Saturn's icy moon Enceladus may have tilted due to collision with asteroid, NASA Cassini probe reveals

Enceladus, the icy moon of Saturn, may have tilted or tipped over in the past, a new data from NASA’s Cassini probe has revealed. The slant may have been caused due to a possible collision with some other celestial body such as an asteroid, says NASA.

Evidence was found by the researchers that Enceladus’ spin axis – the line through the north and south poles – has reoriented. The NASA team examined the features of Saturn’s icy moon Enceladus and showed that it apparently tipped away from its original axis by about 55 degrees. This amounts for more than halfway toward rolling completely onto its side.

“We found a chain of low areas, or basins, that trace a belt across the moon’s surface that we believe are the fossil remnants of an earlier, previous equator and poles,” said Radwan Tajeddine, a Cassini imaging team associate at Cornell University in the US.
The area surrounding the Enceladus’ current south pole is a geologically active region. The long and linear fractures called tiger stripes slice across the surface at this region.

It is speculated that an asteroid may have collided with the region in the past when it was near the equator. “The geological activity in this terrain is unlikely to have been initiated by internal processes,” Tajeddine said.

“We think that, in order to drive such a large reorientation of the moon, it’s possible that an impact was behind the formation of this anomalous terrain,” he said.

Cassini found in 2005 that jets of water vapour and icy particles spray from the tiger stripe fractures - evidence that an underground ocean is venting directly into space from beneath the active south polar terrain.

Researchers said that whether it was caused by an impact or any other process, some of Enceladus’ mass redistributed due to the disruption and creation of the tiger-stripe terrain. This led to the moon rotate unsteadily and wobbly.

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The rotation would have eventually stabilised, likely taking more than a million years. By the time the rotation settled down, the north-south axis would have reoriented to pass through different points on the surface - a mechanism called “true polar wander.”

The polar wander idea helps to explain why Enceladus’ modern-day north and south poles appear quite different. The south is active and geologically young, while the north is covered in craters and appears much older.

The moon’s original poles would have looked more alike before the event that caused Enceladus to tip over and relocate the disrupted tiger-stripe terrain to the moon’s south polar region. The findings are published in the journal Icarus. 

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(With inputs from PTI)