All language subtitles for How the Universe Works - 1X08 Moons

In the universe,

everything seems
to orbit something.

Planets orbit stars,
and moons orbit planets.

Some moons are volcanic,
but the volcanoes are ice.

Others are awash
with great oceans.

There may be more
habitable moons in our galaxy

than there are
habitable planets.

Moons tell the unknown
stories of our solar system

and show us how it all works.

In our own solar system,
there are just eight planets.

But orbiting six
of those planets are moons...

...lots and lots of moons...
more than 300 of them.

Each one is different...

...each one a world all its own.

Well, when we look
out on our solar system,

we see a lot of planets.

But even more than planets,
we see moons.

And in many ways,
they're more interesting

than the planets
that they go around.

We have moons that are airless
and apparently dead, like ours.

Then, out in
the outer solar system,

we have moons
with oceans inside them

and moons with atmospheres
around them.

I'm for moons.
You can keep the planets.

The biggest eruptions...

...the coldest temperatures...

...and the largest oceans
in the solar system...

they're all on moons.

There are moons
with ice volcanoes.

There are moons with lakes of
methane and methane rainfall,

smog clouds...

...moons that are
so volcanically active

that they keep remaking
their surface...

Moons with all kinds of plumes
shooting off into space...

really a much wider range
of environments

than we ever
could have imagined.

Often, when I'm describing

to the general public,
or even to my fellow scientists,

these moons of Saturn
and Jupiter,

I call them "worlds"
because they really do have

the complexity and mystery
of a whole world.

Jupiter and Saturn
have over 60 moons each.

These giant gas planets
and their moons

are like mini solar systems,

and each moon
has a distinct personality.

Lapetus, a two-toned moon
in black and white.

Titan, with a dense,
orange atmosphere.

And icy Enceladus, blasting ice
geysers 200 miles into space.

Each moon is unique.

But they all have
one thing in common.

All moons
are natural satellites,

held in place by gravity.

But moons do more
than just go around planets.

They help stabilize the planets
in their orbits

and keep the machinery
of the solar system

running smoothly.

The diversity of moons

is an interesting combination
of predictable laws of science

and then complete randomness
of just things smashing together

and the chips kind of falling
where they did

in a way that you could
never predict.

Planets and moons
begin the same way.

Once a star turns on,

there's a lot of dust and gas
left over.

Slowly, the dust particles clump
together, forming rocks.

The rocks smash into each other
and form boulders.

Slowly, the objects
get bigger and bigger.

The process
is called accretion.

One can think of it
as forming a snowball

and rolling it down a hill.

As it rolls down the hill,

it collects and gathers up
yet more snow,

which makes it roll
faster and harder.

And so that process
of runaway accretion

actually happens

in the formation of the planets

and in the formation
of moons, as well.

It sounds simple enough,

but nobody knew for sure
how it worked until 2003.

On the International
Space Station,

astronaut Don Pettit was
experimenting in zero gravity.

He put grains of salt and sugar
inside a plastic baggie.

Instead of floating apart,
they began to clump together.

This is how both planets
and moons build up.

But instead of taking shape
around stars,

most big moons take shape
around planets.

If the same process
makes them all,

what makes all of them
so different from each other?

Take two of Jupiter's moons,
Callisto and Ganymede...

...two very different moons,

each born from the same debris
when Jupiter was still young.

Ganymede formed
close to Jupiter,

where there was lots of debris.

Because there was
so much material,

it came together quickly...
in about 10,000 years...

and it was hot.

The heat separated the ice
from the rock.

You can still see it in
Ganymede's distinct landscape.

The primary factor that affects

why moons are the way
they are today

is energy...

how much energy
was put into them

as heat during accretion

and how much energy
has been lost.

All of those factors go
into telling us

why moons behave the way they do

and why they look the way
they do today.

Callisto's surface
tells a different story.

It formed much farther out,

where there was less debris
and less heat.

It took longer
and cooled faster.

Unlike Ganymede,
Callisto's surface is uniform.

Rock and ice never separated.

Where a moon forms
can also mean the difference

between survival
and destruction.

Get too close,

and a planet's gravity
will rip a moon to shreds.

Scientists believe this
is what happened to many moons

when Jupiter was young.

And it's very likely
that Jupiter had

an entire conveyor belt
of large moons

that were wanting to form,

only to be swallowed up
by the planet itself.

The large moons we see today

are only the last ones
that were able to stabilize

right at the end
of that process,

stop their death spiral,

and survive into the position
we see today.

But Jupiter keeps
trying to eat them.

The gravity of the giant planet

reaches out and pulls hard
on the orbiting moons.

It transforms them
from lifeless balls of rock

into strange and dramatic
worlds.

Jupiter is the largest planet

in our solar system.

It has 63 moons.

The four largest are called
the Galilean moons,

named after the astronomer
Galileo,

who discovered them in 1610.

They show how gravity controls

both what moons look like

and how they behave.

The first
of the Galilean moons, lo,

orbits closest to the planet,

just 260,000 miles
above Jupiter.

That's about the same distance
as our Moon is from Earth.

But unlike our Moon,

the surface of lo
has no impact craters.

Scientists realized that meant
the surface was new.

But how could that be?

Every time you look at lo,

with a spacecraft
or even with a telescope,

it's a little bit different.

So the geology on lo changes

like the weather
on other planets.

It's that active.

When NASA first sent
probes to fly past lo,

they were shocked.

They saw dozens
of active volcanoes.

This is footage of an erupting
supervolcano on lo,

blasting 200 miles into space.

Everyone had
the same question...

how could there be
active volcanoes on a moon?

The answer was simple...
gravity.

Jupiter's gravity is so huge

that it reaches out
and crunches the moon.

And it's not just Jupiter's
gravity pulling on lo.

Other nearby moons
also pull on it as they pass by.

So the core of the moon

is being worked back and forth
all the time.

It's called tidal friction

and generates extreme heat
in lo's core.

Almost like bending a
wire coat hanger until it breaks.

And you feel the inside
of the coat hanger there...

it feels rather warm.

That tidal friction...
that internal friction...

heats the interior of lo
until it's become,

actually, one of the most
volcanically active worlds

in the solar system.

The constant
pushing and pulling

generates temperatures
thousands of degrees high

inside lo.

It blasts out
in gigantic eruptions of lava.

Io is the prime example

of tidal forces
and gravitational interactions

in the solar system.

It is constantly being pulled
by Jupiter,

and it's
constantly getting pulled

by the other moons, as well.

And so, as a result,

there's a tremendous amount
of heat created.

The floods of erupting lava

constantly resurface lo,

which is why there are
no visible impact craters

on this moon.

Gravity also heats
lo's neighbor, Europa.

Europa's orbit is farther away
from Jupiter,

so it's much colder.

Instead of lava,
the surface of Europa is ice.

The lowest recorded temperature
in Antarctica

is minus-128 degrees.

Europa's surface
is twice as cold.

But underneath all the ice,

there may be an ocean of water

heated by
the same tidal friction

that makes lo volcanic.

Europa has a subsurface ocean,

almost certainly.

And that subsurface ocean is in
contact with the rocky mantle,

which provides heat

and also provides, probably,

appropriate nutrients
to sustain life.

Someday we'll send a probe

to explore beneath the ice
on Europa.

And maybe we'll discover
life-forms living there

in warm European oceans.

Out beyond lo and Europa
are nearly 60 more moons.

They orbit much further away
from Jupiter,

where the effects
of the giant planet's gravity

are much weaker.

Out here, it's too weak

to generate tidal friction
and heat the moons.

So these remote worlds

are cold and barren...

But not featureless.

They bear the scars
of countless collisions,

and scientists believe
it was collisions that created

the most extraordinary
moon system of them all.

The planet with
the most unusual moon system

is Saturn.

It's spread out
over more than 200,000 miles.

Technically, there are
more than a billion moons.

That's right...
a billion moons.

And all together,
they make up Saturn's rings.

A moon can be a hunk of rock
or ice no bigger than a pebble,

as long as it orbits a planet.

The rings of Saturn are made

of countless pieces
of rock and ice.

They go from the size
of a pebble

up to the size of a city.

We don't refer
to all the ring particles

that can get to be as big
as 10 or 20 meters across.

We don't refer to them
as individual moons.

But when we find a body

that is maybe a kilometer
or two across,

then you can start talking
about it as a moon or a moonlet.

Saturn's rings

are one of the oldest mysteries
of astronomy.

Where did they come from?

To try and find out,

NASA sent the Cassini probe
on a 12-year mission

to study Saturn, its rings,
and its moons.

We took, with Cassini,

probably the most beautiful
picture that's ever been taken,

and I'm not the only one
who has said this.

Cassini was in the shadow
of Saturn, cast by the Sun,

and so you don't see the Sun.

You see the backlit planet of
Saturn and its beautiful rings.

You see the refracted image
of the Sun

poking out from the side
of Saturn.

And nestled
in all of that splendor

is this small little dot.

That tiny dot is not a moon.

That is
the distant planet Earth,

nearly a billion miles away.

Most of what we know
about Saturn,

of its rings and moons,
comes from Cassini.

Before Cassini, we thought
there were only eight rings.

Today we can see over 30.

What we have found at Saturn

has been just literally
an embarrassment of riches.

We're seeing something
that we had seen before,

but now we're seeing it with
a level of detail and clarity

that was just mind-blowing.

Scientists used to think

the rings were made
of the icy leftovers

after Saturn was formed
about 4 billion years ago.

But anything that old

should be covered
with cosmic dust, and dirty.

So why does Saturn's rings

appear bright and clean,
almost new?

To get the answer,

Mission Control maneuvered
Cassini close to the rings.

The probe saw that
all the ice pieces in the rings

are constantly colliding
and breaking up.

And each collision
exposes new surfaces

that are clean and polished.

This is what astronomers
think happened.

When Saturn was young,

it had no rings,
just lots of moons.

At some point, an icy comet

zoomed in from deep space

and smashed
into one of those moons.

The comet broke up
into billions of pieces.

The impact also pushed
the moon closer to Saturn,

where the planet's
enormous gravity broke it up.

Now debris from the moon
and ice from the comet mixed.

Gradually, Saturn's gravity

pulled all those fragments
into rings around it.

The story of moons
is the story of gravity.

Gravity holds them in orbit.

It heats up their insides
and shapes their surfaces.

In the end, it controls
everything about moons,

even their survival
and destruction.

Gravity can even create
new moons

by kidnapping asteroids,
comets, and even whole planets.

We know
that gravity makes moons.

The standard way
is to assemble them

from debris left over
when planets are formed.

But gravity makes moons
a second way, too.

It captures them.

Imagine a wandering comet
or asteroid.

Somehow it gets knocked
off course.

It wanders too close
to a planet.

Gravity acts like
a science-fiction tractor beam

and grabs it.

Not quite enough gravity,
and it escapes.

Too much gravity, and it
collides with the planet.

Just enough,
and the comet or asteroid

goes into orbit
around the planet

and becomes a new moon.

Mars has two tiny moons,
named Phobos and Deimos.

Both are captured asteroids.

One is pushing outward
as it circles the planet

and will eventually break free

and continue on its journey
through space.

The other is circling inwards,

a little closer to Mars
all the time.

Eventually,
it'll smash into it.

This is Cruithne.

It's an asteroid, really,
just three miles across.

But it's sometimes described
as Earth's second moon.

With the little object Cruithne,

which was discovered
back in 1986,

we start to get
into this realm of...

of what does it mean
to be a moon.

Only a few thousand years ago,

Cruithne was
an ordinary asteroid,

orbiting the Sun
like billions of others.

But eventually, it wobbled

out of its orbit
in the Asteroid Belt

and got snagged
by Earth's gravity.

But then Cruithne
did something unusual.

Instead of orbiting
around the Earth,

like a normal moon,

Cruithne began to follow
behind it.

And so one might call it
a sort of a moon of the Earth...

not exactly, though,
because that object is on...

you know, it's
on its own independent orbit

around the Sun, not the Earth.

Sometimes asteroids
capture their own moons.

In 1993, the Galileo spacecraft

flew past the asteroid Ida

and found something
nobody expected...

a tiny half-mile-wide moon.

The fact that we saw a satellite

around only the second asteroid

ever to be encountered
with a spacecraft

immediately tells us

that moons around asteroids
must be incredibly common.

Not all
captured moons are small.

The mother of all
captured moons is Triton.

It orbits the planet Neptune,
and it is big...

about 1,700 miles in diameter.

But Triton is a moon
with an unusual story.

Triton was
a very puzzling problem

for planetary scientists,

because our traditional view

would tend to make
all the moons orbit

in the same direction
that the planet itself spins.

In the case of Triton
around Neptune,

it's the other way around.

Neptune is spinning this way.

Triton is orbiting around
in the opposite direction.

This means
it didn't form like most moons,

out of the debris left over
from the birth of the planet,

or it would orbit
in the same direction.

So something wasn't right.

Triton is huge,
and its orbit is funny.

It's anomalous.

It does not seem
as though it formed

as a part of the Neptune system.

It seems much more
like a captured planet.

Scientists now think Triton

was once a dwarf planet,
like Pluto.

And a giant planet like Neptune
certainly has enough gravity

to capture a moon
the size of Triton.

Triton
was almost certainly formed

way out
in the outer solar system

and then at some point
was captured by Neptune.

Perhaps Triton, early on,
had its own moon,

they both were captured,

and then that moon was destroyed
during the capture process.

But Triton is in danger.

Neptune is dragging it
closer and closer.

Eventually,
it will get too close,

and Neptune's immense gravity
will tear it apart.

Triton the moon will be reborn

as a ring system
around the planet.

But what about our Moon?

How did it get there?

Was it captured?

The truth
is even more extraordinary.

It was born in extreme violence.

Our Moon, like a lot of moons,

is rocky, barren,
and pockmarked with craters.

But in one way, our Moon
is unique in the solar system.

For a long time,

astronomers thought
the Moon formed

from debris left over
from the birth of the Earth.

But researchers in the 1960s

came up with
a radically different idea.

They suggested
it came from a giant impact.

When we first had the idea

of forming the Moon
from a giant impact,

that was not
a terribly popular idea.

And I actually did have good
science friends... colleagues...

coming to me, saying, you know,
we really have to exhaust

all the slow
evolutionary theories

before we start talking
about cataclysms.

The evidence
Bill Hartmann needed

was on the Moon itself.

And the proof had to wait

until Apollo astronauts
finally went there in 1969.

They brought back hundreds
of pounds of Moon rocks.

Scientists analyzed the rocks
and were amazed.

They were identical to rocks
in the Earth's crust,

and they'd been superheated.

So, how did
pieces of the Earth's crust

become superhot
and wind up on the Moon?

Hartmann was pretty sure
he knew.

This whole idea
was that the Earth forms.

Now you hit it with something.

You blow all this light,
rocky material off the top.

That material goes into orbit
and makes the Moon.

The Moon's just made
out of rocky debris.

Lmagine our
chaotic solar system

4.5 billion years ago.

The young Earth is just one

of a hundred or so new planets
orbiting the Sun.

One of them is a Mars-sized
planet called Theia,

and it's on a collision course
with Earth.

They smash into each other

at many thousands of miles
an hour.

Theia is destroyed,
and Earth barely survives.

The impact blasts billions
of tons of debris into space.

The Earth's gravity pulls it
into orbit around the planet.

Now these hunks
of leftover Earth

clump together
and form our Moon.

That's the theory, anyway.
But how do you test it for real?

Here at NASA's
Vertical Gun Range,

they're re-creating
that ancient collision in a lab.

This 30-foot-long gun
fires a tiny projectile

at 18,000 miles an hour.

The projectile is Theia.

This ball represents the Earth.

By changing
the angle of Theia's impact,

the team can figure out
how precise

the ancient collision had to be
in order to make the Moon.

In the first shot,

Theia hits the top of the Earth
with a glancing blow.

So, here's the Earth,
if you will, suspended in space.

And now it's gotten hit.

So, now we see
the planet ejecta

is being ripped
out of the Earth

and is forming
this giant impact basin.

And if this
really were the Earth,

this basin would be
thousands of kilometers...

thousands of miles... across.

In this simulation,

Theia only skims
off the surface of the planet,

and very little debris
is thrown out into space...

not nearly enough
to build our Moon.

The second shot
is a head-on collision.

Ka-pow!

That's the end of planet Earth.
It's gone.

Some of the debris is gonna go
out of the solar system.

Some of the debris
will reaccrete

to form small planetesimals
within the solar system.

There's no Earth left,

so there's no gravity

to gather the debris
and form the Moon.

Now the gun is set
to just the right angle...

halfway between a glancing blow
and a direct hit.

So we'll see what happens
if the Earth barely survives.

Oh, oh, gorgeous!
Oh, my gosh!

Ka-pow!

Now we have the entire part
of the Earth

being ripped apart,

but the vapor plume is...
oh, my gosh.

Aw, geez!

That is gorgeous.

But this was the beginning...
the beginning of our Moon.

The experiment shows

that Theia could have
smashed into the Earth

and formed the Moon.

But the collision
had to be just right.

And lucky for us, it was.

Today, the Moon orbits
250,000 miles from Earth.

But when it first formed,

the Moon orbited
just 15,000 miles

above the Earth's surface.

500 million years
after the Moon formed,

if we looked up in the sky,

the Moon would have comprised
a tremendous portion of the sky.

It would have been enormous,

because the Moon
would have been much closer.

Back then,
the Earth was rotating so fast,

a day lasted just six hours.

But the Moon was so close,
its gravity acted like a brake.

It slowed our planet down

until a day now lasts 24 hours.

The Moon's gravity
also created giant tides

that surged across the planet,

churning up the seas,
mixing minerals and nutrients.

This created
the primordial soup

from which the first forms
of life arose.

Without our Moon, life on Earth
may never have happened.

And there may be other moons
with a link to life, as well.

Moons may be the great biology
experiments of the universe...

the true laboratories
of life itself.

Moons are full of surprises.

There are moons
with giant volcanoes,

moons with vast oceans
sealed under thick ice.

And now we know a few
are rich in organic compounds.

In the right combination,
they might even support life.

In our solar system,
the biological window

through which we can understand
the rest of the universe

may be through these moons
of the outer solar system.

That may be where we find
our second genesis,

and that second genesis

is really
our first deep understanding

of the biological nature
of the universe.

At first glance,
moons don't look ideal for life.

Take Enceladus.

It's a shiny ball of ice,
300 miles across,

orbiting Saturn.

It's the brightest object
in the solar system.

It reflects 100% of the light
that hits it,

so it's superbright,

and that's because
it's water ice.

In 2005, the Cassini probe

spotted ice volcanoes erupting
from the surface of Enceladus.

That meant there had to be
heat under all that ice...

heat that created
oceans of water.

And where there's water,
there's the possibility of life.

So, this is Beehive Geyser
here in Yellowstone,

and it is shooting water vapor
and water

about 150 feet into the sky.

And it's pretty incredible.

So, now imagine if you're
on the surface of Enceladus.

You would see geysers
that look a lot like this,

and they are shooting ice grains
and water vapor into space

thousands of times higher
than this geyser here.

The ice volcanoes
are powered by gravity.

Here's how.

Saturn's gravity works
on the core of the moon,

heating it up.

The underground water expands

and forces its way up through
cracks in the surface ice

and blasts out into space
as ice crystals.

These are some of
the most spectacular eruptions

in our solar system.

They make Beehive Geyser
look like a squirt gun.

From the ice in the volcanoes,

scientists have detected salt
and simple organic compounds.

That means
the water under the ice

is not only warm
but full of nutrients.

Sound familiar?

Heat, water, and nutrients...

that's how life on Earth began.

We realize
you could have all the things

that we associate
with oceans on the Earth

going on inside a moon.

It's the discovery
of a lifetime.

Saturn's
Enceladus has an ocean.

So does Jupiter's Europa.

But these aren't the only moons
where life could emerge.

Saturn has another moon...
Titan...

with an even greater potential
for life.

In 2005, Cassini sent a probe,
called Huygens,

on a one-way mission to Titan.

For just 31/2 hours,

Huygens transmitted
live pictures

from the hostile surface,
nearly a billion miles away.

Then the battery died.

It was just incredible.

This was the first time humans
had ever touched this moon

with something
of our own making.

It was just an event

that should have been
celebrated the world over.

We should have had
ticker-tape parades

in every major city
across the U.S. And Europe

to celebrate this.

It was that history-making
and that astonishing.

Raindrops on Titan

are twice as big
as raindrops on Earth.

But the rain isn't water.

It's methane.

On Earth, methane is a gas,

but on Titan, it's a liquid
because the moon is so cold.

There may be methane icebergs.

There are certainly
methane lakes and rivers,

and there's methane rain
and methane clouds

and maybe bugs
swimming in methane.

Bugs living in liquid methane

may sound unbelievable.

But scientists have discovered

that Enceladus, Europa,
and Titan

are all covered
with a substance called tholin.

Tholin contains
the chemical building blocks

for life to begin.

So could life emerge
on any or all of these moons?

We can't get our hands
on the tholin from the moons,

so Chris McKay
makes it in the lab.

He zaps a mixture of gases
found on Titan with electricity.

What he gets
is a reddish-brown mud.

So, this is
what we make... tholin,

this sort of nonbiological
organic material.

It's produced by chemical energy

put into simple molecules,
like methane and nitrogen,

and here we got it.

And that's the material
we see on Titan.

We see evidence for something
like this on Enceladus.

We see it on the surface

of many of the moons
in the outer solar system.

This is nature's recipe

for making the stuff that life
eventually emerges from.

Somewhere in the outer
reaches of our solar system,

on some remote moon,

life may have already emerged.

But it probably won't be life
as we know it.

Life 2.0 doesn't
necessarily have to have

the same genetics
as life 1.0, right?

In fact, the more different it
is, the more interesting it is.

Whether it's the same
or very different,

the discovery of life
on the moons of our solar system

will change the way
we look at the universe.

I think that,
should we ever find

that life had originated

not once but twice
in our solar system,

then you... you can
easily dismiss any arguments

that say that life
is unique to the Earth.

Moons are small,

but they're still
diverse and dynamic worlds.

They help us understand
how the universe works.

They're essential cogs
in the cosmic machine.

Without any moons,

our solar system would be
a very different place.

Without our Moon, life may
never have evolved on Earth.

And who knows...