NASA’s Cassini spacecraft captured a propeller-shaped disturbance in one of Saturn's rings created by a moon that is too small to be seen here.

Photojournal: PIA12789

July 8, 2010

NASA’s Cassini spacecraft captured a propeller-shaped disturbance in one of Saturn's rings created by a moon that is too small to be seen here.

The moon, likely about a kilometer (half a mile) across, is invisible at the center of the image. However, it is larger than many other "propeller" moons and has cleared ring material from the dark wing-like structures to its left and right in the image. Disturbed ring material closer to the moon reflects sunlight brightly and appears like a white airplane propeller. This propeller appears in the A ring, which is the outermost of Saturn’s main rings.

Taken in 2006, this image is 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. 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 a French aviator named Louis Bleriot. The propeller structure is 5 kilometers (3 miles) in the radial dimension -- the dimension moving directly outward from Saturn. The dark wings appear 1100 kilometers (700 miles) in the azimuthal (longitudinal) dimension, while the central propeller structure is 110 kilometers (70 miles) long.

See Propeller Churns the A Ring to watch a movie of "Bleriot." Giant Propeller in A Ring shows the giant propeller "Earhart" named after another aviator, Amelia Earhart. See Propeller Motion and Locating the Propellers to learn more about propeller shapes and to see smaller propellers.

This image has been re-projected so that orbiting material moves to the right and Saturn is down. The propeller was seen at the edge of the camera's field of view when the image was taken, so some data were missing; the blank space at the top of the image was filled in with a gray color. Scale in the original image was 2 kilometers (1 mile) per pixel. Image scale in this re-projected view is about 1 kilometer (half a mile) per pixel.

This view looks toward the southern, sunlit side of the rings from about 30 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 15, 2006. The view was acquired at a distance of approximately 463,000 kilometers (288,000 miles) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 15 degrees.

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