Pandora and the Rings

The F ring shepherd Pandora is captured here along with other well-known examples of how Saturn’s moons shape the rings. From the narrow F ring, to the gaps in the A ring, to the Cassini Division, Saturn's rings are a masterpiece of gravitational sculpting by the moons.

Pandora (50 miles, or 81 kilometers across), along with its fellow shepherd Prometheus (53 miles, or 86 kilometers across), helps confine the F ring and keep it from spreading.

This view looks toward the unilluminated side of the rings from about 31 degrees below the ringplane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on March 8, 2014.

The view was obtained at a distance of approximately 533,000 miles (858,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 63 degrees. Image scale is 32 miles (51 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/Space Science Institute

Note: For more information, see Shepherd and Flock.

Saturn and Shadows

Saturn's rings cast shadows on the planet, except their shadows appear to be inside out! The edge of the outermost A ring can be seen at the top left corner of the image. Moving towards the bottom of the page, one can see the faint Cassini Division, the opaque B ring and the innermost C ring, which contains several ringlets that appear dark against Saturn in this geometry. The bottom half of the image features the shadows of these rings in reverse order superposed against the disk of the planet: the C ring, the B ring, the Cassini Division and the inner half of the A ring.

This view looks toward the unilluminated side of the rings from about 28 degrees below the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on December 2, 2013 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

The view was acquired at a distance of approximately 750,000 miles (1.2 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 57 degrees. Image scale is 45 miles (72 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

B-Ring Clumps and Strands

Zooming in on clumps in Saturn’s B-ring (lower left), the image also spans the ringlets of the Cassini Division towards the A-ring in the top right. The view looks toward the sunlit side of the rings from about 31 degrees below the ring plane. The image scale is approximately 2 km per pixel.

Photo credit: NASA/JPL/Space Science Institute

Saturn

The giant planet Saturn, as observed with the VLT NAOS-CONICA Adaptive Optics instrument on December 8, 2001; the distance was 1,209 million km. It is a composite of exposures in two near-infrared wavebands (H and K) and displays well the intricate, banded structure of the planetary atmosphere and the rings. Note also the dark spot at the south pole at the bottom of the image. One of the moons, Tethys, is visible as a small point of light below the planet. It was used to guide the telescope and to perform the adaptive optics "refocusing" for this observation. More details in the text.

This image of Saturn, the second-largest planet in the solar system, was obtained at a time when Saturn was close to summer solstice in the southern hemisphere. At this moment, the tilt of the rings was about as large as it can be, allowing the best possible view of the planet's South Pole. That area was on Saturn's night side in 1982 and could therefore not be photographed during the Voyager encounter. The dark spot close to the South Pole is a remarkable structure that measures approximately 300 km across. The bright spot close to the equator is the remnant of a giant storm in Saturn's extended atmosphere that has lasted more than 5 years.

The present photo provides what is possibly the sharpest view of the ring system ever achieved from a ground-based observatory. Many structures are visible, the most obvious being the main ring sections, the inner C-region (here comparatively dark), the middle B-region (here relatively bright) and the outer A-region, and also the obvious dark "divisions," including the well-known, broad Cassini division between the A- and B-regions, as well as the Encke division close to the external edge of the A-region and the Colombo division in the C-region. Moreover, many narrow rings can be seen at this high image resolution, in particular within the C-region.

Photo credit: ESO

Unexpected Chevron Structure on the Edge of Saturn's B-Ring

The outer edge of Saturn's B ring exhibits an unexpected feature in this movie made from images captured by NASA's Cassini spacecraft. The images were obtained early in the planet's equinox "season" -- the period leading up to and away from August 11, 2009 when the Sun was over the planet's equator and lit the rings exactly edge on.

The B ring is shown at the top of the frame. The Cassini Division, a low-density region that separates the A and B rings, dominates the middle of the frame. The inner A ring is at the bottom.

It is apparent in the movie that the outer B ring edge location varies with time. For a more detailed view and explanation for this behavior, see PIA12794.

But, about halfway through, an unusual, 20,000-kilometer-long (12,000-mile-long), chevron-shaped structure can be seen moving along the B ring edge. Higher resolution images, taken during equinox, have shown that this region is the site of vertical structures, as tall as 3.5 kilometers (2.2 miles), whose existence was betrayed by long shadows (see PIA11668).

Cassini imaging scientists found that this chevron feature is one of two sites at the B ring's outer edge that does not follow any of the three newly discovered rotating patterns distorting the ring's edge or another pattern previously known to be caused by the moon Mimas. They have found instead that it orbits Saturn as would an independently orbiting body. As a result, scientists conclude that these are likely sites of massive bodies, or moonlets, embedded near the ring's edge but independently orbiting Saturn. In the particular region shown in this movie, the moonlets are likely big enough to cause ring material streaming past them to be excessively compressed and thrown vertically as a result. The moonlets themselves can't be seen.

This interpretation is supported by Cassini's previous discovery of a moonlet embedded in this region of the B ring (see PIA11665). The imaged moonlet, whose size is estimated at 300 meters (1,000 feet) across, was found only because it was betrayed by the shadow it cast during Saturn's August 2009 equinox period.

This view looks toward the southern, sunlit side of the rings from about 4 degrees below the ring plane.

The movie is a concatenation of 39 images taken about 2 minutes, 40 seconds apart, over the span of 1 hour, 40 minutes. The images, taken on February 25, 2009, were re-projected into the same viewing geometry.

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The images were taken in visible light with the Cassini spacecraft narrow-angle camera. The view was obtained at a distance of approximately 822,000 kilometers (511,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 154 degrees. Image scale is 5 kilometers (3 miles) per pixel.

Video credit: NASA/JPL/Space Science Institute

Note: A continuous loop video of the chevron structure can be found here.

Vertical Structures in Saturn's B-Ring

Vertical structures, among the tallest seen in Saturn's main rings, rise abruptly from the edge of Saturn's B ring to cast long shadows on the ring in this image taken by NASA's Cassini spacecraft two weeks before the planet's August 2009 equinox.

Part of the Cassini Division, between the B and the A rings, appears at the top of the image, showing ringlets in the inner division.

In this image, Cassini's narrow angle camera captured a 1,200-kilometer-long (750-mile-long) section arcing along the outer edge of the B ring. Here, vertical structures tower as high as 2.5 kilometers (1.6 miles) above the plane of the rings -- a significant deviation from the vertical thickness of the main A, B and C rings, which is generally only about 10 meters (about 30 feet).

Cassini scientists believe that this is one prominent region at the outer edge of the B ring where large bodies, or moonlets, up to a kilometer or more in size, are found. It is possible that these bodies significantly affect the ring material streaming past them and force the particles upward, in a "splashing" manner.

This image and others like it (see PIA11669) are only possible around the time of Saturn's equinox, which occurs every half-Saturn-year, or about every 15 Earth years. The illumination geometry that accompanies equinox lowers the Sun's angle to the ring plane and causes structures jutting out of the plane to cast long shadows across the rings. The "season" of equinox allows shadows to appear on the rings in the months before and after equinox, but the actual equinox occurred August 11, 2009, as the Sun shone directly edge-on to the ring plane.

This view looks toward the southern, sunlit side of the rings from about 32 degrees below the ring plane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 26, 2009. The view was acquired at a distance of approximately 336,000 kilometers (209,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 132 degrees. Image scale is 2 kilometers (1 mile) per pixel.

Photo credit: NASA/JPL/Space Science Institute

Galactic Behavior for the Outer B Ring

Keeping a close watch on the outer portion of Saturn's B ring, NASA's Cassini spacecraft records the complex inward and outward movement of the edge of the ring. This ring movement resembles the suspected behavior of spiral disk galaxies.

The position of the outer edge of the B ring, shown here crossing the middle of the frame, varies with time in this concatenation of 301 images taken an average of 1 minute, 50 seconds apart, over the span of about nine hours. The total variation of the edge, from the innermost to outermost locations, is 200 kilometers (120 miles). The eccentric Huygens Ringlet, another very narrow ringlet discovered by Cassini, and the innermost of the bands of ring material in the Cassini Division, a low-density region once thought to be empty, all appear in the top of the frame.

Cassini scientists have determined that the complicated radial variations in the B ring edge are caused by the presence of four scalloped patterns, all independently moving around the ring. One pattern, with two lobes, is present because of the gravitational perturbations from the moon Mimas, which alter the ring particle orbits because of a repetitive configuration of particle and satellite orbital positions known as a Lindblad resonance; this pattern always stays fixed with respect to Mimas.

The other patterns with one, two, and three lobes respectively, travel around the ring with differing speeds and are believed to be natural modes of oscillation of the ring in this vicinity, excited by a process known as "viscous overstability." In this process, the small, random motions of the ring particles feed energy into a wave that propagates outward across the ring from an inner boundary, reflects off the outer edge of the B ring (which becomes distorted as a result), and then travels inward until it reflects off the inner boundary. This continuous back-and-forth reflection is necessary for these wave patterns to grow and become visible as distortions in the outer edge of the B ring.

In supporting these so-called "self-excited" modes, the outer edge of the B ring is behaving the way astronomers believe spiral galaxies behave. However, such modes are not directly observable in galaxies. Cassini's observations of the outer B ring edge constitute the first time such large-scale modes in a broad disk of material have been observed in nature.

The movie repeats twice. The second time the movie runs, the location of the Mimas resonance (marked with a green line), the locations of the inner boundaries for the one-lobed (blue), two-lobed (yellow), and three-lobed (red) modes, and the location of the mean radius of the outer edge of the B ring (white) are all indicated.

The images were re-projected into the same viewing geometry and magnified by a factor of two to increase visibility of features. Image scale was about 2 kilometers (about 1 mile) per pixel in the original images. These images have not been cleaned of cosmic rays that struck the camera's sensor during exposure. These cosmic ray hits appear as small white streaks on the images.

The view looks toward the southern, sunlit side of the rings from about 44 degrees below the ring plane.

The images were taken in visible light with the Cassini spacecraft narrow-angle camera on January 28, 2008. The view was acquired at a distance of approximately 424,000 kilometers (264,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 52 degrees.

Video credit: NASA/JPL/Space Science Institute

Note: For a similar article and video, see PIA12795: Oscillations at B Ring Edge.

Long Spiky Shadows

Vertical structures in the variable outer edge of Saturn's B ring cast shadows in these two images captured by NASA's Cassini spacecraft shortly after the planet's August 2009 northern vernal equinox.

In these two images, Cassini's narrow angle camera captured a 20,000-kilometer-long (12,000-mile-long) section arcing along the outer edge of the B ring in Saturn's rings. This particular section of the ring is known to be the site of vertical structures as tall as 3.5 kilometers (2.2 miles). See PIA11668 to learn more.

The B ring is shown at the top of both frames. The Cassini Division, a low-density ring region that separates the B ring from the A ring, runs from the bottom right to the upper left of the images. The A ring is at the bottom.

Cassini imaging scientists have concluded that this region and another in this vicinity are the sites of massive bodies, or moonlets, embedded near the ring's edge but independently orbiting Saturn. In the particular region shown in this image, the moonlets are likely big enough to cause ring material streaming past them to be excessively compressed and thrown vertically as a result.

This interpretation is supported by Cassini's previous discovery of a moonlet embedded in this region of the B ring (see PIA11665). The imaged moonlet, whose size is estimated at 300 meters (1,000 feet) across, was found only because it was betrayed by the shadow it cast during Saturn's August 2009 equinox period.

This image and others like it are only possible around the time of Saturn's equinox which occurs every half-Saturn-year (equivalent to about 15 Earth years). The illumination geometry that accompanies equinox lowers the Sun's angle to the ring plane and causes structures jutting out of the plane to cast long shadows across the rings. Cassini's cameras have spotted not only the predictable shadows of some of Saturn's moons (see PIA11657), but also the shadows of newly revealed vertical structures in the rings themselves (see PIA11654).

Both panels were re-projected to the same viewing geometry. The right-hand panel is a mosaic of two images. The images of the right-hand panel were taken in visible light with the Cassini spacecraft narrow-angle camera on August 19, 2009. Two stars are visible.

The left-hand panel was taken in visible light with the Cassini spacecraft narrow-angle camera on August 16, 2009. One star is visible.

This view looks toward the northern, sunlit side of the rings from about 11 degrees above the ring plane at a distance of approximately 2.3 million kilometers (1.4 million miles) from Saturn. Image scale is 13 kilometers (8 miles) per pixel.

Photo credit: NASA/JPL/Space Science Institute

The Cassini Division

The Cassini spacecraft looks between Saturn's A and B rings to spy structure in the Cassini Division.

The Cassini Division, occupying the middle and left of the image, contains five dim bands of ring material, but not all of the division is shown in this image. The B ring is on the right of the image. The Huygens Gap is the widest black swath near the middle of the image. See PIA11142, PIA08901 and PIA08330 to learn more. This view looks toward the northern, sunlit side of the rings from about 3 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on September 3, 2010. The view was obtained at a distance of approximately 443,000 kilometers (275,000 miles) from Saturn. Image scale is 2 kilometers (1 mile) per pixel.

Photo credit: NASA/JPL/Space Science Institute