Newfound Moon May Be Source of Outer Saturn Ring

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

Joe Mason 720-974-5859
Space Science Institute, Boulder, Colo.
media@ciclops.org

NEWS RELEASE: 2009-035 March 3, 2009

Newfound Moon May Be Source of Outer Saturn Ring

NASA's Cassini spacecraft has found within Saturn's G ring an embedded moonlet that
appears as a faint, moving pinprick of light. Scientists believe it is a main source of the G
ring and its single ring arc.

Cassini imaging scientists analyzing images acquired over the course of about 600 days
found the tiny moonlet, half a kilometer (about a third of a mile) across, embedded within
a partial ring, or ring arc, previously found by Cassini in Saturn's tenuous G ring.

The finding is being announced today in an International Astronomical Union circular.
Images can be found at http://www.nasa.gov/cassini, http://saturn.jpl.nasa.gov and
http://ciclops.org .

"Before Cassini, the G ring was the only dusty ring that was not clearly associated with a
known moon, which made it odd," said Matthew Hedman, a Cassini imaging team
associate at Cornell University in Ithaca, N.Y. "The discovery of this moonlet, together
with other Cassini data, should help us make sense of this previously mysterious ring."

Saturn's rings were named in the order they were discovered. Working outward they are:
D, C, B, A, F, G and E. The G ring is one of the outer diffuse rings. Within the faint G
ring there is a relatively bright and narrow, 250-kilometer-wide (150-miles) arc of ring
material, which extends 150,000 kilometers (90,000 miles), or one-sixth of the way
around the ring's circumference. The moonlet moves within this ring arc. Previous Cassini
plasma and dust measurements indicated that this partial ring may be produced from
relatively large, icy particles embedded within the arc, such as this moonlet.

Scientists imaged the moonlet on Aug. 15, 2008, and then they confirmed its presence by
finding it in two earlier images. They have since seen the moonlet on multiple occasions,
most recently on Feb. 20, 2009. The moonlet is too small to be resolved by Cassini's
cameras, so its size cannot be measured directly. However, Cassini scientists estimated
the moonlet's size by comparing its brightness to another small Saturnian moon, Pallene.

Hedman and his collaborators also have found that the moonlet's orbit is being disturbed
by the larger, nearby moon Mimas, which is responsible for keeping the ring arc together.

This brings the number of Saturnian ring arcs with embedded moonlets found by Cassini
to three. The new moonlet may not be alone in the G ring arc. Previous measurements
with other Cassini instruments implied the existence of a population of particles, possibly
ranging in size from 1 to 100 meters (about three to several hundred feet) across.
"Meteoroid impacts into, and collisions among, these bodies and the moonlet could
liberate dust to form the arc," said Hedman.

Carl Murray, a Cassini imaging team member and professor at Queen Mary, University of
London, said, "The moon's discovery and the disturbance of its trajectory by the
neighboring moon Mimas highlight the close association between moons and rings that
we see throughout the Saturn system. Hopefully, we will learn in the future more about
how such arcs form and interact with their parent bodies."

Early next year, Cassini's camera will take a closer look at the arc and the moonlet. The
Cassini Equinox mission, an extension of the original four-year mission, is expected to
continue until fall of 2010.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space
Agency and the Italian Space Agency. The Jet Propulsion Laboratory (JPL), a division of
the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission
for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two
onboard cameras were designed, developed and assembled at JPL. The imaging team is
based at the Space Science Institute, Boulder, Colo.

-end-

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