Original subtitles

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.