All language subtitles for How the Universe Works s01e06 Extreme Planets.eng

It used to be
the only planets we knew about

were the ones
that orbit our Sun.

But now we've discovered
rocky worlds

and gas giants
orbiting other stars.

They tell an amazing story.

The early history
of these planets

would have been very,
very violent.

Planets are made
everywhere in the same way.

They form from the dust
and debris

left over
from the birth of stars.

So, if they're all made
the same way,

what makes them all
so different?

The universe
is full of galaxies...

...gas clouds...

stars...

And planets, as it turns out.

Our solar system
has eight planets.

But we now know
they're a tiny group,

compared to the huge
cosmic family of planets

across the galaxy.

It's an extraordinary
moment in scientific history...

To know for sure

that there are other
planetary systems out there.

They're very common.

And out of the 200 billion stars
in our Milky Way galaxy,

there are surely dozens of
billions of planets out there.

In 2009, NASA launched
the Kepler Space Telescope

on a six-year mission

to find new planets
orbiting other stars.

So far, astronomers
have found over 400.

Some are colossal balls
of churning gas

five times the size of Jupiter.

Others are huge, rocky worlds
many times larger than Earth.

Some follow wild,
erratic orbits,

so close to a star
they're burning up.

One thing is clear...
no two planets are the same.

Each is one of a kind.

But most of these new planets
are far away and hard to study.

Most of what we know
about how planets work

comes from the eight
that orbit our own star.

Our own planets
come in two main types.

There are four rocky planets
in the inner solar system...

Mercury...

Venus...

Earth...

And Mars.

And in the outer solar system,

there are four giant
gas planets...

Jupiter...

Saturn...

Uranus...

And Neptune.

Each of the eight planets
is distinct and very different.

Their unique personalities
began to form

at the birth of our solar system
4.6 billion years ago.

When the Sun ignited,

it left behind a huge cloud
of gas and dust.

All eight planets...

the inner rocky
and the outer gas planets...

came from this cloud
of cosmic debris.

The planets
in our solar system

are all made
from the same stuff.

They're made from the same
cloud of gas and dust,

but they formed under
very different conditions.

Some of them formed
in close to the Sun,

where it was much hotter,

some much farther away,
where it was much colder.

And because the conditions were
so different, the end result,

the product of their formation,
was different, as well.

So, you start
the solar system, in my view,

with a pretty
homogeneous mix of silicates

and water vapor and hydrogen,
lots of hydrogen,

and methane and other elements.

These elements
in the dust cloud

are like ingredients in a cake.

They cook differently,
depending on the combination

of the ingredients
and the temperature of the oven.

And just like with the
cake, you'd mix the ingredients.

And then you'd put it
in the oven and bake it,

and it would change.

And so this is kind of what
happened in the solar system.

Overall, the planet cooks
in a slightly different way,

depending on how close
it is to the Sun.

Close in,
where it's hot,

the Sun burns off gases
and boils away water.

Only materials that stay solid
at high temperatures,

like metals and rock,
can survive,

which is why only rocky planets
form close to the Sun.

Move farther away
from the heat of the Sun,

and you get different kinds
of planets cooking.

But it's the ingredients
in the cloud

that determine precisely
what kinds of planets will form.

Well, depending on the type of
cloud a solar system forms in,

you could have solar systems
that don't have rocky planets

because it was just
too poor in the materials

to build something
like the Earth,

and instead you could end up
with more gas giants

and no rocky planets at all.

If you want rocky planets,

you need a cloud
full of metals and rock.

Next step... turn the heat down.

As it cools down,
some of the elements in there

that have a high boiling point
start to condense out as solids.

And you can get these very tiny
little mineral grains forming.

These tiny mineral grains

are the seeds
of a new rocky planet.

Over time,
they start to stick together.

You would have one dust molecule
and another dust molecule,

and they would basically slam
into each other

and become one
slightly bigger dust molecule.

And they would pick up
more and more and more.

This process
is called accretion.

As these things got bigger,
they became basically rocks.

Then rocks slam into
other rocks and form boulders.

Boulders smash together
to form bigger boulders.

Eventually,
you've got something big enough

that it's gravity
was strong enough

that it could
start drawing material in.

So, instead of
just slamming into material

and gaining mass that way,

it was actually
actively pulling material in.

In our own solar system,

there were many growing infant
planets at first... maybe 100.

Most of them didn't make it.

If you go to the Asteroid Belt

and look at the asteroid
4 Vesta,

that is a good indicator of
how big a rocky planet has to be

before it can pull itself
into a spherical shape.

Vesta is only
329 miles across,

not quite big enough
to become a sphere.

For a growing planet
to become round,

it has to reach
500 miles across.

Then it has enough gravity
to crush it into a sphere.

Any smaller,
and it stays an irregular shape.

As round infant planets
keep eating up stuff,

each collision
makes them hotter and hotter,

until they start to melt.

Now gravity begins to separate
the heavy stuff from the light.

Lighter materials tend
to float up into crusty film,

and the heavier materials...
many of the metals...

falling down and forming

a much denser core
at the center of the planet.

The young planets

are finally beginning
to look like planets.

But now they have to
survive a period

of violence and destruction...

...a brutal phase
that determines

which planets will live
and which planets will die.

After the birth of the Sun,

our eight planets all evolved

from the same cloud
of dust and gas,

and yet they ended up
completely different.

There was no real blueprint
for each of the newborn planets.

They did obey the laws
of physics and chemistry,

but the most important things
happened by pure chance.

4.5 billion years ago,

around 100 baby planets
circled our Sun.

It turned
into a demolition derby.

Planet hit planet.
Most were destroyed.

The early history
of these planets

would have been very,
very violent,

with lots of these impacts
taking place

in the final stages
of the growth of each planet.

As these impacts took place,
as objects ran into each other,

certain objects began to grow

at the expense of all the others
in this swarm of planetesimals.

And these planets, these things
that would become planets,

grew and grew,
and as they got bigger,

they swept up all the smaller
planetesimals around them,

the consequence on the surface
of that protoplanet

being an enormous amount
of bombardment

by debris from space.

When it was over,

all that was left were four
very different rocky planets.

Each planet's impact
history left its stamp,

and that's why they're all
so different from each other.

Mars is a frozen wasteland.

Earth flows with liquid water.

Venus is a volcanic hellhole.

And Mercury is tiny,
bleak, and super hot,

the result
of a monster collision.

Mercury, for example,

is extremely dense
and has a very thin crust.

So, it's possible it started off
as a bigger planet.

And then something
hit it at an angle,

and it sheared off
the lighter-weight crust,

leaving only the dense core.

The young Earth
also took a big hit.

Sometime late
in its development,

the Earth was impacted
by another object

that ripped debris
out of the Earth's mantle...

...which then went into orbit
around the Earth

and re-accumulated
to form what is now the Moon.

There's also evidence

that something
crashed into Mars.

The northern hemisphere has a
thinner crust than the southern.

A theory that has emerged
for how this happened

is that early
in the planet's history,

the northern hemisphere of Mars
was whacked by some object

that blasted a lot
of the crust off of it.

And that crust re-accumulated
on the southern half of Mars.

All these collisions
did two things.

They cut down the number
of surviving infant planets.

And they brought more
ingredients to the survivors.

If you had a collision

with something
that was metal-rich,

those chunks
would tend to descend down

into what was
becoming the core...

...where if you collided
with something light or icy,

they would
tend to just float about

and form part
of the crust instead.

The four rocky planets
close to the Sun

were almost complete.

They had a solid, hot-iron core

surrounded
by a layer of liquid iron,

all wrapped in a jacket
of molten rock.

Above that,
an outer surface crust.

These rocky planets all formed
in the same basic way,

from the same basic stuff.

But each of them
was very different...

Different sizes
and very different destinies.

Space may look empty,
but it's not.

It's full of stuff
blown out of the Sun.

The Sun generates
powerful magnetic fields

that rise above the surface
in giant loops.

When they clash, it triggers
a storm of super hot,

highly charged particles
blasting out into space.

It's called the solar wind.

Astronauts in space
can see it...

But only
when they close their eyes.

Occasionally, you see a little
flash with your eyes shut.

And that is
an energetic particle

coming through your head

and interacting with the fluid
inside your eye,

and it makes
a little light flash.

And you see these
every couple of minutes or so

that you're awake
with your eyes shut.

If the astronauts were exposed

to a lot more of the solar wind,
it could be a killer.

During the Apollo program,

in between
two of the Moon missions,

there was an outburst on the Sun

that would have
killed the astronauts

if they had been there.

So, space radiation
is a serious business.

But here on Earth,

the solar wind
isn't much of a threat

because we have
an invisible protective shield,

a magnetic field
generated by the planet's core.

The very center of the Earth
is the solid inner core.

It's a hard, iron,
crystalline ball.

Then there's a thick layer
of liquid iron,

which is convecting
churning motions,

which give rise
to the magnetic field.

Well, that's the theory.

To prove that an iron core
can generate a magnetic shield,

scientists built
their own planet in a lab.

This 10-foot, 26-ton sphere

simulates conditions
deep inside the Earth.

A metal ball in the center
acts as the planet's inner core.

Liquid sodium spins around it
at 90 miles an hour,

imitating
the effects of molten metal

spinning
around the Earth's core.

We built this experiment to
try to generate a magnetic field

to attempt to understand why
the Earth has a magnetic field

and why other planets
do not have magnetic fields.

It works like
the generator in your car,

where rotating coils of wire
produce electricity.

In the experiment, liquid sodium
churns around the core

and generates a magnetic field.

It's very much like
an electrical generator.

You have motion that is able to

generate magnetic fields by
turning the energy, the motion,

into magnetic energy.

The same thing happens
deep inside the Earth.

As the Earth spins,
the hot liquid metal

flows around the solid core,
transforming its energy

into a magnetic field
that emerges from the poles.

It protects the planet's
atmosphere from the solar wind.

And if the planet
has a magnetic field,

that solar wind will be diverted

around the planet
by the magnetic field.

The magnetic field

deflects the solar wind
around the planet,

protecting the atmosphere and
everything on Earth's surface.

Sometimes big storms
of solar radiation

will mix it up
with the magnetic field.

Then we get big light shows
over the poles... the auroras.

Without a magnetic force field,

the solar wind would blast away
Earth's atmosphere and water...

Leaving a dead, arid planet...

A lot like Mars.

Mars formed just like Earth.

But today it's cold and dry,
with little atmosphere.

So, why are the two planets
now so different?

In 2004, NASA sent two robot
explorers to Mars to find out.

The rovers,
named Spirit and Opportunity,

explored
miles of the Martian surface.

They confirmed that Mars
is a dry and hostile desert,

with only 1%
the atmosphere of Earth.

But they did find evidence
of water in the past.

Mars was not always a desert.

We have found
compelling evidence

that water was once beneath the
surface, came to the surface,

and evaporated away.

We also see in a few places
ripples preserved,

of the sort that are formed
when water flows over sand.

So, not only did water exist
below the surface.

It had flowed
across the surface.

If Mars had water once,

it probably also
had a thick atmosphere.

So what happened?

We can see that Mars once
had active volcanoes.

So, it had a hot interior
at some point.

And because it was made
of the same stuff as Earth,

it would have
had a hot-iron core,

surrounded by liquid metal
at its center.

So, it should have
had a magnetic field, too.

The question is...
where did it go?

Early in the planet's history,

Mars apparently
had a strong magnetic field.

And it was probably caused in
the same way as it is on Earth.

But Mars is a smaller planet
than Earth.

It's gonna lose its heat
more rapidly as a consequence.

And what that means is that
liquid core can freeze solid.

Freeze the core solid,
the convection will stop.

The convection stops,
the magnetic field goes away.

As the magnetic shield died,

the solar wind
blasted away the atmosphere,

and the water evaporated.

Mars became a cold,
barren planet.

Mars, Earth, Venus, and
Mercury... the rocky planets...

all formed within
150 million miles of the Sun.

But four times farther out,

the Sun baked
a very different kind of planet.

They're gigantic,
they're made of gas,

and these monsters
have no solid surfaces at all.

So far,
astronomers have discovered

over 400 new planets orbiting
in far-off solar systems.

Nearly all of them
are gigantic and made of gas.

We have four
of these so-called gas giants

in our own solar system.

Jupiter, Saturn,
Uranus, Neptune...

Which all have these very thick,

very soupy atmospheres,
lots of hydrogen,

lots of helium, lots of methane.

Why are these
outer four made of gas

when the inner ones are rocky?

It all has to do with location.

Out here, 500 million miles
from the Sun, it's very cold.

At the start of the solar
system, there was some dust,

but mostly gas and water,
frozen in ice grains.

Where the giant planets
started to form,

it was cold enough
to get solid snow.

And we think we were able to
make ice snowflakes,

and these things
were able to clump together

to form the cores
of the giant planets.

And we think that's maybe

why the giant planets
got to be so big.

There was so much ice
and gas their cores grew huge,

around 10 times larger
than the Earth.

These giant cores
generated a lot of gravity.

They had so much pulling power,

they sucked in
all the surrounding gas

and built up thick,
soupy atmospheres

tens of thousands of miles deep.

The larger they got,
the more gravity they generated.

More and more dust and debris

got pulled in
towards the planets,

and this became the building
blocks of their moons.

Jupiter and Saturn
have over 60 moons each.

The gas planets have another
special feature... rings.

Saturn is unique
among the planets

in that it has
this gorgeous ring system.

It turns out Jupiter
and Uranus and Neptune...

they have ring systems, as well,

but they're really weak
and pathetic

and extremely hard to detect.

But they are there.

All four of the gas giants
have rings,

but Saturn's
are the most obvious.

From a distance, Saturn's rings
look like a single flat disk.

However, they're actually
thousands of separate ringlets,

each only a few miles wide.

When the Cassini Probe
flew past,

it detected billions of pieces
of ice and cosmic rubble

orbiting inside the rings

at speeds of up
to 50,000 miles an hour.

These bits of ice and rock

constantly
crash into each other.

Some grow into tiny moons.
Others smash apart.

But they never form
into larger moons

because Saturn's immense
gravity tears them apart.

Scientists are only
just beginning to figure out

how the rings
formed in the first place.

The theory goes like this...

a comet smashed into a moon
and knocked it out of its orbit

and closer to the planet.

Saturn's gravity
tore it to pieces.

And all of that debris

got trapped in rings
around the planet.

But the real mysteries of the
gas giants lie deep inside them,

tens of thousands of miles
beneath the clouds.

This is where
the real action is.

It's a place so extreme it
challenges the laws of nature.

Most of the new planets

we're finding around
distant stars are gas giants.

They're so huge
they make Jupiter look small.

But what goes on inside
all gas giant planets,

both in our solar system and
way out there, is a mystery.

We know Jupiter's
dense atmosphere

is 40,000 miles deep,

and we can see
high-speed bands of gas

creating violent storms
that rage across its surface.

But what we don't know
is what's going on deep inside,

far beneath the storms.

To find out, NASA launched
the spacecraft Galileo

on a 14-year mission to Jupiter.

Woman:2, 1.

We have ignition
and lift-off of Atlantis

and the Galileo spacecraft
bound for Jupiter.

December 7, 1995.

Galileo dropped a probe
that dove

into Jupiter's atmosphere
at 160,000 miles an hour.

Parachutes slowed it down

as it dropped
through the thick atmosphere.

It detected lightning
in the clouds

and winds of 450 miles an hour.

The probe transmitted data
back to Earth for 58 minutes.

So, people have asked me,

"What happened to the Galileo
probe that we dropped in?"

It didn't hit anything.

It just fell continually
into the Jupiter environment,

and the pressure increased
and increased and increased.

As it descended,
it recorded pressures

23 times greater than on Earth

and temperatures
of over 300 degrees.

When you're in
the gas-giant environment

and you go deeper and deeper
into this hydrogen soup

that has no solid surface,

it nevertheless
can have a tremendous weight.

And so eventually
you would be crushed

by the overlying weight
of the material that's there.

Even though the probe
descended for only 124 miles

before it was crushed,

it gave scientists
a glimpse of Jupiter's interior.

But the dark heart of the planet
still remains a mystery.

Like some rocky planets,

the gas giants
have a magnetic field, too.

But these are off the charts.

Jupiter's magnetic field

is 20,000 times
more powerful than Earth's

and so huge it extends
all the way to Saturn,

more than
400 million miles away.

Like on Earth, the magnetic
field deflects the solar wind

and protects
Jupiter's atmosphere.

When scientists studied
Jupiter's magnetic field,

they discovered it was
affecting Jupiter's moons.

The volcanic moon lo orbits only
217,000 miles from the planet.

Io's volcanoes blast
a ton of gas and dust

into space every second.

And Jupiter's magnetic field
supercharges it,

creating powerful belts
of radiation.

And that makes
the vicinity of Jupiter

very active
in many different ways.

If you point
a radio antenna at Jupiter,

one can hear
all sorts of interactions

happening between the planets
and the magnetic field.

This is the sound
of Jupiter's magnetic field.

Jupiter and Saturn don't need
the solar wind to make auroras.

They have huge magnetic fields
that create their own.

The Chandra Space Telescope

took these images
of Jupiter's auroras.

And NASA's Cassini Probe

took these beautiful pictures
of auroras on Saturn.

These auroras are proof

that gas planets
have magnetic fields, too.

But how do gas planets
generate magnetic fields?

On Earth,
a super-hot liquid metal

spinning around the planet's
solid-iron core does the job.

Gas planets probably
do roughly the same thing.

But gas planets
don't have hot-iron cores.

They formed around frozen cores
of dust and ice.

So, exactly what's going on
deep inside is a mystery.

At the very deepest interior
of Jupiter,

we really don't understand

what composes
those deep interior states.

So, it could be
that the very center of Jupiter

has a solid core.

Or it could actually
just be still fluid.

We may never find out.

No probe could ever
make the 44,000-mile journey

to the planet's center
to investigate.

Galileo was crushed

before it got anywhere
near the planet's core.

So, now scientists are
recreating Jupiter's interior

right here in a lab on Earth.

Here at
the National Ignition Facility

in Livermore, California,

they're simulating
Jupiter's core

using the world's
most powerful laser.

This facility is really designed

to compress hydrogen to extreme
densities and temperatures.

Inside Jupiter,
extreme pressures are created

by the weight of 40,000 miles
of hydrogen gas

crushing down on the core.

In the lab, it's done
by focusing 192 laser beams

on a tiny sample of hydrogen.

As the pressure in the sample

reaches over a million times
the surface pressure on Earth,

the hydrogen
turns into a liquid.

But when it reaches
tens of millions

of times the pressure...
more like at Jupiter's core...

something really weird
happens to the hydrogen.

The pressure is so great

that it actually
re-arranges the hydrogen,

which is a very basic molecule,
until it is able to conduct.

So it changes the structure
of H2 into a metallic form.

Scientists think

this is what's happening
inside Jupiter...

pressure and heat

have transformed the planet's
core into metallic hydrogen.

Jupiter's metallic core works
like the iron core in the Earth.

It generates the gas planet's
gigantic magnetic field.

Gravity and heat
shape how planets evolve,

from their inner cores
to their outer atmospheres.

They're the great creative
forces in planet building.

But there's another ingredient

that has a lot to do
with how planets turn out.

And that ingredient is water.

Planets
may seem fixed and unchanging,

but they never stop evolving.

In our own solar system,

one lost its atmosphere
and became a barren wasteland.

Another heated up and
became the planet from hell.

Planet Earth has changed,
as well,

and the game changer...
was water.

When you look at Earth from
space, you see a lot of water.

We are the Blue Planet,
after all.

So, it must be really wet,
right?

It looks at first glance
that our Earth...

of course,
covered 3/4 by oceans...

it's a very water-rich world.

Not true.

The Earth, by mass,
is only 0.06% water.

There's some water on the
surface in the form of oceans,

some water
trapped in the mantle.

But actually, the Earth
is a relatively dry rock.

All of the inner rocky planets

formed very close to the Sun,
so they started off dry.

Any water they might have had
evaporated away

or was blown away by impacts.

These massive collisions
that formed the Earth

were so energetic...

That any water
that had been here

would have been vaporized
and lost from the Earth.

So, where did Earth

get all the new water
we have today?

It moved here.

When you look farther out

and you look at Jupiter,
Saturn, Uranus, and Neptune,

those planets have
enormous amounts of water

locked up inside them.

And even more dramatically
are the moons.

The moons of Jupiter, Saturn,
Uranus, and Neptune

are at least 50% water.

There was
a lot of water out there.

So, how did some of it
get to planet Earth?

And the answer
almost certainly is

that left farther out
in our solar system

were some asteroids
and some comets,

far enough from the Sun that
they could retain their water.

Millions of these
watery comets and asteroids

came flying
into the inner solar system.

And some of them
smashed into Earth.

Over the eons,
the Earth acquired the water

that had been
a part of the asteroids,

and that indeed
makes up the mass of water

that nearly
covers the Earth today.

But the amount
of water that was delivered?

That was the luck of the draw.

Couldn't it have
been the case that the Earth

would have acquired maybe
half as much water as it did?

If so, the Earth would be
nearly dry on its surface,

if not completely dry,
the sponge of the interior

soaking up
the rest of the water.

No surface water
would have meant no life.

And what about too much water?

We would be a water world,
the oceans much deeper,

covering the continents,
even Mt. Everest.

And so you can ask, then, "If
the Earth were covered by water,

only having twice as much
as it currently has,

would we have had a planet

that was suitable
for technological life?"

Technology requires dry land.

And it's quite likely
that the precise amount of water

that the Earth
just happens to have

has allowed a technological
species like we homo sapiens

to spring forth.

The world as we know it

exists because a blizzard
of comets and asteroids

delivered
just the right amount of water

about four billion years ago.

And just maybe the same thing
is happening right now

somewhere else in the universe.

One thing's for sure... there
is plenty of water out there.

Hydrogen, the most
common atom in the universe,

and o xygen, one of the next most
common atoms in the universe...

H2O is certainly going to be
a very popular molecule...

and indeed it is...
within our universe.

So, water is
everywhere in the universe,

and we're discovering
that planets are, too.

But we still haven't found

another planet
with liquid water.

Scientists have discovered
more than 400 new planets.

None of them
look like our world.

What we have
not yet found is a planet

that is about
the same size and mass

and chemical composition
as the Earth,

orbiting another star.

So, it remains an extraordinary
holy grail for humanity

to find other abodes
that remind us of home.

But we'll keep looking.

We know that there
are around 200 billion stars

in our galaxy alone.

And as many as 40 billion
of them could have planets.

We're still hopeful

that when we discover
terrestrial-style planets

that will help us tremendously
in understanding

how our own inner-solar-system
planets and the Earth

evolved in comparison to
the outer-solar-system planets.

We are entering into
what is gonna be thought of

in the future as the Golden Age
of planetary discovery.

We will really for the first
time begin to truly understand

the actual diversity
that lies out there.

I think it's gonna be
a fantastically exciting time.

Planets form

according to the laws of physics
and chemistry.

What they become... that has
a lot more to do with luck.

Many scientists believe
it's only a matter of time

before we find
another planet like Earth,

one that formed
from the same ingredients,

in the right place, with just
the right amount of water.

One thing's for sure...

there are billions
of planets out there

waiting to be discovered.

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