From: baalke@kelvin.jpl.nasa.gov (Ron Baalke)
Subject: Re: Moon's of Saturn
Followup-To: sci.geo.geology
Summary: more info on 18th moon?
News-Software: VAX/VMS VNEWS 1.3-4   
Reply-To: baalke@kelvin.jpl.nasa.gov
Organization: Jet Propulsion Laboratory
Date: Tue, 7 Apr 1992 23:50:03 GMT

In article <1992Apr2.111433.21420@mailer.cc.fsu.edu>, cain@geomag.gly.fsu.edu (Joe Cain) writes...
>I note that the 25 September 1990 EOS (well, I don't keep completely
>up to date!) announced the discovery of an 18th moon of Saturn,
>temporarily named 1981 S13. Can someone give me a reference noting the
>specifics of this body, its orbit, and official name please?
> 

I posted this back in July 1990.  I believe the moon was named Pan.
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NEW MOON DISCOVERED ORBITING PLANET SATURN

     A new moon orbiting planet Saturn has been discovered by Dr.
Mark Showalter, a researcher at NASA's Ames Research Center,
Mountain View, Calif.  Showalter found the small, bright object
while analyzing images taken by the Voyager 2 spacecraft.
"It was very gratifying to see it," he said.  Showalter used
a computer program he wrote to sort through 30,000 images sent
back to Earth during the Voyager/Saturn encounters in 1980-81.

     When the discovery is certified by the International
Astronomical Union (IAU), it will bring to 18 the number of
Saturnian moons.  The new moon has a diameter of only 12 miles
and is temporarily designated 1981S13.  It orbits in the major
gap, known as Encke's gap, in Saturn's outermost major ring, the
"A" ring.

     Now Saturn's smallest known satellite, the moon pushes
material away from its orbit and is believed to cause the 200
mile-wide Encke's gap.  The same "shepherding effect," Showalter
said, produces Saturn's thin, outermost "F" ring, with moons
orbiting on either side of the ring, constraining the material.

     A wavy pattern in the ring material on both sides of Encke's
gap was first noticed by Ames' ring expert Dr. Jeff Cuzzi while
studying basic ring structure in the mid-1980s.  Adapting a
theory from galactic dynamics, he and Dr. Jeffrey Scargle, also
at Ames, suggested that the disturbance was caused by an unseen
asteroid-sized moon in the gap.

     Showalter further analyzed the disturbance and used this
"moonlet wake" pattern, resembling a motorboat wake, to determine
the position and mass of the unseen body.  The amplitude of the
waves, he said, suggested the mass of the unobserved object and
the wavelength of the ripples revealed the moon's possible
position.

     Showalter's computer program combined information on the
Voyager spacecraft's position and camera direction with his
prediction of the orbit to search through the enormous stock of
Voyager imagery and select the frames where the moon would fall
in the camera's field of view.

     Brian Marsden of the IAU contacted Showalter saying, "I
congratulate you on this modern-day repetition of the discovery
of Neptune.  It's a nice piece of work."  Planet Neptune also was
first predicted by theorists who observed its gravitational
influence on Uranus before sighting it in 1846.

     Showalter's research is supported by the Ames Space Science
Division under a joint agreement with Stanford University.  He is
a research affiliate at the Stanford Center for Radar Astronomy.

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    /_ /|  /____/ \  /_ /|     Ron Baalke         | baalke@kelvin.jpl.nasa.gov
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
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