CICLOPS: Cassini Imaging Central Laboratory for OPerationS

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PIA 14918

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  These three Cassini images show a propeller-shaped structure created by an unseen moon in Saturn's A ring. Propellers and other details of Saturn's rings are greeting scientists for the first time in two years, as Cassini's orbit took the spacecraft out of Saturn's equatorial plane in the spring of 2012, making face-on views of the rings possible again.

For years scientists have tracked this propeller, marked with red arrows here. 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.

This propeller, nicknamed "Sikorsky" after Russian-American aviator Igor Sikorsky, is about 30 miles (50 kilometers) long. See PIA12790, PIA12792 and PIA11672 to learn more about propellers.

In this most recent image, scientists knew they were observing a propeller they had seen before because Sikorsky was found close to the location predicted by a simple model of its motion. But its actual location did trail the predicted location by 6 degrees of longitude (8,000 miles, or 13,000 kilometers), underlining some of the changes known to occur in the orbits of propeller moons. These changes may occur because of interactions between the rings and the propeller moons. Scientists are eager to understand these interactions in Saturn's rings, as they may hold a key to similar systems such as solar systems forming from disks of matter.

In this most recent image, Sikorsky was found to trail its predicted position by 6 degrees of longitude (8,000 miles, or 13,000 kilometers), a discrepancy that underlines the changes that are known to occur in the orbits of propeller moons, possibly due to interactions between the rings and the embedded moons. Scientists are eager to understand these interactions in Saturn's rings, as they may hold a key to similar systems such as solar systems forming from disks of matter.

The Encke Gap of Saturn's A ring is on the right in the images. The A ring is the outermost of Saturn's main rings. This view looks toward the northern, sunlit side of the rings from about 12 degrees above the ringplane.

These images have not been cleaned of the effects of cosmic rays that struck the camera's sensor during exposure. These cosmic ray hits appear as small white specks or streaks on the images. These specks are not features in Saturn's rings. The image has been enhanced to aid visibility of compact objects like the propeller. The enhancement makes the edge of the Encke Gap appear dashed.

The images were taken in visible light with the Cassini spacecraft narrow-angle camera on June 5, 2012. The view was obtained at a distance of approximately 236,000 miles (380,000 kilometers) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 24 degrees. Image scale is 1 mile (2 kilometers) per pixel.

The Cassini Solstice 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.

For more information about the Cassini Solstice Mission visit, and

Credit: NASA/JPL-Caltech/Space Science Institute
Released: July 9, 2012 (PIA 14918)
Image/Caption Information

Alliance Member Comments
NeKto (Aug 30, 2012 at 7:33 AM):
I've been thinking that perhaps these features are not caused by tiny moons. in fluid dynamics, if you have a slow down at one point in a flow, it will produce a wave that moves upstream. eg; if one car slows down 5 mph in 60 mph "bumper to bumper" traffic, a few miles behind that car, traffic will come to a complete stop. the hypothesis i am attempting to communicate is that the propeller "moons" might not be solid bodies at all. perhaps they are rubble concentrations caused by something akin to the wave phenomenon i described. no individual orbiting particle would stay in the sphere of concentration for long. the concentrated mass could be enough to produce the visible propellers. the concentration could move along the orbital path slower, possibly even faster, than orbital velocity.
when i read you found propellers behind predicted positions, i thought my hypothesis might be worth mentioning.
greece (Jul 15, 2012 at 10:00 AM):
Is this S/2009 S 1 or another object?

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