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00:00We all know the familiar faces of our solar system.
00:21The worlds we grew up with.
00:25But there's another side to our solar system we're now discovering.
00:35The misfits and oddballs.
00:42Worlds of freakish shape and size.
00:49Of extreme landscapes.
00:55Mysterious phenomena.
01:02And hidden secrets.
01:09Our neighbourhood is far stranger than we ever imagined.
01:17So how did all these weird worlds come about?
01:25Well, to answer that question, we'll have to explore the force that sculpted and created them.
01:31Gravity.
01:32And the forces that resist its relentless inward pull.
01:37And also, at a deeper level, as there's always a deeper level,
01:42we'll be forced to contemplate why there is anything of complexity and beauty in our universe at all.
01:50Welcome to the solar system of the weird.
02:07From a cloud of gas and dust, gravity, the great sculptor of our universe, fashioned our star and all the worlds and moons around it.
02:33Creating the solar system.
02:42And gravity has continued to shape these myriad worlds ever since.
02:59Let me give you a little 30-second lecture on gravity.
03:14And I'm going to use Newton's picture, not Einstein's, because we don't need the additional accuracy delivered by relativity.
03:21Gravity is a force of attraction between objects.
03:26And it only attracts.
03:28So that means that it tends to clump things together.
03:31And it's a force that only depends on the distance between objects, not the angle.
03:37And so it tends to make spheres.
03:40It's this property of gravity that shaped the moons and planets.
03:59But beyond the near-perfect spheres that dominate our solar system.
04:11Out past the giant orbs of gas and ice.
04:18And ice.
04:19In a distant realm of the solar system.
04:25We found something strange.
04:30Only one craft has been sent to explore the worlds of this distant region.
04:51And on its epic, ongoing journey, the probe caught a glimpse of something truly bizarre moving in the dark.
05:13Not a sphere, like Earth, or even Pluto.
05:26But a giant, 2,000-kilometer-long, egg-shaped world.
05:40Everything around it, two glittering moons.
05:43Mountains, an icy rock, and a faint ring.
05:52If you were standing on Haumea's surface, the stars would wheel above you.
05:57Six times faster than here on Earth.
06:04Haumea is a truly unexpected and bizarre-shaped object.
06:08The first like it ever discovered.
06:11The first like it ever discovered.
06:23Leaving the question.
06:27What created such a seemingly gravity-defying world?
06:39Now, for rocky worlds, the force resisting the inward pull of gravity is created by this rigidity of the rock.
06:49And the thing about pressure is that it acts equally outwards in all directions.
06:56So if you have a force that's squashing everything inwards equally in all directions, and a force that's resisting that squashing equally in all directions, then the shape that's naturally produced is a sphere.
07:09You might say, well, why is something like that not a sphere then?
07:14I mean, it's made of rock.
07:15It's got a gravitational pull.
07:17But it's a very weak gravitational pull because it's not very massive.
07:21And that's the point.
07:23So the gravitational force is on the surface here, trying to squash it down, and nowhere near big enough to overcome the strength of the rock.
07:35So how big does a thing have to be such that the gravitational force is strong enough to overcome the strength of the rock and allow it to deform into a sphere?
07:47And you find, if you wave your hands around a bit, that that size, the radius, is something like 200, 300 kilometres.
07:57It's called a potato radius.
07:59And indeed, you find that if you look out into the solar system, anything that's smaller than about a couple of hundred kilometres in radius looks like that.
08:09And anything that's bigger than a couple of hundred kilometres in radius looks like the Earth.
08:19From what we observe, it seems that the potato radius is a pretty strictly followed rule.
08:27The larger worlds are, the more spherical they become.
08:42Yet it's a rule, Haumea breaks.
08:54Way over the potato radius,
08:56how Haumea should be a round world.
09:01So if its egg shape is not down to its size,
09:05then what is it?
09:08There is a clue,
09:10found by looking at our world,
09:12in a slightly unusual way.
09:17This is a photograph of us working on the beach today.
09:21I use the term loosely.
09:22And what we did is we took a time-lapse.
09:25But it's an interesting time-lapse.
09:27We used an astronomical mount.
09:29And so we fixed the camera at a single point in the sky, the sun.
09:36And then you see what happens.
09:39So it's holding its position.
09:40It doesn't look right because the whole ground is rotating around.
09:45So usually our experience on the surface of the Earth is watching the sky and the sun and the moon and the stars rotate around us.
09:55But if you take that motion out, then what you're seeing here is the Earth rotating beneath the sky.
10:02This unusual view really brings home the fact that we live on a spinning ball of rock.
10:20And there are consequences for sitting on the surface of something that's spinning.
10:34New forces are introduced, forces that are so-called fictitious forces.
10:39But there's nothing fictitious about them, actually.
10:42You'll know that if you try to hang on to a spinning roundabout.
10:45If you let go, you go flying off.
10:48That's not a fiction.
10:49And that force is called the centrifugal force.
10:52Like the Earth, all worlds in the solar system spin.
11:07But Haumea is spinning incredibly quickly.
11:17The entire 2,000-kilometre-long world.
11:22Whips around once every four hours.
11:40And that makes the centrifugal force very powerful indeed.
11:45And I can show you by taking a small thing.
11:52Let's say that's Haumea.
11:56And spinning it really fast.
11:59So, you see what's happening is it was a sphere.
12:03And now it's bulging out.
12:06And it's bulging out along its equator.
12:08Look at that.
12:09That's got the centrifugal force that tends to flatten things.
12:13Oh!
12:20See?
12:23You see that?
12:24I mean, there it is, right?
12:25Those are fictitious forces at work.
12:27And that's essentially, actually, what happened to some bits of Haumea, we think.
12:33We think we're spinning so fast that some bits got thrown off.
12:36And there.
12:38Right, there it is.
12:39So, what you just saw there was a demonstration of how we think this system was created.
12:44This is the best photo we have of that system.
12:47And these bits are essentially that bit that's now over there.
12:50There we are.
12:57See, look.
12:59Haumea.
13:08The battle between spin and gravity has created a truly strange world.
13:14gravity shapes everything in the solar system.
13:22And our next destination has the scars to prove it.
13:28Let the pole from our star draw us inwards.
13:34Pass Neptune.
13:37Until we reach the innermost ice giant.
13:44Uranus is pretty odd to begin with.
13:55The entire planet is knocked over on its side,
14:00likely by a giant impact in the past.
14:05But it's not only the planet that's strange.
14:15Voyager 2 is the only spacecraft to have visited the moon Miranda.
14:30As it flew past the South Pole,
14:33its cameras saw a truly weird patchwork landscape.
14:38A jumble of towering mountains the height of Everest.
14:49And plunging chasms deeper than the Grand Canyon.
14:58One of the most astonishing surfaces in all the solar system.
15:02Where strange cliffs rise to unimaginable heights.
15:15Unlike anything seen on Earth.
15:17So what created the truly bizarre face of Miranda?
15:38The geology of our world is awe-inspiring,
15:41even though we're really familiar with it.
15:43I mean, this island rises two and a half kilometres
15:47from the surface of the Atlantic Ocean.
15:49But just imagine what it would be like standing on the surface of Miranda.
15:53I mean, there's a slope, not unlike this,
15:56that stretches for something like 10,000 metres.
16:01I remember when Voyager soon arrived at Miranda in 1986
16:06and sent back images like this.
16:08Well, that slope is up here.
16:10But one of the scientists at the time said that this world is exotic.
16:15And you can see why.
16:17One of the explanations for why it's like this
16:19was that it must have been hit by something and then reassembled.
16:23It's like a Frankenstein world.
16:25But we now know that the explanation for this strange geology
16:30is, if anything, even more exotic.
16:32We're pretty sure that Miranda must receive the occasional impact.
16:48The result would look like it was playing out in slow motion.
16:59Debris taking the best part of 10 minutes
17:02to slowly tumble to the bottom of those great slopes.
17:05On Earth, it would take only 50 seconds to fall the same distance.
17:19Because on this moon, smaller than the width of the UK,
17:24the pull of gravity is much weaker.
17:26One hundredth of the strength on our world.
17:32Now, the basic explanation for Miranda's strange surface
17:38really is just basic physics.
17:40Miranda's very small.
17:42It's only about 470 kilometres in diameter,
17:45not too far away from the potato radius.
17:46And so its gravity is just not quite strong enough to squash it down into a sphere.
17:53But there's more to the geology, to the surface of a world,
17:58than just basic physical principles.
18:00There's also the history of the world.
18:05Miranda's weak gravity is what makes this landscape possible.
18:10But it's not alone responsible for sculpting it.
18:16Something must have happened to Miranda
18:22to create its battered and scarred surface.
18:27All we have to go on are the glimpses of this world captured as Voyager 2 flew by.
18:38Which suggests this moon had a troubled past.
18:46The key to unlocking the mystery of Miranda is to notice that this surface is not as chaotic as it looks.
18:57It's not entirely random.
18:59There are these three distinct regions, which are known as corona.
19:04And at least on these two external regions, there are ridges, fault lines that surround them.
19:11And to a geologist, that's a smoking gun.
19:13What it suggests is that this surface was not created by external forces,
19:18by impacts from the outside.
19:20It was created from within.
19:23And it's similar to this landscape here.
19:26This is new land.
19:28These are volcanoes.
19:29They were created by a hotspot deep underneath the surface of the Earth.
19:33And by buoyant, hot material rising up through the surface of the Atlantic Ocean.
19:38And we think that's what's happened here.
19:42Buoyant, less dense material rising to the surface, creating these features.
19:48It's thought that it was this internal turmoil that left ruler straight canyons running for hundreds of kilometers across the face of the moon.
20:05Formed when warm material pushing up from the interior caused the surface to crack along fault lines.
20:18Part of the active geology that over millions of years created this Frankenstein world.
20:26But that raises another mystery.
20:31Because Earth's geology is driven by the heat stored away from its formation four and a half billion years ago.
20:38Along with the energy released by radioactive decay.
20:41But Miranda is far too small to have retained any of the heat from its formation.
20:47So where did all that energy come from?
21:01For the answer, you have to look at Miranda's relationship with its parent planet.
21:06And another quirk of gravity.
21:08Probably several times in its history, Miranda was in a more elliptical orbit around Uranus.
21:17That meant that it went close to the planet, far away, close and far away.
21:23And the changing gravitational forces injected the heat into the moon.
21:28And that's what drove its geology.
21:29Gravity, sculpting one of the most tortured landscapes in the solar system.
21:52I think the story of Miranda reveals something quite deep, actually,
21:55about the way that the laws of nature sculpted the strange worlds in our solar system.
22:01And actually, the way that they sculpt everything in the universe.
22:04Because the basic shape, in this case a sphere, reflects the simplicity and beauty and symmetry
22:12of the laws of nature that created it, in this case gravity.
22:16But the detail of the surface, the complexity, reflects a turbulent and often chaotic past.
22:23So you're seeing history frozen in time.
22:27And it is this interaction between simplicity and symmetry and complexity
22:33that truly makes our universe beautiful.
22:36Beautiful and strange.
22:39Travel further into the solar system, and we enter the realm of the outer gas giant.
22:55Home to a site unrivaled in the solar system.
23:12A structure of outrageous size and shape.
23:17Rings of rock and ice.
23:21And ice.
23:27Split into hundreds of ordered, repeating tracks and gaps.
23:32Almost engineered in their precision.
23:36And looping for thousands of kilometres through the void.
23:48So how did nature create the intricate, ordered beauty?
23:53The spiralling gaps and tracks of Saturn's rings?
23:57One of the most obvious things you can say about our universe is that at first sight it is very complicated indeed.
24:17But one of the deepest things you can say about it is that complexity emerges from the action of very simple laws.
24:26Think about this desert landscape.
24:29There's all these beautiful sand dunes and ripples.
24:32But if you look more closely, there's regularity in the ripples.
24:38And if you look at the sand dunes, this angle that they fall away at is always the same.
24:43So there's regularity and beauty and structure emerging from the action of simple laws.
24:50In this case, it's just the wind blowing sand grains and gravity pulling them down to the ground.
24:58And I think the best and certainly the most evocative example of that in the solar system has to be the rings of Saturn.
25:06Yet at first sight there's nothing simple about Saturn's rings.
25:30We think they formed when an icy moon strayed too close to Saturn.
25:34And was pulled apart by its gravity.
25:46Creating a jumble of trillions of individual fragments of ice.
25:57So what turns such chaos into the ordered beauty of Saturn's rings?
26:04NASA's Cassini probe captured the rings in stunning detail.
26:21And orbiting within them, it saw one of the most startling objects in the entire Saturnian system.
26:26Pan is the most wonderful, bizarre object.
26:27I mean, look at these photographs taken by Cassini.
26:29I mean, this is a, it looks like a cross between a UFO and a piece of pasta.
26:33And it's, it's really small.
26:34It's less than 30 kilometers in diameter.
26:35But its impact on the rings is profound.
26:36The shape, actually, is the key to understanding how it is.
26:37It's really small.
26:38It's really small.
26:39It's really small.
26:40It's really small.
26:41It's really small.
26:42It's really small.
26:43It's really small.
26:44It's really small.
26:45It's, it's less than 30 kilometers in diameter.
26:46But its impact on the rings is profound.
26:47The shape, actually, is the key to understanding how it is that Saturn's rings are so wonderfully
26:52complex.
26:53And you can see the basic idea here.
26:58So there's Pan.
26:59And the moon is obviously inside the ring.
27:03And so that means that ring particles can, it can essentially hit them and they fall onto
27:09the surface.
27:10And because Pan has got a very weak gravitational field, it's really, really, really, really,
27:14that it's really, really profound.
27:15And it's really, really profound.
27:16The shape, actually, is the key to understanding how it is that Saturn's rings are so wonderfully complex.
27:20And you can see the basic idea here.
27:24So there's Pan.
27:25And because Pan has got a very weak gravitational field, it's too small, way below the potato
27:30radius, they don't get squashed into a sphere.
27:33They stay there, sort of a ridge.
27:45So part of the explanation for the gaps is that the rings are slowly being eaten.
27:51For millions of years, Pan has been nibbling away, clearing icy particles out of its orbit.
28:06And yet, Pan is only 28 kilometres across.
28:11But it sits within a track that is over 300 kilometres wide.
28:20Clearly far broader than Pan could clear through snacking alone.
28:25This moon doesn't just create a tiny gap in the rings.
28:34It creates a very big gap indeed.
28:36It's so big, in fact, it's called the anchor gap, that that gap was discovered using 19th century telescopes.
28:42It's about ten times the diameter of the moon.
28:44And the way it does that is really key to understanding the complexity of Saturn's rings.
28:51So I have to tell you one thing, a very important thing, about orbits.
28:59Here's Saturn.
29:00And here is Pan orbiting around.
29:04Now, it's a property of orbits that the further away from the planet you are, the slower you move.
29:12That's actually traced back all the way to the beautiful simplicity of Newton's law of universal gravitation.
29:18So that means that ring particles on the inside of Pan are orbiting faster.
29:27They're overtaking the moon.
29:29These particles get a gravitational tug that tends to slow them down.
29:35They are pulled back by Pan's gravity.
29:39And ring particles further out are moving slower.
29:43Now Pan is overtaking them, and that tends to give them a gravitational kick, which speeds them up.
29:50And the effect of that is that Pan's gravitational pull on the particles that are overtaking it tends to cause them to fall down towards the planet.
30:03And its gravitational pull on the particles outside that it's overtaking tend to get raised to a higher orbit around the planet.
30:12And so Pan clears a much bigger gap in the rings than you might otherwise expect.
30:29And Pan is not alone.
30:31Daphnis, a moon a mere eight kilometres across, clears its own track.
30:48Tiny worlds, creating structures on a staggering scale.
30:53What's more puzzling is that so far these are the only moons we've seen directly clearing a track like this.
31:04But there are thousands of looping spirals and gaps, seemingly created by nothing at all.
31:12Including one of the biggest, the Cassini division.
31:19Over 3,000 kilometres wide.
31:24So what's creating these other structures?
31:31Surprisingly, the answer lies not within the rings, but out beyond the discs of ice.
31:46There really is tremendous complexity and structure in Saturn's rings.
31:51Not only gaps, but also sort of structures, density waves that wrap around the planet often several times, like the grooves on a record.
32:01And all those structures ultimately are caused by hundreds of moons, actually over 140 large-ish moons at the last count and countless smaller ones.
32:14And all those have a gravitational influence on the particles in the rings.
32:20One of the key culprits or drivers of complexity is this moon, which looks like a space station, but it's not a space station.
32:31It's a moon, it's called Mimas.
32:37Another truly odd, almost science fiction world.
32:42With its dominant impact crater.
32:44Yet it's not obvious why this moon should influence the rings, as it's about 40,000 kilometres away.
32:57So Mimas, it's orbiting outside the rings such that it goes round Saturn once to every two orbits of particles that would be inside the Cassini division.
33:11So that means that those particles would regularly meet Mimas on its orbit as a gravitational interaction that disrupts the orbits of these particles and moves them out of the division.
33:26Each time the moon and the ice particles align, Mimas's gravity tugs at the fragments of ice and rock like an invisible hand.
33:43Over millions of years, opening up the giant gap.
33:49Opening up the giant gap.
33:57And Mimas is just one of over 140 known moons.
34:04Each capable of creating their own resonances with the rings.
34:08Look at this picture.
34:11This is an image from the Cassini spacecraft.
34:13And you see the complexity here.
34:16It's mind boggling.
34:18This is a resonance with a moon called Prometheus that orbits 14 times around Saturn.
34:27Every 15 orbits of the particles in there.
34:29And that causes this disruption, this structure in the rings.
34:35Here's a moon called Janus that creates a recognisable structure in the rings.
34:39And so on.
34:40And these are just the structures that we've observed.
34:43The orbital dance of Saturn's moons recorded in the rings, creating a pattern we're lucky to see.
35:01Imagine how complicated the gravitational field is around Saturn.
35:05And that's what you're seeing.
35:06It's very beautiful.
35:07It's as if someone had sprinkled ice crystals over the gravitational field so that we can see it.
35:16I suppose that a vinyl record really is a bit like Saturn's rings.
35:20There's a structure here, physical structure, which can give rise to something that we can perceive now.
35:27Sound made solid, in a sense, when you put a needle on there.
35:32And stylus needle.
35:33All right, granddad.
35:34But also, there is, of course, a sense of history about a recording on a record.
35:42It tells you something about the past.
35:47And so it is with a pattern that we see in the rings.
35:51In Saturn's rings, we can see gravity at work, shaping our solar system.
36:09Over half a billion kilometers closer to the sun is a planet on a mind-boggling scale.
36:27So huge, you could fit all the other planets inside it.
36:44Jupiter's immense gravity has helped shape an astonishing world.
36:57Since 2016, NASA's Juno spacecraft has been exploring Jupiter and its moons.
37:12And its moons.
37:18Including the largest moon in the solar system.
37:28Ganymede is a very strange world indeed.
37:31A moon playing at being a planet.
37:41It's the only moon we know of, with an internally generated magnetic field, producing strange aurora.
37:47And elsewhere on its surface, Juno witnessed bizarre scars gouged into its icy crust.
38:06These phenomena suggest Ganymede may be hiding an extraordinary secret.
38:25Ganymede is becoming, I think it's fair to say, one of the most fascinating places in the solar system.
38:30This is one of our best images of Ganymede, taken by Juno.
38:34It is a big moon.
38:36This is the eighth largest object orbiting the sun.
38:39It's bigger than Mercury and not much smaller than Mars.
38:42But it doesn't look particularly different from our moon.
38:45But a series of observations are beginning to suggest to us
38:51that there may be something extremely interesting indeed going on below the surface.
39:00One clue comes from Ganymede's aurora.
39:04Detailed observations have shown that it behaves in an unexpected way.
39:19To have an aurora, then a planet or moon needs two things, basically.
39:22It needs a tenuous atmosphere and it needs a magnetic field.
39:27So what's happening on Ganymede is that charged particles, primarily from Jupiter,
39:32have been funneled down their magnetic field lines to the poles.
39:37And there they hit particles in the atmosphere, they excite them and cause them to emit light, to glow.
39:43And that's the same process that we see here on Earth in the northern and southern lights.
39:48However, Jupiter also has a magnetic field.
39:52And that will affect the aurora on Ganymede.
39:55And so what was done is some computer modelling.
39:58You get Ganymede with its field and its aurora and you get Jupiter with its magnetic field
40:02and you put it all into the computer and you see what happens.
40:05And you find there is a prediction that the aurora on Ganymede should kind of wobble around,
40:10wander in the vicinity of the pole.
40:13And we observed that, but we observed that the aurora wanders far less than it should.
40:20So that implies there's something else going on.
40:33If Ganymede had an additional second magnetic field, it would interfere with the aurora,
40:40causing it to wander less.
40:48But the only way to generate that extra field would be if another layer within the moon conducts electricity.
40:56I believe he was.
41:09I thought we were very good in the lab.
41:11That doesn't work.
41:13Have we got another battery?
41:15Yeah.
41:16Let's plug another battery in.
41:17Here's an electrical circuit.
41:22There's a battery in the bulb.
41:24And if I connect it, the electrons flow and the bulb lights up.
41:29But now, look what happens.
41:31If I take these two wires and connect it by dipping the wires into salt water.
41:38Very cool, isn't it?
41:47So in here, the circuit is being completed.
41:49Salt water is a conductor of electricity.
41:53An electrical current flows.
41:56And that can produce a magnetic field.
41:59So we think that is the origin of that third magnetic field that's making the aurora wander far less than it should.
42:10The implication is that beneath the surface of Ganymede, there's a salt water ocean.
42:17Welcome to the largest ocean of water in the solar system.
42:32It's estimated that there's a layer of water over 100 kilometers deep, wrapped around the moon.
42:40One that never sees the light of day, hidden beneath 150 kilometers of rock hard ice.
42:52But how can liquid water exist in such enormous quantities beneath the frozen surface?
43:05This fascinating theory involves those strange gouges in the surface.
43:17These are impact craters.
43:22Not single craters like those found in other worlds.
43:27But long chains.
43:35There are quite a lot of the answer, actually, of how it came to be that Ganymede has an ocean.
43:49It's the presence of Jupiter.
43:52I can see clouds on the surface of Jupiter through this pretty small telescope, even though tonight it's about 600 million kilometers away.
44:02It can fit over a thousand Earths inside it.
44:05It's massive.
44:07And being massive, it means it's got a strong gravitational pull.
44:11And Jupiter tends to attract things, suck things in, that come within its vicinity and rip them apart.
44:20And we've seen that.
44:22This is a great image.
44:23It's one of the most famous images in astronomy in recent times, actually.
44:27You see that?
44:29So that is Comet Schumacher-Levy 9.
44:32This is a comet that came too close to Jupiter.
44:35It was drawn in by its gravitational field, whipped to bits by its gravitational field, and then ultimately hit Jupiter.
44:43And it hit Jupiter with such ferocity that we saw the impacts in the clouds, and some of them were bigger than the Earth.
44:50Now you look at that, and then look at that, the surface of Ganymede.
45:02Being so close to Jupiter puts Ganymede in the firing line.
45:07Ferocious impacts that create the chain craters.
45:27These scars are just a fraction of what Ganymede has suffered living so close to Jupiter.
45:40And that's the key to understanding how it may have got its hidden ocean.
45:45The early solar system was a much more chaotic place than it is today.
45:59Impacts were common.
46:05Everything got hit.
46:10Jupiter's immense gravity drew in countless asteroids and comets.
46:16And Ganymede was caught in the crossfire.
46:25Impacts delivered enough energy to heat the moon.
46:30And kickstart a process that caused it to melt and separate into layers.
46:37Dense, heavy metals at the core.
46:41And an outer shell made of water and ice.
46:49And we think Ganymede has retained enough of that heat to produce a saltwater ocean with more water, actually, than all the oceans of the Earth combined below the frozen surface of Ganymede.
47:01A strange, giant moon with an ocean and aurora nearly a billion kilometres away from the sun.
47:14We're talking about potentially a habitat for life.
47:15This is a big world, a planet-sized moon, which has a magnetic field and a saltwater ocean and a ready source of energy, it seems.
47:31All the things that we think are necessary for the origin of life.
47:37And it's important because we used to think of what's called a habitable zone around a star, which is where the Earth orbits and indeed Mars and Venus just about.
47:45Which is the zone where you could potentially have liquid water on the world, on the surface of the world in that case.
47:54But now, looking at places like this, we understand that there might be habitable zones far away from stars.
48:01In this case, a habitable zone around a gas giant.
48:06And that habitability, here, is delivered by gravity.
48:21Leaving this distant ocean moon behind, we head inwards on the final leg of our journey.
48:26Passing through the asteroid belt.
48:32Rubble left over from when gravity failed to pull a planet together.
48:42Until we reach the inner rocky planets.
48:44The worlds here are home to phenomena and landscapes that are mesmerizing.
49:08So strange and alien.
49:14But amongst all these wonders, lurks perhaps the strangest world of all.
49:41Welcome to Earth.
49:42It is the biggest rocky world, radius about 6,370 kilometres or so.
49:49It's a bit unusual, in that it's got a single moon.
49:54But the thing that makes it very unusual indeed, is the presence of that liquid water on the surface.
50:01You might not think of Earth as strange, because we live on it.
50:12But it is, in fact, a very rare world.
50:15This is a really wonderful and unusual thing to be able to do in our solar system.
50:30Because there is no other world where the conditions of temperature and pressure on the surface allow liquid water to exist.
50:33It's a very narrow range. And that range is set by the details of our atmosphere.
50:46Tons, tons, tons of atmosphere pressing down on this rock rule to stop it from boiling away.
50:52The nature of our atmosphere is defined by the history of our world, our place in the solar system and gravity.
51:02So, if you imagine that you'd reduce the mass of the planet just a bit, then the pressure would fall and this would boil away.
51:11If I carried on doing that and reduced the gravitational pulse some more, the whole atmosphere would disappear off into space.
51:25All the myriad properties of our planet have combined to allow liquid water to persist here for over four billion years.
51:34Leading to planet Earth's most unique feature.
51:49Life.
52:04As we explore the solar system, we are discovering ever stranger places.
52:12All born of the interplay, between beautifully simple laws of nature.
52:20And the deep history of each and every world.
52:26Creating endless wonders of the solar system.
52:29solar system including us just look at these telescopes our eyes on the universe i find it
52:50so remarkable that on one strange world in our solar system collections of atoms have come
52:56together that can do astronomy because there's nothing particularly special about the earth it is
53:02just another lump of stuff that's found a way to avoid gravitational collapse but somewhere in
53:10between the relentless inward pull of gravity and the sheer bloody mindedness of matter some of that
53:17stuff has found a way to contemplate its place in the universe
53:21no other planet has rings quite like saturn does they're beautiful but it's odd to think that
53:49they might not be there forever far from a permanent structure we now know that these strange loops of
53:55rock and ice are constantly changing and may one day disappear completely we have big questions about
54:05saturn's rings how old are the rings how did they form and what is their evolution like how long are
54:11they going to last nasa's cassini spacecraft studied saturn and its rings for 13 years in search of
54:21answers cassini allowed us to see saturn from closer up than ever before but also from new vantage points
54:29that we had never been able to access from the earth cassini witnessed a series of bizarre moons
54:36clearing paths in the rings but one of the biggest insights came from its encounter with a strange
54:46kind of rain falling onto saturn it was voyager that gave us the first hints that particles could be
54:54falling into saturn but towards the end of the cassini mission when we flew the spacecraft between the
55:00rings and the planet we were able to detect small ring particles that were falling into the planet so
55:07called ring rain the immense gravity of saturn is pulling on these particles eroding the rings ring rain
55:16causes the rings to slowly die but what we don't know is the rate at which the rings are perishing we
55:24just know that they are flying through the icy rain falling from ring to planet was one of cassini's last
55:36endeavors in 2017 the mission came to an end before cassini could find out how long the rings had left
55:45to get a definitive answer on the lifespan of saturn's rings we needed a brand new mission
55:58so jwst isn't like a normal telescope that you would find on earth it's not at the top of the mountain
56:07like the big telescopes that we have here instead it is 1.5 million kilometers away in space
56:13the space telescope is designed to peer into the depths of the universe but its infrared cameras are
56:23also showing us our solar system in a strange new light
56:27illuminating the faint rings around the outer planets normally invisible to us
56:37it's extremely difficult to get to the outer solar system and so an instrument like jwst that can look
56:49at these distant objects is invaluable amongst its targets is saturn and its rings where the hope is
56:59that the telescope will be able to help answer how fast the ring rain is falling
57:04so the rings are made of mostly water ice and some of the smallest pieces flow up the magnetic field
57:11and fall into the planet that happens all the way around so in our observations we see this kind of
57:18infrared glow all the way around the planet that location which indicates that there is ring material
57:23flowing in in the next few years jwst will measure the intensity of the infrared glow in that band
57:32revealing how fast the rings are losing particles i'm very excited to find out how quickly saturn's rings
57:40are eroding today because finding out what's going on today is really important for mapping their past and predicting their future
57:47bringing us ever closer to understanding exactly how long saturn's stunning rings of ice are likely to last
57:56there's something about seeing saturn's rings you have this almost childlike fascination and a professional curiosity
58:06that come together in a very unique way knowing that saturn's rings won't be around forever and that we're here at the exact moment of the planet
58:15and that we're here at the exact moment when they are here is really amazing i feel really lucky that we get to experience them
58:22we're standing on a tightrope wire
58:38they push me but i don't fall down
58:44it's time to continue to end together
58:51forever
58:56forever
58:58forever
59:00forever
59:02forever
59:05forever
59:08forever