Cassini spacecraft finds evidence of football-field sized moonlets in Saturn's A ring

http://www.news.cornell.edu/stories/March06/Tiscareno.Saturn.lg.html

March 29, 2006

By Lauren Gold
lg34@cornell.edu

New observations of propeller-shaped disturbances in Saturn's A ring indicate the presence of four small, embedded moons -- and most likely millions more, Cornell University astronomers report.

This is the first evidence of the existence of moonlets bridging the gap in size between the larger ring moons Pan and Daphnis (several miles each in diameter) and the much smaller ice particles that comprise the bulk of the rings. The discovery could lead to a better understanding of the origin and formation of Saturn's rings and the solar system as a whole.

Matthew Tiscareno, a Cornell research associate, is lead author of a paper describing the discovery in the March 30 issue of the journal Nature.

The four disturbances, which appear as pairs of slightly offset bright horizontal streaks in an otherwise bland region of the ring, were captured in two images taken in 2004 by NASA's Cassini spacecraft. Astronomers say the streaks are indicators of orbiting moons about 100 meters (328 feet) in diameter: about the length of a football field, but still too small for even Cassini's highly sensitive Imaging Science Subsystem (ISS) to see directly, but large enough to exert an observable gravitational pull on the particles around them.

"The discovery of these intermediate-sized particles tells us that Pan and Daphnis are probably just the largest members of the ring population, rather than interlopers from somewhere else," said Tiscareno.