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A new analysis of data returned by the Cassini probe’s studies of Saturn’s moon, Enceladus, reveals that this moon may have tipped over. Researchers have announced that an asteroid impact in the distant past may have caused Enceladus’ spin axis to reorient itself by about 55 degrees from its original orientation. In essence, the moon may have tilted very nearly on its side.

A paper on the subject has been published in the online version of the journal Icarus. This paper’s lead author, Cassini imaging team member Radwan Tajeddine, said of the research, “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.”

The asteroid that caused Enceladus’ current tilt is believed to have hit in the region around the moon’s south pole. This region is known for an icy “tiger stripes” pattern and liquid water vents originating from an underground liquid ocean that indicate geological activity. The activity is an anomaly for Enceladus that is only found at the south pole. The recent data from Cassini indicates that this activity is not internally caused, but could have originated with an asteroid strike.

The strike may also have redistributed some of Enceladus’ mass, which destabilized the moon and caused it to wobble. Over the next million years, the moon restabilized in its current orientation. During the process, the north-south axis reoriented itself to pass through several points on the surface, a process called “true polar wander.”

This explains why the northern hemisphere and southern hemisphere look completely different. The surface of the south pole is relatively young and geologically active, while the northern pole is old and not very active. The original poles would have looked more similar before the asteroid strike.

The announcement of this new discovery came during the seventh of 22 orbits that are part of Cassini’s “Grand Finale,” which brings it between Saturn and its innermost ring on a regular basis. Cassini’s mission is expected to end with a spectacular dive into Saturn’s atmosphere on September 15, 2017.