0:00:04 > 0:00:06We live on a world of wonders...
0:00:08 > 0:00:12..a place of astonishing beauty and complexity.
0:00:14 > 0:00:19We have vast oceans and incredible weather,
0:00:19 > 0:00:23giant mountains and breathtaking landscapes.
0:00:24 > 0:00:27If you think that this is all there is,
0:00:27 > 0:00:30that our planet exists in magnificent isolation,
0:00:30 > 0:00:31then you're wrong.
0:00:34 > 0:00:38As a physicist, I'm fascinated by how the laws of nature
0:00:38 > 0:00:40that shaped all this
0:00:40 > 0:00:44also shaped the worlds beyond our home planet.
0:00:48 > 0:00:54I think we're living through the greatest age of discovery our civilisation has known.
0:00:54 > 0:00:58We've voyaged to the farthest reaches of the solar system.
0:00:58 > 0:01:02We've photographed strange new worlds,
0:01:02 > 0:01:06stood in unfamiliar landscapes, tasted alien air.
0:01:08 > 0:01:13But what makes the wonders of the solar system even more astonishing is
0:01:13 > 0:01:17that it all started as nothing more than a chaotic cloud of gas and dust.
0:01:19 > 0:01:23And it was from that cloud that everything in the solar system formed.
0:01:23 > 0:01:26All this order - the sun,
0:01:26 > 0:01:29the rotating planets, me -
0:01:29 > 0:01:33coalesced from a collapsing cloud of dust.
0:01:37 > 0:01:39In this film, we'll discover
0:01:39 > 0:01:43how the solar system made the journey from chaos into order...
0:01:44 > 0:01:49..and see how that cloud gave rise to the solar system's most beautiful wonder -
0:01:49 > 0:01:52the majestic rings of Saturn.
0:01:55 > 0:01:59We'll discover how Saturn's amazingly varied moons
0:01:59 > 0:02:02govern the intricate patterns of the rings,
0:02:02 > 0:02:06and how another wonder recently discovered on one of those moons
0:02:06 > 0:02:08is changing our ideas
0:02:08 > 0:02:11about the nature of the outer solar system.
0:02:11 > 0:02:12It's cool!
0:02:15 > 0:02:20We'll witness the fundamental forces that control the universe...
0:02:20 > 0:02:22It's beginning to come - the end of the world.
0:02:22 > 0:02:26..and see how those forces were unleashed
0:02:26 > 0:02:29to create the beautifully ordered solar system we live in.
0:02:33 > 0:02:37It's only now that we're beginning to understand the origins of that order,
0:02:37 > 0:02:41and that has implications for our understanding of the entire solar system,
0:02:41 > 0:02:45and, ultimately, of why we are here.
0:03:10 > 0:03:17MUEZZIN CHANTS
0:03:20 > 0:03:24This is the Great Mosque in the city of Kairouan in Tunisia,
0:03:24 > 0:03:27and this mosque is the fourth holiest place in Islam,
0:03:27 > 0:03:33and so for the last 14 centuries, the relentless passing of the days
0:03:33 > 0:03:38has been celebrated by prayers before dawn, at sunrise,
0:03:38 > 0:03:43at noon, at sunset and in the evening.
0:03:43 > 0:03:46MUEZZIN CHANTS
0:03:46 > 0:03:49The calls to prayer mark out
0:03:49 > 0:03:54the passing of time as the sun travels across the sky.
0:03:54 > 0:03:57But it's not the sun that's moving.
0:03:57 > 0:04:02What we're really observing is the movement of the Earth through space.
0:04:09 > 0:04:13This is the ball of rock we live on.
0:04:13 > 0:04:20It carries us through cycles of night and day as it turns on its axis every 24 hours.
0:04:20 > 0:04:24A year is the time it takes to orbit the sun,
0:04:24 > 0:04:29and we have seasons because the Earth's axis is tilted by 23 degrees.
0:04:32 > 0:04:35To see how that works, we need to speed time up
0:04:35 > 0:04:38so a year passes in just ten seconds.
0:04:38 > 0:04:40At this pace,
0:04:40 > 0:04:43we can see how the southern and then northern hemispheres
0:04:43 > 0:04:46are angled towards the warmth of the sun,
0:04:46 > 0:04:50taking us through yearly cycles of summer and winter.
0:04:53 > 0:04:55All the rhythms of our lives are governed
0:04:55 > 0:04:59by how the Earth travels through space,
0:04:59 > 0:05:03and in Tunisia in April, it's springtime.
0:05:18 > 0:05:23This is the seasonal flower market in Kairouan, and it's only here
0:05:23 > 0:05:26for two months of the year,
0:05:26 > 0:05:30because that's when these flowers are in flower.
0:05:30 > 0:05:36And it's a beautiful example of how the structure, the clockwork of the solar system
0:05:36 > 0:05:40affects things here on Earth in the most unexpected of ways,
0:05:40 > 0:05:46because if our Earth's axis wasn't tilted by 23 degrees, then there wouldn't be any seasons,
0:05:46 > 0:05:50and if there weren't any seasons, then seasonal flowers wouldn't have evolved
0:05:50 > 0:05:52and there wouldn't be a flower market.
0:05:59 > 0:06:01But it's not just the Earth.
0:06:01 > 0:06:05The whole solar system is full of rhythms.
0:06:05 > 0:06:09Each planet orbits the sun at its own distinctive tempo.
0:06:11 > 0:06:13Mercury is the fastest.
0:06:13 > 0:06:16Closest to the sun, it reaches speeds
0:06:16 > 0:06:22of 200,000 kilometres an hour as it completes its orbit in just 88 days.
0:06:29 > 0:06:34Venus rotates so slowly that it takes longer to spin on its axis
0:06:34 > 0:06:36than it does to go around the sun,
0:06:36 > 0:06:40so that on Venus, a day is longer than a year.
0:06:44 > 0:06:48Further out, the planets orbit more and more slowly.
0:06:48 > 0:06:54Jupiter, the largest planet, takes 12 Earth years to complete each orbit.
0:06:56 > 0:06:59And at the very furthest reaches of the solar system,
0:06:59 > 0:07:024.5 billion kilometres from the sun,
0:07:02 > 0:07:07Neptune travels so slowly that it hasn't completed a single orbit
0:07:07 > 0:07:10since it was discovered in 1846.
0:07:11 > 0:07:14The solar system is driven by these rhythms,
0:07:14 > 0:07:19so regular that the whole thing could be run by clockwork.
0:07:19 > 0:07:23It seems extraordinary that such a well-ordered system
0:07:23 > 0:07:27could have come into being spontaneously,
0:07:27 > 0:07:29but it is in fact a great example
0:07:29 > 0:07:33of the beauty and symmetry that lies at the heart of the universe.
0:07:35 > 0:07:40I want to explain how that order emerged from the chaos of space,
0:07:40 > 0:07:44because understanding that will help us understand
0:07:44 > 0:07:47the origins and formation of the solar system,
0:07:47 > 0:07:49and the beauty of its wonders.
0:08:11 > 0:08:14These are the Atlas Mountains in North Africa.
0:08:15 > 0:08:20According to Roman legend, they held the heavens above the Earth.
0:08:24 > 0:08:29And they are one of the finest places to come to view the stars.
0:08:33 > 0:08:37From a place like this, it's easy to appreciate the profound effect
0:08:37 > 0:08:41that the night sky would have had on our ancestors.
0:08:48 > 0:08:50You know, from a modern perspective,
0:08:50 > 0:08:55astronomy can seem remote and arcane,
0:08:55 > 0:08:59because we've lost our connection with the night sky.
0:08:59 > 0:09:05From a city you just don't see a sky look anything like this.
0:09:05 > 0:09:11From the darkness of the Atlas Mountains, it's really, truly majestic.
0:09:12 > 0:09:14So for our ancestors,
0:09:14 > 0:09:18the connection with the night sky would have been incredibly intimate.
0:09:20 > 0:09:24They looked into the skies to understand their place in creation,
0:09:24 > 0:09:25and the movement of the stars
0:09:25 > 0:09:28told them one thing -
0:09:28 > 0:09:31they were at the centre of the universe.
0:09:32 > 0:09:36Up there is Polaris, the North Star,
0:09:36 > 0:09:40and it's almost exactly aligned with the Earth's spin axis,
0:09:40 > 0:09:43which means that, as the Earth rotates,
0:09:43 > 0:09:47all the stars rotate through the sky around that point.
0:10:03 > 0:10:07So it looks for all the world as if the Earth
0:10:07 > 0:10:13is at the centre of the universe and the stars rotate around it.
0:10:18 > 0:10:23And that's, of course, what the ancients thought for thousands of years, and why not?
0:10:23 > 0:10:27Because it's obvious...
0:10:27 > 0:10:29but wrong.
0:10:31 > 0:10:34To understand the Earth's real position in the solar system,
0:10:34 > 0:10:36we need to look at the one set of bodies
0:10:36 > 0:10:40that doesn't behave as predictably as the stars.
0:10:40 > 0:10:45The Greeks named them "planetes", or "wandering stars",
0:10:45 > 0:10:48and we have kept the name "planet" to describe them.
0:10:50 > 0:10:56This is Mars, photographed once a week over a period of months.
0:10:56 > 0:10:59Rather than travelling in a straight line
0:10:59 > 0:11:01across the background of the stars,
0:11:01 > 0:11:05it occasionally changes direction and loops back on itself.
0:11:07 > 0:11:10It's very hard to explain these retrograde loops
0:11:10 > 0:11:14if the Earth is at the centre of the universe.
0:11:17 > 0:11:21Understanding the retrograde motion of Mars didn't come easy.
0:11:21 > 0:11:27That's why it took over 2,000 years to work out, but I'm going to explain it using a stick and some rocks.
0:11:27 > 0:11:31The key thing is that the Earth is not at the centre of the solar system.
0:11:31 > 0:11:33The sun is,
0:11:33 > 0:11:37and the Earth and Mars go round it
0:11:37 > 0:11:39in almost...
0:11:39 > 0:11:43circular orbits.
0:11:43 > 0:11:45So when Mars is viewed from the Earth,
0:11:45 > 0:11:49then it's seen on the sky -
0:11:49 > 0:11:52in fact on the constellations of the Zodiac.
0:11:52 > 0:11:56So as Mars orbits around and the Earth orbits around,
0:11:56 > 0:11:57then from that position,
0:11:57 > 0:12:01Mars will look like it's there on the sky.
0:12:01 > 0:12:05Mars moves and the Earth moves in THAT position...
0:12:06 > 0:12:12..and Mars moves in that direction across the sky, and again,
0:12:12 > 0:12:14in that position,
0:12:14 > 0:12:17Mars will be here, so it's moving in a straight line across the sky.
0:12:20 > 0:12:24But what happens when the Earth overtakes Mars?
0:12:24 > 0:12:27Then look at the line of sight.
0:12:27 > 0:12:31Mars has moved back to there.
0:12:31 > 0:12:33It's reversed its direction.
0:12:34 > 0:12:36And it continues to do that
0:12:36 > 0:12:40until the Earth gets round to somewhere like there,
0:12:40 > 0:12:42and Mars is here,
0:12:42 > 0:12:45and the line of sight means it's started moving that way again.
0:12:49 > 0:12:53So Mars has executed that strange looping motion on the sky
0:12:53 > 0:13:00because the Earth overtook Mars on the inside, and that's why
0:13:00 > 0:13:02the retrograde motion happens.
0:13:02 > 0:13:04Simple!
0:13:06 > 0:13:12Understanding the retrograde loops was one of the major achievements of early astronomy.
0:13:12 > 0:13:16It created the concept of the solar system
0:13:16 > 0:13:19and allowed us to build the first accurate maps of the planets
0:13:19 > 0:13:22and their orbits around the sun.
0:13:23 > 0:13:26Once you had this picture of a solar system
0:13:26 > 0:13:28running like clockwork,
0:13:28 > 0:13:31the sun surrounded by the orbiting planets,
0:13:31 > 0:13:34then you might start asking questions like
0:13:34 > 0:13:37why is the solar system so ordered,
0:13:37 > 0:13:40and how did that order come into existence.
0:13:40 > 0:13:47Well, a clue lies in those sweeping, circular motions of the planets.
0:13:58 > 0:14:03- RADIO:- ..Severe storms over western Oklahoma, 70%.
0:14:03 > 0:14:06Other hazardous weather, 80%...
0:14:06 > 0:14:10To understand how the solar system came into being,
0:14:10 > 0:14:15we need to understand the physical principles that govern the whole universe.
0:14:15 > 0:14:20But, of course, the same laws of physics also control the world WE inhabit,
0:14:20 > 0:14:24so to discover how the solar system started,
0:14:24 > 0:14:27we don't need to look out into space or back in time.
0:14:27 > 0:14:30We just need to look around us.
0:14:30 > 0:14:35One of the remarkable things about the laws of nature is that they're universal,
0:14:35 > 0:14:39and that means that the same laws that describe the formation of the solar system
0:14:39 > 0:14:46can also describe the most mundane things here on Earth, like the motion of water as it drains from the sink.
0:14:50 > 0:14:53These spinning spirals are seen all across the universe.
0:14:53 > 0:14:59We see them everywhere because the laws of physics are the same everywhere.
0:15:03 > 0:15:07I've come here to Oklahoma to see how those laws can unleash forces
0:15:07 > 0:15:12that drive some of the most powerful and destructive phenomena in the atmosphere of our planet -
0:15:12 > 0:15:14tornadoes.
0:15:16 > 0:15:20Oklahoma is in the middle of what is known as Tornado Alley.
0:15:20 > 0:15:22- No, no, no! Tornado! Tornado! - Oh, my God!
0:15:22 > 0:15:24Yep, it's huge.
0:15:24 > 0:15:27- Oh, wow!- Big, big, big. - Look at that thing!
0:15:27 > 0:15:28Look at it spin!
0:15:28 > 0:15:33Every year, hundreds of twisters tear across the landscape.
0:15:33 > 0:15:37They're incredibly dangerous and destructive,
0:15:37 > 0:15:40and their key feature is that same spinning spiral.
0:15:51 > 0:15:54Don Giuliano is a professional storm chaser.
0:15:54 > 0:15:59He's going to help me try to get close to a tornado.
0:15:59 > 0:16:02That little developing storm there is this.
0:16:02 > 0:16:06It's a severe thunderstorm that is capable of producing a tornado.
0:16:06 > 0:16:11Anywhere inside that purple area, it's possible that a tornado could be there or is moving that way.
0:16:11 > 0:16:17And what would happen if, in this car, we - deliberately or not - went straight through it?
0:16:17 > 0:16:19It would probably pick up our car and toss it
0:16:19 > 0:16:24a quarter of a mile through the air and crush it into a little ball.
0:16:24 > 0:16:26I'm going to just do a U-turn.
0:16:26 > 0:16:28THEY LAUGH
0:16:32 > 0:16:34'Bizarre as it sounds,
0:16:34 > 0:16:38'the processes that drive these vast storm systems
0:16:38 > 0:16:44'are the same as would have been seen 5 billion years ago at the start of the solar system.'
0:16:49 > 0:16:54Everything that we know and see around us was formed from a nebula -
0:16:54 > 0:16:57a giant cloud of gas and dust.
0:16:58 > 0:17:01Drifting across light years of space,
0:17:01 > 0:17:06that cloud remained unchanged for millions of years.
0:17:06 > 0:17:10But then something happened that caused it to coalesce
0:17:10 > 0:17:12into the solar system we have today.
0:17:16 > 0:17:18It's thought that a supernova,
0:17:18 > 0:17:21the explosive death of a nearby star,
0:17:21 > 0:17:24sent shockwaves through the nebula.
0:17:24 > 0:17:29This caused a clump to form in the heart of the cloud.
0:17:29 > 0:17:33Because it was more dense, its gravitational pull was stronger
0:17:33 > 0:17:37and it started to pull in more and more gas.
0:17:37 > 0:17:42Soon the whole cloud was collapsing, and crucially, it began to spin.
0:17:47 > 0:17:50It's a feature of all things that spin
0:17:50 > 0:17:53that if they contract, they must also rotate faster.
0:17:53 > 0:17:58It's a universal principle called the conservation of angular momentum.
0:17:58 > 0:18:00Just pull off anywhere here.
0:18:00 > 0:18:04'It's this that leads to those spinning spirals,
0:18:04 > 0:18:07'and it applies equally well to the early solar system
0:18:07 > 0:18:10'and storms like these.
0:18:10 > 0:18:12'As the giant thunderheads build,
0:18:12 > 0:18:16'they suck up hot air and contract,
0:18:16 > 0:18:19'and like the cloud that built the solar system,
0:18:19 > 0:18:23'when they contract, they spin faster and faster.'
0:18:26 > 0:18:28On Earth in storms like this,
0:18:28 > 0:18:33conservation of angular momentum means that you get, in the most extreme case, tornadoes.
0:18:33 > 0:18:36You get very rapidly rotating columns of air
0:18:36 > 0:18:42where the wind speeds can rise to 300, 400, even sometimes 500 kilometres an hour.
0:18:42 > 0:18:47It's very similar to the process that occurred early in the formation of the solar system,
0:18:47 > 0:18:52when a collapsing cloud of dust got, for some reason, a little bit of spin,
0:18:52 > 0:18:57and as that dust cloud collapsed, the spin rate has to speed up and speed up.
0:18:57 > 0:19:01That's what you can see in storms like this when tornadoes are formed.
0:19:01 > 0:19:06The spin of the big storm system can become concentrated and speeded up
0:19:06 > 0:19:09in, well, a tornado.
0:19:09 > 0:19:13You get immense wind speeds, although the wind speed isn't too gentle now.
0:19:13 > 0:19:17And it looks pretty wild up there, I've got to say.
0:19:17 > 0:19:19In fact, I've never... Look at that.
0:19:19 > 0:19:23I've rarely seen such dramatic clouds.
0:19:31 > 0:19:36And apparently, we've got about five minutes before the end of the world,
0:19:36 > 0:19:39so we have to get back in the car.
0:19:39 > 0:19:43There's thunder and lightning and there was a report earlier from this storm
0:19:43 > 0:19:47of hail the size of baseballs, and I don't want one of those on my head.
0:19:47 > 0:19:49PATTERING
0:19:49 > 0:19:52- Let's get back to the car.- Let's go.
0:19:52 > 0:19:55It's beginning to come - the end of the world!
0:20:04 > 0:20:10'This storm never developed into a tornado, but when they do,
0:20:10 > 0:20:14'you can really see the conservation of angular momentum in action.'
0:20:14 > 0:20:17Huge tornado, look at that!
0:20:17 > 0:20:22'As the storm contracts, its core rotates faster and faster
0:20:22 > 0:20:27'until a column of violently rotating air descends from the cloud.'
0:20:27 > 0:20:29Man, look at that funnel!
0:20:30 > 0:20:35'The awesome spinning power of tornadoes has incredibly destructive effects,
0:20:35 > 0:20:37'but it's this same phenomenon
0:20:37 > 0:20:42'that is responsible for creating the stability of the solar system,
0:20:42 > 0:20:45'because it was the conservation of angular momentum
0:20:45 > 0:20:48'that stopped the early solar system collapsing completely.'
0:20:48 > 0:20:51Oh, my God, that's going to be violent.
0:20:57 > 0:21:02While gravity caused the nebula to contract, its conserved spin
0:21:02 > 0:21:06gave rise to a force that balanced the inward pull of gravity
0:21:06 > 0:21:09and allowed a stable disc to form.
0:21:12 > 0:21:16When the sun ignited, it lit up this spinning disc.
0:21:18 > 0:21:21And within the disc, the planets formed,
0:21:21 > 0:21:27all orbiting the sun in their regular, clockwork patterns.
0:21:42 > 0:21:44In just a few hundred million years,
0:21:44 > 0:21:49the cloud had collapsed to form a star system,
0:21:49 > 0:21:51our solar system,
0:21:51 > 0:21:53the sun surrounded by planets,
0:21:53 > 0:21:58and the journey from chaos into order had begun.
0:21:58 > 0:22:01And there's no better place to see the results of that journey
0:22:01 > 0:22:06than in what I think is one of the wonders of the solar system.
0:22:12 > 0:22:15Of all the solar system's wonders,
0:22:15 > 0:22:20there is a place we can go where the processes that built the solar system
0:22:20 > 0:22:22are still in action today...
0:22:24 > 0:22:29..a place of outstanding beauty and complexity...
0:22:31 > 0:22:36..a place that has entranced astronomers for centuries...
0:22:39 > 0:22:41..the planet Saturn.
0:22:51 > 0:22:53This is NASA's Jet Propulsion Laboratory,
0:22:53 > 0:22:58and I've known about this place, or its address - Oak Grove Drive, Pasadena, California -
0:22:58 > 0:23:01since I was very small, because I wrote to them in 1975
0:23:01 > 0:23:06to ask for pictures from the surface of Mars taken by Viking, and they sent them.
0:23:06 > 0:23:10But today, this is the control centre for Cassini, which is our one,
0:23:10 > 0:23:14and to date, only, spacecraft in orbit around Saturn.
0:23:24 > 0:23:27Cassini was launched in 1997.
0:23:27 > 0:23:33It is the largest, most sophisticated spacecraft ever sent to the outer solar system.
0:23:39 > 0:23:44Its purpose is to study Saturn and its rings, and since 2004,
0:23:44 > 0:23:48it has been sending back the most amazing pictures.
0:23:50 > 0:23:54They reveal that the rings are impossibly intricate,
0:23:54 > 0:23:59made up of thousands upon thousands of individual bands and gaps.
0:24:01 > 0:24:06The whole system is surrounded by a network of moons.
0:24:09 > 0:24:12Part of Cassini's mission is to discover how the rings
0:24:12 > 0:24:18came to be like this, how all this incredible structure was created.
0:24:20 > 0:24:22Because, strange as it seems,
0:24:22 > 0:24:26these beautiful patterns are as close as we can get
0:24:26 > 0:24:30to the disc that formed the solar system,
0:24:30 > 0:24:35and that is why the Saturnian system has so much to tell us.
0:24:40 > 0:24:43I mean, I like to think of it as like a miniature solar system.
0:24:43 > 0:24:47The moons are the equivalent of the planets and Saturn is the equivalent of the sun.
0:24:47 > 0:24:52'Carl Murray has spent a lifetime studying Saturn's rings.'
0:24:53 > 0:24:57In the rings, we're learning something about our own origins, if you like,
0:24:57 > 0:25:00because the physical processes that go on in the rings
0:25:00 > 0:25:03and their interaction with the small moons
0:25:03 > 0:25:08are probably similar to what went on in the early solar system after the planets formed,
0:25:08 > 0:25:13and there's still a ring or debris left over from the formation of the planets.
0:25:13 > 0:25:18So if you looked at the solar system 4.5 billion years ago, the sun at the centre,
0:25:18 > 0:25:25- you'd have a disc of dust not unlike Saturn's ring system?- That's right.
0:25:25 > 0:25:30But if we can't understand a disc of material that's in our own back yard,
0:25:30 > 0:25:32what chance do we have of understanding
0:25:32 > 0:25:37a disc that's long since disappeared - the one out of which the solar system formed?
0:25:37 > 0:25:42So it's the same processes, but we've got this incredible opportunity with Cassini
0:25:42 > 0:25:45to observe things happening in front of our eyes.
0:25:52 > 0:25:58Using the data from Cassini, we are able to recreate Saturn's rings in incredible detail.
0:26:01 > 0:26:04We can journey from the vast scale of the disc
0:26:04 > 0:26:08to the minute structure of individual ringlets.
0:26:15 > 0:26:21All the rings are in motion, orbiting Saturn at immense speeds.
0:26:21 > 0:26:25Like the planets orbiting the sun, the rings nearest Saturn are
0:26:25 > 0:26:29the fastest, travelling at over 80,000 kilometres an hour.
0:26:31 > 0:26:35And while the rings appear solid, casting shadows onto the planet,
0:26:35 > 0:26:39they are also incredibly delicate.
0:26:39 > 0:26:43The main disc of the rings is over 100,000 kilometres across,
0:26:43 > 0:26:46but as little as three metres thick.
0:27:02 > 0:27:05Saturn's rings are undoubtedly beautiful
0:27:05 > 0:27:10and, when you see those magnificent pictures from Cassini,
0:27:10 > 0:27:16it's almost impossible to imagine that that level of intricacy and beauty and symmetry
0:27:16 > 0:27:20could have emerged spontaneously, but emerge spontaneously it did.
0:27:20 > 0:27:26And for that reason alone, Saturn's rings are one of my wonders of the solar system.
0:27:26 > 0:27:33But there's more than that because, in studying the origin and evolution of Saturn's rings,
0:27:33 > 0:27:40we've begun to gain valuable insights into the origins and evolutions of our own solar system.
0:27:59 > 0:28:05To try to understand the true nature of Saturn's rings, I've come to this glacial lagoon in Iceland.
0:28:11 > 0:28:16There are two things the boat driver told me about these icebergs.
0:28:16 > 0:28:20One is that they can come up from the bottom of the seabed
0:28:20 > 0:28:22without any warning at all,
0:28:22 > 0:28:28fly up to the surface, tip the boat over and then you die.
0:28:28 > 0:28:34Secondly, if you take some of it and take it home, it's absolutely brilliant in whisky
0:28:34 > 0:28:40because the water is pure, a thousand years old,
0:28:40 > 0:28:43no pollutants in it and it makes whisky taste superb.
0:28:43 > 0:28:46So it's either death or whisky.
0:28:46 > 0:28:48That's my kind of pond!
0:28:52 > 0:28:55But I'm really here because the structure of the rings
0:28:55 > 0:29:01is remarkably similar to the way these icebergs float in the lagoon,
0:29:03 > 0:29:07because, despite appearances, the rings aren't solid.
0:29:07 > 0:29:11Each ring is made up of hundreds of ringlets
0:29:11 > 0:29:16and each ringlet is made up of billions of separate pieces.
0:29:17 > 0:29:22Caught within the grasp of Saturn's gravity, the ring particles
0:29:22 > 0:29:27independently orbit around the planet in an impossibly thin layer.
0:29:27 > 0:29:30- Thanks, see you in a minute. - Yeah hopefully.
0:29:32 > 0:29:36But the similarity doesn't end with the layout.
0:29:36 > 0:29:40It also lies in what the rings and the icebergs are made of,
0:29:40 > 0:29:44and that explains why the rings are so bright.
0:29:54 > 0:29:58Well, this is why we can see Saturn's rings from Earth,
0:29:58 > 0:30:00because this is what they're made of.
0:30:00 > 0:30:06They're made of beautiful pure water ice, sparkling in the sunlight,
0:30:06 > 0:30:10billions of these pieces, a billion kilometres away from Earth.
0:30:17 > 0:30:23Most of the pieces are, well, smaller than that, less than a centimetre.
0:30:23 > 0:30:29Many are micron size ice crystals, but some are as big as this iceberg.
0:30:29 > 0:30:31Some are as big as houses.
0:30:31 > 0:30:35Some can be over a kilometre across.
0:30:35 > 0:30:37Imagine sitting on one!
0:30:37 > 0:30:41Imagine this were a piece of Saturn's rings. What a view.
0:30:47 > 0:30:51This is the closest we can get to Saturn's rings on Earth
0:30:51 > 0:30:54and the view would be remarkably similar.
0:30:58 > 0:31:04Billions of chunks of ice shining brightly as they catch the sunlight.
0:31:07 > 0:31:13And the reason the rings shine so brightly is that, like the icebergs,
0:31:13 > 0:31:16the rings are constantly changing.
0:31:18 > 0:31:21As the ring particles orbit Saturn,
0:31:21 > 0:31:25they're continually crashing into each other and collecting into giant
0:31:25 > 0:31:30clusters that are endlessly forming and breaking apart.
0:31:31 > 0:31:34As they collide, the particles shatter
0:31:34 > 0:31:40exposing bright new faces of ice that catch the sunlight.
0:31:40 > 0:31:43It's because of this constant recycling that the rings are
0:31:43 > 0:31:48able to stay as bright and shiny as they were when they formed.
0:31:58 > 0:32:03For me, one of the most remarkable things about Saturn's rings
0:32:03 > 0:32:07is their dynamism, their constant renewal.
0:32:07 > 0:32:10It's because of that dynamism that we can see them at all.
0:32:10 > 0:32:16That's why they're clean, that's why they reflect sunlight and we can see them from Earth.
0:32:16 > 0:32:22It's, I suppose, a bit like a city that people come and go, buildings
0:32:22 > 0:32:27get torn down and rebuilt but the city always remains the same.
0:32:27 > 0:32:29So it is with Saturn's rings.
0:32:29 > 0:32:32They're different today than they were a thousand years ago.
0:32:32 > 0:32:36They'll be different in a hundred or a thousand years' time
0:32:36 > 0:32:43but that structure and that beauty, that magnificence will always remain.
0:32:55 > 0:33:00Saturn's rings are magnificent for more than just their beauty...
0:33:01 > 0:33:03..because by looking at the rings
0:33:03 > 0:33:07we can begin to understand our own origins.
0:33:13 > 0:33:19And the key to understanding the rings can be found orbiting around them.
0:33:26 > 0:33:27Oh!
0:33:27 > 0:33:30That is absolutely incredible.
0:33:30 > 0:33:35You can see the rings are completely end on.
0:33:35 > 0:33:38I mean, when you see that, I've looked at the sky, I've looked
0:33:38 > 0:33:42at Saturn hundreds of times but I've never seen it through a telescope like this
0:33:42 > 0:33:46and you really get a feeling it's a planet.
0:33:47 > 0:33:52I know what Galileo thought when he said that the planet had ears.
0:33:52 > 0:33:55He didn't have one of these telescopes, though.
0:33:55 > 0:33:59And I can see one, two, three,
0:33:59 > 0:34:04four, five moons around the planet.
0:34:04 > 0:34:06It's just incredibly beautiful.
0:34:10 > 0:34:14Seen like this, it's easy to appreciate how Saturn
0:34:14 > 0:34:21is like a mini-solar system with the moons orbiting like planets around the sun.
0:34:21 > 0:34:24From Earth we can only see a few of the larger moons.
0:34:26 > 0:34:30But in total, Saturn has more than 60 moons,
0:34:30 > 0:34:34and seen close up, they are a weird and wonderful bunch.
0:34:36 > 0:34:39Dione is typical of Saturn's icy moons.
0:34:39 > 0:34:45It looks similar to our own moon but its composition is very different.
0:34:45 > 0:34:50It's about two-thirds water but the surface temperature is minus
0:34:50 > 0:34:57190 degrees Celsius, and at those temperatures, the surface behaves pretty much like solid rock.
0:35:00 > 0:35:04Iapetus is known as the yin and yang moon,
0:35:04 > 0:35:07one half clean ice,
0:35:07 > 0:35:11the other coated in black, dusty deposits.
0:35:17 > 0:35:20The giant moon, Titan, is bigger than the planet Mercury.
0:35:20 > 0:35:23But the unique thing about Titan
0:35:23 > 0:35:29is this atmosphere which is four times as dense as the Earth's.
0:35:29 > 0:35:32It's rich in organic molecules and it's thought that the chemistry
0:35:32 > 0:35:38is very similar to that of the primordial Earth before life began.
0:35:42 > 0:35:47And Hyperion is a moon unlike any other.
0:35:47 > 0:35:51It's not even round and its battered surface has the texture of a sponge.
0:35:56 > 0:36:00And one theory for that is that it's actually a captured comet
0:36:00 > 0:36:07that has drifted in from the distant reaches of the solar system and been captured by Saturn's gravity.
0:36:09 > 0:36:13But the moons of Saturn aren't just a celestial freak show.
0:36:13 > 0:36:19They're the driving force behind the beauty and structure of the rings.
0:36:24 > 0:36:29The most remarkable of them is hidden in one of the outer rings.
0:36:29 > 0:36:34Buried in the heart of the E-ring is a moon that is rapidly becoming
0:36:34 > 0:36:40one of the most fascinating places in the solar system - Enceladus.
0:36:42 > 0:36:46Enceladus has long been an astronomical curiosity
0:36:46 > 0:36:50because it's the most reflective object in the solar system,
0:36:50 > 0:36:55but we've known little about it because Enceladus is tiny,
0:36:55 > 0:37:02only 400 kilometres across, and over a billion kilometres away.
0:37:02 > 0:37:05It's only now we have these amazing images from Cassini
0:37:05 > 0:37:10that we can see just how strange it is.
0:37:10 > 0:37:15Its heavily cratered northern hemisphere looks like any other icy moon,
0:37:15 > 0:37:19but the southern hemisphere tells a very different story.
0:37:19 > 0:37:22It's almost completely free from craters,
0:37:22 > 0:37:27which means that the surface is probably newly formed.
0:37:27 > 0:37:31It's scarred by canyons and riven by cracks.
0:37:31 > 0:37:38It all looks remarkably similar to the geology of Earth, but carved in ice rather than rock.
0:37:41 > 0:37:45And right over the South Pole are the Tiger Stripes,
0:37:45 > 0:37:52four parallel trenches over 130 kilometres long, and possibly hundreds of metres deep.
0:37:54 > 0:37:56They look just like tectonic fault lines.
0:38:07 > 0:38:10This is what tectonic faults look like on Earth.
0:38:12 > 0:38:19This is the continental divide in Iceland where the American and European plates are spreading apart.
0:38:21 > 0:38:26The cliffs at the edge of the plates look out over a plain of new crust
0:38:26 > 0:38:31formed from molten lava pushing up from the centre of the Earth.
0:38:40 > 0:38:44Carolyn Porco, head of the Cassini imaging team,
0:38:44 > 0:38:48thinks that something similar may be happening on Enceladus.
0:38:50 > 0:38:56It is one of the most unique places in all the solar system and you can tell that just by looking at it.
0:38:56 > 0:39:00And we think that it's possible that there is something similar
0:39:00 > 0:39:03to what's happening right here, where you might get slushy ice,
0:39:03 > 0:39:07viscous ice that comes up through the cracks, OK?
0:39:07 > 0:39:12And creates more surface ice, the way you get more crust created right here,
0:39:12 > 0:39:17pushing things out to the side and it's buckling by the time it gets to what is now the mountains.
0:39:17 > 0:39:21So it really is similar to Iceland actually where you're getting lava
0:39:21 > 0:39:26welling up from the surface and creating new land, so in the same way you've got ice?
0:39:26 > 0:39:32We think. In fact it gives us an indication of just how this whole system down there may be working.
0:39:33 > 0:39:37The next clue that something was happening under the surface
0:39:37 > 0:39:42came when Cassini flew directly over the South Pole.
0:39:42 > 0:39:46Thermal readings showed hot spots under the Tiger Stripes.
0:39:46 > 0:39:51For some reason, the stripes were much hotter than the rest of the moon.
0:39:51 > 0:39:54Cassini has found the unthinkable.
0:39:54 > 0:39:59It's found that this southern tip of Enceladus is excessively warm.
0:39:59 > 0:40:03There's more heat coming out of the south polar cap, if you will,
0:40:03 > 0:40:06of Enceladus than is coming out of the equatorial regions.
0:40:06 > 0:40:11It would be like saying there's more heat coming out of Antarctica than the Equator on Earth.
0:40:11 > 0:40:14Then, one day in November 2005,
0:40:14 > 0:40:19Cassini photographed Enceladus just as the sun was setting behind it.
0:40:22 > 0:40:29What it saw became one of the most remarkable discoveries ever made in the outer solar system.
0:40:29 > 0:40:36The backlit images reveal giant fountains erupting from the South Pole,
0:40:36 > 0:40:41volcanoes blasting out ice instead of rock.
0:40:41 > 0:40:43And those images blew everybody away.
0:40:43 > 0:40:46I mean that was like game over, you know!
0:40:46 > 0:40:54Here you have these dozen or more narrow jets and they just look ghostly and fantastic.
0:40:57 > 0:41:00Just a few miles away from the continental divide
0:41:00 > 0:41:04is an area that can help us understand the ice fountains.
0:41:06 > 0:41:11This is one of Earth's hot spots where the volcanic heat of
0:41:11 > 0:41:15the planet's core bubbles up to just below the surface.
0:41:15 > 0:41:18Until a few years ago, Enceladus was thought to be an
0:41:18 > 0:41:25unremarkable world, a small frozen barren lump of rock and ice.
0:41:25 > 0:41:31But those fountains of ice erupting thousands of kilometres out into space mean that there's something
0:41:31 > 0:41:34incredibly interesting going on beneath its surface.
0:41:45 > 0:41:49It's here we find the Earthly phenomenon most like the ice fountains...
0:41:52 > 0:41:54..geysers.
0:41:55 > 0:41:58They form when underground pockets of water suddenly boil
0:41:58 > 0:42:01and explode into the air.
0:42:10 > 0:42:14Geysers on Earth require three things.
0:42:14 > 0:42:17They require a ready source of water,
0:42:18 > 0:42:22they require an intense source of heat just below the surface
0:42:22 > 0:42:25and they need just the right geological plumbing.
0:42:25 > 0:42:29So if the geysers on Enceladus are similar, then that raises the
0:42:29 > 0:42:36intriguing possibility that there's an ocean of liquid water beneath the surface of the moon and it
0:42:36 > 0:42:40raises a very interesting question because Enceladus is far too small
0:42:40 > 0:42:46to have retained any meaningful source of heat at its core, so where does that heat come from?
0:42:54 > 0:42:58On Earth, the geysers are driven by the intense temperatures inside the
0:42:58 > 0:43:03planet, hot enough to melt rock and power volcanoes.
0:43:07 > 0:43:13But Enceladus is so tiny that its core should be frozen solid.
0:43:15 > 0:43:20Enceladus must be getting its heat from somewhere else, and it's
0:43:20 > 0:43:26thought that it might come from its peculiar orbit around Saturn.
0:43:27 > 0:43:31So the next thing to investigate was whether or not you could have,
0:43:31 > 0:43:36what we call, tidal forces flex Enceladus,
0:43:36 > 0:43:41and that simply arises because the orbit of Enceladus is eccentric, meaning it's elliptical,
0:43:41 > 0:43:45out of round, and as it encircles Saturn in its orbit,
0:43:45 > 0:43:49it gets close to Saturn and then far away, close and far away,
0:43:49 > 0:43:53and the gravitational pull changes as it moves in its orbit
0:43:53 > 0:43:56so that means the body's flexing and, if it's flexing,
0:43:56 > 0:43:58it means it's undergoing friction inside this.
0:43:58 > 0:44:05This is a major process for injecting energy that turns into heat into a body like Enceladus.
0:44:07 > 0:44:13As Enceladus orbits, Saturn's gravity actually distorts the shape of the moon.
0:44:13 > 0:44:17It's thought that this heats the interior of the moon just enough
0:44:17 > 0:44:22to melt a small underground ocean of water.
0:44:22 > 0:44:28As it contacts the vacuum of space, that water vaporises and explodes out
0:44:28 > 0:44:32of the moon creating this wonder of the solar system.
0:44:39 > 0:44:44These geysers are incredibly impressive natural phenomena
0:44:44 > 0:44:50but they pale into insignificance compared to the ice fountains of Enceladus.
0:44:53 > 0:44:54It's so cool.
0:44:58 > 0:45:04While this geyser erupts every few minutes, blasting boiling water 20 metres into the air...
0:45:07 > 0:45:12..on Enceladus the plumes are thought to be erupting constantly.
0:45:12 > 0:45:14For them, the sky is the limit.
0:45:22 > 0:45:26Bursting through the surface at 1,300 kilometres an hour,
0:45:26 > 0:45:30they soar up into space for thousands of kilometres.
0:45:31 > 0:45:36They must be one of the most impressive sights in the solar system.
0:45:37 > 0:45:42Any liquid water instantly freezes into tiny ice crystals.
0:45:42 > 0:45:47Some of it falls back onto the surface, giving the moon its reflective icy sheen.
0:45:49 > 0:45:53But the rest keeps going all the way round Saturn.
0:45:53 > 0:45:59The ice fountains are creating one of Saturn's rings as we watch.
0:45:59 > 0:46:04The whole E-ring is made from pieces of Enceladus.
0:46:06 > 0:46:10But Enceladus is not the only moon that shapes the rings.
0:46:12 > 0:46:16Saturn's other moons also play a crucial role in creating these
0:46:16 > 0:46:22beautiful patterns and they do so in mysterious ways.
0:46:38 > 0:46:44The Sahara desert may seem an unlikely place to come to explain Saturn's rings,
0:46:44 > 0:46:51but the behaviour of the sand in the desert can help us understand how the moons form the patterns in the rings.
0:46:55 > 0:47:00At first sight the Sahara desert seems an immensely chaotic place,
0:47:00 > 0:47:07just billions of grains of sand being blown randomly around by the desert winds but actually,
0:47:07 > 0:47:12look a little bit closer, and you start to see an immense amount of order.
0:47:12 > 0:47:16There are sand dunes as far as the eye can see,
0:47:16 > 0:47:21and a remarkable thing is that the angles of the front
0:47:21 > 0:47:24of all the sand dunes are exactly the same.
0:47:24 > 0:47:29Now in the Sahara, the emergence of that order is driven by the desert
0:47:29 > 0:47:33winds blowing always in the same direction,
0:47:33 > 0:47:37day after day, year after year, moving the sand around.
0:47:37 > 0:47:42In the Saturnian system, the order and beauty and intricacy
0:47:42 > 0:47:46of the rings is driven obviously not by wind,
0:47:46 > 0:47:49but by a different force, the force of gravity.
0:47:56 > 0:48:02As the moons orbit Saturn, their gravitational influence sweeps through the rings.
0:48:06 > 0:48:12In these amazing images, we can actually watch the moons as they work.
0:48:14 > 0:48:17We can see gravity in action.
0:48:17 > 0:48:21As the moons pass close to the rings, their gravitational pull
0:48:21 > 0:48:27tugs the ring particles towards them, distorting the shape of the rings.
0:48:28 > 0:48:34The F-ring, one of the outer rings, is twisted into a spiral shape
0:48:34 > 0:48:38by two moons, Prometheus and Pandora.
0:48:38 > 0:48:42In this video taken by Cassini, you can see how Prometheus
0:48:42 > 0:48:47drags plumes of material away as it passes close to the rings.
0:48:49 > 0:48:55These short-range gravitational effects account for many of the patterns in the rings.
0:48:58 > 0:49:05But sometimes the moons can exert their pull over much greater distances,
0:49:05 > 0:49:11and the way they do so reveals the subtlety with which gravity can work.
0:49:14 > 0:49:19Well, here's a model of the Saturnian system with Saturn in the middle
0:49:19 > 0:49:23and the magnificent ring system going around the outside,
0:49:23 > 0:49:29and the first thing you notice when you look at the rings is a huge gap called the Cassini division.
0:49:29 > 0:49:32Now what could possibly have caused that?
0:49:32 > 0:49:37Well, it's all down to one of Saturn's moons called Mimas
0:49:37 > 0:49:40which orbits well outside the ring system.
0:49:40 > 0:49:43And how could something that far outside the rings
0:49:43 > 0:49:47have any influence at all on the particles inside the rings?
0:49:47 > 0:49:51Well, it's all down to a phenomena called orbital resonance.
0:49:51 > 0:49:56Now the particles in the Cassini division have an interesting relationship with the moon, Mimas
0:49:56 > 0:50:00because they orbit around Saturn twice for every single
0:50:00 > 0:50:04orbit of Mimas, and that has an interesting consequence.
0:50:04 > 0:50:08Imagine there's a particle inside the Cassini division.
0:50:08 > 0:50:14Then every second year for this particle they meet up with Mimas.
0:50:14 > 0:50:21They end up in the same place in space and that means that this particle will get a kick
0:50:21 > 0:50:26or a tug from Mimas's gravity on a regular basis, every second year.
0:50:26 > 0:50:31Bang, bang, bang! And that alters the orbit of anything that's in
0:50:31 > 0:50:37the Cassini division, and actually has the effect of throwing it out, of clearing a gap in the rings.
0:50:37 > 0:50:43And in fact, much of the complex and beautiful structure of Saturn's rings
0:50:43 > 0:50:46is down to these orbital resonances,
0:50:46 > 0:50:52not only with Mimas, but with one or more of the 61 known
0:50:52 > 0:50:58moons of Saturn that orbit outside, and indeed some inside, the rings.
0:51:08 > 0:51:12And for me, that's part of the wonder of Saturn's rings.
0:51:12 > 0:51:19Their beauty is such a good illustration of how gravity can carve order out of chaos.
0:51:23 > 0:51:28But more than that, understanding how Saturn's moons shape the rings
0:51:28 > 0:51:33can shed light on the events that shaped the early solar system,
0:51:33 > 0:51:36events that helped create the world we live in.
0:51:38 > 0:51:42Resonance can be much more than a delicate sculptor
0:51:42 > 0:51:46because it's not only small moons that can enter orbital resonance.
0:51:46 > 0:51:52It's now thought that billions of years ago the two giants of the solar system, Jupiter and Saturn,
0:51:52 > 0:51:57entered a resonance and that unleashed forces that could move entire planets,
0:51:57 > 0:52:03and that made the solar system an incredibly turbulent and violent place.
0:52:09 > 0:52:16The solar system is full of craters, the record of a long history of cataclysmic impacts.
0:52:24 > 0:52:28But there was one period 3.6 billion years ago
0:52:28 > 0:52:32when the whole solar system was turned inside out
0:52:32 > 0:52:37by the same forces of orbital resonance that shaped Saturn's rings.
0:52:40 > 0:52:46We now believe that the giant planets formed much closer to the sun than they are today.
0:52:49 > 0:52:53Their orbits drifted for hundreds of millions of years
0:52:53 > 0:52:58until Jupiter and Saturn fell into a resonant pattern.
0:52:58 > 0:53:03Once every cycle, the two planets aligned in exactly the same spot,
0:53:03 > 0:53:07creating a gravitational surge
0:53:07 > 0:53:11that played havoc with the orbits of all the planets.
0:53:11 > 0:53:16Neptune was catapulted outwards and smashed into the ring of comets
0:53:16 > 0:53:20surrounding the solar system, with dramatic consequences.
0:53:27 > 0:53:31For a hundred million years, the solar system turned into
0:53:31 > 0:53:36a shooting gallery as a rain of comets ploughed through it.
0:53:39 > 0:53:45Millions of comets were scattered in all directions, peppering the planets.
0:53:45 > 0:53:48It was called the Late Heavy Bombardment.
0:53:53 > 0:53:59It created many of the craters we see throughout the solar system today.
0:53:59 > 0:54:03It left scars all over our moon...
0:54:04 > 0:54:08..and it had a lasting impact on the Earth as well.
0:54:12 > 0:54:14The only impact craters we see on Earth today,
0:54:14 > 0:54:18like this one in Arizona, were made much more recently,
0:54:18 > 0:54:22but they reveal the scale of these impacts.
0:54:29 > 0:54:33Now today, impacts like this are relatively rare,
0:54:33 > 0:54:34although they will happen again,
0:54:34 > 0:54:37but during the Late Heavy Bombardment,
0:54:37 > 0:54:40the Earth was hit by thousands of objects with sizes
0:54:40 > 0:54:43far in excess of the object that made this crater,
0:54:43 > 0:54:47and the environment was changed radically and dramatically.
0:54:47 > 0:54:53But those changes weren't necessarily catastrophic because it's now thought
0:54:53 > 0:54:58that a significant amount of the water in the Earth's oceans was delivered by the impacts of
0:54:58 > 0:55:04water-rich comets and other objects during the Late Heavy Bombardment,
0:55:04 > 0:55:11and that means that impacts could have played a key role in the development of life on Earth.
0:55:16 > 0:55:21Before the Late Heavy Bombardment, the Earth was a barren rock.
0:55:25 > 0:55:30Afterwards, it supported the oceans that would become the crucible for life.
0:55:41 > 0:55:48Without the water delivered in the Late Heavy Bombardment, life on Earth may never have evolved.
0:55:53 > 0:55:57It's quite a thought that all this may have
0:55:57 > 0:56:02been caused by the violent resonances generated by the orbiting planets.
0:56:08 > 0:56:14The story of the solar system is the story of the creation of order out of chaos.
0:56:15 > 0:56:20The planets and their moons were created by the same universal laws,
0:56:20 > 0:56:25the delicate interaction between gravity and angular momentum
0:56:25 > 0:56:28that led to the spinning patterns we see around us today.
0:56:38 > 0:56:45Ultimately, that journey created the finest example of those forces in action...
0:56:47 > 0:56:50..because, in creating the solar system,
0:56:50 > 0:56:55those forces that sculpted order out of chaos also created
0:56:55 > 0:57:02the best and most beautiful laboratory for studying how the solar system works - Saturn's rings.
0:57:12 > 0:57:16It's often the case in science that answers to the most profound
0:57:16 > 0:57:20questions can come from the most unexpected of places.
0:57:20 > 0:57:25Saturn's rings were initially studied because of their beauty, but understanding
0:57:25 > 0:57:30their formation and evolution has led to a deep understanding
0:57:30 > 0:57:35of how form and beauty and order can emerge from violence and chaos.
0:57:35 > 0:57:40And that understanding can be spread across the entire solar system
0:57:40 > 0:57:44and remember that you and me are part of the solar system.
0:57:44 > 0:57:48You and me are ordered structures formed from the chaos
0:57:48 > 0:57:53of the primordial dust cloud 4.5 billion years ago,
0:57:53 > 0:57:56and that is one of the wonders of the solar system.
0:58:24 > 0:58:26Subtitles by Red Bee Media Ltd
0:58:26 > 0:58:28E-mail subtitling@bbc.co.uk