“August 13, 2009. An unusually large propeller feature is detected just beyond the Encke Gap in this Cassini image of Saturn’s outer A ring taken a couple days after the planet’s August 2009 equinox.
The unique geometry of equinox has thrown into relief small moonlets within the rings and the structures they create around them. Propeller-like features, a few kilometers long, centered on and created by the action of small embedded moonlets only about 100 meters across, were discovered early in the mission. These previous findings constituted the first recognition of the presence in Saturn’s rings of bodies bigger than the largest ring particles (about 10 meters, or 30 feet, across) but smaller than the 8-kilometer-wide (5-mile-wide) ring moon, Daphnis, in the outer A ring.
From the 350-kilometer (220-mile) length of the shadow cast by this 130-kilometer-long (80-mile-long) propeller, the heights of these features above the ring plane have been measured to reach about 200 meters (650 feet), indicating the moonlet responsible for the propeller in this image is likely to be 400 meters (1,300 feet) across.
Cassini scientists have tracked several individual propeller moons embedded in Saturn’s A ring over several years. The A ring is the ...