All language subtitles for How the Universe Works - 6X05 Uranus and Rise of the Ice giants

Our solar system
is home to giants.

Gas giants Jupiter and Saturn
seem to dominate,

but two ice giants determine
the fate of the rest...

Neptune and Uranus...

Distant planets
unconnected to us,

or so we thought.

We now know the fate
of the ice giants

is entwined with our own.

They've gone from being
these cold, dull worlds

to actually having in them
the very secret

of why you and I exist at all.

Their story is of
epic migration,

brutal destruction...

Uranus got jabbed
and then knocked on its side.

...Of worlds more
alive than anyone imagined.

They hold the key to the history
of the solar system

and perhaps to life on Earth.

Uranus and Neptune...
Mysterious giants

lurking in the cold outer
reaches of the solar system...

The farthest planets
from the Sun.

Uranus and Neptune are
sort of the sentinels

of the outer solar system.

They're out past
Jupiter and Saturn,

well over, like, 2 billion,
3 billion miles from the Sun.

Their size and location

are a puzzle
to planetary astronomers.

Uranus and Neptune are somewhat
of a mystery because,

in a way, they shouldn't exist,

or at least they shouldn't
exist where they are.

Scientists can't understand

how these giant planets grew
so big so far from the Sun.

The mystery starts
4 1/2 billion years ago...

...with the birth
of the solar system.

In the beginning,
the Sun ignites from a disk

of gas and dust.

The rocky cores of the first
planets start to grow.

They collide with the debris in
the disk as they orbit the Sun.

But the inner planets
have a size limit.

To grow into a giant planet,
you need gas.

Heat from the infant sun blasts
these lighter gas molecules

beyond a point astronomers
call the frost line.

Out here, it's cool enough
for gas molecules like hydrogen

and helium to stabilize.

Jupiter and Saturn
take shape first...

Sweeping in the abundant gas
and quickly becoming gas giants.

But Neptune and Uranus
are different.

Jupiter and Saturn are about
90% hydrogen and helium,

whereas Neptune and Uranus
are more like 20%.

So what does this
difference in gas tell us

about their formation?

We suspect that Uranus and
Neptune came a little bit later

when there was not
as much gas to be swept up.

Uranus and Neptune
have less time to suck up

as much hydrogen and helium
before these gases disappear.

But they're also
forming farther out,

where it's cold enough for
other, heavier gases to freeze.

These are swept up by
the growing outer planets.

Out where Uranus and Neptune
are, tons of ice,

tons of frozen gases
as we might think of them...

Methane, ammonia, water,

and so that's what makes up
their composition predominantly.

They may be smaller
than Jupiter and Saturn,

but these heavy ices
mean they grow dense.

They become ice giants.

But there's a problem.

They're too big.

The disk of gas and ice
around a newborn star

does not last forever,

and material in the far reaches

of the solar system
is spread thin.

As you move further out
in the solar system,

the time scale for two bodies

to find each other and collide
and accrete slows down

because the periods around
the Sun are much longer,

and it just takes
a very, very long time.

Neptune and Uranus
orbit the Sun incredibly slowly,

too slowly to collide
with enough icy material

to grow into the giants
we see today.

So when we look at Neptune
at this very distant orbit,

we don't have enough time
in the solar system

to build a planet like Neptune.

We just don't think
we could build Neptune

where we find it today.

So what happened?

It turns out,
where we see them now

is probably not where
they started out.

One thing we've learned
about solar systems

is that things are
in a delicate balance,

and planets migrate.
They move around.

They don't form in one place
and stay there forever.

So what has enough power

to move a giant planet
like Neptune?

An even bigger one... Jupiter.

One way for planets to move

is by gravitationally
interacting with each other,

so they feel
each other's gravity.

They can tug. They can pull, and
that effect can lead to planets

slowly migrating around
in their planetary systems.

The closer two planets
are, the greater the effect,

and in the early days
of the solar system,

the giant planets
are much closer together.

On top of that,
they may have orbited

in a different order
than we see today...

Jupiter, Saturn,
Neptune, and Uranus.

So what causes Neptune
and Uranus to swap positions?

The answer lies
with Jupiter and Saturn.

The two biggest giants lock
into a gravitational dance.

There's always this
interplay between them.

Think of Capoeira dancers,
balancing and moving together

in a careful, orchestrated way.

Over millions of
years, a rhythm slowly builds.

These giants push
and pull each other

into more elliptical orbits.

But the gravitational dance
reaches a climax.

The stretched orbits
become unstable.

The giants move off course.

As Saturn and Jupiter
twist out from the Sun,

they fling Neptune
out beyond Uranus.

As Neptune moves out
through the solar system,

it pushes debris ahead of it.

These are the leftover icy
fragments from planet formation.

Neptune
snowplows these bodies out.

They because the Kuiper belt,

the band of thousands of
small bodies of ice and rock

just beyond Neptune's orbit.

You can think of the structure
of that Kuiper belt as, like,

blood splatter on the wall
at a murder scene.

It's the record of this
really violent of Neptune

migrating outward
across the solar system.

But Neptune's movement
doesn't just fling

these small icy bodies
out into the Kuiper belt.

It also sends some of them
crashing in towards the Sun.

Some bombard the early Earth.

It's the most violent time
on our planet

since the birth of
the solar system itself,

500 million years after
the Sun flared into life.

It's called
the late heavy bombardment.

During the late heavy
bombardment,

you had rocks literally falling
down from the sky constantly.

This would've been
a terrible time for life.

And yet,
this cascade of icy bodies

also brings something
essential for life.

One characteristic of the outer
solar system bodies

is that we often find organics.

Organics provide the basis

for all living organisms
we find today.

They're carbon-based molecules
that form on the surface

of dust grains
in the early solar system.

The rocky inner planets sweep up
these organics as they grow...

But the scorched surfaces
of the young planets

are too inhospitable

for many of these
delicate molecules to survive.

Yet organics remain intact
on the small, icy bodies

of the outer solar system

that Neptune tosses
towards the early Earth.

Neptune was the solar system's
cosmic delivery service.

As far away as Uranus
and Neptune are,

the existence of ice giants
in the outer solar system

may have been critical for
the existence of Earth today.

And the ice giants may have done

more than give life on Earth
a kickstart.

They may have prevented
our planet

from being completely destroyed.

The ice giants...
Uranus and Neptune,

distant giant worlds

that may have delivered
the elements of life to Earth.

Without them, our planet itself
might not exist at all.

These ice giants are
fascinating worlds,

but they may be even
more important than that.

They might be the reason
we're here.

Around 4 billion years ago,

the young Earth is under threat

from our solar system's bully,
Jupiter.

Positioned between
the rocky inner planets

and the giant outer ones,

Jupiter dominates
the solar system.

When you have a behemoth like
Jupiter in your solar system,

what it does determines in part
what everything else does.

As Jupiter and Saturn lock

into their gravitational dance,

they migrate out,
away from the Sun.

Jupiter's immense gravity
should pull Earth

and Venus along with it.

Earth and Venus' orbits
should stretch

and overlap with each other.

It's a collision
waiting to happen...

...except... It didn't.

So by the fact that we're
talking about this here on Earth

suggests that Earth and Venus

didn't have an impact
early in the solar system

when Jupiter and Saturn
were migrating.

Something appears
to have protected us.

Scientists think
something yanked Jupiter

into a different orbit
before it had a chance to pull

Earth and Venus
on a collision course.

But what could cause
such a large jump

in Jupiter's migration?

This is where the ice giants
enter the story.

Getting Jupiter to make
a big jump in its migration

is not easy,

and so the best way that
the models have been able

to actually recreate this jump
is to have Jupiter

actually eject something
the size of Neptune

out of the solar system
entirely.

Jupiter has a lot of gravity,

and if you get too close to it,

you're going to be accelerated
as you fall in towards Jupiter,

and it's possible that
you can eject a planet

completely out of
the solar system this way.

It's basically slingshotting it.

But a planet the size of Neptune

is heavy, even for Jupiter,

and slingshotting it out
of the solar system

gives Jupiter a kickback.

Jupiter is knocked into a new
orbit, and Earth is saved.

But which ice giant
sacrificed itself for us?

Neptune is still
in the solar system,

and so is Uranus.

If you use computer models

to basically predict
the behavior of the planets,

what you find is that
if you start with Jupiter,

Saturn, Uranus and Neptune,
you can't save the Earth

without ejecting
either Uranus or Neptune,

but they're there,
so we know that's not right.

However, if you add
a third ice giant,

a fifth giant planet out there,

then that actually
makes everything work.

You can save the Earth,

have the planets in
their present configuration,

and that ice giant gets ejected
from the solar system.

Imagine our solar system

starting with three ice giants.

One swings too close to Jupiter.

Our solar system's bully
throws its victim clean

out of the playground.

Jupiter is pushed
into a new orbit

by the ice giant's gravity.

Earth is saved from Jupiter's
deadly gravitational pull,

and the solar system
becomes the safe

and orderly place we see today.

So we have a funny story here.

This ice giant that may have
existed billions of years ago

yanked Jupiter back into
the outer solar system,

preventing it
from destroying the Earth,

but in the meantime,
it sacrificed itself for us,

getting ejected from
the solar system.

We have to thank it
for our existence,

but it's not there anymore.

We humans are really lucky.

Had the dinosaurs not gone
extinct, we wouldn't be here.

Had this planet not been ejected
out of our solar system,

we wouldn't be here.

So where is
this missing ice giant now?

The answer is pretty amazing.

It could be clear across
the other side

of the milky way galaxy.

The Sun moves around
the milky way galaxy

at about half a million miles
an hour,

and in the history of the Earth,

we've been around
about 20 times.

We could've lost that planet
anywhere across the milky way.

But is this third ice giant

really lost or just hiding?

January 2016...
Astronomers at Caltech

make an astonishing
announcement.

They claim to have
found evidence

of a mysterious ninth planet
disrupting icy bodies

far out in the Kuiper belt.

Simulations suggest that if this
so-called planet nine exists,

it is similar in size
to Neptune and Uranus.

Could this be Earth's savior?

Could the solar system's
primordial missing

sacrificial ice giant
be planet nine?

Yes, it could.

Perhaps this third ice giant

wasn't ejected from
the solar system after all.

One type of ejection is
where you just take something

and you throw it out
of the solar system,

but another more gentle kind

is when you don't quite
make it all the way out,

and instead you go on
a very, very long period orbit

around the young solar system.

Planet nine is thought
to be so far out,

it takes up to 20,000 years
for it to travel around the Sun.

Perhaps it's been observing
the dramatic,

dynamical evolution
of the solar system

unfold from its frigid
20,000-year orbit.

Whether planet nine
is a long-lost sibling or not,

ice giants played a huge role
in taming Jupiter.

They made our solar system
the haven it is today.

But they are not
peaceful places.

Somehow, out in the deep freeze,

Neptune is tormented
by wild weather,

mysterious superstorms
and maybe even diamond rain.

Uranus and Neptune...

Their location at the edge
of our solar system

makes them very difficult
to study.

The ice giants Uranus
and Neptune

are very mysterious to us.

They're very far away,
so they're hard to observe

with telescopes
here at the Earth.

As a result,

these planets
have long been overlooked.

The only time we've glimpsed
these distant giants up close

was when voyager 2
flew past them in the 1980s.

The results amazed Heidi Hammel,
part of the voyager 2

imaging team at the time
of the Neptune flyby.

One of the most wondrous
and frustrating things

about planetary flybys
is that you learn so much

that you open a whole
Pandora's box of questions.

One observation
instantly intrigued scientists.

Neptune has the fastest winds
in the solar system.

Here on Earth, our winds
are actually driven

by different temperatures
from sunshine.

Neptune is so far away
from the Sun

that it receives almost
no energy from our star.

Neptune is 3 billion miles
from the Sun.

It's really cold there, so why
does it have such fast winds?

The less energy
a planet receives from the Sun,

the quieter we expect
its weather to be...

But Neptune isn't
tranquil at all.

It's covered in
massive violent storms.

There are storms
that are rivaling

the size of the inner planets.

That's a pretty big storm.

One of the largest
ever recorded on Neptune

is known as the 1989
great dark spot,

a single vast tempest,

large enough to swallow
the Earth whole,

riding on a jet stream
with a mind-blowing wind speed

of 1,500 miles per hour.

Hands down,
Neptune holds the record

for the fastest wind speeds
in the solar system.

The fastest tornado winds
on Earth

are only a few
hundred miles an hour,

and that does
devastating destruction,

so it's hard to imagine
what winds on Neptune would do.

A probe entering
Neptune's upper atmosphere

would record freezing
temperatures,

minus-370 degrees Fahrenheit...

Too cold
to generate the wind we see.

600 miles down,
though, the probe is smashed

by Neptune's relentless
jet stream winds.

And the deeper you go,
the warmer it becomes.

Neptune has almost three times

as much heat coming
from its interior

than you would expect
from a ball of gas

out at Neptune's distance.

The strange thing about
these high-speed Neptune winds

is that they're not powered
by heat energy from the Sun.

In fact, they're powered
by heat energy

from Neptune's own interior.

So where does this
internal heat come from?

When planets form, it's a very
violent, very energetic event,

and the planets are
actually extremely hot,

and it takes billions of years
for that heat to leak away,

so Neptune, it turns out,

probably still has a
tremendous amount of that heat

that is trapped inside of it,
and as that bubbles up,

that's what's actually
heating the atmosphere

and driving this
tremendous weather.

So how does Neptune
retain so much heat?

The secret lies deep
below the atmosphere.

As you go down
and down and down,

you'll just find the pressure
gets more and more intense

until you are eventually
essentially crushed.

That atmosphere will get
thicker and thicker like a fog

until suddenly you would realize
that instead of an atmosphere,

you are in an ocean.

Neptune has
a super-dense fluid mantle

made up of methane,
ammonia, and water.

Really, an ice giant
is not a solid ball of ice,

but rather a moving ocean
of swirling liquid material.

This swirling liquid
traps the heat,

acting like a blanket,
insulating the core.

This is the secret
to Neptune's wild weather,

and the intense interior heat

and pressure
in Neptune's methane-rich mantle

may create another
extraordinary effect.

The pressure is so intense

that the methane breaks up,

and methane is made
of carbon and hydrogen,

so if you take carbon
and you compress it a lot,

you could get diamond formation,

and so it is entirely possible

that literal diamonds
are raining down

in this ocean
of the mantle fluid on Neptune.

From superstorms to
diamond rain,

Neptune is strange,
dynamic beyond expectation,

but Uranus is the real mystery,

the victim of a cosmic
one-two punch with seasons

unlike anything else
in the solar system.

January 1986...

Voyager 2 approaches Uranus
at over 40,000 miles per hour.

Astronomers have been waiting
for this moment for 8 years,

but on voyager's arrival,

all that's revealed is
a bland, pale, blue ball.

That was a little bit
disappointing

from my perspective

as a scientist studying
the atmosphere of the planet.

20 years later,
everything changes.

Telescopes reveal huge storms
raging across the planet.

Why the enormous difference?

The answer lies in the planet's
extreme axial tilt.

If Neptune and Uranus
are siblings,

Uranus is definitely
the wonky sibling.

All the planets are tilted with
respect to the solar system.

The Earth is 23 degrees.

Jupiter is just
a handful of degrees,

but Uranus is
actually on its side.

It's tipped 98 degrees.

Uranus' tilt is almost
four times more extreme

than any other planet
in the system.

It's lying so its poles
are horizontal,

and its rings and moons
are vertical relative

to the plane
of the solar system.

Earth's tilt gives it seasons.

Uranus' extreme tilt
gives it extreme seasons.

Twice a year, its poles are
pointed directly towards

or away from the Sun,

so each pole has a very
intense period of midnight sun

and a dark, cold polar night.

It takes Uranus 84 years
to orbit the Sun,

so those seasons last
for a very long time.

You get, like,
20 years of sunlight

in the northern hemisphere
as its going around the Sun

and 20 years of darkness
in the Southern hemisphere.

Uranus is kind of like
"game of thrones."

You're waiting ages
for winter to come,

and then winter lasts 20 years.

A winter's night
or a summer's day

that lasts for decades.

But what happens in the interim
when the orbit of the planet

means the Sunlight
hits its spinning equator

rather than one of its poles?

When it's off to the side,
the whole planet's lit up.

As it spins, every piece of the
planet is exposed to sunlight.

Sunlight hits the
equator of the spinning planet,

pumping energy into the surface,
warming the atmosphere

and driving air currents
around the planet.

The result...
Spring and Autumn storms.

That extreme change in how
much sunlight is distributed

across that planet's atmosphere

probably has an important role

in driving this remarkable
seasonal change

we see in Uranus' atmosphere.

Unlike its ice giant
sibling, Neptune,

Uranus has seasonal storms
rather than constant ones,

so why does Uranus
roll around the Sun

while other planets
spin like tops?

It goes against everything we
know about planetary formation.

In some ways, forming new
planets in the solar system

was a lot like
making cotton candy.

There was a direction that
everything was coming together.

If you put a stick down in it,

the material would
accumulate around it

in a certain direction,
so that's why all the planets

have roughly the same
orbital axes.

If Uranus started out
with a vertical orbital axis,

how did it end up
flipped on its side?

We know there were a lot
of collisions between planets

or planet-sized objects
in the early solar system.

It's natural to assume
that Uranus probably got hit

as a grazing impact
from another giant object,

which tipped it
over on its side.

But there's a problem
with this assumption.

If you hit Uranus with a single
impact to knock it over

to 98 degrees,

then actually what you expect
is that the rings left over

would be orbiting in
the wrong direction

relative
to the spin of the planet.

What event could be
powerful enough

to flip a planet,

but gentle enough to bring
everything in orbit around it

along for the ride?

A single big collision

is probably not what happened
to Uranus

because that would've
been too disruptive.

It's kind of like boxing.

Instead of one big knockout
blow, it was the old one-two.

One theory suggests that

the newly formed Uranus is hit
by a protoplanet

the size of Earth.

The blow is only glancing.

Uranus is knocked partway
towards its current tilt.

Its ring system
survives the impact

and stays in orbit
around the equator.

As the second object hits,
Uranus is tipped all the way,

and the rings follow.

Uranus got jabbed
and then knocked on its side.

Uranus may orbit
the Sun sideways,

but Neptune's moon, Triton,
has an even stranger trajectory.

It travels around Neptune
in reverse.

But weirder than that,
it seems to be erupting,

and it could even harbor life.

Wherever we see planets,
we expect to see moons.

It seems the larger the planet,
the more moons orbit around it.

Jupiter has 69. Saturn, 61.

Next come the ice giants.

Astronomers have so far detected
27 moons around Uranus

and 13 around Neptune.

But one stands out completely...

Neptune's moon, Triton.

Triton is a bit of an oddball

because instead of orbiting
Neptune in the same direction

that Neptune spins,

it orbits
in the opposite direction,

what we call a retrograde orbit.

A giant planet and its moons

form out of the same swirling
disk of gas,

dust, and rocky material.

The lighter gas falls
into the center more easily,

forming the planet,

while some of
the heavier rocky material

is left over in the disk,
forming the moons.

Typically, the moon travels
in the same direction

that the planet is orbiting,

but in the case
of Triton and Neptune,

that's the complete
opposite case.

We know it couldn't have formed

in that orbit around Neptune.

It had to come were
somewhere else,

and a wonderful clue
to where it came from

is the nearby neighbor, Pluto.

Pluto is a dwarf planet in
the nearby Kuiper belt.

It's only 200 miles
smaller than Triton,

but it's not just size that
makes these two bodies similar.

It's their composition.

Triton is actually
most similar to Pluto.

It has a similar amount
of rock in its interior.

It has a similar
surface composition

with a lot of nitrogen
and methane.

It really looks like
a Pluto-like world,

but it just happens
to be orbiting a planet

instead of orbiting the Sun.

If Triton is like Pluto,

maybe it also started life
in the Kuiper belt.

Could it have been captured
by Neptune's gravity,

pulled into
the gas giant's orbit?

It's not easy to capture a moon
into orbit around a planet.

It's not natural for a body
to come close to another world

and just spiral in.

You've somehow got to put on
the brakes when it's close in.

For Neptune to capture Triton,

Triton had to be slowed down,
but how?

Again, Kuiper belt objects
hold a clue.

Many of the largest
are binary pairs,

two worlds orbiting each other,

like Pluto
and its large moon Charon.

Perhaps Triton was
one of a pair as well.

If Triton was in orbit
with a partner,

each of the pair would
travel at different speeds.

This speed difference is key.

Triton's velocity is just
a little bit slower.

As it's orbiting its companion,
it's slow enough

that it could actually
get captured by Neptune,

while that other one would speed
off across the solar system.

Triton's original dance partner

is flung out and away.

Triton has a new, much
bigger companion, Neptune.

But these unlikely partners
are dancing out of sync.

Capture explains
the backwards orbit,

but there's an even
stranger mystery to solve.

On a moon like Triton,

we'd expect to see
heavily cratered terrain,

the hallmark of
geologically dead worlds.

Instead, voyager 2 reveals a
world that's startlingly alive.

I think one of the most
amazing discoveries

of the entire voyager mission is
that when we flew past Triton,

we saw these jets
of liquid nitrogen

coming up out of the surface.

We had no idea that this
tiny, little cold world

out there would still be alive.

Smooth, icy planes
cover the surface.

Geysers of nitrogen
punch up through the crust

and spew black dust
5 miles into the sky.

We thought it was too far from
the Sun, too cold, too dead.

It was just going
to be an ice ball

like all the other moons
that had tended to be, but, no.

It's a fresh, young surface.

Triton's surface is

a frosty 200 degrees
below freezing.

Where's the heat coming from
to drive these surface features?

The answer lies with
Neptune's capture of Triton.

Triton's orbit is circular,
but it was once elliptical.

As Triton moved closer in
and farther away,

it would have been
repeatedly squashed

and stretched
by Neptune's gravity.

That would generate massive
amounts of friction

inside of Triton.

Might well have completely
melted Triton

due to those forces,

and as that happened,
it would have acted as a brake.

All that friction would have
circularized Triton's orbit

and left it in the orbit
that we see today.

This change in orbit
is what gives Triton its heat.

The surface of Triton
froze over,

but the moon still retains
some of this warmth

deep below the icy shell.

Astronomers think there's enough
heat to melt ice into water,

forming an underground
liquid ocean

on a world 3 billion miles
from the Sun.

Liquid water, heat...
There is only one question,

and it's impossible
not to ask it.

Could there be life?

If there's a source
of energy on Triton,

then perhaps there's a form
of life that figured out

how to take advantage
of that energy source.

An incredible thought.

If life has carved out a niche,
this frozen ball

could be the most distant
habitable world from the Sun.

Neptune's moon, Triton,
might be alive,

but Uranus' moons
are even stranger.

They have a neat trick
to cheat death entirely.

Uranus...
An ice giant with beautiful,

shimmering rings and 27 moons...

And their position is a mystery.

Half exist within
a tightly packed orbit.

It shouldn't be possible
for this many moons

to be in such close
proximity to each other.

The environment around Uranus
is very busy,

and the system appears unstable,

and the moons
should be colliding,

but yet, we see these nice,
well-formed moons.

And what's even more
surprising is that in 2003,

the Hubble space
telescope revealed

two new rings and two new moons...
Cupid and Mab.

Question is, where did
these moons come from?

A clue lies in Uranus' rings.

In addition to the very packed
moon system,

you also have rings
around Uranus,

which is also
somewhat unexpected,

but these two
unexpected qualities

might actually
explain one another.

Anytime you see a ring system,
you're seeing part of a process.

There was probably a time
in Earth's history

when it had a ring, you know,
when our moon was being formed.

It seems that the new
moons are made up of material

from a previous ring system.

But when scientists
model Cupid's future,

they discover it's dangerously
close to another moon, Belinda.

In a few thousand years,
two of the moons in particular,

Cupid and Belinda,
are likely to collide together

as their trajectories intersect.

And this collision
will create a domino effect.

When there is a moon collision,

that sets up a very delicate
gravitational balance,

and it also creates
a lot of debris,

so one collision sets off
a string of collisions.

We think Cupid and Belinda

will destroy
not only each other,

but all of Uranus' inner moons.

A runaway cascade of destruction
grinds Uranus' moons to pebbles.

All of this will happen
in only a few thousand years.

The fact that we are predicting
to have a collision

within a few thousand years
feels kind of contrary

because this system has been
here for billions of years,

so it seems a little bit lucky
that we're looking just now,

and we think there's going to be
a collision in the near future.

What if this cycle
of destruction

is a case of
Uranian groundhog day?

When you look at
the Uranian system,

I like to think of it sort of
like a violent hockey game.

Guys are taking big hits.

They can't continue,
so what must you do?

You have to sub them in and out.

When you look at this game
that's that violent,

you know that the guys
you see on the ice

are not the guys
that started the game.

Whoo!

It's a whole new set of players.

Like hockey subs,

Uranus keeps its moons
fresh by recycling them.

Every time these moons collide,

the debris forms
a ring system around Uranus,

and then over time,

that ring system starts
to spawn new moons.

Over time, the rings of debris

that surround Uranus
form into new moons,

which in turn collide
and grind each other to dust.

Uranus, it turns out,
is actually very Eco-conscious.

Its moons shatter.

They hit each other,
form all this debris,

and then the moons reform
from that material,

and then the whole pattern,
the whole cycle starts up again,

and the moons hit, shatter, and
new moons form all over again.

Ultimately, this eternal
cycle of life and death

that we see with these moons
might be a story

that is actually kind of true
of many things in the universe,

when it comes to stars, planets,

and maybe even
the universe itself.

Uranus and Neptune,

no longer forgotten outposts
of the solar system.

Suddenly, these planets
are revealed to you as worlds.

It's breathtaking.
It's... it's awe-inspiring.

It's humbling,
and it makes you proud

that you're part of a species

that could actually do that,

to get out there
and to see these places.

Dynamic worlds with dramatic,

often violent histories,
stolen moons,

giants flung out into the cold,

saving the Earth
from destruction.

Uranus and Neptune are puzzle
pieces in the solar system.

They are giant planets.

They have a lot to tell us,
not just about themselves

but about everything
in our solar system,

including our own planet, Earth.

Somewhere in the story
of the ice giants

is the reason you and I
are actually here

to talk about it at all,

the reason the Earth was
able to form and stabilize

and become an
environment for life.

It would not be
an exaggeration to say

that the ice giants
are the coolest planets

in the solar system.