When first viewed in the video sequence, Cassini images reveal the moon Prometheus as it slowly collides with the diffuse inner edge of Saturn’s F ring and reminds this viewer of the Silver Surfer cresting on a big wave, only this one is literally out of this world. The Cassini spacecraft focuses on a streamer-channel feature in Saturn’s F ring. These features are created by the moon Prometheus as it closely approaches the ring once per orbit (see Soft Collision). Once during its 14.7-hour orbit of Saturn, Prometheus (102 kilometers, or 63 miles across) reaches the point in its elliptical path, called apoapse, where it is farthest away from Saturn and closest to the F ring. At this point, Prometheus’ gravity is just strong enough to draw a “streamer” of material out of the core region of the F ring.Credit: NASA/JPL/Space Science Institute
Initially the dust-sized material drawn away from the ring appears to form a streamer pointing ahead of Prometheus in its orbit. (All orbital motion is towards the right in the movie.) Over time, the streamer falls increasingly farther behind Prometheus because material in the F ring is orbiting slower than the moon. The streamer gets longer and a darker “channel” starts to be seen (to the left of the streamer in the movie). The video can be seen at this site.
This view looks toward the unilluminated side of the rings from about 36 degrees above the ringplane.The image was taken in visible light with the Cassini spacecraft narrow-angle camera on September 30, 2008. The view was acquired at a distance of approximately 970,000 kilometers (602,000 miles) from Saturn and at a Sun-ring-spacecraft, or phase, angle of 45 degrees. Image scale is 5 kilometers (3 miles) per pixel.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.
The creation of such streamers and channels occurs in a cycle that repeats each Prometheus orbit: when Prometheus again reaches apoapse, it draws another streamer of material from the F ring. But since Prometheus orbits faster than the material in the ring, this new streamer is pulled from a different location in the ring about 3.2 degrees (in longitude) ahead of the previous one. In this way, a whole series of streamer-channels is created along the F ring. In some observations, 10 to 15 streamer-channels can easily be seen in the F ring at one time (see PIA07712 on the left). Eventually, a streamer-channel disappears as shearing forces (i.e., Keplerian shear) act to disperse the constituent dust particles.
The movie shows just under half of a complete streamer-channel cycle. The dark frames in the movie represent the period during which Prometheus and the F ring pass through Saturn’s shadow. The images in the movie were acquired by the Cassini spacecraft narrow-angle camera on November 23 and 24, 2006. The movie sequence consists of 72 clear spectral filter images taken every 10.5 minutes over a period of about 12.5 hours.
The original images were cropped to show only the region around Prometheus and the nearby portion of the F ring. The movie covers the region between 138,000 and 142,000 kilometers (86,000 and 88,000 miles) radially from Saturn and 1 degree in longitude from Prometheus on each side. Each frame was reprojected such that the vertical axis represents distance from Saturn and the horizontal axis represents longitude around Saturn. Image scale is 10 kilometers (6 miles) per pixel in the vertical direction; the images cover 0.005 degrees of longitude in the horizontal direction. Because of the reprojection, the F ring appears straight, rather than slightly curved, as it otherwise would.
Since the F ring has an elliptical shape, its radial distance from Saturn varies by about 1,000 kilometers (620 miles) around the ring. This accounts for the apparent vertical movement of the ring over the course of the movie. Only a very small part of the ring appears in each of the reprojected frames, so the difference in the ring’s radial distance from left to right across any single frame is small enough as to be effectively unnoticeable.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.
