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This mosaic of Saturn's moon Enceladus shows the regional context for close-up views NASA's Cassini spacecraft acquired during its flyby on Aug. 11. Areas that are greenish in appearance are believed to represent deposits of coarser grained ice and solid boulders. ((NASA/JPL/Space Science Institute))

NASA has found the source of the geysers that jet out from Saturn's moon Enceladus, tracing the icy plumes to deep fissures in the moon's south pole.

Astronomers studying Enceladus had suspected the geysers came from these 300-metre deep fissures, called "tiger stripes," but had been unable to pinpoint the exact location within the fractures.

On Monday the Cassini spacecraft made its second close pass of the moon's surface, giving NASA its closest look yet at the region in question, and sent back close-up images of a deeply fissured surface littered with blocks of ice.

NASA confirmed on Thursday these images had pinpointed the locations of the active jets within the fractures. "This is the motherlode for us," said Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colo.

"A place that may ultimately reveal just exactly what kind of environment — habitable or not — we have within this tortured little moon," she said in a statement.

The geysers have attracted broad interest in the scientific community since they were discovered in 2005, with a number of astronomers suggesting they pointed to both volcanic activity and the possibility of liquid water on the moon, both considered important preconditions for the development of life on Earth.

Now that the scientists know the origin of the geysers, the next step is to study the extensive deposits of ice and other material to piece together how the eruptions occur. This information, along with observations from Cassini's other instruments, might help scientists determine whether liquid water exists beneath the moon's surface, NASA said.

It was the second time Cassini has flown to within 50 kilometres of the distant moon. During the first such manoeuvre, in March 2008, Cassini flew through the icy geyser plumes and was able to detect the presence of water vapour as well as trace amounts of methane and simple organic compounds.

Two more Enceladus flybys are planned for October, NASA said. The first of those will bring the spacecraft to within 25 kilometres of the moon's surface.