Moons of Saturn May Be Transient Objects

This false-colour photo shows some of the inner moons around Saturn. It is a composite of 60-second frames obtained with the advanced ADONIS adaptive optics camera at the ESO 3.6-m telescope on La Silla (Chile). This instrument neutralizes the image-smearing effects of the atmospheric turbulence and records very sharp images on an infrared-sensitive 256 x 256 pixel detector with a scale of 0.05 arcsec/pixel. They were taken through the `short K' filter with a central wavelength at 2.2 micron. The angular resolution is about 0.3 arcsec, corresponding to about 1900 km at the distance of Saturn during the observations (1313 million km). North is up and East is to the left.

The frames were obtained shortly before the Earth ring plane crossing (RPX) event at 20:54 UT on August 10, 1995. At this time the Earth was slightly below the ring plane and the Sun was slightly above it, so that the dark side of the rings was visible.

Each frame has a width of 10.4 arcsec. The upper panel shows the Western ansa (from Latin `handle') of Saturn's ring, about 1.5 day before the Earth RPX. The halo to the left is caused by sunlight scattered from Saturn. In addition to the moons Janus and Rhea, Pandora is seen moving westward (to the right), as expected from the ephemerides derived from the Voyager spacecraft observations in 1980/81. This is the one of the very first observations of the small object (diameter about 100 km) since its discovery.

The lower panel is again of the Western ansa, about 12 hours before the moment of the ring plane crossing. The left frame shows the brighter B-ring and the light shining through the Cassini Division (left side of the image), and then the fainter A-ring, plus a brighter clump at the extremity of the ansa, corresponding to the location of the F-ring. The right frame was obtained by subtracting a mirror-inverted image of the Eastern ansa. It enhances the image of this object which is identified with a new Saturnian 'moon', S/1995 S6. It is not excluded, however, that it is not a solid body, but rather a transient condensation of material in the F-ring.