All language subtitles for S05E02 - Mystery of Planet 9.en

We thought we knew
our solar system.

Turns out we were wrong.

Groundbreaking
observations suggest

an unseen ninth planet

may be out there on the
fringes of our solar system.

And it could be huge,

5,000 times
more massive than Pluto

and 10 times
the mass of the Earth.

We don't get a lot
of revolutions in astronomy.

And here we are on the cusp
of a discovery like this.

It's crazy to think that,

as much as we've looked
into the universe,

that there's this ninth planet
out there that we've never seen.

If planet 9 really is out there,

what will it be like?

Is it a rocky super-Earth,

an icy mega-Pluto,

or a gassy mini-Neptune?

Or is planet 9 an alien world

stolen from another star?

And could it provide
an unlikely home for life

100 billion miles from the Sun?

...Captions by vitac...
www.Vitac.Com

Captions paid for by
Discovery communications

Take a look at the night sky.

The pattern of stars

that drifts overhead
appears fixed.

But look for longer,
weeks or months,

and you'll see a handful
of the points move.

These slow-moving points
of light are the planets,

the giant chunks of rock or gas

that orbit our home star,
the Sun.

We thought there were eight.

We were wrong.

You know, we think
we understand something

as simple as our solar system.

We've found all the planets.

And, right in front of us,
we missed something big.

A group of astronomers are
studying the Kuiper belt,

a vast band of icy asteroids

that sits way, way outside
the orbit of Neptune.

Most of these objects move
in a neat, circular formation

around the Sun.

But the astronomers
are puzzled by a small group

that appear to break the rules,

swinging far outside
the main belt

on wild, extended orbits.

Something sitting far outside
the Kuiper belt

seems to be pulling
these asteroids out of line,

something the size
of a giant planet.

Caltech astronomer
Mike Brown hears

about the wild observations

and is determined to prove
the planet theory wrong.

When we saw
these alignments of all

these objects out there,
we thought,

"ugh, everybody's gonna say
there's a planet.

We have to very strongly prove
there's not a planet."

Because, of course, we all know

there's not another planet
out there. That's ridiculous.

Mike asked his
colleague, Konstantin Batygin,

to run a computer simulation

to see what effect
a ninth planet

should have on the Kuiper belt.

Stunningly,
the simulation predicts

elongated orbits identical

to ones already observed.

But the simulation also
spits out a surprise.

There should be
a second set of rogue orbits

that are perpendicular
to the first set.

If Mike can locate these weird

predicted objects
inside the Kuiper belt,

planet 9 is almost
certainly real.

I took these simulation
results to Mike's office

just a couple doors
down from my office.

And I said, "look!" You know,
"we've got a huge problem!"

He said, "no!"

There's an object
called 2012 dr30

"which has an orbit just like
the one you're predicting."

Mike's asteroid fits
the prediction perfectly.

He searches the records for
more and finds another four

that seem to be
in the right area.

But just how closely
will they fit the prediction?

I remember sitting back
and thinking,

"okay, we're going to,
right now, plot the data,

the real observational data
on top of the model."

And Mike said,
"if these two match up,

my jaw is just gonna
drop to the floor."

The theory says they should be
right here and right here.

And I did the
calculations very quickly

to see where they were
and brought them up.

And there they are.
One, two, three, four, five,

right on these lines

exactly where we predicted
they should be.

The moment we saw this,

we went from cautious

to "holy cow!
This really is there!"

We have to make sure
to tell everybody right away

"because it's actually real!"

Mike and Konstantin had unlocked

the solar system's
greatest secret.

Planet 9 was almost
certainly real.

And it had to be huge,

perhaps 10 times
the mass of Earth.

We're not talking about
something like our moon

or Pluto.
We're talking about something

that is literally
planet-sized.

And we're seeing
its gravitational wake

affecting these other objects.

The idea that there
could be a giant planet

that we've never seen
is something I think

most of people
wouldn't have bet on.

But the evidence is remarkable!

To prove planet 9 exists,

astronomers need to see it
with their telescopes.

But there's a problem.

Computer simulations
only give a broad idea

of where to find it.

And planet 9 is incredibly faint

and almost
inconceivably far away.

It's much, much farther out

than we ever expected
to find planets.

It probably spends
most of its life,

if it's on an elliptical orbit,

so far away from the Sun
that we just missed it.

So just how far away
is planet 9?

The only way to truly
appreciate its vast orbit

is to build a scale model,

perhaps the biggest working
model of the solar system

ever attempted.

Planetary scientist Kevin Walsh
is here to call the shots.

And he starts
with the size of the Sun.

So what we've got here,
our kickball,

is going to set the scale of
our mini-solar system today.

So everything is scaled off
of its relative size

compared to the size of the Sun.

Kevin quickly
paces out the position

of the inner rocky planets.

All four sit within 60 yards
of the Sun on this scale.

And each planet would appear
no bigger than a peppercorn.

To make this
a working solar system,

we need to bring on the drones.

Each drone represents
a different planet.

And the orbital speeds

have been scaled
so one Earth year

takes just 30 seconds.

Already, it's clear to see

how tightly bunched
these inner planets are,

and how the closest planets

orbit faster
than those farther out.

Far beyond the tightly
packed rocky planets

lies the first
of the gas giant planets,

on this scale, just over
a football field from the Sun.

So, after this 400-foot walk,
we made to to Jupiter,

the largest planet
in the solar system.

But, even by this size scale,

Jupiter is only about
the size of a lollipop.

Another football-field
length lies ahead

on the walk to Saturn.

As we look back
across the lake bed,

I can barely see the drones.

We covered a huge distance.

The trek out to Uranus
is bigger still,

three football fields

or the length
of an aircraft carrier.

Turns out there's a lot of wind
in the outer solar system!

So I have to yell.

Surprising amount of wind
in the outer solar system.

Tumbleweed, rattlesnakes.

After Uranus, it's around
200 yards out to Neptune.

Before the discovery
of planet 9,

we thought Neptune was the
farthest planet from the Sun,

around half a mile
on the scale of our model.

But Neptune's distant orbit
is nothing

compared to the orbit
of planet 9.

So here we are.

We made it to
the orbit of Neptune.

We're only at the tip
of the iceberg.

We need to stop
measuring in feet.

And we need to start
thinking in miles.

We need a car
to get out to planet 9.

Planet 9 swings out
on a highly elliptical orbit.

Its closest pass to the Sun

is a whopping 19 billion miles.

That's six times wider
than the orbit of Neptune.

But, at its farthest point,

planet 9
is 112 billion miles away.

And, on this scale,
that's an incredible 18 miles

from our kickball-sized Sun.

So we're here, end of the road.

We've driven about 18 miles

from where we first started
setting up the solar system.

But, in the scale
of the solar system,

it's over 100 billion miles.

100 billion miles

to get out to the furthest
part of planet 9's orbit.

So, to scale,

and we don't know
what planet 9 would look like,

but it's probably about
the size of a B.B.

So this is the challenge
for our astronomers.

How do you see a b.B.
From 18 miles away?

This is what we have to do.

It could take years
for our telescopes

to pick out an object
so impossibly faint,

far away as planet 9.

Until then, scientists
can only speculate

on what this mysterious world
might be like.

We're in this wonderful moment
right now

where we suspect
that planet 9 exists.

But we really have
no idea what it's like.

And that means
our imaginations can run wild.

They're informed by science.

But I love it
when creativity takes hold,

and you just run with it.

So what are the options?

Science suggests
three possibilities.

And the first is astonishing.

Planet 9 could be made

from the same materials
as the Earth,

but 10 times more massive,

a rocky super-Earth.

But what would
this giant, rocky planet

look like so far from the Sun?

A bizarre volcanic world
scarred with fire

somehow emerges from the
cold darkness of deep space.

In 2016, astronomers
release astonishing evidence

of a missing ninth planet

on the frozen edges
of our solar system,

100 billion miles from the Sun.

Until our telescopes find it,

we can only guess what this
mysterious planet 9 is like.

But the first option is
perhaps the most surprising.

Planet 9 could be
made from rock,

just like the Earth,

but 10 times more massive,

a so-called rocky super-Earth.

When we looked out
into the universe, we realized

that the most common
type of planet

in the entire galaxy

is something we don't have,

something called a
super-Earth.

The Kepler space
telescope finds alien worlds

by measuring
the tiny dip in light

as a planet passes
in front of its host star.

Most of the alien solar systems
Kepler finds have super-Earths.

So how come our star
doesn't have one?

Could it be possible that planet
9 is our missing super-Earth?

If planet 9 is
a rocky super-Earth,

what will it look like up close?

Planetary geologist Jani
Radebaugh imagines planet 9

as a dramatic world
of fire and ice.

Right now, we're in Iceland.

We're flying over amazing,

beautiful volcanic landscapes
of Iceland.

We think this might be
the perfect landscape

for thinking about what might
be happening on planet 9

if it's a rocky super-Earth.

These black mountains
and lava flows

were created by leftover heat

from the Earth's formation
spilling out onto the surface.

Planet 9, born with so much
more insulating rock,

should have even more of this
leftover heat trapped inside it.

What we're talking
about is a body

that's maybe 10 times
the mass of the Earth.

I'd expect,
because it's so large,

that we should have lots
more internal heat.

And so, even though it's
far away in the solar system,

it's far away from the Sun,

it's still got lots
of its own energy.

Touching down on
the surface of planet 9,

you'd find a world
as inhospitable

as you could imagine.

Billions of miles from the Sun,

the surface is lit
by little more

than the twinkle
of distant stars

and the red glow of intense
geological activity

on the surface.

We can imagine, if we were on

a super rocky Earth planet 9,

we could have a landscape
just like this one.

There should be volcanoes
erupting all the time.

And the other thing
we should see

is lots and lots of ice and
snow blanketing the landscape.

This is because the atmosphere
is so cold

that parts of it have condensed

and settled back down
onto the surface.

You're gonna have volcanoes.
You're gonna have canyons.

You're gonna have plate
tectonics, mountain-building.

All of these processes are still
gonna be going on out there

in what we normally would
think of as the frozen, cold,

and dead world
of the outer solar system.

As hot lava reaches the surface,

it freezes suddenly
in the cold of space,

perhaps forming a weird,

volcanic glass called obsidian,

another feature shared

with the sub-zero
volcanoes of Iceland.

Okay, let's put
this whole thing together.

We have a landscape

that's kind of dimly lit
by starlight,

but maybe also
by the reddish glow

from erupting lavas spreading
across the landscape.

And then, behind you,
you have gases

that are changing
immediately to snow

and falling as snow
down to the surface.

And it would just be a
beautiful, magical landscape.

The case for a giant, rocky
planet 9 is compelling

because it paints
such a vivid picture

of a living volcanic world.

But there's a problem.

If planet 9
is, in fact, a super-Earth,

how did it form?
Where did it form?

We don't have
any other super-Earths

in our solar system.

And the ones we see
around other stars

are typically really
close to their star.

So how did our super-Earth
end up way out there

at the edges
of our solar system?

For planet 9 to be
our rocky super-Earth,

it would've had to have formed
in the inner solar system

and then migrated out
to its current position.

And that's a problem,

because there probably wasn't
enough rocky material left over

in the early solar system

to create both
the massive planet 9

as well as Mercury, Venus,
Earth, and Mars.

It's really hard to imagine

that we could have formed
a 10-Earth-mass planet here

and still formed
the rocky planets

that we see today.

- '- Time for a new theory.

What if planet 9 formed from ice

in the outer solar system?

Calculations tell us
it would have to be 10 times

the mass of the Earth.

And here's the kicker.

An ice world that big

would have an internal ocean
of liquid water.

A new world is revealed

where icy geysers
shoot through cracks

in the frozen crust.

And deep below it

lies the largest body
of liquid water

in the solar system.

The planets that make up
our solar system

seem to follow a pattern.

The four closest to the Sun
are all made from rock.

The next four are giants
made mostly from gas.

Beyond Neptune, gas is replaced

by multiple worlds
made from ice.

This is the Kuiper belt,

a frozen realm
of water-ice asteroids,

millions of them.

The Kuiper belt
is a region of space

outside of Neptune's orbit

that extends out,

eh, about 50 times the distance
from the Earth to the Sun.

So it's really far out there.

And this is populated
by icy bodies.

These are giant chunks of ice

that have some rock
and other things in them.

But they're mostly ice.

Perhaps planet 9 is
made from the same materials,

an overgrown version
of the Kuiper belt's

most infamous citizen, Pluto.

Poor Pluto.

Discovered in 1930
by Clyde Tombaugh,

this tiny ice world,

smaller than our moon,

was quickly proclaimed
the ninth planet.

But, in the 1990s, Mike brown
and others discovered

a host of icy worlds
orbiting out with Pluto.

Pluto was just another
Kuiper belt object

and got demoted to dwarf planet,

to the dismay
of much of the world.

Everybody loves the idea
that I killed Pluto,

and now I'm trying
to atone for my sins

by replacing it
with a new ninth planet.

In fact, even my daughter
suggested this

long before we started
looking for planet 9.

She said, you know,
"you should find a new planet."

And then you can have
found a planet.

And there'll be
nine planets again.

"And everybody
will like you again."

If planet 9
is an icy Kuiper belt world,

it'll be the biggest
we've ever found.

Pluto, the biggest object

we know out there
in the Kuiper belt now,

is less than 1%
the mass of the Earth,

less than that.

Planet 9, we think, is 10
times the mass of the Earth.

So we're dealing with a factor
of thousands of times in mass

between the largest
Kuiper belt object

that we know now

and the size of planet 9.

So you're talking about
super-mega-ultra-Pluto.

It's really, really big.

And it's hard to know
what an ice ball

like that would look like.

It's not crazy to speculate that
there could still be activity,

internal geologic activity,

keeping this world
from being cold

and totally dead.

Peering through the darkness

to a hypothetical
mega-Pluto planet 9,

we discover
a giant world of ice.

There's much less rock
than a super-Earth planet 9.

But the mass of ice alone
creates enough gravity

to generate warmth deep in
the core, even out here.

The real currency of keeping
a planet alive is mass.

Does it have enough mass
to keep the interior warm?

Well, something
that's 5 to 10 times

the mass of the Earth
probably would be warm inside.

Up close, the surface
explodes with activity.

But these volcanoes
spew water ice, not lava.

If something like
a giant Pluto exists,

it must be the most
amazing landscape

to take a walk over.

You'd have these ice volcanoes
spewing out jets

of frozen water,
of ice raining down on you.

Maybe you'd look out
over the landscape

and see hundreds
of these erupting.

This dramatic,
icy vista is a gateway

to a secret world,

a vast, slushy ocean
of liquid water

mixed with ice crystals,

perhaps the largest

single body of water
in the solar system.

There's gonna be enough
internal heat, maybe,

to turn this
into a slushy water world.

So it's not quite
a terrestrial, rocky planet.

And it's not
a Uranus or Neptune.

It's a true mega-ocean world,

but perhaps a very cold one.

Is planet 9 an icy mega-Pluto?

The problem is scale.

Pluto and the other objects
in the Kuiper belt are tiny.

So how could the same
building materials

have come together
to form a giant?

So, the idea that planet 9

is simply a really scaled-up
Pluto, a mega-Pluto,

has some difficulties.

We just don't think that there
was enough mass out there

in the far reaches
of the solar system

to all come together
to build a planet that large.

When you look
at the Kuiper belt,

there are all of these
small, icy bodies.

There's nothing
very big out there.

And we think that's not
a coincidence,

that the disk of dust and gas
that formed the planets

had more stuff
closer to the Sun.

And by the time you got out
to where Pluto is,

there wasn't much material
to build planets out of,

certainly not a planet

5 to 10 times
the mass of the Earth.

So, if planet 9 didn't form
in the icy outer system

and didn't form in the rocky,
inner solar system,

where did it come from?

The more likely option,

planet 9 formed
in the gas-rich zone

in the middle
of our solar system

that also created Jupiter,
Saturn, and Neptune.

A gassy planet 9
could be similar to Neptune,

but perhaps a little smaller,

a mini-Neptune.

But how would it get
so much farther out

than the other gas giants?

And what would it look like?

Imagine a weird,
translucent world

glowing in the dark like a
giant deep-sea creature.

Something on the fringes
of our solar system

is upsetting orbits
and causing a ruckus.

Could it be a planet?

It's incredible to me
that we now know

of thousands of other planets

going around other stars
in the sky,

but we may have
missed a big planet

in our own solar system.

Planet 9, a world
we know almost nothing about,

beyond the possibility
that it exists.

Science suggests
intriguing options...

a giant, rocky world
with a heart of fire,

or an ice world filled

with a giant, slushy ocean.

But problems with each theory
have led to new hunches.

So, if it's not a rocky,
metallic super-Earth

and it's not a gigantic,
ice-ball, mega-Pluto,

what's left?

And the answer is a gas giant.

And that strikes me as being
the most likely prospect.

When you think about
the mass of planet 9

and where it is now,
my best guess,

it's something like a
miniature version of Neptune.

The gas giant planets

are the monsters
of our solar system.

Instead of a solid surface,
like the Earth,

the gas giants have thick,
stormy atmospheres

that descend for tens
of thousands of miles,

shrouding their small,
rocky cores.

Jupiter is
the largest gas giant,

over 300 times
the mass of Earth.

Moving out from Jupiter,

the gas giants
get progressively smaller,

Saturn, then Uranus,
and finally Neptune,

around 17 times
the mass of the Earth.

If planet 9 is a gas giant,

it'll be even smaller,

a mini-Neptune.

If planet 9 is a mini-Neptune,

if it's a lot like Neptune,

then it's not really like

a terrestrial planet,
like Earth.

But it's not really like
a gas giant, like Jupiter.

Neptune is this weird,
in-between thing

where it's probably got
a rocky core.

But it's actually, mostly,
what astronomers call ices.

It's got methane in it and water
and various other substances

and a very, very, very thick
atmosphere on top of that.

Neptune's thick clouds
are stained blue

with molecules of methane.

But planet 9's atmosphere
could be transparent.

It's so cold out there,
you're getting almost

no extra energy from the Sun.

And so then anything
heavy in the atmosphere,

any heavier molecule, over time,

would have probably
fallen to the surface.

And only the lightest elements,

the lightest molecules,
would stay in your atmosphere,

so maybe just almost
pure hydrogen or helium.

And you'd have, maybe,
a really clear atmosphere.

What would
a mini-Neptune look like

that far out from the Sun?

The thing I think of are
things like jellyfish, right?

That sort of beautiful,
translucent look,

where you're looking through to
the innards of the organism.

In this case,
you might look through

to the innards
of the planet in some way.

The atmosphere
may be transparent.

But this planet
is far from calm.

The interior is lit by
the flash of thunderstorms.

And faint lights
dance around the poles

as solar winds
from distant stars

stream down the planet's
magnetic fields.

Looking into the
innards of the planet,

it would look, in some ways,
like these gorgeous,

beautiful deep-sea organisms
that are bioluminescent.

And we may have
the planetary equivalent

of something like out there in
the inky blackness of space,

rather than the inky blackness
of the deep ocean.

Could planet 9
be a mini-Neptune?

Surprisingly, the possibility
of an extra gas giant

in our solar system isn't new.

In 2011, scientists attempted

to replicate the formation

of our solar system
using supercomputers.

But their models didn't work

unless they added an extra
gas giant planet to the mix.

It was really
difficult to reproduce

our current solar system.

But one scientist found that,

if you add a fifth large planet

to our solar system,

then that planet will end up

getting ejected
from our solar system.

And you'd have the planets
that we have today.

Is planet 9
the missing gas giant

predicted by the supercomputers?

The computer model
shows it being ejected

by the immense gravity
of Jupiter.

But did planet 9 instead
cling to our solar system

by the tips of its
gravitational fingers?

Sometimes,
our mathematical models

predict things
that we think are impossible.

And then we find them.

And, for a while,
we've known that,

if you throw a mini-Neptune

into the mix of planets forming,

the models work better.

Maybe we found that key,
finally... planet 9.

We know giant planets
can get thrown around.

Observers have even seen
ejected planets

floating free in the space
between stars.

Did planet 9 almost
suffer the same fate?

It's entirely possible
that there could've been

a planet forming
bigger than Earth,

something like a super-Earth,
well on its way

to becoming a gas giant

in this wonderful area
of the disk,

where it could've drawn in
a lot of material

and become a gas giant
like Jupiter,

except it got
too close to Jupiter.

And, before it could do that,

it was gravitationally
thrown away

from this wonderful
feeding ground

out into the much sparser,

more barren desert
of the outer solar system.

Is planet 9 really
a frozen mini-Neptune

banished to the badlands
of the outer solar system?

Right now, it's our best bet.

But there is one more option.

Some scientists believe

planet 9 may not have formed
around our Sun at all.

Is our most distant planet

an alien world snatched
from another star?

If the mysterious
planet 9 exists,

it is by far
the most distant planet

in the solar system,

20 times farther out
than Neptune.

So how did it get there?

Was it made in the place
it currently occupies?

Or was it flung out
from the inner solar system

as a rocky super-Earth

or, more likely, a
mini-Neptune?

The jury's out.

But there is another option.

And it's out of this world.

So the question is, then,
where did it come from

if neither of these things
is right?

And it's possible that
there is another explanation.

And that is that planet 9
is an alien visitor

from outer space.

The Sun is just 1
of 200 billion stars

orbiting the supermassive
black hole

at the center
of the milky way galaxy.

Most of these stars probably
have multiple planets.

And scientists now believe
that, from time to time,

two stars might pass a little
too close for comfort.

The result... planetary theft.

We know that the Sun moves
around in the galaxy.

We know that there
are other stars

and other solar systems.

Is it possible that
the Sun passed so close

to another solar system

that it stole a planet?

Today, our Sun
drifts through space alone,

like a yacht in the open ocean.

But that wasn't always the case.

Rewind the clock
4.6 billion years,

and our local star cluster
was a much more crowded place,

ideal conditions
for planet 9 to jump ship.

The Sun was born in a nursery

with thousands of other stars.

Just like the boats
in this harbor,

there are so many boats
around, so many neighbors.

It was like that
for the young Sun.

Stars like the Sun
are born in stellar nurseries,

vast clouds of gas that collapse

to form tens of thousands
of stars,

all tightly packed together.

Astronomers think it's possible

that, inside this cramped,
confused playground of stars,

our Sun's gravity
could've stolen planet 9

from a passing neighbor.

Imagine this cool scenario.

You've got an alien star.

And around that star
forms a planet.

This is planet 9.

And here comes the Sun
whizzing by.

The Sun gets so close
that it steals planet 9

on its way out into the galaxy.

It sounds like science fiction.

But our Sun may already
have a criminal record.

There's some evidence that
the comets in our solar system

may not have started
in our solar system.

We may have stolen comets
from other stars.

If that's the case,

it's not totally outrageous

to think that a planet that
formed around another star

somehow made its way
into our solar system

and became part of our family.

But if planet 9 really did
come from another star,

how will we know for sure
that it's an alien visitor?

What we'd like to do
is essentially

a DNA test on planet 9,

scoop up some of its surface

and look for material
that we absolutely know

couldn't have formed
around our Sun,

because we don't see it anywhere
else in our solar system.

We may even have
to send a probe there

to really get a good look at it

and find out what
its chemical composition is,

exactly everything we can
find out about its orbit.

And, that way,
we might be able to see

if there are any
sort of fingerprints,

smoking-gun pieces of evidence

that'll say clearly
this formed here

or it formed out there.

Unfortunately, before we can

we first have to find it.

Astronomers like Mike brown

have made the challenge
a little easier,

using math
to narrow down the zone.

What we know right now
is that planet 9

is in a swath of the sky
that goes about like this.

It's about this big.
It goes across like this.

But we think we even know
a little bit better.

We've pinpointed, or at least
slightly constrained

where it is, to a patch of sky
that's about this big.

It's still a lot of sky
to look at.

But it's a lot less than having
to look at the whole sky.

Mike's patch of sky is close

he's going to wait until fall,

when Orion is highest
in the sky,

to search for planet 9

using the Subaru infrared
telescope on Hawaii.

The telescope is fine-tuned

to pick out the faint
heat signature

of distant objects

against the cold backdrop
of deep space.

Planet 9 may be frozen.

But it will be
warmer than space.

And that tiny difference
in temperature

is all this incredible
telescope needs.

We want to see
two pictures taken

of the same area of the sky
a few weeks apart.

The stars don't move.

But you see this one, little
thing going, "boop, boop, boop,"

as you flash the pictures
back and forth.

That's what happens
when you have an object

moving around the Sun

against the background of stars.

That's how Pluto was discovered.

That's how we're gonna
find planet 9 if it exists.

It could take years
to find planet 9.

But when we do spot it,

scientists will be able
to analyze its light.

And hidden within
that faint glow

could be the chemical signature

for rock, ice, or gas.

If it is, planet 9's identity

will finally be revealed.

What lies in store beyond that
is a mystery.

But perhaps
the most exciting prospect

is planet 9 could be home
to a family of moons.

And it's just possible
one of these moons

could provide a home for life

100 billion miles from the Sun.

Are we alone in the universe?

For decades,
scientists have scoured

our closest planetary neighbor

for signs of
extraterrestrial life.

But so far, not a trace
has been found.

Is it possible we're targeting
the wrong planet?

If planet 9 is real,

it sits on the icy outer
limits of the solar system.

But even here, 100 billion
miles from the Sun,

it's just possible
that life could thrive

not on the planet itself,

but deep inside its moons.

Historically,
we've always thought of moons

as being these little,
insignificant places.

But the incredible thing
is they may be

the best places to find life.

In our solar system alone,

there may be far more chances
for life on moons of planets

than there are
on planets themselves.

Moons excite astrobiologists

because they can sometimes
support liquid water,

no matter how far
they sit from the Sun.

The key is something
called tidal heating.

Moons on elliptical orbits
get squashed

and squeezed by the gravity
of their parent planet.

This generates heat
and melts ice

to form underground
oceans of liquid water,

the key ingredient
for life as we know it.

If planet 9 is
as big as scientists predict,

it could have multiple moons.

And maybe one of those moons

could have warm, salty oceans

primed for simple life.

So, if you have planet 9,

and it's got icy moons,
and these icy moons

are on the right
kinds of orbits,

the heat could be coming
from within, not without.

And so the Sun basically
doesn't matter.

You could have liquid water
below the surface

that's heated from
the internal geology.

You could have geysers of water

like what we see
coming off of moons

around Saturn and Jupiter.

You could have that all the
way out there at planet 9.

Imagine planet 9
with a system of giant moons.

The closest moon
is heated to melting point

by planet 9's immense gravity.

There's no life here.

Any water boiled away
millions of years ago,

creating a hot,
arid ball of rock.

Farther out lies
a second giant moon.

This new world is encased
in bright, white water ice.

But the crust hides a secret...

a vast ocean
of warm liquid water

heated by volcanic vents
on the ocean floor.

This hidden world is rich
with organic chemistry.

And it could even support
a weird, alien zoo

of pale aquatic creatures.

We associate life with the Sun.

That's how we think of life
originating on the Earth.

But we know
you don't need the Sun.

We have tube worms
at the bottom of the ocean

which live off
of hydrothermal vents.

They get all the chemicals
and the heat they need

from, basically,
the interior of the Earth.

This is not out of the question.
You know, decades ago,

you'd have been laughed
out of a lecture hall

if you'd have said
something like that.

But we have learned
so much about life

in extreme environments
since then

that this is now
in the realm of possibility,

talking about life on a planet

beyond Pluto
in our own solar system.

Wherever there's energy,

wherever there's heat,
there can be life,

even all the way
out by planet 9.

There is good news.

If planet 9 does have
an active watery moon,

we should be able to see it
with our telescopes.

The active moons
of Jupiter and Saturn

are the brightest
in the night sky,

thanks to warm water gushing
out from cracks in the surface

and freezing in bright
white layers of fresh ice.

If planet 9's moons
have liquid oceans,

their surfaces should be
just as bright.

The race is on to image
planet 9 and its moons.

But what we'll see
when those pictures come back

is anybody's guess.

I have to admit, there's
some wonderful tension

that I feel right now when it
comes to finding planet 9.

We have giant telescopes

that are scanning the sky
looking for it.

So, any day now, I'm waiting
with baited breath.

My daughter believes

that planet 9 is pink
with purple dots.

Um, she might be right.

One thing's for sure.

If and when we do find planet 9,

we'll never look at our solar
system the same way again.

This is tremendously exciting,

because, if it's there,
it's already telling us

that there's more to know
about our solar system,

that there are more secrets
literally under the Sun

than we have dreamed of
in our philosophy.