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.
These giant, dirty snowballs
slam into planets.
When a big comet hits a planet,
there are megaton-sized explosions in the atmosphere.
But they may also deliver life.
Comets can bring the seeds and the fertilizer of life
to spread across a planet.
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.
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.
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.
Comets aren't wandering icebergs.
They're fragile clumps of ice and rock.
And Shoemaker-Levy 9 had an even bigger surprise.
People realized that this string of comets
is going to actually hit Jupiter,
and so the world was prepared to watch this.
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.
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.
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.
Scientists launched a fleet of spacecraft
to find out more about these cosmic wanderers.
We have ignition and liftoff of a delta ii rocket
carrying deep impact.
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.
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.
Three, two, one, fire.
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.
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.
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.
While Joseph fine-tunes his harpoon,
NASA searches for a suitable target.
A successful rendezvous will depend
on predicting a comet's path.
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.
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.
But scientists can track comets
even when they are far from Earth.
Astronomer Peter Jenniskens searches for signs
in the night sky.
The sky is alive.
You really see the Earth move through space.
You really feel that we are part of the universe.
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.
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.
His software determines the direction
this dust falls to Earth and the path of the comet.
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.
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.
Could these frozen time capsules
reveal how life on Earth began?
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.
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.
Inside this metal can are the dust collection plates.
They're coated with a sticky oil to make particles stick to them.
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.
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.
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.
Zero, and liftoff of the stardust spacecraft
returning a time capsule with the elements
of the formation of our solar system.
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.
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.
Comets began life in the inner solar system,
not in the cold outer regions where we now find them.
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.
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.
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?
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.
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.
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.
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.
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.
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.
What we're finding is that
the chemical signature of this water
is different from that of the ocean's.
But telescopes have analyzed
the chemical signature of water in passing comets.
This may solve Lydia's puzzle.
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.
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?
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?
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.
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?
Scott mixes the gases
and recreates the environment of deep space.
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.
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.
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.
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.
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?
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.
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.
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?
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.
Mark's ocean is a bag of sterile water,
a liquid that contains no trace of life.
Right?
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.
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.
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.
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.
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.