All language subtitles for NOVA.S51E09.Solar.System.Storm.Worlds.1080p.WEB.h264-BAE_track3_[eng]

NARRATOR:
Across the solar system,

spectacular storms are raging.

JAMES DOTTIN:
What we've learned about
weather on other planets

has rewritten the rulebook
on what we thought was possible.

NARRATOR:
From corrosive clouds...

GEORGE DRANSFIELD:
If you were to go skydiving
through the clouds of Venus,

there wouldn't be
a lot of you left at the end.

NARRATOR:
...to global dust storms.

DAVID GRINSPOON:
On Mars, the whole atmosphere
basically freaks out,

and the storm grows to the point

where it engulfs
the entire planet.

We don't have anything
like that on Earth.

NARRATOR:
Storms found
in unexpected places...

DERRICK PITTS:
It's a moon that
looks like this!

How do you have these features
on the moon of a planet?

NARRATOR:
...and made
of bizarre materials.

SHANNON MACKENZIE:
Buckets and buckets of rain

are falling on the surface,
and yet,

it's not water
raining out of the atmosphere,

but liquid methane.

NARRATOR:
Extra-terrestrial weather

makes exploration challenging.

ABIGAIL FRAEMAN:
Seeing the skies get
darker and darker and darker,

we started to realize that,

"Oh, this is actually,
this is a really bad one."

NARRATOR:
But can teach us so much.

PETER GAO:
It opens up the possibilities
of, "What is weather?"

NARRATOR:
What drives these exotic storms
raging across the solar system?

And how do they shape
a planet's destiny?

"Solar System: Storm Worlds."

Right now, on "NOVA."

♪ ♪

♪ ♪

NARRATOR:
It's midsummer.

♪ ♪

A storm is brewing.

♪ ♪

It unleashes torrents of rain...

...forming floods that drain
into rushing rivers...

♪ ♪

...and giant lakes.

♪ ♪

This is the only world
in our solar system

where rainstorms
pummel the surface.

♪ ♪

The only world other than Earth.

Here, more than 800 million
miles from the sun...

...orbits the largest
of Saturn's moons.

In some ways,
Titan is more similar to Earth

than any other place
in the solar system.

But upon closer inspection,

you will find that it's
actually exceptionally alien.

The surface temperature of Titan

is around
-300 degrees Fahrenheit.

NARRATOR:
Far too cold for liquid water.

DOTTIN:
What's fascinating is that

the rain that's falling
out of the sky on Titan

and filling up the lakes

is usually found on Earth
as a flammable gas.

NARRATOR:
Methane.

Titan is a world shaped
by alien storms,

and it is not alone.

MACKENZIE:
It's pretty mind-blowing

that as we look elsewhere
in the solar system,

we see these weather patterns

that look very familiar to us,

and yet there are
also these wild extremes.

♪ ♪

DRANSFIELD:
Some of the storms
we're seeing

are like supersized versions

of the storms
that we see here on Earth.

♪ ♪

NARRATOR:
And the more we explore,

the more weird and wonderful
weather we're finding.

GRINSPOON:
Pretty much every planet
with weather

has some oddity to it
that's surprised us.

NARRATOR:
So what creates the wild
diversity in weather

across the solar system?

GAO:
We're so used to dealing with
our specific brand of weather.

But there's just
so much more out there,

if you look
at these stormy worlds.

♪ ♪

♪ ♪

ALEJANDRO SOTO:
When I hear the word
"weather,"

I get a memory

of when I was a kid,
standing out in a field...

♪ ♪

...when the wind would pick up,
the sky would darken a bit,

and you knew
it was about to rain.

(wind gusting)

And yet it would also be
the best.

NARRATOR:
From towering thunderstorms

to howling blizzards

to choking dust storms,

our atmosphere
is a restless place.

But what causes all this chaos?

JEN GUPTA:
Earth, like all the planets,

is essentially a big ball
floating in space

being heated by the sun.

It's pretty simple, really.

But because of the shape
of a planet,

its spherical geometry,

it's actually really hard
to heat the planet evenly.

For a start,

there's always a side
of the Earth

DOTTIN:
And some parts,

like the Equator,

receive more sunlight

than others, like the poles,

and that creates
an energy imbalance.

But because the Earth is
surrounded by this atmosphere,

this envelope of gas
that's free to move around,

it can carry the heat from
the hot places to the cold

in an attempt to equalize
this imbalance.

LEIGH FLETCHER:
And without that conveyor belt
of energy motion,

we wouldn't have

the incredible diversity of
weather

that we can see around us today.

♪ ♪

NARRATOR:
Wind, rain, and lightning
are all side effects

as our atmosphere balances
hot and cold.

♪ ♪

And what applies here
applies elsewhere, too.

CLARA SOUSA-SILVA:
In our solar system, wherever
there's an atmosphere,

there's weather, no matter how
different

an atmosphere from Earth's.

sometimes they're made
of different things.

And all of these combine

to give these crazy cool weather
systems

that are all so different

across the solar system.

♪ ♪

NARRATOR:
To see this alien weather
in action

across our vast solar system,

we head away
from our shared star...

♪ ♪

...passing a planet so small
and close to the sun

that it has no atmosphere,

to encounter a planet

smothered by one.

PITTS:
Venus looks so beautiful
in the evening sky.

Brilliant, clear, white,

just stunningly lovely to see,

yet it's such a horribly nasty
environment.

we can't actually see
Venus's surface at all.

Instead, all we see are endless,
thick, churning clouds

that completely conceal
the rest of the planet.

♪ ♪

GRINSPOON:
Historically, we thought,
"Oh, Venus has clouds.

"They're probably made out
of water.

It might be sort of nice there."

(laughing): But then,

when we started to actually get
data from spacecraft,

we discovered,
no, they're not water.

In fact, they're battery acid.

♪ ♪

SOUSA-SILVA:
The clouds on Venus are

made up of extremely
concentrated sulfuric acid,

one of the most corrosive
substances we know of.

If you were to go skydiving

through the clouds of Venus,

there wouldn't be a lot of you
left at the end.

NARRATOR:
But if we could
withstand the acid

and took the plunge down
through Venus's clouds...

...we'd reach a landscape
that is eerily calm...

...but with air pressure
more than 90 times greater

than at Earth's surface.

GAO:
Even though we don't realize it,

air has weight.

It's being pulled down by
gravity,

just like the rest of us.

And so, on Venus, where the
atmosphere

is so thick and so massive,

all that air
is being pulled down,

and if we're
on the bottom of it,

then we'll feel
all that pressure.

SOUSA-SILVA:
If you find yourself
on the surface of Venus,

you would almost immediately
be crushed.

But if somehow you survived

and tried to go for a stroll,
it would be exhausting.

The atmosphere is so thick,

it would be like
walking through molasses.

NARRATOR:
The surface of Venus

is comparable to the bottom
of Earth's oceans,

but with a key difference.

At about 900 degrees Fahrenheit,

this is the hottest planetary
surface in the solar system.

And again, Venus's extreme
atmosphere is responsible.

SOUSA-SILVA:
Carbon dioxide
and other molecules

are able to absorb
and radiate heat,

and so, in large enough
quantities,

they can act like
a planetary blanket

that traps
that heat in a planet.

That's what we call
the greenhouse effect.

NARRATOR:
And Venus's incredibly
dense atmosphere

is 96.5% carbon dioxide.

♪ ♪

Even 0.04% CO2 in our atmosphere

is enough to initiate
a climate crisis

in our world right now.

So you can imagine
how bad it is on Venus.

NARRATOR:
Venus's extreme
greenhouse effect

means it's even hotter
than Mercury.

Which is why what
we would find there

is so extraordinary.

♪ ♪

What look like
snow-capped mountains

towering over
the scalding surface.

For generations,
we could only guess

at what lay beneath
Venus's clouds.

But, thanks to radar images

beamed back by
NASA's Magellan orbiter,

we now have detailed maps
of the planet's surface.

So, here we have an image
taken by Magellan,

and what we're looking at

is actually Maxwell Montes.

Maxwell Montes here

is the highest region on Venus.

And what you'll notice
is that around this image,

the surface looks dark.

But in the center,
where Maxwell Montes is,

it's much brighter--
it almost looks white.

We weren't expecting

to have such
radar-bright regions

on the highlands,
in the mountaintops of Venus.

♪ ♪

GUPTA:
When you see those radar images
of Maxwell Montes,

it's hard not to imagine
snow-capped mountains.

♪ ♪

NARRATOR:
But given the conditions
on Venus,

snow as we know it
is impossible.

♪ ♪

In places, it's so hot,

the ground actually glows,

like metal
coming out of a forge.

GRINSPOON:
On Earth, you can imagine

waiting till nighttime
to cool off.

That wouldn't work on Venus.

There's no relief at night
on Venus from the temperature.

And in fact, if you go
from the equator to the pole,

it doesn't get any cooler,
for the same reason--

that thick atmosphere
is very efficient

at redistributing the heat.

NARRATOR:
It is a world where there
is no place for snow to hide.

But there's one way
to cool off on Venus,

and that's to go up a mountain.

♪ ♪

NARRATOR:
A phenomenon that we here
on Earth can also relate to.

♪ ♪

PORT:
Everyone knows
when you go up a mountain,

you should always pack a jacket.

And the reason for that
is because it's much colder.

But why is it colder?

Well, when you go up a mountain,
there's less air,

and that means
there's less pressure.

♪ ♪

NARRATOR:
And as the pressure decreases,

so does the temperature.

PORT:
So, as we go up in elevation,

we cross a threshold

where the temperature
drops low enough

that water can be a solid.

And this is what we call
the snow line.

NARRATOR:
Venus's snow line suggests

something may be freezing
up there.

But even its highest peaks

are far too hot
for that something to be water.

And that points us
to substances

that solidify
at much higher temperatures.

PORT:
So, instead of water,

it actually could be
something like this.

So this is a piece of galena,

also known as a lead sulfide.

On Earth,
it's present as a solid,

as you can see here.

But on Venus,

it may only be a solid
in the highlands.

NARRATOR:
Deep in Venus's lowlands,

like valleys,

it's hot enough for compounds
like lead sulfide

to vaporize,

drift on the wind,

and, as the winds flow up

into the mountains of
Maxwell Montes...

...the temperature drops
just enough for the compounds

to freeze out of the air.

At 820 degrees Fahrenheit,

Venus's atmosphere
may coat its mountaintops

not in snow,

but in a metallic frost.

PORT:
We still don't know for sure

if metal frost can explain
the bright regions

that we're seeing
on the mountaintops.

There's still a lot
that we don't know about Venus,

and that's because
we haven't even sent a lander

to the surface of Venus
since the 1980s.

But it's amazing to think

that something like this
could be condensing

on the mountaintops of Venus.

When we think of the possibility
of metallic frost on Venus,

it sounds crazy, but that's
only crazy for us Earthlings.

If you have
a different atmosphere,

you get different weather,
different phenomena playing out.

♪ ♪

NARRATOR:
Leaving this crushing world
behind...

...we head out in search
of an atmosphere

that could almost be
Venus's opposite.

To reach it,
we bypass our own planet.

Passing two potato-shaped moons

orbiting our other
next-door neighbor,

we encounter an atmosphere

more than 10,000 times thinner
than Venus's.

With little in the way
of cloud cover,

we don't need radar to get
a look at the Martian surface.

Yet, images sent back
by our orbiters

suggest rain may have once
fallen here.

These pictures show
that Mars is covered in features

which appear to have been
created by flowing water.

DOTTIN:
With such a thin atmosphere,

it's really difficult

to retain heat, and certainly

not enough heat to have

liquid water on the surface.

it must have had a much thicker
atmosphere in the past.

FRAEMAN:
In the early 2000s,

we'd seen that there were hints

that liquid water had once been

on the Martian surface

from our orbiters,

but we didn't have
definitive proof

from the surface.

So the goal of the Mars
Exploration Rover mission

was to follow the water.

MAN:
T minus five, four, three,

two, main engine start,

zero, and liftoff

of the Delta rocket
with Opportunity,

a chance to explore

and unlock the secrets
of our neighboring planet.

FRAEMAN:
I was 16 years old
when Spirit and Opportunity

launched and landed on Mars.

But I had the
amazing opportunity

through an outreach program
to actually go to be at NASA,

at the Jet Propulsion
Laboratory,

when the rovers landed.

MAN:
Getting a bounce to signal.

(cheering)

FRAEMAN:
And I was in the room
with the science team

when Opportunity landed on Mars,

and it was the most
amazing experience.

(cheering and applauding)

NARRATOR:
Two rovers named Spirit
and Opportunity

were sent to opposite sides
of the Red Planet

to search for definitive proof

that Mars's dry landscape

was once a water world.

At first glance,
modern Mars doesn't appear

to be a very dynamic place.

With an average
surface temperature

of about
-80 degrees Fahrenheit

and an atmosphere just
one percent as thick as Earth's,

it is a freezing desert.

Typically, we think of
Mars as this dead world.

But we do see changes
on the surface over time.

NARRATOR:
Strange, overlapping lines,

often dozens of feet wide,

can stretch for miles.

Unlike many of Mars's features,

these are not relics.

We see them appear
and disappear.

What are these bizarre,
shape-shifting patterns?

♪ ♪

In January 2004,
Spirit and Opportunity

began to investigate Mars.

♪ ♪

But their mission wasn't
expected to last very long.

GUPTA:
Mars is covered in dust.

It gets everywhere,

including on the solar panels
of Mars rovers.

the power levels
that the rover would have

would get lower
and lower and lower,

and eventually,
they would just stop working.

NARRATOR:
The team hoped the rovers

would last
at least three months,

a feat they surpassed.

But, as the months wore on,

the power levels
continued to drop.

What was really exciting

was, at one point
in the mission,

as we were seeing
the power levels

getting lower
and lower and lower,

all of a sudden,
the power levels were

back up high again.

♪ ♪

Almost as high as they were
when the rovers had landed.

And you can take a look at
the before and after pictures,

and you can see that
it looks like the solar panels

have just been wiped clean.

You could call up AAA
and send them to Mars

with the rag
to clean everything off.

They couldn't have done
a better job.

NARRATOR:
Finally, a clue
to what might be happening

was spotted by Spirit's Navcam.

♪ ♪

In the mid-afternoon sun...

♪ ♪

...heating
of the Martian surface

creates towering vortices,

which can grow miles high.

Dust devils.

GUPTA:
I imagine it would be
absolutely terrifying

to be standing
on the surface of Mars

and see one of these dust devils
coming straight at you.

FRAEMAN:
You might think
that there was this

tornado-force wind
coming towards the rover,

and it might pick the rover up
and spin them around

and do all sorts
of horrible things.

But in reality,

the Martian atmosphere
is actually very, very thin,

and so you can have
a dust devil pass over you

and, and you would
barely even notice it.

But even though a Martian
dust devil

might not be able to
pick you up,

it can certainly pick dust up.

NARRATOR:
It's thought that

as these whirlwinds
traveled over the rovers,

they sucked dust
off the solar panels,

like a vacuum.

So a mission expected
to last just a few months

was extended again,

and again,

and again.

But the cleaning power
of the dust devils

doesn't just work on rovers.

(wind roaring)

♪ ♪

As they travel,

these huge vortices

suck up dust
from Mars's surface,

exposing the darker bedrock
beneath.

Leaving trails so large,

we can see them clearly
from space.

♪ ♪

There are no Martians
creating the lines.

The culprit is
the Martian atmosphere.

Dust devils
might create the tracks,

but something else
wipes them away.

♪ ♪

Just like Earth,

Mars has a tilt
that gives it seasons.

Summer in one hemisphere
means winter in the other.

And with no oceans
or thick atmosphere

to help spread heat
around the globe,

an extreme temperature
difference.

So here, dust helps
drive the action.

♪ ♪

As summer arrives
in the southern hemisphere,

warmer temperatures
drive stronger winds,

which kick dust up into the air.

The dust absorbs sunlight
and heats the air around it...

...further strengthening
the winds,

which lift even more dust...

...until a storm forms...

...wiping away
dust devil trails.

And these storms can combine
and grow so large...

...that they engulf
the entire planet,

sometimes blocking more than
99% of the incoming sunlight

from reaching the surface...

...and the solar panels
of Mars rovers.

In May 2018, with Opportunity
still active on the surface,

a storm began to build.

FRAEMAN:
It only took a couple of days

of seeing the skies get
darker and darker and darker

before we started
to realize that,

"Oh, this is actually,
this is a really bad one."

Um, and by the end of the week,

we knew that this was
the worst dust storm

that we were ever gonna
have to survive.

We knew we were probably gonna
lose communication with Oppy.

So we let her go dark

and we just waited and waited.

NARRATOR:
Mars's low gravity means
the dust in the air

can remain there for months.

♪ ♪

Eventually,
with so little sunlight

reaching the Martian surface,

the temperature differences
which fueled the storm

are dampened,

cutting off
its own energy supply,

and the dust finally settles.

But by the end of 2018,

even after the Martian skies
had cleared,

there was no signal
from Opportunity.

And with winter looming,

it was unlikely
the rover's electronics

would survive the cold.

♪ ♪

On February 13, 2019,

NASA declared
its mission complete.

FRAEMAN:
I know it sounds weird,

'cause it's a robot...
(laughs)

...but it's sort of
the same feeling you have

when you might lose a loved one

who's lived a very full life.

I was a high school student
when they landed.

By the time
Opportunity's mission ended,

I had gone to college,
I had gotten a Ph.D.,

I had done a post-doc,

and then I had been hired
by NASA

to work on this very same
Opportunity rover

that had inspired me when
I was a high school student.

NARRATOR:
Sent to Mars to hunt
for ancient evidence of water,

Opportunity not only succeeded,
but exceeded expectations,

lasting over 14 years
thanks to the Martian weather.

♪ ♪

Despite their differences,

Venus and Mars have
one thing in common.

Their weather is powered
by solar energy.

But beyond the asteroid belt...

...ruled by
the dwarf planet Ceres,

the sun's influence wanes.

And yet,
the next planet we encounter

is a storm world...

...on the grandest scale.

PITTS:
If you were just arriving
at Jupiter in a spacecraft,

you would be stunned by what you
see.

First of all, there's the size.

You can fit 1,300 planet Earths
inside Jupiter.

In fact, you could fit all of
the planets

in the solar system inside
Jupiter

and still have room to spare.

NARRATOR:
Jupiter is a gas giant

on which storms can grow bigger
than Earth itself.

Since 2016,
NASA's Juno spacecraft

has been exploring
this gargantuan planet

and found its weather
is anything but subtle.

(thunder rumbling)

Jupiter's thunderstorms
can produce lightning bolts

ten times more energetic
than anything recorded on Earth.

(thunder rumbling,
lightning crackling)

Most of the flashes lie beneath
thick ammonia ice clouds.

But the most powerful storms
break free,

soaring to the edge of space.

(thunder booming,
lightning crackling)

The scale of Jupiter's storms
may be hard to comprehend.

But Juno found
that the frequency

of its lightning strikes
is remarkably similar

to Earth's thunderclouds.

DRANSFIELD:
It's odd that lightning
is such a common occurrence

here on Earth,

but it's taken us centuries

to really understand how it
works.

NARRATOR:
The substance responsible

for our planet's thunderstorms
is water.

The way that lightning gets
formed

is that it relies on collisions

between icy particles and watery
droplets.

with the icy particles
that are falling downwards,

they're exchanging charge
with each other.

So you get a separation
of charge

from the top of a cloud
to the bottom of the cloud.

And as that separation of charge

becomes bigger
and bigger and bigger,

eventually, the atmosphere
can't cope anymore.

PITTS:
And when that occurs,

now a flow of electricity
can happen.

(lightning crackling)

NARRATOR:
A single bolt of lightning
is so powerful,

it can heat the surrounding air

to temperatures greater
than the surface of the sun.

♪ ♪

So how can clouds
produce so much energy?

HEIDI BECKER:
For all of our history,
lightning has been

something
that humans have feared.

But what's driving it
really is the water cycle.

The sun heats the water,

it evaporates,
becomes water vapor,

rises up into the atmosphere,

cools, and eventually becomes

water droplets in clouds.

And intuitively, as humans,

we actually understand
what's happening very well.

We wet our hand,

and it feels cold because

the water is stealing energy
from our hand,

breaking up the
water molecules,

turning them into
water vapor

so that they can

rise up into
the sky.

NARRATOR:
Water evaporation
requires energy,

whether it's from
our body heat or the sun.

As water turns from a liquid
to a gas, it stores this energy.

And when it turns back into
a liquid, in the form of clouds,

it releases this energy
back into the atmosphere.

What's kind of incredible
to believe

is that a, a small little
cumulus cloud that you might see

floating in the sky, looking
so graceful and peaceful,

is actually the result

of an enormous amount of energy
being released.

It's the same
as hundreds of tons of TNT.

NARRATOR:
And for an average thunderstorm,

the energy released is
equivalent to a nuclear blast.

It's this huge release of heat

that makes thunderclouds
so turbulent,

causing
the countless icy collisions...

(thunder rumbling,
lightning crackling)

...which power
Earth's lightning.

Several missions to Jupiter
have detected water

in its atmosphere.

But the planet receives just
four percent of the sunlight

that reaches Earth,

too little energy to account for
its ferocious lightning storms.

♪ ♪

But looking at the planet
in infrared

reveals a different source
of energy.

Jupiter is radiating heat,

almost twice the energy
it receives from the sun.

FLETCHER:
So, Jupiter itself
is slowly cooling,

and has been over the entire age
of the solar system.

And as it's cooling, the entire
gas giant is slowly shrinking.

And as it shrinks,
it's relinquishing that energy

that was left over
from when Jupiter was born.

That's enough to power

the gargantuan storms
that we see.

(crackling)

NARRATOR:
This internal heat means water.

The chemical powering
Earth's storms

also powers storms on Jupiter.

In vapor form, water rises,

carrying heat energy
from deep inside the planet...

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

(thunder crashes)

...where it's cool enough

to condense into
liquid water droplets

and ice crystals.

The energy released
by this condensing water

powers the growth
of violent thunderstorms.

But because Jupiter
has so much internal heat

that's trying to escape,

in some places, enough energy is
released by condensing water...

...that ice crystals are swept
up into the ice clouds above.

Here, ammonia acts
as an antifreeze...

...allowing thunderclouds
to grow

to more than 35 miles tall

and lightning to strike
at minus 150 degrees Fahrenheit.

♪ ♪

Jupiter and Earth
may be worlds apart,

but both play host
to lightning storms

which are driven by water.

I just find it wicked cool
that on a planet

as different as Jupiter,

the weather is being formed
in much the same way

as it is here on Earth.

NARRATOR:
However, there is one more place
in the solar system

with even more
Earth-like weather.

PITTS:
But what's really interesting
and exciting is,

the liquid that's being shifted
around

isn't water.

from the sun

and encounter another gas giant.

But this isn't our destination.

♪ ♪

Saturn is orbited by
an amazing variety of moons,

so many that it can be hard
to keep track of them all.

Iapetus, Rhea,

Enceladus...

GAO:
Tethys, Mimas, Epimethys.

Helene, Prometheus, uh, Calypso.

Shoot, there's that
really funny one.

Phoebe.

There's Pan,
which is really cool

because it looks like a ravioli.

GRINSPOON (laughing):
I didn't cram for this.

Did I mention Mimas?

GRINSPOON:
What's the little,
really weird...

Hyperion.

Uh...
(chuckles)

Um...

Um, uh, let's see.

And a bunch more.
(laughs)

NARRATOR:
But one is special.

More than 20 times the mass
of all the others combined.

It's the only moon in the solar
system with a thick atmosphere.

In November 1980,
NASA's Voyager 1 spacecraft

revealed Saturn
and its many moons

in greater detail
than ever before.

PITTS:
When the Voyager 1 spacecraft
flew by Titan,

we could see
that it had an atmosphere,

and a thick atmosphere,

but this was only
a tantalizing view.

SOTO:
The images from Voyager of Titan

were exciting but also,
in a way,

infuriating, right?

It confirmed everything that
we had thought about Titan,

but it didn't allow us
to see down to the surface.

With Voyager, we could do some
remote sensing

but in
the right temperature range

so that you might actually have
liquid methane on the surface.

And so we, we just knew that we
had to go back

and, and learn more.

MAN:
Five, four, three, two, one,

and liftoff of
the Cassini spacecraft

on a billion-mile trek
to Saturn.

NARRATOR:
The legendary
Cassini-Huygens mission

took almost seven years
to reach Saturn

and spent over a decade

exploring the planet
and its moons.

And on December 25, 2004,

nearly a quarter of a century
after Voyager 1's flyby...

...the Huygens probe
detached from Cassini

in a bid to become the first
probe ever to land on a body

in the outer solar system.

♪ ♪

You know, there was
so much anticipation

of what that surface
might be like.

But I think in none
of our wildest dreams

was the surface of Titan
as interesting and beautiful

and exotic and exciting
as it turns out to actually be.

NARRATOR:
During its two-and-a-half-hour
descent to Titan,

Huygens captured images
of intricate ridges,

deep gullies,

and, perhaps most strikingly,
river channels.

GRINSPOON:
It was truly like a dream,
but there they are.

These are real pictures coming

from our first-ever descent
to Titan.

And, uh, it's unmistakable
what we're seeing.

And I'll, I'll just
never forget that moment.

PITTS:
It's a moon!

It's a moon
that looks like this!

Not a planet.

How do you, how do you have
these fluvial erosional features

on the moon of a planet?

♪ ♪

NARRATOR:
The team had designed
Huygens to float,

but it landed in what appeared
to be an empty riverbed.

And the river channels it imaged
during its descent were dry.

The probe continued
to transmit data

from Titan's surface
for more than an hour

before its breathtaking mission
came to an end.

But Cassini continued to explore
the surface from afar.

♪ ♪

It saw a landscape
of rolling dune fields,

vast plains,

and more dried-up rivers.

It seemed Titan
was a desert world.

But in 2006, after
many months of searching...

...Cassini's radar instrument
found

what everyone
had been waiting for:

lakes and seas of liquid methane
at the north pole.

Titan's equatorial region
may be a desert,

but Cassini had proved that
its poles were anything but.

FLETCHER:
So that difference we could see

between the deserts

down around the equatorial
region

and the seas that were present

up at high latitudes

had us scratching our heads.

NARRATOR:
What could be carving channels

over a thousand miles away
from the poles?

MACKENZIE:
We think about deserts
as dry places,

and most of the time they are,
but they're carved,

they're shaped, they're defined
by these seasonal rainstorms

that may happen
only once or twice a year.

The question is, could something
similar be happening on Titan?

Saturn happens to be tilted

at about the same angle that the
Earth is.

So as it's going around the sun,

it experiences seasons much
like we do here on the Earth.

But it takes Saturn and Titan
a lot longer

to go around the sun than we do.

It takes 29-and-a-half years.

Titan shares the same orbital
plane as Saturn.

And so it also experiences
seasons

as it's going around the sun.

If we take the southern
hemisphere, for example,

there are seven years of summer

where the southern hemisphere
is pointed

towards the sun and receiving
more energy.

That extra bit of energy,

even though it's only a 100th

of what we experience here
on the Earth,

is enough to pump the atmosphere
full of methane,

thanks to evaporation

from the lakes in the
south pole.

♪ ♪

NARRATOR:
Cassini saw this happening.

It flew by Titan during
the southern summer...

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

But the clouds
didn't stay there.

MACKENZIE:
In 2010, there was a giant cloud

that formed over the equatorial
region in the shape of an arrow.

And as it moved across
the surface of Titan,

we saw that land
that was bright before

darkened, uh,
after the cloud passed over.

And the area that darkened

is equivalent to about
Utah and Arizona put together.

So how did that happen?

What is responsible for that?

Well, we think
the best explanation

is a giant rainstorm.

♪ ♪

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

Monsoons arrive
from the south...

...unleashing torrents
of methane rain.

But because of Titan's low
gravity and dense atmosphere,

the raindrops fall about
six times slower than on Earth.

These storms dump enough liquid
methane onto the surface...

...to create flash floods...

...which drain
into dry riverbeds...

...carving into the landscape...

...before spilling out
onto vast floodplains.

MACKENZIE:
So, thanks to Cassini, we know

that massive floods
are happening on Titan.

And just a few months later,

which is only, like,
five Titan days, that same land

reverted to what it looked
like before, it brightened.

And the clouds themselves

that were responsible for
that rain had already moved on.

♪ ♪

NARRATOR:
In 2022, five years after
the Cassini mission ended,

the James Webb Space Telescope

turned its infrared gaze
towards Saturn's largest moon.

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

and the telescope spotted
something remarkable:

huge clouds over the north pole.

The traveling storms
had reached their destination.

It is now believed
Titan's storm belt

goes on an epic
29-and-a-half-year journey

from one pole to the other
and back again.

Slow-motion seasons

unleashing massive,
slow-motion storms,

creating seasonal rivers
of methane,

in a desert
on one of Saturn's moons.

♪ ♪

MACKENZIE:
It's pretty incredible
to be standing here

in a desert landscape
on the Earth

and think about
how similar that is

to a landscape
a billion miles away

elsewhere in the solar system,

the same processes,
the same desert monsoon systems

we think are at work on Titan,

creating vistas much like
this one that we see here.

And yet the compounds,
the materials

that are involved in that
process are totally different,

and the temperature's
totally different,

and the timescales
are totally different.

And they're leading
to a phenomenal landscape

like the one that we see here.

♪ ♪

SOUSA-SILVA:
On all these worlds,
all this complexity,

all these storms

ultimately come from one
fundamental law of nature.

FLETCHER:
That need to move energy

from where it's plentiful
to where it's scarce.

DOTTIN:
What makes these worlds
so different

are the unique conditions

that are found
in their atmospheres.

(thunder rumbling)

GUPTA:
Because that determines
the chemistry

that drives their storms
and shapes their surfaces.

(thunder rumbling)

GRINSPOON:
You know, it's a pretty
amazing time to be alive

in, in that we have the ability

to be monitoring weather
on other planets.

And yet I feel like
we're in our early stages

of understanding weather
beyond Earth.

DRANSFIELD:
There are hundreds
of billions of stars

out there in the galaxy.

And we now know that planets
around stars is the norm.

GAO:
So that's potentially
billions and billions

of planets orbiting out there,

all each with their own
weather systems and storms.

FRAEMAN:
And I think there are things
that are happening

on these planets that we haven't
even begun to imagine,

because they're gonna be
so different

from anything else
that we've been able

to experience
in our own solar system.

GAO:
And so that
just makes me think of,

what possibilities exist
out there?

What have we not thought of?

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