Dwayne Brown
Headquarters, Washington
202-358-1726
dwayne.c.brown@nasa.gov

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

RELEASE: 08-078

CASSINI SPACECRAFT TO DIVE INTO WATER PLUME OF SATURN MOON

PASADENA, Calif. - NASA's Cassini spacecraft will make an
unprecedented "in your face" flyby of Saturn's moon Enceladus on
Wed., March 12.

The spacecraft, orchestrating its closest approach to date, will skirt
along the edges of huge Old-Faithful-like geysers erupting from giant
fractures on the south pole of Enceladus. Cassini will sample
scientifically valuable water-ice, dust and gas in the plume.

The source of the geysers is of great interest to scientists who think
liquid water, perhaps even an ocean, may exist in the area. While
flying through the edge of the plumes, Cassini will be approximately
120 miles from the surface. At closest approach to Enceladus, Cassini
will be only 30 miles from the moon.

"This daring flyby requires exquisite technical finesse, but it has
the potential to revolutionize our knowledge of the geysers of
Enceladus. The Cassini mission team is eager to see the scientific
results, and so am I," said Alan Stern, associate administrator of
NASA's Science Mission Directorate, Washington.

Scientists and mission personnel studying the anatomy of the plumes
have found that flying at these close distances poses little threat
to Cassini because, despite the high speed of Cassini, the plume
particles are small. The spacecraft routinely crosses regions made up
of dust-size particles in its orbit around Saturn.

Cassini's cameras will take a back seat on this flyby as the main
focus turns to the spacecraft's particle analyzers that will study
the composition of the plumes. The cameras will image Enceladus on
the way in and out, between the observations of the particle
analyzers.

Images will reveal northern regions of the moon previously not
captured by Cassini. The analyzers will "sniff and taste" the plume.
Information on the density, size, composition and speed of the gas
and the particles will be collected.

"There are two types of particles coming from Enceladus, one pure
water-ice, the other water-ice mixed with other stuff," said Sascha
Kempf, deputy principal investigator for Cassini's Cosmic Dust
Analyzer at the Max Planck Institute for Nuclear Physics in
Heidelberg, Germany. "We think the clean water-ice particles are
being bounced off the surface and the dirty water-ice particles are
coming from inside the moon. This flyby will show us whether this
concept is right or wrong."

In 2005, Cassini's multiple instruments discovered that this icy
outpost is gushing water vapor geysers out to a distance of three
times the radius of Enceladus. The moon is only 310 miles in
diameter, but despite its petite size, its one of the most
scientifically compelling bodies in our solar system. The icy water
particles are roughly one ten-thousandth of an inch, or about the
width of a human hair. The particles and gas escape the surface at
jet speed at approximately 800 miles per hour. The eruptions appear
to be continuous, refreshing the surface and generating an enormous
halo of fine ice dust around Enceladus, which supplies material to
one of Saturn's rings, the E-ring.

Several gases, including water vapor, carbon dioxide, methane, perhaps
a little ammonia and either carbon monoxide or nitrogen gas make up
the gaseous envelope of the plume.

"We want to know if there is a difference in composition of gases
coming from the plume versus the material surrounding the moon. This
may help answer the question of how the plume formed," said Hunter
Waite, principal investigator for Cassini's Ion and Neutral Mass
Spectrometer at the Southwest Research Institute, San Antonio.

This is the first of four Cassini flybys of Enceladus this year. In
June, Cassini completes its prime mission, a four-year tour of
Saturn. Cassini's next flyby of Enceladus is planned for August, well
into Cassini's proposed extended mission. Cassini will perform seven
Enceladus flybys in its extended mission. If this encounter proves
safe, future passes may bring the spacecraft even closer than this
one. How close Cassini will be allowed to approach will be determined
based on data from this flyby.

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 and more information about the Cassini mission and the
Enceladus flyby, visit:

http://www.nasa.gov/cassini