Professor Brian Cox goes on a journey to the storm worlds of the Solar System and explores the weird weather that plays out in the atmospheres of distant planets and moons.
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LearningTranscript
00:00It's midsummer, a storm is breaking, unleashing torrents of rain.
00:30Forming floods that drain into raging rivers and giant lakes.
00:51This is the only world in our solar system where raindrops fall to the ground.
00:58Apart from our own planet.
01:121.4 billion kilometres from the sun lies Earth's strange stormy twin.
01:26Saturn's moon Titan is in some ways more like a planet than a moon.
01:31It is larger than Mercury and it is also in some ways more like the Earth than any other place in the solar system.
01:40I could stand on the surface of Titan in a spacesuit and look out over lakes.
01:48And I could look into the sky and I could experience droplets of rain landing on my visor.
01:56But appearances can be deceptive.
02:06Temperatures on Titan hover around minus 180 degrees Celsius.
02:11Far too cold for liquid water.
02:13Instead, these clouds are made of a chemical that on Earth is a flammable gas.
02:25Methane.
02:31Titan is a world sculpted by methane storms.
02:35Titan is the only moon in the solar system with a thick atmosphere.
02:41And that atmosphere is the stage for the methane cycle.
02:45An arena within which liquid can evaporate from lakes, condense as clouds and fall as rain.
02:52But Titan is certainly not the only storm world.
03:01Among the most dynamic and violent worlds in our solar system
03:05are the handful that, like Titan, have a thick atmosphere.
03:18Planets where sulfuric acid storms rage.
03:25Giant dust vortices dance.
03:28And lightning, ten times more powerful than anything found on Earth, lights up the sky.
03:40And worlds whose storms grow so large, they are entirely engulfed.
03:58The sun rises above the high plains of Utah, it's easy to forget that we live in an atmosphere.
04:22But our atmosphere is central to our existence and central to the character of our planet.
04:38Atmospheres behave like fluids.
04:42And that's extremely important for a planet like Earth.
04:46Let me show you what I mean.
04:51You can see that I'm a very experienced camper.
04:56Now, if I build a model of the Earth's atmosphere, which is coffee,
05:02and then if I put some milk in, which is a denser fluid than the coffee,
05:10and so it's sinking down to the bottom of the pan.
05:14And the reason I want to do that is to show you something that happens when I heat a fluid.
05:22When you think about a planet like the Earth, then it's heated from the sun.
05:28That means that there are temperature differences naturally occurring in our atmosphere.
05:33And it's what happens in nature when there are temperature differences that matters.
05:37So what you see here is that that milk at the bottom of the pan is getting hotter than the coffee at the top.
05:46And that temperature difference is trying to equalise.
05:51So it's not that the temperature difference just equalises in a nice uniform way.
05:58Well, you can see it.
06:00There.
06:02See, there are patterns developing.
06:05Tremendous amount of complexity.
06:06And it's exactly the same in our atmosphere.
06:11But in our atmosphere, we call all those patterns and all that turbulence weather.
06:17Wind, rain and storms can almost be thought of as side effects of an atmosphere trying to move energy between hot and cold.
06:33If a world has an atmosphere, it will have some form of weather.
06:43But as the fleet of spacecraft exploring our cosmic backyard have revealed, atmospheres vary hugely by temperature, pressure and chemical makeup.
07:03And that means that while storms might be common in our solar system, on no two worlds are they ever the same.
07:15GRAND
07:28Journeying outwards from our shared star.
07:31Searching for storm worlds.
07:37We dodge past a planet with no atmosphere.
07:45and arrive at a world consumed by one.
07:59From a distance, Venus appears to be a serene, pearlescent orb,
08:05floating in space.
08:07But get a little closer,
08:09and the planet begins to reveal its true nature.
08:20All that can be seen are clouds,
08:23endless, thick, churning storm clouds
08:26that conceal the entire surface from view.
08:34This is just the top of a cloud deck that's 20 kilometres deep.
08:40And whipped up by hurricane-force winds.
08:46Venus is a true storm world.
08:55Now, those clouds on Venus just look like storm clouds here on Earth.
09:00A bit foreboding, perhaps,
09:03but maybe nothing too much to worry about if you were sat beneath them.
09:07Well, they are, actually, something to worry about.
09:11They're not made of water.
09:15They're made of this.
09:17Concentrated sulphuric acid.
09:20Now, even saying that sounds nasty,
09:23but just wait until you see what this stuff does
09:26to the stuff that I'm made of,
09:29the stuff that you're made of,
09:30just organic material,
09:31in this case, sugar.
09:33Now, you see, that's already starting to react.
09:42It's turning brown.
09:43It's starting to bubble.
09:44The concentrated sulphuric acid,
09:47and this is 90-odd percent concentrated,
09:50which is precisely what we find in the clouds of Venus,
09:53is ripping the water out of the sugar.
09:56In fact, that dark material there is carbon.
10:01It's what's left over when you rip all the water out of the sugar.
10:04I can show you.
10:05So, C12H22O11.
10:10So, that's the sugar we've got,
10:11and then sulphuric acid, which is H2SO4.
10:15And that goes to carbon and water,
10:19and I can smell it, actually.
10:22Sulfur dioxide.
10:24That's it.
10:25And a lot of heat.
10:26But just think, that started off as sugar.
10:29Essentially, organic material like this stuff.
10:34I mean, can you look at that?
10:36So, if you were to skydive through the clouds of Venus,
10:40for some reason,
10:41then that's what you'd turn into.
10:44So, I suppose the moral of the story is,
10:46don't.
10:56But ignoring that advice,
10:58and taking the plunge down through Venus's storm clouds.
11:08We reach a surface that's eerily calm.
11:11With air pressure so intense,
11:13it's like being one kilometre beneath the ocean.
11:17But with one key difference.
11:21that's the only thing that we've got to do.
11:24At 460 degrees Celsius,
11:25Venus's surface is hotter than that of any other planet.
11:31which is why one feature leaps out.
11:38Something that shouldn't be possible on this roasting world.
11:44A mountain that seems to be covered in snow.
11:56Could it really be snowing on Venus?
11:59As well as being really nasty and corrosive,
12:10those sulfuric acid clouds are extremely dense.
12:13That's why, if you look at Venus through a telescope,
12:16all you can see is clouds.
12:19Until the 1950s, actually,
12:21we imagined that Venus might be a tropical paradise.
12:24Now, NASA's Magellan probe arrived in the 1990s,
12:28equipped with radar that could peer through the clouds
12:31and image the surface.
12:33And it took pictures like this.
12:36This is a vast mountain range called Maxwell Montes.
12:40And it's huge.
12:41It's much bigger than the size of Wales
12:42to use the standard measure of area.
12:45And there are points on here
12:46that are 11 kilometres in altitude.
12:49Now, I think it's very difficult using,
12:51as we do our brains tuned to the landscapes of Earth,
12:55not to look at that and see that.
13:02The material that coats Venus's mountains reflects radar,
13:06mimicking the appearance of snow.
13:13But Venus's extreme atmosphere means snow is unlikely.
13:18The atmospheric pressure on the surface of Venus
13:22is 90 times the pressure here on Earth.
13:25That's because its atmosphere is extremely dense.
13:28So 96% of it is carbon dioxide.
13:31Now, carbon dioxide is a powerful greenhouse gas.
13:35That means that although it lets the visible light in from the sun,
13:40which heats up the ground,
13:41the heat radiation coming back out again,
13:44the infrared light is trapped.
13:46The result is a runaway greenhouse effect.
13:53Venus is so hot,
13:54it's thought that the ground might actually glow,
13:57like metal coming out of the forge.
14:03It's a world far too hot for snowstorms.
14:10But the fact that this strange material imitates snow
14:14by being found only on mountaintops is a clue.
14:18The key is altitude.
14:32As you go higher and higher in the Earth's atmosphere,
14:35then the atmospheric pressure falls.
14:37And the reason for that is pretty easy to understand
14:40if you think what pressure is.
14:42It's just the weight of air pressing down.
14:45And so imagine going up to 100 kilometres, for example,
14:49then you'd be in space,
14:50there'd be no atmosphere at all,
14:52and the pressure would be zero.
14:59As you increase altitude,
15:00it's not only the pressure that falls,
15:02the temperature as well.
15:09Now, the explanation for that, actually,
15:10is quite complicated.
15:11It's what a physicist would call
15:13slightly non-trivial.
15:15There are a lot of things happening.
15:17One is that, if you imagine a piece of air,
15:20a volume of air down at sea level,
15:22and you lift it up higher and higher,
15:25and the pressure falls,
15:27and so that air expands,
15:29and therefore it cools.
15:30And there's another thing happening as well,
15:32which is related to the greenhouse effect.
15:34So sunlight is coming down
15:36and heating up the ground,
15:38and then the ground is re-radiating the heat
15:40up into the atmosphere, which is trapping it.
15:43And so the closer you are to the ground,
15:45the hotter it is.
15:46The point is that if you climb a mountain on Earth,
15:49then you can get to a point where the temperature is so low
15:52that water freezes out to form snow.
15:55And that dividing line between the two regions
15:59is called the snow line for obvious reasons.
16:02Now, on Venus, we also see something
16:05that looks for all the world like a snow line,
16:08but water isn't involved.
16:11So what is it?
16:17Venus's snow line suggests that something is freezing up there,
16:22something that freezes at much higher temperatures than water.
16:26and that points us to chemicals that,
16:29on much cooler Earth,
16:31are only ever found as solids.
16:36Now, one of the candidates for that bright, snowy stuff
16:39that coats the mountaintops of Venus
16:43is this.
16:45This is lead sulphide.
16:47So the idea is that the lead and sulphur
16:50that are becoming vapour because it's so hot
16:52and heading up into the atmosphere,
16:55cool and condense out onto the mountaintops
16:58and react to coat them in this bright silver.
17:03I mean, we don't really know for sure.
17:06And part of the reason for that
17:07is it's so difficult to explore Venus.
17:09It would be wonderful to drop a spacecraft
17:11onto those mountains.
17:13But we haven't landed a spacecraft successfully
17:15on the surface of Venus
17:17since the Russian probes in the 1980s.
17:19and they didn't last very long.
17:21But just imagine if that's right.
17:23I mean, what a sight that would be.
17:28Instead of water,
17:29it's thought that on Venus,
17:31it's lead and sulphur that vaporise.
17:34In vapour form, they carried on air currents
17:41from lower altitudes
17:43up into mountain ranges
17:50where, because of the altitude,
17:54the temperature dropped just enough
17:56to allow them to crystallise out of the air.
18:02Coating Venus's mountaintops
18:05in glittering metallic frost.
18:09Creating snowy peaks
18:11on a hellish world.
18:16Leaving Venus's crushing atmosphere behind.
18:23We head out in search of a world
18:25that could almost be Venus's opposite.
18:27We head out in search of a world
18:29that could almost be Venus's opposite.
18:31Bypassing our own planet.
18:32Bypassing our own planet.
18:34We head out in search of a world
18:35that could almost be Venus's opposite.
18:38Bypassing our own planet.
18:40Bypassing our own planet.
18:42Bypassing our own planet.
18:44Bypassing our own planet.
18:53And dodging two potato-shaped moons.
18:57and dodging two potato-shaped moons.
19:11We arrive at the farthest rocky planet from the sun.
19:22We've sent more spacecraft to explore Mars
19:25than any other world in the solar system.
19:30And thanks to this robotic army beaming back photographs,
19:38we know that in the deep past,
19:42Earth-like rainstorms carved at the Martian surface.
19:46But around four billion years ago, Mars began to lose its atmosphere,
19:55transforming it into a planet where you wouldn't expect to see any storms at all.
20:00Modern Mars' wisp of an atmosphere is just one percent the density of Earth's.
20:15And it's so dusty, the sunrise is tinted blue.
20:19Temperatures on the surface average minus 60 degrees Celsius.
20:34Mars might appear to be a frozen world.
20:38But all is not what it seems.
20:43Strange lines, often tens of meters wide, are etched on the surface.
20:51Unlike Mars' dry rivers, these are not relics.
20:56We see them appear and disappear.
21:09Almost as if they're being deliberately drawn and then wiped away.
21:16What, on dry-freezing Mars, could be behind these bizarre shape-shifting patterns?
21:28Oh, look at that.
21:40This is, Moab is a, it's just a fascinating place, the uranium building.
21:45This was known as one of the wildest places in the Wild West.
21:49And then in the 1950s, discovered uranium.
21:52So there's a boom, it was like the gold rush.
21:55But it was a uranium rush.
21:57And there's all these echoes of the atomic hair salon over there.
22:02And there's a, there's nuclear coffee, nuclear coffee.
22:07I'm having some of that.
22:09Clues to solving the mystery of the Martian lines,
22:15come from a pair of trailblazing Mars rovers.
22:18Spirit and Opportunity were small rovers.
22:28And unlike the big, nuclear-powered rovers of today, they were purely solar-powered.
22:33And the solar panel's very small, only about this big.
22:37And those rovers were designed to last around three months because Mars is a dry, dusty desert world.
22:44And all the engineers thought that over time, those solar panels would be covered with dust and the power would drop.
22:51And that's indeed what happened for a while.
22:53Thanks to Mars' dusty atmosphere, at first, the solar panel's energy output dropped.
23:03But then, suddenly, the power started leaping up.
23:11Something was sweeping dust from the solar panels, keeping the rovers alive much longer than expected.
23:26Before long, images started to arrive at Earth that hinted at what was going on.
23:41On Mars, as on Earth, the sunlight passes through the atmosphere pretty much unhindered and hits the ground and heats it up.
23:48But on Mars, because the atmosphere is much lower pressure, much more tenuous,
23:52then the temperature gradients you get close to the ground can be far greater.
23:57So I could stand on the equator of Mars, and the ground can be at 20 degrees Celsius.
24:05But my head can be in air that's at minus 10 degrees Celsius.
24:10And that temperature gradient has powerful effects.
24:13It has consequences, because the gradient wants to equalise.
24:17So the air, in contact with the ground, will heat up.
24:21That means that it will rise. Hot air rises.
24:25Under the right conditions, that rising air creates a lower pressure into which colder air can fall.
24:33And so you can get a system where air rises, air falls, the whole thing spins.
24:38And that can form a stable structure, a dust devil.
24:42So this is, again, a beautiful example of a gradient, an imbalance, creating temporary structure.
24:51In this case, a spinning storm of dust.
24:54Now spotted frequently by spacecraft on the surface,
25:03it's thought that dust devils passing over the rovers sucked dust off the solar panels like a vacuum.
25:12Keeping spirit roving for six years and making opportunity seem unstoppable.
25:24But the cleaning power of dust devils doesn't just work on rovers.
25:30Thanks to Mars' thin atmosphere,
25:44Martian dust devils can grow to up to 20 kilometres tall and one kilometre wide.
25:50And as they travel, these spinning vortices suck up dust from Mars' surface, exposing the darker bedrock beneath.
26:03Leaving trails so large, we can see them clearly from our orbiting spacecraft.
26:15There are no Martians behind the lines.
26:22The culprits are spinning Martian windstorms.
26:33But dust devils are just one half of the puzzle.
26:36They might create the tracks.
26:39But it's something else that wipes them away.
26:44Just like the Earth, Mars has a tilt that gives it seasons.
26:56Summer in one hemisphere means winter in the other.
27:01And the planetary temperature gradient that wants to equalise.
27:05But Mars has no oceans or thick atmosphere to help move heat around the globe.
27:18The one thing it does have, however, is dust.
27:24As summer progresses, a huge amount of dust is lifted into the air by the sun's heat.
27:37The dust absorbs sunlight heating up the air around it, causing updrafts and more dust to be lifted.
27:49Until...
27:51A storm is formed.
27:56That wipes away any dust devil trails in its path.
28:00And every few years, these storms grow so large.
28:12They encircle the entire planet.
28:17In 2018, a monster dust storm darkened Mars' skies for months on end.
28:34And for solar-powered Opportunity, it was catastrophic.
28:38This is the last of over 200,000 photographs that Opportunity sent back from the surface of Mars to Earth.
28:47And it's certainly not the most beautiful photograph by any means.
28:51But it is, I think, remarkably poignant.
28:54Because these speckles, they're not stars in the sky.
28:58They're camera noise.
29:00Because it was so dark when this photograph was taken.
29:04And this dark area here, it's not the Martian surface.
29:07It's actually nothing at all.
29:09Because Opportunity ran out of power just before it finished transmitting this photograph back to Earth.
29:18So, after 14 and a half years, this is the final thing that Opportunity saw, defeated by the Martian atmosphere that kept it alive for so long.
29:32But the darkness plays an important role for Mars.
29:43With less sunlight hitting the surface, the temperature difference between the hemispheres is reduced.
29:52And when the storms recede, they leave a slate white clean.
30:01Ready for dust devils to start etching the surface again.
30:06Leaving Mars and its dust cycle behind, we head out in search of a completely different kind of atmosphere.
30:28But first, we must traverse the asteroid belt.
30:34Ruled by the dwarf planet, Ceres.
30:41Until, three times further from the Sun than Mars, we enter the realm of giants.
30:51Twice as massive as all the other planets of the solar system combined.
31:06This is a storm world on the grandest scale.
31:11Made mostly of hydrogen and helium, Jupiter is a gas giant.
31:21On which storms can grow bigger than planet Earth.
31:30Since 2016, NASA's Juno spacecraft has been exploring this gargantuan planet.
31:44And found that the violence of its weather matches its scale.
31:51Lightning strikes here in abundance.
31:57With bolts ten times more powerful than those found on Earth.
32:03Most flashes are trapped under Jupiter's thick outer layer of ammonia ice clouds.
32:13But the most powerful storms break free.
32:20Allowing us to get a proper look at the fireworks.
32:39It's not really fully understood in precise detail how lightning forms on Earth.
32:44You need ice crystals rising and hailstones falling.
32:48And they collide.
32:49And in that process, electrons are exchanged.
32:52And so the electric charges separate.
32:54The top of the cloud and the bottom of the cloud become electrically charged.
32:58I mean, it's just like walking around on the wrong kind of carpet.
33:04And then grabbing a door knob and getting electrocuted.
33:07But the spark is much bigger.
33:09But what we do know is that in the same region of the atmosphere,
33:14for lightning to form, you need all three phases of water to be present.
33:18The vapour, ice and liquid.
33:21Lightning is common on our planet because of Earth's water cycle.
33:33But Jupiter is a very different kind of world.
33:36Five times further from the Sun.
33:42Thanks to Juno, we know that its atmosphere does contain a trace of water.
33:49Around a quarter of one percent.
33:56But could this water really be the cause of Jupiter's lightning?
34:02We all learn about the water cycle at school.
34:05The Sun shines down on the oceans and lakes.
34:08Water evaporates.
34:09The water vapour rises and cools.
34:12Condenses back to form clouds.
34:14And then falls down to the ground again as rain.
34:18But there's something else to the water cycle that's extremely important.
34:22Because it is a very efficient energy transport mechanism.
34:27Let's take some water from the river and pour it into the hot frying pan on the camping stove.
34:33Then the water boils, turns into vapour and disappears off into the atmosphere.
34:42Let's think about what's happening here at a deeper level.
34:46So water molecules, H2O, are bonded together in the liquid.
34:52I have to put energy in from the flame to break those bombs and turn the liquid into vapour.
34:59The reverse must also be true.
35:02So if the vapour, the steam, turns back into liquid again, the bombs reform and all that energy is released.
35:09And that's why steam burns.
35:14And what's happening is the vapour is touching my cooler hand, turning back into liquid.
35:19And as the bonds reform, a tremendous amount of energy is released.
35:24The water cycle acts like a battery.
35:35On Earth, when water evaporates, it absorbs the sun's energy and stores it.
35:45Until re-releasing it into the atmosphere, when it condenses into clouds.
35:53In a typical cloud, the energy release, when the vapour turns to liquid, is hundreds of tonnes of TNT.
36:01Just in a cloud like that, you think of a big storm system like a hurricane,
36:05then over its lifetime, the energy release is more like thousands of atomic bombs.
36:15By funneling the sun's energy into the atmosphere, the water cycle powers Earth's electrical storms.
36:28But the same can't be true on Jupiter.
36:33The planet receives just 4% of the sunlight that we do here on Earth.
36:37And the surface we see, the ammonia ice clouds, is at minus 100 degrees Celsius.
36:50But, looking at the planet in the infrared, provides a clue as to what's going on.
36:56Jupiter is radiating heat, double the amount of energy it receives from the sun.
37:07Jupiter is basically a giant ball of gas.
37:09And there's nowhere really, as you descend into the planet, where the atmosphere ends.
37:13It's just that the pressure increases.
37:15And ultimately, those gases become liquids.
37:18And actually, at the core, strange sorts of metallic solids.
37:23Now, Jupiter is collapsing under its own gravity.
37:27It's been doing that since it formed, about four and a half billion years ago.
37:30And even now, it's collapsing by about one millimetre per year.
37:36But that releases a tremendous amount of this.
37:39It's gravitational potential energy.
37:46That release is heating Jupiter up at the core.
37:50It's 24,000 degrees Celsius.
37:53Huge temperature gradient.
37:55And it's that that powers the storms on Jupiter.
38:03This internal heat allows water to drive storms on Jupiter.
38:07Just as it does here on Earth.
38:14And that's why Jupiter has so much lightning.
38:22In vapour form, water ascends, carrying energy from deep inside the planet.
38:32Until it reaches a place under the ammonia ice clouds.
38:36Where it's cool enough for it to condense into droplets and ice crystals.
38:45The energy released as the water condenses powers the growth of violent thunderstorms.
38:55In places, so much energy is released.
38:56That ice crystals are swept upwards into the ammonia ice clouds.
39:00Here, ammonia acts as antifreeze.
39:01Here, ammonia acts as antifreeze.
39:02The carbon-freeze.
39:03In places, so much energy is released
39:12that ice crystals are swept upwards into the ammonia ice clouds.
39:25Here, ammonia acts as antifreeze.
39:33Allowing liquid water to grow thunderclouds 60 kilometres tall,
39:40even though it's minus 100 degrees Celsius.
39:51Jupiter's about as different from the Earth as you can possibly get.
39:54It's a gas giant, extremes of temperature and pressure,
39:57really different chemical composition.
40:00But there is a water cycle.
40:03There's a region in the atmosphere
40:05where the temperature and pressure is just right
40:07for water to exist in all of its three phases.
40:11And it's that region that plays the dominant role
40:14in allowing the energy from deep inside the planet
40:17to escape into the upper atmosphere,
40:19drive the storm systems that we see,
40:22and ultimately allow energy to flow from inside the planet
40:26and out into space.
40:33We go to Jupiter and we stop spearheading the National问题.
40:34We, we have great Corrine to find a angel
40:36by a giant baby in the реals.
40:42Heading out from Jupiter,
40:46we cross 700 million kilometres of empty space
40:49before we encounter the solar system's other gas giant.
41:07Taking the crown for the planet with most moons,
41:12Saturn is orbited by at least 146.
41:16That we know of.
41:19But one stands out amongst the crowd.
41:26More than 20 times the mass of all Saturn's other moons combined.
41:35The only moon in the solar system to have a thick atmosphere.
41:39But what makes Titan really special
41:50is it's the only place we know of other than Earth.
41:54Where you could see a site like this.
42:06Thanks to Titan's thick nitrogen atmosphere
42:08and temperatures of minus 180 degrees Celsius,
42:12methane, naturally found as a gas here on Earth, can exist as a liquid.
42:26It forms clouds in the sky, falls as rain, and pools in giant lakes.
42:32But lakes like these are not found everywhere on Titan.
42:39They're only located at the poles.
42:43Free in the sky.
42:50Travel beyond and we find a very different world.
42:58Great plains.
43:01Rolling Dunefields.
43:03These are Titan's deserts, but get down closer, and the familiar shape comes into view.
43:29The reason we know so much about Titan is because of the iconic spacecraft Cassini.
43:35It arrived in the Saturnian system in 2004 and spent over a decade exploring the planet
43:41and its moons, and it discovered not only that Titan is a desert world with methane
43:46lakes around the poles, but also it saw features like this, meandering across the deserts,
43:59and this is one of those.
44:12Titan's desert regions are criss-crossed with dry riverbeds, some 3,000 kilometres away from
44:21the methane lakes at Titan's poles.
44:27So we're faced with a mystery.
44:31What is carving these rivers?
44:36The southwestern United States is just covered in canyons like this.
44:41And they're very similar to the canyons that Cassini saw on the surface of Titan.
44:46Now here, they're caused by flash flooding.
44:48So in the summer months, the North American monsoon sweeps across this landscape.
44:53It's a huge amount of moist air that's risen up from the Gulf of California and dumps rain
45:00onto this otherwise parched desert.
45:02It flows down and cuts these canyons.
45:09If Earth's dry rivers have a seasonal origin, could the same also be true for Titan?
45:22Just like Earth, Saturn is tilted on its axis, and that means that just like Earth, Saturn
45:29has seasons.
45:31But Saturn's year is 29 Earth years, and so that means that each season is something like
45:37seven years long.
45:40Now, Titan shares Saturn's tilt in Titan's southern hemisphere summer.
45:48The southern hemisphere points towards the sun, and even though it's a billion miles away,
45:52so there's not much energy falling on the southern hemisphere, there is enough for those seven
45:57years for methane to evaporate from the lakes and up into the atmosphere.
46:07Cassini saw this happening.
46:11It flew by Titan during southern summer, and saw methane clouds swirling around the South
46:18Pole.
46:22All that methane condensing out in Titan's atmosphere releases a tremendous amount of
46:26energy, just like water condensing out in our atmosphere releases energy.
46:32And that energy release seeds the formation of storms.
46:38But the clouds didn't stay at the South Pole.
46:41In 2010, Cassini took this image of Titan.
46:46And I think it's just remarkable, because this is a storm around Titan's equator.
46:51It's worthwhile sometimes just sitting back and realising what this is.
46:55It's a photograph of a storm in the atmosphere of a moon orbiting Saturn.
47:05In Titan's deserts, autumn brings change to the air.
47:11Storms like the one seen by Cassini arrive from the pole, unleashing torrents of methane
47:22rain.
47:25But because the gravity on Titan is even less than that of our moon, the raindrops fall
47:31at one-sixth of their speed on Earth.
47:40Storms in slow motion.
47:43The most powerful thought to drop 30 centimetres of methane rain a day.
47:47Forming flash floods that over millennia carve canyons into the desert landscape before
48:06they spill out into vast floodplains.
48:09And Cassini also took these images.
48:27This one is an image of the surface.
48:30And these dark areas here have been interpreted as liquid methane.
48:36A flood of liquid methane.
48:38It's a few tens of centimetres deep.
48:41But the area of this flood is something like the area of Utah and Arizona combined.
48:47And then, just a few months later, this image was taken of the same region on Titan.
48:54And now you see that the flooding has disappeared.
48:57All that methane has evaporated back up into the atmosphere again over the period of just
49:02a few months.
49:04And the storm moved on.
49:14In 2022, five years after the Cassini mission had ended, the James Webb Space Telescope turned
49:22its infrared gaze towards Saturn's distant moon.
49:28By now, it was late summer in Titan's northern hemisphere.
49:33And the telescope spotted something magical.
49:39Giant clouds over the North Pole.
49:42The travelling storms had reached their destination.
49:45It's now believed that Titan storms go on an epic 29-year migration.
49:56From one pole to the other and back again.
50:03As they travel, they unleash methane floods that over millennia carve canyons into Titan's
50:10deserts, seasonal rivers on a moon 1.2 billion kilometres from Earth.
50:26Titan is a fascinating world.
50:28And although it lives in permanent twilight, and so we might expect it to be frigid and
50:33frozen solid, it has a tremendously dynamic atmosphere.
50:37There are storms and seasonal monsoons that sweep across the surface, not unlike the monsoons
50:43that sweep across Utah and Arizona.
50:46It's just that because of those temperatures, it's not water that carries energy around the
50:52atmosphere.
50:53All of the chemistry is shifted.
50:55And it's methane that takes centre stage.
50:58This, then, is the story of the storm worlds of our solar system.
51:12The beautiful and complex structures we call weather emerge from each atmosphere trying
51:18to do the same thing, move energy to balance out hot and cold.
51:34But what makes these worlds so dazzlingly different?
51:42Is which chemicals play the leading role in carrying that energy?
51:56Chemistry is what happens between the heat of the stars and the cold of space.
52:00And it plays out on the surface of planets and moons.
52:04The arena is the atmosphere.
52:06The storms sculpt the surface of worlds.
52:10On Venus, the mountains might be coated in metal, and methane falls as rain on Saturn's
52:16moon Titan.
52:18Here on Earth, the atmosphere has allowed life to emerge.
52:22And now a solar system is only one of hundreds of billions of solar systems out there in
52:27the Milky Way galaxy alone.
52:29So just imagine what nature that great tinkering chemist might have created out there.
52:40The navigation has confirmed that the parachute has deployed.
53:02Vacuum maneuver has started about 20 meters off the surface.
53:08For decades, NASA has used rovers to explore the Martian surface.
53:19But because Mars is a storm world, a world with an atmosphere, there is another way.
53:33Ingenuity is a helicopter.
53:35It's our first spacecraft that we built to fly on another world.
53:42In 2021, after hitching a ride to Mars with NASA's latest rover, Perseverance, Ingenuity
53:52has made history.
53:58Ingenuity is reporting.
53:59Spin-up, take-off, slide.
54:01Altimeter data confirmed that Ingenuity has performed its first flight of a powered aircraft
54:08to another planet.
54:12Ingenuity's first flight was so cool.
54:15It was one of these, oh my God, it worked moments, you know.
54:19You test and you test and you do your best to design something.
54:22But to actually see it work on the surface of Mars, we called it the Wright Brothers moment,
54:27but for another planet.
54:37The helicopter was designed at NASA's Jet Propulsion Laboratory.
54:40A test vehicle to prove that extraterrestrial flight is possible.
54:47But the major challenge for engineers was Mars' atmosphere.
54:55Mars does not have a lot of atmosphere to speak of.
54:58It's not like here on the Earth it's much thinner.
55:01A couple of molecules bouncing into each other every once in a while is not a lot of stuff
55:08to push against to generate lift.
55:11So, you have to have a helicopter that's very, very, very, very light.
55:15And you have to have rotors that spin very, very, very, very, very fast.
55:20Only designed to fly five short test flights, Ingenuity surpassed all expectations.
55:29But that looks great.
55:31We're right in the vicinity of where we want it to be.
55:35Its mission was finally brought to an end when it sustained rotor damage on its 72nd flight.
55:44But during its active three years on Mars, the helicopter pioneered a new approach to exploring
55:49the storm worlds of our solar system.
55:54Helicopters like Ingenuity open up a new dimension to exploration on the surface of the planet.
55:59And I mean dimension literally.
56:02You can cover so much more ground.
56:05Instead of driving for meters every day, you can drive kilometers.
56:10You're also going to get this bird's eye view of the planet that's going to be very different.
56:16A rover on the surface has got to climb over boulders, climb up hills.
56:20With a helicopter like Ingenuity, you just fly right over it, no big deal.
56:27Which is why NASA's future mission to Titan is going to be a flying one.
56:35Titan is a fabulous place to explore by rotorcraft.
56:38It's smaller, so it has much lower gravity than Mars.
56:43But it also has a much thicker atmosphere.
56:46If you and I were sitting on the surface of Titan and strapped some wings and an oxygen mask
56:53to our face, we would be able to generate enough lift to fly.
56:58So you can build something that's a lot heavier, that has a lot more complicated, intense science instruments.
57:04In 20 to 30 minutes, Dragonfly will cover several kilometers.
57:09Compare this to the rovers on Mars, which go about 100 meters over the course of a day.
57:15This will allow the Dragonfly team to visit many sites with one spacecraft.
57:25Dragonfly's fundamental mission is to give us an understanding of the chemistry on Titan.
57:33What is the surface of Titan actually made of?
57:36That question has huge implications for our understanding of how complex chemistry can become,
57:44which means it's important for our understanding of how life may emerge elsewhere in the universe.
57:51And it's, I think, going to be so cool.
57:54I can't even imagine what Dragonfly is going to see and what we're going to learn.
57:58I can't wait for that mission.
58:05Next time, the ice worlds.
58:10Where mountains of ice float across great frozen plains.
58:15Where strange aurora hang above an icy giant.
58:20Where a moon is torn apart by a monster planet.
58:25Where
58:32ancient museums,
58:32alltium
58:33in the sky
58:35where
58:36imi
58:38Old
58:41and
58:42hill
58:43in the district
58:45in azul
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