How Saturn’s Icy Moon, Enceladus, Got Its ‘Tiger Stripes’

A false-color mosaic of Saturn’s moon Enceladus, taken following a 2008 fly-by of NASA’s Cassini spacecraft.

Of the strange and unexplained terrains in our solar system, the south pole of Saturn’s moon Enceladus is among the most perplexing.

Enceladus is an ocean world, with a vast and briny sea tucked beneath its icy crust; this makes it one of the most tantalizing places in the solar system to look for life beyond Earth. But unlike other frozen moons, Enceladus constantly erupts. The tiny world blasts salty water into space through cracks in its crystalline shell. These fissures, raked across the moon’s southern pole, are roughly parallel and evenly spaced. And ever since scientists first took a good look at this alien moon, they’ve had a tough time explaining those “tiger stripes.”

“What is going on?” said Doug Hemingway of the Carnegie Institution for Science. “In a way, it’s an obvious question — it’s been in the back of everyone’s mind for a long time.”

Now, Dr. Hemingway and his colleagues think they know how the moon got its stripes — and, curiously, why the stripes are found only at the Enceladian south pole. They described their hypothesis Monday in Nature Astronomy. Learning more about how extraterrestrial oceans on worlds such as Enceladus evolve and interact with planetary surfaces is important for understanding how life might exist beyond Earth and how we might find it, Dr. Hemingway said.

In 2005, NASA’s Cassini spacecraft first swooped in and stared at 313-mile-wide Enceladus. The spacecraft saw a stunning array of geysers erupting from the moon’s south pole — eruptions that vent the moon’s ocean into space and sculpt Saturn’s E ring. Later, when Cassini flew through the jets, it tasted an alien soup containing all the ingredients necessary for life as we know it.

The moon’s southern hemisphere is riven by four prominent fractures. Approximately parallel and spaced about 20 miles apart, the massive cracks are, like other features of Enceladus, named after locations in “One Thousand and One Nights.”

Previous ideas about the origins of the cracks — Alexandria, Baghdad, Cairo, Damascus and a smaller crack unpoetically referred to as “E” — included massive impacts, hot spots, strike-slip faulting and a migrating icy shell. Dr. Hemingway and his colleagues modeled the evolution of the moon’s icy shell, accounting for its thickness, elasticity, strength and temperature, and uncovered a simpler, more comprehensive explanation.

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SOURCE: The New York Times, Nadia Drake