The Rosetta mission was an ground-breaking expedition to land on a comet for the very first time; special access reveals what this cutting-edge journey discovered and how these mysterious objects helped create life on Earth.
Thanks for watching. Follow for more videos.
#cosmosspacescience
#howtheuniverseworks
#season9
#episode2
#cosmology
#astronomy
#spacetime
#spacescience
#space
#nasa
#missiontoacomet
#comet
#mineralsoncomet
#rosettamission
#lifeonearth
Thanks for watching. Follow for more videos.
#cosmosspacescience
#howtheuniverseworks
#season9
#episode2
#cosmology
#astronomy
#spacetime
#spacescience
#space
#nasa
#missiontoacomet
#comet
#mineralsoncomet
#rosettamission
#lifeonearth
Category
📚
LearningTranscript
00:00Comets, messengers from the dawn of the solar system.
00:12For the first time, we sent a spacecraft to orbit and land on one.
00:21To go outside of the inner solar system and catch a speeding comet, and then send a lander
00:28down to land on its surface?
00:31That is nuts.
00:33The Rosetta mission answers our most fundamental questions.
00:38Rosetta is really teaching us how comets live in real time.
00:43This is a game changer.
00:45Rosetta changes our understanding of the cosmos forever.
00:50The secrets of life itself may be wrapped up on Comet 67B.
00:58530 million miles from the sun, a tiny lump of ice and rock starts its journey towards
01:14the inner solar system.
01:17Scientifically, comets are more precious than pure gold.
01:21They are actual time capsules.
01:24They are preservations of what the chemistry, the environment was like when our solar system
01:28formed.
01:29And they hold clues as to how our chemistry arrived here on Earth.
01:34Comets are some of the most valuable scientific treasures that exist.
01:39Finding a comet we can study is not an easy task.
01:43Finding the right comet for a mission, it's kind of like you're auditioning them, right?
01:47One comes in and it's like, oh, that orbit's okay, but it's not exactly what we're looking
01:52for and, oh, this one's too big, this one's too little, this one's too active.
01:57What we really want to see is that comet come from outer parts of the solar system and get
02:03heated up as it gets close to the sun, pass around the sun and head back out to the outer
02:07part of the solar system.
02:08So you need to get way out in the solar system and catch a comet on its way in.
02:14Comet 67P fits the bill.
02:17The special thing about comet 67P is how accessible it is here on Earth.
02:22It actually orbits around the sun once every six and a half years.
02:25And its orbit doesn't take it all that far out, only about as far out as the planet Jupiter.
02:30That gives us many chances to actually reach the comet and successfully rendezvous with it.
02:3367P's moment in the spotlight arrived.
02:43The European Space Agency launched the groundbreaking Rosetta probe.
02:49For years, we've studied comets from afar.
02:52We had never seen one up close with cutting edge technology to learn about how comets behave
02:58as they orbit the sun.
03:04Missions to large, planet-sized objects are hard.
03:08The Hubble Space Telescope's blurry images revealed Rosetta's target is just two miles wide.
03:15And not just a small target, a moving one.
03:20Comet 67P races through the solar system at over 33,000 miles an hour.
03:28The precision involved is pretty incredible.
03:31It's like making that hole-in-one golf shot from New York to San Francisco.
03:35But catching comet 67P wasn't just a straight shot.
03:41The spacecraft had to actually get the same sort of velocity as the comet.
03:45And with current propulsion systems, we can't achieve that by flying directly to the comet.
03:52Instead, Rosetta performed a slingshot maneuver that would take 10 years.
03:59So what it's doing, it's actually taking some energy away from the planet.
04:05So it's slowing the planets down a little bit and then imparting that energy into the probe.
04:13Rosetta flew past Jupiter, nearly 100 million miles from the warmth of the sun, and entered
04:20the most dangerous part of its journey, hibernation.
04:26Even though Rosetta had solar panels on it, it still had to be put to sleep.
04:30And the reason for that is that it had to track 67P a ways away from the sun, and there
04:34just was not enough collection area and solar power to be able to power the instruments.
04:40It's normal to put spacecraft into hibernation, but the worrying thing at the back of your
04:44mind is that it had never been done for this long before.
04:48Thirty-one months of hibernation gave Rosetta's team plenty of time to worry about what could
04:54go wrong.
04:56It's dark and cold out there in space.
04:58There's a lot of things going on.
05:00There's a lot of little micrometeorites out there.
05:02And without the constant communication with that spacecraft, it just is a little nerve wracking
05:08when the day comes and it's time to flip the switch and turn it back on.
05:12January 20th, 2014.
05:17After almost ten years in space, it was finally time for Rosetta to wake up, reactivate its communication
05:23system, and phone home.
05:26I mean, the tension was just palpable.
05:30It was just, I mean, how long do we have to wait before we're going to get the signal?
05:35It's got to work.
05:36It has to work.
05:37Oh, gosh.
05:38Maybe it's just not going to turn on at all.
05:39Have we lost the spacecraft?
05:42And then the peak appeared on the graph.
05:44It's like, yes, we've got contact with the spacecraft.
05:50Rosetta began to send back images of its target.
06:07And after months of seeing a small dot in the distance, the comet slowly came into focus.
06:16When I saw this comet crystal clear, this mountain floating in space of ice and rock, my heart
06:23just dropped.
06:24They were some of the most dramatic, beautiful images I have ever seen.
06:28And then as it got closer and we got to see more and more details on it, yeah, that's
06:34when things started getting really strange.
06:36Quite simply, arrival at 67P, we expected to see something shaped like a potato, and we
06:45found something shaped like a rubber duck.
06:4867P is no ugly duckling, but its strange shape created a problem for Rosetta.
06:56Orbiting the comet was going to be far more difficult than anyone had imagined.
07:03A planet has a lot of gravity, so you can send the spacecraft out there and then just slow
07:07it down a little bit with a rocket burn and it'll drop into orbit.
07:11In the case of comet 67P, you're dealing with a very small little rock.
07:15The spacecraft cannot feel the gravity of that rock, at least not until it's right up against
07:19it.
07:20Well, the engineers had to actually plot triangular orbits.
07:24It was a very complicated set of maneuvers.
07:29Once in orbit, Rosetta could start work.
07:33Its first task?
07:35Figure out how 67P formed.
07:38So how did this comet get this weird shape?
07:42There's two main ideas.
07:44One is just that it was eroded somehow in the center, and so it started off as a more spherical
07:50thing and became the shape it is today through some unknown process.
07:56The other idea is that it started as two separate objects.
07:59Space rocks normally hit each other hard.
08:05They collide with an average impact speed of more than 11,000 miles an hour.
08:11That's five times faster than a rifle bullet.
08:15Was 67P involved in a pileup?
08:18A clue came from the distinct layers on the comet's surface.
08:24The layers in Comet 67P are a little like the layers in an onion.
08:29If you see them aligned, that's a clue that perhaps the object formed as a single entity
08:35and only eroded later into its present form.
08:38But if you see those layers misaligned, like we actually do in the comet, that's a big
08:42clue that it started out as two separate objects formed independently, sticking together
08:48to form the comet we see today.
08:50The layers prove that 67P was originally two separate objects that fused together.
08:57The process of potentially putting Comet 67P together from two different pieces is important
09:02because it can teach us about what was happening in the early solar system.
09:06So as far as we can tell, these two separate bodies must have been formed in the same area.
09:12They're very similar in composition.
09:14They are so light and fluffy that they would have destroyed each other if they had hit
09:19fast.
09:20They had a low speed collision and basically stuck together like two wet snowballs.
09:26With one mystery solved, Rosetta began to investigate the chemical makeup of 67P.
09:33The little comet could answer one of the biggest questions in planetary science.
09:38From where did our blue planet get its water?
09:51The Rosetta mission, a four billion mile journey to Comet 67P and a four and a half billion year
09:59trip back in time to the birth of the solar system.
10:04This comet is a remnant of the formation of the solar system itself.
10:10So this is an opportunity to open that time capsule and get a view into the ancient solar
10:17system.
10:20Comet 67P could help us answer one of the most important questions about our planet.
10:26One of the big mysteries that we have about Earth is, where did the water come from?
10:31Today, water covers over two thirds of the Earth's surface.
10:37But it wasn't always that way.
10:414.6 billion years ago, the inner solar system formed from a maelstrom of rocky debris.
10:50Temperatures were so hot, any water on the early Earth boiled away.
10:55What the evidence suggests to us is that Earth's water arrived at Earth after the Earth formed.
11:01And the primary mechanism that we thought were responsible were our comets.
11:07You have to remember that comets are basically just big balls of ice and dirt.
11:12One of the main goals of the Rosetta mission was to analyze the water on this comet and see
11:16if it matched the water on Earth.
11:20Comets come from two regions at the outermost reaches of our solar system.
11:26The Oort Cloud and the Kuiper Belt.
11:30The Kuiper Belt is in the plane of our solar system.
11:33And the member that most people are aware of is Pluto.
11:36But beyond that, there is a spherical distribution of icy bodies, the Oort Cloud.
11:43This is a repository of comets that extend for hundreds of thousands of times further away
11:48from the Sun than we find the Earth.
11:50And it's kind of a big spherical cloud around the Sun that's a kind of deep freeze for a bunch
11:55of big comets.
11:57Billions of icy objects orbit safely beyond the chaos of the inner solar system, locking
12:04in primordial water.
12:07The lifespan of a comet is fascinating.
12:09They might do absolutely nothing out there for over four billion years until the right
12:15tweak of their orbit or tug from a planet changes everything.
12:20And all of a sudden they're on a path in towards the Sun and that ice that's been in deep freeze
12:24for billions of years starts to heat up.
12:29Astronomers believe that Comet 67P's former home turf was the Kuiper Belt.
12:34Until something sent it ricocheting inwards.
12:40The influence of the gravity of Jupiter, because Jupiter is such a massive planet, it actually
12:44attracted the comet and pulled it into the inner solar system.
12:47It slowly was perturbed and migrated into the inner solar system where we see it today.
12:52It's traveled, I mean, not just billions of miles in linear space, but really when you
12:56think of all the orbits it must have made, just trillions upon trillions of miles.
13:01That's quite a journey for such a little object.
13:04Now, 67P loops around the Sun in a six-and-a-half-year orbit that travels as far out as Jupiter and
13:13closer in than Mars.
13:16As it gets nearer to the Sun, its frozen ice begins to heat up, leading to a famous effect,
13:22the comet's tail.
13:25Sunlight comes in and heats up the comet's surface and it gets transferred to the interior
13:29where there's a lot of ice.
13:30And the ice gets heated up and it vaporizes and makes its way to the surface.
13:34And once it's sitting on the surface, the solar wind is bombarding that comet and it drags
13:39all of that material out into a long, beautiful tail.
13:43Rosetta flew into the tail to analyze the water vapor.
13:49Its goal?
13:50Confirm it's the same type of water as we have on Earth.
13:55Water does come in different flavors, and I don't mean salt water or fresh water.
13:59I mean what the water's made of.
14:00It's molecules.
14:02We're talking about the actual chemical makeup on the proton, neutron, and electron level.
14:10So you might have heard of heavy water before, and that just means that there is an extra
14:15neutron.
14:16It's H2O, but one of the hydrogens has an extra neutron, so we call it deuterium.
14:24And so that water actually weighs more than normal water because of that extra neutron in
14:29the mix.
14:32On Earth, there are roughly 160 molecules of heavy water for every million molecules
14:39of normal water.
14:43As Rosetta moved around the comet, it measured the ratio of hydrogen to deuterium in the water
14:49vapor.
14:50An exact match to Earth's ratio would confirm that comets were the source of our oceans.
14:58But Rosetta discovered something surprising.
15:02What Rosetta found was that the deuterium to hydrogen ratio was three times that of the
15:07water in Earth's ocean.
15:08That means a comet like 67P couldn't have been the source of Earth's water.
15:13If it was the same as the measurement of the ocean water, then we could have said that these
15:18comets could have been a delivery mechanism for the water that we see on Earth.
15:22The fact it was three times higher kind of indicates that comets like 67P were not the source of the
15:29water that we see on Earth today.
15:34But although comets like 67P didn't deliver our water, we can't rule out all comets.
15:43We have to keep this in perspective.
15:4667P is but one comet.
15:48And what we know about objects like comets is that they come in families, and these families
15:54have different compositions.
15:56So it could be that some have Earth-like water, and those are the ones that brought water to
16:00Earth.
16:01And some don't.
16:02I don't see wrinkles like this as going back to the drawing board.
16:07Sure, we get more questions sometimes than answers, but that allows us to probe farther
16:13and really expand our knowledge into how planets formed.
16:18The composition of comet 67P rewrites our understanding of the solar system.
16:24And the comet has more secrets to reveal.
16:29The reason we went all the way out to comet 67P, and in fact the reason we study comets
16:33at all, is we're looking for clues about the origins of life.
16:38As Rosetta examined the icy core of the comet, it found a treasure trove of molecules.
16:46Could 67P carry the building blocks of life itself?
16:59Rosetta's mission to comet 67P planned to answer the biggest questions in planetary science.
17:10And none is bigger than figuring out the origins of life on Earth.
17:15Life on Earth got started not long after our planet cooled, something like 4.5 billion years
17:21ago.
17:22We don't know the exact process.
17:24Did all that stuff come together here from molecules on Earth and become more and more
17:28complex?
17:29Or was it brought from space?
17:35Rosetta began to hunt for the building blocks of life, basic organic compounds.
17:40So we always thought that comets probably carry organic materials.
17:45But we really couldn't confirm that until Rosetta.
17:49It detected aliphatic compounds, which are organics rich in carbon and hydrogen.
17:55And that is the first time such a substance has been detected at the surface of a comet.
17:59These materials are the raw building blocks for making things like proteins, which are required
18:05for all life.
18:06And this is really important because this says that possibly these materials were delivered
18:10to Earth by comets.
18:13The idea that comets carry the building blocks for life across the solar system is known
18:19as molecular panspermia.
18:22You can kind of think of comets as being like space delivery trucks, right?
18:27They're forming out there in deep space.
18:28All this stuff is being formed with them.
18:31And then they bring it to Earth.
18:32Now, you know, you don't want your delivery truck smashing through your front door.
18:37But in the case of comets, when they impact the Earth, they can distribute those molecules
18:41all over the place.
18:45But in some way, we're kind of skipping a step, right?
18:46I mean, so the comet may be bringing the ingredients of life to the Earth.
18:52But where did the comet get those ingredients?
18:55The answer may be in deep space, in the matter and radiation floating between star systems
19:01in a galaxy.
19:03It's called the interstellar medium.
19:06The really interesting result is that the overall composition of comet 67P and some of
19:12the really interesting ingredients in that comet are very similar, identical in some cases,
19:18to materials we find out there in the interstellar medium, floating out there in the gas and
19:22dust between the stars.
19:24If this organic chemistry is common on Earth, it's likely to be common across the entire
19:32galaxy.
19:33This chemical kit for making life is universal, and therefore, perhaps life itself is common.
19:39There could be plenty of wet rocks out there in the night sky teeming with life, with this
19:46universal chemistry kit.
19:50But scientists still couldn't figure out the origin of one vital element.
19:55So phosphorus is one of the atoms that is absolutely essential for life, but we don't
20:00really know where it comes from.
20:03Phosphorus is a vital part of DNA, cell membranes, and energy production.
20:08But the problem is it's quite scarce in the universe, and it's certainly scarce on the surface
20:14of the Earth.
20:15Any phosphor that was around would have been locked up in the soluble rock, so that wouldn't
20:20have been available for life to use at that time.
20:24If rocks had locked in all the mineralized phosphorus, where did the phosphorus needed for biological
20:30processes come from?
20:3367P held the key to the mystery.
20:36What we found on the comet is bioavailable forms of phosphorus, not just mineralized phosphorus.
20:47Bioavailable phosphorus is a form that life can use.
20:53But where did Comet 67P get it from?
20:58In January 2020, astronomers combined data from the Rosetta mission with ALMA's observations
21:04of the star-forming region AFGL 5142.
21:09AFGL 5142 is a stellar nursery, a gas cloud where large and small stars are being born simultaneously.
21:17And it's very close to us, which means we can study it in great detail.
21:21The ALMA Observatory takes really high-resolution images of different types of dust and gas in
21:28very, very close to a star that's just formed, so you can actually see the process of formation
21:32happening.
21:33The largest stars live fast and die young, exploding in supernovas.
21:39So the phosphorus itself, we believe, is formed in massive stars, so essentially it's created
21:48as the star gets to the end of its life, and when the star goes supernova, it spews this
21:53phosphorus out into the interstellar median.
21:56When mid-sized stars burst into life, they sent shockwaves and radiation through the cloud,
22:02transforming phosphorus into a form biology can use, phosphorus monoxide.
22:09The phosphorus monoxide can freeze out and get trapped on the icy dust grains that remain
22:13around the star.
22:16These dust grains can come together to form pebbles, rocks, and eventually comets that
22:20become the transporters of phosphorus monoxide.
22:24Scientists trace the cosmic trail of phosphorus and organics from stars to comets to planets
22:31and even to life.
22:35We could, in theory at least, take the sort of chemistry we find preserved in a comet and
22:40use it to construct a cell.
22:44So often people seem to think of astronomy as the study of things that are very far away,
22:48that have absolutely no bearing on our day-to-day life.
22:52Nothing is farther from the truth.
22:53We are looking for the origins of ourselves out there, and we are discovering them.
22:58So a basic question, like how did phosphorus end up in our DNA, when the only place you
23:03seem to find it isn't around young stars, clouds, thousands of light years away.
23:08Now we know the mechanism because we asked the question, and now we understand ourselves
23:12that much better.
23:15The next stage of the mission was to get the lander onto the comet's surface.
23:21But there was a problem.
23:23The craft's landing gear was broken.
23:27Would the team have to abort the mission?
23:40Rosetta had discovered the building blocks for life on 67P.
23:47Now the probe faced its toughest challenge so far, a historic first landing on the surface
23:54of a comet.
23:56One of the biggest challenges about setting the Philae lander down on the surface is having
24:00no idea what the surface is like when you're designing the lander.
24:04Is it going to be like rock or ice and be very stiff?
24:07Is it going to be brittle?
24:10Philae had harpoons to dig into the soft surfaces and top thrusters to stop it from bouncing
24:16off the comet.
24:18The lander team discovered neither system was working properly.
24:23With the odds stacked against them, they decided to go for a landing anyway.
24:32Philae made a slow, 12-mile, 7-hour descent.
24:45Until finally, touchdown.
24:48So when we got the first signal of touchdown, we were relieved.
24:55The lander was down and everything was good to go.
24:59But then we realized things weren't quite going to plan.
25:03The data from the lander was intermittent.
25:06The only possible explanation?
25:09It was tumbling end over end.
25:12It could have bounced and bounced right off the comet and continued on the way into space.
25:17We really didn't know.
25:19We just knew we were not on the ground and we were rotating and tumbling.
25:23Then, 12 minutes later, a ray of hope.
25:26We saw a flash in one of the computers and we huddled around it and we realized that the
25:32lander was actually sending data back as it was programmed to do.
25:35We were actually doing science on the comet and getting the results back.
25:40The lander stopped tumbling.
25:42Philae's solar panels weren't fully operational and the tiny craft's battery had only 60 hours
25:48of power left.
25:50It was a race against time.
25:52We had to completely rip up all our plans of what we wanted to do and then we had to rewrite
25:57everything to maximize the amount of science return in those 60 hours we had available
26:01to us.
26:02Philae got to work.
26:07Its first discovery.
26:08The ground was stranger than expected.
26:10One of the things we found about the surface is the top 40 centimeters were a very fluffy
26:18material.
26:19It's not dense and rocky.
26:22It's pretty fluffy.
26:23You could imagine something on the order of cigar ash.
26:26Imagine the rocks on Comet 67P but imagine them being as light and fluffy as cigar ash.
26:34It's so crumbly that if you had it in your hands you could break it apart with almost
26:37no effort at all.
26:39It has a fraction of the strength of styrofoam.
26:42Philae's bounce landing helped investigate the surface.
26:48By bouncing we actually were able to sample two sites and interestingly both sites were different.
26:54That kind of shows us that the comet is not homogeneous.
26:57It's not all the same material.
27:00Philae's instruments revealed Comet 67P is not just two lobes fused together.
27:07The comet formed from distinct blocks pulled together by gravity.
27:13Philae's onboard camera also fed back vital clues to the lander's final resting place.
27:19The images taken by the lander were really amazing because from those we were actually
27:24able to work out that Philae was on its side.
27:27Philae's location was unknown, far from the planned landing site.
27:33With its battery dead, it couldn't speak to Rosetta.
27:37The problem with not knowing exactly where on the surface of the comet we were was that
27:41some of the instruments needed to know that exact location to actually interpret the data.
27:46And without that information, the results were meaningless.
27:51Time is passing and still no Philae lander is to be found.
27:56Because their hope is all lost.
28:00When you make or follow a space robot, you kind of get invested in that success and the
28:05survival of that robot.
28:07You want it to succeed against the harsh reality of space.
28:09You feel like you've lost a pioneer, you've lost a fellow explorer.
28:19As Rosetta scanned the comet, searching for the lost lander, it faced a new problem.
28:26As this dirty snowball races towards the sun, the radiation from the sun heats it up and
28:33so it starts snapping and popping and cracking, transforming itself.
28:38It's like a fireworks show.
28:41Huge jets blasted material from the surface.
28:44Would the outbursts launch Philae into space?
28:58Rosetta's lander, Philae, was lost somewhere on the surface of Comet 67P, its battery dead
29:04and its solar panels useless.
29:08As Rosetta scanned the comet for the missing probe, it flew less than two miles above the
29:13surface, close enough to cast a shadow.
29:18Seeing the shadow of the spacecraft itself on the comet really brought home the fact that
29:25there was a piece of humanity, one of our machines, right there.
29:32It makes the hair in the back of my neck stand up, it gives me chills.
29:38The low passes allowed Rosetta to smell the comet's surface.
29:42The Rosina instruments allowed us to actually measure the chemicals and the gases coming
29:47off the comet so we can actually put those together to make a comet perfume.
29:54So what we've actually done is impregnated those smells of the comet into a card, a bit like
29:58a scratch and sniff card.
29:59So you can actually smell and that is the smell of the comet.
30:05And it's not very pleasant.
30:06If you can imagine a mixture of something like rotten eggs and cat urine and like bitter almond
30:14stuff, it's like it's not something I would want to have to be able to smell.
30:19To me it kind of smells like baby's nappies and it's a bit of a pungent, quite an unpleasant
30:27smile.
30:30Months passed with no sign of Philae.
30:33The comet isn't terribly big, you know, where could it be hidden?
30:36And if we understood where it was hidden, we would understand the images that it had returned
30:40so much better.
30:41There was sort of that human part of like, where is my buddy?
30:44And also that science part of what was it trying to tell us?
30:47Then, an eagle-eyed researcher spotted something in the corner of an image.
30:54The lander itself was a tiny little speck and you really have to zoom in to actually see
30:58it.
30:59But there was Philae, under a cliff.
31:03Seeing a little Philae lander there, on its side, under a ledge, in the shadows, was
31:10just remarkable.
31:12Pinpointing Philae's location on the smaller lobe solved one final mystery.
31:17It explained data sent back months earlier, revealing this area of the comet is solid.
31:25There was a real sense of closure and there was sort of a Godspeed to it, you know, like
31:30we know what's happened to you, thank you for the science.
31:33And that was its final resting place and it was really wonderful to see.
31:38Philae was an amazing success.
31:41Despite all those problems, we got the lander down.
31:44Despite the bounce and it coming to a rest under the cliff face, we got absolutely amazing
31:48images and some fantastic measurements of the gases and the structure of the comet itself,
31:53which we would never have had had we not tried to put a lander on a comet.
32:00All of a sudden there were these jets that would appear and eject a huge amount of material from
32:16the interior.
32:19When sunlight warms the comet's surface, ice turns directly into gas.
32:24The uneven surface of the comet funnels the escaping water vapor into narrow jets of gas
32:31and dust.
32:34But Rosetta also spotted huge, violent gas outbursts.
32:40We would expect to see jets on comets that kind of gradually rise and fall with the solar
32:47illumination.
32:48But these outbursts were utterly different.
32:50They would just sharply increase and then stop.
32:54These outbursts weren't timed with the sun.
32:56They came out at random times.
32:59So there must be something else going on.
33:02The outbursts exploded in sudden brief high speed events.
33:09As we only take pictures of the surface every 5 to 30 minutes, when we see an outburst in
33:15only one image, we know that the whole event lasted less than that time, which is very mysterious.
33:24So it was like putting together a puzzle and you have a thousand pieces and you're putting
33:28them together and you realize, oh, I only actually have 600 of the thousand pieces and I've got
33:32to make sense of this.
33:33And it's really frustrating.
33:36As the comet swung closer to the sun, Rosetta's cameras captured 34 outbursts in just three
33:42months.
33:44They were all huge.
33:46In the span of only a few minutes, a single jet can release up to 260 tons of material.
33:53And one jet was spotted releasing 40 pounds of material every single second.
34:00The cause of the outbursts was a complete mystery.
34:03Then, in September 2014, close-up images revealed a 230-foot-long, three-foot-wide fracture on
34:13the cliff edge named Aswan.
34:17Less than a year later, Rosetta photographed a large outburst from the same region of the
34:22comet.
34:26When the probe investigated the area, it found a devastated landscape.
34:30The cliff had collapsed in a huge landslide.
34:35This is like a crime scene.
34:37We have the before pictures and the after pictures and we have to solve the mystery of how this
34:44happened.
34:46What links the outburst and the cliff collapse?
34:49We think there's a domino effect going on here where the sun heats up some of the volatiles
34:55deep under the surface and they sublimate and turn into a gas and they find any little
35:00crack or crevice they can to shoot out of the comet.
35:04But that process weakens part of the comet's face.
35:13This is going to release more material and as it does that, it's going to start forcing
35:16gas up through kind of nozzle-like features, having them act like jets.
35:21And as they do that, then that's going to cause even more weakening of the material and maybe
35:26a large-scale collapse, which could actually cause a giant outburst.
35:31We think escaping gas weakens the surface, which triggers a collapse and a release of gas
35:37in a giant outburst.
35:39Like sticking dynamite charges in the side of the cliff and then setting them all off.
35:53Comet 67P revealed the hidden geological activity going on inside these dirty snowballs.
36:01Rosetta spotted another surprising phenomenon, strange shapes moving across the surface, dunes.
36:12Dunes aren't driven by wind.
36:14Well, on an airless comet, how do you have that happen?
36:20Rosetta rewrote the book on how comets form, how they live and how to explore them.
36:36When Rosetta flew close to the surface, it spotted something unexpected, dunes.
36:44These are serious dunes.
36:46They're about six feet high, and they extend for hundreds of feet in every direction.
36:50So we've got to figure out what this mechanism is that it's causing this, you know, pretty
36:54significant geologic structure on the comet.
36:58Janie Radabaugh is a planetary scientist.
37:05She studies space dunes on Earth.
37:07One of the most fascinating things that Rosetta saw on 67P was a set of dune-like features on
37:14an airless body.
37:17These were found up by the neck region in a set of soft sediments.
37:20They actually looked very similar to these ripple-like landforms.
37:25They were spaced about 10 yards across, and there were maybe 10 to 15 of them across
37:31the surface, and we even saw them change over time.
37:36When we first saw these, no one had any idea what could have formed them.
37:39In fact, people even doubted that they were dune-like landforms, because how would they
37:43possibly form on a body that has no atmosphere, let alone any wind?
37:48On Earth, land heated unequally creates winds.
37:53The atmosphere on Earth and the really transient atmosphere on a comet are very different from
37:57each other.
37:58On Earth, it's a stable, thick, dense atmosphere.
38:01It's got constant solar heating that can pick up air masses and move them across the surface
38:05and generate wind.
38:08Comet 67P does have an atmosphere created when the sun heats the surface, releasing gases.
38:16But this atmosphere has a maximum pressure 100,000 times lower than Earth's.
38:24Using Rosetta images, researchers in France modeled the movement of gases on the surface
38:29of the comet.
38:31And they think they've found the answer.
38:33Researchers found that there are winds on the comet's surface.
38:38These are brief, and they form because gases escape on the sunlit side, and then they rush
38:42over to the cold side across the surface.
38:45And this movement of air across the surface is what picks up the sand and forms the dunes.
38:49The grains on the comet are far bigger than sand grains on Earth.
38:57On the Earth, the sand dunes are made of grains about this size.
39:00But on the comet, the sand dune grains are this size.
39:04Gravity also plays a really important role in moving grains around on the comet.
39:08The comet has such a low density that if you were walking around, you'd be able to fly
39:12into orbit very easily.
39:14And so a grain this big but low density would easily be lofted by the very thin air there.
39:22After two years orbiting the sun with comet 67P, Rosetta's mission was almost over.
39:28So the plan was to lower the orbiter down towards the surface in a controlled way.
39:34And this would allow very high resolution images to be taken, and also to get some gas measurements
39:39right close to the surface of the comet.
39:44September 30th, 2016, Rosetta spent 14 hours slowly free falling towards the comet, taking
39:52photos on the way down.
39:59As Rosetta was lowered, it touched the surface, and then the link back to Earth was broken,
40:06and the mission was effectively over.
40:09The thing that's kind of wonderful about it is that there's a little piece of us on that
40:13comet out there right now.
40:15As that comet spins around out to Jupiter and back every six and a half years, it will
40:20always have a little bit of humanity on it.
40:26There was one final twist to Rosetta's story.
40:30We thought we had the last image back from Rosetta before the planned end of the mission,
40:35but it turns out that actually just before touching down, before the comms were able
40:40to finish transmitting back to Earth, an incomplete packet of information was sent back.
40:46The computer discarded this incomplete data packet.
40:51Recently, human experts re-examined it.
40:56The result?
40:57Rosetta's closest photo of 67p.
41:00And the image is amazing because when you actually blow it up and look at it, you can
41:05actually feel like you could reach out and touch the surface.
41:11It's a fitting postscript to the only mission to land on a comet.
41:16It's an incredible chance to learn about the geologic structure at the size scale of a human being
41:24exploring there.
41:25It's a way to look at comets that we've never had before.
41:30The Rosetta mission has transformed our understanding of comets.
41:34Between the strange shape and the measurements of heavy water, we're finding that there's a
41:38big diversity out there of comets.
41:39And that every time we go to visit a new one, we're probably going to be surprised all over
41:43again.
41:45Rosetta may inspire new missions.
41:49We may actually be returning to comet 67P itself.
41:51There's a lot more there to discover about the origin of our lives, ourselves, here on Earth.
41:56There's so much more to learn and so many more mysteries to uncover.