[dramatic music]
[explosions]
NARRATOR: 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.
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 the 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 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.
[explosion]
But 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.
And 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.
[roaring]
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.
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.
MICHAEL MISCHNA: Right
now, our solar system
is kind of a 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.
[explosion]
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.
