Go inside the final moments of NASA's Cassini 20-year mission, which explored Saturn and its moons. Cassini revealed the secrets of strange new worlds that could harbor life, changing what we know about the Solar System.
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LearningTranscript
00:00A billion miles from home, running low on fuel, almost out of time.
00:13We're putting down a fully functioning spacecraft.
00:19After 13 years orbiting Saturn, the spacecraft Cassini is about to plunge to a fiery death.
00:30Becoming part of the very planet it has been exploring.
00:34Cassini was not so much of a mission as a way of life.
00:38I've spent 20 years of my life on this.
00:41What we found was spectacular.
00:44Cassini sent back dramatic visions of strange new worlds.
00:49Nothing of what we had imagined came close to the reality.
00:53It revealed methane lakes, electric dunes, buried oceans.
01:00That moon has an ocean in it that could harbor life.
01:04It's the end of a mission that has not only unveiled the beauty and probed the mysteries of Saturn,
01:10but has changed our view of the solar system forever.
01:28System's lead, mission planning.
01:30Go ahead, mission planning.
01:31Spacecraft has just crossed 30 degrees north latitude.
01:34Altitude is 6,000 miles.
01:36The dead of night.
01:37Friday the 15th of September.
01:40In the control room of NASA's Jet Propulsion Laboratory,
01:43the flight director and her team of engineers are presiding over the death of a spacecraft
01:48that they have nurtured for nearly three decades.
01:54In less than an hour, they will watch as Cassini sends its final transmission.
01:59Next band and this band.
02:01Copy.
02:01It's sad.
02:02It was 27 years of the investment of many lives into this.
02:09Nearby at the California Institute of Technology is the vast family of scientists from around the world
02:15who run the 12 instruments on Cassini,
02:18measuring everything from infrared to radar, magnetic fields and cosmic dust.
02:24In some ways, I just want it to be over now.
02:27You know, you're sort of waiting for it to end and it's really weird.
02:30Very mixed emotions at the moment.
02:32Really strange.
02:33All have played a vital role in exploring Saturn.
02:38But it's Cassini's skills with a camera that have been truly inspirational.
02:44Head of the camera team and guardian of the Cassini image gallery is Carolyn Porco.
02:59Carolyn has been responsible for designing the camera systems,
03:02deciding when, where and which pictures to take
03:06and delivering and processing hundreds of thousands of images of Saturn,
03:11its rings and moons.
03:13This is one of my favorites.
03:15The reason why I love it is because we're seeing the rings edge on
03:18and you just really can tell how thin they are.
03:28You can get the sense of three-dimensionality.
03:34And this is the famous hexagon.
03:38Okay, this is the feature that drives everybody crazy
03:41because they don't expect to see something that is straight-sided in an atmosphere.
03:47It is nothing more than a jet stream, like our jet stream.
03:52Okay, really, you can relax.
03:54This is not the end of the world.
03:57Back at the rings, I mean, have you ever, ever seen anything
04:02just so magnificently regular and beautiful?
04:07With its two on-board cameras, Cassini has unveiled the Saturn system
04:12as a strange, mysterious, and unique place.
04:19Saturn just captivates people because it looks so supernatural.
04:24It engenders the immediate feeling that it can't possibly be real.
04:29But we're lucky to have it.
04:31I think we're damn lucky to have Saturn.
04:33I'm glad I grew up in a solar system that had a planet like Saturn.
04:41But taking and downloading such amazing pictures
04:44when your camera is a billion miles away
04:47through the bleak void of outer space
04:49is no easy feat.
04:56In charge of remotely managing the spacecraft
04:59from NASA's Jet Propulsion Laboratory
05:01is Julie Webster.
05:04You know scientists and engineers are true nerds,
05:06so you'll see a lot of nerd stuff on them.
05:11Julie is Cassini's chief engineer.
05:14She's been caring for the intrepid explorer
05:16since before it left home
05:18and uses a scale model of the spacecraft
05:20to demonstrate its capabilities.
05:23This is a quarter-sized model.
05:25So this is a quarter-sized me.
05:29I'd like to be this weight, not this height.
05:33So you start at the top.
05:35This is a four-meter antenna.
05:38It was also designed for radar.
05:41So this is the composite infrared spectrophotometer.
05:45This is the ultraviolet spectrophotometer.
05:48This is the VIMS, visual and infrared.
05:51And these are the imaging cameras,
05:54the narrow angle and wide angle,
05:56that are used for the actual photos that you see.
06:00So this is the ion and neutral mass spectrometer
06:04that is the most important data
06:06that we're going to get in the last few hours.
06:08And here's part of the magnetometer instrument,
06:11and here's the other half of the magnetometer instrument.
06:15The trick is, the reason you want to put it out on a boom
06:18is you do not want to measure the magnetic field of the spacecraft.
06:23You want to measure the magnetic field of Saturn
06:25or whatever you're at at the time.
06:27Let's see.
06:28That's the nuclear battery.
06:31I actually sat inside this part during the build.
06:35So when I close my eyes and think of Cassini,
06:38I actually see the wiring inside the spacecraft
06:42and the things switching on and off.
06:44And when it goes in,
06:47that's what I'm going to see in my mind
06:49is the aluminum melting on the structure.
06:53So now we're headed back up to the first floor,
06:56to my office.
06:59Cassini divides its time between gathering data,
07:02which it stores on its internal memory,
07:05and then sending it back home.
07:08A typical day, we're out taking pictures,
07:11collecting data, storing it on the solid-state recorder,
07:15and then we'll turn it back to Earth
07:18and we'll play it back for nine hours.
07:21We only have four gigabits of data that we can load up
07:25and it takes nine plus hours to play that data back.
07:30For nine hours at a time, up to six times a week,
07:34Cassini sends its precious images of Saturn
07:37on the billion-mile journey back to Earth.
07:41We have cleared the tower
07:43and the Cassini spacecraft is on its way to Saturn.
07:47So what does it take to get a spacecraft
07:49the size of a bus
07:51with 12 delicate instruments
07:53all the way to Saturn
07:56and to keep it operating for 20 years?
08:00And the solid rocket boosters have been tested.
08:12In the mission to get closer to Saturn than ever before,
08:16getting the Cassini spacecraft to its new home
08:19was a challenge for the team of fearless rocket scientists.
08:24So, we'll go into the, uh, dark room?
08:30Inside the dark room,
08:32the mission support area
08:33is where the whole flight team gathers for critical events,
08:37like the final plunge, launch, or orbit insertion.
08:41It took seven years to get to Saturn,
08:44a spiraling journey that involved four gravity assists,
08:49close flybys past planets
08:50that boost the speed like a slingshot.
08:53It's a flight path designed by head of navigation,
08:57Duane Roth.
08:58We had a Titan 4B.
09:00Titan 4B.
09:01So that, that was the, to get us away from the, the Earth,
09:05but then it still wasn't quite enough
09:07to make it all the way to Saturn.
09:08So we had two Venus flybys,
09:10gravity assists from each of those,
09:12an Earth gravity assist,
09:13and finally we've got a Jupiter gravity assist,
09:16and that got us to Saturn.
09:17Once Cassini was approaching Saturn,
09:20it had to perform possibly its most critical maneuver of the mission,
09:24a perfectly timed engine burn
09:26that would slow it down enough
09:28to be captured in orbit by the giant planet.
09:32Saturn orbit insertion was obviously incredibly nerve-wracking.
09:35We spent seven years guiding the spacecraft
09:39to get to Saturn, to get it into orbit.
09:41If it hadn't done the orbit insertion,
09:44which was a 90-minute burn on the main engine,
09:47if we hadn't done that,
09:49we'd have been a Saturn flyby
09:51and just gone on out in space.
09:53The Doppler has planned out.
10:05During its 13-year stay,
10:08Cassini has revealed Saturn
10:10as a unique jewel in the solar system,
10:12a gas giant with swirling storms,
10:16a dancing sprinkling of moons,
10:18and surrounded by bright but paper-thin rings of ice.
10:25The origin of the rings is still a mystery,
10:29as is the complex gravitational interplay
10:32between rings, moons, and planet.
10:35So this is one of those discoveries we made
10:40that really threw us for a loop.
10:42This is the outer edge of the B-ring,
10:45and these, as you can see,
10:47are spiky shadows that are created
10:49by these features here
10:51that are sticking up 2 1⁄2 miles.
10:532 1⁄2 miles above a sheet of debris
10:56that's only 30 feet thick.
10:58It was just extraordinary.
10:59It was out of science fiction.
11:01That's what this whole mission has been.
11:14But hidden in the images from Cassini
11:17are clues to the formation
11:19of this complex and dynamic system.
11:23Well, we know the rings of Saturn are made of ice.
11:27This is a really solid block of ice here,
11:30but this is not the sort of ice
11:33that the rings are made of.
11:36Carl Murray is part of the imaging team,
11:38trying to work out how rings make moons,
11:41and moons make rings.
11:44He sort of thinks it's more like sort of fluffy ice,
11:46so it's really the difference
11:47between a snowball and a hailstone.
11:50So this would be like a hailstone,
11:51but if you kind of break it up,
11:54you start to get more of a flavor
11:56for what the ring particles might actually be made of.
12:01And the fluffy nature of the ice
12:03kickstarts the process of clumping.
12:06So if the ice is fluffy,
12:08the particles perhaps are more likely to coalesce
12:11rather than to break up or bounce off each other
12:15because there's more surface area
12:17for the particles to stick.
12:21Eventually, gravity can take over,
12:24and a moon can be born.
12:27And it's the moons of Saturn,
12:29rather than the planet itself,
12:31that have offered up many of the most incredible surprises
12:34and mysteries to be solved.
12:37They're incredibly diverse,
12:40ranging in size from a few hundred feet
12:42to bigger than the planet Mercury.
12:48But out of all these moons,
12:50the two standouts are Titan and then Enceladus.
12:57Before Cassini's intrepid voyage,
13:00our best view of Titan was as an orange, foggy blob.
13:04Titan was so mysterious to us before we got there.
13:09At first sight, it may not look like much,
13:12but peer through the fog,
13:15and an astonishing world is revealed.
13:18A world that surprised everyone.
13:22We hadn't let our imaginations go as wild
13:25as nature turned out to be.
13:38On December 24th, 2004,
13:40Saturn's mysterious moon Titan
13:43began revealing its secrets to an eager audience
13:46when Cassini dropped a passenger,
13:49the European-built Huygens probe.
13:52The Huygens deploy,
13:54we actually did that on Christmas Eve in here.
13:57It was the last year my father was alive,
14:00and this was a really important thing for him.
14:04And so he was able to sit up in the balcony
14:07and see his daughter say, you know,
14:10release the probe.
14:18Huygens was designed as a descent module.
14:22Go through the atmosphere
14:23and tell us everything we can find out
14:26about this sister to our own atmosphere.
14:31Planetologist Athena Kustinus
14:33has been with the mission since the beginning.
14:36And as Huygens fell through the orange atmosphere,
14:40she was at the European Space Agency's
14:42Mission Control in Germany,
14:44waiting anxiously for news from Huygens
14:46to find out if it survived the descent.
14:52I remember telling my colleagues,
14:54please remove this image of Mars,
14:57this photograph of Mars here.
14:58We're waiting for Titan.
15:00And then somebody said, it's Titan.
15:01And I said, no, it's Titan.
15:03We can see the pebbles on the ground.
15:06We can see the surface.
15:09And we're there,
15:10and the probe is taking images continuously
15:13of the same spot.
15:15The parachute goes right above,
15:18and so we can see the shadow of the parachute.
15:22That was the first image they saw,
15:25but the best was yet to come.
15:28Huygens was busy gathering valuable data
15:31during the two-and-a-half-hour descent
15:33through the orange gloom.
15:36These are actual images taken during the descent,
15:40joined into a seamless film.
15:42Together with a recording made by Huygens
15:46of the sound of Titan's orange atmosphere.
15:56And we started seeing channels carved through the hills,
16:00and we had this very dark area in the middle
16:03that eventually were identified as a dry lake.
16:06Nothing of what we had imagined
16:09came close to the reality.
16:14Long after Huygens was tasting the atmosphere
16:17and snapping pictures at the surface,
16:20Cassini continued to explore Titan far above.
16:23We went by Titan over 125 times.
16:31Each flyby needs to be incredibly precise,
16:35and to prepare for them,
16:37Julie has a simulation of Cassini
16:39and the universe around it.
16:42Hello.
16:43Hello.
16:43The integrated test laboratory.
16:48A real-time absolute time?
16:50She uses the mock-up
16:52to anticipate every eventuality
16:55and rehearse every maneuver.
16:59We must have run 10,000 simulations.
17:02When you fly spacecraft,
17:04you have to learn how to fly them.
17:05So the first two or three years
17:07were the most difficult
17:08because you're kind of learning
17:09how, how,
17:10what makes the personality
17:12of the spacecraft.
17:15Cassini was originally intended
17:17to orbit Saturn
17:18for just four years.
17:19These are years by color.
17:21But the mission has been so successful,
17:24it's been extended twice.
17:26By the end of the mission,
17:28it will have done a total of 293 orbits,
17:32covering every corner of the system.
17:35Right?
17:35Careful planning
17:36and endless simulations
17:38by Julie and her team
17:39kept Cassini in full working order
17:41even after 20 years in space.
17:44There's engineers
17:45and there's science
17:46and we're the engineers.
17:48So scientists like
17:49to constantly be surprised, right?
17:51They like new data.
17:52They like to say,
17:53oh, I don't know what this means.
17:54I don't know what that,
17:55that can't,
17:56that there's something new.
17:58Engineers do not like
17:59to be surprised.
18:01And Cassini
18:02didn't disappoint the scientists.
18:05It delivered plenty of mystery
18:07and surprise.
18:09These are doom fields
18:11and they're,
18:12the dunes are enormous.
18:13They're several kilometers apart.
18:16They're 100 meters high
18:18and they go on and on
18:21for hundreds of kilometers.
18:23And in all these dark areas
18:25that you see,
18:26it's covered with dunes.
18:31At first look,
18:33these dunes look remarkably like
18:35the very largest dunes
18:36found on Earth.
18:37But a more careful investigation
18:40reveals some very crucial differences.
18:47The sand on Titan's dunes
18:49doesn't blow in the prevailing wind.
18:52And the dunes seem to be resilient
18:54to all but the very strongest of storms.
18:58Joshua Mendez Harper
19:00and George MacDonald
19:01have been trying to work out
19:03what's so special
19:04about Titan's sand.
19:06One idea is that these dunes
19:07are cohesive or sticky,
19:09that the grains that make up these dunes
19:11somehow keep the dunes together.
19:15The question is,
19:16okay,
19:16if these dunes are sticky,
19:17what's causing them to be sticky?
19:22On Earth,
19:23if you want to make sand sticky,
19:25you need to add water
19:26to help it clump together.
19:29But on Titan,
19:31the sand comes not from rocks
19:33or shellfish,
19:34but from Titan's exotic atmosphere.
19:39Ultimately,
19:39it must be coming from
19:41the hydrogen and carbon
19:43that's stored in methane
19:44in the atmosphere.
19:45And so you're basically making sand
19:46from something that's raining out
19:48from the atmosphere.
19:50Titan's sand is thought
19:52to be made up of hydrocarbons,
19:54similar in makeup to plastic.
19:57In their experiments,
20:00Josh and George compared
20:01Earth sand,
20:02which flows freely,
20:03with polystyrene beads
20:05standing in for Titan sand.
20:08And if your sand is made
20:10from something similar
20:11to polystyrene beads,
20:13it can easily build up
20:14a charge of static electricity,
20:16which makes it sticky.
20:18So on Titan,
20:19when these winds blow
20:21these hydrocarbon grains,
20:23particles rub against each other
20:24and charge frictionally.
20:26And so when you do that,
20:27things tend to clump together.
20:30The forces are strong.
20:31It does provide that stickiness.
20:34Titan was already proving
20:36more mysterious
20:37than anyone imagined.
20:39Yet scientists were still searching
20:41for something that eluded them
20:43from up till now.
20:45Surface liquid.
20:50One day,
20:51nearly five years after
20:53Huygens landed,
20:55one of Cassini's instruments
20:56spotted something shining
20:58through the haze.
21:01That is basically the sun
21:03glinting off the sea
21:05of Kraken Mare.
21:08Kraken Mare,
21:10the first alien sea
21:12ever discovered.
21:15And Cassini soon found
21:18a host of seas and lakes
21:19at Titan's North Pole.
21:22I mean,
21:23this could be Earth.
21:26Finally,
21:26Cassini had found
21:27the surface liquid
21:28that everyone was expecting.
21:32In many ways,
21:33this lake is much like
21:34what we would find on Titan,
21:35but in other ways,
21:37it is very different.
21:42First of all,
21:42on Titan,
21:43the liquid is not water,
21:45it's liquid methane,
21:46because the temperatures
21:47are so cold
21:48that methane cannot be a gas,
21:50it's a liquid.
21:51The sky would not be blue,
21:52it would be kind of
21:53a deep orange.
21:56Planetary scientist
21:57Janie Radevaal
21:58is looking at the parallels
21:59between the two worlds.
22:02The mountains surrounding
22:03this lake are made of rock,
22:05but on Titan,
22:06even though the mountains
22:07would look very similar,
22:08they wouldn't be quite as tall,
22:10but they would be heavily eroded,
22:12they'd have river channels,
22:13and they are made of water ice.
22:15And on Titan,
22:16ice is so cold
22:17that it is a solid rock.
22:20Just as the Earth
22:21has a liquid cycle
22:23where water changes
22:24from clouds to rain
22:25to rivers, lakes, and seas,
22:28so Titan has one too,
22:31with methane
22:32taking the place of water.
22:34This methane actually
22:35follows exactly
22:37the same cycle
22:39that water has on Earth,
22:41evaporating from the oceans,
22:43getting into the atmosphere,
22:45making clouds,
22:46clouds of methane on Titan,
22:48falling through the atmosphere
22:50in the form of rain,
22:51rain of methane on Titan.
22:54And with surface liquid,
22:56you find places
22:57with special significance,
22:59the meeting point
23:00between solid, gas, and liquid,
23:03a beach.
23:05We're thinking more and more
23:06about the importance
23:07of beaches
23:08as a possible cradle
23:10for life on the Earth.
23:12What's so vital
23:13about a beach
23:13is you have this space
23:15where there is liquid
23:17interacting with solid materials,
23:19important building blocks,
23:20and the atmosphere.
23:22All three of those things
23:23can exist,
23:24coexist on a beach.
23:27Those things together
23:28basically enable
23:29the right kind of chemistry,
23:31the right chemical conditions
23:32that may lead to life.
23:34Tons of larvae.
23:37Blah, stinky.
23:41Life on Titan's beaches
23:43is extremely unlikely,
23:45but it offers a window
23:47into some early pre-life processes
23:49on our own planet.
23:53Cassini and Huygens together
23:55lifted the veil
23:56of orange fog
23:57and revealed Titan's
23:59treasure trove of secrets,
24:01a moon strangely Earth-like
24:02and yet otherworldly.
24:04But it was another moon
24:06that would offer up
24:07the most delicious
24:09of discoveries,
24:10the tiny ice moon
24:12Enceladus.
24:26The Cassini spacecraft's
24:28revelations about
24:29the ice moon Enceladus
24:31blew everyone away.
24:32They emerged initially
24:35from an unexpected source,
24:37from Cassini's sixth sense,
24:40its ability
24:40to sense magnetic fields.
24:43The magnetometer
24:44is an instrument
24:45run from London's
24:47Imperial College
24:48by Michelle Doherty.
24:50This large boom here,
24:51which is 11 meters in length
24:53on the main spacecraft,
24:54is where we put our instrument.
24:55The main objective
24:57of the magnetometer
24:59is to investigate
25:00the magnetic field
25:01generated by Saturn
25:02to help probe
25:04the inner workings
25:05of the gas giant.
25:06For 20 years,
25:08data has been flowing
25:09from Cassini's magnetometer
25:11a billion miles away
25:13via the Jet Propulsion Laboratory
25:15into this small room
25:17in London.
25:18Coming in the back
25:19is the direct link
25:20to JPL.
25:21Early in 2005,
25:23a stream of data
25:25arrived through these cables
25:26that would radically
25:28change the entire mission.
25:32In 2005,
25:33there were three planned
25:35flybys of Enceladus.
25:37The first flyby
25:38took place on 17th of February,
25:40and it was a distant flyby,
25:42a thousand kilometers
25:43above the surface.
25:44For the magnetometer team,
25:46this was a prospect
25:47no more exciting
25:48than any routine days' worth
25:50of data.
25:51But hidden in the graphs
25:53was the tiniest of glitches.
25:56You can see
25:57there's a little pimple
25:58in the data
25:59just over there,
26:01an anomalous signature.
26:03When I first looked
26:04at that data,
26:05I thought,
26:05oh, I know the spacecraft
26:07was moving really quickly.
26:09Maybe we haven't got
26:11the trajectory right.
26:13You know,
26:13maybe that's why
26:14we're seeing
26:14this funny signature
26:15in the data.
26:16This strange signature
26:18seemed to suggest
26:20that something
26:21on or near Enceladus
26:22was somehow blocking
26:24the magnetic field
26:25of Saturn.
26:26It's almost as if
26:27Enceladus is acting
26:28as a much bigger obstacle
26:30than its physical size.
26:33And one of the ways
26:34you can do that
26:35is if you've got
26:35an atmosphere.
26:36The other thing
26:37we noticed
26:38is there was
26:40a lot of noise
26:41in the data
26:42on either side.
26:44and what we were able
26:45to do
26:46is calculate
26:47what ions
26:49were generating
26:50those waves
26:51and it was
26:51water group ions.
26:53It seemed to suggest
26:54that there was
26:55some kind of atmosphere
26:57around the moon,
26:58an atmosphere
26:59of water
27:00that no one
27:02had anticipated
27:02being there.
27:04A second flyby
27:05a month later
27:06confirmed the results.
27:09One of the reasons
27:10we waited
27:10for the second flyby
27:11is it was really weird
27:12to see that there
27:14was potentially
27:15an atmosphere
27:15on the first flyby
27:16because Enceladus
27:17is small
27:18and so the implication
27:19was there was
27:20something generating
27:21the atmosphere.
27:21So this was
27:22a real surprise.
27:23That's why I was
27:24so wary about
27:25saying anything
27:26until we'd had
27:26the second flyby
27:27just to make sure
27:28because you know
27:30you don't want
27:30to make a fool
27:30of yourself.
27:33Michelle and her team
27:34decided
27:35it was time
27:36to alert
27:36the rest
27:37of the mission.
27:40We knew
27:40for us
27:41to be able
27:41to have a chance
27:42of really seeing
27:43what was going on
27:44at Enceladus
27:44we needed
27:44to get closer
27:46and so
27:48we made
27:49the decision
27:50that I would
27:51go out to JPL
27:52and Trump
27:53dissuade the project
27:54to take us
27:54really close.
27:56And so
27:57armed with her anomalies
27:59Michelle made
28:00the journey
28:00to JPL.
28:04It took a lot
28:05of discussion
28:05not everyone
28:06was supportive
28:08some of the teams
28:09would then
28:09lose some data
28:10because some
28:11of the planned
28:12observations
28:12of Enceladus
28:13would have to change
28:14but the project
28:16talked about it
28:16and they then
28:17decided we would
28:18go much closer
28:19on the third flyby.
28:22And I must confess
28:23I didn't sleep
28:24for two or three nights
28:25before that close flyby
28:26because if we hadn't
28:27seen anything
28:28no one would ever
28:28have believed
28:29anything I said again.
28:30So
28:31but what we found
28:33was spectacular.
28:40when Cassini
28:41returned to Enceladus
28:42in July 2005
28:44it passed
28:45just over
28:46a hundred miles
28:46from the moon.
28:48What it saw
28:49thrilled everyone.
28:53We finally
28:54got to see
28:55the south pole
28:57of Enceladus
28:58and here it is
28:59it's crisscrossed
29:00by these major
29:01fractures.
29:04Nicknamed
29:05the Tiger Stripes
29:06Cassini found
29:07that these fractures
29:08were radiating
29:10heat.
29:11Heat
29:11I mean
29:12who expected
29:13the south pole
29:13of Enceladus
29:15to be hot?
29:16And what we found
29:17was instead of
29:17the atmosphere
29:18covering the entire
29:19surface
29:19it was just
29:20focused at the
29:21south pole.
29:25And that's
29:26not all.
29:28Pouring out
29:28of the Tiger Stripes
29:30were giant
29:30geyser-like jets
29:32spewing water
29:33vapor and ice
29:34particles
29:34from the cracks
29:35in the ice crust.
29:40And the discovery
29:42of the plumes
29:42has revealed
29:43the origin
29:44of Saturn's
29:45outermost ring.
29:46A ghostly ring
29:48called
29:48the E-ring.
29:51Something like
29:52maybe 200 kilograms
29:54a second
29:54of predominantly
29:56water ice
29:57is thrown out
29:59into space
30:00so what it does
30:01is form a ring
30:01and that's
30:02the E-ring.
30:04The question was
30:05where was the
30:07water coming from?
30:09We have been
30:09able to determine
30:11that there is
30:12a large water
30:14pocket
30:14or sea
30:16deep sea
30:17under the
30:19south pole
30:19of Enceladus.
30:21It's about
30:21the size
30:22of Lake Superior
30:24in North America.
30:27Based on this discovery,
30:29many more visits
30:30to Enceladus
30:31were planned.
30:32The closest flyby
30:34was within just
30:3516 miles
30:36of the surface.
30:38By the time
30:39we did that one
30:40we were very confident.
30:41So we flew in
30:42on thrusters
30:43because we didn't know
30:44what Enceladus
30:44would do to us
30:45and then you were
30:46getting like
30:46one thruster pulse.
30:48In the process
30:49of getting good at it
30:50they used up
30:50all the propellant.
30:52It was really
30:52not much choice.
30:53But no,
30:54I think they've been
30:55very good at it
30:55for a long time.
30:57It's just that now
30:57some of these
30:59flybys
31:00are just
31:00exquisitely accurate.
31:02So accurate
31:03and so close
31:04that Cassini
31:05was able
31:06to taste the spray.
31:08And what it found
31:09raised an
31:09extraordinary possibility.
31:12This is now
31:12one of the places
31:13in the solar system
31:14where people think
31:15potentially life
31:17might have formed
31:18in the past
31:18or might be able
31:19to form.
31:20I love this picture
31:21and it's about
31:23as much meaning
31:23as you can get
31:24out of the
31:26Cassini mission
31:27because we know
31:27that that moon
31:29has an ocean
31:31in it that could
31:31harbor life.
31:34If life evolved
31:36on that sealed ocean
31:37then it must have
31:38evolved separately
31:39from life
31:40on our planet.
31:42It would be a sign
31:43of a second genesis.
31:46I think that all
31:47we need to do
31:48is find that life
31:49has independently
31:50arisen just one
31:52other time
31:53and that would
31:55tell us
31:56that it's everywhere.
31:58If it happened
31:59a second time
32:00it probably
32:01has happened
32:01you know
32:02a colossal number
32:03of times
32:04throughout the cosmos
32:05and throughout
32:05its history.
32:08But sadly,
32:09ironically,
32:10it was this
32:11greatest discovery
32:12of Cassini's
32:13that ultimately
32:13sealed its fate.
32:16after 20 years
32:17the great explorer
32:18is running out
32:19of fuel
32:20and when the fuel
32:21is gone
32:21so too
32:23is NASA's ability
32:24to steer
32:25the spacecraft.
32:27We didn't want
32:28to lose
32:29control of
32:30Cassini
32:31and have it
32:31crash on the
32:32surface of Enceladus.
32:34If you discovered
32:35life there
32:36one day
32:36there might be
32:38those doubters
32:39who would say
32:39yes but
32:40a spacecraft
32:41crash landed
32:42and took bacteria
32:43there.
32:46And so
32:47the mission team
32:48decided to use
32:49the last drops
32:50of fuel
32:50to set Cassini
32:52on a final phase
32:53that would take it
32:54closer and closer
32:55to Saturn
32:57before plunging
32:58into the planet
32:59and being destroyed
33:00a phase NASA
33:02called
33:02the grand finale.
33:21In April 2017
33:23mission scientists
33:25gathered at
33:25NASA's JPL
33:26to witness
33:28the beginning
33:28of the end
33:29for the Cassini
33:30spacecraft.
33:31There's a real
33:32buzz here
33:32of excitement
33:33and you know
33:34slight nerves
33:35as well.
33:35The reason
33:36it's so exciting
33:37is this is
33:37the start
33:38of the end
33:38of the mission.
33:39We're running
33:40out of fuel
33:40and we're going
33:42to make sure
33:43we go out
33:44with as much
33:44great science
33:45as we can.
33:47The last phase
33:49of the mission
33:49known as
33:50the grand finale
33:51began with
33:53a hair-raising
33:53dive through
33:54the gap
33:55between the rings
33:56and the cloud tops
33:57of the planet.
33:58It's risky
33:59but with the mission
34:00coming to an end
34:01the team
34:02could afford
34:02to take risks
34:03that would previously
34:04have been unthinkable
34:05and send the spacecraft
34:07exploring closer
34:08to Saturn
34:09than ever before.
34:10Everything looks great
34:12we're just now
34:12waiting for the data.
34:16It was worth
34:17the risk
34:18because flying
34:19inside the rings
34:20will allow the team
34:22to explore
34:23enduring mysteries
34:24such as the mass
34:25and the age
34:26of the rings
34:27the exact length
34:28of Saturn's day
34:29and in its final moments
34:31the actual composition
34:33of the atmosphere.
34:36Ansco Systems
34:37is Cassini Ace
34:38I can confirm
34:39the science playback
34:40is in luck
34:41and starting to run.
34:44The green spike
34:46was the first sign
34:47that Cassini
34:48survived the dive
34:49and was now
34:50sending data
34:51back to Earth.
34:56The grand finale
34:57consists of
34:5822 of these
34:59hair-raising dives
35:01between the rings
35:02and the planet
35:02before the final
35:04plunge into
35:04Saturn's atmosphere.
35:08From this unique
35:09vantage point
35:10Cassini has already
35:12sent back these images
35:14from the atmosphere
35:15taken on the very
35:16first dive
35:17merged here
35:18into a slice
35:20of Saturn
35:20taken from closer
35:22than ever before.
35:24Analyzing images
35:25such as these
35:26will keep scientists
35:27busy for years.
35:30And this
35:31the first ever
35:33series of images
35:34showing the rings
35:36from the inside
35:37looking out.
35:42It's coming in right now.
35:44Yeah, we are at
35:45about two hours
35:47before the plunge.
35:48Critically
35:49for those final moments
35:51of the mission
35:51Julie must ensure
35:53that Cassini
35:54is able to collect
35:55and transmit data
35:56till its dying breath.
36:00So what my team
36:01is doing right now
36:02is simulating
36:04the last four hours
36:06of Cassini's life.
36:07We've cleared off
36:08the solid state
36:09recorders.
36:10We've dumped down
36:11all the pictures.
36:12All we're doing
36:13is as much
36:13real-time data
36:14as we can.
36:16Data can only be sent
36:18as long as the antenna
36:19is pointing
36:20precisely at the Earth.
36:23Something that will get
36:24increasingly difficult
36:25as Cassini starts
36:27to be buffeted
36:27by Saturn's atmosphere.
36:29So what we do is
36:31we let the spacecraft
36:32go until it hits
36:33the two-millaradian
36:34dead band
36:35and then it fires
36:36a thruster
36:37to push it back
36:38and then we let it
36:39drift over
36:40to the other side
36:40and it fires it.
36:41So it's called
36:41bang-bang controlling.
36:43It doesn't know
36:44it's in trouble yet.
36:49Right now they're firing
36:50once every minute or so
36:53and then as they get
36:54into the atmosphere
36:55they'll start firing
36:56more and more
36:57and more and more
36:57in the last few minutes
36:59and what we want to see
37:00is we want to see
37:01how much of the atmosphere
37:02we can see
37:02before we lose
37:03the signal
37:04before it can't fight
37:04the atmosphere anymore
37:06and it goes off point
37:08and then at that point
37:10it starts to burn up.
37:19It goes from 200
37:20to 2,000 degrees
37:21in just a matter
37:23of seconds
37:24and then everything
37:24will start to melt
37:25and disintegrate.
37:29And then it'll go away.
37:31It just will lose
37:33the signal
37:33and that'll be
37:34end of mission.
37:37So pretty much
37:38everybody will know
37:39at the same time
37:40the end of mission
37:41because we'll all see
37:42the carrier signal
37:43go away.
37:50So after dedicating
37:52nearly three decades
37:53of your life
37:53to a spacecraft
37:55how do you say goodbye?
38:10The Cassini-Huygens
38:11scientists and engineers
38:13have faithfully dedicated
38:14over two decades
38:15of their lives
38:16to the mission
38:18and now
38:19it's nearly time
38:20to say farewell
38:21to their beloved friend.
38:25My navigation team
38:26will be sitting
38:27up here.
38:29I will be out
38:29in Pasadena.
38:31I've spent 20 years
38:32of my life on this.
38:33And back here
38:36radio science
38:37is going to be
38:37one of the most
38:38critical positions
38:39because they'll have
38:41the open-loop receivers
38:42and they'll be
38:43the very last signal.
38:45The Cassini is going
38:45to be getting
38:47and transmitting data
38:48to its last breath.
38:50I'm going to cry
38:51my eyes out.
38:52I cried when it launched.
38:54Everybody will be
38:55watching the spacecraft
38:56making sure that
38:57we're getting
38:58all the data.
38:59This will have
39:00a cast of thousands.
39:01Every seat
39:02will be taken.
39:03Project Manager
39:04I usually like
39:05to sit next to Earl
39:06so Earl will be here.
39:07I'm in the
39:08Flight Director's seat.
39:12Flight Director's
39:13just in seat.
39:14Everything is normal.
39:15Copy.
39:16Spacecraft has just
39:16crossed 10 degrees
39:17north latitude
39:18altitude 1,000 miles.
39:20In its final
39:21fatal kiss.
39:23We've just had
39:24the transition
39:25to high-rate mode
39:26and we are
39:27in the atmosphere.
39:29Cassini touched
39:30Saturn's atmosphere
39:31and then began
39:33to burn up.
39:35Becoming part
39:36of the very planet
39:37it had got to know
39:38so well.
39:48At exactly 4.55
39:50and 46 seconds
39:51Pacific time
39:52on Friday,
39:53the 15th of September,
39:55the signal disappeared.
39:56So that would be
39:57the end
39:58of the spacecraft.
39:59Project Manager
40:00off the net.
40:02And Cassini,
40:03unquestionably
40:05one of our most
40:06successful missions
40:07into space,
40:08came to a final
40:09spectacular end.
40:15It's a 20-year-old friend.
40:19I can't imagine
40:20anything topping that,
40:22but we will try
40:23for a new mission.
40:24It's always that way.
40:26It's like a death
40:26in the family.
40:27You know,
40:27it's imminent,
40:29but when it happens,
40:31it's the finality of it
40:32that really is
40:33what you're left with.
40:36Cassini may be gone,
40:37but its revelations
40:39will continue.
40:41Results are already
40:42starting to emerge
40:43from the grand finale orbits.
40:46And we could be
40:47a step closer
40:47to discovering
40:48the length of Saturn's day
40:50by pinning down
40:51the mysterious tilt
40:52of its magnetic field.
40:54If there is a tilt,
40:55it is really small,
40:57but we need to find
40:58that tilt
40:59if we're going to work out
41:00how long a day
41:00on Saturn is.
41:01I would think
41:02we would probably
41:03have a final answer
41:04in three to six months.
41:07It's mission accomplished.
41:09And for us,
41:10it was a long,
41:12long mission.
41:13It was totally appropriate
41:15that it was slightly raining
41:16here as we walked out
41:18because, you know,
41:19I think even the Earth
41:20is crying right now.
41:21That was a great spacecraft.
41:23It did exactly
41:24what we asked it to do
41:26all the way to the end.
41:28No surprises.
41:32And the legacy of Cassini
41:34looks set to continue
41:36long into the future.
41:40Scientists will be
41:41pouring over our images
41:42and all the data
41:43from Cassini
41:44for, I mean it,
41:45a hundred years.
41:47We've got this amazing
41:48amount of information
41:49to pass on
41:50to future generations.
41:55We've only skimmed
41:56the surface
41:56of what's in that data.
42:00Godspeed,
42:01you know,
42:02been a great spacecraft,
42:04a great program.
42:06You know,
42:07thank it and release it.
42:12In its dying hours,
42:15Cassini left us
42:16with these final pictures.
42:20This
42:21is its last ever image.
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