S C I E N C E: Saturn data stuns scientists

New data sent back by the Cassini space probe has left scientists
beguiled by Saturn's seething clouds of gas, the beauty and unexpected
turbulence of its rings and the diversity of its moons, a conference

"The complexity is just dumbfounding," Dennis Matson, senior scientist
with the Cassini project, told a meeting in Cambridge of top US and
European specialists on the solar system.

The last of the big-ticket explorations of the outer planets begun by
the United States four decades ago, Cassini arrived at Saturn in
mid-2004 on a four-year mission to survey the ringed giant and its
satellites. In December, the three billion dollar (2.4 billion euros)
mission sent down the European probe Huygens on a suicide plunge to
Titan, a moon whose bizarre photochemistry -- a smog of methane and
other carbon compounds -- makes it one of the most puzzling objects in
the system.

Extraordinary pictures from Cassini, unveiled at the Cambridge meeting,
had many astronomers gasping in amazement at details that formerly they
could only guess at, through Earth-bound telescopes or a snatched
glance by NASA's Voyager spacecraft. One surprise is the sheer
diversity of the clouds lurking in the depths of the atmosphere of
Saturn, a gas giant like its slightly larger sibling, Jupiter. "Unlike
the hazy, broad, global bands of clouds regularly seen in Saturn's
upper atmosphere, many of the deeper clouds appear to be isolated,
localized features," said Kevin Baines, a member of the visual and
infrared mapping spectrometre team at NASA's Jet Propulsion Laboratory.
"They come in a large variety of sizes and shapes, including circular
and oval shapes, Űring-likeű doughnut shapes, and swirls."

These clouds are deep in the atmosphere, about 30 kilometers (19 miles)
underneath the upper clouds usually seen on Saturn. They also behave
differently from those in the upper atmosphere and consist of different
materials, JPL said. They are made of either ammonium hydrosulphide or
water, but not ammonia -- the chemical generally thought to comprise
the upper clouds.

Saturn's roiling, suffocating atmosphere is also inhabited by huge
thunderstorms the size of an Earth-sized continent. One cataclysmic
event spotted by Cassini's cameras was named "Dragon Storm" because it
coincidentally took the shape of a dragon, Matson said. Saturn's most
famous possession -- the rings, first spotted by Galileo in 1610
according to legend -- is in a continuous state of evolution, the
Cassini team reported.

Far from being a region of circling coherence and tranquility, the
rocky debris of the seven rings bump and clump together and pull part,
enslaved in the gravitational grip of their master and ripped by
passing moons. The A ring -- the outermost -- "is primarily empty
space," as debris becomes clustered, gets torn apart and then
reassembled by Saturn's gravitational forces.

Part of the D ring -- the ring closest to Saturn -- has become dimmer
and moved inward, toward Saturn, by about 200 kilometers (125 miles),
since it was observed by Voyager in 1980 and 1981. The ring system "is
an absolutely dynamic region. The rings are constantly moving, with the
interplay of gravity and possibly magnetic fields," said Carolyn Porco
of the Space Science Institute at Boulder, Colorado. Another big
surprise is that a spiral ring encircles the planet like a coiled
spring. This "spiral arm" exists around the F ring, and could be the
consequences of moons that, themselves tortured by Saturn's giant
gravity, spew out material. This raises the question that the F ring
might be unstable or even short-lived.

As for Saturn's 46 moons, Enceladus has joined Titan as a source of
nagging speculation as to how they were formed -- a process that sheds
light on the birth of Earth and the other rocky planets that orbit
close to the Sun. The south pole of this ice-covered satellite is
streaked with deep, long cracks nicknamed "tiger stripes." Thermal
sensors show this area to be a hot spot, albeit still very cold by
Earth standards, and with a localised atmosphere of water vapour. The
implication is that there is some warm, sub-surface ocean. But how
could this happen? Enceladus is in theory too tiny to develop enough
internal heat to do this.