Ice plumes rise from Saturn's moon, Enceladus.
NASA/JPL/Space Science Institute
NASA's Saturn-orbiting Cassini spacecraft flew through the heart of the icy plumes shooting off the moon Enceladus, a mysterious world that is suspected of harboring liquid water beneath its frozen surface.
Cassini traveled as close as 103 kilometers (64 miles) above the moon last week, its seventh Enceladus encounter. The passage through plumes, which rise like icy versions of the Yellowstone geysers from the moon's south pole, was the probe's closest yet.
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Analysis of data collected during the flyby is under way, but scientists already have learned that the plume extends at least 1,000 kilometers (600 miles) into space and is about half as dense as expected.
At its heart, however, the plume is three times denser than parts flown through during Cassini's previous visits, according to Cassini scientist Bonnie Buratti, with NASA's Jet Propulsion Laboratory in Pasadena, Calif.
With the spacecraft zipping along at about 5 miles per second -- fast enough to fly from Los Angeles to New York in less than nine minutes -- Cassini's trip through the plumes lasted less than a minute.
In addition to directly sampling particles, Cassini used ultraviolet and infrared imaging to map the plume's gases, said science team member Roger Clark, with the U.S. Geological Survey in Denver.
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"The main thing we're seeing is ice everywhere," Clark told Discovery News.
His team is on the lookout for organics and carbon dioxide, both of which have been found on the surface of the moon.
In addition, analysis of the size and distribution of ice grains in the plumes should help scientists understand what is going on beneath Enceladus' surface ice.
"We know that heating by tidal forces is what drives the plumes, but we're not sure exactly how. In addition to a possible liquid subsurface ocean, Enceladus may be harboring a dense mass underneath its surface that helped to start and maintain the moon's current activity," Burratti wrote in a NASA blog.
The last time Cassini flew close enough to sample the plumes, scientists discovered sodium bound in the ice grains, a finding that buoyed the chance for liquid water in the moon.
"It is really quite likely liquid water," said Candice Hansen-Koharcheck, a Cassini scientist at the Jet Propulsion Laboratory in Pasadena, Calif.
"People are trying to understand what's driving the system. There are quite a few (computer) models, each plausible in some ways," added Clak. "It takes a lot of flybys to build up a big picture."
"There's a lot of unanswered questions," he added. "That's the way science goes: You answer 10 questions, and you come up with 100 more. But at least you're making progress."
Tags: Enceladus (moon), Moons of Saturn, NASA, Saturn, Spacecraft
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