0:00:02 > 0:00:03Our sun.
0:00:05 > 0:00:07The heart of the solar system.
0:00:07 > 0:00:10The giver of light, heat...
0:00:12 > 0:00:14..and, of course, life.
0:00:15 > 0:00:17But what does its future hold?
0:00:20 > 0:00:23Scientists are looking to the stars to find out.
0:00:24 > 0:00:28Between these two stars is what's going to happen to our sun.
0:00:31 > 0:00:34Scientists today are almost like modern-day prophets.
0:00:34 > 0:00:37They foresee an apocalyptic future.
0:00:39 > 0:00:41Imagine the ball is Andromeda Galaxy
0:00:41 > 0:00:44on a head-on collision with the Milky Way Galaxy.
0:00:45 > 0:00:49The fate of the Earth hangs in the balance.
0:00:49 > 0:00:50Wow! Look at this!
0:00:50 > 0:00:53The temperature at the surface of the Earth
0:00:53 > 0:00:55will be enough to melt rock.
0:00:55 > 0:00:58Enough to melt the whole surface of the Earth.
0:00:58 > 0:01:02Unfortunately, nobody will be around to see it, which is a pity.
0:01:07 > 0:01:10This is the story of how our sun
0:01:10 > 0:01:13will transform the solar system it binds together.
0:01:16 > 0:01:19Before bringing it to a spectacular end.
0:01:44 > 0:01:45Peoria, Illinois.
0:01:48 > 0:01:50An average city in Midwest America.
0:01:53 > 0:01:56But it has one claim to fame that's out of this world.
0:02:00 > 0:02:04In the middle of the town, there's a 46-foot-wide mosaic of the sun.
0:02:08 > 0:02:12The centrepiece of a huge scale model of our solar system,
0:02:12 > 0:02:15created by local astronomer, Sheldon Schafer.
0:02:16 > 0:02:19And here we are at the sun. And, boy, is it hot!
0:02:19 > 0:02:23It's about 10,000 degrees here at the surface.
0:02:23 > 0:02:26And over a million Earths could fit inside of the sun.
0:02:28 > 0:02:29Peoria's solar system,
0:02:29 > 0:02:3299 million times smaller than the real thing,
0:02:32 > 0:02:37accurately reveals the relative sizes of our sun and its planets.
0:02:37 > 0:02:39OK, we're all together?
0:02:39 > 0:02:41And the distances between them.
0:02:44 > 0:02:47My job title is curator of the solar system.
0:02:47 > 0:02:50And we just went 33 million miles
0:02:50 > 0:02:53until we got to this tiny little two-inch Mercury.
0:02:53 > 0:02:56All right, so we're headed off to Venus!
0:02:58 > 0:03:00From Mercury, the inner planets are strung along
0:03:00 > 0:03:05a picturesque riverside park, all the way to Mars.
0:03:05 > 0:03:08These planets are relatively close together.
0:03:12 > 0:03:15The outer planets are much further away,
0:03:15 > 0:03:17in some bizarre locations.
0:03:20 > 0:03:22Five miles from the image of the sun,
0:03:22 > 0:03:25above the local airport's check-in desks,
0:03:25 > 0:03:28is five-foot-wide Jupiter.
0:03:29 > 0:03:32If you're going to have a planet, you may as well have the biggest!
0:03:32 > 0:03:35So it's fun to have Jupiter.
0:03:35 > 0:03:37Occasionally, we have birds that decorate,
0:03:37 > 0:03:40so we've had to clean it. But not very often.
0:03:42 > 0:03:47While the children's section of a neighbouring town's library
0:03:47 > 0:03:48is home to Saturn.
0:03:56 > 0:03:59Uranus is in Princeville, Illinois.
0:04:01 > 0:04:05From there, it's a 10-mile drive along Route 91,
0:04:05 > 0:04:08or almost a billion miles in cosmic terms,
0:04:08 > 0:04:14to the old railroad depot in Wyoming, Illinois, and Neptune.
0:04:19 > 0:04:22And finally, in a furniture store
0:04:22 > 0:04:2540 Earth miles away from the centre of the sun
0:04:25 > 0:04:29in Kewanee, Illinois is distant Pluto.
0:04:34 > 0:04:39Peoria's models are a perfect likeness of the solar system today.
0:04:39 > 0:04:41But it won't always be this way.
0:04:45 > 0:04:49Scientists know that one day, the sun will fundamentally change.
0:04:52 > 0:04:54And transform the planets.
0:04:57 > 0:05:01Imagine fast-forwarding through the next seven billion years
0:05:01 > 0:05:05to watch the end of the solar system.
0:05:11 > 0:05:14Dr Eva Villaver can predict this future.
0:05:17 > 0:05:19Because everything that will happen to our sun
0:05:19 > 0:05:22is already happening to countless other stars.
0:05:25 > 0:05:28Some, known as solar twins,
0:05:28 > 0:05:30are remarkably similar to our own.
0:05:33 > 0:05:36The studies we are doing is because they are very important
0:05:36 > 0:05:38to understand not only the sun,
0:05:38 > 0:05:42but they tell us how the future of our own solar system will be.
0:05:44 > 0:05:48In 2013, a solar twin called CoRoT Sol 1 was discovered.
0:05:50 > 0:05:54CoRoT is over there, in the constellation of Monoceros.
0:05:54 > 0:05:55It's a star, like the sun,
0:05:55 > 0:05:58and has the same mass. Exactly the same mass.
0:05:58 > 0:06:02But astronomers found one particularly significant difference.
0:06:03 > 0:06:06It had a lower concentration of the element lithium,
0:06:06 > 0:06:10which helped them to accurately calculate its age.
0:06:10 > 0:06:14It's a star that is a little bit older than the sun.
0:06:14 > 0:06:17A few billion years older.
0:06:17 > 0:06:19And if we observe a star that is older than our sun,
0:06:19 > 0:06:22we know what will happen to the sun.
0:06:24 > 0:06:28This older version of our sun was giving out more radiation.
0:06:34 > 0:06:37So it helped us put the pieces together.
0:06:37 > 0:06:39As the sun will get older,
0:06:39 > 0:06:41it will become brighter. Much brighter.
0:06:47 > 0:06:51Our sun's luminosity is slowly increasing
0:06:51 > 0:06:54because of a change deep inside the sun.
0:06:58 > 0:07:01Where two opposing forces are in constant battle.
0:07:04 > 0:07:07Similar forces to those that act on a hot-air balloon.
0:07:12 > 0:07:17Pushing up and out is the immense pressure of hot gas.
0:07:17 > 0:07:20In the sun, this is created by nuclear fusion.
0:07:27 > 0:07:30The sun has been burning hydrogen into helium
0:07:30 > 0:07:33for thousands of millions of years now.
0:07:33 > 0:07:36This is like the propane bottles here.
0:07:36 > 0:07:39It's like generating heat that warms up the air
0:07:39 > 0:07:41that keeps the balloon going.
0:07:41 > 0:07:43That's what happens in the sun, too.
0:07:47 > 0:07:50But pulling down into the core of the sun
0:07:50 > 0:07:54is an equally powerful force - gravity.
0:07:54 > 0:07:58The life of the sun is nothing but a battle against gravity.
0:07:58 > 0:08:01We have the gravitational force trying to pull the stars,
0:08:01 > 0:08:02crush the stars together.
0:08:02 > 0:08:06I mean, like pushing it in, and then we have
0:08:06 > 0:08:09the thermal pressure of the gas pushing outwards.
0:08:09 > 0:08:13So the balance between the two forces is what keeps the sun stable.
0:08:18 > 0:08:20For 4.5 billion years,
0:08:20 > 0:08:23the two forces have been in perfect balance.
0:08:25 > 0:08:28But as time passes, this balance is shifting.
0:08:31 > 0:08:33As the sun fuses hydrogen,
0:08:33 > 0:08:38it produces around 600 million tonnes of helium every second,
0:08:38 > 0:08:40which is a denser gas.
0:08:42 > 0:08:44This change in density
0:08:44 > 0:08:46has a profound effect on the nuclear reactions.
0:08:49 > 0:08:53As the core gets denser, hydrogen is burned at a higher rate.
0:08:53 > 0:08:55It's like turning the burners up.
0:08:55 > 0:08:57I mean, we are increasing the energy
0:08:57 > 0:09:00that is coming out of the core at that point.
0:09:02 > 0:09:07As a result, our sun is getting 10% brighter every billion years.
0:09:11 > 0:09:15So the older it gets, the more it heats up the solar system.
0:09:18 > 0:09:22And scientists know that will one day have serious consequences...
0:09:26 > 0:09:28..for Walter Kinsman's favourite planet.
0:09:30 > 0:09:33The Earth is my favourite planet to paint.
0:09:34 > 0:09:36I never get my fill of it.
0:09:38 > 0:09:42He's painted all the planets in the Peoria solar system model,
0:09:42 > 0:09:45except Jupiter, which was too big to fit in his house.
0:09:47 > 0:09:51He's now painting a spare Earth for the local museum.
0:09:51 > 0:09:54I'm in the process of painting a storm system
0:09:54 > 0:09:57in the southern Indian Ocean.
0:09:57 > 0:09:59The beautiful white clouds
0:09:59 > 0:10:03up against the blue oceans is breathtaking.
0:10:05 > 0:10:08The Earth only has its oceans and clouds
0:10:08 > 0:10:12because it orbits in a band around the sun called the habitable zone.
0:10:14 > 0:10:19Which means it's just the right temperature for liquid water.
0:10:19 > 0:10:21And that makes it the only planet in the solar system
0:10:21 > 0:10:23where we know life can thrive.
0:10:28 > 0:10:30But as the sun becomes more powerful,
0:10:30 > 0:10:33the habitable zone will move.
0:10:37 > 0:10:40For a vision of the Earth in two billion years' time,
0:10:40 > 0:10:44astrobiologist Professor Lynn Rothschild
0:10:44 > 0:10:46believes we should look to Venus.
0:10:54 > 0:10:56Venus is up in the sky there.
0:10:56 > 0:10:59It's the brightest object after the sun and the moon.
0:10:59 > 0:11:01It's right near Jupiter this morning.
0:11:01 > 0:11:04It's just an absolutely spectacular day to see it.
0:11:08 > 0:11:11Venus and the Earth formed out of the same materials.
0:11:11 > 0:11:13They're roughly the same size.
0:11:13 > 0:11:16The difference is that Venus is closer to the sun.
0:11:23 > 0:11:27The surface of Venus is the most hellish planetary surface
0:11:27 > 0:11:28in our entire solar system.
0:11:32 > 0:11:35The winds are ridiculous. They're 350 miles per hour.
0:11:35 > 0:11:38And then the temperature is unbelievably hot,
0:11:38 > 0:11:42about 900 degrees or so Fahrenheit.
0:11:42 > 0:11:45So this is not a place that you'd want to be.
0:11:48 > 0:11:51It's no surprise Venus is warmer than Earth,
0:11:51 > 0:11:54but strangely, Venus is even hotter than Mercury,
0:11:54 > 0:11:57despite being further from the sun.
0:12:08 > 0:12:10In 2006, the Venus Express probe
0:12:10 > 0:12:13launched towards our nearest planet
0:12:13 > 0:12:18to analyse the Venusian atmosphere in unprecedented detail.
0:12:21 > 0:12:24It found a vital clue among the clouds
0:12:24 > 0:12:26to how Venus became so hot.
0:12:28 > 0:12:32Venus Express allowed us to see that
0:12:32 > 0:12:36there was a lot of deuterium, which is a heavy form of hydrogen, left.
0:12:36 > 0:12:40And that's indicative of the fact that there was once water here.
0:12:41 > 0:12:43It soon became clear that in the past,
0:12:43 > 0:12:45Venus was a very different world.
0:12:48 > 0:12:51So here was this beautiful water world,
0:12:51 > 0:12:55not too dissimilar to maybe what the Earth is like today.
0:12:55 > 0:12:58There was liquid water and reasonable atmospheric pressure
0:12:58 > 0:13:00and organic compounds.
0:13:00 > 0:13:03There's no reason that there shouldn't have been life.
0:13:13 > 0:13:17The evidence suggests that Venus was once in the habitable zone.
0:13:20 > 0:13:23But, as the sun grew brighter three billion years ago,
0:13:23 > 0:13:26it would have had a dramatic effect on the planet's water.
0:13:29 > 0:13:31As the sun started to get hotter,
0:13:31 > 0:13:33the surface of Venus started to get hotter.
0:13:33 > 0:13:36And therefore, the water turns into steam.
0:13:36 > 0:13:38And steam is a greenhouse gas,
0:13:38 > 0:13:41so that means it traps the solar radiation.
0:13:41 > 0:13:44And therefore, just like a greenhouse,
0:13:44 > 0:13:46it starts to get hotter and hotter.
0:13:48 > 0:13:50It seems a runaway greenhouse effect
0:13:50 > 0:13:54caused Venus to become the hottest planet in the solar system.
0:13:58 > 0:14:02Mercury, although closer to the sun, has no atmosphere and no water.
0:14:05 > 0:14:07Earth has both.
0:14:07 > 0:14:10And as the brighter sun evaporates our oceans,
0:14:10 > 0:14:14the effect is likely to be far more intense
0:14:14 > 0:14:16than the man-made global warming we see today.
0:14:19 > 0:14:23Over the next two billion years, temperatures on Earth will rocket.
0:14:25 > 0:14:30Life here must adapt...or die.
0:14:48 > 0:14:51Yellowstone National Park in North America
0:14:51 > 0:14:53is a natural laboratory for Lynn to study
0:14:53 > 0:14:56how life can survive in extreme conditions.
0:14:59 > 0:15:02The reason it's so great is that we have the whole range,
0:15:02 > 0:15:07from the top predators, things like wolves and bears and so on,
0:15:07 > 0:15:11all the way down to the beavers and the herbivores
0:15:11 > 0:15:13and down to the very tiny organisms
0:15:13 > 0:15:15and even some incredible microbes.
0:15:19 > 0:15:22Life here is used to dealing with extremes.
0:15:23 > 0:15:26But in about half a billion years' time,
0:15:26 > 0:15:29these extremes will go in the opposite direction
0:15:29 > 0:15:33as temperatures could climb by up to 20 degrees in some places.
0:15:38 > 0:15:42By then, life as we know it will have evolved to be very different.
0:15:45 > 0:15:47But just as some of today's animals
0:15:47 > 0:15:49have adapted to survive harsh winters,
0:15:49 > 0:15:53in the future, they may use similar strategies
0:15:53 > 0:15:55to cope with scorching summers.
0:15:55 > 0:15:58As the sun gets hotter, you could imagine the winter
0:15:58 > 0:16:00as being the very pleasant season
0:16:00 > 0:16:04and the summers become unbearably hot.
0:16:04 > 0:16:08So if you're thinking about a bear that lives in an area like this
0:16:08 > 0:16:10that would normally hibernate in the winter,
0:16:10 > 0:16:13if you turn the thermostat on the Earth high enough,
0:16:13 > 0:16:14it might be the reverse.
0:16:14 > 0:16:17So that now, animals would be hibernating in the summer
0:16:17 > 0:16:19and be active in the winter.
0:16:19 > 0:16:23And grasses would be setting seed now, in the spring,
0:16:23 > 0:16:26the seeds would be what would carry the plant through this harsh summer,
0:16:26 > 0:16:29and then, as the rains started again in the autumn,
0:16:29 > 0:16:33they would germinate and you would get the lush green in the winter.
0:16:38 > 0:16:41In less than a billion years' time,
0:16:41 > 0:16:43the greenhouse effect is expected to take off.
0:16:45 > 0:16:47Sending temperatures soaring.
0:16:54 > 0:16:56As it gets hotter and hotter on the land,
0:16:56 > 0:16:59eventually, even the winters will be too hot
0:16:59 > 0:17:02for most organisms, certainly, to live.
0:17:04 > 0:17:08So if you have a large animal, like, say, a bison,
0:17:08 > 0:17:10that's also warm-blooded, as it gets hotter and hotter,
0:17:10 > 0:17:14it won't be able to cool down and it will eventually die.
0:17:16 > 0:17:19And so ultimately, large animals like that will go extinct.
0:17:21 > 0:17:23In just over a billion years from now,
0:17:23 > 0:17:28the land could be nothing but a parched desert, devoid of life.
0:17:29 > 0:17:33The air is going to heat up much more quickly than water will.
0:17:33 > 0:17:37And so I predict that, just like the ancestors of whales
0:17:37 > 0:17:40and dolphins and so on moved from the land to the water,
0:17:40 > 0:17:43so will the descendants of bison, if they want to survive.
0:17:45 > 0:17:48But models suggest that in two billion years' time,
0:17:48 > 0:17:50even the water will have gone.
0:17:52 > 0:17:57As it boils away, the Earth would increasingly resemble Venus today.
0:18:01 > 0:18:04For those of us who are interested in the future of planet Earth,
0:18:04 > 0:18:08Venus is a really good model system.
0:18:10 > 0:18:13As the sun heats up and the oceans turn into steam,
0:18:13 > 0:18:16we will have a world that's not too dissimilar
0:18:16 > 0:18:17from what you see behind me in Yellowstone,
0:18:17 > 0:18:21where you see the hot water coming up to the surface
0:18:21 > 0:18:24and then turning into steam and going away.
0:18:24 > 0:18:26In less than three billion years' time,
0:18:26 > 0:18:30it's thought that the searing sun and a runaway greenhouse effect
0:18:30 > 0:18:33will have wiped out virtually all life on Earth.
0:18:35 > 0:18:38But intelligent life may just find a way out.
0:18:40 > 0:18:43We have something that the other organisms out there don't have.
0:18:43 > 0:18:45And that is we have technology.
0:18:45 > 0:18:48And we're going to have the option of going to other planets.
0:18:48 > 0:18:52As it gets too hot for the Earth, Mars will start to warm up.
0:18:52 > 0:18:56And so that means that it's just possible
0:18:56 > 0:18:58Mars will become a better place for life.
0:18:58 > 0:19:01Who knows? I have great faith in our descendants.
0:19:01 > 0:19:05By then, Mars is expected to be in the habitable zone.
0:19:06 > 0:19:09So it could provide a refuge.
0:19:09 > 0:19:11But not for ever.
0:19:11 > 0:19:15Because the next threat will be to the entire solar system.
0:19:20 > 0:19:24From 100 billion stars racing towards us.
0:19:27 > 0:19:29The Andromeda Galaxy.
0:19:33 > 0:19:35Scientists have long suspected
0:19:35 > 0:19:39it will one day crash into our galaxy, the Milky Way.
0:19:43 > 0:19:47But until recently, no-one had been able to say for sure.
0:19:51 > 0:19:55In 2012, Dr Tony Sohn stepped up to the plate.
0:19:57 > 0:20:00He and his team set out to precisely measure Andromeda's path
0:20:00 > 0:20:04and discover if it would be a near miss,
0:20:04 > 0:20:06a glancing blow...
0:20:07 > 0:20:08..or a head-on hit.
0:20:10 > 0:20:12To predict the outcome, he used a technique
0:20:12 > 0:20:15familiar to baseball players.
0:20:15 > 0:20:18I ran a experiment that can help explain how we measure
0:20:18 > 0:20:19the motion of Andromeda.
0:20:19 > 0:20:21Imagine a game of baseball.
0:20:21 > 0:20:25The batter is waiting for the ball thrown by the pitcher.
0:20:27 > 0:20:29To work out if the ball is on target,
0:20:29 > 0:20:33the batter needs to see whether it's drifting to the side or not.
0:20:34 > 0:20:37So they instinctively compare the motion of the ball
0:20:37 > 0:20:39against the background.
0:20:41 > 0:20:43Tony needed to apply the same principle
0:20:43 > 0:20:46to discover if Andromeda was heading towards us.
0:20:47 > 0:20:50But in order to measure the galaxy's motion,
0:20:50 > 0:20:54he had to find fixed points behind Andromeda to compare it to.
0:20:56 > 0:20:59A daunting task.
0:20:59 > 0:21:02Most of the stars we see in the sky are in our galaxy,
0:21:02 > 0:21:06so they cannot be used as background objects.
0:21:07 > 0:21:10Instead, Tony had to search for distant galaxies
0:21:10 > 0:21:13hundreds of millions of light-years away.
0:21:14 > 0:21:16Only one telescope was up to the job.
0:21:18 > 0:21:21We used the Hubble Space Telescope to do this project
0:21:21 > 0:21:24because we needed a very stable instrument
0:21:24 > 0:21:26and we needed to be above the Earth's atmosphere
0:21:26 > 0:21:29to get very high resolution of the image.
0:21:29 > 0:21:30With data from Hubble,
0:21:30 > 0:21:34Tony painstakingly tracked stars in Andromeda
0:21:34 > 0:21:36against distant galaxies.
0:21:38 > 0:21:40Just like a batter tracks a ball.
0:21:41 > 0:21:43Imagine the ball is Andromeda Galaxy
0:21:43 > 0:21:47and the fence behind that are background galaxies.
0:21:47 > 0:21:50And what we did was we compared the position
0:21:50 > 0:21:54of the Andromeda galaxies against the background galaxies over time.
0:21:54 > 0:21:57And that's how we measure the sideways motion.
0:21:57 > 0:21:59The results were conclusive.
0:22:01 > 0:22:05The sideways speed of Andromeda we measured was effectively zero.
0:22:05 > 0:22:08So we can say with certainty that Andromeda
0:22:08 > 0:22:11is on a head-on collision with the Milky Way Galaxy.
0:22:13 > 0:22:16Tony's team confirmed that over 100 billion stars
0:22:16 > 0:22:18are on course for a strike
0:22:18 > 0:22:22at 2,000 times the speed of a fastball.
0:22:26 > 0:22:30But since it's so far away, the galaxies won't collide
0:22:30 > 0:22:33until nearly four billion years from now.
0:22:36 > 0:22:39Tony's precise measurements allow him to predict
0:22:39 > 0:22:42how this clash of the titans will look.
0:22:44 > 0:22:48To anyone on Earth, it would be a spectacular sight.
0:22:50 > 0:22:54We'll see the Andromeda Galaxy getting bigger and bigger on the sky
0:22:54 > 0:22:57and then eventually, in about four billion years from now,
0:22:57 > 0:22:59we'll see the collision of the two galaxies.
0:23:06 > 0:23:09On impact, clouds of dust will be crushed together.
0:23:11 > 0:23:13With sensational results.
0:23:16 > 0:23:18What we'll see is a lot of stars getting formed,
0:23:18 > 0:23:22and this will look something like stellar fireworks on the sky.
0:23:30 > 0:23:33Tony can even calculate the odds that our solar system
0:23:33 > 0:23:36will crash into one of Andromeda's billions of stars
0:23:36 > 0:23:38during the collision.
0:23:40 > 0:23:44Perhaps surprisingly, the prognosis is good.
0:23:44 > 0:23:47Galaxies are essentially empty space.
0:23:47 > 0:23:51So the chance of stars colliding with another star is very slim
0:23:51 > 0:23:55because this distance between the stars is vast.
0:23:55 > 0:23:57So when the collision happens, the solar system
0:23:57 > 0:24:00will pass through an empty space between the stars.
0:24:04 > 0:24:07After passing like ghosts in the night,
0:24:07 > 0:24:10the irresistible pull of gravity will draw them back together
0:24:10 > 0:24:13over the next two billion years.
0:24:14 > 0:24:20To finally settle as a new super-galaxy, nicknamed Milkomeda.
0:24:24 > 0:24:27Our galaxy will no longer exist.
0:24:27 > 0:24:32Yet calculations suggest the solar system will survive.
0:24:34 > 0:24:36It will merge into one big galaxy
0:24:36 > 0:24:39and it will look like a giant ball on the sky.
0:24:41 > 0:24:44Sadly, it's unlikely anyone will be on Earth
0:24:44 > 0:24:47to witness this colossal galactic collision.
0:24:52 > 0:24:55But there's a slim chance an extreme form of life
0:24:55 > 0:24:59could be clinging on as the two galaxies meet,
0:24:59 > 0:25:03despite the searing heat from the ageing sun.
0:25:08 > 0:25:12In Yellowstone, Professor Lynn Rothschild has found evidence
0:25:12 > 0:25:16of what those last remaining Earthlings might be like.
0:25:18 > 0:25:22This area of Yellowstone is extremely acidic, and it's also hot.
0:25:22 > 0:25:24You can see the steam rising.
0:25:24 > 0:25:27So in other words, it's sort of like boiling battery acid.
0:25:27 > 0:25:32Very few living things can actually live at this high temperature.
0:25:32 > 0:25:35But there are a couple of organisms that are very well adapted for it
0:25:35 > 0:25:38and you can see the beautiful colours behind me.
0:25:40 > 0:25:43The kaleidoscopic colours of Yellowstone springs
0:25:43 > 0:25:45are caused by heat-loving microbes.
0:25:53 > 0:25:55We can pretty much use these as a thermometer.
0:25:55 > 0:25:57Anything that is green means
0:25:57 > 0:26:00that it's got chlorophyll, just like plants.
0:26:00 > 0:26:05And once they get to a temperature above about 73 degrees or so,
0:26:05 > 0:26:07their chlorophyll breaks down.
0:26:07 > 0:26:10And so when you start getting warmer than that,
0:26:10 > 0:26:12you start to move into other sorts of organisms.
0:26:12 > 0:26:15Organisms that, for example, eat iron.
0:26:15 > 0:26:18And then you see these beautiful orange colours.
0:26:18 > 0:26:21Once all the water on Earth has turned to steam,
0:26:21 > 0:26:24it's possible that heat-loving microbes could continue to live.
0:26:26 > 0:26:28In the clouds.
0:26:29 > 0:26:33We know some of the earliest organisms on the Earth were thermophiles.
0:26:33 > 0:26:35Organisms that lived at high temperature.
0:26:35 > 0:26:38And so at some point, it may be organisms like this
0:26:38 > 0:26:40that once again inherit the Earth.
0:26:43 > 0:26:46The microbes will have their day.
0:26:46 > 0:26:48But their reign will inevitably be cut short.
0:26:52 > 0:26:55Because when the sun is twice the age it is now,
0:26:55 > 0:27:01astronomers foresee a turbulent new phase...written in the stars.
0:27:05 > 0:27:07On a clear night, many of the stars
0:27:07 > 0:27:09you can see with your naked eye today
0:27:09 > 0:27:12are going through this phase.
0:27:12 > 0:27:16You can tell which ones they are because of their colour.
0:27:16 > 0:27:18They're known as red giants.
0:27:22 > 0:27:25It's very easy to see red giant stars because they are very bright.
0:27:25 > 0:27:27They are giant and they are bright.
0:27:27 > 0:27:30So they are everywhere in the sky.
0:27:30 > 0:27:32Some red giants are so large,
0:27:32 > 0:27:36you could fit our own sun inside them - millions of times over.
0:27:38 > 0:27:42Yet astronomers are confident our sun will one day grow
0:27:42 > 0:27:44to become one itself.
0:27:44 > 0:27:48So these stars are a glimpse of our future.
0:27:52 > 0:27:55If we study the stars that grow in size, we can tell the fate
0:27:55 > 0:27:58of the planetary systems that are orbiting in them.
0:27:58 > 0:28:00Stars like that give us already clues
0:28:00 > 0:28:04about what will be the future fate of our own solar system.
0:28:08 > 0:28:11The transformation of our sun into a red giant
0:28:11 > 0:28:14will begin deep below its surface,
0:28:14 > 0:28:17where all the heat is generated.
0:28:20 > 0:28:25The burning core is the only place hot enough for hydrogen to fuse.
0:28:25 > 0:28:28And yet it makes up less than 2% of the sun's total volume.
0:28:31 > 0:28:33For the next five billion years,
0:28:33 > 0:28:36it's thought the core will be stable,
0:28:36 > 0:28:40finely balanced between two phenomenal opposing forces.
0:28:42 > 0:28:44The crushing pull of gravity...
0:28:46 > 0:28:50..and the explosive push of nuclear-heated gas.
0:28:54 > 0:28:55But, like a hot-air balloon,
0:28:55 > 0:28:58the core will eventually run out of fuel.
0:29:00 > 0:29:03Just as gravity pulls the spent balloon down,
0:29:03 > 0:29:08in the sun, gravity will pull on the core, unopposed.
0:29:10 > 0:29:12When the balance is broken,
0:29:12 > 0:29:14because the hydrogen runs out in the core,
0:29:14 > 0:29:16the dominant force will be gravity.
0:29:16 > 0:29:18It will try to squeeze the core.
0:29:20 > 0:29:22But the sun will be far from spent.
0:29:22 > 0:29:24As gravity crushes the core,
0:29:24 > 0:29:27it will trigger a transformation in the rest of the sun.
0:29:29 > 0:29:33For the first time, the hydrogen gas surrounding the core
0:29:33 > 0:29:35will begin to fuse,
0:29:35 > 0:29:39giving the sun access to far more fuel than it's already burnt.
0:29:41 > 0:29:43We ran out already of one bottle of propane,
0:29:43 > 0:29:46but we have three more.
0:29:47 > 0:29:49So...it's like the sun.
0:29:53 > 0:29:57The burning shell of hydrogen releases so much heat
0:29:57 > 0:29:59that gravity is overwhelmed.
0:30:00 > 0:30:03Tipping the balance in favour of rapid expansion.
0:30:04 > 0:30:07Gravity is not winning the battle,
0:30:07 > 0:30:10so the star expands as a red giant.
0:30:14 > 0:30:18Astronomers predict that in about five billion years,
0:30:18 > 0:30:22the sun will start to grow into a vast, seething ball of fire.
0:30:26 > 0:30:28A red giant.
0:30:29 > 0:30:33Sending temperatures soaring across the solar system.
0:30:36 > 0:30:40The inner planets will become far too hot to support any kind of life.
0:30:41 > 0:30:44But the distant outer planets
0:30:44 > 0:30:48will bask in the warm glow of the sun for the first time.
0:30:51 > 0:30:56The habitable zone, where life can exist, will sweep out.
0:31:01 > 0:31:06In Peoria's solar system model, it would mean the habitable zone
0:31:06 > 0:31:09would leave town and head for the outskirts.
0:31:12 > 0:31:17Here, at the airport, is Jupiter.
0:31:17 > 0:31:19You got your bag sheet?
0:31:19 > 0:31:21You're all good, you're going to go to gate number ten.
0:31:21 > 0:31:25- And it is delayed until 1:30? - Yes, ma'am.
0:31:27 > 0:31:30My favourite planet, I would say, is Earth,
0:31:30 > 0:31:32but Jupiter's second, for sure.
0:31:32 > 0:31:34It's very cool. It's very cool.
0:31:39 > 0:31:42When the sun grows, Jupiter will come in from the cold.
0:31:45 > 0:31:47And although life as we know it
0:31:47 > 0:31:49could never survive on gassy Jupiter,
0:31:49 > 0:31:54the solar system's biggest planet has several icy moons.
0:31:57 > 0:32:01These are likely to melt and become cosmic watering holes
0:32:01 > 0:32:05for any refugees fleeing the parched inner solar system.
0:32:07 > 0:32:10Astronomers have speculated that Jupiter could change colour.
0:32:14 > 0:32:17As clouds of ammonia vaporise,
0:32:17 > 0:32:20it might turn a deep shade of blue.
0:32:25 > 0:32:28After Jupiter, astronomers expect the habitable zone
0:32:28 > 0:32:31to move swiftly towards Saturn.
0:32:33 > 0:32:37On Saturdays, we'll have families making that interplanetary trip
0:32:37 > 0:32:39from one planet to the other in our area.
0:32:39 > 0:32:43I think Saturn is more interesting because of the rings.
0:32:46 > 0:32:49If Saturn still has its icy rings by then,
0:32:49 > 0:32:52they're forecast to vaporise and disappear.
0:32:59 > 0:33:04But, like Jupiter, Saturn's icy moons could melt
0:33:04 > 0:33:06and be safe havens for life.
0:33:13 > 0:33:16Then, models predict the habitable zone
0:33:16 > 0:33:18will sweep out faster and faster,
0:33:18 > 0:33:22past the solar system's most distant planets and their moons.
0:33:23 > 0:33:25First, Uranus.
0:33:32 > 0:33:34Then, deep-blue Neptune.
0:33:36 > 0:33:39Astronomers think they, too, will be transformed.
0:33:39 > 0:33:43But exactly how they'll look in the future is still a mystery.
0:33:48 > 0:33:52Eventually, the habitable zone is forecast to pass beyond
0:33:52 > 0:33:54all the planets and their moons.
0:33:58 > 0:34:00But although Neptune's the final planet,
0:34:00 > 0:34:03the solar system doesn't finish there.
0:34:07 > 0:34:10At the Good's furniture store in Kewanee, Illinois...
0:34:12 > 0:34:16..adjacent to a wide selection of cabinets and coffee tables,
0:34:16 > 0:34:19is ex-planet Pluto
0:34:19 > 0:34:22and its large moon, Charon.
0:34:24 > 0:34:28In 2006, Pluto was downgraded to a dwarf planet.
0:34:30 > 0:34:32They say planet Pluto is no longer a planet,
0:34:32 > 0:34:34but to us, it will always be a planet.
0:34:36 > 0:34:39People are so amazed at how small planet Pluto is.
0:34:39 > 0:34:41They get up real close with their camera,
0:34:41 > 0:34:43just a couple of inches away to snap a really close shot.
0:34:46 > 0:34:49Astronomers have tried to predict what will happen
0:34:49 > 0:34:52as this distant outpost of the solar system warms.
0:34:55 > 0:34:58But because it's so small and remote,
0:34:58 > 0:35:01this world was shrouded in mystery...
0:35:03 > 0:35:04..until recently.
0:35:10 > 0:35:14In July 2015, the New Horizons' mission
0:35:14 > 0:35:17finally revealed Pluto's secrets.
0:35:23 > 0:35:27The first clear images ever captured of the dwarf planet
0:35:27 > 0:35:29revealed some startling terrain.
0:35:31 > 0:35:34Strange troughs, cliffs...
0:35:34 > 0:35:36and even dunes.
0:35:43 > 0:35:46Professor Lynn Rothschild is fascinated
0:35:46 > 0:35:50by this tiny world and its potential for life.
0:35:52 > 0:35:54With the New Horizons' mission,
0:35:54 > 0:35:57we really knew almost nothing about Pluto.
0:35:57 > 0:36:02And our knowledge of Pluto has just blossomed enormously.
0:36:02 > 0:36:04In fact, it's not blossomed, it's exploded.
0:36:11 > 0:36:15One of the most unexpected features is a towering series of peaks.
0:36:19 > 0:36:21Much, I think, to everyone's surprise,
0:36:21 > 0:36:24there were huge mountains that were found on Pluto.
0:36:24 > 0:36:26These things are as high as 11,000 feet.
0:36:26 > 0:36:30Sort of like the mountains behind me, here in the Rockies in Montana.
0:36:32 > 0:36:36Here on Earth, the chemical bonds that bind rock
0:36:36 > 0:36:41are strong enough to defy gravity by holding up mountains.
0:36:42 > 0:36:46Yet Pluto's crust is not made of rock, but ice.
0:36:58 > 0:37:01The -220 degree temperatures there
0:37:01 > 0:37:04alter the chemical bonds in Pluto's ice.
0:37:06 > 0:37:09And make it as strong as rock is here.
0:37:11 > 0:37:16Strong enough to hold up ice mountains as high as the Rockies.
0:37:22 > 0:37:25But the arrival of the habitable zone would change this.
0:37:27 > 0:37:29Pluto's frosty peaks could be destroyed.
0:37:32 > 0:37:34As the sun becomes hotter and hotter,
0:37:34 > 0:37:37the ice mountains will start to collapse, I would imagine,
0:37:37 > 0:37:40under their own weight because at that point,
0:37:40 > 0:37:43the ice won't be as hard as it is today.
0:37:43 > 0:37:46And at some point, it may in fact be warm enough
0:37:46 > 0:37:48for all this ice on Pluto to melt.
0:37:50 > 0:37:55Amid the destruction, something remarkable could emerge.
0:37:56 > 0:37:59A water world at the edge of our solar system.
0:38:01 > 0:38:04Once you have liquid water and little energy,
0:38:04 > 0:38:07that's very good news for life.
0:38:07 > 0:38:10At that point, it'll be warm enough
0:38:10 > 0:38:13that even, even Pluto will be in a habitable zone.
0:38:13 > 0:38:16It will finally have its moment in the sun.
0:38:18 > 0:38:21After a 12 billion year long winter,
0:38:21 > 0:38:24the expanding sun may bring spring to Pluto.
0:38:30 > 0:38:33But while the red giant nurtures Pluto...
0:38:34 > 0:38:38..it poses a grave threat to the planets of the inner solar system.
0:38:39 > 0:38:43They face total annihilation.
0:38:48 > 0:38:52In 2012, Dr Eva Villaver stumbled across grisly evidence
0:38:52 > 0:38:56of what red giants can do to their inner planets.
0:38:58 > 0:39:02A search for distant worlds had led to the constellation of Perseus,
0:39:02 > 0:39:07where a star called BD+48740
0:39:07 > 0:39:10caught her attention for two reasons.
0:39:12 > 0:39:16There we have a star, a red giant,
0:39:16 > 0:39:17that was very peculiar
0:39:17 > 0:39:21because the star itself has a very high content of lithium.
0:39:21 > 0:39:24And that's very unusual for this type of star.
0:39:24 > 0:39:29So that was one of the pieces of the puzzle and the other one was
0:39:29 > 0:39:32that it has a Jupiter-like planet orbiting the star
0:39:32 > 0:39:35that has an orbit that is very unusual.
0:39:36 > 0:39:40Eva thought the two strange features must be somehow connected.
0:39:41 > 0:39:43Something had happened that had affected
0:39:43 > 0:39:46both the planet and the star itself.
0:39:49 > 0:39:51The team analysed the possible causes...
0:39:52 > 0:39:56..and concluded there was only one event that could explain both.
0:39:58 > 0:40:02The most simple explanation is that something very violent happened.
0:40:04 > 0:40:07We think that the star had a multiple planetary system
0:40:07 > 0:40:10and what we see is just the leftover planet,
0:40:10 > 0:40:13but there was another planet that was eaten by the star.
0:40:16 > 0:40:21As one planet was engulfed by the star, it destabilised the other.
0:40:23 > 0:40:26Then it triggered lithium production by stirring the hot gases.
0:40:30 > 0:40:33So this star has eaten one of its planets
0:40:33 > 0:40:36as the star became a red giant.
0:40:39 > 0:40:41Eva had found compelling evidence
0:40:41 > 0:40:44that ageing stars can grow so large,
0:40:44 > 0:40:46they devour their inner planets.
0:40:51 > 0:40:53In around 5.5 billion years,
0:40:53 > 0:40:57our own sun will enter this extraordinary phase of its life.
0:40:58 > 0:41:02Evidence suggests its surface will reach out towards Mercury,
0:41:02 > 0:41:05Venus and Earth,
0:41:05 > 0:41:08threatening their very existence.
0:41:11 > 0:41:13Local astronomer Sheldon Schafer
0:41:13 > 0:41:17is leading his weekly inner-planetary bicycle tour.
0:41:18 > 0:41:21With the sun's surface hot on his heels.
0:41:21 > 0:41:24So right now, we're going at about four miles an hour.
0:41:24 > 0:41:26That's about half the speed of light.
0:41:26 > 0:41:33This peaceful Midwestern town is about to go on the ride of its life.
0:41:33 > 0:41:35And here we are, approaching Mercury.
0:41:39 > 0:41:42You can see it's easily a stunt double for the Earth's moon.
0:41:42 > 0:41:44It's a heavily-cratered world
0:41:44 > 0:41:46without an atmosphere, hot in the sun
0:41:46 > 0:41:48and cold in the darkness.
0:41:48 > 0:41:53But the solar system's smallest planet will get hotter still.
0:41:53 > 0:41:55Off to Venus!
0:41:55 > 0:41:56Because astronomers predict
0:41:56 > 0:42:01that less than a billion years into the red giant phase,
0:42:01 > 0:42:03the sun's surface will reach Mercury.
0:42:06 > 0:42:10After more than ten billion years of relative calm,
0:42:10 > 0:42:14the solar system will lose a planet.
0:42:20 > 0:42:23And the sun will continue to expand.
0:42:25 > 0:42:28Growing ever closer to Venus.
0:42:32 > 0:42:36OK, so here we are. We've come about 66 million miles
0:42:36 > 0:42:38and, er...Venus, you might notice,
0:42:38 > 0:42:41is almost exactly the same size as the Earth.
0:42:41 > 0:42:45And for that reason alone, it's been called the Earth's sister planet.
0:42:45 > 0:42:48But Earth will probably lose its sibling.
0:42:50 > 0:42:53Because most models of the sun's evolution
0:42:53 > 0:42:56show it easily enveloping Venus.
0:43:11 > 0:43:17The next planet...is Earth itself.
0:43:19 > 0:43:21You can see from wherever you're standing
0:43:21 > 0:43:24that the Earth is blue, with lots and lots of liquid water.
0:43:25 > 0:43:28By the time the sun engulfs Venus,
0:43:28 > 0:43:32the Earth's oceans are expected to have boiled away.
0:43:34 > 0:43:39The ultimate fate of our world appears to be on a knife edge.
0:43:46 > 0:43:48- A fortune cookie. - SHE CHUCKLES
0:43:50 > 0:43:53For years, scientists have been unsure
0:43:53 > 0:43:54what fortunes await the Earth.
0:43:54 > 0:43:56Uh-oh!
0:43:56 > 0:44:00Will it be swallowed by the sun?
0:44:00 > 0:44:02"The world will end in fire."
0:44:03 > 0:44:07Or will it outlive the sun, to face a frozen eternity in space?
0:44:07 > 0:44:10"The world will end in ice."
0:44:13 > 0:44:15Maybe!
0:44:15 > 0:44:19In 2001, astronomer Dr Robert Smith decided to investigate.
0:44:21 > 0:44:23His first calculations had ominous results.
0:44:25 > 0:44:27What we found, to our disappointment,
0:44:27 > 0:44:31was that the sun will expand to something like
0:44:31 > 0:44:35250 times its present size
0:44:35 > 0:44:40and the Earth's orbit is only about 215 times
0:44:40 > 0:44:41the present size of the sun.
0:44:41 > 0:44:47So it will certainly go beyond the present orbit of the Earth.
0:44:48 > 0:44:51But Robert foresaw that there was still hope for our planet.
0:44:54 > 0:44:57Another factor that could potentially save the Earth
0:44:57 > 0:44:59from the sun's clutches.
0:45:08 > 0:45:10He realised the Earth's destiny
0:45:10 > 0:45:13hangs on something called the solar wind.
0:45:13 > 0:45:17Highly-charged particles that stream out from the sun
0:45:17 > 0:45:20as its hot surface evaporates.
0:45:20 > 0:45:25Like the wind on Earth, this stream of particles is invisible.
0:45:25 > 0:45:26But you can see its effects.
0:45:29 > 0:45:32You can see the tail is always downwind of the kite.
0:45:32 > 0:45:37And you get the same kind of phenomenon with comets, for example.
0:45:37 > 0:45:40You can see that the tail of a comet,
0:45:40 > 0:45:42it's not always behind the direction of the comet,
0:45:42 > 0:45:45it's streaming away, always away from the sun.
0:45:47 > 0:45:50The solar wind also affects the sun itself.
0:45:52 > 0:45:56Solar wind is carrying away particles, so it does reduce the mass.
0:45:57 > 0:45:59As the sun loses mass,
0:45:59 > 0:46:03so the gravitational field of the sun gets weaker.
0:46:03 > 0:46:06It pulls less strongly on the planets
0:46:06 > 0:46:10and so the planets tend to move out, the orbits get bigger.
0:46:12 > 0:46:17As a red giant, the sun will lose a lot of mass through the solar wind.
0:46:18 > 0:46:21Robert wanted to know if it would be enough
0:46:21 > 0:46:23for the Earth to escape the advancing sun.
0:46:23 > 0:46:27So initially, it was just sheer curiosity.
0:46:27 > 0:46:31What happens to the Earth when the sun becomes a red giant?
0:46:34 > 0:46:38Robert and his colleague calculated how the sun would evolve.
0:46:38 > 0:46:41And, in particular, how much mass it would lose
0:46:41 > 0:46:43after it becomes a red giant.
0:46:48 > 0:46:50There was an amazing amount of interest in this.
0:46:50 > 0:46:53We found that the mass of the sun itself
0:46:53 > 0:46:56would go down by something like 20%
0:46:56 > 0:46:58at the end of the red giant stage.
0:47:02 > 0:47:07As the sun loses mass, the planets will shift further from its centre.
0:47:10 > 0:47:13Robert predicts that the Earth will move out millions of miles...
0:47:16 > 0:47:18..as the sun expands.
0:47:22 > 0:47:27So here we are at Mars, the last of the terrestrial planets.
0:47:27 > 0:47:29But in seven billion years' time,
0:47:29 > 0:47:32calculations show that Mars will no longer be here.
0:47:34 > 0:47:38Instead, the red planet is forecast to have moved all the way out
0:47:38 > 0:47:40to where the asteroid belt is today.
0:47:44 > 0:47:46With the Earth in its place.
0:47:49 > 0:47:52According to Robert Smith's calculations in 2001,
0:47:52 > 0:47:54the sun would then stop growing
0:47:54 > 0:47:58when it's still ten million miles away from the Earth.
0:47:59 > 0:48:02And our world would survive.
0:48:02 > 0:48:06We were quite pleased when we found that the Earth would escape.
0:48:06 > 0:48:11Unfortunately, nobody will be around to see it, which is a pity.
0:48:16 > 0:48:20But within a few years, scientists began to realise
0:48:20 > 0:48:23that there was another effect they hadn't considered...
0:48:24 > 0:48:28..which could potentially draw the Earth back towards the sun.
0:48:34 > 0:48:39Dr Eva Villaver has analysed these so-called tidal interactions
0:48:39 > 0:48:42that exist between all red giants and their planets.
0:48:44 > 0:48:46She foresees that the same forces
0:48:46 > 0:48:51will one day act between the sun...and the Earth.
0:48:53 > 0:48:57I have a third experiment that maybe can help understanding
0:48:57 > 0:48:59how the Earth and the sun will interact
0:48:59 > 0:49:02as the sun becomes a red giant.
0:49:02 > 0:49:05Imagine that you have a carousel, which is the sun,
0:49:05 > 0:49:07and you have a bicycle orbiting it,
0:49:07 > 0:49:09going around it, and the bike is the Earth.
0:49:11 > 0:49:15As the sun expands, the rate it spins will slow down.
0:49:15 > 0:49:18So by the time it reaches its maximum size,
0:49:18 > 0:49:21the Earth will be going around the sun
0:49:21 > 0:49:24much faster than the sun itself is turning,
0:49:24 > 0:49:26which has a critical effect.
0:49:28 > 0:49:30The rotation of both is going to be connected.
0:49:30 > 0:49:34So imagine that you have a rope tied on the bike.
0:49:34 > 0:49:37If the carousel rotates more slowly than the bike,
0:49:37 > 0:49:42it will pull whatever is rotating around it.
0:49:42 > 0:49:47And as a consequence of that, the planet will be forced to slow down.
0:49:48 > 0:49:50So that's basically the tidal force,
0:49:50 > 0:49:53this connection between the carousel and the bike.
0:49:54 > 0:49:58As a result, the Earth would lose speed.
0:49:58 > 0:50:01The planet will be moving more slowly
0:50:01 > 0:50:03and as a consequence of that,
0:50:03 > 0:50:06the Earth would get closer to the surface of the sun.
0:50:08 > 0:50:11Our world would be drawn towards the sun.
0:50:21 > 0:50:23Could the Earth be doomed after all?
0:50:25 > 0:50:27Dr Robert Smith went back to work
0:50:27 > 0:50:31to calculate whether the tidal force pulling the Earth in
0:50:31 > 0:50:33could counteract the solar wind
0:50:33 > 0:50:35reducing the sun's grip on our planet.
0:50:37 > 0:50:39Unfortunately, we found that
0:50:39 > 0:50:42the tidal effect was really quite important.
0:50:42 > 0:50:47And it caused the Earth to spiral in towards the sun.
0:50:47 > 0:50:49And the overall effect was that
0:50:49 > 0:50:52the Earth actually was swallowed by the sun.
0:51:01 > 0:51:04Well, that was a very disappointing result
0:51:04 > 0:51:08because we had hoped that the Earth would still nonetheless escape,
0:51:08 > 0:51:11but unfortunately, that's the way things are.
0:51:11 > 0:51:15And the Earth, by that stage, wouldn't have been liveable on,
0:51:15 > 0:51:18so perhaps it doesn't matter too much.
0:51:24 > 0:51:27For a vision of those final days on Earth,
0:51:27 > 0:51:33Dr Eva Villaver has come to a unique facility in Odeillo, France.
0:51:33 > 0:51:36The world's largest solar furnace.
0:51:39 > 0:51:41As the sun becomes a red giant,
0:51:41 > 0:51:46we will have a red star occupying most of the sky.
0:51:46 > 0:51:49And the energy that every single inch of the Earth
0:51:49 > 0:51:51will receive will increase.
0:51:51 > 0:51:54And here, this is exactly what these mirrors are doing.
0:51:56 > 0:51:59Around 10,000 mirrors focus the sun's rays,
0:51:59 > 0:52:02like a giant magnifying glass.
0:52:03 > 0:52:07Which allows them to replicate the conditions the Earth will face
0:52:07 > 0:52:10when the sun becomes a red giant.
0:52:15 > 0:52:18Eva calculates that the radiation shining on the Earth's surface
0:52:18 > 0:52:22will be nearly 3,000 times more intense than today.
0:52:29 > 0:52:31So, to simulate our future,
0:52:31 > 0:52:36the solar furnace has magnified the sun's power by 3,000 times.
0:52:40 > 0:52:42We are focusing the light of the sun in a bin
0:52:42 > 0:52:45and trying to see what will be the effect on a rock.
0:52:45 > 0:52:48Because the Earth is a rock floating around the sun.
0:52:56 > 0:52:58Wow, look at this!
0:53:04 > 0:53:05There it goes.
0:53:11 > 0:53:14The temperature at the surface of the Earth at that point
0:53:14 > 0:53:17will be of the order of 1,400 degrees.
0:53:17 > 0:53:20Enough to melt rock.
0:53:20 > 0:53:22Enough to melt the whole surface of the Earth.
0:53:27 > 0:53:31It's thought the planet will be covered in a vast ocean of molten lava.
0:53:34 > 0:53:36But even after the Earth's surface has melted,
0:53:36 > 0:53:41the heat is expected to increase further as the planet is engulfed.
0:53:42 > 0:53:44The maximum intensity of the solar furnace
0:53:44 > 0:53:49is 16,000 times the sun's power today.
0:53:51 > 0:53:54Still only a fraction of what the Earth would encounter
0:53:54 > 0:53:56inside the red giant.
0:53:59 > 0:54:00The rock would be stripped away,
0:54:00 > 0:54:03leaving just the planet's iron core.
0:54:12 > 0:54:14Wow, look at this!
0:54:14 > 0:54:16Just the sun's radiation.
0:54:18 > 0:54:21That's iron being melted by the radiation of the sun.
0:54:23 > 0:54:26This is how the last moments of our world would be.
0:54:28 > 0:54:31So everything, the whole material of the Earth,
0:54:31 > 0:54:33will melt all the way down through the core.
0:54:33 > 0:54:35Even the iron core will melt.
0:54:35 > 0:54:39The whole material of the Earth will be part of the material of the sun.
0:54:39 > 0:54:41Everything will be mixed together.
0:54:42 > 0:54:44According to the latest calculations,
0:54:44 > 0:54:47the world will end in fire.
0:54:51 > 0:54:54But our solar system's story is not quite over yet.
0:54:56 > 0:54:58Because the final phase of the sun's life
0:54:58 > 0:55:01will be the most spectacular of all.
0:55:04 > 0:55:06- There's Seven Sisters... - It's like an upside-down owl.
0:55:06 > 0:55:08Nick, you wanted to see the Andromeda?
0:55:08 > 0:55:11- It's really cool.- Wow!
0:55:11 > 0:55:13In Peoria, every Saturday night,
0:55:13 > 0:55:16the Astronomy Society meets
0:55:16 > 0:55:19by the Northmoor Observatory at the edge of town.
0:55:20 > 0:55:23And between these two stars is the remnant
0:55:23 > 0:55:26of what's going to happen to our sun.
0:55:27 > 0:55:29So we're going to move the telescope
0:55:29 > 0:55:31and, Brian, do you want to move the dome?
0:55:32 > 0:55:36Tonight, Sheldon is searching for a distant, dying star.
0:55:38 > 0:55:40The Ring Nebula.
0:55:42 > 0:55:44OK, that's good, Brian.
0:55:46 > 0:55:47Ha! I think it's there.
0:55:49 > 0:55:52OK. So come on over and take a look.
0:55:52 > 0:55:55Look through the eyepiece and you should see a lot of stars
0:55:55 > 0:55:57and then right in the middle, do you see that little smoke ring?
0:55:57 > 0:56:01- Yes.- It's just barely there, right? - Yeah.
0:56:01 > 0:56:06- Wow!- So this is a star that, after the red giant stage,
0:56:06 > 0:56:08it puffs off shells of itself.
0:56:08 > 0:56:13It expels most of its matter into, like, bubbles of gas.
0:56:14 > 0:56:17The planetary nebulae produced by dying stars
0:56:17 > 0:56:21are some of the most spectacular celestial objects in the night sky.
0:56:23 > 0:56:26When our sun dies, it, too, could make a nebula.
0:56:28 > 0:56:32Astronomers have calculated that up to half of the sun's mass
0:56:32 > 0:56:36would be thrown off into space as gas and dust.
0:56:37 > 0:56:40Including much of the material that came from the Earth.
0:56:43 > 0:56:46And then the star itself shrinks from the red giant
0:56:46 > 0:56:47down to a white dwarf,
0:56:47 > 0:56:50which is a star about the size of the Earth.
0:56:50 > 0:56:52Very, very hot, but extremely tiny.
0:56:52 > 0:56:55And, er...then the shells of gas
0:56:55 > 0:56:58are really the only thing that's left to see.
0:57:01 > 0:57:04The vaporised remains of half the solar system
0:57:04 > 0:57:08would glow brilliantly for around 10,000 years.
0:57:12 > 0:57:15Then, as it spreads into space,
0:57:15 > 0:57:17the light would slowly fade.
0:57:20 > 0:57:23And our solar system will end.
0:57:27 > 0:57:31But in a sense, it's just a new beginning.
0:57:35 > 0:57:37The materials that make up our bodies
0:57:37 > 0:57:43may well ultimately get spat out into the cosmos
0:57:43 > 0:57:47and be the raw materials for another generation of stars,
0:57:47 > 0:57:49planets and maybe even life forms.
0:57:53 > 0:57:57We're all famously made of star stuff.
0:57:59 > 0:58:01One day, we may return to a star.
0:58:03 > 0:58:05Our sun.
0:58:08 > 0:58:13But then, in an extraordinary process of cosmic rebirth,
0:58:13 > 0:58:17the sun would return our atoms to interstellar space.
0:58:19 > 0:58:22To form new worlds...
0:58:24 > 0:58:27..and perhaps new life.