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00:00Comets are a celestial mystery.
00:07They are messengers from deep space itself.
00:12Time machines from the early universe.
00:15Comets could unlock the deepest secrets of our cosmos.
00:20If we can establish a correlation between amino acids on comets and life on Earth,
00:26that would be one of the most significant findings in science.
00:31They threaten our very survival.
00:34We're talking about something the size of a mountain.
00:36So the amount of energy that this thing would release upon impact is devastating.
00:41Yet without comets, we might not be here.
00:46We may owe a great cosmic debt to comets
00:48because they may have been responsible for bringing the chemicals that we require for life to the Earth.
01:18A dramatic streak of light across the sky.
01:21A passing comet is an astonishing sight.
01:28They're beautiful. These fuzzy glowing balls with the tail coming off.
01:32It's really something. You just don't get to see an object like that very often.
01:37Comets are extraordinary. If you get to see a comet for the very first time, it'll stick with you forever.
01:43The journey of a comet as it sails through the solar system is the most fantastic of all astronomical objects.
01:54It loops in toward the sun from the depths of space.
01:58An odyssey that can last millions of years.
02:04Many pass by the Earth so often, they're almost like old friends.
02:13Every comet is a frozen mass of rock and ice several miles across.
02:21But all we see is a glowing ball of light and a long, sweeping tail.
02:28Yet comets are more than cosmic fireworks.
02:37They could help unlock some of the deepest mysteries in science.
02:47We're trying to figure out as scientists where we came from.
02:50And that means everything from the beginning of the universe to the beginning of the solar system to how life started.
02:55Comets really fit into that. They really give us clues about how the solar system formed.
03:00If we can't understand comets, we don't understand how we got here.
03:08Comets may even be the source of life itself.
03:13We may owe our existence to the fact that comets billions of years ago came to Earth and brought the necessary ingredients for life.
03:22They can also cause enormous destruction.
03:36Comets could kill us all.
03:39If a comet were to hit the Earth, watch out. It would be a planet buster.
03:44It would be an object sufficient to wipe out all life as we know it on the planet.
03:51Learn about comets, and just maybe we will learn how to survive them
03:58and begin to understand how the universe works.
04:06When we study them, we're learning what the solar system was like when it was first forming.
04:11And we can learn about what other solar systems were like as well.
04:14And hopefully that will teach us a tremendous amount about how stars form and how planets form
04:19and how comets themselves were originally formed.
04:27Comets date back to the birth of our solar system four and a half billion years ago.
04:39They were made by the same force that created the solar system, gravity.
04:46It began in a maelstrom of chaos.
04:51A giant cloud of gas and dust collapsed to form a whirling disk.
04:58Close to the sun it was burning hot.
05:04But further out, it was cool enough for gas clouds to condense and freeze.
05:11Ice crystals fused with grains of dust.
05:16They slowly pulled together into larger and larger masses.
05:23Over time, these sort of snowballed, like a snowball rolling downhill,
05:27picking up more and more and more material.
05:32Eventually, they formed gas giants like Jupiter and Saturn.
05:38But not all the debris in the disk turned into planets.
05:43Trillions of lumps of dirty ice were left behind.
05:47The comets.
05:49You could almost think of comets as sort of the frozen leftovers of the formation of the solar system.
05:55They're almost unchanged to this day.
05:59They're pristine time capsules, and if you could crack one open and see what was inside,
06:03you could literally see what the solar system was first made out of.
06:07That's remarkable.
06:10But the comets did not stay put.
06:12Several hundred million years later, the solar system plunged into turmoil once again.
06:20Encounters with debris pulled the gas giants out of position.
06:25The giants' immense gravity then hurled comets in every direction,
06:30flinging trillions of tons of material from the dawn of the solar system
06:35into the cold outer reaches of space.
06:40Some comets settled in a region 4,000 million miles from the sun,
06:46the Kuiper Belt.
06:49But most were tossed even farther out
06:52to form a giant sphere around the entire solar system.
06:59We call it the Oort Cloud.
07:03This is a region of our solar system that's farthest away from the sun.
07:07The sun is just a tiny little dot, one of many stars.
07:10And the whole area of space around you is virtually empty.
07:14There's nothing there, very little.
07:16And just occasionally you'll find the odd comet floating out there in deep freeze,
07:21cold, dark, and very much alone.
07:25In this remote ice cloud, there are more than a trillion comets.
07:30They can take millions of years to orbit the sun.
07:34But they don't always stay here.
07:37The orbit of every comet is a delicate gravitational balance.
07:42The smallest nudge can tip the scale.
07:46Most comets spend their entire lifespan in orbit.
07:51Most comets spend their entire lifespan billions of miles from the sun motionless, inert,
07:57simply waiting for something to happen.
08:00But then perhaps a random collision takes place.
08:03Perhaps a passing star nudges it.
08:06And then the gravitational force of the sun inevitably pulls it toward the inner solar system.
08:20Gravity, the force that created the comets,
08:24then flung them to the edge of the solar system,
08:27now pulls them back in.
08:32Our comet begins its epic odyssey to spread life, or death, across the solar system.
08:40NASA Jet Propulsion Laboratory, California Institute of Technology
08:49More than a trillion comets circle the sun at the frozen edges of our solar system.
08:56But many do not stay here.
08:59The smallest gravitational disruption can knock them out of their orbit.
09:04It could be a nearby star going by.
09:07It could be us going through a denser part of the galaxy.
09:10Anything that just gives a little gravitational hit to a comet can cause it to fall in towards us.
09:16Our comet has been disturbed.
09:19Now the sun's immense gravity takes over.
09:26You can think of the gravity of our solar system sort of like being a hillside.
09:30At the bottom there's the sun, and comets are way at the top of that hill.
09:34When they get dislodged, there's only one way for them to go.
09:37They have to fall down in towards the sun.
09:41Our comet accelerates towards the sun, but its path is far from straight.
09:48Gravity from the planets can throw comets off course, or out of the solar system completely.
09:56If they escape these obstacles, comets continue their journey toward the sun.
10:02Now they begin one of the most remarkable transformations known to science.
10:09A chrysalis to a butterfly. They become the most spectacular things the universe has to offer.
10:17As it passes Jupiter, our comet begins to change.
10:24As it starts to move a little bit faster, it starts getting closer and closer to the sun,
10:28and it starts feeling the heat of the sun.
10:31That's when things really start to change.
10:40500 million miles from the sun, heat brings our comet to life.
10:45Frozen gases start to vaporize.
10:48Grains of ice and dust rise from the surface.
10:53As the comet continues to approach the sun and gets warmer, more and more gas is released.
10:58The comet becomes a fuzzy ball.
11:00There's a solid part in there, but it's surrounded by a much larger sort of cloud of material.
11:07This cloud of dust and gas forms an atmosphere, or coma, around the comet.
11:14And it also creates the comet's huge tail.
11:22It's all driven by the sun, and it's not over yet.
11:27There's something called the solar wind.
11:29It's actually a huge wave of charged particles originating from the sun.
11:33This fills our solar system.
11:35And as a comet begins to move further and further in towards the sun, the solar wind gets stronger.
11:41Like a cosmic hurricane, the solar wind blasts gas molecules from our comet out into space.
11:50They form a second giant tail.
11:58The solid part of the comet might only be a few miles across,
12:02and the fuzzy part might be a few thousand or tens of thousands of miles across.
12:06The tail that gets swept back as that material is blown off by the solar wind
12:10can be millions or tens of millions of miles long.
12:15Our comet hurtles through space at 50,000 miles an hour.
12:21It's about to enter the most violent phase of its journey.
12:25200 million miles from the sun, water ice begins to vaporize.
12:31The ground would start to shift and quake, and as the material beneath my feet is literally thawing,
12:37we'd have great big jets of carbon dioxide and water ice starting to come out.
12:42And that would not be a very good place to be standing.
12:45The surface cracks open.
12:48Gases explode.
12:51Debris fires in all directions.
12:55The force of these eruptions makes the comet tumble erratically.
13:01Every jet that turns on is literally like a little jet engine attached to the comet.
13:07Like a dragster on a racetrack, our comet explodes to life.
13:22Incredible speed.
13:24Irresistible energy.
13:26And a vast plume of debris.
13:29Our comet transforms into a cosmic hot rod.
13:34But speed and energy are a volatile mix.
13:39Our comet could blow apart at any moment.
13:52The cloud around our comet is now bigger than Jupiter.
13:57Its tail stretches for 100 million miles.
14:04An object 4.5 billion years old emerges from the dark.
14:11Every arrival of a new comet is like a gift from the universe.
14:15We've never seen this little bit of the solar system before.
14:18This little building block, this little baby picture, it's completely new to us.
14:24It's a chance to study the origin of our solar system.
14:28And what we're learning is a revelation.
14:32Comets are far more hostile and alien than we imagined.
14:50With modern telescopes, we can study comets in more detail than ever before.
14:57But to really understand them, we need to get close to the very heart of a comet.
15:03Its nucleus.
15:06One of the holy grails of comet science is to really understand what is in a comet's nucleus.
15:12What is actually on the surface? What is the chemical composition?
15:15What are the characteristics of the rocks and the materials, the volatiles that are on that surface?
15:21The nucleus is the fundamental building block of the solar system
15:25that we as scientists really want to investigate.
15:28That's where the mysteries really are.
15:31There have been more than a dozen missions to comets in the past three decades.
15:36Every one of them has been a revelation.
15:40We've learned about the chemistry of them.
15:42We've learned about the physical interaction they have with the sun.
15:45We've learned about their physical surface, their terrain.
15:47And how they're different even if you were to go from one spot on a comet to another.
15:50So we're really learning that these things are worlds unto themselves.
15:57Scientists thought comets were white, like a snowball.
16:06That changed in 1986 when the JATO space probe beamed back these images of Halley.
16:13For the first time in history, we had a snapshot of the very center of that comet.
16:18That comet that entered human history on many occasions.
16:22And we found a cold, dead world.
16:24We found an object shaped like a peanut.
16:30Halley was no snowball.
16:32A thick layer of black dust.
16:34But Halley was still a comet.
16:37Halley was no snowball.
16:39A thick layer of black dust covered its surface.
16:44There were pits and hills.
16:46And Halley was nine miles long.
16:50Far bigger than anyone expected.
16:56Scientists thought that all comets were the same.
17:00They were wrong.
17:02They were wrong.
17:04In 2004, the Stardust probe flew into the tail of comet Vilt II.
17:12And captured thousands of tiny dust particles.
17:18When Stardust brought those samples back on Earth, we realized that in fact every comet is a unique object.
17:23Just like every planet is different, it looks like every comet is different.
17:26It has its own history to tell.
17:28Different materials went into its formation.
17:30Different heat sources were injected into its interior.
17:33Different chemical processes and geologic processes occurred.
17:36Each one is a unique world waiting to be explored.
17:42Some comets are truly strange.
17:49These are real images of Hartley II.
17:53A comet so weird, it snows.
17:59It's so strange.
18:00We were able to see that there are golf ball sized chunks of dry ice that are following the comet around.
18:05Up to a million miles away from the nucleus.
18:08This thing is just making a big mess.
18:10Hartley II is just amazing.
18:12It looked like you were in the middle of a snow globe.
18:14And you shook it up and there are all these little things.
18:17Kind of like flies buzzing around food.
18:20Just kind of floating out there.
18:22It's just not right.
18:25Hartley II is a hyperactive comet.
18:30It tumbles faster and spits out more debris than most others its size.
18:38Comets are alien worlds.
18:42On Comet Tempel 1, there are smooth plateaus.
18:49Craters and cliffs 60 feet high.
18:53Layers of rock lie on top of each other like a stack of pancakes.
19:00Each comet seems to have its own unique history.
19:07Tempel 1 gave scientists their biggest breakthrough.
19:12In 2005, the Deep Impact Space Probe slammed a projectile into its surface.
19:20The explosion dug out a crater 150 yards across.
19:25Talk about a spectacular Fourth of July.
19:27Can you imagine anything better?
19:29We actually blew a hole in a comet.
19:31That's got to be one of the more amazing things that NASA has ever done.
19:35The material the impact ejected allowed us to see inside a comet's nucleus for the first time.
19:42It was completely unexpected.
19:44We found things like rubies and peridot, gemstones.
19:47Tiny little things inside the comet.
19:50And we found all kinds of organic molecules.
19:53The very sorts of things we're made of.
19:58Scientists now believe that comets play a critical role in our universe.
20:06Where do the ingredients of life come from?
20:08Where were they all mixed together?
20:10Where did all this liquid water come from?
20:13Comets could hold a key to understanding the nature of life itself.
20:19But opportunities to study them up close are rare.
20:23Our comet is now moving at incredible speed toward a place where no spacecraft could ever survive.
20:32The sun.
20:43Four billion years ago, gravity hurled comets to the edges of our solar system.
20:51The same force can pull them back in.
20:56Our comet passes Earth and enters the most violent stage of its journey.
21:03It rockets toward the sun at 100,000 miles per hour.
21:09The surface of the comet is now sizzling.
21:13Sizzling with activity.
21:14Blistering temperatures are being created.
21:16Enormous geysers of ice crystals and gas being shot off the surface.
21:21Jets are erupting all over the place.
21:23It's tumbling.
21:24The rotational state is changing.
21:26And the very surface is kind of cracking up underneath our feet.
21:30Inside the comet, pockets of gas explode and fling huge rocks into space.
21:37It's losing mass.
21:38It's shrinking.
21:39And as we get closer and closer to the sun and more and more of the volatiles are starting to come off of its surface,
21:44this can actually change the rotational state of the comet.
21:46It can make it tumble.
21:47It can actually even push it in its orbit.
21:49It can actually change the orbit of the comet.
21:51Comets can shed 50 tons of ice and gas every second.
21:57Enormous pressures build up inside the nucleus.
22:01It could become unstable.
22:02It could even break apart into pieces at any time.
22:07As comets reach their closest point to the sun, their existence is on a knife edge.
22:14Many will not survive.
22:18We've been able to actually see images of comets just getting swallowed up by the sun.
22:22And you can actually see them just pelting in there.
22:24And the whole body, whether it's a mile across or 10 miles across, just gets completely and utterly destroyed.
22:32A solar observatory recorded these extraordinary images.
22:36They show small comets, called sun grazers, diving towards the sun.
22:46Here, they're exploding.
22:49Here, they're exposed to immense gravity and torched by the ferocious heat of the sun.
23:05Many are vaporized.
23:08Even in deep space, vast explosions can tear comets apart.
23:15In 2007, Comet Holmes was heading away from the sun when something extraordinary happened.
23:23In less than a day, it grew half a million times brighter.
23:28The cloud around it ballooned back into the sky.
23:31In less than a day, it grew half a million times brighter.
23:35The cloud around it ballooned into space.
23:39It's actually relatively common for a coma, the fuzzy part around a comet,
23:43to expand large enough to be bigger than Jupiter, 100,000 miles across.
23:48But that can take days and weeks and months to build up.
23:52To have a single event, something that happened, boom, all at once, some catastrophe,
23:56to create this shell around Comet Holmes that could be bigger than Jupiter is amazing to me.
24:03We had never seen something like this before.
24:05In fact, the coma of the comet was actually larger than the sun itself.
24:10Briefly, it was the largest object in the entire solar system, something that was unprecedented.
24:21Without warning, Comet Holmes blew apart.
24:26The largest cometary explosion ever recorded.
24:32The debris stretched for a million miles.
24:37What caused it is still unclear.
24:41One theory is that perhaps Comet Holmes slammed into an asteroid of some sort,
24:46creating this gigantic megaflare in outer space.
24:50Another possibility is perhaps the comet was unstable,
24:53and perhaps there was an explosion caused by expanding gas and ripped the entire comet apart.
24:59At the present time, we simply don't know.
25:04The life of all comets hangs by a thread.
25:10Our comet survives its encounter with the sun, but it's paid a price.
25:17Its geography has been totally rearranged.
25:20Huge chunks, mountaintops worth of rock, have disappeared.
25:25An object which could be perhaps 10, 20 miles across has lost literally hundreds,
25:30perhaps thousands of tons of rock and ice on its journey.
25:36As our comet leaves the sun behind, activity on its surface subsides.
25:43On its outward journey, a comet gradually begins to shut down.
25:46It becomes cooler, less active, the jets begin to turn off, the coma begins to blow away,
25:51and you're left with this little ball of ice and dirt.
25:56It returns to the depths of space, dormant once again.
26:06But the sun is just one of many challenges.
26:10Comets must also survive the gravitational pull of the planets.
26:17Our gravity is way too small to have any effect on this comet,
26:20but Jupiter is a very large planet.
26:24It has 300 times the mass of the Earth.
26:27If the comet passes within even a few million miles of Jupiter, that can change its orbit.
26:34The consequences can be catastrophic.
26:39In 1994, a comet called Shoemaker-Levy 9 flew too close to Jupiter.
26:47Scientists watched the planet's immense gravity tear it apart.
26:53The remains headed straight toward Jupiter.
26:57Many people thought that the impacts wouldn't do anything to Jupiter,
27:00that Jupiter would just sort of swallow it up without a burp.
27:03And that's not what happened at all.
27:0621 comet fragments smashed into Jupiter's atmosphere.
27:13Each impact released more energy than all the world's nuclear arsenals combined.
27:21Comet Shoemaker-Levy 9 was not a particularly massive comet.
27:24It wasn't even a very dense one.
27:26It actually had the consistency of cotton candy.
27:28You could have pulled bits of it apart with your fingers.
27:31But this rather tenuous little icy creature created unimaginable destruction.
27:37The impacts hurled plumes of debris thousands of miles high
27:43and scarred Jupiter's atmosphere with dark lesions.
27:49The event rocked the scientific community.
27:54To actually see it for ourselves, to actually see the immense destructive power
27:59by an object that's really not that much bigger than a hill,
28:03was really pretty terrifying.
28:05Even though we knew the math, to see it for ourselves was amazing.
28:08The Shoemaker-Levy 9 impact really woke astronomers up to the fact
28:12that impacts can happen now, and they can happen here.
28:17If a comet just a few miles across hit our planet,
28:22the result would be catastrophic.
28:25Tidal waves would devastate the land.
28:29Debris would rain from the sky.
28:34Life as we know it would end.
28:39Yet comet impacts can also be a creative force.
28:45They could even trigger the birth of life itself.
28:52NASA Jet Propulsion Laboratory, California Institute of Technology
29:12Across the universe, comets cause massive destruction.
29:18They could be moving 50 or more times faster than a rifle bullet.
29:23And we're talking about something the size of a mountain.
29:26So the amount of energy that this thing would release upon impact is devastating.
29:31But they're not always destructive.
29:34They have another side.
29:37Scientists believe they can shape entire worlds.
29:42Titan
29:44This is Titan, the largest of Saturn's moons.
29:48It's the only moon in our solar system with a thick atmosphere.
29:55Rivers and lakes of liquid methane cover its surface.
30:04Titan was transformed by comets.
30:08Radar images reveal a moon shaped by a blizzard of comets
30:12that rained down over millions of years.
30:18Each comet vaporized when it hit,
30:21releasing gases from inside its nucleus.
30:26Gradually, they built up a rich, organic atmosphere
30:30and this strange liquid landscape.
30:35Comets turned a space rock into an Earth-like world.
30:40Comets, in some sense, are the ultimate engineers of the solar system.
30:44Cometary impacts could give us the chemicals which give us the atmosphere,
30:48not just of Titan, but even perhaps the Earth itself.
30:54So if comets have the power to reshape entire worlds,
30:58what part did they play in the history of our own planet?
31:03To find out, we need to get closer to a comet than ever before.
31:10We need to land on one.
31:15In March 2004, the Rosetta Mission launched.
31:22The Rosetta Mission is named after the Rosetta Stone
31:26because, just like the stone gave linguists the keys to the ancient language,
31:32we're hoping that the comet will give us the keys
31:36to understanding the ancient solar system.
31:40November 11, 2014, will be a landmark in space exploration.
31:46For the very first time, a spacecraft will touch down on the surface of a comet.
31:57Previous missions to comets were basically flybys,
32:00and they basically gave us tantalizing evidence
32:03that there was a greater mystery yet to be solved.
32:06Now, we're going to land on a comet.
32:08We're going to be up close and dirty with a live comet streaming through outer space,
32:14and this is unprecedented.
32:20Rosetta is around the size of a car.
32:23It's flying through space at 20,000 miles per hour.
32:31It's heading for this.
32:35A comet with a nucleus three miles wide, orbiting the sun every six and a half years.
32:46A robotic lander will drop down to the surface,
32:50beginning the most detailed study of a comet ever attempted.
32:57It's going to look at what the surface looks like.
33:00It's going to take samples. It's going to look at the terrain.
33:02It's going to be able to actually probe inside the comet
33:05and see what it's made of and how it's put together.
33:08We're hopefully going to learn more from this mission about one comet
33:12than we have about just everything we've known about comets for centuries.
33:21Rosetta should answer some very simple questions.
33:28Is it porous? Is it like a sponge? Is it like a bunch of tubes?
33:34Is it like a snowflake, you know, with this sort of fairy castle structure?
33:41These things will help us to understand how the heat flows within
33:45and see what causes certain portions of it to become a jet and other portions not.
33:51But this is just the beginning.
33:54For an entire year, Rosetta will study the comet on its epic journey around the sun.
34:01Using technology so advanced, it mimics the five human senses.
34:08We've got instruments that can see.
34:12We've got a kind of an ultrasound experiment.
34:14We've got different instruments that are the equivalent of your hands.
34:17So we'd like to understand everything possible about this comet's journey around the sun
34:24from when it's quiet to when it's at its most active.
34:30But we'll have to get there first.
34:33Just to reach the comet, scientists must overcome enormous technical challenges.
34:40Rosetta must hit a target just three miles wide, traveling at 34,000 miles per hour.
34:50Landing on it will be even harder.
34:53Comets have very little gravity.
35:00There's not anything that you know is going to pull you down to the surface.
35:04And there's no atmosphere, so you can't unfurl a parachute
35:08and sail down until you touch down.
35:11You've got to figure out a way to get your lander to actually reside and rest on the surface.
35:23Technicians have an ingenious solution.
35:26The lander is equipped with shock absorbers and a harpoon.
35:32When it makes contact with the surface, at the same time,
35:35the harpoon will be released down into the substrate
35:39and it will have prongs that will open that will prevent it from coming back up.
35:49Rosetta will attempt to solve some of science's deepest mysteries.
35:56We would very much like to know why is it that Earth has liquid water
36:00and so much of it compared to any place else that we've ever seen.
36:03So, how is it that the water got here?
36:06Now, there is a theory that says that comets delivered the water to the Earth long ago.
36:10But the question is, can we actually prove it?
36:16To find out, the lander will collect water molecules to compare with water from Earth.
36:22But scientists hope to go even further.
36:26We're on the brink of making an extraordinary discovery.
36:31We may find proof that life itself has an extraterrestrial origin.
36:37That it was brought to Earth by comets.
36:41Life has existed on our planet for at least three and a half billion years.
36:48But we still don't understand its beginnings.
36:53We used to think life originated on Earth itself.
36:58That volcanic eruption was the beginning of life on Earth.
37:04We used to think life originated on Earth itself.
37:09That volcanic gases and water vapor formed oceans and an atmosphere.
37:15Lightning added the creative spark for early life to begin.
37:21Now, we think that's wrong and the evidence is in space.
37:27In 1997, comet Hale-Bopp appeared, one of the biggest and brightest comets ever recorded.
37:36Scientists found it was packed with water, gases, and carbon, the basic ingredients for life.
37:46That discovery raised profound questions.
37:50We're all used to the idea that life originated here on Earth.
37:53And it probably did, at least complex life.
37:55But where did the building blocks come from?
37:57Where did the water that makes up our body,
37:59the organic molecules that make up the very essence of life,
38:02they actually may not have been intrinsically part of the Earth to begin with.
38:06They came from somewhere else.
38:13Hale-Bopp suggested that the world was made up of water.
38:18Hale-Bopp suggested that the raw materials for life might have an extraterrestrial origin.
38:27Since then, scientists have found further evidence.
38:33Astrobiologist Dante Loretta discovered that dust from Comet Wild 2 contained minerals
38:40that could only form in heat and liquid water.
38:45We had the sulfide minerals, we had iron oxides, we had carbonate minerals,
38:49which are the same kind of materials that marine organisms use to build their shells,
38:53unlike anything we thought was possible to be formed in the early solar system.
38:59Scientists have even found that Comet Wild 2 contains amino acids.
39:07That's incredibly exciting because amino acids are the building blocks of proteins,
39:11and proteins are essential biomolecules for all life on Earth.
39:17These discoveries have transformed our understanding of comets.
39:25Many scientists now believe they're more than just frozen time capsules.
39:32Perhaps they play a central role in the history of our planet.
39:38We have learned from the study of a single comet and the results of the Stardust mission
39:42that they are complex chemical laboratories where the ingredients of life could form.
39:47These materials likely did not arise naturally on the surface of the Earth from processes on our planet.
39:53Instead, they had to be delivered by these messengers from the outer solar system.
39:58The idea that we may owe our existence to comet impacts is astounding.
40:04But not everyone is convinced.
40:08There's pretty good circumstantial evidence that a comet might have been important to life.
40:13But we don't really have, you know, if we're CSI, if we're the comet science investigators trying to prove it,
40:19we haven't got the proof lined up yet.
40:25It's quite possible that what we have out there has nothing to do with life as we know it on Earth.
40:35Scientists hope the Rosetta mission will resolve the issue.
40:42If we can establish a correlation between amino acids on comets and the amino acids we have on Earth,
40:49life on Earth, that would be one of the most significant findings in science.
40:57The story of life on Earth began four and a half billion years ago
41:03When our planet formed, it was a barren, hostile world.
41:08700 million years later, the solar system plunged into turmoil.
41:14Gravity ripped comets from their orbits and hurled them in all directions, many into the inner solar system.
41:24They rained down on the early Earth for 300 million years.
41:32They released gases and organic material, creating an atmosphere and the oceans.
41:41Finally, life could begin.
41:49It's a dramatic story.
41:52But is it true?
41:55Only time is going to tell, if we keep studying these mysterious objects,
41:58whether or not we can really pin down exactly the mechanisms and find out how it all got started.
42:02In a hundred years time, hopefully we'll look back and say,
42:05wouldn't it be cool to have been a living at that time, to be a witness,
42:10to be one of the first to make these incredible discoveries.
42:15In the meantime, the search for proof continues.
42:22I can't say for sure if comets brought all of these raw ingredients to the Earth
42:27and that we evolved from these materials, but it's certainly possible.
42:33And it's absolutely poetic to think that we came from out there.
42:57NASA Jet Propulsion Laboratory, California Institute of Technology