Original subtitles

Our sun...

The heart of the solar system...

The giver of light, heat,

and, of course, life.

But what does its future hold?

Scientists are looking to the stars to find out.

Between these two stars is what's gonna happen to our sun.

Scientists today are almost like modern-day prophets.

They foresee an apocalyptic future.

Imagine the ball is Andromeda galaxy

on a head-on collision with the Milky Way galaxy.

The fate of the Earth hangs in the balance.

Wow! Look at this.

The temperature of the surface of the Earth

will be enough to melt rock.

Enough to melt the whole surface of the Earth.

This is the story of how our sun

will transform the solar system

it binds together...

Before bringing it to a spectacular end.

Captions by vitac... www.Vitac.Com

captions paid for by Discovery communications

Peoria, Illinois,

an average city in midwest America,

but it has one claim to fame that's out of this world.

In the middle of town,

there's a 46-foot-wide mosaic

of the Sun,

the centerpiece of a huge-scale model

of our solar system

created by local astronomer Sheldon Schafer.

And here we are at the Sun.

And, boy, is it hot.

It's about 10,000 degrees here at the surface.

And over a million Earths could fit inside of the Sun.

Peoria's solar system,

99 million times smaller than the real thing,

accurately reveals the relative sizes

of our sun and its planets...

Okay, we're all together?

And the distances between them.

My job title is curator of the solar system.

And we just went 33 million miles,

until we got to this tiny little two-inch Mercury.

All right. So, we're headed off to Venus.

From Mercury,

the inner planets are strung along

a picturesque riverside park,

all the way to Mars.

These planets are relatively close together.

The outer planets are much further away,

in some bizarre locations.

Five miles from the image of the Sun,

above the local airport's check-in desks,

is five-foot-wide Jupiter...

Well, if you're gonna have a planet,

you may as well have the biggest one, right?

So, it's fun to have Jupiter.

Occasionally we have birds that decorate,

so we've had to clean it. But not very often.

While the children's section

of a neighboring town's library is home to saturn.

Uranus is in princeville, Illinois.

From there, it's a 10-mile drive

along route 91,

or almost a billion miles in cosmic terms,

to the old railroad depot in Wyoming, Illinois,

and Neptune.

And finally,

in a furniture store

40 Earth miles away from the center of the Sun,

in kewanee, Illinois, is distant Pluto.

Peoria's models

are a perfect likeness of the solar system today.

But it won't always be this way.

Scientists know that one day,

the Sun will fundamentally change,

and transform the planets.

Imagine fast-forwarding through the next seven-billion years

to watch the end of the solar system.

Dr. Eva Villaver can predict this future...

Because everything that will happen to our sun

is already happening to countless other stars.

Some, known as solar twins,

are remarkably similar to our own.

We study solar twins because they are very important

to understand not only the Sun,

but to tell us how the future of our own solar system will be.

In 2013,

a solar twin called corot sol 1 was discovered.

Corot is over there, in the constellation of monoceros.

It's a star like the Sun, and it has the same mass.

Exactly the same mass.

But astronomers found

one particularly significant difference...

It had a lower concentration of the element lithium,

which helped them to accurately calculate its age.

It's a star that is a little bit older

than the Sun, a few billion years older.

And if we observe a star that is older than our sun,

we know what will happen to the Sun.

Eva and her team discovered

that this older version of our sun

was giving out more radiation.

So, it helped us put the pieces together.

As the Sun will get older,

it will become brighter, much brighter.

Our sun's luminosity is slowly increasing

because of a change deep inside the Sun,

where two opposing forces are in constant battle.

Similar forces to those that act on a hot-air balloon.

Pushing up and out is the immense pressure of hot gas.

In the Sun, this is created by nuclear fusion.

The Sun has been burning hydrogen into helium

for thousands of millions of years now.

This is like the propane bottle here.

It's generating heat that warm up the air

that keeps the balloon going.

That's what happens in the Sun, too.

But pulling down into the core of the Sun

is an equally powerful force... Gravity.

The life of the Sun is nothing but a battle against gravity.

We have the gravitational force trying to pull the star,

crash the star together. I mean like pushing it in.

And then we have the thermal pressure

of the gas pushing outwards.

So, the balance between the two forces

is what keeps the Sun stable.

For 4.5-billion years,

the two forces have been in perfect balance.

But as time passes, this balance is shifting.

As the Sun fuses hydrogen,

it produces around 600 million tons

of helium every second,

which is a denser gas.

This change in density

has a profound affect on the nuclear reactions.

As the core gets denser,

hydrogen is burned at a higher rate.

It's like turning the burners up.

I mean, we are increasing the energy

that is coming out of the core at that point.

As a result,

our sun is getting 10% brighter every billion years.

So the older it gets,

the more it heats up the solar system.

And scientists know that will one day

have serious consequences.

The Earth has oceans and clouds

because it orbits a band around the Sun

called the habitable zone,

which means it's just the right temperature for liquid water.

And that makes it the only planet in the solar system

where we know life can thrive.

But as the Sun becomes more powerful,

the habitable zone will move.

For a vision of the Earth in two-billion years' time,

astrobiologist professor Lynn Rothschild

believes we should look to Venus.

Venus is up in the sky, there.

It's the brightest object after the Sun and the moon.

It's right near Jupiter this morning.

It's just an absolutely spectacular day to see it.

Venus and the Earth formed out of the same materials.

They're roughly the same size.

The difference is that Venus is closer to the Sun.

It's no surprise Venus is warmer than Earth.

But strangely, Venus is even hotter than Mercury

despite being further from the Sun.

In 2006, the Venus express probe

launched towards our nearest planet

to analyze the venusian atmosphere

in unprecedented detail.

It found a vital clue among the clouds

to how Venus became so hot.

Venus express allowed us to see

that there was a lot of deuterium,

which is a heavy form of hydrogen, left.

And that's indicative of the fact

that there was once water here.

It soon became clear that in the past,

Venus was a very different world.

So, here was this beautiful water world

not too dissimilar to, maybe,

what the Earth is like today.

There was liquid water

and reasonable atmospheric pressure

and organic compounds.

There's no reason that there shouldn't have been life.

The evidence suggests

that Venus was once in the habitable zone.

But as the Sun grew brighter three-billion years ago,

it would have had a dramatic effect on the planet's water.

As the Sun started to get hotter,

the surface of Venus started to get hotter,

and therefore the water turns into steam.

And steam is a greenhouse gas,

so that means it traps the solar radiation.

And therefore, just like a greenhouse,

it starts to get hotter and hotter.

It seems a runaway greenhouse effect caused Venus

to become the hottest planet in the solar system.

Mercury, although closer to the Sun,

has no atmosphere and no water.

Earth has both.

And as the brighter sun evaporates our oceans,

the affect is likely to be far more intense

than the man-made global warming

we see today.

Over the next two-billion years,

temperatures on Earth will rocket.

Life here must adapt or die.

Yellowstone national park is a natural laboratory

for Lynn to study how life can survive in extreme conditions.

The reason it's so great

is that we have the whole range, from the top predators...

Things like wolves and bears and so on,

all the way down to the beavers and the herbivores,

and down to the very tiny organisms,

and even some incredible microbes.

Life here is used to dealing with extremes.

But in about a half-billion years' time,

these extremes will go in the opposite direction,

as temperatures could climb by up to 20 degrees in some places.

By then, life as we know it

will have evolved to be very different.

But just as some of today's animals have adapted

to survive harsh winters, in the future,

they may use similar strategies to cope with scorching summers.

As the Sun gets hotter,

you could imagine the winter as being the very pleasant season,

and the summers become unbearably hot.

So, if you're thinking about a bear

that lives in an area like this

that would normally hibernate in the winter,

if you turn the thermostat on the Earth high enough,

it might be the reverse,

so that now animals would be hibernating in the summer

and be active in the winter.

And grasses would be setting seed now in the spring.

The seeds would be what would carry the plant

through this harsh summer.

And then, as the rain started again in the Autumn,

they would germinate,

and you would get the lush green in the winter.

In less than a billion years' time,

the greenhouse effect is expected to take off,

sending temperatures soaring.

As it gets hotter and hotter on the land,

eventually even the winters will be too hot for most organisms,

certainly, to live.

So, if you had a large animal

like, say, a bison,

that's also warm-blooded, as it gets hotter and hotter,

it won't be able to cool down, and it will eventually die.

And so, ultimately,

large animals like that will go extinct.

In just over a billion years from now,

the land could be nothing but a parched desert, devoid of life.

The air is gonna heat up much more quickly

than water will, and so I predict

that, just like the ancestors of whales and dolphins

and so on moved from the land to the water,

so will the descendants of bison if they want to survive.

But models suggest that in two-billion years' time,

even the water will have gone.

As it boils away,

the Earth would increasingly resemble Venus today.

In less than three-billion years' time,

it's thought that that the searing sun

and a runaway greenhouse effect

will have wiped out virtually all life on Earth.

But intelligent life may just find a way out.

We have something that the other organisms

out there don't have, and that is we have technology.

And we're gonna have the option of going to other planets.

As it gets too hot for the Earth,

Mars will start to warm up.

And so that means that it's just possible

Mars will become a better place for life.

Who knows? I have great faith in our descendants.

By then, Mars is expected

to be in the habitable zone,

so it could provide a refuge, but not forever.

Because the next threat will be the entire solar system...

from 100-billion stars racing towards us...

the Andromeda galaxy.

Scientists have long suspected it will one day

crash into our galaxy, the Milky Way.

But until recently, no one had been able to say for sure.

In 2012, Dr. Tony sohn stepped up to the plate.

He and his team set out

to precisely measure Andromeda's path,

and discover if it would be a near miss,

a glancing blow,

or a head-on hit with our galaxy.

To predict the outcome,

he used a technique familiar to baseball players.

I found a thought experiment

that can help explain how we measure the motion of Andromeda.

Imagine a game of baseball.

The batter is waiting for the ball,

thrown by the pitcher.

To work out if the ball is on target,

the batter needs to see

whether it's drifting to the side or not.

So the instinctively compare the motion of the ball

against the background.

Tony needed to apply the same principle

to discover if Andromeda was heading towards us

but in order to measure the galaxy's motion,

he had to find fixed points behind Andromeda

to compare it to...

A daunting task.

Most of the stars we see in the sky are in our galaxy,

so they cannot be used as background objects.

Instead, Tony had to search for distant galaxies

hundreds of millions of light-years away.

Only one telescope was up to the task.

We used the hubble space telescope to do this project

because we need a very stable instrument,

and we need to be above the Earth's atmosphere

to get very high resolution of the image.

With data from hubble, Tony painstakingly tracked stars

in Andromeda against distant galaxies,

just like a batter tracks a ball.

Imagine the ball is Andromeda galaxy,

and the fence behind that are background galaxies.

And what we did was we compared

the position of the Andromeda galaxy

against the background galaxies over time,

and that's how we measure the sideways motion.

The results were conclusive.

The sideways speed of Andromeda we measured

was effectively zero,

so we can say with certainty

that Andromeda is on a head-on collision

with the Milky Way galaxy.

Tony's team confirmed

that over 100-billion stars

are on course for a strike at 2,000 times

the speed of a fast ball.

But since it's so far away,

the galaxies won't collide

until nearly four-billion years from now.

Tony's precise measurements allow him to predict

how this clash of the titans will look.

To anyone on Earth, it would be a spectacular sight.

We'll see the Andromeda galaxy

getting bigger and bigger in the sky.

And then eventually, in about four-billion years from now,

we'll see the collision of the two galaxies.

On impact,

clouds of dust will be crushed together,

with sensational results.

What we'll see is a lot of stars getting formed.

And this will look something like

stellar fireworks in the sky.

Tony can even calculate the odds

that our solar system

will crash into one of Andromeda's billions of stars

during the collision.

Surprisingly, the prognosis is good.

Galaxies are essentially empty space.

So the chances of stars colliding with another star

is very slim,

because the distance between the stars is vast.

So when the collision happens,

the solar system will pass through an empty space

between the stars.

After passing like ghosts in the night,

the irresistible pull of gravity will draw them back together

over the next two-billion years

to finally settle as a new supergalaxy nicknamed milkomeda.

Our galaxy will no longer exist.

Yet calculations suggest the solar system will survive.

It will merge into one big galaxy,

and it will look like a giant ball in the sky.

Sadly, it's unlikely anyone will be on Earth

to witness this colossal galactic collision.

But there's a slim chance an extreme form of life

could be clinging on as the two galaxies meet

despite the searing heat from the aging sun.

In yellowstone, professor Lynn Rothschild has found

evidence of what those last remaining Earthlings

might be like.

This area of yellowstone

is extremely acidic, and it's also hot.

You can see the steam rising.

So, in other words, it's sort of like boiling battery acid.

Very few living things can actually live

at this high temperature,

but there are a couple of organisms

that are very well-adapted for it.

You can see the beautiful colors behind me.

The kaleidoscope colors

of yellowstone's Springs

are caused by heat-loving microbes.

We can pretty much use these as a thermometer.

Anything that is green means

that it's got chlorophyll, just like plants.

And once they get to a temperature

above about 73 degrees or so,

their chlorophyll breaks down.

And so when you start getting warmer than that,

you start to move into other sorts of organisms.

Organisms that, for example, eat iron,

and then you see these beautiful orange colors.

Once all the water on Earth has turned to steam,

it's possible that heat-loving microbes

could continue to live in the clouds.

We know some of the earliest organisms

on the Earth were thermophiles,

organisms that lived at high temperature.

And so at some point,

it may be organisms like this

that once again inherit the Earth.

The microbes will have their day,

but their reign will inevitably be cut short.

Because when the Sun is twice the age it is now,

astronomers foresee a turbulent new phase written in the stars.

On a clear night,

many of the stars you can see

with your naked eye today are going through a phase.

You can tell which ones they are because of their color.

They're known as red giants.

It's very easy to see red giant stars,

because they are very bright.

They are giant and they are bright.

So, they are everywhere in the sky.

Some red giants are so large

you could fit our own sun inside them millions of times over.

Yet astronomers are confident

our sun will one day grow to become one itself.

So these stars are a glimpse of our future.

If we study stars that grow in size,

we can tell the fate of the planetary systems

that are orbiting them.

Stars like that give us already clues

about what will be the future fate of our own solar system.

The transformation of our sun into a red giant

will begin deep below its surface,

where all the heat is generated.

The burning core

is the only place hot enough for hydrogen to fuse.

And yet it makes up less than 2%

of the Sun's total volume.

For the next five-billion years,

it's thought the core will be stable.

Finally balanced between two phenomenal opposing forces...

The crushing pull of gravity

and the explosive push of nuclear heated gas.

But like a hot-air balloon,

the core will eventually run out of fuel.

Just as gravity pulls the spent balloon down,

in the Sun, gravity would pull on the core.

When the balance is broken

because the hydrogen runs out in the core,

the dominant force will be gravity.

It will try to squish the core.

But the Sun will be far from spent.

As gravity crushes the core,

it will trigger a transformation in the rest of the Sun.

For the first time,

the hydrogen gas surrounding the core will begin to fuse,

giving the Sun access to far more fuel

than it's already burned.

We run out already of one bottle of propane,

but we have three more.

So, it's like the Sun.

The burning shell of hydrogen releases so much heat

that gravity is overwhelmed,

tipping the balance in favor of rapid expansion.

Gravity's not winning the battle.

So, the star expands as a red giant.

Astronomers predict that in about five-billion years,

the Sun will start to grow into a vast,

seething ball of fire...

A red giant,

sending temperatures soaring across the solar system.

The inner planets will become far too hot

to support any kind of life.

But the distant outer planets

will bask in the warm glow of the Sun

for the first time.

The habitable zone, where life can exist, will sweep out.

In Peoria's solar system model,

it would have meant the habitable zone

would leave town and head for the outskirts.

Here at the airport is Jupiter.

When the Sun grows, Jupiter will come in from the cold.

And although life as we know it

could never survive on gassy Jupiter,

the solar system's biggest planet has several icy moons.

These are likely to melt and become cosmic watering holes

for any refugees fleeing the parched inner solar system.

Astronomers have speculated that Jupiter could change color.

As clouds of ammonia vaporize,

it might turn into a deep shade of blue.

After Jupiter, astronomers expect the habitable zone

to move swiftly towards saturn.

If saturn still has its icy rings by then,

they're forecast to vaporize and disappear.

But like Jupiter, saturn's icy moons

could melt and be safe havens for life.

Then models predict the habitable zone

will sweep out faster and faster,

past the solar system's most distant planets and their moons.

First, uranus.

Then deep-blue Neptune.

Astronomers think they, too, will be transformed.

But exactly how they'll look in the future is still a mystery.

Eventually, the habitable zone is forecast to pass beyond

all the planets and their moons.

Although Neptune's the final planet,

the solar system doesn't finish there.

In July 2015,

the New Horizons mission finally revealed Pluto's secrets.

The first clear images ever captured of the dwarf planet

revealed some startling terrain.

Strange troughs, cliffs,

and even dunes.

After a 12-billion-year-long winter,

the expanding sun

may bring spring to Pluto.

But while the red giant nurtures Pluto,

it poses a grave threat

to the planets of the inner solar system.

They face total annihilation.

Studying the night sky,

Dr. Eva Villaver uncovered grisly evidence

of what red giants can do to their inner planets.

A search for distant worlds

had led to the constellation of perseus,

where a star called bd+48 740

caught her attention for two reasons.

There we have a star, a red giant,

that was very peculiar,

because the star itself has a very high content in lithium,

and that's very unusual for these type of stars.

So, that was one of the pieces of the puzzle.

And the other one was that it has a Jupiter-like planet

orbiting the star that has an orbit that is very unusual.

Eva thought the two strange features

must be somehow connected.

Something had happened

that had affected both the planet and the star itself.

In around 5.5-billion years,

our own sun will enter this extraordinary phase of its life.

Evidence suggests its surface will reach out towards Mercury,

Venus, and Earth,

threatening their very existence.

Local astronomer Sheldon Schafer

is leading his weekly interplanetary bicycle tour,

with the Sun's surface hot on his heels.

And here we are, approaching Mercury.

You can see it's easily a stunt double for the Earth's moon.

It's a heavily cratered world without an atmosphere.

Hot in the Sun and cold in the darkness.

But the solar system's smallest planet will get hotter still.

Off to Venus.

Because astronomers predict that less than a billion years

into the red giant phase,

the Sun's surface will reach Mercury.

After more than 10-billion years

of relative calm,

the solar system will lose a planet.

And the Sun will continue to expand,

growing ever closer to Venus.

The next planet is Earth.

By the time the Sun engulfs Venus,

the Earth's oceans are expected to have boiled away.

The ultimate fate of our world appears to be on a knife's edge.

For a vision of those final days on Earth,

Dr. Eva Villaver has come to a unique facility

in odeillo, France...

The world's largest solar furnace.

As the Sun becomes a red giant,

we will have a red star occupying most of the sky.

And the energy that every single inch of the Earth

will receive will increase.

I hear that this is exactly what these mirrors are doing.

Around 10,000 mirrors focus the Sun's rays

like a giant magnifying glass,

which allows them to replicate the conditions

the Earth will face when the Sun becomes a red giant.

Dr. Eva Villaver is calculating the temperature

of the Earth's surface when the Sun's radiation

will be nearly 3,000 times more intense than today.

So, to simulate our future,

the solar furnace has magnified the Sun's power by 3,000 times.

We are focusing the light of the Sun in a beam

and trying to see what will be the effect on a rock,

because the Earth is a rock floating around the Sun.

Wow! Look at this.

There it goes.

The temperature of the surface of the Earth

at that point will be of the order of 1,400 degrees...

Enough to melt rock,

enough to melt the whole surface of the Earth.

It's thought the planet will be covered

in a vast ocean of molten lava.

But even after the Earth's surface is melted,

the heat is expected to increase further

as the planet is engulfed.

The maximum intensity of the solar furnace

is 16,000 times the Sun's power today.

Still only a fraction

of what the Earth would encounter inside the red giant.

The rock would be stripped away,

leaving just the planet's iron core.

Wow! Look at this.

Just sun radiation.

That's iron being melted by the radiation of the Sun.

This is how the last moments of our world would be.

So, everything, the whole material of the Earth,

will melt, all the way down to the core.

Even the iron core will melt.

And the whole material of the Earth

would be part of the material of the Sun.

Everything would be mixed together.

According to the latest calculations,

the world will end in fire.

But our solar system's story is not quite over yet,

because the final phase of the Sun's life

will be the most spectacular of all.

There's seven sisters.

Like an upside down "l."

Nick, you wanted to see the Andromeda?

It's really cool.

Wow.

In Peoria, every Saturday night,

the astronomy society meets by the northmoor observatory

at the edge of town.

Between these two stars is the remnant

of what's gonna happen to our sun.

So, we're gonna move the telescope.

And, Brian, do you want to move the dome?

Tonight, Sheldon is searching for a distant,

dying star...

The ring nebula.

Okay. That's good, Brian.

Ha! I think it's there.

Okay. So, come on over and take a look.

Look through the eyepiece.

And you should see a lot of stars.

And then right in the middle, do you see that little smoke ring?

Yes.

- It's just barely there, right? - Yeah.

Wow.

And, so, this is a star

that, after the red giant stage,

it puffs off shells of itself.

It expels most of its matter into, like,

bubbles of gas.

The planetary nebulae produced by dying stars

are some of the most spectacular celestial objects

in the night sky.

When our sun dies, it too could make a nebula.

Astronomers have calculated that up to half of the Sun's mass

could be thrown off into space as gas and dust.

Including much of the material that came from the Earth.

The vaporized remains of half the solar system

would glow brilliantly for around 10,000 years.

Then, as it spreads into space,

the light would slowly fade...

And our solar system will end.

But in a sense, it's just a new beginning.

The materials that make up our bodies

may well ultimately get spit out into the cosmos

and be the raw materials

for another generation of stars, planets,

and maybe even life forms.

We're all famously made of star stuff.

And one day, we may return to a star...

Our sun.

But then, in an extraordinary process of cosmic rebirth,

the Sun would return our atoms

to interstellar space

to form new worlds,

and perhaps new life.