Wednesday, June 22, 2011

Saturn's 'ice queen' captured

Saturn's Ice Queen
NASA's Cassini orbiter has captured another close-up view of the Saturnian moon Helene, clearing the way for a global map of the 20-mile-wide "ice queen."

The spacecraft got its latest look at the icy moon on Saturday from a distance of 4,330 miles (6,968 kilometers), more than a year after its closest-ever Helene flyby in March 2010. This time, the pictures provided sunlit views of the moon's Saturn-facing side, improving on last year's imagery. Taken together, these pictures will enable astronomers to finish a global map that could shed additional light on the grooved, pockmarked moon's impact history, NASA's Jet Propulsion Laboratory said in today's image advisory.

Helene sticks out among Saturn's more than 60 moons for a couple of reasons: First of all, it is gravitationally bound in the same orbit as another, much larger icy moon called Dione. This makes it one of four "Trojan moons" in the Saturnian system, along with Polydeuces (which is also bound to Dione) and Telesto and Calypso (both bound to Tethys).

Helene's surface also reveals a network of gully-like features that may have been created by landslides (or, in this case, dustslides or iceslides). Working up a detailed map of the moon should help astronomers get a better grip on the gullies' genesis.

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