Cassini Shows Saturnian Roller Derby, Strange Weather

Cassini Shows Saturnian Roller Derby, Strange Weather

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-090&cid=release_2010-090

From our vantage point on Earth, Saturn may look like a peaceful orb with rings worthy
of a carefully raked Zen garden, but NASA's Cassini spacecraft has been shadowing the
gas giant long enough to see that the rings are a rough and tumble roller derby. It has also
revealed that the planet itself roils with strange weather and shifting patterns of charged
particles. Two review papers to be published in the March 19 issue of the journal Science
synthesize Cassini's findings since arriving at Saturn in 2004.

"This rambunctious system gives us a new feel for how an early solar system might have
behaved," said Linda Spilker, a planetary scientist and the new Cassini project scientist at
NASA's Jet Propulsion Laboratory in Pasadena, Calif. "This kind of deep, rich data can
only be collected by an orbiting spacecraft, and we look forward to the next seven years
around Saturn bringing even more surprises."

In the paper describing the elegant mess of activity in the rings, lead author Jeff Cuzzi,
Cassini's interdisciplinary scientist for rings and dust who is based at NASA Ames
Research Center, Moffett Field, Calif., describes how Cassini has shown us that collisions
are routine and chunks of ice leave trails of debris in their wakes. Spacecraft data have
also revealed how small moons play tug-of-war with ring material and how bits of rubble
that would otherwise join together to become moons are ultimately ripped apart by the
gravitational pull that Saturn exerts.

During equinox, the period when sunlight hits the rings exactly edge-on, Cassini
witnessed rings that are normally flat – about tens of meters (yards) thick – being flipped
up as high as the Rocky Mountains.

The spacecraft has also shown that the rings are composed mostly of water ice, with a
mysterious reddish contaminant that could be rust or small organic molecules similar to
those found in red vegetables on Earth.

"It has been amazing to see the rings come to life before our very eyes, changing even as
we watch, being colorful and taking on a tangible, 3-D nature," Cuzzi said. "The rings
were still a nearly unstructured object in even the best telescopes when I was a grad
student, but Cassini has brought us an intimate familiarity with them."

Cuzzi said Cassini scientists were surprised to find such fine-scale structure nearly
everywhere in the rings, forcing them to be very careful about generalizing their findings
across the entire ring disk. The discovery that the rings are clumpy has also called into
question some of the previous estimates for the mass of the rings because there might be
clusters of material hidden inside of the clumps that have not yet been measured.

In the review paper on Saturn's atmosphere, ionosphere and magnetosphere, lead author
Tamas Gombosi, Cassini's interdisciplinary scientist for magnetosphere and plasma
science who is based at the University of Michigan in Ann Arbor, describes how Cassini
helped scientists understand a south polar vortex that has a diameter 20 to 40 times that
of a terrestrial hurricane, and the bizarrely stable hexagon-shaped jet stream at the planet's
north pole. Cassini scientists have also calculated a variation in Saturn's wind speeds at
different altitudes and latitudes that is 10 times greater than the wind speed variation on
Earth.

According to Gombosi's paper, Cassini has also shown us that the small moon Enceladus,
not the sun or Saturn's largest moon Titan, is the biggest contributor of charged particles
to Saturn's magnetic environment. The charged particles from Enceladus, a moon that
features a plume of water vapor and other gases spraying from its south polar region, also
contribute to the auroras around the poles of the planet.

"We learned from Cassini that the Saturnian magnetosphere is swimming in water,"
Gombosi said. "This is unique in the solar system and makes Saturn's plasma environment
particularly fascinating."

Of course, Cassini's intense investigation has opened up a host of new mysteries. For
example, Cassini has shown us images of occasional cannon-ball-like objects that rocket
across one of the outer rings known as the F ring, without many clues about where they
came from or why they quickly disappear.

Learning more about a kind of radio emission known as "kilometric radiation" at Saturn
has unsettled debates about the planet's rotation rate rather than settled them. While the
regular periods of kilometric radiation have given scientists a sense of the rotation rate at
Jupiter, Saturn has clocked different periods for the radiation during NASA's Voyager
flybys in 1980 and 1981 and the nearly six years of Cassini's investigations. The
modulations vary by about 30 seconds to a minute, but they shouldn't be varying at all.
The inconsistency may be related to a source in the magnetic bubble around the planet
rather than the core of the gas giant, but scientists are still debating.

"Cassini has answered questions we were not even smart enough to ask when the mission
was planned and raised a lot of new ones," Cuzzi said. "We are hot on the trail, though."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space
Agency and the Italian Space Agency. JPL manages the project for NASA's Science
Mission Directorate in Washington. The Cassini orbiter was designed, developed and
assembled at JPL.

More Cassini information is available, at http://www.nasa.gov/cassini and
http://saturn.jpl.nasa.gov.

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui.c.cook@jpl.nasa.gov

Rachel Prucey 650-604-0643
NASA Ames Research Center, Moffett Field, Calif.
rachel.l.prucey@nasa.gov.

2010-090
-end-

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