Cassini Spacecraft to Dive Into Water Plume of Saturn Moon

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Carolina Martinez 818-354-9382
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Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown@nasa.gov

NEWS RELEASE: 2008-040 March 10, 2008

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 200 kilometers (120 miles) from the surface. At closest approach to Enceladus,
Cassini will be only 50 kilometers (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 500 kilometers
(310 miles) in diameter, but despite its petite size, it's 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 400 meters per second (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, 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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