11x01 - The Moons of Saturn

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Orbiting the magnificent
ringed planet, Saturn,

are a series of
extraordinary moons.

The closer that we look,

the more that we see its moons
are like worlds of their own...

So dynamic, so Earth-like.

Almost a billion miles
from the Sun,

these icy worlds could be
home for Life 2.0.

The moons of Saturn
offer possibly the best

chance of finding
extraterrestrial life

in our solar system.

With each new mission,
we get closer

to unraveling the mysteries of
Saturn's moons.

October 2019.

Astronomers discover


orbiting the gas giant, Saturn.

These tiny,
three-mile-wide objects

bring the ringed planet's
moon count to over 80,

the most of any planet
in our solar system.

You hate to play favorites,
but I'm gonna say it...

Saturn is my favorite
planetary system.

It is unbelievably beautiful,
with this incredible system of

rings and moons,

and there's a lot of mystery
kind of all bound up in there.

The Voyager spacecraft
gave us our

first close look at Saturn
and its rings.

Two decades later,
Cassini got us even closer

to many of Saturn's moons.

There's Prometheus, Pandora,
and Atlas.

Its largest moon, Titan,
is a moon that's shrouded

in mystery.

There's Mimas,
that's fairly small,

and then Tethys and Dione
are a bit larger.

There are a pair of moons...
Janus and Epimetheus...

That were perhaps
one moon in the past.

Iapetus, half of it's
bright white.

The other half of it is
sort of as

dark as coal,
sort of yin and yang.

Each of the moons of Saturn

had remarkable stories to tell.

In 2005, Cassini discovered that

one moon's story was
particularly exciting.

Yeah, Enceladus.

Enceladus is one of Saturn's
wee little moons.

It's about 300 miles across...
For scale,

it's roughly the size
of Colorado.

The spacecraft's
cameras spot plumes of

water vapor sh**ting
out from Enceladus

at 800 miles an hour.

Three times as powerful than

all the hot springs
in Yellowstone.

The discovery of
geysers gushing out of tiny,

little Enceladus that should
have been cold and dead,

completely changed our view of
what that moon exactly was.

It's alive.
That moon is alive.

I'd like to be standing there
on the surface of Enceladus to

see with the... this water vapor

and ice crystals booming
out of the surface

at supersonic speeds.

Cassini's sensors
probe deep beneath

the frozen surface of Enceladus,

detecting hints of a rocky core

and something else
even more remarkable.

Underneath that
thick layer of ice,

there is liquid water ocean.

The measurements
suggest his is a huge part of

Enceladus's interior volume,

about six miles deep,
because it was making Enceladus

wobble in its orbit.

Imagine putting liquid inside
a ball and rolling it.

You see the natural wobble of

the ball as the liquid
sloshes around.

Giant liquid oceans
on an alien world,

opening up exciting
new possibilities.

Where you find water,
you could possibly find life.

If you had asked me 20 years
ago where there might be life

in the solar system
besides Earth,

I think Saturn's moons would
have been the last place

I would have picked.

But against all odds,
it's looking like this tiny icy

moon orbiting Saturn

nearly a billion miles from
the Sun may be one of

the best places
to look for life.

July 2021.

A new study reexamines
Cassini's plume data

and finds huge quantities
of methane.

This large amount can't be

explained by just
geochemical processes.

The methane might be from
primordial organic matter

breaking down in
Enceladus's oceans,

or even processes
we've never seen before.

But it could be that

living microorganisms helped
generate the methane,

just like they do on Earth.

Enceladus might actually look
a lot like early Earth in its

deepest oceans,
when life was first arising,

because we know that there are
some chemical pathways that are

likely occurring on Enceladus
that happened on Earth.

These chemical pathways
start with

hot, hydrothermal vents
on Earth's

cold sea floor, releasing
important life-giving chemicals

into the oceans.

Having hydrothermal vents
are a real

boon to the evolution of life.

These are cracks in
the Earth's crust, where

hot material can then spew out
into the ocean.

And that's the energy

that life needs
to be able to form,

and then water so everything
is present, and things

are able to just grab all
these resources and energy

and just start to evolve.

On Earth, hydrothermal
vents produce methane,

but only in small amounts.

Microbial life

living around the vents
makes the rest.

Maybe microorganisms do the same

at the bottom of Enceladus's
deep oceans.

Hydrothermal vents on
Enceladus could offer

the perfect location
for chemistry

becoming biochemistry
becoming life.

Hydrothermal vents
normally require

heat from a hot core.

So what's going on
inside Enceladus?

This is an icy moon out there
in the cold outer solar system.

Where is all this heat
coming from?

Cassini spotted
Enceladus's plumes

sh**ting out
from parallel cracks

in the surface,
called tiger stripes.

The cracks are a clue to
the origin of the geysers

and the energy that powers them.

We look to the orbit of
Enceladus itself.

It's not in a perfectly
circular orbit

around the planet.

It's on a slightly elliptical
orbit, and that means that

the tidal forces acting on
the moon change over time.

It's a little bit like
the forces on a rubber ball.

When the moon is closer to
the planet, it's stretched out,

and when the moon is
farther from the planet,

it's relaxed back a little bit,
so you're gonna squeeze

and deform and squish
the body of

that moon over time, which is
gonna heat its interior.

The warm, rocky core
heats up the ocean,

which both powers the geysers
as they burst

through the surface

and creates conditions that
could support life.

We see the energy source
kicking the water

out of the Enceladus subsurface.

You combine that energy source

and liquid water,
that harkens to putting

us on the same path
that early life

may have taken
here on the Earth.

And if that's the case,

there could be little beasties
swimming underneath the surface

of one of Saturn's moons.

Saturn's squeezing of
Enceladus may

have transformed it into
a living world,

but other moons
weren't as lucky.

They've been torn apart in
vicious fights

to the death.

There are a huge variety
of moons orbiting Saturn,

from Titan, a moon larger
than the planet Mercury,

to objects about the size of
a sports stadium.

There must be
something dramatic that happened

to create a system

that's so complicated
and changing

before our very eyes.

To understand such
a marked difference in size,

scientists look for clues in
the moon's orbits around

Saturn itself.

Most of the moons of that system
orbit in the same direction.

That's obviously not
a coincidence.

That's motion left over
from the formation

of our solar system.

This suggests the moons
formed around

the same time as Saturn did.



the ringless gas giant
grows from gas,

rock, and ice in
the protoplanetary disk,

along with a family of moons.

This origin story works for
most of Saturn's moons,

but not for the recently
discovered objects orbiting

in the opposite direction of
the planet's rotation.

If there's a moon orbiting in
the other direction,

it couldn't have formed with
the planet.

It must have come from
somewhere else.

Saturn captured these moons.

But from where?

We think there was a huge
upheaval in the solar system

over four billion years ago,

where the giant planets

went from a close and compact
configuration, started

having interactions
with each other,

moved each other around
to end up into the orbits

that they find today.

During that process, a lot of
smaller bodies,

like asteroids
from the distant part

of the solar system
got scattered

every which direction.

During this ancient upheaval,

Saturn grabs some of
the scattered objects.

Many bodies now crowd
the region around the planet,

and that means collisions.

Some are destructive.

Others form new moons.

In the cosmic pinball,

some moons are thrown
out of the system,

and others, into Saturn.

Only one large moon
survives the carnage.

And all of a sudden,
most of the mass

of all the satellites is in
that single moon, Titan.

Titan may have formed
from the material in

the protoplanetary disk at
the same time as Saturn,

but then gorged on the debris
created in the later

lunar collisions.

It amassed 96 percent of
the material orbiting Saturn

and grew so large that it
developed a dense atmosphere.

When Voyager photographed Titan,

it clearly showed that Titan
had a thick atmosphere,

which was so
incredibly exciting,

but it was so dense
and impenetrable,

that was all we could see.

Two decades after Voyager,

the Huygens Probe
launched from Cassini

and plunged through the murky
depths of Titan's atmosphere.

Our first images of what

the Titanic landscape was like

were utterly and truly
mind-blowing.

It showed there were mountains

and there was sort of erosion

on those mountains
that looked like liquid

had fallen down the mountains
and brought material with it.

That liquid must
have come from somewhere.

And where else than rain,

the weather on Titan?

We've only found
two places in the solar system

with rivers and rain...

Earth and Titan.

Out of this thick gloom,

this is the most similar place
to Earth we've ever seen.

Similar, but not identical.

That rain filling lakes and
rivers on Titan isn't water.

It's liquid methane.

It's like if every oil well,
if every gas station on

Earth started leaking
all over the place,

that is what we see on
this world.

The methane is a liquid on Titan

because the surface temperature
is 290 degrees below zero,

which is a big problem for life

as we understand it.

We don't know of any organism
that can really survive past

negative 4 degrees Fahrenheit,
and that's just because

cells will tend to freeze there.

The cells that we have,

what they're made up from,
these proteins and fatty

material, stop working,
and everything would die.

That's what happens to
Earth's water-based cells.

But could methane-based life
survive in extreme cold?

The ALMA telescope spotted
a clue in Titan's nitrogen-

and-methane-rich atmosphere.

With sunlight hitting
the atmosphere of Titan,

things like methane and
nitrogen can get broken apart

and reassembled,
like playing with LEGO blocks,

and then these molecules
recombine to

make new ones,
like vinyl cyanide.

Artist depiction.

Used on Earth to make
plastics, vinyl cyanide can

build long chains of molecules,

the type you need to build
cell membranes.

But unlike Earth's
water-based cells,

the extreme cold wouldn't
destroy them.

It could survive
at those low temperatures.

So on Titan, it could be that
this vinyl cyanide is able

to form the membranes

that are required
for cells to develop,

which are required
for life to happen.

And good news...

There's a lot of this stuff
on Titan right now.

There's as much as 10 billion
tons of this vinyl cyanide

in just one of the lakes.

If you want to start
making creatures out of it...

Say, I don't know,
a giant squid...

Do you like giant squids?

I hope so, because you could
make billions

of giant squids out of
this vinyl cyanide.

Saturn's geyser moon, Enceladus,

could have life as we know it.

Titan might have
something truly alien.

It is an unrelentingly brutal,

cold place compared to Earth.

But for Titanic life,
it might just be ideal.

As we search for life
beyond Earth,

it still comes with a bias of
life as we know it.

And so it's great,
as we continue

to explore and continue to
evolve our definitions,

we can expand our view
of how to search for life.

Maybe the Saturn system
has two living worlds.

But for life to thrive
on Titan's surface,

it must survive a storm of
deadly particles

racing out of the Sun

at over a million miles an hour.

The sun provides
light and warmth...

and something else,
something very dangerous...

The solar wind.

These lethal solar particles
can strip away

atmosphere from planets
and moons.

Without an atmosphere,

Earth would be
a barren desert, right?

There wouldn't be any water,
it would just all boil away.

There wouldn't be any life,

Luckily, Earth has
a built-in defense system.

In the center of our Earth,

we have a solid iron core, and
surrounding that is liquid iron

that is constantly moving
and swirling and convecting,

and these complex motions

power up a global-scale
magnetic field

And this acts like a force field

against the solar wind,
pushes it away,

pushes it around us
so it doesn't hit us.

We think
that Saturn's moon, Titan,

has no molten iron core

and therefore no protective
magnetic field.

So it's at the mercy of
the solar wind.

It kind of begs the question,
why does Titan

have such a thick,
dense atmosphere?

Titan retaining
an atmosphere without

a protective shield
makes no sense.

Titan doesn't have
a magnetic field,

but Saturn does.

So maybe there's some sort of
interaction between

the atmosphere of Titan and
Saturn's giant magnetic field.

The gas giant Saturn
generates a magnetic field

around 600 times larger
than Earth's,

large enough to shield Titan
from the solar wind.

So Titan by itself
is vulnerable.

Saturn is like the mother ship.

It has this giant force field

that it can use
to protect Titan.

Despite Saturn's embrace,
Titan still loses

some of its atmosphere,
because occasionally,

the moon wanders away from its
protective parent.

Titan orbits inside of
that magnetic field...

mostly, most of the time.

Its orbit isn't
perfectly circular.

It's slightly elliptical.

So as Titan orbits the planet,
for a little bit of time,

about 5 percent of its orbit,

it's actually slightly outside
the magnetic field

before dipping back in again.

But these short forays into

the f*ring line don't cause
any lasting damage.

What's really weird is that
there's sort of a residual

magnetic effect on Titan.

When it leaves Saturn's
protective field,

it should just immediately
drop to nothing.

But there still is
this residual field,

protecting it from
the solar wind.

It can maintain the
memory of that magnetic field

and still preserve some
of that protection.

It's almost like Saturn is
trying to teach

Titan how to have
a magnetic field,

and Titan can remember
for a little bit,

but then it needs to come
back home.

This magnetic memory could help

support any life on
Titan's surface,

providing a safe haven that's
protected from the solar wind.

And Cassini spots a way

Saturn's magnetism
might also allow

its moons to develop life.

One of the most amazing
discoveries around Saturn was

that its magnetic field is not

just transporting
charged particles from,

say, the sun, but it's also
transporting material

from one moon to another.

Saturn's magnetic field
helps boost

the chance of life on Titan

by stealing material
from its sister moon, Enceladus.

Magnetism is
a strong force, of course,

but to act on a scale
and a range

like this and maybe transport
matter from moon to moon,

that's pretty cool.

Saturn's magnetic field
smashes apart

water molecules blasted out
from Enceladus's geysers

and carries the leftover oxygen
to Titan.

The magnetic field of Saturn

acts like an inter-lunar highway

in the Saturn system,
transporting oxygen

from Enceladus all the way
to Titan.

But there's a problem
when the oxygen tries to

take the Titan exit off of
this inter-lunar highway.

Normally, this oxygen
wouldn't survive

in the atmosphere of Titan.

It would react with the methane
there and create carbon dioxide.

To get to the surface

in one piece, oxygen hitches

a ride with something
called a fullerene.

Fullerenes are these sort of

soccer ball shaped molecules
that are hollow.

If the oxygen atom
gets in there,

it can be safely transported
through Titan's atmosphere.

Once on the surface,
the oxygen could help create

amino acids,

the essential building blocks
of proteins,

another stepping stone for
life to emerge.

Think of all
the complex coincidences

that have to happen

for these chemical reactions
to take place.

If Titan's orbit
was any different,

it simply wouldn't exist.

Saturn protects
any potential life on its moons.

And as it turns out, the moons

return the favor
by helping create

and maintain
Saturn's iconic rings.

At 170,000 miles in diameter,

but only 30 feet thick
in places,

Saturn's beautiful rings have
always stolen the show,

but their origin is still
a mystery.

Saturn has these beautiful
rings that really

define it as a planet,

but its unique in the solar
system in the sense that no

other planet has such
a big ring system.

All of the other gas
giants have remnants of a ring,

kind of small, thin, dark rings,
but nothing like Saturn.

So something very different
happened around Saturn.

A clue comes from
the rings' composition.

They're around


giving the rings
their sparkling appearance.

This leads astronomers
to a bold theory.

We do not know how Saturn's
icy rings formed.

We're not even sure
how old they are,

but one idea is that
they formed from ice that was

existing previously on a moon.

How amazing is that?

Several billion years ago,
Saturn may have been ringless,

with a large, icy moon.

The moon was big enough that
its gravity drew heavier

stuff like rock to its core

and lighter stuff like ice
floated to the top.

We think the moon
strayed too close to Saturn.

The gravity from Saturn
could tear it apart,

and it could separate the ices
from the rocky parts

and the ices could stay in
orbit and form our rings,

and the rocky parts would get
swallowed up by Saturn.

The death of a large moon
may have built the rings,

but they owe their current
appearance to the moons that

are still alive.

When you go back
to Saturn's rings,

time and time again,
they're all slightly different.

They are changing, they are
braiding in and out of

each other... we had no idea
there would be

so much beauty and so much
mystery in the rings.

The behavior of two of
Saturn's moons,

Prometheus and Atlas,

which are embedded in the rings

is especially surprising.

Some of these smallest moons

are interspersed within
the ring system.

Some of them are doing
something really bizarre.

In some cases, it looks like
the moons were shepherding

the edges of the rings and
keeping them in their place.

The moon's gravity
cleans up the rings,

sometimes, sculpting shapes
in their wake.

Saturn's rings aren't static,
and there's some really

fascinating interactions where
moons are clearly pushing on

the rings and causing weird
and cool waves,

making the rings just
that much more beautiful.

The whole dance between
Saturn and its moons,

its rings, how they all

are interconnected, is just
completely fascinating.

It's a dynamic, amazing,

living, geologically
vibrant place.

Saturn's moons may keep
the rings orderly,

but they can't explain
why the rings are so clean,

almost pristine.

They're too shiny.

If they were billions of
years old,

they should have collected
a lot of dust by now

and be a lot darker.

The fact that they're shiny
kind of implies that

maybe they're a lot younger
than we first thought.

Perhaps the rings we see today

are a more recent upgrade.

The rings might only be


about the time of the dinosaurs.

So if the dinosaurs
had invented telescopes,

they could have seen Saturn
without rings.

And it makes you wonder, is this

the first ring system that
Saturn had?

Or was there another ring system

that may be slowly eroded away?

Perhaps a comet or a body came
in too close to Saturn,

and Saturn's gravity
literally tore it apart,

and then we got a brand-new
ring system.

The later dinosaurs could have
watched the rings form,

and then they would have been
wiped out by an asteroid.

Yeah, should have built
better telescopes,

dinosaurs, sucks to be you.

We still don't know
why the rings of Saturn

are so clean.

It could be that the rings
really are old, and they have

some sort of cleaning system,

which removes the dust
from them,

making them look young, or they
may actually be young, and this

may be the seventh or eighth
or whatever generation rings.

It is so different than
any other planetary system.

And those mysteries still exist.

We have some idea what went on,

but there's a lot that
we don't know about Saturn.

Cassini is changing that.

It's discovered a whole new
moon-making process,

with the rings taking the lead.

Midway through its 13-year
mission to Saturn,

Cassini captures
an intriguing image,

a bright feature at the edge

of one of Saturn's
outermost rings,

something we'd never
seen before.

I was really excited when
we saw these images of Saturn's

rings, and it looked
like there was a lump,

maybe a moon forming there,
which they nicknamed Peggy.

Named after the mother-in-law

of the scientist
who discovered it,

Peggy was still too small
to be considered

a fully-formed moon,
but nearby orbits

a group of objects that are
just big enough to be moons,

and they are really weird.

These moons are really unusual.

We don't think of them as like
anything else we've seen.

They're kind of
little fuzzy potatoes or maybe

even like a ravioli is another
one or a croissant.

Why do we always come up
with food?

But at the same time, that's
exactly what they look like.

The most bizarrely-shaped moon
of Saturn is Pan.

It's got these
crisscrossing cracks,

just like bread,
and then around the outside

is a belly band,
it's undulatory.

How would this get there?

Cassini discovered a clue.

Like Saturn's rings,

these moons were made almost
entirely of water ice.

They must have grown from

tiny lumps trapped
within the rings.

They're going to be
extremely fragile,

kind of like a snowflake
orbiting Saturn.

They can start drawing in
material and then can grow.

You can actually imagine
rolling up a snowball

and accumulating more and more
particles on the outside.

And in the same way,
you could accumulate

these clumps in the rings.

And if they're near
the edge of the rings,

perhaps they actually break free
and go out to form tiny moons.

The size of
these space snowballs,

tens of miles across or less,

helps explain
their unusual shapes.

The size of the moon actually
affects its shape in that once

you get below a certain
size threshold,

you cannot be round anymore.

That's because the strength of
the rock or the ice

in this case is too great
to be overcome by gravity,

and so the kind of oblong
shapes can be maintained.

Add in a few collisions,

and you get Saturn's ravioli-
and croissant-shaped moons.

It's a bizarre process but
leads to a beautiful form.

We know the moons affect
the rings, but it looks

like in this case, the rings
affect the moons, too.

They're connected
in both directions.

The rings form a moon factory,

capable of building countless
generations of new worlds.

This is a dance of physics.

If moonlets can form
by these icy ring particles,

they'll grow, and then
their natural gravitational

interaction with the rings will
make them move out.

They keep growing
as they move out.

But then another moon forms
where the first one was.

So you keep getting these
growing moons, right,

and this process repeats
like on a conveyor belt.

And what you wind up with is
bigger moons orbiting

farther out from Saturn
and smaller ones

orbiting closer in.

But Saturn's conveyor belt
will eventually break down.

When ultraviolet light from

the sun interacts with
ring particles,

it throws their steady orbit
around Saturn out of whack.

The sun energizes the rings,
and it gives them a charge.

This charge means
they can get picked

up by the magnetic field
of Saturn.

So these little tiny charged
particles then are lifted

out of the rings,

follow along
the magnetic field lines,

rain down into
Saturn's atmosphere.

The charged particles
are tiny ice crystals.

They rain down onto Saturn,

enough to fill
an Olympic-sized swimming pool

every second.

In less than 100 million years,

Saturn's rings will be gone.

There will be no material
to build new moons.

Saturn's moons and rings,

they almost make me feel
bittersweet, because they

show you the beauty of
what physics can create,

But also the fleeting-ness.

They'll be gone soon,
and that makes me sad.

The closer we look,

the more intriguing
the Saturn system becomes.

And now, scientists

have an audacious new plan

to fly a drone on one of
Saturn's moons.

Saturn is one of
the most dynamic places

in the solar system.

We want to go back there,

to explore its moons up close

and hunt directly
for Life 2.0.

For so long, we've been
emphasizing that to have

a habitable planet,

you have to be warm, you have
to be close to your star.

In fact, the most likely
chance we have to find

life maybe way in the outer
solar system in Saturn's moons.

But we won't know for sure
until we send

another mission there,
specifically to look for life.

The Huygens Probe gave us

a tantalizing glimpse of
Titan's surface,

but it wasn't equipped
to search for life.

Now, scientists are
developing Dragonfly,

a space helicopter that can
search for life.

Dragonfly is an amazing mission.

We're sending this to Titan
to better

understand how life might
arise in a very different

context than Earth.

One thing we know
absolutely for certain

is that Titan has interesting,
complex chemistry.

The question now is,

does that chemistry actually
turn into biology?

The million-dollar question,
is this a living world?

April 2021.

We test the concept
of a space helicopter.

Ingenuity making
the first remote flight on

another world launches into
the thin Martian atmosphere.

Mars is a really difficult
place to fly,

because the atmosphere is 100
times thinner than Earth's.

And remember, it's
the atmosphere that provides

the support and the lift
for a helicopter to fly.

So in order
for Ingenuity to fly,

it had to spin
very fast in order

to even get itself
off the ground.

Fortunately, Titan's
thick atmosphere

is much more
helicopter friendly.

The contrast between Ingenuity
and the Dragonfly mission

is really funny,

because Mars has almost
no atmosphere,

less than 1 percent the
atmospheric pressure of Earth.

On Titan,
you have exactly the opposite.

The air pressure near
the surface of Titan can be

four times as much as
the air pressure on Earth.

So for a helicopter
or something like a drone,

something like an octocopter,

the lower the gravity is
and the denser the atmosphere,

the better you can fly.

So Titan just begs to be
explored, because you get

a lot of lift, and you can
actually carry heavy

instruments with you.

It allows you to fly
through the atmosphere,

collect samples, and determine
what the prebiotic chemistry

is on that moon.

If ever there was a world
built for flying drones,

it's Titan.

Dragonfly is scheduled
to launch in 2027,

arriving at Titan
around seven years later,

completing the journey of moon
discovery that began

with Voyager and Cassini.

We completely transformed

our picture of the Saturn
system, the rings and the moons.

It's a far more complex

environment than
we ever dreamed possible.

The moons have come
alive, right?

They're not boring, dead
ice balls, and it just

begs generation after generation
of spacecraft follow up.

We're only just beginning to

unravel the secrets of
Saturn's moons.

And with more than 80 to
explore, the Saturn system is

a gift that'll keep on giving.

Saturn was the very first
thing I ever

saw through a telescope
when I was a kid.

And here I am... clearly,
I was inspired by Saturn,

by its beauty.

Saturn has always been
my favorite planet.

Everything you want

is there... v*olence,
colliding moons,

how new rings form, new moons
form over time.

And there might be life there.

There might be life in
more than one place there.

One destination, one planetary
zip code, gives you all of that.

I say go back to Saturn.