Planetary Oceanography: Enceladus
|An image taken by the Cassini spacecraft of Saturn's moon Enceladus backlit by the sun. Note the the fountain-like sprays of material being ejected from the south polar region (bottom left). (NASA/JPL/Space Science Institute)|
|Temperature map of Enceladus retrieved by the Cassini spacecraft. Note the intense hot spot at the south pole (bottom). Higher resolution images of this area show even hotter temperatures, associated with young cracks in the crust.|
|The overall shape of Enceladus is unusual as well. (The deviations are highly exaggerated in this picture.) The distance from pole to pole (c) is somewhat smaller than one would expect, if the planet were composed of differentiated rock (tan) and ice (white) layers. We feel this can be explained by the presence of a molten "sea" (blue) beneath the south pole. The south polar surface would be depressed as the ice changed to liquid and contracted.|
Geoffrey Collins (Wheaton College)
When Cassini, NASA?s ongoing mission to Saturn, turned its cameras to the small icy moon Enceladus, the results stunned the planetary science community (Porco et al, 2006). They showed a dramatic geyser-like plume of gas and ice being ejected from the south polar zone, along with an enigmatic hot spot and a violently cracked and disrupted south polar surface. The overall shape of the planet is also somehow affected: it is more oblate than would be expected from its size, orbital position, and likely internal structure.
We believe that the formation of a south polar ?sea? of liquid water beneath the ice crust can explain all these observations. Using the same sorts of models previously applied to Europa and Snowball Earth, we demonstrate (Goodman and Collins, 2006b) that melt-contraction of a thick ice layer would distort the planetary figure, producing the observed oblate shape, while also producing the observed surface terrain disruption and thermal output.
And yet, this is only the beginning. The Cassini spacecraft has only just begun to explore the Saturnian system, and continually poses new puzzles for interested fluid dynamicists, from the sea and geysers of Enceladus to the hydrocarbon rains and rivers of the giant moon Titan.
Porco, C.C., and 24 colleagues, 2006. Cassini observes the active south pole of
Enceladus. Science 311, 1393-1401.
Goodman, J. C. and G. C. Collins, 2006b. Enceladus?s South Polar Sea. Submitted to Icarus.