Saturn's ring-plane crossings of August and November 1995: A model for the new F-ring objects

We analyze observations made in August and November 1995 during the Earth and Sun crossings of Saturn's ring plane, respectively. The August 1995 observations combine data taken with the Adonis adaptive optics system at the European Southern Observatory (ESO) and images from the Hubble Space Telescope (HST), The November 1995 data are based on HST images only. We report here the detections of four new objects (three in August, one in November) orbiting near, or within, the F ring of Saturn. Two of the objects observed at ESO in August 1995 are most probably S/1995 S5 and S/1995 S6, reported by P. D. Nicholson et al, (1996, Science 272, 509-515) from the HST observations on August 10, 1995, The third object, S/1995 S20 cannot be clearly linked with any other objects reported by other observers, An elongated object, or are, is tracked in November 1995, acid can be connected to one of the arcs also reported by Nicholson et al. Our combined measurements improve the determination of the orbital parameters of S/1995 S5 and the are, indicating that these objects orbit, within the error bars (less than or similar to +/-140 km), in the F ring. We discuss the nature and origin of these F-ring features. We propose that they are clouds of regolith ejecta resulting from collisions between large particles, or "parent bodies," within the F ring. From the available constraints (brightness and lifetime of the objects), we show that the observations ate consistent with the presence of several hundred l-km-sized (and/or several thousand 100-m-sized) unseen parent bodies embedded in the F ring, each of which is covered by a regolith layer tens of centimeters to similar to 1 m in thickness (C) 2000 Academic Press.