Take a walk on planet Earth.
It's a wonderful place.
But don't take it for granted, because one day it might just vanish - forever.
This is the story of the universe we live in...
..and the dangers we face just by being here.
We'll fly with the comets and asteroids which threaten all life on our planet.
Here on Earth, we'll recreate our sun's headlong plunge around the galaxy
and watch disasters unfold which could spell the end for us all.
Our planet is under threat.
Our mission...
..is to stay alive.
If you're a gambler, this is the planet to live on,
because just by being here, we're all taking a risk.
And the odds are stacked against us.
Do you feel lucky? You should do.
You may not realise it, but we are all winners.
We human beings are lucky to be here,
because the universe keeps trying to wipe us out.
Trying...
..and failing.
We have survived every disaster the universe has ever thrown at us - so far.
But our run of luck won't last forever.
When it ends, our planet and our entire species will cease to exist...
..unless we can do something about it.
Could our whole planet really be in danger?
What could threaten a globe 13,000 km across, or 6 billion people?
To understand the threat, you have to see it first hand.
I want to show you planet Earth as it was in its earliest days.
(WHOOSHING AND CRACKLING)
This is where it all begins.
We're lucky there's even a planet here for us to live on,
because it was very nearly blown apart before life had even begun.
This is planet Earth, billions of years ago, at the very beginning of its life.
As you can see, it is under attack.
These are asteroids, rocks left over from the creation of the planets themselves.
Some of them were vast, and one of them was on a collision course with Earth.
This collision nearly smashed our Earth to pieces.
We were hit by a ball of molten rock the size of Mars travelling at colossal speed.
(EXPLOSION)
The impact ripped huge chunks out of our planet.
Somehow it survived. But what about the future?
Smaller chunks of rock are still flying around our solar system today.
We call them asteroids,
and they could put an end to human civilisation.
Asteroids range in size from pebbles to mountains, or even bigger.
And they're dangerous. They're flying around at incredible speeds.
To get an idea of the damage they can do, just take a trip to the moon.
(MISSION CONTROL) Three, two one, zero. All engines running.
(BROADCAST) Man, a species born and who's lived all his life on Earth,
moves with this journey out into the solar system.
What can you say about a sight like that?
(MISSION CONTROL) You are go to continue power descent.
In 1969, for the first time ever,
human beings walked on the surface of another world...
(BANG, FOLLOWED BY ASTRONAUT'S VOICE)
..the moon.
Tranquillity Base here. The eagle has landed.
(MISSION CONTROL) Roger, Tranquillity, we copy.
And what a world it was - airless, barren, hostile.
And bearing the disturbing evidence of a terrifying threat.
The moon is scarred with craters,
the marks of countless asteroids that have slammed into it.
The moon is under attack.
And travelling through space, alongside the moon, is another planet,
the one we call home.
So why aren't we taking the same pounding?
There's a simple answer to that...
we are.
This crater was formed in a few seconds about 49,000 years ago.
It's almost 1.2 kilometres in diameter. It's almost 200 metres deep.
It was caused by an asteroid about 40 metres in diameter.
It came in with a velocity of about 25 km/second,
and it exploded with the force of a 15-megaton hydrogen bomb.
(EXPLOSIONS)
This is Meteor Crater in Arizona.
Geologist Jeff Wynn thinks that what happened here could happen again, soon.
Local effects would have been devastating.
Anything within the circumference of the crater would have been obliterated.
If you were an animal grazing within a few kilometres, you would have been killed.
If you were beyond that, depending on where the wind was blowing,
the ejector coming down would have killed you.
This is just one example of what could happen if one of these things did hit.
Geologists are discovering more and more evidence of asteroid impacts here on Earth.
Meteor Crater would be hard to miss.
Other impacts are more difficult to spot.
But we have seen them. We've photographed them from space.
These are the remains of titanic collisions, some of them vast, 20 or 30 km across.
The Earth is being pounded all the time.
Siberia, 1908, an entire forest was flattened.
There was an impact in Saudi Arabia in 1933.
(MUFFLED ROAR)
This was caught on camera in Canada in 1972.
A near miss - it flew back out into space. If it had crashed on Earth,
it would have exploded with more force than an atom bomb.
Amazingly, in all these events, no one at all was killed.
But even if an asteroid doesn't hit us, it could do something even more dangerous.
It could hit the sea.
If a big asteroid smashes into the ocean, it could create a huge deadly wave
that could wipe out entire cities.
(WYNN) I think there's a realistic possibility
that something like this could cause serious problems to human civilisation
some time in the next century or two.
It's not an appealing thought, but the threat is real.
Whole cities could be obliterated from space.
Whether it's your city comes down to luck.
But before you feel too lucky, think about this.
It may not matter where you live.
There are things out there which could wipe all life from the face of the planet.
Space contains dangers that make asteroids...
..seem utterly insignificant.
Our telescopes have captured images of truly colossal disasters.
This photograph shows a star a hundred times bigger than our sun
blasting incandescent gas out into space.
And this is a black hole
spewing out jets of super-hot matter at close to the speed of light.
If these had been near us, there's almost no chance that we'd have survived.
It looks as though fortune has been on our side.
At least it has so far.
But for how much longer?
Professor Mike Rampino thinks the odds for long-term survival of life on Earth are slim.
Luck plays a big role in the existence of life on the planet Earth.
You have to realise that the galaxy is a very violent place.
If we get unlucky, that could put an end to complex life on the planet.
Here's the problem.
We don't notice it, but planet Earth is on the move.
While we get on with our lives,
the world is hurtling around our galaxy at 230 kilometres a second.
And high speed means high risk - some you win, some you lose.
We may not realise it, but we're on the ride of our lives.
Think of the Earth's orbit as a kind of cosmic roller-coaster ride.
As we move in this orbit, we're moving past gas clouds.
We can come close to black holes.
We can get close to stars.
We can come close to supernova explosions.
Any of these objects could cause catastrophes on the Earth.
Sound incredible? It's very real.
Life on Earth has been all but eradicated on 20 separate occasions.
And to make matters worse, it's going to happen again.
After all, remember what happened to the dinosaurs.
Flying through space is a dangerous business.
It's not just that we're moving, it's where we're going.
Planet Earth regularly flies through some of the most dangerous areas of the galaxy.
(RAMPINO) If one could speed up time
and watch the orbit of the Earth through the galaxy and around the galaxy,
it would look like a very, very fast carousel -
the sun and the planets moving up and down,
and at the same time moving around the galaxy very rapidly.
We go around the galaxy about once every 250 million years.
But, also, we go through the densest part of the galaxy every 30 million years.
That's the danger zone.
Every 30 million years, planet Earth travels through a region heavily packed with stars.
And it so happens that it's every 30 million years or so
that life on Earth comes close to being wiped out.
Coincidence?
Here is our galaxy, a huge flat pancake of 400,000 million stars, all whirling around.
The brightest areas are where the stars are most tightly packed.
These are the danger zones.
And this star is our sun.
At the moment...
..it's just there, just another pinprick in the cloud of stars that makes up our galaxy.
But take a closer look and see how it's moving.
It doesn't just go round the galaxy. It also goes up and down.
And where the sun goes, the Earth goes.
So, regular as clockwork, we plunge through the danger zone.
And every time we do so, the odds are stacked against us.
Here's how it works.
This is our sun, and each of those other dots is a star.
As our sun bobs up and down through the galaxy,
we're passing them by the million.
And where the stars are densest, the danger is greatest.
The reason those other stars are dangerous
is the powerful effect of their gravity on our solar system.
Fly outwards from the sun, away from the Earth and the other planets,
and eventually you encounter these: chunks of ice, trillions of them,
a vast cloud in space.
If another star comes too close, its gravity disturbs the cloud...
..and catapults ice chunks in towards the sun.
More than 10 km across, travelling at 40 km a second,
it begins its million-year journey into the heart of our solar system.
We know these huge snowballs by another name.
This is a comet.
As it plunges towards the sun, it warms up and belches out a haze of gas and dust.
An immense cloud trails through space behind it...
..the comet's tail.
But this comet doesn't hit the sun. It skims round it and out.
It drifts past Mercury, and the planet's gravity swings it onto a new path.
Finally, it shoots past the moon
and on to a collision course with Earth.
This is what happened to the dinosaurs 65 million years ago.
How much time have WE got?
(RAMPINO) So far we've been lucky. If you look at the history of life on the Earth,
the average lifetime of a species is just a few million years.
Human beings have been around for a few million years.
It doesn't bode well for the future of the existence of human beings on the Earth.
We last passed through the danger zone one million years ago.
But that doesn't mean we're safe yet.
Because a million years is how long it takes for comets to enter our solar system.
And in July 1994, one smashed straight into Jupiter,
drawn in by its immense gravity.
These blurred photographs reveal a colossal explosion.
It covered an area bigger than our entire planet.
If Jupiter hadn't intercepted that comet, if it had hit the Earth instead,
it could have been the end of us.
I told you we were lucky.
It's not just that Jupiter saved us six years ago. It's saved us thousands of times.
It's been doing so since the dawn of our solar system.
Without Jupiter, life on Earth would never even have got started.
Remember all those asteroids in the early solar system?
There were so many of them flying around that life couldn't even get started.
What changed that was Jupiter.
Its powerful gravity sucks in anything that comes too close.
You're watching at a million years per second.
Jupiter made life on Earth possible.
It drew the asteroids' fire and shielded our planet.
It's still catching asteroids today.
But unfortunately for us, the number of asteroids out there is all but limitless.
Sooner or later our luck will run out, just as it did for the dinosaurs.
Jupiter can't catch them all. And one is all it takes.
This one, for example.
The question is, what on earth are we going to do about it?
It seems we have a problem.
This asteroid is huge, 50 km across,
100 billion tonnes of rock surrounded by clouds of dust and debris.
It's travelling at 40 km a second.
And it's heading straight towards Earth.
So what ARE we going to do about it?
The American military are on alert.
The man who runs Earth's asteroid detection system is Sergeant Rob Medrano.
Comets and asteroids represent
the most significant threat that we have from space.
They do impact the Earth routinely, but mostly objects that are very small.
We're concerned about those large objects that penetrate the Earth's atmosphere.
With that in mind, on average we're discovering about four a month.
The asteroid passes Mars. It is now only 45 days from the Earth.
Already time is running out for us all.
Detecting the threat is not enough. The point is to DO something about it.
(WYNN) There are several possibilities.
One is to send a rocket up with a nuclear device and blow it to pieces.
Another possibility is to put chemical rockets on the object
and try to shove it out of the way.
This all requires that we have time to mount a project and do something about it.
There are two possibilities for human beings to survive far into the future.
One is some kind of planetary protection.
The other is insurance - moving off of this planet onto other planets...
..so if there are catastrophes on this individual planet,
it wouldn't wipe out human beings entirely.
The potential exists for an asteroid to impact the Earth
that would essentially wipe out life as we know it.
(MUFFLED ROAR)
(ALARM)
In terms of defending ourselves today,
predicting where the asteroid is going to actually impact, that's really all that we have.
(MUFFLED ROAR)
So far, we have survived.
But what about the future? To safeguard that, we should be acting now.
One day our planet's luck will run out. It's a matter of time.
We must develop the technology to defend ourselves.
Because if we're not prepared, the odds are that one day...
(ROAR)
..one day the human race may cease to exist.