New Scientist’s Maggie McKee reckons that Enceladus has one set (not two) of polar vents because it — er... knew — enough to rotate itself a little to promote its own stability. Clever chunk of rock, that one.
Shown like this, it seems surprising that the jets weren’t seen much, much earlier... but it turns out to be all a matter of perspective — or, rather, “of spectrum”. The large but simple jets don’t show up on all scanners.
The heating is probably caused by Saturn's gravity – or tidal effect – which causes Enceladus to stretch and compress slightly as it moves around in its orbit. But the observation was surprising because not all theoretical models can account for the high degree of tidal heating apparently taking place.
Researchers were also perplexed at the location of the hotspot and geysers. "That was a puzzle as soon as we found all this activity - it's absolutely perfectly centred around the south pole," says Cassini team member John Spencer [...]
Researchers expect polar regions to be tidally heated more than equatorial regions, says Francis Nimmo [...]. That is because tidal stresses are spread over a larger area at the equator, diluting the heat they produce there. But any extra heating should warm up both poles, and the effect on Enceladus is only seen at the south pole.
I guess our sixth planet kind of Saturn that one?
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