Enceladus may have been tipped over

Saturn's icy moon may have been knocked on its side by a collision with a smaller body in its past.

Maps of Enceladus looking towards its southern hemisphere, with purple representing lower terrain and red representing higher. These maps show how Enceladus’s orientation may have dramatically changed following an impact with a smaller body. Credit: NASA/JPL-Caltech/Space Science Institute/Cornell University
Published: May 31, 2017 at 12:00 pm
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Saturn’s icy moon Enceladus may have been tipped on its side as a result of a collision with a smaller body in its past, data from the Cassini mission has shown.

The tipping may have caused a reorientation of the moon so that terrain closer to its original equator was relocated to the poles.

A team of scientists working with data collected by the Cassini spacecraft found that Enceladus appears to have rolled away from its original axis by about 55 degrees.


The theory would explain why Enceladus’s current north and south poles appear quite different.

The south is young and geologically active, while the north is covered with craters indicating it is much older.

The area around the current south pole boasts long, linear fractures across its surface. These are referred to as ‘tiger stripes’.

It is suspected that these features are the result of a collision between Enceladus and a smaller body in the past.

This impact could have caused some of the moon’s mass to be redistributed, causing its rotation to become unsteady.

After a period of over a million years, its rotation would have eventually settled down, but with the north-south axis passing through different points on the surface.

"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," says Radwan Tajeddine, a Cassini imaging team associate at Cornell University and lead author of the paper.

"The geological activity in this terrain is unlikely to have been initiated by internal processes.


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."


Iain Todd, BBC Sky at Night Magazine
Iain ToddScience journalist

Iain Todd is BBC Sky at Night Magazine's Staff Writer. He fell in love with the night sky when he caught his first glimpse of Orion, aged 10.


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