ROWE: Orbiting the magnificent ringed planet, Saturn,
are a series of extraordinary moons.
LANZA: The closer that we look,
the more that we see its moons are like worlds of their own --
so dynamic, so Earth-like.
ROWE: 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.
ROWE: With each new mission, we get closer
to unraveling the mysteries of Saturn's moons.
[electricity sparking]
[explosion blasts]
ROWE: 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.
ROWE: 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.
ROWE: In 2005, Cassini discovered that
one moon's story was particularly exciting.
PLAIT: 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.
ROWE: 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.
RADENBAUGH: 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.
DURDA: 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.
ROWE: 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.
CHRISTIANSEN: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
PLAIT: These are cracks in the Earth's crust, where
hot material can then spew out into the ocean.
RADEBAUGH: 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.
ROWE: 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.
ROWE: 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?
ROWE: Cassini spotted Enceladus's 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 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.
ROWE: 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.
DURDA: 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.
ROWE: 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.
ROWE: 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.
RADEBAUGH: There must be something dramatic that happened
to create a system
that's so complicated and changing
before our very eyes.
ROWE: 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.
ROWE: 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 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.
ROWE: Saturn captured these moons.
But from where?
WALSH: 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.
ROWE: 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.
WALSH: And all of a sudden, most of the mass
of all the satellites is in that single moon, Titan.
ROWE: 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.
CHRISTIANSEN: 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.
ROWE: Two decades after Voyager,
the Huygens Probe launched from Cassini
and plunged through the murky depths of Titan's atmosphere.
DARTNELL: Our first images of what
the Titanic landscape was like
were utterly and truly mind-blowing.
HOWETT: 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?
ROWE: 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.
ROWE: 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.
ROWE: 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.
HOWETT: The cells that we have,
what they're made up from, these proteins and fatty
material, stop working, and everything would die.
ROWE: 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.
ROWE: 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.
HOWETT: 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.
ROWE: 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.
ROWE: 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.
COOPER: 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.
ROWE: 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.
ROWE: 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,
ROWE: Luckily, Earth has a built-in defense system.
SUTTER: 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
PLAIT: And this acts like a force field
against the solar wind, pushes it away,
pushes it around us so it doesn't hit us.
ROWE: 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?
ROWE: Titan retaining an atmosphere without
a protective shield makes no sense.
SUTTER: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
SUTTER: 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.
ROWE: 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.
ROWE: 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.
ROWE: Saturn's magnetic field smashes apart
water molecules blasted out from Enceladus's geysers
and carries the leftover oxygen to Titan.
SUTTER: The magnetic field of Saturn
acts like an inter-lunar highway
in the Saturn system, transporting oxygen
from Enceladus all the way to Titan.
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
THALLER: 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.
ROWE: 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?
ROWE: 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.
ROWE: We think the moon strayed too close to Saturn.
WALSH: 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.
THALLER: 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.
ROWE: 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.
ROWE: 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.
HOWETT: 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.
ROWE: Saturn's moons may keep the rings orderly,
but they can't explain why the rings are so clean,
almost pristine.
PLAIT: 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.
ROWE: 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 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.
ROWE: 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.
ROWE: Cassini is changing that.
It's discovered a whole new moon-making process,
with the rings taking the lead.
ROWE: 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.
ROWE: 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?
ROWE: 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.
PLAIT: 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.
ROWE: 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.
ROWE: 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.
ROWE: The rings form a moon factory,
capable of building countless generations of new worlds.
This is a dance of physics.
PLAIT: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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.
ROWE: 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?
ROWE: 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.
ROWE: 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.
LANZA: 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.
ROWE: 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.
DURDA: 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.
ROWE: 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.
THALLER: Saturn has always been my favorite planet.
Everything you want
is there -- violence, colliding moons,
how new rings form, new moons form over time.
PLAIT: 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.