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
"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,
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
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
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
Jet Propulsion Laboratory, Pasadena, Calif.