Cassini Plans Doubleheader Flybys of Saturn's Geyser Moon

MEDIA RELATIONS OFFICE
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Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
carolina.martinez@jpl.nasa.gov

NEWS RELEASE: 2008-185 Oct. 6, 2008

Cassini Plans Doubleheader Flybys of Saturn's Geyser Moon

PASADENA, Calif. -- As major league baseball readies for the World Series, NASA's Cassini
team will come to bat twice this month when the spacecraft flies by Saturn's geyser moon,
Enceladus.

The Oct. 9 flyby is an inside pitch—the closest flyby yet of any moon of Saturn, at only 25
kilometers (16 miles) from the surface. The Oct. 31 flyby is farther out, at 196 kilometers (122
miles).

Scientists are intrigued by the possibility that liquid water, perhaps even an ocean, may exist
beneath the surface of Enceladus. Trace amounts of organics have also been detected, raising
tantalizing possibilities about the moon's habitability.

While Cassini's cameras and other optical instruments were the focus of an Aug. 11 flyby, during
Cassini's Oct. 9 flyby, the spacecraft's fields and particles instruments will venture deeper into
the plume than ever before, directly sampling the particles and gases. The emphasis here is on
the composition of the plume rather than imaging the surface.

"We know that Enceladus produces a few hundred kilograms per second of gas and dust and that
this material is mainly water vapor and water ice," said Tamas Gambosi, Cassini scientist at the
University of Michigan, Ann Arbor. "The water vapor and the evaporation from the ice grains
contribute most of the mass found in Saturn's magnetosphere.

"One of the overarching scientific puzzles we are trying to understand is what happens to the gas
and dust released from Enceladus, including how some of the gas is transformed to ionized
plasma and is disseminated throughout the magnetosphere," said Gambosi.

On Oct. 31, the cameras and other optical remote sensing instruments will be front and center,
imaging the fractures that slash across the moon's south polar region like stripes on a tiger.

These two flybys might augment findings from the most recent Enceladus flyby, which hint at
possible changes associated with the icy moon. Cassini's Aug. 11 encounter with Enceladus
showed temperatures over one of the tiger-stripe fractures were lower than those measured in
earlier flybys. The fracture, called Damascus Sulcus, was about 160 to 167 Kelvin (minus 171 to
minus 159 degrees Fahrenheit), below the 180 Kelvin (minus 136 degrees Fahrenheit) reported
from a flyby in March of this year.

"We don't know yet if this is due to a real cooling of this tiger stripe, or to the fact that we were
looking much closer, at a relatively small area, and might have missed the warmest spot," said
John Spencer, Cassini scientist on the composite infrared spectrometer, at the Southwest
Research Institute, Boulder, Colo.

Results from Cassini's magnetometer instrument during the August flyby suggest a difference in
the intensity of the plume compared to earlier encounters. Information from the next two flybys
will help scientists understand these observations.

Four more Enceladus flybys are planned in the next two years, bringing the total number to
seven during Cassini's extended mission, called the Cassini Equinox Mission. The next
Enceladus doubleheader will be November 2 and 21, 2009.

The Enceladus geysers were discovered by Cassini in 2005. Since then, scientists have been
intrigued about what powers them, because the moon is so tiny, roughly the width of Arizona at
only 500 kilometers (310 miles) in diameter.

"The October doubleheader gives Cassini two more opportunities to hit the ball out of the park,"
said Bob Pappalardo, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena,
Calif. "With high scores in geology, surface heat, watery plumes and magnetospheric effects,
Enceladus could win the 'world championship' title this year!"

Scientists anticipate reporting results from the two flybys in November and early December.

Cassini has been orbiting Saturn since 2004. The Cassini-Huygens mission is a cooperative
project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the
Cassini-Huygens mission for NASA's Science Mission Directorate. The Cassini orbiter was
designed, developed and assembled at JPL.

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 .

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