Once-wet Mars has long been the primary focus of the search for life on other planets. But Saturn's moon Enceladus could be an even more promising place to start the search for extraterrestrials.
Startling new images from NASA's Cassini spacecraft indicate that Enceladus may contain pockets of liquid water below its icy crust.
These pockets, described in an article published today in the journal Science, may be ideal habitats for life-forms similar to those found in hydrothermal vents beneath the Earth's oceans.
"This is extraordinary," said Carolyn Porco, a Cassini team leader at the Space Science Institute in Boulder, Colorado and primary author of the new study.
"I think our results are significant enough to redirect the planetary exploration program, placing Enceladus as the primary target of astrobiological interest in our solar system."
(See our interactive solar system map.)
Thar She Blows
Launched in 1997, the Cassini orbiter has conducted numerous flybys of Saturn's frigid moons.
When Cassini imaged Enceladus's south pole early last year, researchers noticed plumes of what appeared to be a steamlike substance spewing from the 300-mile-wide (480-kilometer-wide) moon's crust.
At first Porco's team thought the billows might be water vapor rising from subsurface ice deposits. Then the scientists realized they were seeing something unprecedented: outer-space liquid-water geysers not unlike Yellowstone's Old Faithful.
What causes these geysers to form? According to Porco and her colleagues, unknown heat sources inside Enceladus melt ice into deposits of subsurface water. Under pressure, these water pockets burst through the icy crust in fountainlike jets.
"Once the water comes out it freezes, and that produces copious amounts of ice particles," Porco said.
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