Name: 土星の不思議な月 (Saturn's Mysterious Moons)
Uploaded: 2021-01-14T04:42:33.000Z
Duration: 25 min 15 s
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Launched three years before the new century... a spacecraft wound its way through the empty

倒置法（否定的な副詞がある場合）

On Earth, its progress was little noted, as it swung twice by the planet Venus, then our

moon. And Earth. The asteroid belt. And Jupiter.

Almost seven years later, on the first of July 2004, the Cassini probe entered the orbit

of Saturn. It then began to compile what has become one of the greatest photographic collections

of all time, of a giant gas planet, surrounded by colorful rings, guarded by a diverse collection

Within this record, is a trail of clues... pointing to the energy sources and complex

chemistry needed to spawn life. What are these mysterious worlds telling us about the universe,

In the outer reaches of the solar system, a billion and a half kilometers from the Sun...

there is a little world known as Enceladus. Nearly all of the sunlight that strikes its

icy surface is reflected back into space, making it one of the brightest objects in

At its equator, the average temperature is minus 198 degrees Celsius. It can rise about

70 degrees higher in grooves that stretch across the south pole like tiger stripes.

Looming over it is the giant planet Saturn.

In myth, Saturn - the Roman name for the primal Greek God Chronos - was the youngest son of

Wielding a scythe provided by his mother, the story goes, Saturn confronted his abusive

father, castrating him. The blood of Uranus flowed into the seas, fertilizing the Earth

and giving rise to Enceladus and other giant offspring.

Saturn's moon Enceladus has its own tangled story. In 2005, the Cassini spacecraft spotted

plumes of water vapor shooting out into space from several locations near its south pole.

More recent close encounters have revealed jets of water, flavored by slightly salty

chemical compounds, spewing out from vents in the rough, cracked polar terrain. That

may mean that Enceladus harbors a remarkable secret below its frigid surface: A liquid

ocean, and perhaps, a chemical environment that could spawn simple life forms.

It's not the only promising stop in the realm of Saturn. The moon Titan is often said to

resemble Earth in its early days. It is lined with volcanoes and a hazy atmosphere rich

While Enceladus is the size of Great Britain, Titan is ten times larger, 50% larger than

our moon, and the second largest moon in our solar system.

We've known about Titan since the astronomer Christian Huygens discovered it in 1655, and

Enceladus since William Herschel spotted it in August 1789, just after the start of the

Scientists began to investigate these moons in earnest with the launch of the two Voyager

spacecraft in 1977. The lineup of outer planets in the solar system allowed the spacecraft

Along the way, they 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 toward

interstellar space - made discoveries about the chemical environments that have turned

these planets into gigantic works of abstract art.

They also disclosed new details about their magnetic fields, atmospheres, ring systems,

and inner cores. But what really turned heads were the varied shapes and surfaces of their

They've all been pummeled over the millennia by wayward asteroids and comets. A few appear

to be sculpted by forces below their surfaces. Neptune's largest moon Triton has few craters.

It's marked with circular depressions bounded by rugged ridges. There are also grooves and

folds that stretch for dozens of miles, a sign of fracturing and deforming.

Triton has geysers too, shooting some five miles above the surface. But on this frigid

moon - so far from the Sun - the liquid that spouts is not water but nitrogen.

Tiny Miranda, one of 27 known moons that orbit Uranus, wears a jumbled skin that's been shaped

Jupiter's moon Io - orbiting perilously close to the giant planet is literally turning itself

inside out. Rivers of lava roll down from open craters that erupt like fountains.

What's causing these tiny moons to come to life? The surface of Jupiter's moon Europa

offers a window into the churning activity at its core.

Flying by Europa, Voyager documented a complex network of criss-crossing grooves and ridges.

In the 1990s, the Galileo spacecraft went back to get a closer look. 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?

Europa orbits Jupiter in a slight ellipse, diving in close before swinging wide. That

allows the massive planet's gravity to constantly tug at its rocky center. The friction of rock

rubbing on rock causes that core to heat up.

Then, heat rising up through a subsurface ocean of liquid water cracks, and shifts,

and spreads the icy surface in a thousand different ways. Europa's neighbors, Callisto

and Ganymede, show similar features, suggesting they too may have liquid oceans below their

Crossing outward to Saturn, Voyager found a similar surface on the moon Enceladus. So

when the Cassini spacecraft arrived in 2004, it came looking for answers to a range of

burning questions: if this moon and others have subsurface oceans? Do they also have

the ability to cook up and support life? And what could they tell us about the origin of

Cassini came equipped with 12 separate instruments to analyze light waves, to figure out the

composition of dust, measure magnetic fields, and more.

After a year in orbit, Cassini let go of its traveling companion, the Huygens probe...

and sent it parachuting down to the surface of Titan.

Unexpected crosswinds buffeted Huygens' parachute, but the probe was able to snatch a wealth

Its on-board radar showed a complex topography with ridges, rivers, and lakes, and even rocks

Titan's atmosphere is thick and cold. Like Earth, the air here is mostly nitrogen gas.

What's more, Titan's muddy, wet terrain is laced with organic compounds. On our planet,

it's water that cycles from ice to steam. On Titan, it's methane.

Methane gurgles up from the ground in liquid form and flows into lakes. It freezes in spots,

or floats off as gas in orange clouds. This image shows a flash of sunlight reflecting

off a sprawling 400,000 square kilometer lake known as Kraken Mare.

Scientists consider Titan to be a possible mirror of Earth in its early days with the

chemistry of life still in its earliest stages. That's why they are so eager to explore its

varied landscapes. So far, radar passes by Cassini have revealed expansive dune fields,

wetlands, hilly terrain, and the occasional crater.

Scientists mapped an area near Titan's south pole called Sikun Labyrinthus. The image shows

a network of canyons and cliffs sculpted by liquid methane.

Nearby, methane flows into a lake called Ontario Lacus. A little smaller than Lake Michigan,

it's bounded by bays, river deltas, beaches, and other familiar features.  And here, in a region called Sotra Facula.

Cassini mapped what looks like a volcano. Thousand meter high peaks tower over craters

Are these features the result of an internal heat source, like the grooves that line Enceladus

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土星の不思議な月 (Saturn's Mysterious Moons)

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