Scientists for NASA's Cassini mission noticed some weird-looking propeller-like shapes in the outer edge of Saturn's A ring. What could be creating these unusual contours? A closer look revealed they were being formed by dozens of moving moonlets. Normally, these kilometer-sized moons would have been almost impossible to see, since they are embedded within the rings. "However, their presence is betrayed by the large tell-tale 'propeller' structures they generate in the ring material on either side of them," said Carolyn Porco, leader of the Cassini imaging team, and co-author on a new paper on these propeller moons. In an email, Porco said similar features had been seen earlier in other locations in Saturn's rings, but were "much smaller, harder to see, and so numerous that there was no hope of following any one of them. The new propellers, and the moonlets that create them, are some ten times larger and much easier to identify and follow from image to image and year to year."