I've come to Cape Town in South Africa
to do something that I have always wanted to do
but I never thought I'd get the chance.
I'm about to fly incredibly high,
to the very edge of the Earth's atmosphere.
From here, I'm hoping to see something that only a handful of people
have ever seen.
The thin blue line,
the fragile strip of gas that surrounds our whole planet.
And this is what's going to take me there.
So this is an English Electric Lightning,
the most beautiful fighter aircraft ever built.
This is when…
when England built the best aircraft in the world.
The Lightning is no longer in service.
But this piece of magnificently overpowered engineering
is going to take me 18 kilometres straight up.
Actually, I read somewhere that the…
when you read about the altitude of the Lightning,
it says altitude estimated 60,000 feet,
ceiling classified.
So don't know how high these can go.
I've heard rumours they can go to 80,000 feet,
which is amazing.
My journey will take me beyond
almost all the molecules of gas that make up our atmosphere.
- If you feel you're going to get sick… - Yeah.
- ..use a bag, OK? - Right.
Hopefully not.
To get there, I'm going to experience what made the Lightning famous.
Vertical takeoff.
It takes just seconds to reach nine kilometres up,
but I'm still in the thickest layer of the atmosphere, called the troposphere.
But the further I climb, the thinner the atmosphere becomes.
Up at 58,000 feet,
90% of the atmosphere is below me.
The only people above me are on the space station.
So beautiful.
I'm now at 60,000 feet, 18 kilometres up
and the highest I can go.
Above me, the sky is a deep, dark blue.
And that is what I've come to see:
our atmosphere.
Really is the thin blue line that protects us.
So fragile and so tenuous.
Just a tiny sliver of blue.
Amazing.
The Mars rovers have really captured our imaginations.
I suppose, because they genuinely are explorers in the old-fashioned sense.
You know, they're the extension of our senses to the surface of another world.
But they've also been very important scientifically, because
you can't really get to know another planet from orbit.
You've got to get down on to the surface,
you've got to touch it,
you've got to dig down and examine it microscopically.
And the rovers really have,
by doing that, made some extremely important scientific discoveries.
One of the most significant of those discoveries was made in November 2004.
The Opportunity rover was examining an impact feature called the Endurance crater
when it detected deposits of a remarkable mineral.
This is the world's largest salt works, on the Baja peninsula in Mexico.
And what they do here is just pump seawater
into these lagoons and let it evaporate.
Now what they're after is this stuff, which is sodium chloride, table salt.
But at different stages different salts, different minerals, crystallise out.
So all the things really that are in seawater emerge, crystallise out,
at different stages of the process.
In one of the lagoons, Pond Number Nine,
the seawater is at exactly the right concentration
to precipitate out these beautiful crystals
that cover the entire floor of the lagoon.
This is gypsum.
And it's exactly the same stuff that Opportunity found on the surface of Mars.
Now, what's interesting about that discovery is how you make gypsum.
You see, its chemical formula
is CaSO4 –
so it's calcium sulphate –
dihydrate, 2H2O – that's water.
So the only way we know of,
the only way to make gypsum here on Earth,
is to have calcium and sulphate ions in the presence of liquid water.
So large deposits of gypsum on the surface of Mars tells you
that there must have been big areas of water present
for a very long time.
The discovery of gypsum
has helped build a picture of an ancient Mars
that was much warmer and wetter.
Subsequent discoveries of gypsum in networks of sand dunes
suggest that large areas of Mars were once covered in standing water.
And where there is standing water,
there is the chance of life.
This is the Matanuska glacier in Alaska.
It really is one of the most astonishing places I've ever seen.
And this whole landscape is testament to the erosive power of this stuff,
this mixture of ice and rock, as it rolls down this valley over
hundreds of thousands of years and creates this astonishing landscape.
But the reason it can do that is because of the delicate
balance of the Earth's atmosphere.
See, our planet is just at the right temperature and pressure
to allow water to exist as solid, as liquid
and as gas, as vapour in the clouds.
And so the sun can
heat up the oceans and it can move the water
over the top of the mountains.
It can fall as rain, turn to ice,
become a glacier and then sweep down the valley to sculpt this
astonishing landscape.
Just as our atmosphere allows all this to exist,
the atmosphere of Titan is the perfect temperature and pressure
to allow something to exist that has never been seen before
on a world beyond Earth.
This is a picture taken of the south pole of Titan by Cassini in June 2005,
and it's subsequently become one of the most important
and fascinating pictures in the history of space exploration.
The interesting thing is this black blob here.
Now, this fascinated the Cassini scientists,
but the explanation as to what that is had to wait just over a year,
until July 2006, when this picture was taken.
And it's a radar image, this time of the north pole of Titan.
And you see, again, these huge black areas.
Black in this case means that
the radar waves that bounced on to them didn't come back.
So they're completely black.
And there's only one really good explanation for that.
That is that they're incredibly flat surfaces.
In fact, they're surfaces of liquid.
So this picture combined with this picture,
means that this is the first observation of a liquid,
a lake, on the surface of a body other than the Earth
in the solar system.
But these lakes, of course, cannot be lakes of liquid water
because the surface temperature on Titan is -180 degrees Celsius.
And at those temperatures, water
is frozen as hard as steel.
So if these are not lakes of water,
then what are they?
Well, this is the Cueva de Villa Luz in Tabasco, Mexico –
the Cave of the House of Light.
And it is the definition of a hostile environment to me,
because it's full of hydrogen sulphide gas,
hence the gas monitor, which says at the moment
one part per million hydrogen sulphide.
Very toxic for me,
which is why I've got this gas mask in case it all gets too much.
So it's a place where you,
at first sight, would not expect
a great many life forms to survive and flourish.
Although the cave is a death trap for us,
that doesn't mean that nothing lives here.
In fact, it's teeming with life.
But look at these fish, just everywhere in the cave water.
And they're adapted to live in these conditions.
In fact, if you look at them closely, they're quite pink.
And that's thought to be because they've got lots of haemoglobin
because there's not that much oxygen down there
and so they need to have an efficient way of moving oxygen
around their bodies. Beautiful.
But the really interesting life
is found in the depths of the caves,
where the concentration of poisonous gas
is high enough to set off my alarm.
Down here, far from the light of the sun,
are organisms whose energy source comes from the air around them.
They use the hydrogen sulphide gas
bubbling up through these springs.
The same gas that could be fatally poisonous to me
is their source of life.
Well, these things are what I came deep underground to see.
These are snottites
and you can see why they're called that.
They're really one of the most alien
life forms that I can conceive of on the…
on the Earth, because they metabolise hydrogen sulphide.
So they metabolise this faintly acidic
and nasty gas that I'm just breathing in now.
You can almost feel it on your tongue, actually, the acidity of it.
They metabolise it, they react it with oxygen,
and they produce sulphuric acid.
So their breathing process, if you like,
their version of what I do,
I breathe in oxygen, react that with sugars and produce… breathe out CO2 and get energy,
these guys breathe in hydrogen sulphide and oxygen and produce sulphuric acid.
In fact, I can test it here with this.
Yeah, you see, look at that.
That-that… Well, what looks like water, that secretion dripping off the snottites,
has actually got a pH of… well, it's now about between point-five and zero.
I mean, that's strong acid. That's as strong as battery acid.
It's actually highly concentrated sulphuric acid.
So what a strange organism.
It's alien in every sense of the word,
except that it's present on the…
well, just below the surface of our planet.