All language subtitles for Wonders of the Solar System E02 Order out of Chaos 1080p AC3+DTS_Subtitles06.ENG

We live on a world of wonders...

..a place of astonishing beauty and complexity.

We have vast oceans and incredible weather,

giant mountains and breathtaking landscapes.

If you think that this is all there is,

that our planet exists in magnificent isolation,

then you're wrong.

As a physicist, I'm fascinated
by how the laws of nature

that shaped all this

also shaped the worlds beyond our home planet.

I think we're living through the greatest
age of discovery our civilisation has known.

We've voyaged to the farthest
reaches of the solar system.

We've photographed strange new worlds,

stood in unfamiliar landscapes, tasted alien air.

But what makes the wonders of the
solar system even more astonishing is

that it all started as nothing more
than a chaotic cloud of gas and dust.

And it was from that cloud that
everything in the solar system formed.

All this order - the sun,

the rotating planets, me -

coalesced from a collapsing cloud of dust.

In this film, we'll discover

how the solar system made the
journey from chaos into order...

..and see how that cloud gave rise to the
solar system's most beautiful wonder -

the majestic rings of Saturn.

We'll discover how Saturn's amazingly varied moons

govern the intricate patterns of the rings,

and how another wonder recently
discovered on one of those moons

is changing our ideas

about the nature of the outer solar system.

It's cool!

We'll witness the fundamental
forces that control the universe...

It's beginning to come - the end of the world.

..and see how those forces were unleashed

to create the beautifully
ordered solar system we live in.

It's only now that we're beginning to
understand the origins of that order,

and that has implications for our
understanding of the entire solar system,

and, ultimately, of why we are here.

MUEZZIN CHANTS

This is the Great Mosque in the
city of Kairouan in Tunisia,

and this mosque is the fourth
holiest place in Islam,

and so for the last 14 centuries,
the relentless passing of the days

has been celebrated by prayers
before dawn, at sunrise,

at noon, at sunset and in the evening.

MUEZZIN CHANTS

The calls to prayer mark out

the passing of time as the
sun travels across the sky.

But it's not the sun that's moving.

What we're really observing is the
movement of the Earth through space.

This is the ball of rock we live on.

It carries us through cycles of night and
day as it turns on its axis every 24 hours.

A year is the time it takes to orbit the sun,

and we have seasons because the
Earth's axis is tilted by 23 degrees.

To see how that works, we need to speed time up

so a year passes in just ten seconds.

At this pace,

we can see how the southern
and then northern hemispheres

are angled towards the warmth of the sun,

taking us through yearly
cycles of summer and winter.

All the rhythms of our lives are governed

by how the Earth travels through space,

and in Tunisia in April, it's springtime.

This is the seasonal flower market
in Kairouan, and it's only here

for two months of the year,

because that's when these flowers are in flower.

And it's a beautiful example of how the
structure, the clockwork of the solar system

affects things here on Earth in
the most unexpected of ways,

because if our Earth's axis wasn't tilted by 23
degrees, then there wouldn't be any seasons,

and if there weren't any seasons,
then seasonal flowers wouldn't have evolved

and there wouldn't be a flower market.

But it's not just the Earth.

The whole solar system is full of rhythms.

Each planet orbits the sun at
its own distinctive tempo.

Mercury is the fastest.

Closest to the sun, it reaches speeds

of 200,000 kilometres an hour as it
completes its orbit in just 88 days.

Venus rotates so slowly that it
takes longer to spin on its axis

than it does to go around the sun,

so that on Venus, a day is longer than a year.

Further out, the planets
orbit more and more slowly.

Jupiter, the largest planet,
takes 12 Earth years to complete each orbit.

And at the very furthest
reaches of the solar system,

4.5 billion kilometres from the sun,

Neptune travels so slowly that it
hasn't completed a single orbit

since it was discovered in 1846.

The solar system is driven by these rhythms,

so regular that the whole thing
could be run by clockwork.

It seems extraordinary that
such a well-ordered system

could have come into being spontaneously,

but it is in fact a great example

of the beauty and symmetry that
lies at the heart of the universe.

I want to explain how that order
emerged from the chaos of space,

because understanding that will help us understand

the origins and formation of the solar system,

and the beauty of its wonders.

These are the Atlas Mountains in North Africa.

According to Roman legend,
they held the heavens above the Earth.

And they are one of the finest
places to come to view the stars.

From a place like this,
it's easy to appreciate the profound effect

that the night sky would
have had on our ancestors.

You know, from a modern perspective,

astronomy can seem remote and arcane,

because we've lost our
connection with the night sky.

From a city you just don't see
a sky look anything like this.

From the darkness of the Atlas
Mountains, it's really, truly majestic.

So for our ancestors,

the connection with the night sky
would have been incredibly intimate.

They looked into the skies to
understand their place in creation,

and the movement of the stars

told them one thing -

they were at the centre of the universe.

Up there is Polaris, the North Star,

and it's almost exactly aligned
with the Earth's spin axis,

which means that, as the Earth rotates,

all the stars rotate through
the sky around that point.

So it looks for all the world as if the Earth

is at the centre of the universe
and the stars rotate around it.

And that's, of course, what the ancients
thought for thousands of years, and why not?

Because it's obvious...

but wrong.

To understand the Earth's real
position in the solar system,

we need to look at the one set of bodies

that doesn't behave as predictably as the stars.

The Greeks named them "planetes",
or "wandering stars",

and we have kept the name
"planet" to describe them.

This is Mars, photographed once
a week over a period of months.

Rather than travelling in a straight line

across the background of the stars,

it occasionally changes direction
and loops back on itself.

It's very hard to explain these retrograde loops

if the Earth is at the centre of the universe.

Understanding the retrograde
motion of Mars didn't come easy.

That's why it took over 2,000 years
to work out, but I'm going to explain
it using a stick and some rocks.

The key thing is that the Earth is not
at the centre of the solar system.

The sun is,

and the Earth and Mars go round it

in almost...

circular orbits.

So when Mars is viewed from the Earth,

then it's seen on the sky -

in fact on the constellations of the Zodiac.

So as Mars orbits around and
the Earth orbits around,

then from that position,

Mars will look like it's there on the sky.

Mars moves and the Earth moves in THAT position...

..and Mars moves in that direction
across the sky, and again,

in that position,

Mars will be here, so it's moving
in a straight line across the sky.

But what happens when the Earth overtakes Mars?

Then look at the line of sight.

Mars has moved back to there.

It's reversed its direction.

And it continues to do that

until the Earth gets round
to somewhere like there,

and Mars is here,

and the line of sight means it's
started moving that way again.

So Mars has executed that strange
looping motion on the sky

because the Earth overtook Mars
on the inside, and that's why

the retrograde motion happens.

Simple!

Understanding the retrograde loops was one of
the major achievements of early astronomy.

It created the concept of the solar system

and allowed us to build the first
accurate maps of the planets

and their orbits around the sun.

Once you had this picture of a solar system

running like clockwork,

the sun surrounded by the orbiting planets,

then you might start asking questions like

why is the solar system so ordered,

and how did that order come into existence.

Well, a clue lies in those sweeping,
circular motions of the planets.

RADIO:..Severe storms over western Oklahoma, 70%.

Other hazardous weather, 80%...

To understand how the solar
system came into being,

we need to understand the physical
principles that govern the whole universe.

But, of course, the same laws of physics
also control the world WE inhabit,

so to discover how the solar system started,

we don't need to look out
into space or back in time.

We just need to look around us.

One of the remarkable things about the
laws of nature is that they're universal,

and that means that the same laws that
describe the formation of the solar system

can also describe the most mundane
things here on Earth, like the motion
of water as it drains from the sink.

These spinning spirals are
seen all across the universe.

We see them everywhere because the laws
of physics are the same everywhere.

I've come here to Oklahoma to see
how those laws can unleash forces

that drive some of the most
powerful and destructive phenomena
in the atmosphere of our planet -

tornadoes.

Oklahoma is in the middle of
what is known as Tornado Alley.

No, no, no! Tornado! Tornado! Oh, my God!

Yep, it's huge.

Oh, wow!Big, big, big. Look at that thing!

Look at it spin!

Every year, hundreds of twisters
tear across the landscape.

They're incredibly dangerous and destructive,

and their key feature is
that same spinning spiral.

Don Giuliano is a professional storm chaser.

He's going to help me try
to get close to a tornado.

That little developing storm there is this.

It's a severe thunderstorm that is
capable of producing a tornado.

Anywhere inside that purple area,
it's possible that a tornado could
be there or is moving that way.

And what would happen if,
in this car, we - deliberately or
not - went straight through it?

It would probably pick up our car and toss it

a quarter of a mile through the air
and crush it into a little ball.

I'm going to just do a U-turn.

THEY LAUGH

'Bizarre as it sounds,

'the processes that drive these vast storm systems

'are the same as would have been seen 5 billion
years ago at the start of the solar system.'

Everything that we know and see
around us was formed from a nebula -

a giant cloud of gas and dust.

Drifting across light years of space,

that cloud remained unchanged
for millions of years.

But then something happened
that caused it to coalesce

into the solar system we have today.

It's thought that a supernova,

the explosive death of a nearby star,

sent shockwaves through the nebula.

This caused a clump to form
in the heart of the cloud.

Because it was more dense,
its gravitational pull was stronger

and it started to pull in more and more gas.

Soon the whole cloud was collapsing,
and crucially, it began to spin.

It's a feature of all things that spin

that if they contract,
they must also rotate faster.

It's a universal principle called the
conservation of angular momentum.

Just pull off anywhere here.

'It's this that leads to those spinning spirals,

'and it applies equally well
to the early solar system

'and storms like these.

'As the giant thunderheads build,

'they suck up hot air and contract,

'and like the cloud that built the solar system,

'when they contract, they spin faster and faster.'

On Earth in storms like this,

conservation of angular momentum means that
you get, in the most extreme case, tornadoes.

You get very rapidly rotating columns of air

where the wind speeds can rise to 300, 400,
even sometimes 500 kilometres an hour.

It's very similar to the process that occurred
early in the formation of the solar system,

when a collapsing cloud of dust got,
for some reason, a little bit of spin,

and as that dust cloud collapsed,
the spin rate has to speed up and speed up.

That's what you can see in storms
like this when tornadoes are formed.

The spin of the big storm system can
become concentrated and speeded up

in, well, a tornado.

You get immense wind speeds,
although the wind speed isn't too gentle now.

And it looks pretty wild
up there, I've got to say.

In fact, I've never... Look at that.

I've rarely seen such dramatic clouds.

And apparently, we've got about five
minutes before the end of the world,

so we have to get back in the car.

There's thunder and lightning and there
was a report earlier from this storm

of hail the size of baseballs,
and I don't want one of those on my head.

PATTERING

Let's get back to the car.Let's go.

It's beginning to come - the end of the world!

'This storm never developed into
a tornado, but when they do,

'you can really see the conservation
of angular momentum in action.'

Huge tornado, look at that!

'As the storm contracts,
its core rotates faster and faster

'until a column of violently rotating
air descends from the cloud.'

Man, look at that funnel!

'The awesome spinning power of tornadoes
has incredibly destructive effects,

'but it's this same phenomenon

'that is responsible for creating
the stability of the solar system,

'because it was the conservation
of angular momentum

'that stopped the early solar
system collapsing completely.'

Oh, my God, that's going to be violent.

While gravity caused the nebula
to contract, its conserved spin

gave rise to a force that balanced
the inward pull of gravity

and allowed a stable disc to form.

When the sun ignited,
it lit up this spinning disc.

And within the disc, the planets formed,

all orbiting the sun in their
regular, clockwork patterns.

In just a few hundred million years,

the cloud had collapsed to form a star system,

our solar system,

the sun surrounded by planets,

and the journey from chaos into order had begun.

And there's no better place to
see the results of that journey

than in what I think is one of
the wonders of the solar system.

Of all the solar system's wonders,

there is a place we can go where the
processes that built the solar system

are still in action today...

..a place of outstanding beauty and complexity...

..a place that has entranced
astronomers for centuries...

..the planet Saturn.

This is NASA's Jet Propulsion Laboratory,

and I've known about this place,
or its address - Oak Grove
Drive, Pasadena, California -

since I was very small,
because I wrote to them in 1975

to ask for pictures from the surface of
Mars taken by Viking, and they sent them.

But today, this is the control centre
for Cassini, which is our one,

and to date, only, spacecraft
in orbit around Saturn.

Cassini was launched in 1997.

It is the largest, most sophisticated
spacecraft ever sent to the outer solar system.

Its purpose is to study Saturn
and its rings, and since 2004,

it has been sending back
the most amazing pictures.

They reveal that the rings
are impossibly intricate,

made up of thousands upon thousands
of individual bands and gaps.

The whole system is surrounded
by a network of moons.

Part of Cassini's mission is
to discover how the rings

came to be like this, how all this incredible
structure was created.

Because, strange as it seems,

these beautiful patterns
are as close as we can get

to the disc that formed the solar system,

and that is why the Saturnian
system has so much to tell us.

I mean, I like to think of it as
like a miniature solar system.

The moons are the equivalent of the planets
and Saturn is the equivalent of the sun.

'Carl Murray has spent a lifetime
studying Saturn's rings.'

In the rings, we're learning something
about our own origins, if you like,

because the physical processes
that go on in the rings

and their interaction with the small moons

are probably similar to what went on in the
early solar system after the planets formed,

and there's still a ring or debris left
over from the formation of the planets.

So if you looked at the solar system 4.5
billion years ago, the sun at the centre,

you'd have a disc of dust not unlike
Saturn's ring system?That's right.

But if we can't understand a disc of
material that's in our own back yard,

what chance do we have of understanding

a disc that's long since disappeared - the
one out of which the solar system formed?

So it's the same processes, but we've got this
incredible opportunity with Cassini

to observe things happening in front of our eyes.

Using the data from Cassini,
we are able to recreate Saturn's
rings in incredible detail.

We can journey from the vast scale of the disc

to the minute structure of individual ringlets.

All the rings are in motion,
orbiting Saturn at immense speeds.

Like the planets orbiting the
sun, the rings nearest Saturn are

the fastest, travelling at over
80,000 kilometres an hour.

And while the rings appear solid,
casting shadows onto the planet,

they are also incredibly delicate.

The main disc of the rings is
over 100,000 kilometres across,

but as little as three metres thick.

Saturn's rings are undoubtedly beautiful

and, when you see those
magnificent pictures from Cassini,

it's almost impossible to imagine that that
level of intricacy and beauty and symmetry

could have emerged spontaneously,
but emerge spontaneously it did.

And for that reason alone, Saturn's rings are
one of my wonders of the solar system.

But there's more than that
because, in studying the origin
and evolution of Saturn's rings,

we've begun to gain valuable insights into the
origins and evolutions of our own solar system.

To try to understand the true nature
of Saturn's rings, I've come to this
glacial lagoon in Iceland.

There are two things the boat driver
told me about these icebergs.

One is that they can come up
from the bottom of the seabed

without any warning at all,

fly up to the surface,
tip the boat over and then you die.

Secondly, if you take some of it and take it
home, it's absolutely brilliant in whisky

because the water is pure, a thousand years old,

no pollutants in it and it
makes whisky taste superb.

So it's either death or whisky.

That's my kind of pond!

But I'm really here because
the structure of the rings

is remarkably similar to the way
these icebergs float in the lagoon,

because, despite appearances,
the rings aren't solid.

Each ring is made up of hundreds of ringlets

and each ringlet is made up of
billions of separate pieces.

Caught within the grasp of Saturn's
gravity, the ring particles

independently orbit around the
planet in an impossibly thin layer.

Thanks, see you in a minute. Yeah hopefully.

But the similarity doesn't end with the layout.

It also lies in what the rings
and the icebergs are made of,

and that explains why the rings are so bright.

Well, this is why we can see
Saturn's rings from Earth,

because this is what they're made of.

They're made of beautiful pure water
ice, sparkling in the sunlight,

billions of these pieces,
a billion kilometres away from Earth.

Most of the pieces are, well,
smaller than that, less than a centimetre.

Many are micron size ice crystals,
but some are as big as this iceberg.

Some are as big as houses.

Some can be over a kilometre across.

Imagine sitting on one!

Imagine this were a piece of
Saturn's rings. What a view.

This is the closest we can get
to Saturn's rings on Earth

and the view would be remarkably similar.

Billions of chunks of ice shining
brightly as they catch the sunlight.

And the reason the rings shine so
brightly is that, like the icebergs,

the rings are constantly changing.

As the ring particles orbit Saturn,

they're continually crashing into
each other and collecting into giant

clusters that are endlessly
forming and breaking apart.

As they collide, the particles shatter

exposing bright new faces of
ice that catch the sunlight.

It's because of this constant
recycling that the rings are

able to stay as bright and shiny
as they were when they formed.

For me, one of the most remarkable
things about Saturn's rings

is their dynamism, their constant renewal.

It's because of that dynamism
that we can see them at all.

That's why they're clean, that's why they reflect
sunlight and we can see them from Earth.

It's, I suppose, a bit like a city
that people come and go, buildings

get torn down and rebuilt but the
city always remains the same.

So it is with Saturn's rings.

They're different today than
they were a thousand years ago.

They'll be different in a hundred
or a thousand years' time

but that structure and that beauty,
that magnificence will always remain.

Saturn's rings are magnificent for
more than just their beauty...

..because by looking at the rings

we can begin to understand our own origins.

And the key to understanding the rings
can be found orbiting around them.

Oh!

That is absolutely incredible.

You can see the rings are completely end on.

I mean, when you see that,
I've looked at the sky, I've looked

at Saturn hundreds of times but I've never
seen it through a telescope like this

and you really get a feeling it's a planet.

I know what Galileo thought when
he said that the planet had ears.

He didn't have one of these telescopes, though.

And I can see one, two, three,

four, five moons around the planet.

It's just incredibly beautiful.

Seen like this, it's easy to appreciate how Saturn

is like a mini-solar system with the moons
orbiting like planets around the sun.

From Earth we can only see
a few of the larger moons.

But in total, Saturn has more than 60 moons,

and seen close up, they are a weird
and wonderful bunch.

Dione is typical of Saturn's icy moons.

It looks similar to our own moon but
its composition is very different.

It's about two-thirds water but
the surface temperature is minus

190 degrees Celsius, and at those temperatures,
the surface behaves pretty much like solid rock.

Iapetus is known as the yin and yang moon,

one half clean ice,

the other coated in black, dusty deposits.

The giant moon, Titan,
is bigger than the planet Mercury.

But the unique thing about Titan

is this atmosphere which is four
times as dense as the Earth's.

It's rich in organic molecules and
it's thought that the chemistry

is very similar to that of the
primordial Earth before life began.

And Hyperion is a moon unlike any other.

It's not even round and its battered
surface has the texture of a sponge.

And one theory for that is that
it's actually a captured comet

that has drifted in from the distant
reaches of the solar system and been
captured by Saturn's gravity.

But the moons of Saturn aren't
just a celestial freak show.

They're the driving force behind the
beauty and structure of the rings.

The most remarkable of them is
hidden in one of the outer rings.

Buried in the heart of the E-ring
is a moon that is rapidly becoming

one of the most fascinating places
in the solar system - Enceladus.

Enceladus has long been an astronomical curiosity

because it's the most reflective
object in the solar system,

but we've known little about
it because Enceladus is tiny,

only 400 kilometres across,
and over a billion kilometres away.

It's only now we have these
amazing images from Cassini

that we can see just how strange it is.

Its heavily cratered northern hemisphere
looks like any other icy moon,

but the southern hemisphere
tells a very different story.

It's almost completely free from craters,

which means that the surface
is probably newly formed.

It's scarred by canyons and riven by cracks.

It all looks remarkably similar to the geology
of Earth, but carved in ice rather than rock.

And right over the South
Pole are the Tiger Stripes,

four parallel trenches over 130 kilometres
long, and possibly hundreds of metres deep.

They look just like tectonic fault lines.

This is what tectonic faults look like on Earth.

This is the continental divide in
Iceland where the American and
European plates are spreading apart.

The cliffs at the edge of the plates
look out over a plain of new crust

formed from molten lava pushing
up from the centre of the Earth.

Carolyn Porco, head of the Cassini imaging team,

thinks that something similar
may be happening on Enceladus.

It is one of the most unique places
in all the solar system and you can
tell that just by looking at it.

And we think that it's possible
that there is something similar

to what's happening right here,
where you might get slushy ice,

viscous ice that comes up through the cracks, OK?

And creates more surface ice,
the way you get more crust created right here,

pushing things out to the side and it's buckling
by the time it gets to what is now the mountains.

So it really is similar to Iceland
actually where you're getting lava

welling up from the surface and creating new
land, so in the same way you've got ice?

We think. In fact it gives us an
indication of just how this whole
system down there may be working.

The next clue that something
was happening under the surface

came when Cassini flew
directly over the South Pole.

Thermal readings showed hot
spots under the Tiger Stripes.

For some reason, the stripes were much
hotter than the rest of the moon.

Cassini has found the unthinkable.

It's found that this southern tip
of Enceladus is excessively warm.

There's more heat coming out of
the south polar cap, if you will,

of Enceladus than is coming
out of the equatorial regions.

It would be like saying there's more heat coming
out of Antarctica than the Equator on Earth.

Then, one day in November 2005,

Cassini photographed Enceladus just
as the sun was setting behind it.

What it saw became one of the most remarkable
discoveries ever made in the outer solar system.

The backlit images reveal giant
fountains erupting from the South Pole,

volcanoes blasting out ice instead of rock.

And those images blew everybody away.

I mean that was like game over, you know!

Here you have these dozen or more narrow jets
and they just look ghostly and fantastic.

Just a few miles away from the continental divide

is an area that can help us
understand the ice fountains.

This is one of Earth's hot spots
where the volcanic heat of

the planet's core bubbles up
to just below the surface.

Until a few years ago,
Enceladus was thought to be an

unremarkable world, a small frozen
barren lump of rock and ice.

But those fountains of ice erupting
thousands of kilometres out into
space mean that there's something

incredibly interesting going
on beneath its surface.

It's here we find the Earthly phenomenon
most like the ice fountains...

..geysers.

They form when underground
pockets of water suddenly boil

and explode into the air.

Geysers on Earth require three things.

They require a ready source of water,

they require an intense source
of heat just below the surface

and they need just the right geological plumbing.

So if the geysers on Enceladus
are similar, then that raises the

intriguing possibility that there's
an ocean of liquid water beneath
the surface of the moon and it

raises a very interesting question
because Enceladus is far too small

to have retained any meaningful source of heat
at its core, so where does that heat come from?

On Earth, the geysers are driven by
the intense temperatures inside the

planet, hot enough to melt
rock and power volcanoes.

But Enceladus is so tiny that
its core should be frozen solid.

Enceladus must be getting its heat
from somewhere else, and it's

thought that it might come from
its peculiar orbit around Saturn.

So the next thing to investigate
was whether or not you could have,

what we call, tidal forces flex Enceladus,

and that simply arises because the orbit of
Enceladus is eccentric, meaning it's elliptical,

out of round, and as it encircles
Saturn in its orbit,

it gets close to Saturn and then
far away, close and far away,

and the gravitational pull
changes as it moves in its orbit

so that means the body's
flexing and,if it's flexing,

it means it's undergoing friction inside this.

This is a major process for injecting energy
that turns into heat into a body like Enceladus.

As Enceladus orbits, Saturn's gravity
actually distorts the shape of the moon.

It's thought that this heats the
interior of the moon just enough

to melt a small underground ocean of water.

As it contacts the vacuum of space,
that water vaporises and explodes out

of the moon creating this
wonder of the solar system.

These geysers are incredibly
impressive natural phenomena

but they pale into insignificance compared
to the ice fountains of Enceladus.

It's so cool.

While this geyser erupts every few minutes,
blasting boiling water 20 metres into the air...

..on Enceladus the plumes are
thought to be erupting constantly.

For them, the sky is the limit.

Bursting through the surface
at 1,300 kilometres an hour,

they soar up into space for
thousands of kilometres.

They must be one of the most
impressive sights in the solar system.

Any liquid water instantly
freezes into tiny ice crystals.

Some of it falls back onto the surface,
giving the moon its reflective icy sheen.

But the rest keeps going all the way round Saturn.

The ice fountains are creating one
of Saturn's rings as we watch.

The whole E-ring is made from pieces of Enceladus.

But Enceladus is not the only
moon that shapes the rings.

Saturn's other moons also play a
crucial role in creating these

beautiful patterns and they
do so in mysterious ways.

The Sahara desert may seem an unlikely
place to come to explain Saturn's rings,

but the behaviour of the sand in the
desert can help us understand how the
moons form the patterns in the rings.

At first sight the Sahara desert
seems an immensely chaotic place,

just billions of grains of sand being blown
randomly around by the desert winds but actually,

look a little bit closer, and you start to see
an immense amount of order.

There are sand dunes as far as the eye can see,

and a remarkable thing is
that the angles of the front

of all the sand dunes are exactly the same.

Now in the Sahara, the emergence of
that order is driven by the desert

winds blowing always in the same direction,

day after day, year after
year, moving the sand around.

In the Saturnian system,
the order and beauty and intricacy

of the rings is driven obviously not by wind,

but by a different force, the force of gravity.

As the moons orbit Saturn, their gravitational
influence sweeps through the rings.

In these amazing images, we can actually
watch the moons as they work.

We can see gravity in action.

As the moons pass close to the
rings, their gravitational pull

tugs the ring particles towards them,
distorting the shape of the rings.

The F-ring, one of the outer rings,
is twisted into a spiral shape

by two moons, Prometheus and Pandora.

In this video taken by Cassini,
you can see how Prometheus

drags plumes of material away as
it passes close to the rings.

These short-range gravitational effects
account for many of the patterns in the rings.

But sometimes the moons can exert their
pull over much greater distances,

and the way they do so reveals the
subtlety with which gravity can work.

Well, here's a model of the Saturnian
system with Saturn in the middle

and the magnificent ring system
going around the outside,

and the first thing you notice when
you look at the rings is a huge gap
called the Cassini division.

Now what could possibly have caused that?

Well, it's all down to one of
Saturn's moons called Mimas

which orbits well outside the ring system.

And how could something that far outside the rings

have any influence at all on
the particles inside the rings?

Well, it's all down to a phenomena
called orbital resonance.

Now the particles in the Cassini division have
an interesting relationship with the moon, Mimas

because they orbit around
Saturn twice for every single

orbit of Mimas, and that has
an interesting consequence.

Imagine there's a particle
inside the Cassini division.

Then every second year for this
particle they meet up with Mimas.

They end up in the same place in space and
that means that this particle will get a kick

or a tug from Mimas's gravity on a
regular basis, every second year.

Bang, bang, bang! And that alters
the orbit of anything that's in

the Cassini division, and actually
has the effect of throwing it out,
of clearing a gap in the rings.

And in fact, much of the complex and
beautiful structure of Saturn's rings

is down to these orbital resonances,

not only with Mimas, but with one or
more of the 61 known

moons of Saturn that orbit outside,
and indeed some inside, the rings.

And for me, that's part of
the wonder of Saturn's rings.

Their beauty is such a good illustration of
how gravity can carve order out of chaos.

But more than that, understanding
how Saturn's moons shape the rings

can shed light on the events that
shaped the early solar system,

events that helped create the world we live in.

Resonance can be much more
than a delicate sculptor

because it's not only small moons
that can enter orbital resonance.

It's now thought that billions of
years ago the two giants of the
solar system, Jupiter and Saturn,

entered a resonance and that unleashed
forces that could move entire planets,

and that made the solar system an
incredibly turbulent and violent place.

The solar system is full of
craters, the record of a long
history of cataclysmic impacts.

But there was one period 3.6 billion years ago

when the whole solar system was turned inside out

by the same forces of orbital
resonance that shaped Saturn's rings.

We now believe that the giant planets formed
much closer to the sun than they are today.

Their orbits drifted for
hundreds of millions of years

until Jupiter and Saturn fell
into a resonant pattern.

Once every cycle, the two planets
aligned in exactly the same spot,

creating a gravitational surge

that played havoc with the
orbits of all the planets.

Neptune was catapulted outwards and
smashed into the ring of comets

surrounding the solar system,
with dramatic consequences.

For a hundred million years,
the solar system turned into

a shooting gallery as a rain
of comets ploughed through it.

Millions of comets were scattered in
all directions, peppering the planets.

It was called the Late Heavy Bombardment.

It created many of the craters we see
throughout the solar system today.

It left scars all over our moon...

..and it had a lasting
impact on the Earth as well.

The only impact craters we see on Earth today,

like this one in Arizona,
were made much more recently,

but they reveal the scale of these impacts.

Now today, impacts like this are relatively rare,

although they will happen again,

but during the Late Heavy Bombardment,

the Earth was hit by thousands
of objects with sizes

far in excess of the object that made this crater,

and the environment was changed
radically and dramatically.

But those changes weren't necessarily
catastrophic because it's now thought

that a significant amount of the water in the
Earth's oceans was delivered by the impacts of

water-rich comets and other objects
during the Late Heavy Bombardment,

and that means that impacts could have played a
key role in the development of life on Earth.

Before the Late Heavy Bombardment,
the Earth was a barren rock.

Afterwards, it supported the oceans that
would become the crucible for life.

Without the water delivered in the Late Heavy
Bombardment, life on Earth may never have evolved.

It's quite a thought that all this may have

been caused by the violent resonances
generated by the orbiting planets.

The story of the solar system is the story
of the creation of order out of chaos.

The planets and their moons were
created by the same universal laws,

the delicate interaction between
gravity and angular momentum

that led to the spinning
patterns we see around us today.

Ultimately, that journey created the finest
example of those forces in action...

..because, in creating the solar system,

those forces that sculpted
order out of chaos also created

the best and most beautiful
laboratory for studying how the
solar system works - Saturn's rings.

It's often the case in science
that answers to the most profound

questions can come from the
most unexpected of places.

Saturn's rings were initially studied
because of their beauty, but understanding

their formation and evolution
has led to a deep understanding

of how form and beauty and order
can emerge from violence and chaos.

And that understanding can be spread
across the entire solar system

and remember that you and me
are part of the solar system.

You and me are ordered
structures formed from the chaos

of the primordial dust cloud
4.5 billion years ago,

and that is one of the
wonders of the solar system.

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