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New insights into the nature of Saturn's rings are revealed in this panoramic mosaic of 15 images taken during the planet's August 2009 equinox.
Not only has equinox created the opportunity to discover brand new phenomena in the rings, but it has shed new light on those previously known.
Beginning at the left, closest to Saturn, we find ringlets within the innermost D ring showing up in this geometry as relatively bright ...an indication that they are extending sufficiently above the ringplane to catch the direct rays of the sun.
The edges and ringlets of some of the gaps in the C ring and elsewhere are also now relatively bright, indicating these features are vertically thicker and more extended out of the ringplane than previously known. To sweeten the sight, clumps are seen in some of the narrow, and here very bright, ringlets in the C ring ...a circumstance not previously anticipated.
The gentle, spiraling 30-kilometer-wavelength undulation that had been discovered in 2006 extending across 800 kilometers of the D ring is now seen, under better viewing conditions, to extend fully across the C ring, right up to the inner B ring. In 2006, imaging scientists speculated that a collision with a comet or asteroid may have disturbed the D ring. That explanation seems less likely now that this and other new images show the effect spread over a much broader radial range. It covers a total radial distance of about 19,000 kilometers (12,000 miles). This startling result calls into question the initial conjecture that an early-1980s impact of an object, a few meters across, into the D ring initiated the wave disturbance. The enormous extent of the corrugation now makes its existence more mysterious than ever, and imaging scientists are struggling to understand its origin. See PIA11671 to learn more.
Waves in the inner B ring, first seen in Saturn orbit insertion images, are now obvious and distinct.
Bright spokes, consisting of tiny particles elevated above the ring plane and surrounded by the dark outer B ring, can also be seen near the middle of the mosaic. See PIA08877 to learn more about these ghostly markings.
Several ringlets within the Cassini Divison, like those in the C ring, have become brighter in this geometry.
Farther outward, a bending wave, created by a resonance with the moon Iapetus, can be easily seen just beyond the Cassini Division, leading into the inner A ring.
The shadow of the moon Dione is seen in several locations on the rings because of the shadow's motion across the rings during the time the mosaic images were being acquired.
Ringlets residing in the Encke gap are now very bright, and density waves in the outer A ring are dramatically illuminated under the conditions of equinox. These waves can be seen on the right of the mosaic, right up to the outer A ring edge. (See PIA10452 to learn more about these types of waves.) The equinox images now show that these are regions where compression within the strongest part of the wave is severe enough to force material out of the ringplane and into broad sunlight.
Shadows, barely visible on the bright F ring on the far right of the mosaic, are being cast by structures in the ring itself.
This view and others like it (see PIA11664) 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 ringplane, significantly darkens the rings, and causes out-of-plane structures 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 PIA11665).
This view looks toward the southern side of the rings from about 5 degrees below the ringplane. The rings, illuminated only by light reflected off the planet and by edge-on light from the sun, are very dim at this time. The rings have been brightened in this mosaic to enhance visibility. Background stars are visible shining through the rings, and the image has not been cleaned to remove cosmic rays which struck the camera's detector during the exposures.
The images were taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 10, 2009. The view was acquired at a distance of approximately 868,000 kilometers (539,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 158 degrees. Image scale is 5 kilometers (3 miles) per pixel.
[Caption updated March 31, 2011.]
The Cassini Equinox Mission is a joint United States and European endeavor. 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 was designed, developed and assembled at JPL. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.