Two moons of Saturn are shaped a bit like flying saucers, as seen in these images from the orbiting Cassini spacecraft. The top images show Atlas from the side (left) and almost above, while the bottom images show Pan (at right, bisected by Saturn's rings). These small moons acquired their saucer shapes by pulling in bits of ring material, which build up around their waists. [NASA/JPL/SSI]
Flying saucers orbit the planet Saturn. They're not piloted by Saturnians, though -- or anyone else, for that matter. That's because they're moons that skim along with Saturn's rings.
Pan and Atlas are chunks of rock and ice that are about 20 miles across. They're only about a third as far from Saturn as our moon is from Earth.
Both moons have tall ridges around their equators -- up to two or three miles high in some places. The ridges give the moons their saucer-like appearance.
The ridges probably are made of ice and dust from Saturn's rings. Atlas is at the outer edge of Saturn's main rings, while Pan is inside the rings. In fact, it clears a gap in the rings that's a couple of hundred miles wide.
As the moons orbit Saturn, their gravity pulls at the nearby ring material -- tiny bits of ice and rock. That creates ripples in the rings that radiate outward like the wake of a boat. It also pulls some ring material into the paths of the two moons. They sweep up this material, building the ridges -- ridges that make Pan and Atlas look like flying saucers.
Saturn is in good view tonight. It looks like a fairly bright golden star, just a whisker above the orange planet Mars. Much-brighter Venus -- the "evening star" -- is off to their lower right. Saturn's rings are visible through telescopes. Pan and Atlas are far too small to see even with a telescope, but they continue to skim along at the outer edge of the rings.
Script by Damond Benningfield, Copyright 2010
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