Cassini Prepares to Swoop by Saturn's Geyser-Spewing Moon

http://www.jpl.nasa.gov/news/news.cfm?release=2008-156

Cassini Prepares to Swoop by Saturn's Geyser-Spewing Moon
Jet Propulsion Laboratory
August 07, 2008

Fractures, or "tiger stripes," where icy jets erupt on Saturn's moon
Enceladus will be the target of a close flyby by the Cassini
spacecraft
on Monday, Aug. 11.

Cassini will zoom past the tiny moon a mere 50 kilometers (30 miles)
from the surface. Just after closest approach, all of the spacecraft's
cameras -- covering infrared wavelengths, where temperatures are
mapped,
as well as visible light and ultraviolet -- will focus on the fissures
running along the moon's south pole. That is where the jets of icy
water
vapor emanate and erupt hundreds of miles into space. Those jets have
fascinated scientists since their discovery in 2005.

"Our 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
Ithaca, NY. "From this data we may learn more about how eruptions,
tectonics, and seismic activity alter the moon's surface. We will get
an
unprecedented high-resolution view of the active area immediately
following the closest approach."

Seeing inside one of the fissures in high resolution may provide more
information on the terrain and depth of the fissures, as well as the
size and composition of the ice grains inside. Refined temperature
data
could help scientists determine if water, in vapor or liquid form,
lies
close to the surface and better refine their theories on what powers
the
jets.

Imaging sequences will capture stereo views of the north polar
terrain,
and high resolution images of the south polar region will begin
shortly
after closest approach to Enceladus. The image resolution will be as
fine as 7 meters per pixel (23 feet) and will cover known active spots
on three of the prominent "tiger stripe" fractures.

In addition to mapping the moon's surface in visible light as well as
infrared and ultraviolet light, Cassini will help determine the size
of
the ice grains and distinguish other elements mixed in with the ice,
such as oxygen, hydrogen, or organics.

"Knowing 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 Amanda Hendrix, Cassini ultraviolet imaging spectrograph
team member at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Other instruments will measure the temperatures along the fractures,
which happen to be some of the hottest spots on the moon's surface.

"We'd 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 Bonnie Buratti of JPL, team member on
Cassini's
visual and infrared mapping spectrometer.

Cassini discovered evidence for the geyser-like jets on Enceladus in
2005, finding that the continuous eruptions of ice water create a
gigantic halo of ice and gas around Enceladus, which helps supply
material to Saturn's E-ring. This marks Cassini's second flyby of
Enceladus this year. During Cassini's last flyby of Enceladus in
March,
the spacecraft snatched up precious samples and tasted comet-like
organics inside the little moon. Two more Enceladus flybys are coming
up
in October, and they may bring the spacecraft even closer to the moon.
The Oct. 9 encounter is complimentary to the March one, which was
optimized for sampling the plume. The Oct. 31 flyby is similar to this
August one, and is again optimized for the optical remote sensing
instruments.

For images, videos and a mission blog on the flyby, visit:
http://www.nasa.gov/cassini . More information on the Cassini mission
is
also available at http://saturn.jpl.nasa.gov .

Editors: A pre-flyby videofile with animation, images and interview is
available on NASA TV. The videofile airs at 12 p.m. Eastern on the
Media
Channel with replays at 4 p.m., 8 p.m. and 10 p.m Eastern. In the
continental United States, NASA Television's Public, Education and
Media
channels are carried by MPEG-2 digital C-band signal on AMC-6, at 72
degrees west longitude, Transponder 17C, 4040 MHz, vertical
polarization. They're available in Alaska and Hawaii on an MPEG-2
digital C-band signal accessed via satellite AMC-7, transponder 18C,
137
degrees west longitude, 4060 MHz, vertical A Digital Video Broadcast
(DVB)-compliant Integrated Receiver Decoder (IRD) with modulation of
QPSK/DVB-S, data rate of 36.86 and FEC is needed for reception.

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Media contact: Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
carolina.martinez@xxxxxxxxxxxx

2008-156
.

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