Original subtitles

İn 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 45 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.

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 we have an asteroid slam in at high speed,

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

and, inevitabiy, some of those chunks will hit Earth.

So if you think Earth is a safe haven, think again.

From the oldest cataciysm that rocked the planets,

to the ultimate disaster that will öone day blow them to oblivion.

Fasten your seatbelts,

as we count down the 10 greatest catastrophes that changed the planets.

Planet Earth, peaceful today,

has suffered its share of collisions,

massive eruptions

and mass extinctions.

But most Earthiy disasters

pale in comparison with the apocalyptic ttaumas

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 protoplanets

colliding with one another or going close past öone 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 in.

As the surviving planets took shape, the violence only intensified.

First, and earliest, on our countdown of the 10 worst planetary cataclysms,

the Mercury Mantle Disaster.

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 404 of the volume of the planet.

Whereas on Earth, for example,

the core is only about 204 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.

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

İt's almost like a pure piece of steel.

How did that little planet get so dense?

Öne 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,

-and seat İt. -Yeah.

We take our cannonball

and set that in, start it,

and 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 İt,

-and we're ready to fire. -All right. Let's fire this cannon.

-Okay. Fire in the hole! -All right.

Oh, yeah!

-İt hit... -Did you see that?

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

-We gotta take a look at that. -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.

This is exactiy 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.

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 four 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.

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

guite the same vaporization as the outer rocky shell did.

NASA's Messenger spacecraft is currentiy 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 four billion years ago.

Number nine on our countdown of planetary catastrophes,

Saturn's Shattered Moon.

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?

And perhaps most puzzling of all,

why are Saturn's iconic rings mostiy 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.

İt looks a little strange, though.

İt 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.

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.

Of Saturn's 60 remaining moons, Titan is the largest.

İtf's one and a half 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 helplessiy plunged into the planet,

with the last moon creating the bands of rings.

The model, realliy, for the first time,

explains the ice-rich nature of those rings.

You know, you'd expect kind of an egual 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.

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.

İt 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 determined 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.

Eariy 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,

the Orbital Maelstrom.

Five hundred 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 2:1 resonance.

2:1 resonance is a very strong gravitational interaction,

when taken over millions of years.

And having Jupiter and Saturn in a 2:1 resonance

leads to profound conseguences throughout the solar system.

İt shakes the orbits of the other objects up.

İt leads to crossing orbits, and it can lead to giant impacts.

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 2:1 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.

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

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.

İtf'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's 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.

But the 2:1 resonance was just the beginning.

As the gas giants searched for stable orbits 41 billion years ago,

they ignited the most wide-ranging cataciysm

ever to engulf the solar system, so far, anyway.

Number seven in our countdown,

the Late Heavy Bombardment.

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 protoplanets

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 41 billion years ago.

And then the 2:1 resonance of Jupiter and Saturn

channeled some of those asteroids into the inner solar system,

creating the era of heavy bombardmenit.

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 cataciysm."

Proof of this disaster was discovered in 1969,

when NASA's Apollo 11 mission put the first man on the Moon.

İt'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 four 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.

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 Mars Mega-Meteorite Impact.

The tumultuous Late Heavy Bombardment

that pounded the solar system between 4.1 and 3.8 billion years ago

disrupted more than just comets and asteroids,

entire planets were thrown off-course.

And a NASA space orbiter recentiy uncovered evidence that one of them,

a world the size of Pluto, plunged into Mars,

drastically reshaping the Red Planet.

İt was a very large impact that struck the planet at a very low angle,

a very obligue angle, and essentially skimmed off

the surface of the northern hemisphere of Mars.

Think ofit almost as if

a knife were slicing through a melon, for example.

The impact carved out the Borealis basin,

which covers over 4006 of Mars' surface.

İt'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.

İt was just sort of sunken down on the edges.

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,

the Mars Magnetic Disaster.

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 impacit,

this one with life-altering implications.

We're not exactiy sure why Mars has only a weak magnetic field.

ÖOne 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.

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 deadliy 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.

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.

İt could be that Mars is simply a small planet,

and so it lost its internal heat

relatively gulickly compared to the Earth.

And without the heat, it would have a solid iron core,

and it wouldn't create a magnetic field.

İn any case, once Mars lost its atmosphere,

it was unable to support liguid water on the surface,

because the pressure was too İow.

Without liguid water on the surface, surface life would have perished.

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.

İt's very clear that all the giant planets

have moved substantially from where they originaliy 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.

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 profoundiy 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 pummael into planets,

rampant volcanism can occur on planets.

There are all sorts of ways in which catastrophes can occur on the planets.

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,

the Mars Super Eruptions.

The Mars Express spacecraft recentiy revealed

that the Red Planet has been ravaged at least five times

by episodes of catastrophic volcanism,

giving Mars a unigue complexion,

unlike anything else in the solar system.

İn 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.

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.

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 Mears.

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

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 volcanoces, like Olympus Mons.

On Earth, there's plate tectonics.

So, for example, the volcanic islands of Hawali 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.

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,

the Great Venus Meltdown.

Our closest planetary neighbor, Venus, may have begun guite Earthlike.

İt was born at roughiy the same time

and made with the same cosmic materials,

but something transformed Venus into Earth's evil twin.

İf you could penetrate through its thick atmosphere,

you'd see that about 906 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 EFarth'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 neariy 900 degrees Fahrenheit.

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

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

he would be baked and very guilckly totally crushed.

The hellish conditions on Venus could have been caused

by an extreme runaway greenhouse effect over three 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.

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 dramaticalliy.

If we are able to understand what happened on Venus,

we can apply those lessons learned here on Earth.

İf an eco-disaster evaporated the liguid 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, e-mailed us.

Jack, that's a really fascinating guestion.

İt turns out that Venus may have had oceans

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

İf so, primitive life, by which l 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.

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 originaliy so warm and Earthlike,

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 Fahrenhett,

almost double that of Mercury.

But Earth's next-door neighbor may have taken a different road to ruin.

Öne 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 elemenits,

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.

Proponenits 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 guite 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.

The fate of Venus is a telling reminder

that even temperate conditions, like those on Earth,

can never be taken for granted.

İf 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.

The Shoemaker-Levy 9 llmpacts.

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.

Jupiter, the largest gas giant,

has been our solar system's planetary punching bag.

İts gravitational force deflects renegade comets

that break loose from their orbital prisons

in the Öort 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.

İn a sense, Jupiter is asking for trouble.

Jupiter has taken a lot of nasty hits,

including one of the most violent celestial catastrophes

ever witnessed by mankind.

İn July, 1994, the world watched as achain 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 six 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 airburst 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.

The fragments didn't produce craters,

because Jupiter doesn't have a solid surface.

İnstead, 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 telis an important tale, that if you have an object that's

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.

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, oftentimes, very violent weather patterns.

So, no matter how destructive that airburst 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.

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 four billion years of planet-altering catastrophes.

İn 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.

NASA has recentiy 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.

İf 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.

July, 1994, marks the date of the Shoemaker-Levy 9 impact evenit.

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 the ripples that we still see today.

İn 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 it on the side.

Shoemaker-Levy 9 wasn't the only comet

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

İn July, 2009,

another asteroid smashed into the gas giant near its south pole.

When it impacted Jupiter,

it brought up a İlot 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 Öcean on the Earth.

İt was gduite large.

İt'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 ihe 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 essentialiy a sitting duck for all the debris,

the comets and the asteroids that were falling in towards the Sun,

creating vastİy larger numbers of catastrophes on Earth

than we've experienced through our history.

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,

Planetary Armageddon.

İn 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 the planets do affect each other gravitationalliy.

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 ecceniric.

It becomes progressively more elongated,

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

it's actually crossing Venus' orbit.

İf Mercury's orbit ever gets to the situation

where it's crossing Venus' orbit,

then basicalliy all hell can break İoose.

Scientists have calculated one Of four disastrous conseguences.

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 190 chance that Mercury's orbit will go haywire.

And within that 196 chance,

there's a small probability that things will unfold

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

Mercury is hardiy 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 Earth,

repeating the disaster that gave rise to the Moon.

And it's not just planets.

Nearby stars periodicaliy 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 expecit,

the Andromeda Galaxy ultimately collides with the Milky Way,

the galactic pileup could shatter our solar system's deceptive calm.

The ultimate planetary catastrophe, Il think, is still in our future.

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 İife,

and how we might protect it and us from the catastrophes of the future.