How the Universe Works (2010–…): Season 5, Episode 1 - The Mystery of Planet 9 - full transcript
Scientists have discovered a mysterious ninth planet on the very edge of our solar system. Ten times the size of Earth, this strange world could have moons with extraterrestrial life.
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 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.
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 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.