Comet of the Century: A Horizon Special Horizon

In the hills of Arizona,

one of America's most sophisticated telescopes

is preparing for a visitor

from the furthest reaches of the solar system.

It's moving along.

-The field is 12 arc minutes.

-Yeah.

So you can go 2 arc minutes or so, I think.

It's 4.6 billion years old

and started travelling towards our sun millions of years ago.

-The same amount again.

-One more time?

-Yeah.

-Go 75 arc seconds.

-OK.

This is Comet ISON.

It's no ordinary comet.

-This thing is moving so quick.

-Yeah.

In one week's time, millions of us should be able

to see it with our naked eye.

'A really bright comet like Comet ISON is extremely rare.'

It's extraordinarily exciting.

This is probably a once-in-a-lifetime experience.

A comet is one of the most spectacular sights in the night sky.

And Comet ISON could be the most STUNNING for a generation.

You should see a beautiful tail stretching upwards from the horizon

and millions of people will be able to see it.

Everybody should go out

and see it because you may never get that chance again.

ISON will be much more than just a celestial spectacle.

Comets are relics from the earliest days of the solar system,

so ISON could help us solve

some of the great scientific mysteries about where we come from.

It won't just tell us about comets.

It'll tell us about the entire evolution

and origin of the solar system.

THIS is the comet of the century.

It's September the 12th at the Discovery Telescope in Arizona.

In the next few minutes,

Comet ISON will be visible from Earth for the first time.

Dr Matthew Knight has been preparing for this moment all year.

For the past three months, ISON has been obscured by the sun.

Now the comet is about to emerge into view.

-Jason, what's the humidity doing?

-Coming up on 80%.

Are you ready for one more?

He is pinpointing its position...

Move has been issued.

..so that he can photograph it for the first time.

METALLIC CREAKING

-And... And stable. All right.

-That should have us in the right spot.

For the astronomers, the waiting is nearly over.

-COMPUTERISED VOICE:

-'Series complete.'

BEEPING

BEEPING

It's going to be out in about 10 seconds,

so...

There we go.

JASON CHUCKLES

So this looks fantastic.

It's there, it's bright, it just like we expected it to be.

There is a nice tail. I'm very excited to see it.

Every 30 seconds, a new image of the comet is taken.

When I was in grad school

thinking about comets like this,

I thought, "Sometime, hopefully in my lifetime, I'll get to see one."

And here, 5 years after I got my PhD,

I am the first professional astronomer

to image this at a professional telescope.

So it's very exciting.

Comets are one of the solar system's

most spectacular and unusual objects.

We like to think of comets as dirty snowballs.

They're balls of rock and ice.

And, by ice, I mean frozen gases.

So frozen water, frozen carbon dioxide.

And they come from the outer solar system, where it is very, very cold,

into the inner solar system, where it really heats up.

Seen from Earth, they display huge tails of dust and gas,

sometimes up to hundreds of millions of kilometres

in length, as their ices are melted by the heat of the sun.

The distance from Earth means that comets appear to be stationary

but, in fact, they can be travelling at speeds of over

1 million km/h.

As an astronomer, comets are really, really exciting because

they change a lot, they're unpredictable,

and you don't know what they'll do. There's a pretty high chance

of finding out something new and really cool, so it's quite

different from many other branches of astronomy where nothing changes

from this billion years to the next billion years.

Comets change literally from hour to hour.

Thousands of comets fly through our solar system every year.

Most we never see with the naked eye

and even with telescopes it's hard to learn anything about them.

But this one is special.

Comet ISON is 4.6 billion years old

and is heading on an extraordinary journey

which will take it through the sun's corona.

This is a rare class of comet called a sungrazer.

A sungrazer is a comet that comes very, very close to the sun,

much closer than normal comets.

It passes so close to the sun that it gets extremely hot

and also risks breaking up

due to the gravitational pull of the sun.

But nobody knows what's going to happen

after its close encounter with the sun.

Although it could be spectacular,

Dr Knight thinks there are three scenarios for ISON.

The first is based on what happened to another sungrazer -

Comet Lovejoy, seen here from the International Space Station.

So here we are seeing Comet Lovejoy in late 2011,

as it is going right behind the sun.

And when Comet Lovejoy got so close to the sun,

it was under incredible forces.

It was very hot, it was losing mass very rapidly and it was feeling

the gravitational pull of the sun.

And what happens there is that

the side of the comet that's closer to the sun

is being pulled more strongly than the side of the comet further away,

which caused it to stretch apart

and, probably a few hours or maybe a day or so after close approach,

it actually caused it to break up.

So could ISON disintegrate just as Comet Lovejoy did?

A key factor is its size.

We think from these Hubble images that it is probably about...

possibly as big as 2km in size, maybe 1km,

but it is on the edge of where I feel comfortable

predicting whether it will survive or not.

The second scenario is based on Comet Encke,

seen here in 2007 as it flies into the sun's corona.

It has already been through the inner solar system

about 70 times since it was first observed.

Comet Encke, which you can see here,

is a very old comet. It has been around the sun many times,

in the inner solar system, where it is very hot and it is therefore

running out of the ices and gases that drive its activity

because those things boil away.

As you can see here, it's starting to peter out and doesn't look quite like

you normally think of an active comet looking. It's fizzling out.

This is the moment when the tail is broken off

by a blast of solar particles.

We think that's a possibility

for what might happen for Comet ISON as well.

Although it took many orbits before Comet Encke burnt off all its gases

and started to fizzle out...

..the great heat of the sun could have the same effect on ISON

on its one and only passage.

But there is a 3rd scenario.

It's what happened to Comet Ikeya-Seki in 1965...

..the brightest comet in living memory.

Ikeya-Seki went very close to the sun, like ISON,

and it created this large tail that you can see here.

It was just a fantastic comet, spectacular.

People would go outside with their naked eye and they could see this

massive tail which stretched from the horizon all the way overhead.

This would be the perfect...the ideal scenario for Comet ISON.

We can only hope that Comet ISON will be as impressive as that.

However, even an experienced comet-watcher like Dr Knight

is just going to have to wait and see.

It's quite nerve-racking not knowing what's going to happen.

We can make our best guesses,

hope that we can predict what's going to happen,

but we really won't know until it actually gets close to the sun.

Whichever scenario turns out to be correct,

for scientists, the spectacle isn't the main point.

Comet ISON will provide an extraordinary opportunity

to study MORE than just the fate of these most mysterious bodies.

This is our solar system, seen from over 7 trillion km away.

From here, the sun and the planets look like a single point of light.

But the solar system extends much further out to a belt of comets -

the Oort Cloud.

And THIS is where ISON has come from.

Millions of years ago, ISON's orbit was disturbed.

The gravity from a neighbouring star in our galaxy

deflected it out of the Oort Cloud.

Since then, it's been travelling towards our sun.

Because ISON was formed at the beginning of the solar system

and has not changed since then,

it offers scientists a wonderful opportunity

to understand how our solar system formed.

Comet ISON is rather like excavating a dinosaur skeleton

from the birth of the solar system.

It's a fossilised, deep-frozen relic from that time

when the sun and the planets came together.

We know, however, that this is that first time into the sun

and it's never coming back,

so this is a once-in-a-lifetime opportunity.

We are going to get an insight into the past 4½ billion years

of our solar system - when it first formed.

We know that 5 billion years ago

the solar system was just a swirling mass of dust and gas.

And we know that 4.6 billion years ago the sun formed

at the centre of the nebula.

But the next stage in the origins of our solar system -

the formation of the planets - still holds many mysteries.

The first question is

how did the dust and gas of the solar nebula

coalesce to build the planets?

If we consider the universe, we think of stars and galaxies,

but hardly anybody thinks about dust particles.

For Professor Jurgen Blum,

the first stage in the formation of the planets

can be seen all around us.

This is my dusty basement, as you can see, and the dust here

acts in the same way as the dust in the young solar system.

When dust particles collide or stick to a wall, they really stick by

the very same forces as in the young solar system.

The forces are the same here on Earth and any place in the universe.

This is Europe's biggest drop tower -

a massive instrument for testing these forces.

Professor Blum's team is creating an experiment

to discover how these tiny particles of dust began to form into planets.

They fill a cylinder with a phial of dust and monitoring equipment,

which is hoisted up 120m to the top of the tower.

It's then released and plummets to Earth,

in the process, dramatically reducing the gravity inside

and creating conditions similar to those in space.

The drop takes mere seconds,

but high-speed cameras inside the cylinder record the dust responding.

In the near absence of gravity,

the tiny particles start to bond together.

Here we see two dust particles that collide at very low speeds

and then they stick together

by a force that we call the van der Waals' force,

and this is caused by a very weak bonding

between the atoms of the two particles.

The dust particles have negatively charged electrons surrounding them.

At their centre are positively charged protons.

Negative electrons from one particle of dust are attracted

to the positive protons of another and form a weak bond.

It's called the van der Waals' force.

This force holds dust particles together

when they collide in the emptiness of space.

But it's only strong enough to create bodies

1cm in diameter.

So the next question is, how did they grow beyond that size?

There are two theories.

The first is called the mass transfer theory.

According to this, dust particles crash together at great speed.

To test this they are moulded into a small pellet

to simulate the centimetre-sized body.

This is loaded into the top of another drop tower

where it is bombarded with tiny dust particles.

Here, a small dust particle is smashed into a large dust particle

at rather high speeds.

The velocities are indeed so high that the small particle

fragments into pieces that we can see here

and transfers part of its mass to the large particle.

And the large particle grows in mass by each subsequent collision.

And, according to this theory, the bodies can grow big enough

to become the seeds of the planets.

But there is another theory about how the planets grew

which is inspired by an activity close to Prof Blum's heart.

I cycle every day, I use my bike to go to work

and this gives me enough time to think about

the origin of the solar system.

Professor Blum thinks that the physical forces which operate

on riders in a cycle race are the same as those affecting

centimetre-sized bodies of dust in the early solar system.

He calls this the peloton theory.

'They feel the friction of the nebula gas,

'and the gas friction slows them down on their orbit.'

However, if they form groups just by chance,

like the peloton in a bicycle race,

only the front particles of the peloton face the gas friction,

so the back particles push the front particles

so that they catch up with individual dust particles on their way

and grow in mass until the combined gravity

is so strong that they form a single body.

The peloton theory is a much gentler way of forming a planet,

because the particles gradually coalesce to form bodies.

If planets formed this way, they should be less dense

than those formed by the multiple high-speed collisions

of the mass transfer theory.

ISON will be the ultimate test of which theory is correct,

because comets are formed in the same way as planets.

If ISON explodes after passing the sun,

it's a clear sign that it's bound together extremely weakly,

and that clearly supports the peloton theory.

So the fate of Comet ISON, as it circles the sun,

could answer the question of how the dust from the solar nebula

formed into planets.

Although the planets might have all started off in the same way,

there is one further mystery about the formation of the solar system.

Why are the planets so different?

In the inner solar system there are the smaller rocky planets...

..Mercury, with its huge temperature range...

..Venus, its volcanic surface hidden beneath swirling clouds...

..our own watery Earth...

..and Mars, with its striking red surface.

Although superficially different,

they are all basically made of the same stuff -

silicate rock and metals.

Further out, the planets are very different.

Jupiter - 2½ times the size

of all the other planets put together...

..Saturn with its rings...

..Uranus, surrounded in clouds of methane...

..and Neptune, with its wind speeds of 2,100 km/h.

These are the gas giants.

Although they have a core made of dust,

they are mostly made up of gas.

Dr David Walsh has been working on a theory to explain

where and why these two types of planets were created.

It's important to explain

the early history and evolution of the solar system.

The key of it was trying to understand

what temperature different things formed at in the solar system.

It's really critical.

According to this theory, the creation of the different

types of planet can be explained by the way temperature decreases

the further away you travel from the sun.

The smaller planets close to the sun can only have been built

in the inner solar system, where there was enough heat

to fuse together the metals from which they were made.

We think that in the early solar system history

there was kind of a natural temperature gradient,

where things much closer to the sun were much hotter.

So, naturally, in the inner part of the solar system

we build our rocky planets

made of materials that formed at higher temperatures,

and in the outer part we build something completely different.

Only further out in the solar system was it cold enough to condense

the gases which formed the gaseous giants around their solid cores.

When we look at the solar system

we see that probably the first planet to form

was the largest planet in our solar system, Jupiter.

Jupiter is a gas giant, and that tells us that

it must have formed in the distant solar system,

where the temperature was low enough for the gas to survive.

The temperature gradient across the early solar system

gives an explanation of how the different types of planets formed...

..and why the rocky planets are close to the sun...

..while the gas giants are further away.

But there is a problem with the theory.

It centres around the two furthest planets from the sun -

Uranus...

and Neptune.

Scientists have realised that the solar nebula

did not have enough dust to form these planets

where they are now orbiting.

Where they formed and how they formed

is a big mystery for scientists.

The temperatures of the gases and the solids that they accreted

when they were forming is really important to understanding

their entire history, when and where they formed.

Comet ISON could hold the key to the mystery of the formation

of these two planets, because scientists believe that ISON

originally formed in the same part of the solar system as Neptune.

According to the new theory, all the gas giants,

including Neptune and Uranus,

were formed much closer to the sun than they are today.

They were also much closer together.

What's more, millions of comets left over from the formation

of the solar system were orbiting near Neptune.

But then the orbits of Jupiter and Saturn

came so close together that they started to react against each other,

creating huge gravitational forces.

These pushed them both further away from the sun

and, in the process, also knocked Uranus and Neptune

further out into the solar system.

This great disturbance sent comets hurling all over the place.

We think that Comet ISON was kicked by one of these giant planets

to the furthest extent of the solar system,

which is the Oort Cloud.

And it's been sitting out there frozen, essentially,

for 4.5 or 4.6 billion years.

And the material that it was made of is essentially frozen in,

it's locked in and it hasn't really changed at all.

Then, millions of years ago, the gravity from a neighbouring star

shunted ISON out of the Oort Cloud

and it started heading back into the centre of the solar system.

Its arrival will provide a rare opportunity for scientists

to test their theory of how the solar system came together.

ISON originated next to Neptune.

Analysing its gases will tell them not only the temperature

at which the comet formed, but also that of the planet.

From this they can work out where Neptune was created.

So, when comet ISON comes close to the sun,

astronomers are going to look really closely

at the gas coming off its surface.

Hopefully, we'll see enough gas in enough detail

that we can really zoom in and look at the some

of the chemical signatures to some of these different gases.

Specifically, something like the nitrogen isotopes

will tell us a lot about the temperature at which the material,

the gases in ISON, formed at.

If the result shows it formed closer to the sun than Neptune is today,

then it will suggest that their theory is correct.

This is a really unique opportunity, a really powerful opportunity.

We could learn a lot about

the entire formation process of all our planets.

But every time we think we have something nailed,

every time we think we really understand something,

we get surprised, and we go back to the drawing board,

and that's what really, really fun about science.

So, maybe Comet ISON will be that thing

that sends us back to the drawing board.

We're just going to have to wait and see.

Comets like ISON may do more than provide evidence

of how the solar system formed.

Many scientists now believe that they may help answer

one of the biggest questions about Earth.

Where did all our water come from?

There are over a billion cubic km of water

on the surface of the Earth.

The amount hasn't changed for at least 3.8 billion years.

So, how did all this water arrive on the surface of our planet?

Dr Melissa Morris, from Arizona State University,

believes that the Comet ISON could help us find the answer.

The arrival of Comet ISON is so exciting

because scientifically it helps us settle questions that go to the very

nature of our origin and what brought life-sustaining water to our planet.

This is the Coso Volcanic Field in southern California,

where water vapour steams from below the surface of the Earth.

For many decades, scientists thought that this was how the Earth

got its water - released from rocks deep inside the planet.

It's called the accretion theory.

So the accretion theory is one theory to explain

the delivery of Earth's water.

And what that means is that the Earth was put together

from smaller rocky bodies that had high a water content,

and then the water came out from the interior of the Earth,

much like at this site here.

It then condensed out of the atmosphere

to form the Earth's oceans.

The theory suggests that when the early Earth formed,

it was covered in volcanoes, which belched out steam.

The water vapour cooled in the atmosphere and formed clouds.

These rained water down onto the Earth's surface

for thousands of years, the longest rainstorm in history.

But for some, this theory is flawed.

You might imagine that the water came from inside the Earth,

that it was trapped in the Earth when the Earth formed.

The trouble with that is that the Earth formed hot.

And hot materials are not that good at holding water.

So, in the lab, if you want to make something dry,

you stick it in the oven and it loses the water.

That means that perhaps the Earth formed dry

and water came from space, after the Earth had cooled down a bit.

This theory that the Earth's water was delivered from outer space

was controversial.

But evidence to support it can be seen in the night sky.

Our moon is covered in craters. Many were caused by comets

which crashed during the period when the changing orbits of

the gas giants sent comets all over the solar system.

Some scientists believe they also crashed into Earth,

bringing water with them.

Comets are made of roughly 50% water,

and so, after the Earth formed, during that period of heavy

bombardment, the comets brought the water along, impacted on the

surface of the Earth, and that the oceans came from cometary water.

It sounds far-fetched, but there is a way of proving whether comets

played a role in supplying the Earth's water.

There are two types of water that exist.

Most of the water we find on Earth is the sort we are familiar with.

But there is another kind,

with a slightly different atomic composition.

Well, it may surprise you to find that not all water is the same.

This is ordinary drinking water

and this is what we call heavy water,

and it contains deuterium, which is a form of hydrogen that contains

an extra proton, so it has a greater mass than the ordinary water.

So, to demonstrate the difference between ordinary water

and heavy water, we are going to do this simple experiment.

So, what I will do is pour this ordinary water,

which has 150 parts of deuterium per million

and has a density of 1g per cubic cm, into this beaker.

And then, I'm going to take an ordinary glass stopper,

and we are going to place it in this beaker full of ordinary water,

and we'll see what happens.

GLASS TINKLES

So, it sinks. The glass stopper sinks in ordinary water.

To see the difference, we are going to pour the heavy water

into this other beaker.

And heavy water has a higher percentage of deuterium,

so it has 320 parts per million...

..and a density of 1.15g per cubic cm.

And I'm going to do the same thing,

we are going to take an identical glass stopper

and we are going to place it in the heavy water and see what happens.

GLASS TINKLES Voila!

It floats in the heavy water, where it sinks in the ordinary water.

Heavy water doesn't occur naturally on Earth,

so if comets turned out to be made of heavy water, it would be

bad news for the theory that comets filled up the oceans.

What the scientists needed was to sample water from a comet

and find out whether it was heavy or ordinary water.

First stage ignition and take-off!

In 1986, the Giotto spacecraft was launched,

heading for the most famous comet of all, Halley's comet.

For the first time, a space probe could fly past a comet

and analyse the gases in its tail.

They found heavy water.

A few years later, a telescope on Earth examined the water gases

from another comet, Hyakutake.

It too had a tail full of heavy water.

Measurements of Comet Halley

and Comet Hyakutake suggest that comets contain more heavy water than

we see in the oceans, and the importance of that is pretty

straightforward, that means if you just melt a bunch of comets,

you get water which doesn't look like the oceans,

and therefore, the oceans cannot consist of melted comets.

It seemed that the theory of comets delivering the water for

Earth's oceans had received a serious setback.

But to be sure,

what scientists needed was more data from more comets.

So, NASA decided to send high altitude planes

into the Earth's stratosphere.

Their mission was to collect space dust there,

captured on adhesive panels attached to their wings.

The hope was that the dust had come from distant comets

and would contain molecules of water.

Professor Kevin McKeegan was one of the chief scientists on the mission.

Well, this is an electron microscope image of a dust particle

collected by NASA in the stratosphere of the Earth.

This particle came to Earth through interplanetary space,

and particularly this kind of dust particle,

with a lot of pore space and sort of a fairy castle structure,

may have been from a comet. You see all of these holes,

all of these pores in the particle here,

may have had in them

at one time water ice, or other ices, which are no longer there.

It was tantalisingly close.

But still, a sample of water from a comet eluded them.

Then, Professor McKeegan examined a second group of particles.

This is another dust particle collected from the stratosphere.

In this case, there is a lot of clay minerals,

so the water is trapped in the mineral layers, and the deuterium to

hydrogen ratio in the water that is trapped in those minerals is

similar to that, for example, in the ocean.

So, could this water from space, which was so like our own,

be the proof scientists needed that comets had brought it to Earth?

We've been studying these interplanetary dust particles,

we know that some of them have water,

some have structures which look like they could have had ices in them.

But frustratingly, this result wasn't quite what it seemed.

The problem, the fundamental problem is, we don't know where any one

dust particle that we collected in Earth's atmosphere comes from.

In the end, space dust could not provide definitive proof.

The scientists could not be certain where it came from.

-As descent sees it...

-Above Mars.

But then, in 2006, they made a breakthrough.

Well, that's cool.

The capsule returned to Earth from an epic journey through

-the solar system.

-Quite a trail. Near spec has a great view.

On board was the first ever dust actually

collected from the tail of a comet.

Wow, we got that, boys!

-MCKEEGAN:

-Personally, I have been studying dust

for some 25 years or so,

but comet dust had never been collected before,

because it is exceedingly difficult,

because comets come by the Earth at a very great speed.

This was the Stardust mission.

Its aim, to collect the dust on special gel attached to

the wings of a spacecraft.

Stardust was an extremely exciting event for us,

and the Stardust spacecraft flew through the dust tail

of Comet Wild 2, and the speed was 6km/second.

So, you're trying to collect something that is microscopic, that

you can't see, and it's going six times faster than a speeding bullet.

We have confirmation...

When the capsule finally landed,

scientists waited to see what it might reveal.

I was there when the sample canister was opened.

But of course, the dust is microscopic, so when you

first look at the collector, you don't necessarily see anything.

There was a little bit of unspoken nervousness, that uh-oh,

maybe we didn't collect anything, maybe it didn't open, or whatever.

But then, the dust was found and everybody was very excited,

there were high-fives and cheering and all of these kind of things.

And then, the real work gets to begin.

Now, actual particles of dust

which definitely came from a comet were examined.

The hope was that they would contain molecules of water within them.

Here is an image of an impact of an actual grain from Comet Wild 2,

this image is magnified 3,000 times.

And what you can see is that there is debris in the hole

and surrounding the hole, and those are bits of the comet.

After years of planning and waiting,

could they finally have the evidence they needed?

Unfortunately, because the dust was travelling so fast

when it hits the target, the dust is very badly damaged.

And one of the things is that the ices, water,

other volatile materials, are not preserved in the process.

Bringing a sample of a comet back to Earth was a technical triumph.

But it did not shed any light on the origins of Earth's water.

Finally, in 2010, there was a breakthrough.

It came from a telescope, out in space.

Newly-developed infrared scanners

on board the Herschel Space Observatory

analysed vaporised water gases from Comet Hartley 2.

So, then something very exciting happened.

The measurements came back

and it was much more similar to the signature of Earth's ocean water.

And so, that tells us

that at least one comet has a signature very similar to Earth,

and that we need to measure more comets to resolve that question.

The evidence from Hartley 2 suggested it was carrying

water like that on Earth.

So now, the data we have is contradictory.

When ISON tears through the sun's corona in a few days' time,

the evidence it provides could prove crucial.

So, if Comet ISON has a water signature that is similar to

Earth, just as Hartley 2 did, that is going to

change the balance of that argument and bring validity that

comets could very well have delivered water to our Earth.

Comets are central to the story of how the solar system formed.

But they are also helping us address one of the most intriguing

and profound questions humans have ever asked.

Are we alone in the universe?

At the heart of the mystery of the origins of life is how simple

chemical reactions between water, minerals

and air turned into living organisms.

So far, we have only been able to look at our Earth for evidence.

The creation of life requires a critical first step.

Chemicals have to combine in order to produce amino acids.

These are the most fundamental building blocks of life.

All life that we know of is based on these compounds.

We know these amino acids were created on Earth,

but could they also have formed in other environments,

across the universe?

Some scientists think comets could provide the answer.

One of the big questions in this field is,

can you make the building blocks of life in space,

despite the fact that the environment is quite hostile?

You have temperatures of extremely low, you have radiation

levels that are very high, you are in a vacuum, you have no air.

All of these things are the kind of things that you normally

would expect to stop chemistry, not promote chemistry.

Although they travel through the freezing vacuum of space,

comets contain all the necessary ingredients for amino acids.

But in these hostile conditions,

can the chemicals combine to form these building blocks of life?

Dr Sandford has built a comet in his lab to try and find out.

This is kind of our kitchen. It's where we mix our gases.

So if we want to simulate a comet,

we want to put in the molecules that we expect to be in comets

like water, methanol, ammonia, very simple molecules.

And this is a system we use to mix them all into one bulb

so that we can take this down to our machine,

where we'll simulate the kind of things

that may have played a role in getting life started.

Having created the chemicals that are thought to exist on a comet,

Dr Sandford must recreate the conditions in outer space.

OK, well, we are trying to simulate the surface of a comet

in the outer solar system, so we want a very low temperature.

Right now, this is running at about 15 degrees Kelvin,

which is minus 257 degrees centigrade.

This is probably five times colder than Siberia

in the middle of the winter.

He then replicates the effect of our sun on a comet

in the far reaches of our solar system

by firing a UV light onto the ices in the vacuum chamber.

We have a hydrogen lamp here which we use to simulate the radiation

that comes from the sun or other stars

and that's the radiation that goes in and hits our sample

and does the chemistry. So the photons from this lamp

come down over here and come into the sample chamber.

Now, a comet in the outer solar system

will only get a little bit of radiation at any given time

because it is far from the sun,

but since a comet is in orbit around the sun for over four billion years,

the radiation can build up

and you can actually get quite a large dose this way.

The extreme cold of outer space

and the radiation of the sun would seem to destroy any prospects

of creating even the building blocks of life in outer space.

But Dr Sandford has discovered

the radiation that reaches a comet seems to have an unexpected effect.

The radiation that's hitting the ice in our samples

breaks chemical bonds in these very simple compounds that are there,

and that allows them to rearrange into more complex molecules,

including a number of the amino acids,

some of the building blocks of life on Earth which are used to build,

for example, the proteins which play a large role in our biochemistry.

And we always see that we make these amino acids in our samples

and since our samples are made under an environment

attempting to simulate the kinds of environments that are out in space,

like in comets, we would anticipate

these amino acids being produced in space as well,

not just here on Earth.

Dr Sandford's work suggests that amino acids could form on comets.

But it's unlikely you can create life on them.

However, scientists think

there is a way in which comets could help create life on a planet.

Bizarrely, the destructive force of comets hitting a planet

could actually be the key to creating life.

On impact with a planet, a medium-sized comet would explode

with a force 15 times that of the entire nuclear arsenal on Earth.

At the University of Kent, scientists have created

an experiment to investigate what happens to the chemicals on a comet

when they are subjected to a massive impact.

Dr Mark Price is mixing the chemicals

most commonly found on comets

and freezing them to the low temperatures found in outer space.

But this simulated icy comet

has been placed at the end of a gun chamber.

And this tiny projectile is about to be fired at it

to mimic a collision between a planet and a comet.

So what I'm doing here

is loading the gun with a 1mm stainless steel projectile,

which will travel down the gun at a speed of approximately 18,000km/h,

which is approximately ten times faster than a normal gun.

This is the first time we've taken these compounds,

which give us a comet, and fired into it at very high speed.

During such an event, we get very high temperatures,

something of the order of 1,000 degrees centigrade,

and very high pressures, of the order of half a million atmospheres.

Two, one, go!

The gun produces a massive explosion

in the frozen chemicals held in the vacuum chamber.

OK, so, here is our comet in a lab.

We have just impacted this with a full projectile at 18,000km/h.

The residue from the explosion is analysed by Dr Zita Martins

at Imperial College in London, to find out what has happened to it.

Instead of being destroyed,

a remarkable transformation seems to have taken place.

So our results are extremely exciting

because we have proved experimentally

for the first time ever that

we can actually produce amino acids

when a comet impacts the surface of a planet.

Here you can see, actually,

one of the amino acids we produce,

also the tiny peaks are another amino acid,

so the amino acids are the building blocks of life.

It seems that the explosion creates the conditions

for a major reorganisation of the chemicals on a comet.

When the impact shock occurs,

the pressure and the temperature increases

and the bonds between the atoms of very simple molecules will break,

and there is reorganisation and formation of more complex molecules,

the building blocks of life, the amino acids.

It now seems likely that complex amino acids can form

both in the frozen wastelands of space on board icy comets,

and also when the comet crashes into a planet.

This suggests that the business of creating amino acids

could be happening all over the universe.

We know that impacts occur throughout our solar system

because we can see craters in planetary surfaces.

So our study shows that life may originate

not only here on Planet Earth but throughout our solar system

and probably in other parts of our universe.

So far, the search for amino acids on comets

has relied on creating artificial comets in the lab.

Now, scientists desperately need to sample a real comet,

to find out if it is home to amino acids.

That won't happen with ISON, as it was only discovered a year ago.

Six, cinq, quatre, trois...

But another comet has been lined up for just such a sampling mission.

In 2004, the European Space Agency launched the Rosetta spacecraft

with the aim of landing on the surface of a comet

and searching for amino acids in its nucleus.

It's the first ever spacecraft to attempt to do so.

So what we see here is a model of the spacecraft of Rosetta,

nearly identical to the one flying to the comet

and the main feature is the main antenna of the spacecraft

pointing towards Earth,

and you need a big antenna because the thing is far away,

in order to get your signals down to Earth.

What else you can see over there is this little tiny cone sticking out.

That's one of the little jet engines that turn the thing around.

There's about 12 of them,

so you can twist it, you can make it point the way you want it,

so that the thing you are interested in is in your field of view.

The spacecraft should reach the comet Churyumov-Gerasimenko

in November next year, after a 10-year journey.

The rendezvous will take place just as the comet passes Jupiter,

but the technical challenges are enormous.

If you want to investigate a comet,

you have to be fast in order to catch up with the comet.

Currently Rosetta is doing 3,600km/h more than the comet does.

That's about 1.5 times the maximum speed of the old Concorde.

But you can't do much in order to brake, so it's a very careful balance

between speeding up in order to get there

and not being too fast, otherwise you will crash into it or fly past.

The rendezvous is going to be the easy part of the mission.

Attached to the side of the spacecraft is the Philae lander,

which will descend onto the surface of the comet.

It's very challenging in terms of timing

and there is no possibility to make mistakes.

We have a limited period of time to approach the comet

and eventually land.

The first challenge we have in approaching the landing

is really to fly to an environment that is not known to us.

Of the comet we know almost nothing.

The major problem is that so little is known about the cometary nucleus,

the central, supposedly solid, body.

It could be either having a crust on the top,

so it could be like an eggshell with something soft underneath,

or the whole surface could be very, very soft.

The extreme case would be something like cigarette ash,

so the whole lander may fall into something very fluffy,

we simply don't know yet.

And the last thing you want is the thing to bounce off the surface

because then it would be lost to space.

So you need to do everything you can to stick to the cometary nucleus.

One idea is to make it kind of sticky, so that it doesn't jump off.

The second idea is ice screws in the feet that try to go into the surface

and there's also two harpoons

that are going to be fired into the cometary nucleus,

with the hope that with the ropes attached to these little harpoons,

the cometary lander, Philae, will stay where it is.

It's frightening, because so little is known about the parameters

you have to encounter.

For the engineers, that was pure horror.

If the Rosetta mission is successful, it will confirm

not only the presence of amino acids

but also whether they are any more developed

than the ones found in the laboratories.

So if we find complicated amino acids in the nucleus of a comet,

it would provide another building block in the story of biology.

Currently biology is Earth-centred,

because that's the only source of biology we know,

and it's the only example of biology we have.

But if we find the really, really complicated biomolecules,

it could point in the direction

that biology is a much more general phenomenon in the universe

and that other places that could harbour life would do so

in an almost inevitable way.

Personally I'd be amazed

if there isn't life on other planets out there.

It's quite possible that the vast majority would be very simple stuff,

kind of pond scum kind of things,

but we know from the history of our own planet

that some pond scum evolves,

so this could happen on other planets as well.

So the possibility there's other intelligent life out there

is certainly one well worth exploring.

From December 3rd, one of the greatest comets of our lifetime

could fly through our skies.

It won't just be scientists who will wonder at its glory.

If Comet ISON survives its solar passage,

then I'm hoping it's going to be

a glorious sight in the early morning skies,

the pre-dawn skies in early December.

Looking towards the east before sunrise,

you should see a beautiful tail stretching upwards from the horizon.

Millions of people will be able to see it, everybody should go out

and see it, because a truly great comet is a wonderful sight.

We never know when one is going to come around,

we never know when the next one's coming.

If you've got the chance, you should take it.

In the next few days, Comet ISON and its secrets will be revealed.

Subtitles by Red Bee Media Ltd