Their findings, entitled “Saturn's Small Inner Satellites: Clues to Their Origins,” are published in the December 7, 2007 issue of the journal Science. Besides Porco, the co-authors are P. C. Thomas, J. W. Weiss, and D. C. Richardson.

Their abstract states, “Cassini images of Saturn's small inner satellites (radii of less than  100 kilometers) have yielded their sizes, shapes, and in some cases, topographies and mean densities. This information and numerical N-body simulations of accretionary growth have provided clues to their internal structures and origins. The innermost ring-region satellites have likely grown to the maximum sizes possible by accreting material around a dense core about one-third to one-half the present size of the moon. The other small satellites outside the ring region either may be close to monolithic collisional shards, modified to varying degrees by accretion, or may have grown by accretion without the aid of a core. We derived viscosity values of 87 and 20 square centimeters per second, respectively, for the ring material surrounding ring-embedded Pan and Daphnis."

It concludes: "These moons almost certainly opened their respective gaps and then grew to their present size early on, when the local ring environment was thicker than it is today.”

A complementary article (“The Equatorial Ridges of Pan and Atlas: Terminal Accretionary Ornaments?”), also in the December 7th issue of Science describes the flying-saucer shaped moonlets of Atlas and Pan. The lead author of the study is French astrophysicist Sebastien Charnoz at University of Paris Diderot in France. He was joined in the article by: André Brahic, Peter C. Thomas, and Carolyn C. Porco, who is also associated with the first article mentioned here.

In the abstract to this paper: “In the outer regions of Saturn's main rings, strong tidal forces balance gravitational accretion processes. Thus, unusual phenomena may be expected there. The Cassini spacecraft has recently revealed the strange "flying saucer" shape of two small satellites, Pan and Atlas, located in this region, showing prominent equatorial ridges. The accretion of ring particles onto the equatorial surfaces of already-formed bodies embedded in the rings may explain the formation of the ridges. This ridge formation process is in good agreement with detailed Cassini images showing differences between rough polar and smooth equatorial terrains."

It concludes: "We propose that Pan and Atlas ridges are kilometers-thick "ring-particle piles" formed after the satellites themselves and after the flattening of the rings but before the complete depletion of ring material from their surroundings.”


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