Close-up Look at Saturn’s Rings

The Encke Gap. Image Credit: JPL/NASA

Cassini continued today to perform as expected, sending back more than 60 stunning close-up images of Saturn’s complex system of rings. Some of the images confirmed ideas that scientists who study the rings already suspected; others, however, showed entirely novel phenomena that left ring specialists scratching their heads.

The majority of the images were taken by Cassini’s narrow-angle camera just after the spacecraft completed a maneuver that put it into orbit around the planet. The first ring image arrived at about 5:30 a.m. PDT Thursday; additional images continued to arrive at a rate of one a minute for the next hour or so.

In the banner image of Saturn’s A and F rings, the broad white band is Saturn’s broad A ring; the thinner white band to the right and bottom is the much narrower F ring. Within the A ring, the large dark gap is the Enke Gap; the smaller gap, farther out, is the Keeler Gap. The tiny white dot in the lower right of the full image, is Saturn’s moon Prometheus, a mere 100 kilometers (62 miles) in diameter. Prometheus, which orbits just inside the F ring, and Pandora, which orbits just outside the F ring, serve to "shepherd" the ring, containing it within narrow confines. This image was captured by Cassini’s wide-angle camera on the sunlit side of Saturn’s rings.

Cassini took this first batch of 43 images on the unlit side of rings, while the orbiter was still above Saturn’s ring plane. Even this backlit view of segments of the A, B and C rings showed rich detail, including instances of phenomena known as "density waves" and "bending waves."

In the first views of these density and bending waves, two types of dynamic wave patterns are visible in the close-up image (right) of Saturn’s A ring. The pattern in the lower left is a density wave, a series of changes in the density of ring particles that ripples through a ring when a passing moon exchanges energy with the material in the ring. The pattern in the upper left is a banding wave. Banding waves are also induced by the gravitational energy of a passing moon, but, unlike density waves, result from ring particles being lifted above the plane in which they normally orbit. This image was taken by Cassini’s narrow-angle camera on the backlit side of the rings.

The Mysterious F Ring. Image Credit: JPL/NASA

Cassini captured the second batch, consisting of an additional 18 images, on the sunlit side of the rings after the spacecraft dipped back down below the ring plane. These were taken from a greater distance from the rings than the first batch of images and included several wide-angle shots as well as narrow-angle ones.

The large gap in Saturn’s A ring (upper right image), known as the Encke Gap, is the 2nd largest gap in Saturn’s ring system. The gap is produced by Pan, a 20-kilometer-wide (12-mile-wide) moonlet that orbits within the gap. As Pan orbits around Saturn, it perturbs the inner edge of the Encke Gap, causing the scalloped-edge effect visible in the center of the image. Pan is a bit of a mystery to scientists because Saturn’s gravitational pull, in theory, should prevent a moon from forming so close to Saturn. One possible explanation is that Pan formed farther out from Saturn and later migrated inward. This image was take by Cassini’s narrow-angle camera on the sunlit side of Saturn’s rings.

The Keeler Gap (middle left) is shown as a narrow gap near the outer edge of Saturn’s A ring and is a mere 30 kilometers (19 miles) wide. Scientists speculate that a tiny moon, as yet undiscovered, orbits within the gap. They are hopeful that, if there is a moon there, Cassini will find it. They plan to study this and other images of the Keeler Gap for the telltale scalloping effect, seen in the image of the Encke Gap above, that would signal the presence of a moon. This image was taken by Cassini’s narrow-angle camera on the backlit side of the rings.

The bizarre formation (bottom left) on the inner edge of Saturn’s F ring is 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.