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0:00:01 > 0:00:03- Jupiter.
0:00:04 > 0:00:08- The biggest and most important - of all the planets.
0:00:09 > 0:00:13- All the planets in the solar system - would fit into Jupiter.
0:00:13 > 0:00:16- Without Jupiter, - we would not be here today.
0:00:18 > 0:00:22- It controls - everything that surrounds us.
0:00:22 > 0:00:27- Jupiter's huge effect on our solar - system can be seen even today.
0:00:28 > 0:00:33- In this programme, we discover why - life on earth relies on this planet.
0:00:33 > 0:00:38- Jupiter is the shepherd - of our solar system.
0:00:39 > 0:00:41- We reveal - Jupiter's biggest secrets...
0:00:42 > 0:00:46- ..and ask if this is the best place - to find alien life in the cosmos.
0:00:48 > 0:00:52- If we had to name the places - where alien life is most possible...
0:00:54 > 0:00:57- ..Jupiter would be - at the top of that list.
0:01:15 > 0:01:17- Jupiter.
0:01:27 > 0:01:31- Named after the Roman king - of the gods - the god of the sky.
0:01:34 > 0:01:39- If I looked at our solar system - from afar, I wouldn't see the earth.
0:01:39 > 0:01:40- It's too small.
0:01:40 > 0:01:42- I would see our sun.
0:01:43 > 0:01:46- Jupiter would probably be - the only visible planet.
0:01:54 > 0:01:59- This vast planet has had a huge - influence on our solar system.
0:02:03 > 0:02:08- But despite its size, we know very - little about the planet itself.
0:02:10 > 0:02:12- In the Roman myth...
0:02:13 > 0:02:17- ..Jupiter drew a veil of clouds - around him to hide his mischief.
0:02:17 > 0:02:21- That, to some extent, is what's - happened when we look at Jupiter.
0:02:22 > 0:02:26- We're seeing not the surface of - a planet but the edge of a cloud.
0:02:27 > 0:02:29- It has no surface.
0:02:29 > 0:02:32- You can't stand on it, - not even in a space suit.
0:02:33 > 0:02:35- It's all gas.
0:02:38 > 0:02:41- This shroud of gas - hides Jupiter's deepest secrets.
0:02:43 > 0:02:48- What lies behind the clouds - and the beautiful bands of colour?
0:02:49 > 0:02:51- It's a mystery.
0:02:54 > 0:02:58- But we do know that - what's happening inside Jupiter...
0:02:58 > 0:03:00- ..gives the planet its power.
0:03:01 > 0:03:04- One of the big mysteries of Jupiter - is what is its core?
0:03:05 > 0:03:07- It's something we don't know yet.
0:03:09 > 0:03:13- What we do know is that the planet's - atmosphere is very dangerous.
0:03:15 > 0:03:17- The atmosphere is so thick...
0:03:19 > 0:03:23- ..the atmospheric pressure - at Jupiter's core...
0:03:23 > 0:03:28- ..would be thousands of times - greater than earth's atmosphere.
0:03:33 > 0:03:38- Travelling in a jet plane from the - cloud tops to the planet's centre...
0:03:38 > 0:03:40- ..would take three days.
0:03:41 > 0:03:46- The descent would be difficult, - dangerous and maybe impossible.
0:03:50 > 0:03:52- We know that from experience.
0:03:53 > 0:03:55- The Galileo spacecraft...
0:03:55 > 0:03:59- ..dropped a probe into - Jupiter's atmosphere 20 years ago.
0:04:03 > 0:04:08- The Galileo spacecraft orbited - Jupiter and its moons for years.
0:04:09 > 0:04:10- At the end of its life...
0:04:10 > 0:04:14- ..they decided to send a probe - into the atmosphere.
0:04:18 > 0:04:24- The probe travels through the clouds - at speeds of 106,000 miles per hour.
0:04:28 > 0:04:33- Jupiter is so big and dense, - gravity is very strong.
0:04:34 > 0:04:36- Before hitting the clouds...
0:04:37 > 0:04:41- ..the probe accelerated - to exceptionally high speeds.
0:04:43 > 0:04:45- When it hit the atmosphere...
0:04:45 > 0:04:48- ..it had to be very dense - to decelerate...
0:04:48 > 0:04:53- ..and lose the immense heat - that was created outside the probe.
0:04:54 > 0:04:59- The Galileo probe reached pressure - levels much higher than the earth...
0:05:00 > 0:05:04- ..after entering the first - tiny percentage of the atmosphere.
0:05:11 > 0:05:15- On its journey through the clouds, - the probe's sensors reveal...
0:05:16 > 0:05:20- ..that hydrogen makes up - 90% of Jupiter's atmosphere.
0:05:23 > 0:05:24- It's a fierce place.
0:05:25 > 0:05:28- Temperatures soar - to over 300 degrees.
0:05:29 > 0:05:31- Winds rage at 400 miles per hour.
0:05:37 > 0:05:41- Under an hour after - entering Jupiter's atmosphere...
0:05:41 > 0:05:43- ..the probe vaporizes.
0:05:47 > 0:05:49- Jupiter's core remains a mystery.
0:05:53 > 0:05:57- The journey to Jupiter's centre - remains impossible...
0:05:58 > 0:06:01- ..so scientists try to recreate it - in a lab.
0:06:01 > 0:06:06- At the National Ignition Facility - near San Francisco...
0:06:06 > 0:06:10- ..they aim to achieve this - by using the world's largest laser.
0:06:12 > 0:06:15- There are a lot of other facilities - where we can generate...
0:06:15 > 0:06:18- ..states that are found - at the centre of the earth...
0:06:19 > 0:06:21- ..or some of the other - terrestrial planets.
0:06:22 > 0:06:26- This is the only place you can - recreate the interior of Jupiter.
0:06:29 > 0:06:34- They take hydrogen, the most common - element in Jupiter, and freeze it.
0:06:36 > 0:06:40- They then fire the laser - through a series of chambers...
0:06:40 > 0:06:44- ..a process which increases - the probe's size and power.
0:06:46 > 0:06:49- Eventually, the beams converge.
0:06:55 > 0:06:57- For a fraction of a second...
0:06:57 > 0:07:01- ..the laser bombards the hydrogen - with huge energy.
0:07:04 > 0:07:07- At those very extreme pressures...
0:07:07 > 0:07:10- ..100 million atmospheres - of pressure...
0:07:11 > 0:07:14- ..chemistry is completely different.
0:07:17 > 0:07:20- Instead of distorting - the chemical bond...
0:07:21 > 0:07:25- ..you're distorting - how the atom itself behaves.
0:07:25 > 0:07:29- Matter behaves - in a fundamentally different way...
0:07:29 > 0:07:33- ..than we experience it - here, on earth.
0:07:35 > 0:07:39- The atoms break down, transforming - the hydrogen gas into a liquid.
0:07:41 > 0:07:42- A liquid metal.
0:07:43 > 0:07:48- Essentially, you would have - this very dense structure...
0:07:48 > 0:07:52- ..and it would perhaps look like - this massive ball of mercury...
0:07:53 > 0:07:55- ..at the centre of Jupiter.
0:08:01 > 0:08:03- At the centre of the planet...
0:08:03 > 0:08:08- ..it seems hydrogen creates - something similar to metal.
0:08:15 > 0:08:18- The core rotates - at an immense speed...
0:08:18 > 0:08:23- ..generating a vast, highly - radioactive electromagnetic field.
0:08:23 > 0:08:27- The magnetic field around Jupiter - is very strong.
0:08:27 > 0:08:31- When you turn on a TV - and you pick some static...
0:08:32 > 0:08:36- ..some of it was caused - by Jupiter's magnetic field.
0:08:36 > 0:08:40- Jupiter can interfere - with our television signals!
0:08:40 > 0:08:44- Immense heat - is created inside Jupiter...
0:08:46 > 0:08:50- ..and we can see its effects - on the planet's surface.
0:08:56 > 0:09:00- Heat comes from the core, - warming the atmosphere.
0:09:01 > 0:09:04- We can see the clouds simmering...
0:09:04 > 0:09:08- ..as they carry chemicals - from the centre of the atmosphere.
0:09:09 > 0:09:13- That's why we see these wonderful - colours in Jupiter's clouds.
0:09:16 > 0:09:21- On earth, the sun's heat - drives our weather.
0:09:23 > 0:09:24- But not on Jupiter.
0:09:32 > 0:09:35- Heat rises - from the centre of the planet.
0:09:37 > 0:09:41- A mixture of chemicals and gas - creates colourful clouds.
0:09:46 > 0:09:51- Jupiter rotates faster than any - other planet in our solar system.
0:09:57 > 0:10:01- It rotates once every ten hours, - which is much faster the earth.
0:10:04 > 0:10:08- Like the sun, its equator - rotates quicker than its poles.
0:10:13 > 0:10:15- Looking through a telescope...
0:10:16 > 0:10:20- ..we can see the planet is wider - at its equator than pole to pole.
0:10:20 > 0:10:24- It rotates so quickly, - its centre bulges out.
0:10:25 > 0:10:28- This marriage of heat and motion...
0:10:28 > 0:10:32- ..creates one of the largest storms - in the cosmos.
0:10:33 > 0:10:38- As far as we know, Galileo was the - first person to see the red spot...
0:10:38 > 0:10:41- ..back in the 17th century...
0:10:42 > 0:10:46- ..so we know it's been there for - at least 400 years, if not longer.
0:10:47 > 0:10:51- And it's a huge storm, - like a hurricane on earth.
0:10:52 > 0:10:55- From space, you can see - these terrifying hurricanes...
0:10:57 > 0:10:59- ..as things spin around.
0:10:59 > 0:11:03- These storms are created - by the planet's rotation.
0:11:03 > 0:11:06- The Coriolis Force - causes these storms to form.
0:11:08 > 0:11:11- On earth, cyclones weaken - when they hit land.
0:11:12 > 0:11:15- But Jupiter has no land - to stop its storms.
0:11:19 > 0:11:22- It's a storm - which has lasted at least 400 years.
0:11:23 > 0:11:25- When we experience a storm - on earth...
0:11:25 > 0:11:28- ..we know it will only last - for a few days.
0:11:29 > 0:11:32- Even the worst hurricanes - will last only a week or two.
0:11:33 > 0:11:35- They eventually lose their energy.
0:11:36 > 0:11:39- A 400-year storm - would be a huge problem.
0:11:40 > 0:11:43- Galileo spotted it - and it's still there.
0:11:43 > 0:11:47- I'm sure it will continue - for hundreds of years.
0:11:50 > 0:11:55- Because of its size, Jupiter's - storms will last into the future.
0:12:02 > 0:12:05- But how did Jupiter become so big?
0:12:08 > 0:12:12- To answer this, we must go back - over four billion years.
0:12:13 > 0:12:17- In the dust and gas left over - from the sun's formation...
0:12:17 > 0:12:20- ..the first planet forms - Jupiter.
0:12:22 > 0:12:27- Jupiter is five times further - from the sun than the earth...
0:12:27 > 0:12:30- ..and probably formed - earlier than the others.
0:12:31 > 0:12:36- It pulled in much more of the disc - around the sun before the others.
0:12:40 > 0:12:43- The fact it's big - and started out so big...
0:12:43 > 0:12:47- ..means it mopped up matter - around the solar system...
0:12:47 > 0:12:49- ..including comets, dust and gases.
0:12:52 > 0:12:56- Jupiter forms at the right time - and in the right place.
0:12:59 > 0:13:02- Just at the point - where water vapour turns to ice.
0:13:06 > 0:13:09- Jupiter is right at the point - where ice can form.
0:13:10 > 0:13:13- At this point, - ice and water can exist.
0:13:16 > 0:13:18- So when Jupiter was created...
0:13:19 > 0:13:23- ..one of the reasons it grew so much - was that ice could exist here.
0:13:23 > 0:13:27- Planets like earth, Venus - and Mars are made of rock...
0:13:27 > 0:13:30- ..so they can't expand hugely.
0:13:31 > 0:13:35- But in icy conditions, - mass can bind together.
0:13:35 > 0:13:37- Once this had happened...
0:13:37 > 0:13:41- ..it was possible to pull in - all these gases around Jupiter.
0:13:42 > 0:13:44- And as Jupiter grew bigger...
0:13:45 > 0:13:48- ..its ability to pull in more mass - also increased.
0:13:49 > 0:13:52- That resulted in the huge planet - we see today.
0:13:53 > 0:13:56- We're lucky to exist at all - because Jupiter is so big...
0:13:57 > 0:14:00- ..it could have mopped up everything - before the earth formed.
0:14:03 > 0:14:06- The planet - eats everything in its reach...
0:14:07 > 0:14:09- ..to become the giant we see today.
0:14:12 > 0:14:14- Had it continued to grow...
0:14:15 > 0:14:18- ..it's likely Jupiter - would have turned into a star.
0:14:21 > 0:14:24- What turns into a star - depends on its mass.
0:14:25 > 0:14:29- You reach a point - where something is big enough...
0:14:30 > 0:14:34- ..to start nuclear reactions, - which turns it into a star.
0:14:35 > 0:14:38- Jupiter generates energy - from its core...
0:14:39 > 0:14:43- ..but it's not big enough - to start the nuclear reactions...
0:14:44 > 0:14:46- ..which would turn it into a star.
0:14:46 > 0:14:49- So you could describe Jupiter - as a failed star.
0:14:50 > 0:14:54- The night sky and the day sky - would look very different.
0:14:54 > 0:14:57- We'd have two stars.
0:14:57 > 0:15:00- And night might not be night, - it might be day.
0:15:01 > 0:15:05- Four fifths of all the stars we see - in the night sky...
0:15:06 > 0:15:08- ..are two stars orbiting each other.
0:15:13 > 0:15:16- So why didn't Jupiter become a star?
0:15:18 > 0:15:22- Jupiter is immense. It's 1,000 times - the mass of the earth.
0:15:22 > 0:15:26- But the sun is a million times - the mass of the earth.
0:15:26 > 0:15:29- It's too small - for the processes at its centre...
0:15:30 > 0:15:35- ..to heat it to the level necessary - to fuse hydrogen into helium.
0:15:38 > 0:15:42- After billions of years - gathering gases and dust...
0:15:42 > 0:15:44- ..Jupiter is finally created.
0:15:47 > 0:15:51- But the planet is drifting, - and is moving towards the sun.
0:15:52 > 0:15:57- In early days of the cosmos, - the sun pulls Jupiter closer.
0:15:59 > 0:16:03- So what will save the planet - from a fiery death?
0:16:07 > 0:16:08- .
0:16:18 > 0:16:18- Subtitles
0:16:18 > 0:16:20- Subtitles- - Subtitles
0:16:32 > 0:16:36- Jupiter is the biggest planet - with the biggest influence.
0:16:38 > 0:16:41- But beyond our solar system, - Jupiter is not unique.
0:16:44 > 0:16:49- Scientists discovered the first - planet beyond our solar system...
0:16:49 > 0:16:51- ..some 20 years ago.
0:16:51 > 0:16:54- 51 Pegasi b - is a giant gas planet...
0:16:55 > 0:16:59- ..similar to Jupiter in every way, - except one thing.
0:17:03 > 0:17:08- The planets we've discovered tend to - be far closer to their star...
0:17:08 > 0:17:11- ..than Jupiter is to our sun.
0:17:11 > 0:17:16- Astronomers have since identified - over 1,000 similar planets.
0:17:19 > 0:17:22- Many orbit - extremely close to their star.
0:17:24 > 0:17:26- The planet WASP-33 b...
0:17:26 > 0:17:30- ..orbits so close to its star, - it's scorching.
0:17:32 > 0:17:36- It's the hottest planet - ever observed in our galaxy.
0:17:38 > 0:17:43- Some of the planets - are very close to their stars.
0:17:44 > 0:17:47- But Jupiter - is relatively far from the sun.
0:17:49 > 0:17:53- Some people suggest Jupiter formed - much further out...
0:17:53 > 0:17:55- ..and has moved closer to the sun.
0:17:56 > 0:18:00- It currently sits five times further - away from the sun than earth.
0:18:01 > 0:18:05- The theory is that other - Jupiter-like planets formed...
0:18:05 > 0:18:08- ..at similar distances - to where our Jupiter is.
0:18:09 > 0:18:13- A reaction to the disc of dust - in the early system...
0:18:13 > 0:18:17- ..caused these planets - to move closer to their star.
0:18:17 > 0:18:22- So the next question is, why didn't - this happen in our system?
0:18:25 > 0:18:29- To answer this, scientists - created a computer model...
0:18:29 > 0:18:34- ..to examine how the planets - in our solar system were formed.
0:18:38 > 0:18:40- We would build our models.
0:18:40 > 0:18:43- We'd get a Venus right where Venus - is supposed to be.
0:18:43 > 0:18:47- We'd get an earth right where - the earth is supposed to be.
0:18:47 > 0:18:49- But where Mars is today...
0:18:49 > 0:18:52- ..we were usually getting a Venus - or earth-mass planet.
0:18:53 > 0:18:57- No matter how we changed the model, - we always got a really big Mars.
0:18:57 > 0:19:00- Our simulations show that Mars - where it is in the disc...
0:19:01 > 0:19:03- ..should be at least ten times - the mass it is.
0:19:04 > 0:19:07- Something came in - and literally ate Mars as lunch.
0:19:08 > 0:19:10- And that something was Jupiter.
0:19:12 > 0:19:16- Jupiter was formed much closer - to the sun than it is today.
0:19:19 > 0:19:21- In the beginning...
0:19:21 > 0:19:26- ..it collides with the debris - left over from the sun's formation.
0:19:27 > 0:19:29- The sun's gravity - then pulls it closer.
0:19:31 > 0:19:33- Jupiter spirals inwards...
0:19:33 > 0:19:38- ..hoovering up the raw materials - that should have made Mars.
0:19:42 > 0:19:47- Seeing a great solution to the small - Mars problem was the Eureka moment.
0:19:47 > 0:19:49- Maybe there's a mechanism out there.
0:19:50 > 0:19:54- We know that planets migrate, - so let's put these things together.
0:19:55 > 0:19:57- As Jupiter travels inwards...
0:19:57 > 0:20:01- ..it bulldozes the material - that lies in its path.
0:20:01 > 0:20:05- On the inward migration - there's a lot of material there...
0:20:05 > 0:20:08- ..and it pushes - about 80% of it inward.
0:20:08 > 0:20:12- When we make the movies in a certain - way it looks like a snowplough.
0:20:14 > 0:20:18- It looks like Jupiter - will plummet into the sun.
0:20:23 > 0:20:26- Then, unexpectedly, - it changes direction.
0:20:28 > 0:20:32- A massive force is needed - to turn such a huge planet.
0:20:32 > 0:20:37- It seems our second-biggest planet, - Saturn, has saved the day.
0:20:42 > 0:20:46- It looks like Jupiter - starts moving closer to the sun...
0:20:46 > 0:20:50- ..but then Saturn's gravity - pulls Jupiter back out.
0:20:50 > 0:20:52- Saturn is also a large planet.
0:20:53 > 0:20:56- After a while, - the same process starts again.
0:20:57 > 0:21:02- Jupiter moving closer to the sun - and Saturn pulling it back out.
0:21:04 > 0:21:06- Over a long period of time...
0:21:06 > 0:21:10- ..it seems likely that Jupiter - will stay where it is today.
0:21:12 > 0:21:16- Saturn helps Jupiter - move away from the sun.
0:21:20 > 0:21:25- Both planets travel back - and reach their current position.
0:21:30 > 0:21:34- Because Saturn was formed - at the same time...
0:21:35 > 0:21:38- ..that reaction - between Jupiter and Saturn...
0:21:39 > 0:21:43- ..helped to position both planets - in their current orbit.
0:21:43 > 0:21:45- Saturn saves Jupiter.
0:21:48 > 0:21:52- And all this allows another planet - to grow - the earth.
0:21:55 > 0:22:00- Because when Jupiter moves out, - it leaves rocky debris behind.
0:22:04 > 0:22:08- It's from this debris - that the earth forms.
0:22:15 > 0:22:18- Our planet - and all the rocky planets exist...
0:22:19 > 0:22:22- ..because of Jupiter's epic journey.
0:22:27 > 0:22:30- When the biggest thing in the solar - system moves this far this fast...
0:22:31 > 0:22:33- ..it changes everything around it.
0:22:35 > 0:22:39- Five million years - after it first formed...
0:22:39 > 0:22:42- ..Jupiter reaches its present orbit.
0:22:43 > 0:22:47- But this is still not - the solar system that we see today.
0:22:48 > 0:22:52- By examining the solar system - in its early days...
0:22:54 > 0:22:58- ..it seems their distances - from the sun have changed.
0:22:59 > 0:23:04- That's because Jupiter and its huge - gravity influences their orbit.
0:23:05 > 0:23:07- Jupiter settles into its orbit...
0:23:08 > 0:23:12- ..but from its new position, - it can still wreak havoc.
0:23:12 > 0:23:16- It even threatens to destroy - our earth.
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0:23:29 > 0:23:29- Subtitles
0:23:29 > 0:23:31- Subtitles- - Subtitles
0:23:43 > 0:23:46- Over four billion years ago, - Jupiter forms...
0:23:47 > 0:23:50- ..and orbits - between the other planets.
0:23:52 > 0:23:58- From this vantage point, it controls - the other planets and wreaks havoc.
0:24:04 > 0:24:08- It's an incredibly violent time - in solar system history.
0:24:08 > 0:24:10- We refer to that timescale...
0:24:11 > 0:24:15- ..several hundred million years - after the planets formed...
0:24:15 > 0:24:18- ..as the Late Heavy Bombardment.
0:24:19 > 0:24:21- This was a horrific period.
0:24:25 > 0:24:27- We're going back 4.2 billion years.
0:24:30 > 0:24:32- The solar system - was a very busy place.
0:24:33 > 0:24:36- All sorts of rocks and planets - were moving around.
0:24:37 > 0:24:42- In a relatively short space of time, - they all collided...
0:24:42 > 0:24:46- ..and created the dance - we have at the moment.
0:24:51 > 0:24:53- If you were on earth then...
0:24:53 > 0:24:58- ..rocks would constantly fall - from space, hitting the planet...
0:24:58 > 0:25:03- ..and throwing gases, rocks and dust - into the atmosphere.
0:25:04 > 0:25:07- It would not have been - a very safe place to live.
0:25:19 > 0:25:23- That period of chaos has ended.
0:25:25 > 0:25:29- The earth is transformed - and the scars have disappeared.
0:25:32 > 0:25:36- But the evidence is still there - if we look up to the moon.
0:25:38 > 0:25:44- If you look up today at our moon, - we can see these ancient craters.
0:25:44 > 0:25:48- They were created - 4.6 billion years ago...
0:25:48 > 0:25:52- ..when Jupiter was throwing rocks - around our solar system...
0:25:53 > 0:25:55- ..hitting the earth and the moon.
0:25:56 > 0:25:59- The moon doesn't have - an atmosphere...
0:25:59 > 0:26:01- ..so it has no weather.
0:26:01 > 0:26:05- Without wind to blow the dust, - we can still see the craters.
0:26:06 > 0:26:08- If you look at the moon, - you can see them today.
0:26:11 > 0:26:16- Five years ago, the Spitzer Space - Telescope reveals a similar scene...
0:26:16 > 0:26:18- ..around a distant star.
0:26:20 > 0:26:23- Astronomers see a vast disc - of gas and dust...
0:26:23 > 0:26:26- ..circling a young star - called Eta Corvi.
0:26:28 > 0:26:32- Comets and asteroids swarming - into each other.
0:26:32 > 0:26:38- Four billion years ago, the same - thing happened in our solar system.
0:26:40 > 0:26:43- And in that early stage - of our history...
0:26:43 > 0:26:47- ..Jupiter started to - throw her weight around.
0:26:50 > 0:26:52- Many comets and asteroids...
0:26:53 > 0:26:57- ..were travelling around the sun - between the planets.
0:26:57 > 0:27:02- When approaching Jupiter, they were - thrown out or in, closer to the sun.
0:27:04 > 0:27:09- With Saturn's help, Jupiter pushes - the other two planets further out.
0:27:10 > 0:27:12- Uranus and Neptune swap places.
0:27:19 > 0:27:23- Neptune slams into - frozen dust and gas...
0:27:24 > 0:27:26- ..in the solar system's - outer reaches.
0:27:28 > 0:27:31- Debris is scattered far and wide.
0:27:36 > 0:27:39- They collide - with the asteroid belt...
0:27:40 > 0:27:43- ..orbiting the planets - close to the sun.
0:27:44 > 0:27:50- The asteroids are then thrown out, - hitting planets like earth.
0:27:56 > 0:28:00- But this destruction - contains the seeds of creation...
0:28:01 > 0:28:06- ..because the icy comets - deliver a precious cargo - water.
0:28:08 > 0:28:12- We're learning more and more - about the asteroids...
0:28:13 > 0:28:16- ..travelling - between Mars and Jupiter.
0:28:17 > 0:28:21- On less than a dozen of those, - we've discovered ice...
0:28:21 > 0:28:25- ..which means there's water - close to the surface.
0:28:26 > 0:28:29- They act as comets for part - of their journey around the sun.
0:28:30 > 0:28:35- And if many of the asteroids which - hit earth during its formation...
0:28:35 > 0:28:37- ..carried ice like this...
0:28:37 > 0:28:43- ..it's likely that's where the water - in our lakes and seas came from.
0:28:46 > 0:28:51- Every river, every raindrop - existing because of Jupiter.
0:28:57 > 0:29:00- The giant planet - may even have started life itself...
0:29:03 > 0:29:06- ..as water reached earth - on board one of these comets.
0:29:11 > 0:29:17- Jupiter helped create life - but it also protects life.
0:29:21 > 0:29:24- NASA scans the skies every day...
0:29:24 > 0:29:29- ..for asteroids and comets - which could hit the earth.
0:29:30 > 0:29:33- So far, they've spotted - over 10,000 of them.
0:29:36 > 0:29:40- And it only takes one to hit - the earth to cause a catastrophe.
0:29:42 > 0:29:44- Just three miles wide...
0:29:45 > 0:29:49- ..this small comet is big enough - to wipe out life on earth.
0:29:49 > 0:29:51- Luckily, Jupiter is in the way.
0:29:53 > 0:29:54- As Jupiter expanded...
0:29:55 > 0:29:58- ..it became the protector - of other planets.
0:29:58 > 0:30:02- Its gravity pulled any stray rocks - and comets towards it.
0:30:05 > 0:30:08- Some say Jupiter - allowed life to form on earth.
0:30:09 > 0:30:12- It has protected us - from most cosmic collisions...
0:30:13 > 0:30:15- ..for billions of years.
0:30:17 > 0:30:22- The way objects move in the solar - system is like a roller derby.
0:30:24 > 0:30:29- All these objects moving around - the sun in the same direction...
0:30:29 > 0:30:34- ..but they have gravity and they - can interact with each other.
0:30:34 > 0:30:37- The skater in white is an icy comet.
0:30:39 > 0:30:44- The skaters in black - are gas planets, like Jupiter.
0:30:45 > 0:30:48- The comet veers towards the planet.
0:30:51 > 0:30:53- Until it encounters Jupiter.
0:30:54 > 0:30:57- The comet is caught - by Jupiter's gravity.
0:30:58 > 0:31:02- And it's catapulted - in another direction.
0:31:06 > 0:31:09- It would be swung and escorted away.
0:31:10 > 0:31:14- You could describe Jupiter as - the shepherd of our solar system.
0:31:20 > 0:31:25- In the 1990s, astronomers - spotted a comet close to Jupiter.
0:31:25 > 0:31:27- Too close to get flung out.
0:31:29 > 0:31:34- Instead, Jupiter's gravity - rips the comet apart.
0:31:36 > 0:31:41- These comets are fragile and - the effects of Jupiter's gravity...
0:31:41 > 0:31:44- ..is strong enough - to rip them apart.
0:31:46 > 0:31:50- The original comet - was a few kilometres long.
0:31:50 > 0:31:54- I watched it through - a very small telescope in Surrey...
0:31:55 > 0:31:58- ..along with 12 other people.
0:31:59 > 0:32:02- As the comet hit - the dark side of Jupiter...
0:32:02 > 0:32:05- ..a few minutes later, - the planet turned...
0:32:06 > 0:32:10- ..and we could see black marks - in the planet's clouds.
0:32:12 > 0:32:15- As the comet passed through - Jupiter's atmosphere...
0:32:16 > 0:32:20- ..it left black soot marks, and - these could be seen in the clouds.
0:32:21 > 0:32:23- It was amazing to watch this unfold.
0:32:25 > 0:32:29- Some 200 times more comets - and asteroids smash into Jupiter...
0:32:30 > 0:32:33- ..than smash into the earth.
0:32:33 > 0:32:36- Jupiter is bigger - than the other planets...
0:32:37 > 0:32:41- ..so its gravity is stronger than - anything else in the solar system.
0:32:41 > 0:32:45- That's why things are pulled - in Jupiter's direction.
0:32:51 > 0:32:53- Our lives rely on Jupiter.
0:32:58 > 0:33:02- As new planets are discovered - orbiting other stars...
0:33:02 > 0:33:07- ..without a partnership between - more than one large planet...
0:33:07 > 0:33:10- ..to keep the biggest one - in position...
0:33:11 > 0:33:15- ..it's difficult to find a system - similar to ours.
0:33:15 > 0:33:19- Having a pair of big planets - like Saturn and Jupiter...
0:33:19 > 0:33:23- ..made it possible for small planets - like ours to exist.
0:33:26 > 0:33:32- Jupiter makes life on earth possible - and helps protect that life.
0:33:37 > 0:33:40- And it may even nurture alien life.
0:33:43 > 0:33:44- .
0:33:54 > 0:33:54- Subtitles
0:33:54 > 0:33:56- Subtitles- - Subtitles
0:34:06 > 0:34:09- Jupiter dominates - everything around it.
0:34:13 > 0:34:16- The largest planet - in our solar system...
0:34:16 > 0:34:19- ..also has - the largest number of moons.
0:34:20 > 0:34:26- There are dozens of moons orbiting - Jupiter - over sixty of them.
0:34:28 > 0:34:31- Some of those are made of rock.
0:34:31 > 0:34:35- Others are made of gases - and others a combination of both.
0:34:36 > 0:34:39- Each one has different attributes.
0:34:42 > 0:34:45- Jupiter has a huge influence - over all the moons.
0:34:46 > 0:34:49- And perhaps making - one of them home to life.
0:34:52 > 0:34:54- March 1st, 2007.
0:34:55 > 0:34:59- The New Horizon space probe - flies past a moon called Io.
0:35:00 > 0:35:03- As it passed Jupiter and the moon...
0:35:03 > 0:35:08- ..the probe turned around - and it saw something near Io.
0:35:11 > 0:35:14- At first, scientists were confused.
0:35:15 > 0:35:17- What could it be?
0:35:18 > 0:35:22- They then realized - it was a huge volcanic eruption.
0:35:25 > 0:35:30- This moon is the solar system's - most volcanic location.
0:35:31 > 0:35:34- It's home to at least - 400 active volcanoes.
0:35:36 > 0:35:40- Io orbits Jupiter - in an elliptic orbit...
0:35:41 > 0:35:45- ..similar to the orbit - our moon takes around the earth.
0:35:46 > 0:35:49- The moon's shape - changes all the time.
0:35:49 > 0:35:54- Just like squeezing a tennis ball - in your hand over and over again...
0:35:55 > 0:35:57- ..and the ball tennis heats up...
0:35:57 > 0:36:02- ..the effect of Jupiter's gravity - heats up the Io moon.
0:36:06 > 0:36:10- So much heat is released - by this process...
0:36:10 > 0:36:13- ..volcanoes appear - all over its surface.
0:36:14 > 0:36:19- It's likely Io has been - twisted and turned many times.
0:36:21 > 0:36:25- Sulphur dioxide - is emitted from the volcanoes...
0:36:25 > 0:36:31- ..and Jupiter's magnetic field - strips molecules of their electrons.
0:36:33 > 0:36:38- They're carried along - the magnetic field around Jupiter...
0:36:40 > 0:36:45- ..creating auroras like the - Northern Lights we have on earth.
0:36:49 > 0:36:53- Jupiter's magnetic field - transports chemicals...
0:36:53 > 0:36:57- ..from Io - to its neighbouring moon, Europa.
0:37:00 > 0:37:04- That's why this place is our - best hope of finding alien life.
0:37:07 > 0:37:11- When you look at pictures - of Europa's surface....
0:37:11 > 0:37:13- ..you can see ice...
0:37:15 > 0:37:18- ..which contains huge fractures.
0:37:18 > 0:37:22- It's similar to the landscape - of our North and South Poles.
0:37:25 > 0:37:28- These cracks and ridges - on Europa's surface...
0:37:29 > 0:37:33- ..show that ice has moved here - at some point in the past.
0:37:35 > 0:37:38- As there has been - so much movement...
0:37:38 > 0:37:42- ..it seems the layer of ice - on Europa's surface is quite thin.
0:37:49 > 0:37:52- Jupiter's gravity - pushes and pulls Europa.
0:37:54 > 0:37:57- It seems this sea is created...
0:37:57 > 0:38:01- ..because Jupiter's gravity, - along with the other moons...
0:38:02 > 0:38:03- ..warms Europa.
0:38:05 > 0:38:10- It's warm enough for there to be - water as liquid under the surface...
0:38:10 > 0:38:14- ..but not hot enough to create - volcanoes like the ones on Io.
0:38:17 > 0:38:20- We knew most of the moon - was covered in ice.
0:38:22 > 0:38:26- But significant interest - has developed recently...
0:38:26 > 0:38:31- ..after geysers that push water out - from under this ice were found.
0:38:34 > 0:38:36- November 2013.
0:38:36 > 0:38:41- Analysing photographs - from the Hubble Space Telescope...
0:38:41 > 0:38:44- ..scientists spot - two giant geysers...
0:38:44 > 0:38:47- ..spewing water - above Europa's south pole.
0:38:51 > 0:38:56- It's the best evidence yet of liquid - water beneath Europa's frozen crust.
0:38:59 > 0:39:02- These geysers - are a significant discovery.
0:39:03 > 0:39:07- It means there must be - liquid water underneath the ice.
0:39:12 > 0:39:16- For life to evolve, - it needs water and other chemicals.
0:39:17 > 0:39:22- And that's where Jupiter's - magnetosphere is important...
0:39:22 > 0:39:27- ..transporting chemicals from - the volcanic moon Io to Europa.
0:39:28 > 0:39:33- Scientists think this delivers - sulphur, carbon and other minerals.
0:39:38 > 0:39:43- Finding water elsewhere in - the solar system is very exciting.
0:39:44 > 0:39:49- If we named one place where life - could exist in our solar system...
0:39:49 > 0:39:52- ..Europa would be - at the top of the list.
0:39:53 > 0:39:56- So Europa's geysers - are a major discovery.
0:39:56 > 0:40:00- One of the exciting aspects - of seeing this geyser on Europa...
0:40:00 > 0:40:05- ..is it means the liquid ocean under - the surface has a way to get out.
0:40:05 > 0:40:09- Maybe there's a way for stuff from - the surface to get into the ocean.
0:40:10 > 0:40:12- It could be that in this ocean...
0:40:13 > 0:40:16- ..there's a nutrient-rich - supply of food.
0:40:20 > 0:40:23- Life needs water and food. - And something else.
0:40:24 > 0:40:26- You also need an energy source.
0:40:27 > 0:40:30- On the earth, that's the sun. - Its light warms the surface.
0:40:31 > 0:40:35- On Europa, if you're in that ocean - it's probably pitch black.
0:40:37 > 0:40:42- But here on earth, - life can exist without the sun.
0:40:45 > 0:40:50- Around 11% of our planet's surface - is covered by glaciers.
0:40:50 > 0:40:54- Underneath these glaciers, - there is life.
0:40:58 > 0:41:03- They're extreme conditions - - zero degrees Celsius all year round.
0:41:03 > 0:41:06- No energy from the sun reaches it...
0:41:06 > 0:41:11- ..and there is very little organic - matter or food for life to exist.
0:41:11 > 0:41:15- So we have water and we have heat - coming from inside the moon.
0:41:18 > 0:41:22- The seas under the layer of ice - on Europa's surface...
0:41:22 > 0:41:25- ..is one of a few places - in the solar system...
0:41:26 > 0:41:29- ..where we know the conditions - could sustain life.
0:41:40 > 0:41:46- If there is life beneath Europa's - surface, it may outlive us all.
0:41:48 > 0:41:53- Because, five billion years - from now, the sun is going to die.
0:41:59 > 0:42:02- We know for certain - that the sun will die.
0:42:03 > 0:42:08- In five billion years, that will be - the beginning of the end.
0:42:12 > 0:42:16- When the sun reaches the end - of its life, it will expand...
0:42:17 > 0:42:20- ..and swallow - some of the planets closest to it.
0:42:20 > 0:42:23- Mercury, Venus and the earth...
0:42:23 > 0:42:27- ..will probably be swallowed - by the sun as it expands.
0:42:29 > 0:42:32- The inner planets burn up.
0:42:33 > 0:42:35- Will Jupiter be next?
0:42:40 > 0:42:44- It's likely the sun will expand - very close to the earth's orbit.
0:42:45 > 0:42:48- There's a degree of uncertainty - about this.
0:42:49 > 0:42:55- But the planets further away - from the sun will not be engulfed.
0:42:59 > 0:43:02- It's likely that, - as the sun expands...
0:43:03 > 0:43:08- ..the larger planets further away - will get more light and heat.
0:43:10 > 0:43:15- There is water present on moons - around Jupiter and Saturn.
0:43:16 > 0:43:19- We could see life flourish - on those moons.
0:43:23 > 0:43:28- Moons like Europa will be far more - habitable than they are today.
0:43:30 > 0:43:34- We could see the ice on Europa melt.
0:43:41 > 0:43:45- Perhaps Europa will be - life's last refuge as the sun dies.
0:43:47 > 0:43:49- In the distant future...
0:43:49 > 0:43:55- ..Jupiter could enjoy temperatures - which are similar to earth's today.
0:43:56 > 0:44:01- So in billions of years, - maybe the moons orbiting Jupiter...
0:44:02 > 0:44:05- ..will be a place - where people could live.
0:44:08 > 0:44:10- In our dying solar system...
0:44:10 > 0:44:13- ..Jupiter's moons - may offer a safe haven.
0:44:14 > 0:44:15- But for how long?
0:44:17 > 0:44:21- The sun's outer layers - will gradually disappear...
0:44:22 > 0:44:25- ..but the core, - the white dwarf, will remain.
0:44:26 > 0:44:29- Over time, it will gradually - get darker and darker.
0:44:30 > 0:44:34- You wouldn't see the sun - from the surface of Jupiter...
0:44:34 > 0:44:37- ..when the sun - undergoes its final stage...
0:44:37 > 0:44:41- ..to become a piece of nuclear waste - drifting in outer space.
0:44:47 > 0:44:51- Jupiter and its moons - will become dark once more.
0:44:52 > 0:44:58- The white dwarf will lose its energy - and get darker and darker.
0:45:00 > 0:45:05- The gases and dust left over - from the sun will still be there...
0:45:08 > 0:45:12- ..but it will be a dark and cold - area of the universe.
0:45:13 > 0:45:16- Jupiter, because of its size, - will still be there...
0:45:18 > 0:45:21- ..orbiting what is left - of the sun forever.
0:45:29 > 0:45:30- Jupiter will live on.
0:45:32 > 0:45:35- And with it lives the hope of life.
0:45:36 > 0:45:41- Any remaining water in places - like Europa will turn back to ice.
0:45:45 > 0:45:47- It will be extremely cold.
0:45:47 > 0:45:51- People couldn't live there - but bacteria could survive.
0:45:54 > 0:45:58- Five billion years from now, - Jupiter will take centre stage.
0:46:04 > 0:46:08- Before long, we can reveal - more of Jupiter's secrets.
0:46:11 > 0:46:16- In August 2016, the Juno spacecraft - will go there...
0:46:16 > 0:46:20- ..opening a new chapter in the - big story of this huge planet.
0:46:27 > 0:46:32- Jupiter has had a huge influence - on our solar system.
0:46:33 > 0:46:34- That's evident.
0:46:37 > 0:46:41- Jupiter has been here - since the beginning...
0:46:41 > 0:46:43- ..and it will be here until the end.
0:46:46 > 0:46:49- Creator, protector, - nurturer and survivor.
0:46:51 > 0:46:54- Jupiter shaped the solar system - that we see today...
0:46:55 > 0:46:59- ..making life possible on earth, - and perhaps beyond.
0:47:00 > 0:47:04- We certainly owe Jupiter - a huge debt of gratitude.
0:47:34 > 0:47:36- S4C subtitles by Eirlys A Jones
0:47:36 > 0:47:37- .