If you have access to a copy of The New Solar System by Beatty, O'Leary and Chaikin, chapter 13, Planetary Rings, has a nice diagram and description of how a mass of particles (or gas for that matter) in randomly inclined orbits around a central body will over time collapse into the <i>LaPlacian plane</i>.<br /><br /><br /><br />Good reference book to have around on general principle.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>