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Saturn's tides drive icy moon's plumes

Enceladus' chilly jets ebb and flow in time with the planet’s tug

PIERCING PLUMES  Icy jets  burst out of the south pole of Saturn’s moon Enceladus. The plumes, shown here in a 2009 image from the Cassini spacecraft, emerge in response to Saturn’s tides.

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Icy geysers repeatedly erupting from Saturn’s moon Enceladus owe their Old Faithful-esque regularity to the planet’s tidal pull. An analysis of 252 images captured by NASA’s Cassini spacecraft proves what many scientists have suspected since the probe discovered the regular eruptions in 2005.

In 2007, Cassini scientists developed a mathematical simulation suggesting that the jets are powered by Saturn’s gravitational pull, which waxes and wanes throughout Enceladus’ egg-shaped 33-hour orbit. The study predicted that Enceladus’ fractures would open most readily when Saturn was farthest away and then close up as the planet neared.

Researchers report July 31 in Nature that the simulation was correct: The Cassini images show that cracks at the moon’s south pole spew out four times as much of their icy innards when Enceladus and Saturn are farthest apart as they do when the two bodies move closest together.

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