October 28th, 2015. The Cassini probe captures one of its final
images of a mysterious moon orbiting Saturn. Its name? Enceladus. Its diameter is just 310 miles, less than
15 percent of our own moon. But these photos reveal what appear to be
volcanic geysers spewing from its surface. Scientists are trained not to jump to conclusions,
so we weren't gonna say, "Definitely, we've found, you know, we've found something." We thought, you know, you know, Toto, we're
not in Kansas anymore. This is, this is something really really outstanding
and something very significant. Why do these plumes exist? What is inside them? To me, it eclipses everything else we know
about the other worlds in the solar system. This is the single most important and interesting
place for our solar system beyond the Earth. Could this tiny ball of ice actually contain
the ingredients necessary for life? In 1977, NASA launches two spacecrafts on
a 12-year journey to the outer edge of the solar system. The Voyager probes send back the first detailed
images and data of the gas giants beyond the asteroid belt. But one planet captures the heart of Carolyn
Porco. I was a graduate student when Voyager flew
by Saturn. I did my thesis on Saturn's rings, and it's,
you know, like your first love. There's the, the jolt that we scientists get
is you know, finding something new that nobody else knows about. And all that happened for me at Saturn. But one moon seems to hold more mysteries
than the others. Covered in a thick orange atmosphere, its
name is Titan. It was Titan, completely enshrouded in haze,
and we didn't know when we got there with Voyager, whether or not we'd be able to see
down to the surface, and it, with our cameras, and it turned out we couldn't. Unable to see past the atmosphere, Voyager
cannot solve the mystery of what lies beneath. Titan was an object of immense interest. This was the place that we need to go back
to. So, when NASA put out this announcement of
opportunities saying, you know, "Come, apply to be involved in our next adventures at Saturn,"
I applied, and I'm so grateful that I had the chutzpah to think, "I'm not just gonna
be a member of the imaging team, I'm gonna lead it." In 1990, Carolyn's dream comes true. NASA places her in charge of the imaging team
for Cassini, and this mission will be different. Voyager, mind you, was a reconnaissance mission. It was just a flyby, and the whole purpose
was just to see what's there in the brief period of time that you're allowed. But Cassini will enter Saturn's system and
stay there for years. Imaging the planet and its moons with high
powered cameras and scientific instruments. Three, two, one. And lift off of the Cassini spacecraft on
a billion-mile trek to Saturn. In July, 2004, Cassini arrives at Saturn. And right away, it delivers on its promise,
taking the most detailed images ever of the ringed planet and its moons. I had been thinking about Voyager imagery,
and then I walk into my lab and I see this picture. And it's incredibly detailed. And that's when I thought, "Oh my god, this
is gonna be just spectacular. This is gonna be a wondrous thing, what we're
gonna be doing at Saturn." The Cassini mission brought us a wealth of
scientific discoveries about Saturn, for example, it helped discover four new moons. Cassini revealed entirely new detail about
Saturn's amazing rings, and the way that they are moving around the planet. Talk about an age exploration. Imagine sending an observatory out to Saturn
to stay there for years. You don't even really know what you're gonna
discover, so you can hang around, and even go back to places again and again, to look
for what's changing over time, to investigate things that you never knew were there, until
you actually got to Saturn. So, when I think of Cassini, I think about
these amazing pictures of this beautiful planet. There's nothing like Saturn to me that really
evokes this poetic response. The, the sheer beauty of it. And we found so many amazing things. We learned about how giant planets operate. But we know about the rings now, from Cassini
being out there. I mean, it just completely changed our view
of the most beautiful of the planets. But for astrobiologist Chris McKay, the real
star of the show is Titan. The reason Titan was so interesting for astrobiology
was that it is so rich in organics. There's an organic haze in the atmosphere. We thought that there would be organic liquids
on the surface. Organics are the carbon-based molecules needed
for life. Could organic liquids indicate some form of
life on the surface of Titan? Carolyn and the team have equipped Cassini
to do what Voyager could not. See beneath the haze. And it will happen by sending a probe called
Huygens right down to the surface. So, Huygens was designed to drop from the
Cassini probe and descend through the atmosphere and make a soft landing on Titan, sending
back information the whole way about what Titan was actually like, and finally giving
us a chance to peer through these murky clouds on the surface. On January 14th, 2005, Huygens makes its descent. When the Huygens probe descended through Titan's
atmosphere on a parachute, it was taking images of the surface. We didn't know what to expect. But it showed what looked like shorelines. When we got pictures of the surface, it was
very clear that there had been liquid of some kind on the surface for a long time. But Titan's surface is nearly minus 200 degrees
Celsius, so that liquid cannot be water. So, Titan has clouds, it has rain, it has
rivers, it has seas. But it's methane and ethane. And the real question for astrobiology is,
is there some sort of chemistry that could make life, that could live in this kind of
liquid? For life to exist on Titan, it would have
to be so alien, that it survived on methane instead of water. Although Chris McKay is hopeful, it's a long
shot. But Titan is not the only moon orbiting Saturn. Enceladus was a moon that we knew from Voyager
was unique. It was the whitest object in the solar system,
it was the brightest object in the solar system. It was associated with a very big ring of
very very fine smoke sized particles that had been discovered around Saturn in the 1960s. Enceladus was the place that we were just
puzzled about, and other than Titan, Enceladus was the moon that on Cassini we had planned
to have the greatest number of flybys. Carolyn Porco turns her attention towards
Enceladus. And once Cassini arrives, a single photograph
transforms the entire mission. I was focused on Titan but then my world changed. For me it was really an "Oh my god" moment. In February 2005, the Cassini space probe
makes a shocking discovery on Saturn's icy moon, Enceladus. Some of the first images coming back from
Enceladus are sort of centered on the moon itself, and there's not much space besides,
it's just the moon in the image. And if you look closely, there's kind of this
whiteish glow near the south pole. And I can imagine people at first wondering
"Was that some trouble with the image? Did the calibration not go right?" And then all of a sudden you realise there's
something coming out of that moon. And our first observation turned out to have
something coming off the south pole. And it was clear. Everybody just went all abuzz with this, like,
"Wow, there's something coming off the south pole." Everybody was getting excited. Scientists knew that the moons of Saturn were
cold. And then they suddenly see these images of
Enceladus and they noticed a kind of activity that you don't expect from some sort of cold,
dead moon. The image shows a plume of material streaming
miles above Enceladus. The Cassini team suspects that it's water,
somehow ejected by a powerful amount of heat and energy. Carolyn Porco immediately contacts Chris McKay
with the news. Carolyn calls me up. I'm in a meeting, but I know if it's Carolyn
it's an important message, so I ducked out of the meeting, and I listened to the phone
call, and I was stunned. And that's when I learned about all the interesting
stuff coming back from Enceladus. Evidence of energy coming from a sub-surface
ice environment. My world changed. The reason why this discovery mattered so
much, is that it meant there might be an enormous amount of really interesting chemistry going
on there. The kind of chemistry that might be similar
to what we saw in the early days of the Earth, maybe replicating the kinds of conditions
that might give rise to life. Our first thought was, "We gotta get a closer
look, OK? And we gotta figure this thing out." A few months later, the probe makes another
flyby of Enceladus. And this time, there's no mistaking the power
hiding underneath the icy surface of this moon. And that's when we really had our, you know,
our socks blown off, because that's the picture where you see about a dozen narrow jets coming
off the south pole. We found out that heat was coming from these
four fractures. But what is producing something so extreme? Scientists believe the gravitational forces
of Saturn are tugging on Enceladus, creating friction inside the moon. The evidence indicates Enceladus has massive
amounts of water, and a powerful source of energy. Two key ingredients in the search for life. If you've ever spent any time by the ocean,
you know about tides. On Earth the water rises and falls, you know,
a couple of times a day, and that has to do with the gravity of the sun and the moon,
actually tugging on the Earth, kind of stretching the planet. Now in the outer solar system, you have some
big planets. You know, Saturn is on the order of 95 times
the mass of the Earth, so there's a lot of gravity there. And some of Saturn's moons actually orbit
very very close in to that planet, so there's tidal forces, and so these moons are stretched
and pulled back and forth. And friction is simple. You know, you, you rub your hands together
and you can feel the warmth. The rocks sliding back and forth, being stretched
by the tides, generates heat. In fact, enough heat that underneath the ice,
you get liquid water, lots of it. And how else could a little moon like Enceladus
so far out from the sun, part of the outer solar system, how could it be warm enough
to have liquid water? It's the tides that warms the interior of
Enceladus. And the next step is, can we say something
from the molecules we see about the conditions of what's going on in the sub-surface? Can we say anything about the presence of
biology? Can we see anything that could be consistent
with biology? The team looks to find signs of organic material
in the plumes. And what Cassini finds provides even more
evidence that the building blocks of life may be brewing underneath the icy surface. We have found that the particles in the plume
close to the surface, were salty. And they had a salinity comparable to the
Earth's oceans. And that said that this body of water had
to be under the ice shell, and in contact with a core. In contact with a rocky core. It could be an environment similar to hydrothermal
vents at the bottom of Earth's oceans, a place where life exists. So, all of this put together said that we
had a zone that could possibly sustain life. Ok? It had the basic ingredients. It doesn't mean it has the secondary and tertiary
ingredients, but could it possibly be a place where you know, if biological activity is
not taking place now, it might be well on its way to taking place. Over the next several years, Cassini continues
to gather data and photos from Enceladus and its plumes. But in December 2015, after ten years of flybys,
Cassini approaches Enceladus for the last time. Carolyn and Chris are among the first people
to see the final images. This is the last flyby of Enceladus by Cassini. These are the last close ups? That's right. Are you strapped in? Here we go. Look, oh my god. What? Oh, those are just craters, but look at them. It's incredible isn't it? Really nice. Wow, I wasn't expecting that. We're gonna be working with this now defined
set for a long time. Oh, a very long time. I, I mean, Cassini's been so incredibly rich. I, you know, it'll be... I but, I bet we'll be working with Cassini
data for 50 years. But this final pass by Cassini doesn't study
the plumes on Enceladus. If scientists are going to continue looking
for signs of life, a new probe will have to go back because in September 2017, Cassini
will end its mission and plunge into the atmosphere of Saturn. For scientists who were looking for possibilities
of life in the outer solar system, seeing these jets on Enceladus, this is winning the
World Series and the Super Bowl, all rolled into one. This is the, the best possible discovery they
could make. Imagine being one of those planetary scientists
where you just have your universe stood on its head. You go out to the outer solar system expecting
things to be frozen solid, you're so far away from the sun, you know, where are you gonna
get the heat? And all of a sudden, now you realise that
underneath the ice of Enceladus, there is a lot of liquid water, an ocean's worth. And it even looks very interesting, there's
neat chemistry in the water. So, this may be one of the best places to
look for life. Your entire career has just been changed. Sometimes the universe just does you a favor. Enceladus, in some ways, is kind of the holy
grail of looking for life, because you know that there is warm liquid water. You know that there's interesting organic
chemistry in the water, but there's nowhere else in the solar system where that water
is flying out in geysers that are hundreds of miles tall. Which means you can fly your spacecraft right
through it. The universe delivers the sample right to
us. Nowhere else in the solar system do you know
that there is a vent of liquid water coming out right here. So, we could send a lander to actually land
near one of these geysers, maybe even go down one of the vents. That's why Dr Porco and her team are determined
to return with a new spacecraft. We're not sure that there's life there. We just have strong indications that there's
at least an environment there that could support life. And maybe even an environment where life might
have originated. So, the thing that many of us wanna do, is
we wanna go back and if at all possible, eventually bring back a sample to Earth. To me it eclipses everything else we know
about the other worlds in the solar system. This is the single most important and interesting
place for astrobiology in our solar system, beyond the Earth. Can you tell I'm enthusiastic about it?
