NARRATOR: In the beginning, 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. MICHAEL MISCHNA: 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. GREG LAUGHLIN: 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 10
greatest catastrophes that changed the planets. 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. ALEX FILIPPENKO: The
birth of the solar system was full of violence. There were all sorts of
planetesimals and proto-planets colliding with one another or
going close past one another and ejecting each other
or sending each other down toward the sun. So only a few planets survived. MICHAEL MISCHNA: The early
solar system was very much like a cosmic pinball machine. 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. The 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 is 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. DAN DURDA: Mercury is a bit of a
conundrum in planetary science. It's like the solar system's
big ball bearings 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 going to 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, feed it. Yep. We take our cannonball. We'll set that in, start it. Set that on top of the powder. How fast is this
thing going to 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, Alec? Right, and my
glasses here, right? And your glasses. OK. All I have left to do is prime
it, and we're ready to fire. All right, let's
fire this cannon. OK, fire in the hole. Oh, yeah! It hit! You blasted it! High five. Woohoo!
Excellent. - Ready to go take a look at it?
- Absolutely. Yeah, let's go take a look.
- OK. Wow, there's stuff
all over the place. 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. ALEX FILIPPENKO: So this nicely
explains how dense Mercury is. It has this big iron core
because 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 crackup would have ejected Mercury's
mantle into the sun and flung it as far as Jupiter. The wreckage rained down
for up to 4 million years. ALEX FILIPPENKO: 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? MICHAEL MISCHNA: 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 then 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. 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, Saturn's shattered moon. LAURA DANLY: 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 recreated Saturn and one of its icy moons to help us
visualize a new theory, how a lunar catastrophe could have
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. LAURA DANLY: 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. 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 into orbit. The moon itself fell into
Saturn leaving no trace behind, but it left the glorious rings
that we see with Saturn today, which are made mostly of ice. NARRATOR: Of Saturn's
60 remaining moons, Titan is the largest. It's 1 and 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. DAN DURDA: The model,
really, for the first time explains the ice rich
nature of those rings. You'd expect 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 and
you 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 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. ALEX FILIPPENKO: Early in the
history of the solar system, Jupiter and Saturn 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. NARRATOR: 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. 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 2 to 1 resonance. GREG LAUGHLIN: 2 to 1
resonance is a very strong gravitational interaction when
taken over millions of years. And having Jupiter and
Saturn in a 2 to 1 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. LAURA DANLY: When Jupiter and
Saturn reached that 2 to 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. 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. DAN DURDA: It's
almost a certainty that our solar system has
lost planets along the way, during this 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. NARRATOR: But the
2 to 1 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 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. ALEX FILIPPENKO: The wandering
around of Jupiter and Saturn would have created gravitational
tugs on the proto-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 2 to 1 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. DAN DURDA: 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 four billion years ago here in the
inner solar system. We had the geologic
evidence ever since Apollo, in the dating of the
rocks from the moon that showed this period of
dates at that time. GREG LAUGHLIN: 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 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
recently uncovered evidence that one of them, a
world the size of Pluto, plunged into Mars, drastically
reshaping the red planet. MICHAEL MISCHNA: It was a
very large impactor that struck the planet at a very
low, 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. 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. LAURA DANLY: We see evidence
for impacts on other planets because they form craters
that all follow the same sort of pattern, nice excavated
pit, there's 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 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,
the Mars Magnetic Disaster. Spacecraft orbiting Mars
revealed 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. ALEX FILIPPENKO:
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. MICHAEL MISCHNA: 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. ALEX FILIPPENKO: 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. GREG LAUGHLIN: It's very clear
that all of 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 facelift 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 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. MICHAEL MISCHNA:
In some respects, the shield volcanoes on Mars are
similar to some volcanoes here on Earth, such as in 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, 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. GREG LAUGHLIN: When we look
at Mars's 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 unmarked. If a 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. GREG LAUGHLIN: On Mars, there
was never large scale plate tectonics of the type
that we have on Earth. And 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
in 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 homegrown violence. Next on our countdown
of planetary disasters, the Great Venus Meltdown. 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. ALEX FILIPPENKO: 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. The hellish conditions
on Venus could have been caused by an extreme
runaway greenhouse effect over three billion years ago. ALEX FILIPPENKO:
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. GREG LAUGHLIN: We know from
sampling Venus's 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 e-mailed us, did life once thrive on Venus? Jack, that's a really
fascinating question. It turns out that Venus
may have had oceans for the first half a 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. GREG LAUGHLIN: 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. ALEX FILIPPENKO: 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. The Shoemaker Levy 9 Impacts. LAURA DANLY: 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. Its gravitational force
deflects renegade comets that break loose from
their orbital prisons in the Oort Cloud
and Kuiper Belt. ALEX FILIPPENKO: 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. DAN DURDA: 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 half a mile across striking an
object the size of the Earth, the dust fall from that
impact would 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. GREG LAUGHLIN: Jupiter has very
vigorous and oftentimes 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 four 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. 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. DAN DURDA: 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 degrees
passed through its rings, tilting and twisting
them into the ripples that we still see today. DAN DURDA: 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 it 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. MICHAEL MISCHNA: 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. LAURA DANLY: The fact that
we've seen several of these suggests 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. MICHAEL MISCHNA: 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, Planetary Armageddon. 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. tggftttyt Right now,
our solar system is the paradigm of
clockwork regularity. But it turns out that
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's orbit. If Mercury's orbit ever
gets to the situation where it's crossing
Venus's 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. GREG LAUGHLIN: 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 is a small probability that things will
unfold in such a way that Earth itself is
impacted by Mercury. 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
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.
