Cassini Buzzes Saturn's Dinky Moon Helene : Big Pic
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June 20, 2011 -- Two days ago, NASA's Cassini spacecraft flew within 6,968 km (4,330 miles) of Saturn's moon Helene. Measuring in at only 36 × 32 × 30 km (22 × 20 × 19 miles), this dinky moon was only discovered in 1980 when astronomers realized it shared its orbit with the larger Saturnian moon Dione -- Helene trails Dione, sitting in the Saturn-Dione Lagrangian (L4) point. Helene is therefore known as a "Trojan moon," one of four known to exist in the Saturnian system.*
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As Helene is so small, it doesn't have a significant gravitational field to shape its body into a smooth sphere -- a state known as hydrostatic equilibrium. It is therefore a very lumpy moon. Helene also features impact craters and gully-like structures. Interestingly, the moon also features "two faces" -- one side is smooth and apparently covered in dust, while the other side is craggy and pockmarked in craters.
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Although this was a close pass, in March 2010, Cassini got even closer to Helene during a 1,820 km (1,131 mile) flyby. However, on this occasion, Cassini imaged Helene's night side to its sunlit side, catching a beautiful crescent in the process (pictured below).
*Interestingly, this is how Helene got its name; after Helen of Troy, the granddaughter of Cronus (Saturn) in Greek mythology.
-- by Ian O'Neill
Credit/source: NASA/JPL-Caltech/Space Science Institute
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