Word: mooning
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Even viewed from Earth, the 310-mile-diameter moon appears bright white, almost as if covered in ice or snow; when the Voyager 1 spacecraft arrived at Saturn in 1981, it confirmed that long-distance impression. More intriguing was the way Enceladus behaved. Embedded inside Saturn's E ring - the outermost of the eight bands that make up the ring system - Enceladus seemed to orbit with a thick clump of ring matter trailing behind it, almost as if it were dragging the material in its gravitational wake. What astronomers suspected instead - and what Voyager confirmed - was that Enceladus...
...biologists, that's huge. The only way to account for that particular chemistry is if the salts have dissolved out of rocks in the interior of Enceladus into a large quantity of standing water, as would occur if the moon had a subsurface ocean. "Both components [table salt and carbonates] are in concentrations that match the predicted composition of an Enceladus ocean," says Postberg. "The carbonates also provide a slightly alkaline pH value, which could provide a suitable environment on Enceladus for life precursors...
...moon that hangs in the frigid depths of the solar system could keep water in a liquid state is not much of a mystery. Too small to have a molten core and too far from the sun to feel even a flicker of its heat, Enceladus does have other moons - principally outlying Tethys and Dione - orbiting nearby. Each time those moons pass, they give Enceladus a gravitational tug, which causes it to flex slightly. Do that enough times - and the 4 billion years the solar system has been around is more than enough - and the pulsing moon heats...
...book on Enceladus is by no means closed, and Cassini has two more flybys of the moon scheduled for November. Scientists aren't expecting to find proof of biology there anytime soon - but now, at least, they've got a good reason to look...
...interactive graphic of landing sites on the moon...