A University of Colorado at Boulder professor involved with
the Cassini-Huygens mission is reporting an ever-changing vista at
the frontiers of Saturn, featuring wayward moons, colliding
meteoroids, rippling rings and flickering auroras.

Larry Esposito of the Laboratory for Atmospheric and Space
Physics said CU-Boulder’s Ultraviolet Imaging Spectrometer, or UVIS,
riding on Cassini is revealing a dynamic dance in the Saturn system.
“Instead of a quiet panorama, UVIS sees rapidly changing phenomena,
including interactions between the rings, moons, radiation belt,
solar wind and the planet Saturn,” said Esposito, the principal
investigator for the $12.5 million UVIS instrument.

The instrument has detected oxygen atoms in an immense cloud
surrounding Saturn, the result of moonlets in the ring system
colliding, shattering and releasing ice particles. The ice grains
are bathed by Saturn’s radiation belt, liberating the oxygen atoms
that reflect sunlight and which makes them visible to the ultraviolet
spectrometer, said Esposito.

A UVIS analysis of Phoebe — a tiny, dark moon about
one-fifteenth the diameter of Earth’s moon — confirms the suspicions
of many space scientists that it was born elsewhere, likely in the
Kuiper Belt. The Kuiper Belt is a region beyond Neptune believed to
populated with thousands of small, icy moons created during the
formation of the solar system more than four billion years ago.

“UVIS sees the absorption signature of water ice on its
surface, showing Phoebe was born in the outer solar system,” Esposito
said. Exhibiting an unusual retrograde, or backward, orbit, Phoebe
likely was lassoed by Saturn’s powerful gravitational field during
the planet’s formative years, he said.

Esposito presented his findings at the 36th annual Division
of Planetary Sciences Meeting held in Louisville, Ken. Nov. 8 to Nov
12.

The UVIS research team also has noted significant brightening
of the auroras at Saturn’s poles as the solar wind periodically ramps
up to speeds of 250 miles, or 400 kilometers, per second, Esposito
said. “Dense puffs of the charged particles from the sun excite the
hydrogen molecules in Saturn’s upper atmosphere to glow more
brightly.”

In addition, UVIS continues to zero in on the fabulous ring
system. “At the time Cassini went into orbit around Saturn, UVIS
produced the highest detail images of Saturn’s rings ever made in UV
light,” he said. “These images show the amount of water-ice varies
in the ring particles’ surfaces.”

The variation is caused by the contamination of the rings
with meteoric dust, and by the subsequent transfer of material
between the ring particles from collisions and meteoroid bombardment,
Esposito said.

“The fluctuations we see can be explained by the recent
destruction of small moons within the rings, and by wave action in
the rings that dredges fresh material onto the surfaces of the ring
particles,” Esposito said. “This indicates that the material in the
rings is continually recycled from rings to moons and back.”

The UVIS instrument was used to obtain the highest resolution
observations of the ring particles ever by focusing on the
fluctuations of light from a distant star as it passed behind the
rings, he said.

The team also detected a density wave – a ripple-like feature
in the rings caused by the influence of Saturn’s moons — – in the
so-called Cassini Division. The Cassini Division is the gap between
the bright A and B rings of Saturn that are visible from Earth using
backyard telescopes, he said. “Analysis of such waves determines the
size, mass and velocity of the ring particles,” said Esposito.

The UVIS instrument also is showing a bright glow in the
upper atmosphere of Titan, the most intriguing of Saturn’s 33 known
moons and which will be targeted by the Cassini-Huygens probe slated
for release by the spacecraft Christmas Eve. “Observations of Titan
show the glow of nitrogen atoms, molecules and ions energized by
electrons striking the upper atmosphere,” he said.

Launched in 1997, the Cassini-Huygens spacecraft achieved
Saturn orbit June 30. During the spacecraft’s four-year tour of the
Saturn system, the UVIS team will continue to track the dynamic
interactions of the planet’s rings, moons and radiation belts,
Esposito said.

The Cassini-Huygens mission is a cooperative project of NASA,
the European Space Agency and the Italian Space Agency. The Jet
Propulsion Laboratory, a division of the California Institute of
Technology in Pasadena, manages the Cassini-Huygens mission for
NASA’s Science Mission Directorate, Washington, D.C.