NATURE|Vol 440|16 March 2006 NEWS

Signs of warm water on ’s moon

Astrobiologists have welcomed by volcanic activity; there was no may be much the news that Saturn’s small sign of craters left by meteorite warmer than anyone expected, moon Enceladus has a huge impacts, suggesting they had a possibility that has excited geyser that spews water vapour been wiped away. Astronomers astrobiologists. and dust thousands of also speculated from Voyager “We have found another kilometres into space. It means data that Saturn’s E ring of fine environment in our Solar the satellite may be hiding particles was being fed by System, in a very surprising one of the most accessible material from Enceladus. place, that could host living reservoirs of liquid water in The latest observations organisms,” says Caroline the . support that idea, Porco of the Space Evidence for the geyser was and suggest that “Pockets of liquid Science Institute in discovered by NASA’s Cassini the geyser could water may be no Boulder, Colorado, probe during three fly-bys in in part be driven who leads Cassini’s 2005. “Cassini essentially flew by heat from the more than tens imaging team. through it,” says planetary movement of of metres below That makes scientist Jonathan Lunine of the Enceladus’ the surface.” Enceladus an , Tucson. insides, which attractive place According to a suite of slosh around as the moon is to explore, says Lunine. The ice- papers in last week’s Science pulled back and forth by its covered oceans of ’s large (see Science311,1388; 2006), neighbours’ gravity. Heating moon Europa remains the main the plume, which also contains from the decay of radioactive target of astrobiologists’ carbon dioxide, methane, elements also contributes to the interest. But its frozen crust may nitrogen and propane, is process. The Cassini team be kilometres thick. “What’s probably fed by a reservoir of estimates that at least 150 different here is that pockets of liquid water that nestles just kilograms of material a second liquid water may be no more beneath the icy surface. comes from the plume, which is than tens of metres below the The idea that material could more than enough to supply surface,” says Andrew Ingersoll, be welling up beneath the Saturn’s E ring. an atmospheric scientist at surface of Enceladus isn’t new. But the probe did not find the California Institute of When the Voyager probes flew any ammonia — previously Technology, Pasadena. Cassini’s past in 1980 and 1981, they suggested as the antifreeze next close fly-by in spring spotted a flat area around the that helps keep internal water 2008 should help to find out south pole that looked as though liquid in this chilly part of the for sure. ■ it had recently been resurfaced Solar System. So parts of Mark Peplow

Smooth patches on Enceladus’ surface suggest material is welling up from below. NASA/JPL/SPACE SCIENCE INSTITUTE INSTITUTE SCIENCE NASA/JPL/SPACE

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