Well this is cool. It appears that Saturn’s moon Enceladus has tipped over on its side sometime in the recent past. It didn’t happen last week, but sometime after the moon formed and was reasonably stable, something happened to cause it to roll over. It probably wasn’t collision with something else, but more likely was due to the motion of material inside this moon. That would have rearranged the mass distribution (that is, where the mass is located) inside, and caused it to tip over. The result is that a warm, low-density blob of material is now currently at Enceladus’s south pole. Now, you’d expect the south pole to be the coldest place on Enceladus, but it’s not, and this temperature anomaly in Cassini’s data is what clued scientists into the unusual explanation.

Enceladus has always been considered something of an unusual place in the Saturnian system (which has its share of odd moons, including Titan). It is continually heated due to the gravitationally caused tidal stretching and squeezing as it orbits Saturn. The heat has to escape from the core somehow, and as it does it expands and rises toward the surface. This causes the surface to expand, and since the surface is icy cold, it cracks under the stress from the upwelling material. It’s a continual squeeze play that changes the surface all the time.

I remember the first time I saw Enceladus in a picture sent back by the Voyager 2 spacecraft. It was astonishing to see an icy world with such evidence of activity underneath. Only at the time, nobody was sure what we’d see. Now that Cassini is giving us more views over a long time period, it’s clear that this moon is far from a frozen, dead world. In the words of many a bad science fiction character, geologically speaking, “It’s alive!!!”