Helene is a tiny moon of Saturn that shares an orbit with the much larger moon Dione. Helene reposes at a gravitationally stable position called a Lagrange point. Helene orbits Saturn ahead of Dione, and viewed from above the centres of Dione, Saturn and Helene form a vast equilateral triangle. Moons located at Lagrangian points are known as Trojan satellites. In this case, this is highly appropriate for this little moon is named for the mythical Helen, daughter of Zeus and Leda, whose abduction by Paris was the casus belli for the Trojan Wars.

image of helene

NASA's Cassini spacecraft obtained this image of Saturn's moon Helene on June 18, 2011. ( Image credit: NASA/JPL-Caltech/Space Science Institute)


Dark and a mere 36km wide, Helene was discovered  by French astronomers in 1980 and was originally designated S/1980 S6. Virtually all we know of this world comes from visits by the superb Cassini probe. The moon can be seen to have an unusually smooth surface with few impact craters and strange gully-like features. It seems that some dry material flows into low-lying regions, filling them and erasing craters. However this is true of only the face of Helene turned towards  Saturn, the other is as cratered as one would expect. Why Helene should be so two-faced is unknown.


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