Original subtitles

Narrator: Comets --

Mysterious visitors from the edge of our solar system.

A comet is a giant chunk of ice and rock the size of a mountain

That is hurtling through space at 300 miles per second.

Narrator: These giant, dirty snowballs

Slam into planets.

Plait: When a big comet hits a planet,

There are megaton-sized explosions in the atmosphere.

Narrator: But they may also deliver life.

Comets can bring the seeds and the fertilizer of life

To spread across a planet.

Narrator: Where do comets come from,

And what can we learn from landing spacecraft

On a distant comet?

To find out, we will strip comets apart.

We'll pull off their spectacular tails

And crack open their icy cores

To reveal the secrets locked inside.

♪

-- Captions by vitac -- www.Vitac.Com

Captions paid for by discovery communications

♪

Comets.

They appear without warning and blaze across the sky.

They seem very distant and very tiny,

But really, they're some of the most dramatic things

You could possibly look at.

They would appear out of nowhere.

They'd be huge.

They'd be bright, and they were omens to ancient people.

We've seen them as omens as war or good times, bad times.

Narrator: Now pioneering missions and experiments

Are revealing there is far more to comets than we thought.

♪

Comets travel in huge orbits around the sun,

Up to hundreds of thousands of miles per hour.

In their wake, they leave a tail millions of miles long.

♪

Pulling away this dusty trail reveals a glowing sphere

Of dust and gas.

Hidden deep inside

Tumbles the cold, rocky heart of the comet, the nucleus.

♪

Beneath its crust lies a glistening prize --

Rocks and ice frozen since the dawn of the solar system.

Understanding comets could unlock the secrets

Of our planet's evolution.

♪

For centuries, comets were astronomical curiosities,

Cosmic wanderers that orbit the sun

Until a truly cataclysmic event.

♪

Jupiter -- 1,000 times bigger than earth,

Its gravitational field reaches far into space.

♪

In 1993, astronomers watched as this giant planet

Captured a comet called shoemaker-levy 9.

Shoemaker-levy 9 was a comet that came close to jupiter

And broke apart,

And it formed what we call the string of pearls.

Narrator: As the comet fractured into 21 fragments,

Scientists gained new insights into these balls of ice.

When you say a comet is a big chunk of ice,

You might think about a big iceberg

Careening across the sky.

But, in fact, as shoemaker-levy

Fell into the gravity field of jupiter,

It was pulled apart very easily,

And the strength of it was more than, like, cotton candy.

Narrator: Comets aren't wandering icebergs.

They're fragile clumps of ice and rock.

And shoemaker-levy 9 had an even bigger surprise.

Sykes: People realized that this string of comets

Is going to actually hit jupiter,

And so the world was prepared to watch this.

♪

Narrator: The fragments of shoemaker-levy 9

Hurtled toward jupiter.

♪

Stripping the planet apart shows how they pierce the atmosphere

At over 100,000 miles per hour.

♪

The biggest chunks exploded with hundreds of times

More energy than earth's entire nuclear arsenal.

♪

The impacts left dark scars the size of earth.

It was spectacular.

So every time one of these cometary fragments

Struck the jupiter atmosphere, there was a huge explosion,

You know, like a multi-megaton explosion in the atmosphere.

Narrator: Shoemaker-levy 9 was a wake-up call.

When we first knew that comet shoemaker-levy

Was going to collide with jupiter,

We scientists thought we were looking at

A once-in-a-lifetime opportunity

To see an incredibly dramatic event, but that changed.

Now we understand that it happens far more often

Than we were aware of.

Narrator: Astronomers spotted evidence of massive impacts

Right across the solar system,

Causing damage on a planetary scale.

Shoemaker-levy really changed our idea

Of what living in our solar system is actually like.

Narrator: Scientists launched a fleet of spacecraft

To find out more about these cosmic wanderers.

Woman: We have ignition and liftoff of a delta ii rocket

Carrying deep impact.

Narrator: Nasa fired their deep impact probe into a comet,

Hoping to unlock its secrets...

...And the european space agency's rosetta mission

Steered a lander onto a comet's surface.

♪

On November 12, 2014,

The philae lander touched down on the surface of comet 67p.

This was the first-ever landing on a comet.

[ cheers and applause ]

♪

Missions to comets like rosetta have given us

Glimpses of the nucleus.

It's one of the darkest objects in the solar system.

A jet-black coating on its surface

Absorbs 98% of all light.

So far, no mission has ever brought back a sample

Of what lies beneath.

♪

The dark crust conceals

A cosmic time capsule of rocks and gas,

Untouched since the birth of our solar system.

♪

♪

Today's comet chasers are planning a mission

To pierce this time capsule.

Joseph nuth is developing a comet-penetrating harpoon.

He uses a giant crossbow to fire a missile into samples

That mimic a comet's nucleus.

We're testing the system to see exactly what can go wrong,

And we're pushing it to try to make things go wrong.

Man: Three, two, one, fire.

♪

Narrator: Joseph designs his missile

To bring a sample back to earth.

The tethers retract the system back up into the spacecraft.

The spacecraft flies away,

Eventually brings the sample home to us.

Narrator: But for the mission to succeed,

Joseph must pierce the crust surrounding the nucleus,

And he has no way of knowing how hard it is.

♪

A comet starts life with no tail and no crust.

As it approaches the sun,

The increasing heat vaporizes the ice on the surface,

Exposing a dark, powdery layer of dust.

♪

It forms a thin sheet covering the icy core of the comet.

♪

But with each orbit, the heat of the sun

Bakes the dust into a harder and harder crust.

When joseph's machine intercepts a comet,

He will have just one shot at piercing the crust.

So he tests his harpoon on a range of surfaces.

Nuth: This is like going into cement.

Okay. -List is at 900.

That sounds of tension.

Ready?

Three...

Two...

One.

Fire!

♪

We hit.

It barely penetrated.

It actually rolled over.

This is the kind of thing we want to avoid, and we will.

We'll just have to work on it a little more.

Narrator: While joseph fine-tunes his harpoon,

Nasa searches for a suitable target.

A successful rendezvous will depend

On predicting a comet's path.

♪

♪

Narrator: Comets are frozen enigmas.

Until recently, we've known little about

Their immense journeys through space...

...Because we could only see them

When they ventured close to our planet.

There's always a lot of fanfare

When a really large comet comes in towards earth,

And you can actually see it in the sky.

But, in fact, we live in an environment of comets.

There are many small comets that we never see from earth.

Narrator: When we do see comets from our planet,

It is because of their iconic tails,

And comets only produce these spectacles

When they are close to the sun.

♪

The source of a comet's tail is inside the nucleus.

As the comet approaches the sun, pockets of frozen gas heat up

And erupt in icy jets.

♪

They rip up to 3 tons of dust and gas

From the core every second.

♪

This forms a glittering tail,

Reflecting sunlight and making it glow white.

They have a long tail streaming off, which sometimes

Can be bright enough to see with the unaided eye.

And they circle around the sun, moving across the sky

Over the course of a few weeks or months.

And then they disappear into the dark,

And sometimes never to be seen again.

♪

Narrator: But scientists can track comets

Even when they are far from earth.

Astronomer peter jenniskens searches for signs

In the night sky.

Jenniskens: The sky is alive.

You really see the earth move through space.

You really feel that we are part of the universe.

Narrator: Peter uses cameras to pinpoint the glowing debris

Comets leave behind.

When a comet's orbit takes it close to the sun...

...Its dust tail leaves behind a stream of debris.

♪

Every time the comet returns, the tail leaves more dust.

When the earth passes through this gritty trail,

These dust particles burn up on the atmosphere,

Creating a meteor shower.

♪

Every morning, peter checks what his cameras have detected.

Jenniskens: At the beginning of the night,

You see these thick streaks, which are airplanes,

And here, the clouds are gradually fading,

And the stars are coming in view,

And all these short streaks are little bits of comet dust.

Narrator: His software determines the direction

This dust falls to earth and the path of the comet.

Jenniskens: That allows us to calculate the comet orbit.

If we know what the orbit of the comet is,

Then in principal, you could look along that comet orbit

And see a comet coming close to the earth

That could potentially hit us.

Narrator: Peter's team has mapped the orbits

Of nearly 4,000 comets just from their dust.

♪

But comets don't just trail dust.

They also produce a mysterious blue tail.

The power behind it is the sun.

Our star emits massive amounts of ultraviolet radiation...

...And it also ejects the solar wind,

A vast stream of electrons and protons

That shoot deep into space.

This combines with ultraviolet radiation

To form the comet's blue tail.

♪

When ultraviolet radiation hits the gassy sphere

Around the nucleus, it creates a bright blue plasma.

♪

Then the solar wind pushes this blue plasma

Out in a straight line,

Producing what scientists call the plasma tail.

♪

This makes comets even more spectacular

When they fly past earth.

But this blue tail is vulnerable.

The sun can make it and break it.

♪

Comet encke orbits the sun very tightly.

But in 2007, it hit trouble.

A massive solar storm blasted the comet...

♪

...And ripped off its plasma tail.

A nasa probe captured this extraordinary event,

The first proof that comets can lose their plasma tail.

♪

Encke never wanders far from the sun,

But other comets have orbits

That stretch to the very edge of the solar system.

These long-distance travelers hold clues

About one of the biggest mysteries in science.

When we see comets flying around,

They are the leftover remnants

Of the formation of our solar system.

Narrator: Could these frozen time capsules

Reveal how life on earth began?

♪

♪

Narrator: 4.6 billion years ago,

Our solar system was born.

The shock wave from a supernova forced cosmic dust

Into a gigantic rotating ring.

Most of this debris clumped together

To make the sun and the planets.

But how did the comets form?

♪

Today, comets orbit two main areas of our solar system.

The nearest comets come from a region

Just beyond neptune called the kuiper belt,

A huge ring of icy debris.

But 1,000 times farther out,

Almost a light-year away...

...Comets swarm together to form the oort cloud.

♪

It's a gigantic sphere, a cosmic snow globe

Teeming with an estimated 2 trillion icy dirt balls.

♪

Comets are at the very edge of our solar system

And go as far as, like,

A quarter of the way to our nearest star.

So they're way out there.

There are comets that are so far out, we will never see them.

Narrator: We now find comets across the solar system.

But where were they born?

Mike zolensky sends planes to the edge of space to find out.

♪

He attaches dust traps to a modified spy plane.

Zolensky: Inside this metal can are the dust collection plates.

They're coated with a sticky oil to make particles stick to them.

Narrator: The sticky collector deploys at 60,000 feet.

♪

But capturing comet dust so high in the atmosphere

Puts the flight crew at risk.

♪

At that altitude, the pressure is so low,

The blood boils at body temperature.

So the crew must wear a life-preserving pressure suit.

♪

♪

Each flight lasts up to 8 hours,

But even the most successful mission

Collects less than 100 tiny grains of comet dust.

Zolensky: We started collecting these particles in 1981.

The goal is to have the plane fly many times

So we have a large selection of comet grains to sample.

Narrator: Mike takes these samples

To an ultra-clean storage facility,

The cosmic dust laboratory,

The largest collection of comet debris on the planet.

♪

Here, mike and his team analyze the dust for clues

About where the comet was born.

Their collection includes dust that came from much farther away

Than earth's atmosphere.

Man: Zero, and liftoff of the stardust spacecraft

Returning a time capsule with the elements

Of the formation of our solar system.

Narrator: In 2000, nasa's stardust mission captured dust

From the tail of a comet, and 6 years later,

It brought these samples back to earth.

This tray was the capture tray for the spacecraft.

It's always scary to have the entire tray out

And in the lab at one time because you could destroy,

You know, a large amount of samples all at once.

This was a $220 million mission, which means each of these cells

Technically cost about $1 million.

Narrator: Scientists used to think that comets formed

In the icy outer reaches of the solar system,

Where we find them today.

But chemical analysis of this comet dust

Shattered this theory.

Really, you'd be surprised to find not only was that wrong,

It was really wrong.

We see minerals that consist entirely of titanium

And calcium, aluminum oxides.

Those must have formed at very high temperature,

Thousands of degrees c,

Obviously right up next to the sun.

Narrator: Comets began life in the inner solar system,

Not in the cold outer regions where we now find them.

Zolensky: That's why it's so exciting

To do this kind of mission, because you head off

In new directions you never thought of before.

Narrator: How did material that formed near the sun

End up trillions of miles away in the oort cloud?

♪

4.6 billion years ago,

Our solar system was a swirling cloud of dust and gas.

This fused together to forge giant planets like jupiter.

♪

Its gravity captured some of the remaining dust and rocks

And slung the rest out trillions of miles into outer space.

These rocks mixed with frozen gas and ice

To form the comets that we now find in the oort cloud.

♪

The reason the oort cloud is there

Is when the planets were forming,

The gravity kicked out lots of material very, very far away.

Some of it escaped the solar system entirely.

So when you see a comet coming back from the oort cloud,

In some cases, it's come from nearly a light-year

Or 2 light-years away.

It's had a very long journey to get to us.

Narrator: Comets are our long-distance travelers.

From the depths of the solar system,

They can tear towards the sun

At hundreds of thousands of miles an hour.

And sometimes, comets throw us a curveball.

♪

Just beyond the orbit of saturn,

Astronomers tracked a slow-moving rocky object

Over 100 miles across.

At first, they thought it was a new planet

Until the dead rock suddenly got brighter...

...And grew a tail.

It's both a planet and a comet.

Named chiron,

This was the first of a new breed of cosmic bodies --

Centaurs,

The biggest comets roaming our solar system.

The discovery of centaurs reminds us

That our understanding of comets is still evolving.

Scientists now think comets also hold clues

About our planet's remarkable appearance.

Could they be the reason water covers

So much of the earth's surface?

♪

♪

Narrator: Comets are far more than balls of ice.

They smash into planets, causing massive damage.

♪

Their dust ignites into dramatic meteor showers,

And they preserve fragments from the birth of the solar system,

But they also hold clues about our own planet's past.

♪

Today, water covers 70% of the earth's surface,

Making our home unique in the solar system.

Plait: If we were too much closer to the sun,

A lot of that water could have evaporated off.

We would have gotten a runaway greenhouse effect,

And the earth would be very hot, like venus.

And if we would have been farther out,

It would have been much cooler,

And we could have turned into mars.

But as it is, we're in just the right spot from the sun.

We're at the sweet spot

Where we can have liquid water on the surface

And keep it there for billions of years.

Narrator: But where did earth's oceans come from?

♪

Comets carry a hidden payload.

Under the dark, baked-on crust...

...They are crammed with dust and rocks.

But much of their core is frozen water.

Comets can carry hundreds of billions of gallons

Of this vital liquid.

♪

But did they bring water to earth's oceans?

To help solve this 4 1/2-billion-year-old mystery,

Scientists first need to find water created

During the violent birth of our planet.

♪

Geologist lydia hallis has special permission to hunt

For this ancient liquid on the volcanic island of staffa.

♪

We've got the columns of basalt that rise out of the ocean.

And inside this basalt, there's trapped water,

Hidden water in the rock.

Narrator: The rocks captured this water as our planet formed.

Some of it is still sealed inside.

This is just a piece of basalt

That's fallen from these cliffs up there.

Let's see if we can break it open.

Inside, there are tiny crystals that look sparkly,

And that's what we're interested in analyzing in the laboratory.

Narrator: Lydia examines the rock samples

Under a powerful electron microscope

To pinpoint the ancient water.

Here's the electron image of the basalt sample.

What I'm looking for in this sample

Are these darker regions in the image.

Narrator: Lydia extracts water from these areas

And checks its chemical signature,

A molecular label that reveals the water's origin.

If this water is the source of earth's oceans,

Their chemical signatures should match.

Hallis: What we're finding is that

The chemical signature of this water

Is different from that of the ocean's.

♪

Narrator: But telescopes have analyzed

The chemical signature of water in passing comets.

This may solve lydia's puzzle.

Hallis: If we mix the chemical signature

Of this water that was trapped when the earth was born

With a chemical signature of the water inside comets,

It matches that of the earth's oceans.

So comets must have made some contribution

To the earth's oceans.

♪

Narrator: Nearly 4 billion years ago

In a period called the late heavy bombardment...

...A barrage of comets hit our planet.

They exploded on the surface and released their watery cargo

In huge plumes of vapor.

♪

This created a layer of thunderclouds

That made it rain for millions of years.

♪

The water from the comets mixed with the water

Already on the earth,

And together,

They made the earth the blue planet it is today.

Recent findings bring this model into question,

But if comets did deliver water to the earth,

Could they have done the same thing elsewhere?

There's evidence on mercury.

Airless and sun-blasted, it's the last spot

In the solar system you'd expect to find water,

But some places at mercury's poles

Are forever locked in shadow.

Craters that could be comet impacts riddle these areas...

...And deep inside them, a layer of dark dust...

...Conceals hundreds of billions of tons of frozen water.

♪

Comets may be part

Of the universe's water delivery service.

But could they carry an even more precious cargo?

Did comets seed life on earth?

♪

♪

Narrator: Comets --

Dirty snowballs made from rock and ice.

When they collided with the ancient earth,

Comets may have helped form our oceans.

But could they have delivered something else to our planet?

Are comets also the bringers of life?

As far as we can tell, the early earth was mostly

A hot, dead rock, and yet here we are,

This wonderful, rich environment of life.

Well, where did that come from?

What actually brought the building blocks of life

To the earth?

Narrator: The answer lies hidden deep

Under a comet's glistening shroud.

♪

The comet's core contains a cosmic chemistry set...

...Frozen ammonia, methane, and carbon dioxide...

...Molecules that can combine to form amino acids,

The building blocks of life.

♪

But could amino acids really form on a comet

Hurtling through the cold vacuum of space?

♪

♪

Nasa scientists are trying to answer this question.

Scott sanford is building an artificial comet.

Sanford: On a comet, we would be taking very simple things,

Like water, methanol, carbon dioxide.

But we can mix them in the proportions

We think are actually in comets.

So one of the things we're obviously interested in knowing

Is amino acids, which we know are critical for life on earth,

Are these made under these conditions?

Narrator: Scott mixes the gases

And recreates the environment of deep space.

Sanford: Well, if we're gonna simulate a comet,

We want very low temperature and we want to be in a vacuum.

So that's what this device does for us,

And this device here is a cryocooler,

Which is cooling our samples down to a temperature

Right now of about 16 kelvin.

So that's minus 430 fahrenheit.

No one is allowed to put their tongue on this.

Narrator: Scott sprays the mixed gases

Onto a revolving piece of metal foil,

And then adds one final ingredient --

Ultraviolet radiation that mimics sunlight.

But this radiation provides energy

That triggers chemical reactions,

And these reactions could produce amino acids.

So here we have data taken from our experiments.

Each one of these peaks

Represents one or more compounds,

New chemicals we made in our experiment.

Amongst all the other things we made

In our cometary simulation, we made amino acids.

Narrator: This experiment shows that the building blocks of life

Can form in the extreme conditions of deep space...

...And comets are good at delivering payloads to earth.

♪

These impacts may have been a key stage

In the formation of life

By fusing amino acids together to form proteins.

These complex molecules can survive that collision.

And not only that,

Simple organic molecules can be cooked

Into even more complex molecules.

So comets can bring the seeds and the fertilizer of life

To spread across a planet.

Narrator: There are trillions of comets in our solar system.

If each of these had the ability to seed a planet,

Then maybe we're not alone.

If life here is somehow related to comets

Bringing these wonderful, rich organics here,

It very well may have happened

Elsewhere in the solar system as well.

Narrator: Comets might be seeding life

All over the cosmos.

♪

60 light-years away from the sun...

...Far beyond the kuiper belt and the oort cloud...

...Astronomers have spotted a huge band of comet dust

Wrapped around a younger star called eta corvi.

♪

The dust could be evidence that comets are raining down

On the planets orbiting this star.

♪

They might be seeding life on this alien world

At this very moment.

♪

But what if comets could spread

More than the building blocks of life across the cosmos?

What if they could also deliver living organisms?

♪

♪

Narrator: Life, as far as we know it,

Only exists in one place --

Earth.

But what if life came here from elsewhere?

What if comets brought organisms from outer space.

Oluseyi: One huge unanswered question that we have is,

How did life on earth originate?

And one idea is what we call panspermia,

And that is the idea that life came to earth

Via some space rock or a comet.

Narrator: According to panspermia,

Primitive organisms survive deep inside the comet's nucleus...

...With a dark crust and thick ice protecting them

From the harsh conditions of outer space,

But could these fragile life forms really survive

A massive collision with a planet?

♪

In England, scientists are about to find out.

It's an exciting question,

And if you don't study the exciting questions,

What are you doing?

Narrator: Mark burchell uses a giant gun

To simulate comet impacts.

He works with plankton,

A form of life that has existed for billions of years on earth.

So we're taking a solution of it

And loading it into our projectile

As if it were a comet which has been seeded with life.

We then place it in our gun,

Ready to fire at our ocean.

Narrator: Mark's ocean is a bag of sterile water,

A liquid that contains no trace of life.

Right?

Narrator: And this is no ordinary gun.

Compressed gas accelerates the projectile

To over 14,000 miles per hour.

♪

♪

That was the gun firing,

And now we hopefully have a successful shot.

Narrator: Could anything survive this immense collision?

The water is what we're interested in.

Mark cultures the water, and 3 days later,

The change is dramatic.

Life has more than survived.

It has flourished.

Most of what we fire will die,

But about 1 in 100,000 will survive.

And that doesn't sound a lot,

But that's all you need here on earth

To seed an ocean with life from space.

Narrator: Mark's research suggests that life could survive

The massive forces of a comet impact.

And it raises a vital question.

If life didn't begin on earth, where did it come from?

There's this wonderful push to try to find life

Outside the earth, to try to find alien life.

Well, the amazing thing is, maybe all you need to do

Is look in the mirror.

The building blocks of life did not start here.

They came from somewhere else.

So the aliens are us.

Narrator: Our understanding of comets

Has changed dramatically over the past 20 years.

♪

Comets wreak havoc when they collide with planets.

♪

But these impacts also bring ingredients

Vital to the formation of life.

Comets can bring life to a planet.

They can bring water to a planet.

But also, they can destroy life on a planet.

They were omens to ancient people.

They were omens of good and they were omens of bad.

And now, in modern science,

We're finding that this is absolutely correct.

Narrator: Comets are fleeting visitors from deep space...

♪

...Traveling time capsules from the dawn of the solar system.

Without comets, our world might be very different --

Earth may not be the blue planet we see today...

...And humans might not even exist.

♪