Pan, its name, was discovered in 1990 from images taken by the spaceship Voyager 2 nine years ago.
Pan is the innermost of the known moons of Saturn. It revolves around the Ring A Encke Division, just 134,000 kilometres from the planet's atmosphere. Complete a revolution in just 13.8 hours.
In its motion along the orbit, Pan exerts a gravitational influence on the little particles that make up the ring. The overall motions of the particles in turn generate a wave-like phenomenon that propagates for several hundred kilometers within the rings.
It was by studying these perturbations that two astronomers in 1985 predicted the existence of a moon within the Encke division, which was discovered five years later.
The particles forming the ring may also be responsible for the appearance of the moon's flying saucer. These particles, attracted by the gravity of Pan, would fall on its surface to form the equatorial ridge visible in the images. Currently, that is only a hypothesis; to have more reliable answers, we will need other missions in orbit around Saturn.
Credit: NASA, JPL.
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