find
'we've scoured the galactic neighbourhood
'for all of the big planets there are to be found.'
Planet-hunters have now discovered
more planets around stars outside our solar system
than there are around our sun.
But these new-found planets are very different
from anything that was expected.
It was thought impossible
for a giant planet to exist close to its star.
They should only form far out,
in the coldest ice-bound regions of a solar system.
'The image we had of formation of planets'
was very much based on one system, ours.
And so we...thought we had understood the process
by just looking at one system.
Now, here it comes, and they're totally different.
'The 15 we know are not at all like the solar system.
'So we have the 15 on one side,
'and the solar system on the other.
'And now it's the solar system that looks different.'
These must be strange worlds
and some scientists question whether they really are planets.
Some argue that until we have seen them we cannot be sure.
Others remain convinced.
'The chances that this is not a planet'
are so remote that nobody believes it.
It would be incredible.
it would even be more incredible
to have something that mimics the presence of a planet,
than having a planet itself.
The easiest interpretation at this stage
is that if it walks like a duck and quacks like a duck,
what we've found are ducks.
I think that's the best argument that we've found planets.
But how much can be found out
about these other worlds?
With Michel Mayor, Athena Coustenis
is looking at extraordinary new data
from 51 Pegasus.
She has developed a new technique
that identifies the chemical make-up of the planet,
something previously thought impossible to measure.
Three years ago we had no idea
we can access the chemistry of a planet.
Sometimes science is exciting.
The idea we had was to use the star itself
to tell us something
about what the planet is made of.
They cannot see the planet,
but they can see changes in the light from the star.
Interaction between wind from the star
and the planet's atmosphere
create a tail flowing away from the planet,
and if the line of sight
'goes through this tail,
'you have access to the chemistry of the planet.'
By analysing the changing light from the star,
they hope to find out
what the atmosphere of the planet is made of.
If we detect an atmosphere,
it's definite proof
that this is a planet.
But the future of planet hunting lies in space missions.
200 miles above us,
the Hubble Space Telescope is the first witness
to the exotic nature of the cosmos.
Among the thousands of galaxies Hubble has photographed,
there must be a myriad of other planets.
But to see even the planets in our own galaxy,
we need a vast telescope in space.
Probably the most important telescope
for the Origins programme
is a device called the Planetfinder.
This is a large telescope called an interferometer.
'It's really more than one telescope.
'It'll be four or five small telescopes
'that will mimic a very large telescope.'
Telescopes like Planetfinder will let us see
extrasolar planets for the first time,
bringing the unimaginable into sharp focus.
'The Planetfinder will provide us'
not with a picture in the sense we're used to seeing
from satellites in orbit around the Earth.
What we will get is...a dot, in terms of the image,
but the signal from that dot will be the key thing.
But what can a dot of light
tell us about another planet, far away in the universe?
Before the probe Galileo headed for Jupiter
it looked at Earth
to see if life could be detected from space.
'Galileo showed us'
that these molecular signatures
we think are indicative of life were really there,
so it gave us some confidence
that by looking for similar signatures
in atmospheres of other planets,
we could infer that life was there as well.
The signs of life as we know it are universal.
The combinations of chemicals on Earth
could be repeated on any planet in space,
and these chemicals are now identifiable from a distance.
'We'll be looking for things like water,
'carbon dioxide - indicating a substantial atmosphere -
'ozone - which says there's oxygen.
'And all these together tell you something
'about the likelihood that the planet is inhabited
'or maybe habitable.'
If you can find methane, especially with oxygen,
it's a slamdunk, as we say in America in basketball,
that you can conclude that life is on that planet.
In the right place in a solar system,
many now believe the combination of these elements
will almost certainly mean life.
'Hand a biochemist a planet with a rocky surface,
'with a temperature that's not too cold,'
so that water is frozen into ice,
and not so hot that water is evaporated into steam,
but, in the words of Goldilocks, is "just right"
for liquid water.
'It will pool into lakes and rivers and streams and oceans,
'and biochemists are unanimous
'that the laws of chemistry will take over.
'You'll end up with complicated organic molecules
'that we, in fact, would call life.'
But we've yet to find a planet
that falls within this "Goldilocks" zone,
and is rocky and small enough to be suitable for life,
like the Earth.
I would be happy to find an Earth-like planet,
even cold, or far away, or too hot, or anything,
I'd like to see that these exist,
because if I find one, I'd be sure there are others
that might be more suitable for life.
I think the major question is to see one,
then we'll start being picky.
Like Voyager looking back at our family of planets,
telescopes in space may allow us to look at distant worlds.
Earth is very insignificant in a cosmic sense.
Very significant to us.
But in the cosmic sense
it's that pale blue dot in the distance.
And the Origins programme
is about the search for another pale blue dot.
'Some 500 years ago Copernicus, in effect,
'removed the Earth from the centre of the universe.
'We have since shown that the sun is nothing special,
'neither is our galaxy.
'But we only have evidence for one example of life,
'and that's the life on this planet.'
'We are so obsessed'
with finding other lifeforms,
and understanding how life originated.
It's like life needs to seek out itself.
That's manifest in our thinking.
'Almost certainly, any expedition we mount
'to another solar system
'will be to a solar system
'that looks like it's going to be most like our own.'
'It's not beyond the stretch of imagination
'to think of sending a probe, an automated probe.'
Imagine you're sitting at a control room,
50 or 60 years after this probe is launched,
and suddenly this signal comes back,
and you scratch the archives -
and this probe is one we sent to Beta Hydra -
and it's telling us what that place is like.
I think that would be very exciting.
It was curiosity about what lay beyond our atmosphere
that drove us into space.
But the further we venture in our search for new worlds,
the more we are struck by the beauty of our own planet.
Our tiny Earth remains, for us,
the most inspiring body in the universe.