Some 900 million miles from the Sun... in the outer regions of our Solar System... orbiting
the planet Saturn....
...lies a mysterious world.
Enceladus is enveloped in ice. Because nearly all of the sunlight that manages to hit its
surface is reflected back into space, it's one of the brightest objects in the solar
system.
At its equator, the temperature is -315 degrees Fahrenheit.
But, at the poles, the temperature is at least 15 degrees warmer... and as much as 65 degrees
warmer in grooves that stretch across the south like tiger stripes.
In 2005, the Cassini spacecraft spotted a complex plume of water vapor shooting out
into space from several locations near the south pole.
That may mean that Enceladus harbors a remarkable secret below its frigid surface:
A liquid ocean... and maybe... some forms of life.
This discovery was the culmination of a search that began over three decades ago. .
Back in 1979, the outer planets of the solar system lined up in such a way that mission
planners were able to dispatch the Voyager spacecraft to fly past each of them ...
The two Voyagers sent back tens of thousands of images... of planetary realms more diverse
than anyone had imagined.
These long-distance marathon flyers - both now headed out towards interstellar space
- made discoveries about the planetary chemistry that make these gas giants appear to us as
gigantic works of abstract art.
The Voyagers disclosed new details about their magnetic fields, atmospheres, ring systems,
and even the nature of their inner cores.
Voyager turned up some surprising new mysteries too:
a huge dark spot - a storm in fact - on Neptune...
They found that Uranus is tipped 90 degrees to one side...
That Saturn is less dense than water; if you had a bathtub big enough, Saturn would float!
...And that you'd need the mass of three Saturns to make just one Jupiter!
But what really knocked the scientists' socks off were the moons that orbit these gas giants.
All of them have been pummeled over the millennia by wayward asteroids and comets...
But a few appear to also be sculpted by forces below their icy surfaces.
Neptune's largest moon Triton has few craters. It's marked with circular depressions bounded
by rugged ridges that may mean the icy surface is collapsing.
There are also grooves and folds in the land that stretch for dozens of miles, a sign of
fracturing and deforming.
Triton has geysers too. But these are not spurts of water. On frigid Triton - so far
from the Sun - the liquid that spouts some five miles above the planet is nitrogen. No
one yet knows exactly what drives them.
Tiny Miranda... one of 27 known moons that orbit Uranus... wears a jumbled skin that's
been shaped and reshaped. Most likely, its outer crust is slipping and sliding on a molten
core.
The moon called Io - orbiting perilously close to giant Jupiter is literally turning itself
inside out! Rivers of sulfurous lava roll down from open craters that are constantly
erupting.
What was causing these tiny moons to generate so much energy from within? The answer may
well be here... on Jupiter's Europa - just slightly smaller than Earth's Moon.
Voyager saw no signs of volcanic activity, but -but instead documented a complex network
of criss-crossing grooves and ridges.
In the 1990s, the Galileo spacecraft was sent back to get a closer look at Europa and its
sister moons. .
It found that Europa's surface is a crazy quilt of fractured plates, cliff faces and
gullies... amid long grooves like a network of superhighways.
How did it get like this?
Well, as it orbits around Jupiter in a nearly circular ellipse, the massive planet's gravity
constantly tugs at Europa's rocky core.
The friction of rock rubbing on rock causes that core to heat up.
That heat rises up through an ocean of liquid water... then cracks and spreads the icy surface
in a thousand different ways.
Callisto and Ganymede also show such features... suggesting they have - or perhaps once had
-liquid oceans below their surfaces too!
Crossing outward to the Saturn system, Voyager's images from the late 1970's showed that the
moon Enceladus had a similar surface...
The same was presumed of Saturn's by far largest moon, Titan... enshrouded in heavy clouds.
So when the Cassini spacecraft arrived in 2004 to scrutinize the kingdom of Saturn,
it came ready to answer a range of burning questions...
Can such moons really have liquid oceans beneath their surfaces... and do those oceans have
the ability to cook up and then support life?
After a year in orbit, Cassini let go of its traveling companion, the Huygens probe...
and sent it parachuting down towards the surface of Titan.
It's the largest moon in the solar system, larger in size - in fact - than the planet
Mercury... and massive enough to hold an atmosphere.
Unexpected crosswinds buffeted Huygens' parachute... but the probe was able to snatch a wealth
of revealing information.
During Huygens' descent, its on-board radar showed a complex topography... with ridges,
rivers, and lakes... and even individual rocks on the ground.
Titan's atmosphere is thick and cold, the thermometer hovering just above minus 300
Fahrenheit. Like Earth, the air here is mostly nitrogen gas.
And like Earth in its very early years, Titan's muddy, wet terrain is a stew of organic compounds.
But while the liquid that cycles from ice to steam here on Earth is water, Titan's ever-changing
fluid is methane.
On Titan, methane gurgles up from the ground in liquid form and flows into lakes...freezes
into hydrocarbon icebergs ... and puffs off as gas in orange clouds and pinkish fog.
It may not be completely crazy to imagine a primitive form of life arising out of this
chaotic, cold carbon-rich chemistry.
Once again, the evidence points toward a moon with a rocky core, heated by the tidal gravity
of a massive planet... and layers of liquid and ice near the surface that burst forth
in cold volcanoes and icy geysers.
All this activity has left a profound imprint upon the landscape.
Repeated radar passes by Cassini reveal expansive dune fields of methane mud... wetlands...
structures that look like volcanic vents... and the occasional crater.
And there's at least one continent... now known as Xanadu.
To reach us, these images had to travel nearly a billion miles. At the end of the journey...
...they were picked up by the Deep Space Network... think of the DSN as the early prototype for
an interplanetary internet.
Within just a few years, Cassini had transmitted one of the most impressive photographic records
of all time...
Of a fascinating ringed planet... a turbulent gas giant.
It saw a storm that raged across Saturn's southern hemisphere for months - generating
lightning strikes thousands of times more powerful than those on Earth.
Cassini witnessed a giant cyclone larger than Earth ... spinning around at Saturn's south
pole, - a huge hurricane with a eye so big you could drop the entire continental United
States into it without touching the cloud walls...
And Cassini radioed back unprecedented new details of Saturn's most famous feature...
its rings.
The Italian astronomer Galileo Galilei discovered these broad, flat concentric bands of ice
and dust, four hundred years ago, in 1610.
But he didn't realize they were actually rings... And he couldn't have had any clue how intricate
they truly are.
Even today, we don't yet know just where they came from.
Nor how old - or young - they actually are.
The chunks and particles range from boulders the size of houses down to tiny granules,
finer than baby powder.
They may contain the remains of two moons that collided and shattered. But something
may also be continually adding material.
The rings stretch more than 150,000 miles across - but, in any one place, they are less
than a mile from top to bottom.
Saturn is almost like a solar system unto itself:
Everything acts upon everything else.
The planet's moons - more than 60 have been named so far - and countless small moonlets
pull and tug on the Ring particles - shaping and twisting and clearing lanes - making them
dance to the combined music of their masses.
The medium-sized moon Mimas - orbiting close in to Saturn - has hollowed out a large gap
called the Cassini Division.
Some tiny moons actually ride within the rings.
Other moons continually sculpt the rings... gently shepharding the granules with their
gravity.
And across the ring plane, spokes of different colored dust occasionally cling like strands
of hair on a cold dry day.
Like the rings, each of Saturn's sixty-plus moons tells a different story... enticing
us in for a closer look.
There's dense little Dione - hard rock covered by ice - pummeled on one side by asteroids...
causing craggy cliffs to spring up on the other.
Hyperion... looks like a sponge... an odd-shaped world pocked with odd-shaped craters...it
tumbles around so chaotically, it's really tough to predict its exact orbit.
Iapetus... looks like a cosmic Yin-Yang symbol - with one hemisphere brighter than snow
and the other darker than tar.
A strange ridge system of mountains - like the spine of a rhino - runs around its equator,
in places more than 12 miles tall.
But it's one of Saturn's smallest moons, Enceladus, that really steals the show. That's Saturn's
second largest moon, Rhea, passing behind it.
Compared to many of its sister moons, Enceladus has fewer craters. The largest is relatively
small, only 22 miles across.
Like Europa... Enceladus has a finely textured landscape - with at least five different kinds
of terrain... a sign that it's frequently remade by geologic activity.
It's fractured and wrinkled surface is most obvious around its south pole. But there is
something else going on down here among these ridges.
Enceladus lies outside of Saturn's bright inner rings, in the wide and diffuse E Ring.
With Cassini's camera pointed at just the right angle to the sun, Saturn's E Ring lit
up. Enceladus is the bright object in the center of the frame.
What is all this hazy stuff made of? Could it be coming from the moon itself?
The plan had been to let Cassini tour the Saturn system until the middle of 2008.
But the mission was clearly too successful - and too intriguing - to let it end... And
the Cassini science team suspected that they were onto something big.
So they went to work: plotting new orbital paths... building a new target list... preparing
to have another go at Enceladus.
They set the spacecraft on course for a set of close flybys of its south pole... down
to as close as 25 miles above its surface.
This is what Cassini saw...
Plumes of vapor rising out of the ice.
Scientists began to think of them as geysers, much like those in geologic hot spots on earth.
If the team could find out what these jets are made of, they might just have some major
clues to what's going on deep inside Enceladus.
And if there truly are liquid oceans, what's in them?
To get some answers, Cassini sampled particles that make up the E Ring. It found crystals
of water, and within them, it detected the presence of a simple compound well known on
Earth... salt.
Salt dissolved in water tastes like evidence to a scientist... evidence that friction from
a rocky core jostled by Saturn's gravity warms a reservoir of liquid water below the icy
surface of Enceladus... and sends it bursting through!
Now, to be accurate, Enceladus' jets could possibly form without liquid water.
And even if they begin as liquid, they may boil up out of a few water-filled caverns,
rather than a huge ocean.
But if this tiny moon's waterspouts do originate in a sizeable subterranean sea, the possibilities
for life throughout the galaxy may be that much greater.
How amazing that, even out here... almost 900 million miles from the Sun...
...far beyond the orbit of Earth...
and far outside what many call the "Goldilocks Zone" ... this distant little moon might just
harbor the conditions needed for chemistry to become biology.
So we continue to mine the kingdom of Saturn for knowledge and images.
And not just from space. For eight years, astronomers at the Gemini Telescope in Hawaii
had been monitoring...
...The infrared light streaming in from the Saturn system.
For the first time, on Titan, they saw evidence of a massive and unlikely storm erupting over
what's thought to be a vast equatorial desert. If nothing else, it shows how much we still
have to learn about these mystery worlds.
Meanwhile, Cassini keeps adding to its unprecedented photographic collection.
With Saturn now at its farthest point from the Sun, the angle of the light allows objects
to cast long shadows across the rings... like this little moon, never before seen.
Or these ones that seem to have punched through the F Ring.
Who knows whether Saturn's moons have ignited the spark of life.
Since Galileo, they have certainly ignited our imaginations.
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