New-found Moon PDF Print E-mail
On Tue, 3/3/09, NASA JPLwrote:
Subject: Newfound Moon
            May Be Source of Outer Saturn Ring
NASA's Cassini spacecraft has found within
Saturn's G ring n embedded moonlet that
appears as a aint, moving pinprick of light.
Scientists believe it is a ain 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,
and .
"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 niversity in Ithaca, N.Y. "The discovery
of this moonlet, together with other Cassini data,
should help s 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 elatively 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 arger, 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.
Last Updated ( Tuesday, 03 March 2009 )
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