All language subtitles for How.the.Universe.Works.S11E05.Solar.System.Special.1080p.AMZN.WEB-DL.DDP2.0.H.264-BurCyg_track3_[eng].1

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.

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