Comet of the Century: A Horizon Special Horizon


Comet of the Century: A Horizon Special

Similar Content

Browse content similar to Comet of the Century: A Horizon Special. Check below for episodes and series from the same categories and more!

Transcript


LineFromTo

In the hills of Arizona,

0:00:070:00:08

one of America's most sophisticated telescopes

0:00:080:00:11

is preparing for a visitor

0:00:110:00:14

from the furthest reaches of the solar system.

0:00:140:00:18

It's moving along.

0:00:180:00:19

-The field is 12 arc minutes.

-Yeah.

0:00:190:00:21

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

0:00:210:00:24

It's 4.6 billion years old

0:00:240:00:29

and started travelling towards our sun millions of years ago.

0:00:290:00:33

-The same amount again.

-One more time?

-Yeah.

-Go 75 arc seconds.

-OK.

0:00:330:00:36

This is Comet ISON.

0:00:360:00:40

It's no ordinary comet.

0:00:400:00:42

-This thing is moving so quick.

-Yeah.

0:00:420:00:45

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

0:00:450:00:48

to see it with our naked eye.

0:00:480:00:51

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

0:00:510:00:55

It's extraordinarily exciting.

0:00:550:00:56

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

0:00:560:01:00

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

0:01:030:01:06

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

0:01:060:01:11

You should see a beautiful tail stretching upwards from the horizon

0:01:130:01:17

and millions of people will be able to see it.

0:01:170:01:19

Everybody should go out

0:01:190:01:20

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

0:01:200:01:23

ISON will be much more than just a celestial spectacle.

0:01:250:01:28

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

0:01:290:01:34

so ISON could help us solve

0:01:340:01:36

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

0:01:360:01:40

It won't just tell us about comets.

0:01:410:01:43

It'll tell us about the entire evolution

0:01:430:01:45

and origin of the solar system.

0:01:450:01:47

THIS is the comet of the century.

0:01:490:01:51

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

0:02:050:02:09

In the next few minutes,

0:02:100:02:12

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

0:02:120:02:15

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

0:02:190:02:23

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

0:02:240:02:29

Now the comet is about to emerge into view.

0:02:290:02:33

-Jason, what's the humidity doing?

-Coming up on 80%.

0:02:380:02:40

Are you ready for one more?

0:02:400:02:42

He is pinpointing its position...

0:02:420:02:45

Move has been issued.

0:02:450:02:46

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

0:02:460:02:50

METALLIC CREAKING

0:02:510:02:54

-And... And stable. All right.

-That should have us in the right spot.

0:02:540:02:58

For the astronomers, the waiting is nearly over.

0:03:010:03:05

-COMPUTERISED VOICE:

-'Series complete.'

0:03:060:03:08

BEEPING

0:03:100:03:12

BEEPING

0:03:140:03:15

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

0:03:220:03:24

so...

0:03:240:03:25

There we go.

0:03:250:03:28

JASON CHUCKLES

0:03:310:03:33

So this looks fantastic.

0:03:330:03:35

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

0:03:350:03:38

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

0:03:380:03:41

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

0:03:410:03:45

When I was in grad school

0:03:500:03:51

thinking about comets like this,

0:03:510:03:53

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

0:03:530:03:56

And here, 5 years after I got my PhD,

0:03:560:03:58

I am the first professional astronomer

0:03:580:04:00

to image this at a professional telescope.

0:04:000:04:02

So it's very exciting.

0:04:020:04:03

Comets are one of the solar system's

0:04:150:04:17

most spectacular and unusual objects.

0:04:170:04:20

We like to think of comets as dirty snowballs.

0:04:310:04:34

They're balls of rock and ice.

0:04:340:04:36

And, by ice, I mean frozen gases.

0:04:360:04:38

So frozen water, frozen carbon dioxide.

0:04:380:04:40

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

0:04:400:04:43

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

0:04:430:04:46

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

0:04:470:04:53

sometimes up to hundreds of millions of kilometres

0:04:530:04:56

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

0:04:560:05:00

The distance from Earth means that comets appear to be stationary

0:05:020:05:06

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

0:05:060:05:09

1 million km/h.

0:05:090:05:11

As an astronomer, comets are really, really exciting because

0:05:160:05:19

they change a lot, they're unpredictable,

0:05:190:05:21

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

0:05:210:05:24

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

0:05:240:05:26

different from many other branches of astronomy where nothing changes

0:05:260:05:30

from this billion years to the next billion years.

0:05:300:05:32

Comets change literally from hour to hour.

0:05:320:05:35

Thousands of comets fly through our solar system every year.

0:05:400:05:44

Most we never see with the naked eye

0:05:440:05:47

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

0:05:470:05:50

But this one is special.

0:05:520:05:54

Comet ISON is 4.6 billion years old

0:05:570:06:02

and is heading on an extraordinary journey

0:06:020:06:05

which will take it through the sun's corona.

0:06:050:06:08

This is a rare class of comet called a sungrazer.

0:06:100:06:14

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

0:06:140:06:17

much closer than normal comets.

0:06:170:06:19

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

0:06:190:06:22

and also risks breaking up

0:06:220:06:24

due to the gravitational pull of the sun.

0:06:240:06:26

But nobody knows what's going to happen

0:06:270:06:29

after its close encounter with the sun.

0:06:290:06:32

Although it could be spectacular,

0:06:340:06:36

Dr Knight thinks there are three scenarios for ISON.

0:06:360:06:40

The first is based on what happened to another sungrazer -

0:06:430:06:46

Comet Lovejoy, seen here from the International Space Station.

0:06:460:06:51

So here we are seeing Comet Lovejoy in late 2011,

0:06:550:06:57

as it is going right behind the sun.

0:06:570:06:59

And when Comet Lovejoy got so close to the sun,

0:06:590:07:03

it was under incredible forces.

0:07:030:07:04

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

0:07:040:07:07

the gravitational pull of the sun.

0:07:070:07:09

And what happens there is that

0:07:090:07:11

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

0:07:110:07:13

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

0:07:130:07:16

which caused it to stretch apart

0:07:160:07:17

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

0:07:170:07:20

it actually caused it to break up.

0:07:200:07:22

So could ISON disintegrate just as Comet Lovejoy did?

0:07:250:07:29

A key factor is its size.

0:07:320:07:33

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

0:07:370:07:41

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

0:07:410:07:44

but it is on the edge of where I feel comfortable

0:07:440:07:46

predicting whether it will survive or not.

0:07:460:07:48

The second scenario is based on Comet Encke,

0:07:530:07:56

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

0:07:560:08:01

It has already been through the inner solar system

0:08:010:08:04

about 70 times since it was first observed.

0:08:040:08:07

Comet Encke, which you can see here,

0:08:120:08:13

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

0:08:130:08:16

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

0:08:160:08:19

running out of the ices and gases that drive its activity

0:08:190:08:21

because those things boil away.

0:08:210:08:24

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

0:08:240:08:27

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

0:08:270:08:30

This is the moment when the tail is broken off

0:08:320:08:35

by a blast of solar particles.

0:08:350:08:37

We think that's a possibility

0:08:390:08:40

for what might happen for Comet ISON as well.

0:08:400:08:42

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

0:08:450:08:49

and started to fizzle out...

0:08:490:08:51

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

0:08:540:08:58

on its one and only passage.

0:08:580:09:00

But there is a 3rd scenario.

0:09:030:09:06

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

0:09:080:09:12

..the brightest comet in living memory.

0:09:140:09:16

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

0:09:190:09:21

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

0:09:210:09:24

It was just a fantastic comet, spectacular.

0:09:240:09:27

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

0:09:270:09:30

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

0:09:300:09:33

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

0:09:330:09:36

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

0:09:360:09:39

However, even an experienced comet-watcher like Dr Knight

0:09:420:09:47

is just going to have to wait and see.

0:09:470:09:49

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

0:09:530:09:56

We can make our best guesses,

0:09:560:09:58

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

0:09:580:10:00

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

0:10:000:10:03

Whichever scenario turns out to be correct,

0:10:080:10:11

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

0:10:110:10:14

Comet ISON will provide an extraordinary opportunity

0:10:170:10:21

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

0:10:210:10:26

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

0:10:320:10:37

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

0:10:390:10:43

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

0:10:450:10:50

the Oort Cloud.

0:10:500:10:52

And THIS is where ISON has come from.

0:10:520:10:55

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

0:10:580:11:01

The gravity from a neighbouring star in our galaxy

0:11:020:11:05

deflected it out of the Oort Cloud.

0:11:050:11:08

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

0:11:100:11:13

Because ISON was formed at the beginning of the solar system

0:11:150:11:18

and has not changed since then,

0:11:180:11:21

it offers scientists a wonderful opportunity

0:11:210:11:23

to understand how our solar system formed.

0:11:230:11:27

Comet ISON is rather like excavating a dinosaur skeleton

0:11:270:11:31

from the birth of the solar system.

0:11:310:11:34

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

0:11:340:11:37

when the sun and the planets came together.

0:11:370:11:40

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

0:11:420:11:45

and it's never coming back,

0:11:450:11:47

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

0:11:470:11:50

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

0:11:500:11:53

of our solar system - when it first formed.

0:11:530:11:55

We know that 5 billion years ago

0:12:010:12:03

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

0:12:030:12:07

And we know that 4.6 billion years ago the sun formed

0:12:090:12:13

at the centre of the nebula.

0:12:130:12:15

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

0:12:170:12:20

the formation of the planets - still holds many mysteries.

0:12:200:12:24

The first question is

0:12:260:12:27

how did the dust and gas of the solar nebula

0:12:270:12:30

coalesce to build the planets?

0:12:300:12:32

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

0:12:460:12:49

but hardly anybody thinks about dust particles.

0:12:490:12:52

For Professor Jurgen Blum,

0:12:550:12:57

the first stage in the formation of the planets

0:12:570:13:00

can be seen all around us.

0:13:000:13:02

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

0:13:040:13:08

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

0:13:080:13:11

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

0:13:120:13:17

the very same forces as in the young solar system.

0:13:170:13:19

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

0:13:210:13:25

This is Europe's biggest drop tower -

0:13:310:13:35

a massive instrument for testing these forces.

0:13:350:13:38

Professor Blum's team is creating an experiment

0:13:400:13:44

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

0:13:440:13:49

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

0:13:520:13:57

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

0:13:570:14:02

It's then released and plummets to Earth,

0:14:090:14:14

in the process, dramatically reducing the gravity inside

0:14:140:14:18

and creating conditions similar to those in space.

0:14:180:14:21

The drop takes mere seconds,

0:14:390:14:42

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

0:14:420:14:47

In the near absence of gravity,

0:14:510:14:53

the tiny particles start to bond together.

0:14:530:14:57

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

0:15:000:15:04

and then they stick together

0:15:040:15:06

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

0:15:060:15:08

and this is caused by a very weak bonding

0:15:080:15:11

between the atoms of the two particles.

0:15:110:15:13

The dust particles have negatively charged electrons surrounding them.

0:15:140:15:18

At their centre are positively charged protons.

0:15:180:15:22

Negative electrons from one particle of dust are attracted

0:15:220:15:26

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

0:15:260:15:29

It's called the van der Waals' force.

0:15:290:15:33

This force holds dust particles together

0:15:340:15:37

when they collide in the emptiness of space.

0:15:370:15:40

But it's only strong enough to create bodies

0:15:400:15:43

1cm in diameter.

0:15:430:15:45

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

0:15:460:15:50

There are two theories.

0:15:520:15:55

The first is called the mass transfer theory.

0:15:550:15:59

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

0:16:000:16:05

To test this they are moulded into a small pellet

0:16:050:16:08

to simulate the centimetre-sized body.

0:16:080:16:11

This is loaded into the top of another drop tower

0:16:120:16:15

where it is bombarded with tiny dust particles.

0:16:150:16:18

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

0:16:250:16:29

at rather high speeds.

0:16:290:16:31

The velocities are indeed so high that the small particle

0:16:310:16:34

fragments into pieces that we can see here

0:16:340:16:36

and transfers part of its mass to the large particle.

0:16:360:16:40

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

0:16:450:16:49

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

0:16:530:16:57

to become the seeds of the planets.

0:16:570:17:00

But there is another theory about how the planets grew

0:17:150:17:18

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

0:17:180:17:22

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

0:17:240:17:27

and this gives me enough time to think about

0:17:270:17:29

the origin of the solar system.

0:17:290:17:31

Professor Blum thinks that the physical forces which operate

0:17:330:17:37

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

0:17:370:17:40

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

0:17:400:17:45

He calls this the peloton theory.

0:17:450:17:48

'They feel the friction of the nebula gas,

0:17:480:17:50

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

0:17:500:17:53

However, if they form groups just by chance,

0:17:580:18:01

like the peloton in a bicycle race,

0:18:010:18:04

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

0:18:040:18:08

so the back particles push the front particles

0:18:080:18:11

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

0:18:110:18:15

and grow in mass until the combined gravity

0:18:150:18:18

is so strong that they form a single body.

0:18:180:18:21

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

0:18:230:18:27

because the particles gradually coalesce to form bodies.

0:18:270:18:31

If planets formed this way, they should be less dense

0:18:310:18:34

than those formed by the multiple high-speed collisions

0:18:340:18:37

of the mass transfer theory.

0:18:370:18:39

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

0:18:430:18:48

because comets are formed in the same way as planets.

0:18:480:18:52

If ISON explodes after passing the sun,

0:18:540:18:57

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

0:18:570:19:01

and that clearly supports the peloton theory.

0:19:010:19:05

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

0:19:080:19:12

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

0:19:120:19:16

formed into planets.

0:19:160:19:19

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

0:19:300:19:33

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

0:19:330:19:38

Why are the planets so different?

0:19:390:19:42

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

0:19:450:19:49

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

0:19:510:19:55

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

0:19:580:20:03

..our own watery Earth...

0:20:050:20:07

..and Mars, with its striking red surface.

0:20:100:20:14

Although superficially different,

0:20:160:20:18

they are all basically made of the same stuff -

0:20:180:20:21

silicate rock and metals.

0:20:210:20:23

Further out, the planets are very different.

0:20:260:20:29

Jupiter - 2½ times the size

0:20:300:20:34

of all the other planets put together...

0:20:340:20:37

..Saturn with its rings...

0:20:390:20:41

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

0:20:460:20:49

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

0:20:520:20:58

These are the gas giants.

0:21:010:21:04

Although they have a core made of dust,

0:21:050:21:08

they are mostly made up of gas.

0:21:080:21:10

Dr David Walsh has been working on a theory to explain

0:21:130:21:17

where and why these two types of planets were created.

0:21:170:21:21

It's important to explain

0:21:230:21:24

the early history and evolution of the solar system.

0:21:240:21:28

The key of it was trying to understand

0:21:280:21:30

what temperature different things formed at in the solar system.

0:21:300:21:33

It's really critical.

0:21:330:21:34

According to this theory, the creation of the different

0:21:360:21:39

types of planet can be explained by the way temperature decreases

0:21:390:21:43

the further away you travel from the sun.

0:21:430:21:45

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

0:21:470:21:51

in the inner solar system, where there was enough heat

0:21:510:21:54

to fuse together the metals from which they were made.

0:21:540:21:57

We think that in the early solar system history

0:21:590:22:01

there was kind of a natural temperature gradient,

0:22:010:22:03

where things much closer to the sun were much hotter.

0:22:030:22:06

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

0:22:060:22:08

we build our rocky planets

0:22:080:22:10

made of materials that formed at higher temperatures,

0:22:100:22:12

and in the outer part we build something completely different.

0:22:120:22:15

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

0:22:190:22:22

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

0:22:220:22:28

When we look at the solar system

0:22:290:22:31

we see that probably the first planet to form

0:22:310:22:33

was the largest planet in our solar system, Jupiter.

0:22:330:22:36

Jupiter is a gas giant, and that tells us that

0:22:360:22:38

it must have formed in the distant solar system,

0:22:380:22:41

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

0:22:410:22:45

The temperature gradient across the early solar system

0:22:480:22:51

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

0:22:510:22:55

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

0:22:580:23:01

..while the gas giants are further away.

0:23:030:23:06

But there is a problem with the theory.

0:23:100:23:13

It centres around the two furthest planets from the sun -

0:23:130:23:16

Uranus...

0:23:160:23:18

and Neptune.

0:23:180:23:20

Scientists have realised that the solar nebula

0:23:210:23:24

did not have enough dust to form these planets

0:23:240:23:27

where they are now orbiting.

0:23:270:23:29

Where they formed and how they formed

0:23:310:23:33

is a big mystery for scientists.

0:23:330:23:34

The temperatures of the gases and the solids that they accreted

0:23:340:23:38

when they were forming is really important to understanding

0:23:380:23:41

their entire history, when and where they formed.

0:23:410:23:43

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

0:23:460:23:50

of these two planets, because scientists believe that ISON

0:23:500:23:54

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

0:23:540:23:59

According to the new theory, all the gas giants,

0:24:000:24:04

including Neptune and Uranus,

0:24:040:24:06

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

0:24:060:24:09

They were also much closer together.

0:24:110:24:15

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

0:24:150:24:19

of the solar system were orbiting near Neptune.

0:24:190:24:22

But then the orbits of Jupiter and Saturn

0:24:270:24:30

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

0:24:300:24:34

creating huge gravitational forces.

0:24:340:24:37

These pushed them both further away from the sun

0:24:400:24:45

and, in the process, also knocked Uranus and Neptune

0:24:450:24:48

further out into the solar system.

0:24:480:24:50

This great disturbance sent comets hurling all over the place.

0:24:560:25:00

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

0:25:050:25:08

to the furthest extent of the solar system,

0:25:080:25:10

which is the Oort Cloud.

0:25:100:25:12

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

0:25:150:25:19

for 4.5 or 4.6 billion years.

0:25:190:25:21

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

0:25:210:25:25

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

0:25:250:25:28

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

0:25:300:25:34

shunted ISON out of the Oort Cloud

0:25:340:25:37

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

0:25:370:25:40

Its arrival will provide a rare opportunity for scientists

0:25:420:25:46

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

0:25:460:25:50

ISON originated next to Neptune.

0:25:520:25:55

Analysing its gases will tell them not only the temperature

0:25:550:25:59

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

0:25:590:26:01

From this they can work out where Neptune was created.

0:26:030:26:07

So, when comet ISON comes close to the sun,

0:26:100:26:12

astronomers are going to look really closely

0:26:120:26:14

at the gas coming off its surface.

0:26:140:26:16

Hopefully, we'll see enough gas in enough detail

0:26:160:26:19

that we can really zoom in and look at the some

0:26:190:26:21

of the chemical signatures to some of these different gases.

0:26:210:26:24

Specifically, something like the nitrogen isotopes

0:26:240:26:27

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

0:26:270:26:31

the gases in ISON, formed at.

0:26:310:26:33

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

0:26:350:26:39

then it will suggest that their theory is correct.

0:26:390:26:43

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

0:26:450:26:48

We could learn a lot about

0:26:480:26:50

the entire formation process of all our planets.

0:26:500:26:52

But every time we think we have something nailed,

0:26:520:26:55

every time we think we really understand something,

0:26:550:26:58

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

0:26:580:27:00

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

0:27:000:27:03

So, maybe Comet ISON will be that thing

0:27:030:27:05

that sends us back to the drawing board.

0:27:050:27:07

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

0:27:070:27:09

Comets like ISON may do more than provide evidence

0:27:150:27:19

of how the solar system formed.

0:27:190:27:21

Many scientists now believe that they may help answer

0:27:230:27:26

one of the biggest questions about Earth.

0:27:260:27:29

Where did all our water come from?

0:27:320:27:35

There are over a billion cubic km of water

0:27:370:27:41

on the surface of the Earth.

0:27:410:27:43

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

0:27:430:27:48

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

0:27:510:27:55

Dr Melissa Morris, from Arizona State University,

0:28:070:28:11

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

0:28:110:28:14

The arrival of Comet ISON is so exciting

0:28:160:28:18

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

0:28:180:28:22

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

0:28:220:28:27

This is the Coso Volcanic Field in southern California,

0:28:310:28:35

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

0:28:350:28:40

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

0:28:420:28:45

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

0:28:450:28:49

It's called the accretion theory.

0:28:510:28:53

So the accretion theory is one theory to explain

0:28:540:28:57

the delivery of Earth's water.

0:28:570:28:58

And what that means is that the Earth was put together

0:28:580:29:01

from smaller rocky bodies that had high a water content,

0:29:010:29:05

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

0:29:050:29:08

much like at this site here.

0:29:080:29:09

It then condensed out of the atmosphere

0:29:090:29:12

to form the Earth's oceans.

0:29:120:29:14

The theory suggests that when the early Earth formed,

0:29:160:29:19

it was covered in volcanoes, which belched out steam.

0:29:190:29:23

The water vapour cooled in the atmosphere and formed clouds.

0:29:240:29:29

These rained water down onto the Earth's surface

0:29:290:29:32

for thousands of years, the longest rainstorm in history.

0:29:320:29:37

But for some, this theory is flawed.

0:29:380:29:42

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

0:29:420:29:45

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

0:29:450:29:48

The trouble with that is that the Earth formed hot.

0:29:480:29:51

And hot materials are not that good at holding water.

0:29:510:29:56

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

0:29:560:29:58

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

0:29:580:30:00

That means that perhaps the Earth formed dry

0:30:000:30:02

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

0:30:020:30:06

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

0:30:070:30:10

was controversial.

0:30:100:30:13

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

0:30:130:30:17

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

0:30:220:30:27

which crashed during the period when the changing orbits of

0:30:270:30:30

the gas giants sent comets all over the solar system.

0:30:300:30:34

Some scientists believe they also crashed into Earth,

0:30:380:30:42

bringing water with them.

0:30:420:30:44

Comets are made of roughly 50% water,

0:30:460:30:49

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

0:30:490:30:52

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

0:30:520:30:56

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

0:30:560:31:00

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

0:31:010:31:06

played a role in supplying the Earth's water.

0:31:060:31:09

There are two types of water that exist.

0:31:090:31:12

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

0:31:120:31:16

But there is another kind,

0:31:160:31:19

with a slightly different atomic composition.

0:31:190:31:23

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

0:31:230:31:27

This is ordinary drinking water

0:31:270:31:29

and this is what we call heavy water,

0:31:290:31:31

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

0:31:310:31:35

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

0:31:350:31:40

So, to demonstrate the difference between ordinary water

0:31:400:31:43

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

0:31:430:31:46

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

0:31:460:31:50

which has 150 parts of deuterium per million

0:31:500:31:53

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

0:31:530:31:58

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

0:31:580:32:02

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

0:32:020:32:05

and we'll see what happens.

0:32:050:32:06

GLASS TINKLES

0:32:070:32:08

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

0:32:100:32:15

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

0:32:150:32:18

into this other beaker.

0:32:180:32:20

And heavy water has a higher percentage of deuterium,

0:32:200:32:23

so it has 320 parts per million...

0:32:230:32:26

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

0:32:280:32:33

And I'm going to do the same thing,

0:32:340:32:36

we are going to take an identical glass stopper

0:32:360:32:40

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

0:32:400:32:44

GLASS TINKLES Voila!

0:32:450:32:48

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

0:32:480:32:53

Heavy water doesn't occur naturally on Earth,

0:32:530:32:56

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

0:32:560:33:00

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

0:33:000:33:04

What the scientists needed was to sample water from a comet

0:33:080:33:12

and find out whether it was heavy or ordinary water.

0:33:120:33:16

First stage ignition and take-off!

0:33:160:33:19

In 1986, the Giotto spacecraft was launched,

0:33:190:33:24

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

0:33:240:33:28

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

0:33:320:33:36

and analyse the gases in its tail.

0:33:360:33:39

They found heavy water.

0:33:430:33:45

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

0:33:480:33:52

from another comet, Hyakutake.

0:33:520:33:55

It too had a tail full of heavy water.

0:33:550:33:57

Measurements of Comet Halley

0:33:570:33:59

and Comet Hyakutake suggest that comets contain more heavy water than

0:33:590:34:04

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

0:34:040:34:08

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

0:34:080:34:10

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

0:34:100:34:13

and therefore, the oceans cannot consist of melted comets.

0:34:130:34:17

It seemed that the theory of comets delivering the water for

0:34:190:34:24

Earth's oceans had received a serious setback.

0:34:240:34:27

But to be sure,

0:34:270:34:28

what scientists needed was more data from more comets.

0:34:280:34:33

So, NASA decided to send high altitude planes

0:34:400:34:42

into the Earth's stratosphere.

0:34:420:34:45

Their mission was to collect space dust there,

0:34:480:34:51

captured on adhesive panels attached to their wings.

0:34:510:34:55

The hope was that the dust had come from distant comets

0:34:580:35:01

and would contain molecules of water.

0:35:010:35:05

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

0:35:110:35:15

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

0:35:190:35:22

collected by NASA in the stratosphere of the Earth.

0:35:220:35:25

This particle came to Earth through interplanetary space,

0:35:250:35:28

and particularly this kind of dust particle,

0:35:280:35:32

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

0:35:320:35:35

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

0:35:350:35:38

all of these pores in the particle here,

0:35:380:35:40

may have had in them

0:35:400:35:42

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

0:35:420:35:46

It was tantalisingly close.

0:35:480:35:50

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

0:35:500:35:55

Then, Professor McKeegan examined a second group of particles.

0:35:550:35:59

This is another dust particle collected from the stratosphere.

0:35:590:36:03

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

0:36:030:36:06

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

0:36:060:36:10

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

0:36:100:36:13

similar to that, for example, in the ocean.

0:36:130:36:17

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

0:36:190:36:23

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

0:36:230:36:28

We've been studying these interplanetary dust particles,

0:36:300:36:33

we know that some of them have water,

0:36:330:36:35

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

0:36:350:36:39

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

0:36:390:36:44

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

0:36:440:36:49

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

0:36:490:36:53

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

0:36:550:36:59

The scientists could not be certain where it came from.

0:36:590:37:03

-As descent sees it...

-Above Mars.

0:37:090:37:12

But then, in 2006, they made a breakthrough.

0:37:120:37:16

Well, that's cool.

0:37:160:37:19

The capsule returned to Earth from an epic journey through

0:37:190:37:23

-the solar system.

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

0:37:230:37:27

On board was the first ever dust actually

0:37:270:37:30

collected from the tail of a comet.

0:37:300:37:32

Wow, we got that, boys!

0:37:340:37:35

-MCKEEGAN:

-Personally, I have been studying dust

0:37:380:37:40

for some 25 years or so,

0:37:400:37:41

but comet dust had never been collected before,

0:37:410:37:45

because it is exceedingly difficult,

0:37:450:37:47

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

0:37:470:37:49

This was the Stardust mission.

0:37:510:37:54

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

0:37:540:37:58

the wings of a spacecraft.

0:37:580:38:00

Stardust was an extremely exciting event for us,

0:38:040:38:08

and the Stardust spacecraft flew through the dust tail

0:38:080:38:12

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

0:38:120:38:15

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

0:38:150:38:19

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

0:38:190:38:22

We have confirmation...

0:38:220:38:24

When the capsule finally landed,

0:38:240:38:27

scientists waited to see what it might reveal.

0:38:270:38:30

I was there when the sample canister was opened.

0:38:330:38:36

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

0:38:360:38:39

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

0:38:390:38:43

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

0:38:430:38:46

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

0:38:460:38:50

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

0:38:500:38:54

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

0:38:540:38:57

And then, the real work gets to begin.

0:38:570:38:59

Now, actual particles of dust

0:39:010:39:04

which definitely came from a comet were examined.

0:39:040:39:07

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

0:39:090:39:14

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

0:39:170:39:22

this image is magnified 3,000 times.

0:39:220:39:24

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

0:39:240:39:28

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

0:39:280:39:32

After years of planning and waiting,

0:39:320:39:35

could they finally have the evidence they needed?

0:39:350:39:38

Unfortunately, because the dust was travelling so fast

0:39:400:39:43

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

0:39:430:39:46

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

0:39:460:39:50

other volatile materials, are not preserved in the process.

0:39:500:39:55

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

0:39:560:40:01

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

0:40:010:40:05

Finally, in 2010, there was a breakthrough.

0:40:090:40:13

It came from a telescope, out in space.

0:40:130:40:17

Newly-developed infrared scanners

0:40:200:40:22

on board the Herschel Space Observatory

0:40:220:40:25

analysed vaporised water gases from Comet Hartley 2.

0:40:250:40:30

So, then something very exciting happened.

0:40:320:40:34

The measurements came back

0:40:340:40:36

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

0:40:360:40:40

And so, that tells us

0:40:400:40:42

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

0:40:420:40:45

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

0:40:450:40:49

The evidence from Hartley 2 suggested it was carrying

0:40:510:40:55

water like that on Earth.

0:40:550:40:56

So now, the data we have is contradictory.

0:40:580:41:00

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

0:41:040:41:08

the evidence it provides could prove crucial.

0:41:080:41:12

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

0:41:130:41:16

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

0:41:160:41:19

change the balance of that argument and bring validity that

0:41:190:41:23

comets could very well have delivered water to our Earth.

0:41:230:41:26

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

0:41:320:41:36

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

0:41:380:41:43

and profound questions humans have ever asked.

0:41:430:41:46

Are we alone in the universe?

0:41:460:41:49

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

0:41:580:42:02

chemical reactions between water, minerals

0:42:020:42:05

and air turned into living organisms.

0:42:050:42:08

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

0:42:090:42:15

The creation of life requires a critical first step.

0:42:190:42:24

Chemicals have to combine in order to produce amino acids.

0:42:240:42:29

These are the most fundamental building blocks of life.

0:42:290:42:34

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

0:42:340:42:38

We know these amino acids were created on Earth,

0:42:380:42:41

but could they also have formed in other environments,

0:42:410:42:45

across the universe?

0:42:450:42:46

Some scientists think comets could provide the answer.

0:42:590:43:04

One of the big questions in this field is,

0:43:110:43:13

can you make the building blocks of life in space,

0:43:130:43:15

despite the fact that the environment is quite hostile?

0:43:150:43:18

You have temperatures of extremely low, you have radiation

0:43:180:43:21

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

0:43:210:43:25

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

0:43:250:43:28

would expect to stop chemistry, not promote chemistry.

0:43:280:43:31

Although they travel through the freezing vacuum of space,

0:43:320:43:36

comets contain all the necessary ingredients for amino acids.

0:43:360:43:41

But in these hostile conditions,

0:43:410:43:43

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

0:43:430:43:47

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

0:43:550:43:59

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

0:44:030:44:06

So if we want to simulate a comet,

0:44:060:44:07

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

0:44:070:44:10

like water, methanol, ammonia, very simple molecules.

0:44:100:44:14

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

0:44:140:44:16

so that we can take this down to our machine,

0:44:160:44:19

where we'll simulate the kind of things

0:44:190:44:21

that may have played a role in getting life started.

0:44:210:44:23

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

0:44:280:44:32

Dr Sandford must recreate the conditions in outer space.

0:44:320:44:37

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

0:44:370:44:39

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

0:44:390:44:42

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

0:44:420:44:45

which is minus 257 degrees centigrade.

0:44:450:44:48

This is probably five times colder than Siberia

0:44:480:44:51

in the middle of the winter.

0:44:510:44:52

He then replicates the effect of our sun on a comet

0:44:530:44:57

in the far reaches of our solar system

0:44:570:45:00

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

0:45:000:45:05

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

0:45:070:45:10

that comes from the sun or other stars

0:45:100:45:12

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

0:45:120:45:14

and does the chemistry. So the photons from this lamp

0:45:140:45:17

come down over here and come into the sample chamber.

0:45:170:45:21

Now, a comet in the outer solar system

0:45:210:45:23

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

0:45:230:45:26

because it is far from the sun,

0:45:260:45:27

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

0:45:270:45:31

the radiation can build up

0:45:310:45:32

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

0:45:320:45:35

The extreme cold of outer space

0:45:350:45:38

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

0:45:380:45:42

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

0:45:420:45:46

But Dr Sandford has discovered

0:45:470:45:49

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

0:45:490:45:54

The radiation that's hitting the ice in our samples

0:45:560:45:59

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

0:45:590:46:02

and that allows them to rearrange into more complex molecules,

0:46:020:46:06

including a number of the amino acids,

0:46:060:46:08

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

0:46:080:46:11

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

0:46:110:46:15

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

0:46:150:46:19

and since our samples are made under an environment

0:46:190:46:21

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

0:46:210:46:25

like in comets, we would anticipate

0:46:250:46:27

these amino acids being produced in space as well,

0:46:270:46:29

not just here on Earth.

0:46:290:46:31

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

0:46:360:46:41

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

0:46:430:46:46

However, scientists think

0:46:480:46:50

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

0:46:500:46:54

Bizarrely, the destructive force of comets hitting a planet

0:46:580:47:03

could actually be the key to creating life.

0:47:030:47:05

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

0:47:100:47:15

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

0:47:150:47:20

At the University of Kent, scientists have created

0:47:270:47:30

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

0:47:300:47:34

when they are subjected to a massive impact.

0:47:340:47:37

Dr Mark Price is mixing the chemicals

0:47:400:47:43

most commonly found on comets

0:47:430:47:45

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

0:47:450:47:49

But this simulated icy comet

0:47:510:47:53

has been placed at the end of a gun chamber.

0:47:530:47:56

And this tiny projectile is about to be fired at it

0:47:570:48:01

to mimic a collision between a planet and a comet.

0:48:010:48:05

So what I'm doing here

0:48:070:48:08

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

0:48:080:48:13

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

0:48:130:48:17

which is approximately ten times faster than a normal gun.

0:48:170:48:21

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

0:48:240:48:26

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

0:48:260:48:30

During such an event, we get very high temperatures,

0:48:300:48:32

something of the order of 1,000 degrees centigrade,

0:48:320:48:35

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

0:48:350:48:39

Two, one, go!

0:48:430:48:45

The gun produces a massive explosion

0:48:510:48:54

in the frozen chemicals held in the vacuum chamber.

0:48:540:48:56

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

0:49:050:49:08

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

0:49:080:49:12

The residue from the explosion is analysed by Dr Zita Martins

0:49:150:49:19

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

0:49:190:49:23

Instead of being destroyed,

0:49:240:49:27

a remarkable transformation seems to have taken place.

0:49:270:49:30

So our results are extremely exciting

0:49:330:49:35

because we have proved experimentally

0:49:350:49:37

for the first time ever that

0:49:370:49:39

we can actually produce amino acids

0:49:390:49:42

when a comet impacts the surface of a planet.

0:49:420:49:45

Here you can see, actually,

0:49:450:49:47

one of the amino acids we produce,

0:49:470:49:49

also the tiny peaks are another amino acid,

0:49:490:49:52

so the amino acids are the building blocks of life.

0:49:520:49:55

It seems that the explosion creates the conditions

0:49:580:50:02

for a major reorganisation of the chemicals on a comet.

0:50:020:50:06

When the impact shock occurs,

0:50:080:50:10

the pressure and the temperature increases

0:50:100:50:13

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

0:50:130:50:17

and there is reorganisation and formation of more complex molecules,

0:50:170:50:22

the building blocks of life, the amino acids.

0:50:220:50:25

It now seems likely that complex amino acids can form

0:50:290:50:32

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

0:50:320:50:36

and also when the comet crashes into a planet.

0:50:360:50:40

This suggests that the business of creating amino acids

0:50:460:50:50

could be happening all over the universe.

0:50:500:50:53

We know that impacts occur throughout our solar system

0:50:570:51:01

because we can see craters in planetary surfaces.

0:51:010:51:04

So our study shows that life may originate

0:51:050:51:08

not only here on Planet Earth but throughout our solar system

0:51:080:51:11

and probably in other parts of our universe.

0:51:110:51:14

So far, the search for amino acids on comets

0:51:210:51:25

has relied on creating artificial comets in the lab.

0:51:250:51:28

Now, scientists desperately need to sample a real comet,

0:51:290:51:33

to find out if it is home to amino acids.

0:51:330:51:36

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

0:51:400:51:44

Six, cinq, quatre, trois...

0:51:470:51:50

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

0:51:500:51:54

In 2004, the European Space Agency launched the Rosetta spacecraft

0:52:030:52:09

with the aim of landing on the surface of a comet

0:52:090:52:11

and searching for amino acids in its nucleus.

0:52:110:52:14

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

0:52:170:52:22

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

0:52:270:52:31

nearly identical to the one flying to the comet

0:52:310:52:34

and the main feature is the main antenna of the spacecraft

0:52:340:52:37

pointing towards Earth,

0:52:370:52:39

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

0:52:390:52:42

in order to get your signals down to Earth.

0:52:420:52:44

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

0:52:440:52:48

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

0:52:480:52:52

There's about 12 of them,

0:52:520:52:53

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

0:52:530:52:57

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

0:52:570:53:01

The spacecraft should reach the comet Churyumov-Gerasimenko

0:53:040:53:08

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

0:53:080:53:12

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

0:53:130:53:18

but the technical challenges are enormous.

0:53:180:53:21

If you want to investigate a comet,

0:53:210:53:24

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

0:53:240:53:26

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

0:53:260:53:32

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

0:53:320:53:36

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

0:53:360:53:40

between speeding up in order to get there

0:53:400:53:43

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

0:53:430:53:47

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

0:53:490:53:53

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

0:53:530:53:57

which will descend onto the surface of the comet.

0:53:570:54:00

It's very challenging in terms of timing

0:54:020:54:04

and there is no possibility to make mistakes.

0:54:040:54:07

We have a limited period of time to approach the comet

0:54:070:54:09

and eventually land.

0:54:090:54:11

The first challenge we have in approaching the landing

0:54:110:54:13

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

0:54:130:54:17

Of the comet we know almost nothing.

0:54:170:54:19

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

0:54:210:54:25

the central, supposedly solid, body.

0:54:250:54:28

It could be either having a crust on the top,

0:54:280:54:32

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

0:54:320:54:35

or the whole surface could be very, very soft.

0:54:350:54:37

The extreme case would be something like cigarette ash,

0:54:370:54:40

so the whole lander may fall into something very fluffy,

0:54:400:54:44

we simply don't know yet.

0:54:440:54:45

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

0:54:450:54:48

because then it would be lost to space.

0:54:480:54:50

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

0:54:500:54:54

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

0:54:540:54:58

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

0:54:580:55:03

and there's also two harpoons

0:55:030:55:05

that are going to be fired into the cometary nucleus,

0:55:050:55:08

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

0:55:080:55:12

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

0:55:120:55:16

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

0:55:160:55:20

you have to encounter.

0:55:200:55:21

For the engineers, that was pure horror.

0:55:210:55:24

If the Rosetta mission is successful, it will confirm

0:55:260:55:29

not only the presence of amino acids

0:55:290:55:32

but also whether they are any more developed

0:55:320:55:35

than the ones found in the laboratories.

0:55:350:55:38

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

0:55:400:55:44

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

0:55:440:55:49

Currently biology is Earth-centred,

0:55:490:55:51

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

0:55:510:55:53

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

0:55:530:55:57

But if we find the really, really complicated biomolecules,

0:55:570:56:01

it could point in the direction

0:56:010:56:04

that biology is a much more general phenomenon in the universe

0:56:040:56:08

and that other places that could harbour life would do so

0:56:080:56:11

in an almost inevitable way.

0:56:110:56:12

Personally I'd be amazed

0:56:230:56:24

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

0:56:240:56:26

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

0:56:260:56:29

kind of pond scum kind of things,

0:56:290:56:31

but we know from the history of our own planet

0:56:310:56:34

that some pond scum evolves,

0:56:340:56:36

so this could happen on other planets as well.

0:56:360:56:38

So the possibility there's other intelligent life out there

0:56:380:56:40

is certainly one well worth exploring.

0:56:400:56:42

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

0:56:480:56:53

could fly through our skies.

0:56:530:56:56

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

0:56:560:57:00

If Comet ISON survives its solar passage,

0:57:010:57:04

then I'm hoping it's going to be

0:57:040:57:06

a glorious sight in the early morning skies,

0:57:060:57:08

the pre-dawn skies in early December.

0:57:080:57:10

Looking towards the east before sunrise,

0:57:100:57:13

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

0:57:130:57:17

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

0:57:170:57:20

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

0:57:200:57:24

We never know when one is going to come around,

0:57:240:57:27

we never know when the next one's coming.

0:57:270:57:29

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

0:57:290:57:32

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

0:57:330:57:39

Subtitles by Red Bee Media Ltd

0:58:020:58:05

Download Subtitles

SRT

ASS