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.
Captions by vitac... www.Vitac.Com
captions paid for by discovery communications
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.