Enceladus presents a puzzle for Cassini team

Weird stuff afoot around Saturn

So, on 14 July this year, Cassini flew within 176km of the surface of the moon, and returned some spectacular images.

The data it gathered during that fly-by revealed that the moon does indeed have an atmosphere, and a very strange one at that. "It is probably around the entire body, but seems to be concentrated at the south pole," Dougherty explains, comparing the plume of material emanating from the moon to a cometary jet.

Temperature data from the surface revealed that the south pole is conspicuously hot, in contrast to the researchers' expectations.

John Spencer from the Southwest Research Institute in Colorado, analysed the data from the Composite IR Spectrometer said that they had expected the hottest temperatures - no more than 80 Kelvin - to be found near the equator, at noon when the sun was shining directly overhead.

What they actually found was a hotspot of around 85 Kelvin over the south pole. Zooming in for a closer look revealed that the temperature directly over one of the crevasses was 91 Kelvin: "Distinctly warmer than its surroundings," Spencer confirms.

Data from the visual IR mapping spectrometer provided more evidence of some kind of internal heat source.

The ice crystals near the tiger stripes are highly crystalline, as compared to the less ordered ice covering the rest of the moon. Bob Brown from the University of Arizona says that this forces the conclusion that the surface in that area is either very hot, or very young, or both.

The researchers also found simple chains of carbon on the surface near the fractures. "There is something very special about the fractures," Brown said.

Cassini has two more flybys of Enceladus scheduled, and the researchers will be keen to get more data from those to help them unravel the mystery. ®

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