August 8, 2008

Cassini Prepares for Monday Flyby of Saturn Moon

Cassini spacecraft is going to get another up-close-and-personal look at
Saturn's moon Enceladus on Monday. Scientists hope the glimpse at fractures on
the icy moon's surface will provide clues as to how the jets spewing from them

spacecraft will zoom past the tiny moon just 30 miles (50 kilometers) over the
surface. Immediately after closest approach, Cassini will train its cameras onto
the fissures that run along Enceladus' south pole.

Jets of icy
water vapor, first discovered by Cassini in 2005, erupt hundreds of miles into
space from these large cracks. The eruptions
create a giant halo of ice and gas around Enceladus that helps supply material
to Saturn's E-ring.

cameras, which collect light in the infrared, visible and ultraviolet
wavelengths, will aim to take high resolution images, as fine as 23 feet (7
meters) per pixel, of the known active spots on three of the prominent
"tiger stripe" fractures.

main goal is to get the most detailed images and remote sensing data ever of
the geologically active features on Enceladus," said Paul Helfenstein, a
Cassini imaging team associate at Cornell University in New York. "From
this data we may learn more about how eruptions, tectonics and seismic activity
alter the moon's surface."

observations, which detect temperatures on the surface, could help scientists
determine if water, in vapor or liquid form, lies close to the surface.

like to refine our numbers and see which fracture or stripe is hotter than the
rest because these results can offer evidence, one way or the other, for the
existence of liquid water as the engine that powers the plumes," said
Cassini team member Bonnie Buratti of NASA's Jet Propulsion Laboratory in
Pasadena, Calif.

observations should also help determine the size of the ice grains that spew
from the jets
, as well as distinguish any other elements mixed in with the
ice, such as oxygen, hydrogen or organics.

the sizes of the particles, their rates and what else is mixed in these jets
can tell us a lot about what's happening inside the little moon," said
Cassini team member Amanda Hendrix, also of JPL.

This next
flyby follows a previous
close approach
in March during which Cassini was to sample the material
emanating from the plumes. A software glitch kept the spacecraft from carrying
out its sampling mission, but it did return the most detailed images
of the moon to date.

flyby will be followed by two more in October. The attempt on Oct. 9 will also
try to sample one of the icy plumes, while the Oct. 31 flyby will image the
surface again. Cassini, currently on an extended two-year mission following the
June 30 completion of its four-year primary mission, entered orbit at Saturn
July 1, 2004.