Shepherd Satellites

This image taken by the Voyager 2 spacecraft of Saturn's A-ring shows the
thin F-ring bracketed by its two shepherding satellites. Because the inner
moon revolves around the planet slightly faster than the outer one, the
satellites lap each other every 25 days.

This picture was taken on August 15, 1981, when Voyager 2 was 10.5 million
kilometers (6.6 million miles) from Saturn. At that instant, the shepherds
were less than 1,800 kilometers (1,100 miles) apart.