0:00:07 > 0:00:08In the hills of Arizona,
0:00:08 > 0:00:11one of America's most sophisticated telescopes
0:00:11 > 0:00:14is preparing for a visitor
0:00:14 > 0:00:18from the furthest reaches of the solar system.
0:00:18 > 0:00:19It's moving along.
0:00:19 > 0:00:21- The field is 12 arc minutes.- Yeah.
0:00:21 > 0:00:24So you can go 2 arc minutes or so, I think.
0:00:24 > 0:00:29It's 4.6 billion years old
0:00:29 > 0:00:33and started travelling towards our sun millions of years ago.
0:00:33 > 0:00:36- The same amount again.- One more time?- Yeah.- Go 75 arc seconds.- OK.
0:00:36 > 0:00:40This is Comet ISON.
0:00:40 > 0:00:42It's no ordinary comet.
0:00:42 > 0:00:45- This thing is moving so quick.- Yeah.
0:00:45 > 0:00:48In one week's time, millions of us should be able
0:00:48 > 0:00:51to see it with our naked eye.
0:00:51 > 0:00:55'A really bright comet like Comet ISON is extremely rare.'
0:00:55 > 0:00:56It's extraordinarily exciting.
0:00:56 > 0:01:00This is probably a once-in-a-lifetime experience.
0:01:03 > 0:01:06A comet is one of the most spectacular sights in the night sky.
0:01:06 > 0:01:11And Comet ISON could be the most STUNNING for a generation.
0:01:13 > 0:01:17You should see a beautiful tail stretching upwards from the horizon
0:01:17 > 0:01:19and millions of people will be able to see it.
0:01:19 > 0:01:20Everybody should go out
0:01:20 > 0:01:23and see it because you may never get that chance again.
0:01:25 > 0:01:28ISON will be much more than just a celestial spectacle.
0:01:29 > 0:01:34Comets are relics from the earliest days of the solar system,
0:01:34 > 0:01:36so ISON could help us solve
0:01:36 > 0:01:40some of the great scientific mysteries about where we come from.
0:01:41 > 0:01:43It won't just tell us about comets.
0:01:43 > 0:01:45It'll tell us about the entire evolution
0:01:45 > 0:01:47and origin of the solar system.
0:01:49 > 0:01:51THIS is the comet of the century.
0:02:05 > 0:02:09It's September the 12th at the Discovery Telescope in Arizona.
0:02:10 > 0:02:12In the next few minutes,
0:02:12 > 0:02:15Comet ISON will be visible from Earth for the first time.
0:02:19 > 0:02:23Dr Matthew Knight has been preparing for this moment all year.
0:02:24 > 0:02:29For the past three months, ISON has been obscured by the sun.
0:02:29 > 0:02:33Now the comet is about to emerge into view.
0:02:38 > 0:02:40- Jason, what's the humidity doing? - Coming up on 80%.
0:02:40 > 0:02:42Are you ready for one more?
0:02:42 > 0:02:45He is pinpointing its position...
0:02:45 > 0:02:46Move has been issued.
0:02:46 > 0:02:50..so that he can photograph it for the first time.
0:02:51 > 0:02:54METALLIC CREAKING
0:02:54 > 0:02:58- And... And stable. All right.- That should have us in the right spot.
0:03:01 > 0:03:05For the astronomers, the waiting is nearly over.
0:03:06 > 0:03:08- COMPUTERISED VOICE: - 'Series complete.'
0:03:10 > 0:03:12BEEPING
0:03:14 > 0:03:15BEEPING
0:03:22 > 0:03:24It's going to be out in about 10 seconds,
0:03:24 > 0:03:25so...
0:03:25 > 0:03:28There we go.
0:03:31 > 0:03:33JASON CHUCKLES
0:03:33 > 0:03:35So this looks fantastic.
0:03:35 > 0:03:38It's there, it's bright, it just like we expected it to be.
0:03:38 > 0:03:41There is a nice tail. I'm very excited to see it.
0:03:41 > 0:03:45Every 30 seconds, a new image of the comet is taken.
0:03:50 > 0:03:51When I was in grad school
0:03:51 > 0:03:53thinking about comets like this,
0:03:53 > 0:03:56I thought, "Sometime, hopefully in my lifetime, I'll get to see one."
0:03:56 > 0:03:58And here, 5 years after I got my PhD,
0:03:58 > 0:04:00I am the first professional astronomer
0:04:00 > 0:04:02to image this at a professional telescope.
0:04:02 > 0:04:03So it's very exciting.
0:04:15 > 0:04:17Comets are one of the solar system's
0:04:17 > 0:04:20most spectacular and unusual objects.
0:04:31 > 0:04:34We like to think of comets as dirty snowballs.
0:04:34 > 0:04:36They're balls of rock and ice.
0:04:36 > 0:04:38And, by ice, I mean frozen gases.
0:04:38 > 0:04:40So frozen water, frozen carbon dioxide.
0:04:40 > 0:04:43And they come from the outer solar system, where it is very, very cold,
0:04:43 > 0:04:46into the inner solar system, where it really heats up.
0:04:47 > 0:04:53Seen from Earth, they display huge tails of dust and gas,
0:04:53 > 0:04:56sometimes up to hundreds of millions of kilometres
0:04:56 > 0:05:00in length, as their ices are melted by the heat of the sun.
0:05:02 > 0:05:06The distance from Earth means that comets appear to be stationary
0:05:06 > 0:05:09but, in fact, they can be travelling at speeds of over
0:05:09 > 0:05:111 million km/h.
0:05:16 > 0:05:19As an astronomer, comets are really, really exciting because
0:05:19 > 0:05:21they change a lot, they're unpredictable,
0:05:21 > 0:05:24and you don't know what they'll do. There's a pretty high chance
0:05:24 > 0:05:26of finding out something new and really cool, so it's quite
0:05:26 > 0:05:30different from many other branches of astronomy where nothing changes
0:05:30 > 0:05:32from this billion years to the next billion years.
0:05:32 > 0:05:35Comets change literally from hour to hour.
0:05:40 > 0:05:44Thousands of comets fly through our solar system every year.
0:05:44 > 0:05:47Most we never see with the naked eye
0:05:47 > 0:05:50and even with telescopes it's hard to learn anything about them.
0:05:52 > 0:05:54But this one is special.
0:05:57 > 0:06:02Comet ISON is 4.6 billion years old
0:06:02 > 0:06:05and is heading on an extraordinary journey
0:06:05 > 0:06:08which will take it through the sun's corona.
0:06:10 > 0:06:14This is a rare class of comet called a sungrazer.
0:06:14 > 0:06:17A sungrazer is a comet that comes very, very close to the sun,
0:06:17 > 0:06:19much closer than normal comets.
0:06:19 > 0:06:22It passes so close to the sun that it gets extremely hot
0:06:22 > 0:06:24and also risks breaking up
0:06:24 > 0:06:26due to the gravitational pull of the sun.
0:06:27 > 0:06:29But nobody knows what's going to happen
0:06:29 > 0:06:32after its close encounter with the sun.
0:06:34 > 0:06:36Although it could be spectacular,
0:06:36 > 0:06:40Dr Knight thinks there are three scenarios for ISON.
0:06:43 > 0:06:46The first is based on what happened to another sungrazer -
0:06:46 > 0:06:51Comet Lovejoy, seen here from the International Space Station.
0:06:55 > 0:06:57So here we are seeing Comet Lovejoy in late 2011,
0:06:57 > 0:06:59as it is going right behind the sun.
0:06:59 > 0:07:03And when Comet Lovejoy got so close to the sun,
0:07:03 > 0:07:04it was under incredible forces.
0:07:04 > 0:07:07It was very hot, it was losing mass very rapidly and it was feeling
0:07:07 > 0:07:09the gravitational pull of the sun.
0:07:09 > 0:07:11And what happens there is that
0:07:11 > 0:07:13the side of the comet that's closer to the sun
0:07:13 > 0:07:16is being pulled more strongly than the side of the comet further away,
0:07:16 > 0:07:17which caused it to stretch apart
0:07:17 > 0:07:20and, probably a few hours or maybe a day or so after close approach,
0:07:20 > 0:07:22it actually caused it to break up.
0:07:25 > 0:07:29So could ISON disintegrate just as Comet Lovejoy did?
0:07:32 > 0:07:33A key factor is its size.
0:07:37 > 0:07:41We think from these Hubble images that it is probably about...
0:07:41 > 0:07:44possibly as big as 2km in size, maybe 1km,
0:07:44 > 0:07:46but it is on the edge of where I feel comfortable
0:07:46 > 0:07:48predicting whether it will survive or not.
0:07:53 > 0:07:56The second scenario is based on Comet Encke,
0:07:56 > 0:08:01seen here in 2007 as it flies into the sun's corona.
0:08:01 > 0:08:04It has already been through the inner solar system
0:08:04 > 0:08:07about 70 times since it was first observed.
0:08:12 > 0:08:13Comet Encke, which you can see here,
0:08:13 > 0:08:16is a very old comet. It has been around the sun many times,
0:08:16 > 0:08:19in the inner solar system, where it is very hot and it is therefore
0:08:19 > 0:08:21running out of the ices and gases that drive its activity
0:08:21 > 0:08:24because those things boil away.
0:08:24 > 0:08:27As you can see here, it's starting to peter out and doesn't look quite like
0:08:27 > 0:08:30you normally think of an active comet looking. It's fizzling out.
0:08:32 > 0:08:35This is the moment when the tail is broken off
0:08:35 > 0:08:37by a blast of solar particles.
0:08:39 > 0:08:40We think that's a possibility
0:08:40 > 0:08:42for what might happen for Comet ISON as well.
0:08:45 > 0:08:49Although it took many orbits before Comet Encke burnt off all its gases
0:08:49 > 0:08:51and started to fizzle out...
0:08:54 > 0:08:58..the great heat of the sun could have the same effect on ISON
0:08:58 > 0:09:00on its one and only passage.
0:09:03 > 0:09:06But there is a 3rd scenario.
0:09:08 > 0:09:12It's what happened to Comet Ikeya-Seki in 1965...
0:09:14 > 0:09:16..the brightest comet in living memory.
0:09:19 > 0:09:21Ikeya-Seki went very close to the sun, like ISON,
0:09:21 > 0:09:24and it created this large tail that you can see here.
0:09:24 > 0:09:27It was just a fantastic comet, spectacular.
0:09:27 > 0:09:30People would go outside with their naked eye and they could see this
0:09:30 > 0:09:33massive tail which stretched from the horizon all the way overhead.
0:09:33 > 0:09:36This would be the perfect...the ideal scenario for Comet ISON.
0:09:36 > 0:09:39We can only hope that Comet ISON will be as impressive as that.
0:09:42 > 0:09:47However, even an experienced comet-watcher like Dr Knight
0:09:47 > 0:09:49is just going to have to wait and see.
0:09:53 > 0:09:56It's quite nerve-racking not knowing what's going to happen.
0:09:56 > 0:09:58We can make our best guesses,
0:09:58 > 0:10:00hope that we can predict what's going to happen,
0:10:00 > 0:10:03but we really won't know until it actually gets close to the sun.
0:10:08 > 0:10:11Whichever scenario turns out to be correct,
0:10:11 > 0:10:14for scientists, the spectacle isn't the main point.
0:10:17 > 0:10:21Comet ISON will provide an extraordinary opportunity
0:10:21 > 0:10:26to study MORE than just the fate of these most mysterious bodies.
0:10:32 > 0:10:37This is our solar system, seen from over 7 trillion km away.
0:10:39 > 0:10:43From here, the sun and the planets look like a single point of light.
0:10:45 > 0:10:50But the solar system extends much further out to a belt of comets -
0:10:50 > 0:10:52the Oort Cloud.
0:10:52 > 0:10:55And THIS is where ISON has come from.
0:10:58 > 0:11:01Millions of years ago, ISON's orbit was disturbed.
0:11:02 > 0:11:05The gravity from a neighbouring star in our galaxy
0:11:05 > 0:11:08deflected it out of the Oort Cloud.
0:11:10 > 0:11:13Since then, it's been travelling towards our sun.
0:11:15 > 0:11:18Because ISON was formed at the beginning of the solar system
0:11:18 > 0:11:21and has not changed since then,
0:11:21 > 0:11:23it offers scientists a wonderful opportunity
0:11:23 > 0:11:27to understand how our solar system formed.
0:11:27 > 0:11:31Comet ISON is rather like excavating a dinosaur skeleton
0:11:31 > 0:11:34from the birth of the solar system.
0:11:34 > 0:11:37It's a fossilised, deep-frozen relic from that time
0:11:37 > 0:11:40when the sun and the planets came together.
0:11:42 > 0:11:45We know, however, that this is that first time into the sun
0:11:45 > 0:11:47and it's never coming back,
0:11:47 > 0:11:50so this is a once-in-a-lifetime opportunity.
0:11:50 > 0:11:53We are going to get an insight into the past 4½ billion years
0:11:53 > 0:11:55of our solar system - when it first formed.
0:12:01 > 0:12:03We know that 5 billion years ago
0:12:03 > 0:12:07the solar system was just a swirling mass of dust and gas.
0:12:09 > 0:12:13And we know that 4.6 billion years ago the sun formed
0:12:13 > 0:12:15at the centre of the nebula.
0:12:17 > 0:12:20But the next stage in the origins of our solar system -
0:12:20 > 0:12:24the formation of the planets - still holds many mysteries.
0:12:26 > 0:12:27The first question is
0:12:27 > 0:12:30how did the dust and gas of the solar nebula
0:12:30 > 0:12:32coalesce to build the planets?
0:12:46 > 0:12:49If we consider the universe, we think of stars and galaxies,
0:12:49 > 0:12:52but hardly anybody thinks about dust particles.
0:12:55 > 0:12:57For Professor Jurgen Blum,
0:12:57 > 0:13:00the first stage in the formation of the planets
0:13:00 > 0:13:02can be seen all around us.
0:13:04 > 0:13:08This is my dusty basement, as you can see, and the dust here
0:13:08 > 0:13:11acts in the same way as the dust in the young solar system.
0:13:12 > 0:13:17When dust particles collide or stick to a wall, they really stick by
0:13:17 > 0:13:19the very same forces as in the young solar system.
0:13:21 > 0:13:25The forces are the same here on Earth and any place in the universe.
0:13:31 > 0:13:35This is Europe's biggest drop tower -
0:13:35 > 0:13:38a massive instrument for testing these forces.
0:13:40 > 0:13:44Professor Blum's team is creating an experiment
0:13:44 > 0:13:49to discover how these tiny particles of dust began to form into planets.
0:13:52 > 0:13:57They fill a cylinder with a phial of dust and monitoring equipment,
0:13:57 > 0:14:02which is hoisted up 120m to the top of the tower.
0:14:09 > 0:14:14It's then released and plummets to Earth,
0:14:14 > 0:14:18in the process, dramatically reducing the gravity inside
0:14:18 > 0:14:21and creating conditions similar to those in space.
0:14:39 > 0:14:42The drop takes mere seconds,
0:14:42 > 0:14:47but high-speed cameras inside the cylinder record the dust responding.
0:14:51 > 0:14:53In the near absence of gravity,
0:14:53 > 0:14:57the tiny particles start to bond together.
0:15:00 > 0:15:04Here we see two dust particles that collide at very low speeds
0:15:04 > 0:15:06and then they stick together
0:15:06 > 0:15:08by a force that we call the van der Waals' force,
0:15:08 > 0:15:11and this is caused by a very weak bonding
0:15:11 > 0:15:13between the atoms of the two particles.
0:15:14 > 0:15:18The dust particles have negatively charged electrons surrounding them.
0:15:18 > 0:15:22At their centre are positively charged protons.
0:15:22 > 0:15:26Negative electrons from one particle of dust are attracted
0:15:26 > 0:15:29to the positive protons of another and form a weak bond.
0:15:29 > 0:15:33It's called the van der Waals' force.
0:15:34 > 0:15:37This force holds dust particles together
0:15:37 > 0:15:40when they collide in the emptiness of space.
0:15:40 > 0:15:43But it's only strong enough to create bodies
0:15:43 > 0:15:451cm in diameter.
0:15:46 > 0:15:50So the next question is, how did they grow beyond that size?
0:15:52 > 0:15:55There are two theories.
0:15:55 > 0:15:59The first is called the mass transfer theory.
0:16:00 > 0:16:05According to this, dust particles crash together at great speed.
0:16:05 > 0:16:08To test this they are moulded into a small pellet
0:16:08 > 0:16:11to simulate the centimetre-sized body.
0:16:12 > 0:16:15This is loaded into the top of another drop tower
0:16:15 > 0:16:18where it is bombarded with tiny dust particles.
0:16:25 > 0:16:29Here, a small dust particle is smashed into a large dust particle
0:16:29 > 0:16:31at rather high speeds.
0:16:31 > 0:16:34The velocities are indeed so high that the small particle
0:16:34 > 0:16:36fragments into pieces that we can see here
0:16:36 > 0:16:40and transfers part of its mass to the large particle.
0:16:45 > 0:16:49And the large particle grows in mass by each subsequent collision.
0:16:53 > 0:16:57And, according to this theory, the bodies can grow big enough
0:16:57 > 0:17:00to become the seeds of the planets.
0:17:15 > 0:17:18But there is another theory about how the planets grew
0:17:18 > 0:17:22which is inspired by an activity close to Prof Blum's heart.
0:17:24 > 0:17:27I cycle every day, I use my bike to go to work
0:17:27 > 0:17:29and this gives me enough time to think about
0:17:29 > 0:17:31the origin of the solar system.
0:17:33 > 0:17:37Professor Blum thinks that the physical forces which operate
0:17:37 > 0:17:40on riders in a cycle race are the same as those affecting
0:17:40 > 0:17:45centimetre-sized bodies of dust in the early solar system.
0:17:45 > 0:17:48He calls this the peloton theory.
0:17:48 > 0:17:50'They feel the friction of the nebula gas,
0:17:50 > 0:17:53'and the gas friction slows them down on their orbit.'
0:17:58 > 0:18:01However, if they form groups just by chance,
0:18:01 > 0:18:04like the peloton in a bicycle race,
0:18:04 > 0:18:08only the front particles of the peloton face the gas friction,
0:18:08 > 0:18:11so the back particles push the front particles
0:18:11 > 0:18:15so that they catch up with individual dust particles on their way
0:18:15 > 0:18:18and grow in mass until the combined gravity
0:18:18 > 0:18:21is so strong that they form a single body.
0:18:23 > 0:18:27The peloton theory is a much gentler way of forming a planet,
0:18:27 > 0:18:31because the particles gradually coalesce to form bodies.
0:18:31 > 0:18:34If planets formed this way, they should be less dense
0:18:34 > 0:18:37than those formed by the multiple high-speed collisions
0:18:37 > 0:18:39of the mass transfer theory.
0:18:43 > 0:18:48ISON will be the ultimate test of which theory is correct,
0:18:48 > 0:18:52because comets are formed in the same way as planets.
0:18:54 > 0:18:57If ISON explodes after passing the sun,
0:18:57 > 0:19:01it's a clear sign that it's bound together extremely weakly,
0:19:01 > 0:19:05and that clearly supports the peloton theory.
0:19:08 > 0:19:12So the fate of Comet ISON, as it circles the sun,
0:19:12 > 0:19:16could answer the question of how the dust from the solar nebula
0:19:16 > 0:19:19formed into planets.
0:19:30 > 0:19:33Although the planets might have all started off in the same way,
0:19:33 > 0:19:38there is one further mystery about the formation of the solar system.
0:19:39 > 0:19:42Why are the planets so different?
0:19:45 > 0:19:49In the inner solar system there are the smaller rocky planets...
0:19:51 > 0:19:55..Mercury, with its huge temperature range...
0:19:58 > 0:20:03..Venus, its volcanic surface hidden beneath swirling clouds...
0:20:05 > 0:20:07..our own watery Earth...
0:20:10 > 0:20:14..and Mars, with its striking red surface.
0:20:16 > 0:20:18Although superficially different,
0:20:18 > 0:20:21they are all basically made of the same stuff -
0:20:21 > 0:20:23silicate rock and metals.
0:20:26 > 0:20:29Further out, the planets are very different.
0:20:30 > 0:20:34Jupiter - 2½ times the size
0:20:34 > 0:20:37of all the other planets put together...
0:20:39 > 0:20:41..Saturn with its rings...
0:20:46 > 0:20:49..Uranus, surrounded in clouds of methane...
0:20:52 > 0:20:58..and Neptune, with its wind speeds of 2,100 km/h.
0:21:01 > 0:21:04These are the gas giants.
0:21:05 > 0:21:08Although they have a core made of dust,
0:21:08 > 0:21:10they are mostly made up of gas.
0:21:13 > 0:21:17Dr David Walsh has been working on a theory to explain
0:21:17 > 0:21:21where and why these two types of planets were created.
0:21:23 > 0:21:24It's important to explain
0:21:24 > 0:21:28the early history and evolution of the solar system.
0:21:28 > 0:21:30The key of it was trying to understand
0:21:30 > 0:21:33what temperature different things formed at in the solar system.
0:21:33 > 0:21:34It's really critical.
0:21:36 > 0:21:39According to this theory, the creation of the different
0:21:39 > 0:21:43types of planet can be explained by the way temperature decreases
0:21:43 > 0:21:45the further away you travel from the sun.
0:21:47 > 0:21:51The smaller planets close to the sun can only have been built
0:21:51 > 0:21:54in the inner solar system, where there was enough heat
0:21:54 > 0:21:57to fuse together the metals from which they were made.
0:21:59 > 0:22:01We think that in the early solar system history
0:22:01 > 0:22:03there was kind of a natural temperature gradient,
0:22:03 > 0:22:06where things much closer to the sun were much hotter.
0:22:06 > 0:22:08So, naturally, in the inner part of the solar system
0:22:08 > 0:22:10we build our rocky planets
0:22:10 > 0:22:12made of materials that formed at higher temperatures,
0:22:12 > 0:22:15and in the outer part we build something completely different.
0:22:19 > 0:22:22Only further out in the solar system was it cold enough to condense
0:22:22 > 0:22:28the gases which formed the gaseous giants around their solid cores.
0:22:29 > 0:22:31When we look at the solar system
0:22:31 > 0:22:33we see that probably the first planet to form
0:22:33 > 0:22:36was the largest planet in our solar system, Jupiter.
0:22:36 > 0:22:38Jupiter is a gas giant, and that tells us that
0:22:38 > 0:22:41it must have formed in the distant solar system,
0:22:41 > 0:22:45where the temperature was low enough for the gas to survive.
0:22:48 > 0:22:51The temperature gradient across the early solar system
0:22:51 > 0:22:55gives an explanation of how the different types of planets formed...
0:22:58 > 0:23:01..and why the rocky planets are close to the sun...
0:23:03 > 0:23:06..while the gas giants are further away.
0:23:10 > 0:23:13But there is a problem with the theory.
0:23:13 > 0:23:16It centres around the two furthest planets from the sun -
0:23:16 > 0:23:18Uranus...
0:23:18 > 0:23:20and Neptune.
0:23:21 > 0:23:24Scientists have realised that the solar nebula
0:23:24 > 0:23:27did not have enough dust to form these planets
0:23:27 > 0:23:29where they are now orbiting.
0:23:31 > 0:23:33Where they formed and how they formed
0:23:33 > 0:23:34is a big mystery for scientists.
0:23:34 > 0:23:38The temperatures of the gases and the solids that they accreted
0:23:38 > 0:23:41when they were forming is really important to understanding
0:23:41 > 0:23:43their entire history, when and where they formed.
0:23:46 > 0:23:50Comet ISON could hold the key to the mystery of the formation
0:23:50 > 0:23:54of these two planets, because scientists believe that ISON
0:23:54 > 0:23:59originally formed in the same part of the solar system as Neptune.
0:24:00 > 0:24:04According to the new theory, all the gas giants,
0:24:04 > 0:24:06including Neptune and Uranus,
0:24:06 > 0:24:09were formed much closer to the sun than they are today.
0:24:11 > 0:24:15They were also much closer together.
0:24:15 > 0:24:19What's more, millions of comets left over from the formation
0:24:19 > 0:24:22of the solar system were orbiting near Neptune.
0:24:27 > 0:24:30But then the orbits of Jupiter and Saturn
0:24:30 > 0:24:34came so close together that they started to react against each other,
0:24:34 > 0:24:37creating huge gravitational forces.
0:24:40 > 0:24:45These pushed them both further away from the sun
0:24:45 > 0:24:48and, in the process, also knocked Uranus and Neptune
0:24:48 > 0:24:50further out into the solar system.
0:24:56 > 0:25:00This great disturbance sent comets hurling all over the place.
0:25:05 > 0:25:08We think that Comet ISON was kicked by one of these giant planets
0:25:08 > 0:25:10to the furthest extent of the solar system,
0:25:10 > 0:25:12which is the Oort Cloud.
0:25:15 > 0:25:19And it's been sitting out there frozen, essentially,
0:25:19 > 0:25:21for 4.5 or 4.6 billion years.
0:25:21 > 0:25:25And the material that it was made of is essentially frozen in,
0:25:25 > 0:25:28it's locked in and it hasn't really changed at all.
0:25:30 > 0:25:34Then, millions of years ago, the gravity from a neighbouring star
0:25:34 > 0:25:37shunted ISON out of the Oort Cloud
0:25:37 > 0:25:40and it started heading back into the centre of the solar system.
0:25:42 > 0:25:46Its arrival will provide a rare opportunity for scientists
0:25:46 > 0:25:50to test their theory of how the solar system came together.
0:25:52 > 0:25:55ISON originated next to Neptune.
0:25:55 > 0:25:59Analysing its gases will tell them not only the temperature
0:25:59 > 0:26:01at which the comet formed, but also that of the planet.
0:26:03 > 0:26:07From this they can work out where Neptune was created.
0:26:10 > 0:26:12So, when comet ISON comes close to the sun,
0:26:12 > 0:26:14astronomers are going to look really closely
0:26:14 > 0:26:16at the gas coming off its surface.
0:26:16 > 0:26:19Hopefully, we'll see enough gas in enough detail
0:26:19 > 0:26:21that we can really zoom in and look at the some
0:26:21 > 0:26:24of the chemical signatures to some of these different gases.
0:26:24 > 0:26:27Specifically, something like the nitrogen isotopes
0:26:27 > 0:26:31will tell us a lot about the temperature at which the material,
0:26:31 > 0:26:33the gases in ISON, formed at.
0:26:35 > 0:26:39If the result shows it formed closer to the sun than Neptune is today,
0:26:39 > 0:26:43then it will suggest that their theory is correct.
0:26:45 > 0:26:48This is a really unique opportunity, a really powerful opportunity.
0:26:48 > 0:26:50We could learn a lot about
0:26:50 > 0:26:52the entire formation process of all our planets.
0:26:52 > 0:26:55But every time we think we have something nailed,
0:26:55 > 0:26:58every time we think we really understand something,
0:26:58 > 0:27:00we get surprised, and we go back to the drawing board,
0:27:00 > 0:27:03and that's what really, really fun about science.
0:27:03 > 0:27:05So, maybe Comet ISON will be that thing
0:27:05 > 0:27:07that sends us back to the drawing board.
0:27:07 > 0:27:09We're just going to have to wait and see.
0:27:15 > 0:27:19Comets like ISON may do more than provide evidence
0:27:19 > 0:27:21of how the solar system formed.
0:27:23 > 0:27:26Many scientists now believe that they may help answer
0:27:26 > 0:27:29one of the biggest questions about Earth.
0:27:32 > 0:27:35Where did all our water come from?
0:27:37 > 0:27:41There are over a billion cubic km of water
0:27:41 > 0:27:43on the surface of the Earth.
0:27:43 > 0:27:48The amount hasn't changed for at least 3.8 billion years.
0:27:51 > 0:27:55So, how did all this water arrive on the surface of our planet?
0:28:07 > 0:28:11Dr Melissa Morris, from Arizona State University,
0:28:11 > 0:28:14believes that the Comet ISON could help us find the answer.
0:28:16 > 0:28:18The arrival of Comet ISON is so exciting
0:28:18 > 0:28:22because scientifically it helps us settle questions that go to the very
0:28:22 > 0:28:27nature of our origin and what brought life-sustaining water to our planet.
0:28:31 > 0:28:35This is the Coso Volcanic Field in southern California,
0:28:35 > 0:28:40where water vapour steams from below the surface of the Earth.
0:28:42 > 0:28:45For many decades, scientists thought that this was how the Earth
0:28:45 > 0:28:49got its water - released from rocks deep inside the planet.
0:28:51 > 0:28:53It's called the accretion theory.
0:28:54 > 0:28:57So the accretion theory is one theory to explain
0:28:57 > 0:28:58the delivery of Earth's water.
0:28:58 > 0:29:01And what that means is that the Earth was put together
0:29:01 > 0:29:05from smaller rocky bodies that had high a water content,
0:29:05 > 0:29:08and then the water came out from the interior of the Earth,
0:29:08 > 0:29:09much like at this site here.
0:29:09 > 0:29:12It then condensed out of the atmosphere
0:29:12 > 0:29:14to form the Earth's oceans.
0:29:16 > 0:29:19The theory suggests that when the early Earth formed,
0:29:19 > 0:29:23it was covered in volcanoes, which belched out steam.
0:29:24 > 0:29:29The water vapour cooled in the atmosphere and formed clouds.
0:29:29 > 0:29:32These rained water down onto the Earth's surface
0:29:32 > 0:29:37for thousands of years, the longest rainstorm in history.
0:29:38 > 0:29:42But for some, this theory is flawed.
0:29:42 > 0:29:45You might imagine that the water came from inside the Earth,
0:29:45 > 0:29:48that it was trapped in the Earth when the Earth formed.
0:29:48 > 0:29:51The trouble with that is that the Earth formed hot.
0:29:51 > 0:29:56And hot materials are not that good at holding water.
0:29:56 > 0:29:58So, in the lab, if you want to make something dry,
0:29:58 > 0:30:00you stick it in the oven and it loses the water.
0:30:00 > 0:30:02That means that perhaps the Earth formed dry
0:30:02 > 0:30:06and water came from space, after the Earth had cooled down a bit.
0:30:07 > 0:30:10This theory that the Earth's water was delivered from outer space
0:30:10 > 0:30:13was controversial.
0:30:13 > 0:30:17But evidence to support it can be seen in the night sky.
0:30:22 > 0:30:27Our moon is covered in craters. Many were caused by comets
0:30:27 > 0:30:30which crashed during the period when the changing orbits of
0:30:30 > 0:30:34the gas giants sent comets all over the solar system.
0:30:38 > 0:30:42Some scientists believe they also crashed into Earth,
0:30:42 > 0:30:44bringing water with them.
0:30:46 > 0:30:49Comets are made of roughly 50% water,
0:30:49 > 0:30:52and so, after the Earth formed, during that period of heavy
0:30:52 > 0:30:56bombardment, the comets brought the water along, impacted on the
0:30:56 > 0:31:00surface of the Earth, and that the oceans came from cometary water.
0:31:01 > 0:31:06It sounds far-fetched, but there is a way of proving whether comets
0:31:06 > 0:31:09played a role in supplying the Earth's water.
0:31:09 > 0:31:12There are two types of water that exist.
0:31:12 > 0:31:16Most of the water we find on Earth is the sort we are familiar with.
0:31:16 > 0:31:19But there is another kind,
0:31:19 > 0:31:23with a slightly different atomic composition.
0:31:23 > 0:31:27Well, it may surprise you to find that not all water is the same.
0:31:27 > 0:31:29This is ordinary drinking water
0:31:29 > 0:31:31and this is what we call heavy water,
0:31:31 > 0:31:35and it contains deuterium, which is a form of hydrogen that contains
0:31:35 > 0:31:40an extra proton, so it has a greater mass than the ordinary water.
0:31:40 > 0:31:43So, to demonstrate the difference between ordinary water
0:31:43 > 0:31:46and heavy water, we are going to do this simple experiment.
0:31:46 > 0:31:50So, what I will do is pour this ordinary water,
0:31:50 > 0:31:53which has 150 parts of deuterium per million
0:31:53 > 0:31:58and has a density of 1g per cubic cm, into this beaker.
0:31:58 > 0:32:02And then, I'm going to take an ordinary glass stopper,
0:32:02 > 0:32:05and we are going to place it in this beaker full of ordinary water,
0:32:05 > 0:32:06and we'll see what happens.
0:32:07 > 0:32:08GLASS TINKLES
0:32:10 > 0:32:15So, it sinks. The glass stopper sinks in ordinary water.
0:32:15 > 0:32:18To see the difference, we are going to pour the heavy water
0:32:18 > 0:32:20into this other beaker.
0:32:20 > 0:32:23And heavy water has a higher percentage of deuterium,
0:32:23 > 0:32:26so it has 320 parts per million...
0:32:28 > 0:32:33..and a density of 1.15g per cubic cm.
0:32:34 > 0:32:36And I'm going to do the same thing,
0:32:36 > 0:32:40we are going to take an identical glass stopper
0:32:40 > 0:32:44and we are going to place it in the heavy water and see what happens.
0:32:45 > 0:32:48GLASS TINKLES Voila!
0:32:48 > 0:32:53It floats in the heavy water, where it sinks in the ordinary water.
0:32:53 > 0:32:56Heavy water doesn't occur naturally on Earth,
0:32:56 > 0:33:00so if comets turned out to be made of heavy water, it would be
0:33:00 > 0:33:04bad news for the theory that comets filled up the oceans.
0:33:08 > 0:33:12What the scientists needed was to sample water from a comet
0:33:12 > 0:33:16and find out whether it was heavy or ordinary water.
0:33:16 > 0:33:19First stage ignition and take-off!
0:33:19 > 0:33:24In 1986, the Giotto spacecraft was launched,
0:33:24 > 0:33:28heading for the most famous comet of all, Halley's comet.
0:33:32 > 0:33:36For the first time, a space probe could fly past a comet
0:33:36 > 0:33:39and analyse the gases in its tail.
0:33:43 > 0:33:45They found heavy water.
0:33:48 > 0:33:52A few years later, a telescope on Earth examined the water gases
0:33:52 > 0:33:55from another comet, Hyakutake.
0:33:55 > 0:33:57It too had a tail full of heavy water.
0:33:57 > 0:33:59Measurements of Comet Halley
0:33:59 > 0:34:04and Comet Hyakutake suggest that comets contain more heavy water than
0:34:04 > 0:34:08we see in the oceans, and the importance of that is pretty
0:34:08 > 0:34:10straightforward, that means if you just melt a bunch of comets,
0:34:10 > 0:34:13you get water which doesn't look like the oceans,
0:34:13 > 0:34:17and therefore, the oceans cannot consist of melted comets.
0:34:19 > 0:34:24It seemed that the theory of comets delivering the water for
0:34:24 > 0:34:27Earth's oceans had received a serious setback.
0:34:27 > 0:34:28But to be sure,
0:34:28 > 0:34:33what scientists needed was more data from more comets.
0:34:40 > 0:34:42So, NASA decided to send high altitude planes
0:34:42 > 0:34:45into the Earth's stratosphere.
0:34:48 > 0:34:51Their mission was to collect space dust there,
0:34:51 > 0:34:55captured on adhesive panels attached to their wings.
0:34:58 > 0:35:01The hope was that the dust had come from distant comets
0:35:01 > 0:35:05and would contain molecules of water.
0:35:11 > 0:35:15Professor Kevin McKeegan was one of the chief scientists on the mission.
0:35:19 > 0:35:22Well, this is an electron microscope image of a dust particle
0:35:22 > 0:35:25collected by NASA in the stratosphere of the Earth.
0:35:25 > 0:35:28This particle came to Earth through interplanetary space,
0:35:28 > 0:35:32and particularly this kind of dust particle,
0:35:32 > 0:35:35with a lot of pore space and sort of a fairy castle structure,
0:35:35 > 0:35:38may have been from a comet. You see all of these holes,
0:35:38 > 0:35:40all of these pores in the particle here,
0:35:40 > 0:35:42may have had in them
0:35:42 > 0:35:46at one time water ice, or other ices, which are no longer there.
0:35:48 > 0:35:50It was tantalisingly close.
0:35:50 > 0:35:55But still, a sample of water from a comet eluded them.
0:35:55 > 0:35:59Then, Professor McKeegan examined a second group of particles.
0:35:59 > 0:36:03This is another dust particle collected from the stratosphere.
0:36:03 > 0:36:06In this case, there is a lot of clay minerals,
0:36:06 > 0:36:10so the water is trapped in the mineral layers, and the deuterium to
0:36:10 > 0:36:13hydrogen ratio in the water that is trapped in those minerals is
0:36:13 > 0:36:17similar to that, for example, in the ocean.
0:36:19 > 0:36:23So, could this water from space, which was so like our own,
0:36:23 > 0:36:28be the proof scientists needed that comets had brought it to Earth?
0:36:30 > 0:36:33We've been studying these interplanetary dust particles,
0:36:33 > 0:36:35we know that some of them have water,
0:36:35 > 0:36:39some have structures which look like they could have had ices in them.
0:36:39 > 0:36:44But frustratingly, this result wasn't quite what it seemed.
0:36:44 > 0:36:49The problem, the fundamental problem is, we don't know where any one
0:36:49 > 0:36:53dust particle that we collected in Earth's atmosphere comes from.
0:36:55 > 0:36:59In the end, space dust could not provide definitive proof.
0:36:59 > 0:37:03The scientists could not be certain where it came from.
0:37:09 > 0:37:12- As descent sees it...- Above Mars.
0:37:12 > 0:37:16But then, in 2006, they made a breakthrough.
0:37:16 > 0:37:19Well, that's cool.
0:37:19 > 0:37:23The capsule returned to Earth from an epic journey through
0:37:23 > 0:37:27- the solar system.- Quite a trail. Near spec has a great view.
0:37:27 > 0:37:30On board was the first ever dust actually
0:37:30 > 0:37:32collected from the tail of a comet.
0:37:34 > 0:37:35Wow, we got that, boys!
0:37:38 > 0:37:40- MCKEEGAN:- Personally, I have been studying dust
0:37:40 > 0:37:41for some 25 years or so,
0:37:41 > 0:37:45but comet dust had never been collected before,
0:37:45 > 0:37:47because it is exceedingly difficult,
0:37:47 > 0:37:49because comets come by the Earth at a very great speed.
0:37:51 > 0:37:54This was the Stardust mission.
0:37:54 > 0:37:58Its aim, to collect the dust on special gel attached to
0:37:58 > 0:38:00the wings of a spacecraft.
0:38:04 > 0:38:08Stardust was an extremely exciting event for us,
0:38:08 > 0:38:12and the Stardust spacecraft flew through the dust tail
0:38:12 > 0:38:15of Comet Wild 2, and the speed was 6km/second.
0:38:15 > 0:38:19So, you're trying to collect something that is microscopic, that
0:38:19 > 0:38:22you can't see, and it's going six times faster than a speeding bullet.
0:38:22 > 0:38:24We have confirmation...
0:38:24 > 0:38:27When the capsule finally landed,
0:38:27 > 0:38:30scientists waited to see what it might reveal.
0:38:33 > 0:38:36I was there when the sample canister was opened.
0:38:36 > 0:38:39But of course, the dust is microscopic, so when you
0:38:39 > 0:38:43first look at the collector, you don't necessarily see anything.
0:38:43 > 0:38:46There was a little bit of unspoken nervousness, that uh-oh,
0:38:46 > 0:38:50maybe we didn't collect anything, maybe it didn't open, or whatever.
0:38:50 > 0:38:54But then, the dust was found and everybody was very excited,
0:38:54 > 0:38:57there were high-fives and cheering and all of these kind of things.
0:38:57 > 0:38:59And then, the real work gets to begin.
0:39:01 > 0:39:04Now, actual particles of dust
0:39:04 > 0:39:07which definitely came from a comet were examined.
0:39:09 > 0:39:14The hope was that they would contain molecules of water within them.
0:39:17 > 0:39:22Here is an image of an impact of an actual grain from Comet Wild 2,
0:39:22 > 0:39:24this image is magnified 3,000 times.
0:39:24 > 0:39:28And what you can see is that there is debris in the hole
0:39:28 > 0:39:32and surrounding the hole, and those are bits of the comet.
0:39:32 > 0:39:35After years of planning and waiting,
0:39:35 > 0:39:38could they finally have the evidence they needed?
0:39:40 > 0:39:43Unfortunately, because the dust was travelling so fast
0:39:43 > 0:39:46when it hits the target, the dust is very badly damaged.
0:39:46 > 0:39:50And one of the things is that the ices, water,
0:39:50 > 0:39:55other volatile materials, are not preserved in the process.
0:39:56 > 0:40:01Bringing a sample of a comet back to Earth was a technical triumph.
0:40:01 > 0:40:05But it did not shed any light on the origins of Earth's water.
0:40:09 > 0:40:13Finally, in 2010, there was a breakthrough.
0:40:13 > 0:40:17It came from a telescope, out in space.
0:40:20 > 0:40:22Newly-developed infrared scanners
0:40:22 > 0:40:25on board the Herschel Space Observatory
0:40:25 > 0:40:30analysed vaporised water gases from Comet Hartley 2.
0:40:32 > 0:40:34So, then something very exciting happened.
0:40:34 > 0:40:36The measurements came back
0:40:36 > 0:40:40and it was much more similar to the signature of Earth's ocean water.
0:40:40 > 0:40:42And so, that tells us
0:40:42 > 0:40:45that at least one comet has a signature very similar to Earth,
0:40:45 > 0:40:49and that we need to measure more comets to resolve that question.
0:40:51 > 0:40:55The evidence from Hartley 2 suggested it was carrying
0:40:55 > 0:40:56water like that on Earth.
0:40:58 > 0:41:00So now, the data we have is contradictory.
0:41:04 > 0:41:08When ISON tears through the sun's corona in a few days' time,
0:41:08 > 0:41:12the evidence it provides could prove crucial.
0:41:13 > 0:41:16So, if Comet ISON has a water signature that is similar to
0:41:16 > 0:41:19Earth, just as Hartley 2 did, that is going to
0:41:19 > 0:41:23change the balance of that argument and bring validity that
0:41:23 > 0:41:26comets could very well have delivered water to our Earth.
0:41:32 > 0:41:36Comets are central to the story of how the solar system formed.
0:41:38 > 0:41:43But they are also helping us address one of the most intriguing
0:41:43 > 0:41:46and profound questions humans have ever asked.
0:41:46 > 0:41:49Are we alone in the universe?
0:41:58 > 0:42:02At the heart of the mystery of the origins of life is how simple
0:42:02 > 0:42:05chemical reactions between water, minerals
0:42:05 > 0:42:08and air turned into living organisms.
0:42:09 > 0:42:15So far, we have only been able to look at our Earth for evidence.
0:42:19 > 0:42:24The creation of life requires a critical first step.
0:42:24 > 0:42:29Chemicals have to combine in order to produce amino acids.
0:42:29 > 0:42:34These are the most fundamental building blocks of life.
0:42:34 > 0:42:38All life that we know of is based on these compounds.
0:42:38 > 0:42:41We know these amino acids were created on Earth,
0:42:41 > 0:42:45but could they also have formed in other environments,
0:42:45 > 0:42:46across the universe?
0:42:59 > 0:43:04Some scientists think comets could provide the answer.
0:43:11 > 0:43:13One of the big questions in this field is,
0:43:13 > 0:43:15can you make the building blocks of life in space,
0:43:15 > 0:43:18despite the fact that the environment is quite hostile?
0:43:18 > 0:43:21You have temperatures of extremely low, you have radiation
0:43:21 > 0:43:25levels that are very high, you are in a vacuum, you have no air.
0:43:25 > 0:43:28All of these things are the kind of things that you normally
0:43:28 > 0:43:31would expect to stop chemistry, not promote chemistry.
0:43:32 > 0:43:36Although they travel through the freezing vacuum of space,
0:43:36 > 0:43:41comets contain all the necessary ingredients for amino acids.
0:43:41 > 0:43:43But in these hostile conditions,
0:43:43 > 0:43:47can the chemicals combine to form these building blocks of life?
0:43:55 > 0:43:59Dr Sandford has built a comet in his lab to try and find out.
0:44:03 > 0:44:06This is kind of our kitchen. It's where we mix our gases.
0:44:06 > 0:44:07So if we want to simulate a comet,
0:44:07 > 0:44:10we want to put in the molecules that we expect to be in comets
0:44:10 > 0:44:14like water, methanol, ammonia, very simple molecules.
0:44:14 > 0:44:16And this is a system we use to mix them all into one bulb
0:44:16 > 0:44:19so that we can take this down to our machine,
0:44:19 > 0:44:21where we'll simulate the kind of things
0:44:21 > 0:44:23that may have played a role in getting life started.
0:44:28 > 0:44:32Having created the chemicals that are thought to exist on a comet,
0:44:32 > 0:44:37Dr Sandford must recreate the conditions in outer space.
0:44:37 > 0:44:39OK, well, we are trying to simulate the surface of a comet
0:44:39 > 0:44:42in the outer solar system, so we want a very low temperature.
0:44:42 > 0:44:45Right now, this is running at about 15 degrees Kelvin,
0:44:45 > 0:44:48which is minus 257 degrees centigrade.
0:44:48 > 0:44:51This is probably five times colder than Siberia
0:44:51 > 0:44:52in the middle of the winter.
0:44:53 > 0:44:57He then replicates the effect of our sun on a comet
0:44:57 > 0:45:00in the far reaches of our solar system
0:45:00 > 0:45:05by firing a UV light onto the ices in the vacuum chamber.
0:45:07 > 0:45:10We have a hydrogen lamp here which we use to simulate the radiation
0:45:10 > 0:45:12that comes from the sun or other stars
0:45:12 > 0:45:14and that's the radiation that goes in and hits our sample
0:45:14 > 0:45:17and does the chemistry. So the photons from this lamp
0:45:17 > 0:45:21come down over here and come into the sample chamber.
0:45:21 > 0:45:23Now, a comet in the outer solar system
0:45:23 > 0:45:26will only get a little bit of radiation at any given time
0:45:26 > 0:45:27because it is far from the sun,
0:45:27 > 0:45:31but since a comet is in orbit around the sun for over four billion years,
0:45:31 > 0:45:32the radiation can build up
0:45:32 > 0:45:35and you can actually get quite a large dose this way.
0:45:35 > 0:45:38The extreme cold of outer space
0:45:38 > 0:45:42and the radiation of the sun would seem to destroy any prospects
0:45:42 > 0:45:46of creating even the building blocks of life in outer space.
0:45:47 > 0:45:49But Dr Sandford has discovered
0:45:49 > 0:45:54the radiation that reaches a comet seems to have an unexpected effect.
0:45:56 > 0:45:59The radiation that's hitting the ice in our samples
0:45:59 > 0:46:02breaks chemical bonds in these very simple compounds that are there,
0:46:02 > 0:46:06and that allows them to rearrange into more complex molecules,
0:46:06 > 0:46:08including a number of the amino acids,
0:46:08 > 0:46:11some of the building blocks of life on Earth which are used to build,
0:46:11 > 0:46:15for example, the proteins which play a large role in our biochemistry.
0:46:15 > 0:46:19And we always see that we make these amino acids in our samples
0:46:19 > 0:46:21and since our samples are made under an environment
0:46:21 > 0:46:25attempting to simulate the kinds of environments that are out in space,
0:46:25 > 0:46:27like in comets, we would anticipate
0:46:27 > 0:46:29these amino acids being produced in space as well,
0:46:29 > 0:46:31not just here on Earth.
0:46:36 > 0:46:41Dr Sandford's work suggests that amino acids could form on comets.
0:46:43 > 0:46:46But it's unlikely you can create life on them.
0:46:48 > 0:46:50However, scientists think
0:46:50 > 0:46:54there is a way in which comets could help create life on a planet.
0:46:58 > 0:47:03Bizarrely, the destructive force of comets hitting a planet
0:47:03 > 0:47:05could actually be the key to creating life.
0:47:10 > 0:47:15On impact with a planet, a medium-sized comet would explode
0:47:15 > 0:47:20with a force 15 times that of the entire nuclear arsenal on Earth.
0:47:27 > 0:47:30At the University of Kent, scientists have created
0:47:30 > 0:47:34an experiment to investigate what happens to the chemicals on a comet
0:47:34 > 0:47:37when they are subjected to a massive impact.
0:47:40 > 0:47:43Dr Mark Price is mixing the chemicals
0:47:43 > 0:47:45most commonly found on comets
0:47:45 > 0:47:49and freezing them to the low temperatures found in outer space.
0:47:51 > 0:47:53But this simulated icy comet
0:47:53 > 0:47:56has been placed at the end of a gun chamber.
0:47:57 > 0:48:01And this tiny projectile is about to be fired at it
0:48:01 > 0:48:05to mimic a collision between a planet and a comet.
0:48:07 > 0:48:08So what I'm doing here
0:48:08 > 0:48:13is loading the gun with a 1mm stainless steel projectile,
0:48:13 > 0:48:17which will travel down the gun at a speed of approximately 18,000km/h,
0:48:17 > 0:48:21which is approximately ten times faster than a normal gun.
0:48:24 > 0:48:26This is the first time we've taken these compounds,
0:48:26 > 0:48:30which give us a comet, and fired into it at very high speed.
0:48:30 > 0:48:32During such an event, we get very high temperatures,
0:48:32 > 0:48:35something of the order of 1,000 degrees centigrade,
0:48:35 > 0:48:39and very high pressures, of the order of half a million atmospheres.
0:48:43 > 0:48:45Two, one, go!
0:48:51 > 0:48:54The gun produces a massive explosion
0:48:54 > 0:48:56in the frozen chemicals held in the vacuum chamber.
0:49:05 > 0:49:08OK, so, here is our comet in a lab.
0:49:08 > 0:49:12We have just impacted this with a full projectile at 18,000km/h.
0:49:15 > 0:49:19The residue from the explosion is analysed by Dr Zita Martins
0:49:19 > 0:49:23at Imperial College in London, to find out what has happened to it.
0:49:24 > 0:49:27Instead of being destroyed,
0:49:27 > 0:49:30a remarkable transformation seems to have taken place.
0:49:33 > 0:49:35So our results are extremely exciting
0:49:35 > 0:49:37because we have proved experimentally
0:49:37 > 0:49:39for the first time ever that
0:49:39 > 0:49:42we can actually produce amino acids
0:49:42 > 0:49:45when a comet impacts the surface of a planet.
0:49:45 > 0:49:47Here you can see, actually,
0:49:47 > 0:49:49one of the amino acids we produce,
0:49:49 > 0:49:52also the tiny peaks are another amino acid,
0:49:52 > 0:49:55so the amino acids are the building blocks of life.
0:49:58 > 0:50:02It seems that the explosion creates the conditions
0:50:02 > 0:50:06for a major reorganisation of the chemicals on a comet.
0:50:08 > 0:50:10When the impact shock occurs,
0:50:10 > 0:50:13the pressure and the temperature increases
0:50:13 > 0:50:17and the bonds between the atoms of very simple molecules will break,
0:50:17 > 0:50:22and there is reorganisation and formation of more complex molecules,
0:50:22 > 0:50:25the building blocks of life, the amino acids.
0:50:29 > 0:50:32It now seems likely that complex amino acids can form
0:50:32 > 0:50:36both in the frozen wastelands of space on board icy comets,
0:50:36 > 0:50:40and also when the comet crashes into a planet.
0:50:46 > 0:50:50This suggests that the business of creating amino acids
0:50:50 > 0:50:53could be happening all over the universe.
0:50:57 > 0:51:01We know that impacts occur throughout our solar system
0:51:01 > 0:51:04because we can see craters in planetary surfaces.
0:51:05 > 0:51:08So our study shows that life may originate
0:51:08 > 0:51:11not only here on Planet Earth but throughout our solar system
0:51:11 > 0:51:14and probably in other parts of our universe.
0:51:21 > 0:51:25So far, the search for amino acids on comets
0:51:25 > 0:51:28has relied on creating artificial comets in the lab.
0:51:29 > 0:51:33Now, scientists desperately need to sample a real comet,
0:51:33 > 0:51:36to find out if it is home to amino acids.
0:51:40 > 0:51:44That won't happen with ISON, as it was only discovered a year ago.
0:51:47 > 0:51:50Six, cinq, quatre, trois...
0:51:50 > 0:51:54But another comet has been lined up for just such a sampling mission.
0:52:03 > 0:52:09In 2004, the European Space Agency launched the Rosetta spacecraft
0:52:09 > 0:52:11with the aim of landing on the surface of a comet
0:52:11 > 0:52:14and searching for amino acids in its nucleus.
0:52:17 > 0:52:22It's the first ever spacecraft to attempt to do so.
0:52:27 > 0:52:31So what we see here is a model of the spacecraft of Rosetta,
0:52:31 > 0:52:34nearly identical to the one flying to the comet
0:52:34 > 0:52:37and the main feature is the main antenna of the spacecraft
0:52:37 > 0:52:39pointing towards Earth,
0:52:39 > 0:52:42and you need a big antenna because the thing is far away,
0:52:42 > 0:52:44in order to get your signals down to Earth.
0:52:44 > 0:52:48What else you can see over there is this little tiny cone sticking out.
0:52:48 > 0:52:52That's one of the little jet engines that turn the thing around.
0:52:52 > 0:52:53There's about 12 of them,
0:52:53 > 0:52:57so you can twist it, you can make it point the way you want it,
0:52:57 > 0:53:01so that the thing you are interested in is in your field of view.
0:53:04 > 0:53:08The spacecraft should reach the comet Churyumov-Gerasimenko
0:53:08 > 0:53:12in November next year, after a 10-year journey.
0:53:13 > 0:53:18The rendezvous will take place just as the comet passes Jupiter,
0:53:18 > 0:53:21but the technical challenges are enormous.
0:53:21 > 0:53:24If you want to investigate a comet,
0:53:24 > 0:53:26you have to be fast in order to catch up with the comet.
0:53:26 > 0:53:32Currently Rosetta is doing 3,600km/h more than the comet does.
0:53:32 > 0:53:36That's about 1.5 times the maximum speed of the old Concorde.
0:53:36 > 0:53:40But you can't do much in order to brake, so it's a very careful balance
0:53:40 > 0:53:43between speeding up in order to get there
0:53:43 > 0:53:47and not being too fast, otherwise you will crash into it or fly past.
0:53:49 > 0:53:53The rendezvous is going to be the easy part of the mission.
0:53:53 > 0:53:57Attached to the side of the spacecraft is the Philae lander,
0:53:57 > 0:54:00which will descend onto the surface of the comet.
0:54:02 > 0:54:04It's very challenging in terms of timing
0:54:04 > 0:54:07and there is no possibility to make mistakes.
0:54:07 > 0:54:09We have a limited period of time to approach the comet
0:54:09 > 0:54:11and eventually land.
0:54:11 > 0:54:13The first challenge we have in approaching the landing
0:54:13 > 0:54:17is really to fly to an environment that is not known to us.
0:54:17 > 0:54:19Of the comet we know almost nothing.
0:54:21 > 0:54:25The major problem is that so little is known about the cometary nucleus,
0:54:25 > 0:54:28the central, supposedly solid, body.
0:54:28 > 0:54:32It could be either having a crust on the top,
0:54:32 > 0:54:35so it could be like an eggshell with something soft underneath,
0:54:35 > 0:54:37or the whole surface could be very, very soft.
0:54:37 > 0:54:40The extreme case would be something like cigarette ash,
0:54:40 > 0:54:44so the whole lander may fall into something very fluffy,
0:54:44 > 0:54:45we simply don't know yet.
0:54:45 > 0:54:48And the last thing you want is the thing to bounce off the surface
0:54:48 > 0:54:50because then it would be lost to space.
0:54:50 > 0:54:54So you need to do everything you can to stick to the cometary nucleus.
0:54:54 > 0:54:58One idea is to make it kind of sticky, so that it doesn't jump off.
0:54:58 > 0:55:03The second idea is ice screws in the feet that try to go into the surface
0:55:03 > 0:55:05and there's also two harpoons
0:55:05 > 0:55:08that are going to be fired into the cometary nucleus,
0:55:08 > 0:55:12with the hope that with the ropes attached to these little harpoons,
0:55:12 > 0:55:16the cometary lander, Philae, will stay where it is.
0:55:16 > 0:55:20It's frightening, because so little is known about the parameters
0:55:20 > 0:55:21you have to encounter.
0:55:21 > 0:55:24For the engineers, that was pure horror.
0:55:26 > 0:55:29If the Rosetta mission is successful, it will confirm
0:55:29 > 0:55:32not only the presence of amino acids
0:55:32 > 0:55:35but also whether they are any more developed
0:55:35 > 0:55:38than the ones found in the laboratories.
0:55:40 > 0:55:44So if we find complicated amino acids in the nucleus of a comet,
0:55:44 > 0:55:49it would provide another building block in the story of biology.
0:55:49 > 0:55:51Currently biology is Earth-centred,
0:55:51 > 0:55:53because that's the only source of biology we know,
0:55:53 > 0:55:57and it's the only example of biology we have.
0:55:57 > 0:56:01But if we find the really, really complicated biomolecules,
0:56:01 > 0:56:04it could point in the direction
0:56:04 > 0:56:08that biology is a much more general phenomenon in the universe
0:56:08 > 0:56:11and that other places that could harbour life would do so
0:56:11 > 0:56:12in an almost inevitable way.
0:56:23 > 0:56:24Personally I'd be amazed
0:56:24 > 0:56:26if there isn't life on other planets out there.
0:56:26 > 0:56:29It's quite possible that the vast majority would be very simple stuff,
0:56:29 > 0:56:31kind of pond scum kind of things,
0:56:31 > 0:56:34but we know from the history of our own planet
0:56:34 > 0:56:36that some pond scum evolves,
0:56:36 > 0:56:38so this could happen on other planets as well.
0:56:38 > 0:56:40So the possibility there's other intelligent life out there
0:56:40 > 0:56:42is certainly one well worth exploring.
0:56:48 > 0:56:53From December 3rd, one of the greatest comets of our lifetime
0:56:53 > 0:56:56could fly through our skies.
0:56:56 > 0:57:00It won't just be scientists who will wonder at its glory.
0:57:01 > 0:57:04If Comet ISON survives its solar passage,
0:57:04 > 0:57:06then I'm hoping it's going to be
0:57:06 > 0:57:08a glorious sight in the early morning skies,
0:57:08 > 0:57:10the pre-dawn skies in early December.
0:57:10 > 0:57:13Looking towards the east before sunrise,
0:57:13 > 0:57:17you should see a beautiful tail stretching upwards from the horizon.
0:57:17 > 0:57:20Millions of people will be able to see it, everybody should go out
0:57:20 > 0:57:24and see it, because a truly great comet is a wonderful sight.
0:57:24 > 0:57:27We never know when one is going to come around,
0:57:27 > 0:57:29we never know when the next one's coming.
0:57:29 > 0:57:32If you've got the chance, you should take it.
0:57:33 > 0:57:39In the next few days, Comet ISON and its secrets will be revealed.
0:58:02 > 0:58:05Subtitles by Red Bee Media Ltd