Original subtitles

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 20 new moons 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 is...

it sort of as dark as coal, sort of yin and yang.

Each of the moons of Saturn have 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

shooting 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's alive!

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

to see what 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 this is a huge part

of Enceladus' 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 would ask me 20 years ago

where there might be life in the Solar System besides Earth,

I think Saturn's moons would've 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 re-examines 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' 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' 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's all this heat coming from?

Cassini spotted Enceladus' plumes

shooting 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 looked at 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.

And 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.

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 sport 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.

Well, 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.

4.6 billion years ago, the ringless gas giant grows

from gas, rock and ice in the protoplanetary disc,

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've come from somewhere else.

Saturn captured these moons...

...but from where?

We think there's 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, 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 disc

at the same time as Saturn,

but then gorged on the debris

created in the later lunar collisions.

It amassed 96% 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,

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, than 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.

Titan's atmosphere has nitrogen, like ours.

But, instead of oxygen, it has methane.

Plus, the atmosphere is 50% thicker than Earth's.

Imagine the smoggiest, nastiest day you've ever imagined,

and multiply it by ten,

and then envelop the moon in that.

That's kind of what its atmosphere was like.

And the physics of this smog

can lead to some truly bizarre possibilities.

One consequence of Titan's very thick atmosphere

is that rain falls much more slowly.

So, if you were singing a song, likeSinging in the Rain,

you'd probably want to do it a little bit slower

because the rain is coming down more gently.

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's 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 definition,

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?

Using Cassini data to model Titan's atmosphere,

scientists spot a clue at the moon's poles.

So the Cassini spacecraft saw these swirls, almost cyclones

of hydrogen cyanide in the atmosphere of Titan.

This is a very strange pattern to find in the poles of Titan.

The closest analog we have to how these molecules

look and behave on Titan is the aurora on Earth, of all things.

When solar particles hit the magnetic shield

around the Earth, the field lines funnel the particles

down to the poles, both North and South,

triggered the light shows we call the auroras.

Titan's atmospheric vortices follow a similar pattern.

These vortices, the pattern of the gas here

is a little bit of a paradox.

It's a bit of a mystery because it's almost as though

the gas is clumped along

and formed along magnetic field lines near the pole.

Titan doesn't have an Earth-like magnetic field.

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 mothership.

It has this giant forcefield 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% of its orbit,

it's actually slightly outside the magnetic field

before dipping back in again.

But these short forays into the firing 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.

Saturn doesn't just help out its moons,

it communicates with them,

and sometimes we're able to listen in to that conversation.

Near the end of its mission,

Cassini gathered one last bit of data, of signal,

And it was radio emission from Saturn itself.

It tuned in to Radio Saturn.

You can convert sound into electromagnetic energy.

This is how radios work.

You take somebody singing,

you convert it into fluctuations of an electromagnetic field.

Then you can beam that to somebody's radio

and then they can hear it again as music.

Well, Enceladus interacts with Saturn's magnetic field

and creates a changing, fluctuating energy field around it,

and you can take that and can convert it into audio.

This is beautiful.

This is a conversation of electromagnetic radiation

that that we got to listen in to this very private, intimate moment

between Saturn and its moon.

Yeah, that's creepy as hell. I don't wanna hear that on the radio.

I wanna hear that on Halloween, right?

That's really weird. Creepy.

But what that is showing us is that Enceladus

is reacting to Saturn's magnetic field.

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.

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 99 percent water ice,

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, 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 100 million years old,

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 maybe 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.

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

may be 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.

Violence, 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.

Subtitling by Iyuno