August 21, 2008
This high-resolution view shows incredible detail within a spiral density wave within Saturn's A ring.
A spiral density wave is a spiral-shaped massing of particles that tightly winds many times around the planet. These waves decrease in wavelength with increasing distance from the planet.
The wave that covers a broad strip across the center of the image is created by a gravitational resonance with the moon Janus. For every sixth orbit of the ring particles at this radius from Saturn, Janus makes five orbits, meaning that the moon is continually providing a gravitational kick to particles in this region of the rings.
A couple of the peaks in the broad Janus-created wave appear bunched together, possibly owing to Janus' orbit being changed when it swaps places with its co-orbital moon Epimetheus (see The Dancing Moons).
This view looks toward the sunlit side of the rings from about 34 degrees below the ringplane.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 21, 2008. The view was acquired at a distance of approximately 170,000 kilometers (106,000 miles) from Saturn. Image scale is 669 meters (2,194 feet) 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, Colo.
Credit: NASA/JPL/Space Science Institute