The two large craters on the right of this image are overprinted with smaller, more recent craters in this Cassini spacecraft view of Saturn's moonRhea.
Rhea, at 1,528 kilometers, or 949 miles, across, is Saturn's second largest moon. This view is centered on terrain at 17 degrees South latitude, 235 degrees West longitude.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on October 17, 2010. The view was acquired at a distance of approximately 44,000 kilometers (27,000 miles) from Rhea. Image scale is 259 meters (850 feet) per pixel.
Enceladus (504 kilometers, or 313 miles across) is the largest moon in this image and appears at the bottom. Janus (179 kilometers, or 111 miles across) orbits beyond the rings near the center of the image. Epimetheus (113 kilometers, or 70 miles across) orbits beyond the rings near the top of the image. Atlas (30 kilometers, or 19 miles across) appears as a tiny speck between the main rings and the thin F ring on the right. Daphnis (8 kilometers, or 5 miles across), which orbits in the narrow Keeler Gap of the A ring, appears as a small, bright speck on the left of the image. Pan (28 kilometers, or 17 miles across), which orbits in the Encke Gap of the A ring, also appears as a bright speck on the left of the image. Daphnis is farther to the left of the image than Pan.
Although Enceladus appears to be in the foreground here, that moon, at a distance of 3.1 million kilometers (1.9 million miles), is actually farthest away from Cassini in this image. Janus is 3 million kilometers (1.9 million miles) from the spacecraft. The view was obtained at a distance of approximately 2.8 million kilometers (1.7 million miles) from Epimetheus.
Enceladus is a very reflective body. To enhance visibility, the other moons and the rings have been brightened by a factor of 3.4 relative to Enceladus.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on October 6, 2010. Image scale is approximately 19 kilometers (12 miles) per pixel on Enceladus, about 18 kilometers (11 miles) per pixel on Janus and about 17 kilometers (11 miles) per pixel on Epimetheus.
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 moonMimas. 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 orbitingSaturn. 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.
...
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.
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).
Cassiniscientists 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 Earthyears. 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.
This fractured terrain covers the trailing hemisphere of Dione (1,123 kilometers, or 698 miles across). See PIA10560 to learn more. This view is centered on terrain at 53 degrees north latitude, 209 degrees west longitude.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on October 17, 2010. The view was acquired at a distance of approximately 61,000 kilometers (38,000 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 32 degrees. Image scale is 363 meters (1,190 feet) per pixel.
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.
Cassiniscientists 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 moonMimas, 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.
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 Earthyears). 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.
Lit terrain seen here is on leading hemisphere of Mimas (396 kilometers, or 246 miles across). North on Mimas is up and rotated 1 degree to the left.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on October 16, 2010. The view was obtained at a distance of approximately 103,000 kilometers (64,000 miles) from Mimas and at a Sun-Mimas-spacecraft, or phase, angle of 113 degrees. Image scale is 613 meters (2,011 feet) per pixel.
