Order Out of Chaos Wonders of the Solar System


Order Out of Chaos

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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 and incredible weather,

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giant mountains and breathtaking 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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As a physicist, I'm fascinated by how the laws of nature

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that shaped all this

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also shaped the worlds beyond our home planet.

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

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

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We've photographed strange new worlds,

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stood in unfamiliar landscapes, tasted alien air.

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

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

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

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All this order - the sun,

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the rotating planets, me -

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coalesced from a collapsing cloud of dust.

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In this film, we'll discover

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

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

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the majestic rings of Saturn.

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We'll discover how Saturn's amazingly varied moons

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govern the intricate patterns of the rings,

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and how another wonder recently discovered on one of those moons

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is changing our ideas

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about the nature of the outer solar system.

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It's cool!

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

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

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..and see how those forces were unleashed

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to create the beautifully ordered solar system we live in.

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

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

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and, ultimately, of why we are here.

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MUEZZIN CHANTS

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

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and this mosque is the fourth holiest place in Islam,

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

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has been celebrated by prayers before dawn, at sunrise,

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at noon, at sunset and in the evening.

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MUEZZIN CHANTS

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The calls to prayer mark out

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

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

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

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This is the ball of rock we live on.

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

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

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

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

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so a year passes in just ten seconds.

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At this pace,

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we can see how the southern and then northern hemispheres

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are angled towards the warmth of the sun,

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taking us through yearly cycles of summer and winter.

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All the rhythms of our lives are governed

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by how the Earth travels through space,

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and in Tunisia in April, it's springtime.

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

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for two months of the year,

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because that's when these flowers are in flower.

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

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

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

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

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and there wouldn't be a flower market.

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But it's not just the Earth.

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The whole solar system is full of rhythms.

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Each planet orbits the sun at its own distinctive tempo.

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Mercury is the fastest.

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Closest to the sun, it reaches speeds

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

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

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than it does to go around the sun,

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

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Further out, the planets orbit more and more slowly.

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

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And at the very furthest reaches of the solar system,

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4.5 billion kilometres from the sun,

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

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since it was discovered in 1846.

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The solar system is driven by these rhythms,

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

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It seems extraordinary that such a well-ordered system

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could have come into being spontaneously,

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but it is in fact a great example

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

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

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because understanding that will help us understand

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the origins and formation of the solar system,

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and the beauty of its wonders.

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These are the Atlas Mountains in North Africa.

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

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

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

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that the night sky would have had on our ancestors.

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You know, from a modern perspective,

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astronomy can seem remote and arcane,

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

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

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

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So for our ancestors,

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

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

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and the movement of the stars

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told them one thing -

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they were at the centre of the universe.

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Up there is Polaris, the North Star,

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

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which means that, as the Earth rotates,

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all the stars rotate through the sky around that point.

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So it looks for all the world as if the Earth

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

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

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Because it's obvious...

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but wrong.

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

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we need to look at the one set of bodies

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that doesn't behave as predictably as the stars.

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

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

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

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Rather than travelling in a straight line

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across the background of the stars,

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it occasionally changes direction and loops back on itself.

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It's very hard to explain these retrograde loops

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if the Earth is at the centre of the universe.

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

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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.

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

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The sun is,

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and the Earth and Mars go round it

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in almost...

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circular orbits.

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So when Mars is viewed from the Earth,

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then it's seen on the sky -

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in fact on the constellations of the Zodiac.

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So as Mars orbits around and the Earth orbits around,

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then from that position,

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

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

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

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in that position,

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

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But what happens when the Earth overtakes Mars?

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Then look at the line of sight.

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Mars has moved back to there.

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It's reversed its direction.

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And it continues to do that

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until the Earth gets round to somewhere like there,

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and Mars is here,

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

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So Mars has executed that strange looping motion on the sky

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

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the retrograde motion happens.

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Simple!

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

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It created the concept of the solar system

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

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and their orbits around the sun.

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Once you had this picture of a solar system

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running like clockwork,

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the sun surrounded by the orbiting planets,

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then you might start asking questions like

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why is the solar system so ordered,

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and how did that order come into existence.

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

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-RADIO:

-..Severe storms over western Oklahoma, 70%.

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Other hazardous weather, 80%...

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To understand how the solar system came into being,

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

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

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so to discover how the solar system started,

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

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We just need to look around us.

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

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

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

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These spinning spirals are seen all across the universe.

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

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

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

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tornadoes.

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

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-No, no, no! Tornado! Tornado!

-Oh, my God!

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Yep, it's huge.

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-Oh, wow!

-Big, big, big.

-Look at that thing!

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Look at it spin!

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Every year, hundreds of twisters tear across the landscape.

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They're incredibly dangerous and destructive,

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and their key feature is that same spinning spiral.

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Don Giuliano is a professional storm chaser.

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

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That little developing storm there is this.

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

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

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

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It would probably pick up our car and toss it

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

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

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THEY LAUGH

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'Bizarre as it sounds,

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'the processes that drive these vast storm systems

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

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

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a giant cloud of gas and dust.

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Drifting across light years of space,

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that cloud remained unchanged for millions of years.

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But then something happened that caused it to coalesce

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into the solar system we have today.

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It's thought that a supernova,

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the explosive death of a nearby star,

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sent shockwaves through the nebula.

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

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Because it was more dense, its gravitational pull was stronger

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and it started to pull in more and more gas.

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

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It's a feature of all things that spin

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that if they contract, they must also rotate faster.

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

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Just pull off anywhere here.

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

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'and it applies equally well to the early solar system

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'and storms like these.

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'As the giant thunderheads build,

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'they suck up hot air and contract,

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'and like the cloud that built the solar system,

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

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On Earth in storms like this,

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

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You get very rapidly rotating columns of air

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

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

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

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

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

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

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in, well, a tornado.

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

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

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

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I've rarely seen such dramatic clouds.

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

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so we have to get back in the car.

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

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

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PATTERING

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-Let's get back to the car.

-Let's go.

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

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

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

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Huge tornado, look at that!

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

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

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Man, look at that funnel!

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

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'but it's this same phenomenon

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

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'because it was the conservation of angular momentum

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'that stopped the early solar system collapsing completely.'

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

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While gravity caused the nebula to contract, its conserved spin

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

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and allowed a stable disc to form.

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

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And within the disc, the planets formed,

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all orbiting the sun in their regular, clockwork patterns.

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In just a few hundred million years,

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the cloud had collapsed to form a star system,

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our solar system,

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the sun surrounded by planets,

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and the journey from chaos into order had begun.

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

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

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Of all the solar system's wonders,

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

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are still in action today...

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

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

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..the planet Saturn.

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This is NASA's Jet Propulsion Laboratory,

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

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

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

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

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

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Cassini was launched in 1997.

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

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

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it has been sending back the most amazing pictures.

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They reveal that the rings are impossibly intricate,

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

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The whole system is surrounded by a network of moons.

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

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

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Because, strange as it seems,

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these beautiful patterns are as close as we can get

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to the disc that formed the solar system,

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

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

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

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

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

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because the physical processes that go on in the rings

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and their interaction with the small moons

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

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

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

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-you'd have a disc of dust not unlike Saturn's ring system?

-That's right.

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

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what chance do we have of understanding

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

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

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to observe things happening in front of our eyes.

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

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We can journey from the vast scale of the disc

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to the minute structure of individual ringlets.

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

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

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

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

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they are also incredibly delicate.

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

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but as little as three metres thick.

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Saturn's rings are undoubtedly beautiful

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and, when you see those magnificent pictures from Cassini,

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

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could have emerged spontaneously, but emerge spontaneously it did.

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

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

0:27:260:27:33

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

0:27:330:27:40

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

0:27:590:28:05

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

0:28:110:28:16

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

0:28:160:28:20

without any warning at all,

0:28:200:28:22

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

0:28:220:28:28

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

0:28:280:28:34

because the water is pure, a thousand years old,

0:28:340:28:40

no pollutants in it and it makes whisky taste superb.

0:28:400:28:43

So it's either death or whisky.

0:28:430:28:46

That's my kind of pond!

0:28:460:28:48

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

0:28:520:28:55

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

0:28:550:29:01

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

0:29:030:29:07

Each ring is made up of hundreds of ringlets

0:29:070:29:11

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

0:29:110:29:16

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

0:29:170:29:22

independently orbit around the planet in an impossibly thin layer.

0:29:220:29:27

-Thanks, see you in a minute.

-Yeah hopefully.

0:29:270:29:30

But the similarity doesn't end with the layout.

0:29:320:29:36

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

0:29:360:29:40

and that explains why the rings are so bright.

0:29:400:29:44

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

0:29:540:29:58

because this is what they're made of.

0:29:580:30:00

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

0:30:000:30:06

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

0:30:060:30:10

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

0:30:170:30:23

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

0:30:230:30:29

Some are as big as houses.

0:30:290:30:31

Some can be over a kilometre across.

0:30:310:30:35

Imagine sitting on one!

0:30:350:30:37

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

0:30:370:30:41

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

0:30:470:30:51

and the view would be remarkably similar.

0:30:510:30:54

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

0:30:580:31:04

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

0:31:070:31:13

the rings are constantly changing.

0:31:130:31:16

As the ring particles orbit Saturn,

0:31:180:31:21

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

0:31:210:31:25

clusters that are endlessly forming and breaking apart.

0:31:250:31:30

As they collide, the particles shatter

0:31:310:31:34

exposing bright new faces of ice that catch the sunlight.

0:31:340:31:40

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

0:31:400:31:43

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

0:31:430:31:48

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

0:31:580:32:03

is their dynamism, their constant renewal.

0:32:030:32:07

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

0:32:070:32:10

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

0:32:100:32:16

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

0:32:160:32:22

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

0:32:220:32:27

So it is with Saturn's rings.

0:32:270:32:29

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

0:32:290:32:32

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

0:32:320:32:36

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

0:32:360:32:43

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

0:32:550:33:00

..because by looking at the rings

0:33:010:33:03

we can begin to understand our own origins.

0:33:030:33:07

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

0:33:130:33:19

Oh!

0:33:260:33:27

That is absolutely incredible.

0:33:270:33:30

You can see the rings are completely end on.

0:33:300:33:35

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

0:33:350:33:38

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

0:33:380:33:42

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

0:33:420:33:46

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

0:33:470:33:52

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

0:33:520:33:55

And I can see one, two, three,

0:33:550:33:59

four, five moons around the planet.

0:33:590:34:04

It's just incredibly beautiful.

0:34:040:34:06

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

0:34:100:34:14

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

0:34:140:34:21

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

0:34:210:34:24

But in total, Saturn has more than 60 moons,

0:34:260:34:30

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

0:34:300:34:34

Dione is typical of Saturn's icy moons.

0:34:360:34:39

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

0:34:390:34:45

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

0:34:450:34:50

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

0:34:500:34:57

Iapetus is known as the yin and yang moon,

0:35:000:35:04

one half clean ice,

0:35:040:35:07

the other coated in black, dusty deposits.

0:35:070:35:11

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

0:35:170:35:20

But the unique thing about Titan

0:35:200:35:23

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

0:35:230:35:29

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

0:35:290:35:32

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

0:35:320:35:38

And Hyperion is a moon unlike any other.

0:35:420:35:47

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

0:35:470:35:51

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

0:35:560:36:00

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

0:36:000:36:07

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

0:36:090:36:13

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

0:36:130:36:19

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

0:36:240:36:29

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

0:36:290:36:34

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

0:36:340:36:40

Enceladus has long been an astronomical curiosity

0:36:420:36:46

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

0:36:460:36:50

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

0:36:500:36:55

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

0:36:550:37:02

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

0:37:020:37:05

that we can see just how strange it is.

0:37:050:37:10

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

0:37:100:37:15

but the southern hemisphere tells a very different story.

0:37:150:37:19

It's almost completely free from craters,

0:37:190:37:22

which means that the surface is probably newly formed.

0:37:220:37:27

It's scarred by canyons and riven by cracks.

0:37:270:37:31

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

0:37:310:37:38

And right over the South Pole are the Tiger Stripes,

0:37:410:37:45

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

0:37:450:37:52

They look just like tectonic fault lines.

0:37:540:37:56

This is what tectonic faults look like on Earth.

0:38:070:38:10

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

0:38:120:38:19

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

0:38:210:38:26

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

0:38:260:38:31

Carolyn Porco, head of the Cassini imaging team,

0:38:400:38:44

thinks that something similar may be happening on Enceladus.

0:38:440:38:48

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

0:38:500:38:56

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

0:38:560:39:00

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

0:39:000:39:03

viscous ice that comes up through the cracks, OK?

0:39:030:39:07

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

0:39:070:39:12

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

0:39:120:39:17

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

0:39:170:39:21

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

0:39:210:39:26

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

0:39:260:39:32

The next clue that something was happening under the surface

0:39:330:39:37

came when Cassini flew directly over the South Pole.

0:39:370:39:42

Thermal readings showed hot spots under the Tiger Stripes.

0:39:420:39:46

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

0:39:460:39:51

Cassini has found the unthinkable.

0:39:510:39:54

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

0:39:540:39:59

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

0:39:590:40:03

of Enceladus than is coming out of the equatorial regions.

0:40:030:40:06

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

0:40:060:40:11

Then, one day in November 2005,

0:40:110:40:14

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

0:40:140:40:19

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

0:40:220:40:29

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

0:40:290:40:36

volcanoes blasting out ice instead of rock.

0:40:360:40:41

And those images blew everybody away.

0:40:410:40:43

I mean that was like game over, you know!

0:40:430:40:46

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

0:40:460:40:54

Just a few miles away from the continental divide

0:40:570:41:00

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

0:41:000:41:04

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

0:41:060:41:11

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

0:41:110:41:15

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

0:41:150:41:18

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

0:41:180:41:25

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

0:41:250:41:31

incredibly interesting going on beneath its surface.

0:41:310:41:34

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

0:41:450:41:49

..geysers.

0:41:520:41:54

They form when underground pockets of water suddenly boil

0:41:550:41:58

and explode into the air.

0:41:580:42:01

Geysers on Earth require three things.

0:42:100:42:14

They require a ready source of water,

0:42:140:42:17

they require an intense source of heat just below the surface

0:42:180:42:22

and they need just the right geological plumbing.

0:42:220:42:25

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

0:42:250:42:29

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

0:42:290:42:36

raises a very interesting question because Enceladus is far too small

0:42:360:42:40

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

0:42:400:42:46

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

0:42:540:42:58

planet, hot enough to melt rock and power volcanoes.

0:42:580:43:03

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

0:43:070:43:13

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

0:43:150:43:20

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

0:43:200:43:26

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

0:43:270:43:31

what we call, tidal forces flex Enceladus,

0:43:310:43:36

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

0:43:360:43:41

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

0:43:410:43:45

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

0:43:450:43:49

and the gravitational pull changes as it moves in its orbit

0:43:490:43:53

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

0:43:530:43:56

it means it's undergoing friction inside this.

0:43:560:43:58

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

0:43:580:44:05

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

0:44:070:44:13

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

0:44:130:44:17

to melt a small underground ocean of water.

0:44:170:44:22

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

0:44:220:44:28

of the moon creating this wonder of the solar system.

0:44:280:44:32

These geysers are incredibly impressive natural phenomena

0:44:390:44:44

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

0:44:440:44:50

It's so cool.

0:44:530:44:54

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

0:44:580:45:04

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

0:45:070:45:12

For them, the sky is the limit.

0:45:120:45:14

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

0:45:220:45:26

they soar up into space for thousands of kilometres.

0:45:260:45:30

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

0:45:310:45:36

Any liquid water instantly freezes into tiny ice crystals.

0:45:370:45:42

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

0:45:420:45:47

But the rest keeps going all the way round Saturn.

0:45:490:45:53

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

0:45:530:45:59

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

0:45:590:46:04

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

0:46:060:46:10

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

0:46:120:46:16

beautiful patterns and they do so in mysterious ways.

0:46:160:46:22

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

0:46:380:46:44

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

0:46:440:46:51

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

0:46:550:47:00

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

0:47:000:47:07

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

0:47:070:47:12

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

0:47:120:47:16

and a remarkable thing is that the angles of the front

0:47:160:47:21

of all the sand dunes are exactly the same.

0:47:210:47:24

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

0:47:240:47:29

winds blowing always in the same direction,

0:47:290:47:33

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

0:47:330:47:37

In the Saturnian system, the order and beauty and intricacy

0:47:370:47:42

of the rings is driven obviously not by wind,

0:47:420:47:46

but by a different force, the force of gravity.

0:47:460:47:49

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

0:47:560:48:02

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

0:48:060:48:12

We can see gravity in action.

0:48:140:48:17

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

0:48:170:48:21

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

0:48:210:48:27

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

0:48:280:48:34

by two moons, Prometheus and Pandora.

0:48:340:48:38

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

0:48:380:48:42

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

0:48:420:48:47

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

0:48:490:48:55

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

0:48:580:49:05

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

0:49:050:49:11

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

0:49:140:49:19

and the magnificent ring system going around the outside,

0:49:190:49:23

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

0:49:230:49:29

Now what could possibly have caused that?

0:49:290:49:32

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

0:49:320:49:37

which orbits well outside the ring system.

0:49:370:49:40

And how could something that far outside the rings

0:49:400:49:43

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

0:49:430:49:47

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

0:49:470:49:51

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

0:49:510:49:56

because they orbit around Saturn twice for every single

0:49:560:50:00

orbit of Mimas, and that has an interesting consequence.

0:50:000:50:04

Imagine there's a particle inside the Cassini division.

0:50:040:50:08

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

0:50:080:50:14

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

0:50:140:50:21

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

0:50:210:50:26

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

0:50:260:50:31

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

0:50:310:50:37

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

0:50:370:50:43

is down to these orbital resonances,

0:50:430:50:46

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

0:50:460:50:52

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

0:50:520:50:58

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

0:51:080:51:12

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

0:51:120:51:19

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

0:51:230:51:28

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

0:51:280:51:33

events that helped create the world we live in.

0:51:330:51:36

Resonance can be much more than a delicate sculptor

0:51:380:51:42

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

0:51:420:51:46

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

0:51:460:51:52

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

0:51:520:51:57

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

0:51:570:52:03

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

0:52:090:52:16

But there was one period 3.6 billion years ago

0:52:240:52:28

when the whole solar system was turned inside out

0:52:280:52:32

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

0:52:320:52:37

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

0:52:400:52:46

Their orbits drifted for hundreds of millions of years

0:52:490:52:53

until Jupiter and Saturn fell into a resonant pattern.

0:52:530:52:58

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

0:52:580:53:03

creating a gravitational surge

0:53:030:53:07

that played havoc with the orbits of all the planets.

0:53:070:53:11

Neptune was catapulted outwards and smashed into the ring of comets

0:53:110:53:16

surrounding the solar system, with dramatic consequences.

0:53:160:53:20

For a hundred million years, the solar system turned into

0:53:270:53:31

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

0:53:310:53:36

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

0:53:390:53:45

It was called the Late Heavy Bombardment.

0:53:450:53:48

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

0:53:530:53:59

It left scars all over our moon...

0:53:590:54:03

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

0:54:040:54:08

The only impact craters we see on Earth today,

0:54:120:54:14

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

0:54:140:54:18

but they reveal the scale of these impacts.

0:54:180:54:22

Now today, impacts like this are relatively rare,

0:54:290:54:33

although they will happen again,

0:54:330:54:34

but during the Late Heavy Bombardment,

0:54:340:54:37

the Earth was hit by thousands of objects with sizes

0:54:370:54:40

far in excess of the object that made this crater,

0:54:400:54:43

and the environment was changed radically and dramatically.

0:54:430:54:47

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

0:54:470:54:53

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

0:54:530:54:58

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

0:54:580:55:04

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

0:55:040:55:11

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

0:55:160:55:21

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

0:55:250:55:30

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

0:55:410:55:48

It's quite a thought that all this may have

0:55:530:55:57

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

0:55:570:56:02

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

0:56:080:56:14

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

0:56:150:56:20

the delicate interaction between gravity and angular momentum

0:56:200:56:25

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

0:56:250:56:28

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

0:56:380:56:45

..because, in creating the solar system,

0:56:470:56:50

those forces that sculpted order out of chaos also created

0:56:500:56:55

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

0:56:550:57:02

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

0:57:120:57:16

questions can come from the most unexpected of places.

0:57:160:57:20

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

0:57:200:57:25

their formation and evolution has led to a deep understanding

0:57:250:57:30

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

0:57:300:57:35

And that understanding can be spread across the entire solar system

0:57:350:57:40

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

0:57:400:57:44

You and me are ordered structures formed from the chaos

0:57:440:57:48

of the primordial dust cloud 4.5 billion years ago,

0:57:480:57:53

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

0:57:530:57:56

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