Space Forum / Space Science / April 2005

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
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http://www.jpl.nasa.gov

Carolina Martinez (818) 354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

Steve Koppes (773) 702-8366
University of Chicago News Office

Press Release: 2005-063                          April 26, 2005

Cassini Finds Particles Near Saturn's Moon Enceladus

The Cassini spacecraft has discovered intriguing dust particles
around Saturn's moon Enceladus.  The particles might indicate the
existence of a dust cloud around Enceladus, or they may have
originated from Saturn's outermost ring, the E-ring.

"We are making measurements in the plane of the E-ring," said Dr.
Thanasis Economou, a senior scientist at the University of
Chicago's Enrico Fermi Institute.  Economou is the lead
researcher on the high rate detector, part of a larger instrument
on Cassini called the cosmic dust analyzer.  "It will take a few
more flybys to distinguish if the dust flux is originating from
the E-ring as opposed to a source at Enceladus."

Enceladus is rapidly becoming a very interesting target for
Cassini.  So much so that scientists and engineers are planning
to revise the altitude of the next flyby to get a closer look.
Additional Cassini encounters with Enceladus are scheduled for
July 14, 2005, and March 12, 2008.  The July 14 flyby was to be
at an altitude of 1,000 kilometers (620 miles), but the mission
team now plans to lower that altitude to about 175 kilometers
(109 miles).  This will be Cassini's lowest-altitude flyby of any
object during its nominal four-year tour.

Earlier this year Cassini completed two flybys of Enceladus.  On
February 17, Cassini encountered Enceladus at an altitude of
1,167 kilometers (725 miles). On that date, the cosmic dust
analyzer with its high rate detector recorded thousands of
particle hits during a period of 38 minutes. Cassini executed
another flyby of Enceladus on March 9 at an altitude of 500
kilometers (310 miles). "Again we observed a stream of dust
particles," said Economou.  The largest particles detected
measure no more than the diameter of a human hair -- too small to
pose any danger to Cassini.

Scientists have speculated that Enceladus is the source of
Saturn's E ring, the planet's widest, stretching 302,557
kilometers (188,000 miles). It's possible, the scientists say,
that tidal interactions between Enceladus and Mimas, two other
moons of Saturn, have heated Enceladus' interior causing water
volcanism.

"These measurements are extremely important in order to
understand the role of Enceladus as the source of the water ice
particles in the E ring," said Dr. Ralf Srama, of the Max Planck
Institute for Nuclear Physics, Heidelberg, Germany.  Srama is
principal investigator of the cosmic dust analyzer science team.
This study requires precise measurements of dust densities near
the Enceladus region, "but without the high rate detector this
would not be possible," said Srama.

Another of Cassini's instruments, the magnetometer, recently
discovered water ions which could be part of a very thin
atmosphere around Enceladus. Enceladus is a relatively small
moon.  The amount of gravity it exerts is not enough to hold an
atmosphere very long.  Therefore a strong, continuous source is
required to maintain the atmosphere.

Enceladus measures 500 kilometers (310 miles) in diameter and
reflects nearly 100 percent of the light that hits its ice-
covered surface.  It orbits Saturn at a distance of approximately
237,378 kilometers (147,500 miles), about two-thirds the distance
from Earth to the moon.

The cosmic dust analyzer provides direct observations of small
ice or dust particles in the Saturn system in order to
investigate their physical, chemical and dynamical properties.
It is made up of two detectors.  The University of Chicago built
the high rate detector, which made these observations.  With
further analysis, the cosmic dust analyzer might be able to
determine whether the particles are made of ice or dust.

For images and information on the Cassini mission visit
http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini .

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. The Jet
Propulsion Laboratory, a division of the California Institute of
Technology in Pasadena, manages the Cassini-Huygens mission for
NASA's Science Mission Directorate, Washington, D.C. The Cassini
orbiter was designed, developed and assembled at JPL.

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