Mysterious 'tiger stripes' on Saturn's moon Enceladus explained by scientists

Scientists are now in a position to explain the 'tiger stripes' that cover the surface of Saturn's moon Enceladus. The icy moon has long drawn a captivating curiosity among the scientific community with speculation of the celestial body's possibility of nurturing life. The vast ocean that hides beneath its surface may be home to extraterrestrial life but that's just one facet of the mysteries surrounding it.

Unique landscape spotted by NASA's Cassini

One of those mysteries is the four stripes that cover its south pole, which are like nothing else known in our solar system. Researchers have now revealed the physics behind the giant fissures that open up and spill ocean water out of the icy surface and create those stripes. The discovery of the tiger stripes was done by US space agency NASA's Cassini mission in 2015 which took its deepest dive into the plume of vapour and particles emanating from cracks in Enceladus.

"First seen by the Cassini mission to Saturn, these stripes are like nothing else known in our Solar System," lead author Doug Hemingway explained. "They are parallel and evenly spaced, about 130 kilometers long and 35 kilometers apart. What makes them especially interesting is that they are continually erupting with water ice, even as we speak. No other icy planets or moons have anything quite like them."

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Observers puzzled

At first, the astronomers were uncertain of the reasons behind the stripes and their sole location on Enceladus at the south pole. They also scratched their heads to figure out why the tiger stripes were so evenly spaced across that surface. The landscape looked like human veins artistically drawn on the surface.

Max Rudolph, assistant professor of earth and planetary sciences at the University of California, Davis and a colleague of Hemingway, said, "We want to know why the eruptions are located at the south pole as opposed to some other place on Enceladus, how these eruptions can be sustained over long periods of time and finally why these eruptions are emanating from regularly spaced cracks."

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What have researchers concluded?

Among other conclusions, one was the realisation that there was nothing special about that south pole. The stripes at the south pole opened up first and it could have formed at any other side of Enceladus. The other major breakthrough was the discovery that when the cracks formed in the surface, ocean water gushed out of the gap that was left. That allowed three more cracks to form neatly across the surface. "Our model explains the regular spacing of the cracks," Rudolph said in the statement. He further explained that the weight of the icy material falling back to the edges of the first crack "caused the ice sheet to flex just enough to set off a parallel crack about 35 kilometres (22 miles) away."

They additionally found that the cracks stay open and continue to erupt in part because of the tidal effects of Saturn's gravity which changes with the moon's strange orbit. The fissures continue to widen and narrow, bringing water through them. This prevents them from closing up for good.

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The discovery was made using numerical modelling, which allowed scientists to understand the forces that act on the icy shell that encases Enceladus. Tidal forces are exerted on Enceladus as it is pulled by Saturn's gravity which heats and cools the surface. As that happens, water solidifies into the ice beneath the outer shell and expands in volume, pushing up against the ice until it cracks. Those cracks are kept open because the water underneath is continually sloshed around and so it cannot freeze shut. As the water spills out of those cracks, it drops back down as ice, which builds up at the edge of the fissure and weighs it down. That means the ice sheet flexes, and so led to the neat cracks about 20 miles away, the researchers say.

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