How the Universe Works - S07E10 - Cassini's Final Secrets
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00:00For 13 years, the Cassini spacecraft explored astounding worlds, Saturn and its moons.
00:13We discovered things we never imagined.
00:16All of these strange, bizarre landscapes, geysers erupting out of moons.
00:22We were so stunned by the images.
00:26I mean, people were just going around in shock.
00:37But Cassini started running out of fuel.
00:41Scientists at NASA had to decide what to do next, and the answer was actually pretty spectacular.
00:49Cassini goes where no spacecraft has gone before, a death flight revealing the deepest
00:56secrets of Saturn.
01:20Far beyond Jupiter lies Saturn, a planet circled by multiple moons and rings.
01:27It's like a miniature solar system.
01:32Imagine having a mission with the power, the instruments, the capability to explore all
01:36aspects of the Saturn system.
01:39That mission was Cassini.
01:50It would become our eyes and ears in the Saturnian system for over 13 years.
01:59But by September 2017, Cassini was almost out of fuel.
02:06Cassini has been orbiting Saturn and studying the Saturn system for over a decade.
02:11End the mission.
02:12We're going to lose control soon.
02:14So rather than let it just go derelict, we headed into Saturn, go out with a bang.
02:22The Cassini team goes for broke.
02:25They programmed the probe to head straight for the planet.
02:30How cool is it to sort of sacrifice everything you've got to sort of learn your last bit
02:34of information and then crash and burn?
02:37We are in the atmosphere.
02:42As Cassini was careening toward its death, it still had instruments that continued to
02:46work and as each instrument died, there was still a set sending back data and information.
02:52Cassini wasn't designed to plunge through Saturn's atmosphere.
02:56No one knew how long it would last before burning up.
03:04I remember sitting in a room with my colleagues on Cassini and watching that radio signal,
03:15that sharp green peak that told us Cassini was still linked to the Earth.
03:21We could monitor the atmosphere as we flew into it and right up until the last it was
03:25sending back signs.
03:27I was really impressed by how long Cassini lasted in the Saturn atmosphere.
03:32I mean, go NASA engineering.
03:36As Cassini plummeted down at 77,000 miles an hour, it was bombarded by gas molecules
03:43in Saturn's atmosphere.
03:49Friction started tearing Cassini apart as it struggled to maintain contact.
04:01As the antenna turned away, we actually saw a secondary little peak and we thought, okay,
04:05Cassini, hang in there, keep fighting.
04:08And then just that green flat line.
04:11We just heard the signal from the spacecraft was gone and we have in the next 45 seconds
04:18so far in the spacecraft.
04:21Cassini's heartbeat was gone and we knew the mission had ended.
04:26It just vaporized in the Saturnian atmosphere and so it has become a part of Saturn itself.
04:40Cassini's death plunge was the last of a series of daring dives.
04:52Prior to ending Cassini's mission by sending it into Saturn's atmosphere, NASA's engineers
04:57and scientists came up with an idea.
04:59Let's do dives into the region between the tops of Saturn's clouds and the innermost
05:05area of Saturn's rings.
05:09Starting in April of 2017, Cassini ventured between Saturn and its rings 22 times.
05:18Scientists called it the grand finale.
05:23On these dives, Cassini got closer to Saturn's cloud tops than any spacecraft ever had before.
05:33Saturn is an enormous ball of hydrogen and helium, a gas giant.
05:39Fundamentally it's a really very different kind of planet than we're used to in our everyday
05:44lives.
05:46Cassini snaps close-ups of the planet's gaseous surface.
05:50The pictures reveal a turbulent and stormy world.
05:55We think of some storms on Earth as being particularly violent.
05:57If you've ever been in a hurricane, that's not a fun place to be.
06:01The storms on Saturn, the wind patterns on Saturn, can make that look like a mere breeze
06:05in comparison.
06:08On Saturn, one storm stands out.
06:11Its location is marked by a distinct shape.
06:16One of the really weird things is that once the bands go around Saturn, they're all circular
06:21until you get to the pole, and then there's a hexagonal band up there.
06:26No one expected that.
06:29During its lifetime, Cassini took multiple images of the hexagon.
06:35Whenever we posted an image of the hexagon, the hits to the website went through the roof.
06:41I think people thought it was so mysterious.
06:44When I first saw this, I was blown away.
06:46I mean, who could imagine having something this regular, almost geometric, on the atmosphere
06:51of a planet?
06:52It's really just phenomenal.
06:55In 2018, Cassini data reveals this hexagonal storm could be a towering structure hundreds
07:03of miles in height.
07:05It's this gigantic structure.
07:07It's many thousands of miles across, and right in the center, right at the pole, is this
07:11sort of permanent vortex, a permanent hurricane.
07:14So it's kind of a creepy eye-like thing staring back at us.
07:19Each side of the hexagon is as wide as the Earth.
07:24It seems artificial.
07:26How do you get a hexagon-shaped storm or cloud structure on Saturn?
07:38Scientists think that Saturn's spin interacts with air currents to create this symmetrical
07:44shape.
07:45But they don't know why it's lasted for decades.
07:50That's the puzzle.
07:51How can you get a six-sided jet stream that's stable for so long?
07:58But while the hexagon's shape is stable, the color has altered.
08:04Over four years, it changed from mostly blue to golden brown.
08:11The transformation is linked to Saturn's seasons.
08:19The seasons on Saturn are caused by the same thing on Earth.
08:22It's the tilt of the planet.
08:24And so as Saturn is going around the sun and its north pole is tipping toward the sun,
08:29you start to get more light up there.
08:32This sunlight interacts with the atmosphere, producing suspended particles called aerosols.
08:40It actually looks a lot like smog.
08:41It turns things more orange.
08:43So over time, the hexagon went from blue to orange.
08:48The color change happened during one of Saturn's northern hemisphere summers.
08:53But mysteriously, the very center of the hexagon remained blue.
08:59Now this could have been for two reasons.
09:01Maybe the haze never formed in the eye because the eye was shielded from the sun.
09:05And the sun is responsible for creating the brownish haze that we see on Saturn.
09:10Another reason is maybe the actual vortex is sucking the haze down.
09:15Maybe there's something like the eye of a hurricane.
09:17There's haze that forms over it, but it gets sucked down into the eye.
09:27But the storms on Saturn aren't the only extraordinary thing about the weather.
09:33When Cassini dives through the rings, it discovers rain.
09:39Falling onto the planet from space.
09:55April 2017.
09:58Cassini embarked on its grand finale, following a daring new path.
10:06We decided to dive in between the rings and the planet, to go to a place no spacecraft
10:12had ever flown before, and make a unique set of measurements.
10:17It was uncharted territory.
10:21They didn't know exactly what they were going to find.
10:23There could be stuff there that could have destroyed the Cassini spacecraft.
10:28Instead, Cassini encountered something totally unexpected.
10:35Rain.
10:44On Earth, it rains quite a bit.
10:46We're getting that rain from rain clouds, which are basically just a few miles up.
10:51On Saturn, it also rains, but it turns out it's raining onto the top of the upper atmosphere.
10:57And that rain is coming from space.
11:01In 2018, Cassini data revealed the colossal weight of the downpour.
11:08Icy-grained rain hits Saturn at a rate of several tons per second.
11:17It's completely unlike anything we've ever seen.
11:19Suddenly we've discovered rain at Saturn, but there aren't any rain clouds.
11:23Where is it coming from?
11:27The answer is Saturn's rings.
11:36The first thing you think of when you hear the word Saturn is the rings.
11:39They're the most dramatic and unique aspect of that planet.
11:45From afar, Saturn's rings look like just one whole structure.
11:50But when you look up close, it's actually a bunch of ice crystals and ice rocks
11:54that make Saturn's rings.
11:58The size of the ring material ranges from dust grains to boulders to houses.
12:11Saturn's rings are well above the atmosphere of Saturn.
12:15They're way out in space.
12:16And under normal circumstances, those particles of ice making up the rings
12:21would just orbit Saturn forever.
12:23But things are a little bit weird.
12:27Something is making these orbiting ice particles fall inward as a kind of cosmic hail.
12:38Material is dripping inwards from the rings and falling into the clouds of Saturn.
12:44It's like a rain with no rain cloud.
12:46Like a cosmic rain trickling in and falling down.
12:49Cassini discovers the rain is a mix of different kinds of ice particles,
12:54but doesn't reveal why they actually rain down.
12:59Then, the researchers realized the ice grains were statically charged.
13:06Ultraviolet light from the sun, for example, can blow off an electron.
13:10And that gives these particles a charge, just like rubbing a balloon on your hair
13:14makes it stick to a wall.
13:16Well, if you have particles that are like that, they can be affected by magnetism.
13:21And Saturn has a very strong magnetic field.
13:26Earth's magnetic field springs from its spinning molten iron core.
13:31Although Saturn probably has a rocky center, it's mostly a giant ball of hydrogen.
13:37We don't have enough data to know exactly what's going on in Saturn's interior,
13:42but we do know the broad strokes.
13:44Within Saturn's interior, extreme pressures and temperatures force hydrogen
13:50to move through the atmosphere.
13:52And that's what we're looking at right now.
13:53So, we're looking at what's going on in the interior of Saturn.
13:57And we're looking at what's going on in the interior of Saturn.
14:00And we're looking at what's going on in the interior of Saturn.
14:03Extreme pressures and temperatures force hydrogen to stop acting like a gas,
14:10turning it into spinning liquid metallic hydrogen.
14:14You've got this band of electrons that can just wander freely through that fluid.
14:18So, in that way, liquid hydrogen under high extreme pressure can act like a metal.
14:25The magnetic field generated by the spinning metallic hydrogen outer core
14:31pulls the ice particles from the rings.
14:34These charged ice particles are then drawn in by Saturn's field.
14:39They follow the magnetic field lines and rain down onto the atmosphere of Saturn.
14:47Cassini had revealed several tons of material is raining down on Saturn every second.
14:52But how much stuff is actually in the rings?
14:56Again, Cassini provides the answer.
14:59In the final days of Cassini, we actually flew in between the planet Saturn and the rings.
15:04And the gravity data was able to separate out how much mass is coming from the planet
15:08and how much is coming from the rings.
15:11And the surprise was the rings are actually not very massive at all.
15:17Even though they cover an area as big as the moon's orbit around Earth,
15:21Saturn's rings are 100,000 times less massive than our own small planet.
15:29They're lighter than we thought. There's not as much material there.
15:37The mass of the rings is a valuable clue about their age.
15:42A more massive ring can hold itself together for much longer than a less massive ring.
15:48So, if there's not a lot of stuff there, it must be younger.
15:51So, how long have Saturn's rings been in place? And what is keeping them there?
15:57It's something that I don't even think I could have imagined if I tried.
16:01As Cassini orbited Saturn, it revealed incredible insights into the planet's rings.
16:20As Cassini orbited Saturn, it revealed incredible insights into the planet's rings.
16:34The photos that came from Cassini of the rings are unlike anything that I could ever imagine.
16:40If I was an alien visiting our solar system, I don't know what would stand out to me more,
16:45the blue marble or Saturn and its amazing rings.
16:51One of the biggest questions about the rings is how old are they?
16:55Could something like that really have existed from the beginning of the solar system,
16:58or is it relatively recent?
17:03Cassini provided an answer.
17:06The rings could be as young as only 100 million years old. A couple of clues, the low mass
17:12and the fact that they're so bright and icy that it hasn't had time to get polluted from
17:16all the micrometeoroids and darkened over a long time like the age of the solar system.
17:23So the amazing thing is that, you know, if you were on Earth about the time of the dinosaurs,
17:27there might have been a Saturn in the sky with no rings.
17:35So if the rings didn't form at the same time as Saturn,
17:39how did they form? And what's keeping them in place?
17:46To form the rings 100 million years ago, you need to find an object, maybe a comet,
17:51or a moon gets too close to Saturn, Saturn's gravity tears it apart and forms the rings.
18:00As the object is torn apart, the pieces spread out around Saturn to form the rings.
18:07They keep colliding, breaking into smaller and smaller pieces.
18:11Like pebbles on a beach, subsequent jostling and self-collisions between each other will
18:16take the sharp edges off of them, creating rounded particles.
18:23From a distance, Saturn's rings appear incredibly thin and almost perfectly flat,
18:29but appearances can be deceptive.
18:33One of our last results from the Hubble Space Telescope is that Saturn's rings
18:38were not uniform. One of our last results from Cassini, as it took its final plunge into Saturn,
18:44was as we flew past those rings, we noticed that the rings were actually not a uniform density.
18:51That's something that nobody had seen. I mean, you had to get really close to see that,
18:54and it wasn't expected. I'm a ring scientist, and I just love seeing that detail
19:01and trying to figure out why do Saturn's rings look the way they do?
19:06There are very intricate structures, knife-edge little ringlets, and almost like the grooves in a
19:12record. Begs the question, of course, where do those structures come from?
19:23The clue is hidden within the rings.
19:27There's not five rings. There's not 500 rings. There's thousands of rings. There's potentially
19:33millions of tiny little ringlets with small gaps between them, and sometimes large gaps.
19:40And Cassini saw that there are moons embedded inside the rings.
19:51These moons and moonlets seem to be shaping the rings.
19:58When I think about the rings of Saturn, I almost hear symphonies playing in my head.
20:02It's all about this wonderful structure and these harmonies,
20:05the balances between gravity. So we use the word resonance.
20:12Saturn's moons stir the ring particles with their gravitational pull, creating waves.
20:22There's a special place where the resonance exists. Imagine where the ring particles would
20:29go around twice for each single time the moon goes around. It's like pushing someone on a swing.
20:34If you push them at just the right rate, they go higher and higher.
20:38And these places are where the waves generated.
20:42So there's this ballet, this dance between the ring and the moons.
20:45It is one of the most elegant things I've ever seen.
20:48But the rings aren't just being shaped into waves by the moons.
21:01They're being held in place by them.
21:04Through gravitational interactions, these moons might be shaping the rings,
21:09shepherding them, keeping their flock in a nice tight orbit around the planet.
21:19In 2017, Cassini reveals there are more than one or two moons shepherding the rings.
21:26A whole team of moons hold Saturn's outermost visible ring, the A-ring, in place.
21:35One of the really cool things that Cassini discovered during its death dive
21:38was that there are seven moons of Saturn that are all working together to keep that
21:42ring system in configuration. So it's like the Magnificent Seven holding this thing together.
21:48Of the seven Magnificent Moons, the biggest is Mimas.
21:57It's one-eighth the size of our moon.
22:02The smallest, Pan, is only 20 miles across.
22:08Acting in combination, these moons hold all of Saturn's rings in check.
22:13So it's these seven moons working together, forming the ring system that we see today.
22:29Cassini has truly opened our eyes to the wonder of Saturn's rings and many moons.
22:36Saturn has a lot of moons. I mean, a lot of moons. And they're all really interesting and different.
22:43Coming up with an exact number is a little difficult,
22:44because it almost changes every year as we discover new ones.
22:50The latest count is over 60 moons, each with a different character.
22:55But one has a split personality and a very dark side.
23:13May 2017. Cassini was on its grand finale.
23:23The probe snapped its last photo of a strange moon two million miles from Saturn.
23:33Iapetus. Iapetus was discovered hundreds of years ago. And right from the start,
23:39it was recognized that one side of it was very bright and the other side was as dark as dark can be.
23:48This dark and light moon confused Italian astronomer
23:51Giovanni Cassini when he first spotted it in 1671.
23:58It's been puzzling scientists ever since.
24:02So we get there with Cassini. And of course, Iapetus was a very major target for us,
24:07because we were interested to know what was with this crazy two-toned moon.
24:18Cassini reveals that the answer lies even farther out from Saturn, in the form of another moon.
24:25There's one pretty big but really dark moon, Phoebe,
24:29that's outside of Iapetus and is orbiting the opposite direction around Saturn.
24:35Phoebe orbits Saturn four times farther out than Iapetus. As it travels around the planet,
24:42micrometeorite impacts on the moon's surface generate a cloud of dark dust.
24:47The dust from Phoebe actually creates a large ring.
24:52A ring of dark, dusty material that's drifting inwards towards Saturn, going the opposite
24:56direction of Iapetus, which is the perfect material for Iapetus to sweep up in its orbit
25:01to create one dark side.
25:10Iapetus has one dark side because it's orbiting the opposite direction around Saturn.
25:15Iapetus has one dark side because it's tidally locked to Saturn.
25:22One side always faces the planet,
25:27while another side drives forward through the dust.
25:32It's plowing through a bunch of dust that's sticking to the front side,
25:36kind of like bugs on a windshield.
25:38Cassini discovered this dark dust makes the leading side warmer than the trailing bright
25:44side by 50 degrees Fahrenheit.
25:47When you have something that's dark, like the dust on the leading edge of Iapetus,
25:51that gets warmer. It absorbs sunlight better. And if it's warmer, then things that can evaporate
25:57more easily, like water, for example, tends to blow off the surface.
26:04The front side gets darker and warmer.
26:08Any visible ice turns to vapor and makes its way to the colder trailing side where it refreezes.
26:19So the white side gets whiter and the dark side gets darker.
26:24So you have the self-sustaining dark side and bright side,
26:27and you wind up with this two-faced moon.
26:34Iapetus's two sides are strange.
26:38But Cassini discovers that they're not the weirdest thing about this moon.
26:45The weirdest thing is that it is a walnut.
26:54Iapetus has a mountain range that exactly circles its equator
26:57all the way around the moon, a mountain range higher than the Himalayas.
27:08These mountains are over 12 miles high,
27:12more than twice the altitude of Earth's highest peak, Mount Everest.
27:19It's crazy. It's this huge, crazy ridge on this really strange moon.
27:27How do you form a smooth equatorial mountain ridge around an entire world?
27:32A really interesting idea is that for some period of time,
27:36just like Saturn itself has this gigantic ring system, Iapetus had a ring system as well.
27:43Over time, Iapetus's ring collapsed, falling in a circle around the moon.
27:52As it fell to the surface, it built up a mountain range right below where the ring was orbiting,
27:58it built up a mountain range right below where the ring was orbiting,
28:01so that all that material just built up and built a mountain range
28:04ringing the equator all the way around.
28:11Walnut-shaped Iapetus is not the only strange moon around Saturn.
28:16Cassini discovered a moon hiding many secrets beneath its icy surface,
28:22Enceladus, a moon that could even harbor life.
28:28Enceladus
28:41August 2017. Cassini captured six images of Enceladus,
28:50one of the most intriguing moons in the solar system.
28:53Enceladus
28:54Enceladus is a relatively small moon of Saturn that's pretty easy to ignore,
29:00but once you pay attention to it, hosts a lot of surprises.
29:10We've known something was unusual about this icy world
29:14ever since the Voyager mission took photographs in 1980.
29:18We thought that Enceladus would be frozen solid, and yet we knew from Voyager data
29:23the surface of Enceladus was bright white.
29:27And we could see on the surface that vast tracts of it were smooth,
29:32at least at the resolution that we had with Voyager,
29:35and that immediately says that there's been internal activity,
29:40because that's really on an airless moon, that's the only process that could erase craters.
29:48Cassini
29:49Scientists suspected something was actively resurfacing Enceladus,
29:55filling in its craters to make it smooth and bright.
30:00Then, Cassini sent back pictures of Enceladus backlit, and all was revealed.
30:08We saw these icy jets shooting out from Enceladus, and everyone was so amazed that a moon so tiny
30:15and assumed to be a frozen solid ice cube could be so active.
30:26Jets of almost luminous material sprang out of geysers.
30:32When I first saw a picture of a geyser on Enceladus, I mean, I was floored.
30:37That's amazing. I had no idea that that was even possible.
30:41The Cassini discovery of geysers on Enceladus was a game-changer.
30:46All of a sudden, here's water jetting out.
30:50It was, like, too good to be true.
30:53Cassini revealed the geysers are blasting out liquid water.
30:58Enceladus is not a solid ball of ice.
31:02As we got more data from Cassini, we found that Enceladus had a wobble
31:07that was too large for a body that was frozen solid all the way through,
31:12and that told us that a liquid water ocean circled a rocky core.
31:17Enceladus has liquid water under its surface, and it may very well be
31:21an ocean basically covering the inside of that moon.
31:25But where's the heat coming from?
31:29When planets and moons form, their cores are incredibly hot.
31:33But over time, they cool down.
31:36The smaller the planet, the faster it cools.
31:41A tiny world like Enceladus, over a billion miles from the sun,
31:45should have frozen solid by now.
31:50That's what we expected.
31:51If things are smaller, then they would be roughly dead,
31:53and they'd be covered by craters.
31:55But Enceladus shows us that that's not the case at all.
31:58How could a tiny moon so far from the sun have enough warmth for liquid water?
32:03One idea is tidal heating.
32:08If you've ever played racquetball, you know as you play the game, the ball heats up.
32:11And this is because as the ball hits the racquet or the wall,
32:14it's getting squished and then it relaxes.
32:20Saturn's gravity squishes and relaxes Enceladus as it orbits the sun.
32:25Saturn's gravity squishes and relaxes Enceladus as it orbits the planet,
32:30heating it like a racquetball.
32:35But this alone wouldn't generate enough heat to stop Enceladus's water from freezing.
32:41Something else must be going on in the core.
32:46What if the core of Enceladus is actually kind of gravelly?
32:51Instead of it just being solid,
32:53all put together,
32:54then what happens is as the tides are stretching and squeezing it,
32:58those rocks are rubbing together,
33:00and that actually generates even more energy.
33:062017, a computer model based on Cassini data
33:11revealed this tidal friction generates more energy than America's biggest power station.
33:18Water, heated to 194 degrees Fahrenheit, rises to the surface.
33:24It sprays through cracks in the moon's south pole, creating misty plumes.
33:33As we flew seven times through and tasted and sampled the gas and the particles,
33:38we found salty particles, that the ocean was salty, very much like the Earth's ocean.
33:44We found hydrocarbons, methane, carbon dioxide, ammonia.
33:49We found the key ingredients for life coming out of the jets of Enceladus.
33:55So remarkable.
34:00In 2018, scientists reanalyzed the Enceladus data and found something even more remarkable.
34:09Complex organic molecules.
34:14What they found were larger organic compounds than initially thought there.
34:19At first it was just dust and water and some basic organics.
34:22Now they're seeing more complex stuff coming up from Enceladus's interior,
34:27and that asks the question, what else is down there?
34:32On Earth, we find life huddled around hot vents on the seabed.
34:37Could the same be true in the oceans of Enceladus?
34:41Could these complex organic molecules be signs of life?
34:47My favorite name for them is goo.
34:49They're gooey things.
34:51And think of life as a collection of gooey-like molecules.
34:54Now that doesn't mean that all gooey molecules are biological,
34:57but certainly biology makes use of these complex organic molecules.
35:03Deep in Enceladus's oceans, heat from hydrothermal vents drives chemical reactions.
35:11Combining simple molecules like methane and hydrogen
35:15into longer, complex organic molecules.
35:20Complex molecules that could serve as the precursors to life.
35:26What's amazing is the chemistry of that ocean.
35:29Everything needed for life is there.
35:32The internal question is, is there life in the universe?
35:34And Enceladus is a great place to try and answer that question.
35:40And Cassini revealed secrets of another moon of Saturn with amazing chemistry.
35:50A giant moon with Earth-like features.
35:54Rivers, lakes, and dunes.
35:57Titan.
36:11September, 2017.
36:15Four days before the mission ended,
36:17Cassini flew past one of Saturn's most spectacular moons, Titan.
36:25Here's why I like Titan.
36:26Not just because it has a name that means big and strong, which makes you think of me,
36:31but because it has an extensive atmosphere that's made primarily of nitrogen, just like Earth's.
36:41Titan's always been a mystery.
36:43What is hiding underneath that thick atmosphere?
36:51Feud through a telescope, this moon seemed little more than a hazy orange ball.
36:57Then, Cassini launched the Huygens probe.
37:00It traveled beneath the clouds and sent back images of Titan's surface.
37:06I almost can't describe how thrilling it was.
37:12The landing of the Huygens probe on the surface of Titan.
37:15It was like a Jules Verne adventure come true.
37:26The images that you see as you're coming through the atmosphere and the world emerges,
37:31and it's this incredible world that looks so familiar.
37:35Mountains and these streams flowing into this ocean.
37:38Wow.
37:40You might be standing on the shores of a lake, but this lake doesn't look like water.
37:46Instead, it's methane.
37:47It's much darker.
37:49It's a frigid, bizarre world with geologic features that look familiar,
37:54but in a very, very alien setting.
37:57Titan is like a home away from home.
37:59It's just colder, by about 350 degrees Fahrenheit.
38:05The Cassini mission revealed that Titan is really exactly like Earth in terms of its landscape.
38:10In fact, almost a quarter of the body is covered in sand dunes, exactly like what you see behind me.
38:21But Cassini reveals Titan's dunes are not what they seem.
38:26The dunes on Titan are made of something completely different than sand dunes on the Earth.
38:30We know most sand on the Earth is made of quartz,
38:32but on Titan, sand dunes, it turns out, are made entirely of organics.
38:39Titan's sand is made from tiny particles of organic gunk called hydrocarbons.
38:46These organic dunes contain the building blocks of life.
38:51For scientists, this is a tantalizing hint.
38:56Could Titan harbor life?
39:03Here on Earth, there's life that exists in the form of particles of life.
39:07And in the form of life, there's life that exists in the form of particles of life.
39:12Here on Earth, there's life that exists in so many extreme environments,
39:16so it's not impossible to think that life could have evolved
39:20to use the methane and all of the other chemical constituents on Titan.
39:25If life has developed on Titan, it's going to look really weird.
39:29It's going to be really different from life on Earth.
39:32To me, there's going to be this wonderful moment in history
39:35when we really do have another example of how life can be.
39:38And if I had to place my bets on it, I think we're going to find it in the Saturn system.
39:44But Cassini's discovery of potential life sentenced the probe to death.
39:52We didn't want to leave it just indefinitely in orbit
39:54because there was this fear that, you know,
39:58should there be any earthly contamination on the spacecraft,
40:01you don't want it crashing into Titan or Enceladus.
40:09Cassini interacted with Titan one last time.
40:14With a gentle nudge from Titan's gravity, we call it Titan's goodbye kiss,
40:20we ended the mission with a plunge into Saturn's atmosphere,
40:25vaporizing Cassini and saying goodbye to our friend.
40:29I hope you're all as deeply proud of this amazing accomplishment.
40:41I'm going to call this the end of mission.
40:44Project manager off the net.
40:54Although Cassini is gone, its legacy lives on.
41:00Now we're sifting through all of the data collected, still finding discoveries,
41:06putting together the pieces of the puzzle to understand Saturn, the rings and the moons.
41:12Cassini is going to go down in history as one of the most scientifically productive
41:17interplanetary missions that humanity has ever flown.
41:22I'm immensely proud and feel enormously privileged to have been a part of it.
41:37Besides the amazing science Cassini returned,
41:41just the beauty of this planet, I think, sparks something inside of us.
41:47Whenever I look up at Saturn now,
41:50I know that Cassini is there too.
41:52And so Saturn is even a more special place.