All language subtitles for Cosmic Front 12of18 Saturns Moon Titan Another Earth 720p

Saturn.

The rings are made of ice particles.

We also now know that Saturn is orbited

by over 60 natural satellites.

The largest of Saturn's satellites
is a moon called Titan.

It is enveloped in a thick atmosphere,

one filled with orange haze.

In 2005,

a NASA probe penetrated
the veil of mystery,

and sent back the first
images of the surface.

The terrain looked amazingly familiar.

Black lines branched out over the surface.

They looked just like rivers.

And numerous lakes were discovered.

This was the first time any
celestial object had been found

with liquid on its surface.

The more the probe investigated,

the more Earth-like Titan seemd to be.

It was at this point that
scientists began to suspect

that life might be present.

Maybe in the seas, more
interesting things happen.

Maybe you get self-replicating
chemical systems

much like those that are the first steps

towards living systems that
are deep in our own history.

So Titan gives us a whole
new set of possibilities.

There's the possibility that
maybe there is life on Titan

that has somehow found a way to make use

of all of these building blocks

that the atmosphere is making for it.

However, the temperature on Titan

is -180 degrees Celsius.

Could life really exist there?

How do we know it's too cold?

Imagine you're living on Titan

and you're looking at the Earth.

You'd say, "Oh, there's a
liquid, there's organics",

"there's energy, but it's too hot."

Titan has both an atmosphere and liquids.

Could life exist there?

This planetary body, very similar to Earth.

Saturn's moon, Titan.

Imagine the journey from Earth to Titan.

If you could travel at the speed of light,

you'd pass Mars about four
minutes into the voyage.

At the 30-minute mark or so,

you would pass the giant ball
of gases known as Jupiter.

Then, some 70 minutes after departure,

you would finally arrive at Saturn

surrounded by those beautiful rings.

Like Jupiter, Saturn is
a large gaseous planet.

Finally, you'd reach Titan.

With a diameter of 5,000 kilometers,

Titan is about three-fourths
the size of Mars.

It's a moon the size of a planet.

Fully cloaked in that orange haze,

Titan's true appearance was not known

until the 21st century.

1997 saw the launch of the
Cassini-Huygens mission.

The Cassini orbiter equipped with cameras

and other instruments, and
carrying the Huygens probe

was sent to investigate
Saturn and its moons,

especially Titan.

In 2004, seven years after liftoff,

Cassini-Huygens reached
the vicinity of Saturn,

1.4 billion kilometers from the Sun.

Cassini then proceeded to enter
into orbit around the planet

and its satellites, and to
commence scientific observations.

It took this image of Titan.

For the first time,

Titan's true features began to show

from under that thick haze.

The day was approaching when
we would finally be able

to see the surface of Saturn's giant moon.

In December 2004,

the Huygens probe separated from Cassini,

and coasted to Titan.

The target landing site
was near Titan's equator.

What that site would
be like, no one knew.

Titan's atmosphere is
1,000 kilometers thick.

The probe entered it.

Huygens deployed a parachute
and drifted down,

jettisoning its heat shield.

This image, taken from a
height of 152 kilometers,

was Huygens' fist view of Titan,

which was still obstructed by haze.

Huygens was shooting still
images as it descended.

Its microphone also captured the sound

of the wind rushing by.

This was the first sound recording ever

made of an alien environment.

These images of Titan's surface

were taken by Huygens from
16,000 kilometers up.

Black veins like the branchings
of a river are visible.

It does look as though they're flowing

to the mouth of a river.

Now, from 8,000 meters above Titan.

It looks just like the sort of coastline

we're used to seeing on Earth.

Finally, the landing.

This is an image taken by
Huygens just after landing.

What look like rocks and pebbles

strewn about over a flat plain,

are actually chunks of ice.

The surface temperature
is -180 degrees Celsius.

Atmospheric pressure is a
little higher than Earth's,

1.5 bars.

The horizon seems blurred by mist.

This is exactly like some rocky
desert landscape on Earth.

High above, the Cassini orbiter
continued its observations.

In the equatorial region where
the Huygens probe landed,

Cassini discovered a strange pattern.

Some sort of regular striping.

Further observations
found similar striations

covering some 20% of Titan's surface.

Ralph Lorenz has dedicated himself

to investing the strange striped pattern.

He is trying to solve the
mystery of Titan's stripes

by comparing them to
patterns he finds on Earth.

This is the Mojave Desert

in the western United States.

Lorenz believes Titan's stripes

are like the peaks and troughs
of desert sand dunes.

There are, indeed, real similarities.

It's remarkable somehow that despite

the different gravity,
the thicker atmosphere,

and the different material
that the sand is made of,

somehow the landscape ends up looking

almost exactly the same
as many places on Earth.

By comparing the shape of the dune

and the interaction with the
rest of the environment,

we can get an understanding

of how these structures formed.

For example, different shapes of dunes

form in different wind patterns.

So the goal is to solve the mystery

of Titan's stripes by investigating

terrestrial desert dunes.

Lorenz's first step is to
send up a kite with a camera

for an aerial overview.

He is looking for a place

that has a striped pattern like Titan's.

Next, he mounts a dune
buggy equipped with GPS.

He wants to measure the heights of dunes

and the angles of their slopes.

The shapes of sand dunes
change by the minute.

Lorenz plants a stake
with a streamer attached.

In fact, he plants a whole
line of them along this slope.

This will show what sort of
wind creates this type of dune.

The wind is blowing from screen
left across a gentle slope.

Then it swirls around

as if to carve out that slope to the right.

So it's become clear that here,

the wind flows from the milder slope

over and down the sharper slope.

Lorenz believes that the stripes on Titan

are also wind-sculpted sand dunes.

A closer look at that
image of Titan's stripes

shows ridges with milder
and sharper slopes,

similar to those in the Mojave Desert.

So Lorenz conjectures
that the wind on Titan

must've been blowing from left to right.

The winds blowing on
Titan's dunes, however,

are thought to be weaker
than the winds on Earth.

The reason for that is that
Titan's gravitational force

is only one-seventh of Earth's.

A relatively small lashing
can produce a big result.

So on Titan, effects similar
to those seen on Earth

are being produced by mild winds.

Titan is still an active world

where, geologically speaking,

processes are still happening.

And the fact that we can see
sand dunes for example,

suggest that the winds
that move the sand around

are still active, that we're
seeing a dynamic planet

much like the Earth.

There was another unexpected aspect

to those images taken by Huygens.

Look closely at those chunks
of ice on the ground.

They are reminiscent of
stones turned over and over

by rivers on Earth.

Sharp edges are worn down.

They're rounded like pebbles.

So there may well be liquid on Titan.

This discovery attracted
attention and astonishment.

Meanwhile, the Cassini orbiter

made a surprising discovery of its own.

Black spots and blotches were visible

near Titan's north pole.

Radar observations showed them to be lakes

filled with some liquid.

They number in the hundreds,

and some of them are huge.

This is the first time liquid
has been found on the surface

of any celestial body other than Earth.

The lakes are dotted with
islands and fed by rivers.

But with a surface
temperature of -180 degrees,

any water on Titan would've frozen.

What liquid could it be in
these lakes and rivers?

This is it.

Liquid methane.

On Earth, it's normally a vapor,

but at extremely low temperatures,

it condenses into a liquid.

Methane melts at -182 degrees Celsius.

It boils at -161 degrees.

In the 20 degree range
between those two extremes,

it exists in a liquid state.

The temperatures on Titan's surface

are just right for liquid methane.

Methane is composed of one carbon atom

and four hydrogen atoms.

It's the simplest hydrocarbon,

and it constitutes the bulk of
the liquid in Titan's lakes.

A portion of the liquid is ethane,

another hydrocarbon with
similar characteristics.

Scientists at the Jet Propulsion
Laboratory are trying

to determine how Titan's
methane lakes were created

by conducting experiments here on Earth.

Christophe Sotin is an
expert on bodies of ice

found in the solar system.

This device is called the Titan Chamber.

With internal air pressure at 1.5 bars

and a temperature of -180 degrees Celsius,

it reproduces Titan's
environmental conditions.

Inside is placed a disc of ice

standing in for the terrain on Titan.

They then release droplets
of liquid methane

onto the surface of the ice.

The methane disappears immediately,

absorbed by the ice,

like water being swallowed
up by a thirsty earth.

So it was a big surprise,
something we did not expect,

is that when the methane falls on the ice,

actually the methane got
sucked into the ice.

It gets absorbed.

It doesn't run on the ice.

However, if methane continues to drip

onto the ice, eventually,

it begins to pool on the surface.

This suggests that wherever
there are lakes on Titan,

the surrounding ice must
be saturated with methane.

During its landing on Titan,

Huygens measured the
concentration of methane.

That concentration gradually rose

the closer the probe got to the surface.

Then, the moment it landed,
there was a sharp increase.

It is thought that this was
due to the heat from Huygens

vaporizing the methane
that permeates the ice.

On Titan, liquid methane acts in ways

similar to water on Earth.

In June 2012, for example,

Cassini observed a strange phenomenon

near Titan's south pole.

An oddly-shaped mass seemed
to be squirming about

in the atmosphere.

It was a cloud swirling.

A cloud made up of methane.

On Earth, water is recycled
as water vapor and rain.

One of the factors prompting
this is seasonal change.

On Titan, the same sort of
mechanism seems to be at work.

Titan is tilted on its axis,

some 26 degrees off vertical.

The Earth has a 23.4 degree tilt.

It's another point of similarity.

Along with its parent planet,
Saturn, not shown here,

Titan takes 30 Earth
years to orbit the Sun.

The tilt of its axis gives
birth to different seasons.

At this location, Titan's
northern hemisphere

experiences the long days of summer.

The northern hemisphere is warm,

producing rising atmosphere currents.

Liquid methane on Titan's
surface evaporates

and is carried southward.

Near the south pole, it is winter.

The methane gases cool

condensing into a liquid
or even solid state.

It can form clouds

like that huge swirling
cloud Cassini spotted.

When it's winter in the
northern hemisphere,

the cycle reverses.

Now, the methane cloud
forms near the north pole.

Underneath that cloud,
methane rain begins to fall.

Since methane is more viscous than water,

its raindrops are larger,

with diameters of about a centimeter.

But as Titan's gravity
is weaker than Earth's,

the droplets fall more slowly,

about one meter per second,

like a soft snow on Earth.

They soak the icy ground
on Titan and form lakes.

Wind blows.

Rain falls.

When people could finally
see Titan close-up,

they were astonished at how
much it resembles Earth.

In 2007,

the Cassini orbiters spotted
something truly peculiar

on Titan's surface.

A land formation, some 70 kilometers across

in the shape of a flower.

What could it be?

Perspective can be gained
by combining images

taken from two different points of view.

A three-dimensional image
of the topography emerges.

That strange formation turns
out to be a rugged mountain,

featuring a 1,500-meter high peak.

There is also a chasm that looks

like it might be a volcanic crater.

From that, one can infer a
formally-active volcano.

That volcano has been an
object of particular interest

to Jonathan Lunine,

an expert on Titan's internal structure.

He says that the volcano did not spew lava.

Rather, it pumped up a mixture
of ammonia and water.

One thing to remember is that when water

is mixed with ammonia, it can stay liquid

down to very low temperatures.

Down, in fact, to -100 Celsius.

But at that point, within a
few degrees of that point,

the liquid is actually very viscous.

It's almost like basalt.

So if that is what is
flowing out on the surface,

we would see very thick flows.

Lunine believes that under the ice

beneath the volcano, there's an ocean.

He came to this conclusion due
to changes in Titan's shape.

Titan completes its elliptical
orbit around Saturn

once every 16 days.

During that time, it regularly
feels the changing effect

of Saturn's gravity.

In short, it experiences tidal forces.

At its farthest point from Saturn,

Titan is almost perfectly spherical.

But at its closest point

where Saturn's gravitational
pull is the strongest,

Titan grows fatter.

Its diameter alters by
as much as 10 meters.

Lunine says that Titan can
transform so dramatically

because internally, it is not
made entirely of solid rock.

Lunine's observations suggest
the following picture

of Titan's structure.

The outer crust of ice is some
50 to 100 kilometers thick.

The center is comprised
of two types of bedrock.

In between the ice and the rock, however,

is a layer of liquid water.

The bedrock generates heat, says Lunine,

permitting the water to
remain in a liquid state.

This ocean layer is some
300 kilometers deep.

Ammonia, present in Titan since its origin,

has also dissolved into the water.

It is thanks to this ocean layer

that Titan can change shape so flexibly.

The interior's warm enough
that really only liquid water

is a suitable, stable
material in that region,

so we're pretty sure from
the gravity experiment

that Titan has a liquid water
layer under its surface.

According to Lunine,

the tidal forces caused by Saturn, in turn,

stimulate volcanic activity.

Tidal forces cause friction
along the boundary

between ice and the subsurface ocean.

The water heated in this way
melts some of the icy crust.

It builds up by terretrial magma,

and eventually forces its
way up above the surface.

This ammonia-laden water flows out

from Titan's volcanoes like lava.

Lunine believes such volcanoes are proof

of an underground ocean.

Beneath Titan's icy shell,

a whole new world lies hidden.

Saturn has over 60 moons.

Among them are Enceladus,
ice-covered like Titan.

And Hyperion, pockmarked with craters.

Mimas has this huge crater.

Those are just a few of Saturn's moons,

but they all have
practically no atmosphere.

Only Titan boasts an
atmosphere that extends

as far as 1,000 kilometers into space.

Actual measurements reveal
that this atmosphere

is 98% nitrogen.

The rest is largely methane.

Why is Titan the only one of Saturn's moons

with a thick atmosphere?

Solving that mystery through
experimentation on Earth

has been a preoccupation
of Yasuhito Sekine.

Sekine believes that Titan's
atmosphere was generated

by an extraordinary mechanism.

The mechanism?

Collisions with small celestial objects.

Sekine is trying to reproduce
that effect using a laser.

When Titan was first formed,

its icy land mass contained
about 1% ammonia.

So inside a vacuum chamber,

a disc of ammonia-water ice
stands in for the young Titan.

The laser beam enters from
the left of your screen.

It strikes a projectile,

which then impacts the ammonia disc.

That was the laser shot.

Gases released by the impact are measured.

One is nitrogen

released by the disintegration
of the ammonia.

Titan's thick atmosphere contains
large amounts of nitrogen.

According to Sekine's calculations,

based on his experiments,

repeated impacts by small celestial objects

could have produced just
such an atmosphere.

For example, Enceladus,

one of Saturn's other moons,

is merely 500 kilometers across.

That is one-tenth of Titan's diameter.

Saturn's other satellites are also small,

with weak gravitational fields.

So even if they've been similarly impacted,

they haven't been able to
hold on to any atmosphere.

But did Titan, in fact,
experience repeated bombardment

by small celestial objects?

Hal Levison uses computers to calculate

the history of the solar system.

He has advancd the revolutionary theory

that some four billion years ago,

the entire solar system was
shaken by a massive event.

Levison argues that when the
solar system was forming

4.6 billion years ago,

Uranus and Neptune were closer to the Sun

than they are now.

He inputs the location
and size of the planets

and also of the small celestial objects

that lie further out.

Then the simulation begins.

At first, the basic situation
did not change much.

But some 600 million years later,

Uranus and Neptune were suddenly flown

to the outer realms of the solar system.

Du, du, du, du, then out.

And that caused the giant
planets to slowly spread.

It was infinitesimal, you
wouldn't have noticed it

but the orbits were slowly changing.

And that continued until Jupiter and Saturn

got to the point where Jupiter
was going around the Sun

exactly twice every time
Saturn went around once,

and that configuration

is what set the whole instability off.

So you went, almost overnight,

from a time when there was
a little bit going on

but not much, to this very violent period

where all hell breaks loose.

The smaller celestial objects
shown here in green,

had formed a ring at the outer
edge of the solar system.

But then the gravitational
force of Uranus and Neptune

violently scattered these objects.

The result was that in the
period from four billion

to 3.9 billion years ago,

the planets of the solar system encountered

a barrage of small celestial objects.

During this period, Titan
also was hit repeatedly,

developing a nitrogen-rich atmosphere.

That made it a very special moon.

1977 saw the lauch of Voyager one.

Its mission.

To explore and observe the outer planets

from Jupiter to Neptune.

This was its view of Titan.

It was a close look,

but still, the moon was shrouded
in a thick orange haze.

However, even then,

one scientist maintained that the haze

held the secret to sparking life below.

Bishun Khare has been trying to penetrate

the mystery of Titan's haze
since the early 1970s.

He participated in the Voyager mission.

He is focused on the haze as being itself,

a source of life.

Khare introduces a nitrogen-methane
mix into a sealed flask

to simulate Titan's atmosphere.

The flask is fitted with electrodes.

Now Khare discharges them.

This is meant to reproduce
the effect of lightning

or other energy surges
on Titan's atmosphere.

It's about 10 hours since the
start of the experiment.

A reddish-brown substance
has become visible

inside the flask.

Khare claims that this is
the very same substance

as the haze enveloping Titan.

So what happened inside that glass vessel?

First off, the electrical
surges split apart

the molecules of nitrogen and the methane.

Their atoms recombine with carbon

and other atoms in all sorts of ways

forming a variety of new organic compounds.

Analysis showed that some 200
types of organic compounds

had been created in this experiment.

Organic compounds are the materials

out of which our own bodies are made.

They are the building blocks of life.

It was thanks to Khare's
work that Titan came

to be considered one of
the celestial objects

on which life might exist.

The Cassini orbiter's close-up
observations of Titan

have come some 30 years
after Khare's experiments.

Will they confirm that
Titan's hazy atmosphere

has in fact given rise to organics?

The INMS is a device that
measures molecular mass.

Cassini has used it to
determine the composition

of Titan's atmosphere.

Cassini's data were streamed back to Earth,

where they were analyzed by
Hunter Waite and his colleagues.

Waite led the team that designed
the INMS instrument package

carried aboard Cassini.

Waite's lab was able to reproduce
and confirm Cassini's data

by utilizing the same INMS system.

They could then analyze
accurately whatever molecules

or compounds the instrument had detected.

The results were astonishing.

Rendered in the form of a chart,

each of the different molecules
identified by Cassini

is represented by its own colored area.

Various organic substances were created

in Titans' atmostphere,

ranging from ones with a single carbon atom

to more complex ones with
six or seven carbon atoms.

When Cassini sent back data,

we found out that the upper atmosphere

was much more relevant
than we ever thought,

that most of the chemistry
seemed to be going on

in the upper atmosphere,

that very large molecules
were being created

in the upper atmosphere way
beyond our expectations.

Titan is one of the best

organic factories in the solar system.

Bathed in ultraviolet and cosmic rays,

Titan's upper atmosphere
is continually engaged

in converting nitrogen and methane

into a rich array of organic compounds.

As these compounds collect
in the lower atmosphere,

they produce Titan's famous orange haze.

Finally, they are precipitated
with methane rain

onto the surface as well.

It's been four billion years

since Titan's atmosphere was formed.

During that time, it is estimated

the organic settling onto the surface

have created a layer
dozens of meters thick.

The dunes discovered near Titan's equator

are thought to be a large
deposit of these organics.

Now on Titan, the sand is made,

we think, from organic material.

And we think that material comes down

and gets built up into sand-size particles

that are then accumulated by the wind

to form dunes much like these.

Amidst this accumulation of organics

on Titan's surface,

are substances of vital importance
to the emergence of life.

That finding was made by a young researcher

with a specialty in organic
chemistry, Sarah Hörst.

Hörst has undertaken a minute examination

of the organic compounds
discovered in Titan's atmosphere.

She's written her own
computer program to do that.

Based on Cassini's observational data,

she faithfully simulates the composition

of Titan's atmosphere and
produces the same organics.

Next, she uses her computer program

to determine the molecular
structure of every compound.

These peaks right here are
the masses of the ions

in the mass spectrum data,

and then it's the number
of carbon, nitrogen,

oxygen, and hydrogen in
each of those peaks.

So then what the code
does is it goes through

and compares this information
to a list that I've given it

of all of the amino acids and nucleobases

that we're looking at.

Here, we have 136, we have the
molecular formula of adenine

which is five carbons that matches,

it has five nitrogens that matches,

no oxygen, and then five hydrogens.

So we know from this that we
have the molecular formula

of adenine in this sample.

Genetic information for all life on Earth

is encoded in DNA.

Adenine is one of its four major components

or nucleobases.

And all four had been produced
in Hörst's experiments.

If these nucleobases combine

in such a way that they create DNA,

then a huge step forward
will have been taken

towards life itself.

With this discovery,
speculation mounted that Titan

might actually be capable
of harboring life.

Life on Titan?

It may, in fact, already exist.

If it does, what
would it look like?

The search is on for the answer.

Trinidad and Tobago form an island country

in the Southern Caribbean.

They have a population
of about 1.3 million.

They also have one of the most
unusual lakes in the world.

It's called Pitch Lake.

It contains not water,

but naturally-occurring asphalt.

It bubbles up from an oil
field that lies underneath,

creating a lake of asphalt
that's 40 hectares in area

and 80 meters deep.

Strangely enough,

Pitch Lake is the side
of fieldwork being done

by astrobiologist, Dirk Schulze-Makuch.

He thinks that Titan is the best candidate

for the location of extraterrestrial life.

He's come here to try to envision

what lifeforms on Titan might be like.

Asphalt, like methane,

is a hydrocarbon comprised
entirely of carbon and hydrogen.

You wouldn't think this was a
substance that harbors life.

But Schulze-Makuch says it actually does

contain microorganisms.

This is one of the few environments

where it's similar to Saturn's moon, Titan,

where we know that we have
hydrocarbon lakes on the surface.

Obviously, Titan is very cold,

so it's still different from over here.

But we do have the liquid
methane and ethane

which are also hydrocarbons.

And if we can find out
what kind of organisms

are living here in the asphalt lake

and how they adapt to
living in the hydrocarbons,

we think we can get some ideas to how life

could operate on a moon like Titan.

Asphalt contains almost no water.

Did you say that there's microbes in there?

Yes, there's microbial organisms
in the liquid asphalt.

In this thing?

In this thing, yeah.

Like maybe one, two?

Millions.

Millions?
Yeah.

Genetic analysis identified
some 600 new types

of microorganisms living in the asphalt.

Most are archaebacteria

related to the primordial microorganisms

that live in extreme environments.

So for them, actually,
it's a great environment,

it's a great food source,

and basically, a
never-running-out food source

because it's getting supply
from deep down there.

On Earth, there are microorganisms

that can use asphalt for
sustenance instead of water.

Schulze-Makuch is convinced
that in Titan's lakes,

there must be lifeforms
that exploit methane

in a similar way.

Another scientist, Chris McKay,

holds that the methane lakes on Titan

contain creatures so unlike Earth creatures

that they exceed our wildest imaginations.

Think of fish living in water

and ask them to imagine a
bird which lives in air.

They probably can't conceive of an organism

that is so much denser than
the medium in which it lives.

Fish move through water by floating,

so they would imagine a
bird must float in the air.

We humans live in an
environment called Earth.

We produce energy by causing oxygen

and organic matter to interact.

That is our lifestyle.

But McKay is arguing that on Titan,

lifeforms would be based
on a Titan lifestyle

that makes use of what's
available on Titan.

Titan's atmosphere
contains minuscule amounts

of hydrogen and acetylene.

McKay thinks that there
may be lifeforms on Titan

that exist by deriving
energy from the interaction

of those two substances
in a methane environment.

McKay says that life could very
well already exist on Titan.

So instead of being small and round,

I would guess that a
single-celled organism on Titan

might be big and flat like a sheet of paper

to maximize its contact with the nutrients

in this thin soup.

It's living in an environment
where there's not a lot

of food, so it's gotta access
the food with big area

and maybe on this area,
it has active molecules.

So it's like a big flat sheet of paper

with little traps on it to collect food.

To that lifeform,

that will be the normal environment.

It was not until the 21st century

that Titan's thick veil was lifted.

Now that we're getting a closer look,

what new discoveries await?

So Titan gives us a whole
new set of possibilities

and there are, for sure, perhaps hundreds,

maybe millions of worlds like
Titan around other stars.

Do those have life?

Titan maybe can give us some clues.

If life is found on Titan,

humanity's view of the
universe will surely change.

The best place for me, in terms of finding

another type of life, would be Titan.

Because if we find it on Titan,

then we know that it really is two.

It's not the same as us.

When we go to Mars, we
may find life on Mars

but we won't be sure that it's
not the same life as Earth.

So my best hope would be
we find life on Titan

'cause then I know that we found

two completely different types of life.

Then I can go on to some
other science problem.

There is only one body in space

that we know of other than Earth,

that has a thick atmosphere and lakes.

Titan.

If life is found on Titan,

it will instantly increase the possibility

that life exists in many other places

in the universe as well.

We may not be alone in the universe.

We may have many comrades.

The quest to find out for sure continues.

Clues to solving that great mystery

lie hidden on Titan.