Prometheus Steals Ring

Saturn’s F rings distorted by shepherd moon, Prometheus. Click image for larger view. Image Credit: NASA/JPL

Cassini took this amazing photograph of Prometheus, one of Saturn’s small shepherd moons as it’s tugging material away from the planet’s F ring. The F ring resolves into 5 separate strands, and you can see how tiny Prometheus has a stream of material flowing towards it. Prometheus is only 102 km (63 miles) across, and scientists still aren’t sure exactly why it creates the different knots and breaks in the F ring.

As it completed its first orbit of Saturn, Cassini zoomed in on the rings to catch this wondrous view of the shepherd moon Prometheus (102 kilometers, or 63 miles across) working its influence on the multi-stranded and kinked F ring.

The F ring resolves into five separate strands in this closeup view. Potato-shaped Prometheus is seen here, connected to the ringlets by a faint strand of material. Imaging scientists are not sure exactly how Prometheus is interacting with the F ring here, but they have speculated that the moon might be gravitationally pulling material away from the ring.

The Mysterious F Ring. Image Credit: JPL/NASA

The ringlets are disturbed in several other places. In some, discontinuities or "kinks" in the ringlets are seen; in others, gaps in the diffuse inner strands are seen. All these features appear to be due to the influence of Prometheus.

The inner moon Prometheus and the outer moon Pandora use their gravitational attraction to define Saturn ‘s outermost ring. Were any of the smaller chunks of ice and rock that compose Saturn’s F Ring to stray, the ring particle would be gravitationally pulled back into place by one of these passing moons. This complex interaction creates a ring structure with two narrow braids and several unusual knots.

The image was taken in visible light with the narrow angle camera on Oct. 29, 2004, at a distance of about 782,000 kilometers (486,000 miles) from Prometheus and at a Sun-Prometheus-spacecraft, or phase, angle of 147 degrees. The image scale is 4.7 kilometers (2.9 miles) per pixel. The image has been magnified by a factor of two, and contrast was enhanced, to aid visibility.

The bizarre formation (middle left) on the inner edge of Saturn’s F ring was one of the first great surprises of the Cassini mission. Scientists have never seen anything like it before, and don’t know what mechanism is reponsible for it. The image was taken by Cassini’s narrow-angle camera on the sunlit side of the rings.

Saturn shown half-lit using a visible-red filter. Image Credit: NASA/JPL

Around 1655, the Dutch scientist, Huygens first recognized that Saturn was "girdled by a thin, flat ring, nowhere touching it." The rings may be composed of icebergs and/or snowballs from a few centimeters to a few meters in size. As a milestone for marrying theoretical and observational astronomy, scientists predicted that an undiscovered ring might be formed here, and only in 1980 was their "F-ring" hypothesis confirmed by Voyager I during its Saturn flyby. The lettering scheme, "A through F", refers to the historical order of the ring divisions’ discoveries, and does not relate easily to their distance from Saturn. In the case of the thin F and G rings, the last discovered gaps, these debris fields do lie outside the more prominent "A through D" system.





Related Web Pages

Saturn Edition, Astrobiology Magaz.
Saturn’s Rings in UV
Cassini Closes In on Saturn

Saturn– JPL Cassini Main Page
Lord of the Rings
Space Science Institute, Imaging Team Boulder, Colorado
Saturn: The Closest Pass
Prebiotic Laboratory
Planet Wannabe
Where is Cassini Now?