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What's going on inside Saturn moon? Geysers offer intriguing new clue.

Enceladus is thought to have liquid water – and perhaps life – beneath its surface. New findings showing that geysers of water vary with tidal changes offer a glimpse of the mechanics inside.

By Staff writer / July 31, 2013

Geyser-like eruptions of ice particles and water vapor shoot from the south pole of Saturn's moon Enceladus. A new study suggests that the plumes vary in intensity as the moon orbits Saturn.

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Plumes of ice crystals erupting from Saturn's moon Enceladus wax and wane in a pattern that could help reveal the inner workings of a body widely seen as a potential habitat for life beyond Earth, according to a new study.

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The moon is thought to have either a global ocean under its icy crust or a sea underlying the crust in the south polar region. Theories suggest that frictional heat generated in Enceladus's interior keeps the sea from freezing. The friction is generated as Saturn's gravity tightens and relaxes its grip on the moon during each orbit.

Previous research revealed the south polar region as a hot spot whose surface is radiating up to 16 billion watts of power – roughly equal to the heat generated by 16 large nuclear power plants.

Now, it appears that tidal action is changing the amount of ice the region ejects as well – repeatedly opening and nearly closing four parallel, 80-mile-long "tiger stripe" fissures associated with the geysers feeding the plumes.

Stresses in Enceladus's crust overpower Saturn's gravity and widen the fissures when the moon reaches the most distant point in its orbit. At closest approach, Saturn's gravity overcomes the stresses and nearly shuts the fissures.

The results a reported by a team led by Cornell University planetary scientist Matthew Hedman are and set to appear in Thursday's issue of the journal Nature.

The plumes have captivated planetary scientists ever since the features were discovered in 2005. It marked the first time researchers could study a geologically active icy moon as events were happening. The material in the plumes provided a window on the chemical processes going on below the surface. The ices contain organic compounds and hydrocarbons that have piqued the interest of astrobiologists hunting for other potential habitats for life in the solar system.

Now, researchers say, they have a direct measure of the stresses at work on the crust.

In 2007, researchers published the results of modeling experiments suggesting that the moon underwent this process. That triggered a hunt to detect the effect, Dr. Hedman explains. Two other groups tried, but failed, to detect a consistent venting pattern in the different approaches they tried.

His team wasn't even looking for this effect when it started to review data gathered by Cassini's Visual Infrared Mapping Spectrometer, Hedman says. Instead, the researchers were trying to analyze the range of particle sizes in the plumes, which are known to feed one of Saturn's rings, known as the E ring.

But in poring over the data, Catherine Gosmeyer, an undergraduate student at Indiana University serving as a research assistant at the time, noted pronounced changes in the brightness of the plumes with time. Looking at the pattern, and particularly at the intensity of the changes, "I thought, 'That can't possibly be right,' " Hedman recalls.

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