Original subtitles

A small black star floats through space.

This is the Sun,

billions of years in the future.

It's all that remains of our solar system.

The sole survivor of a dramatic history of elegant beauty

and extreme violence.

Just because things look really nice and serene now

doesn't mean it's always been that way.

There are a lot of planets that could have made it but didn't.

And we just happen to be one of the lucky ones that did.

The players in our solar system story are more tangled up

than we ever imagined.

The more we look at this stuff, the more we realize

that everything affects everything else, including us.

How did we go from a vibrant family of planets orbiting the yellow Sun

to a lone dead zombie star?

It's an old familiar story.

A bunch of planets orbit a yellow star

in a quiet suburb of the Milky Way galaxy.

But it's not the whole story.

Over the past decade, our vision of our solar system

has been completely revamped.

Think of the solar system as an old-fashioned Mafia crime family.

The Sun is the don,

his quarrelling children, the planets.

Their story, like any good mob movie,

is an epic tale of empire building, sibling rivalry,

greed and ultra-violence.

The origin of the solar system was chaotic and violent.

Planets colliding, planets even changing places.

Now a shift in our understanding reveals a tale of tangled alliances

between family members.

Just think about how much our view of the solar system has changed.

The planets used to be so far away from each other

and of course they had nothing to do with each other.

And now the history is all about the interaction.

So the idea that everything is just its own world

and doesn't interact is completely wrong.

We like to think of astronomy as looking up,

looking outward away from ourselves.

But the more we do that, the more we realize

how connected we are to everything out there.

You probably have some material in your body

from pretty much every world that existed in the solar system.

Like any good mobster movie,

our story starts with the humble rise of the godfather.

In this tale, that's the birth of the Sun.

But exactly how that happens is a mystery.

Well, we're trying to figure out how the solar system began.

We don't have a time machine,

so what can we use to find out about how it formed?

The solar system has the answer,

its own time machines, meteorites.

Meteorites are pieces of the solar system from the distant past

and they've remained unchanged since then.

So they're like little time capsules.

They're like fossils from before our solar system even formed.

By studying them, we can really study what was happening,

what was going on in the very early days of our own solar system.

2020.

Scientists study ancient material trapped inside a meteorite

found in Murchison, Australia.

The Murchison meteorite contains tiny crystals

called pre-solar grains

that pre-date our sun.

And trapped within them is evidence of the history

of the formation of our solar system.

The pre-solar grains are made up of elements like silicon

that form inside giant stars.

When these stars die,

they blow out huge clouds of gas and grains of dust.

The term "pre-solar grain" doesn't sound very romantic.

But actually, we might call those stardust.

These materials are things that were made

in stars that no longer exist.

The Murchison meteorite contains grains

from at least 46 different stars.

What the Murchison meteorite tells us

is that the material that came together

that formed our solar system

had its origination in dozens of different stars.

These stars died and blew out all of these materials...

...and then created this huge cloud of gas and dust called a nebula.

The sources of the material in that cloud

can come from one of a number of places.

The material from lots of stars' atmospheres could be mixed in there.

In the mix were the ingredients to build the solar system.

But we don't know what triggered the gas and dust to form the Sun.

A 2020 study may have the answer.

One of the coolest things we've discovered

in the last couple of decades about the Milky Way

is there's a giant stream of stars

that's stretching across virtually the whole sky.

These stars were not born in the galaxy, they're not from here.

If not from our galaxy then from where?

We think these stars actually came

from the Sagittarius Dwarf Galaxy which orbits the Milky Way.

Over five billion years ago, the Sagittarius Dwarf Galaxy

wanders too close to the Milky Way.

Our galaxy's powerful gravity drags Sagittarius towards it.

The galaxies collide.

As this is happening, the Milky Way is tearing Sagittarius apart,

ripping stars out of it.

This is truly intergalactic cosmological drama at play.

This collision shakes up the Milky Way.

When a body passes through the disc of our galaxy,

it's gonna set off ripples.

And that's gonna compress the gas clouds

and that's gonna create star formations.

The Sagittarius Dwarf smashing into the Milky Way

is like dropping a boulder into a pond.

It sends out ripples of density.

And it disturbs everything in the galaxy

but it doesn't disturb everything equally.

It causes some clumps of dust and gas

to start accumulating together.

The disruption in one galactic zip code leads to new activity in others

across the Milky Way.

The ripples trigger gas and dust left over from the dying stars

to split into clumps, sparking a frenzy of star formation.

Look, if you were an observer,

suddenly out of these little clumps of gas

come bright ignition sparks all at once.

If you were to stand there long enough

watching this stellar nursery,

it might look kind of like a field at night

with fireflies blinking on.

Perhaps the Sun formed in this starburst.

The passage of the Sagittarius Dwarf through our galaxy

correlates in time to the formation and birth of our sun.

So maybe our solar system came about

as a result of the Sagittarius Dwarf passing through our galaxy

over five billion years ago.

Of course we don't know for sure

if this is what triggered the formation of our sun

but the timing does fit.

4.6 billion years ago,

part of the cloud seeded with material from dying stars

grows denser until it gets so massive it collapses.

As the gas cloud collapses,

it gets hotter and hotter and spins faster and faster,

forming a dense core at its center.

The core is the protostar that will later become our sun.

The protostar drags in more and more gas and dust,

creating a region of material spinning around it

called the protoplanetary disc.

As the Sun builds up more mass,

it's getting compressed gravitationally

and so the core is getting hotter and hotter and hotter.

The densities are increasing.

The new don, the head of our solar mobster family,

immediately reveals a ferocious nature,

blasting out supercharged jets of radiation.

The early Sun was not the calm glowing orb we see in our sky today.

It was far more chaotic.

It's sort of like in its toddler phase.

It was acting up all the time.

It has all of this energy that pushes material off of the surface

and launches it into what we call the solar wind.

The blizzard of particles races out at over a million miles an hour.

It smashes into the protoplanetary disc

and blows the gas away.

At the same time, the Sun's core heats up

to 18 million degrees Fahrenheit,

triggering the fusion of hydrogen into helium.

And that releases a tremendous amount of energy

that eventually works its way back to the surface of the star

and comes out as light.

Finally the Sun becomes the recognizable Sun

that we see in our sky today.

The Sun is now the godfather,

pulling the strings of the solar system.

The young don's rise to the top

triggers a power struggle with its willful children, the planets.

It's a brutal fight for survival.

4.6 billion years ago.

Our mob family rises in a quiet suburb of the Milky Way.

Its godfather, the Sun, forms from a collapsed stellar nebular.

The greedy star scarfs down most of the cloud of gas and dust.

But just enough is left over to build the planets.

We're standing here on a big planet.

And we look up in the sky and see other planets going around the Sun

and it's an obvious and challenging question to ask,

where do these planets come from?

How did the leftover gas and dust build the planets?

To solve the mystery, scientists study other star systems

across the Milky Way.

We can't go back in time and watch our own solar system forming.

But we can look at other new solar systems as they're forming

and use that to understand how our own might have formed.

Star system PDS 70 is one such system.

It's young, just 5.4 million years old.

And nestled inside the protoplanetary disc

are two infant planets feeding on gas and dust.

We can see these baby exo-planets pulling in material

and creating these gaps in the disc.

It's an amazing discovery. It's kind of mind-blowing that we can see

a new solar system being born.

These snapshots, these systems like PDS 70

are so valuable because they let us test our theories.

We thought planets formed from these discs of dust and gas

but we hadn't seen it until now.

What we couldn't see was how gas and dust bind together

to grow into planets.

That took an astronaut on the space station,

messing around with breakfast.

Don Pettit, this one astronaut, took a bag full of salt and sugar

and coffee grounds and just shook it to see what would happen in zero G.

And to his astonishment, he saw that they immediately clumped up.

It's effectively electrostatic forces

that are causing those clumps to form.

The salt grains rub around with each other

and they develop a charge, an electrical charge.

And so those clumps very naturally form.

These clumps were strong.

They didn't fall apart when they hit the sides of the bag.

And sitting down on the ground, down at mission control,

was astronaut Stan Love, going,

"Oh, my God, Don, you've solved the first steps of planetary formation."

A very similar process went on in the early protoplanetary disc.

Instead of salt it's mineral grains.

So the dust grains that you start with stick to each other

because of electrostatic forces, basically static cling.

And it's almost identical to how a dust bunny forms in your room.

These are cosmic dust bunnies

that will someday grow up into giant planets.

Astronomers call these cosmic dust bunnies pebbles.

We think clumping dust particles formed trillion of pebbles

each around an inch in diameter.

It's the first step in planet construction.

The next step in forming a planet involves planetesimals.

These are objects that are roughly half a mile to 100 miles in size.

But how pebbles build planetesimals was a mystery.

Because pebbles don't play well together.

Grains of protoplanetary material

stick together because of static charge.

The problem is, once they get too big, that force isn't enough

and they'll just bounce off each other.

Yet we know we have to get

all the way up to hundreds of miles across to build our planetesimals.

How do you build a bigger structure

when the particles that you're trying to lump together

are bouncing off of each other?

So a new idea came forward about how to make this big jump

from pebble-sized things all the way up to planetesimals.

And this relies on the interaction of a huge number of pebbles

moving together through the gas around the star.

In the disc of gas and dust that encircles the young sun,

pebbles will begin to coalesce into these big clouds

much in the same way that individual fish will form schools of fish.

More and more pebbles join the cloud.

Eventually you get enough of them together

that they collapse under their own gravity

and make one big planetesimal.

The planetesimals face a race against time.

To grow into planets, they must grab enough building material

from the protoplanetary disc

before their don, the Sun, blasts it all away.

4.6 billion years ago.

A fierce battle erupts between the head of the family, the Sun,

and his children, the growing planets.

The godfather is armed and dangerous

and threatening to destroy the planets' food source

with his weapon of choice, the solar wind.

There's this strong wind of high-energy particles

coming out of the Sun.

That blows away the disc of gas.

The planets must fight to grab hold of the remaining resources

before the Sun drives them away.

So it's a race against time.

Jupiter is racing the Sun to capture as much material as it can

before the Sun blows it all away.

And what we see from studying other solar systems

is that those discs only last for about 5 million years.

We used to think of the solar system's protoplanetary disc

like an old-school diner where the mob family came to eat.

The first-born child, Jupiter, grows by wolfing down planetesimals

followed by a second course of gas.

The old model of planet formation is the idea

that these largish planetesimals that are miles across

collide and stick to each other kind of like modelling clay

until you get a bigger and bigger object

that can eventually get so massive it starts to then pull in

the more diffuse gas around it to form a gaseous atmosphere.

It's a simple idea but with a big problem.

Time.

By that old model, it would take upwards of 100 million years

to accumulate enough planetesimals to do that.

Way too long for Jupiter to grow

before the Sun blows all the gas away.

We found a clue to how Jupiter beat the problem of the disappearing gas

in 2017, when the Juno spacecraft investigated the gas giant's core.

The traditional theories predict that Jupiter's core

would be kind of like a big ball of solid iron or rock

surrounded by a giant gaseous atmosphere.

Juno instead found that Jupiter's core is fuzzy.

There's no boundary between hard rock and then gaseous atmosphere.

There's just a gradual transition as you move outwards

from mostly rock and icy to mostly gassy.

This fuzzy transition from rock-ice core to gas

suggests that young Jupiter didn't eat a la carte,

with separate courses of planetesimals and then gas.

Instead it devoured the whole buffet in one sitting.

These fuzzy cores suggest that as Jupiter's core was forming,

it was actually incorporating a mixture of gas and ice and rocks

all together in its formation.

This was possible because there was still lots of gas

in the protoplanetary disc.

Everything was moving through this very thick disc of dust and gas.

That means everything was actually being slowed down by the drag.

Things the size of pebbles, they were feeling the drag too.

That meant they lost energy

and it made it easier for Jupiter to pull them in.

The young planetesimals grabbed millions of pebbles

along with lots of gas.

They're drawing in gas as well as these pebbles.

The pebbles basically run out and they keep drawing this gas in

and get bigger and bigger and bigger.

This formation model allows you to grow a planet like Jupiter

much more quickly, because it's gobbling up everything at once

at a very rapid pace and that allows it to potentially beat the Sun

and grow within a few million years before the Sun blows everything away.

Both Jupiter and Saturn won their race against the Sun and grew large.

But the inner planets were not so lucky.

The godfather ruthlessly limited the food on their menu.

So the planets that formed depend upon what you have to begin with.

If you're making a cake and you only have certain ingredients,

you can only make a cake out of those ingredients.

The planets are the same way.

They could only be made out of things in their vicinity.

In the inner solar system, where it's much warmer,

volatiles like water and ammonia had evaporated, been blown away.

So the only materials found here for building planets

were rocky metallic materials.

So the planets that formed in this inner region are rocky planets

with metallic cores.

The ice giants feasted on materials that only survive

far from the Sun's harmful influence.

When you get further out, the distances Uranus and Neptune are at,

ammonia and methane start to turn into their own frozen ices.

That's why we call them ice giants.

They're formed primarily out of solid ices.

And there were plenty of these ices to gorge on.

The further you are from the Sun, the less effect the solar wind has.

It's a bit like standing next to a fan.

Right next to it you really feel it.

Step back a few paces, it's not as blowy.

It's the same thing happening in the outer solar system.

It's not able to strip away the gases and the rock quite as much.

The ice giants grew to over 14 times the mass of Earth.

The godfather, the Sun, ruthlessly controls the family.

But first-born Jupiter has grown large.

He craves power and attempts a hostile takeover

of the inner solar system,

triggering mass murder and mayhem.

We used to think that all star systems were similar to our own.

That's because our solar system was the only one we knew.

It's hard to get a perspective on your home

if you've not been anywhere else.

We thought it was typical, but now we've discovered hundreds of others

it's the weird one.

It may surprise you that we've never found a solar system

around another star that really resembles our own,

with all of these small rocky planets in the middle of the system

and these big gas giants farther out.

We've found star systems with super puff planets,

rocky worlds orbiting tiny red stars.

Giant stars with super-heated planets that rain liquid iron.

Water worlds and planets orbiting zombie white dwarf stars.

But none that look like our home system.

Every solar system we'd look at,

ours just looked like it's standing off in a corner all by itself.

The other systems may be very different from our own,

but they can still show us how the solar system developed.

In 2021, scientists discover six planets

orbiting a small orange star called TOI-178.

They range from a bit more massive than the Earth, about 1.5 times,

to a bit more than seven times the mass of the Earth.

These are called super-earths and it turns out

these are really abundant out in the universe.

Around 40% of the star systems we've found

contain at least one super-earth.

One of the most peculiar aspects about our solar system

is that we don't have any super-earths.

We see these things everywhere. Not here.

The first clue to solving the mystery of the missing super-earths

comes from an asteroid called Psyche.

It orbits in the asteroid belt,

a band of rocky objects between Mars and Jupiter.

The asteroid Psyche appears to be a fascinating world

made almost entirely of metal, of iron and nickel.

We think it's the core of a now destroyed planet.

You can think of Psyche as a metallic kernel of a nut

whose shell was smashed off in a huge collision.

Psyche is not the only evidence of the mayhem in the inner solar system

In 2020, scientists studying the Sahara Desert

discover a meteorite called Erg Chech 002.

The Erg Chech 002 meteorite is so exciting

because it's the very oldest volcanic rock ever found.

This rock almost predates the solar system itself.

It's just over 4.5 billion years old.

We know that this meteorite was once flowing like lava

because of the size of the crystals in it and also their composition.

Its lava-like nature tell us its origin.

In order for this meteorite to be a volcanic fragment,

it had to come from something molten.

And the only thing in the solar system in those days that was molten

were large things.

What this tells us is that there was an ancient protoplanet

that was big enough to have volcanism

but doesn't exist any more, it was destroyed somewhere in the past.

The asteroid belt is full of similar debris,

like blood splatter at a Mafia murder scene.

It points to serious felonies taking place in the early solar system.

We think that there were once dozens of rocky protoplanets

orbiting around the young sun.

Now we only have four.

We find clues to what caused this planetary homicide

in distant star systems.

The first exo-planets that we found orbiting stars like the Sun

are what we call hot Jupiters.

Nobody expected these.

These are planets as big or bigger than Jupiter

but orbiting super close in to their star.

When the young star is forming,

it blows out all of the material that's very close to it,

the sheer force of the solar winds.

Nothing could've formed right there.

How the heck did you get a planet that big that close to a star?

Hot Jupiters forced scientists to consider a radical idea.

We always assumed that planets were formed where we see them today.

But these hot Jupiters couldn't have been formed there.

They must have migrated in from further out.

That made us look at our solar system through a different lens.

All of a sudden we started seeing signs that,

"Oh, yeah, maybe this happened here."

One million years after the birth of the Mafia-family-like solar system

many small rocky planets grow

in the inner part of the protoplanetary disc.

Under boss Jupiter makes a move to take control of the family.

The giant planet's gravity creates spiraling waves

in the protoplanetary disc,

which drag on Jupiter, slowing it down.

Jupiter slows down just a little bit in its orbit around the Sun

and as it slows down, it falls inwards towards the Sun

and migrates closer and closer.

Jupiter crashes into the inner solar system.

In its path, the infant rocky planets.

You can't take something with 300 times the mass of the Earth

and let it roam around the inner solar system

and hope it's not gonna do anything.

Jupiter is like a monster truck at a stock car rally race.

It's just ploughing through everything, chaos everywhere.

So here we are, forming our lovely young solar system.

There are all kinds of new planets forming,

settling in to nice orderly orbits.

And here comes Jupiter, the big bully on the block.

Enforcer Jupiter pushes its smaller siblings around.

Gravitationally, it starts to destabilize the inner planets.

So nice circular orbits start to go all haywire.

And things begin to actually play pinball in the early solar system.

The growing inner planets fly off in all directions.

Some collide violently. Many die in the melee.

This is a solar system demolition derby

in the early days of the formation of the planets

where things are smashing into each other

and destroying little planets right and left.

This cosmic carnage could explain why we don't have any super-earths.

Perhaps our solar system once had large rocky planets

but debris from the colliding inner planets slowed down their orbits,

dragging the young super-earths into the Sun.

These primordial super-earths get pushed onto the Sun

and destroyed altogether.

It only takes 100,000 years to destroy the primordial group

of super-earths that would have formed in the inner solar system.

But not everyone agrees with this version of events.

This is a pretty cool idea. But I'm not convinced by it.

We have a lot of ideas of why we are the way we are today.

What we need is more evidence to be able to separate these ideas out.

An alternative theory suggests that Jupiter stole everyone else's lunch,

starving the inner solar system of food,

so the planets couldn't grow into super-earths.

Evidence for this event comes from the young star system PDS 70.

In 2021, the Hubble Space Telescope measured

how fast the two planets around PDS 70 are growing.

Hubble's showing us that this second outer planet is still forming.

It's still expanding, it's still growing at a steady rate.

Whereas the inner planet seems to be slowing down.

This suggests that the outer planets might be able

to starve the inner planets of their food.

Probably by their gravitational effects.

As they're getting bigger and bigger in the outer regions,

their gravitational effect prevents the dust that would normally

be gradually flowing inwards towards the star through the disc

from continuing to do so, it stalls or stops it on its way in.

And that means the inner planets run out of their fuel supply.

The growth rate of the inner planet is slowing

because the outer planet is a hog and is eating all this food.

The same thing may have happened in the early solar system.

As Jupiter gets bigger and bigger, eventually it's so massive

that it's able to prevent material from flowing past it

into the inner parts of the solar system.

So material like dust and pebbles

that would normally feel the Sun's gravity and drift in towards the Sun

is arrested, is stopped on its way inwards.

And now the nascent inner planets are no longer able

to have new fuel to continue growing.

So without Jupiter, Earth and Venus and Mars

might have just kept on growing and growing.

We might have had a bunch of super earths in the inner solar system.

Mob underboss Jupiter's unprovoked assault

on his smaller siblings in the inner solar system continued.

The attack caused many casualties

and nearly put our planet in an early grave.

For thousands of years, people have looked up at the sky

and seen the planets orbiting the Sun in harmony.

They've seen all of this wonderful order.

And that's what we thought, everything formed together,

the Sun, the planets,

almost like this beautiful clockwork set up in the heavens.

Now we know that actually that was far from the truth.

Around two million years after the birth of the godfather, the Sun,

the underboss, Jupiter, makes a power grab

and crashes into the inner solar system.

If Jupiter had continued its journey toward the Sun,

it would have ejected a lot of the stuff left.

There would be no inner rocky planets, it would just be Jupiter.

Fortunately we avoid complete slaughter.

Something stops Jupiter's murderous attack.

Lucky for us, we had an ace in the hole.

We had a friend, and that friend is so beautiful in the sky today.

And we call that friend Saturn.

Saturn is also migrating inward towards the Sun.

But the rate it's moving in depends on the mass of the planet.

Saturn is less massive than Jupiter so it's moving in more rapidly.

Peace-making consigliere Saturn

catches up with Jupiter and brokers a deal.

When they reach each other, they don't collide.

They get stuck in a complicated orbital dance with each other.

Their cosmic tango strips out gas from the disc

clearing a path for Saturn and Jupiter to move back outwards.

So this can actually reverse their migration

and suddenly we have the two planets

moving outward in the solar system.

It's like Saturn has a trailer hitch and is towing Jupiter

back to the outer solar system where we find them today.

Saturn saved the Earth, basically.

If it hadn't been there to pull Jupiter

back out from the inner solar system,

Jupiter would have thrown all the inner planets out.

So no Mercury, no Venus, no Mars, no Earth.

Three million years after the birth of the Sun,

around 20 baby planets survive Jupiter's ransacking

of the inner solar system.

But the carnage isn't over.

The inner solar system's kind of in turmoil.

The gravitational interaction from Jupiter was severe.

Everything is excited. Orbits are out of control and crazy

and things are interacting and having violent collisions.

The inner solar system is like a congested highway.

Planets cross lanes, collisions are frequent.

As the bloodshed continues, the young Earth

wanders into the path of a smaller planet.

There's a theory, and it's a pretty good one,

that the Earth a long time ago was hit by another relatively big planet

and we've called that planet Theia.

Theia hit Earth at over 25,000 miles an hour.

The impact destroyed Theia

and nearly wiped out Earth.

When Earth was struck by Theia,

it was unlike any event before or since.

We think about the event that wiped out dinosaurs as a huge collision.

Oh, this one dwarfs that one.

The Earth was completely turned inside out.

The surface was new, it was molten

and it was raining fire literally.

Lava rock was raining down from the heavens.

Earth was badly wounded but survived.

Material from Theia mixed with Earth rock,

building a bigger planet and a new companion.

This collision was so huge, it blasted off

a tremendous amount of material off the Earth's surface.

And this coalesced to form the Moon.

That theory may now become fact.

We found two massive chunks of rock buried deep beneath Earth's surface.

These massive lumps of rock

have a different density, a different composition

than the rest of the mantle rock around them.

A new study in 2021 suggests they don't come from Earth.

It could be that these dense blobs of material deep in our mantel

are remnants of Theia.

Throughout the inner solar system, protoplanet hit protoplanet.

Some high-speed crashes ended in catastrophe.

There was drama, a lot of drama.

It's as much a story of destruction as it is of creation.

There are a lot of planets that could have made it but didn't.

And we just happen to be one of the lucky ones that did.

Slower impacts glued the colliding worlds together,

building hybrid planets from the wreckage.

The four terrestrial planets, Mercury, Venus, Earth and Mars,

emerged from the ashes of the 20 protoplanets

and joined the mob family.

The planets are connected.

You probably have some material in your body

from pretty much every world that existed in the solar system.

Everything mixed around.

That mixing made Earth larger and better equipped to survive.

The bloodbath also left its mark on the other surviving planets.

What's strange about Venus

is it actually spins in the opposite direction.

All the other planets spin sort of with a right-hand spin

from the west to the east.

And Venus spins from the east to the west.

And also, Venus's spin is very slow.

It's 243 times slower than that of Earth.

You can imagine a big protoplanetary embryo

almost the size of Venus itself, smashing almost head-on to Venus.

Just in the right angle to stop the rotation, slow it down,

even actually reverse it slightly.

And now it's still spinning like that today.

Mercury carries horrific scars from Jupiter's assault

on the inner solar system.

Mercury has always seemed to be a bit of an odd planet

because it really is sort of a cannon ball.

It has a giant core compared to the rest of the planet.

The question is, how do you get this large core but very little rock,

very little mantle and crust around it?

We think Mercury hit another planet hard.

The outer layers of Mercury, its rocky mantle was blasted off,

leaving behind just the dense iron cannonball core of this planet,

which ricocheted off and then settled in Mercury's current orbit

close to the Sun.

That leaves one last rocky planet member of the Mafia family.

Mars.

It's older and much smaller than its neighbors Venus and Earth.

One way to interpret Mars in this scenario

is that Mars was one of those original 20 or 30 planetary embryos,

or protoplanets, and it just survived.

It avoided this big violent endgame

of the giant impact stage of planet formation.

Mars sat on the sidelines,

far enough away from the action to be safe from physical harm.

But enforcer Jupiter's violent raid on the inner solar system

still prevented Mars from reaching its full potential.

One big effect of Jupiter's incursion

into the inner solar system

is to blast away a bunch of material

around where we find Mars today.

In some ways, Jupiter kind of ate Mars's lunch.

So Mars just didn't have as much stuff to work with

and it never became a very big planet.

After 60 million years of family feuding,

the battle of the planets is finally over.

Out of all the mayhem and chaos of the early solar system,

four terrestrial planets remained.

One of them was Earth.

Given everything we've now learned about how violent it was,

we understand just how vulnerable we've been all the way along.

Planets colliding, planets even changing places.

In some ways now, it's amazing the Earth even survived.

Our planet emerged as one of the winners from underboss Jupiter's

homicidal assault on the inner planets.

But Jupiter's return to the outer solar system

soon triggered more mayhem.

Mayhem that would threaten Earth

with the biggest bombardment in its history.

The Mafia family we call the solar system

has survived underboss Jupiter's attack on the inner planets.

But faces more disruption from its enforcer

when the giant gas planet heads out to where Uranus and Neptune grow.

A journey that may help explain several mysteries

about the solar system,

including the size of the ice giants.

The biggest problem with the outer solar system is literally bigness.

Uranus and Neptune are too big for where they are.

The problem is the availability of building materials.

This far out from the Sun,

there wasn't enough gas and dust in the protoplanetary disc

to construct such large planets.

One way of solving the riddle of how Uranus and Neptune are so big

is that they didn't form where they are now.

So we think they formed further in and then maybe moved out.

This is what we think happened.

Five million years after the birth of the Sun,

Jupiter and Saturn reached the same region of space

as Uranus and Neptune.

The four quarrelling children call a truce and orbit together.

Orbits are on a razor's edge of stability as it is.

And so one thing that helps to stabilize our solar system

in the early days was that it was in this cloud of gas and dust

that was this protoplanetary disc.

Gas in the protoplanetary disc can slow down planets

so they migrate.

But it can also stabilize their orbits.

Like sand on the side of a racing track

that's there to slow down the cars and help them get back on track,

the gas allows the planets to not veer off too much

away from their stable compact configuration.

The ceasefire between the gas planets is short-lived.

Once the godfather Sun blows away the last of the gas,

the largest mafiosi children set off on another crime spree.

So when the gas goes away,

you no longer have this damping effect

on the orbits of the giant planets.

And they can start interacting with each other.

And Jupiter is free to be a bully again,

only this time he's got a big sidekick, Saturn.

Former peacekeeper Saturn joins forces with Jupiter

and they start messing with Uranus and Neptune.

So the two largest kids team up together

and start pushing everyone else around.

When you put really big planets that are really massive

really close to each other,

they push on each other's orbits and the orbits get excited.

The whole thing starts to unravel and eventually culminates

in a violent and beautiful instability.

Gravitational shoves from Jupiter and Saturn

push the ice giants outwards.

Uranus still bears the scars from this power move.

For one thing, it's orbiting the Sun on its side.

Instead of having its rotation axis sort of straight up and down,

it's tipped way over so its pole is pointing more or less toward the Sun

instead of up and down, that's really weird.

Recent studies suggest a giant impact

caused Uranus's strange orientation.

Over four billion years ago, a large icy object

hits the ice giant with a glancing blow.

The planet starts to tip over.

Then the attacker comes around and smashes into Uranus a second time.

This one-two punch knocks the ice giant onto its side.

A clue to the cause of the collision comes from Neptune's moon, Triton.

What's odd about Triton is that it orbits the wrong way around Neptune.

That's the wrong way for the whole solar system.

Everything's going in this direction Triton's going the other way.

The other thing's Triton is made of slightly different things

than it should be at the orbit of Neptune.

Its color, its density are just a little bit off.

What we think that means is it probably didn't form there.

We find pointers to Triton's origin on the dwarf planet Pluto.

Pluto sits in the Kuiper Belt,

a band of millions of icy objects beyond Neptune.

When we looked at Triton and compared it with Pluto

from telescopes from Earth,

we recognized these two are very similar.

On Triton, there's nitrogen ice,

carbon monoxide ice, carbon dioxide ice.

These are the same types of ices that we see on Pluto.

This similarity in chemical composition

suggests that Pluto and Triton formed in the same place,

an ancient band of icy objects called the Trans-Neptunian Belt.

When the giant planet orbits go berserk,

Uranus and Neptune get tossed into this Trans-Neptunian disc.

It's like a big bowling ball coming in and knocking off

bowling pins left and right.

Chaos ensues, as the two outer planets,

get pushed through all of this stuff,

throwing things left, right and center.

All kinds of collisions are inevitable.

One of these collisions knocks Uranus over.

Another small planet heads towards Neptune.

The ice giant grabs it, creating the moon Triton.

The other Trans-Neptunian objects scatter outwards

forming the Kuiper Belt.

Tremors from this planetary bowling match

spread far and wide,

sparking a cataclysmic onslaught of the inner solar system

billions of miles away.

The Kuiper Belt, this very, very distant collection

of small rocky bodies in the outer solar system.

You'd think we have no connection to that.

But instead it may be responsible for helping life to start on Earth.

4.6 billion years ago.

A cloud of gas collapses in a quiet suburb of the Milky Way.

It's the birth of our mobster family solar system.

The godfather, the Sun, ignites and takes control.

His children, the planets, grow from the disc of gas and dust

left over from the birth of the star.

Gas planets form in the cold outer suburbs,

rocky ones in the warm, inner real estate.

But the Sun's fearsome nature threatens the young Earth.

The early Earth, right after its formation,

was not a great place to be alive.

In fact, it would not have been possible to be alive

because it was so hot, it had no atmosphere,

it had been blown away.

It wasn't even fully solid and it had no water to speak of.

The Earth is too close to the Sun to have formed

with the amount of water that we see today.

The protoplanetary disc was just too hot for water to condense.

And water vapor would have been blown away by the stellar wind.

For the same reason, it was also lacking in carbon

and volatile organic materials.

This raises a big mystery. Where did all that material

ultimately come from that we now obviously have in abundance?

on planet Earth?

Nasa's Dawn mission to the dwarf planet Ceres provided a clue.

Ceres sits in the asteroid belt,

a band of rocky debris left over

from Jupiter's attack on the inner planets.

The Dawn mission showed us that Ceres is actually

a really wet world, we thought it was just rock.

But instead, Ceres is rich in water, ammonia and carbon.

These chemicals are essential for life.

Analysis of other asteroids found lots of this volatile material.

This is surprising, because this close in,

the Sun should have vaporized them.

They could not have formed in the asteroid belt.

Temperatures were way too high for those materials

water, ammonia, to be able to condense.

They must have formed in the outer solar system

and then been transported to the inner solar system.

A 2019 study discovered evidence of a storm of icy objects

raining inwards around 4.48 billion years ago.

The same time the giant gas planets

were tearing through the outer solar system.

As Jupiter and Saturn, Uranus and Neptune

were migrating back outwards in the solar system,

they're excavating a whole slew of icy planetesimals,

like a snow plow bursting through a snowdrift,

scattering these things all through the solar system.

The outer planets hurl millions of icy objects in towards their don,

the Sun.

Some, like Ceres, stop in the asteroid belt.

Others continue and smash into the inner planets...

...including Earth.

We are being rained down on by giant asteroids, comets.

The entire surface of the Earth is molten again.

I mean, it is a rain of the largest objects you can imagine

onto the surface of the Earth.

Everything just would have been completely smashed to pieces.

Imagine something like the dinosaur-killing impact

happening once a month.

The onslaught lasts for 30 million years.

It pulverizes the Earth's surface...

...but brings fresh chemicals to replace material

blasted away by the Sun.

All of these asteroids and comets raining down on Earth,

of course are causing massive amounts of destruction.

But they're bringing the building blocks of life as well,

the carbon-based molecules that make us up,

the water that every bit of life on Earth needs.

All the conditions necessary to life were brought by the bombardment.

If that chaotic bombardment hadn't happened,

it's just possible that we wouldn't be here today.

Even though some of our mob family

now live in the outer reaches of the solar system,

family ties to the planets in the inner regions are still strong.

The distances between all of the planets

in our solar system are large.

You get a sense of that if you go into the night sky

and Jupiter and Saturn are pinpricks of light.

But really they're all interconnected in a very complex way

Gravity has this huge effect

and can go over long distances.

The solar system has this huge violent past

as these giants have moved and interacted.

It's really remarkable how interconnected

all these planetary bodies really are

even though we think of them as very separate.

This interaction between planets billions of miles apart

transformed the inner solar system

and primed Earth for life.

But our planet was still uninhabitable.

The early Earth right after the bombardment

would have been a complete hellscape.

It would have been really hot, magma everywhere,

big impact craters with impact melt all across the floors.

It would have been unrecognizable.

Not only was it incredibly hot,

but it also didn't have an atmosphere.

And at the time, there was no liquid water on the surface yet.

Early Earth could not have supported life.

For life to start, Earth must cool down

and build a new atmosphere.

The Earth developed its second atmosphere using materials

delivered by the great bombardment.

All of these volatiles like water and carbon, organic materials

were incorporated into the Earth's crust.

And then volcanoes were able to outgas all these materials,

forming a very thick layer of gas.

The new atmosphere had a composition that was mostly water vapor,

carbon dioxide and nitrogen.

Over the next 30 million years,

Earth cools, a solid surface forms.

As the planet is cooling, the water vapor in the atmosphere

is going to be raining out.

That's gonna form pools of liquid water on the surface of the Earth.

The earliest evidence for liquid water on Earth

was 4.3 billion years ago.

Remember, that's just 200 million years after its formation,

which is really fast.

Trillions of gallons of water rain down.

Torrential rains, imagine monsoon rains for, you know,

tens and tens of thousands of years.

All this water would have rained onto the surface,

rained, rained and eventually filled up our oceans.

The oceans pull life-forming chemicals from the rocks

and the atmosphere,

creating the primordial soup.

Life can begin.

We used to be so disconnected from each other,

each planet just living entirely separately.

Now we know things mix around.

Now we know that probably the building blocks of life itself

and the water in my body actually came from the outer solar system.

I like that.

A series of interconnecting and often violent incidents

going right back to the start of the solar system,

led to our existence.

If you look at what the solar system has been through,

what has to happen for life to happen,

when you add all of those thing up, we shouldn't exist.

We just shouldn't be here, the chances are so, so slim.

And yet here we are.

The Earth has managed to survive a lot of the nonsense

the solar system has thrown at it

and some of that is probably just luck of the draw.

So I think even on our worst days we should remember

we're pretty lucky just to be here.

Earth won the cosmic game of chance.

But were the other mafiosi children as lucky?

Did Mars and Venus also develop environments

capable of supporting life?

200 million years after the birth of the Sun,

the Mafia family prospers.

The inner planets have the building blocks of life

thrown in from the outer solar system.

So in theory, they could be habitable.

But when the Russian probe Venera landed on Venus in 1970,

it found a scorching, hostile world.

The conditions on Venus are crazy.

The temperature on the surface is over 800 degrees Fahrenheit,

so it's hot enough to melt lead.

The first probes that landed on Venus functioned for a little while,

then they were crushed like a tin can and melted.

It has a huge crushing atmosphere pressure

which is 90 times that on the Earth's surface.

And that's entirely carbon dioxide.

It gets worse still because gases in the atmosphere have combined

to make really this concentrated solution of acid.

So you've got this noxious, acidic, corrosive environment

coupled with very, very high temperatures.

Life as we know it could not survive on the surface of Venus

as it is today.

New climate models suggest that 4 billion years ago,

Venus was a very different planet to the one we see today.

These models suggest that in the past,

Venus had actually a cooler surface temperature

and had a better composition for habitability.

We think it once had a much thinner atmosphere

much more like Earth's atmosphere today.

It would have had a climate which was much, much cooler

and therefore even the possibility of liquid water on the surface.

Maybe Venus had oceans in the way that we find on Earth still today.

It even makes sense that Venus would be similar to Earth

because it formed out of basically the same materials

close to the same location from the Sun.

And ended up being even almost the same size.

Really we are twin planets.

The barrage of icy objects from the outer solar system

that struck Earth also hit Venus.

Just like Earth, Venus got a whole bunch of volatiles from bombardments

and those in turn were recycled and produced a very nice atmosphere

and allowed water to exist on the surface as a liquid.

These early conditions on Venus could have provided a habitat,

the right sort of conditions for life to have got started.

What about Mars? Was it also habitable?

Looking at it today, all we see is a frozen barren wasteland.

Part of the reason it's so cold

is it's further from the Sun and doesn't have a very thick atmosphere

so it's very hard for it to retain heat.

It also has extremely low atmospheric pressure,

which means any liquid water on the surface would just boil away.

And any current water that's in the planet is locked up in ice.

However, recent surveys of Mars reveal a very different planet,

once capable of supporting life.

As you look across the landscape of Mars,

you can see these physical features that give us hints

that water used to exist there, like dried lake beds and river beds.

We see abundant evidence of river channels, drainages,

all across the landscape.

The best way, I think the only way to form these is by rainfall.

There had to have been clouds and rain in Mars's past.

And there's also sediments and mineral deposits

that could only form in the presence of liquid water.

We calculate that Mars once had 5 million cubic miles

of liquid water on the surface.

That's enough for an ocean bigger than the Earth's Arctic Ocean.

So we think that Mars had an ocean in its northern hemisphere.

To have oceans, Mars must have had a thick atmosphere.

And recently, a space probe orbiting the Red Planet

found evidence.

The MAVEN Mission revealed that Mars is losing its atmosphere rapidly.

I mean, this is something like a quarter pound a second of atmosphere

being stripped away by the solar wind.

We can take those MAVEN loss rates from Mars's atmosphere

and extrapolate back in time and we can see Mars had an atmosphere

as thick as Earth's in the past.

With a thicker atmosphere, Mars would have been able

to retain heat much more effectively

and would have had increased atmospheric pressure

which would have allowed liquid water to persist on the surface.

In the past, Mars would have been just a beautiful landscape

filled with running rivers and lakes.

And that water could have potentially sustained ancient life.

All of the observations that we have of Mars today

just tell us that it was absolutely a habitable world.

So now we have an Earth that had kind of settled down

after the heavy bombardment, Venus that might have water on the surface

and a thinner atmosphere and Mars with a thicker atmosphere

and water on the surface.

Water on all three surfaces. Maybe all three were right for life.

It's actually remarkable to think that all three of these planets

could have been habitable at the same time.

But this golden age of habitability is short lived.

Another battle erupts between the planets and their don, the Sun.

Venus and Mars suffer serious collateral damage.

Four billion years ago, the mob family,

the solar system, is thriving.

The children, Earth, Mars and Venus,

have the conditions to sustain life.

2020. Scientists investigate how Mars became uninhabitable.

They detect faint magnetic traces coming from lava

spewed out by ancient volcanic eruptions.

The magnetic lava on Mars

tells us that when that lava was molten,

there was a strong global magnetic field on that planet.

Dating the rocks tells us that Mars's magnetic field was active

4.5 billion years ago.

Having a magnetic field really helps a planet retain its atmosphere.

That's just because a magnetic field protects the planet's atmosphere

from incoming radiation, solar wind, cosmic rays, you name it.

On Earth, liquid iron churning around the hot molten core

generates a magnetic field.

The younger Mars would have still had a much hotter core

with churning convection currents in its interior.

And these would have generated a global magnetic field

in exactly the same way that Earth creates its magnetic field.

Mars couldn't maintain its magnetic field

because Jupiter's violent assault on the inner solar system

stole the Red Planet's lunch.

Jupiter migrated in about where Mars is today.

So that means most of the material

was actually swallowed up by the gravity of Jupiter.

So Mars just got unlucky.

Small planets lose heat faster.

Tiny Mars cooled down.

And so as Mars's core cooled,

the convection in that core would have slowed down

to the point where no magnetic field would be generated.

Once the magnetic field at Mars is shut off,

that's the end of the protection for the atmosphere.

3.7 billion years ago,

the Sun attacks the defenseless Mars.

The solar wind just bombards it

and strips away the atmosphere very quickly over time.

Without its thermal blanket, Mars's surface freezes

and the atmospheric pressure plummets.

As the atmospheric pressure drops,

surface water gradually evaporates or even boils away.

Earth was luckier.

Jupiter didn't steal our food.

So we grew larger.

The fact that the Earth is a larger planet than Mars

means it can retain its interior heat for a lot longer.

And so Earth still has vigorous convection currents

in its interior

and it's still able to generate a global magnetic field.

Earth's bigger size also means that it has more gravity than Mars.

The combination of our strong gravity and our magnetic field

keep our planet protected and keeps the atmosphere thick.

And that allows our planet to stay warm and wet.

Venus also suffered a climate catastrophe.

We find clues on its surface.

Like all planetary sized bodies in the solar system,

Venus has impact craters on it from asteroids smacking into it.

But there aren't that many, which is a little odd.

They're not damaged like the craters we see on other worlds.

They look pristine,

as if nothing has modified them, as if they happened yesterday.

So that suggests these craters and the surface on which they reside

are both very young.

There are several theories suggesting that volcanic eruptions

resurfaced the planet around 500 million years ago.

One idea is that Venus has a very thick crust

and it doesn't move around in place like Earth's does.

So it's just a lid over the planet.

Eventually the pressure builds up and builds up and builds up

until, boom, it lets out all at once.

A catastrophic event that overturned the entire crust of Venus

and resurfaced it.

An alternate theory suggests the resurfacing happened

over millions of years.

A series of large volcanic eruptions

that would have completely resurfaced the planet.

Imagine watching this event on Venus.

I mean, the overturn of an entire crust?

That's just completely awe-inspiring.

Volcanic events release huge amounts of gas.

Icelandic volcano Eyjafjallajokull

blasts out up to 300,000 tons of carbon dioxide every day.

Venus's planet wide volcanism would have been off the charts.

Such a huge worldwide bout of volcanic activity

would release huge amounts of carbon dioxide into the Venusian atmosphere

Scientists think this enormous release of gas

may have triggered the Venusian climate change.

Carbon dioxide built up in Venus's atmosphere,

trapping heat from the Sun.

As soon as the climate on Venus started to warm up a little,

there's greater evaporation coming off the oceans.

And that water vapor in the atmosphere

is itself a greenhouse gas.

The climate gets even warmer.

Venus reaches 880 degrees Fahrenheit.

Any chance for life broils away.

The Earth also faces a searing hot future,

when the ageing godfather, the Sun,

bloats up and attacks his family once again...

...transforming into a lethal weapon of mass destruction.

For the last four billion years,

our mob family, the solar system, lived in harmony.

But nothing lasts forever.

The godfather, the Sun, will grow old, fat and mean.

The Sun is getting hotter.

Eventually it will overwhelm Earth.

It's estimated that in just under a billion years,

the Sun is gonna tip the Earth into a runaway greenhouse.

The oceans will eventually boil away.

And the Earth is gonna become very much like Venus.

Eventually Earth is gonna be too hot for life.

But this global heating is only the warm-up act.

In five billion years, the battle between the Sun and the planets

will enter a new phase.

And there will only be one winner.

Stars like the Sun only have enough hydrogen

to fuse for about 10 billion years.

So that means that in about 5 billion years,

the Sun will actually run out of hydrogen.

With no hydrogen fuel left, fusion stops.

The core collapses and reignites, fusing helium.

The energy released by all of this fusion

causes the star to balloon outwards and become a red giant.

The red giant is like a bitter old gangster.

Bloated and aggressive, it attacks the inner planets.

Mercury and Venus are gonna be engulfed by the Sun

as it becomes a red giant.

It burns up both planets.

Next in line, Earth.

Then the universe throws us a lifeline.

As the Sun expands outward as it enters its red giant phase,

it's actually going to be losing mass.

The red giant blows off gas.

And as it loses mass, its gravity is weakening.

So this means that the Sun's grip on the planets that orbit it

is gonna be weakening.

And so they sort of start moving away from the Sun.

It's almost like they're running away from the heat.

If you can't stand the heat, get out of the solar system.

Can Earth and Mars outrun the expanding red giant?

So it's a race, right?

Who will get far enough from the Sun to escape being engulfed by it?

The eventual fate of the Earth is not clear.

It's possible that the Earth will be completely swallowed up

by the Sun's atmosphere.

Its new, bloated, red atmosphere.

Even if the Earth escapes being directly engulfed by the Sun,

it's still not a good day for our planet.

Because the Sun is gonna be really, really close.

So imagine something basically red hot, glowing, covering the sky.

The Earth will be molten, in fact a lot of it will vaporize.

So it's not like you're gonna want to be here anyway.

As I look at the scenario,

what's clear is that life isn't gonna make it on Earth.

Mars had a head start and escapes complete destruction.

It'll be cooked, it'll be a molten planet but it'll still be there.

The ageing don wipes out life in the inner solar system.

But may help it survive elsewhere.

The Sun's red giant phase may initially bring

new opportunities for life in the outer solar system.

Right now the outer solar system is locked in ice,

it's way too cold.

But when our sun becomes a red giant,

it will become much, much brighter.

It will warm up the outer system.

And transform the gas giants' icy moons.

Europa and Enceladus, that orbit Jupiter and Saturn respectively,

are currently frozen worlds.

They have icy crusts

and are believed to have liquid oceans below those crusts.

Scientists believe that these sub-surface oceans

may harbor life.

As the temperature increases, their frozen exteriors

are gonna be thawed and they'll become entirely ocean worlds.

Any lifeforms already evolving in their oceans

will have a whole new world of possibility open to them.

If life isn't there yet, it would certainly have a chance to evolve.

We may have explosions of life on the other outer solar system bodies.

But this burst of new life may be short-lived.

Even though these ocean worlds may seem like a great place to move to

after the inner solar system is engulfed,

I would not start packing yet.

The red giant will grow to over 250 times its current size.

As the Sun continues to expand,

these new ocean worlds will start getting hotter and hotter

and eventually all of the water will evaporate away.

Any new life dies out.

But bodies in the furthest reaches of the solar system fare better.

The key to surviving the Sun turning into a red giant

is basically distance.

So the farther out you are from the Sun now,

the better off you are then.

The best bet might be the distant dwarf planets like Pluto.

Or Neptune's moon, Triton.

Today, Pluto and Triton are frozen worlds,

coated in frozen water, frozen carbon dioxide,

frozen methane and frozen nitrogen.

Current temperatures on Pluto and Triton

are a freezing minus 390 degrees Fahrenheit.

But in the distant future,

the red giant will make them more like Florida

with beaches and oceans.

At first, the really exotic ices, the nitrogen and the methane

will evaporate away and start to make an atmosphere.

And then the surface of water ice might melt

to make a liquid water ocean.

So now we have these objects that might actually become

the most Earth-like bodies in the solar system.

These may be our lifeboats.

I mean, they won't have breathable atmospheres

and it's not like they're gonna be great places to live.

But the Earth is gonna be basically toast at that point

so what choice do you have?

Humanity may use the warm outer bodies

as stepping stones to a new home

because when the godfather Sun gets very old,

he becomes frail and unable to stop other more powerful dons

from destroying the solar system forever.

Six billion years in the future.

The ageing godfather's attack on his children ends.

The bloated red giant dies, releasing a burst of energy

which blasts the outer regions of the star,

plus the remains of the vaporized planets out into space...

...ready to build new stars and new planets.

What's left are veils of beautiful colored gas

called a planetary nebula.

The surviving planets,

and at the heart, the remains of the Sun,

now nothing but a burnt-out core.

We call those leftover cores from small stars white dwarf stars.

And they're much smaller than the Sun.

The white dwarf will be about half the Sun's original mass

and all contained into the size of the Earth.

The dense white dwarf doesn't burn fuel so it can't generate energy.

The solar system cools.

We'll start seeing freezing

from the outer solar system to the inner system.

We'll start with Pluto...

...then Enceladus around Saturn...

...and then Europa around Jupiter.

And then finally Mars.

So they've already had any volatiles sent away,

their surfaces are now gonna be metallic and rocky.

You're gonna end up with these very frozen, rocky metallic worlds.

The near-dead godfather is now a shadow of his former self.

And the solar system is at the mercy of more powerful mobster stars.

The white dwarf of the Sun has about half the mass of the Sun today.

Which means gravity is half as strong.

So the planets and their orbits will move further out.

These outer planets which survived the Sun turning into a red giant,

their orbits are now much, much larger than they were before,

up to about a factor of two.

That's an issue because there are other stars in the galaxy.

We're part of the Milky Way galaxy.

Our best estimate is there are something like 100 billion

other suns like ours orbiting our galaxy.

Every 20 million years, something like that,

one of them will pass by close enough

to affect the orbits of these planets.

So in this distant future where our sun is a white dwarf,

as our orbits are larger and things are moving slower,

we're way more susceptible to the effects of passing stars.

You can imagine this as ships passing each other in the ocean

where as one whizzes by another,

it creates waves that knock the other one around.

Passing stars will give the planets little nudges,

little kicks.

The giant planets will enter a chaotic phase

where everything except for Jupiter

will be scattered out of the solar system.

Fifty billion years in the future,

the solar system faces another ruthless gangster

out on the make.

Its gravity is gonna yank Jupiter away from the Sun

and fling it out into interstellar space,

and Jupiter will become a rogue planet.

All that's left of our once strong Mafia family,

the Sun, eight planets and countless moons,

is the small, weak white dwarf.

Eventually a white dwarf cools so much

that it no longer emits radiation.

And it becomes what we call a black dwarf.

And this is basically just a burnt-out shell of a star

composed of oxygen and carbon.

It can form a carbon crystal, which we happen to call diamonds.

So think of a black dwarf as a diamond in the sky.

A cosmic gem destined to wander the galaxy for eternity.

Our solar system formed from chaos

but grew from collaboration between the planets and the Sun.

We know the planets affect us, we know the Sun affects us.

In a few billion years, the Sun will really affect us.

The more we look at this stuff,

the more we realize that everything affects everything else,

including us.

Without all of these things interplaying,

the Earth wouldn't have the stable environment we have today

and life wouldn't be able to exist.

And so the chances are small but it's worked out well for us.

As we piece together the events that

we think have shaped our solar system,

step back and think about all the moving parts,

all of the chance encounters,

all of the chaos.

It's hard not to think we're really lucky to be sitting on Planet Earth.

In the future, our Mafia family will be gone.

But somewhere out in the Milky Way,

a new mobster star system may rise from the ashes of our own.

One of the trends that we see in our universe

is that destruction leads to creation.

The fact that our star is gonna one day die

doesn't mean that it's the end of anything.

It's the beginning of something new.

I think in the future, it's only going to get more complicated,

more interesting.

We'll find out just how dynamic a place the universe really is.

Subtitling by Iyuno