All language subtitles for How the Universe Works - 7X10

For 13 years,
the cassini spacecraft explored

astounding worlds --
saturn and its moons.

We discovered things
we never imagined.

All of these strange,
bizarre landscapes --

geysers erupting out of moons.

We were so stunned
by the images.

I mean, people were just
going around in shock.

But cassini started
running out of fuel.

Scientists at nasa had to decide
what to do next,

and the answer was actually
pretty spectacular.

Cassini goes where no
spacecraft has gone before --

a death flight revealing
the deepest secrets of saturn.

out beyond jupiter lies saturn,

a planet circled
by multiple moons and rings.

It's like a miniature
solar system.

Imagine having a mission
with the power, the instruments,

the capability to explore all
aspects of the saturn system.

That mission was cassini.

it would become our eyes
and ears

in the saturnian system
for over 13 years.

but by September 2017,
cassini was almost out of fuel.

Cassini has been
orbiting saturn

and studying the saturn system
for over a decade.

End the mission -- we're
going to lose control soon,

so rather than let it
just go derelict,

we headed into saturn.

Go out with a bang.

The cassini team goes for broke.

They program the probe to head
straight for the planet.

How cool is it to sort
of sacrifice

everything you've got
to sort of learn

your last bit of information,
and then crash and burn?

Man:
We are in the atmosphere.

As cassini was careening
toward its death,

it still had instruments
that continued to work,

and as each instrument died,

there was still a set sending
back data and information.

Cassini wasn't
designed to plunge

through saturn's atmosphere.

No one knew how long it
would last before burning up.

spilker:
I remember sitting in a room

with my colleagues on cassini

and watching that radio signal,

that sharp green peak
that told us cassini

was still linked
to the earth.

We could monitor the
atmosphere as we flew into it,

and right up until the last,
it was sending back science.

I was really impressed
by how long cassini lasted

in the saturn atmosphere.

I mean, go nasa engineering.

As cassini plummeted down

at 77,000 miles an hour,

it was bombarded
by gas molecules

in saturn's atmosphere.

friction started tearing
cassini apart

as it struggled
to maintain contact.

spilker:
As the antenna turned away,

we actually saw
a secondary little peak,

and we thought, "okay, cassini.
Hang in there. Keep fighting."

and then just
that green flatline.

Just heard the signal
from the spacecraft is gone,

and in the next 45 seconds,
so will be the spacecraft.

Cassini's heartbeat
was gone,

and we knew
the mission had ended.

It just vaporized
in the saturnian atmosphere,

and so it has become
a part of saturn itself.

Cassini's death plunge

was the last of a series
of daring dives.

Prior to ending
cassini's mission

by sending it
into saturn's atmosphere,

nasa's engineers and scientists
came up with an idea --

"let's do dives
into the region

between the tops
of saturn's clouds

and the innermost area
of saturn's rings.

Beginning in April of 2017,

cassini ventured between saturn
and its rings 22 times.

Scientists called it
the grand finale.

On these dives, cassini got
closest to saturn's cloud tops

than any spacecraft
ever had before.

Saturn is an enormous
ball of hydrogen and helium,

a gas giant.

Fundamentally, it's a really
very different kind of planet

than we're used to
in our everyday lives.

Cassini snaps close-ups
of the planet's gaseous surface.

The pictures reveal
a turbulent and stormy world.

Durda:
We think of some storms on earth
as being particularly violent.

If you've ever been
in a hurricane,

it's not a fun place to be,

but the storms on saturn,
the wind patterns on saturn,

can make that look like
a mere breeze in comparison.

On saturn,
one storms stands out.

It's location is marked
by a distinct shape.

One of the really weird
things is that

whereas the bands go
around saturn,

they're all circular
until you get to the pole,

and then there's
a hexagonal band up there.

No one expected that.

During its lifetime,

cassini took multiple
images of the hexagon.

Whenever we posted
an image of the hexagon,

the hits to the website
went through the roof.

I think people thought
it was so mysterious.

When I first saw this,
I was blown away.

I mean, who could imagine
having something this regular,

almost geometric,
on the atmosphere of a planet?

It's really just phenomenal.

In 2018, cassini data
reveals this hexagonal storm

could be a towering structure
hundreds of miles in height.

Plait:
It's this gigantic structure.

It's many thousands
of miles across,

and right in the center,
right at the pole,

is this sort of
permanent vortex,

a permanent hurricane.

So, it's kind of
a creepy eye-like thing

staring back at us.

Each side of the
hexagon is as wide as the earth.

It seems artificial.

How do you get
a hexagon-shaped storm

or cloud structure on saturn?

Scientists think
that saturn's spin

interacts with air currents to
create this symmetrical shape.

But they don't know
why it's lasted for decades.

That's the puzzle.

How can you get
a six-sided jet stream

that's stable for so long?

But while
the hexagon shape is stable,

the color has altered.

Over four years, it changed from
mostly blue to golden brown.

The transformation is linked
to saturn's seasons.

plait:
The seasons on saturn are caused
by the same thing on earth.

It's the tilt of the planet,

and so as saturn
is going around the sun

and it's north pole
is tipping toward the sun,

you start to get
more light up there.

This sunlight
interacts with the atmosphere,

producing suspended particles
called aerosols.

It actually looks
a lot like smog.

It turns things more orange,

so over time the hexagon
went from blue to orange.

The color change happened

during one of saturn's
northern hemisphere summers,

but mysteriously,
the very center of the hexagon

remained blue.

Now, this could have been
for two reasons.

Maybe the haze never formed
in the eye

because the eye was shielded
from the sun,

and the sun is responsible
for creating the brownish haze

that we see on saturn.

Another reason is maybe
the actual vortex

is sucking the haze down.

Maybe there's something like
the eye of a hurricane.

There's haze that forms over it,

but it gets sucked down
into the eye.

But the storms on saturn

aren't the only extraordinary
thing about the weather.

When cassini dives through
the rings, it discovers rain,

rain falling onto
the planet from space.

April 2017, cassini
embarked on its grand finale,

following a daring new path.

We decided to dive in
between the rings of the planet,

to go to a place no spacecraft
had ever flown before

and make a unique
set of measurements.

It was uncharted territory.

Oluseyi:
They didn't know exactly
what they were going to find.

There could be stuff there
that could have destroyed

the cassini spacecraft.

Instead, cassini encountered

something totally
unexpected -- rain.

plait:
On earth it rains quite a bit.

We're getting that rain
from rain clouds

which are basically
just a few miles up.

On saturn it also rains,
but it turns out it's raining

onto the top
of the upper atmosphere,

and that rain
is coming from space.

In 2018, cassini data
revealed the colossal weight

of the downpour.

Icy-grained rain hits saturn

at a rate of several tons
per second.

It's completely unlike
anything we've ever seen.

Suddenly we've discovered
rain at saturn,

but there aren't
any rain clouds.

Where was it coming from?

The answer is saturn's rings.

thaller:
The first thing you think of

when you hear the word
saturn is the rings.

They're the most dramatic
and unique aspect

of that planet.

from afar, saturn's rings look
like this one whole structure,

but when you look up close it's
actually a bunch of ice crystals

and ice rocks
that make saturn's rings.

The size of the ring
material ranges from dust grains

to boulders to houses.

saturn's rings are well
above the atmosphere of saturn.

They're way out in space.

And under normal circumstances
those particles of ice

making up the rings would
just orbit saturn forever,

but things are
a little bit weird.

Something is making
these orbiting ice particles

fall inward
as a kind of cosmic hail.

Material is dripping
inwards from the rings

and falling into
the clouds of saturn.

It's like a rain
with no rain cloud.

A cosmic rain trickling in
and falling down.

Cassini discovers the rain

is a mix of different kinds
of ice particles,

but doesn't reveal why
they actually rain down.

Then the researchers realized
the ice grains

were statically charged.

Ultraviolet light from the sun,
for example,

can blow off an electron,

and that gives these
particles a charge,

just like rubbing
a balloon on your hair

makes it stick to a wall
because of the static charge.

Well, if you have particles
that are like that,

they can be affected
by magnetism,

and saturn has
a very strong magnetic field.

Earth's magnetic field springs

from it's spinning,
molten-iron core.

Although saturn probably has
a rocky center,

it's mostly a giant ball
of hydrogen and helium,

but deep in its interior,
scientists think something

much more exotic is going on.

We don't have enough data

to know exactly what's going on
in saturn's interior,

but we do know
the broad strokes.

Within saturn's interior,

extreme pressures
and temperatures force hydrogen

to stop acting like a gas,

turning it into spinning
liquid-metallic hydrogen.

You've got this band
of electrons

that can just wander
freely through that fluid,

so in that way, liquid hydrogen
under extreme pressure

can act like a metal.

The magnetic field generated

by the spinning
metallic-hydrogen outer core

pulls the ice particles
from the rings.

Plait:
These charged ice particles

are then drawn in
by saturn's field.

They follow
the magnetic field lines

and rain down onto
the atmosphere of saturn.

Cassini had revealed
several tons of material

is raining down
on saturn every second,

but how much stuff
is actually in the rings?

Again, cassini provides
the answer.

Thaller:
In the final days of cassini,

we actually flew in between
the planet saturn and the rings,

and the gravity data
was able to separate out

how much mass is coming
from the planet

and how much is coming
from the rings,

and the surprise was the rings

are actually not
very massive at all.

Even though they cover an area

as big as the moon's orbit
around earth,

saturn's rings are 100,000 times
less massive

than our own small planet.

They're lighter than we thought.

There's not as much
material there.

The mass of the rings is
a valuable clue about their age.

A more massive ring
can hold itself together

for much longer
than a less massive ring,

so if there's not a lot of stuff
there, it must be younger.

So, how long have
saturn's rings been in place,

and what is keeping them there?

It's something that I don't
even think I could have imagined

if I tried.

As cassini orbited saturn,

it revealed incredible insights
into the planet's rings.

the photos that came
from cassini of the rings

are unlike anything
that I could ever imagine.

If I was alien
visiting our solar system,

I don't know what would
stand out to me more,

the blue marble or saturn
and its amazing rings.

One of the biggest
questions about the rings

is how old are they.

Could something like that
really have existed

from the beginning
of the solar system,

or is it relatively recent?

Cassini provided an answer.

The rings could be as young
as only 100 million years old.

A couple of clues --
the low mass and the fact

that they're so bright and icy

that it hasn't had time
to get polluted

from all the micrometeoroids
and darkened

over a long time like the age
of the solar system.

Thaller:
So, the amazing thing is

that, you know,
if you were on earth

about the time of the dinosaurs,

there might have been a saturn
in the sky with no rings.

So, if the rings didn't form

at the same time as saturn,
how did they form,

and what's keeping them
in place?

to form the rings
100 million years ago,

you need to find an object --

maybe a comet or a moon
gets too close to saturn.

Saturn's gravity tears it apart
and forms the rings.

As the object is torn apart,

the pieces spread out around
saturn to form the rings.

They keep colliding, breaking
into smaller and smaller pieces.

Like pebbles on a beach,
subsequent jostling

and self collisions
between each other

will take
the sharp edges off of them

creating rounded particles.

From a distance,
saturn's rings appear

incredibly thin
and almost perfectly flat,

but appearances
can be deceptive.

One of our results
from cassini

as it took its final plunge
into saturn

was as we flew past those rings,

we noticed that the rings were
actually not a uniform density.

That's something
that nobody had seen.

I mean, you had to get
really close to see that,

and it wasn't expected.

Spilker:
I'm a ring scientist,

and I just love seeing
that detail

and trying to figure out

why do saturn's rings
look the way they do.

There are
very intricate structures,

knife-edge little ringlets

and, like, almost like
the grooves in a record.

It begs the question, of course,

where do those structures
come from.

The clue is hidden
within the rings.

There's not five rings.
There's not 500 rings.

There's thousands of rings.

There's potentially millions
of tiny, little ringlets

with small gaps between them,
and sometimes large gaps,

and cassini saw that there are
moons embedded inside the rings.

These moons and moonlets
seem to be shaping the rings.

When I think about
the rings of saturn,

I almost hear symphonies
playing in my head.

It's all about this wonderful
structure and these harmonies,

the balances between gravity.

So, we use the word "resonance."

Saturn's moons
stir the rings particles

with their gravitational pull,
creating waves.

There's a special place
where the resonance exists.

Imagine where the ring particles
are going around twice

for each single time
the moon goes around.

It's like pushing someone
on a swing.

If you push them
at just the right rate

they go higher and higher,

and these places are
where the waves generated.

So, there's
this ballet, this dance,

between the ring and the moons.

It is one of the most elegant
things I've ever seen.

But the rings aren't
just being shaped

into waves by the moons.

They're being held
in place by them.

Through
gravitational interactions,

these moons might be shaping
the rings, shepherding them,

keeping their flock in a nice,
tight orbit around the planet.

In 2017, cassini reveals

there are more
than one or two moons

shepherding the rings.

A whole team of moons holds
saturn's outermost visible ring,

the "a" ring, in place.

One of the really cool things
that cassini discovered

during its death dive

was that there are
seven moons of saturn

that are all working together

to keep that ring system
in configuration,

so it's like
the magnificent seven

holding this thing together.

Of the seven magnificent moons,
the biggest is mimas.

It's one-eighth
the size of our moon.

the smallest, pan,
is only 20 miles across.

acting in combination,

these moons hold
all of saturn's rings in check.

So, it's these
seven moons working together

forming the ring system
that we see today.

Cassini has truly
opened our eyes to the wonder

of saturn's rings
and many moons.

Saturn has a lot of moons --
I mean, a lot of moons,

and they're all really
interesting and different.

Coming up with the exact number
is a little difficult

'cause it almost changes every
year as we discover new ones.

The latest count
is over 60 moons,

each with a different character,

but one has a split personality
and a very dark side.

May 2017.

Cassini was
on its grand finale.

the probe snapped its last photo
of a strange moon

2 million miles
from saturn...

Iapetus.

Iapetus was discovered
hundreds of years ago,

and right from the start
it was recognized

that one side of it
was very bright,

and the other side
was as dark as dark can be.

This dark and light moon

confused italian astronomer
giovanni cassini

when he first spotted
it in 1671.

It's been puzzling scientists
ever since.

so, we get there with cassini,
and of course iapetus

was a very major target for us

because we were interested
to know

what was with this crazy
two-toned moon.

Cassini reveals that
the answer lies even farther out

from saturn
in the form of another moon.

There's one pretty big
but really dark moon,

phoebe, that's
outside of iapetus

and is orbiting the opposite
direction around saturn.

Pheobe orbits saturn four times
farther out than iapetus.

As it travels around the planet,
micrometeorite impacts

the moon's surface generate
a cloud of dark dust.

The dust from phoebe
actually creates a large ring.

A ring of dark, dusty
material that's drifting inwards

toward saturn going the
opposite direction of iapetus,

which is the perfect
material for iapetus

to sweep up in its orbit
to create one dark side.

Iapetus has one dark side

because it's tidally
locked to saturn.

One side always faces
the planet

while another side drives
forward through the dust.

It's plowing through
a bunch of dust

that's sticking to
the front side,

kind of like bugs
on a windshield.

Cassini discovered
this dark dust

makes the leading side warmer

than the trailing bright side
by 50 degrees fahrenheit.

When you have something
that's dark like the dust

on the leading edge of iapetus,
that gets warmer.

It absorbs sunlight better,

and if it's warmer then things
that can evaporate more easily,

like water for example,
tends to blow off the surface.

The front side
gets darker and warmer.

any visible ice turns to vapor

and makes its way
to the colder trailing side

where it refreezes.

so, the white side gets whiter
and the dark side gets darker.

So, you have
this self-sustaining dark side

and bright side, and you wind up
with this two-faced moon.

Iapetus' two sides are strange,

but cassini discovers
that they're not

the weirdest thing
about this moon.

The weirdest thing
is that it is a walnut.

iapetus has a mountain range
that exactly circles its equator

all the way around the moon,

a mountain range higher
than the himalayas.

These mountains are
over 12 miles high,

more than twice the altitude
of earth's highest peak,

mount everest.

It's crazy.
It's this huge crazy ridge

on this really strange moon.

how do you form a smooth
equatorial mountain ridge

around an entire world?

A really interesting idea
is that for some period of time,

just like saturn itself
has this gigantic ring system,

iapetus had
a ring system, as well.

Over time,
iapetus' ring collapsed,

falling in a circle
around the moon.

Walsh:
As it fell to the surface,

it built up a mountain range

right below
where the ring was orbiting

so that all that material
just built up

and built a mountain range

ringing the equator
all the way around.

Walnut-shaped iapetus

is not the only
strange moon around saturn.

Cassini discovered a moon

hiding many secrets
beneath its icy surface --

enceladus, a moon
that could even harbor life.

August 2017,

cassini captured six images
of enceladus,

one of the most intriguing moons
in the solar system.

Enceladus is a relatively
small moon of saturn

that's pretty easy to ignore,

but once you pay attention
to it, hosts a lot of surprises.

We've known something
was unusual about this icy world

ever since the voyager mission
took photographs in 1980.

We thought that
enceladus would be frozen solid,

and yet we knew from voyager
data the surface

of enceladus was bright white.

Porco:
And we could see on the surface

that vast tracks of it
were smooth,

at least at the resolution
that we had with voyager,

and that immediately says that
there's been internal activity

because that's really,
on an airless moon,

that's the only process
that could erase craters.

Scientists suspected something

was actively
resurfacing enceladus,

filling in its craters
to make it smooth and bright.

Then cassini sent back pictures
of enceladus backlit,

and all was revealed.

We saw these icy jets
shooting out from enceladus,

and everyone was so amazed
that a moon so tiny

and assumed to be a frozen-solid
ice cube could be so active.

Jets of almost luminous material
sprang out of geysers.

When I first saw a picture
of a geyser on enceladus,

I mean, I was floored.
That's amazing.

I had no idea
that was even possible.

The cassini discovery of geysers
on enceladus was a game changer.

All of the sudden,
here's water jetting out.

It was, like,
too good to be true.

Cassini revealed the geysers
are blasting out liquid water.

Enceladus is not
a solid ball of ice.

As we got more data
from cassini,

we found that enceladus
had a wobble

that was too large
for a body

that was frozen solid
all the way through,

and that told us
that a liquid water ocean

circled a rocky core.

Enceladus has
liquid water under its surface,

and it may very well
be an ocean

basically covering
the inside of that moon,

but where's the heat
coming from?

When planets and moons form,

their cores are incredibly hot,

but over time they cool down.

The smaller the planet,
the faster it cools.

A tiny world like enceladus over
a billion miles from the sun

should have frozen solid by now.

Oluseyi:
That's what we expected.

If things are smaller,
then they would be roughly dead,

and they'd be
covered by craters,

but enceladus shows us
that that's not the case at all.

How could a tiny moon
so far from the sun

have enough warmth
for liquid water?

One idea is tidal heating.

If you've ever played
racquetball,

you know as you play the game
the ball heats up,

and this is because as the ball
hits the racket or the wall,

it's getting squished,
and then it relaxes.

saturn's gravity squishes
and relaxes

enceladus as it orbits
the planet,

heating it like a racquetball,

but this alone
wouldn't generate enough heat

to stop enceladus' water
from freezing.

Something else must be
going on in the core.

Plait:
What if the core of enceladus
is actually kind of gravelly?

Instead of it just being solid,
it's actually made of rocks

and pebbles
and gravel all put together.

Then what happens is
as the tides are stretching

and squeezing it, those rocks
are rubbing together,

and that actually generates
even more energy.

2017, a computer model
based on cassini data

revealed this tidal friction
generates more energy

than america's biggest
power station.

Water heated to 194 degrees
fahrenheit rises to the surface.

It sprays through cracks
in the moon's

south pole
creating misty plumes.

As we flew seven times
through and tasted and sampled

the gas and the particles,
we found salty particles,

that the ocean was salty very
much like the earth's ocean.

We found hydocarbons, methane,
carbon dioxide, ammonia.

We found the key ingredients
for life

coming out of the jets
of enceladus -- so remarkable.

In 2018, scientists
reanalyze the enceladus data

and found something
even more remarkable --

complex organic molecules.

What they found were
larger organic compounds

than initially thought there.

At first, it was just dust and
water and some basic organics.

Now they're seeing more
complex stuff

coming up
from enceladus' interior,

and that asks the question
what else is down there.

On earth, we find life huddled
around hot vents on the seabed.

Could the same be true
in the oceans of enceladus?

Could these complex organic
molecules be signs of life?

My favorite name
for them is "goo."

they're gooey things,
and think of life

as a collection
of gooey-like molecules.

Now, that doesn't mean that all
gooey molecules are biological,

but certainly biology makes use

of these complex
organic molecules.

Deep in enceladus' oceans,

heat from hydrothermal vents
drives chemical reactions...

Combining simple molecules
like methane and hydrogen

into longer, complex
organic molecules,

complex molecules that could
serve as the precursors to life.

What's amazing is the chemistry
of that ocean.

Everything needed for life
is there.

The eternal question is
is there life in the universe,

and enceladus is a great place
to try and answer that question.

And cassini revealed secrets

of another moon of saturn
with amazing chemistry,

a giant moon
with earth-like features --

rivers, lakes, and dunes --

titan.

September 2017,

four days
before the mission ended,

cassini flew past
one of saturn's

most spectacular moons,
titan.

Here's why I like titan --
not just because it has a name

that means "big" and "strong,"
which makes you think of me,

but because it has
an extensive atmosphere

that's made primarily
of nitrogen, just like earth's.

sutter:
Titan's always been a mystery.

What is hiding underneath
that thick atmosphere?

Viewed through a telescope,

this moon seemed little more
than a hazy orange ball.

Then cassini launched
the huygens probe.

It traveled beneath the clouds

and sent back images
of titan's surface.

I almost can't describe
how thrilling it was,

the landing of the huygens probe
on the surface of titan.

It was like a jules verne
adventure come true.

lanza:
The images that you see

as you're coming
through the atmosphere

and the world emerges,

and it's this incredible world
that looks so familiar.

Mountains and these streams
flowing into this ocean.

Wow!

You might be standing
on the shores of a lake,

but this lake
doesn't look like water.

Instead, it's methane.

It's much darker.

Durda:
It's a frigid, bizarre world

with geologic features
that look familiar,

but in a very,
very alien setting.

Titan is like a home
away from home.

It's just colder by about
350 degrees fahrenheit.

The cassini mission
revealed that titan is

really exactly like earth
in terms of its landscape.

In fact, almost a quarter
of the body

is covered in sand dunes exactly
like what you see behind me.

But cassini reveals titan's
dunes are not what they seem.

The dunes on titan
are made of something

completely different
than sand dunes on the earth.

You know, most sand on the earth
is made of quartz,

but on titan sand dunes,
it turns out,

are made entirely of organics.

Titan's sand is made
from tiny particles

of organic gunk
called hydrocarbons.

these organic dunes contain
the building blocks of life.

For scientists,
this is a tantalizing hint.

Could titan harbor life?

Here on earth,
there's life that exists

in so many extreme environments,

so its not impossible
to think that life

could have evolved
to use the methane

and all of the other
chemical constituents on titan.

If life has developed on titan,
it's going to look really weird.

It's going to be really
different from life on earth.

To me, there's going to
be this wonderful moment

in history
when we really do have

another example
of how life can be,

and if I had to place
my bets on it,

I think we're going to find it
in the saturn system.

But cassini's
discovery of potential life

sentenced the probe to death.

We didn't want to leave
it just indefinitely in orbit

because there's this fear
that, you know,

should there be any earthly
contamination on the spacecraft,

you don't want it crashing
into titan or enceladus.

Cassini interacted
with titan one last time.

With a gentle nudge
from titan's gravity,

we call it titan's goodbye kiss.

We ended the mission with a
plunge into saturn's atmosphere,

vaporizing cassini and saying
goodbye to our friend.

I hope you're all
as deeply proud

of this
amazing accomplishment.

I'm going to call this
the end of mission.

Project manager
bob mitchell.

[ applause ]

Although cassini
is gone, its legacy lives on.

Spilker:
Now we're sifting through

all of the data collected,
still finding discoveries,

putting together the pieces
of the puzzle to understand

saturn, the rings,
and the moons.

Cassini is going to
go down in history

as one of the most
scientifically productive

interplanetary missions
that humanity has ever flown.

I'm immensely proud
and feel enormously privileged

to have been a part of it.

Besides the amazing
science cassini returned,

just the beauty
of this planet

I think sparked something
inside of us.

Whenever I look up
at saturn now,

I know that cassini
is there, too,

and so saturn is even
a more special place.