(dramatic music)
Saturn is the jewel in the crown of the solar system.
It's the truly beautiful, majestic planet.
Saturn just makes us gasp at its beauty.
The Saturnian system is an absolute wonderland.
Saturn, second largest of the planets,
nearly 800 times the volume of Earth, a true gas giant,
adorned by and adored for its mysterious, captivating rings.
The study of Saturn's rings has inspired
great theoretical musings for centuries.
Almost 300,000 kilometers in diameter,
the ring system is just 20 meters thick.
The rings capture the imagination
to the point you have to understand where they came from
and what do they mean?
To try and answer these questions,
humans designed, built, and launched
some of the most advanced spacecraft ever conceived.
It was and is the largest outerplanetary spacecraft
that's ever been built.
This is a massive piece of machinery.
This is the story of the exploration of Saturn,
its rings and moons, told by those who dared to do it,
a place that turns out to be much more
than just a celestial beauty spot.
The building blocks of life could form
in the interiors of these icy bodies.
The kind of conditions we see
are probably present on tens of billions
of environments across the Milky Way.
Saturn could hold the key
to understanding our true place in the universe.
It's definitely the most
interesting place in the solar system.
(title resonates)
To the naked eye, the night sky
is filled with points of light.
Zoom into almost all of them and they remain just that:
shining points in a dark universe.
But one celestial object revealed
to an Italian polymath that it was special.
Galileo wasn't the inventor of the telescope,
but he was one of the first people to use it
for astronomical observations.
It was 1610 when Galileo first observed the Saturn system.
His drawing showed what were described
as ears or jug handles either side of the planet.
So Saturn's my face, it appeared that there
were these weird globes.
And so he thought well, these might be moons
but stuck one on each side of the planet Saturn.
He didn't know Newtonian mechanics, it hadn't been invented.
He didn't know that moons have to go
all away around a planet.
When he went back to look at Saturn
a couple of years later,
he noticed that those features had gone.
(spirited music)
Galileo even suggested that Saturn had eaten
his own children as in the ancient Greek myth,
and that's why the moons had disappeared.
Galileo lived in Italy, but he was aware
of other major figures in his time,
including Constantijn Huygens from the Netherlands,
and in fact it was Huygens' son, Christiaan Huygens,
who eventually solved the puzzle
that was posed by the disappearing handles of Saturn.
Christiaan Huygens turned his telescope towards Saturn.
As technology develops, optics developed,
and he was able to see more.
And what he saw meant that he was able
to come up with this radical idea
that Saturn was surrounded by a ring system,
and he was able to link back to what Galileo saw
because if the ring system was tilted
at an angle to our view from Earth,
it means that sometimes you'll see the rings tilted
and you'll see them sort of almost face-on,
and other times when the planet has moved,
they'll be edge-on.
So at particular times, we'd look at the rings edge-on
and they completely disappear.
In fact even today when Hubble,
the best optical telescope we have, looked at Saturn
across through the ring plane, the rings disappeared.
But not only that, Christiaan Huygens
made another amazing discovery:
that Saturn has a moon and it turns out
that this moon is a really curious place,
and is perhaps even more curious
than the rings of Saturn itself.
After the discovery by Huygens of Saturn's first moon,
Giovanni Domenico Cassini discovered
four more in the next decades,
and moons continued to be discovered
over the next few hundred years.
Mimas.
Enceladus.
Hyperion.
However, from the first there were
big questions posed by Saturn's rings.
What were the rings made of?
How did they arise?
What's the origin of the rings of Saturn?
And why does Saturn have rings and not the other planets?
The only way to answer that question
is to actually get up close, we need to go to Saturn.
But getting to planets in the outer solar system
obviously requires a huge amount of fuel,
but a large amount of fuel means
you have an expensive mission
because you're trying to launch a lot of mass into space
and you need more fuel to be able to do that.
So you start to think about, well,
what are the other ways that you
can accelerate your spacecraft
without requiring lots of fuel?
And one technique that's used
is what's called a gravitational assist.
(monitor beeping)
(inquisitive music)
As a spacecraft passes a planet
that is itself moving around the sun,
it would get dragged along
and accelerated by the planets during the encounter,
gaining extra speed like a skateboarder
briefly holding onto a passing car.
What's more, a huge opportunity suddenly presented itself.
It was discovered that the outer planets
would actually align in a way
that they hadn't since Thomas Jefferson had been president.
So we realized that you could fly past Jupiter,
get a kick, go to Saturn, get a kick,
go to Uranus, get a kick, go on to Neptune.
This gravity assist trajectory was called The Grand Tour.
And if we were gonna go and do this,
take advantage of this alignment,
we'd better get going and launch that spacecraft soon.
NASA quickly responded to the opportunity
by preparing some pathfinding spacecraft,
one that would go to Jupiter
and one that could use a gravity assist
from Jupiter to go on to Saturn.
And that was called Pioneer 11.
(spacecraft beeping)
(flames roaring)
The primary purpose of those Pioneers
was really to pave the way for later spacecraft.
And that mission was called Voyager.
(upbeat music)
And the Voyager mission had two components,
Voyager 1 and Voyager 2.
Each of them would get a gravity assist
from Jupiter to go on to Saturn.
But that's then where the missions deviated,
because Voyager 1 was given an extra special task.
It was to go and visit the moon
that Christiaan Huygens had discovered in 1655, Titan.
Titan would become almost
as important a destination as Saturn itself.
Titan is a really intriguing moon.
This is a massive moon,
probably not worthy of the word moon.
This is a body which is bigger than Mercury,
so it's a big moon.
Its mass is lower than that of Mercury,
but in terms of size, it's bigger than our smallest planet.
As we've been looking around the solar system,
many people have been fixated on Mars
as the place beyond the Earth most likely to hold life,
but there's another place in the solar system
which is probably just as exciting,
and for some people even more so, and that's Titan.
The atmosphere of Titan was hinted at a century ago
and confirmed in the 1940s.
It's the only satellite in the solar system
with a dense atmosphere.
In fact, its atmosphere is actually
denser than our atmosphere here on Earth.
Titan is the most interesting moon
in the solar system, hands-down.
But getting to Titan
meant a change of direction,
curtailing the exploration of the outer plants.
So Voyager 1 going off to visit Titan
meant that it was no longer able
to slingshot on to visit Uranus and Neptune.
If Voyager 1 had not been able
to achieve that objective for whatever reason,
Voyager 2 was going to be diverted to do that job
at the expense of going on to Uranus and Neptune.
(upbeat music)
But that's how they felt about Titan, the importance.
7-4-6-S-1-9.
15 seconds.
When Pioneer 11 eventually arrived at Saturn
six years after flying by Jupiter,
it was an immense, exciting moment.
Five, four, three, two, one.
We made it! (people cheering)
Hooray!
(intriguing music)
The rings of Saturn were big and beautiful in our pictures
and we stood in awe at the closeup views.
My task was to see if we might discover any new rings,
and amazingly, I watched the first images
appear on the television screen
and there was clearly a new ring of Saturn.
The rings of Saturn had originally
been named A, B, and C, in order
from the outermost known ring to the innermost,
but in the 20th century, we began to discover
new rings which were then assigned alphabetically
in the order of discovery, first the D Ring,
then the E Ring, so the next available letter was F,
and so I named that ring Ring F of Saturn.
(tense music)
Pioneer 11 passed Titan by quite a large distance,
couple hundred thousand miles away.
And really all it told us about Titan
was that it was very, very cold,
too cold for life as we know it to exist.
But actually we needed to go back
and look at this thing in much more detail.
Fortunately, two more spacecraft
were already on their way.
4-7-4-7-4-6-U-S-4-9.
The Pioneers had told us it was safe,
it's okay, we can go there.
(triumphant music)
So just a year later, Voyager 1,
equipped with better instruments and better cameras
was preparing to take a look at Saturn and its rings.
The encounter was an amazingly thrilling
and rapid experience,
all happened within a matter of a few days,
and even before you could explain
some of the new phenomena we saw,
Voyager was off on its way out of the solar system.
(people cheering) (people applauding)
Many people referred to that flood of data,
the camera pictures and other observations,
as like drinking from a fire hose.
The estimate is.
(people chattering)
(people cheering) (people applauding)
Do you guys have any questions?
After the Voyager flybys, we knew there were
thousands of rings, and it's that moment
that we stopped naming them with letters.
It was just impossible, exceeded the alphabet.
We saw waves propagating through the rings,
we saw the edges of the rings wiggling.
A ring could be maintained between two moons,
one outside the ring and one inside the ring.
And that's the beauty of this idea of moonlets
that are sitting within the rings,
shepherding the gravitational motion
of the particles within it.
(intriguing music) (people chattering)
Maybe it's a scientific prerequisite
to start with a simple idea,
but we had imagined the rings were ancient,
unchanging, and completely uniform,
and this picture of the rings was completely shattered.
The rings were changing in time, changing in space,
they're dynamically changing with waves
lapping across the rings, so this idea of symmetry,
of constant persistence of the rings,
all were immediately questioned.
(people chattering)
(inquisitive music)
But what was the origin of the rings?
Where did they come from?
When an object gets closer to the planet
it gets stretched out, and so a basketball might look
more like an American football under this stress.
The question is, can that stress
be withstood by the object?
For most competent objects, including humans,
we can withstand that stress.
For objects that are piles of rubble or dust
or are big, say larger than 50 or 100 kilometers,
they cannot withstand that force.
If a large moon had once strayed
too close to Saturn, this destructive force
would've been enough to tear it into tiny pieces.
So Saturn once had a moon,
say an object about the size of Titan,
if it were dragged in toward the planet by friction,
first the ice would shatter
and then later the core, which is made of metal,
would shatter or might even end up inside the planet,
and the pieces of ice formed a ring around Saturn.
And now the mission
turned to the prize that was worth
missing out Neptune and Uranus: Titan.
(tense music)
The scientific community and the public
watched with great interest as Voyager 1
made the first flyby of Titan.
What Voyager 1 encountered was still this mysterious veil.
There was an organic haze that encircled the surface
and you couldn't see the surface as a result.
That atmosphere is simultaneously
the bane of my research because it blocks the surface,
but it's also the reason why Titan is so interesting.
All of those hazes that mean that you and I
can't actually see the surface
with light that our eyes can see,
make Titan this organic chemistry wonderland.
One of the other things we figured out was that there was
methane present in the atmosphere of Titan.
Now this is important because
both pressure and temperature measurements
that Voyager 1 took indicated that
it gets incredibly close to the triple point of methane.
This opened the really, really tantalizing possibility
for lakes and oceans on the surface.
Some people think if we look in these methane lakes,
perhaps we'll find a different way of organizing matter,
a different way of organizing life.
(monkey calls)
Titan was still hiding all its mysteries from us,
so that laid down the gauntlet of the challenge.
We must now go to the surface of Titan.
Fortunately, Voyager 1 made
excellent observations of Titan,
so thankfully Voyager 2 was allowed
to go on to the next planet, Uranus, and then to Neptune.
(triumphant music)
The Uranian rings had been discovered
from the ground om 1977,
Voyager itself discovered the ring of Jupiter in 1979,
and while we were on our way to the planet Uranus,
the rings of Neptune were also discovered.
So by the time the Voyager mission had completed,
we knew that all of the giant planets had rings,
just the opposite of what the question had been
before those missions of why only Saturn has rings,
but leaving us with deeper questions about Saturn's rings.
What were they made of?
How old were they?
And why are Saturn's rings so particularly different,
so big and so bright compared to
the narrower, less massive, darker rings
of Jupiter, Uranus, and Neptune?
The rapid flybys that Voyager provided were insufficient
to answer these questions in more detail,
but then those failings could be addressed
by a mission that went into orbit around Saturn
and stayed for many years.
(people chattering)
We already knew that the value of orbiting a system
and the amount of understanding you can gain
by being there for a long period of time
is so amazing that the next step
was clearly gonna be an orbital mission.
And if we're going to send another mission to Saturn
that stays there, it should have a part of it
that lands on the surface of Titan.
Planning began in 1982
for a mission that will be more ambitious and advanced
than anything that had gone before,
a mission called Cassini Huygens.
The spacecraft was about the size of a school bus.
If you saw it when they were putting it together,
it was pretty impressive, you just looked up.
It was a monster.
It was and is the largest outerplanetary spacecraft
that's ever been built, and may,
in my lifetime, ever be built.
Pressures are excellent.
T plus 20 seconds.
The mission was a collaboration
with the European Space Agency,
who designed and built a lander called Huygens.
And this was the vehicle to take us
down through the clouds, down to the surface of Titan.
(dramatic music)
The Huygens probe was actually
designed to be able to float in liquid
as well as land on a solid surface
because we didn't know at the time whether it was going to
land in a liquid or on a solid surface.
So we designed the mission to cope
with as many characteristics as possible.
No one's ever tried to measure the depths of an ocean
and how hard a rock is
depending on which one you're gonna land on.
We knew from Hubble images that there
probably wasn't a global ocean,
but whether there were other liquids was still not known.
Huygens' team had to prepare for that
but also a very hard landing, or maybe you can imagine
a very squish surface full of organic goop.
(liquid gurgling)
20 seconds and counting.
This is Titan Launch Control.
Without any doubt, the most risky element
of any space mission is the launch.
T minus 15 seconds.
It was a nighttime launch, so you had to get on the bus
something like two in the morning or something to go out,
and we did that, and we went out to the launch site,
and the first opportunity, the launch was scrubbed.
And so we did the same thing again two days later.
T minus 10.
When you've put eight years of your life
into designing and building and testing something
which is going to go into space--
Nine, eight, seven.
And then seeing on the top of a rocket
that's being vibrated on its way to Saturn,
it is quite a feeling.
One.
(explosion booms) (dramatic music)
When it did go off, it created a huge amount of light,
(flames crackling)
and then the rocket went behind the cloud.
When it went behind that cloud, it was very impressive.
The whole cloud lit up.
We all thought oh goodness, has something gone wrong?
United Station, our fly ring data.
And then the nose cone came out
and you were getting all, phew.
(inquisitive music)
(people chattering)
Wait, do I come?
Go ahead Aswar, come.
One of the things you have to do
when you arrive at a big planetary body
is slam the brakes on pretty quick.
You need to slow yourself down and get yourself into orbit.
You typically do this by going
very close to the planet to slow you down,
so you get captured by the gravitational pull of Saturn.
It was an incredibly complex sequence
that we had basically worked on for two years.
Even after Pioneer and Voyager, we didn't know enough
about the possible dangers of the Saturn system.
And because the Cassini spacecraft was moving
at about 10 miles per second,
even hitting a grain of sand or a chunk of ice
could be deadly to the spacecraft,
and so we took a number of ways to remove that risk,
(dramatic music)
and the best was to turn so that
the spacecraft antennae was facing forward.
The high-gain antennae, which is a thing
which communicates back to Earth,
was actually protecting it from
potentially being hit by dust particles,
so it couldn't be in communication with Earth at that time.
This was an incredibly nervous
and dangerous maneuver to do given the unknowns.
Once Cassini had crossed
the plane of Saturn's rings,
the spacecraft had to reorient itself again.
The thrusters had to be turned
so that they would point in the direction of motion
to be able to capture it into orbit.
During the 90 minutes
that Cassini's engines were firing,
the spacecraft was completely shielded from Earth.
At its closest approach, the spacecraft
was just 20,000 kilometers from the cloud tops of Saturn.
All the mission controllers on Earth could do was wait.
We all held our breath waiting for the signal to return.
But then we got a signal which was dead-on.
The doppler has landed.
And we knew at that moment we had
successfully gone into orbit, and there was a huge cheer.
(people cheering) (people applauding)
It was really a fist pump moment.
People were jumping up and hugging.
(people cheering) (people applauding)
I was watching it in the middle of the night
via the internet, and I must've went into a huge cheer
which woke everybody else up in the house.
When the burn was completed,
we knew we were in orbit, so we turned away from the Earth
and photographed the dark side of the rings
and then after we come back through
the ring plane crossing again,
we turn back to the Earth to start play back that data,
and those images I'll never forget them.
We've had much prettier images but my gosh,
to see the ripples and the structure in those rings,
it was absolutely, like I said, I'll never forget it.
(triumphant music)
It's one of those moments you'll take to your grave.
Cassini Huygens had arrived
at the Saturnian system, an enormous gas giant
with 82 moons at present count,
orbiting on the outside and within
the hundreds of rings of varying shades and colors.
We could now truly start to appreciate
the awesome beauty and complexity of this planetary system.
(gentle music)
From a mission engineer's point of view,
the rings are a hazard. (laughs)
But once we've discovered that the environment's safe,
then we can start to open up the stops a little bit
to allow more activity.
We knew that we'd have long, consecutive pieces of data
to test our theories, but we didn't realize
that because we could orbit Saturn hundreds of time,
the same aspect could be seen over multiple times
by all the 12 instruments,
and that hit us in the head sometimes.
Oh, this is something unexpected that's happening.
It's very easy to think of the system as isolated parts,
especially when you're working with a spacecraft mission
and you target this feature
and then you target the satellite.
Any speculation, any idea we had had from the years
between Voyager and Cassini, could now be tested.
And as for the origins of the rings and moons,
the Cassini team made a further discovery.
(dramatic music)
As we have seen quite clearly,
Saturn's rings are made out of ice,
which is the fragments of shattered icy moons.
But the alternate is also true.
Cassini showed us that the pieces of the ring
are sticking together to make new moons.
So the rings are collecting in places to make moons,
and the moons are being shattered to make new rings.
So this is sort of a cosmic recycling of material.
So not only are the rings of Saturn
most likely made of moons, but they also make new moons.
One of the best measurements that Cassini made
was to measure the total mass of the rings.
This determines how long this recycling process could go on.
The amount of pollution, the amount of meteoric dust,
the combination of those two facts
say that the rings are about 100 million years old.
This can be extended, perhaps, to a billion years or two,
but the current one is the rings
that the dinosaurs would've seen.
(dinosaur roars)
(gentle music)
(intriguing music)
If we were to look closely,
many of the ring particles would appear fluffy to your hand.
They're fairy castle structures sort of like snow.
You would see a range in particle sizes
continually colliding, but at a relatively low velocity,
maybe a millimeter a second,
which is gentle enough that the surfaces
might be slightly compressed.
But occasionally, particles will hit each other
at a much higher velocity, which will knock off
a spray of small particles of snow and ice
which eventually are recaptured by other clumps,
so the equilibrium, the balance between these two processes,
leads to a distribution of sizes from dust to mountains,
and each of the objects being like a pile of rubble
with a coating of snow on the top.
(inquisitive music)
After six months in orbit,
Cassini was scheduled to deploy the Huygens lander
on December the 25th, 2004.
We had Christmas dinner at my home
and had a lot of the European and American contingent
because we were all spending Christmas at JPL.
My whole family was here.
I made them come to JPL and they watched
as we released the probe that night.
(people chattering)
(people cheering) (people applauding)
A few days later we turned around
to take a picture of where the probe was supposed to be.
It's a little speck and it's not very exciting,
but it was a genuine confirmation
it was exactly where we thought it was going to be.
Because what happens with a probe
is essentially when you release it,
you've turned on a little three-week egg timer.
(dramatic music) (timer ticking)
Your worst nightmare is silence.
That's happened too many times to people in space missions
and it's just a punch in the gut.
But three weeks later, right on schedule,
we get the signal back.
When we arrive at Titan,
we're traveling at incredible speeds,
and what you gotta do is go from ballistic,
incredibly fast speeds at the top of the atmosphere
to zero speed at the bottom
of the atmosphere on the surface,
and this is pretty hard to do.
There are several elements in order
to get yourself down to the surface.
The first is a heat shield.
Titan has a huge atmosphere,
and Huygens was just screaming in.
And if we were to send the probe
in without protection, it will burn immediately.
So you have the sacrificial heat shield
in front of the probe, so the fireball that's created
as the probe slows down doesn't destroy the lander itself.
And in the case of Huygens,
the heat shield was made of many of those tile.
While the heat shield
was slowing the probe down,
Huygens experienced a deceleration of 15G.
Once it had got to an altitude of 170 kilometers
and was only traveling at a mere 400 meters per second,
Huygens deployed the first of its three parachutes.
The drogue parachute stabilized the probe
and pulled off the back cover,
which deployed the main parachute,
at which point the spent heat shield was discarded.
(clock ticking)
But Titan's atmosphere is so thick
that if we kept that parachute on,
the batteries would've run out before it got to the surface.
It was gonna go a little slowly.
So it actually deployed that parachute
and then dropped the last chute
which allowed it to descend at a more reasonable pace.
You get horizontal winds coming across
and swinging the probe about,
so as it descends through the atmosphere
it's not perfectly still, it's swinging like a pendulum.
The images from descent show channels on the surface
and there was no doubt, there were no questions,
it was obvious what we were seeing.
And it was just so spectacular to see something
and know what it was on the surface of Titan
and for it to be river channels.
(introspective music)
It then landed on the surface
and it started transmitting back to Cassini,
which was way up overhead.
The spacecraft, meanwhile, is flying over the top
and pointing at the point on
the surface of Titan where the probe is.
And eventually the spacecraft goes over the horizon.
The batteries were still going
even after we lost sight of it.
The spacecraft turned back
and started to play the data back.
Imaging guys turned around an image
of the surface very, very quickly.
(keyboard keys clacking)
And it flickered up on the screen.
And everybody looks up and goes,
"What's going on here?"
It was almost like it was fake.
To see something like that on a moon
in the outer solar system, it was just spectacular.
It still gives me goosebumps to think about
all of that working so well.
Seeing something that no human in history
had ever seen before, it was truly awe-inspiring.
It was a moment I will never, ever forget.
It was sitting on this flat lake bed
and the things that appeared as rocks in the background
were actually pebbles of ice that had been frozen.
Titan is an icy satellite.
Its bedrock is made of water ice.
But when we look at the surface of Titan
with the spectrometer, it's actually really hard
to find any pure water ice spectral signatures,
and I think that the key there
is all these atmospheric products
that are continually falling out across the surface.
Titan's atmosphere is actually
mostly nitrogen like Earth's atmosphere,
but it's cold in the outer solar system,
and the next most common constituent in the atmosphere
is methane, and methane in Titan's atmosphere
plays a role very much like water on Earth.
So the methane in the atmosphere
can condense to form clouds,
it can actually rain out onto the surface,
it can run across the surface in rivers,
form lakes and seas, and there may even be
methane aquifers in the subsurface as well.
So it really does have a complete hydrological cycle
where methane plays the role that water does on Earth.
Carl Sagan and his research partners, Khare and Thompson,
gave us a really interesting insight
by doing experiments where they mixed
nitrogen with methane and then provided
some free energy source, some light or some particles
(light booms)
to break them apart or to ionize them,
and it led to this incredible organic chemistry
that was beyond the wildest dreams,
created this stuff in the laboratory the called tholins.
The methane dissociates at the top of the atmosphere,
recombines to form very complex molecules,
and all of that material falls out onto the surface.
How long that process has been going on
is still not well understood,
but if Titan has had an atmosphere like it has today
for the entirety of the solar system,
that's going to produce a volume of sediments
that means that Titan's crust is not just water ice
but also has a bunch of organic sediments
that have been built up over time.
All of these organic materials have been
sitting around littering the surface of this moon
where there's the opportunity, potentially,
for them to have mixed with liquid water.
If you react water with these precursor molecules,
what's been demonstrated is these tholins
that have been studied in a lab can form amino acids.
And the universe provides us that mechanism
when impacts hit the surface of Titan,
(object whooshes) (impact booms)
because every impact has enough kinetic energy
to melt some of the crust.
The bigger your impacter, the more kinetic energy
you impart, and so the more melt you can generate.
And then based on how much melt you generate,
you have this pool of liquid in the near subsurface
that's going to cool slowly over time,
and based on the sizes of impact craters
that we've seen on Titan,
this can be anywhere from hundreds
to tens of thousands of years.
So we know that Titan has all the ingredients
necessary for life as we know it,
and it's been doing these chemistry experiments
for hundreds of millions of years.
You also have the opportunity for organic material
to mix with a different solvent
in the form of liquid methane,
and so perhaps there are other prebiotic systems on Titan
that have progressed that are completely alien
to the water-based biology we have on Earth.
It's hard to conceive how a methane-based
form of life would work, but nature has repeatedly
surprised us as demonstrated by all the findings
of the Cassini mission, so I'm not willing to rule out
the possibility of life in the liquid methane lakes.
I'm personally skeptical that we would find that.
There are some difficulties with that.
So for example long-chained carbon molecules,
organic molecules, tend not to dissolve very well
in liquid methane, they'll precipitate out.
So you could imagine an inverted structure almost
where because cells are a mixture
of insoluble and soluble parts,
it's possible it could work the other way around,
and I find it much more difficult
to conceive how that could work.
Certainly it would be very exotic
and at present we have no indications
in any of the current measurements
from the Cassini or Huygens part of the mission
that there's anything bizarre
that we might need to attribute to the activity of life.
But the only way to find out is to go and look,
and so you have with Titan this wonderful possibility
that we might find life as we know it
or we might find life as we don't know it.
In any case, just going to look around
will be a fantastic thing to do,
so what's not to like, really?
But as exciting as Titan was,
there were even more intriguing discoveries to be made.
When Cassini was approaching Saturn for the first time
at the end of 2003, our experiment,
the ultraviolet imagining spectrograph,
was systematically scanning
back and forth on the planet Saturn,
and we were amazed to discover
that the system was filled with molecules of oxygen,
and the oxygen was completely unexpected
and we mapped this out and we noticed
that the peak in the distribution
was just a distance four times Saturn's radius
from the center of the system.
We knew that the moon Enceladus
was orbiting just at that distance.
Enceladus is a tiny moon
just 500 kilometers in diameter
with a surface area slightly larger than Texas.
It coexists with one of Saturn's
fainter rings, the E Ring.
The E Ring is just a ring
of icy grains in the micron range.
It was tenuous enough ring that we could
fly through it and examine it.
We had these tentative ideas that maybe
there was a connection between the E Ring and Enceladus
because they were pretty co-located,
but we didn't really have any understanding
of how they were playing together.
Enceladus originally was on the itinerary,
but only marginally so.
It was another very interesting Saturn moon,
small, very shiny, very white, very bright,
but other than that too small to be interesting.
(dramatic music)
And it was in the first close flyby
that the magnetometer team detected
something interesting that they didn't expect.
The magnetic field instrument observed
that the magnetic field lines didn't quite
come down to the moon the way they should.
This significant deflection in the magnetic field
was extremely unexpected.
The magnetometer team said
it looks like it has an atmosphere.
Well, anybody that knows anything about moons
says that's too tiny, can't have an atmosphere,
it's way too small to hold onto anything.
A moon as small as Enceladus
has a tiny gravitational field,
far too week to hold onto an atmosphere.
What's more, the atmosphere that was there
didn't seem to be evenly spread out.
If you flew by the south pole
it looked like there was an atmosphere,
but if you flew by at the equator
you didn't see anything at all.
But then we went back again and again
and explored with more instruments
and then took some images,
and all of the sudden realized
that not only it had an atmosphere,
it was an icy atmosphere,
but it had these plumes coming out of the southern pole.
And here's water geysers on a tiny moon.
(intriguing music)
And that water that was coming out of
what we've later found out to be an interior ocean
was what was forming the E Ring.
We were able to measure the amount
of water in those plumes exactly enough
to explain the ring of oxygen around Saturn
that we had seen before that approach.
What an amazing development that the geysers
on the moon Enceladus are continually erupting
water molecules broken down by the sun
to form atoms of oxygen that we could see
even millions of miles away from the planet Saturn.
And as we flew through these plumes
coming out of the south pole, some of that plume material
was captured by the instrument.
And we used that to learn more
about the interior ocean chemistry.
Not only did it contain water vapor,
but it had traces of ammonia, methane, H2, CO2,
and then there was a whole host
of organic compounds that we could also see.
The experiment that we did here at Colorado
is very similar to that.
We didn't actually fly through the plume
but we watched a star set through the plume.
And now we can put all that information together
to get a picture of the shape of the eruption
and also the material that's being
erupted from inside of Enceladus,
and amazingly enough that material
has the basic building blocks of life.
We've been dominated as biologists
with a fixation on the idea that all life on Earth
is powered ultimately by the sun.
Any formation of life going on on Enceladus
is going to be happening beneath the icy crust
and the oceans underneath where we see
the same kind of hydrothermal vent systems
releasing hydrogen gas into the oceans there,
which we know for a fact would've
been present on the early Earth,
and they don't strictly require the sun.
We think based on the types of molecules
and other chemicals we're finding in the plume
that this process called serpentinization is happening.
Serpentinization is a geological process.
It's a fancy way of saying how
liquid water can react with rocks,
and serpentinization is thought to be
really important for supporting microorganisms
and the base of an ecosystem outside of these
hydrothermal vents because it makes abundant hydrogen,
and hydrogen is sort of like rocket fuel
for a microorganism, it's a great way
to have a food that can be burned to provide energy.
To me, Titan is less exciting than Enceladus
because Enceladus has oceans
with alkaline fluids from hydrothermal vents going into it,
and therefore it's exactly analogous
to how I think life started on Earth.
This says to me that would be a good place to go,
measure those plumes, maybe drill down
and see if there's any form of life there.
So Enceladus may have
just the right conditions for life
to get started far away from the sun,
and the evidence for its mysterious inner workings
can be seen in the enormous, diffuse E Ring.
This is just another case of how the moons make rings,
so by grinding of their surface,
which throws dust into orbit around the planet,
by erupting of geysers, or by shattering them to bits,
the moons are the parents of the rings that we see,
but also the children because the rings in some cases
can collect up to form new moons.
(whimsical music)
Cassini would spend
more than 13 years at the Saturnian system
and completely 294 orbits of the planet,
but eventually its fuel would run out.
Everything has to end, including Cassini.
(melancholic music)
We went through this amazing time
at the end of the mission,
ending up with orbits which went inside Saturn's rings,
but we knew at the end, of course,
that the idea was to actually
burn the spacecraft up in the atmosphere of Saturn,
and that's to avoid it hitting these
astrobiologically feasible places like Enceladus and Titan.
The last thing we would want to do
would be contaminate those with something sent from Earth.
You can go where you've never been before.
You can get science you will never have
any other opportunity of getting,
and you'll keep Enceladus safe.
No brainer. (laughs)
But the emotions were all over the map.
All good things must come to an end, (laughs) right?
Yes, it's sad in a way, but.
The spacecraft was oriented so it could
communicate with the deep space network here on Earth,
but then the other axis was set
so that the spacecraft could get the best measurements
of Saturn's atmosphere as we plunged into it.
We have loss of signal in X-ray band and CR-band.
Total loss of signal at 11:55:46
for the S-band, so that would be the end of the spacecraft.
I don't think any of us were ready.
If you ever had pets, and I've gone through
eight cats and two dogs during
the 23 years I worked on Cassini,
and when you know it's time, it's time,
and it was time to end the spacecraft.
Now I, don't get me wrong,
I'm very sentimental about it, but it wasn't a pet,
it was just an amazing instrument, a robot,
that did some incredible things at our behest.
Signal from the spacecraft is gone
and within the next 45 seconds, so will be the spacecraft.
I hope you're all as deeply proud
of this amazing accomplishment.
Congratulations to you all.
This has been an incredible mission,
an incredible spacecraft,
and you're all an incredible team.
I'm gonna call this the end of mission.
Project manager off the net.
(people applauding)
Cassini was only made possible
by the hard work of hundreds of scientists and engineers
from even before I was born,
so to be able to be there with them
for the end of the mission was supremely humbling
because of the gift that they gave us.
And I cried like a baby (laughs) the whole time.
(inquisitive music)
I've always loved the rings of Saturn.
The Cassini exploration has allowed us
to see them really close up, changing before our eyes.
The idea of oceans beneath the ice
that might support life is far from the old paradigm.
It opens up a whole new idea of how life
might form in solar systems in the cosmos.
If you were to say to me,
"Where would I most want to send a rocket?"
it would be to Enceladus and it would be to look at
the plumes and alkaline hydrothermal vents under the surface
because to me, that's the environment
that's most likely to drive the origin of life.
Finding life on Enceladus
or underneath the surface of Titan
would drastically change our view of the universe
and our place in it, and it's a future test
to search out and find out if those ingredients
have led to the evolution of life on those celestial bodies.
In the summer of 2019,
NASA announced that it had approved a mission
called Dragonfly that would return to the surface of Titan.
Dragonfly is a mission that's going to Titan
to study its prebiotic chemistry.
It's an octocopter.
By being a mobile lander, Dragonfly is going to allow us
to truly discover what the surface of Titan is like.
And it would spend most of its time on the surface
making scientific measurements,
but then we'd be able to fly from place to place
so that we could measure the chemistry
in different environments.
Dragonfly's main goal is to taste the surface of Titan
and tell us what the end product
of all of this fantastic chemistry that Cassini revealed is.
And really understand how far
prebiotic chemistry can progress in an environment we know
has all the key ingredients for life.
Dragonfly is scheduled
to leave Earth for the Saturn system in 2026
and should arrive at Titan in 2034,
55 years after Pioneer 11
gave us our first encounter with Saturn.
(intriguing music)