All language subtitles for The universe S06E01 Catastrophes that Changed the Planets

Male narrator: In the beginning,
there was darkness,

and then, bang,

giving birth to an endless
expanding existence

of time, space, and matter.

Every day, new discoveries
are unlocking the mysterious,

the mind-blowing,
the deadly secrets

of a place we call
The Universe.

Throughout its
4.5 billion-year history,

our solar system has witnessed
carnage on a colossal scale.

Time and again,

catastrophes have shattered
the planetary peace.

- A large impact
striking at the right location

could have caused the whole
planet to go off kilter.

Narrator: Worlds have collided

or been paved over
by runaway volcanism

or even ejected
from the Sun's grasp.

No planet
has provided sanctuary

from the solar system's
reign of terror.

- If you have an asteroid
slam in at high speed,

then little bits of Mercury
will go flying off the surface,

and inevitably,

some of those chunks
will hit Earth.

Narrator: So, if you think
Earth is a safe haven,

think again.

From the oldest cataclysm
that rocked the planets

to the ultimate disaster

that will one day
blow them to oblivion,

fasten your seat belts
as we count down

the ten greatest catastrophes
that changed the planets.

[dramatic music]

♪ ♪

Planet Earth,
peaceful today,

has suffered its share
of collisions,

massive eruptions,

and mass extinctions.

But most earthly disasters
pale in comparison

with the apocalyptic traumas

that befell our siblings
in the solar system.

The solar system
was born in a maelstrom,

as billions
of rocky boulders collided

to form the planets
we know today.

- The birth of the solar system
was full of violence.

There were all sorts of
planetesimals and pro to planets

colliding with one another

or going close past one another
and ejecting each other,

or sending each other
down toward the Sun.

So, you know,
only a few planets survived.

- The early solar system
was very much

like a cosmic pinball machine

where you had lots of impacts

and lots of collisions
taking place,

destroying planets,
forming planets,

breaking apart planets,

creating everything
that we see today.

But long ago, it would not
be the type of place

that we'd want to live.

Narrator: As the surviving
planets took shape,

the violence only intensified.

First and earliest
on our countdown

of the ten worst
planetary cataclysms:

Mercury, the closest planet
to our sun,

is also the runt
of the solar system.

Now scientists think
the puniest planet

was dealt one
of nature's mightiest blows.

- Mercury's a mystery
to scientists.

The iron core
inside Mercury

is about 40%
of the volume of the planet,

whereas on Earth,
for example,

the core is only about 20%
of the Earth's total volume,

even though Earth is about
three times larger than Mercury.

- Mercury is
a bit of a conundrum

in planetary science.

It's like the solar system's big
ball bearing sitting out there.

It's almost like
a pure piece of steel.

How did that little planet
get so dense?

Narrator: One theory holds

that a planetary collision
was the culprit.

But how could an impact
make a planet dense?

By envisioning Mercury's cosmic
attacker as a cannonball,

we can help re-imagine
what happened.

- Let's fire cannonballs from
this American Revolution cannon

at a bowling ball
covered with plaster

40 yards away.

Now, that bowling ball
covered with plaster

represents
the early Mercury,

where the plaster
is the mantle and crust.

Now, Gary Harper,
our weapons expert,

is gonna fire this cannon
for us.

Gary, how do we do this?

- Well, fairly simple.

We use the appropriate
powder charge,

insert it into the bore...

Seat it.
- Yeah.

- We take our cannonball.

We'll set that in, start it,

set that
on top of the powder.

- How fast
is this thing gonna go?

- Should be going
about 300 feet per second.

- Wow.
That's about 200 miles an hour.

Should do some real damage.

- Now, how about
some hearing protection, Alex?

- Right.
And my glasses here, right?

- And your glasses.
- Okay.

- Now all we have left to do
is prime it,

and we're ready to fire.

- All right.
Let's fire this cannon.

- Okay.
Fire in the hole!

- All right.

Oh! Yeah!

It hit!
- [laughs] Did you see that?

- You blasted it! High five!
- We did it.

- Whoo-hoo!
- [laughs]

- We got to go
take a look at that.

- Yeah, let's go take a look.
- Okay.

Wow, there's stuff
all over the place here.

- Oh, yeah, the plaster
has been knocked off.

Look at that.

Narrator: This is exactly

how scientists think
Mercury's crust was blown away,

leaving the remaining planet
an iron core.

- So this nicely explains
how dense Mercury is.

It has this big iron core
'cause the rest of this stuff

was largely stripped away
by the collision.

So good job aiming the cannon
at this bowling ball.

Narrator:
The celestial crack-up

would've ejected
Mercury's mantle into the Sun

and flung it
as far as Jupiter.

The wreckage rained down
for up to 4 million years.

- The debris went
throughout the solar system

and could even have landed
on planets.

In fact,
there are some estimates

that up to 16 million billion
tons of material

from Mercury
landed on Earth.

Narrator. But proponents
of the cosmic hit-and-run theory

face a forensic dilemma.

If the collision happened,

why didn't it leave
a visible scar on the surface?

- Other ideas for the formation
of Mercury's large core

involve the local environment
of Mercury being so hot,

due to fluctuations
in the solar output,

that the entire planet
actually vaporized,

the rocky mantle
actually became rock vapor,

and the solar wind
blew that rock vapor away

out into space.

So that's another
possible explanation

for why the core survived,
because it was made of metal

and didn't suffer
quite the same vaporization

as the outer rocky shell did.

[electronic beeping
and whirring]

Narrator:
NASA's Messenger spacecraft

is currently orbiting Mercury,

hoping to unlock the mysteries
of its turbulent past.

But it wasn't just
the innermost planet

that took a beating.

Today Saturn's
spectacular rings

rotate in calm serenity,

but they owe their beauty

to a makeover
of the most violent kind

over 4 billion years ago.

Number nine on our countdown
of planetary catastrophes:

- Although Saturn's rings are

one of the most noticeable
things in the solar system,

they've also been
one of the big mysteries

of the solar system.

How long ago did they form?
How did they form?

Narrator: And perhaps
most puzzling of all,

why are Saturn's iconic rings
mostly made of ice,

33 million billion tons of it?

Sculptor Roland Hernandez
has re-created Saturn

and one of its icy moons

to help us visualize
a new theory:

how a lunar catastrophe

could've given birth
to Saturn's rings.

- We have a beautiful
2-foot version of Saturn,

and we also have its wonderful
moon made out of ice.

- Wow.
It's just beautiful.

It looks
a little strange, though.

It doesn't look
like the Saturn that we know

because it doesn't have
any rings.

But that's why we're here,

because we want to take ice
off the surface of this moon

and create rings around Saturn.

Oh, yeah.

Narrator: Many scientists
now believe

an ancient, ice-covered moon
fell into Saturn.

As it did,
Saturn's powerful gravity

pulled off the moon's ice,
and swept it into orbit.

- This sander acts like
the tidal force of Saturn,

pulling the icy mantle
of this moon off and in orbit.

The moon itself
fell into Saturn,

leaving no trace behind,

but it left the glorious rings
that we see in Saturn today,

which are made mostly of ice.

Narrator. Of Saturn's
60 remaining moons,

Titan is the largest.

Its 1 1/2 times bigger
than the Earth's moon.

But new simulations show
that Saturn could have begun

with several larger moons
that were all lost

as they helplessly
plunged into the planet,

with the last moon
creating the bands of rings.

- The model really,
for the first time,

explains the ice-rich nature
of those rings.

You know, you'd expect
kind of an equal mix

of rock and ice and stuff

if they were just a battered,
broken-apart moon,

but this whole idea
that you had a moon spiral in

and had its outer icy mantle
stripped off

as the rest of the core
continues inward

to make the rings
out of the icy mantle.

Narrator: The origin
of Saturn's rings illustrates

that even
its most beautiful features

were born in violence.

But while the disasters

that shaped Saturn and Mercury
were localized,

one catastrophe ripped
the entire solar system apart.

It not only affected
every planet we see today;

it even hurled planets
right out of the Sun's grasp

and into the dark exile
of interstellar space.

Cosmic catastrophes,

like the early disasters
that destroyed Mercury's mantle

and formed Saturn's rings,

have shaped almost every aspect
of the solar system,

but now,
as we move forward in time,

disasters even determine

the order in which
the planets line up.

Today,
traveling out from the Sun,

the order
of the outer gas giants

is Jupiter, Saturn,
Uranus, and Neptune.

But once,
things were very different.

- Early in the history
of the solar system,

Jupiter and Saturn
kind of wandered around

at different distances
from the Sun,

and that's because they were
continually interacting

with the leftover planetesimals
in the solar system.

That affected their orbits.

As the orbits of Jupiter
and Saturn fluctuated,

they set off
a cosmic chain reaction

that tore
the solar system apart.

Number eight in our countdown

to the ultimate planetary
catastrophe:

500 million years
after the planets formed,

Jupiter elbowed inwards
toward the Sun

while Saturn, Uranus,
and Neptune drifted outwards.

Jupiter eventually
orbited around the Sun

exactly twice for every one time
that Saturn did.

This pivotal moment is known
as the two-to-one resonance.

- Two-to-one resonance

is a very strong
gravitational interaction,

when taken
over millions of years,

and having Jupiter and Saturn
in a two-to-one resonance

leads to profound consequences
throughout the solar system.

It shakes the orbits
of the other objects up.

It leads to crossing orbits,

and it can lead
to giant impacts.

Narrator: Saturn and Jupiter's
resonant gravity

destabilized the orbits
of Uranus and Neptune.

The resulting game
of planetary musical chairs

ignited the largest

and most long-lasting
catastrophe

ever to shake the solar system.

- When Jupiter and Saturn
reached that two-one resonance,

it imparted
a lot of gravitational energy

that essentially stirred up
the outer solar system.

Neptune and Uranus were thrown
into much higher orbits,

and they even switched places.

So now the order
is Uranus, Neptune.

In the beginning, it used to be
Neptune followed by Uranus.

Narrator: Neptune and Uranus
may have switched orbits

not once
but several times.

But they were the lucky ones.

Several planets
were most likely

hurled out of the solar system
altogether,

doomed to wander forever

in the blackness
of interstellar space.

- It's almost a certainty

that our solar system
has lost planets along the way,

during this sort of
celestial billiards

that's played
and planets swapping places.

There is even
some evidence, perhaps,

that Jupiter and Saturn
may have wandered

into the inner solar system,

to near the position
where the Earth is today,

before wandering back out
to their present locations.

Narrator:
But the two-to-one resonance

was just the beginning.

As the gas giants
searched for stable orbits

4.1 billion years ago,

they ignited
the most wide-ranging cataclysm

ever to engulf
the solar system...

so far, anyway.

Number seven
in our countdown:

The orbital dance
of Saturn and Jupiter

didn't just throw the outer
gas giants into turmoil;

it also ignited
a system-wide maelstrom.

- The wandering around
of Jupiter and Saturn

would have created gravitational
tugs on the pro to planets

that were forming in the region
of the asteroid belt.

That would have caused them
to smash together,

shattering them
into a bunch of asteroids,

probably before
4.1 billion years ago.

And then
the two-to-one resonance

of Jupiter and Saturn

channeled
some of those asteroids

into the inner solar system,

creating the era
of heavy bombardment.

Narrator: We can see
the dramatic results

every time we gaze up
at the Moon.

Most of the scars
on its pockmarked face

are the result
of this bombardment,

also known
as the lunar cataclysm.

Proof of this disaster
was discovered in 1969,

when NASA's Apollo 11 mission

put the first man on the Moon.

- It's a really fun
detective story

connecting
the dynamical models

that are giving us
an explanation

for the geologic evidence
that we see

for a late heavy bombardment

about 4 billion years ago
here in the inner solar system.

We had the geologic evidence
ever since Apollo

and the dating of the rocks
from the Moon

that showed this period of dates
at that time.

- The cratering record tells us
that in various spots

in the solar system, especially,
for instance, on the Moon,

that there was a sudden increase
in the number

of really large objects
slamming into the planets.

Narrator: But while the Moon
merely suffered cosmetic scars,

one planet received
such a cataclysmic blow,

it may have lost
its ability to harbor life.

Number six
on our countdown

to the solar system's
greatest catastrophe:

The tumultuous
late heavy bombardment

that pounded the solar system

between 4.1 billion
and 3.8 billion years ago

disrupted more
than just comets and asteroids.

Entire planets
were thrown off course,

and a NASA space orbiter
recently uncovered evidence

that one of them,
a world the size of Pluto,

plunged into Mars,

drastically reshaping
the Red Planet.

- It was a very large impact
that struck the planet

at a very low angle,

a very oblique angle,

and essentially skimmed off
the surface

of the northern hemisphere
of Mars.

Think of it almost
as if a knife

were slicing through a melon,
for example.

Narrator: The impact carved out
the Borealis Basin,

which covers
over 40% of Mars' surface.

It's the largest impact crater
in the solar system,

large enough to hold
the continents of Asia,

Europe, and Australia.

- We see evidence for impacts
on other planets

because they form craters

that all follow
the same sort of pattern:

nice excavated pit,
usually a rim around the edge,

sometimes a spray of material
coming out.

But those kinds of evidence
were not clear on Mars.

The lines of evidence
have to do

with both the gravity
of the interior of Mars

and the topography
of the surface of Mars.

Those, taken together,
show that there was a crater:;

it was just sort of
sunken down on the edges.

Narrator:
At least five huge impacts

pummeled Mars during
the late heavy bombardment.

But a far worse fate
was in store for the Red Planet.

And our next catastrophe
may have done more

than gouge out a hefty chunk
of the Martian surface.

It may have changed
the planet's destiny.

Number five
on our countdown:

Spacecraft orbiting Mars
reveal that the planet

carries only
the faint remains

of its once-protective
magnetic field.

Scientists speculate
that the culprit

was yet another impact,

this one
with life-altering implications.

- We're not exactly sure

why Mars has
only a weak magnetic field.

One idea is that Mars was hit
by a gigantic object,

and that heated
the crust and mantle,

and that decreased
the temperature difference

between the core
and the mantle.

Without there being
a big temperature difference,

there wouldn't be
convective motions,

the churning motion
in the interior of Mars.

Without them,
you don't get a magnetic field.

Narrator. On Earth,
our global magnetic field

deflects
dangerous solar particles

away from our atmosphere.

But on Mars,
its very weak magnetic field

covers only
a few regions of the planet.

So deadly solar particles
could have eroded away

much of its atmosphere.

- And over billions of years,

you can tend to erode

a large fraction
of the atmosphere,

and that includes things like
water vapor, carbon dioxide,

things that are
excellent greenhouse gases,

which have caused the planet
to become very cold,

and hence, the planet
that we see today

is a very cold, dry desert.

Narrator: The loss
of magnetism on Mars

may have made it impossible
for life to evolve and survive

on the frigid, arid planet.

But some scientists
are skeptical

that its magnetism died
with a colossal bang.

- It could be that
Mars is simply a small planet,

and so it lost its internal heat
relatively quickly

compared to the Earth,

and without the heat,

it would have
a solid iron core,

and it wouldn't create
a magnetic field.

In any case,

once Mars
lost its atmosphere,

it was unable to support
liquid water on the surface

because the pressure
was too low.

Without liquid water
on the surface,

surface life
would have perished.

Narrator: By the time
the late heavy bombardment

slowly came to an end
3.8 billion years ago,

every planet
in the solar system

had received
some kind of makeover.

- It's very clear
that all the giant planets

have moved substantially from
where they originally formed.

We see that Neptune
clearly migrated outward,

because it picked up
the smaller bodies,

like Pluto and
the other Kuiper belt objects

in its gravitational sway,

and pushed them out
along with it.

Narrator: The planets eventually
settled into stable orbits,

but now, as they matured,

new catastrophes
began erupting from within,

and in some cases,

these volcanic,
homegrown disasters

would exceed anything
from outer space.

Our solar system
was profoundly shaped

by the chaotic collisions
and bombardments

that marked
its earliest days.

But as the planets finally
eased into stable orbits

3.8 billion years ago,

new threats arose.

And in some cases,
they were as bad

as anything bearing down
from outer space.

- Catastrophes
in the solar system didn't end

with the era
of late heavy bombardment.

There have been catastrophes
since that time.

Asteroids and comets
can pummel into planets.

Rampant volcanism
can occur on planets.

There are all sorts of ways

in which catastrophes
can occur on planets.

Narrator: The next disaster
gave one of the planets

an ill-fated face-lift
that left it

with the most towering blemish
in the solar system.

Number four
on our countdown

to the solar system's
worst disaster:

[electronic beeping
and whirring]

The Mars Express spacecraft

recently revealed
that the Red Planet

has been ravaged
at least five times

by episodes
of catastrophic volcanism,

giving Mars
a unique complexion

unlike anything else
in the solar system.

- In some respects,
the shield volcanoes on Mars

are similar to some volcanoes
here on Earth,

such as at Hawaii.

You've got a large magma chamber
beneath the surface

that's erupting
lots of lava onto the surface,

creating the volcano.

However, on Mars,
these types of volcanoes

are 10 to 100 times larger
than they are on Earth.

So, all across the planet,
you've got these eruption events

that are occurring here
and then here and then here,

and over time,
sort of the whole surface

gets filled in
with this lava.

Narrator: Mars is home
to about 20 major volcanoes,

including Olympus Mons,

the largest
in the solar system.

This towering relic
provides an eerie glimpse

into the planet's
fiery past.

- When we look
at Mars' geologic record,

we can tell
how old things are

by looking at how many craters
are on the surface.

If the surface
is relatively young,

then there has been
relatively little time

for craters to build up,

and so we see a surface that's
largely flat and unmarred.

If the surface is very old,

then we see
large numbers of craters.

And so through crater dating

and through careful mapping
of the Martian surface,

it looks like there were perhaps
five very major episodes

of volcanic activity on Mars.

Narrator: Just as with
shield volcanoes on Earth,

magma chambers rose
to the surface of Mars,

broke through,
and spewed basaltic lava

in centuries-long eruptions.

But there was a key difference
between Earth's shield volcanoes

and the behemoths on Mars.

- On Mars, there was never
large-scale plate tectonics

of the type
that we have on Earth.

So, on Mars,
when a volcano gets going,

it just sits there and keeps
piling lava out and out and out,

and it builds up
enormous shield volcanoes,

like Olympus Mons.

- On Earth,
there's plate tectonics.

So for example,
the volcanic islands of Hawaii

are in a chain.

Because the plate
is moving north,

the hot spot
is relatively fixed,

and new islands
keep on popping up.

But on Mars, it's the same
island all the time,

and it just keeps getting
bigger and bigger.

Narrator: Massive volcanism

radically changed
the surface of Mars

time and time again.

But it wasn't
the only terrestrial planet

that fell victim to episodes
of extreme home-grown violence.

Next on our countdown
of planetary disasters:

Our closest
planetary neighbor, Venus,

may have begun quite Earth like.

It was born
at roughly the same time

and made
with the same cosmic materials,

but something transformed Venus
into Earth's evil twin.

- If you could penetrate
through its thick atmosphere,

you'd see that about 90%
of the surface of Venus

is covered by solidified lava
from previous volcanism.

And the thick, noxious
atmosphere

consists mostly
of carbon dioxide,

and it has
an atmospheric pressure

about 90 times
that on Earth's surface.

Wow.

That's like being 3,000 feet
below the surface of the ocean.

That's what you'd feel.

Moreover,
the temperature on Venus

is nearly
900 degrees Fahrenheit.

That's huge.
It's enough to melt lead.

So if a human were suddenly
placed on the surface of Venus,

he would be baked

and very quickly
totally crushed.

Narrator:
The hellish conditions on Venus

could have been caused

by an extreme
runaway greenhouse effect

over 3 billion years ago.

- So what happened
to the oceans of Venus,

if they were there
to begin with?

Well, the Sun gradually
grew brighter,

and that led to more
evaporation of the oceans,

increasing the water vapor
content of the atmosphere.

Well, water is
a greenhouse gas,

so that led to a greater
increase in temperature,

which led to more evaporation,
more greenhouse gases,

a runaway greenhouse effect

that eventually evaporated away
the oceans of Venus.

Narrator:
Evidence of these lost oceans

may exist
above the cloud decks of Venus.

- We know
from sampling Venus' atmosphere

that there is
a high concentration

of the form of heavy hydrogen
called deuterium.

Most of the hydrogen
escaped to space,

and the small dregs of hydrogen
that did remain

are this special heavy form
called deuterium.

- Venus provides a great example
of what can happen to a planet

when the climate changes
dramatically.

If we are able to understand
what happened on Venus,

we can apply those
lessons learned here on Earth.

Narrator: If an Eco-disaster

evaporated the liquid
surface water on Venus,

were there living creatures
that also perished?

That's what one viewer
wanted to ask The Universe.

So Jack Kershaw from
Fort Worth, Texas, emailed us:

- Jack, that's
a really fascinating question.

It turns out that Venus
may have had oceans

for the first half billion or
billion years of its existence.

If so, primitive life,

by which I mean
microbes and bacteria,

may have formed
in those oceans.

We just don't know.

But on Earth,
primitive life formed

shortly after the end
of the late heavy bombardment.

If the same thing
happened on Venus,

then Venus once had life.

Narrator: According
to the greenhouse theory,

the surface of Venus
became bone-dry gradually

over millions of years,

but not everyone agrees.

Some scientists argue
that the water on Venus

actually disappeared
not slowly

but in one disastrous day.

Of all the catastrophes that
have swept the solar system,

perhaps the most puzzling
is what happened to Venus.

A planet originally
so warm and Earth like,

it might have harbored life.

For decades,
scientists theorized

that a runaway
greenhouse effect

slowly raised the planet's
average temperature

to a scorching
860 degrees Fahrenheit,

almost double that of Mercury.

But Earth's
next-door neighbor

may have taken
a different road to ruin.

- One way that Venus
may have lost

a substantial chunk of its water
all at once

is through a giant impact.

A giant impact
will hit the planet,

basically strip off a huge
amount of the outer layer.

That provides
an incredible amount of energy,

an incredible amount of heat,

and so volatile elements,

like water or ammonia
or methane,

are simply lost
to interplanetary space.

And after the giant impact
has occurred,

after everything has died down,
you're left with a planet

that's much drier
and made of material

that has a much higher
vaporization temperature.

Narrator:
Proponents of the theory

claim the cosmic punch
was so powerful,

it actually spun the planet
off its axis.

- Venus spins in the direction

opposite that
of most of the planets,

and we don't know
quite why that is,

but one idea is that
it was hit by a gigantic object

early in the history
of the solar system,

and that effectively
either flipped it

or just reversed
the sense of rotation,

depending on exactly
how the object hit Venus.

Narrator: The fate of Venus
is a telling reminder

that even temperate conditions,
like those on Earth,

can never be taken
for granted.

If we didn't know that
already,

number two in our countdown
of planetary catastrophes

drove the point home.

And this time,
the whole world was watching.

- We used to think that

the outer planets
were pretty stable.

There wasn't
a lot happening to them.

But in fact, now we see impacts
hitting the outer planets

all the time.

Narrator: Jupiter,
the largest gas giant,

has been our solar system's
planetary punching bag.

It's gravitational force
deflects renegade comets

that break loose
from their orbital prisons

in the Oort cloud
and Kuiper belt.

- The rate of impacts on Jupiter
is greater than that

of any other planet
for two reasons:

first,
Jupiter is the biggest planet,

so it presents
the biggest cross section.

Things are more likely
to hit it.

Second,
Jupiter has a huge mass,

so it pulls objects
in toward it.

In a sense,
Jupiter is asking for trouble.

Narrator: Jupiter has taken
a lot of nasty hits,

including one of the most
violent celestial catastrophes

ever witnessed by mankind.

In July, 1994,

the world watched as a chain
of 21 comet fragments

raced towards the giant planet

and struck it
with colossal force.

Shoemaker-Levy 9,
named after its discoverers,

delivered the energy

of 6 million megatons
of TNT.

- During the Shoemaker-Levy 9
impact on Jupiter,

you had this ripped-up comet
coming in

at tens of kilometers
per second

and impacting Jupiter
in one air burst after another

as Jupiter spun
underneath the comet.

And so that led to a series
of impacts being spread

along a particular latitude
of Jupiter's surface

and leaving these scars,

which were visible
in telescopes from the Earth.

Narrator: The fragments
didn't produce craters,

because Jupiter
doesn't have a solid surface.

Instead, they struck
the gas giant's dense atmosphere,

dredging up material
that erupted

in a trail of venting scars.

- The impact scars,
the dark cloud features,

were about the size
of our planet Earth,

and that tells
an important tale,

that if you have an object
that's, you know,

a half a mile across striking
an object the size of the Earth,

the dust pall
from that impact

will encompass
our entire planet.

So that's the lesson we learned
from the Jupiter impacts,

is, it really brought home
the story of impacts

right here on Earth.

Narrator: The dark imprints left
on the cloud decks of Jupiter

were only visible
for several months

before being mixed
into its turbulent atmosphere.

- Jupiter has very vigorous

and, often times,
very violent weather patterns.

So no matter how destructive
that air burst might be,

over a period
of weeks to months,

the currents, the airflow
in Jupiter's atmosphere

takes the pollutants

and disperses them
through the planet.

And the evidence
for the catastrophic impact

dissipates and disappears.

Narrator. Shoemaker-Levy 9
is a scary reminder

of the cosmic unrest
in our solar system,

but scientists warn
that the ultimate catastrophe

still looms in the future.

And for Earth,
there can be no escape.

Our solar system has weathered
over 4 billion years

of planet-altering
catastrophes.

In some cases,
the effects are obvious,

like the craters
of the late heavy bombardment

that still litter the Moon.

In others, the evidence
has long since disappeared.

But scientists
recently discovered

that number two
on our countdown of catastrophes

has created a ripple effect
they never imagined.

[electronic whirring]

NASA has recently compared
images of Jupiter

from the Cassini
and new horizons missions

and made
a stunning discovery.

Like Saturn,
Jupiter also has rings,

though much fainter.

But something
has disrupted them.

- If you look
at the rings of Jupiter,

they actually have
little corrugations,

little ripples in them,

and those ripples are formed

when a portion of the ring
is tilted,

and then as it continues
to spin and evolve over time,

those ripples wander out,

propagate out
through the ring system.

If you unwind that system
and work back out the ripples,

you can find out

the point in time
when that ring plane

had gotten tilted over.

That point when
that ring got tilted

was right around
July of 1994,

narrator: July 1994
marks the date

of the Shoemaker-Levy 9
impact event.

The scientific sleuths
had made a key discovery.

As the cometary fragments
struck Jupiter itself,

much smaller debris
passed through its rings,

tilting and twisting them

into ripples
that we still see today.

- In the case
of a disrupted comet

like Shoemaker-Levy 9,

you've got
an entire pall of dust,

a large mass of material

distributed across
the disk of the rings

raining through
that system.

And so rather than displacing
only one or two ring particles,

you can do
the entire cloud at once,

tipping on the side.

Narrator. Shoemaker-Levy 9
wasn't the only comet

to leave its calling card mark
on Jupiter in recent times.

In July 2009,
another asteroid

smashed into the gas giant
near its south pole.

- When it impacted Jupiter,
it brought up a lot of material

from deep
within the atmosphere

and created a huge scar
on the surface of the planet

that was visible
for many weeks.

The size
of this black ash cloud

was perhaps the size of
the Pacific Ocean on the Earth.

It was quite large.

Narrator: It's now estimated
that an asteroid or comet

hits Jupiter
every 10 to 15 years,

which is 5,000 times higher

than the rate
of impacts on Earth.

- The fact that we've seen
several of these

suggests that it's happening
all the time,

because there are all the ones
we don't see.

So there's a lot more
impact activity

on the outer gas giants
than we ever thought.

- If Jupiter was not
in our solar system,

the Earth would be essentially
a sitting duck

for all the debris,
the comets and the asteroids

that were falling in
towards the Sun,

creating vastly larger
numbers of catastrophes on Earth

than we've experienced
through our history.

Narrator:
But as our solar system ages,

new threats will likely arise,

and Earth itself will face
a cosmic day of reckoning

that nothing,
not even Jupiter, can prevent.

Which brings us to number one

on our countdown
of catastrophes:

In several billion years,

many scientists believe Jupiter,
the largest planet,

and Mercury, the smallest,

will face off
in an orbital duel,

and an innocent bystander,
Earth, just might find itself

in the line of fire.

- Right now, our solar system

is kind of the paradigm
of clockwork regularity.

But it turns out that,
you know,

the planets do affect
each other gravitationally.

The planetary orbits are,
over very long periods of time,

vibrating in and out
and turning.

Jupiter and Mercury
will begin to turn their orbits

at the same rate,
and if that happens,

Mercury's orbit becomes
progressively more eccentric.

It becomes
progressively more elongated

until the point where,
at its far point from the Sun,

it's actually
crossing Venus ' orbit.

If Mercury's orbit
ever gets to the situation

where it's crossing
Venus' orbit,

then basically,
all hell can break loose.

Narrator:
Scientists have calculated

one of four
disastrous consequences.

Mercury might collide
with the Sun,

might be ejected
from the solar system,

might smash into Venus.

Or, in a worst-case scenario,

Mercury might
collide with the Earth,

blasting away
our mantle and atmosphere

and sterilizing our planet.

- As far as we can tell
from computer simulations,

there's about a 1% chance

that Mercury's orbit
will go haywire.

And within that 1% chance,

there's a small probability
that things will unfold

in such a way that the Earth
itself is impacted by Mercury.

Narrator: Mercury is hardly
the only threat we face

from within the solar system.

According to some scenarios,

Mars also faces orbital chaos
in the future.

And it, too,
may slam into the Earth,

repeating the disaster
that gave rise to the Moon.

And it's not just planets.

Nearby stars periodically
disrupt comets in the Oort cloud,

which could send them
on a kamikaze mission

through the solar system

and set off
a new late heavy bombardment.

And if, as most expect,

the Andromeda galaxy ultimately
collides with the milky way,

the galactic pileup

could shatter our solar system's
deceptive calm.

- The ultimate
planetary catastrophe,

I think, is still
in our future.

Narrator: Catastrophes
have always played

a violent yet vital role
in our solar system's history.

Without them, our neighborhood
would be a very different place.

By learning
about these volatile events,

we can better understand
how they helped form the planet

that gave us life

and how we might protect it
and us

from the catastrophes
of the future.