All language subtitles for How.the.Universe.Works.S11E05.Solar.System.Special.1080p.AMZN.WEB-DL.DD+2.0.H.264-playWEB_track4_[eng]

ROWE: 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.

ROWE: The players in
our solar system's 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.

ROWE: 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.

ROWE:
Think of the solar system as

an old-fashioned mafia
crime family.

The sun is the Don,
his quarreling children,

the planets.

Their story,
like any good mob movie,

is an epic tale of empire building,

sibling rivalry, greed,
and ultra violence.

THALLER: The origin of
the solar system was chaotic

and violent--
planets colliding,

planets
even changing places.

ROWE: 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

ever existed
in the solar system.

ROWE:
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.

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

you know, we don't have
a time machine.

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

ROWE: 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 and what was going

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

ROWE: 2020--

scientists study ancient
material trapped inside

a meteorite found in
Murchison, Australia.

The Murchison meteorite
contains tiny crystals called

presolar grains
that predate our sun.

OLUSEYI: And trapped
within them is evidence of

the history of the formation
of our solar system.

ROWE: The presolar 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 presolar grain
doesn't sound very romantic,

but actually,
we might call those stardust,

because these materials
are things that were

made in stars
that no longer exist.

ROWE: 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.

OLUSEYI: The sources of
the material in that cloud

could come from one of
a number of places.

The material
from lots of stars'

atmospheres
could be mixed in there.

ROWE: 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.

BULLOCK: 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.

ROWE:
If not from our galaxy,

then from where?

We think these stars actually
came from

the Sagittarius Dwarf galaxy,
which orbits the Milky Way.

ROWE:
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 going to compress

the gas clouds, and that's gonna
create star formation.

The Sagittarius Dwarf smashing
into the Milky Way

is like dropping a boulder
into a pond.

It sets 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.

ROWE: 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.

LANZA: 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.

ROWE: Perhaps the Sun formed in
this starburst.

OLUSEYI: 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 million 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.

ROWE:
4.6 billion years ago,

part of the cloud
seeded with

material from dying stars
grows denser,

until it gets so massive,
it collapses.

NANCE:
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.

ROWE: The protostar drags in
more and more gas and dust,

creating a region of materials
spinning around it

called the protoplanetary disk.

OLUSEYI: 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.

ROWE: 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

that 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.

ROWE: The blizzard of
particles races out

at over a million miles
an hour.

It smashes into
the protoplanetary disk

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.

ROWE: The sun is now
the Godfather,

pulling the strings on
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.

ROWE:
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 nebula.

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 we see other
planets going around the Sun,

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

where did these planets
come from?

ROWE: How did the leftover gas
and dust build the planets?

To solve the mystery,

scientists study
other star systems

across the Milky Way.

HOPKINS:
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.

ROWE: Star system PDS 70
is one such system.

It's young,
just 5.4 million years old.

And nestled inside
the protoplanetary disk are

two infant planets
feeding on gas and dust.

We can see these baby
exoplanets pulling in

material and creating
these gaps in the disk.

It's an amazing discovery--
it's kind of mind-blowing

that we can see a new
solar system being born.

CHRISTIANSEN: 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.

ROWE: 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.

Ah.

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 0G.

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.

ROWE:
These clumps were strong.

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

DURDA: 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 disk.

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 exactly
identical to how

a dust bunny forms
in your room.

SUTTER: These are cosmic dust
bunnies that

will some day grow up
into giant planets.

ROWE: Astronomers call these
cosmic dust bunnies pebbles.

We think clumping dust
particles formed trillions

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
and these are objects that are

roughly half a mile
to 100 miles in size.

ROWE: 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 that 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?

WALSH: 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.

BATYGIN: In the disk
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.

ROWE: 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.

ROWE: The planetesimals
face a race

against time to grow
into planets.

They must grab enough
building material

from the protoplanetary disk
before their Don,

the Sun,
blasts it all away.

ROWE:
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 planet's
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 disk
of gas.

ROWE: 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 disks only last for
about five million years.

ROWE: We used to think
of the solar system's

protoplanetary disk
like an old-school diner

where the mob family
came to eat.

The firstborn child, Jupiter,
grows by wolfing down

planetesimals, followed by
a second course of gas.

HOPKINS: The old model of planet
formation is the idea that

these large-ish planetesimals
that are miles across

collide and stick to
each other,

kind of like modeling clay,
until you get a bigger

and bigger object that can

eventually get so massive that
it starts to then pull in

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

ROWE: 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.

ROWE: 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.

HOPKINS: 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.

SUTTER: 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.

ROWE: 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.

HOPKINS: 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.

ROWE: This was possible
because there was still

lots of gas in
the protoplanetary disk.

Everything was moving through

this very thick disk
of dust and gas.

That means that everything
was actually

being slowed down by the drag.

Things were the size
of pebbles,

they were feeling
the drag, too.

That meant they lost energy
and made it easier for Jupiter

to pull them in.

ROWE: The young planetesimals
grab 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.

HOPKINS: 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.

ROWE: 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.

HOWETT:
And 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,

and the planets
are the same way.

They could only be made out

of things that are in
their vicinity.

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

volatiles like water
and ammonia

had evaporated
and get 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.

ROWE: The ice giants feasted
on materials that

only survive far from
the Sun's harmful influence.

HOPKINS:
When you get further out,

the distances that Uranus
and Neptune are at, ammonia

and methane start to turn into
their own frozen ices.

That's why we call them
ice giants, because

they're formed primarily
out of these solid ices.

ROWE: And there were plenty
of these ices to gorge on.

HOWETT: The further you are
from the Sun,

the less the effect
the solar wind has.

It's a bit like if you're
standing next to a fan, where if

you're right next to it,
you're really gonna feel it.

You step back a few paces,

it's not as blowy,
and so it's

the same thing happening in
the outer solar system.

It's not able to strip away

the gasses and the rock quite
as much.

ROWE: The ice giants
grew to over

14 times the mass of Earth.

The Godfather, the Sun,

ruthlessly controls the family.

But firstborn Jupiter has
grown large.

He craves power

and attempts a hostile takeover
of the inner solar system,

triggering mass murder
and mayhem.

ROWE: 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.

OLUSEYI: It's hard to get
a perspective on

your home if you've not been
anywhere else.

We thought it was typical,
but now that we've discovered

hundreds of others,
it's the weird one.

It may surprise you to learn
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 solar system
and these big gas giants

farther out.

ROWE: We've found star systems
with super puff planets,

rocky worlds orbiting
tiny red stars,

giant stars
with superheated 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 look at, ours

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

ROWE: The other systems may be
very different from our own,

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

2021.

Scientists discover
six planets orbiting

a small orange star

called TOI-178.

And they range from just
a little 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.

ROWE: Around 40 percent
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.

ROWE: 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.

LANZA: 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.

ROWE: 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.

PLAIT: The first exoplanets
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, so

there's nothing that could
have formed right there.

How the heck did you get

a planet that big,
that close to a star?

ROWE:
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.

WALSH: That made us look
at our solar system

through a different lens.

And all of a sudden, we started
seeing signs that, oh, maybe--

yeah, maybe this happened here.

ROWE: 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 disk.

Underboss Jupiter makes
a move to take control of

the family.

The giant planet's gravity
creates spiraling waves in

the protoplanetary disk,
which drag on Jupiter,

slowing it down.

So 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.

ROWE:
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, right?

It's just plowing through everything,

just chaos everywhere.

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

and there are
all kinds of new planets

forming, and they're settling
into nice orderly orbits.

And here comes Jupiter,

the big bully on the block.

ROWE: 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.

ROWE: The growing inner planets
fly off in all directions.

Some collide violently.

Many die in the melee.

DURDA: This is like
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.

ROWE: 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.

ROWE: 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.

ROWE: 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.

WALSH: Without Jupiter, Earth
and Venus and Mars might

have just kept on growing
and growing and growing.

We might have ended up with
a bunch

of super-Earths
in the inner solar system.

ROWE: 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.

ROWE: For thousands of years,
people have looked up at

the sky and seen the planets
orbiting the Sun in harmony.

THALLER: 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.

ROWE: 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.

PLAIT: If Jupiter had continued
its journey toward the Sun,

it would have ejected a lot
of the stuff that was left.

There would be
no inner rocky planets.

It would just be Jupiter.

ROWE: 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 toward 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.

ROWE: 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.

ROWE: 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 all of
a sudden, we have

the two planets moving outward
in the solar system.

So it's like Saturn has
a trailer hitch, and it's towing

Jupiter back to the outer
solar system,

where we find them today.

PLAIT: Saturn saved
the earth, basically.

If it hadn't have 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.

ROWE: 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.

WALSH: 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 big,

violent collisions.

ROWE: 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.

PLAIT: 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 call that planet Theia.

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

The impact destroyed Theia

and nearly wiped out Earth.

OLUSEYI: When Earth
was struck by Theia,

it was unlike any event
before or since.

We think about the event
that wiped

out the 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.

ROWE: 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.

ROWE: 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.

ROWE:
A new study in 2021 suggests

they don't come from Earth.

It could be that
these dense blobs of

material deep in our mantle
are remnants of Theia.

ROWE: 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 happened 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 ever 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.

RADEBAUGH: What's strange
about Venus is that

it actually spins in
the opposite direction.

All the other planets spin
sort of with--

with a righthand spin,
from the west to the east,

and Venus spins from the east
to the west.

LANZA: And also
Venus's spin is very slow.

It's 243 times slower
than that of Earth's.

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.

ROWE: Mercury carries horrific
scars from Jupiter's

assault on the inner
solar system.

THALLER: Mercury has always
seemed to be a bit of

an odd planet, because it really
is sort of a cannonball.

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

So the question is,
how do you get

this large core,
but very little rock,

very little mantle
and crust around it?

ROWE: We think Mercury
hit another planet, hard.

DARTNELL: 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.

ROWE: 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 end game

of the giant impact stage of
planet formation.

ROWE:
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.

THALLER: In some ways,
Jupiter kinda ate Mars's lunch.

So Mars just didn't have as
much stuff to

work with, and it never became
a very big planet.

ROWE: After 60 million years of
family feuding,

the battle of the planets is
finally over.

OLUSEYI: Out of all the mayhem
and chaos of the early

solar system, four
terrestrial planets remained.

One of them was Earth.

THALLER: 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.

ROWE: 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.

ROWE: 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 towards
where Uranus and Neptune grow,

a journey that may help
explain several mysteries about

the solar system,

including the size
of the ice giants.

PLAIT: The biggest problem with
the outer solar system is

literally bigness.

Uranus and Neptune are too big
for where they are.

ROWE: The problem is
the availability of

building materials.

This far out from the Sun,

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

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 that they formed

further in
and then maybe moved out.

ROWE:
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 quarreling children
call a truce and orbit together.

OLUSEYI: Orbits are on
the razor's edge of stability

as it is, and so one thing that
helped to stabilize

our solar system
in the early days

was that it was in
this cloud of gas and dust

that was this
protoplanetary disk.

ROWE: Gas in
the protoplanetary disk 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.

ROWE: The ceasefire between
the gas planets is short-lived.

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

the largest Mafioso children
set off on another crime spree.

So when the gas goes away,

you no longer have this
dampening 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.

ROWE: 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,

over time,
they start to push on each

other's orbits, and their
orbits start to get excited.

The whole thing starts
to unravel

and eventually culminates in
a violent

and beautiful instability.

ROWE: Gravitational shoves
from Jupiter

and Saturn pushed
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,

more or less, it's tipped
way over, so its pole is

pointing more or less towards
the Sun instead of up and down.

That's really weird.

ROWE: 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 1-2 punch knocks
the ice giant onto its side.

A clue to the cause of

the collision comes from
Neptune's moon, Triton.

RADEBAUGH: What's odd about
Triton is that it orbits

the wrong way around Neptune,
and that's

the wrong way for
the whole solar system,

so everything is going in this
direction, Triton is going

the other way.

The other thing is that 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 that

it probably didn't form there.

ROWE: 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.

RADEBAUGH: When we looked
at Triton and compared it

with Pluto from
telescopes from Earth,

we recognize these two are
very similar to each other.

On Triton,
there's nitrogen ice,

carbon monoxide ice,
there's carbon dioxide ice.

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

ROWE: 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 disk.

it's like a big bowling bowl
coming in and knocking off

bowling pins left and right.

THALLER:
Chaos ensues,

and as the two outer
planets get pushed through

all of this stuff,

throwing things left,
right, and center, all kinds of

collisions are inevitable.

ROWE: 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.

THALLER: The Kuiper belt--

this very, very distant
collection of small,

rocky bodies in the outer
solar system--

you would think that we have
no connection to that at all.

But instead, it may be
responsible for helping life

get started on Earth.

ROWE:
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 disk 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 disk 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.

DURDA: This raises a big
mystery-- where did all that

material ultimately
come from

that we now obviously have
in abundance on planet Earth?

ROWE: 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.

ROWE: 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, because

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.

ROWE: A 2019 study discovered
evidence of a storm of

icy objects raining inwards
around 4.48 billion years ago.

At the same time,
the giant gas

planets were tearing
through the outer solar system.

As Jupiter and Saturn,
Uranus and Neptune,

are migrating back outwards in
the solar system,

they're excavating a whole
slew of icy planetesimals,

like a like a snowplow 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.

ROWE: 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 of the conditions
necessary for life

were brought by
the bombardment.

If that chaotic bombardment
hadn't happened, it's just

possible that we wouldn't be
here today.

ROWE: Even though some of our
mob family now live in

the outer reaches
of the solar system,

the family ties to the planets

in the inner regions are
still strong.

HOWETT: 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.

ROWE: This interaction
between planets,

billions of miles apart,

transformed
the inner solar system

and primed Earth for life.

But our planet was
still uninhabitable.

RADEBAUGH: The early Earth,
right after the bombardment,

would have been
a complete hellscape,

and 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 that time,

there was no liquid water
on the surface yet.

Early Earth could not
have supported life.

ROWE: 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 of these materials, forming
a very thick layer of gas.

This new atmosphere had
a composition that was mostly

water vapor, carbon dioxide,
and nitrogen.

ROWE: Over the next
30 million years,

Earth cools--
a solid surface forms.

DURDA: 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.

RADEBAUGH: 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.

ROWE: Trillions of gallons
of water rain down.

Torrential rains for, I mean,
you know, imagine monsoon rains

for, you know, tens and tens
of thousands of years.

RADEBAUGH: All this water
would have rained

onto the surface, rained,

rained, and eventually
filled up our oceans.

ROWE: The oceans pull
life-forming chemicals from

the rocks and the atmosphere,
creating the primordial soup.

Life can begin.

THALLER: 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.

ROWE: A series of
interconnecting and often

violent incidents
going right back

to the start of the solar
system led to our existence.

HOWETT: 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
things up, we shouldn't exist.

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

And yet here we are.

PLAIT: 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 that we're
pretty lucky just to be here.

Earth won the cosmic
game of chance,

but were the other
Mafioso children as lucky?

Did Mars and Venus

also develop environments
capable of supporting life?

ROWE: 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.

RADEBAUGH: 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,
and then they were

crushed like a tin can
and melted.

LANZA: It has a huge, crushing
atmospheric pressure,

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

and that's entirely
carbon dioxide.

DURDA: And it gets worse still,
because gasses in

the atmosphere have combined

to make really this concentrated
solution of gasses.

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.

ROWE: New climate models suggest
that four 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.

LANZA: 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 away

from the Sun, and it 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 that any liquid
water on the surface would just

boil away,
and any current water

that's on the planet
is locked up in ice.

ROWE: However, recent surveys
of Mars reveal

a very different planet, once
capable of supporting life.

COOPER: 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 riverbeds.

RADEBAUGH: 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.

ROWE: We calculate that Mars
once had five 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.

ROWE: To have oceans,

Mars must have had
a thick atmosphere.

And recently,
a space probe

orbiting the red planet
found evidence.

RADEBAUGH: 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 for Mars's atmosphere

and extrapolate back in time,

and we can see that 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 to date

just tell us that it was
absolutely a habitable world.

RADEBAUGH: So now we have
an Earth that had kind of

settled down after the heavy
bombardment of 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.

ROWE: But this golden age
of habitability

is short-lived.

Another battle erupts
between the planets

and their Don, the Sun.

Venus and Mars suffers
serious collateral damage.

ROWE:
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.

ROWE: 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, and that's just
because a magnetic field

protects the planet's atmosphere
from incoming radiation.

Solar wind, cosmic rays,
you name it.

ROWE: 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 the Earth
creates its magnetic field.

ROWE: Mars couldn't maintain
its magnetic field,

because Jupiter's violent
assault on the inner

solar system stole
the red planet's lunch,

THALLER: Jupiter migrated in
about where Mars is today.

So that means that most of
the material

was actually swallowed up by
the gravity of Jupiter.

So Mars just got unlucky.

ROWE: 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,

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

ROWE:
3.7 billion years ago,

the Sun attacks
the defenseless Mars.

The solar wind just
bombards it and strips it

away of the atmosphere
very quickly over time.

ROWE:
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.

ROWE: 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.

ROWE:
They're not damaged

like the craters we see
on other worlds.

LANZA: 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.

ROWE: 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
plates like Earth's does.

So it's just a lid over
the planet, and eventually,

the pressure builds up
and builds up

and builds up until it--
boom, lets out all at once.

RADEBAUGH: A catastrophic event
that overturned

the entire crust of Venus
and resurfaced it.

ROWE:
An alternate theory suggests

the resurfacing happened over
millions of years.

RADEBAUGH: 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.

ROWE: 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
in the Venusian atmosphere.

ROWE: 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.

DARTNELL: 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.

ROWE: Venus reaches
880 degrees Fahrenheit.

Any chance
for life broils away.

The Earth also faces
a searing hot future

when the aging Godfather,

the Sun, bloats up and attacks
his family once again,

transforming into a lethal
weapon of mass destruction.

ROWE: 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.

Stars like the Sun
only have enough

hydrogen to fuse for about
10 billion years.

So that means that
in about five billion years,

the Sun will actually
run out of hydrogen.

ROWE: With no hydrogen
fuel left, fusion stops.

The core collapses
and reignites, fusing helium.

NANCE: The energy released by
all of this fusion causes

the star to balloon outwards
and become a red giant.

ROWE: 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.

OLUSEYI: 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.

ROWE: Can Earth and Mars outrun
the expanding red giant?

So it's a race, right?
Who is going to get

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

MINGARELLI: 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.

PLAIT: So imagine basically
something red-hot, glowing,

covering the sky.

The earth will be molten,
and in fact, a lot of it

will vaporize.

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

OLUSEYI:
As I look at this scenario,

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

ROWE: Mars had a head start and
escapes complete destruction.

It'll be cooked, I mean,
it'll be a molten planet,

but it'll still be there.

The aging 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.

SUTTER: 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.

ROWE: And transform the gas
giant's 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.

ROWE: Scientists believe
that these subsurface oceans

may harbor life.

As the temperature increases,

their frozen exteriors are
gonna be thawed,

and they'll become
entirely ocean worlds.

CHRISTIANSEN: Any life forms
already evolving in their oceans

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

Or if life isn't there yet,

then it would certainly have
a chance to evolve.

We may have explosions of life

on these other outer
solar system bodies.

ROWE: 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.

ROWE: 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.

ROWE:
Any new life dies out,

but bodies
in the furthest reaches

of the solar system
fare better.

PLAIT: 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.

ROWE: The best bet might be
the distant dwarf planets,

like Pluto.

So now we have these objects
that might actually

become the most Earth-like
bodies in the solar system.

These may be our lifeboats.

PLAIT: I mean, they won't have
breathable atmospheres,

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

but, you know, the Earth is
gonna be basically toast at

that point, so, you know,
what choice do you have?

ROWE: Humanity may use the warm
outer bodies as stepping stones

to a new home,
because when

the Godfather's sun
gets very old,

he becomes frail and unable to
stop other more powerful Dons

from destroying
the solar system forever.

ROWE: Six billion years
in the future.

The aging 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.

ROWE: 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 solar system--
we'll start with Pluto.

Then Enceladus around Saturn.

And then Europa
around Jupiter,

and then finally Mars.

So, you know, they've already
had any volatiles sent away.

Their surfaces are now gonna
be metallic and rocky,

and you're gonna end up with
these very frozen, rocky,

metallic worlds.

ROWE:
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 in 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, and our best estimate

is that there is something like
100 billion other suns like ours

orbiting our galaxy.

PLAIT: 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 like
ships passing each other in

the ocean, where there's one
whizzes by another,

it creates waves that knock
the other one around.

BATYGIN: 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.

ROWE: 50 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.

ROWE: 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.

OLUSEYI:
It can form a carbon crystal,

which we happen
to call diamonds.

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

ROWE: 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.

PLAIT:
We know the planets affect us.

We know the Sun affects us--
in a few billion years,

the Sun is really gonna
affect us.

The more we look at
this stuff,

the more we realize that
everything affects everything

else, including us.

HOWETT: Without all of
these things interplaying,

the Earth wouldn't have
the stable environment

that 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.

WALSH: As we piece together
the events that have

we think shaped
our solar system,

we step back and think about
all the moving parts,

all of the chance encounters,
all of the chaos.

And it's hard not to think
that we're really

lucky to be sitting here
on this planet Earth.

ROWE: 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.

OLUSEYI: 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.

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

more complicated,

more interesting, and we're
gonna find out just how dynamic

a place the universe really is.