Astronomers discover origin of Enceladus’ strange ‘tiger stripes’

9 Dec 2019503 Views

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Image: © Peter Jurik/Stock.adobe.com

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Astronomers looking at the icy moon Enceladus have determined what is creating its strange ‘tiger stripes’ features.

Along with Europa, Saturn’s moon Enceladus is considered one of the most likely places in the solar system to harbour alien life. The icy outpost, covered in mysterious grooves often described as ‘tiger stripes’, has a vast ocean underneath which astronomers on Earth are eager to investigate.

Now, a team from the Carnegie Institute of Science has published findings that claim to have gotten to the bottom of what’s causing these grooves near its south pole.

First discovered by Cassini, the lines are parallel and evenly spaced, being approximately 130km long and 35 km wide.

Still spewing water

“What makes them especially interesting is that they are continually erupting with water ice, even as we speak,” said Doug Hemingway, lead author of the research. “No other icy planets or moons have anything quite like them.”

Using models, the team investigated the physical forces acting on Enceladus that allow the tiger stripe fissures to remain in place. They also wanted to understand why they only occur on its south pole and why the cracks are so evenly spaced.

The modelling revealed it to be a simple case of chance as the fissures could have formed on either pole, but just happened to occur in the south. Key to their formation was the fact the moon’s poles experience the greatest amount of gravitational stretching caused by its eccentric orbit, so the ice sheet is thinnest over these lengths.

Orbital image of Enceladus with 'tiger stripe' fissures on its surface.

First seen by the Cassini mission to Saturn, Enceladus’ ‘tiger stripes’ are like nothing else known in our solar system. Image: NASA/ESA/JPL/SSI/Cassini Imaging Team

Ground zero: Baghdad

During cooling periods, the moon’s subsurface ocean will freeze. As water expands when frozen and the icy crust thickens from below, the pressure in the ocean builds until it cracks open to leave a fissure. Also, because ice is thinner at the poles, this region is more prone to cracking.

The team said that one fissure, nicknamed Baghdad, was ground zero for the fissures. As it stayed open allowing water to spew from it, it created three additional parallel cracks.

The fissures stay open because of the tidal effects of Saturn’s gravity. In effect, these open wounds never getting the chance to heal. On a larger moon, its own gravity would be enough to prevent this from happening.

“Since it is thanks to these fissures that we have been able to sample and study Enceladus’ subsurface ocean, which is beloved by astrobiologists, we thought it was important to understand the forces that formed and sustained them,” Hemingway said.

Colm Gorey is a senior journalist with Siliconrepublic.com

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