Sat­urn’s larg­est, most compact ring con­sists of tightly packed clumps of par­t­i­cles sep­a­rat­ed by nearly emp­ty gaps, ac­cord­ing to new find­ings from NASA’s Cas­si­ni space­craft.

These clumps in Sat­urn’s B ring are neatly or­gan­ized and con­stantly col­lid­ing, which sur­prised sci­en­tists, they said.

“We orig­i­nally thought we would see a un­iform cloud of par­t­i­cles,” said Lar­ry Es­pos­ito, prin­ci­pal in­ves­ti­ga­tor for the Cas­si­ni ul­tra­vi­o­let im­ag­ing spec­tro­graph at the Un­ivers­ity of Col­o­rad­o, Boul­der. 

This false-color im­age of Sat­urn's rings was made us­ing a Cas­si­ni in­stru­ment called the ultra­violet im­ag­ing spec­tro­graph. Sci­en­tists used it to rec­ord oc­cul­ta­tions, in which a star's bright­ness changes as the rings pass in front of it, re­veal­ing the amount of ring ma­te­ri­al be­tween the craft and the star. Cas­si­ni gave sci­en­tists the most de­tailed view yet of the B ring and found that this part of the rings is dense­ly packed with con­stant­ly col­lid­ing clumps called self-gravity wakes, sep­a­rat­ed by gaps. The clumps, 30 to 50 me­ters (100 to 160 feet) across, are too small to be seen di­rect­ly, but re­search­ers can map their dis­tri­bu­tion, shape and ori­en­ta­tion. Col­ors here in­di­cate their ori­en­ta­tion; bright­ness in­di­cates den­si­ty of ring par­t­i­cles. Those in the yel­low zone are too dense­ly packed for star­light to pass through. (Cre­dit: NA­SA/JPL/Uni­ver­s­ity of Co­lo­ra­do)

“In­stead we find that the par­t­i­cles are clumped to­geth­er with emp­ty spaces in be­tween. If you were fly­ing un­der Sat­urn’s rings in an air­plane, you would see these flashes of sun­light come through the gaps, fol­lowed by dark and so forth. This is dif­fer­ent from fly­ing un­der a un­iform cloud of par­t­i­cles.” 

Be­cause pre­vi­ous in­ter­preta­t­ions as­sumed the ring par­t­i­cles were dis­trib­ut­ed un­iformly, sci­en­tists un­der­es­ti­mated the to­tal mass of Sat­urn’s rings, re­search­ers said: the mass may ac­tu­ally be two or more times pre­vi­ous es­ti­mates. 

“These re­sults will help us un­der­stand the over­all ques­tion of the age and hence the or­i­gin of Sat­urn’s rings,” said Josh Col­well of the Un­ivers­ity of Cen­tral Flor­i­da, Or­lan­do, and a team mem­ber of the Cas­si­ni ul­tra­vi­o­let im­ag­ing spec­tro­graph. 

A pa­per de­tail­ing the re­sults ap­pears in the April 13 early on­line is­sue of the re­search jour­nal Ic­a­rus.

Courtesy NASA and World Science staff