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Path: utzoo!snell
From: snell@utzoo.UUCP (Richard Snell)
Newsgroups: net.space
Subject: Re: New planet formation theory
Message-ID: <6291@utzoo.UUCP>
Date: Wed, 15-Jan-86 14:29:52 EST
Article-I.D.: utzoo.6291
Posted: Wed Jan 15 14:29:52 1986
Date-Received: Wed, 15-Jan-86 14:29:52 EST
References: <407@decwrl.DEC.COM>
Organization: U of Toronto Zoology
Lines: 40

A front page article in a U of Toronto newspaper "The Newspaper"
refers to the "shepard theory" of Prof. Scott Tremaine (Canadian Institute
of Theoretical Astrophysics), Prof. Peter Goldreich (California
Inst. Technology), and Dr. Nicole Borderies (Pic-du-Midi Observatory,
France).  Portions of this article are reproduced:

"Uranus is known to have five satellites surrounding it.  The scientists
believe that 10 additional satellites are the only plausible theory
to explain why the rings of Uranus are so narrow.  In theory, the 
constant jostling of one ring particle against another should have
spread any narrow ring-like structure into a much broader diameter.
Despite the fact that Uranus's rings are some 300,000 kilometres in
circumference, the width of the rings themselves is only 2-3 kilometres.

"[They] suggest that if each ring was accompanied by small satellites
or moons - on inside and one outside - the gravitational forces of
these moons could overcome the natural tendency of a ring to spread...

""The satellites act somewhat like shepards keeping a flock of unruly
sheep in order and hence are called `shepard' satellites...   It is difficult
to understand without shepard satellites how such perfectly sharp 
and well-defined structures (ringsystem) could be maintained over
the age of the solar system," [Tremaine] added.

"In response to a question of what a sucessful prediction whould (sic)
mean to the discipline, Tremaine responded, "It certainly won't 
revolutionaize my thinking... but one broad implication
for the study of planetart rings is it gives you clues as to how the 
system (of disks and planets) works that can be applied to other systems
of galaxies and solar systems."

"... when the Voyager 2 mission went past Saturn, it discovered a 
previously unknown ring that shares characteristics with the Uranus
structure. The Saturn ring was narrow and accompanied by two shepard
satellites on either side of it
-- 
Name:   Richard Snell
Mail:   Dept. Zoology, Univ. Toronto
        Toronto, Ontario, Canada    M5S 1A1
UUCP:   {allegra,ihnp4,linus,decvax}!utzoo!snell