NASA boffins find an explanation for Saturn's wonky moon

Enceladus might have been knocked over by an asteroid

Southern end of Enceladus (Image credit: NASA/JPL/Space Science Institute)

Enceladus, Saturn’s watery moon, may have been tipped on its axis after being battered with an asteroid, new evidence reveals.

NASA’s Cassini mission may be entering its Grand Finale stage, but the data collected is still a treasure trove for discovery. Results published last month in Icarus, a planetary science journal, show that Enceladus has spun away from its axis by 55 degrees, almost completely rolling on 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,” Radwan Tajeddine, lead author of the paper and a member of the imaging team for the Cassini mission at Cornell University in Ithaca, New York, said on Tuesday.

Tajeddine and his colleagues have also narrowed down on a possible impact region: the south pole. It’s home to a series of diagonal grooves, which are Enceladus’ most striking feature, and has been nicknamed the “tiger stripes.”

It’s an active region driven by complex geological processes. Spouts of water vapor and icy particles have erupted from the tiger stripes, leading scientists to believe the moon could be hiding an ocean beneath its surface.

Tajeddine believes the asteroid may have struck there because the activity is unlikely down to internal mechanisms. “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,” Tajeddine said.

The creation of these stripes could have caused some of the moon’s mass to be shuffled, making it wobbly and unstable and prone to rotation. By the time the icy satellite stabilized, after more than a million years, the north-south axis would have pointed in different directions. Researchers call this process “true polar wander.”

The idea also explains the difference between the current poles on Enceladus. The north pole is pocked with crater marks, while the southern end is more dynamic, and smoother. The poles would have been more similar before the asteroid smashed into it causing it to tip over and move the tiger stripes to the south pole.

Researchers are heavily focused on Enceladus. Last month, NASA announced it had detected hydrogen, reinforcing the idea that alien life may exist elsewhere in the Solar System. It will also be the target for an ultraviolet camera onboard NASA’s Europa Clipper spacecraft, which is expected to launch in the 2020’s. ®

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