Saturn’s moon Enceladus may indeed hide an underground reservoir of water. Scientists analyzed the plumes seen spewing from the moon with the Cassini spacecraft, and found water vapor and ice. “There are only three places in the solar system we know or suspect to have liquid water near the surface,” said Joshua Colwell Cassini team scientist from the University of Central Florida. “Earth, Jupiter’s moon Europa and now Saturn’s Enceladus. Water is a basic ingredient for life, and there are certainly implications there. If we find that the tidal heating that we believe causes these geysers is a common planetary systems phenomenon, then it gets really interesting.”
Using data from Cassini’s Ultraviolet Imaging Spectrograph (UVIS), the team’s findings support a theory that the plumes observed are caused by a water source deep inside Enceladus. An Earth analog is Lake Vostok in Antarctica, where liquid water exists beneath thick ice.
Scientists suggest that in Enceladus’s case, the ice grains would condense from the vapor escaping from the water source and stream through the cracks in the ice crust before heading into space. That’s likely what Cassini’s instruments detected in 2005 and 2007, the basis for the team’s investigation.
The team’s work also suggests that another hypothesis is unlikely. That theory predicts that the plumes of gas and dust observed are caused by evaporation of volatile ice freshly exposed to space when Saturn’s tidal forces open vents in the south pole. But the team found more water vapor coming from the vents in 2007 at a time when the theory predicted there should have been less.
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Instead, their results suggest that the behavior of the geysers supports a mathematical model that treats the vents as nozzles that channel water vapor from a liquid reservoir to the surface of the moon. By observing the flickering light of a star as the geysers blocked it out, the team found that the water vapor forms narrow jets. The authors theorize that only high temperatures close to the melting point of water ice could account for the high speed of the water vapor jets.
Although there is no solid conclusion yet, there may be one soon. Enceladus is a prime target of Cassini during its extended Equinox Mission, underway now through September 2010. Cassini launched from the Kennedy Space Center in 1997 and has been orbiting Saturn since July 2004.
The team’s findings are reported in the Nov. 27 issue of the journal Nature.