All language subtitles for How the Universe Works - 1X07 Solar Systems

Our solar system...

8 planets and over 300 moons

circling the Sun like clockwork.

But it didn't start that way.

Our solar system
has a long history of violence.

The solar system we see today

is really just the final
survivors of the early chaos.

And in the future,
that chaos will return.

The entire house of cards
that is our solar system

will completely fall apart.

From start to finish,

this is how solar systems work.

There are billions of stars
in the Milky Way galaxy.

One of them is our Sun.

And around the Sun orbits
a system of planets and moons...

a solar system.

Our solar system is clearly
a precious planetary system.

And it begs the question,

are there other
planetary systems like ours

orbiting other stars?

To find out, Marcy
scans the skies with the Keck...

one of the world's largest
optical telescopes.

Perched at 14,000 feet,
on top of Mauna Kea in Hawaii,

it hunts for new,
distant solar systems.

The marvelous reality is
that our own Milky Way galaxy

contains some
200 billion stars or so,

and many of those stars have
their own planetary systems.

Our solar system,
with its eight major planets,

is not alone.

There are other
brethren planetary systems

out there by the billions.

Of course, astronomers
hope to find another solar system

with a planet like Earth,
and they're off to a good start.

So far, Marcy
and other astronomers

have discovered over 360 stars
with orbiting planets.

One of the exciting
discoveries that we've made

is that stars
tend to be orbited

not just by one planet

but usually two, three, four,
or a multitude of planets.

Planets come in families,

not unlike the family of planets

we enjoy here
around our own Sun.

For the first time,

scientists can study them
in some detail.

We can actually observe
how planets heat up

as they go around their sun.

For example, we actually saw
that one planet

got hotter and colder
as it orbited its star.

And we realized
that we were actually seeing

the night side of the planet

and then the day side
of the planet.

That was
the temperature difference.

We were observing sunrise
and sunset on a planet

in another solar system.

But that planet
is nothing like Earth,

and most of these newly
discovered solar systems

are nothing like our own.

Their planets are huge...
much bigger than Jupiter.

Some follow wild orbits,

some orbit
in the opposite direction,

and some shoot billions
of miles out into space,

then dive back
toward their star.

A few orbit so close
to the star,

their surfaces vaporize.

It's bizarre, at the least,
if not completely frightening.

Planetary systems
offer a wide diversity

of different architectures,
sizes,

masses of the planets,
and so on,

rendering our solar system
just one type

of a planetary system
out of thousands.

It could be that each and
every solar system is a one-of-a-kind.

But they all have one thing
in common...

each one begins with a star.

First, a star is born in a cloud
of dust and gas called a nebula.

This is the Eagle nebula.

These are the Pillars
of Creation.

And this is
the Horsehead nebula,

an enormous star nursery.

What scientists have been
trying to figure out

is what triggers
the star-making process.

One possibility is that
a nearby supernova explosion

took place...

...and rammed into

this otherwise innocuous
molecular cloud...

...smushing it, smashing it,

compressing it down so that
gravity could take over.

Once gravity takes over,

the cloud begins to shrink,

sucking in more and more gas
into a giant, spinning disk.

Gravity at the center
crushes everything

into a dense, superhot ball...

...that gets hotter and hotter.

Suddenly,
atoms in the gas begin to fuse,

and the star ignites.

The leftover dust and debris

forms a disk spinning around
the new star.

It contains the seeds

of planets, moons, comets,

and asteroids.

In 2001,
the Hubble space telescope

was scanning the Orion nebula

and took this image
of a young star

surrounded by
one of these disks.

It's a picture of
a solar system being born.

Whenever I look at these
beautiful pictures of nebulae,

the thing that really gets me

is that these are baby pictures
of our own solar system.

We looked like that once.

These fuzzy images
have opened the door

to understanding
how planetary systems form.

We have this
marvelous first-ever tool

by which we can take pictures
of planets

caught in the act of formation.

It's quite
a marvelous opportunity

for us to see the planets
around other stars forming,

thereby giving us a glimpse

as to how our own solar system
must surely have formed.

Scientists understood
where stars come from

but not how planets grow
from the disk of gas and dust.

The answer was discovered
by accident

aboard the International
Space Station.

Astronaut Don Pettit

was experimenting with grains
of sugar and salt

in the weightlessness of space.

Stanley Love was watching
from Mission Control

when Pettit stumbled
onto the process

of how planets form
from cosmic dust.

Well, one of Don's

Saturday-morning
science projects

was to take the bags
that we store drinks in

and he put other stuff in it,
like salt and sugar,

and there was one bag that he
just left the coffee powder in.

Then he inflated the bags,

and with these particles
in them,

noticed that the particles would
just clump up immediately.

They make a little dust bunny.

We'll be spending
some time watching that.

I said,
"Don, this is incredible!

You've just solved a 40-year-old
problem in planetary science!"

Astronaut Pettit
had discovered something big.

In the zero gravity of space,

particles of dust
don't float apart,

they clump together.

This is how mighty planets
are made from cosmic dust.

The dust particles would collide
and stick and grow

into ever larger dust particles

and eventually rocks
and eventually boulders.

The bigger the boulder,

the more gravity it has.

It begins to eat up everything
around it and grows bigger.

It becomes larger, heavier,

and consumes bigger
and bigger rocks.

Eventually, some of these rocks
grow into planets.

This is what happened
in our solar system

4.6 billion years ago.

There were
about 100 young planets

all orbiting the new Sun.

Collisions were inevitable.

At the beginning,
solar systems are violent.

Ours was no different.

It began with about
100 small, new planets.

So, how did it go
from 100 small planets

to the 8 major planets of today?

We got the answer

by studying the evolution
of other solar systems.

We see solar systems
forming planets,

and all of a sudden, they had
these giant disks around them.

Those disks must be
from huge collisions.

If planets are smashing
together in other systems,

they probably smashed together
in our own.

We now know that
all solar systems do this

before they settle down.

It's the way they're built.

The nice, neat, orderly
solar system that we see today

has not always been the case.

In the early days... a few
million years, basically,

after the planets
started forming...

there were dozens, maybe even
hundreds of these young planets

that were bouncing around
the solar system.

They would smash
into each other.

Sometimes they would collect
and get to be bigger planets.

Sometimes they would smash
each other

and turn into little bits.

There was heavy traffic
in the new solar system,

objects of all sizes.

They were bound to collide.

Some of the planets
grew larger,

and so did the collisions.

I like to try to imagine
what it would have been like

to actually stand
on the early Earth

and look up into the night sky.

Things would have looked
different.

Planet hit planet.

Only the largest survive.

The rest are smashed to pieces.

Something very large struck
the young planet Mercury.

It blew the crust off

and left behind
just the iron core.

And the young planet Earth
did not escape, either.

A planet-sized object

slammed into the Earth
off-center

and blew a huge amount of
the Earth's crust into space.

The debris circled
around the Earth...

And eventually coalesced
to become the moon.

This demolition derby
raged for 500 million years.

What we see now...

Mars and Earth and Mercury
and Venus...

these planets
in the inner solar system...

they're the survivors.

They're the ones who lived
through these giant impacts.

Debris
from smashed infant planets

ended up in the Asteroid Belt...

a junkyard of rocky,
leftover planet parts.

Most of the big impacts
happened

in the inner solar system.

But one of
the outer planets, Uranus,

was also hit
and knocked on its side.

A mystery, since the outer
planets formed mostly from gas

and largely escaped the violence
of the inner solar system.

These rocky cores formed.
The gas accumulated around them.

This process actually happened
very rapidly,

in astronomical terms,
in only about a million years.

And those are the giant planets
we see today.

Beyond the gas giants,
Jupiter and Saturn,

are Uranus and Neptune.

These two are made
of gas and ice.

And beyond them
lies the Kuiper Belt,

a band of orbiting icy rocks
and dwarf planets.

We used to think that one
Kuiper Belt object, Pluto,

was the ninth planet.

We've since decided that Pluto
is, in fact, a dwarf planet...

one of many orbiting
more than 3 billion miles

from the Sun.

There are millions
of these things out there.

They're so far away and so faint
that they're hard to see.

These are left over
from the formation

of the solar system itself.

The Kuiper Belt marks
the edge of the Sun's influence.

There is no warmth
and not much light

way out here.

But the Kuiper Belt is not
the end of our solar system.

A shell of trillions
of icy objects,

called the Oort Cloud,
is even further out.

The Oort Cloud is so far away,

light from the Sun
takes a full year to reach it.

From the cold outer edge
to the hot star at the center,

our solar system seems stable.

Everything appears orderly
and in its proper place.

But something isn't right.

Uranus and Neptune
are in the wrong place.

The planets of the solar system

grew from a giant disk
of dust and gas...

the four inner rocky planets
close to the Sun,

and the giant gas planets
farther out.

But Uranus and Neptune
seem out of place.

There wasn't enough stuff
this far from the Sun

to make such big planets.

So, what are they doing
out here?

That led us to a theory
where Uranus and Neptune

formed very close to the Sun

and were actually
violently pushed outward.

So, what could shove
two massive planets

clear across the solar system?

We believe
that Jupiter and Saturn

got into this funny
configuration

where Jupiter went around
the Sun exactly twice

every time
Saturn went around once.

And that configuration

allows the planets
to kick each other more

as they pass one another,

and that caused the
whole system to go nuts.

The combined gravity
of Jupiter and Saturn

yanked hard on Uranus
and Neptune

and pulled them
away from the Sun.

As they moved outward,

the two planets plowed through
asteroids and other debris

left over from the formation
of the other planets.

This sent billions of chunks of
rock flying in all directions.

Some rocks
formed the Asteroid Belt.

But most were thrown out
to create the vast Kuiper Belt.

The analogy I like to
use is, think of a bowling match.

And the bowling balls go down,
and the pins just go kaplooey.

That's what happened in the
outer part of the solar system.

The gravitational push

from Jupiter and Saturn
was so strong,

it may have reversed
the position of the two planets.

It looks like it's possible
that Uranus and Neptune

actually formed
in the opposite order.

Neptune was closer
to the Sun than Uranus,

but these gravitational
interactions

actually swapped
their positions.

It was the blizzard of rocks

that Uranus and Neptune
ran into

that acted like a brake

and slowed them into the orbits
they keep today.

The idea of planets changing
orbits may sound crazy,

but scientists have seen it
happen in other solar systems.

So now they think it's just
the way all solar systems work.

When we look out into the galaxy

and look at planets
around other stars,

we see lots of evidence

of those kind of events
happening elsewhere.

In one far-off system,

scientists have spotted

something completely
off the charts...

a planet as big as Jupiter,

but it's not acting
like the Jupiter we know.

Some of these giant planets

are found orbiting very close
to their host star,

taking only days...
a few days...

to go around the host star.

Obviously,
such close-in Jupiters

are blowtorched by the star,

raising the temperature
of the planet

up to 1,000 or 2,000
degrees Celsius.

There's no way a gas giant
could have formed this close in.

It's way too hot.

The only explanation is that
it must have formed out there

and then moved in here.

The same thing
could have happened

in our own solar system.

Scientists have found large
amounts of the element lithium

on the surface of the Sun.

Lithium doesn't normally
exist in stars,

but it is found in gas planets.

Maybe there was
another gas giant

in our own solar system

that spiraled in
and crashed into the Sun.

That would explain
how the lithium got there.

Something very violent happened.

Could it have been one
of these Jupiter-size planets

getting thrown in
toward the Sun long ago?

In the beginning,

solar systems
are violent and messy,

but, over time, they settle down
and become more stable.

But stability is an illusion.

Any planet in the solar system

is always in danger
of total annihilation.

There are all kinds
of solar systems

in the Milky Way galaxy.

Most seem strange
compared to our own.

Some planets
follow crazy orbits.

Some smash into each other.

Others dive into their stars.

So, why are the orbits
of our own planets

so regular and stable?

Well, that's because all the
planets have motion left over

from the formation
of the solar system.

When the nebula collapsed
around the Sun,

as the Sun was forming,
there was an intrinsic motion,

and that gave our planet
a velocity.

Literally, we are falling freely
toward the Sun at all times,

but we're going so fast,
we keep missing it.

That's what an orbit is.

Think of a merry-go-round.

The faster it spins,

the farther and farther
you're thrown from the center.

When it slows down,

you lose momentum
and fall back inwards.

It's something like that
with planets.

The disk that gave birth
to the planets was spinning,

and the momentum
left over from that

keeps everything going around
to this day.

Moving at 66,000 miles an hour,

the Earth takes one year
to orbit the Sun.

Planets farther from the Sun
have bigger orbits,

move slower, and take longer.

Saturn orbits the Sun
once every 29 years.

Neptune takes 164 years.

Each planet stays on
a precise path around the Sun,

and for us, that's a good thing.

Our solar system
has a somewhat fortunate

spacing of the planets,

with nearly circular orbits,

which keeps
the whole house of cards

from falling apart, crumbling,
scattering to the wind.

If our solar system did not have

nice, neat, stable,
nearly circular orbits,

the Earth wouldn't be here

and we wouldn't be here
talking about it.

The planets
are on safe, stable orbits...

...but billions of comets
and asteroids are not.

Many come streaking
into the inner solar system.

And when they do, watch out.

The meteor crater
which we see here today

formed as a result of
a 150-foot rocky iron object

coming in
and slamming into the Earth

roughly 50,000 years ago.

Some of the objects
coming our way can be much bigger.

Look at the moon.

It's covered
with large impact craters.

Earth has been hit, too...
a lot.

But the craters have eroded.

We know that a huge asteroid
smashed into the Earth,

off the coast of Mexico,
65 million years ago.

It was going
45,000 miles an hour,

and when it hit,

it released more energy
than 5 billion Hiroshima bombs.

It wiped out 70% of life
on Earth.

A few more impacts like that
could destroy all life on Earth.

But, believe it or not,
Earth has a giant bodyguard.

Jupiter is more
than just another pretty face

through the telescope.

It's actually really important
for life on Earth.

Jupiter's gravity is so huge

and it's just in the right place
in the solar system,

that it protects the Earth
from comets

that come from deep
in the solar system

and swing by the Sun and could
possibly hit the Earth.

Jupiter plays the role

of the biggest baseball bat
in the solar system.

As these comets come by,

most of them get knocked out
of the solar system by Jupiter.

In 1994,

comet Shoemaker-Levy 9 raced
toward the inner solar system.

But it never got past Jupiter.

Astronomers watched
as Jupiter tore it to pieces

and dragged its remains
down to the planet's surface.

We have seen comets
smash into Jupiter,

creating fireballs that were
bigger than the Earth.

They were
the biggest explosions

ever seen in our solar system.

Had that comet hit us,

it would have resurfaced
the planet.

It would have been the end
of life as we know it.

If Jupiter wasn't there,

we believe that the impact rate
on the Earth

would be something like 1,000
times more than we see today.

Lucky for us,
Earth has the perfect orbit.

Jupiter protects us
from asteroids and comets.

We're close enough to the Sun
for liquid water

but not so close
that it boils away.

It's just the right combination
for life.

Question is,

if our solar system could create
the perfect conditions,

could other solar systems
do it, too?

Planet hunters have spotted
a solar system

20 light-years away,

and it has a planet
just the right size

in just the right place.

Astronomers around the
world are looking for new planets

in distant solar systems.

So far, they've discovered
more than 420.

Most are huge gas giants,
like Jupiter...

...but they're either very close
to the star

or much farther away.

Then, in 2005, astronomers
made an exciting discovery.

They detected a solar system
with rocky planets like our own.

These planets orbit a star
called Gliese 581.

This star, Gliese 581,
and its 4 planets

is, frankly, quite bizarre
relative to our solar system.

The four planets we know of

all orbit very close
to the host star,

all four of them orbiting closer

than the planet Mercury,
our closest planet,

orbits the Sun.

But Gliese 581 is a small star.

It doesn't burn as brightly

or give off as much heat
as our Sun,

so the planets can orbit
much closer

without being vaporized.

We know of four
planets going around this star,

and a few of them
are quite interesting.

There's one that's only
about twice the mass of Earth.

Now, that particular one
is very close to the star.

It's probably very hot...
too hot for life.

But there's another one,

about eight times the mass
of the Earth,

which is getting far enough away
from the star

that it might be
in the habitable zone.

Like Earth,

this planet orbits at a distance
where water is a liquid.

And where there's liquid water,
there could be oceans and life.

In March 2009, NASA launched
the Kepler Space Telescope.

Its mission...

to search for planets
similar to our own

in new solar systems.

We may find planets that
have methane atmospheres...

...that have
ammonia atmospheres.

We may find planets that are
covered in heavy organics...

...a tarlike material.

We may find some
that are covered by water.

I think one of
the glorious quests here

in the next decade or two

is to learn the full diversity

of the family
of Earth-like planets

that may be out there
in the universe.

With Kepler,

astronomers expect
to discover hundreds,

possibly thousands,
of new solar systems.

Think about
our own Milky Way galaxy.

The galaxy has roughly
500 billion to a trillion stars.

Some fairly large percentage
of that have planets.

Now, think about how many
galaxies we know of.

We certainly haven't found
all the galaxies

in the universe yet.

But the ones
we can take a picture of

are actually
about 60 billion galaxies.

When you look up
at the night sky tonight,

simply in the path
of your sight,

even if you can't see it,

there are billions of
solar systems all around you.

And there could be
a solar system

with a planet just like Earth.

If it happened once,
it could happen again.

Solar systems
don't last forever.

Orbits fall apart.

Planets collide.

It might happen to us.

But even if it doesn't,

in another 5 billion years,

a catastrophe will end
our solar system as we know it.

Nothing lasts forever,
not even solar systems.

Ours may seem stable now,

but, actually,
it's very slowly coming apart.

If the solar system
was chaotic in the past,

that doesn't mean
it's all settled down now.

There is still a possibility

of a little bit of chaos
in the future.

In the future,

the gravitational pull
of the planets on each other

will gradually disrupt
their orbits.

Perhaps,
over the billions of years,

the planets will jostle each
other in this gravitational way

so that, eventually,

two of the planets
will come close to each other.

When that happens...
and it will...

those two planets will engage
in a sort of a do-si-do,

flinging one or the other
of them, maybe both,

into wild orbits,

perhaps ejecting one or both
of them from the solar system.

Mars could be thrown
out of the solar system,

and Mercury might crash
into the Earth.

The entire house of cards
that is our solar system

would completely fall apart.

Solar systems begin and end

with a lot of collisions
and destruction.

But don't panic yet.

This is gonna take
billions of years,

but over the lifetime
of the solar system,

these are eventualities
that could come to pass.

But one way or another,

our solar system is doomed.

Like all solar systems,
the end will come

when the star
at the center dies.

In 5 billion years,

our own star
will run out of fuel

and become a red giant.

It'll heat up, swell,
and engulf the inner planets.

The Earth's surface
will be scorched...

...the seas will evaporate...

And the land will melt.

The Sun will become about
as big as where the Earth's orbit is,

so a likely scenario for the end
of the world

is that we're going to be inside
the Sun for a while.

The Earth's gonna get
swallowed right up into the Sun,

and it's gonna be toast...
vapor, literally.

After a while,

the red giant
will fall apart, too,

leaving behind a tiny corpse
of a star called a white dwarf.

Lt'll be
about the size of the Earth,

and it will cool off over many
millions or billions of years.

That will be the real end
of our solar system.

From the Earth...

this dead, rocky planet
that used to harbor

an enormously vibrant
civilization...

we will look out...

And there will be this fairly
faint dot which is our Sun,

now a white dwarf,
a dying, almost dead star.

The remains
of the inner planets

will continue to orbit
the white dwarf.

But the giant outer planets
will live on, untouched.

They will have warmed up

during the red-giant phase
of the Sun.

But once the Sun
is a white dwarf,

those giant planets
will survive just as well,

holding on to their hydrogen
and helium,

albeit colder
than they used to be,

because that white dwarf will
no longer be warming them up.

Even though this is
5 billion years in the future

for our solar system,

it may already have happened

to many other systems
throughout the universe.

Our solar system
emerged from chaos

to eventually support life.

We were lucky.

We've just the right amount
of planets,

in the right place,

at the right distance
from each other,

all orbiting
the right type of star.

But it could have been
a very different story.

There are so many things

that are fortunate
about our solar system,

starting with the Sun.

The Sun is a very stable,
easy star...

a perfect thing
for life to evolve around.

That's probably not
a coincidence that we're here.

An extraordinary
chain of events

over billions of years

have made our solar system
the perfect place

for life to evolve.

What we see today is not
the way things have always been

and not the way things
will always be.

We're not unique,

but it is just the way
things worked out.

The Earth has to be
in the right place.

The planets had to be
in the right place.

The giant planets have to be
in the right place

to protect us from impacts.

All that has to be right
in order to get life on Earth.

Ours is the only
planetary system we know

that supports life.

As solar systems go,

does that make us extraordinary
or perfectly normal?

We don't know.

But every week,

we're discovering
new solar systems

with new planets.

It could be
just a matter of time

before we discover...

We're not alone.