Propeller Churns the A Ring

July 8, 2010
PIA NumberPIA12792
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This movie created from images obtained by NASA’s Cassini spacecraft shows a propeller-shaped structure created by a hidden, embedded moon moving through one of Saturn's rings.

The moon, likely about a kilometer (half a mile) across, can't be seen at this resolution. However, it is larger than many other "propeller" moons and has cleared ring material from the dark wing-like regions to its left and right in these images. Disturbed ring material closer to the moon reflects sunlight brightly and appears like a white airplane propeller.

Taken in 2005, these images are part of a growing catalogue of "propeller" moons that, despite being too small to be seen, enhance their visibility by creating larger disturbances in the surrounding fabric of Saturn's rings. The motion here occurs in Saturn’s outermost main ring, known as the A ring. Cassini scientists now have tracked several of these individual propeller moons embedded in Saturn's disk over several years.

These images are important because they represent the first time scientists have been able to track the orbits of objects in space that are embedded in a disk of material. Continued monitoring of these objects may lead to direct observations of the interaction between a disk of material and embedded moons. Such interactions help scientists understand fundamental principles of how solar systems formed from disks of matter. Indeed, Cassini scientists have seen changes in the orbits of these moons, although they don't yet know exactly what causes these changes.

Imaging scientists nicknamed the propeller shown here "Bleriot" after the French aviator Louis Bleriot. The propeller structure is 5 kilometers (3 miles) in the radial dimension (the dimension moving outward from Saturn which is far out of frame above this image). The dark wings appear 1,100 kilometers (700 miles) in the azimuthal (longitudinal) dimension.

Giant Propeller in A Ring shows the giant propeller "Earhart" named after the aviatrix Amelia Earhart. See Propeller Motion and Locating the Propellers to learn more about propeller shapes and to see smaller propellers.

This movie is a concatenation of seven images taken during a span of about 20 minutes. This view looks toward the southern, sunlit side of the rings from about 21 degrees below the ring plane.

The images were taken in visible light with the Cassini spacecraft narrow-angle camera on May 1, 2005. The view was obtained at a distance of approximately 1.2 million kilometers (746,000 miles) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 28 degrees. Image scale is 7 kilometers (4 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, Calif., 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.

For more information about the Cassini-Huygens mission visit The Cassini imaging team homepage is at

Image Credit: NASA/JPL/SSI