[meteorite-list] Newfound Moon May Be Source of Outer Saturn Ring

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 3 Mar 2009 12:47:40 -0800 (PST)
Message-ID: <200903032047.MAA24906_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2009-035

Newfound Moon May Be Source of Outer Saturn Ring
Jet Propulsion Laboratory
March 03, 2009

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.

Media contacts: Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
carolina.martinez at jpl.nasa.gov

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

2009-035
Received on Tue 03 Mar 2009 03:47:40 PM PST