SAN FRANCISCO – New research casts doubt on the existence of water near the surface of a tiny Saturn moon — a finding that, if confirmed, could set back the hunt for extraterrestrial life.
Scientists speculated the eruptions were driven by shallow pools of water lurking just below the icy surface.
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In an alternative view published in Friday's issue of the journal Science, other researchers propose that buried ice clathrates — not liquid water — are responsible for releasing the towering plumes through a sudden tectonic shift in the crust that causes cracks in the ice and gas to vent.
The study doesn't address whether liquid might be present anywhere else on the moon, said lead author Susan Kieffer, a planetary scientist at the University of Illinois at Urbana-Champaign, who has studied geysers on Earth and on the moons of Jupiter and Neptune.
"We didn't go into this trying to disprove liquid water," said Kieffer, adding that in her model, "there is no liquid water required."
The alternative theory shows scientists still don't really know what causes plumes to rise from Enceladus and until that's sorted out, it's premature to send a spacecraft to search for extraterrestrial life, said Bruce Jakosky, an astrobiologist at the University of Colorado at Boulder.
Jakosky noted that if liquid water is not easily accessible on Enceladus, it doesn't bode well for life.
"This would mean that Enceladus would not be a viable place for life. It makes a big difference!" he wrote in an e-mail.
Cassini found the geysers were a mix of water vapor and ice particles containing significant amounts of carbon dioxide and trace amounts of methane.
Kieffer said methane cannot completely dissolve in liquid water, but can exist in ice clathrates, lattice-like structures that trap water ice and organic particles.
Carolyn Porco, a Cassini scientist who first raised the idea of an underground water reservoir on Enceladus, said that while the new model sounds plausible, it doesn't rule out her own model or the possibility of water flowing further down.
She also said the new study shouldn't deter any future missions from probing whether microbial life can exist in such an environment.
"There's reason to believe that there's enough warmth on Enceladus to support liquid water," Porco said.
Enceladus, at only 300 miles wide, was a virtual unknown until Cassini imaged the jets bubbling from a warm zone in its southern polar region.
The discovery vaulted the tiny moon into an exclusive club of celestial bodies that might favor life.
Scientists generally agree that Mars and Jupiter's icy moons might have — or once had — conditions conducive to life.