The sun -
brilliant, powerful, giver of life.
But this is the story of how the sun will one day become our enemy.
If we are to survive, we will have to leave the Earth.
We'll need to seek out new homes in amazing new places.
And change other worlds to re-create the Earth we left behind.
In the far future, our sun will become a monster.
It will burn all life from our planet, destroy entire worlds.
And finally, our sun will even destroy itself.
It's going to happen. Our sun will die and we'll go with it.
It's time to think about the future.
For five billion years,
the sun has nourished the Earth.
It is the sun that provides energy for plants to grow.
It is the sun that makes life on Earth possible.
But that will change.
Slowly, unstoppably, our sun is getting hotter and hotter.
Once it gave life to us all.
But what it gave...
..it can also take away.
If human beings are to have a long-term future,
we must leave our planet behind and search for new places to live.
One day, our homes will be out there...
..somewhere in space.
In the distant future, this could be our home.
Out here in space, we'll have to seek refuge
on new worlds where we could settle and live.
And the reason is, we have to escape from our sun.
Some new worlds may be difficult to adapt to.
Others may be very like our own.
But what is it that makes our planet so special?
And why is it so dependent on the sun?
Here is the sun as it is today,
in the centre of our solar system.
The Earth goes round it about there.
And there are the other planets.
The reason our planet is the one with life on it
is that it's the right distance from the sun.
Closer in and we'd boil, further out and we'd freeze.
We live in a kind of safe zone that's perfect for life.
Trouble is, that zone is moving.
The sun is getting hotter
and the region where life can exist is shifting further out.
Ultimately, the safe zone will leave Earth behind.
When it does, we'll be in serious trouble.
Our planet will die.
This is how it will happen.
As the sun burns up its nuclear energy, it'll become ever hotter.
By the time it's 5% hotter, plant life everywhere will be dying.
10% hotter and animals, too, will begin to die.
15% hotter, rivers and oceans will evaporate,
creating huge cloud banks, trapping more and more heat.
In the far future,
life on Earth will become impossible.
And there's nothing we can do about it.
What will happen to us then?
Astronautical engineer Robert Zubrin
believes he has the answer.
He wants to find us a new place to live.
The only real choice that we have
is to grow, expand, become a space-faring civilisation,
or become extinct.
Not only would WE become extinct,
but unless we bring Earth life out with us into the universe,
all life on Earth will become extinct.
Robert Zubrin's goal is to make us a home...on Mars.
Today, Mars is cold and lifeless.
Temperatures regularly drop to 100 below freezing.
Its atmosphere is 200 times thinner than ours.
A person standing unprotected on the surface would die in seconds.
Yet some scientists believe we could learn to call this home.
Mars is the only other planet in our solar system
that has all the resources needed to support life.
It has water, albeit frozen as ice and permafrost.
It's got carbon dioxide and nitrogen in the atmosphere.
If humans go to Mars and develop the craft of using these resources,
then we can make Mars a place where we can sustain ourselves.
A world for our posterity.
No species can expect to last long if it stays in one place.
In a sense, humans aren't native to the Earth.
We're not native to America or Europe.
We're native to Kenya - long arms, no fur.
But humans were able to leave there
and colonise the Earth by becoming creative.
That's how we coped with Ice Age Europe
and it's how we'll cope with Mars.
In a remote part of Canada,
researchers have already been preparing for life on Mars.
Living in a space pod did prove difficult, but they coped.
Zubrin is optimistic.
We're ready to take this on.
Frankly, if we shrink from this challenge, what it will mean
is that we've become much less than the kind of people we once were.
We are much better prepared today to send humans to Mars
than we were to send people to the moon in 1961 at the start of Apollo.
I believe this nation should commit itself
to achieving the goal of landing a man on the moon
and returning him safely to Earth.
(ZUBRIN) We were there eight years later.
Nothing in this is beyond our technology.
It's a question of showing moxie.
For Zubrin, it's not the technology that's lacking. It's the will.
But technology and willpower alone may not be enough.
Just look at what we'd leave behind.
This is our life support system -
the plants that create oxygen, countless species of animal.
How will we fare without them?
Our survival depends on the living things we share our planet with.
The air we breathe, the food we eat -
all this is created by other forms of life.
If Mars is to be our home,
it must be home to all this, too.
15 years ago, we thought we knew the answer.
This is Biosphere Two -
a huge glass dome covering three acres of Arizona Desert
completely sealed off from the planet.
The theory was that people could survive in it
because it was self-sustaining.
Trees would provide oxygen.
Artificial clouds and oceans would regulate the climate.
But the experiment failed. Food rapidly ran short.
Extra air had to be pumped in.
On Mars, that failure would have killed them all.
If we're ever going to call the red planet our home,
clearly something's going to have to change.
And the easiest thing to change may be Mars itself.
It's an idea called terra forming.
The aim is to transform a planet from somewhere we couldn't survive,
to one where we could.
NASA scientist Chris McKay believes we can turn Mars
into something surprisingly like Earth.
When we think about going into space, we focus on humans.
In fact, it's easier for plants and micro organisms to go to Mars first.
They'll be the first Martians.
In Death Valley, California,
McKay is seeking the Earth's hardiest creatures.
Creatures that might survive on Mars.
That's our guy!
These green smears are algae,
microscopic organisms that can thrive
even in the harsh variable climate of Death Valley.
And they could thrive on Mars, too,
sucking in its thin atmosphere of carbon dioxide,
and pumping out oxygen in its place.
Except, at the moment, even the algae would find Mars deadly.
The first step to making Mars habitable
is to warm it up a bit.
Right now, it's too cold and dry for any type of life from Earth.
Warming up a planet is something we know. We're doing it on Earth.
The pollution on Earth would be the medicine on Mars.
It's a strange twist.
The best way to make Mars a place we could live may be to pollute it.
Here's how it would work.
First, a spacecraft has to drop off the pollution-creating machines.
The machines' job is to suck up a mixture of dust and atmosphere
and process it into new chemicals.
It belches out these greenhouse gases to warm the planet
and dark soot to soak up heat from the sun.
If we send enough machines, over time,
Mars will warm enough to allow these algae to survive.
The algae will begin to give Mars an oxygen atmosphere.
But for speed, we'd need more efficient oxygen makers.
And the best that we know are plants and trees.
The real goal is to get trees growing there.
Those trees will be the ones that make a habitable world.
Then things will really start happening.
As the oxygen level rose, insects then larger animals could survive.
We could change Mars.
If I laid out a timescale, I'd say, 50 years humans go to Mars,
and soon thereafter the algae and bacteria go to Mars.
Maybe 30 years later, the trees go to Mars
and then the humans come back,
but this time to a setting biologically suitable for them.
And then we've learned to become a lifeform
that lives on two planets. Not just humans, all life.
It's a bold and astonishing plan.
If it works, we could turn Mars into a planet very like Earth.
But even Mars will not last forever.
Even there, we could never escape the power of the sun.
As the sun keeps getting hotter,
the safe zone for life moves further out.
This is Mars.
Now Earth's dead, this is our home.
Thanks to our terra forming, it looks a lot like Earth,
and thanks to a hotter sun, it's now in a safe zone.
The only trouble is, the sun is still getting hotter.
Eventually, the safe zone will leave Mars behind, too.
With Mars dead, where next?
Once again, human beings will be looking for a new home.
And, once again, we'll have to move further from our brightening sun.
But the planets further out are impossibly hostile worlds.
Gas giants like Jupiter and Saturn
are not places we could ever hope to transform.
If we're going to survive on these alien worlds,
it won't be the planets we'll have to change...
..we may have to change ourselves.
David Brin is a science fiction writer.
He imagines future worlds for a living.
It's a big universe and the Earth is a very specialised environment.
We won't find many Earths out there.
If we want to spread out,
then we're going to have to adapt to the universe.
It's not easy for humans to get accustomed to that idea
because we're used to making the universe adapt to us.
(CHILDREN) Five, four, three, two, one!
As the sun becomes hotter, new worlds will form into life.
This is Europa, one of Jupiter's huge moons.
We know it today as a frozen planet -
airless, with a crust of iron-hard ice.
But in the future, it will be something else entirely.
The ice will have melted. Europa will become an ocean world.
After Mars, perhaps we'll come here and make this our new home.
We could live in cities at the bottom of an alien sea.
But David Brin thinks that, in the end, a life behind glass
may not be the solution.
Now we're thinking of going to other planets.
At first, we'll arrive in spacesuits, live in domes,
bring environments with us.
But we'll want to get out of those domes,
so we'll have to change ourselves to fit into new environments.
Our ancestors evolved for life on Earth.
But Brin thinks our descendants may redesign themselves
for a future on other worlds.
Human beings have been wonderfully inventive
in the last 20 million years.
And yet, other species have not been idle.
Birds developed lungs in which the air flows
from one side to the other so that all the lungs are used.
We only use half our lung capacity.
If we genetically engineered ourselves
so our lungs flowed through,
think of the thin atmospheres we could live in.
Wouldn't it be great to hibernate like a bear?
We'd be able to travel to far planets, possibly even far stars.
And if they live and work in zero gravity,
they'll get tired of pulling around these useless legs,
which are only good occasionally for pushing us against walls.
Why have legs if you're in zero gravity,
when you could have additional arms?
Wouldn't it be more functional
jumping all over the place like gibbons?
Can genetic engineering achieve any of these things? Who knows?
We're just at the beginning of this grand adventure.
But it's an extravagant version of tomorrow
that we should be thinking about.
Wouldn't it be a desirable thing
if we're happy, creative, productive,
part of a great civilisation?
Vive la différence!
We can only guess at the future.
What will our descendants be like? We'll have to wait and see.
And where will they live?
The only certainty is, it cannot possibly be here.
It's not just that the sun will have seared all life from Earth.
It's that the planet itself will no longer exist.
Everything we know will have disappeared.
In the far future, our sun will turn into a monster.
It's going to consume the solar system.
Its first victim is the closest planet - Mercury.
Next, Venus is transformed into a molten fireball...
and, ultimately, boiled away.
And still the sun grows.
It's 160 times its original size, 2,000 times hotter!
And its next victim is the Earth.
Long since seared barren by the sun,
the place we once called home now melts and is engulfed.
Seven billion years from now, the Earth will be gone.
For us today, one question remains.
Is the future of our planet also OUR future?
Can we really survive the death of Planet Earth?
Look at how far we have come.
Compared to the world of 100 years ago,
we're living in a science fiction universe
with skyscrapers 100 storeys tall!
Who can believe, seeing that,
that looking forward 100 years,
there will not be a new civilisation on Mars?
And look back 1,000 years - the world lit only by fire.
Who can say that 1,000 years from now,
there will not be hundreds of new branches of human civilisation
filling worlds, orbiting hundreds of stars
and listening to the galaxy?
Some people think that we are living at the end of history,
but I think we're living at the beginning of time.
We're present at the creation. It's a glorious time to live.
(JOHN MCKAY) For all we know,
we might be the only lifeform in the universe.
If that's true, that really deepens the importance
of spreading life beyond the Earth.
If we're the only spark of life,
we certainly don't want that spark to go out.
Our scientists today are already imagining
strange, far-off tomorrows for our kind.
And, if we do survive, perhaps we will be there
to witness the moment when our sun's transformations finally end.
It was first the giver of life, then the destroyer of worlds...
..and now, it, too, is doomed.
This is the sun at the end of its life.
Layer after layer, it is blowing itself apart.
Huge clouds of star stuff drift into space.
It's a slow process that takes millions of years.
What follows is inevitable - the death of our sun.
It casts off one final layer,
and its spark is extinguished forever.
So, the sun will one day go out.
Will it be significant to our descendants in billions of years?
I don't think so. They will have observed similar phenomena
on innumerable other stars before then.
But, if they did think about it, they'd note with gratitude
that their ancestors did not stay on that one little world
and await their doom,
but spread into the universe and made their life possible.
No one can know our future,
but our sun's future is certain.
There will come a time when we must leave our Earth behind.
Our planet will be gone.
Our home will be in space.