All language subtitles for NOVA.S51E13.Wandering.Worlds.1080p.WEB.h264-BAE_track3_[eng]

NARRATOR:
Our solar system is filled
with mysterious worlds...

...wandering between
and beyond the planets.

(collision pounds)

MALENA RICE:
The objects that lie
between the planets

are actually the key
to understanding

how our solar system formed.

NARRATOR:
Imposters, and oddballs,

rewriting our understanding
of our place in space.

JESSICA SUNSHINE:
It is two pieces
that are stuck together.

It was really quite remarkable.

(explodes)

QUEENIE HOI SHAN CHAN:
It is possible that after
30 million years,

Mars might have a ring
of its own.

♪ ♪

NARRATOR:
Studying these wandering worlds

allows scientists to explore
regions of the solar system

we have no chance of visiting.

WANDA DÍAZ MERCED:
I cannot go to
the asteroid belt,

so when a meteorite
lands on Earth,

we will have a chunk of history
right in our hands.

ASHLEY KING:
The Winchcombe meteorite

was like a little treasure box
for planetary scientists.

(geyser bursts)

NARRATOR:
And the misfits
of our solar system

are full of surprises.

VERONICA BRAY DURFEY:
There are many, many worlds
out there

that we are yet to discover

and that we haven't
even imagined yet.

SCOTT SHEPPARD:
It's like a box of chocolates.

You never know what you're
gonna get in our images.

This model of the solar system,

it's missing all
of the most interesting bits.

NARRATOR:
What secrets do
these wandering worlds

reveal about our solar system?

And what else
is lurking out there

in the dark?

(bursting)

"Solar System:
Wandering Worlds,"

right now on "NOVA."

♪ ♪

♪ ♪

NARRATOR:
There's something out there
in the darkness.

We don't know for sure
where it came from

or how long it's been there.

But we know it's not alone.

It was discovered in 2018.

A world with no official name.

So distant,
it has been called simply

FarFarOut.

SHEPPARD:
FarFarOut,

as its name implies, is very
far away.

So, it's just a, a very faint
point of light

that, uh, we discovered

with one of the largest
telescopes in the world.

JANE LUU:
Its notoriety
comes from the fact

that it's
the most distant object

that we have found
in the solar system.

SHEPPARD:
And the big question is,
what do we call the next one?

Do we just add another "far"
or not?

LUU:
"ExtremelyFarOut,"
and then "StupendouslyFarOut,"

and it just keeps going.
(laughs)

♪ ♪

NARRATOR:
12 billion miles from the sun,

FarFarOut is not alone.

Out here, there could be
countless other worlds

yet to be discovered,

wandering in the dark.

Even closer to home,
we are only just beginning

to explore the vast spaces
between the planets.

Home to a myriad of worlds,

many too small or too dark
to see.

NANCY CHABOT:
When we think about
our solar system,

we think about the sun,
it's in the center,

everything else is
kind of going around it,

and we've got the big planets,
Jupiter and Saturn,

and the most important planet,
Earth.

But there are so many more
secrets and mysteries

than just these planets
that are shown in the model.

So, to me,
the most exciting thing

about studying the solar system
is not the planets themselves,

but it's all the bits
in between the planets.

NARRATOR:
These worlds could provide clues
to our own planet's story.

RICE:
In a lot of ways,
studying the solar system

is a way of trying
to understand ourselves.

How did we come to be
in the first place,

and what does it mean
that we're on this rock

that is sailing through space?

NARRATOR:
With distances so vast,
there's still much to discover.

KING:
There's so much stuff

that we just don't know
about our solar system,

and what we do know is,
it is constantly surprising us.

So we need to go out there,
look at these wandering worlds.

NARRATOR:
And many questions
remain unanswered.

LYNNAE QUICK:
Are these lost
and wandering worlds

worthy of exploration
in their own right?

CHABOT:
How far do these
dark regions extend

beyond, to the edge
of our solar system?

Are there more planets
in the dark region

waiting to be discovered?

♪ ♪

(dog barking in distance)

NARRATOR: It was the sound
that most people noticed.

(explosion echoing in distance)

A sonic boom in the night.

But this was no fighter jet.

Traveling at around
30,000 miles per hour,

it tore through the atmosphere.

♪ ♪

Broke up.

And rained down
across the fields.

A visitor from a distant realm.

One of the biggest chunks

landed on a driveway
in front of a house.

KING:
When I first saw it,
it was kind of a splat.

I mean, it's so soft, it kind of
just made a powder

SARA RUSSELL:
The Winchcombe meteorite fall

was the first U.K. meteorite
fall recovered for 30 years,

so we've been waiting
such a long time.

KING:
I couldn't believe that we had
a new meteorite in the U.K.

Yeah, it was incredibly
exciting.

And all meteorites are
scientifically priceless.

RUSSELL:
I feel amazed and privileged

to be able to hold something

that may tell us about the
secrets

of the origins of our solar
system,

and how we got to be here.

NARRATOR:
It's estimated as many as 50
meteorites hit Earth every day.

Many burn up in our atmosphere,

creating shooting stars
and meteor showers.

But some of the largest ones
do make it to Earth.

In 2018,
the Hamburg meteor fireball

streaked across
the American Midwest sky.

WOMAN:
What was that?

Did you see a light flash
out there?

It's particularly pristine,
because it landed

on a frozen lake, so that
keeps it in cold storage.

It was like the meteor selected
where to land,

because it wanted to be studied.

NARRATOR:
A few years later,

a meteorite the weight
of a grand piano

exploded in the skies
near McAllen, Texas.

(explosion pounds in distance)

MERCED:
Ah!

It's like a,
like an explosion of dynamite.

(explosion echoes)

That big explosion,
that was a sonic boom.

♪ ♪

NARRATOR:
The cows weren't
the only witnesses

that night in Winchcombe.

Doorbell and CCTV cameras
never sleep.

And networks of dedicated
meteor cameras

captured it
from different angles.

That meant it was possible
to calculate its trajectory.

(cows mooing)

Back over the skies of England,

out of Earth's atmosphere,

past the orbit of Mars,

into the dark.

This is where
the meteorite's journey began,

a mysterious realm
of countless rocky worlds,

rubble left over from the
formation of the solar system:

asteroids.

There could be at least
a million out here.

But they're so dark,
reflecting little light,

they're incredibly difficult
to detect.

But asteroids don't always
stay in the asteroid belt.

(collision pounds)

When two collide,

they blast fragments
in all directions,

sending some out of
the asteroid belt forever.

Sometimes wreaking havoc
on planets they encounter.

♪ ♪

Including our own.

And asteroids
that leave the belt

can transform planets nearby.

♪ ♪

A planet covered in scars
from the asteroid belt is Mars.

Around 80 fresh impact sites
are found on Mars every year.

♪ ♪

And some amazing meteorites

have even been snapped
by NASA's rovers.

But there's
another dark rock here,

imaged by
the Perseverance rover,

not on Mars's surface,
but orbiting overhead...

♪ ♪

...captured during an eclipse,

as it passed
in front of the sun.

This is Mars's moon Phobos.

Today, the orbiting probe
Mars Express

regularly flies
between Mars and Phobos.

♪ ♪

Its high-resolution camera

captured incredibly detailed
images of Phobos,

showing a surface covered
in strange grooves.

Phobos looks like someone has
ridden a giant bike all over it.

Astrophysicist Sean Raymond
is investigating

how objects like Phobos
could have formed.

Phobos is a strange-looking
moon.

Like this beach, it's covered in
grooves.

You might say it's

the grooviest moon
in the solar system.

NARRATOR:
The magnificent grooves
here in Spain

are formed
by geological processes

and erosion
from relentless, crashing waves.

RAYMOND:
It's so cool--
the grooves are amazing here.

NARRATOR:
But Phobos isn't anything
like Earth,

so what's going on?

RAYMOND:
Phobos certainly looks
like an asteroid.

It's covered in craters,
and it's dark in color.

So you might think
it's just an asteroid that got

too close to Mars
and then was captured in orbit.

NARRATOR:
It turns out
it's not that simple.

Phobos orbits Mars
in an almost perfect circle,

right along Mars's equator,

and this makes us question
whether Phobos

is really the asteroid
it appears to be,

because captured asteroids
usually orbit planets

on very elliptical orbits

that sometimes take them
very far from their planet

and sometimes being much closer.

NARRATOR:
So, if it's not an asteroid,

where did this funny
little moon come from?

CHABOT:
So, in planetary science,

the joke is that you just add
an impact event,

and an impact event can explain
everything.

That might actually be true in
this case, though.

that an object hit Mars,

and Phobos is the result
of that impact collision

between those objects,
and that's what we're seeing.

♪ ♪

NARRATOR:
Phobos may not be
a captured asteroid at all,

but formed from debris
thrown into orbit

after a massive asteroid impact.

However,
this still doesn't explain

why it's covered in grooves.

Phobos is about 3,700 miles
from Mars's surface,

and every hundred years,
moves closer by about six feet.

And as it does, the tidal forces
caused by Mars's gravity

become stronger.

RAYMOND:
So, just like the moon
pulls on the Earth,

dragging the oceans
and causing the tide,

Mars pulls on Phobos,
causing tides, as well.

So, as you can see
behind me right now,

the tide is coming in
as the moon is pulling on

the water on the Earth.

The same process
happens on Phobos, due to Mars,

except on Phobos, it's sand
and rock that's moving,

instead of water.

NARRATOR:
Those tidal forces
are pulling Phobos apart.

And with every orbit,
the grooves widen and deepen.

Eventually,
Phobos will drift so close,

Mars's gravity will destroy it.

As Phobos breaks apart...

...most of the debris will fall
to the surface of Mars.

♪ ♪

But the rest will remain
in close orbit,

spreading out to encircle
the entire planet,

giving Mars a wispy ring.

CHAN:
It would be quite impressive.

I love ring planets,
I love Saturn,

and it's not bad to have another
ring planet in our solar system.

NARRATOR:
It seems Mars will one day
be transformed

by the asteroid belt.

But the asteroid belt itself
is still an enigma.

We've flown several spacecraft

through this
mysterious region,

but only one
has orbited the rocks

in the asteroid belt itself:

NASA's Dawn probe.

Most of these ancient remnants
are misshapen boulders.

But one stands out.

Ceres is much bigger
than the others

and almost perfectly spherical.

QUICK:
I joined the Dawn mission

right after it reached Ceres,

and it was so exciting.

Dawn collected thousands
of images of Ceres.

They showed us areas
of the surface

that we'd never seen before.

We thought that it's kind of

a dead planetary body.

Looking at those images,

we could not, basically,
believe our eyes,

and it was, like, "Uh,
what's going on over there?"

♪ ♪

NARRATOR:
At first, it appears dark
and heavily cratered,

like its fellow asteroids.

But Ceres is different.

Its surface is peppered
with white crystals.

But what are they?

Clues come from another planet
in our solar system,

where white crystals
are also found on the surface.

Earth.

HAKEEM OLUSEYI:
This mountain is made up
almost entirely of sea salt,

the exact same stuff
that you put on your food

at the dinner table.

NARRATOR:
40 million years ago,

this whole area
was under an ancient sea.

Over time, it dried out,

leaving behind a layer of salt
a mile thick.

Holy moly!

Whoa!

♪ ♪

It's definitely salty.

And the thing about
salt deposits like this

is that they're only formed
in the presence of water.

So, that raises
an intriguing possibility.

Could the white spots on Ceres
also be salts

that were deposited by water?

NARRATOR:
Finding water on Ceres today

would be
an astonishing discovery.

♪ ♪

Dawn made tight orbits
of Ceres.

And by bouncing light
off the crystal deposits,

it determined
what they were made of:

sodium carbonate,
a common type of salt.

A tantalizing sign that Ceres,

which is 13 times smaller
than Earth,

had an ocean in the past.

Flying just over 20 miles
from the surface,

Dawn finds something else
in the white spots:

hydrohalite crystals,

another salt found on Earth
in the presence of water.

Could Ceres still be
a water world today?

So, "hydro" is water
and "halite" is salt--

table salt.

So, if you imagine a table salt

that's got water molecules
in the structure,

that's what hydrohalite is.

It was very surprising
that there were hydrohalites

on the surface of Ceres.

CHAN:
Hydrohalite would be
very unstable

at the surface of Ceres.

At that pressure,

the water molecule
would have been vaporized.

That implies that water
was recently emplaced on Ceres,

bound to salt crystals within
the past few hundred years.

This replenishment
of hydrohalite

at Ceres' surface
leads us to wonder

if Ceres might be an ocean world

that's masquerading
as an asteroid.

♪ ♪

NARRATOR:
Scientists suspect
that pools of salty water exist

about 25 miles underground,

raising another question:

how did these salts
end up on the surface?

A clue lies in Ceres' location,

right in the heart
of the asteroid belt,

where collisions are common...

(collision pounds)

...and incoming asteroids
can form cracks in the surface

reaching the pools below.

Exposed to the vacuum of space,

the water vaporizes,

leaving its cargo of salt behind

and peppering Ceres
with white spots.

QUICK:
There's still one big twist

to the story of Ceres' past.

The Dawn spacecraft found
ammonia salts on the surface.

NARRATOR:
Ammonia salts could be traces
of ammonia ices

that once covered
Ceres' surface.

Frozen ammonia is common
in colder parts

of the solar system,
but not here.

CHAN:
Ammonia doesn't really exist
as ice at where Ceres is now.

It has to be formed
at a distance

further away from the sun,

where the distance
is cold enough

for ammonia to exist as ice.

This suggests
that Ceres didn't form

where it stands currently
in our solar system.

NARRATOR:
Instead, scientists think
it formed much farther out,

and as it wandered
towards the sun,

the ammonia ices melted,

leaving behind the ammonia salts
we see today.

An imposter
lurking in the asteroid belt,

exposed by its salty secrets.

Ceres has
a journey of relocation

just written
all across the surface.

NARRATOR:
But just how did Ceres end up
where it is today?

OLUSEYI:
The best explanation
is that it wandered.

Well, actually, it was pulled.

So let's say this is Ceres.

Okay?

We think that Ceres
formed beyond

what is known
as the ice line

for ammonium ices.

NARRATOR:
Beyond this ice line,

ammonia freezes,

and this is where Ceres
likely started forming,

alongside Neptune
and Uranus.

OLUSEYI: And here we have
Saturn and Jupiter.

Now, normally, these planets

aren't lined up
like this.

They're moving
around the solar system.

And what happens is,
as Ceres

orbited the solar system,

Jupiter tugged on it
with its gravity,

and Ceres ended up
right there,

in the asteroid belt,
where we find it today.

NARRATOR:
In the heart
of the asteroid belt,

Ceres, once a much icier world,

has migrated
far from where it formed,

evidence that our solar system
is ever changing.

♪ ♪

Ceres isn't
the only displaced world.

Farther from the sun,
there is another icy world

that doesn't seem to belong
where it's found today.

Beyond Jupiter,

the space between the planets
gets wider

and wider.

And temperatures plummet.

♪ ♪

And a billion miles past Uranus,

we finally reach the farthest
planet from the sun.

Neptune.

♪ ♪

Wrapped in a dense blue blanket,

Neptune has
no detectable surface,

with clouds
of methane and ammonia.

But there are rocky worlds
nearby.

Neptune has at least 16 moons.

And one is very unusual.

Triton is the largest
of Neptune's moons.

Its surface is coated with ice.

And, unlike the other moons,

Triton is an active world.

(geyser bursts)

Geyser-like plumes
of gas and dust

stretch five miles high
into Triton's atmosphere...

...which flattens them abruptly

by 90 degrees,

creating a vista so strange,

it's hard to believe it's real.

How did a moon
2.8 billion miles from the sun

become so active?

A clue lies
with how the planets and moons

move around each other
in the solar system.

CARLY HOWETT:
Every day, the sun rises
in the east

and sets in the west.

And the moon follows
the same course.

And there's a reason for that.

NARRATOR:
To understand why,

we need to go all the way back.

To the birth
of the solar system.

DURFEY:
In the beginning of our
solar system,

the sun was surrounded

by a disc of dust and gas.

And it was within
this spinning disc

that the planets formed.

PAREKH:
So that's the reason

the planets and the moon
continued

orbiting also
in the same direction

around the sun.

NARRATOR:
Moons that form
around their planets

tend to follow this pattern,

orbiting and spinning
in the direction

of the planet's rotation.

But while the inner moons orbit
Neptune in the same direction,

Triton goes the other way,

suggesting it didn't form
alongside Neptune,

but came from elsewhere.

HOWETT:
What a planet's made from

can tell you where it formed
in our solar system.

And that's because,
in our early solar system,

the ingredients that
a planet could be built from

varied as the distance
from the sun.

So if we take Earth,
for example,

it's got a lot of rocks and
metals, too:

aluminium and iron.

And Mars is pretty
similar.

Iron, metals, and other rocks.

So these can be paired together.

If we do the same thing

for the ice giants,
Neptune and Uranus,

with big atmospheres
made of hydrogen,

helium, and a bit of methane,

they're huge, too.

So we can pair those together.

So how does Triton fit in?

Well, its surface
is mainly nitrogen ice,

and it's much smaller.

It doesn't fit with either
of these two groupings.

To understand
where it could fit,

we have to look at Pluto.

Pluto has a, a nitrogen
ice surface with methane,

carbon monoxide, and water ice.

And it's about the same size
as Triton, too.

These are a good pairing.

NARRATOR:
With such similar ingredients,

Triton and Pluto could've
formed in the same place,

but they aren't
anywhere near each other today.

HOWETT:
Triton's located
one billion miles from Pluto.

So how did that happen?

NARRATOR:
Neptune might be the farthest
planet from the sun,

but it's not the edge
of our solar system.

Not even close.

Almost a billion miles
farther out

lies Pluto.

And it's not alone.

There are hundreds of thousands
of other worlds out here.

This is the Kuiper Belt,

a vast, doughnut-shaped ring
of icy bodies

billions of miles wide.

So dark and distant,

it remained undiscovered
until 1992.

LUU: We had been searching for,
uh, the Kuiper Belt

for, uh, for five years
before we finally found it.

So when we spotted
the first Kuiper Belt object,

1992 QB1,

there was jumping up
and down, and there was...

I think we gave each other
a high five.
(laughs)

The discovery of the Kuiper Belt

helped us to better understand
our solar system

as it is now,
and also its history.

LUU:
The Kuiper Belt is
really the frontier

if you want to understand
the solar system.

But it is very difficult
to study it,

because it is so far away.

NARRATOR:
Despite the challenges,

more than 4,000
Kuiper Belt objects

have been discovered to date.

And scientists estimate

there may be 200 dwarf planets.

Some have rings and moons.

Some are bizarre and misshapen.

But they
all share one thing in common.

They're made of icy materials,
similar to Triton.

This is where Triton belongs.

So how did it end up
around a billion miles away,

in orbit around Neptune?

♪ ♪

HOWETT:
So, to understand Triton,

you have to understand
the Kuiper Belt.

If this is our sun,

the one population
of Kuiper Belt objects

orbit it in a nice circle.

Another population
of Kuiper Belt objects

have a highly elliptical orbit.

So the question is,
why are these so different?

What caused them to be
in this weird orbit?

Well, the answer is,
some of these objects

are in resonance with
another planet, Neptune.

Resonance is when two objects
have paths

that meet up occasionally.

And we see this
throughout the solar system.

If you look, for example,
at Pluto,

it'll go around

on this elliptical orbit
twice

in the same time Neptune has
gone around three times.

And this resonance is an
important clue

in understanding
how disruptive

Neptune is to Kuiper
Belt objects.

♪ ♪

NARRATOR:
Scientists think Neptune formed

much closer to the sun,

then slowly drifted out.

Its huge gravity
disrupted the orbits

of the Kuiper Belt worlds
it encountered,

kicking them into
the elliptical orbits

we see today.

DURFEY:
The early solar system
was complete chaos,

filled with small bodies
growing larger

and smashing into each other,

sometimes destroying.

Complete chaos.

NARRATOR:
During all the commotion,

Triton became trapped
by Neptune's gravity,

slipping into its
backward orbit.

And being this close
to a giant has consequences.

Just as our moon raises tides
on Earth,

Neptune raises tides on Triton,

stretching and squashing it
like a stress ball,

heating it up.

HOWETT:
Triton being captured
by Neptune

fundamentally changed
how it works.

On Earth, we experience energy
every day.

You might be able to hear it
in the roar

that comes from the tide
coming in underneath us.

(waves pounding)

Tidal energy can force water
up through cracks

in the Earth, like the one
in front of us,

creating plumes
erupting up to the sky.

NARRATOR:
On Triton, the plumes are
even more spectacular.

HOWETT:
The plumes on Triton
would be magnificent to behold.

Erupting from the surface,
cracks like this,

but going five miles
into the sky.

I mean, it'd just be
absolutely phenomenal.

(geyser bursts)

NARRATOR:
What creates Triton's plumes
is a mystery.

But one theory lies
in its unusual orbit.

HOWETT:
It's highly tilted,
and Triton orbits backwards.

Meaning as it goes
around Neptune,

its pull and push
that it receives

from Neptune and its moons
changes.

This creates a kind of friction,

similar to the one
that you get

when you rub your hands together
on a cold day.

Your hands warm up,
and so might Triton.

We call that kind of energy
tidal heating.

NARRATOR:
As Neptune's gravity
stretches and squashes

its giant moon...

(plume roaring)

...the tidal heating produced

melts Triton's frozen
interior...

♪ ♪

...powering its spectacular
plumes.

DURFEY:
Triton is a great example

of how interconnected
our solar system is.

And it also serves as a good
example

of how a large, giant planet

straying into a belt of objects

can really mess up your system.

NARRATOR:
Triton was plucked
from the Kuiper Belt,

a distant realm
filled with mysterious worlds

so far away

we can't make them out
in much detail.

But we have sent one spacecraft.

It took over nine years
for New Horizons to get here

and home in
on its primary target.

♪ ♪

The tiny spacecraft captured
the first close-up images

of this Kuiper Belt world,

revealing unexpectedly complex

and dynamic surface features:

mountains as high as the Alps,
made from water,

frozen as hard as granite.

But there's something else odd
out here.

Another world close by.

How did Charon and Pluto
end up almost touching?

Charon orbits about 12,000 miles

from the surface of Pluto,

which sounds like a really large
number,

but is actually really close

for the scale
of the Kuiper Belt.

It's very common
in our solar system

for moons that are close enough
to their parent body

to become tidally locked.

And that is where one orbit

will also be one spin,

so that the same face
of that moon

is presented to the planet
at all times.

NARRATOR:
All large moons
in the solar system,

including our own,
are tidally locked,

only showing one face
to their parent planet.

But in the case of Pluto
and Charon,

it isn't just Charon that is
tidally locked to Pluto.

Pluto is also tidally locked
to Charon.

Both worlds constantly
face each other at all times.

RICE:
And what that means is,
if you're on the side of Pluto

where you're able to see Charon,

then it'll look like it's just
hanging there all the time.

It's not going to rise,
it's not going to set.

It's just going to
constantly be in your sky.

♪ ♪

NARRATOR:
This isn't just a dwarf planet
and its moon,

but a binary pair.

♪ ♪

New Horizons is still studying
Kuiper Belt worlds today.

During the most distant
fly-by in history,

it encountered Arrokoth,

a bizarre snowman-shaped
object.

SUNSHINE:
It is two pieces
that are stuck together,

and those two pieces must have
come together very gently.

To actually see it
was really quite remarkable.

Any time you see a new world,
it's remarkable.

NARRATOR:
Why do the worlds out here
in the Kuiper Belt

form these partnerships?

LUU:
Things become slower and slower

as you go further away
from the sun.

In the Kuiper Belt,
things might collide

at the speed of a few
hundred feet per second.

They occur at such
low-impact velocity

that a lot of the collisions
are constructive

rather than destructive.

NARRATOR:
At some point in their history,
Pluto and Charon collided.

But their slow movements

meant this was less of an impact

and more of an embrace.

The Kuiper Belt is so vast
and far from the sun

that many mysteries
still remain.

I am often pretty amazed
that we're actually able

to study things
like the Big Bang

and the early universe
and distant galaxies,

and yet we still actually
don't know everything

that there is to know
about our own solar system

and our own backyard.

I'm very confident that
there are many, many worlds

out there that we are yet
to discover,

and that we haven't even
imagined yet.

♪ ♪

NARRATOR:
We can see distant stars
in the night sky

because they burn so bright.

Telescopes can detect planets

as they pass in front
of their parent stars.

Seeing worlds
in our own solar system

is much harder,

but not impossible.

♪ ♪

In 2018,

a faint point of light
was detected

about 12 billion miles
from the sun.

It's thought to be
a dwarf planet

nicknamed FarFarOut.

This is the most distant object
yet seen in our solar system

by some of our most
powerful telescopes.

But it's not the limit
of what could be out there.

♪ ♪

OLUSEYI:
How far do you expect
the solar system to extend?

You may imagine that it ends

at the last major planet,
Neptune.

However, that's not
exactly the case,

and let me show you why.

Here I'm gonna make a model
of the solar system.

This rock is my sun,

and I'm gonna place it
right there,

and an inch away,
I'm gonna place the Earth.

And so this will be my scale,
one inch equals

the average distance
between the Earth and the sun.

So now, if I go a second inch,

I arrive at the asteroid belt.

And to get to the most distant
major planet, Neptune,

that's gonna be about 30 inches.

Now, we have to keep
going and going,

because out here is

the most distantly
observed object ever

in the history
of our solar system,

11 feet away from the sun,

132 inches,

12 billion miles,

is FarFarOut.

NARRATOR:
But the solar system
doesn't end here.

OLUSEYI:
I have to walk
another 50 paces...

...another 186 billion miles,

and now we've reached
our destination,

a vast region known
as the Oort Cloud.

♪ ♪

NARRATOR:
Clinging on at the very edge

of the sun's
gravitational influence,

the Oort Cloud is
our solar system's largest

and most mysterious realm.

It's so deep into the darkness,

it's almost impossible
to imagine,

let alone see,

filled with billions
upon billions

of strange worlds.

Most are thought to be
icy objects

the size of mountains.

But it's likely
some are made of rock.

And if we were able to go there,
we'd discover they are pristine.

♪ ♪

Barely changed since the dawn
of the solar system.

It's thought some could be older
than the sun.

The Oort Cloud's existence
is hypothetical,

but science doesn't deal
in fairy tales,

so how do we know it's actually
there if we've never seen it?

♪ ♪

NARRATOR:
For as long as we've been
looking into the night sky,

we've seen signs
that the Oort Cloud is real.

And this is one of them.

For hundreds of years,

it's been locked in a deep,
frozen slumber.

♪ ♪

But now it stirs.

♪ ♪

As it nears the sun,

warm rays bathe its surface...

...and it begins to thaw.

(hissing)

♪ ♪

So much debris is torn
from the surface,

it stretches out,
forming a tail...

...around 14 million miles long.

This is the comet Nishimura.

It's visible from Earth
for just a few weeks,

before eventually heading back
into the darkness,

just the latest in a long line
of icy visitors.

Hale-Bopp.

Neowise.

They lit up our skies for weeks,
or even months, on end.

Humans have been
captivated by comets

because, frankly,
they're spectacular.

CHABOT:
And the fact that they do wander

around the solar system
from time to time

really is a unique scientific
opportunity.

NARRATOR:
When scientists followed
the trajectories

of these comets back,

they discovered they came
from the same region,

more than 200 billion miles
from the sun.

SUNSHINE:
If you calculate

where the orbit
took you back to,

it was way out,

unbelievably far out,
what we now call the Oort Cloud.

NARRATOR:
It's thought the gravity
of other objects in the galaxy

can occasionally knock
these icy objects inwards.

SUNSHINE:
But the really interesting thing

was that they were coming
from all directions in space,

and there had to be a cloud.

♪ ♪

NARRATOR:
Although we can't see
this far out,

comets with orbits
starting in the Oort Cloud

streak across our skies.

RICE:
The Oort Cloud is
kind of incredible.

No one's actually been there,

no one's actually observed
anything within the Oort Cloud.

They've only seen the wanderers
that have escaped

from the Oort Cloud
for a brief moment,

which I think is what makes it

so spectacular
and so exciting to me.

CHABOT:
If I could visit
one of those dark regions,

I would have to choose
the Oort Cloud.

We don't know that region
at all,

we haven't ever explored it,
so for me,

that would be
the most exciting place to go.

♪ ♪

NARRATOR:
We think of the solar system

as the sun and all the planets.

But that's just
what's close to Earth.

As wandering worlds give us
rare glimpses

into what is beyond

and technology improves,

we're discovering
more and more.

RUSSELL:
We're really only
scratching the surface,

so there are millions
of these tiny bodies out there,

and we still have so many
secrets to unlock from them.

MERCED:
There is so much information
in darkness.

If we pay more attention

and we trust what we perceive

with all our senses,

we will gain
much more information

from those dark regions
of not only our solar system,

but of the universe.

This model of the solar system,

it's missing all of the most
interesting bits.

♪ ♪

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