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Lift off of Messenger
on Nasa's mission to Mercury.
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The Void by Muse
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♪ They'll say no-one can see us
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♪ That we're estranged and all alone
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♪ They believe nothing can reach us
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♪ And pull us out of
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♪ The boundless gloom
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♪ They're wrong
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♪ They're wrong
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♪ They're wrong. ♪
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Beyond the warm worlds
of the inner Solar System...
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beyond the gas giant Jupiter...
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00:01:21,280 --> 00:01:24,240
in the freezing regions
far beyond the Sun...
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lies Saturn...
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a planet made unique, thanks to
a nearly 300,000km-wide ring
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of frozen water.
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Here, trillions of pieces of ice
have been sculpted by gravitational
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forces into some of the
Solar System's most stunning vistas.
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Here on Earth, water takes
many forms - oceans and clouds
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and rivers, but it's
in its crystalline form, ice,
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that it's at its most beautiful.
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Here, ice just adorns the landscape,
but in the Outer Solar System,
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where Saturn lives,
ice is so abundant that, well,
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it's become a building material.
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Now, there's no more beautiful
sight in the Solar System than
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the ice rings of Saturn.
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It's almost as if a god had taken
snowflakes and sprinkled them
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over a gravitational field,
so we could see it, but how could
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something so intricate be sculpted
out of something so simple?
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Well, as is always
the case in science,
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the true beauty lies in the story.
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Saturn is a planet that has
undergone some of the most
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radical transformations
in the Solar System.
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A planet that has
seen destruction...
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and creation.
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A planet that harbours
hidden worlds...
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where, just perhaps,
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there may exist a second home
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for life.
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Imagine a place with
no surface to stand.
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Just an endless atmosphere.
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00:05:01,320 --> 00:05:04,480
Compared to Earth,
Saturn is so alien
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that it's hard to imagine
how it could have grown
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from the same ingredients.
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But go far enough back in time
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and Saturn would appear to be
surprisingly familiar.
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Saturn began life as tiny
worlds of rock and ice...
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tumbling chaotically
through space.
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Just like Earth, Mars,
Venus and Mercury,
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they began to merge
and clump together and grow.
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But unlike the planets of the
inner Solar System, Saturn was
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forming on the other side of a
boundary we call the Snow Line...
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a place where the Sun is so
distant and it's so cold,
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water exists only in its frozen,
solid state.
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Out here, trillions of particles
of ice behave just like rock,
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providing huge amounts of extra
planetary building material.
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Under the force of gravity,
this abundant ice and rock collided
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and combined...
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helping the young Saturn
to grow into a giant.
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00:07:18,760 --> 00:07:21,960
The details of how the planets
formed in the Solar System is
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not fully understood. It's
cutting-edge scientific research.
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We're talking about events that
happened over 4.5 billion years ago,
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but it seems likely that Saturn was
once a world of rock and ice,
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perhaps ten or even 20 times the
mass of the Earth and it's almost
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possible, in your dreams,
to imagine standing on its surface.
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But because of its immense mass
and its place
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in the Solar System, Saturn didn't
remain a rocky, icy world for long.
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As it grew older, Saturn became a
radically different kind of planet.
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In the region in which the young
world was forming, there was
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more than just ice and rock -
there were large amounts of gas.
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00:08:20,200 --> 00:08:22,560
And Saturn began to gain
an atmosphere...
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but on a scale unlike anything
we experience here on Earth.
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00:08:37,120 --> 00:08:40,760
It's not until you see the Earth's
atmosphere from space that
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you appreciate
just how thin it really is.
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00:08:54,520 --> 00:08:56,920
And it's a similar
story for the other
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worlds of the inner Solar System.
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Despite being relatively thin,
these atmospheres can exert
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powerful forces on the planetary
surfaces beneath.
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On Earth, you can see the effects
of an atmosphere with nothing
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more than a sealed container.
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It's easy to forget that the
atmosphere has a weight.
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There's a column of air stretching
up 100km above my head.
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That's a lot of molecules
and it exerts a pressure.
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You really see it if you
look at what happens to this bottle.
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We've filled it with air from
the top of the mountain, which is
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about 3,000 metres.
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00:10:08,200 --> 00:10:12,000
Now, up there, the atmosphere
is about 25% less dense
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than it is down there at sea level.
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So, as we descend, the atmospheric
pressure outside is increasing
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and the pressure in
here is just what it
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was at the top of the mountain
and so, you see visually that
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force in action
and that is squashing the bottle.
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Physics in action!
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It's brilliant, isn't it?
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While just a few hundred metres
of atmosphere can crush a bottle...
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if an atmosphere gets big enough,
it can transform an entire planet.
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Within just a few million
years of its birth...
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Saturn had grown as large as it
could, from rock and ice alone.
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00:11:12,280 --> 00:11:15,360
And now, it turned to another
building material -
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the hydrogen and helium gas left
over from the formation of the Sun.
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This gas would have been
too light for the smaller
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worlds of the inner Solar System
to hold on to.
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But Saturn's great mass created
gravitational forces powerful
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enough to draw it in.
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Trillions upon
trillions of tonnes of hydrogen
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and helium gas began to
envelope the planet.
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And as this new atmosphere grew,
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it transformed the surface below.
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Enormous pressures, created by the
weight of this gas, heated rock
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and ice so much, they began to glow.
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As Saturn matured, the pressure
at the surface rose
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to ten million times the
atmospheric pressure on Earth.
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Under those kind of pressures,
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matter behaves in extremely
strange ways.
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The very idea of a surface becomes
meaningless and Saturn was
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transformed from an icy,
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rocky world into a completely
different class of planet -
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a gas giant.
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Saturn was now so big,
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it could contain
nearly 5,000 Earth-size worlds.
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00:13:00,880 --> 00:13:06,000
But this vast, wild protoplanet
was totally unlike the Saturn
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we see today.
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To discover how that world emerged,
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we had to send spacecraft
to meet it close up.
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We have ignition and we have liftoff
of the Titan Centaur carrying
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the first of two Voyager spacecraft
to extend Man's senses
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farther into the Solar System
than ever before.
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00:13:54,760 --> 00:13:58,120
Reports coming back indicate those
twin large solid motors are
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functioning perfectly, producing
1.2 million pounds of thrust each.
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The guidance data coming back shows
that we're right on the money.
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It's there!
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Voyager 2 has reached Saturn
after four years in space.
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It got there just a bit early,
2.7 seconds early, to be exact,
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after a flight of a billion
and a quarter miles.
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00:14:54,320 --> 00:14:58,920
The Voyager probes gave us
our first detailed look at Saturn,
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revealing the planet
in exquisite resolution.
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00:15:07,240 --> 00:15:10,080
There's just an amazing
harvest of pictures.
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00:15:10,120 --> 00:15:13,360
You know, there's tens of thousands
of photographs of Saturn
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and its rings and its moons
taken by the Voyager 2 spacecraft.
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For the very first time,
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we were able to study Saturn's
vast atmosphere in detail.
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Saturn itself is
composed of hydrogen and helium.
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And we are seeing an exotic
meteorology here.
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Voyager showed, beyond doubt,
that Saturn's upper atmosphere was
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made almost entirely of helium
and hydrogen...
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the very same gases so abundant
in the early Solar System.
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But this once chaotic gas
was now organised
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into intricate weather systems.
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And one, above all others,
took the Voyager team by surprise.
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A huge hexagonal
structure in the clouds,
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so big it could fit our
entire planet within it,
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nearly four times over.
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The atmosphere of Saturn was
revealing itself to be stranger
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and more dynamic than
we could ever have imagined.
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Atmospheres are some
of the most spectacular
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and complex planetary environments.
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Not many people see the Alps
like this! Seriously! It's so great!
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I was afraid that you'd just get too
sick or something. It's awesome!
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Man! It's fun, man!
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This IS fun!
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The atmosphere of every planet
takes on its own unique character.
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But what powers them
and the weather systems within
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depends on where
you are in the Solar System.
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Most of the weather on the Earth
is driven by the Sun.
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It heats the ground up down there
and that, in turn,
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heats the air up close to the
ground, makes it expand,
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and that means that the air becomes
less dense and the hot air rises.
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That means you get thermals,
so energetic
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movements of air from the ground
into the upper atmosphere.
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And that's what we're
exploiting now, to glide.
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All this beautiful weather is
driven by the Sun heating the land
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and causing air to move around.
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So we're sailing around...
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Sailing around in a turbulent,
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moving ocean of air.
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But travel further
out into the Solar System
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and the driving forces within
an atmosphere must change.
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Now, there's been weather on Saturn
for over four billion years,
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but Saturn is a long
way from the Sun, and so
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those weather systems are not
primarily driven by the Sun's heat.
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And yet the storms on Saturn
are amongst the most violent
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found anywhere in the Solar System.
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With sunlight almost 100 times
weaker on Saturn than it is
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here on Earth...
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it means something else is helping
drive its weather...
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and the huge, complex forms that
arise in its atmosphere.
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By studying the cloud tops of Saturn
and its great storm systems,
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we can now infer a great deal about
the strange world that lies beneath.
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And the energy source that helps
power this planet.
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Below the upper atmosphere,
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great clouds of water grow.
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Lightning 10,000 times more powerful
than on Earth illuminates the sky.
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This lightning transforms methane
gas into huge clouds of soot.
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Deeper still,
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the pressures grow
so great that these
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chunks of soot are likely
transformed into diamonds.
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00:21:35,760 --> 00:21:39,400
But even these diamonds will
succumb to the pressures of Saturn,
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eventually liquefying.
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It's not until 40,000km down
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that the major source of Saturn's
energy is revealed.
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00:22:05,600 --> 00:22:09,480
Here, pressures are so intense,
gases behave like liquid metal.
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00:22:09,520 --> 00:22:14,880
Molten helium falls
like rain through hydrogen...
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00:22:16,360 --> 00:22:19,160
and releases incredible
amounts of heat.
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And we think that this is
the extraordinary heat source
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that has been helping to drive
Saturn's weather.
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00:22:56,040 --> 00:22:59,680
Within just a few hundred million
years of its birth,
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Saturn had lived a life of drama.
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00:23:03,400 --> 00:23:07,380
Now, it remained largely
unchanged for billions of years,
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although still very different
from the planet we know today.
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But in time, this great size
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would lead to one more iconic
transformation.
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Saturn is a planet
defined by its rings.
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00:23:37,300 --> 00:23:40,320
You get a child to draw a planet
and quite
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a lot of the time, they'll draw
something that looks like Saturn.
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00:23:43,640 --> 00:23:47,960
Close up, they are almost impossibly
delicate and intricate.
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00:23:48,000 --> 00:23:52,280
They're made up of trillions of ice
crystals, most of them
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00:23:52,320 --> 00:23:56,320
no bigger than snowflakes,
but some of them as large as houses.
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00:23:56,360 --> 00:23:58,560
Now,
if you look through a telescope,
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00:23:58,600 --> 00:24:00,000
they're highly reflective.
220
00:24:00,040 --> 00:24:04,880
They reflect sunlight back just
as powerfully as the planet itself.
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00:24:04,920 --> 00:24:07,800
But that raises
an interesting question,
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00:24:07,840 --> 00:24:10,720
because the Solar System
is full of dust.
223
00:24:10,760 --> 00:24:13,080
Any ice crystals that hang around
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00:24:13,120 --> 00:24:15,800
for any amount of time
will get dirty,
225
00:24:15,840 --> 00:24:20,380
and so they won't reflect sunlight
back, they won't be as bright.
226
00:24:20,420 --> 00:24:24,960
So, the question is, why then
are Saturn's rings so reflective?
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00:24:29,560 --> 00:24:33,080
The answer came from one
of the most audacious
228
00:24:33,120 --> 00:24:36,600
and successful missions
to the Outer Solar System.
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00:24:36,640 --> 00:24:43,000
Five, four, three, two, one, and
liftoff of the Cassini spacecraft
230
00:24:43,040 --> 00:24:45,920
on a billion-mile trek to Saturn.
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00:24:48,480 --> 00:24:52,720
We have cleared the tower. T plus
20 seconds. All systems are go.
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00:24:52,760 --> 00:24:56,480
The Cassini probe was designed
to study Saturn and its moons
233
00:24:56,520 --> 00:24:59,760
and rings up close,
to shed new light on their origins.
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00:25:00,880 --> 00:25:03,480
All systems continuing to be go.
235
00:25:03,520 --> 00:25:06,760
But whereas the Voyager probes
spent only days at Saturn,
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00:25:06,800 --> 00:25:11,480
as they sped by, Cassini was built
to enter Saturnian orbit...
237
00:25:11,520 --> 00:25:14,680
Solid rocket boosters have
been jettisoned.
238
00:25:14,720 --> 00:25:17,360
Velocity 4,378 miles per hour.
239
00:25:17,400 --> 00:25:20,040
And explore the system for years.
240
00:25:26,960 --> 00:25:30,440
Many times more massive than
Voyager, Cassini had to take
241
00:25:30,480 --> 00:25:33,480
a different route to enter
orbit around Saturn.
242
00:25:37,040 --> 00:25:40,240
To conserve fuel,
it flew by multiple planets,
243
00:25:40,280 --> 00:25:43,440
slingshotting past them
to pick up speed
244
00:25:43,480 --> 00:25:47,040
and change direction over
the course of seven years.
245
00:25:53,760 --> 00:25:56,400
As Cassini finally
approached its target,
246
00:25:56,440 --> 00:26:00,560
it was travelling at almost
100,000 kilometres per hour
247
00:26:00,600 --> 00:26:04,160
and had to slow itself
with exquisite precision.
248
00:26:38,120 --> 00:26:41,640
After its 3.5 billion-kilometre
journey,
249
00:26:41,680 --> 00:26:45,200
Cassini was now able to see
Saturn's rings like never before.
250
00:26:57,760 --> 00:27:02,160
What's more, during its long stay
at Saturn, Cassini would be able
251
00:27:02,200 --> 00:27:05,440
to take physical
samples for the very first time.
252
00:27:24,760 --> 00:27:28,160
By measuring the way that the dust
from the Solar System falls
253
00:27:28,200 --> 00:27:31,920
onto the rings, Cassini
made a startling discovery.
254
00:27:38,880 --> 00:27:42,640
If the rings have been around Saturn
for billions of years,
255
00:27:42,680 --> 00:27:46,440
they should have been darkened
and dimmed by the dust.
256
00:27:48,280 --> 00:27:50,640
But they are pristine and bright.
257
00:27:55,240 --> 00:27:58,440
And the reason is
because they are young.
258
00:28:01,120 --> 00:28:06,080
Nearly 4.5 billion years
younger than Saturn itself.
259
00:28:15,720 --> 00:28:19,760
The mystery of the origin of the
rings is an active area of research.
260
00:28:21,360 --> 00:28:24,840
And the evidence that Cassini
delivered hints that the solution
261
00:28:24,880 --> 00:28:27,760
lies not with the planet itself,
262
00:28:27,800 --> 00:28:31,720
but with the world's
tracked in orbit around it -
263
00:28:31,760 --> 00:28:33,640
Saturn's moons.
264
00:28:38,560 --> 00:28:41,840
Saturn has 62 large moons
and countless smaller ones -
265
00:28:41,880 --> 00:28:43,680
we're still discovering them.
266
00:28:43,720 --> 00:28:47,040
So it's like a
mini solar system in itself.
267
00:28:47,080 --> 00:28:50,200
And those moons range in size
from planetary-size objects,
268
00:28:50,240 --> 00:28:54,080
like Titan, to small
irregular-shaped lumps of rock.
269
00:28:54,120 --> 00:28:57,560
And there's so much diversity
in size and form
270
00:28:57,600 --> 00:29:01,640
and surface features, that the whole
system is like a history book.
271
00:29:01,680 --> 00:29:05,040
And if we learn to read it
then we see that Saturn
272
00:29:05,080 --> 00:29:09,080
has had a very violent
and changeable past.
273
00:29:09,120 --> 00:29:12,880
Look at this, this is Mimas, which
is often called the Death Star moon
274
00:29:12,920 --> 00:29:14,480
for obvious reasons.
275
00:29:14,520 --> 00:29:20,120
It has this huge impact crater,
which tells you that once, long ago,
276
00:29:20,160 --> 00:29:22,840
there was a very violent impact
277
00:29:22,880 --> 00:29:26,040
that almost - but not quite -
destroyed the moon.
278
00:29:27,480 --> 00:29:29,840
And this is Iapetus.
279
00:29:29,880 --> 00:29:32,800
It's a very large moon,
almost planetary-size.
280
00:29:32,840 --> 00:29:35,520
It's about 1,500 kilometres across.
281
00:29:35,560 --> 00:29:39,360
And half of it is white,
and half of it is dark.
282
00:29:42,000 --> 00:29:44,920
Iapetus also has another
distinctive feature
283
00:29:44,960 --> 00:29:48,240
which is this ridge all the way
around the equator, and you can see
284
00:29:48,280 --> 00:29:50,560
the scale of it
from this photograph.
285
00:29:50,600 --> 00:29:52,360
And this is clearly visible.
286
00:29:52,400 --> 00:29:55,880
It's one of the highest mountain
ranges in the Solar System,
287
00:29:55,920 --> 00:29:59,600
20km from peak to the ground below.
288
00:30:05,680 --> 00:30:10,720
And it's thought that this formed
because a ring that was once
289
00:30:10,760 --> 00:30:15,680
around the moon, just like Saturn's
rings, collapsed onto its surface.
290
00:30:23,360 --> 00:30:28,800
As Cassini continued its journey,
it revealed in detail multiple moons
291
00:30:28,840 --> 00:30:31,040
made almost entirely of ice.
292
00:30:33,480 --> 00:30:36,960
And many of them had taken
on extraordinary forms
293
00:30:37,000 --> 00:30:39,360
in and around the rings.
294
00:31:01,000 --> 00:31:05,020
As Cassini analysed the ice moons
in ever greater detail,
295
00:31:05,060 --> 00:31:09,080
it became apparent that many of them
were made of exactly
296
00:31:09,120 --> 00:31:12,200
the same material
as the rings themselves.
297
00:31:15,360 --> 00:31:18,840
The rings and moons
were profoundly linked.
298
00:31:23,040 --> 00:31:26,240
But for all the
moons that Cassini saw,
299
00:31:26,280 --> 00:31:29,480
it now seemed likely
that one was missing.
300
00:31:49,480 --> 00:31:51,480
When dinosaurs roamed the Earth,
301
00:31:51,520 --> 00:31:56,600
we now suspect Saturn had a moon
in orbit that no longer exists.
302
00:32:00,760 --> 00:32:03,920
A moon perhaps 400km across
303
00:32:03,960 --> 00:32:06,600
and formed almost entirely of ice.
304
00:32:10,640 --> 00:32:12,680
But this world was doomed.
305
00:32:15,720 --> 00:32:20,160
It found itself orbiting too close
to resist the immense forces
306
00:32:20,200 --> 00:32:22,040
of Saturn's gravity.
307
00:32:34,600 --> 00:32:38,260
Gravity is the sculptor
of the Saturnian system
308
00:32:38,300 --> 00:32:41,920
but also the instigator
of change within it.
309
00:32:41,960 --> 00:32:46,480
We tend to think of gravity as a
force that pulls things together,
310
00:32:46,520 --> 00:32:50,120
but it can also act
to rip things apart.
311
00:32:50,160 --> 00:32:53,600
Think of the tides here on Earth,
they're caused by the difference
312
00:32:53,640 --> 00:32:57,480
in gravitational pull of the moon
from one side of the Earth
313
00:32:57,520 --> 00:32:59,080
to the other.
314
00:32:59,120 --> 00:33:02,960
And that difference which can be
quite subtle is also powerful,
315
00:33:03,000 --> 00:33:04,880
it can move entire oceans.
316
00:33:04,920 --> 00:33:09,880
It's called tidal gravity, but
the Earth also has a tidal effect
317
00:33:09,920 --> 00:33:13,240
on the moon, and because
the Earth is an entire planet
318
00:33:13,280 --> 00:33:16,320
that effect is much more powerful.
319
00:33:20,680 --> 00:33:24,560
The pull of the Earth is enough
to deform the moon's surface.
320
00:33:26,280 --> 00:33:30,440
The effect was particularly strong
4.5 billion years ago
321
00:33:30,480 --> 00:33:33,680
when the moon was
nearly 17 times closer.
322
00:33:35,960 --> 00:33:39,840
Back then, the pull from the Earth
caused a tide of solid rock
323
00:33:39,880 --> 00:33:41,800
to rise and fall.
324
00:33:46,600 --> 00:33:50,200
If the moon had been any nearer
it would have crossed what we call
325
00:33:50,240 --> 00:33:55,400
the Roche limit, a place where tidal
gravitational forces are so strong,
326
00:33:55,440 --> 00:33:58,080
moons can get ripped apart.
327
00:34:07,520 --> 00:34:11,720
The Romans named the planet Saturn
after their god of time and harvest.
328
00:34:11,760 --> 00:34:15,900
And in one of the more gruesome
tales from classical mythology,
329
00:34:15,940 --> 00:34:20,080
Saturn actually ate his newborn
babies in order to prevent them
330
00:34:20,120 --> 00:34:21,840
from taking his power.
331
00:34:21,880 --> 00:34:25,920
What's sort of interesting is,
that what we've learned from Cassini
332
00:34:25,960 --> 00:34:30,000
is that, at least metaphorically
speaking, they weren't far wrong.
333
00:34:43,240 --> 00:34:47,400
Just beyond Saturn's atmosphere,
our leading theory suggests
334
00:34:47,440 --> 00:34:50,940
an icy moon must
have approached close to
335
00:34:50,980 --> 00:34:54,480
or even just inside
the planet's Roche limit.
336
00:34:58,600 --> 00:35:01,900
As Saturn's immense tidal
gravitational forces
337
00:35:01,940 --> 00:35:05,240
acted across the moon,
it began to rupture.
338
00:35:09,840 --> 00:35:13,160
Saturn began to devour its child.
339
00:36:02,280 --> 00:36:05,680
Up to 15,000 trillion tonnes of ice
340
00:36:05,720 --> 00:36:09,120
broke apart in orbit around Saturn.
341
00:36:21,640 --> 00:36:25,120
Because of the speeds the ice
fragments were travelling,
342
00:36:25,160 --> 00:36:28,640
it's likely that in just a few days
they spread out
343
00:36:28,680 --> 00:36:30,760
to encircle the great giant.
344
00:36:37,000 --> 00:36:40,640
Saturn's iconic ring had been born.
345
00:37:01,120 --> 00:37:03,720
Today, the giant ring has evolved.
346
00:37:05,840 --> 00:37:09,440
Saturn's powerful gravitational
field has helped keep
347
00:37:09,480 --> 00:37:11,800
its near perfect circular shape.
348
00:37:12,920 --> 00:37:16,400
But collisions within
have caused it to flatten out.
349
00:37:21,120 --> 00:37:24,720
Now this debris forms
a disc wider than Jupiter,
350
00:37:24,760 --> 00:37:28,320
yet, on average,
just ten meters thick.
351
00:37:33,560 --> 00:37:37,800
Within, moon-sized chunks
of ice orbit the structure
352
00:37:37,840 --> 00:37:40,600
clearing great voids.
353
00:37:42,360 --> 00:37:44,240
Turning one ring...
354
00:37:45,680 --> 00:37:47,480
into many.
355
00:37:53,040 --> 00:37:57,640
In places, moons have pulled
particles of ice upwards
356
00:37:57,680 --> 00:38:01,600
to create strange peaks
over 2km high.
357
00:38:04,160 --> 00:38:06,320
And in just the right conditions,
358
00:38:06,360 --> 00:38:09,800
they cast spectacular shadows
across the rings.
359
00:38:18,000 --> 00:38:21,320
This once tiny world
of rock and ice...
360
00:38:23,720 --> 00:38:26,960
that has undergone so many
great transformations...
361
00:38:33,480 --> 00:38:36,880
has today become
the Solar System's jewel.
362
00:38:50,640 --> 00:38:54,400
Cassini had deepened our
understanding of the origin
363
00:38:54,440 --> 00:38:56,160
and evolution of Saturn.
364
00:38:57,240 --> 00:38:59,840
But its mission was far from over.
365
00:38:59,880 --> 00:39:04,320
Because just beyond the rings
it discovered another treasure.
366
00:39:05,920 --> 00:39:10,200
A place that may hold answers
to some of our deepest questions
367
00:39:10,240 --> 00:39:14,520
about the possibility of life
in the Solar System and beyond.
368
00:39:34,880 --> 00:39:39,120
Over a billion kilometres
from the warmth of the sun,
369
00:39:39,160 --> 00:39:42,480
just on the outer edge
of Saturn's rings,
370
00:39:42,520 --> 00:39:44,960
lies the icy moon Enceladus.
371
00:39:48,200 --> 00:39:50,000
Enceladus is quite a small moon,
372
00:39:50,040 --> 00:39:53,040
it's only about the size
of Iceland actually.
373
00:39:53,080 --> 00:39:55,720
But that does not make it dull.
374
00:39:55,760 --> 00:39:59,320
It is the most reflective
object in the solar system -
375
00:39:59,360 --> 00:40:03,560
over 90% of the light
that hits it bounces back,
376
00:40:03,600 --> 00:40:07,680
and that's because its surface
is covered in pure ice.
377
00:40:07,720 --> 00:40:10,480
It's also crisscrossed by crevasses
378
00:40:10,520 --> 00:40:13,280
like this one you see
in this glacier,
379
00:40:13,320 --> 00:40:15,440
but on a much grander scale.
380
00:40:15,480 --> 00:40:18,360
The largest,
known as the tiger stripes,
381
00:40:18,400 --> 00:40:20,080
are over 100km long.
382
00:40:20,120 --> 00:40:22,740
But for all its surface beauty,
383
00:40:22,780 --> 00:40:25,290
it's what's going on below the ice
384
00:40:25,330 --> 00:40:27,840
that makes Enceladus so special.
385
00:40:33,800 --> 00:40:37,680
What we found beneath Enceladus's
shell of ice must rank
386
00:40:37,720 --> 00:40:41,720
as one of the greatest discoveries
in 21st-century space exploration.
387
00:40:43,560 --> 00:40:47,400
But it was a discovery
that had been hiding in plain sight.
388
00:40:58,040 --> 00:41:02,120
This is a photograph taken
by Voyager 1 of Enceladus in 1980.
389
00:41:02,160 --> 00:41:06,240
Now, nobody noticed anything
remarkable about it at the time
390
00:41:06,280 --> 00:41:10,240
but this image has been enhanced
and now you can see
391
00:41:10,280 --> 00:41:14,240
this sort of misty blob
off one side of the moon.
392
00:41:14,280 --> 00:41:16,800
Now, that is fascinating.
393
00:41:16,840 --> 00:41:21,560
It means something is rising
up from inside Enceladus.
394
00:41:21,600 --> 00:41:26,600
Now, when Cassini got back there 24
years later it saw the same thing,
395
00:41:26,640 --> 00:41:29,440
but this time in much more detail.
396
00:41:33,080 --> 00:41:37,720
As Cassini approached Enceladus,
the anomaly revealed itself.
397
00:41:41,160 --> 00:41:46,200
Giant plumes of water vapour and
ice were erupting from its surface.
398
00:41:49,960 --> 00:41:55,000
Over 200kg of material
was being released every second.
399
00:41:59,840 --> 00:42:02,920
But this material
was not lost to space.
400
00:42:02,960 --> 00:42:06,560
It seemed to be feeding one
of Saturn's outside rings,
401
00:42:06,600 --> 00:42:08,640
helping to replenish it.
402
00:42:16,080 --> 00:42:19,840
And these discoveries
inspired an audacious risk.
403
00:42:22,400 --> 00:42:25,760
Piloted from over a
billion kilometres away,
404
00:42:25,800 --> 00:42:29,680
Cassini was guided
dangerously close to the plumes.
405
00:42:46,080 --> 00:42:50,480
The craft passed within just
48km of the surface
406
00:42:50,520 --> 00:42:52,160
of Enceladus.
407
00:42:55,040 --> 00:42:58,160
And Cassini was able
to touch the plumes.
408
00:43:08,520 --> 00:43:11,840
What we discovered,
thanks to a series of these flybys,
409
00:43:11,880 --> 00:43:13,840
was breathtaking.
410
00:43:15,480 --> 00:43:20,440
The ice in the plumes was actually
frozen particles of salty water.
411
00:43:22,440 --> 00:43:26,480
We had found a subsurface ocean
leaking into space.
412
00:43:31,320 --> 00:43:33,680
Far, far from the sun,
413
00:43:33,720 --> 00:43:37,800
Enceladus was harbouring
an ocean of liquid water.
414
00:43:39,120 --> 00:43:41,640
And it was there because of Saturn.
415
00:43:48,520 --> 00:43:52,160
Enceladus orbits Saturn
in an elliptical orbit,
416
00:43:52,200 --> 00:43:55,280
which means the gravitational forces
across the moon
417
00:43:55,320 --> 00:43:57,280
are constantly changing.
418
00:44:00,000 --> 00:44:03,960
It's maintained in this orbit by
the pull of another larger moon -
419
00:44:04,000 --> 00:44:05,360
Dione.
420
00:44:07,400 --> 00:44:11,560
These ever shifting gravitational
forces stretch and squeeze
421
00:44:11,600 --> 00:44:15,640
its heart, warming and melting
its icy interior.
422
00:44:22,480 --> 00:44:26,280
But Cassini's data had
one more surprise in store.
423
00:44:29,720 --> 00:44:33,800
As the plumes of water ice were
analysed in ever greater detail,
424
00:44:33,840 --> 00:44:37,440
we discovered complex
organic compounds
425
00:44:37,480 --> 00:44:40,720
and silica particles
that could only have come
426
00:44:40,760 --> 00:44:43,480
from hot hydrothermal vents.
427
00:44:48,480 --> 00:44:52,920
In the frozen outer reaches
of the Solar System
428
00:44:52,960 --> 00:44:56,480
we had found a warm watery oasis.
429
00:45:06,440 --> 00:45:10,800
Cassini has given us a glimpse
beneath the ice of Enceladus,
430
00:45:10,840 --> 00:45:15,760
and it is fascinating genuinely
in a scientific sense because many
431
00:45:15,800 --> 00:45:20,720
biologists believe that hydrothermal
vents like those that are almost
432
00:45:20,760 --> 00:45:24,000
certainly present on the floor
of Enceladus's ocean
433
00:45:24,040 --> 00:45:26,400
were the cradle of life on Earth.
434
00:45:26,440 --> 00:45:28,760
All the ingredients are present -
435
00:45:28,800 --> 00:45:32,000
there's hot water in touch
with ice and minerals.
436
00:45:32,040 --> 00:45:35,360
That's a reactive cauldron
of chemistry.
437
00:45:35,400 --> 00:45:37,680
There are reactive gases - methane.
438
00:45:37,720 --> 00:45:41,320
Cassini found molecular hydrogen
in the plumes,
439
00:45:41,360 --> 00:45:46,240
and that was one of the food sources
of primitive organisms on Earth.
440
00:45:46,280 --> 00:45:50,120
So there really is a possibility
that there is life
441
00:45:50,160 --> 00:45:53,240
in orbit around Saturn today.
442
00:46:01,440 --> 00:46:05,080
The prospect of life on Enceladus
is exciting.
443
00:46:06,760 --> 00:46:10,080
But if it's there, it's likely
to be only the simplest
444
00:46:10,120 --> 00:46:12,600
and most primitive of organisms.
445
00:46:16,280 --> 00:46:21,200
And given how violent and changeable
Saturn's past has been,
446
00:46:21,240 --> 00:46:24,320
this world of ice and liquid water
may only have arisen
447
00:46:24,360 --> 00:46:26,440
relatively recently.
448
00:46:29,680 --> 00:46:31,400
Now, we don't know how long
449
00:46:31,440 --> 00:46:35,760
Enceladus has been geologically
active, how long its had an ocean.
450
00:46:35,800 --> 00:46:40,120
If it was only tens of millions or
even hundreds of millions of years,
451
00:46:40,160 --> 00:46:44,600
that may not have been enough
time for life to get going.
452
00:46:44,640 --> 00:46:49,040
But if there is life there
then we can glimpse its future
453
00:46:49,080 --> 00:46:54,280
because there are still hydrothermal
vent systems present on Earth today
454
00:46:54,320 --> 00:46:58,640
and life doesn't just
survive there, it thrives.
455
00:47:17,160 --> 00:47:22,120
Often found in the deep oceans along
fault lines in the Earth's crust,
456
00:47:22,160 --> 00:47:25,800
hydrothermal vents are some
of the richest and most complex
457
00:47:25,840 --> 00:47:28,000
ecosystems on Earth.
458
00:47:29,760 --> 00:47:33,120
Feeding off the abundant bacteria
that breed there,
459
00:47:33,160 --> 00:47:38,000
these habitats support a multitude
of strange and complex organisms.
460
00:47:49,800 --> 00:47:54,260
Whilst creatures like this will
never exist on Enceladus,
461
00:47:54,300 --> 00:47:58,720
billions of years from now,
it is just possible that this
462
00:47:58,760 --> 00:48:03,080
distant world may become home
to its own unique forms of life.
463
00:48:14,080 --> 00:48:18,520
But for Cassini, the brave new world
under the ice of Enceladus
464
00:48:18,560 --> 00:48:21,080
was a bittersweet discovery.
465
00:48:34,960 --> 00:48:38,440
13 years after it arrived at Saturn,
466
00:48:38,480 --> 00:48:42,040
Cassini's fuel
finally began to run dry.
467
00:48:43,920 --> 00:48:48,360
NASA couldn't risk letting
this probe crash land on Enceladus
468
00:48:48,400 --> 00:48:52,200
and contaminate
a potential habitat for life.
469
00:48:52,240 --> 00:48:53,680
Systems, ACS One.
470
00:48:53,720 --> 00:48:56,040
We've just had transition
to high rate mode.
471
00:48:59,000 --> 00:49:03,560
And so the decision was made to send
Cassini on one final journey.
472
00:49:07,000 --> 00:49:08,760
A journey that would take it
473
00:49:08,800 --> 00:49:11,320
into the atmosphere
of Saturn itself.
474
00:49:12,840 --> 00:49:16,240
A journey from which
it would never return.
475
00:49:21,600 --> 00:49:24,300
And we are in the atmosphere.
476
00:49:24,340 --> 00:49:27,040
Radio signal still holding.
477
00:49:27,080 --> 00:49:28,520
30 seconds.
478
00:49:49,400 --> 00:49:53,040
Just heard the
signal from the spacecraft is gone
479
00:49:53,080 --> 00:49:57,240
and that, within the next 45
seconds, so will be the spacecraft.
480
00:50:00,880 --> 00:50:04,640
The planet that had borne witness
to some of the greatest dramas
481
00:50:04,680 --> 00:50:08,440
in the history of the Solar System
was now consuming the craft
482
00:50:08,480 --> 00:50:11,480
that had told its
extraordinary story.
483
00:50:24,080 --> 00:50:28,840
Cassini and Saturn had now become
inseparable companions.
484
00:50:51,840 --> 00:50:55,360
We journeyed out to Saturn
to experience and explore
485
00:50:55,400 --> 00:50:57,080
this great beauty.
486
00:51:03,360 --> 00:51:07,840
But in the end we were rewarded
with insights closer to home.
487
00:51:16,600 --> 00:51:19,460
Cassini and her team of scientists
and engineers
488
00:51:19,500 --> 00:51:22,360
should be counted amongst
our greatest of explorers.
489
00:51:22,400 --> 00:51:24,320
The mission had all
the ingredients -
490
00:51:24,360 --> 00:51:27,800
a vessel and a crew drawn
by the prospects of beauty
491
00:51:27,840 --> 00:51:32,600
and new knowledge across an
uncharted ocean to an alien world.
492
00:51:32,640 --> 00:51:35,800
And, as is so often the case
in exploration,
493
00:51:35,840 --> 00:51:39,360
the real treasure was found
in the unexpected shadows.
494
00:51:39,400 --> 00:51:42,360
In this case,
in the shadow of the rings,
495
00:51:42,400 --> 00:51:45,320
where we found this tiny world,
Enceladus,
496
00:51:45,360 --> 00:51:49,360
that may harbour life
and provide us with reassurance
497
00:51:49,400 --> 00:51:52,360
that we are not alone
in the universe.
498
00:51:52,400 --> 00:51:55,560
See? The beauty is in the story.
499
00:51:55,600 --> 00:51:59,080
Would it matter really
if we found life on Enceladus?
500
00:51:59,120 --> 00:52:01,360
It would only be microbes after all.
501
00:52:01,400 --> 00:52:03,560
Yes, it would matter.
502
00:52:03,600 --> 00:52:08,360
We are at a time in our history,
I think, where we need reassurance
503
00:52:08,400 --> 00:52:13,100
or perhaps a reminder that
there is beauty and knowledge
504
00:52:13,140 --> 00:52:17,840
and perhaps even life and meaning
beyond our shores.
505
00:52:28,840 --> 00:52:33,360
We will, I'm sure, go back
to Saturn and its moons,
506
00:52:33,400 --> 00:52:35,800
explore deeper, stay longer,
507
00:52:35,840 --> 00:52:39,360
and maybe one day
even visit ourselves.
508
00:52:42,840 --> 00:52:45,040
We don't know what we'll discover
509
00:52:45,080 --> 00:52:49,600
but we can be sure that the story
has only just begun.
510
00:53:18,080 --> 00:53:22,360
Cassini has been one of the most
successful probes ever flown.
511
00:53:23,360 --> 00:53:27,040
But constructing a machine
that could survive 13 years
512
00:53:27,080 --> 00:53:31,640
in the outer Solar System was a huge
challenge for everyone involved.
513
00:53:33,360 --> 00:53:35,560
T plus 20 seconds.
514
00:53:35,600 --> 00:53:38,080
Even when they were proposing
Cassini, I thought,
515
00:53:38,120 --> 00:53:40,320
"No, no, this is never
going to happen."
516
00:53:40,360 --> 00:53:42,640
It's, like, maybe too ambitious
or something.
517
00:53:47,000 --> 00:53:49,840
It's difficult to put a number
on how many people
518
00:53:49,880 --> 00:53:52,320
were involved in Cassini.
519
00:53:52,360 --> 00:53:54,480
Tens of thousands, I would say.
520
00:53:57,360 --> 00:53:59,840
This is a very, very complex effort.
521
00:53:59,880 --> 00:54:02,320
There's over ten miles of wiring
522
00:54:02,360 --> 00:54:05,000
and you have to check out
every wire.
523
00:54:06,360 --> 00:54:11,880
So it took us two and a half years
to put the thing together.
524
00:54:14,600 --> 00:54:19,360
All of us spent a lot of effort
to get to that moment
525
00:54:19,400 --> 00:54:22,080
so there's a lot of emotion
attached to it.
526
00:54:23,080 --> 00:54:25,320
And then you see it launch
527
00:54:25,360 --> 00:54:30,600
and you know that it's on a journey
to a very, very distant place...
528
00:54:31,600 --> 00:54:34,360
and so you feel like
you're going too.
529
00:54:42,360 --> 00:54:46,600
When Cassini first began to send
close-up pictures back to Earth...
530
00:54:48,840 --> 00:54:51,600
it was a special moment
for the whole team.
531
00:54:56,840 --> 00:54:59,600
I was sitting in what they call
the Blue Room
532
00:54:59,640 --> 00:55:03,440
being interviewed while they were
beaming for the first time
533
00:55:03,480 --> 00:55:06,080
and then one of these pictures
came on and I just went,
534
00:55:06,120 --> 00:55:07,800
"Wow, look at that!"
535
00:55:07,840 --> 00:55:11,360
That was really the jumping
out of the chair moment for me.
536
00:55:13,480 --> 00:55:15,600
And it was just the first day.
537
00:55:18,600 --> 00:55:22,360
What we were seeing was the highest
resolution that had ever been seen.
538
00:55:23,600 --> 00:55:26,040
I saw phenomena that I'd only seen
539
00:55:26,080 --> 00:55:28,560
in, kind of, computer simulations
before
540
00:55:28,600 --> 00:55:31,080
and now I was seeing it
for the first time
541
00:55:31,120 --> 00:55:33,400
and realising all this was real.
542
00:55:35,600 --> 00:55:38,680
And we were seeing details
in the rings
543
00:55:38,720 --> 00:55:42,600
that were shocking... shocking.
544
00:55:43,600 --> 00:55:47,080
We just lacked the imagination
that it would require
545
00:55:47,120 --> 00:55:49,280
to predict what it would look like.
546
00:55:51,600 --> 00:55:56,080
For me, when that great
backlit picture came out,
547
00:55:56,120 --> 00:55:58,600
that's when it hit for me.
548
00:56:00,360 --> 00:56:05,360
"Oh, my God, we've done something
really unique and wonderful."
549
00:56:08,360 --> 00:56:13,040
It was like, "This is going to be...
This is going to be huge."
550
00:56:16,360 --> 00:56:19,080
Over Cassini's 13 years at Saturn...
551
00:56:20,080 --> 00:56:23,400
it explored the planet's
incredible storms.
552
00:56:24,400 --> 00:56:27,080
The formation of its rings.
553
00:56:29,040 --> 00:56:32,360
And discovered the oceans
of Enceladus.
554
00:56:35,360 --> 00:56:39,080
But Cassini's greatest insights
may be yet to come.
555
00:56:40,360 --> 00:56:43,840
There's such a wealth
of information in the data.
556
00:56:43,880 --> 00:56:47,320
I think we've just skimmed
the top of the data.
557
00:56:47,360 --> 00:56:52,360
I think people will continue to make
discoveries from Cassini data
558
00:56:52,400 --> 00:56:55,120
for another 30 to 40 years.
559
00:56:56,840 --> 00:57:00,040
The data Cassini collected
in its final moments
560
00:57:00,080 --> 00:57:03,400
is already changing our
understanding of the planet.
561
00:57:04,400 --> 00:57:07,220
It has revealed the rings
are disappearing.
562
00:57:07,260 --> 00:57:10,290
As much as 10,000 kilograms
of material
563
00:57:10,330 --> 00:57:13,360
is falling into the planet
each second.
564
00:57:15,360 --> 00:57:19,360
It now seems likely that just
100 million years from now,
565
00:57:19,400 --> 00:57:22,840
Saturn's great rings
will be no more.
566
00:57:26,840 --> 00:57:31,360
Cassini has shown us that
we have been uniquely fortunate
567
00:57:31,400 --> 00:57:33,840
to behold this great beauty.
568
00:57:46,360 --> 00:57:48,680
We head into the darkness.
569
00:57:51,600 --> 00:57:55,360
To the ice giants -
Uranus and Neptune.
570
00:57:56,920 --> 00:57:58,880
And beyond,
571
00:57:58,920 --> 00:58:03,080
to a world 4.5 billion kilometres
from the sun.
572
00:58:06,600 --> 00:58:08,360
Pluto.
573
00:58:11,600 --> 00:58:14,800
Journey through our Solar System
with this free poster, produced
574
00:58:14,840 --> 00:58:19,080
by the Open University, and discover
more about its planets and moons.
575
00:58:20,600 --> 00:58:24,400
Order your free copy by calling...
576
00:58:27,360 --> 00:58:29,800
or go to...
577
00:58:33,360 --> 00:58:36,360
and follow the links
to the Open University.
49885
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