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We live on a world of wonders.
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A place of astonishing
beauty and complexity.
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We have vast oceans
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and incredible weather.
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Giant mountains and
spectacular landscapes.
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If you think
that this is all there is,
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that our planet exists
in magnificent isolation,
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then you're wrong.
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We're part of
a much wider eco-system,
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that extends way
beyond the top of our atmosphere.
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I think we are living through
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the greatest age of discovery
our civilisation has ever known.
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We've voyaged to the farthest
reaches of the solar system,
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photographed strange new worlds,
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stood in unfamiliar landscapes,
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tasted alien air.
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Amongst all these wonders
sits our Earth -
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an oasis of calm amidst the
violence of the solar system.
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And all that separates us
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from what's out there
is a thin, flimsy envelope of gas -
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our atmosphere.
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And it's thanks to this
"thin blue line"
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that we have the air
that we breathe,
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the water that we drink
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and the landscape that surrounds us.
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Atmospheres define all the
planets in the solar system.
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They have the power
to create dynamic worlds
that are alien and chaotic.
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But, remarkably, in the
frozen wastes of the solar system...
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..one atmosphere has created
the most unexpected wonder -
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a moon that looks a lot like home.
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I've come to Cape Town
in South Africa
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to do something that
I have always wanted to do,
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but never thought
I would get the chance.
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I'm about to fly incredibly high,
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to the very edge
of the Earth's atmosphere.
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From here, I am hoping to see
something that only a handful
of people have ever seen -
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the thin blue line,
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the fragile strip of gas
that surrounds our whole planet.
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And this
is what's going to take me there.
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This is an English
Electric Lightning,
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the most beautiful
fighter aircraft ever built.
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This is when England built
the best aircraft in the world.
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The Lightning
is no longer in service,
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but this piece of magnificently
overpowered engineering
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is going to take me
18 kilometres, straight up.
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Actually, I read somewhere that
when you read about the altitude
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of the Lightning, it says
"Altitude: Estimated, 60,000 feet.
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"Ceiling: Classified."
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So I don't know
how high these can go.
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I have heard rumours they can
go to 80,000 feet, which is amazing.
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My journey will take me beyond
almost all the molecules of gas
that make up our atmosphere.
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If you feel you're going to
get sick... Yeah? ..use a bag, OK?
Right. Hopefully not.
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To get there,
I'm going to experience
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what made the Lightning famous -
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a vertical take-off.
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Whoo-hoo!
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'It takes just seconds to
reach nine kilometres up,
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'but I'm still in the thickest
layer of the atmosphere,
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'called the troposphere.
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'But the further I climb,
the thinner the atmosphere becomes.'
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Up at 58,000 feet.
90% of the atmosphere is below me.
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The only people above me
are on the space station.
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So beautiful.
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I'm now at 60,000 feet.
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'18 kilometres up.
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'And the highest I can go.'
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Above me, the sky is a deep,
dark blue.
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'And that is what
I've come to see - '
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our atmosphere.
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That really is the thin blue
line that protects us.
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So...fragile and so tenuous.
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Just a tiny sliver of blue.
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Amazing.
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Between 55 and 60,000 feet,
inverted,
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the curvature of the Earth there.
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5G, vertical ascent.
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That is just a ride!
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It is remarkable to see that.
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You can see
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the...thinness and fragility,
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you can see the atmosphere
going from light blue,
to dark blue, to black.
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It really is astonishing.
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The thin blue line makes the Earth
the wonderfully diverse place it is.
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It acts as a soothing blanket,
that traps the warmth of the sun...
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..yet protects us from the
harshness of its radiation.
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Its movements can be traced
in the gentlest breeze.
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And the most devastating hurricane.
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The oxygen and water
the atmosphere holds
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plays a fundamental role
in the ongoing survival
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of millions of different species
living on the planet.
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In this film, I want to explain
how the laws of physics
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that created our unique atmosphere
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are the same laws that created many
diverse and different atmospheres
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across the solar system.
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When perfectly balanced,
a world as familiar
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and beautiful as the Earth
can evolve beneath the clouds.
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But the slightest changes can
lead to alien and violent worlds.
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There are planets in our solar
system that have been transformed
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into hellish worlds, by nothing more
than the gases in their atmosphere.
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And just as atmospheres
can choke a planet to death,
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they are also powerful enough
to shape their surfaces.
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And there are worlds out there
which are all atmosphere.
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Giant balls of churning gas,
where storms three times
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the size of the Earth
have raged for hundreds of years.
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All atmospheres in the
solar system are unique,
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but the ingredients and forces
that shape them are universal.
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At the heart of each
is the glue which holds
the solar system together,
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a fundamental force of nature -
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gravity.
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Gravity is, by far, the weakest
known force in the universe.
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You can see that
because it's really easy for me
to pick a rock up off the ground,
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even though there's a whole planet,
Earth, pulling the rock down.
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I can just lift it up.
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Incredibly weak,
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but incredibly important,
because it's the only force there is
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to hold an atmosphere to the planet.
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The more massive the planet,
the greater its gravitational force.
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Earth has enough mass to keep a
tight grip of the gas molecules
that make up our atmosphere.
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It holds them against the surface
and allows us to breathe.
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00:11:04,420 --> 00:11:06,820
Now, we don't really
notice the presence
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00:11:06,820 --> 00:11:10,860
of our atmosphere, I suppose,
because we live in it, all the time.
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But there's a lot of it.
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There's five million billion
tons of air surrounding the Earth.
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That's the equivalent
of a weight of one kilogram
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pressing down on every square
centimetre of our bodies.
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Or, put it another way,
if I'm about a metre square,
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that's ten tons of weight
pressing down.
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Now I say pressing down,
but that's not entirely right,
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that's not how air pressure works.
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It presses in every direction
at once. I can demonstrate that.
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This is a glass full of water,
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so if I put a piece of paper
on there, turn it upside down.
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Now, if I'm right,
then the air pressure is pushing
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in every direction on this glass
of water, the air pressure is
pushing up as well as down.
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00:12:02,020 --> 00:12:04,860
And it has no problem in
holding the water in the glass.
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Cool.
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Where did you get this water from?
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CREW LAUGH
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Life on the surface
of this planet survives,
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surrounded by this enormous mass
of gas. We're like lobsters,
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scuttling around
on the ocean floor.
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But our atmosphere does more
than allow us to breathe.
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It protects us
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from the most powerful force
in the solar system...
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..our sun.
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If you ask yourself the question,
"Why is Earth
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"the temperature that it is?"
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Then, the obvious answer
might seem to be,
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"Well, because it's
150m kilometres away from the sun".
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But actually,
things aren't quite that simple.
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This is the Namib desert in Namibia,
in south-western Africa.
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And as the sun sinks below the
horizon, the temperature change,
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from day to night, can be
as much as 30 degrees Celsius.
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That's an immense amount
in just a few hours,
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much more than in somewhere
like Manchester, for example.
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The reason is that this is also one
of the driest places on the planet
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and so there is very little
water vapour in the atmosphere.
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That means that the atmosphere
is not a very good insulator,
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so when the sun disappears, the heat
just disappears quickly into space.
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Now, there's a planet
in the solar system,
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somewhere over there, near the sun,
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where the temperature shift,
from day to night,
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is not a mere 30 degrees Celsius,
but an immense amount bigger.
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Roughly 58 million kilometres from
the sun
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is the smallest planet
in the solar system...
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..Mercury.
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This tortured piece of rock
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suffers the biggest temperature
swings of all the planets,
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from 450 degrees Celsius in the day,
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to minus 180 degrees at night.
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And all because Mercury
has been stripped naked.
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It has virtually
no atmosphere at all.
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Like all the rocky inner planets
of the solar system,
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Mercury had an atmosphere
when it was formed,
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but it lost it very quickly.
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Here on Earth,
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at sea level, then...
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Well, in a volume
about the size of this pebble,
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there are 10 billion
billion molecules of gas.
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On Mercury, in the same volume,
there would be around a 100,000,
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that's 10 million million
times less.
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Now, planets hang on to their
atmosphere by the force of gravity.
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It's the only way they can
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stop that thin blue line of gas
disappearing off into space.
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So, the bigger the planet,
the more massive the planet,
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the stronger the gravitational pull
and the easier it is for the planet
to keep hold of its atmosphere.
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So, Mercury was just too small and
too hot to hang onto its atmosphere
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and the consequences for the planet
were absolutely devastating.
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Atmospheres may be just
a thin strip of molecules,
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but they are a planet's
first line of defence.
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Without them, a planet like Mercury
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is at the mercy
of our violent solar system.
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This is Saskatchewan in
western Canada and it is a
cold place to be in November.
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About a year ago, in November 2008,
a piece of asteroid,
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a space rock,
weighing about ten tons,
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entered the atmosphere
right over here and actually landed
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about 30 kilometres that way,
at a place called Buzzard Coulee.
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Now, it's not unusual for rocks
that big to hit the Earth.
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On average,
that happens about once a month.
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What was unusual about this one
was that it was over quite
a densely-populated area.
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So tens of thousands,
if not hundreds of thousands,
of people saw it and heard it.
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But most spectacularly, it was
captured by a lot of CCTV cameras,
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including that one, in this garage.
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These are the actual CCTV
images captured around the city.
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They show the meteorite,
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as it streaked across the sky
at 20 kilometres per second.
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The fireball was brighter than the
moon and turned the night sky blue.
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Scientists used these
remarkable images
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to triangulate the impact site
of the meteorite.
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They traced it to a field, just
outside the city of Lloydminster.
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A team of meteorite hunters have
been searching the debris
left by the enormous explosion.
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They are led by Dr Alan Hildebrand.
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How much energy
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does a rock like this have, then?
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00:18:24,420 --> 00:18:28,500
You know, what is it,
a ten-ton rock travelling
at 50 times the speed of sound?
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You know, it would be
like if you'd stocked up,
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say, 400 tons of TNT to explode.
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I mean, it's really quite dramatic.
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400 tons that just dissipates away
in the Earth's atmosphere? Yes.
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Atmosphere slowing it down,
of course, causing it to break up.
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In just five seconds,
it's almost all over and, of course,
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you know it's an extreme friction,
makes the light show.
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10% of the energy goes in light
and it's like a billion-watt bulb
shining high in the sky.
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So, what are we looking for?
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What does a piece of
that asteroid look like?
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They... Going through the atmosphere,
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the surface has got melted, so you
end up with a dark crust on them.
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So, essentially, you're looking
for an oddly-sculpted dark rock.
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Yeah. Well, in all fairness, you've
got to be able to tell it from,
you know the cow patties and so on.
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But... I could probably manage that.
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Once you get your eye in,
you'll have no trouble.
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We've got one right here.
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I'll pick that up.
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Astonishing.
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It's just been
completely rounded off.
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Yeah, the heat melted
the surface of the rock.
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I mean, how hot does something
have to be to do that? Yeah.
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6,000 degrees C would do it.
239
00:20:10,340 --> 00:20:14,460
So, this little rock
has had an amazing history.
240
00:20:14,460 --> 00:20:18,620
I mean, it approached Earth
as part of this bigger fragment,
241
00:20:18,620 --> 00:20:23,900
at about, what,
18, 19, 20 kilometres per second.
242
00:20:23,900 --> 00:20:27,260
It hit the Earth's atmosphere.
243
00:20:27,260 --> 00:20:32,500
About 85 kilometres up,
it began to feel the effects
244
00:20:32,500 --> 00:20:34,340
of the Earth's atmosphere.
245
00:20:34,340 --> 00:20:38,940
It began to squash the air in front
of it, creating a pressure wave,
246
00:20:38,940 --> 00:20:43,140
essentially, which, in turn,
causes this thing to heat up.
247
00:20:43,140 --> 00:20:47,660
And it would have heated up to
something like the temperature
of the surface of the sun.
248
00:20:47,660 --> 00:20:52,460
It would have been 5 or 6,000
degrees Celsius as it plummeted
through the atmosphere,
249
00:20:52,460 --> 00:20:57,780
lit up the sky over here
and then, quite literally,
250
00:20:57,780 --> 00:21:03,780
exploded in a series of explosions
and peppered these fields
with lumps of rock this big.
251
00:21:03,780 --> 00:21:08,540
Can you imagine
standing here on that night
and having this, these things -
252
00:21:08,540 --> 00:21:11,460
and this is heavy, right -
253
00:21:11,460 --> 00:21:13,020
raining down from the sky?
254
00:21:13,020 --> 00:21:15,260
It must have been quite incredible.
255
00:21:17,660 --> 00:21:20,340
If the meteorite
had hit the ground intact,
256
00:21:20,340 --> 00:21:26,180
the explosion would have been been
equivalent to 400 tons of TNT
257
00:21:26,180 --> 00:21:28,020
and left a crater 20 metres wide.
258
00:21:31,220 --> 00:21:36,300
The Earth was spared this
colossal impact by nothing more
259
00:21:36,300 --> 00:21:39,340
than the tenuous strip of gases
that surrounds us.
260
00:21:39,340 --> 00:21:43,420
But not all planets have
this protective blanket.
261
00:21:48,620 --> 00:21:51,340
When a meteorite hits naked Mercury,
262
00:21:51,340 --> 00:21:56,580
there is no atmosphere to
break it up or slow it down.
263
00:21:58,780 --> 00:22:03,340
It strikes the ground at full speed
and completely intact.
264
00:22:04,900 --> 00:22:08,100
For the last 4.6 billion years,
265
00:22:08,100 --> 00:22:14,180
Mercury has been bombarded with
countless asteroids and comets.
266
00:22:15,500 --> 00:22:22,580
The whole history
of the planet's violent past
is laid out on its surface,
267
00:22:22,580 --> 00:22:28,100
a world pitted with
hundreds of thousands of craters.
268
00:22:29,060 --> 00:22:33,940
Craters inside craters,
inside craters.
269
00:22:56,380 --> 00:22:58,700
Mercury was damned from the start.
270
00:22:58,700 --> 00:23:01,860
It's simply
too small and too hot
271
00:23:01,860 --> 00:23:05,700
to have retained any
meaningful traces of atmosphere.
272
00:23:05,700 --> 00:23:07,580
We, on the other hand,
273
00:23:07,580 --> 00:23:11,020
are big enough and cold enough
274
00:23:11,020 --> 00:23:14,140
to have retained
this envelope of gases.
275
00:23:17,660 --> 00:23:19,460
That, in turn, allows
276
00:23:19,460 --> 00:23:22,700
living things, like me, to evolve
277
00:23:22,700 --> 00:23:27,220
and to use that atmosphere,
to breathe and to live.
278
00:23:27,220 --> 00:23:30,780
But there are places out there
in the solar system
279
00:23:30,780 --> 00:23:34,820
whose atmospheres have
the same ingredients as our own,
280
00:23:34,820 --> 00:23:39,220
but when the formula
is even slightly remixed,
281
00:23:39,220 --> 00:23:42,900
it leads to worlds
that couldn't be more different.
282
00:23:53,740 --> 00:23:57,100
Roughly 108 million kilometres
from the sun
283
00:23:57,100 --> 00:24:01,980
sits the brightest planet
in the solar system, Venus.
284
00:24:02,900 --> 00:24:05,500
This footage shows the
luminescent world appear
285
00:24:05,500 --> 00:24:08,420
from behind our cratered moon.
286
00:24:11,860 --> 00:24:15,060
Venus and Earth
share many similarities.
287
00:24:15,060 --> 00:24:18,100
We sit next to each other in space,
288
00:24:18,100 --> 00:24:21,100
we were formed from
the same material
289
00:24:21,100 --> 00:24:26,580
and we're roughly the same size and
share a similar mass and gravity.
290
00:24:28,020 --> 00:24:30,820
But that's where
any similarities end.
291
00:24:30,820 --> 00:24:33,900
Venus is a tortured world,
292
00:24:33,900 --> 00:24:39,740
where thick clouds of sulphuric
acid are driven along by high winds
293
00:24:39,740 --> 00:24:43,300
and temperatures are hot enough
to melt lead.
294
00:24:43,300 --> 00:24:49,380
All because this planet's atmosphere
created a runaway greenhouse effect.
295
00:24:52,140 --> 00:24:55,140
The "greenhouse effect"
has become a well-known phrase.
296
00:24:55,140 --> 00:24:58,620
You know, it's synonymous
with global warming.
297
00:24:58,620 --> 00:25:00,700
But what is it?
298
00:25:00,700 --> 00:25:07,060
Well, a planet, like the Earth,
absorbs energy from the sun
as visible light.
299
00:25:07,060 --> 00:25:13,820
Now, atmospheres don't absorb
much visible light, as you can see,
because you can see the sun.
300
00:25:13,820 --> 00:25:19,580
The ground absorbs
the visible light, heats up
and then re-radiates it.
301
00:25:19,580 --> 00:25:24,300
But it re-radiates it
as infrared radiation,
heat radiation, if you want.
302
00:25:24,300 --> 00:25:29,060
And atmospheric gases, particularly
carbon dioxide, are very good
303
00:25:29,060 --> 00:25:34,460
at absorbing in the infrared
and so they trap the heat
and the planet heats up.
304
00:25:39,060 --> 00:25:43,140
On Earth, greenhouse gases
are essential to our survival.
305
00:25:43,140 --> 00:25:47,140
Without them our planet
would be 30 degrees colder,
306
00:25:47,140 --> 00:25:50,900
too cold to support life
as we know it.
307
00:25:57,060 --> 00:26:02,340
But Venus's atmosphere
was flooded with greenhouse gases.
308
00:26:02,340 --> 00:26:06,580
The nearby sun slowly
boiled away its oceans,
309
00:26:06,580 --> 00:26:09,380
pumping water vapour
into the atmosphere.
310
00:26:10,540 --> 00:26:15,020
And carbon dioxide, from
thousands of erupting volcanoes,
311
00:26:15,020 --> 00:26:17,420
added to the stifling mix.
312
00:26:19,140 --> 00:26:22,740
Venus grew hotter and hotter.
313
00:26:22,740 --> 00:26:25,380
The planet was slowly
choked to death.
314
00:26:28,180 --> 00:26:33,100
Venus is a planet with an
atmosphere in overdrive,
315
00:26:33,100 --> 00:26:37,580
but Earth's other rocky neighbour
tells quite a different story.
316
00:27:01,540 --> 00:27:03,300
Get it!
317
00:27:08,300 --> 00:27:11,260
These are the dunes
in the Namib desert.
318
00:27:11,260 --> 00:27:14,740
It's an absolutely
spectacular place.
319
00:27:21,500 --> 00:27:23,060
This place is not the hottest,
320
00:27:23,060 --> 00:27:26,460
nor the driest, desert in the world,
but these dunes
321
00:27:26,460 --> 00:27:29,900
are some of the oldest sand dunes
in the world.
322
00:27:33,420 --> 00:27:35,780
And the reason we're here
in the Namib desert
323
00:27:35,780 --> 00:27:39,060
is that this is a great analogue
324
00:27:39,060 --> 00:27:40,340
for the surface of Mars.
325
00:27:40,340 --> 00:27:44,060
This is what the surface of Mars
looks like and these dunes,
326
00:27:44,060 --> 00:27:46,900
called barchan dunes,
these crescent-shaped dunes,
327
00:27:46,900 --> 00:27:51,100
are the same
as the sand dunes on Mars.
328
00:27:57,300 --> 00:28:01,340
So, if you want to get a
feel for what it would be
like on the surface of Mars,
329
00:28:01,340 --> 00:28:07,420
and you want to know what driving
a 4x4 around on it would be like,
then this is the place to come.
330
00:28:12,980 --> 00:28:18,140
Incredibly, there is a vehicle
driving across the surface
of the "red planet" today...
331
00:28:23,260 --> 00:28:26,300
..a space rover, named Opportunity.
332
00:28:31,580 --> 00:28:35,100
The rovers and spacecraft
that circle the planet
333
00:28:35,100 --> 00:28:39,340
have sent back images which
reveal Mars in exquisite detail.
334
00:28:49,180 --> 00:28:52,700
Mars has vast dunes,
335
00:28:52,700 --> 00:28:57,300
enormous volcanoes
336
00:28:57,300 --> 00:29:00,420
and giant ice sheets.
337
00:29:03,620 --> 00:29:07,420
It has canyons and river valleys.
338
00:29:08,620 --> 00:29:15,900
Mars is a dry, frozen version of our
home, covered in red dust and sand.
339
00:29:15,900 --> 00:29:21,420
And it's all due to the fact that
Mars has virtually no atmosphere.
340
00:29:29,260 --> 00:29:31,460
But there are clues
341
00:29:31,460 --> 00:29:34,220
that things weren't always this way.
342
00:29:35,180 --> 00:29:40,900
These are pictures taken from the
surface of Mars in August 2009.
343
00:29:43,300 --> 00:29:48,860
And they caused quite a bit of
excitement, because of this,
344
00:29:48,860 --> 00:29:53,100
this rock sat on the surface
of Mars in front of the rover.
345
00:29:53,100 --> 00:29:55,540
This rock is about...
346
00:29:55,540 --> 00:29:56,860
Well, here's a close-up.
347
00:29:56,860 --> 00:29:59,300
It's actually
a nickel iron meteorite
348
00:29:59,300 --> 00:30:03,100
and it's about,
what, 60 centimetres across,
349
00:30:03,100 --> 00:30:04,980
weighs half a ton.
350
00:30:04,980 --> 00:30:08,500
It came from space,
351
00:30:08,500 --> 00:30:11,980
came through the Martian atmosphere
and landed on the ground.
352
00:30:11,980 --> 00:30:16,820
But the mystery is that a meteorite
this big, if it hit Mars today,
353
00:30:16,820 --> 00:30:19,180
would disintegrate
when it hit the surface.
354
00:30:19,180 --> 00:30:21,820
It would be travelling too fast
and that's because
355
00:30:21,820 --> 00:30:26,060
Mars's atmosphere is too thin,
too diffuse to slow it down.
356
00:30:27,580 --> 00:30:29,940
But that meteorite
is very definitely there
357
00:30:29,940 --> 00:30:33,500
so how could it
have made it to the ground?
358
00:30:33,500 --> 00:30:37,900
Well, it must be that, in the past,
when this meteorite hit Mars,
359
00:30:37,900 --> 00:30:41,180
Mars' atmosphere
was significantly denser,
360
00:30:41,180 --> 00:30:45,060
dense enough to slow
this piece of rock down enough
361
00:30:45,060 --> 00:30:48,660
that it could land
on the surface intact.
362
00:30:52,340 --> 00:30:58,740
But why did Mars lose its thick
atmosphere and become the
barren planet we see today?
363
00:31:01,260 --> 00:31:06,780
There are so many ways for planets
to lose their atmospheres
364
00:31:06,780 --> 00:31:09,620
that it feels like a miracle
that we've still got ours.
365
00:31:09,620 --> 00:31:11,660
But with Mars,
it's thought that one of
366
00:31:11,660 --> 00:31:14,860
the dominant mechanisms was
interaction with solar winds.
367
00:31:20,140 --> 00:31:25,780
The solar wind
is a stream of super-heated,
electrically-charged particles
368
00:31:25,780 --> 00:31:31,620
that constantly stream
away from the sun at over
one million kilometres per hour.
369
00:31:35,620 --> 00:31:41,300
This wave of smashed atoms
has the power to strip
a planet of its atmosphere.
370
00:31:48,340 --> 00:31:52,940
On Earth, we're protected from this
onslaught by an invisible shield
371
00:31:52,940 --> 00:31:59,100
that completely surrounds our
planet, known as the magnetosphere.
372
00:32:03,900 --> 00:32:09,820
The magnetosphere is created deep
within the Earth's molten iron core.
373
00:32:09,820 --> 00:32:14,180
As the core spins, it generates
a powerful magnetic field
374
00:32:14,180 --> 00:32:18,700
which shoots out of the pole
and cocoons the whole planet.
375
00:32:20,220 --> 00:32:26,540
This magnetic shield is
strong enough to deflect most of
the solar wind that comes our way.
376
00:32:28,820 --> 00:32:32,340
Now, we know that at some
point in the past, Mars
377
00:32:32,340 --> 00:32:36,660
would also have had a molten core
and did have a magnetic field.
378
00:32:36,660 --> 00:32:39,780
But because Mars is a
smaller planet than the Earth,
379
00:32:39,780 --> 00:32:43,980
it lost its heat more quickly
and the core solidified.
380
00:32:43,980 --> 00:32:48,100
Electric currents could no
longer flow and its field vanished.
381
00:32:48,100 --> 00:32:53,340
And that was a major factor
in the solar wind being allowed to
382
00:32:53,340 --> 00:32:57,180
blast the planet and
strip away its atmosphere.
383
00:33:05,300 --> 00:33:10,740
With no atmosphere to insulate it,
this once Earth-like world
384
00:33:10,740 --> 00:33:14,540
transformed into the
frozen desert we see today.
385
00:33:17,100 --> 00:33:19,420
A shadow of its former self.
386
00:33:28,060 --> 00:33:31,300
Although Mars has lost
most of its atmosphere,
387
00:33:31,300 --> 00:33:38,220
those few molecules that remain
still have the power to sculpt
and transform the surface.
388
00:33:38,220 --> 00:33:42,700
And that power,
that transformative effect,
389
00:33:42,700 --> 00:33:46,780
is present on every planet in the
solar system that has an atmosphere.
390
00:33:48,300 --> 00:33:54,900
You can see it transforming the
surface of the Namibian desert
today as we speak.
391
00:33:54,900 --> 00:34:02,060
It is, of course, the force
of nature that we call weather.
392
00:34:07,940 --> 00:34:12,420
We've got to go. Wow!
393
00:34:12,420 --> 00:34:16,100
Weather is a feature of every
planet with an atmosphere.
394
00:34:18,780 --> 00:34:24,460
Our world is transformed
as this huge mass of air
moves across its surface.
395
00:34:27,020 --> 00:34:29,820
But as we look out
into the solar system,
396
00:34:29,820 --> 00:34:35,820
we see it only takes
the slightest atmosphere to
produce extraordinary weather.
397
00:34:38,980 --> 00:34:45,140
Every few years,
Mars all but disappears
under a maelstrom of dust.
398
00:34:48,460 --> 00:34:53,540
Global dust storms are so huge
they dwarf Olympus Mons,
399
00:34:53,540 --> 00:34:56,940
a volcano three times bigger
than Everest.
400
00:35:00,940 --> 00:35:05,500
But to experience
the most extreme and violent
weather in the solar system,
401
00:35:05,500 --> 00:35:08,180
we need to travel to Jupiter.
402
00:35:08,180 --> 00:35:14,300
This banded gas giant is over
140,000 kilometres in diameter.
403
00:35:16,020 --> 00:35:21,460
Its atmosphere isn't
a thin blue line, it's many
thousand of kilometres thick
404
00:35:21,460 --> 00:35:25,820
and in a constant state
of seething motion.
405
00:35:28,300 --> 00:35:32,780
The whole surface boils
with gigantic storms.
406
00:35:35,620 --> 00:35:40,060
Yet, this most alien world shares
a feature with our own planet.
407
00:35:42,180 --> 00:35:44,580
RUMBLING
408
00:35:44,580 --> 00:35:49,460
Jupiter crackles to the sound
of electrical storms.
409
00:35:49,460 --> 00:35:54,820
The bolts of lightning are
thousands of times brighter
than lightning here on Earth.
410
00:36:12,540 --> 00:36:18,180
The physics of storms on Jupiter is,
of course, the same as the physics
of storms on Earth.
411
00:36:18,180 --> 00:36:24,940
The warm moist air deep
in the atmosphere starts to rise,
and as it rises it cools.
412
00:36:24,940 --> 00:36:27,940
And the moisture
condenses out to form clouds.
413
00:36:27,940 --> 00:36:33,100
Now, that rising air leaves a gap
beneath it, a low pressure area,
414
00:36:33,100 --> 00:36:37,940
and so more warm, moist
air is sucked in and that
fuels the rise of the storm.
415
00:36:37,940 --> 00:36:42,980
Now, on Earth, those storm systems
are driven by the power of the sun.
416
00:36:42,980 --> 00:36:47,900
But therein lies a mystery because
the storm systems on Jupiter are
far more powerful
417
00:36:47,900 --> 00:36:52,900
and yet Jupiter is five times
further away from the sun
than the Earth is,
418
00:36:52,900 --> 00:36:57,900
which means it receives
25 times less solar energy.
419
00:36:57,900 --> 00:37:02,980
So, what mechanism could it be that
powers those intensely violent
storms on Jupiter?
420
00:37:08,780 --> 00:37:14,940
The secret to Jupiter's storm-tossed
atmosphere lies hidden deep
within the gas giant.
421
00:37:23,740 --> 00:37:28,900
On Earth, we have clear
boundaries between the gaseous sky,
422
00:37:28,900 --> 00:37:32,660
the liquid oceans
and the solid ground.
423
00:37:32,660 --> 00:37:35,660
But on Jupiter, there
are no such boundaries.
424
00:37:40,380 --> 00:37:45,500
It's a gas giant, made of the two
lightest and most abundant elements
in the universe,
425
00:37:45,500 --> 00:37:47,500
hydrogen and helium.
426
00:37:47,500 --> 00:37:51,260
But as you go deep
into Jupiter's atmosphere,
427
00:37:51,260 --> 00:37:55,700
something very strange and
interesting happens to those gases.
428
00:37:59,300 --> 00:38:03,940
Jupiter's atmosphere is so thick and
its gravitational pull so strong
429
00:38:03,940 --> 00:38:07,820
that 20,000 kilometres
beneath the cloud tops,
430
00:38:07,820 --> 00:38:13,460
the pressure is 2,000,000
times greater than the surface
pressure here on Earth.
431
00:38:15,700 --> 00:38:19,420
Under such immense pressure,
the hydrogen gas in the atmosphere
432
00:38:19,420 --> 00:38:23,700
is transformed
into a strange metallic liquid.
433
00:38:25,700 --> 00:38:30,780
As the gases are squeezed,
a vast amount of energy is released,
434
00:38:30,780 --> 00:38:35,500
enough energy to fuel some of the
biggest storms in the solar system.
435
00:38:39,140 --> 00:38:42,900
The biggest of them all
is the Great Red Spot.
436
00:38:47,220 --> 00:38:52,100
This giant anti-cyclone
has raged for hundreds of years
437
00:38:52,100 --> 00:38:56,260
and is large enough to swallow
the Earth three times over.
438
00:38:58,540 --> 00:39:02,860
The Great Red Spot is an
awesome sight.
439
00:39:02,860 --> 00:39:07,420
But this giant
isn't one of my wonders.
440
00:39:07,420 --> 00:39:10,580
My wonder is a much smaller world.
441
00:39:12,460 --> 00:39:18,620
A moon that orbits the gas giant
Saturn, 1.5 billion kilometres
from Earth.
442
00:39:20,540 --> 00:39:26,500
What we have found on this
small world is simply astonishing.
443
00:39:49,580 --> 00:39:57,100
If you thought of our moon as
the archetypal moon of the solar
system, if you like,
444
00:39:57,100 --> 00:40:02,580
then... Well, you might think that
all the other moons out there,
445
00:40:02,580 --> 00:40:07,660
hundreds of them, would be dead,
uninteresting worlds.
446
00:40:07,660 --> 00:40:10,340
I mean not uninteresting
places to visit.
447
00:40:10,340 --> 00:40:15,780
I mean that is, in my view,
the greatest thing that
humans have ever achieved,
448
00:40:15,780 --> 00:40:23,420
landing on the surface of the moon
but it's a dead and lifeless place.
449
00:40:23,420 --> 00:40:27,540
But as we've begun to visit those
worlds, as we've flown spacecraft
450
00:40:27,540 --> 00:40:34,340
to within hundreds of miles of their
surfaces, we've found that the moons
in the outer solar system
451
00:40:34,340 --> 00:40:42,100
are of an astonishingly interesting
and varied and fascinated
bunch of worlds.
452
00:40:42,100 --> 00:40:45,300
This is Jupiter's moon, Europa.
453
00:40:45,300 --> 00:40:51,020
This is Jupiter's moon, Io, the most
volcanic object in the solar system.
454
00:40:51,020 --> 00:40:57,660
But of all the worlds out there,
this one - Saturn's moon, Titan -
is unique, because of that.
455
00:40:57,660 --> 00:41:01,820
That is an atmosphere,
and what an atmosphere it is!
456
00:41:01,820 --> 00:41:08,340
It's 1,000 kilometres deep,
it's four times denser than
the atmosphere of the Earth.
457
00:41:08,340 --> 00:41:10,460
I mean imagine that,
458
00:41:10,460 --> 00:41:17,180
a moon around a distant planet
in the icy, distant reaches
of the solar system
459
00:41:17,180 --> 00:41:22,460
with an atmosphere
denser and thicker than our own.
460
00:41:29,660 --> 00:41:35,700
Titan has the most
Earth-like atmosphere in
the entire solar system,
461
00:41:35,700 --> 00:41:41,540
a thick blue line, rich in
nitrogen and containing methane.
462
00:41:43,060 --> 00:41:49,420
At first sight, a world this small
shouldn't be able to hold
onto such a dense atmosphere,
463
00:41:49,420 --> 00:41:54,580
except Titan lies in one of the
coldest regions of the solar system,
464
00:41:54,580 --> 00:41:57,620
and that makes all the difference.
465
00:42:03,700 --> 00:42:08,420
Temperature for gases like this,
the gases in our atmosphere,
466
00:42:08,420 --> 00:42:13,380
is really a measure
of how fast the molecules
of the gas are moving around,
467
00:42:13,380 --> 00:42:19,900
and I can demonstrate that with this
thing, which is a Chinese lantern.
468
00:42:22,260 --> 00:42:25,180
If I light this fuel,
469
00:42:25,180 --> 00:42:26,860
then what's going to happen...
470
00:42:28,620 --> 00:42:32,940
is that the gas inside
is going to heat up.
471
00:42:34,740 --> 00:42:38,500
And as you heat up a gas,
472
00:42:38,500 --> 00:42:42,980
what that basically means is that
you speed all the molecules up.
473
00:42:45,220 --> 00:42:49,500
As the molecules of air heat up and
move faster,
474
00:42:49,500 --> 00:42:52,940
the air pressure inside
the lantern begins to increase.
475
00:42:52,940 --> 00:42:59,940
That means that molecules are
forced out, making the air inside
less dense than the air outside,
476
00:42:59,940 --> 00:43:02,660
and the lantern gets lighter.
477
00:43:04,500 --> 00:43:08,900
And eventually the lantern
is so light...
478
00:43:10,420 --> 00:43:16,300
..that it will just float away in
the atmosphere of our planet.
479
00:43:36,980 --> 00:43:43,780
Hot gases have more energy to escape
a planet's gravitational pull
than cold gases.
480
00:43:43,780 --> 00:43:51,380
Now Titan is a much smaller
body than the Earth. It has much
weaker gravitational pull,
481
00:43:51,380 --> 00:43:54,620
and if it were in the same region
of the solar system as we are,
482
00:43:54,620 --> 00:43:57,620
then it would not be able to
hold onto its atmosphere.
483
00:43:57,620 --> 00:44:01,700
But it's a lot further away
from the sun than we are
484
00:44:01,700 --> 00:44:09,020
and so that means that it's colder,
its atmospheric molecules are moving
around much more slowly than ours.
485
00:44:09,020 --> 00:44:16,060
That means that its weak gravity
is enough to hold on to that
thick dense atmosphere.
486
00:44:18,300 --> 00:44:23,100
Titan's thick atmosphere
was an unexpected discovery,
487
00:44:23,100 --> 00:44:25,540
but it took an audacious mission
488
00:44:25,540 --> 00:44:30,180
to reveal the world that lies
beneath the blanket of clouds.
489
00:44:33,420 --> 00:44:38,020
We have lift off of the Cassini
spacecraft on a billion-mile
trek to Saturn.
490
00:44:38,020 --> 00:44:42,500
In 1997,
Cassini began its journey to Titan.
491
00:44:45,860 --> 00:44:53,220
It carried with it the Huygens
probe, a lander designed to
set down on this frozen moon.
492
00:44:58,380 --> 00:45:00,420
On Christmas Day 2004,
493
00:45:00,420 --> 00:45:06,020
Huygens was released from Cassini
and it began the bumpy ride
494
00:45:06,020 --> 00:45:09,980
through one of the most intriguing
atmospheres in the solar system.
495
00:45:13,100 --> 00:45:15,420
And then, for the first time,
496
00:45:15,420 --> 00:45:20,580
the thick clouds parted and
the surface of Titan was revealed.
497
00:45:29,020 --> 00:45:33,020
These are the actual images
taken by Huygens
498
00:45:33,020 --> 00:45:36,620
as it slowly
parachuted to the surface.
499
00:45:41,980 --> 00:45:43,540
The world it revealed
500
00:45:43,540 --> 00:45:47,660
was more familiar than we
could have possibly imagined.
501
00:46:00,900 --> 00:46:02,660
One of the first people to see
502
00:46:02,660 --> 00:46:06,540
these incredible images was a man
who helped design the probe,
503
00:46:06,540 --> 00:46:08,740
Ralph Lorenz.
504
00:46:08,740 --> 00:46:13,020
It was amazing because we
just had no idea what to expect.
505
00:46:13,020 --> 00:46:19,420
We didn't know whether it would be,
you know, cratered like the moon or
just sort of a flat expanse of sand
506
00:46:19,420 --> 00:46:24,020
and then these first pictures
came back and it was just
astonishingly familiar.
507
00:46:24,020 --> 00:46:28,420
Did that picture,
that initial series of pictures...
508
00:46:28,420 --> 00:46:32,020
I suppose it did look somewhat
like this, didn't it? It did.
509
00:46:32,020 --> 00:46:35,820
It could have been there.
It could have been right here.
I do see that.
510
00:46:35,820 --> 00:46:37,300
I could sit here,
511
00:46:37,300 --> 00:46:39,780
look at that and that's what
that picture looks like.
512
00:46:39,780 --> 00:46:41,620
I could take it with a camera.
513
00:46:41,620 --> 00:46:45,780
The camera on the probe was about
the height of your knee, so yeah,
514
00:46:45,780 --> 00:46:48,980
the view the Huygens probe had
is just like this.
515
00:46:48,980 --> 00:46:51,540
Rounded stones dot the landscape.
516
00:46:51,540 --> 00:46:57,660
They're smooth and look like they
have been eroded by tumbling water,
517
00:46:57,660 --> 00:47:01,060
similar to stones found on
river beds, here on Earth.
518
00:47:02,940 --> 00:47:07,020
It sounds to me like this was one of
the easiest pictures to interpret
519
00:47:07,020 --> 00:47:09,260
in the history of space exploration.
520
00:47:09,260 --> 00:47:15,300
You know, the way you tell it, it's
just that's a river bed with these
stones. I mean, is it that simple?
521
00:47:15,300 --> 00:47:17,460
Because you can be misled easily,
with...
522
00:47:17,460 --> 00:47:19,740
The devil is always in the details,
523
00:47:19,740 --> 00:47:22,300
but I think there were
very few people
524
00:47:22,300 --> 00:47:26,020
disputed the interpretation
of a river channel.
525
00:47:26,020 --> 00:47:31,140
I mean it's just such a familiar
thing to so many people on Earth,
there really wasn't much doubt.
526
00:47:33,340 --> 00:47:36,660
It was an extraordinary discovery.
527
00:47:36,660 --> 00:47:41,300
Evidence of flowing rivers had
never been found before on a moon.
528
00:47:42,900 --> 00:47:47,780
But it wasn't the only surprise
Titan held in store.
529
00:48:06,340 --> 00:48:10,020
This is the Matanuska glacier
in Alaska.
530
00:48:12,020 --> 00:48:17,180
It really is one of the most
astonishing places I've ever seen.
531
00:48:19,540 --> 00:48:26,940
And this whole landscape
is testament to the erosive power
of this stuff,
532
00:48:26,940 --> 00:48:31,300
this mixture of ice and rock
533
00:48:31,300 --> 00:48:35,860
as it rolls down this valley over
hundreds of thousands of years
534
00:48:35,860 --> 00:48:38,940
and creates this
astonishing landscape.
535
00:48:48,140 --> 00:48:49,500
But the reason it can do that
536
00:48:49,500 --> 00:48:53,980
is because of the delicate balance
of the Earth's atmosphere.
537
00:48:53,980 --> 00:49:01,580
You see, our planet is just at
the right temperature and pressure
to allow water to exist as solid,
538
00:49:01,580 --> 00:49:06,780
as liquid and as gas,
as vapour in the clouds.
539
00:49:06,780 --> 00:49:13,900
And so the sun can heat up the
oceans and it can move the water
over the top of the mountains.
540
00:49:13,900 --> 00:49:18,980
It can fall as rain, turn to ice,
become a glacier
541
00:49:18,980 --> 00:49:24,620
and then sweep down the valley to
sculpt this astonishing landscape.
542
00:49:35,700 --> 00:49:40,460
Just as our atmosphere
allows all this to exist,
543
00:49:40,460 --> 00:49:47,020
the atmosphere of Titan
is the perfect temperature and
pressure to allow something to exist
544
00:49:47,020 --> 00:49:51,500
that has never been seen before
on a world beyond Earth.
545
00:49:57,580 --> 00:50:01,580
This is a picture taken
of the south pole of Titan
546
00:50:01,580 --> 00:50:03,620
by Cassini in June 2005,
547
00:50:03,620 --> 00:50:10,020
and it's become
one of the most important
and fascinating pictures
548
00:50:10,020 --> 00:50:13,660
in the history of
space exploration.
549
00:50:13,660 --> 00:50:16,820
The interesting thing is
this black blob, here.
550
00:50:18,420 --> 00:50:24,060
Now this fascinated the Cassini
scientists but the explanation
as to what that is
551
00:50:24,060 --> 00:50:28,020
had to wait just over a year
till July 2006,
552
00:50:28,020 --> 00:50:30,220
when this picture was taken,
553
00:50:30,220 --> 00:50:34,540
and it's a radar image, this time
of the north pole of Titan,
554
00:50:34,540 --> 00:50:39,260
and you see, again,
these huge black areas.
555
00:50:39,260 --> 00:50:45,580
The black in this case means
that the radar waves that
bounced onto them didn't come back
556
00:50:45,580 --> 00:50:50,700
so they're completely black,
and there's only one
really good explanation for that.
557
00:50:50,700 --> 00:50:55,620
That is that they are incredibly
flat surfaces.
558
00:50:55,620 --> 00:50:59,420
In fact, they're surfaces of liquid
559
00:50:59,420 --> 00:51:03,620
so this picture combined
with this picture
560
00:51:03,620 --> 00:51:09,780
means that this is the first
observation of a liquid,
561
00:51:09,780 --> 00:51:15,580
a lake on the surface of a body
other than the Earth
in the solar system.
562
00:51:20,260 --> 00:51:25,180
But these lakes, of course, cannot
be lakes of liquid water because
563
00:51:25,180 --> 00:51:30,140
the surface temperature on Titan
is minus 180 degrees Celsius and,
at those temperatures,
564
00:51:30,140 --> 00:51:35,740
water is frozen as hard as steel.
565
00:51:35,740 --> 00:51:40,540
So if these are not lakes of water,
then what are they?
566
00:52:04,340 --> 00:52:10,260
This is Lake Eyak in Alaska,
just on Prince William Sound,
567
00:52:10,260 --> 00:52:16,860
and I've come here to collect
a molecule or a substance that's
very abundant on Titan.
568
00:52:16,860 --> 00:52:21,100
In fact, it's abundant throughout
the solar system, but here on Earth
569
00:52:21,100 --> 00:52:25,820
it exists as a gas and it bubbles up
from the floor of this lake.
570
00:52:38,540 --> 00:52:46,060
The floor of Lake Eyak is covered in
rotting vegetation, you know, dead
leaves and bits of trees, twigs,
571
00:52:46,060 --> 00:52:49,260
and that's been broken down by
bacteria which produce the gas
572
00:52:49,260 --> 00:52:52,020
that bubbles up
from the floor of the lake.
573
00:52:52,020 --> 00:52:56,540
That gas is methane and we've
been collecting it all night
574
00:52:56,540 --> 00:52:59,060
underneath this upturned boat
575
00:52:59,060 --> 00:53:02,500
so that I can take a sample of it in
this bag.
576
00:53:05,220 --> 00:53:10,420
Now, on Earth,
methane is very unstable.
577
00:53:10,420 --> 00:53:12,260
If you give it...
578
00:53:12,260 --> 00:53:15,140
a little kick...
579
00:53:15,140 --> 00:53:20,100
in the presence of oxygen,
then you get what chemists
call an exothermic reaction.
580
00:53:20,100 --> 00:53:25,780
Methane plus oxygen goes to water
plus carbon dioxide, and...
581
00:53:25,780 --> 00:53:27,300
some energy.
582
00:53:29,340 --> 00:53:32,460
The Earth's temperature
and atmospheric pressure
583
00:53:32,460 --> 00:53:36,500
means methane can only exist
as a highly-flammable gas.
584
00:53:40,460 --> 00:53:43,980
But Titan's atmospheric pressure
and temperature
585
00:53:43,980 --> 00:53:50,140
is perfect to allow methane
to exist as a solid,
a gas and, most importantly,
586
00:53:50,140 --> 00:53:52,140
a liquid.
587
00:53:55,580 --> 00:54:01,580
So the images Cassini captured were
gigantic lakes of liquid methane...
588
00:54:04,260 --> 00:54:07,140
..the first ever liquid discovered
589
00:54:07,140 --> 00:54:12,140
pooling on the surface of another
world in the solar system.
590
00:54:12,140 --> 00:54:15,140
This is Kraken Mare.
591
00:54:15,140 --> 00:54:18,460
At over 400,000 square kilometres,
592
00:54:18,460 --> 00:54:22,460
it's the biggest
body of liquid on Titan.
593
00:54:24,260 --> 00:54:28,220
It's almost five times
the size of Lake Superior,
594
00:54:28,220 --> 00:54:30,900
North America's greatest lake.
595
00:54:46,620 --> 00:54:54,220
On Titan,
methane plays exactly the same role
that water does here on Earth.
596
00:54:56,740 --> 00:55:01,020
So, where we have clouds of water,
597
00:55:01,020 --> 00:55:05,700
Titan has clouds of methane
with methane rain.
598
00:55:05,700 --> 00:55:13,340
Whereas we have
lakes and oceans of water,
Titan has lakes of liquid methane.
599
00:55:13,340 --> 00:55:19,540
And whereas, here on Earth,
the sun warms the water
in the lakes and oceans,
600
00:55:19,540 --> 00:55:22,740
and fills our atmosphere
with water vapour,
601
00:55:22,740 --> 00:55:25,340
on Titan the sun lifts the methane
602
00:55:25,340 --> 00:55:30,300
from the lakes and saturates
the atmosphere with methane.
603
00:55:30,300 --> 00:55:37,180
So, whereas on Earth we have a
hydrological cycle, on Titan
there's a methanological cycle.
604
00:55:39,340 --> 00:55:43,700
And rain would be an
absolutely magical sight on Titan.
605
00:55:43,700 --> 00:55:48,980
Because the atmosphere is so dense
and the gravity of the moon
is so weak,
606
00:55:48,980 --> 00:55:54,220
the drops of methane rain would
grow to over a centimetre in size
607
00:55:54,220 --> 00:56:01,620
and they would fall to the ground
as slowly as snowflakes fall
onto the surface of our own planet.
608
00:56:03,580 --> 00:56:09,020
Thousands and thousands
of gallons of liquid methane
609
00:56:09,020 --> 00:56:12,620
must have slowly rained down
onto the surface,
610
00:56:12,620 --> 00:56:17,300
making rivers and streams
swell and burst.
611
00:56:17,300 --> 00:56:21,780
Deep gullies were cut
into the frozen water landscape...
612
00:56:21,780 --> 00:56:25,260
Which looks so familiar
because it is familiar.
613
00:56:25,260 --> 00:56:33,260
It's this. You know, the atmosphere
of Titan shapes the surface
in exactly the same way
614
00:56:33,260 --> 00:56:38,540
that the atmosphere here on Earth
shapes the surface of our planet.
615
00:56:49,660 --> 00:56:55,780
Titan is like a primordial Earth
caught in a deep freeze.
616
00:56:55,780 --> 00:57:00,180
It's almost like looking back in
time over four billion years
617
00:57:00,180 --> 00:57:06,260
and observing our planet
before life began,
and began to modify our atmosphere,
618
00:57:06,260 --> 00:57:10,980
to change it into the oxygen-rich
atmosphere that we see today.
619
00:57:14,900 --> 00:57:19,780
In many ways,
Titan looks so familiar.
620
00:57:19,780 --> 00:57:25,580
It's a place with rivers
and lakes and clouds and rain.
621
00:57:25,580 --> 00:57:30,100
It's a place with water, albeit
frozen as hard as steel,
622
00:57:30,100 --> 00:57:37,260
and a place of methane, albeit so
cold that methane is now a liquid
623
00:57:37,260 --> 00:57:42,860
and flows and shapes the landscape
just like water does here on Earth.
624
00:57:47,220 --> 00:57:51,340
For me, the most
important thing about Titan
625
00:57:51,340 --> 00:57:55,420
is we now have two Earth-like
worlds in our solar system
626
00:57:58,820 --> 00:58:04,820
One in this warm region,
93 million miles away from the sun,
627
00:58:04,820 --> 00:58:10,020
and the other in deep freeze,
a billion miles away from our star
628
00:58:10,020 --> 00:58:16,060
in orbit around another planet,
and that must greatly increase
the probability
629
00:58:16,060 --> 00:58:19,260
that there are other
Earth-like planets in orbit
630
00:58:19,260 --> 00:58:25,900
around the hundreds of billions of
stars out there in the universe.
631
00:58:33,420 --> 00:58:40,140
# Somewhere over the rainbow
632
00:58:40,140 --> 00:58:47,100
# Skies are blue
633
00:58:47,100 --> 00:58:55,100
# And the dreams
that you dare to dream
634
00:58:55,100 --> 00:58:58,220
# Really do come true. #
635
00:58:58,220 --> 00:59:00,460
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