We've Just Solved Some Mysteries of Saturn's Icy Moon Enceladus

Scientists have achieved a deeper understanding of the "tiger-stripe" fissures in the icy crust of Saturn's moon Enceladus, pictured in this composite image of two photographs. Cassini Imaging Team/SSI/JPL/ESA/NASA

There's something curious about the icy moon of Saturn called Enceladus. Take a look at its southern hemisphere, and you'll see wide swaths of color that've been given the nickname "tiger stripes." Discovered in 2005, these four stripes are actually massive fissures in the ice crust that covers a hidden global ocean discovered in 2015. Gigantic plumes composed of salty liquid water and other materials regularly erupt out of these fissures thanks to the tidal pull of Saturn and the 61 other objects — 52 of which have official names — in orbit around the planet.

The diameter of Enceladus is only 314 miles (505 kilometers), meaning the entire moon is comparable to the United Kingdom, as this artist's interpretation shows.
NASA/JPL/Space Science Institute

Tide goes out, water recedes. Tide comes in, water's blasted out of these cracks, and in the process is vaporized by energy generated, and the "water smoke" drifts all the way into space. In fact, this constant expulsion of material from the subsurface sea annually replenishes Saturn's E-ring, the planet's most exterior of its seven main rings. (The rings' letter names go in order of discovery, not by alphabetical order, which is why the E-ring isn't the fifth, as you might imagine).

Scientists have known about the plumes since the Cassini space probe — named after an astronomer who discovered four of Saturn's moons in the late 1600s — sent back data a decade ago, identifying the southern hotspot. And we already knew that the E-ring has been constantly growing since astronomers first identified it in 1966, which means we can assume Enceladus has been feeding it for the past 50 years — and likely for thousands of years before that.

A map of Saturn's moons shows Enceladus at the inner edge of the outermost E-ring.
Encyclopaedia Britannica/Getty Images

But what hasn't been understood until now is just how those plumes have been sustained. Why don't these slots freeze over when the tide's out? Why don't they grow too large? According to new research published today in the journal PNAS, scientists examining the most recent Cassini data have created a working model to understand the physics. 

The research shows that Enceladus' stripes exist in a Goldilocks zone of just the right size — neither too large nor too small. As the water's pumped out and sucked back in by the tides, according to the recently developed model, the friction of liquid against frozen material creates enough heat and physical disruption to prevent the slots from freezing over.

Enceladus is named after mythological Greek Giant of the same name. An enemy of the goddess Athena, Enceladus is said to be buried beneath the Sicilian volcano Etna, and responsible for its tremors and eruptions.

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