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.