Pan, this is its name, was discovered in 1990 from images taken by the Voyager 2 probe nine years earlier.
Pan is the innermost of Saturn's known moons. In fact, it orbits inside the Encke division of ring A, at a distance of only 134,000 km from the planet's atmosphere. It completes one revolution in just 13.8 hours.
In its movement along its orbit, Pan gravitationally influences the small particles that make up the ring. The overall motions of the particles in turn generate a phenomenon similar to waves that propagate for several hundreds of kms inside the rings.
It was by studying these perturbations that two astronomers in 1985 predicted the existence of a moon located within Encke's division, which was discovered five years later.
The particles making up the ring may also be responsible for the moon's saucer-like appearance. These particles, attracted by Pan's gravity, would in fact fall on its surface, forming the equatorial crest visible in the images. At present this remains only a hypothesis; to have more certain answers, other missions in orbit around Saturn will be needed.
Credit: NASA, JPL.
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