All language subtitles for Solar.System.2024.S01E02.1080p.BluRay.x264-DRCOX_track3_[eng]

- (THUNDER ROLLS)
- (WIND WHISTLES)

It's midsummer.

A storm is breaking...

... Unleashing torrents
of rain...

... forming floods that drain
into raging rivers...

..and giant lakes.

This is the only world
in our solar system

where raindrops
fall to the ground...

.. apart from our own planet.

1.4 billion kilometres
from the sun

lies Earth's strange,
stormy twin.

Saturn's moon Titan is,
in some ways,

more like a planet than a moon.

It is larger than Mercury,

and it is also, in some ways,
more like the Earth

than any other place
in the solar system.

| could stand on the surface
of Titan in a spacesuit

and look out over lakes,

and | could look into the sky,

and | could experience droplets
of rain landing on my visor.

But appearances can be
deceptive.

Temperatures on Titan

hover around
minus 180 degrees Celsius,

far too cold for liquid water.

Instead, these clouds are made
of a chemical that, on Earth,

is a flammable gas.

Methane.

Titan is a world sculpted
by methane storms.

Titan is the only moon
in the solar system

with a thick atmosphere,

and that atmosphere is the
stage for the methane cycle,

an arena within which liquid
can evaporate from lakes,

condense as clouds,
and fall as rain.

But Titan is certainly not
the only storm world.

Among the most dynamic
and violent worlds

in our solar system...

..are the handful that,
like Titan,

have a thick atmosphere.

Planets where
sulphuric acid storms rage...

... giant dust vortices dance...

..and lighting ten times
more powerful

than anything found on Earth
lights up the sky...

...and worlds whose storms
grow so large,

they are entirely engulfed.

(THUNDER ROLLS)

On a perfectly still morning
like this...

..as the sun rises
above the high plains of Utah,

it's easy to forget
that we live in an atmosphere.

But our atmosphere
is central to our existence,

and central to the character
of our planet.

Atmospheres behave like fluids,

and that's extremely important
for a planet like Earth.

Let me show you what | mean.

You can see that
I'm a very experienced camper!

Now, if | build a model
of the Earth's atmosphere -

which is coffee -

and then,
if | put some milk in...

...which is a denser fluid
than the coffee,

and so it's sinking down
to the bottom of the pan.

And the reason
| want to do that

is to show you something that
happens when | heat a fluid.

You think about a planet
like the Earth,

then it's heated from the sun.

That means that there are
temperature differences

naturally occurring
in our atmosphere,

and it's what happens
in nature

when there are temperature
differences that matters.

So what you see here
is that that milk

at the bottom of the pan

is getting hotter
than the coffee at the top.

And that temperature difference
is trying to equalise.

So it's not that
the temperature difference

just equalises
In a nice uniform way.

But you can see it...there.

See? There are patterns
developing.

A tremendous amount
of complexity.

And it's exactly the same
in our atmosphere.

But in our atmosphere,
we Call all those patterns

and all that turbulence
weather.

Wind, rain and storms

can almost be thought of
as side-effects

of an atmosphere
trying to move energy

between hot and cold.

lf a world has an atmosphere,

it will have some form
of weather.

But as the fleet of spacecraft

exploring our cosmic back yard
have revealed...

..atmospheres vary hugely

by temperature, pressure
and chemical make-up.

And that means that,

while storms might be common
in our solar system,

on no two worlds
are they ever the same.

Journeying outwards
from our shared star,

searching for storm worlds...

...we dodge past a planet
with no atmosphere...

...and arrive at a world
consumed by one.

From a distance, Venus appears
to be a serene pearlescent orb

floating in space.

But get a little closer...

..and the planet begins to
reveal its true nature.

(WIND WHISTLES)

All that can be seen
are clouds.

Endless, thick,
churning storm clouds

that conceal the entire surface
from view.

This is just the top of a cloud
deck that's 20km deep...

..and whipped up
by hurricane-force winds.

Venus Is a true storm world.

Now, those clouds on Venus

just look like storm clouds
here on Earth.

They're a bit foreboding,
perhaps,

but maybe nothing too much
to worry about

if you were sat beneath them.

Well, they are actually
something to worry about.

They're not made of water.

They're made of this.

Concentrated sulphuric acid.

(LAUGHS) Now, even saying that
sounds nasty,

but just wait till you see
what this stuff does

to the stuff that I'm made of,
the stuff that you're made of,

just organic material -
in this case, sugar.

Now, you see that's
already starting to react -

it's turning brown,
it's starting to bubble.

The concentrated
sulphuric acid -

and this is 90-odd percent
concentrated,

which is precisely what we find
in the clouds of Venus -

is ripping the water
out of the sugar.

In fact, that dark material
there is carbon.

It's what's left over

when you rip all the water
out of the sugar.

| can show you.

So, C12H22011...

So that's the sugar we've got.

And then sulphuric acid,

which is H2SO4,

and that goes
to carbon and water,

and... (LAUGHS)
| can smell it, actually!

... sulphur dioxide.

- That's it. And a lot of heat.
- (BUBBLING)

But just think,

that started off as sugar,

essentially organic material
like this stuff.

| mean, look at that!

So if you were to skydive
through the clouds of Venus,

for some reason,

then that's what you'd
turn into.

So | suppose the moral
of the story is...don't.

(WIND WHISTLES)

But ignoring that advice

and taking the plunge down
through Venus's storm clouds...

...we reach a surface
that's eerily calm,

with air pressure so intense,

it's like being 1km
beneath the ocean,

but with one key difference.

At 460 degrees Celsius,
Venus's surface is hotter

than that
of any other planet...

...Which is why one feature
leaps out.

Something that shouldn't
be possible

on this roasting world...

...a mountain that seems to be
covered in snow.

Could it really be snowing
on Venus?

Now, as well as being
really nasty and corrosive,

those sulphuric acid clouds
are extremely dense.

That's why, if you look at
Venus through a telescope,

all you can see is clouds.

Until the 1950s, actually,

we imagined that Venus
might be a tropical paradise.

Now, NASA's Magellan probe
arrived in the 1990s

equipped with radar that could
peer through the clouds

and image the surface.

And it took pictures like this.

This is a vast mountain range
called Maxwell Montes.

And it's huge, it's much bigger
than the size of Wales,

to use the standard measure
of area.

And there are points on here
that are 11km in altitude.

Now, | think it's very
difficult using, as we do,

our brains, tuned to
the landscapes of Earth,

not to look at that...

..and see that.

The material that coats Venus's
mountains reflects radar,

mimicking the appearance
of snow.

But Venus's extreme atmosphere

means snow is...unlikely.

The atmospheric pressure
on the surface of Venus

is 90 times the pressure
here on Earth.

That's because its atmosphere
is extremely dense,

and 96% of it
is carbon dioxide.

Now, carbon dioxide
is a powerful greenhouse gas.

That means that,

although it lets the visible
light in from the sun,

which heats up the ground,

the heat radiation
coming back out again,

the infrared light, is trapped.

The result is a runaway
greenhouse effect.

Venus is so hot,

it's thought that the ground
might actually glow,

like metal coming out
of a forge.

It's a world far too hot
for snowstorms.

But the fact that this
strange material imitates snow,

by being found only
on mountaintops, is a clue.

The key is altitude.

As you go higher and higher
in the Earth's atmosphere,

then the atmospheric
pressure falls.

And the reason for that
is pretty easy to understand,

if you think what pressure is.

It's just the weight
of air pressing down.

And so, imagine going up
to 100km, for example -

then you'd be in space -

there'd would be
no atmosphere at all,

and the pressure would be zero.

As you increase altitude,

then it's not only
the pressure that falls,

it's the temperature as well.

Now, the explanation for that,
actually, is quite complicated.

It's what a physicist would
call slightly nontrivial.

There are a lot of things
happening.

One is that,
if you imagine a piece of air,

a volume of air
down at sea level,

and you lift it up
higher and higher,

and the pressure falls,

and so that air expands,

and therefore it cools.

But there's another thing
happening as well,

which is related to
the greenhouse effect.

So sunlight is coming down
and heating up the ground,

and then the ground
is re-radiating the heat

up into the atmosphere,
which is trapping it.

And so the closer you are
to the ground,

the hotter it is.

The point is that if you climb
a mountain on Earth,

then you can get to a point
where the temperature is so low

that water freezes out
to form snow.

And that dividing line
between the two regions

is called the snowiline,
for obvious reasons.

Now, on Venus, we also see
something that looks

for all the world
like a Snowline,

but water isn't involved.

So what is it?

Venus's snowline suggests

that something is freezing
up there -

something that freezes at much
higher temperatures than water.

And that points us to chemicals
that, on much cooler Earth,

are only ever found as solids.

Now, one of the candidates
for that bright snowy stuff

that coats the mountaintops
of Venus...

...1S this.

This is lead sulphide.

So the idea is that
the lead and sulphur

that are becoming vapour,
because it's so hot,

and heading up
into the atmosphere,

cool and condense out
onto the mountaintops,

and react to coat them
in this bright silver.

| mean, we don't really know
for sure,

and part of the reason for that

is it's so difficult
to explore Venus.

It would be wonderful
to drop a spacecraft

onto those mountains,

but we haven't landed
a spacecraft successfully

on the surface of Venus

since the Russian probes
in the 1980s,

and they didn't last very long.

But just imagine
if that's right.

| mean,
what a sight that would be.

Instead of water,
it's thought that, on Venus,

it's lead and sulphur
that vaporise.

In vapour form, they're carried
on air currents

from lower altitudes...

...Up into mountain ranges...

...where,
because of the altitude,

the temperature drops
just enough...

(CRACKING)

...to allow them to crystallise
out of the air...

...coating Venus's mountaintops
in glittering metallic frost...

.. creating snowy peaks
on a hellish world.

Leaving Venus's crushing
atmosphere behind...

...we head out in search
of a world

that could almost be
Venus's opposite.

Bypassing our own planet...

..and dodging two
potato-shaped moons...

...we arrive at the farthest
rocky planet from the sun.

We've sent more spacecraft
to explore Mars

than any other world
in the solar system.

And thanks to this robotic army
beaming back photographs...

...we know that
in the deep past...

...Earth-like rainstorms
carved the Martian surface.

But around 4 billion years ago,

Mars began to lose
its atmosphere,

transforming it into a planet
where you wouldn't expect

to see any storms at all.

Modern Mars's
wisp of an atmosphere

is just 1% the density
of Earth's...

(WIND WHISTLES)

..and it's so dusty,
the sunrise is tinted blue.

Temperatures on the surface

average
minus 60 degrees Celsius.

Mars might appear to be
a frozen world...

...but all is not
what it seems.

Strange lines,
often tens of metres wide,

are etched on the surface.

Unlike Mars's dry rivers,
these are not relics.

We see them appear
and disappear...

.. almost as if they're being
deliberately drawn

and then wiped away.

What, on dry, freezing Mars,

could be behind these bizarre
shapeshifting patterns?

Oh, look at that!

This is...

Moab is just
a fascinating place,

the uranium building.
This was known as

one of the wildest places
in the Wild West.

And then, in the 1950s,
they discovered uranium,

so there was a boom.
It was like the Gold Rush.

But it was a uranium rush,

and there's all these echoes
of the...

There's the Atomic Hair Salon
over there,

and there's nuclear coffee!
(CHUCKLES)

Nuclear coffee -
I'm having some of that.

Clues to solving the mystery
of the Martian lines...

...come from a pair
of trailblazing Mars rovers.

Spirit and Opportunity
were small rovers, and unlike

the big nuclear-powered
rovers of today,

they were purely solar powered,

and the solar panels were very
small, only about this big.

And those rovers
were only designed to last

around three months,

because Mars is a dry, dusty
desert world,

and all the engineers
thought that, over time,

those solar panels would be
covered with dust,

and the power would drop.

And that's indeed
what happened...for a while.

Thanks to Mars's
dusty atmosphere,

at first, the solar panels'
energy output dropped.

But then, suddenly...

... the power started
leaping up.

Something was sweeping dust
from the solar panels,

keeping the rovers alive
much longer than expected.

Before long, images started
to arrive at Earth...

.. that hinted at
what was going on.

On Mars, as on Earth,

the sunlight passes through
the atmosphere

pretty much unhindered,

and hits the ground
and heats it up.

But on Mars,

because the atmosphere
is much lower pressure,

much more tenuous,

then the temperature gradients
you get close to the ground

can be far greater.

So | could stand
on the equator of Mars,

and the ground can be
at 20 degrees Celsius,

but my head can be in air

that's at minus 10 degrees
Celsius.

And that temperature gradient
has powerful effects,

it has consequences, because
the gradient wants to equalise.

So the air in contact with
the ground, will heat up,

and that means
that it will rise.

Hot air rises.

Under the right conditions,

that rising air creates
a lower pressure

into which colder air can fall,

and so you can get a system
where air rises, air falls,

the whole thing spins,

and that can form
a stable structure,

a dust devil.

So this is, again, a beautiful
example of a gradient,

an imbalance,

creating temporary structure -

in this case,
a spinning storm of dust.

Now spotted frequently
by spacecraft on the surface...

. It's thought that dust
devils passing over the rovers

sucked dust off the solar
panels like a vacuum...

.. keeping Spirit roving
for six years...

..and making Opportunity
seem unstoppable.

But the cleaning power
of dust devils

doesn't just work on rovers.

Thanks to Mars's
thin atmosphere,

Martian dust devils can grow
up to 20km tall

and 1km wide.

And as they travel,

these spinning vortices suck up
dust from Mars's surface,

exposing the darker bedrock
beneath...

... leaving trails so large,

we can see them clearly
from our orbiting spacecraft.

There were no Martians
behind the lines.

The culprits are spinning
Martian windstorms.

But dust devils are just
one half of the puzzle.

They might create the tracks...

...but it's something else
that wipes them away.

Just like the Earth, Mars has
a tilt that gives it seasons.

Summer in one hemisphere
means winter in the other,

and a planetary
temperature gradient

that wants to equalise.

But Mars has no oceans
or thick atmosphere

to help move heat
around the globe.

The one thing it does have,
however...

...1S dust.

As summer progresses,

a huge amount of dust is lifted
into the air by the sun's heat.

The dust absorbs sunlight,
heating up the air around it...

... causing updraughts
and more dust to be lifted...

...Until a storm is formed...

(WIND WHISTLES)

... that wipes away any
dust devil trails in its path.

And every few years,
these storms grow So large...

.. they encircle
the entire planet.

In 2018, a monster dust storm
darkened Mars's skies

for months on end...

..and for solar-powered
Opportunity,

it was catastrophic.

This is the last
of over 200,000 photographs

that Opportunity sent back from
the surface of Mars to Earth.

And it's certainly not
the most beautiful photograph,

by any means,

but it is, | think,
remarkably poignant,

because these speckles,
they're not stars in the sky.

They're camera noise,

because it was so dark
when this photograph was taken.

And this dark area here,
it's not the Martian surface.

It's actually nothing at all,

because Opportunity
ran out of power

just before it finished
transmitting this photograph

back to Earth.

So, after 14.5 years,

this is the final thing
that Opportunity saw,

defeated by the Martian
atmosphere

that kept it alive for so long.

But the darkness plays
an important role for Mars.

With less sunlight
hitting the surface,

the temperature difference
between the hemispheres

is reduced.

And when the storms recede...

. they leave a slate
wiped clean...

... ready for dust devils

to start etching the surface
again.

Leaving Mars
and its dust cycle behind...

...we head out in search
of a completely different

kind of atmosphere.

But first, we must traverse
the asteroid belt...

...fuled by the dwarf planet
Ceres...

..uUNtil, three times further
from the sun than Mars,

we enter the realm of giants.

Twice as massive
as all the other planets of

the solar system combined...

.. this is a storm world
on the grandest scale.

Made mostly of hydrogen
and helium,

Jupiter is a gas giant...

...on which storms can grow
bigger than planet Earth.

Since 2016,
Nasa’'s Juno spacecraft

has been exploring
this gargantuan planet...

...and found that the violence
of its weather

matches its scale.

Lightning strikes here
in abundance...

...with bolts ten times
more powerful

than those found on Earth.

Most flashes are trapped under
Jupiter's thick outer layer

of ammonia ice clouds.

But the most powerful storms
break free...

...allowing us to get
a proper look at the fireworks.

It's not really fully
understood in precise detail

how lightning forms on Earth.

You need ice crystals rising
and hailstones falling,

and they collide,
and in that process

electrons are exchanged,

and so the electric charges
separate.

The top of the cloud
and the bottom of the cloud

- become electrically charged.
- (THUNDER ROLLS)

| mean, it's just like
walking around

on the wrong kind of carpet,

and then grabbing a door knob
and getting electrocuted,

but the spark is much bigger.

But what we do know is that,

in the same region
of the atmosphere

for lightning to form,

you need all three phases
of water to be present -

the vapour, ice and liquid.

Lightning is common
on our planet

because of Earth's
water cycle.

But Jupiter is a very different
kind of world,

five times further
from the sun.

Thanks to Juno,
we know that its atmosphere

does contain
a trace of water...

... around a quarter of 1%.

But could this water really be

the cause
of Jupiter's lighting?

We all learn about
the water cycle at school.

The sun shines down
on the oceans and lakes,

water evaporates, the water
vapour rises and cools,

condenses back to form clouds,

and then falls down
to the ground again as rain.

But there's something else
to the water cycle

that's extremely important,

because it is a very efficient
energy transport mechanism.

If | take some water
from the river

and pour it into the hot frying
pan on the camping stove...

..then the water boils,
turns into vapour,

and disappears off
into the atmosphere.

Let's think what's happening
here at a deeper level.

So water molecules, H2O,

are bonded together
In the liquid.

Now, | have to put energy in
from the flame

to break those bonds

and turn the liquid
into vapour.

The reverse must also be true,

so the vapour, the steam,
turns back into liquid again,

the bonds reform, and all that
energy is released.

And that's why steam...burns.

What's happening is the vapour
is touching my cooler hand,

turning back into liquid,
and as the bonds reform,

a tremendous amount of energy
is released.

The water cycle acts like
a battery.

On Earth,
when water evaporates,

it absorbs the sun's energy
and stores it...

.. Until re-releasing it
into the atmosphere,

when it condenses into clouds.

In a typical cloud,
the energy release,

when the vapour turns
to liquid,

is hundreds of tonnes of TNT.

Just in a cloud like that.

If you think of a big storm
system, like a hurricane,

then over its lifetime,
the energy release is more like

thousands of atomic bombs.

By funnelling the sun's energy
into the atmosphere,

the water cycle powers
Earth's electrical storms.

But the same can't be true
on Jupiter.

The planet receives
just 4% of the sunlight

that we do here on Earth.

And the surface we see,
the ammonia ice clouds,

is at minus 100 degrees
Celsius.

But looking at the planet
in the infrared...

... provides a clue
as to what's going on.

Jupiter is radiating heat...

... double the amount of energy
it receives from the sun.

Jupiter is basically
a giant ball of gas,

and there's nowhere, really,
as you descend into the planet,

where the atmosphere ends,

just that the pressure
increases,

and ultimately,
those gases become liquids,

and actually, at the core,

strange sorts of
metallic solids.

Now, Jupiter is collapsing
under its own gravity.

It's been doing that
since it formed

about 4.5 billion years ago.

And even now,

it's collapsing
by about 1mm per year.

But that releases
a tremendous amount of this.

It's gravitational
potential energy.

That release
is heating Jupiter up.

At the core,
it's 24,000 degrees Celsius -

a huge temperature gradient -

and it's that that powers
the storms on Jupiter.

This internal heat allows water
to drive storms on Jupiter,

just as it does here on Earth.

And that's why Jupiter has
so much lighting.

In vapour form, water ascends,

carrying energy from
deep inside the planet...

.. Until it reaches a place
under the ammonia ice clouds...

... where it's cool enough
for it to condense

into droplets and ice crystals.

The energy released
as the water condenses

powers the growth
of violent thunderstorms.

In places,
so much energy is released...

...that ice crystals
are swept upwards

into the ammonia ice clouds.

Here, ammonia acts as
antifreeze...

.. allowing liquid water

to grow thunder clouds
60km tall...

...even though it's
minus 100 degrees Celsius.

Jupiter's about as different
from the Earth

as you can possibly get.

It's a gas giant, extremes
of temperature and pressure,

a really different
chemical composition.

But there is a water cycle.

There's a region
in the atmosphere

where the temperature
and pressure is just right

for water to exist
in all of its three phases.

And it's that region that plays
the dominant role in allowing

the energy from deep inside
the planet to escape

into the upper atmosphere,

drive the storm systems
that we see,

and ultimately allow energy
to flow from inside the planet

and out into space.

(DEEP RUMBLING)

Heading out from Jupiter...

...we cross 700 million
kilometres of empty space...

...before we encounter the
solar system's other gas giant.

Taking the crown for
the planet with most moons,

Saturn is orbited by
at least 146...

... that we know of.

But one stands out
amongst the crowd.

More than 20 times

the mass of all Saturn's
other moons combined.

The only moon
in the solar system

to have a thick atmosphere.

But what makes Titan
really special...

. 1S It's the only place
we know of, other than Earth...

...where you could see
a sight like this.

Thanks to Titan's
thick nitrogen atmosphere

and temperatures of
minus 180 degrees Celsius...

..methane, naturally found
as a gas here on Earth,

can exist as a liquid.

It forms clouds in the sky,
falls as rain,

and pools in giant lakes.

But lakes like these are not
found everywhere on Titan.

They're only located
at the poles.

Travel beyond, and we find
a very different world.

Great plains...

...folling dune fields...

... these are Titan's deserts.

But get down closer...

..and a familiar shape
comes into view.

The reason we know
so much about Titan

is because of the iconic
spacecraft Cassini.

It arrived in the Saturnian
system in 2004,

and spent over a decade

exploring the planet
and its moons.

And it discovered not only
that Titan is a desert world

with methane lakes
around the poles, but also...

... It saw features like this,
meandering across the deserts.

And this...is one of those.

Titan's desert regions
are crisscrossed

with dry river beds...

...some 3,000km away

from the methane lakes
at Titan's poles.

So we're faced with a mystery.

What is carving these rivers?

The southwestern United States

is just covered in canyons
like this,

and they're very similar
to the canyons that Cassini saw

on the surface of Titan.

Now, here they're caused
by flash flooding.

So in the summer months,
the North American monsoon

sweeps across this landscape.

So a huge amount of moist air

that's risen up
from the Gulf of California,

and dumps rain onto
this otherwise parched desert,

and it flows down
and cuts these canyons.

If Earth's dry rivers
have a seasonal origin,

could the same also be true
for Titan?

Just like Earth,
Saturn is tilted on its axis,

and that means that, just like
Earth, Saturn has seasons.

But Saturn's year
is 29 Earth years,

and so that means
that each season

is something like
seven years long.

Now,
Titan shares Saturn's tilt.

In Titan's southern hemisphere
summer,

the southern hemisphere
points towards the sun,

and even though
it's a billion miles away,

so there's not much energy

falling on
the southern hemisphere,

there is enough
for those seven years

for methane to evaporate
from the lakes

and up into the atmosphere.

Cassini saw this happening.

It flew by Titan during
southern summer...

..and saw methane clouds
swirling around the south pole.

All that methane condensing
out in Titan's atmosphere

releases a tremendous amount
of energy,

just like water condensing
out in our atmosphere

releases energy,

and that energy release
seeds the formation of storms.

But the clouds didn't stay
at the south pole.

In 2010, Cassini took
this image of Titan,

and | think it's just
remarkable,

because this is a storm
around Titan's equator.

It's worthwhile sometimes
just sitting back

and realising what this is.

It's a photograph of a storm
in the atmosphere

of a moon orbiting Saturn.

In Titan's deserts, autumn
brings change to the air.

Storms like the one seen by
Cassini arrive from the pole...

... Unleashing torrents
of methane rain.

But because the gravity
on Titan

is even less than that
of our moon...

...the raindrops fall

at one-sixth of their speed
on Earth.

Storms in slow motion...

... the most powerful
thought to drop

30cm of methane rain a day...

... forming flash floods...

..that, over millennia,

carve canyons
into the desert landscape...

... before they spill out
into vast flood plains.

Now, Cassini also took
these images.

This one is an image
of the surface,

and these dark areas here

have been interpreted as
liquid methane,

a flood of liquid methane.

It's a few tens of centimetres
deep,

but the area of this flood

is something like the area
of Utah and Arizona combined.

And then,
just a few months later,

this image was taken
of the same region on Titan,

and now you see that
the flooding has disappeared.

All that methane has evaporated

back up
into the atmosphere again

over the period
of just a few months,

and the storm moved on.

In 2022,

five years after the Cassini
mission had ended...

...the James Webb
Space Telescope

turned its infrared gaze
towards Saturn's distant moon.

By now, it was late summer
in Titan's northern hemisphere,

and the telescope spotted
something magical.

Giant clouds
over the north pole.

The travelling storms
had reached their destination.

It's now believed
that Titan's storms

go on an epic
29-year migration...

...from one pole to the other
and back again.

As they travel,

they unleash methane floods
that, over millennia,

carve canyons
into Titan's deserts...

...Seasonal rivers on a moon

1.2 billion kilometres
from Earth.

Titan is a fascinating world,

and although it lives
in permanent twilight -

and so we might expect it
to be frigid and frozen solid -

it has a tremendously
dynamic atmosphere.

It has storms
and seasonal monsoons

that sweep across the surface -

not unlike the monsoons that
sweep across Utah and Arizona.

It's just that,
because of those temperatures,

it's not water that carries
energy around the atmosphere.

All of the chemistry
is shifted,

and it's methane
that takes centre stage.

This, then, is the story

of the storm worlds
of our solar system.

The beautiful and complex
structures we call weather

emerge from each atmosphere
trying to do the same thing...

...move energy to balance out
hot and cold.

But what makes these worlds
so dazzlingly different...

...1S which chemicals
play the leading role

in carrying that energy.

Chemistry is what happens
between the heat of the stars

and the cold of space,

and it plays out on the surface
of planets and moons.

The arena is the atmosphere.

Storms sculpt the surface
of worlds.

On Venus, the mountains
might be coated in metal,

and methane falls as rain
on Saturn's moon, Titan.

Here on Earth, the atmosphere
has allowed life to emerge.

But our solar system is only
one of hundreds of billions

of solar systems out there
in the Milky Way galaxy alone.

So just imagine what nature -

that great tinkering chemist -

might have created out there.

COMMS: Navigation has confirmed
that the parachute

has deployed.

Back in manoeuvre has started.

About 20 metres
off the surface.

PROF COX: For decades,
NASA has used rovers

to explore the Martian surface.

But because Mars
is a Storm world...

...@ world
with an atmosphere...

.. there is another way.

NEW SPEAKER: Ingenuity
is a helicopter. It's our first

spacecraft that we've built
to fly on another world.

PROF COX: /n 20217,
after hitching a ride to Mars

with NASA's latest rover,
Perseverance...

... Ingenuity made history.

COMMS: Ingenuity's reporting
spin up, takeoff, climb.

- Altimeter data confirmed...
- (CHEERING)

...that Ingenuity has performed
its first flight

of a powered aircraft
on another planet!

NEW SPEAKER: Ingenuity's
first flight was so cool!

It was one of these,
"Oh, my God,

"it worked," moments, you know?

You test and you test,

and you do your best
to design something,

but to actually see it work
on the surface of Mars...

We called it
the Wright brothers moment...

...but for another planet!

(APPLAUSE)

PROF COX:
The helicopter was designed

at NASA's
Jet Propulsion Laboratory,

a test vehicle to prove

that extraterrestrial flight
is possible.

But the major challenge
for engineers

was Mars's atmosphere.

Mars does not have a lot
of atmosphere to speak of.

It's not like here on
the Earth. It's much thinner.

DR FRAEMAN:
A couple of molecules

bouncing into each
other every once in a while

is not a lot of stuff
to push against

to generate lift.

So you have to have
a helicopter

that's very, very,
very, very light,

and you have to have rotors

that spin very, very, very,
very, very fast.

PROF COX: Only designed to
fly five short test flights,

Ingenuity surpassed
all expectations.

COMMS: The lat looks great.

We're right in the vicinity
of where we wanted to be.

(CHEERING)

PROF COx: /ts mission was
finally brought to an end

when it sustained rotor damage
on its 72nd flight.

But during its active
three years on Mars,

the helicopter pioneered
a new approach

to exploring the storm worlds
of our solar system.

NEW SPEAKER: Helicopters
like Ingenuity open up

a new dimension to exploration
on the surface of a planet.

And | mean dimension literally.

DR FRAEMAN: You can cover
so much more ground.

Instead of driving

for metres every day,
you can drive kilometres.

You're also going to get this
bird's-eye view of the planet

that's going to be
very different.

DR SOTO: A rover on the surface
has got to

climb over boulders,
climb up hills.

With a helicopter like
Ingenuity,

you just fly right over it,
no big deal.

PROF COX: Which is why NASA's
future mission to Titan

is going to be a flying one.

Titan is a fabulous place
to explore by rotor craft.

It's smaller, so it has
much lower gravity than Mars...

...but it also has
a much thicker atmosphere.

DR MACKENZIE:
lf you and | were sitting

on the surface of Titan,

and strapped some wings
and an oxygen mask

to our face,

we would be able to generate
enough lift to fly.

DR FRAEMAN: So you can build
something that's a lot heavier,

that has a lot more
complicated,

intense science instruments.

DR MACKENZIE:
In 20 to 30 minutes,

Dragonfly will cover
several kilometres.

Compare this to
the rovers on Mars,

which go about 100 metres
over the course of a day.

PROF COX: This will allow
the Dragonfly team

to visit many sites
with one spacecraft.

DR MACKENZIE:
Dragonfly's fundamental mission

is to give us an understanding
of the chemistry on Titan.

What is the surface of Titan
actually made of?

That question
has huge implications

for our understanding

of how complex chemistry
can become,

which means it's important
for our understanding

of how life may emerge
elsewhere in the universe.

DR FRAEMAN: And it's,
| think, going to be so cool.

| can't even imagine
what Dragonfly is going to see,

and what we're going to learn.

| can't wait for that mission.